Climate forcing,primary production and the distribution of Holocene biogenic sediments in the Gulf of California |
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| Institution: | 1. Department of Geology, University of Salamanca, 37008 Salamanca, Spain;2. Institute of Earth Sciences, Université de Lausanne, CH-1015 Lausanne, Switzerland;3. Oceanología, Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), 22860 Ensenada, Mexico;1. Centro Interdisciplinario de Ciencias Marinas–IPN (CICIMAR), Av. Instituto Politécnico Nacional s/n, Col. Playa Palo de Santa Rita, La Paz B.C.S. 23096, Mexico;2. Laboratorio de Paleomagnetismo y Paleoambientes, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad universitaria, Coyoacan 04510, D.F., México;1. U.S. Geological Survey, Menlo Park, CA, United States;2. Department of Earth Sciences, University College London, London WC1E 6BT, UK;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei 430074, PR China;2. School of Earth Science, China University of Geosciences, Wuhan, Hubei 430074, PR China;1. Geological Survey of Denmark and Greenland—GEUS, Department of Marine Geology and Glaciology, Denmark;2. Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Ensenada—UABC, Mexico;3. Centre Européen de Recherche et d''Enseignement des Géosciences de l''Environnement—CEREGE, France |
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| Abstract: | The Gulf of California is a marginal seaway under the influence of a monsoon climate that produces cool, dry winters and warm, humid summers. Winds, tidal mixing and coastal-trapped waves forced by climate and the Pacific Ocean control nutrient advection and primary productivity (PP). Strong northwest winds from the subtropical East Pacific High Pressure system begin in November and last until April and drive coastal upwelling along the mainland margin, especially in the central and southern Gulf. In the northern Gulf, particularly around the midrift island, tidal mixing and turbulence occurs year round, advecting nutrients into the mixed layer and high productivity. During summer and early fall months, winds are variable, of less intensity and mainly blow cross-basin except in the most northern Gulf. Summer PP is generally low in the central and southern Gulf except along the mainland where coastal-trapped waves associated with tropical surges and hurricanes generate mixing over the continental shelf. Mesoscale eddies or gyres often associated with jets and filaments extend to depths of 1000 m and transport nutrient-enriched upwelled waters and plankton detritus across the Gulf. The largest and most persistent gyres rotate in an anti-cyclonic direction (east to west) and are a principal source of the plankton export to the peninsula margin.Two major biogenic sediment patterns are present in core-top sediments. Hemipelagic biosiliceous-rich muds are accumulating beneath upwelling areas of high productivity in the central Gulf and along the mainland margin. Calcium carbonate- and organic carbon-rich (OC) sediments are concentrated along the peninsula margin, generally beneath lower productivity waters with the highest OC content in areas with the lowest productivity. The high, uniform biosiliceous content in Guaymas basin, extending southward into Carmen basin reflects the redistribution by mesoscale gyres of phytoplankon debris produced in mainland coastal upwelling and tidally forced areas around the midrift islands.Holocene biogenic patterns are similar to the present day with the major difference in rates of accumulation. Phytoplankton production prior to about 8200 yr BP was significantly higher in the central and southern Gulf, decreased though the mid-Holocene and has been reasonably steady for the past 2500 yr. The strong north–south and east–west gradients in present-day phytoplankton productivity patterns are also reflected in the Holocene sediment record. A series of depositional cycles occur in the biogenic record with the strongest peaks of variability at about 150 (144±18), 200 (198±5) and 350 (350±40) yrs. Longer periodicities are present prior to 3200 yr BP but the 350 yr cycle dominates in the late Holocene where it is best expressed as productivity/dissolution cycles in the carbonate record. |
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