Bio-optical characteristics along the Strait of Magallanes

LUTZ, V.; FROUIN, R.J.; NEGRI R.M.; SILVA, R.I.; POMPEU, M.; RUDDORF, N.

San Francisco

Simposio; The Second International Ocean Color Science Meeting; 2015

International Ocean-Colour Coordinating Group

The Strait of Magallanesat the tip of South-America connects the Atlantic and Pacific Oceans.Artisanal fisheries, as well as aquaculture, are actively developed in theregion. Here we analyze the variability in the absorption by phytoplankton (aph(440)), non-pigmentedparticles, NPP (aNPP(440)),and CDOM (ay(440))measured along the strait in late summer 2011. MODIS-Aqua PAR, 4-km, Level 3monthly composite data showed that the western sector was a permanent low-lightenvironment (~ 25 mol quanta m-2d-1, due to heavy cloudsand rainy conditions) while the eastern sector had relatively higherirradiances (~ 40 mol quanta m-2d-1). In the PatagonianShelf total absorption was dominated by phytoplankton (maximum aph(440)=0.265 m-1),while in the Atlantic Sector of the strait, the majorcontributor was NPP (maximum aNPP(440)=0.138m-1), and in the Pacific Sector of the strait CDOM contributed up to80% of the total absorption (ay(440)=0.232m-1). These changes could be related to the input of fresh waterfrom glaciers melting and rain on the Pacific Sector (ay(440) vs salinity rS -0.98). Chlorophyll-aconcentration (Chla) ranged from 4.77 mg m-3 in the Patagonian Shelf to 0.55 mg m-3 in the Pacific Sector. The carbon biomass (C) wascomposed in its majority by pico-phytoplankton and secondly by thenano-phytoplankton, with exception of the Atlantic Sector where themicro-phytoplankton dominated. C:Chla ratios were very low (average 6.9) as aresult from photo-acclimation to this extreme low light environment, whichseems to be the major factor affecting phytoplankton in this region.