A COMPARISON OF MODERN SEDIMENTOLOGY FOR SEVERAL HYPERSALINE

A COMPARISON OF MODERN SEDIMENTOLOGY FOR SEVERAL HYPERSALINE LAKES OF SAN SALVADOR ISLAND, BAHAMAS: FRENCH POND, TRIANGLE POND, NO NAME POND, AND STORR’S LAKE Craven, David, James Madison University and Park, Lisa, The University of Akron ON LOCATION French Sodium • San Salvador is unique in its many inland hypersaline lakes. Four of these lakes are the objects of this study: French Pond, Triangle Pond, No Name Pond, and Storr’s Lake. Each of these is host to certain biological activities with cyanobacterial mats being of primary interest. • Conditions in these lakes can be quite harsh in terms of life support – shallow waters, high salinity, intense radiation, high temperatures, and lack of naturally occurring nutrients. • Relatively little is known about the sedimentary dynamics of these lakes and ponds, especially those containing cyanobacterial mats. A better understanding would be helpful in realizing the utility of the sediments as archives of local, regional, and global paleoclimatic events. • In this project, the sediments of the four subject lakes will be examined as well as certain water properties. The objective will be to compare sediments within and across lakes to determine similarities and differences. Of particular interest are the relationships that exist between the cyanobacterial mats and the sediments. The purpose of this project is to gain a better understanding of the characteristics of these lakes and to gain some degree of insight into what factors, such as salinity, cyanobacterial mats, or other elements of the environment, are controlling the processes in these lakes. • Knowledge of the modern sediment of these four lakes could open up new discoveries for the cyanobacterial mats. It may help determine important aspects of the past environment and possibly the future environment. 20 20 20 0 10 20 30 40 50 40 French Pond Carbon Oxygen Magnesium Silicon Aluminum 15 30 45 60 40 0 0 20 20 0 10 20 30 40 50 0 40 40 40 20 20 20 0 0 10 20 30 40 50 15 30 45 60 0 0 40 40 20 20 0 10 20 30 40 50 0 0 15 30 45 60 0 40 40 20 20 0 0 10 20 30 40 50 0 15 30 45 60 40 40 20 20 0 10 20 30 40 50 0 0 15 30 45 60 0 40 40 20 20 0 10 20 30 40 50 0 80 French Pond average Average, all lakes Triangle Pond average Average, all lakes 20 40 60 80 20 0 40 0 60 40 40 0 10 20 30 40 50 20 40 40 0 0 San Salvador, the Bahamas, and the Four Lakes of Interest. Sediment sampling transects shown with red arrows. 0 20 0 Triangle Pond 40 0 Calcium 0 10 20 30 40 50 20 0 Sulfur 0 0 15 30 45 60 0 20 40 60 80 Na Cl C 0 20 40 60 80 0 20 40 60 S Ca Mg Si Al French Pond No Name Pond average Average, all lakes Na Cl C O S Ca Mg Si Al Triangle Pond Storr’s Lake average Average, all lakes Halite Molysite Simonkolleite Na. Cl Fe. Cl 3 Zn 5(OH)8 Cl 2 • H 2 O Pyrite Chalcocite Herzenbergite Hauerite Covellite Metacinnabar Realgar Greigite Smythite Djurleite Fe. S 2 Cu 2 S Sn. S Mn. S 2 Cu. S Hg. S As. S Fe 3 S 4 Fe 9 S 11 Cu 31 S 16 Celestine Anglesite Bassanite Vanthoffite Langite Blodite Nickelblodite Sr. SO 4 Pb. SO 4 Ca. SO 4 • 0. 5 H 2 O Na 6 Mg(SO 4)4 Cu 4(SO 4)(OH)6 • 2 H 2 O Na 2 Mg(SO 4)2 • 4 H 2 O Na 2 Ni(SO 4)2 • 4 H 2 O Purpurite Whitlockite (Mg) Monazite (Ce) Farringtonite Turquoise Isokite (Mn, Fe)PO 4 (Ca, Mg)3(PO 4)2 Ce. PO 4 Mg 3(PO 4)2 Cu. Al 6(PO 4)4(OH)8 • 4 H 2 O Ca. Mg(PO 4)F Bunsenite Monteponite Cuprite Molybdite Bixbyite Corundum Ni. O Cd. O Cu 2 O Mo. O 3 Mn 2 O 3 Al 2 O 3 80 O S Ca Mg Si Al No Name Pond Na Cl C O S Ca Mg Si Al Storr’s Lake 20 40 60 80 Comparison of Average Lake Sediment Elemental Content Chemical Formula F T NS French Pond Fe. O(OH) (Ta, Mn, Nb, Sn)O 2 Fe. Ti. O 3 Ca. Ti. O 3 Mg. Ti. O 3 Mn. Fe 2 O 4 Zn. Al 2 O 4 Mg. Al 2 O 4 Ca 2 Fe 2 O 5 Si. O 2 Ca. Si. O 3 Mg 3 Si 2 O 5(OH)4 Mn 2 Si. O 4 Ca 2 Mg. Si 2 O 