Productivity controls on the redox variation in the southeastern Arabian Sea sediments during the past 18 kyr

Abstract

Redox-sensitive elements (uranium, molybdenum and cadmium) and productivity proxies (total organic carbon, calcium carbonate and phosphorous) were analysed to assess the importance of productivity on redox variation for the last ∼18 kyr in a sediment core off Cochin at a water depth of 280 m in the southeastern Arabian Sea. These proxies document a combination of higher productivity and intense suboxic conditions during the last deglaciation (∼18–13 kyr) and late Holocene (5.5 kyr to Present) versus lower productivity and less suboxic conditions between these intervals (∼13–5.5 kyr). The productivity and redox proxies behave similar to one another suggesting that the variations in productivity controlled the redox conditions. This relationship is supported by patterns during the last deglaciation, when a decrease in productivity at ∼16 kyr preceded improved deep water oxygenation by ∼14 kyr. Therefore, productivity changes were responsible for the development of reducing conditions in shallow waters in the southeastern Arabian Sea.