Contrasting productivity and redox potential in Arabian Sea and Bay of Bengal

Abstract

Understanding the past and present changes is critical for evaluating the future climatic changes. In order to understand the paleoproductivity and depositional environments of Northern Indian Ocean, two sediment cores were collected, one each from the Arabian Sea (lat. 16°51.40′N and long. 71°54.37′E, water depth 803 m) and the Bay of Bengal (lat. 13°05.35′N and long. 91°28.21′E, water depth 3 054 m). The surface seawater samples indicate higher pCO2 values in Arabian Sea as compared to the Bay of Bengal. The sediment organic carbon variations along with sedimentological and other geochemical parameters were studied. Sediment organic carbon varied from 0.5%–4.7% and 0.3%–1.22% in Arabian Sea and the Bay of Bengal, respectively. In Arabian Sea, low productivity, oxic conditions and less intense southwest monsoon prevailed during the deglacial period, whereas productivity has increased from last 16 kyr to the modern age. In the Bay of Bengal, organic carbon decreased from the Last Glacial Maxima (LGM) to the modern age, indicating higher productivity in the past as compared to modern age. Fe was associated with organic carbon in the Bay of Bengal and increased during LGM, showing similar trend to that of organic carbon, indicating that Fe may be the limiting factor for the growth of phytoplankton in the Bay of Bengal in the modern age. In the Bay of Bengal, Mn is enriched during modern age and is depleted during LGM, whereas chromium showed the opposite trend indicating anoxic conditions during the LGM, whereas in Arabian Sea the trends are opposite to the Bay of Bengal.