Chromophoric Dissolved Organic Matter in the Laptev Sea (Siberian Arctic) : a Comparison of In-situ Observations, Laboratory Measurements,and Remote Sensing

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.