Light attenuance measurements of suspended particulate matter, northeastern Gulf of Mexico

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Light attenuance measurements of suspended particulate matter, northeastern Gulf of Mexico

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Title:
Light attenuance measurements of suspended particulate matter, northeastern Gulf of Mexico
Creator:
Steward, Robert G.
Place of Publication:
Tampa, Florida
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University of South Florida
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English
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ix, 140 leaves ; 29 cm.

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Subjects / Keywords:
Marine sediments -- Mexico, Gulf of ( lcsh )
Dissertation, Academic -- Marine science -- Masters -- USF ( FTS )

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General Note:
Thesis (M.S.)--University of South Florida, 1981. Bibliography: leaves 107-112.

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University of South Florida
Holding Location:
Universtity of South Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
028625142 ( ALEPH )
08162225 ( OCLC )
F51-00016 ( USFLDC DOI )
f51.16 ( USFLDC Handle )

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Graduate Council University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Is THESIS This is to certify that the Haster's Thesis of Robert G. Steward with a major in Harine Science has been approved by the Examining Committee on 24 November 1980 as satisfactory for the thesis requirements for the Easter of Science degree. Thesis Committee: aajor Professor: Dr. Frank T. Hanheim Hajor Professor: Dr. Kendall L. Carder Hember: Hr. Hurice 0. Rinkel Hember: Dr. Peter R. Betzer

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ACK.i'l'OHLEDGEHENTS I wish to extend my deepest gratitude to the surviving members of my Frank_ T. Manheim, Kendall L. Carder, Murice Rinkel, and Peter R. Betzer for their sustained interest and support over the many years involved in this work. Special thanks are due Dr. Carder for the financial and moral support for the final push, and to Rink for his unsurpassed insight into the northeastern Gulf of Hexico and for his relentless supplications and threats to "get it done." The data collection was supported by environmental baseline contracts (#08550-CT-5-30 and AA 550-CR7-34) from the Bureau of Land Management. The data could not have been successfully collected without the aid of the captains and crews of the Tursiops, Bellows, Java Seal, and Indian Seal. Lee Edmiston, Ted White, and Ken Haddad were responsible for much of the data collection and reduction. Much of the support for personnel during the data reduction and writing came from the Office of Naval Research grant #N00014-75-C-0539. Finally, in recognition of their valiant attempts to reconcile my proofed copy with the English language, I thank my typists, Melissa Rochkind and Ginger McGough. ii

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TABLE OF CONTENTS LIST OF FIGURES ABSTRACT INTRODUCTION The Study Area Characteristics of SPM Motion Inducing Forces on the MAFLA Shelf METHODS RESULTS DISCUSSION Northwest Region 11iddle Grounds West Florida Shelf Loop Current Hurricane Eloise Temporal Variability Implications and Recommendations CONCLUSIONS LIST OF REFERENCES APPENDIX iii iv vii 1 4 6 7 8 15 21 26 47 57 71 84 91 102 104 107 113

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Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. LIST OF FIGURES The Mississippi, Alabama, Florida Lease Area 0 1AFLA) Sample stations comprising three years of environmental baseline studies in the 1 Histogram of cp (m ) for five MAFLA \-later masses defined by salinity: The Subtropic Unden!ater (>36.55/00), Eastern Gulf of Mexico Water (36.5536.40/00), Outer Continental Shelf Water (36.4-36.2/00), Inner Continental Shelf Water (36.2-35.55/00), Runoff Influenced Water (<35.55/00) Graph of Cp values (m1 ) versus gravimetric SPM (Mg/liter) from Betzer and Peacock (1976) and Betzer et al. (1977). A linear regression line g ives the correlation. betwee n SPM and cp o f 1.25 E xemplary Cp Profiles: Type A: Three layer, Type B: Completely mixed, Type C & E: \-lave generated near bottom lay e r Typ e D: Current generated near bottom layer Transect 2600 Salinity July 8-9, 1976 Transect 2 600 Attenuance July 8-9, 1 976 T im e S .eri e s 2 639 Att e nuance July 10-15, 1976 T ime Series 263 9 Salini t y July 10-15 197 6 Tra nsect 1400 Attenuance J anuary 1123 1 976 i v 3 13 1 7 20 23 28 30 3 3 3 5 38

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Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Time Series 2639 Attenuance February 20-25, 1978. Upper bar graph wind velocity (knots) with sea state and predominant wind direction. Time Series 2538 Attenuance February 15-19, 1978. Upper bar graph shows wind velocity (knots) with sea state and predominant wind direction Time Series 2315 Attenuance July 23-28, 1976 Horizontal contour map of midwater minimum attenuance from October 26 November 11, 1977 Horizontal contour map of surface salinity from October 26 November 11, 1977 Time Series 2315 Attenuance February 8-13, 1978 Time Series 2747 Attenuance August 2-4, 1976 Transect 1100 Attenuance February 6-10, 1976 Transect 1100 Salinity February 6-8, 1976 Transect 1100 Salinity February 6-10, 1976 Time Series 2747 Attenuance February 2-7, 1978 Transect 2200 Attenuance November 12-13, 1977 Transect 2200 Salinity November 12-13, 1977 Transect 2100 Attenuance November 15-17, 1977 Transect 2100 Salinity November 15-17, 1977 Transect 2900 Attenuance November 16-17, 1977 v 40-41 46 50 52 55-56 60 62 65 67 69-70 73 75 77 79 81

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Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Transect 2900 Salinity November 16-17, 1977 Combined Time Series 1207 and Transect 1200 Attenuance September 27-30, 1975 Combined Time Series 1207 and Transect 1200 Salinity September 27-30, 1975 Combined Time Series Attenuance Profiles from summer sampling in the Northwest Region Combined Time Series Attenuance Profiles from winter sampling in the Northwest Region Combined Time Series Attenuance Profiles from the Middle Grounds Region Combined Time Series Attenuance Profiles f rom the West Florida Shelf Region vi 83 86 88 94 96 98 100

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LIGHT ATTENDANCE MEASUREMENTS OF SUSPENDED PARTICULATE MATTER: NORTHEASTERN GULF OF MEXICO by Robert G. Steward An Abstract A thesis submitted in partial fulfillment of the requirements for the degree of Haster of Science in the Department of Marien Science in the University of South Florida August, 1981 Major Professor: Dr. Frank T Hanheim Dr. Kendall L. Carder vii

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ABSTRACT Three years of transmissometer measurements over the northeastern Gulf of Mexico. Shelf (north of 26N and east of 89W) were used to characterize the concentration and distribution of suspended particulate matter (SPM). The one meter pathlength Hydro Products 912 transmissometer was calibrated to give an absolute attenuation coefficient at 550 nm. The data set consists of contoured attenuance cross sections from cross shelf transects and from 12, 24, and 120 hour time series stations. Collaborative data in the form of nearly simultaneous salinity and temperature cross sections, SPIJ concentrations and trace metal composition plus plankton sampling aided in interpretation of the attenuance measurements. These data defined regional and seasonal characteristics including sources and controlling advective mechanisms. The Northwest Region covered the narrow shelf from the eastern edge of the Mississippi Fan to Cape San Blas. In summer, this area was dominated by highly stratified attenuance profiles due to runoff lenses at the surface and bottom resuspension by internal waves and/or tides. The remainder of the West Florida Shelf was divided into the Middle Ground Region (from Cape San Blas to Cedar Key) and the West Florida Shelf Region. These displayed similar characteristics in summer: little or no runoff beyond a few kilometers of the shore, extremely low SPt1 concentrations except for spurious biogenicpeaks and minor bottom resuspension. In viii

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all three regions during winter, the dominant SPH mechanism Has atmospheric frontal passage which completely mixed the water column and resuspended bottom sediment. \vater associated with the Loop Current was shoHn to be some of the most particulate free in the -1 sampling area (attenuance values of 0.02-0.05 m ) and a major control-ling mechanism by its influence on shelf circulation and bottom resuspension during on shelf intrusion. The data set includes one such intrusion of the Loop Current (1977) plus a similar near bottom turbidity layer resulting from Hurricane Eloise (1975). All three regions displayed periodic events either in the presence of sharp density interfaces during surmner and fall or follmving v7inter frontal passage. The oscillations after both a tropical storm and atmospheric frontal storms suggest that the basin is responding to the stress by seiching. Ho.-..Jever, the nearness of frequency of the inertial, diurnal tide, and the fundamental harmonic period prevents the isolation of any one causal agent in this data. Abstract approved: ix Professor T. l!anheim Hajor Professor Kendall L. Carder November 24, 1980 Date of Approval

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1 INTRODUCTION The distribution of suspended particulate matter (SPM) in oceanic water is a function of dynamic physical, chemical, biological, and geological processes. Only by studying concentration, composition, and transportation of SPM is it possible to understand not only these natural processes but also to predict the ultimate fate and impact of anthropogenic particulates with absorbed trace metals, hydrocarbons, and other potentially toxic material. Three years of transmissometer measurements were collected during Bureau of Land Management environmental impact studies in the Nississippi, Alabama, Florida Lease Area (MAFLA). These data have been utilized here to assess the dominant SPM characteristics over the HAFLA shelf and to relatively categorize the importance of particulate source and major advective events in controlling SPM patterns. To date, there are only two publishe d reports concerning SPM measurements over the MAFLA, that outer shelf area bounded by 89W and 26N (Figure 1). Manheim et al. (1972) measured surface SPH during a six \veek period of late fall 1966. Carder and Schlemmer (1973) and Schlemmer (1971) reported the initial optical characteristics and particulate size distribution of the major northeastern Gulf circulatory feature, the Loop Current, from a multiple ship, synoptic survey (EGMEX) in 1970. Other studies have include d the northern Gulf waters, but have not extended onto the shelf

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2 Figure 1. The Mississippi, Alabama, Florida Lease Area (MAFLA)

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29 28 27" 26 w

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(Jacobs and Ewing, 1969; Harris, 1972; Feely, 1975). Thus, the cross shelf transect and time series data of this study provides the most extensive and most recent attempt at characterization of the spatial and temporal variation in the MAFLA shelf suspended matter. This thesis will examine the strengths and limitations of the light attenuation technique in evaluation of the SPM. The variability of the SPM distribution both vertically in the water column and horizontally across the shelf have been categorized by season. An attempt has been made to show the synoptic validity of point sampling within the water column in different regions of the MAFLA. Finally, the relative effect on the SPM distribution has been quantified for such phenomenon as near bottom oceanic intrusions of Loop Current waters and associated spin off eddies, seasonal atmospheric frontal passage, and hurricane passage. The Study Area Historically, the MAFLA shelf has been subdivided by bathymetry and physical oceanography (SUSIO, 1975), and by lithofacies (Gould and Stewart, 1955; Ludwick, 1964; Doyle et al., 1977). These criteria were utilized by the environmental studies program managers in designating cruise tracks and sampling stations. The subdivisions of the shelf facilitate the discussion of the background factors affecting suspended particulate matter and also orient the data and discussion of the results in this survey. The three most important divisions of the shelf are: 1) Northwest Region, from 87W to Cape San Blas; 2) the Middle Ground Region, from Cape San Blas to approximately Cedar Key; and 3) the West Florida Shelf Region, from Cedar Key south. The sampling was generally confined to the band 4

