A Southern Ocean-wide examination of Multi-year Trends in Sea Ice, Chlorophyll Concentration, and Marine Aerosol Optical Depth

We examined the seasonal variation and causal influences on monthly averages of marine tropospheric aerosols arising from physical and biological interactions across the Southern Ocean (SO). This work is based on a newly developed method for quantifying tropospheric marine aerosol with the NASA Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), which we term marine aerosol optical depth (MAOD). MAOD may be retrieved in nighttime conditions of high-latitude winter and is devoid of cloud contamination, thereby advancing upon prior aerosol optical depth (AOD) measurements linked with biogenic aerosols. Seasonal increases in MAOD were observed alongside seasonal increases in chl-a and sea ice melt across various spatial scales from 2007 to 2020. In order to examine what variables affected change in the tropospheric marine aerosol signal, we utilized empirical dynamic modeling and convergent cross mapping and observed that different factors were important in different regions. For example, changes in chl-a and ice causally forced changes in MAOD for the Bellingshausen Sea region of the western Antarctic Peninsula, with changes in chl-a still significantly affecting changes in MAOD once the seasonality in all variables is accounted for. These results indicate a biogenic component to tropospheric marine aerosol presence across the SO. We will put the results from the Bellingshausen Sea in the context of patterns in MAOD, chl-a, and sea ice across multiple seas of the SO, and examine whether the MAOD signal is causally linked to pulses in wind speed and therefore sea spray. Our work extends upon our previous findings of MAOD trends in the Bellingshausen Sea and will more fully characterize MAOD across the SO.