Hand-held photographs taken from earth orbit are a unique resource for investigating whitings, which are the precipitation of calcium carbonate from the water column on the Great Bahama Bank. This work maps the spatial and temporal distribution of whitings, and models the lime mud budget of the Great Bahama Bank. Seventy eight photos from 37 missions and 69 mission days were selected from the Space Shuttle Earth Observations Project (SSEOP) database from the Gemini 5 mission in August, 1965, to the STS 55 flight in April, 1993. All the photos were plotted individually. The distribution of whitings mapped from the photography demonstrates that 75-85% of the whitings were concentrated in a northern basin centered around 25 N, 78' w. Whitings distribution boundaries approximately follow the 5 m bathymetry contour. The northern boundary corresponds to 25' N and the southern boundary to 23' N. The temporal data suggest that whitings occur throughout the year, and some winter whitings may be initiated by the passage of cold fronts. The size of individual whitings is as much as 200 km2 The distribution of whitings coincides with the mud and pellet mud facies on the bank top as well as the mud deposit at the lower slope depo-center along the western margin of the bank. Modeling of the lime mud vii
WHITINGS ON THE GREAT BAHAMA BANK: DISTRIBUTION IN SPACE AND TIME USING SPACE SHUTTLE PHOTOGRAPHS by YUCONG TAO A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology University of South Florida August 1994 Major Professor: Lisa L. Robbins, Ph.D.
Graduate School University of South Florida Tampa, Florida CERTIFICATE OF APPROVAL Master's Thesis This is to certify that the Master's Thesis of YUCONG TAO with a major in Geology has been approved by the Examining Committee on May 5, 1994 as satisfactory for the thesis requirement for the Master of Science degree Examining Committee: Lisa L. Robbins. Ph.D. Member : Mallk T. S taWatt, ....Ph). D
ACKNOWLEDGMENTS I wish to express my gratitude for the helpful, scholarly advice of Dr. Lisa L. Robbins, without whose concerned guidance this thesis would not have come to fruition. The remote sensing work was completed with the help of Dr. Cynthia A Evans and her colleagues, with the Flight Science Branch/Space Shuttle Earth Observations Project. Special thanks are due to Dr. Mark T. Stewart and Dr. Richard A. Davis, Jr., who were always there when I needed assistance and assurance. I will forever be appreciative of the inspiration and support of my wife, Zhiqin, who provides me with a lifetime supply of love, motivation, self confidence. To all my fellow students in the Geology Department who have helped me at some time throughout this project, I extend my very sincere thanks. This thesis was financially supported by the Electric Power Research Institute (EPRI)
TABLE OF CONTENTS LIST OF TABLES ......................................... iii LIST OF FIGURES ......................................... i v ABSTRACT ................................................ vi l.INTRODUCTION Site Description ................................... 2 Previous work ....................................... 6 Origins of Bahamian Whitings Fish Muds and Whitings ........................ 7 Physical Chemistry of Whitings ................ 8 Biologically Induced Precipitation ............ 9 Whitings as Turbulent-Flow Phenomena ......... 10 Former Research of Whitings Distribution .......... 11 Great Bahama Bank Whitings Investigation Project .. 12 2.METHODS Remote Sensing Methods ............................ 14 Photos Acquisition ........................... 15 Image Processing ...... ......... .............. 16 Data Analysis .................... . .......... 18 In situ Observation Sediment Traps and Sediment Collecting ....... 19 Sediment Processing and Analysis ....... ...... 20 3.RESULTS AND DISCUSSION Whitings Spatial Distribution Mapping of Areal Extent of Whiting ............ 23 Whitings Size and Size Distribution .......... 28 Time Series Whitings Observations ............. 30 Seasonal Variation ................................ 35 Sediment Trap Data ................. ............... 38 4.LIME MUD BUDGET OF GREAT BAHAMA BANK Lime Mud Budget Model of Great Bahama Bank ......... 41 Holocene Whitings Production via Whitings .......... 46 Holocene Lime Mud Deposit on Bank-Top ............. 48 Off-Bank Transport of Lime Mud .................... 49 Balance Analysis of Lime Mud Budget ................ 51 i
5 CONCLUSIONS ............................... ............ 54 REFERENCES . . . ......... .......... .. ........ ...... ... 5 6 APPENDICES .............................................. 60 APPENDIX 1. CUMULATIVE WHITINGS AREA AND NUMBER OF WHITINGS IN EACH PHOTOS ................ 61 APPENDIX 2. LARGE WHITINGS (SIZE>10 km2 ) SIZE AND LOCATION LIST .......................... 64 APPENDIX 3 WHOLE-BANK COVERAGE PHOTO LIST ......... 66 APPENDIX 4 DISTRIBUTIO N OF WHITINGS ON GREAT BAHAMA BANK IN JANUARY ................ 67 APPENDIX 5. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN MARCH ................... 68 APPENDIX 6. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN APRIL ................... 69 APPENDIX 7. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN MAY ..................... 70 APPENDIX 8. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN JUNE .................... 71 APPENDIX 9. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN JULY .................... 72 APPENDIX 10. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN AUGUST .................. 73 APPENDIX 11. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN SEPTEMBER ............... 74 APPENDIX 12. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN OCTOBER ............ ..... 75 APPENDIX 13. DISTRIBUTIO N OF WHITINGS ON GREAT BAHAMA BANK IN NOVEMBER .. ... ... ... ..... 76 APPENDIX 14. DISTRIBUTION O F WHITINGS ON GREAT BAHAMA BANK IN DECEMBER ................ 77 ii
Table 1 Table 2. Table 3. Table 4. Table 5 Table 6 LIST OF TABLES Hand-Held Photographs Employed for This Study ....................................... 1 7 Whitings Area and Location Observed in August Cruise, 1993 ......................... 31 Whitings Area and Location During STS-52 Mission ............ .................. 33 Monthly Cumulative Whitings Area, Mission Day, Number of Whitings, and Monthly Frequency index ................. 36 Sediment Data From Sediment traps ........... 38 Presentation of the Results of Budgetary Considerations of Lime Mud Production via Whitings on Great Bahama Bank ........... 52 iii
Figure 1. Figure 2 Figure 3. Figure 4 Figure 5. Figure 6 Figure 7. Figure 8 Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. LIST OF FIGURES Map of Great Bahama Bank ........ ........ .. 3 Sediment Facies Map on Great Bahama Bank ............................... 4 General Cross Section of Bahama Banks from Florida Strait to Tongue of Ocean ... ... 5 Sediment Trap Construction Diagram ....... .. 20 Sediment Trap Locations on Northern Great Bahama Bank ...... . .................. 21 Space Shuttle Photo in Mission STS-52 ...... 24 Spatial Distribution of 885 Whitings Mapped from 78 Space Shuttle Photos ........ 25 Bank-Top Photo Coverage Contour Correlated to Whitings Distribution Map ... 27 Whitings Distribution Map Registered with the Bathymetry Contour ........... ... 29 Statistical Distribution of the Size of Whitings ....................... .... 31 Mean Daily Atmosphere Temperature and Wind Speed during Oct. 18 to Oct. 31, 1992 . . 34 Seasonal Distribution of Whitings .......... 37 Conception of the Origins, Pathways and Final Deposition of Lime Mud, in a Shallow Bank-Top Lagoon ............... 41 Isopach Map of Holocene Sediment Thickness along Western Great Bahama Bank .44 Whitings Distribution Map Superimposed on Sediment Facies Map of Great Bahama Bank ... 45 i v
Figure 16. Conceptional Diagram of Lime Mud Budget Model of Great Bahama Bank ......... 47 Figure 17. Isopach Map of Holocene Sediment on Great Bahama Bank ....................... 50 v
WHITINGS ON THE GREAT BAHAMA BANK: DISTRIBUTION IN SPACE AND TIME USING SPACE SHUTTLE PHOTOGRAPHS by YUCONG TAO An Abstract Of a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology University of South Florida August 1994 Major Professor: Lisa L Robbins, Ph. D vi
budget on the Great Bahama Bank indicates that whitings could be a major mechanism for lime mud production. Abstract Major Professor: Lisa L. Robbins Ph.D. Associate Professor, Department of Geology Date of Approval: viii
1 1. INTRODUCTION Whitings, distinct drifting patches of lime mud, have fascinated scientists for at least 30 years (Cloud, 1962) Waters turbid with calcium carbonate mud are particularly common in subtropical seawater overlying carbonate platforms such as the Great Bahama Bank, Persian Gulf, Turk and Caicos Islands, and northwest Australian Coast (Cloud, 1962; Wells & Illing, 1964; Shinn et al., 1989; Robbins & Blackwelder, 1992). Among these, the Great Bahama Bank is the most extensively studied area. Numerous geochemical, geological and biological investigations have been conducted to document the origin of Bahamian whitings, yet their origin is still being debated. To answer the question of the origin of whitings, data on areal extent and seasonal variations in occurrence are essential, especially as they might be related to the distribution of biological, geochemical, and hydrographical conditions or even fish habitats and tidal currents. Although some aerial surveying work has already been undertaken (Morse et al., 1984; Shinn et al. 1989; Boss & Neumann, 1993), a systematic survey has not been performed and a lime-mud budget model has not been established.