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from three to five kilometers offshore to the shelf break. The designation of these regions in this thesis is descriptive only and does not necessarily coincide with other historical or geographic divisions. The Northwest Region consists of the Alabama-Mississippi coastal plain and continental shelf which is bisected by the DeSoto Canyon (Brooks, 1973). The lateral boundaries are the St. Bernard Prodelta facies of the Mississippi Fan in the west and Cape San Blas to the east. The lithography of this narrow shelf is comprised of the MAFLA Sand Sheet inshore out to a paleoreef remnant on the canyon rim at 100 m. The eastern side of the region consists of several transitional facies: the Florida Quartz Sand Sheets and the Carbonate-Quartz zones al., 1977; Ludwick, 1964; Gould and Stewart, 1955). From Cape San Blas to Cedar Key is commonly known as the Big Bend area or the Middle Grounds Platform. The lithofacies are comprised of an inshore zone of the West Florida Quartz Sand Sheet with a broad transition zone of clastic carbonates and quartz sand. The rejuvenated coral and algal reef complex from which the platform gets its name is surrounded by an area of scattered pinnacle and ledge reefs and carbonate sands (Doyle et al, 1977; Brooks, 1973). All the continental shelf off the west coast of Florida may be included in the term, West Florida Shelf; but for this report it w ill refer only to the shelf extending south from the Middle Grounds Region. The lithofacies here are the same as for the Middle Grounds Region, less the massive oute r shelf reef co mplex. All three regions have a common facies, the West Florida Lime Huds, \vhich are located 5

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at the base of the Florida Escarpment in about 100 m of water (Doyle et al., 1977;.Brooks, 1973). These regions can also be distinguished by their runoff characteristics (Schroeder, 1975). The Northwest Region is dominated by the eastern Mississippi-Mobile river systems. These rivers reach flood stage in April through June, and have a clay mineralogy in the suspended load by smectites (Huang, 1976; Griffen, 1962). 6 The combined annual discharge within this region equals 20% of the total annual Mississippi River flow. In the Middle Grounds Region, the dominant rivers are the Suawnee, Steinhatchee, and Apalachacola which tend to reach flood stages in early summer. This region receives less than 7% of the total runoff in the MAFLA which is equivalent to 9% of the total Hississippi River flow (Rinke!, 1976). Discharge into the West Florida Shelf Region is concentrated in late summer and amounts to less than 1% of the total MAFLA runoff. The clay components of the suspended load in the later two regions are dominated by kaolinites and chlorites (Huang, 1976; Griffen, 1962). Characteristics of SPM The limited studies of SPH over the HAFLA shelf demonstrate a very wide range of concentrations to be normally present. During late fall, from Cape San Blas westward, al. (1972) found concentrations of greater than 1.0 mg/liter within 10 kilometers of shore, and less than 0.125 mg/liter at the shelf break. Henry and Bader (1961) and Ouillette (1970) reported concentrations of 10-20 mg/liter extending 1-5 kilometers seaward of the western edge of the Hississippi Delta. The opposite edge of the spectrum is represented by the Loop Current which is relatively particulate free

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7 (Carder and Schlemmer, 1973; Schlemmer, 1971). These authors concluded that although the Loop consists of very low concentrations of biogenic detritus, the high velocity and volume of this Caribbean water represents a major particulate transport mechanism both directly and indirectly by control of shelf circulation. Hotion Inducing Forces on the MAFLA Shelf Maul and Molineri (1975) have summarized the advective forces active on the MAFLA shelf, the effects of those forces on shelf waters, the area of shelf affected, the seasonality, the spatial and temporal scale of the induced motion, and the adequacy of the data base. The forces contained in that work included: 1) the Loop Current and associated eddies; 2) wind forcing by trade winds and frontal passage; 3) tides and inertial motions; and 4) river runoff. In all cases, the data base as of 1975 was cited as inadequate to test or initialize force modelling, or even, to attempt prediction of water parcel trajectories. Data collected in this thesis will suggest that seiching, tropical storms, and hurricanes should be included as forcing mechanisms.

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HETHODS The transmissometer used in this study, a Hydro Products 912, measures the attenuation of a 20 mm diameter, collimated, white light beam across a one meter or ten centimeter pathlength. The beam diameter and one meter pathlength configuration used throughout this study has an inherent forward scatter error of less than 0.5% (Preisendorfer, 1958). The silicon cell light receptor is most sensitive to incident light at 550 nanometers with the 50% sensitivity at 50 nanometers. This narrow bandpass eliminates the effect of shorter wavelength light attenuancebywater and dissolved matter, making the resultant attenuance most dependent on suspended particulates (Jerlov, 1968; al., 1974). To make an absolute attenuance measurement each instrument must be calibrated to eliminate the attenuance due to the optics. Since this is a time consuming, if not impossible, task for each unit; most commercially available transmissometers have an optical readout relative to a prepared turbidity standard or filtered water. The Hydro Products 912 was adjusted at the factory to read maximum transmittance in particulate-free, distilled water. A subsequent "in air" measurement then provides a repeatable standard for field calibration. As a result, all measurements made at this test setting are relative to the clarity of the prepared standard used by the manufacturers. Early in the program it was found that often the outer 8

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continental shelf waters in the MAFLA would give transmittance values in excess of 100% when using the manufacturers calibration point. Therefore, the following recalibration was undertaken. The dual pathlength plus the well collimated beam of the Hydro Products instrument make an absolute attenuance measurement of a test water possible. Using this value, a new "in air" field calibration point was derived. The basic equation of attenuance is 1. F X F 0 -ex e where F is the light flux at light source, 0, and at x meters; and c is the attenuance coefficient. The relationship between the 0.1 m and 1.0 m pathlengths for the same parcel of water can be expressed as 2. F (0 .1) Fo -c(O.l) e F(l.O) -c(l.O) and Fo e ln (FO.l/Fl.O) c= 0.9 3. The "in air" calibration factor, G, can be written as 4. 5. 6. F = F G 0 (1. 0) air F (1.0) G F (1.0) air -c F(l.O) aire -c e The attenuation coefficient is composed of factors due to the medium (em)' dissolved matter (cd), and particulates (cp). Thus, 9

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7. c = em + cd + cp ; respectively. For our purposes, we assume that cd is insiginficant at 550 nm, and c is zero by the way the instrument is calibrated to be maximally m 10 transmitting in optically pure water. The attenuance due to particu-lates may now be written 8. substituting 9. -(c-ern) e F(l.O) F (1.0) Fo G F (1.0) air -c e m where 10. H = G -c e m -c e e-cm F(l.O) air H At 550 nm, e-cm is equal to 0.933 (Clarke and Jones, 1939). So 11. H = 0.933 G. Experimental values of G and H were determined for the air calibration points used during the three years of this data collection. The corrected c has been utilized as the data base for this report, and p I is referred to, simply, as attenuance hereafter. The data were collected during outer continental shelf environ-mental baseline studies contracted by the Bureau of Land Management. The contracts encompassed five cruises between the summer of 1975 to the winter of 1978. As a contractual study, the methodology, location, and timing of the sampling was prearranged to fit rigid guidelines established by the contracting agency and two management groups (State [Florida] University System Institute of Oceanography, 1975-76; Dames and Hoare, 1977). Deviation from the sampling program to

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11 satisfy scientific curiosity was not permitted. The two concerns of the water column investigation were the spatial and temporal variation of water column parameters which may be related to the uptake and/or transportation of hydrocarbons over the continental shelf. Therefore, cross shelf transects were designated to characterize the regions of the and time series stations were planned to measure in situ variability. The sampling stations for the three years of this study are shown in Figure 2. The first two cruises, September 1975 and January-February 1976, were conducted on four transects with two 24-hour time series stations per season (1412, 1207). The master stations comprising the transects shown in Figure 2 were occupied for one day each while a rigid time schedule of sampling was conducted. Just prior to dawn, the transmissometer was hand-lowered to near bottom or to the limit of the 80 m conducting cable. The percent transmittance was hand-logged either at fixed intervals of two meters in highly variable waters, near the surface and bottom, and throughout shallow depth stations; or at intervals of five to ten meters below the thermocline in homogenous waters. The other water column parameters were collected in the next 7-8 hours. At the midpoint between the master stations, additional transmissometer and salinity/temperature/depth (STD) casts were collected upon arrival. During the 24-hour stations, four to five transmissometer and STD casts were made. The in situ variability was further measured during the summer of 1976 at three, 140-hour time series stations: 2639, 1207, and 2747 (Figure 2). Transmissometer and STD casts were made every other hour. The transmissometer depth range was extended to 300 m with a

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Figure 2. Sample stations comprising three years of environmental baseline studies in the 12

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sgo 87" M/2 r-. 26389 \!I. 9 2640 2528 1309. 2531 @ 1!) 19756 1977-8 & TRANSECT 2600 (1976) 0 100 km 9 2645 9 9 9 9 /3/& 1311 @ 2426 2427 85" 2423 1204 @ 1205 '@-2318 1206 @ 2315 1207 83" 2313 2212 @ 1103 2211 2208 2207 2209 @ (!) 1102 1!01 02748 02747 "2746 2106 2104 2957 2958 2959 8i"W 30 29 28" 27 2102 26" 2960

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winch-lowered conducting cable. The sampling interval and logging technique remained the same as the earlier seasonal cruises. 14 Another seasonal cruise was added in November 1977 to compensate for the hurricane-modified cruise in the fall of 1975. The sampling schedule was modified with 15 additional stations on the West Florida Shelf (Figure 2). The water column and benthic sampling investigations were combined on. a single, much larger vessel than used previously on the water column program. The transmissometer and STD casts were made upon arrival at the station without regard to time of day. Four 12-hour time series stations were conducted with transmissometer and STD casts every other hour. During this cruise, the transmissometer was deployed with a depth sensor. Both depth and percent transmission were continuously recorded on a XYY' analog chart recorder. During the winter of 1978 (February) in situ variability was measured for 140 hours at the same three time series stations as the summer of 1976 plus station 2528. The alternate hourly casts were made with the transmissometer in the same configuration as the November 1977 cruise.

