Phytoplankton Biomass near a Receding Ice-Edge in the Ross Sea

Summary

Ice-edge zones have been hypothesized to be major sites of primary production and energy transfer within the Southern Ocean, and large biomass accumulations of upper-trophic-level organisms (birds and mammals) occur in these zones. However, few data exist to determine if these ice-edge regions support elevated levels of phytoplankton and enhanced rates of primary production. During 2 cruises on the USCGC Glacier in January-February, 1983, the chlorophyll distribution was measured in different areas of the Ross Sea. Our primary study area was located off the coast of southern Victorialand (76° 30′ S) in a region of receding pack-ice. We occupied 34 stations in a 100 × 300 km area of variable ice concentration. In comparison to control stations and previous data, chlorophyll levels were high, averaging 4.08 ± 1.46 mg chl-a m⁻³ at the depth of the chlorophyll maximum in the water column, and 128.2 ± 91.7 mg m⁻² when integrated from the surface to 150 m. High surface chlorophyll levels appeared to be highly correlated with a stable surface layer at the edge of the receding ice-pack. At stations outside of the ice-edge bloom, stability at the surface was reduced and chlorophyll concentrations were markedly lower. Water column stability appeared to be a major factor in the initiation and maintenance of ice-edge phytoplankton blooms, and the roles of these blooms in the overall estimates of biogenic production and energy flux of the Southern Ocean need to be re-evaluated.