Origins of Carbon Isotope Signals in Tropical and Polar Oceans: 0-25,000 Years B.P.

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The carbon-isotopic signal of the Southern Ocean surface waters near the polar front is enriched in delta C-13 by 1.0 per mil. However, downcore the planktonic forams in the polar front region show a greater variation in C-13 because of the migrations of the front through time, linked to changes in carbon-isotopic composition of the Antarctic Intermediate Water (AAIW). In the tropics the delta C-13 signal is small and its origin is debated. The objective of the proposed research is to isolate global, transient, thermodynamic, and "Redfield" changes in the tropical and polar surface water isotopic records. Funds are provided for a two years' stable-isotopic study of cores from the topical to polar waters spanning the past 250 k.yrs. to decipher the origin of the carbon-isotopic signal. The study will help resolve the changes in the position and intensity of the polar front. The analyses of Cd/Ca ratios of forams Cibicides sp. along with their carbon-isotopic analyses may help determine if the decoupling of the two systems can be used to identify the presence of AAIW.