Ocean Colour remote sensing in the Southern Laptev Sea: evaluation and applications

Abstract

Enhanced permafrost warming and increased arctic river discharges have heightened concern about the input of terrigeneous matter into Arctic coastal waters. We used optical operational satellite data from the Ocean Colour sensor MERIS onboard the ENVISAT satellite mission for synoptic monitoring of the pathways of terrigeneous matter in the southern Laptev Sea. MERIS satellite data from 2006 on to 2011 were processed using the Case2Regional Processor, C2R, installed in the open-source software ESA BEAM-VISAT. <br><br> Since optical remote sensing using Ocean Colour satellite data has seen little application in Siberian Arctic coastal and shelf waters, we assess the applicability of the calculated MERIS parameters with surface water sampling data from the Russian-German ship expeditions LENA2010 and TRANSDRIFT-XVII taking place in August and September 2010 in the southern Laptev Sea. The surface waters of the southern Laptev Sea are characterized by low transparencies, due to turbid river water input, terrestrial input by coastal erosion, resuspension events and, therefore, high background concentrations of Suspended Particulate Matter, SPM, and coloured Dissolved Organic Matter, cDOM. <br><br> The mapped calculated optical water parameters, such as the first attenuation depth, Z<sub>90</sub>, the attenuation coefficient, k, and Suspended Particulate Matter, SPM, visualize resuspension events that occur in shallow coastal and shelf waters indicating vertical mixing events. The mapped optical water parameters also visualize that the hydrography of the Laptev Sea is dominated by frontal meanders with amplitudes up to 30 km and eddies and filaments with diameters up to 100 km that prevail throughout the ice-free season. The meander crests, filaments and eddy-like structures that become visible through the mapped MERIS C2R parameters indicate enhanced vertical and horizontal transport energy for the transport of terrigenous and living biological matter in the surface waters during the ice-free season

Space–time dynamics of carbon and environmental parameters related to carbon dioxide emissions in the Buor-Khaya Bay and adjacent part of the Laptev Sea

“…In the ESAS, CDOM is colored because riverine runoff is loaded with humic acids, which are representative of Arctic/sub-Arctic carbon cycling. Note that satellite data available for the ESAS often treat CDOM, incorrectly, as a fraction of ocean-color-derived Chl a, resulting in an overestimation of primary production rates by an order of magnitude (Heim et al, 2013). In our previous studies, we found a strong positive correlation between river-borne DOC and CDOM Shakhova et al, 2009b;Pugach and Pipko, 2013), which allowed us to further treat CDOM as a parameter indicative of riverine DOC.…”

“…This is because the Laptev Sea and the western East Siberian Sea are strongly influenced by riverine runoff enriched in humic substances Pipko et al, 2008Pipko et al, , 2011aPugach and Pipko, 2013). Low transparencies are reflected by in situ Secchi depths of less than 0.5 m near the Bykovsky channel outlet (summer 2008, by Heim et al, 2013) and 0.2-0.4 m in Neelov Bay and the Bykovsky channel (summer 2003, authors' data).…”

“…Nevertheless, field data show that NPP in the highly productive Chukchi Sea is one to two orders of magnitude higher (up to 200-400 g C m −2 yr −1 ) than in the oligotrophic Laptev Sea and western part of the East Siberian Sea (Walsh et al, 1989;Sorokin and Sorokin, 1996). Thus, the proposed NPP increase based on interpretation of satellite data must be validated with observational data (Heim et al, 2013;Fichot et al, 2013). Meanwhile, the observed increase in the Lena River discharge of up to 37 % (2008) since the 1990s suggests that increased levels of annual primary production could be explained by an increasing load of humic acids delivered to shelf water; the color resulting from the presence of CDOM in this water mimics the color resulting from the presence of Chl a when seen from space.…”

“…Note that the 2005 Lena River discharge was the which induced higher levels of coastal erosion and winddriven surface sediment resuspension (Heim et al, 2013) that contributed to the OM supply to the shelf water. At the same time more frequent and longer-lasting storms caused intense water mixing down to the very bottom and consequent release of CO 2 to the atmosphere, allowing significant unloading of the water column CO 2 (Fig.…”

Phytoplankton community structure in the Lena Delta (Siberia, Russia) in relation to hydrography

“…Importantly, the satellite imagery also revealed the presence of a large meander, indicating a high degree of instability between the principal hydrographic zones on smaller than seasonal scales (Heim et al, 2013), making the interpretation of biological signals in the area even more difficult as the extent of these meanders is also related to the discharge magnitude from the major river branches. Longterm changes in discharge/run-off patterns from the Lena Delta, including Trofimov and Bykov channels, have already been shown, probably due to recent climate warming (Berezovskaya et al, 2004;Yang et al, 2002).…”