Description: 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. 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. The mapped calculated optical water parameters, such as the first attenuation depth, Z90, 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.

Description: The Lena River strongly influences physical, biological and chemical processes on the Laptev Sea shelf through vast amounts of freshwater runoff. The Lena river water is poor in nutrients and carries high concentrations of dissolved organic matter (DOM) and colored dissolved organic matter (CDOM). Here we present CDOM absorption complemented by profiles obtained with an in situ WETstar fluorometer during expeditions in August 2010 and 2011, in order to study the vertical and horizontal CDOM distribution on this shelf. The results show that the river Lena dominates the supply of CDOM which exhibits a conservative mixing behavior over a wide range of salinities. The low light penetration of the CDOM-rich river water in conjunction with low concentrations of dissolved phosphate and nitrate and a strong density stratification of the water column result in low chlorophyll a concentrations within and beneath the river plume. Outside of the river plume increased water transparency and the upward transport of phosphate and nitrate from nutrient enriched bottom waters lead to the formation of deep chlorophyll maxima at the pycnocline.

Description: Important for the carbon export to the Deep Sea, Transparent Exopolymer Particles (TEP) also serve as nutritional substrate and attachment surfaces for bacteria, supporting biological oxygen consumption. Spatial distribution of TEP in the Eastern South Pacific Ocean (ESP), an area influenced by a highly productive upwelling system and underlying extensive Oxygen Minimum Zone (OMZ), is largely unknown. In attempt to recognize how TEP stocks are affected by complex biogeochemistry of ESP and vice versa, we determined TEP distribution in the ESP (12°-14°S, 76°-79°W) during the Meteor 93 cruise (February - March 2013). Highest TEP concentrations (〉1900µgXeq/l) were observed close to the coast, coinciding with upwelling of nutrient-rich waters. Generally TEP accumulated in the oxygenated photic layer and correlated significantly with chlorophyll-a-fluorescence (r=0.7, n=323, P〈0.05). At the upper boundary the OMZ (70 m), TEP concentrations were moderate (〈80µgXeq/l), slightly attenuating toward its lower border (〈60µgXeq/l; 500m depth). The role of TEP for organic matter cycling in the ESP and their potential influence on oxygen and carbon fluxes in the OMZ are discussed.

Description: Terrestrial dissolved organic matter (DOM) is continuously discharged by rivers into the ocean. The enhanced permafrost thawing and increased arctic river discharges over the last decades have heightened concern about the input of terrestial materials into the Arctic coastal waters. Chromophoric dissolved organic matter (CDOM) is the optically active component of DOM formed by organic compounds that absorb light at both ultraviolet and visible wavelength bands. This DOM fraction has a strong impact in the carbon cycle and other elements mediating photochemical reactions and, hence, modulates light attenuation in the ocean. Therefore, CDOM interferes with satellite estimations of chlorophyll a and primary production. The objective of this work is to analyze the field CDOM data set including: 202 water samples and 18 vertical CDOM fluorescence profiles taken at oceanographic stations carried out during the TRANSDRIFT-XVII expedition to the Laptev Sea, and 15 water samples from the Lena2010 expedition. Thirty satellite images capturing the Laptev Sea region in September 2010 were processed to reveal the spatial distribution of optical parameters in the surface layer and to correlate the field CDOM and turbidity data with remote sensing data. A relationship between salinity, absorption, slopes and CDOM fluorescence was found and conservative CDOM mixing between riverine and marine waters was observed. This implies that strong in situ sources and/or sinks in CDOM concentration are absent. Within the range of salinities from 0 to 22 the spectral slope of the absorption (S) over the wavelength band of absorption coefficients was in the typical range of CDOM of terrestrial origin. Saltier waters with lower CDOM concentration showed high scattering of S. Optical parameters determined by satellite measurements show a significant covariance with the field observations CDOM and salinity observations while turbidity has not shown reliable coincidence. We suggest that the high concentration of CDOM is the reason of the low influence particular matter concentration on the optical properties of the surface water. Linear regressions were obtained between surface CDOM concentrations and satellite parameters helping to trace the spatial distribution of both salinity and CDOM at the sea surface. Anyhow, further investigations are required to develop an algorithm of calculation of CDOM and salinity based on remote sensing data.