7 Ca 14 Mg 2(Si. O 4)8 Ca. Fe. Si 2 O 6 Ca. Mn. Si 2 O 6 Ca. Ti(Si. O 4)O Na. Ca 2 Si 3 O 8(OH) (Fe, Mg)2 Si. O 4 Mn 2+Mn 3+6[O 8 Si. O 4] Ca. Mn 14 Si. O 24 Cummingtonite (Mg) (Mg, Mn, Fe)7 Si 8 O 22(OH)2 Sulfides Sulfates Phosphates Oxides • In elemental profile graph above, horizontal axis is distance from starting shoreline (m). • In both graphs, vertical axis is relative abundance. Storr’s Lake Stilpnomelane (Fe) K 5(Fe, Mg)48[Si 63 Al 9]O 168 (OH)48 • 12 H 2 O Moissanite Ferdisilicite Vernadite Crocoite Si. C Fe. Si 2 Mn(OH)4 Pb. Cr. O 4 • Element associations Ø Na, Cl – Halite (strong in French Pond). Ø C – Organic content; some carbonate. Ø O – Carbonate; some organic content. Ø S – Sulfides & sulfates (some are nutrients). Ø Ca – Carbonate as aragonite & calcite. Ø Mg – Magnesian calcite, (Ca, Mg)CO 3. Ø Si, Al – Silicates & alumino-silicates. French Pond Triangle Pond Characterization of collected samples • Water properties measurements taken directly in the lakes: Temperature, Dissolved oxygen, Dissolved solids, Conductivity, Salinity, p. H, and Alkalinity. Storr’s Lake Triangle 35 80 m Far northwest shore, heading southeast toward north basin center Storr’s 22 No Name 27 Comparison of Lake Mineral Diversity Profiles • Graph above shows mineral diversity profiles by providing mineral counts at sampling locations. • Table above lists the minerals found in lake sediments by x-ray diffraction pattern matching. • This gives some idea of how allochthonous matter may enter and become distributed over a lake. • Mineral occurrence in each lake is indicated by an “x” in the lake columns (F = French, T = Triangle, N = No Name, & S = Storr’s). • In general, mineral diversity tends to be higher close to shoreline areas and more subdued moving into the lake interiors. • Surprisingly wide variety of minerals in a carbonate environment; most are allochthonous. 0 Temperature Dissolved Oxygen Dissolved Solids Conductivity 0 34 cm 0 0 35 cm 10 0 30 cm 0 20 32 cm 0 30 37 cm 0 38 cm 40 French Pond 19 cm 50 0 30. 5 cm Analysis Methods • Visual characterization of sediments. – Texture, color, grain size and distribution. Preparation for grain size analysis - Wet oxidation using hydrogen peroxide Storr’s Lake 26 cm • Wet & dry sediment bulk densities are generally low; water content is high. • Loss on Ignition (LOI) – Employs three heating stages to remove: 1) water, 2) organic content, 3) carbon dioxide from carbonates. – Determines sediment density and water content. – Determines bulk composition of sediments – organic content, carbonate content, and residual matter. • Sediment texture is generally “fluffy” and composed of silt-sized particles. Sediment Composition as Determined by LOI Analysis Precise grain size analysis results – % Mud • Surprisingly large percentage of residual matter. 34 cm 0 35 cm 0 31 cm Temperature Dissolved Solids Conductivity 0 30 cm 0 32 cm 0 35 cm 0 Temperature 33 cm Dissolved Oxygen Dissolved Solids Conductivity Salinity Triangle Pond 10 20 30 40 50 Ternary Grain Size Chart Includes all sediment samples. % Silt Water Properties Profile for French & Triangle Ponds. Scale: Temp – °C, Dissolved O 2 – mg/L, Dis. Solids – g/L, Conductivity – m. S/cm, Salinity – ppt. % Sand No Name Pond 10 20 0 38 cm 0 70 cm 30 0 82 cm 40 50 60 66 0 118 cm 0 134 cm Temperature Dissolved Oxygen Dissolved Solids Increasing depth Conductivity Salinity p. H = 7 (neutral) Storr’s Lake 15 20 40 60 • Lake differences – Proportions of sediment content are different. French and Triangle Ponds contain the highest level of organic content. Storr’s Lake contains the least. Mineral distribution and diversity also favor French and Triangle Ponds. • Sedimentation characteristics: – All sediments more or less dominated by calcium carbonate. – Sediments driven by organic and inorganic processes. – Carbonate