2 Site Description The Great Bahama Bank comprises one of the most extensive modern-carbonate depositional systems. The region is isolated from all terrigenous sediments sources by deep channels and straits with depths in excess of 650 m (Gebelein, 1974) (Fig. 1). Great Bahama Bank itself covers about 20,000 km2 and rises abruptly up to 4 km above the surrounding depths. Throughout most of the platform, the water depth is shallower than 10 m. The general profile resembles a shallow saucer with the edges of the bank exhibiting shallower depth than the center. Tidal range is only about 0 5 m and is markedly influenced by wind. Tidal currents are greatest over the edge of the bank and become negligible near the center (Ginsburg & Hardie, 1975) The bank top water is warm (24-30C) and saline (35-42/00) Considerable effort has been expended in examining the sediments of the Great Bahama Bank (Enos, 1974; Gebelein, 1974; Wilson & Jordan, 1983). Essentially all of the major carbonate-sediment facies are represented on the bank, including extensive tidal flats (Newell & Rigby, 1959; Gebelein, 1974) A generalized map of the distribution of these lithofacies is presented in 2. Although reefs are not widespread, they are well developed along part of the west side of the Tongue of the Ocean, a deep reentrant into the bank. Skeletal sand is associated with the reefs
3 79' 78' 77 Great Bahama Bank 213" 25' 24' 24" 7f! 7fJ 77 FIGURE 1. Map of Great Bahama Bank.
79' 7f5' 79' 78" 77 77 FIGURE 2. Sediment Facies Map on the Great Bahama Bank (From Purdy, 1963). 4 28" 25' 24'
and is widespread along the bank margin throughout the northern half. Ooids are associated with relatively high-velocity tidal currents which occur along the northwest Wtsl Aodros lslond Coral aiQOI reefs Eost Moonlowtidseolevel a"io ....... ::. FIGURE 3. General Cross Section of Bahama Banks from Florida Straits to Tongue of the Ocean (From Blatt et al., 1980, p. 706). margin of the bank. The interior of the bank is a relatively low wave-energy environment and is dominated by lime mud and pellet mud. Mud is in the central area and pelleted mud covers an extensive region west of Andros Island. Probably the most extensive lithofacies is pellet sand and mud. This includes grapestones, the aggregates of pellets, ooids, or other peloid particles. These sediment 5 facies can be depicted by a general cross section across the Bahama Bank (Fig. 3).
6 Previous Work Many origins have been proposed for lime mud on Great Bahama Bank. Several workers in the early 1900s (Smith, 1926; Black, 1933; Smith, 1940a,b) favored biologically mediated inorganic precipitation, noting the supersaturated levels of calcium carbonate within the warm, hypersaline waters leeward of Andros Island. Inorganic precipitation fell from favor, however, when Lowenstam and Epstein (1957) used stable-isotope data to suggest that the Great Bahama Bank muds could be precipitated by codiacean green algae, particularly Halimeda and Penicillus. Their argument was strongly supported by Neumann and Land (1975), who showed that the standing stocks and assumed productivity of codiacean algae in the Bight of Abaco could produce more than twice the amount of fine-grained aragonite that has accumulated in the Bight. For many years the main detractor of the algal origin was Cloud (1962) who reported the low population of calcareous algae relative to the amount of aragonite mud and called upon chemical precipitation. A reconsideration of whitings led Shinn et al. (1989) to conclude that these suspended carbonates represent carbonate precipitation from the water column rather than resuspension of bottom sediment. More recently, the algal aragonite mud production estimated by Steinen et al. (1988) was as low as 20 g / m2/yr. In addition, strontium concentrations of the
Great Bahama Bank lime mud analyzed by Milliman et al. (1993) strongly support the inorganically precipitated origin. Macintyre and Reid (1992) indicated different crystal morphologies between the whitings and algal mud using scanning electron microscopy. Origins of Bahamian Whitings 7 Numerous lines of research have suggested that whitings are the major source of lime mud on Great Bahama Bank. Research has been conducted to address the whitings origin and several hypotheses of the origin of whitings have been proposed. Fish Muds and Whitings It has long been suggested that whitings are generated by the activity of bottom-feeding fish. Indeed, this idea is deeply entrenched in the common wisdom of the Bahamian people. According to this idea, schools of bottom-feeding fish ingest large quantities of bottom-sediment, extract the edible components, and eject remaining fine-grained sediment into the water column through their gills or use their heads to churn bottom sediments to generate whitings (Boss & Neumann, 1993). However, the fish-mud hypothesis suffers from several unresolved issues. First, no credible witness
8 has been able to produce tangible documentation of fish engaged in the act of generating whitings on Great Bahama Bank, despite rather sophisticated attempts to do so (Shinn et al., 1989). Second, there are presently no data to indicate that fish occur in appropriate numbers on Great Bahama Bank to account for the large number of whitings which can be observed at any one time. Third, the largest whitings (up to tens kilometers in length and breadth) would seem to require large schools of fish which have never been reported from the shallow platforms of the Bahamas (Boss & Neumann, 1993). Physical Chemistry of Whitings A reexamination of the physical chemistry of waters on Great Bahama Bank (Broecker & Takahashi, 1966; Morse et al., 1984), with respect to the relatively long residence times, provides a frame of reference from which the chemical basis for whitings phenomena may be evaluated. The critical contribution to the understanding of the carbonate system on the Great Bahama Bank was the determination of the relatively long residence time of bank top waters by Broecker & Takahashi (1966). Of particular importance was the observation that aragonite activity declined progressively from the bank margins to the bank interior, coincident with the increase in relative water age. The
9 activity, an effective ion concentration index, declined from approximately 3.5 (250% supersaturation) near the bank margins to a value of 1 .95 (95% supersaturation) in the oldest water parcel west of Andros Island (Broecker & Takahashi, 1966). The value of activity at 1 .95 suggest that the bank top water approached equilibrium CaC03 concentration during its 8 month (250 day) residence. Early studies indicated that the pH and alkalinity of waters surrounding and within whitings were nearly constant and was interpreted that CaC03 in whitings was a product of direct precipitation in seawater (Broecker & Takahashi, 1966; Morse et al., 1984). However a recent investigation demonstrates shifts in alkalinity and pH inside a whiting (Robbins & Yates, 1992). Theoretical calculations show that precipitation of aragonite within whitings will produce a significant change in both pH and alkalinity of the whiting water parcel (Morse et al. 1984). Biologically Induced Precipitation Recent observations of fine-grained calcium carbonate associated with organic floccules filtered from whitings have led to the suggestion that whitings result from largescale carbonate precipitation following cyanobacterial blooms (Robbins & Blackwelder, 1990; 1992). Biochemical data suggest that the macromolecules from carbonate
10 suspended in Great Bahama Banks whitings are distinct from those found in the lime mud sediment producer Penicillus and from the bottom sediment. Direct ultrastructural evidence indicates that mineralization occurs on the surfaces of picoplankton cells and degrading organic cellular components (Robbins & Blackwelder, 1992; Robbins & Yates, 1992; Yates & Robbins, 1994). The observed calcium carbonate crystals are distinct from skeletal debris in both molecular weight fractions and amino acid compositions. Biological mechanisms continue to be investigated. Whitings as Turbulent-Flow Phenomena Another potential mechanism involves resuspension of bottom sediment by ocean currents (Boss & Neumann, 1993). A theoretical argument was presented which illustrated the probable effects of turbulent bursts on bottom-sediment stability, entrainment and suspension during water movement over Great Bahama Bank. The bursting process is a primary source of turbulence resulting from flow boundaries and can generate velocity excursions which deviate from mean flow velocity by a factor of 4. Thus the velocities during the bursting process will be in excess of empirically determined threshold sand-transport velocities. The whole theory of the turbulent bursts (Boss & Neumann, 1993) is based on laboratory observation, and validation of the hypothesis
11 needs to be tested in the field. Former Research of Whitings Distribution Some work has been undertaken to address the distribution of the whitings on bank-top by Boss and Neumann ( 1993) The information regarding the geographic distribution (Boss & Neumann, 1993) of whitings on Great Bahama Bank was collected principally from satellite photographs obtained intermittently from 1983-1985 (personal collection of A.C. Neumann) and 1972-1975 (Morse et al., 1984) These data suffer limited temporal and regional coverage of the studied area, being restricted to only the northern part of the bank over a short period of time. These studies however offer an insight into the areal distribution of whitings in the northern part of the bank, leaving the temporal distribution untouched. Boss and Neumann (1993) concluded that the distribution of whitings on Great Bahama Bank is not random. When superimposed on Purdy's (1963) map of Bahamian sediment facies, over 90% of whitings occur over mud or pellet-mud sediment facies of central Great Bahama Bank. Of the 40 whitings observed by Shinn et al. (1989) over a three year period, 39 whitings occur over these facies (Boss & Neumann, 1993)
12 Great Bahama Bank Whitings Investigation Project This project investigates the spatial and temporal distribution of whitings using remotely-sensed imagery from a space platform. The extensive temporal and areal coverage of the Space Shuttle photographs offers a statisticallysignificant resource for investigating whitings on the Great Bahama Bank. Whitings were compiled and mapped as seen in photographs, and compared to findings of ground-based studies of the characteristics and origin of the whitings. Utilizing the information on the spatial and temporal distribution of whitings, the lime-mud budget of the bank was modeled. The work has been carried out in conjunction with Dr. Cynthia A Evans, Johnson Space Center, NASA. Information collected from the imagery includes: 1) frequency of whitings occurrence (percentage of the time are whitings actually observed) ; 2) spatial distribution, with respect to sediment facies and bathymetic condition; 3) number of whitings at a given time and area covered by whitings over time; 4) whiting size and size distribution. In situ observations were also performed. Sediment samples were collected during 3 research cruises using 3-6 sediment traps deployed at different sites on the bank. Data from the sediment traps were compared to the remote
13 sensing data, and served as the confirming evidence. A study of the natural sinks of C02 such as whitings, has been a major concern in recent years due to the role of C02 in global climate change. Whitings are, at least in part, biologically-induced precipitation from the water column (Shinn et al., 1989; Robbins & Blackwelder, 1992; Robbins & Yates, 1992), and have significant implications in the global carbon cycle and C02 budget. Whitings may also be a modern analog to the formation of ancient occurrences of lime mud, and serve as the model for understanding ancient or global carbon cycles.
