Polar cooling due to increases of phytoplankton and DMS emission

Marine phytoplankton play a key role not only in marine ecology but also in climate change. The link to climate change begins with the fact that phytoplankton produce the biogenic gas, dimethyl sulfide (DMS), that is emitted to the air above the sea surface and oxidized eventually to become sulfate aerosols, which are the major source of cloud condensation nuclei (CCN) over the oceanic regions remote from pollution sources. Effects of increased DMS emission due to increased marine phytoplankton activity are examined using Hadley Centre Global Environmental Model version 2 - Atmosphere-Ocean (HadGEM2-AO). Several previous studies suggested that the increased phytoplankton biomass could enhance global warming and amplify Arctic warming by SST increase and sea ice melting. However increased phytoplankton biomass emit more DMS, thus the increased sulfate CCN concentration can induce global cooling effects, which are known as the aerosol direct and indirect effects. In this study, we demonstrate that, as the DMS emission flux from the ocean is increased more, cooling trend becomes stronger. This cooling trend is pronounced especially over the polar regions due to increase of sea ice fraction and albedo. Despite the importance of phytoplankton response mechanisms, most climate models do not include both the positive and negative feedback mechanisms that involve phytoplankton. Both the warming and cooling effects of marine phytoplankton should be properly reflected in future climate models for better estimation of climate change, especially over the polar regions. More detail will be discussed at the conference.