Description: Enhanced permafrost warming and increased Arctic river discharges have heightened concern about the input of terrigenous matter into Arctic coastal waters. We used optical operational satellite data from the ocean colour sensor MERIS (Medium-Resolution Imaging Spectrometer) aboard the ENVISAT satellite mission for synoptic monitoring of the pathways of terrigenous matter on the shallow Laptev Sea shelf. Despite the high cloud coverage in summer that is inherent to this Arctic region, time series from MERIS satellite data from 2006 on to 2011 could be acquired and were processed using the Case-2 Regional Processor (C2R) for optically complex surface waters installed in the open-source software ESA BEAM-VISAT. 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 C2R parameters with surface water sampling data from the Russian–German ship expeditions LENA2008, LENA2010 and TRANSDRIFT-XVII taking place in August 2008 and August and September 2010 in the southern Laptev Sea. The shallow Siberian shelf waters are optically not comparable to the deeper, more transparent waters of the Arctic Ocean. The inner-shelf waters 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 and coloured dissolved organic matter. We compared the field-based measurements with the satellite data that are closest in time. The match-up analyses related to LENA2008 and LENA2010 expedition data show the technical limits of matching in optically highly heterogeneous and dynamic shallow inner-shelf waters. The match-up analyses using the data from the marine TRANSDRIFT expedition were constrained by several days' difference between a match-up pair of satellite-derived and in situ parameters but are also based on the more stable hydrodynamic conditions of the deeper inner- and the outer-shelf waters. The relationship of satellite-derived turbidity-related parameters versus in situ suspended matter from TRANSDRIFT data shows that the backscattering coefficient C2R_bb_spm can be used to derive a Laptev-Sea-adapted SPM algorithm. Satellite-derived Chl a estimates are highly overestimated by a minimum factor of 10 if applied to the inner-shelf region due to elevated concentrations of terrestrial organic matter. To evaluate the applicability of ocean colour remote sensing, we include the visual analysis of lateral hydrographical features. The mapped turbidity-related MERIS C2R parameters show that the Laptev Sea is dominated by resuspension above submarine shallow banks and by frontal instabilities such as frontal meanders with amplitudes up to 30 km and eddies and filaments with horizontal scales up to 100 km that prevail throughout the sea-ice-free season. The widespread turbidity above submarine shallow banks indicates inner-shelf vertical mixing that seems frequently to reach down to submarine depths of a minimum of 10 m. The resuspension events and the frontal meanders, filaments and eddies indicate enhanced vertical mixing being widespread on the inner shelf. It is a new finding for the Laptev Sea that numerous frontal instabilities are made visible, and how highly time-dependent and turbulent the Laptev Sea shelf is. The meanders, filaments and eddies revealed by the ocean colour parameters indicate the lateral transportation pathways of terrestrial and living biological material in surface waters.

Description: Enhanced permafrost warming and increased arctic river discharges have heightened concern about the input of terrigenous matter into Arctic coastal waters. The IPY project 'ocOC- from Ocean Colour to Organic Carbon' (2008-2010) uses Ocean Colour (OC) data for synoptic monitoring of the input of terrigenous Organic Carbon (OC) from fluvial and coastal sources into Arctic coastal waters. Every late summer, Russian-German ship expeditions take part in the southern Laptev Sea (Arctic Siberia, Russia). The multi-year expedition data are the base for understanding the optico-chemico properties of the coastal waters. The coastal waters are characterized by low transparencies, resuspension events and high cDOM concentrations. The Laptev Sea Region has become an ESA CoastColour investigation site to support the use of the ground data. Ocean Colour MERIS data from 2008 on to 2010 are processed using the VISAT Beam Case2Regional Processor (C2R). The expedition data show that Siberian Arctic coastal waters are highly specific in terms of high cDOM background concentrations. Therefore, all remote sensing chlorophyll products are overestimated by an order of magnitude due to the high cDOM concentrations. The optical C2R parameters such as absorption, attenuation and the first attenuation depth are of immediate value to show the hydrographic dynamics of the Laptev Sea coastal waters