Comparison Between Early and Late 21stC Phytoplankton Biomass and Dimethylsulfide Flux in the Subantarctic Southern Ocean

Abstract

Time-series of chlorophyll-a (CHL), a proxy for phytoplankton biomass, and various satellite-derived climate indicators are compared in a region of the Subantarctic Southern Ocean (40°−60°S, 110°−140°E) for years 2012−2014. CHL reached a minimum in winter (June) and a maximum in late summer (early February). Zonal mean CHL decreased towards the south. Mean sea surface temperature (SST) ranged between 8℃ and 15℃ and peaked in late February. CHL and SST were positively correlated from March to June, negatively correlated from July to September. CHL and wind speed (WIND) were negatively correlated with peak WIND occurred in winter. Wind direction (WIRD) was mostly in the southwest to westerly direction. The Antarctic Oscillation index (AAO) and CHL were negatively correlated (R = −0.58), indicating that as synoptic wind systems move southwards, CHL increases, and conversely when wind systems move northwards, CHL decreases. A genetic algorithm is used to calibrate the biogeochemical DMS model’s key parameters. Under 4 × CO2 (after year 2100) Regional mean SST increases 12%−17%, WIND increases 1.2 m s−1, Cloud Cover increases 4.8% and mixed layer depth (MLD) decreases 48m. The annual CHL increases 6.3%. The annual mean DMS flux increase 25.2%, increases 37% from day 1 to day 280 and decrease 3% from day 288 to day 360. The general increase of DMS flux under 4 × CO2 conditions indicates the Subantarctic regional climate would be affected by changes in the DMS flux, with the potential for a cooling effect in the austral summer and autumn.