Late Quaternary carbonate dissolution cycle recorded in southern Drake Passage

Abstract

Changes in deep sea carbonate chemistry might have played an important role in controlling the glacial-interglacial variation in atmospheric carbon dioxide (pCO2) concentration. However, contribution of deep ocean to glacial-interglacial pCO2 variation is still elusive, partly due to deficiency of carbonate data in critical regions such as those proximal to the source of global deep water. Here we present the carbonate content of six gravity cores from 2710 to 4090 m water depths of the southern Drake Passage (SDP). A gravity core from 2710 m contains carbonate of 16 to 63%, and shows high-carbonate interglacial and low-carbonate glacial pattern, reflecting higher primary carbonate productivity during interglacial periods. The other SDP cores from deeper water depths, however, contain much lower carbonate of 0 to 26%, and are characterized by virtually no carbonate during interglacial periods for the last ~800 kyr. This difference in glacial-interglacial carbonate variability pattern among different water depths suggests that dissolution of carbonate on the seafloor has been more intense during interglacial periods than glacial periods during the late Quaternary in the SDP. We interpret this is due to highly corrosive nature of interglacial deep water originated from the Weddell Sea. Oceans bathed by the deep water originated from the Weddell Sea and probably from the Antarctic margins should have been affected by the corrosive interglacial deep water, and the so-called ‘Pacific-type’ carbonate pattern of low carbonate interglacial and high carbonate glacial periods can be made in those regions. This study emphasizes the active role of Antarctic-sourced deep water, especially during interglacial periods, in controlling deep sea carbonate saturation state. Wider shelf area and more extensive ice shelves in interglacial periods compared with glacial periods might have facilitated the production of corrosive deep water in the Antarctic margin.