Late Quaternary Chronostratigraphy, Carbonate Mass Accumulation Rates and Palaeoceanography of the Andaman Sea

Abstract

The Andaman Sea, the least explored semi-enclosed marginal sea in the northern Indian Ocean, is one of the great repositories of palaeo-sedimentary archives for Quaternary climate and oceanographic studies due to its physiographic setting. This marginal sea has some unique features with respect to its response to the past climate change and the difference in the deep-water characteristics with the adjacent Bay of Bengal (BoB). Himalayan Rivers including those traversing Indo-Burmese mountain ranges have one of the world�s highest physical and chemical erosion rates contributing enormous quantity of sediments to the BoB and the Andaman Sea which provides a continuous record of climate variability. Based on ten available accelerator mass spectroscopy (AMS) dated cores retrieved from deeper water depths (>1240 m), the estimated average sedimentation rate for the Andaman basin is ~13 cm/ka and thus the basin is a valuable sedimentary archive for Quaternary climate both in the Andaman Sea and the source areas in Myanmar watersheds. The basin is also characterized by high variability in spatial as well as temporal sedimentation rate. The highest sedimentation rate of ~860 cm/ka reported in the northern part of the Andaman Sea at the Ayeyarwady River mouth with a water depth of ~500 m, whereas the lower rate of sedimentation (~3.1 cm/ka) is witnessed on some rises and mounts in the Western Andaman Sea. These spatial and temporal variations are mainly attributed to the complex bottom topography with valleys and seamounts and the varying oceanography and climate. The basin contains a substantial amount of carbonate sediments which are valuable archives for palaeoceanographic data. Mass accumulation rate (MARs) of carbonate skeletons (Pteropods, planktonic and benthic foraminifera), CaCO3 and total organic carbon in this basin was quantified and were found to be highly comparable with temporal variations in terrigenous input to the basin suggesting that the carbonate productivity within the water column and erosion and weathering processes on Myanmar watersheds were in tandem reflecting the response to the variations in Indian Summer Monsoon (ISM). Very high (~3.0 � 105 no./cm2/ka) MARs of foraminifera was seen during last glacial-Holocene transition, which coincides with relatively higher sedimentation rate and summer insolation at 30� N latitude. The MARs of skeletal carbonate (planktonic and benthic foraminifera) was high during early to mid-MIS 3 and characte