Apparent optical properties of the Canadian Beaufort Sea – Part 1: Observational overview and water column relationships

Abstract

Abstract. A data set of radiometric measurements collected in the Beaufort Sea (Canadian Arctic) in August 2009 (Malina project) is analyzed in order to describe apparent optical properties (AOPs) in this sea, which has been subject to dramatic environmental changes for several decades. The two properties derived from the measurements are the spectral diffuse attenuation coefficient for downward irradiance, Kd, and the spectral remote sensing reflectance, Rrs. The former controls light propagation in the upper water column. The latter determines how light is backscattered out of the water and becomes eventually observable from a satellite ocean color sensor. The data set includes offshore clear waters of the Beaufort Basin as well as highly turbid waters of the Mackenzie River plumes. In the clear waters, we show Kd values that are much larger in the ultraviolet and blue parts of the spectrum than what could be anticipated considering the chlorophyll concentration. A larger contribution of absorption by colored dissolved organic matter (CDOM) is responsible for these high Kd values, as compared to other oligotrophic areas. In turbid waters, attenuation reaches extremely high values, driven by high loads of particulate materials and also by a large CDOM content. In these two extreme types of waters, current satellite chlorophyll algorithms fail. This questions the role of ocean color remote sensing in the Arctic when Rrs from only the blue and green bands are used. Therefore, other parts of the spectrum (e.g., the red) should be explored if one aims at quantifying interannual changes in chlorophyll in the Arctic from space. The very peculiar AOPs in the Beaufort Sea also advocate for developing specific light propagation models when attempting to predict light availability for photosynthesis at depth.

Pan-Arctic optical characteristics of colored dissolved organic matter: Tracing dissolved organic carbon in changing Arctic waters using satellite ocean color data

“…This important task remains to be made in further studies. The significant contribution of Raman scattering on R rs (λ) for Arctic waters is somewhat contradictory because this effect is more pronounced in typical Morel and Prieur (1977)'s case 1 water than in case 2 waters Gentili, 1991, 1993;Gordon, 1999); Arctic waters are often classified as case 2 water due to high proportion of CDOM absorption relative to scattering (Antoine et al, 2013;Matsuoka et al, 2011Matsuoka et al, , 2014. However, it is logical that upwelling radiance in the water column within the remote sensing domain (up to 37°from the sun zenith) is contributed by Raman scattering when single scattering prevails in case 2 water (Loisel and Morel, 2001).…”

“…Subsurface L u values at null depth (i.e., L u (0 − , λ)) were calculated using the slope and intercept by fitting the least-squares linear equation to the logtransformed upwelled radiance versus z for MALINA, ICESCAPE2010, and ICESCAPE2011 data. The depth interval was chosen following the method described by Antoine et al (2013). Briefly, a centered depth z0 and +/− Δz was first set within homogeneous surface layer.…”

Dissolved organic matter at the fluvial–marine transition in the Laptev Sea using in situ data and ocean colour remote sensing

“…DOC concentration maps with high spatial and temporal resolution will improve our understanding of DOC dynamics in fluvial-marine transition zones and better quantify carbon cycling. However, most OCRS retrieval algorithms have focused on optically deep (Case 1) waters, which usually correspond to open ocean where all optical water con-stituents are coupled to chlorophyll concentration (Antoine et al, 2014;Mobley et al, 2004;Morel and Prieur, 1977). Generally, the Laptev Sea coastal to central-shelf waters and Lena River water can be classified as extreme-absorbing and high-scattering waters with high optical complexity (Case 2) (Heim et al, 2014).…”

Assessment of ocean color data records from MODIS-Aqua in the western Arctic Ocean

“…Initial assessments of IOP time-series from SAAs in the Arctic Ocean have shown potential for improving remote sensing C a retrievals in the Arctic (Bélanger et al, 2007;Ben Mustapha et al, 2012). Only very recently have the broad datasets necessary for this task been assembled as the direct result of programs such as ICESCAPE, Malina, and Takuvik (Antoine et al, 2013;Matsuoka et al, 2013b;Zheng et al, in press).…”