14 2. METHODS The data collected for this study are composed of Space Shuttle photographs and sediment samples. Remote Sensing Methods This study focused on the geographical extent and seasonality of whitings on the Great Bahama Bank. Data used here were drawn from more than 100,000 frames of NASA space photos taken since Mercury-Redstone 3 in July 1962 to the most recent Space Shuttle mission STS 56 in April 1993 from the Space Shuttle Earth Observations Project (SSEOP) Database. The hand-held imagery has been proved to be a significant resource for geological application by numerous workers (Helfert & Lulla, 1989; Lulla et al., 1993; Andreae, 1993). Details on the camera systems and videographic systems used during these space flights have been addressed in Amsbury and Bremer (1989) and Lulla and Helfert (1989). Two types of cameras are used for most photos: Hasselblad and Linhof systems. Most photos of Earth are acquired using NASA-modified Hasselbald SOOEL/ M 70 mm cameras. Standard lenses include a Zeiss 50-mm, a 100-mm and a 250 mm. The Linhof system was flown on eleven Space Shuttle missions and
15 was fitted with interchangeable Linhof 90-mm and Linhof Tele-Arlon 250-mm lenses. This camera provided excellent large format photos that cover a much larger area than the Hasselblad 70 mm photographs, yet it has the same resolution. The Hasselblad cameras provided areal coverage of 65x65 km to 330x330 km, and resolutions of about 30 to 150 m, depending on the focal length of the lens employed. Oblique photos show broad regions stretching out to the horizon. Two types of films were employed including color visible (Kodak 5017/6017 Professional Ektachrome, ASA 64) and color infrared (Kodak Aerochrome 2443). Photo Acquisition The SSEOP database is public-domain which is accessible on-line via computer networks at the following address Internet sseop.jsc.nasa.gov The username and password are both "photos". The photo list can be sorted by several queries, including LL (latitude/longitude), LLM (latitude/longitude+ mission), GEO (geographic location), GLL (latitude/longitude + geographic location), GMS (geographic location + mission) as well as MRF (mission + roll + frame). In this project, GEO and GLL were used as searching queries, and up to 1,000 photos were downloaded in this way. The photos are available at
Lunar and Planetary Institute Planetary Image Center 3303 NASA Rd.l Houston, TX 77058. Image Processing Approximately 1,000 photo transparencies from the 1960's Gemini flight, the Skylab missions (1970's) to the Space Shuttle missions (1981 to present) were screened and 359 photographs covering the Great Bahama Bank were selected. These photo transparencies were inspected in detail and 78 of the photographs showing whitings from 69 16 individual mission days of 37 missions were selected (refer to Table 1) Another 35 photographs either did not cover the whole study area or were highly oblique or hazy. We classified these 35 photos as non-usable instead of non-whitings. Interpretation of the selected earth-viewing photography was based on a priori knowledge of the geography of the Great Bahama Bank. Whitings were clearly visible from space; the features are large (from a few hundred meters to tens of kilometers), and the milky water contrasts well with the surrounding clear, blue water. These characteristics were used in photo-interpretation. A Bausch & Lomb Zoom Transfer Scope was employed for photo rectification and registration. Landscape features were utilized for visual matching between adjacent and
TABLE 1. Hand Held Photographs Employed for This Study. Mission Date (MM-RR-FR) (YY-MM-DD) GEM 05-01-45759 65-08 GEM 12-08-63420 66-11-11 SL 02-05424 73-11-06 STS 05-39-1058 82-11-15 STS 41G-12097 84-10-STS 51C-36-35 85-01-25 STS 51835-67 85-05-01 STS 51J-143-5 85-10-STS 618-12150 85-11-27 STS 26-32-1 7 88-09-29 STS 29-9380 89-03-15 STS 33-87-34 89-11-26 STS 31-731 90-04-25 STS 31-8108C 90-04-27 STS 39-72-85 91-04-28 STS 4079-42 91-06-11 ST$43-76-87,88,89 91-08-03 STS 48604-102 91-09-15 STS 41-151-3,5 91-10-07 STS 45-78-16 92-03-26 STS 49-85-63 92OS -11 STS 49-92-88 92-05-13 STS 5081-29 92-07-02 STS 46-8330 92-08-01 STS 46-75-58 92-08-04 STS 52-151-52 92-10-23 STS 52-153-71 92-10-25 STS 52-153-236 92-10-29 STS 53-75-69 92-12-03 STS 53109Q 92-12STS 54-7409 93-01-14 STS 54-151-162 93-01-17 STS 5610078 93-04-14 STS 55-78-26 93-04-28 STS 55-152A-47 93-04-30 MM: mission number RR: film roll number FR: frame number Mission Date (MM-RR-FR) (YY-MM-DD) GEM 07-22-63825 65-12-05 GEM 12-17-62903 66-11-12 SL 04-139-3919 74-01-22 STS 0639190 83-04-04 STS 41G-39-97 84-10STS 51C-44-67 85-01-26 STS 518-147-2 85-05-03 STS 61A-20098 85-11-03 STS 618-121-115 85-11-28 STS 29908 89-03-14 STS 3076-18 89-05-05 STS 36-78-99 90-03-02 STS 3 1-151-157 90-04-26 STS 37-76-5 91-04-09 STS 4075-39 91-06-08 STS 40-613-50 91-06STS 43-151106 91-08-09 STS 48-78-28 91-09-16 STS 448096 91-12-01 STS 49-88-104,105 92-05-08 STS 49-79-59 92-05-12 STS 49-9960 92-05-15 STS 50-77-35,45,46 92-07-04 STS 46-86-65 92-08-02 STS 47-78-49 92-09-14 STS 52-151-256 92-10-24 STS 52-153102 92-10-26 STS 52-77-93,94,95 92-10-30 STS 53-81-82 92-12-06 STS 538078 92-12-08 STS 54-152-243 93-01-16 STS 56-91-26 93-04-11 STS 55-72-77 93-04-27 STS 55-73-35 93-04-29 17
18 overlapping photographs to ensure the matching of boundaries. 1 :1,000,000-scale Operational Navigation Charts (ONCs) were used to derive the whitings edges and to locate whitings features. The photographs, representing 69 mission days, were registered to 69 ONCs maps. Data Analysis Once the whitings were registered on the ONCs, the outlines of whitings for each set of photographs and for each mission date were digitized by a PC-based Bio-Scan system. The whitings size and center of mass were then computed and recorded in a spreadsheet format into 69 files representing 69 ONCs maps (see Appendix 1 ) Spreadsheet files were saved in ASCII format, which were then imported into Lotus. The range, mean and standard deviation were calculated for each file. Size distribution of whitings was calculated by combining the entire files. Seasonal variation of whitings was calculated by grouping the files according to the month when the photo was taken. Because the Bio-Scan system lacks mapping ability, the ONCs maps were digitized into AutoCad. In AutoCad, each whiting is represented by a circle, the centroid of the circle is the center of mass of the whiting and the size of the circle represents the size of the whiting. Since the Space Shuttle photographs are not temporally
