Transfer of the Sr isotopic signature of the Himalayas to the Bay of Bengal

The Sr isotopic signal of the Himalayas is transferred to the sea by riverine water and carbonate particles. The isotopic composition of the carbonate fraction of the sediment is used to trace the sedimentary input into the Bay of Bengal by the Ganges–Brahmaputra river system. Carbonate with 87Sr/86Sr>0.7100 marks the main areas of recent sediment deposition: the submarine delta, the shelf canyon “Swatch of No Ground”, and the connected active channel–levee system of the Bengal fan up to a distance of at least 1100 km from the mouth of the rivers. In contrast, the isotopic signal of the Sr dissolved in the river disappears with the first mixing with the seawater. Sr isotopic composition of tests of surface-dwelling foraminifera (Globigerinoides ruber) prove that the average value of the seawater in the northern Bay of Bengal has not changed during the last 40,000 years. Increasing 87Sr/86Sr ratios of the total carbonate since the end of the Younger Dryas correlate with decreasing δ18O values of the planktonic foraminifera, which are interpreted to result from increasing fresh water input and supply of detrital carbonate in response to increasing intensity of the SW summer monsoon.