sediments are mostly inorganic precipitation with a natural tendency toward aragonite over calcite. This may be organically influenced since calcite is more stable form. – Presence of sulfate ion (SO 42 -) tends to inhibit aragonite and overall carbonate precipitation. – Cyanobacterial mats can alter allochthonous mineral matter as part of their metabolic processes. – Mats also alter texture of sediments from compacted to “fluffy” silt mud. – Surprisingly large amount of allochthonous minerals in sediments – over 20% for some French Pond samples. • Sediment influence on cyanobacterial mats: – Mats are dependent on the allochthonous minerals for nutrients. – Where minerals are present, biological activity is generally rich; where they are lacking, so also is organic content. • Effects of salinity – Salinity did not appear to have a significant adverse effect on the microbial mat communities. French sediments had the highest levels of halite, but also were high in organic content. Mat communities have probably adapted to wide ranges of salinity. – Salinity did not appear to impact inorganic sedimentation processes as well. – Probably salinity is a necessary component to preserve the organic-saline-carbonate ecosystems as they have existed. • Current lake conditions indicate a recent freshening – carbonate concentrations are below saturation, salinity levels are moderate. REFERENCES 1. Carew, J. L. and Mylroie, J. E. , 1995, Geology and Karst of San Salvador Island, Bahamas: A Field Trip Guidebook, Bahamian Field Station, San Salvador, Bahamas, 32 p. Water Properties Profile for No Name Pond & Storr’s Lake. Scale: Temp – °C, Dissolved O 2 – mg/L, Dis. Solids – g/L, Conductivity – m. S/cm, Salinity – ppt. Lake Alkalinity Measurements • In graphs above, horizontal sampling positions are segments separated by vertical black lines. Horizontal Profile Only • Vertical profiles are indicated within segments, moving from left boundary to right boundary. Saturated Carbonate Is About 150 mg/L French Pond No Name Pond 3. Chen, J. H. , Curran, H. A. , White, B. , and Wasserburg, G. J. , 1991, Precise chronology of the last interglacial period: 234 U– 230 Th data from fossil coral reefs in the Bahamas, in Geological Society of America Bulletin, 103, p. 82– 97. 4. Corwin, B. N. , 1985, Paleoenvironments, using Holocene Ostracoda, in Storr’s Lake, San Salvador, Bahamas: [M. S. Thesis]: University of Akron, Ohio. 5. Crotty, K. J. and Teeter, J. W. , 1984, Post Pleistocene salinity variations in a blue hole, San Salvador Island, Bahamas, as Interpreted from the Ostracode Fauna, in Teeter J. W. , ed. , Proceedings of the 2 nd Symposium on the Geology of the Bahamas: CCFL Bahamian Field Station, p. 3 -17. 6. Dix, G. R. , Patterson, R. T. , and Park, L. E. , 1999, Marine saline ponds as sedimentary archives of late holocene climate and sea-level variation along a carbonate platform margin: Lee Stocking Island, Bahamas, in Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 150, Number 3, p. 223 -246. 7. Lewis, M. F. , 2006, Dissolved Oxygen: U. S. Geological Survey Techniques of Water-Resources Investigations, book 9, chap. A 6. , section 6. 2, June, accessed Nov. , 2009 from http: //pubs. water. usgs. gov/twri 9 A 6/. 8. Mackenzie, F. T. , Vink, S. , Wollast, R. , and Chou, L. , 1995, Comparative biogeochemistry of marine saline lakes, in Lerman A. , Imboden, D. , and Gat J. , eds. , Physics and Chemistry of Lakes, 2 nd edition, Springer-Verlag, Berlin, p. 265 -278. 9. Teeter, J. W. , 1985, Holocene lacustrine depositional history, in Curran, H. A. , ed. , Pleistocene and Holocene Carbonate Environments on Salvador Island, Bahamas: Guidebook for Geological Society of America, CCFL Bahamian Field Station, p. 133 -145. 