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RESULTS Profiles and cross sections are the most important formats of the transmissometry data used in this work. The c values as a p function of depth for each instrument deployment are designated to be a profile. Depending on the cruise, the profiles have been com-bined and contoured either temporally or spatially to form cross sections. The transect and time series corss sections have been 15 chronologically arranged in the Appendix to facilitate further utili-zation of the data. The cross sections are also included in the text immediately after the first reference to each. Since particulate content has been shown to be an inherent property of some water masses (Jerlov; 1968; 1976), the accuracy and calibration of the instrument can be checked against these values. In the MAFLA, the most conservative water mass (with respect to optical properties) is the Subtropic Underwater As the core of the Loop Current 1964), this water retains its physical integrity throughout the transit of the Gulf of Mexico (Molineri et al., 1977). These authors have defined this core water as having salinity in excess of 36.5 /oo and a temperature range of 19-23C. F igure 3 is a histogram of c values for five categories of p MAFLA shelf >-.Tater masses as defined by salinity (Rinkel, 1976). The c values were selected from homogenous zones of water away from p obvious particulate sources (e.g., planktonic blooms, bottom

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Figure 3. Histogram of c (m1 ) for five water masses p defined by salinity: The Subtropic Underwater (>36.55/oo), Eastern Gulf o f Mexico Water (36.5536.4/00), Outer Continental Sh elf Wat e r (36.436.2/00), Inner Continental Shelf Water (36.2 35.55/00), Runoff Influence d Water ( <35.55/0 0 ) 16

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> u z w 0 w 0: LL. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 o.B > 36.55 %o 36.55-36.40%. 1L 30 20 36.40-36.20 %o 10 20 36.20-35.55 %o 10 < 35.55 %o 10

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resuspension, etc.). The water in excess of 36.55 /oo clearly represents the low end member of the c distribution with a peak at p 0.02 to 0.05 m -1 Jerlov (1970) has reported a value of c-c or c w p 0.05 -1 at 440 rum for Sargasso Sea water where ilieSW downwells m form the core of the Loop Current (Wust, 1964). Kullenburg et al. (1970) has also reported a slightly lower range of 0.03 m-l at 633 to 484 nm and 0.05 m-l at 440 nrn for these waters. Based on these to comparisons, the accuracy of the transmissometer appears to be quite good for low particulate concentrations. 18 The relationship between c and gravimetric SPM concentration is p complex and dependent on several factors (shape, size, index of refraction, etc). A general, working estimate (SPM = 1.25 c ) has p been graphed in Figure 4. This has been prepared from gravimetric data collected during the project by Betzer and Peacock (1976) and Betzer et al. (1978) in areas of low spatial and temporal attenuance variability. The need for such criteria was dictated by the sampling program which separated by as much as six hours the gravimetric and optical sampling. The graph provides a reasonable correlation of light attenuance to inorganic SPM concentration, but does not cover the wide disparity which organic particulates m a y cause (e.g., see Carder and Betzer, 1974).

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Figure 4. Graph of c values (m1 ) versus gravimetric SPH p (Mg/liter) from Betzer and Peacock (1976) and Betzer et al. (1977). A linear regression line gives the correlation between SPM and c of p 1.25 19

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2.0 1.5 SPM mg I liter 1.0 0.5 G G 0.5 Q 1.0 Cp 0 G & 1975-6 Q 1978 2.0 20

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DISCUSSION The SPM distributional trends as determined by the c data can p be described as a 3x3x3x2 matrix: three cross shelf or horizontal zones; three vertical positions within the water column; the three 21 geographic regions 'vi thin the MAFLA; and t'v o seasons. The first two dimensions of the matrix are classic SPM patterns over most continen-tal shelves (e.g. see Stanley and Swift, 1975). The last three factors are unique to each study area and serve as the body of the discussion divided under the regional subheadings. Of the two classic SPH patterns, the most common is a decrease in concentration going offshore. Typically, there is an inshore zone of high concentration due to: runoff, h igher wave erosion and/or resuspension of bottom material, and higher productivity A transi-tion zone separates this inner zone from the outer shelf area over which usually is found nearly particulate-free water. The division between these zones is open to definition, and will shif t in location due to such factors as river discharge stage, wave energy bottom sediment type, and biogenic productivity. The vertical zonation of the water column refers to the distribu-tion of the c maxima "'ith resp ect to d epth (de /dz) for a s ingle p p profile. The three layer zonatio n reflects t h e t w o most important source depths of SPM: the surface due to fluvial and aeolian inputs plus prim a r y producti v i t y and t h e botton d ue to r esuspe n s ion of

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Figure 5. Exemplary c Profiles: Type A: Three layer, p Type B: Completely mixed, Type C & E: Wave generated turbulence in a near bottom layer, Type D: Current generated turbulence in a near bottom layer 22

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cP .1s I I 0/oo 36.5 0 30.so 1.0 I I 30.0 TYPE A TIME SERIES 2639 0100 JULY 13, 1976 .25 1.00 36.65 36.50 140-1601.4 I I 26. 5 .56 .58 .60 36.0 36.1 10-20-//// ///// TYPE 8 TIME SERIES 2315 1130 FEBRUARY 9, 1978 23 .so .60 .70 36.ll 36.09 36.07 tO-20-TYPE C TIME SERIES 2315 0120 FEBRUARY 9, 1978 1.75 .60 .70 .80 .90 36.30 10-20-30-35.70 35.60 35.50 35.40 TYPE E TIME SERIES 2528 tao 1500 FEBRUARY 15,1978 TYPE 0 TRANSECT STATION 2957 1730 NOVEMBER 16, 1977

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24 sediments and benthic productivity. As with the cross shelf zonation, there is an arbitrarily defined transitional area, a midwater bolus of relatively lower particulate concentration. The greatest advantage of the is that it instantaneously measures and outputs in real time the attenuance profile for an entire water column. Since the w eight of this work rests upon these profiles, Figure_ S was prepared to exemplify the predominant patterns seen during the program. The e xamples are utilized throughout the discussion to h elp describe the regional attenuance distributions. However, it should not be implied that the causal agents for each of the examples in Figure S are universally in effect when similar profiles are encountered i n the f ield. The most common attenuance p atterns seen duri n g the survey took the shape of F igure Sa and Sb for the stations over the middle to inner shelf. T h e first, or T ype A is common throughout m ost of the year e x c ept durin g high energ y conditions. This example s hows a surface layer of high attenuance and low salinity due to runoff, an extremely low attenuance midwater zone from 10 to 30 meters, and a three thick bottom layer o f hig her attenuance which is due to resus p e n sion by t i d a l currents or internal w a ves. Figure Sa s how s a greater influence o f runoff tha n would be t ypical for most o f the MAFLA, but t h e profile pattern i s still r epresentative o f most of the middle t o inne r s helf area s d uring p eriods o f q uiescence ThP. surfac e layer in areas unaffected b y the amount of runoff, as thi s example in the Northwest Region, would seldom b e over 10 2 0 % higher than t h e rnidwater values. The oppo s i t e example or Type B, i s a conditi o n where the e ntire water column has been mixed, the typical winter

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25 profile for most of the sample area. The near.bottom concentration of SP11 is an important indicator of the amount of kinetic energy in the boundary layer and of its affect on the sediments (Lesht, 1979; Chris and Pak, 1977; Lavalle al., 1978; Gust and Walger, 1976). In this study, t\vO conditions were found to predominate in this section of the water column. These conditions or patterns_of attenuance may be described by the change in attenuance, de with respect to a limited near bottom layer, dz. p The first is a bottom layer in which c is relatively large when p compared to the overlying \vater and is nearly constant within the bottom depth interval, or de /dz=O or is very small. Such a layer was p usually the result of resuspension by near bottom currents having a salinity and temperature signature distinct from the overlying water. One of the best examples of this type of bottom layer can be seen in Figure Sd v1hich shov1s the result of a rather strong intrusion of the Loop Current onto the West Florida Shelf. The advective forces of the moving water and the settling velocity of resuspended grains appear to have been temporarily balanced to give a uniform layer with a distinct upper interface. The second type of bottom layer is that where de increases p towards the bottom, or de /dz=constant. This type (Figures Sc and Se) p occurred generally during the onset or abatement of unusually high energy events at the surface, eg. atmospheric frontal passage. Under extreme conditions, this type of bottom layer could be expected to reach the surface, but shipboard conditions prevented sampling during the height of such events. Figure Se is an example of such a bottom layer. By the time such high energy events had subsided enough to

PAGE 35

26 permit sampling, the water column mixing was sufficient to produce a completely mixed profile (Type B). Northwest Region The dominant summer profile in this region was Type A, displaying sharp gradients from the surface and bottom maxima to the midwater bolus of relatively clear water. On the west side of the DeSoto Canyon the surface attenuance did not increase near shore, but was confined to one or two surface lenses (5-15 m thick) over the middle shelf. -1 The c range of these lenses was from 1.2 to 0.6 m the p highest values measured on the surface during the entire project. On the east side, no such lenses were found as the attenuance always -1 increased toward shallower water to values around 0.4 m The -1 -1 midwater values ranged from 0.10 m at the shelf break to 0.25 m inshore on both sides of the canyon. The bottom attenuance was of Type E and was not spatially continuous across either side of the canyon. Occasionally, the midwater values were found to extend down to the sediment/water interface. In general, the c values for the p surface and near bottom on the western side of the DeSoto Canyon were about 20% higher than those of corresponding depth and distance off-shore on the eastern side. The single transect and time series measurement at station 2639 in 1976 revealed more about the physical mechanisms which control the attenuance patterns over this region than did other transects. Comp-arisen of salinity and attenuance cross sections on Transect 2600 (Figures 6 and 7), show that the high surface c is due to two low p salinity, runoff lenses: the outermost (labelled Northwest) is due to the River, and the innermost (labelled West) is due to

PAGE 36

27 Figure 6. Transect 2600 Salinity July 8-9, 1976

PAGE 37

(f)a: w fw Northwest 36. 4 30. 0 0030 9/7 0300 9/7 0500 9/7 2639 I 0700 9/7 36. 0 0900 9/7 29. 0 d 1030 9/7 km West 1200 9/7 -50 -100 -]50 -200 N co

PAGE 38

29 Figure 7. Transect 2600 Attenuance July 8-9, 1976

PAGE 39

1815 8/7 0510 9/7 2639 0710 9/7 km -50 -100 -150 -200 w 0

PAGE 40

31 to combined Mississippi and Alabama drainage areas (Rinkel, 1975). These lenses are best viev1ed as currents of lower density water streaming sinuously across the surface of the Northwestern shelf region. During an unusually high discharge season with a strong northern intrusion of the Loop Current, this runoff water was detected as far away as the Georgia coast (Atkinson and Wallace, 1975). During this survey, the were not optically detected on the eastern DeSoto Canyon transect. While this may indicate that the canyon fs a sink for some of the faster settling particles, it could also have resulted from simple dilution or having the surface stream located further offshore than the eastern canyon transect extended. Time series measurements at Station 2639 (Figure 8), the high salinity, low attenuance ridge between the lenses demonstrated that the currents associated with the lenses migrate rapidly and were noticed to have a leading edge at the picnocline. The maximum atten-uance pockets were preceded by increases along the thermocline (Figure 9) at 0300 and 1300 Day 2, 2300 Day 3, 1900 Day 4, and 1300 Day 5. The lenses can appear or disappear at a fixed station within the two hour sampling interval; e.g. 0300 Day 2, 1500 and 1900 Day 3, and 1300 Day 5. The bottom c values ranged from 0.4 to 0.8 (m1 ) in Type E p profiles and are much more difficult to explain. The nearly periodic occurrence of the high c pockets (on a 16-24 hour frequency) could p have been generated by the large amplitude internal waves (e.g. 1900 Day 3, 1500 Day 4, and 1300 Day 5) and by tidal currents. Boston (1964) and Dowling (1966) reported such low frequency internal waves associated with bathymetrically focused internal tides in this region.