continuous, analysis of seasonal distribution was achieved by the use of a whitings frequency index: monthly cumulated whitings area Frequency Index mission days 19 This method is used to eliminate at least some of the bias introduced by the uneven distribution of the mission days (Andreae, 1993). The frequency index variation in this work is assumed to represent the monthly variation of whitings. In situ Observation To measure rates of deposition of calcium carbonate, sediment samples from six sediment traps were analyzed. Sediment Traps and Sediment Collecting Three sediment traps were constructed using two removable PVC pipes mounted on a 0.6x0.6 m cement base (Fig. 4) Anti-fouling paint was brushed on the outside of the pipes to prevent the growth of encrusting organisms. The bottom of each pipe was filled with 1 liter 5% buffered Formalin in a hypersaline seawater, as a preservative, and the remainder of the pipe was filled up with sea water (Knauer et al., 1979). The sediment trap locations are listed in Figure 5. The traps were placed at field
CABLE DIAGRAM OF SEDIMENT TRAP PVC PIPE BAFFLE CEMENT BASE HOSE CLAMP FIGURE 4. Sediment Trap Construction Diagram. 20 locations in reference to the whiting distribution. The first set of sediment samples were obtained after a 6.5 month residence time on the bank top (Dec., 1992 -May, 1993). Two samples were impregnated and four were dried and weighed. The second set of sediment samples were collected after 2 5 months (May, 1993 -Aug. 1993). During this period, two of the sediment traps were buried in the sand and only 4 valid samples were obtained. Sediment Processing and Analysis Once the sediment traps were collected, some of the
79" 78" Great Bahama Bank 26" 10 9 8 7 1211 D D D D D D 5 6 2 0 D 77" Cruise 1( 12/92-05/93) 2. 25"10'N,78"24'W 3 25"10'N,78"24'W Cruise2(05/93-08/93) 4. O'N, 76"24 5. 25"13'N,78"23'W 6. 25"14'N,78"17'W Cruise3(08/93-Presenl) 7. 25"23'N,78"30'W 8 25"23'N,78"36'W 9 26"23'N,78"41'W 10. 25"23'N,?8'46'W 11. 25"23'N,7B"55'W 12. 25"20'N,7B"55'W 25" 79" 78" 77' FIGURE 5 Sediment Traps Locations on Northern Great Bahama Bank. 26" 25" N .......
22 holders were air-dried and impregnated with resin so that depositional rrevents11 could be evaluated. Because storm activity can resuspend bottom sediment, it was expected that a coarse layer might be observed in the impregnated sediment section. The remainder of the sediment was oven dried and weighed. Yearly calculations from the weight data provide an estimate of the carbonate sediment accumulation rates. These data were then compared to the remote sensing results.
23 3. RESULTS AND DISCUSSION Whitings Spatial Distribution The large number of photos from the NASA/Space Shuttle Earth Observation Project (SSEOP) database provides an significant resource to investigation spatial and temporal systematic of whitings. Figure 6 is a sample of a near vertical photograph of whitings on the northwest section of Great Bahama Bank. The photograph was taken from Space Shuttle Mission STS-52 (Oct 25,1992). Approximately 30 individual whitings are concentrated in the Northwestern region of the bank. The turbid water contrasts well with the background clear blue water. The largest whiting is nearly 31 km2 while the smallest is only 0 .64 km2 S-SE winds were moderate at 20 km /hr. The cumulative whiting size was calculated to be 97 km2 and center of mass was at 2503' N, 78' W Mapping of Areal Extent of Whitings Figure 7 is a map of spatial distributions of whitings documented during 37 missions. 69 ONCs maps, totalling 885
24 FIGURE 6. Space Shuttle Photo Taken in Mission STS52, showing whitings, elongate and white features on the northern part of the bank.
25 79" 78" 77" Great Bahama Bank 28" 25" 24" FIGURE 7. Spatial Distribution of 885 Whitings Mapped from 78 Space Shuttle Photos. Whitings demonstrate dense distribution in the northwestern part of the bank around 2 5 N 1 7 8 50 I w.
26 individual whitings were registered on the Great Bahama Bank. Whitings were represented by circles, the centroid of the circle is the whiting center of mass and the size of the circle is the same as that of whitings. The whitings distribution is not random. As noted, numerous whitings overlapped each other showing a very concentrated distribution on the northwest region of the bank. The northern boundary of whitings distribution is approximately at 2530' N while the southern boundary is about 2345' N Approximately 885 whitings are centerP.d near 2502' N, 7848' W, and that area accounts for about 75-85% of whitings occurrence. However, whitings were also often found in the southern central part of the bank. These whitings are much smaller and more spatially dispersed than their northern counterparts. This is the first time that whitings have been documented in the southern area where in situ observations are limited. Our data show that the restricted whiting distribution on the Great Bahama Bank is not biased by the photo coverage. Figure 8 is a photo coverage map of the bank top. The highest percent of coverage is at the center of the bank, however, the regions outside the whiting distribution boundary still have photo coverage of no less than 40%. In addition, there is a conspicuous offset between the center of the whitings distribution and the highest photo coverage. Therefore, our photos have an unbiased coverage of the
Great Bahama Bank 28" 25. 24. 79' 7B" 77 FIGURE 8. Bank Top Photo Coverage Contour Correlated to Whitings Distribution Map, showing that the regions to the extreme north and south part of the bank still have at least 40% photo coverage. 27
28 entire study area; there are not any whitings formed in the regions at the extreme northern and southern part of the Great Bahama Bank. Figure 9 is another whitings distribution map coregistered on a Coastal & Geodetic Survey map. The bathymetric data is from Cloud (1962) Bathymetric contours in Figure 9 show two shallow basins on the bank top. Both of them are located at the central region of the bank with one in the north and another in the south. The whitings appear to be concentrated within these shallow basins. In addition, the boundaries of the area of highest whiting concentration loosely follow contours. The 3 fathom contour marks the western boundary while the 4 fathom contour marks the eastern boundary. The high concentration of whitings in the northern basin raises the question of why there is such a high concentration of whitings in this area and makes it a worthwhile area to study in detail. Whitings Size and Size Distribution In a review of 78 photographs, almost all the large whitings (individual size >10 km2 ) occurred in the northwest corner of Great Bahama Bank (see Appendix 2). In contrast, along eastern part of the bank, as well as the southern part, no large whitings were observed. The data show that among 57 big whitings events, 53 (93%) occurred in the
25' 24" 79' 79" 78" Great Bahama Bank 76' 0 tl} .,..... -3-fathom 9-' 29 77 26' 25" 24" 77 FIGURE 9 Whitings Distribution Map Registered on the Bathymetry Contour (From Cloud, 1962). The whitings are located in the relatively deep basins, but concentrated in the northern basin at 25 N.
