Distribution of normalized water-leaving radiances at UV and visible wave bands in relation with chlorophyll a and colored detrital matter content in the southeast Pacific

Abstract : [1] In-water radiometric measurements were performed in the southeast Pacific (8°S-35°S, 141°W-72°W) from October to December 2004 during the Biogeochemistry and Optics South Pacific Experiment cruise. Normalized water-leaving radiances (nL w (l)) were determined at eight wave bands within the ultraviolet (UV) (305, 325, 340, and 380 nm) and visible (412, 443, 490, and 565 nm) spectral domains. The highest nL w (l) (mW cm À2 sr À1) were recorded in the hyperoligotrophic waters of the South Pacific Gyre, with values increasing with wavelength from 305 (nL w = 0.64) to 380 nm (nL w = 3.18) in the UV range and decreasing from 412 (nL w = 4.46) to 565 nm (nL w = 0.23) in the visible region. The intense nL w (l) observed in the violet-blue domains were attributed to very low absorptions of colored detrital matter (CDM), likely related to a strong photobleaching of colored dissolved organic matter in the surface waters. We evaluated the relationships between the UV, violet, or blue/green wave band ratios of nL w (l) and surface total chlorophyll a (TChl a) concentration and CDM absorption (a CDM (l)). For TChl a, the best correlation was found with the blue/green ratio at 443 nm: TChl a (mg m À3) = 2.37[nL w (443)/nL w (565)] À1.51 (r 2 = 0.86 and RMS error (RMSE) = 23%). By contrast, for a CDM (l), the best correlation was observed when using the UV/green ratio at 325 nm: a CDM (325) (m À1) = 0.16[nL w (325)/nL w (565)] À0.69 (r 2 = 0.82 and RMSE = 16%). These results show the potential role of nL w (l) at UV wave bands for the assessment, through empirical algorithms, of colored detrital matter in the surface oceanic waters. Citation: Tedetti, M., B. Charrière, A. Bricaud, J. Para, P. Raimbault, and R. Sempéré (2010), Distribution of normalized water-leaving radiances at UV and visible wave bands in relation with chlorophyll a and colored detrital matter content in the southeast Pacific,
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Marc Tedetti, Bruno Charrìère, Annick Bricaud, Julien Para, Patrick Raimbault, et al.. Distribution of normalized water-leaving radiances at UV and visible wave bands in relation with chlorophyll a and colored detrital matter content in the southeast Pacific. Journal of Geophysical Research, American Geophysical Union, 2010, 115 (C010), pp.1-12. ⟨10.1029/2009JC005289⟩. ⟨hal-00456621⟩

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