PAGE 41

32 Figure 8. Time Series 2639 Attenuance July 10-15, 1976

PAGE 42

;) c: l;J : .. #.. .... \ 20-)_, V' 30->1. 0 0300 JULY 13 1300 10-20-30-w w

PAGE 43

34 Figure 9. Time Series 2639 Salinity, July 10-15, 1976

PAGE 44

0100 13 00 0 100 10---35 2036 30-1300 10-20-30-

PAGE 45

36 Recent studies of temporal variability of bottom attenuance have shovltl that a few short period fluctuations in shear stress (such as low frequency internal waves) are more statistically related to entrainment of non-cohesive sediment than the mean stress (Lesht, 1979; Gordon, 1975). These short term fluxes near bottom would best explain the occasional occurences of high c p The dominant cp P .rofile during winter in the North\vest Region was Type B and, for a brief period following atmospheric frontal passage, Type C. The values found ran about 3-4 times higher (0.5-3.3 at the inshore stations generally -1 m ) for the corresponding stations and depth than during summer. Each frontal passage established a new c pattern as shown by the sampling hiatus in Transect 1400 p (Figure 10) and by the increase in c following wind velocity increases p and direction shifts due to frontal passage during the time series stations 2639 (Figure 11) and 2523 (Figure 12). The highest values in both time series occurred near bottom following a frontal passage. Given the lack of synopticity in the sampling and the dynamic changes with respect to each front, it is difficult to determine a steady state c value or to compare values from the two transects within this p region. Iim.rever, it was noticed that the c values on the western p side of the DeSoto Canyon were about 5-10% higher than those for corresponding depths on the immediate western side under similar energy conditions. The transrnissoneter data during winter in this region displayed r.mch smoother gradients than summer in respect to vertical depti1 within the \vater colur.m, horizontal distance from shore, and time. This indicates a dominance of the mixing mechanisms for this season over the stratifyin:; mechanisms of summer.

PAGE 46

37 Figure 10. Transect 1400 Attenuance January 11-23, 1976

PAGE 47

(/) a:: w tw 2 1415 q 1830 23/1 2 2100 22/1 1414 2300 2 2/1 SAMPLING HIATUS -60 DEPTH SAMP LED 80 __ ,c-_ .. 0 25 km

PAGE 48

Figure 11. Time Series 2639 Attenuance February 20-25, 1978. Upper bar graph shows wind velocity (knots) with sea state and predominant wind direction. 39

PAGE 49

4 330 20 4 310 ,__ 0 10 3 350 :.: 3 210 I 0 10 0100 FEBRUARY 2 1 0101) FEBRUARY 22 .a .s 10-<./1 Q: w 1-....! 2C 30-

PAGE 50

I / / 2 260 01'.:10 FEBRUARY 2:3 35 Kts 5 265 0100 FEBRUARY 24 I 260 I 260 01'.:10 25

PAGE 51

Figure 12. Time Series 2528 Attenuance February 15-19, 1978. Upper bar graph shows wind velocity (knots) with sea state and predominant wind direction. 42

PAGE 52

10-1/l n: 9 w w .5 :::;: 20-30-/\0 .J:-w

PAGE 53

Vl f-. 0 z :.: Vl cr w t-w :::;-20 1 0 0 0100 FEBRUARY 18 10-20-.30-0100 FEBRUARY 19 5 p .6 .6 .6 > 6 > 5 > .6, 0 6 6 I 320

PAGE 54

45 Figure 13. Time Series 2315 Attenuance July 23-28, 1976

PAGE 55

l/) 0:: w 1w 0200 JULY23 lQ20-1200 JULY 25 10-20-0000 JULY 24 0000 JULY 26 2315 0000 JUL Y 25 02 .2 2 2 2 .3 .3 > 2 ) .I ).1 2 0000 JULY 27

PAGE 56

47 The transmissometer bottom measurements h t e gravimetric SPM, and trace element ratios (Betzer and Peacock, 1976, B 1 etzer et 1978) indicated that resuspended bottom sediment is the chief compon-ent of the winter water column particulates. The silicon/aluminum ratio was much lower in winter than summer, reflecting a switch in dominance from high silica in organic particulates to inoroanics 0 such as the alumino-silicate minerals. Due to these inorganics vJhich are more efficient light attenuators per unit volume and have more continuous distribution compared to plankton patchiness, there was a greater correlation between the gravimetric SPM measurements and c Most of the high c values in Figure 4 were.selected from the p p time series under these conditions. Although riverine input is still present during winter, it is not as easily detectable. Winter is the period of lowest discharge during the year for the rivers in this region (Rinkel, 1976). The only place where distinct near surface c maxima \vere found \vas at p the shallowest stations near the river mouth, 1412 and 2639 (Figure 10 and 11). All corresponding salinity profiles taken during the time series were completely isohaline with depth even when the transmisso-meter measured a c maxima at the surface. Under these conditions, p the transmissometer provides a more sensitive measurement of water column mixing or advection than does an STD. Hiddle Grounds The predominant profile type found over the Middle Grounds Region in summer was Type A with s!Tlall de at the surface and bottom. p profiles showed secondary maxima or "spikes" at various depths Host h h h 1 Usuallv t .hese spikes were too spurious t1 roug out t e water co uQn. J

PAGE 57

or isolated to be recorded or graphically represented. Typical c p 48 values ranged from <0.10 to 0.20 m-l over most of the shelf in depths greater than 30 m and from 0.20 to 0.30 m-l in a narrow inshore zone and as "spikes" throughout the reg1.'on. h T e spikes as well as the more stable attenuance maxima gave no discernably periodic pattern as can be seen in Figure 13. The lack of distinct patterns and the high degree of makes it difficult to correlate the attenuance with ancillary sampling done at different times. The best explanation for the highly irregular nature of the suspensates over the Hiddle Grounds Region in summer was found in the neuston and plankton sampling by biology co-investigators (Alexander al., 1977). Both reported high degrees of patchiness in the plankton tows, often h aving large quantities of a single species being caught in the same area as extremely little on different tows. The trace metal composition reflected very lmv levels of riverine borne elements (Betzer and Peacock, 1976; Betzer e t al., 1978). In an area of high productivity such as Grounds (Steidinger, 1973), the organic particulates will be an important component of the total attenuance. In a near shore zone of hig h productivity off Beach, California, Ball and La F ond (1964 ) attributed all attenuance to organic particles. It should be noted here that due to the low index of refraction and larger size o f these particles, their attenuance is much lower than the same volume concentration of inor-ganics (see Carder and Betzer, 197 4). The predominance of organic particles in the summer Hiddle d to the lack Of inorganic matter contributed Grounds is primarily ue h b tt Partially, the lack o f by rivers or resuspended off t e o om.

PAGE 58

Figure 14. Horizontal contour map of midwat e r min imum attenuance from October 26 November 11, 1977 49

PAGE 59

89 87 85 83 .05 ATTENUANCE MIDWATER MINIMUM 0 81W 30 29 28 27 26 Ln 0

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Figure 15. Horizontal contour map of surface salinity from October 26 November 11, 1977 51

PAGE 61

89 87" 85 .//r-35 7 35. 2 . /343 :rr36. 1 36.36. 2 / -;------_._ 36. SURFACE SALINITY %o 0 100 km I M lW 83 91w 36.4 /. 30 29 28 27 26 1..11 N

PAGE 62

53 evidence for riverine input is due to the design of the sampling program which was concentrated on the middle to outer shelf except for the 1977 transect cruise. The midater minimum c and surface salin-p ity horizontal cross sections (Figure 14 and 15, respectively) from this cruise show the only evidence of runoff derived particulates, a limited area near Cape San Blas. More importantly, the figures show that the the Cape acts as a topographic barrier to longshore exchange of riverine materials between the Middle Grounds and Northwest Region. The limited inshore zone of runoff means that there is a broad transition zone from the inshore to offshore attenuance values and patterns. As can be seen in Figure 13 and 14, the broad transition zone is confined to the Big Bend area suggesting a rotary circulation. In fact, there are several historical lines of evidence that support the idea of a semi-permanent gyre centered over the Middle Grounds Platform (Nowlin, 1971; Leipper, 1970). Salinity and temperature data from this area over several years (Rinkel, 1976) have delineated the area as having a circulation regime differing from the surround-ing areas. Bed forms determined by side scan sonar also suggest the presence of a regular rotary current in this area (Neurauter, 1979). The presence of such a gyre ,.muld help maintain the broad transition zone and further prevent intrusion of lovl salinity waters from peak river discharge in the Northwest Region. Throughout the Hiddle Grounds Region in winter, vertical homo1 't ter,1perature, and attenuance Has the most common genlty ln sa lnl y, profile (Type B). Hm.,rever, secondary c maxima or spikes at variable p depths ere found similar to those in summer Each front established a nevT at tenuance resime. These were frequent enough to prevent

PAGE 63

54 Figure 16. Time Series 2315 Attenuance Febraury 8-13, 1978

PAGE 64

c.J) 1-0 z 20-0-0700 FEBRUARY 8 c.J) 5 10-1w 20.5 .5 >.5 0 0100 FEBRUARY 9 NO DATA 2315 0100 FEBRUARY 10 .5 .4 \Jl \Jl

PAGE 65

203 -2-3 2-3 180 (fl ..__ 75 0 10-I z 20 0-1700 FEBRUARY 10 1300 0100 FEBRUARY 12 0100 .6 c. 10.4 (fl 0::: ">.4 ).4 .4 w .4 ..__ >.3 ) .4 .5 >.5 w 20.4 30-2315 cont.

