Department of Earth System Science

Satellite remote sensing estimates of surface chlorophyll, temperature, wind speed, and sea ice cover are examined in the region of the Southern Ocean Iron Experiment (SOFeX). Our objectives are to place SOFeX into a regional context and highlight regional mesoscale spatial and monthly temporal variability. SOFeX fertilized two patches with iron, one south of the Antarctic Polar Front (PF) and one north of the PF but south of the Subantarctic Front (SAF). Satellite-observable phytoplankton blooms developed in both patches. The spring sea ice retreat near the south patch site was delayed in the 2001–2002 season, in turn delaying the naturally occurring, modest spring bloom in this region. Ambient surface chlorophyll concentrations for the area surrounding the southern patch during January 2002 are low (mean 0.26 mg/m³) compared with climatological January values (0.42 mg/m³). Regions east and west at similar latitudes exhibited higher mean chlorophyll concentrations (0.79 and 0.74 mg/m³, respectively). These modest phytoplankton blooms were likely stimulated by melting sea ice via changes in the light-mixing regime and release of iron and were smaller in magnitude than the iron-induced bloom within the SOFeX southern patch (>3 mg/m³). Iron inputs from melting ice may drive much of the natural spatial and temporal variability within the seasonal ice zone. Mean chlorophyll concentrations surrounding the SOFeX northern patch site were similar to climatological values during the SOFeX season. The northern patch was stretched into a long, thin filament along the southern boundary of the SAF, likely increasing the mixing/dilution rate with surrounding waters.