BIOOPTICAL PROPERTIES OF THE SOUTHWESTERN ROSS SEA

The bio-optical properties of the southwestern Ross Sea were measured as part of the Antarctic research program Research on Atmospheric Vari ability and Atmospheric Response in the Ross Sea (ROAVERRS), The study area contained three distinct phytoplankton blooms, distinguishable b y species composition, The largest in area was located to the north of the Ross Ice Shelf and was dominated by the prymnesiophyte Phaeocysti s antarctica; chlorophyll a (Chl a) ranged from 0.45 to 8.2 mg m(-3). Beam attenuation and particle absorption at 435 nm were as high as 3.4 m(-1) and 0.35 m(-1), respectively. A bloom of diatoms was more spati ally restricted, located to the north and west of the P. antarctica bl oom, with Chl a generally below 4 mg m(-3). Neither diatoms nor P. ant arctica exhibited evidence of the level of pigment packaging measured in waters near the Antarctic Peninsula during the Research on Antarcti c Coastal Ecosystem Rates (RACER) program, possibly because of their s maller sizes. A much smaller cryptophyte bloom, located south of the D rygalski Ice Tongue, displayed a lower pigment-specific absorption spe ctra than did P. antarctica or diatoms, a sign of greater pigment pack aging. Pigment-specific diffuse attenuation coefficients were consiste nt with the pigment-specific particle absorption coefficients (a (ph) ), both being similar to 3 times greater than similar measurements mad e during RACER. Spectral absorption by solutes determined through regr ession analysis of K-d against Chl a for the ROAVERRS data set was nea rly identical to that measured during RACER, Total diffuse attenuation spectra at a given station could be reconstructed by summing the inhe rent optical properties of the major optical components (pure water, s oluble material, detritus, phytoplankton) measured there. Differences in the absorption ratio of a(ph)(lambda) at 490 nm to a(ph)*(lambda) at 555 nm among the three dominant phytoplankton taxa in the southwest ern Ross Sea were responsible for most of the variability in the ratio of remote sensing reflectance (R-rs) at these same wavelengths. At a given concentration of Chl a, the ratio log [R-rs(490):R-rs(555)] was greatest in cryptophyte-dominated waters, which also possessed the low est a(ph)(490): a(ph)*(555) ratio, and lowest in P. antarctica-domina ted waters. These bio-optical differences suggest that no simple empir ical relationship between Chl a and log [R-rs(490): R-rs(555)] will ap ply to all three taxonomically distinct phytoplankton blooms in the so uthwestern Ross Sea.