Arctic deep-water anoxia and its potential role for ocean carbon sink during glacial periods

Abstract

Deep water freshening beneath pan-Arctic ice shelves has recently been proposed based on the absence of excess thorium in glacial Arctic sediments. This profound proposal requires scrutiny of Arctic paleohydrology during past glacial periods. Here, we present structural and geochemical results of inorganic authigenic carbonates in deep-sea glacimarine sediments from the Mendeleev Ridge, western Arctic Ocean over the last 76 kyr. Our results suggest that Polar Deep Water in the western Arctic became brackish and anoxic during stadial periods. We argue that sediment-laden hyperpycnal meltwater discharged from paleo-ice sheets filled much of the water column depending upon the density, substantially reducing the salinity and oxygen content of the Polar Deep Water. Our findings suggest that this phenomenon was more extreme in the western Arctic Ocean and may point to the potential role of the western Arctic Ocean as an additional carbon reservoir in the global carbon cycle across glacial-interglacial cycles. Freshening and oxygen depletion of the polar deep waters of the Amerasian Basin during the last glacial periods probably resulted in significant carbon burial, according to geochemical analyses of inorganic authigenic carbonates in Arctic Ocean sediments.