Bio-optical characteristics along the Straits of Magallanes

LUTZ, V.; FROUIN, R.J.; NEGRI R.; SILVA R; POMPEU, M.; RUDORFF, N.; CABRAL, A.; DOGLIOTTI, A.I.; MARTINEZ, G.

CONTINENTAL SHELF RESEARCH

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 119 p. 56 - 67

0278-4343

The Straits of Magallanes at the tip of South America connects theAtlantic and Pacific Oceans. The variabilityin the absorption characteristics by phytoplankton (aph(440)), non-pigmented particles, NPP (aNPP(440)), and chromophoric dissolvedorganic matter, CDOM (ay(440)),measured along the Straits in late summer 2011 (R/V Melville MV1102 cruise),was analyzed. Satellite-derived monthly PAR data showed that at the time of thecruise the western sector was exposed to a low-light environment (~ 16 molquanta m-2d-1) while the eastern sector received higherirradiance (~ 28 mol quanta m-2d-1). In the PatagonianShelf total absorption was dominated by phytoplankton (up to 76%; aph(440)=0.265 m-1),while in the Atlantic Sector of the Straits, the major contributor was NPP (upto 42%; aNPP(440)=0.138 m-1),and in the Pacific Sector of the Straits CDOM contributed up to 80% of thetotal absorption (ay(440)=0.232m-1). These changes could be related to the input of fresh waterfrom glacier melting and rain in the Pacific Sector (ay(440) vs salinity rs=-0.98). The carbonbiomass (C) was composed in its majority by pico-phytoplankton and secondly bynano-phytoplankton, with exception of the Atlantic Sector where themicro-phytoplankton dominated. Carbon to chlorophyll-a ratios (C:Chla) werevery low throughout the Straits (average of ~ 6) because of photoacclimation tothe extremely low light. Complementary pigments data obtained in spring 2003 bythe BEAGLE expedition indicated the predominance of diatoms all along the Straits,but the bio-optical trend resembled the one found in late summer 2011, i.e., NPP dominated the absorption inthe well mixed Atlantic Sector, phytoplankton in the Middle Sector, and CDOM inthe Pacific Sector. These results emphasize that underwater light is the majorfactor affecting phytoplankton growth and physiology, and that prevalentphysical and geochemical conditions play an important role regulating thebio-optical properties in this heterogeneous area. These effects should beconsidered to adjust parameters (such as C:Chla) when running biogeochemicalmodels for this region.