10. Zabielski, V. P, 1991, The Depositional History of Storr’s Lake: San Salvador, Bahamas, [M. S. Thesis]: University of North Carolina, Chapel Hill, NC, 107 p. 80 Distance from Starting Shoreline, meters • Most measurements taken over horizontal and vertical (depth) sampling profiles. • Allows plotting of all measurements on one graph. • Lake similarities – The four lakes studied all support organic-saline-carbonate ecosystems. Sediments from lakes contain similar matter: carbonate, organic matter, and allochthonous minerals. 2. Carew, J. L, Mylroie, J. E. , Wehmiller, J. F. , and Lively, R. A, 1984, Estimates of Late Pleistocene sea level highstands from San Salvador, Bahamas, in Teeter, J. W. , ed. , Proceedings of the Second Symposium on the Geology of the Bahamas: Fort Lauderdale, Florida, CCFL Bahamian Field Station, p. 153 -175. CURRENT CONDITIONS – Water Measurements • LOI compositional analysis generally shows high levels of carbonate as well as organic content. Final LOI ignition stage at 1000 °C 0 Salinity Distance from Starting Shoreline, meters SEDIMENT PROPERTIES – LOI & Grain Size Results 36 cm Increasing depth 0 Preparation for XRD – Crushing sediments into powder 0 Distance from Starting Shoreline, meters Storr’s Lake Sediment Bulk Densities and Water Content 33 cm No Name Pond 0 • Environmental Scanning Electron Microscopy (ESEM). – High resolution, magnified sediment images (500 x). – Elemental analysis through emitted x-ray detection. 0 Dissolved Oxygen Distance from Starting Shoreline, meters No Name Pond • X-Ray Diffraction analysis (XRD) – Analyzes crystal lattice structures. – Mineral identification through diffraction pattern matching against known structures. 66 m Southwest shore, heading northwest ending at opposite shore Others Increasing depth Sample Collection • Sediment samples collected along transects into lake interiors at uniformly spaced intervals. • Precise grain size determination using Malvern Mastersizer and analysis software. – Size similarity clustering & principal component analysis. No Name Pond Lake center Aluminum Silicates Ca. Al 2 Si 2 O 7(OH)2 • H 2 O Ca 2 Al[Al. Si. O 7] Fe. Al 2 Si. O 5(OH)2 Na. Al. Si 3 O 8 Al 2 Si 2 O 5(OH)4 Ca 2(Al, Fe)3(Si. O 4)(Si 2 O 7)O(OH) (Ca, Na 2, K 2)Al 2 Si 10 O 24 • 7 H 2 O Ca(Mg, Fe, Al)(Si, Al)2 O 6 Ca 2 Al 2 Mn(Si. O 4)(Si 2 O 7)O(OH) Ca 2(Fe, Mn)Al 2 BO 3 Si 4 O 12(OH) K(Na, K)3 Al 4(Si. O 4)4 (Mg, Al, Fe)3[Al. Si. O 5](OH)4 (Mg, Al)6(Si, Al)4 O 10(OH)8 Mn 2 Al 3(Si. O 4)(Si 2 O 7)(OH)3 (Mn 5 Al)(Si 3 Al)O 10(OH)8 Mineral Content at or Above XRD Correlation Score of 2. 0. METHODS • Samples reflect recent sedimentology – only top 2 cm included. 50 m Lake Profiles for Sediment Elemental Content ELEMENTAL ANALYSIS – ESEM Results No Name Pond 50 m North shore, heading southwest toward center LAKE MINERALOGY – XRD Results Gerace Research Center DISCUSSION and CONCLUSIONS Triangle Pond Lawsonite Gehlenite Chloritoid Albite Kaolinite Epidote Mordenite Augite (Al) Piemontite Ferro-axinite Nepheline Amesite Clinochlore Sursassite Pennantite French 54 Lake center South center shore, heading northwest toward center Silicates Quartz Tridymite Wollastonite Clinoenstatite Lizardite Tephroite Akermanite Bredigite Hedenbergite Johannsenite Titanite Pectolite Fayalite (Mg) Braunite II Lake Total Mineral Count 0 F T N S Mineral Name Goethite Wodginite Ilmenite Perovskite Geikielite Jacobsite Gahnite Spinel Srebrodol’skite Halides 80 Na Cl C 0 O Ca. CO 3 (Ca, Mg)CO 3 Ca. CO 3 Mg. CO 3 Fe. CO 3 Zn. CO 3 Na 2 Ca(CO 3)2 Na 2 Ca 2(CO 3)3 Mg 2 CO 3(OH)2 • 3 H 2 O Ca 4 Al 6(Si. O 4)6(SO 4, CO 3) Multipurpose Scale (see figure caption) • The Bahamas began as an accretionary platform for calcium carbonate sediments deposited by marine algae. Today, the islands are composed of limestone, several miles in depth, with numerous subterranean cavities and conduits for water storage and transport. 