30 northern basin which was centered around 25' N, 7850' W. Only 4 (7%) of the whitings occurred in the southern basin. The probability of occurrence of large whitings increases with the overall frequency of whiting occurrence. It is possible that large whitings are made up of a series of parallel elongate whitings with their boundaries fused together. This is one possible explanation based on photo observation, however geochemical research is needed to further investigate of the relationship between the spatial distribution and size variation of whitings (up to 53 km2 ) The individual whitings size statistics (Fig. 10) show that whitings range from 0.1 km2 to 53 km2 in size, but the 885 whitings studied hav e a 3 7 km2 a verage size and 4.5 km2 standard deviation. This means that 70% of the whitings fall in the 0-8 km2 size range. In situ measurements of five whitings were conducted in August 1993 from the RV Bellows, a 22 m research vessel operated by the Florida Institute of Oceanography. Sizes and locations of the whitings were registered using an onboard Loran system (Table 2). Although the ground data lack statistical significance, the 3.1 km2 average whiting size is close to the remote sensing results. Time Series Whitings Observations As noted, a group of whitings lasting for seven days
0.3 ().25 0,2 0.15 ..u 0.1 o .ce \ \ 0 0 10 20 30 size (km2) FIGURE 10. Statistical Distribution of Size of Whitings. eo 70 TABLE 2 Whiting Area and Location Observed In August Cruise, 1993. Date Latitude Longitude Size (km2 ) (N) (W) 8 /14/93 2511'75" -78'50" 1. 58 8 /15/93 2511'75" -787'60" 1. 69 8/15/93 2510'75" -78'25" 3.93 8 /16/93 2510 I 2511 -78'25" 3.39 8/16/93 251 00 II -78'00" 4.73 31
32 was documented during mission STS52 (Oct. 23, 1992 to Oct. 29, 1992). Five photographs from Oct. 23-29, documented the evolution of a group of whitings from immature to an advanced stage. The whiting sizes and locations are listed in Table 3 These data show that the group of whitings not only changed location, but also changed in size while retaining shape and spatial arrangement. This is the longest duration of any documented whitings. This event may have lasted even longer because whitings were still prevalent on the last day of the photo coverage, Oct. 29, 1992. In a previous study, in situ observation indicated the longest duration of individual whiting was 72 hours (Shinn et al., 1989). Weather information during this period of time was retrieved through daily NOAA broadcasts. Figure 11 is the mean atmosphere temperature and the mean wind speed from Miami weather station during Oct. 15-Nov. 15, 1992. During Oct. 23-24, the temperature decreased rapidly during NE and N winds, some as strong as 50 km /hr, indicating passage of a cold front. Once the cold front passed over the bank, the temperatures were low and weak SE-S winds dominated during Oct. 25-29. Thus, during these seven days (Oct. 23-29, 1992), the first two days' weather (Oct. 23-24) showed a rapid temperature drop and strong NE-N winds; the remaining five days (Oct. 25-29) had low temperatures and weak winds. In addition, the observations from these photos show that
33 Photo ID STS52STS52-STS52-STS52STS52151-52 151-256 153-71 153-102 153-236 Date 92-10-23 92-10-24 92-10-25 92-10-26 92-10-29 (YY-MM-DD) Whitings 26 28 30 20 27 Number(ea) Area Per 60 50 97 145 120 Scene (km2 ) Location 2507' N 2509' N 2503 I N 2506' N 2506' N 7850' w 78 49' w 7847' w 7851' w 7843' w TABLE 3. Whitings Area and Location During STS-52 Mission the bank water was turbid and cloud cover was as much as 70% during Oct. 23-24, 1992; whereas in the remaining photos, taken on Oct. 25-29, 1992, the sea was calm, the water was clear, and the cloud cover was no more than 20%. Therefore, the data indicate that the group of whitings documented in STS 52 mission coincided with strong NE and N winds and the rapid drop in temperature when the cold front swept across the bank. After passage of the cold front, whitings doubled their size and kept enlarging during the extended period of weak winds and low temperatures. In addition, photos in STS 52 show that elongate whitings evolved during this weather change over the seven days. Whitings in the first two days (Oct. 23-24) were unidirectional, oriented toward the south, which was the wind direction. Whitings in the remaining days had two different orientations. The whitings along the western
r.r.. 0 Q) H ::l .j..) m H Q) 0., E Q) .j..) Q) H Q) ..c: 0., UJ 0 E .j..) m s:: m Q) E H ..c: .......... .Q '"0 Q) Q) 0., UJ '"0 s:: -rl 82 82 80 78 78 74 72 70 I W//1 W/1 WA WA W/1 V/41 V/A W//1 V/A V/A WA WA W/11 V<1 1 ...,'b -\ n"-r# Cf r#IJ' Cf1J> d'i1' / rP"' cl / / / or' 50 50 50 1........................................... "17"7771 -------Photo-Coverage -45 I-. . P7 Cold Front 40 35 30 25 ro I V//1 V///1 V/U1 V///1 V/A I V/Ld WLA V///l V// /1 V///1 V/%1 V///1 V///1 r// /A I d'i ... fb c;IJ' Of"J> Of
35 margin were oriented east-west and those whitings in the north were oriented northwest-southeast. These orientations do not reflect the wind direction, suggesting that these whitings may be influenced by tidal currents, as stated by Shinn et al. (1989). Therefore, the long axis of whitings appear to be oriented by currents. Current directions are determined by wind, by tide, or by combination of both. Seasonal Variation In reviewing the entire database, there are 78 photographs showing whitings and 35 photos with obscured views. The data indicate that whitings occur year-round. Figure 12a is a frequency index graph of the whiting area, showing a bimodal distribution with one peak of up to 74.7 km2 of whitings per day in April. Other peaks occur in October, November and December at 72. 1 50.46, 51.9 km2 per day, respectively. The low frequency months are May, June, July, August and September, with about 30 km2 of whitings per day. Because the frequency index is correlated to the mission distribution, the April peak may be a bias induced by the uneven mission days (April has 13 photos whereas February has no data) Summer months also may show this bias of less mission days. The mission day and frequency index value are listed in Table 4. In order to a void bias, a statistical test was run which randomly chose two photos
36 from each month, and the whiting frequency index was represented by the sum of the whiting area from these two photos. The results remain the same (Fig. 12b) however. According to the data, whitings may occur more frequently in the winter. As observed fro m the STS 52 photos, more winter whitings may be due to t h e frequency o f the passage of winter cold fronts. It is possible that as the cold front passes, strong NE-N winds sweep through the shallow bank, stirring up bank sediment. After passage of the cold front, however whitings appear t o persist, despite calm conditions. This suggests that they may be influenced by a geochemical or biological processes. Our temporal data contradict earlier observations that whitings d o not seem t o be more prevalent during the winter storm season than at other times (Shinn et al. 1989) However, whitings are TABLE 4 Monthly Cumulative Whitings Area, Mission Day, Number of Whitings, and Monthly Frequency Index Jan Feb Mar A p r M a y Jun Jul Aug S e p Oct Nov Dec whiting area (km2 ) 177 N / A 113 971 220 95 6 5 183 63 721 404 311 day s 6 N / A 4 13 8 3 2 6 4 10 8 6 no. of 46 N / A 28 133 28 24 9 77 1 6 229 107 113 whiting(ea) f r equen c y 30 N / A 58 75 76 32 33 31 1 6 72 50 52 Inde x ( k m2/ d ) averag e 3 9 N / A 2 7 3 4 7 2 4 3 4 3 size (km2 )
X Q) '0 c H-:>, ;:..,rrs u'O C Q)"' ;::l = 0'..1<: t:I.. X Q) '0 c H ;:..,_ U N c = Q)..l<: Q) t:I.. IKl 70 l. . . ......................... .. IKl F........... ........................... :[ ....... :: ::::::: 30 F, > > > > ........... ...... ... 20 10 O l;f////d t'////1 1////d V///d V///1 [(///,j V///d V//61 V//(d 1////.j V/f /c1 I J8n Feb Mer Apr liXI 250 200 1!50 100 !50 May Jun .lJI Aug Whldf"ll seasonal vartatlon on Greet Behe1n11 Bank (A) Sep Oct Nov Dec 0 CV/// A (////! 1/ ///d V/(/d V///tl V/(/ J r///(L ... V///4 r////] [////1 (////! I Jan Feb Mer Apr May Jun Aug S8p Oct Nov Dec Whiti'lQ aeeeona1 verlation on Greet Bahema Benk (B) FIGURE 12. Seasonal Distribution o f Whitings. (A) Frequency Index: whitings area normalized to mission days. (B) Whitings area from 2 photos chosen randomly each month. w -..]
38 much more difficult to observe from ships in the rough water of winter. Sediment Trap Data According to the whiting distribution map (Fig 7), whitings usually occur in the northwestern part of the bank, centered at about 25 N latitude. Sediment traps were deployed approximately 8 kilometer apart on a transect along 25 N latitude between Andros Island and western edge of Great Bahama Bank The sediment trap locations and the sediment data are listed in Table 5. In the May, 1993 cruise, 6 samples were retrieved. Sample 1-4 were o ven-dried and weighed. Sample 5-6 were air-dried, and TABLE s. Sediment Data From Sediment Traps. Cruise Sample Mean Sediment Sediment weight Weight accumulation accumulation rate date No. (gram) (gram) time (month) (gram/month) 1 88.13 2 100.9 May, 3 38.72 6.5 1993 93.13 (Dec. 92 May, 93) 14. 3 4 144.78 5 N / A 6 N/A 1 4 .82 A u g 2 4 .41 2.5 1993 4 6 (May, 9 3 Au g 93) 1.8 3 N/A 4 N/A
39 impregnated. Sample 5 contained as much as 10% of sand, which were composed of biogenic debris. The size of debris ranged from 0.5 mm to 2.4 mm, including bivalves, corals, gastropods. The thin sections from the samples 5-6 do not show coarse storm layer within mud portion, however, the coarse biogenic debris in sample 5 formed a 5 mm layer on the top of impregnated sample. Four samples were collected in the August cruise. Sample 1-2 were oven-dried and weighed, while sample 3 4 were air-dried. As noted, there were no sand size sediment and no coarse layer found in this set of samples. In addition, the average sediment accumulation rate of samples collected in the May cruise was much higher than that in the August. While it is inappropriate to conclude much concerning the two sets of samples. However, the impregnated sample didn't show any storm stratification, the storm effect could not be excluded.
