Sea ice ecosystems in the instrumental period

This page is part of the topic Marine biology in the instrumental period

It is now clear that decreasing sea ice cover in the southwest Atlantic is due to a decline in ice production along the Peninsula. This can significantly reduce the supply of iron to the surface layer. The formation and presence of sea ice has several effects on the underlying water column and benthos. Deep convection due to brine discharge during ice formation can mix the entire water column down to the sea floor. Downward transported organic particles from the productive surface layer thus become available to benthic filter feeders. This mechanism will be a major source of food supply to the sponge-dominated fauna of Antarctic shelves and explains the apparent lack of gearing of reproduction of the shelf benthos to the ice–free period, when vertical particle flux from the overlying water column is at its maximum. Upward mixing of water that has contacted the sediment surface will bring iron to the surface layer. This mechanism of convective upward iron transport and subsequent fuelling of surface phytoplankton blooms has been reported from the Peninsula and around islands with shallow shelves where convective winter mixing is sufficient to reach the sediment surface without ice formation. It follows that the ongoing retreat of winter sea ice along the western Peninsula will result in declining depths of winter mixing and hence also in the supply of iron to the water column overlying deeper shelves, where surface warming reduces ice formation. A decrease in downstream spring productivity can be expected, which might be a factor contributing to krill decline in this region. However, it cannot be the only factor because the krill decline began before the retreat of the sea ice.