PAGE 66

57 sampling of an entire transect without interuption. During the most severe conditions sampled in this region (20 knot winds and 6 m seas), the maximum cp did not exceed 0.66 m-l (Figure 6). Generally, the attenuance values were found to be on the order of 0.25-0.45 m-1 during the interludes between fronts. Quite often the cleanest water of the profile was found near the bottom. Power spectral analysis of the near bottom c from time series 2315 gave peaks p (10.6 hours and 40 hours) corresponding about one half (10.6 hours) and twice (40 hours) of the diurnal tide frequency (Carder and Haddad, 1973). Resuspended sediment from frontal winds, waves, and currents appears to be the dominant suspended particulate matter over the winter Middle Grounds. The water column acts as a reservoir of the finer portion of this sediment and further advective activity has only a minor affect on the overall concentration. Tidally driven currents are usually not sufficient to erode enough material to affect the atmospheric frontally controlled suspended particulate concentra-tion. In fact, the tidal currents usually introduce cleaner offshore waters near the bottom. There was insufficient evidence to determine the effect of, or even delineate the presence of the Middle Grounds gyre. In winter, as was found in summer, isolated concentrations of dense algal blooms were found by the biological co-investigators al., 1977). This biogenic patchiness i s again the bes t explanation for the attenuance spikes. West Florida Shelf Summe r conditi on s ove r the \Jest Florida S h elf Region were sam pled only during 46 hours of a 120 hours time series station at 2 747 in

PAGE 67

August, 1976. The remainder of the "summer" transect sampling took place in October 1975 and November 1977 due to dictates by the con-tracting agency. These samples were collected after the onset of 58 winter fronts and exhibit more mixing than would be expected for the calmer sunmer months. To further complicate these data, the October cruise was collected about a week after a hurricane had traversed the western MAFLA, and_ the November cruise occurred after a strong intrusion of the Loop Current. Because of the size of the West Florida Shelf Region, its exposure to both cold and warm frontal winds, and its interaction with the Loop Current and eddies, this region is the most complex of the three. In light of the data, only a cursory view can be drawn on the SFM characteristics. The summer time series at 2747 (Figure 7) shows that Type A profiles are most common. There \ laS a very small de within the p surface and bottom layers. Secondary attenuance maxima were found throughout the water column. Typical values of the maxima were from -1 -1 0.25-0.35 m w1th extremely lm.v values (<0.01 m ) common in the mid\vater column. The source of particulate matter in the midwater co lumn and surface of this outer shelf station is most likely to be biogenic. This area like the Hiddle Grounds is known for extensive algal blooms (Steidinger, 1973) At the time of sampling, extensive windrO\vS of Oscillatorea were noted. Unfortunately, corresponding salinity temperature, SPH measurements, and biological samples do not exist or are unreliable due to vagaries of the contracting agency. The w inte r sampling ove r the West Florida She l f was comprised of 1976 d ne 1?0 hour time series in 1978. one 1nterupted transect 1n an o -

PAGE 68

59 Figure 17. Time Series 2747 Attenuance August 2-4, 1976

PAGE 69

1100 AUGUST 2 0100 AUGUST 3 1300 0100 AUGUST 4 10-\ \ \ IQ 1 \j I .2 I 1 \ I "' 30} 2 If ll I II ) II llf \ In I 2 w 1w I II II I II I 1\111 I I 3 soI r1 II I II \ J I I Q 70I \II I II I.Jo I I cr 2747 "' 0

PAGE 70

61 Figure 18. Transect 1100 Attenuance February 6-10, 1976

PAGE 71

(/) 0::: w 1w 110 3 "" .3 _/ // 0730 6/2 .2 1102 11 01 DEPTH SAMPLED _ .... ., 0 25 km -40 -60 -so -100 "' N

PAGE 72

63 The typical profiles seen within this limited data base included both Type A and B . The vertically mixed profiles were most commo; over the shelf in depths less than 40 m. The three layer profiles were most common on the outer shelf where clean water was available to form the midwater minimum c The actual values found on the two cross p sections are representative only of the condition at that time and would be untenable if presented as typical values for the whole region in winter. The cross sections do, however, present excellent examples of how this section of the shelf responds to winter frontal passage. The 1976 c transect (Figure 8) shows an unusual cross shelf p gradient resulting from sustained northeasterly winds (10-15 knots). The maximum c of this transect was found at midshelf (Station 1102) p after winds caused higher salinity water to be upwelled onto the shelf (compare Figures 19 and 20). The major source of material in the water was most likely due to bottom erosion and advection associated with this upwelling. In addition, the upwelling could have supported algal blooms which are not uncommon in this area in winter (Steidinger, 1973). This attenuation gradient is similar in nature, but does not occur at the 25.4 sigma-t contour which Niiler (1976) specifies as the cross shelf boundary of the winter atmospheric frontal mixing zone. Another feature of frontal passage is depicted in the time series measurements at station 2747 (Figure 21). Power spectral analysis of the bottom attenuance gave peaks corresponding to the half seiche frequency as found on the Middle Grounds Region (Carder and Haddad, 1978). It appears that frontal passage is sufficient to initiate

PAGE 73

64 Figure 19. Transect 1100 Salinity February 6-8, 1976

PAGE 74

(j) 0::: w 1w 1103 1310 6/2 110 2 < 36.4 0 1 1 01 >35.2 35.8 35.6 35 4 36.0 -40 -60 25 km -so -100

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66 Figure 20. Transect 1100 Salinity February 6-10, 1976

PAGE 76

(.{) 0:: w 1w 1103 1310 6/2 1101 < 36.4 -40 -6o 0 25 km -so -100

PAGE 77

68 Figure 21_ Time Series 2747 Attenuance February 2-7, 1978

PAGE 78

20 (j) I-0 10 z :.:: oo 0 0100 FEBRUARY 3 0130 FEBRUARY 4 01 30 FEBRUARY 5 IQ-20.2 (j) a: w I-40w {) ::i .2 I 50-60-70-G .3 eo-2747 Q'\ \0

PAGE 79

(f) t o z :.:: (/) a:: w 1w ::E 20 10 0 10-20-30-40-50-60-70so0100 FEBRUARY 6 0100 FEBRUARY 7 .2 2 r .2 D .I .I C3j '"'-2747 cont. ......, 0

PAGE 80

seiching which by frequency is co-oscillatory with diurnal tides (see Platzmon, 1973). The ebb1' d fl d' ng an oo 1ng of such currents is sufficient to resuspend bottom sediment on the outer shelf. Price and Mooers (1974) also found large amplitude inertial oscillation due to frontal passage over the West Florida Shelf. Loop Current The Loop Current regime comprises the most important current system in the Gulf by virtue of its volume (20-30 x 106m3/second) and velocity (1-4 knots) (SUSIO, 1975; Nowlin, 1971). Influence of 71 the current has been reported for the entire shelf (Leipper, 1970) and can upwell through the DeSoto Canyon in summer (Jones, 1973) and winter (Molineri et al., 1977; Huh et al., 1981). The recession of flow is often accompanied by detatchment of eddies propagate along the southern continental shelves of all three regions (Nowlin, 1971; Capurro and Reid, 1972; Rinke!, 1976; Huh et.al., 1981). The data within this study shows that the affects of the Loop Current regime will usually predominate over other SPH mechanisms either by resuspending bottom sediment; upwelling clear, nutrient-rich water near the shelf break; and/or modifying shelf circulation and strati-fication. However, no data has been collected to determine the relative influence of Loop Current water and winter frontal activity. The most pronounced occurrence of the Loop Current during the sampling was found in November 1977 when the SUH was found at the shelf edges of all transects. In the Northwest Region, the occurrence of water in excess of 36.6 /00 salinity at 80-100 m coincided with a midwater bolus of 0.10 m-l water on the outer shelf. As has.been reported in the past (Rinke!, 1976), this forcing causes the two

PAGE 81

72 Figure 22. Transect 2200 Attenuance November 12-13, 1977

PAGE 82

(/) 0:: w Iw 2212 \ .05 ) 1530 13/11 2211 l 2210 2209 2208 2207 6 -so -100 '--0 25 km -150 -200

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74 Figure 23. Transect 2200 Salinity November 12-13, 1977

PAGE 84

(f) n:: w 1--w 2212 1530 13/11 2211 36.3 2210 2209 2208 2207 -50 -100 --o 25 km 150 -200

PAGE 85

76 Figure 24. Transect 2100 Attenuance November 15-17, 1977

PAGE 86

(f) 0: w w 2106 -\ .05 -1830 16/11 2104 2102 2101 3 4 s 6 -100 -I 0 20 km -200

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78 Figure 25. Transect 2100 Salinity November 15-17, 1977

PAGE 88

(f) a:: 2106 I w _;;;;;;_____ 36.5 w 2 -36.3 1830 16/11 2104 \ MD I o 20 km 2102 I I 2101 I >35.0 17 /ll -so -100 -]50 -200

PAGE 89

80 Figure 26. Transect 2900 Attenuance November 16-17, 1977

PAGE 90

so(.f) 0:: w ...... 100w 150-19Q2957 / .0 5 1730 16/11 2958 0 1 2959 2960 >0. 3 . . 0 25 km

PAGE 91

82 Figure 27. Transect 2900 Salinity November 16-17, 1977

PAGE 92

(.{) n: w so-2957 I-100w 150->36. I 190-1730 17 /11 36. 5 2958 2959 .. 0 > 36. 1 25 km 2960 CX> w

PAGE 93

84 surface lenses to merge while migrating 1nshore. N o resuspension due to this event was measured near the bottom in either the Northwest or Middle Grounds Regions. The major influence in these regions, because it is exceptionally clean \vater, was to enhance the cross shelf c gradient (see Figures 14 and 15). p The highest attenuance values measured in sununer in the HAFLA were a direct result of a near bottom intrusion of the SUW onto the Hest Florida Shelf. As can be seen in Figures 22 through 27, the attenuance and salinity cross sections, the influence of the greater than 36.5 /00 water caused near bottom c p -1 values in excess of 2.0 m This bottom layer was homogenous (de /dz<
PAGE 94

Figure 28. Combined Time Series 1207 and Transect 1200 Attenuance September 27-30, 1975 85

PAGE 95

(/) 0:: w 1w :E 2030 L-29/9---.J 1700 28/9 1206 .. 0 1205 1204 6 <(.6 -10 -20 -30 25 km

PAGE 96

Figure 29. Combined Time Series 1207 and Transect 1200 Salinity September 27-30, 1975 87

PAGE 97

l/) 0:: w fw r---1207---, 34. 5 I '--29 /9 ----J 1700 28/9 35-0 1206 0530 28/9 0 1205 25 km 1204 32. 0 -10 -20 -30 00 00