40 4 LIME MUD BUDGET OF GREAT BAHAMA BANK Studies of the rates of deposition of widespread lime mud on the Great Bahama Bank are necessary if we are to properly understand the role of whitings in this process. The long term aerial photo data offer an unique insight into the budget of lime mud. This mud budget model is modified from Neumann and Land (1975), who discussed the major sources of sediment influx and outflux on the Little Bahama Bank in detail (Fig. 13). They included mechanical processes, biological disintegration, chemical precipitation, bacterial precipitation, and erosion of tidal flat. Howe ver, the y used a simple model for calculation where benthic algal disintegration was regarded as mass influx, off bank transport as mass outflux and bank-top deposition as mass storage. In addition to factors included in the Neumann and Land (1975) model, this study includes whitings events as a major source of lime mud production on the Great Bahama Bank. Lime Mud Budget Model of Great Bahama Bank Robbins and Yates (1992) indicated the presence of picoplankton species in whiting water, and suggested that
41 B..ia.bt of Ba!J,qm.R .c;r Cl4t-'\ICAL i>P"r. ?PT. BL..U-RfEI'J t PPr. 01= TIOAL MUD Ol=FA?-Jk T'RA.N S?oRT LOSSES FIGURE 13. Conception of the Origins, Pathways and Final Deposition of Lime Mud, Particularly Aragonitic Mud in a Shallow Carbonate Bank-Top Lagoon. The speckled portion represents that route believed to be most significant (From Neumann & Land, 1975).
the cells of these blue green algae, Synechococcus and Synechocystis, may undergo epicellular precipitation of calcium carbonate induced by photosynthesis to form whitings. Therefore, it is proposed that whitings are the major mud producer on the Great Bahama Bank. There are several line of evidences which support this hypothesis. 42 Wilber et al. (1990) complied a map of mud thickness at the lower depo-center along the western margin of the bank. They noted an asymmetric progradation of the lower slope depo-center (Fig. 14). The maximum progradation is in the middle of the profile at about 25 N. Sediment thickness decreases gradually toward the south and decreases rapidly toward the north from 25 N. The progradation abruptly ends at 2530' N. The lower slope deposit at the Bimini/Riding Rocks area is separated from the southern depo-center and has less lateral progradation. The data presented here show that the progradation of the mud deposit (Wilber et al. 1990) has a similar latitudinal range as the whiting distribution (Fig. 7). The northern whitings boundary is at 2530' N and the southern end at 2345' N, with the maximum occurrence of whitings at 2502' N. This indicates that distribution of whitings may be related to the progradation of mud at the lower depo-center along the western margin of the bank. Furthermore, Wilber et al. (1990) addressed the lithologic similarity between the mud from lower depo-center and the bank top aragonite mud and suggested that the mud in
43 the lower depo-center is transported from the bank top. If a map of distribution of whitings is superimposed on Purdy's (1963) sediment facies map, most whitings occur within the mud facies in the central part of the bank and the pellet-mud facies in the east-central part of the bank. Some occurrences of whitings fall within the oolitic and grapestone facies. However, the distribution of whitings largely coincides with the distribution of mud on the bank top. All of these observations are indications that whitings may be the major mud producer on the bank. The distribution of whitings determines the distribution of the mud facies on the bank top and the location of the lower depo-center. Most of the mud produced on the bank top is transported off-bank. Neumann and Land (1975) reported that following a three-day period of high northerly winds in October, 1965, plumes of muddy white water poured off the Great Bahama Bank near Cat Cay, south of Bimini on an ebb tide. Later work by Wilson and Roberts (1992) suggests an accelerated off-bank transport of sediment by sediment-charged hyperpycnal (super-dense) platform water. High-resolution seismic stratigraphy by Wilber et al. (1990) suggests large-scale export of bank top sediment and rapid progradation of the slope during the Holocene. Therefore, lime mud transported off-bank is assumed to be the major outlet.
24'00'+ HOLOCENE SEDIMENT THICKNESS -Weslvn Gr.(lf Bohomo lk'flt-.1. 79'CJS I 7lr.tj FIGURE 14. Isopach Map of Holocene Sediment Thickness Along Western Great Bahama Bank. Isopleths in meters. Figure is longitudinally exaggerated Sx (From Wilber et al., 1990}. 44
28. 25. 79. 78. 77 Great Bahama Bank 26" ef L:J u wtone I 25. ud 24. 79. 7o 77 FIGURE 15. Whitings Distribution Map Super imposed on Sediment Facies Map on Great Bahama Bank (From Purdy, 1963) 45
46 In the following section, a model of lime mud budget is presented (Fig. 16), which uses mass influx from mud produced by whitings and the lime mud produced by codiacean green algae. Mass outflux is off-bank transport and mass storage is the volume of lime mud on the bank-top within the area of the mud and pellet mud facies. The mass balance of this system follows the equation: Massstorage = Massinflux -Massoutflux (1) Holocene Lime Mud Production via Whitings The Holocene began no earlier than the last glacial retreat, 9000 years BP (Cloud, 1962). Neumann and Land (1975) calculated the rate of mud production on Little Bahama Bank and suggested 5,500 years BP as the beginning of Holocene deposition. Recent work on Holocene sea level in Bahamas (Boardman et al., 1988) indicated 6,000 years BP as the initiation of Holocene deposition in Bahamas. This date estimation is similar to that used by Neumann and Land (1975) and is used in this study as the date for initiation of Holocene deposition on the Great Bahama Bank. The cumulative daily area of whitings is as much as 200 km2 with an average whiting area of 35 km2 As previously noted, about 85% of the photos hav e only partial coverage of the study area. In order to minimize bias from partial
lifest Mass Outflux: Off Bank Tranport Major mass influx: tlhitings Andros Is East Mass Storage: Bank Top Mean low tide sea FIGURE 16. Conceptional Diagram of Lime Mud Budget Model of Great Bahama Bank. Whitings is the major mud producer, some of the mud deposit on the bank while most of them offbank transported. ....,J
48 photo coverage, 10 whole bank coverage photos were selected. From these photos, the average daily whitings area was calculated to be 70 km2 (see Appendix 3). The 70 km2 a day case is likely to be encountered in nature, whereas a chance of 200 km2 a day whitings area is rather small and the 35 km2 a day whitings area is also an underestimate of the whitings areal extent. Each of these three cases is discussed below. The 70 km2 a day case will be used as a average condition, and the 35 km2 a day case is used as the lower limit while the 200 km2 a day case is discussed as the upper limit. Using the assumptions that the water column is 5 meters deep, the specific gravity of wet aragonite mud is 1,150 kg/m3 (Neumann & Land, 1975), the average whitings density is 10.6 g/m3 (Shinn et al. 1989), and assuming the mud production rate has been constant during the Holocene, at 35, 70, 200 km2 daily whitings area, whitings could produce 0. 35x1010 m3 0. 7x101 0 m3 and 2 Ox1010 m3 of mud respectively, over the 6,000 years period of deposition. Holocene Lime Mud Deposit on Bank-Top Strontium concentration data led Milliman et al. (1990) to conclude that only about 25% of the mud on the Great Bahama Bank is produced by codiacean algal aragonite, corroborating with an estimate made earlier by Cloud (1962) Assuming 25% algal aragonite, whitings aragonite accounts
