Abstract
As consequences of global warming sea-ice shrinking, permafrost thawing and changes in fresh water and terrestrial material export have already been reported in the Arctic environment. These processes impact light penetration and primary production. To reach a better understanding of the current status and to provide accurate forecasts Arctic biogeochemical and physical parameters need to be extensively monitored. In this sense, bio-optical properties are useful to be measured due to the applicability of optical instrumentation to autonomous platforms, including satellites. This study characterizes the non-water absorbers and their coupling to hydrographic conditions in the poorly sampled surface waters of the central and eastern Arctic Ocean. Over the entire sampled area colored dissolved organic matter (CDOM) dominates the light absorption in surface waters. The distribution of CDOM, phytoplankton and non-algal particles absorption reproduces the hydrographic variability in this region of the Arctic Ocean which suggests a subdivision into five major bio-optical provinces: Laptev Sea Shelf, Laptev Sea, Central Arctic/Transpolar Drift, Beaufort Gyre and Eurasian/Nansen Basin. Evaluating ocean color algorithms commonly applied in the Arctic Ocean shows that global and regionally tuned empirical algorithms provide poor chlorophyll-a (Chl-a) estimates. The semi-analytical algorithms Generalized Inherent Optical Property model (GIOP) and Garver-Siegel-Maritorena (GSM), on the other hand, provide robust estimates of Chl-a and absorption of colored matter. Applying GSM with modifications proposed for the western Arctic Ocean produced reliable information on the absorption by colored matter, and specifically by CDOM. These findings highlight that only semi-analytical ocean color algorithms are able to identify with low uncertainty the distribution of the different optical water constituents in these high CDOM absorbing waters. In addition, a clustering of the Arctic Ocean into bio-optical provinces will help to develop and then select province-specific ocean color algorithms.
Highlights
The Arctic Ocean basin receives 11% of the global freshwater input with its volume representing only 1% of the global ocean [1]
The permanent loss of sea-ice may lead to an increase in light penetration in the Arctic surface layer [13] and to changes in the composition of phytoplankton assemblages [14], the overall primary production in the Arctic Ocean [15,16], and the degradation of terrestrial material transported to that basin [17,18]
Based on the temperature and salinity profiles five water masses were identified within the surface layer (0−200 m) of the sampled area, which are in agreement with previous studies in the region [45,69]: Upper Halocline Water (UHW), Barents Sea Branch Water (BSBW) and Laptev Sea Shelf Water (LSSW) at the surface; and Lower Halocline Water (LHW) and Atlantic Water (AW) in the beneath layer (Fig 2A)
Summary
The Arctic Ocean basin receives 11% of the global freshwater input with its volume representing only 1% of the global ocean [1]. Together with the fresh water, high loads of terrestrial material (organic and inorganic; dissolved, colloidal and particulate) are introduced in that basin, in particular through the wide Siberian continental shelves [2,3,4,5,6]. By this the Arctic Ocean presents a large carbon reservoir and plays an important role in the planet’s carbon cycle. The permanent loss of sea-ice may lead to an increase in light penetration in the Arctic surface layer [13] and to changes in the composition of phytoplankton assemblages [14], the overall primary production in the Arctic Ocean [15,16], and the degradation of terrestrial material transported to that basin [17,18]
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