The response of the deep convection to the Antarctic Meltwater

Observations indicate that the mass loss from the Antarctic ice sheet has been increasing over the past several decades. This loss is projected to accelerate significantly into the future. Deep convection in the Southern Ocean is expected to bear the brunt of meltwater from a retreating Antarctic Ice Sheet. Here, we present the responses of deep convection and Antarctic Bottom Water (AABW) formation using six coupled climate models with a constant rate of freshwater flux anomaly. Six models all show a significant decrease in the strength of deep convection, albeit the magnitude and location of the changes vary greatly across models. Models that convect more strongly in the base state decrease more in deep convection. We found that the big difference in response between models is surprisingly consistent with their respective base states. With the cessation of deep convection, the AABW becomes warmer and of contraction, and the sea ice concentration and area increase significantly, accompanying surface cooling. However, the link between the responses in deep convection and sea ice area is more complicated than simply meaning more reduction in deep convection corresponds to more increase in sea ice. We suggest that this complexity is partly because some models convect over too large an area and the freshwater forcing is rather strong. Our results suggest that increasing Antarctic meltwater into the ocean will reduce AABW formation, amplifying the warming rate of deep and abyssal waters and reducing the melting rate of sea ice caused by heat input, and reducing vertical exchange due to intensified stratification.