20 Aragonite Calcite (Mg) Calcite Magnesite Siderite Smithsonite Nyerereite Shortite Artinite Meionite Multipurpose Scale (see figure caption) INTRODUCTION 40 Chemical Formula Carbonates Mineral Name Storr’s 40 0 Chlorine No Name 40 Multipurpose Scale (see figure caption) The island of San Salvador, Bahamas is formed of calcium carbonate, accreted from marine sediments dating back to the Jurassic period. There are many inland lakes of various sizes across the island. Most of these are hypersaline with salinity levels widely varying over time and have been reported as high as 300 ppt. These conditions lead to somewhat unique saline-carbonate lacustrine environments that provide support for limited biological activities. Among the organisms thriving in these lakes are microbial mats composed of cyanobacteria along with other microorganisms all working as a synergetic community. At present, little is known about the relationships that exist with the mats, involving a pond’s salinity and carbonate environment. The goal of this project is to compare and contrast the activities occurring in several of the hypersaline lakes of San Salvador from a recent sedimentological perspective. The lakes selected for this purpose are: French Pond, Triangle Pond, No Name Pond, and Storr’s Lake. In June, 2009, surface sediment samples were collected from each of the four lakes along a transect from shoreline to depocenter. Measurements of the lake waters, including temperature, salinity, conductivity, dissolved ion content, dissolved oxygen, p. H, alkalinity, and depth also were taken. After noting physical properties, the sediments were later analyzed for grain size, density, water content, and composition, using various additional techniques. Loss on ignition was used to determine bulk organic, carbonate, and residual content. X-ray diffraction was used to determineral content, while ESEM was used for elemental analysis. The results from the sediment and water analyses indicate that the four lakes studied were generally similar: sediments were dominated by calcium carbonate, but also contained substantial amounts of organic matter and varying amounts of residual mineral matter. No evidence was found indicating detrimental effects from salinity, but rather salinity appears to serve a critical role in protecting the established ecosystems. A key factor to sustaining the microbial mats appears to be allochthonous mineral matter entering the lakes. Conversely, the biological communities of the lakes appear to have at least some influence over the form and composition of lake sediments. Triangle 40 Multipurpose Scale (see figure caption) ABSTRACT Triangle Pond Storr’s Lake Distance from Starting Shoreline (meters) ACKNOWLEDGEMENTS I am grateful to the National Science Foundation for providing funding for this research project through grant number NSF-EAR-0851847; REU Site: Field Research on Bahamian Lakes--Exploring Records of Anthropogenic and Climate Change. These funds were sufficient to cover all costs, including air fare, food and lodging, and a stipend for me. I thank Dr. Tom Rothfus and the Gerace Research Centre for authorizing as well as supplying the food and lodging, and materials necessary for us to conduct the research project. This research was conducted under Research Permits: MAF/FIS/12, MAF/FIS/17, 01/31 and 01/15. I thank Dr. Lisa Park and Andy Michelson for guiding me throughout the workings of the research project at San Salvador as well as at the University of Akron. I thank Dr. Thomas Quick for teaching me how to perform Electron Scanning Microscopy and X-ray Diffraction. I thank Matt Kemp for taking me to Kent State University and teaching me how to use the Malvern Mastersizer. I thank all of the mentors and students for helping to gather the data necessary to produce the research project.