49 for 75% in a two element case. Figure 17 is isopleth map of bank-top sediment (Cloud, 1962) Because the contour follows the mud and pellet mud facies boundary of Purdy (1963), the contours are used as thickness of mud layers. The mud volume is thus simplified to the summation of three layers, which is composed of a one meter contour layer, a two meter contour layer and a three meter contour layer. Digitizing the contours, the volume of these closed contours is about 1.1x101 0 m3 0. 4x1010 m3 and 0. 012x1010 m3 respectively. The total volume is thus no more than 1. 7x1010 m3 According to Steinen' s estimation (Wilber et al., 1990) the lime mud fraction of the mud facies is about 20-40%. However, the vibrocore samples taken from the Great Bahama Bank indicate that the mud portion is only 10% (Davis per. comm.). We use 20% as a best estimate here. Thus, the bank-top lime mud volume will be 0.34x101 0 m3 If whitingsproduced aragonite accounts for 75% of the total volume, then the total whitings produced lime mud on the bank-top is about 0. 25x1010 m3 Off-Bank Transport of Lime Mud Excluding the Bimini/Riding Rock area, the data indicate that the southern part of the mud deposit along leeward slope of the bank contains a contribution from whitings events. According to Wilber et al. (1990, Table 1),
25' 24' 79' 79' 78' Great Bahama Bank 78' e: 0 tl} -3-mete r ? p.. 77 77 FIGURE 17. Isopach Map of Ho locene Sediment on Great Bahama Bank (From Cloud, 1962) 50 25 24'
51 the lower-slope depo-center is 200 km long and 7 km wide. The average sediment thickness is 15 meters. Assuming 90% of mud portion (Wilber et al., 1990), the total mud deposit volume is 1. 9xl010 m3 Assuming that 75% of fraction is produced by whitings, the total lime mud produced by whitings during the Holocene and deposited off the bank-top would be 1. 4x101 0 m3 Balance Analysis of Lime Mud Budget Now we can compare the figures found earlier for the total mass of aragonite mud on the bank top and lower slope depocenter with that derived from the whitings carbonate produced within the range of aerial photo data (Table 6) The data indicate that in the past 6,000 years, 0.7xl010 m3 of lime mud would be produced at an average daily area of 70 km2 ; 0 35x101 0 m3 of mud would be produced at the minimum daily whiting area of 35 km2 ; and 2. Oxl01 0 m3 of lime mud would be produced at the maximum whitings area of 200 km2 Comparing these figures with the mass of aragonitic mud in the bank-top Holocene sediments (0. 25xl01 0 m3), the results show that even the lowest whitings production rate can produce the observed volume of lime mud on the bank-top. There is an overproduction of 40%, 140%, and 700% respectively using a whitings area of 35, 70 and 200 km2 Assuming 200 km2 of whitings area as typical, there is
52 2. Ox1010 m3 of lime mud produced by whitings. Subtracting 0 25x1010 m3 of mud on the bank-top, the remaining 1. 75x1010 m3 of lime mud volume is large enough to accommodate both the mud transport off-bank (1.4x1010 m3 ) and the selective dissolution of aragonite. Considering a more realistic whitings area of 70 km2 a day, there would be 0. 7x1010 m3 of Lime Mud Produced by Whtitings: Daily whitings area (km2 ) Upper limit: 200 Average: 70 Lower limit: 35 Average water depth(m) :5 Average sediment in 0.25 whitings (kg/m3): 0.01061 Density (kg/m3): 1,1502 Time (yr) : 6, 0003 Mud production (x1010 m3) Maximum: 2.0 Average: 0.7 Minimum: 0.35 Mud Over-production over bank top sediment: 700%. 140%, 40% Lime Mud on Bank-Top: Total mud volume (x1010m3): 1.64 Mud fraction (%) : 207 Portion of mud produced by whitings: (%): 755 Mud produced by whitings (x101 0 m3 ) : Mud Transported Off-Bank Lower depo-center mud volume (x1010 m3 ) : 1. 96 Portion of mud produced by whitings (%) : 755 Mud produced by whitings (x1010 m3 ) : 1 4 If daily whitings area is 200 km2 lime mud produced by whiting in Holocene can account both the mud on the bank top and the mud transported off-bank. If daily whitings area is 70 km2 lime mud produced by whitings in Holocene can't balance the budget, but it can account for more than 40% the budget. 1 From Shinn et al. (1989) 4 From Cloud ( 1962) 2 From Neumann and Land(1975)5 From Milliman et al. (1993) 3 From Boardman et al. (1988) 6 From Wilber et al. (1990) 7 Steinen, in Wilber et al. (1990) TABLE 6. Presentation of the Results of Budgetary Considerations of Lime Mud Production via Whitings on Great Bahama Bank.
53 lime mud produced by whitings in the past 6,000 years. Although the amount of mud can't account for both the mud on bank-top and those at the lower slope deposit, when compare with the right side of the mass conservation equation ( 1 4xl01 0+0 25xl01 0 m3 ) 0 7xl01 0 m3 of mud production in Holocene can account for more than 40% of the mud v olume both on the bank-top and transported off-bank and thus appear to be significant.
54 5. CONCLUSIONS The data presented here represent an attempt to understand the spatial and temporal distribution of whitings and to model the lime mud budget on the Great Bahama Bank. The data suggest that whitings usually occur in two basins in the central part of the Great Bahama Bank, loosely following the bathymetric contours. However, 75-85% of the whitings occur in the northern basin around the 25' N and 7848' W area. The whitings distribution corresponds to mud and pellet-mud facies on the bank-top, as well as the lower slope depo-center at the lee of the western margin. Whitings, however, are also found in other facies as well. Whitings are year-round events. Greater frequency of whitings in winter may be due to passage of cold fronts. Whitings are evolving features, aligned subparallel to the direction of bank top currents, whose shape is determined either by wind, tide or by both. The collection aerial photos taken over a 25-year period offer an unique insight into the budget of lime mud deposition. Assuming 200 km2 of daily whitings area as typical, the total production is large enough to account for the bank top deposition, off-bank transport, and selective dissolution of aragonite and magnesium calcite. Although
the mass conservation equation is not balanced, mud production, at a more realistic estimate of 70 km2 a day whitings area, is still able to account for 40% of mud volume on the bank-top and that transported off-bank. 55
56 REFERENCES Amsbury, D and J. Bremer, 1989, Medium-format cameras used by NASA Astronauts. Geocarto International, 4(3) 59-63. Andreae, M.O. 1993, Global distribution of fires seen from space. EOS, 74 (12) :129. Black, M., 1933, The precipitation of calcium carbonate on the Bahama Bank. Geological Magazine, 70:455-466. Blatt, H., G.V. Middleton, and R .C. Murray, 1980. Origin of sedimentary rocks. 2nd (ed.) Prentice-Hall, Englewood Cliffs, M .J., 782. Boss, S.K. and A.C. Neumann, 1993, Physical versus chemical processes of "whitings" formation in the Bahamas. Carbonates and Evaporites, 8(2) :135-148. Boardman, M R Neumann, A C and K .A. Rasmussen, 1988, Holocene sea level in the Bahamas. Fourth Symposium on Geology of the Bahamas. San Salvador, Bahamas, 45-52 Broecker, W.S T Takahashi, 1966, Calcium carbonate precipitation of the Bahama Banks. Journal of Geophysical Research, 71:1575-1602 Cloud, P.E. Jr., 1962, Environment of calcium carbonate deposition west of Andros Island, Bahamas. U.S.Geological Survey Professional Paper, 350:1-138. Davis, R.A. Jr., 1992, Depositional Systems, Introduction to Sedimentology and Stratigraphy, Prentice-Hall, INC., Englewood Cliffs, N.J., 669 Enos, P., 1974, Surface sediment facies map of FloridaBahama Plateau. Geological Society of America,S. Gebelein, C.D., 1974, Guide book for modern Bahamian platform environments. Geological Society of America Annual Meeting. Miami, 93 Ginsberg, R.N., L.W. Hardie, 1975, Tidal and storm deposits, northeastern Andros Island, Bahamas, in Ginsburg, R N (ed.), Tidal Deposits, Springer-Verlag, N.Y., 201-208.
