Biological modification of carbonate chemistry in dense water outflows from the Mertz Polynya, East Antarctica

Polynyas, areas of open water with in the sea-ice pack, are often biologically productive, and are sites of enhanced air–sea exchange. The Mertz polynya is formed in East Antarctica by persistent katabatic winds and an ice barrier created by the Mertz Glacier Tongue. The region plays a significant role in the formation of dense shelf water (DSW) primarily due to salt rejection during intense sea-ice formation. Physical and biogeochemical observations indicate that primary production over the shelf in spring/summer preconditions the dense water outflows, supplying both organic material, and water depleted in CO2, to coral and sponge communities on the continental slope. The formation and export of DSW also plays a role in the transfer of anthropogenic CO2 to the deep ocean. In February 2010 a large piece of ice (~70 km long and ~35 km wide) calved from the Mertz Glacier Tongue, dramatically changing the regional fast-ice and pack-ice distributions. The physical and biogeochemical consequences of this event (based on observations pre- and post-calving) included significant surface freshening, a twofold enhancement of biological production, and an increase in the carbonate saturation state.