PAGE 98

89 most of the outer transect, and the eye passed directly over deep ocean environmental data buoy, EB-10 (Hithee and Johnson, 1975). Moored in 1313 fathoms at 27'N, 88l'W, this buoy was collecting hourly data on standard oceanographic and meterologic parameters at the surface, 50 m, 200m, and 500 m. Combined with the transect sampling, the buoy data gives the first empirical view of how the outer shelf circulation responds to nearly catastrophic storm stress. The attenuance and salinity cross sections display three effects of the storm (Figures 28 and 29). The first was the mixing of upper water column \vhich by other data was shmm to extend to a depth of about 50 m, a depth greater than the shelf break in the Middle Grounds (Rinkel, 1976). The second was appearance of a distinct, near bottom layer of high salinity (36.2-36.4 /00), high attenuance -1 (0. 6 7-1.03 m ) and low temperature water. This layer was quite similar to the Loop Current intrusion found in 1977 in that the near bottom layer was homogenous and had a sharp interface with the upper \l8ter column. The third effect Has three 12 m vertical deflections of the interface that occurred about 12 hours apart (1700 Sept. 28, 0530 and 1630 Sept. 24). Similar oscillations but of longer periods (26-27 hours) were seen in ocean temperature, salinity, current, and pressure at EB-10 following the storm. A progressive vector diagram of the currents at 50 m revealed a classic inertial current pattern superimposed with a t I n part, this complex current southeasterly translatory curren diagram is due to position of Loop Current tvaters. by the level of the 20C isotherm that Molineri (1976) shows

PAGE 99

90 after the sotrm, two eddies of Loop water were situated on the North-west Region shelf break. EB-10 was located directly between these eddies which occupied a depth from 80-170 m. The main core of the Loop Current was located south of 25N, and probably, had very little influence on the MAFLA sampling during this cruise, but the eddies may have had an important effect on the Middle Ground transect. The following scenario has been formulated to account for the effect of Hurricane Eloise on suspended particulate matter over the Middle Grounds. The onset of high winds and waves caused mixing of the water column and bottom erosion. This effect of the storm is very similar to that of the initial atmospheric front of winter with one important difference. The wind and wave direction from a hurricane are continuously changing whereas a single cold or warm front has a relatively constant wind pattern. Therfore, the hurricane most probably does not have as large a net transportation of suspended material as frontal passage unless there are secondary currents in operation (Schnabel and Goodel, 1968). The presence of the distinct near bottom layer suggests the occurrence of such secondary currents. Direct upwelling is known to occur along the track of hurricanes (Icheye, 1972). As the storm center passed over EB-10 the upwelling could have caused either a single Loop Current eddy to separate into two, or at least have caused two existing eddies to migrate further apart. Either the water h Or Water forced by the velocity field directly upwelled by t e storm of the eastern eddy onlapped the shelf of the Hiddle Grounds Region. Should have then behaved as a contour current This denser water Under ;nfluence from the ambient currents: flowing downslope the

PAGE 100

91 Middle Grounds gyre, residual wind circulation, the Loop Current eddy, and/or inertial currents. The t\vo layer water column with sharp interface provides the ideal situation for propagation of internal waves which can be up several times the amplitude of the surface excitation (Roberts, 1975) and have a period near the inertial frequency (Crepon, 1971). As mentioned earlier, the exact source of periodic events in the are difficult to isolate due to the proximity of frequency of the diurnal, inertial, and fundamental harmonic periods. The amplitude of the Middle Grounds oscillation suggest a somewhat more intense disturbance than the normal periodic events. It is most likely that internal seiching was occurring due to the release of the storm surge. The most important information that this internal wave reveals is that under nearly catastrophic sized internal waves, the suspended particulate concentration on the outer shelf was not significantly more than would be expected from a series of intense winter storms. Temporal Variability The time series cross sections are the key factors to in-depth comprehension of the SPH distributions and their controlling mechanisms. Due to the lack of synopticity in transect cross sections (a problem inherent in the program design), it is possible to assume the Cross Sh elf patterns and major mechanisms, only generalities about such as runoff lenses, the Loop Current, and resu s p e nsion. As seen h 1 measurement of even the cross shelf patterns 1n t e w1nter samp 1ng was not possible du e to the hig h fre qu ency of atmosph eric frontal passage. meas u r e m ents c a n co nclu sion s be Only f rom tim e ser1es h transect SPH patterns and individual drawn on how representative t e

PAGE 101

92 fixed depth SPM samples are. To facilitate further usage of the time series data, the combined profiles for each region and season have been simplified in Figures 30 through 33. Each is broken up into four bar graphs representing the cp' s from the surface, 10 m, mid\vater minimum, and bottom; all as a function of time. The surface and bottom were included since these are the most important source depth of particu-lates. Host of the co-investigators of SPH collected their samples at or near the 10 m depth. Therefore, this trace is an example of the potential variability within these data. The midwater minimum is a variable depth view of the most particulate free water at each site. Combining the data in this manner allows a visual comparison of the amount and range in concentration of SPM on regional and seasonal basis. The relative amplitude and phase coherence of the two midwater graphs with respect ot the surface and bottom graphs gives an indication o f the vertical influence of these source depths. Of all regions, the Northwest consistently displayed the widest range of attenuance in both the summer and winter sampling In large part, this i s due to the station bei ng located between the two runoff lenses and in the shallowest water o f the time series sites. The summer graph (Figure 29) shows that the surface is the most variable trand and usually dominates all other depths. This can be accounted for b y internal waves propagating along the d e nsity interface when the lenses are present. The internal waves could then provide additional e n e r gy to resuspe nd bottom sediment. In winter, bottom resuspension was ovenvhelming d omi n ant and exhibited the d ( of attenuance measured Hi thin the two hour est range >

PAGE 102

Figure 30 Combined Time Series Attenuance Profiles from summer sampling in the Northwest Region 93

PAGE 103

SURFACE 10m MIDWATER MINIMUM Cp 1.0 1 0 0 0 1.0 1.0 0 BOTTOM 0 SUMMER 2639 2639 2529

PAGE 104

Figure 31. Combined Time Series Attenuance Profiles from winter sampling in the Northwest Region 95

PAGE 105

Cp WI N TE R 1.0 SURFACE 0 1.0 10m 1.0 0 MIDWATER MINIMUM 0 1.0 BOTTOM 0 2639 1412 2528

PAGE 106

Figure 32. Combined Time Series Attenuance Profiles from the Middle Grounds Region 97

PAGE 107

Cp 1.0 SURFACE 1.0 0 SUMMER WINTER "' 00

PAGE 108

Figure 33. Combined Time Series Attenuance Profiles from the West Florida Shelf Region 99

PAGE 109

r-' 0 0

PAGE 110

101 sampling interval (Figure 30). This supports Lesht's (1979) conclu-sian that in actively eroding areas the near bottom SPM concentrations are dependent on nearly instantaneous advective events. Also, it suggests that ther is a short resident time of particles in the near bottom layer as the larger fraction rapidly resettles out after the event. The time series in the Hiddle Grounds of \vest Florida Shelf regions were located on the edge of the outer shelf, and displayed very similar characteristics in both summer and winter (Figures 32 and 33). Both were fairly coherent with depth and had a rather small variation of c about the mean. The highest values were p usually found at the bottom. Both characteristics were more pro-nounced in winter as the water was better mixed and more resuspension was apparent. These time series graphs illustrate one of the best applications of the transmissometer, the determination of proper depth to conduct ancillary sampling. During the winter in all regions, a single sample from about 3-5 m above the bottom will usually be representative of the SPM for the entire water column. This is also true for the outer shelf of the Hiddle Grounds and Hest Florida Shelf regions during the summer. In these latter regions, it is important to avoid sample collection within one of the isolated, high density biogenic patches. This would be most easily done by use o f a transOver the Northwest Region, the mid\vater minimum represent the most stable area of the water column, the best criterion to use in establishing a baseline value. It is the opinion of the author that attempting to establish such numbers for the SPN

PAGE 111

102 distribution over the MAFLA without consideration of the controlling mechanisms present is, at best, haphazard. Due to the dynamic nature of the relatively low levels of found over most of this area, the only realistic baseline values would be for the most pristine water in this area, the Loop Current. Implication and Recommendations The sedimentary implication of this work with regard to the stratigraphic record is that the processes seen in the northeastern Gulf of Mexico affect only the upper most surficial sediments. Given the sensitivity of the transmissometer ( 0.01 m-l for c p to 0.40 m1 ) and the correlation with gravimetric SPM (SPM = 1.25 c), p the relative changes in the SPM are on the order of 10 mg/1 for most of the outer shelf. Volumetric calculation of the amount of material needed to change an entire water column SPM concentration by this amount were compared to the amount of fine material available in the box core samples from throughout the MAFLA al., 1977). The calculations show that the resuspension of the fine fraction from less than the upper 5 em (ranging up to 10 em from the coarser West Florida Shelf sediments) would be more than sufficient to account for the water column attenuances. Resuspension by winter storms, oceanic intrusions, hurricanes, and internal currents or waves is the most important sedimentary event shown by this study. Riverine derived material was found to be limited to the Northwest Region during this study. In the Middle Grounds and West Florida Shelf Regions, the runoff must either be minimal or confined to the near shore zone that was not included in the study. In these regions, the chief source of particulates is biogenic. However,

PAGE 112

with the continuous resuspension taking place in all regions even minor near bottom currents could provide significant transport. 103 Some of the most desirable data to have in conjunction with the attenuance cross section would be simultaneous measurement of the advective energy, current vectors, plus a few more concentrations and compositions by independent means. The most pertinent ancillary sampling of the study was the salinity and temperature cross sections. These were pertinent due to the fact that the sampling casts were generally taken less than 30 minutes apart. Due to the high degree of variability of SPM over most of the shelf even in areas of low concentration, it is imperative that sampling be simultaneously to assure accurate interpretations. It should be realized that the transmissometer is so sensitive to SPM changes that analysis of each causal agent would be impractical and unbeneficial. This study strongly recommends the use of long term, multi-component, in situ array s to further compliment this work in comprehension of the SPM d ynamics over the

PAGE 113

104 CONCLUSIONS Transmissometry by itself provides an adequate and rapid means of measuring the spatial and temporal variations in SPM. The technique is best suited to areas characterized by a nearly homogeneous suite of constituents in the SP}1 (constant size, and index of refraction). For such material there is a fairly linear relationship between c p and gravimetric concentration. In other areas, it is advisable to simultaneously collect samples for compositional analysis. Combination of this optical technique with salinity, temperature, wave and current measurements providessomeof the most up to data information on suspended particulate dynamics and bottom sediment stability. In an area of repeated vertical mixing, the transmissometer is a better indicator of the amount of advection than is an STD, since the salinity and temperature seldom change after the first few events. Summer SPM conditions over the l1AFLA can be characterized by three layer stratificaiton. This is most pronounced in the Northwest Region which is dominated by runoff lenses. The presence of a sharp density interface usually coincides with internal oscillations that cause bottom erosion. The stratification is not as pronounced over the Middle Grounds or West Florida Shelf Regions due to the lack of runoff or its limitation to a narrow inshore belt. In these regions, biogenic particulates are, therefore, more pronounced, and the rather low levels of attenuance maxina are more depth variable.

