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Cariaco Basin
The Cariaco Basin lies off the north central coast of Venezuela and forms the Gulf of Cariaco. It is bounded on the east by Margarita Island, Cubagua Island, and the Araya Peninsula; on the north by Tortuga Island and the Tortuga Banks; on the west by Cape Codera and the rocks known as Farallón Centinela; and on the south by the coast of Venezuela.
The Cariaco Basin is an east-west trending pull-apart basin〔Schubert, C. (1982). Origin of the Cariaco Basin, Southern Caribbean Sea. Mar. Geol., 47: 345-360.〕 located on the continental shelf off the eastern coast of Venezuela. It is a deep depression composed of two sub-basins, the eastern basin and the western basin, each of ~1400 m depth, separated by a saddle of ~900 m. To the south, the basin confines with the wide (~50 km) Unare Platform.
It is connected to the open Caribbean Sea through two shallow (~140 m) channels, to the north the (Tortuga Channel) and to the west the (Centinela Channel). Water circulation inside the basin is restricted, which, combined with the high annual primary productivity of the region (~500 gCm−2yr−1), causes the basin to be permanently anoxic, below ~250 m.〔Muller-Karger, F. E., R. Varela, R. Thunell, M. Scranton, R. Bohrer, G. Taylor, J. Capelo, Y. Astor, E. Tappa, T. Y. Ho, and J. J. Walsh. (2001). (Annual Cycle of Primary Production in the Cariaco Basin: Response to upwelling and implications for vertical export. ) J. of Geophys. Res. 106:C3. 4527-4542.〕〔Muller-Karger, F. E., R. Varela, R. Thunell, Y. Astor, H. Zhang, and C. Hu. (2004). (Processes of Coastal Upwelling and Carbon Flux in the Cariaco Basin. Deep-Sea Research II. ) Special Issue: Views of Ocean Processes from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Mission: Volume 2 - Edited by D. A. Siegel, A. C. Thomas and J. Marra. Vol 51/10-11 pp 927–943.〕 This naturally occurring anoxic basin allows for sediments to be deposited without bioturbation, forming varves of alternating light and dark color, which correspond to the dry or rainy season.〔Haug, G. H., K. A. Hughen, D. M. Sigman, L. C. Peterson and U. Rohl (2001). Southward Migration of the Intertropical Convergence Zone Through the Holocene. Science, 293: 1304-1308〕 Its unique geography and undisturbed sediment record provides an excellent history of tropical climate change and is particularly sensitive to shifts in the Intertropical Convergence Zone (ITCZ) 〔Peterson, L. C., G.H. Haug (2006). Variability in the mean latitude of the Atlantic Intertropical Convergence Zone as recorded by riverine input of sediments to the Cariaco Basin (Venezuela). Palaeogeography Palaeoclimatology Palaeoecology 234(1):97-113〕 and has been the subject of extensive paleoclimatological research, amongst other sedimentological studies,〔Peterson, L.C., Haug, G.H., Murray, R.W., Yarincik, K.M., King, J.W., Bralower, T.J., Kameo, K., Rutherford, S.D. and Pearce, R.B. 2000b: Late Quaternary stratigraphy and sedimentation at site 1002, Cariaco Basin (Venezuela). In Leckie, R.M., Sigurdsson, H., Acton, G.D. and Draper, G. (eds.): Proceedings of the Ocean Drilling Program, Scientific results 165, 85–99, College station, TX (Ocean Drilling Program).〕〔Peterson, L.C. & Haug, G.H. 2006: Variability in the mean latitude of the Atlantic Intertropical Convergence Zone as recorded by riverine input of sediments to the Cariaco Basin (Venezuela). Palaeogeography, Palaeoclimatology, Palaeoecology 234, 97-113.〕〔Piper, D. & Dean, W.E. 2002: Trace-element deposition in the Cariaco Basin under sulfate reducing conditions—a history of the local hydrography and global climate, 20 ka to the present. US Geological Survey Professional Paper 1670, 41 pp.