Masters Thesis

Sedimentary controls on foraminifera deposition in the Bay of Bengal

Recent IODP expeditions to the Bay of Bengal present an excellent opportunity for better understanding the links between terrestrial and oceanographic climate variability over a variety of timescales. However, foraminifera in Bengal fan sediments may have been transported via turbidity currents. Given the variability in SST and SSS between the southern Bay of Bengal (29.0±0.8°C; 33.9 ±0.3%o) and the northern Bay of Bengal where foraminifera may be transported from (28.0±1.4°C; 31.6±0.8%o), it is important to determine the source of foraminifera to the sediment cores before attempting paleoceanographic reconstructions. We present single foraminifera Mg/Ca and δ18O data from mudline samples of IODP Expedition 354 site U1454 (8.4°N, 85.5°E, 3721 m water depth) near the modem active channel and more likely to be influenced by transport and site U1449 (8.4°N, 88.7°E, 3653 m water depth) far from channel activity. We compare individual Globigerinoides sacculifer from these sites to the core-top sample of site 342KL (19°97'N, 90°03'E, 1256 m water depth) located on the continental shelf. Each foraminifera lives ~2-4 weeks and the distribution of 70 to 80 data points therefore reflects the seasonal range of SST and SSS at the location in which the foraminifera calcified. Foraminifera at site far from channel activity reconstruct the modem seasonal SST (-1.0°C difference) and δ180 (-0.9%o difference) signal of the southern Bay of Bengal. Foraminifera at site near the active channel reflect the SST (1.3°C difference) and 5180 (0.4%o difference) signal also recorded in foraminifera from the continental shelf. This suggests a portion of foraminifera at this site have been transported from the northern Bay of Bengal. Our data shows that foraminifera can be used to reconstruct SST and δI80 in this complex depositional environment, but caution must be taken when the down-core lithology indicates turbidites and possible sediment transport.

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