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59 Wilson, P A and H.H. Roberts, 1992, Carbonate-periplatform sedimentation by density flows: a mechanism for rapid off bank and vertical transport of shallow water fines. Geology, 20:713-716. Yates, K K L L Robbins, 1994, Experimental evidence for a CaC03 precipitation mechanism for marine Synechocystis. The seventh International Symposium on Biomineralization, Monaco, in press
APPENDIX 1 mission SL4-139-3919 STS51C-36-35 STS51C-44-67 STS54-74-9 STS54-152-243 STS54-151-162 STS29-90-8 STS29-93-80 STS36-78-99 STS45-78-16 STS6-39-190 STS31-73-1 STS31-151-157 STS31-81-0BC STS37-765 STS39-72-85 STS56-91-26 STS56-100-78 STS55-72-77 STS55-78-26 STS55-73-35 STS55-152A-47 STS51B-35-67 STS51B-147-2 STS30-76-18 61 CUMULATIVE WHITINGS AREA AND NUMBER OF WHITINGS IN EACH PHOTOS. date month year total no. (ea) area (km2 ) 22 1 74 34.96 3 25 1 85 11.99 14 26 1 85 22.03 17 14 1 93 92.5 10 16 1 93 8.31 1 N/A 1 93 7.6 1 14 3 89 26.39 15 15 3 89 37.53 1 8 2 3 90 3 .47 1 0 26 3 92 45.93 15 4 4 83 105.49 14 25 4 90 73.97 8 26 4 90 40.4 2 27 4 90 29.1 2 9 4 91 9.93 2 28 4 91 95.26 16 11 4 93 105.56 12 1 4 4 93 194.05 33 27 4 93 176.89 18 28 4 93 18.15 4 29 4 93 63.68 14 30 4 93 32.74 6 1 5 85 22.65 6 3 5 85 43.31 2 1 5 5 89 10.91 2 STS49-88-104,105 8 5 92 13.21 9 STS49-85-6 3 11 5 92 39.31 10 STS49-79-59 12 5 92 28.34 15
6 2 APPENDIX 1 (Continued) mission date month year total no. (ea) area ( k m2 ) S T S 49-92-88 13 5 92 32.56 8 STS40-75-39 8 6 91 16.16 4 STS40-79-42 11 6 9 1 31.59 9 STS40-613-50 N/A 6 9 1 47.66 11 STSS0-81-29 2 7 92 26.4 3 STSS0-77-35,45,46,47 4 7 92 38.66 6 GEMOS-1-45759 N/A 8 65 10.8 3 S TS43-76-87,88,89 3 8 9 1 21.54 10 STS4 3-15 1-106 9 8 91 53.25 13 S TS46-83-30 1 8 92 60.02 28 STS46-86-65 2 8 92 20.81 10 STS46-75-58 4 8 92 1 6 .92 13 STS26-32-17 29 9 88 11.98 6 STS48-604-12 15 9 9 1 2.95 1 S TS48-78-28 16 9 9 1 5.77 4 STS47-78 -49 14 9 92 41.95 5 STS41G-120-97 N /A 10 84 62.49 18 STS41G-39-97 N /A 1 0 84 56.77 22 STS51J-143-5 N/A 10 85 96.92 36 STS41-151-3,5 7 10 91 18.89 13 STS52-151-52 23 10 92 56.96 26 STS52-151-256 24 10 92 49.67 28 STS52-153-71 25 10 92 97.02 30 STS52-153-102 26 10 92 145.49 20 S TS52-153-236 29 10 92 120 27 STS52-77-93,94,95 30 10 92 17.25 9 GEM12-8-63420 11 11 66 45. 2 1 5 GEM12-17-62903 12 11 66 56.59 8
63 APPENDIX 1 (Continued) mission date month year total no. (ea) area (km2 ) SL2-5-424 6 11 73 37.13 17 STS5-39-1058 15 11 82 32.57 14 STS61A-200-98 3 11 85 20.32 10 STS61B-121-50 27 11 85 38.34 6 GEM07-22-63825 5 12 65 56.51 1 4 STS44-80-96 1 12 91 81.26 38 STS53-75-69 3 12 92 40.75 14 STS53-81-52 6 12 92 50.12 17 STS53-80-78 8 1 2 92 71.85 19 STS53-109-Q N/A 12 92 10.99 11
APPENDI X 2. LARG E WHITIN G S (SIZE>lO km2 ) SIZE AND LOCATIO N LIST. No Size Lat (Nl Lon_qlHl 1 10.75 24.44 78.53 2 14.67 24.45 79.01 3 10. 9 24.45 79.02 4 12.67 24.52 79. 0 1 5 14.52 24.57 78.59 6 31.22 25.12 78.46 7 41.63 25.14 78.48 8 19.14 25.12 78.39 9 10.37 2 4.59 78.46 10 11.27 25.11 78.42 11 13.19 25.16 78.56 12 24.96 25.06 78.55 13 11.63 25.13 78.51 14 28.33 25.12 78.36 15 38.97 24.49 78.54 16 13.03 24.56 78.51 17 30.01 24.5 78.54 18 10.39 24.56 78.53 19 18.2 24.53 78.55 20 10.9 24.57 78.55 21 11.81 25.09 79.04 22 16.06 25.02 78.57 23 16.12 24. 5 7 78.53 24 15.9 25.21 79.03 25 11.72 2 4.48 78.56 26 11.59 25.19 78.58 27 13.9 24.14 79.0 28 11.64 24.54 "78 52 29 10.36 24.58 78 5 6 4
65 APPENDIX 2. (Continued) No Size Lat(N) Lono(W) 31 11.06 24.59 78.58 32 13.46 25.14 78.59 33 11.93 25.17 78.52 34 19.85 25.15 78. 4 35 18.02 25.22 78.43 36 10.2 25.07 78.34 37 13.69 25.04 78.5 6 38 12.45 25.08 78.53 39 20.54 24.57 78.47 4 0 19.75 25.09 78.44 41 17.72 25.08 78.4 42 18.28 25. 0 5 78.33 43 10.79 24.56 78.4 7 44 15.82 24.59 78.55 45 14.74 24.58 78.58 46 18.82 25.06 78.51 47 53.63 25.02 78.43 4 8 13.36 25.14 78. 5 4 9 22.18 24.57 78.44 50 1 7.85 24.56 78.46 51 16.49 24.56 78.46 52 10.27 24.21 79.02 53 11.27 24.23 79.03 54 12.48 25.07 78.37 55 12.64 24.59 78.39 56 16.22 25.04 78.49 57 11.57 25.09 78.47 Sum (km2 } 957.96 Average Location tnt"' 1 <:.7 ?t;001 'Ill 7R0t;O'W
APPENDIX 3. WHOLE-BANK COVERAGE PHOTO LIST. Mission (MM-RR-FF) Date (YY-MM-DD) STS 51J-143-5 STS29-93-80 STS 31-151-157 STS 40-613-50 STS 46-86-65 STS 52-151-256 STS 52-153-71 STS 52-153-102 STS 52-153-236 STS 53-80-78 Average MM: mission number, RR: film roll number, FF: film frame number. 85-10-89-3-15 90-4-26 91-6-92-8-2 92-10-24 92-10-25 92-10-26 92-10-29 92-12-8 Size (km2 ) 96.92 37.53 40.4 47.66 20.81 49.67 97.02 145.49 120 71.85 72.74 66
APPENDIX 4. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN JANUARY. 79" 78" 77 Great Bahama Bank 26" oo.o 0 25. 25. 0 0 0 til 0 ..... .. 24" 24. 79. 78" 77 67
APPENDIX 5 DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN MARCH. 79' 78' 77 Great Bahama Bank 28" 25' 24" 79' 7f) 77 68
APPENDIX 6. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN APRIL. 79' 78' 77 Great Bahama Bank 26" 25' '; 25' 0 0 0 (f) 0 0 0 0 0 0 9-' 24' 24' 79' 7fJ 77 69
APPENDIX 7. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN MAY. 79" 78" 77 Great Bahama Bank 28' . :0 .41' \ 2 5 25" 00 0 0 0 0 0 0 oO .. Oo o 0 0 (J) 0 : 0 \I 0 0 ;..-' 0 p. 0 2 4 24" 79' 78' 77 70
APPENDIX 8. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN JUNE Great Bahama Bank 26" 25" 24" 79" 78" 7 7 71
APPENDIX 9 DISTRIBUTION O F WHI TINGS ON GRE A T BAHAMA BANK IN JULY. G r eat Bahama Bank 28' 25' 25' 0 (J) 0 'tP ;...-' p.. 24' 24' 79' 78' 77 72
APPENDIX 10. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN AUGUST. 79. 7fJ' 77 Great Bahama Bank 2fJ' 2fJ' Berry \ Island l 0 0 00 O,p<>'o oO 0 25. l) 25. 24. 79. 7fJ 77 73
25' 24' APP E NDIX 11. DISTRIBUTION O F WHITINGS ON GREAT BAHAMA BANK IN SEP TEMBE R 79' 78' 77' Great Bahama Ban k 2fr .. 0 0 25' 0 tJ) .. y; p.o 24' 79' 7fr 77' 74
APPENDIX 12. DISTRIBUT ION OF WHITINGS ON GREAT BAHAMA BANK IN OCTOBER. '79 '78" '77 Great Bahama Bank 28" 25" 25 0 e.: 0 0 -: tl} 'tP ;..-' .. . .. .. 0o f .. p. 24" 24" 00 79" 78" 77 75
APPENDIX 13. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN NOVEMBER. 79" 78. 7 7 Great Bahama Bank 2 fi Q_ 0 0 cP 0 0 o o 0 0 oo 0 IJ 25" 24" 79. 7fJ 7 7 76
APPENDIX 14. DISTRIBUTION OF WHITINGS ON GREAT BAHAMA BANK IN DECEMBER. 79" 78" 7 7 Great Bahama Bank 26" 25" 79" 78" 77 77