Case 2 Antarctic Coastal Waters: the Bio-optical Properties of Surface Meltwater

In the Antarctic region, melting of sea ice and continental glaciers can create a surface lens of meltwater in coastal waters. When ice melts, particles concentrated within the ice are released into the water and can cause turbidity. Under these conditions, the optical properties of the water column are no longer related primarily to the phytoplankton and associated breakdown products (i.e., Case 1) and would be classified as Case 2. Using bio-optical data collected in conjunction with the Palmer Long Term Ecological Research Project, we compare the remote sensing reflectance spectra for meltwater conditions with the typical Case 1 spectra found in these waters. The Case 2 waters have significantly higher reflectance across all wavelengths than the Case 1 conditions, which is indicative of higher levels of backscattering. Measurements of backscattering conducted with the Hydroscat instrument further confirm that backscattering is high and uncorrelated to chlorophyll when the surface lens of meltwater is present. These results are discussed in the context of ocean color remote sensing of meltwater and the associated impact of meltwater on the biomass within the water column. Instrument records over the last half-century have shown a statistically significant warming trend in air temperature along the Antarctic Peninsula that is also evident by the destruction of the Larsen Ice Shelf and the retreat of continental glaciers. Thus, meltwater conditions may become more prevalent and have important implications for bio-optical properties of surface waters and, subsequently on the primary production in this climatically sensitive region.