The Ross Sea, Antarctica’s most pristine region, is experiencing anomalously marked increase in sea ice concentration. Future changes in atmospheric temperatures and wind speeds, however, will likely produce a noticeably different environment. Smith et al. examines the effect of projected changes in atmospheric temperatures and winds on aspects of ocean circulation and its implications for primary production of the Ross Sea.
A high-resolution sea ice – ice shelf – ocean model is used under future atmospheric forcing to simulate projections of oceanographic parameters such as summer mixed layer depth, duration of yearly ice-free periods and on-shelf flux of warm nutrient rich Circumpolar Deep Water for 2050 and 2100.
By 2050 and 2100 duration of yearly ice-free periods increases by 43% and 125% respectively. These modifications are accompanied by respective decreases of 24% and 8% in the amount of modified Circumpolar Deep Water entering the upper 50 m of the water column. Ice-free conditions allow greater irradiance to penetrate the water column, restricting Circumpolar Deep Water’s contribution of nutrients onto the continental shelf. The study also analyzes the depth of the mixed layer, which represents future changes in the vertical structure of the water column across the continental shelf. Projections for 2050 and 2100 showed a decrease in the summer mixed layer by 12% and 44% respectively. These large changes in mixed layer depth and the reduction of CDW fluxes have implications for the vertical replenishment of surface nutrients at the start of the growing season. These changes have implications for biological processes in the Ross Sea: the large reduction in summer sea-ice allows more phytoplankton growth, future reduction in the mixed layer depth implies that ocean stays stratified for a longer period resulting in a modification of the surface plankton composition from haptophytes to diatoms, which overall increases annual primary production by 14%. The study highlighted how changes in production can alter other components of the Ross Sea food web, with unpredictable impacts on this still unspoiled Ross Sea ecosystem.
Smith Jr.WO, Dinniman MS, Hofmann EE, Klinck JM (2014) The effects of changing winds and temperatures on the oceanography of the Ross Sea in the 21st century. Geophysical Research Letters 41: 1624-1631