Elemental Ratios of Bioactive Trace Metals in the Bay of Bengal

The Bay of Bengal is heavily influenced by a variety of anthropogenic and natural inputs. Rivers and run-off, dust, and industry all supply trace metals (TMs) of biological importance. In addition, the subsurface waters of the Bay of Bengal are not well-ventilated, and the resulting low-oxygen waters can affect both the supply and removal of TMs between the surface and the sediments. To better understand the sources and cycling of trace elements in the Bay of Bengal and the Indian Ocean, suspended particulate matter (SPM) samples were collected during the I8S/I9N and I5 CLIVAR/CO2 Repeat Hydrography Indian Ocean transects (2007-2009). These samples, collected on 0.4 um Nuclepore PCTE filters, were digested and analyzed by ICP-MS at the National High Magnetic Field Laboratory (Tallahassee, Florida, USA) for a suite of trace (e.g., Fe, Mn) and major (e.g. Al, P) elements. Particulate Fe and Mn concentrations are highest below the surface (100-200m) and suggest lateral transport of sediments from the northern coast. High particulate P concentrations are found with high bioactive TM concentrations, such as Cd, Cu, and Ni. However, a secondary subsurface maximum is also observed in these TMs, concurrent with low oxygen concentrations and possibly indicating the presence of insoluble sulfide species, which has been proposed in other low oxygen systems. Elemental ratios of these particles (e.g., Cd/P, Mn/Al) will also be compared with literature values of microbial TM quotas and crustal abundances, to further explore biological and redox cycling in the Indian Ocean.