PAGE 114

105 Winter SPM conditions are dependent almost entirely on atmospheric frontal mixing which gives either a homogenous water column or an increasing SPH concentration with depth. The areas of finer sediments in the west tended to provide higher SPM concentra-tions. These concentrations are a function of the erodability of the sediment, the energy imparted by the front, the water depth, and the time interval since the onset of the front. After passage of several fronts, the upper water column appears to approach a steady state condition with SPH concentrations that equal the amount of fine material in the upper 5-10 em of sediment. The Loop Current is a source of nearly particulate-free water on the outer shelf of the Extreme northern intrusions of the core and eddies tend to modify shelf circulation, enhance the cross shelf attenuance gradient, and cause the Northwest Region runoff lenses to migrate shoreward. Onshelf intrusions of the Loop Current, usually only on the West Florida Shelf Region in fall, can resuspend extremely high amounts of sediment. Given the amount of resuspension seen year-round in the the Loop Current could be considered a significant transport mechanism by direct and indirect control of shelf circulation. Time series analysis of SPH concentration demonstrates that there is a highly complex periodicity to near bottom resuspension throughout the year. Seiching in response to hurricane passage and due to winter frontal passage has been suggested in this data. During reriods of intense stratification of the \vater column such as durina or in the presence of Loop Current intrusions, the 0 sharp density interface can be expected to oscillate roughly near the

PAGE 115

106 inertial frequency. Due to the amount and regularity of resuspension seen over the entire shelf, the bottom sediments should not be considered a safe sink for pollutants. These pollutants which adhere or are concentrated on particulates will have a long term effect on the water column. Given the number of transporting mechanisms in the MAFLA, e.g. the Loop Current system and wind ciruclation, such contaminated particles will have a likely chance of wide-spread distribution over the northeastern Gulf of Mexico.

PAGE 116

107 LIST OF REFERENCES Alexander, J. E., White, T. T., Turgeon, K. E. and Blizzard, A. W., 1977. Baseline monitoring studies Mississippi, Alabama, Florida outer continental shelves 1975-1976. National Technical Information Service Report No. BLH-ST-78-33, IV, Discussion. Atkinson, L. P., and Wallace, D., 1975. The source of unusually low surface salinities in the Gulf Stream off Georgia. Deep Sea Res., 23: 913-916. Austin, H. M., and Jones, R. I., 1971. Seasonal variation in bulk plankton on the Florida Hiddle Grounds, and its relation to water masses on the West Florida Shelf. Quart. Jour. Fla. Acad. Sci. pp. 17-24. Ball, T. F., and LeFond, E. C., 1964. Turbidity of water off Mission Beach. In: J. E. Tyler (Editor), Physical Aspects of Light In the Sea. Symposium Pacific Scientific Congress (lOth), pp. 37-44. Betzer, P. R., and Peacock, M.A. B., 1976. Trace metal composition of suspended matter. Final Report to Bureau of Land Management Contract 08550-CT5-30. Betzer, P. R., Peacock, H. A. B., and Jolley, R. R., 1978. Trace metals in suspended matter and zooplankton of the northeastern Gulf of Hexico. Final Report to Bureau of Land Management Contract AA550-CT7-34. Bogdanov, D. V., Sokolov, V. A., and Khromov, N. S., 1969. Regions of high biological and commercial productivity in the Gulf of Mexico and Caribbean Sea. Oceanol., 8(3): 371-381. Boston, N. E. J., 1964. Observations of tidal periodic internal waves over a three day period off Panama City, Florida. Texas A & M Research Foundation Project 286 D. Brooks, H. K., 1973. Geological oceanography. In: A Summary of the Knowledge of the Eastern Gulf of Mexico, coordinated by the State University of Florida Institute of Oceanography.

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108 Carder, K. L., Betzer, P.R., and Eggimann, D. W., 1974. Physical, chemical, and optical measures of suspended particle concentrations: their inter-comparison and application to the west African shelf. In: R. Gibbs (Editor), Suspended Solids in Water. Plenum, N.Y., pp. 173-193. Carder, K. L. and Haddad, K. D., 1978. Transmissometry on the eastern Gulf of Hexico shelves, MAFLA Survey 1976-1978. Final Report to the Bureau of Land Nanagement Contract AA550-CT7-34. Carder, K. L., and Schlemmer, F. C., 1973. Distribution of particles in the surface water of the eastern Gulf of Hexico: an indicator of circulation. Jour. Geophys. Res., 78(27): 6286-6299. Capurro, R. A., and Reid, R. 0., 1972. Contributions on the Physical Oceanography of the Gulf of Hexico. Gulf Publishing Co., Houston, Texas. Chriss, T. M., and Pak, H. J., 1977. Optical evidence of sediment resuspension, Origon continental shelf. E.O.S., 58(6): 410. Clark, G. L., and Jones, H. R., 1939. Laboratory analysis of the selective absorption of light by seawater. Jour. Opt. Soc. Amer., 29: 43-55. Crepon, M., 197. Generation of internal waves of inertial period in a t\vo layer ocean. Rapports et Proces-Verbaux, International Council Expl. Sea (Copenhagen), 162: 85-88. Doyle, L. J., Birdsall, B., Harward, G., Lehman, L., Szydlik, S., and Warren, E., 1977. MAFLA baseline study standard sediment parameters. Final Report to Bureau of Land Contract 08550-CTS-30. Dowling, G. B., 1966. Low frequency shallow water internal waves at Panama City, Florida. U. S. Navy Hine Defense Laboratory Rept., 313. 59 p. Feeley, R. A., 1975. rfajor element composition of particulate matter in the near-bottom layer in the Gulf of Hexico. Har. Chern., 3: 121-156. G "bb R J 1974 Suspended Solids in \.,Tater. Plenum Press, N.Y. l s, . 320 p. G d C 1975 Sediment entrainment and suspension in a or on, ., turbulent tidal flow. Har. Geol., 18: M57-N64 d S R H 1955 Continental terrace sedi-Gould, H. R., an tew art, .. ments in the northeastern Gulf o f Mexico. In: J. Hough and H. w. M e n ard (Editors), Finding A ncient Shorelines. Soc. Econ. Paleontol. and Nine ralog., Spec. P ubl. 3, N e w H a v en, Conn., pp. 1-19.

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109 Griffen, G. M., 1962. Regional clay mineral facies: products of weathering and current distribution in the northeastern Gulf of Mexico. Geol. Sco. Amer. Bull., 73: 737-768. Gust, G., and Halger, E., 1976. The influence of suspended cohesive sediment on boundary layer structure and erosive activity of turbulent seawater flow. Geol., 22: 189-206. Haddad, K. D. and Carder, K. L., 1979. Oceanic intrusion: one possible initiation mechanism of red tide blooms on the west coast of Florida. In: Taylor and Selinger (Editors), Toxic Dinoflagellate Blooms. Elsevier North Holland, Inc., pp. 269-274. Harris, J. E., 1972. Characterization of suspended matter in the Gulf of Mexico I. Spatial distribution of suspended matter. Deep Sea Res., 19: 719-726. Haung, ll. H., 1976. Mineralogy of suspended matter. Final Report to Bureau of Land Management Contract 08550-CT5-30. Henry, V. J., and Bader, R. G., 1961. Recent sedimentation and related oceanographic factors in the west Mississippi Delta area. Texas A & M, Dept. Oceano. Meteorol. Ref. 61-6T and 61-lOF. 187 p. Hopkins, T. L., 1973. Zooplankton. In: J. I. Jones, R. E. Ringe, 0. Rinkel, and R. E. Smith (Editors), A Summary of Knowledge of the Eastern Gulf of Mexico. S.U.S.I.O., St. Petersburg, Fla., pp. IIIF-1IIIF-10. Huh, 0. K., Wiseman, Jr., W. J., and Rouse, Jr., L. J., 1981. Intrusion of Loop Current waters onto the West Florida Continental Shelf. Jour. Geophys. Res., 86: 4186-4192. Icheye, T., 1972. Circulation changes caused by hurricanes. In: L. R. A. Capurro, and J. L. Reid (Editors), Contribution on the Physical Oceanography of the Gulf of Nexico. Gulf Publishing Co., Houston, Texas. 288 p. J b M B and Ewl.ng, M., 1969. Mineral source and transport in aco s, .. the waters of the Gulf of Hexico and Caribbean Sea. Science, 163: 805-809. J 1 N G 1968 Optical Oceanography. Elsevier, Amsterdam. er ov, . _ _ 194 p. J 1 G 1976 Optics. Elsevier Scientific Publishing er ov, t. Co., Amsterdam, Netherlands. 231 p.

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llO Jones, J. I., 1973. Physical Oceanography of the northeastern Gulf of Mexico and Florida continental shelf area. In: J. Jones, R. E. Ring, M. 0. Rinkel, and R. E. Smith (Editors), A Summary of Knowledge of the Eastern Gulf of Mexico. S.U.S.I.O., St. Petersburg, Fla. pp. IIB-1 -IIB-69. Khromov, N. W., 1965. Distribution of plankton in the Gulf of Mexico and some aspects of its seasonal dynamics. In: A. S. Bogdanov (Editor), Soviet-Cuban Fishery Research. U. W. Document TT 69-59016. Kullenberg, G., Lundren, B., Malmberg, S. A., Nygard, K., and Hojerster, N. K., 1970. Inherent properties of the Sargasso Sea, Univ. Copenhagen Instit. Phys. Oceano. Rept., 11. 18 p. Lal, D., 1977. The oceanic microcosm of particles. Science, 198 (431): 997-1009. Lavelle, J. W., Young, R. A., Swift, D. J. P., and Clarke, T. L., 1978. Near bottom sediment concentration and fluid velocity measurements on the inner continental shelf. Jour. Geophys. Res., 83: 6052-6062. Leipper, D. F., 1970. A sequence of current patterns in the Gulf of Mexico. Jour. Geophys. Res. 75: 637-657. Lesht, B. M., 1979. Relationship between sediment resuspension and the statistical frequency distribution of bottom shear stress. Mar. Geol., 32: Ml9-M27. Ludwick, J. C., 1964. Sediments in the northeastern Gulf of Mexico. In: R. L. Miller (Editor), Papers in Marine Geology: Shepard Commemorative Volume. NacMillan Co., N.Y., pp. 204-238. Manheim, F. T., Hathaway, J. C., and Uchupi, E., 1972. Suspended matter in surface waters of the northern Gulf of Mexico. Limnol. and Oceano., 17: 17-27. Maul, G. A., and Molineri, R. L., 1975. Pollutant trajectories. In: State University System Institute of Oceanography (Editors), Compilation and Summation of Historical and Existing Physical Oceanographic Data from the Eastern Gulf of Mexico. Final Report to Bureau of Land Management Contract 08550-CT4-16. Mol1 ner1 R L Ba1"o Behringer, D. W., Maul, G. A., and . "'' Legeckis, R., 1977. Winter intrusion of the Loop Current. Science, 198(4316): 505-506. M 1 R L 1976 Topography of the 20C isotherm levels in 10 1ner1, . the eastern Gulf of Mexico. In: M. 0. Rinkel (Editor), Physical Oceanography -Interdisciplinary Environmental Support Data. Final Report to the Bureau of Land Hanagement Contract 08550-CT5-30. 139 P