〕 geochemical studies, with alkenones,〔Herbert, T.D. & Schuffert, J.D. 2000: Alkenone unsaturation estimates of sea-surface temperatures at site 1002 over a full glacial cycle. Proceedings of the Ocean Drilling Program, Scientific Results 165, 239-247〕 Mg/Ca,〔Lea, D.W., Pak, D.K., Peterson, L.C. & Hughen, K.A. 2003: Synchroneity of Tropical and High-Latitude Atlantic temperatures over the Last Glacial Termination. Science 301, 1361-1364.〕 and micropaleontological, with foraminifera,〔Peterson, L.C., Overpeck, J.T., Kipp, N.G. and Imbrie, J. 1991: A high–resolution late Quaternary upwelling record from the anoxic Cariaco Basin, Venezuela, Paleoceanography 6, 99–119.〕〔Lin, H.-L., Peterson, L.C., Overpeck, J.T., Trumbore, S.E. & Murray, D.W. 1997: Late Quaternary climate change from δ18O records of multiple species of planktonic foraminifera: high-resolution records from the anoxic Cariaco Basin, Venezuela. Paleoceanography 12, 415-427.〕 pollen and spores,〔González, C., Dupont, L.M., Behling, H. & Wefer, G. 2008a: Neotropical vegetation response to rapid climate changes during the last glacial period: palynological evidence from the Cariaco Basin. Quaternary Research 69, 217-230.〕 dinocysts〔González, C., Dupont, L. M., Mertens, K.N., Wefer, G. (2008). Reconstructing the history of marine productivity of the Cariaco Basin during the Marine Isotope Stages 3 and 4 using organic-walled dinoflagellate cysts. Paleoceanography 23, PA3215, doi:10.1029/2008PA001602.〕〔Mertens, K. N., González, C., Delusina, I. & Louwye, S. (2009). 30000 years of productivity and salinity variations in the late Quaternary Cariaco Basin revealed by dinoflagellate cysts. Boreas 38, 647-662.〕 and coccoliths.〔Mertens, K.N., Lynn, M., Aycard, M., Lin, H.-L. & Louwye, S. (2009). Coccolithophores as paleoecological indicators for shift of the ITCZ in the Cariaco Basin. Journal of Quaternary Science 24 (2), 159-174.〕
Because of its anoxia, the Cariaco Basin has also a unique chemistry. Bacteria inhabit both the oxic and anoxic portions of the water column, with a maximum around the interface where oxygen disappears.〔Taylor, G. T., M. I. Scranton, M. Iabichella, T.-Y. Ho, R. C. Thunell, R. Varela, and F. E. Muller-Karger. 2001 (Chemoautotrophy in the redox transition zone of the Cariaco Basin: A significant source of mid-water organic carbon production. ) Limnology and Oceanography. Vol. 46, no. 1. 148-163.〕 This 'interface' oscillates between 200 and 300 meters. As such unique location, the Cariaco Basin has been the site of a variety of studies since the mid-1950s. Since 1995, an international (Venezuela and United States) program has expanded the research in the basin. The CARIACO (Carbon Retention in a Colored Ocean; ()) program consists of a time series station in the eastern deep of the basin which is visited on a monthly basis to collect hydrographic, nutrient and primary productivity measurements. A suite of other measurements, including a sediment trap mooring, microbiological studies and current measurements are also conducted at this site. The work that has resulted from the CARIACO ocean time series program has demonstrated that this anoxic basin is quite dynamic and has helped understand the paleoclimatic record stored in the basin's sediments.〔Smoak, JM, Benitez-Nelson, C., Moore, WS, Thunell, RC, Astor, Y. and F. Muller-Karger (2004) ("Radionuclide fluxes and particle scavenging in Cariaco Basin" ) ''Continental Shelf Research'' 24, 1451-1463.〕〔Thunell, R., R. Varela, M. Llano, J. Collister, F. Muller-Karger, and R. Bohrer. (2000). (Organic carbon flux in an anoxic water column: sediment trap results from the Cariaco Basin. ) Limnology and Oceanography. 45. 300-308.〕〔Tedesco, K. and Thunell, R., (2003) Seasonal and interannual variations in planktonic foraminiferal flux and assemblage composition in the Cariaco Basin, ''Venezuela. Journal of Foraminiferal Research'' 33, 192-210.〕
== References ==
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