Phytoplankton size-structure on the western shelf of the Antarctic Peninsula: a remote-sensing approach

摘要

Remote-sensing models based on total (b_b) and particle (b_(bp)) backscattering are proposed for estimating phytoplankton size-structure characteristics over the Western Antarctic Peninsula (WAP) waters. It is hypothesized that phytoplankton assemblages with larger cells will have lower spectral b_b and b_(bp) slopes (γ). Likewise, a higher concentrations of total chlorophyll a (chl_T) will coincide with larger phytoplankton cells. Values of γ_(b_(bp)) , derived from satellite and in situ remote-sensing reflectance (R_(rs)) measurements were matched up with field determinations of chlorophyll a concentration fractions (chl_(( > 20μm)) and chl_)((0.45-20μm)) collected between 1997 and 2006 as part of the Palmer-LTER project. Functionalities between in situ measurements of γ_(b_b) and chlorophyll α fractions were also investigated. A consistent inverse relationship between chl_(( > 20μm))/chl_T and γ (b_b and b_(bp)) values was found and verified with two approaches: spatial matchup of satellite monthly composites and time-space matchup of photosynthetic pigment markers. Based on satellite data, a γ_(b_(bp)) value of 1.668 was a fair predictor to differentiate WAP waters dominated by 'large' (chl_(( > 20μm))/chl_T ≥ 0.5, γ_(b_(bp)) ≤ 1.668) vs 'small' (chl_(( > 20μm))/chl_T < 0.5, γ_(b_(bp)) > 1.668) phytoplankton cells. A significant negative linear relationship between 19'-butanoylox-yfucoxanthin, fucoxanthin, and γ_(b_(bp)) values suggest that Phaeocystis aggregates and large diatoms ( > 20μm) would explain most of the chl_(( > 20 μm))/chl_(T-γ) variability. No relationships were evident between chl_T values and γ values. Although our results cannot be generalized to other oceanic regions, this work is the first to provide evidence about the significant influence of phytoplankton size distributions on spectral backscattering of WAP waters. Furthermore, and based on chlorophyll a fraction analysis, it was the > 20μm phytoplankton cells that were responsible for such γ variations seen on satellite and in situ values.