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111 No_ oers, C. N. K., and Van Leer, J. C 1975 Mot1."on 1."nduced by an atmospheric cold front on the edge of the West Florida Shelf on 9 February 1973. Jour. Phys. Oceano. Neurauter, T. H., 1979. Bed forms on the Hest Florida Shelf as detected with side scan sonar. M.S. Thesis, Dept. ofMarine Science, University of South Florida. 144 p. t;iiler, P. P., 1976. Observations of lm-1 frequency currents on the west Florida continental shelf. Memoires Socete Royale des Sciences de Liege, 6e serie, tome X: 331 -358. Nowlin, W. D., 1971. Gulf of Mexico. Water masses and general circulation of the Oceanology International, February, pp. 28-33. Ouellette, D. J., 1970. Suspended sediment and water characteristics. Naval Oceano. Office, Informal Report 70-7. 49 p. Platzman, G. W., 1972. Two dimensional free oscillation in natural basins. Jour. Phys. Oceano., 2(2): 117-138. Preisendorfer, R. W., 1958. A general theory of perturbed light fields with applications to forward scattering effect in beam transmittance measurements. Scripps Instit. of Oceanog. Ref. 58-37. 19 p. Price, G. F., and Mooers, C. N. K., 1974. Current meter data report from the winter, 1973. NSF Continental Shelf Dynamics Program, Univ. of Miami, Rosenstiel School of Marine and Atmospheric Science, Report No. UM-RSHAS-74020. 78 p. Rinkel, }1. 0., 1976. Physical oceanography-interdisciplinary environmental support data. Final Report to Bureau of Land Management Contract 08550-CT5-30 139 p. Roberts, J., 1975. Internal Gravity Waves in the Oceans. Marcel Dekker, Inc., N.Y. 274 p. Royer, T. c., and Reid, R. 0., 1966. Gravity waves in a rotating basin, normal modes. Texas A & M, Department of Oceanography, Ref. 66-27T. 85p. Schnable, J. E., and Goodell, H. G., 1968. PleistoceneRecent stratigraphy: evolution and development of the Apalachicola coast, Florida. Geol. Sco. Amer. Special Paper 12. 72 p. Schlemmer III, F. c., 1971. Concentration of particulate matter in the eastern Gulf of Mexico: an indicator of surface circulation patterns. M.S. Thesis, Dept. of Marine Science, University of South Florida. 82 p.

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112 Schroeder, W. W., 1975. River run-off. In: State University System of Florida Institute of Oceanography (Editors), Compilation and Summation of Historical and Existing Physical Oceano graphic Data from the Eastern Gulf of Mexico. Final Report to Bureau of Land Management Contract 08550-CT4-16. Stanley, D. J., and Swift, D. J.P., (Editors), 1976. Marine Sediment Transport. John Wiley and Sons, N.Y. 602 p. Steidinger, K. A., 1973. Phytoplankton ecology: A conceptual review based on eastern Gulf of Mexico research. In: C. R. C. Critical Reviews in Microbiology, 3(1): 49-68. The Chemical Rubber Co., N.Y. SUSIO, 1975. Compilation and Summation of Historical and Existing Physical Oceanographic Data from the Eastern Gulf of Mexico. Final Report to Bureau of Land Management Contract 08550-CT4-16. Swift, D. J.P., Duane, D. B., and Pilkey, 0. H. (Editors), 1972. Shelf Sediment Transport. Dowden, Hutchinson, and Ross, Inc., Stroudsburg, Penn. Tyler, J. E., Austin, R. H., and Petzold, T. J., 1974. Beam transmissometers for oceanographic measurement. In: R. J. Gibbs (Editor), Suspended Solids in Hater. Plenum Press, N.Y., pp. 51-59. Withee, G. W. and Johnson, Jr., A. J., 1975. Data Report: Buoy observations during Hurricane Eloise (September 19 to October 11, 1975). National Oceanographic Data Center, Environmental Data Service, Washington, D.C. r.T G 1964 Stratification and Circulation in the AntilleanIVUS t, Caribbean Basins. Columbia University Press, New York and London. 201 p.

PAGE 122

APPENDIX A chronological arrangement of the transect and time series attenuance cross sections from the three years of sampling that comprise the data base for this thesis Pages Months Year 114-115 September-October 1975 116 --119 January-February 1976 120 123 July-August 1976 124 132 October-November 1977 133140 February 1978 113

PAGE 123

.--1207----. 2030 L-29/9----..J 1700 28/9 1206 1205 0 25 km 1204 I 6 .(.6 -10 -20 -30

PAGE 124

(/) cr. w rw 1103 0600 1/10 .2 >.2 110 2 1 1 01 >' -40 -7MAXIMUM DEPTH SAMPLED -60 0 25 km 80

PAGE 125

(/) a:: w t w -1415 1830 23/1 .2 2100 22/J 1414 2300 2 2/1 :4 1413 1800 23/1 1100 11/l 0600 11/1 1412 9 .8 -20 -40 SAMPLING HIATUS -60 DEPTH SAMPLED -80 0 25 km

PAGE 126

1311 ff) a: w rw // 0700 21/1 < .2 .f' 1700 20/1 1310 .2 1'/ 0630 21/ 1 1'/ 0800 23/1 1309 0800 16/1 0 1308 s 3 -20 1040 15/1 .... -40 1700 15/1 -60 MAXIMUM DEPTH SAMPLED. -"' 25 km -80

PAGE 127

.-----12 0 7-----. 7 I 0030 0700 1200 1730 5/2 1830 4/2 1206 .3 0 1205 1204 > 2 1 0 20 30 -25 km

PAGE 128

(/) a:: w 1w 1103 # 0730 6/2 2 1102 1101 9/2 -40 DEPTH SAMPLED -60 -0 25 km -so -100

PAGE 129

181S 8/7 2639 .5 OS 10 0710 9/7 9/7 km -so -100 -lSO -200 N 0

PAGE 130

1700 JULY 10 0100 JULY II 10-20-j 0100 JULY 12> 1300> 8 0100 .I 2 3:)->10 w w 1300 0100 JULY 14 > .9 1300 0100 JULY 15 10-202639 :>. 9

PAGE 131

(/) a::: w 1w 0200 JULY 23 lQ20-1200 JULY 25 lQ-).1 2 2 20-0000 JULY 24 ).1 0000 JULY 26 0000 JULY 27 2315 0000 JULY 25 3 > 2 .2 1-' N N

PAGE 132

1100 AUGUST 2 10. 1 30(f) .2 a::: w 1w so70-0100 AUGUST 3 1300 0 1 1 2747 2 .2 J 0100 AUGUST 4 .2 Q 3 f-' N w

PAGE 133

0730 I ) _.1 10-.OS 1./) 0::: w 1w 802747 OCTOBER 26 llJO I 1500 1

PAGE 134

(/) a:: w w 2645 I 2640 2 J 2 2639 .6 0330 0030 2200 L--5-6 /ll .. ...... 0 2638 4 4 6 -25 -so 25 km -75 -100

PAGE 135

(f) a::: w 1w 2536 1 -/ 2531 .1 >.05 .. .. 0 2528 3 .2 2 1600 7/11-50 -100 -150 10km

PAGE 136

2427 (./") a:: w 1-w :E I \ 0600 8/11 .05 2426 \ I 2423 2419 \ \ I .3 3 2 -so -100 M WI o 25 k m -150

PAGE 137

(f) 0::: w ..... w 2313 2300 9/11 2316 2 0 2skm 2318 1200 9/11 -so -lQO -150 1--' N 00

PAGE 138

2212 1530 13/11 2211 1 2210 2209 2208 .:-' 0 25 km 2207 6 -so -100 150 -200

PAGE 139

(/) a:: w t w 2746 1100 15/11 2747 .1 2748 > 1 -30 -90 o 25 km -120

PAGE 140

<.n 0:: w so100w 150-1902957 / --...... .05 1730 16/11 2958 2959 2960 > 0.3 o.1 17/11 0 25 km

PAGE 141

(j) 0:: w rw 2106 \ -1830 16/11 .05 2104 2102 2101 3 4 .5 .6 -100 -I 0 20 km -200

PAGE 142

20 (/) t-0 10 z ::r:: oo 0 0100 FEBRUARY :3 01:30 FEBRUARY 4 01:30 FEBRUARY 5 -' 10-20. 2 (/) 0:: w t-40w /) ::l: .2 I 50-60.3 .:3 eo< ) 2747

PAGE 143

20 3 tfl 4 360 3 I4 0 10 40 z 340 ::.:: Q 0 100 FEBRUARY 6 0 100 FEBRUARY 7 10.2 20-30. 2 r (f) 2 a:: w 0 I-40w .I 50-60-70-C 3 j so" 2747 cont. ,_... w .p-

PAGE 144

\J') 1-0 z :::s::: \J') 20-0-0700 FEBRUARY 8 10-1w 20. 5 .5 ).5 0 0100 FEBRUARY 9 NO DATA 2315 0100 FEBRUARY 10 .5 4 1-' w l.n

PAGE 145

203 2-3 2-3 180 lf) 1-10-75 0 z 295 o -1700 FEB RUARY 10 1300 0100 FEBRUARY 12 0100 6 05 10.4 lf) 0:: '>. 4 ) 4 4 w ,4 1-') 3 ) 4 .5 >.5 w 20-,4 30-2315 cont.

PAGE 146

20 2 I 2 Vl 355 1-135 IQO 0 10 60 z :.:: 2 50 0 0130 FEBRUARY 16 0130 FEBRUARY 1 7 .5 10-Vl 0:: w 1w 20-30-

PAGE 147

20 "' 12 I I 0 10 320 320 z 35 :X:: 0 0 100 FEBRUARY 1 8 0100 FEBRUARY 19 "' 10.5 0 0: w 1.5 w 5 :::;; .I:) 6 .6 6 20->.6 >.5 >.61 6 30. 6

PAGE 148

20 ' ..... 0 1 0 ').: 3 I 210 0 10 0100 FEBRUARY 21 5 10-
PAGE 149

:0 0 w I-w 9 / 2 260 0100 FEBRUARY 23 8 35 Kts 5 265 7 6 1 7 0100 FEBRUARY 24 I 260 Ot00 25 1.2


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