Paleoclimate Variability Recorded in Deep Sea Sediment Recovered From the Eastern Equatorial Pacific Ocean

Marine sediment cores can provide a fairly continuous record of paleoclimatic conditions at varying timeframes and resolutions. The top portion of the composite core extracted by Leg 202 of the Ocean Drilling Program from Cocos Ridge in the equatorial Pacific region off the coast of Panamá at Site 1242 contain both marine and terrigenous (continental) sediment deposits and represent a record of ~2.5 million years. By dissolving out carbonate and silicate life forms as well as oxides and hydroxides that come from the ocean environment, the terrigenous component is isolated, including grains transported from the continent by both eolian (wind-blown) and hemipelagic (riverine) processes. Comparison of the weight of the sample before and after this chemical extraction allows the calculation of terrigenous mass accumulation rates. These data can be reflective of continental climatic factors, including precipitation and erosion on the continent. For the samples analyzed, terrigenous weight percents ranged from 51% to 72%, and terrigenous mass accumulation rates ranged from 4.1 g/cm2/ky to 10.9 g/cm2/ky. Eventually, the samples will also be subject to grain size analysis, which, when combined with an investigation of grain alignment (through determination of magnetic fabrics), can indicate the speed of the current at the time of sediment deposition