Late Miocene to Early Pleistocene Deep Water Circulation in the Arabian Sea

Abstract:

Indian Ocean is a major part of Global Overturning Circulation (GOC) as it hosts a significant part of the ocean circulation conveyor belt. Thus, it is essential to understand how the Indian Ocean deep water circulation has changed in the past, in response to the global climate and tectonic changes. Few studies from the Bay of Bengal and the central Indian Ocean have investigated past water mass circulation using authigenic Nd isotope (ε_Nd, a proxy for water mass tracer), however, no such study has been carried out in the north-western Indian Ocean (the Arabian Sea) to the best of our knowledge.

In the present study, we attempted to reconstruct the deep water mass circulation in the Arabian Sea using authigenic neodymium isotope (ε_Nd) compositions of the sediment collected during the IODP expedition 355 from the site U1457 (17°9.94’N, 67°55.81’E, 3523 m) for the time period from late Miocene to early Pleistocene (11-2 Ma). Our high-resolution record of authigenic ε_Nd shows large variability with the values ranging from -4.5 to -10.8 and more radiogenic values during 11 - 6 Ma. The large variability reflected in the ε_Nd record could be due to the changes in relative contributions of various water masses, weathering inputs and/or aeolian dust input. The higher values (ε_Nd ~-5) can be a result of enhanced contributions from Arabian dust or weathering of Deccan Basalt (ε_Nd -2 to -5) or the changes in the source region of the Antarctic Bottom Water (AABW) formation. Whereas the less radiogenic values can be attributed to the strengthening of North Atlantic Deep Water (NADW) (ε_Nd -13) and export of deep water masses similar to modern time.