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Oceanic emissions of the climate-relevant trace gases carbonyl sulfide (OCS) and carbon disulfide (CS2) are a major source to their atmospheric budget. Their current and future emission estimates are still uncertain due to incomplete process understanding and therefore inexact quantification across different biogeochemical regimes. Here we present the first concurrent measurements of both gases together with related fractions of the dissolved organic matter (DOM) pool, i.e., solid-phase extractable dissolved organic sulfur (DOSSPE, n=24, 0.16±0.04 µmol L−1), chromophoric (CDOM, n=76, 0.152±0.03), and fluorescent dissolved organic matter (FDOM, n=35), from the Peruvian upwelling region (Guayaquil, Ecuador to Antofagasta, Chile, October 2015). OCS was measured continuously with an equilibrator connected to an off-axis integrated cavity output spectrometer at the surface (29.8±19.8 pmol L−1) and at four profiles ranging down to 136 m. CS2 was measured at the surface (n=143, 17.8±9.0 pmol L−1) and below, ranging down to 1000 m (24 profiles). These observations were used to estimate in situ production rates and identify their drivers. We find different limiting factors of marine photoproduction: while OCS production is limited by the humic-like DOM fraction that can act as a photosensitizer, high CS2 production coincides with high DOSSPE concentration. Quantifying OCS photoproduction using a specific humic-like FDOM component as proxy, together with an updated parameterization for dark production, improves agreement with observations in a 1-D biogeochemical model. Our results will help to better predict oceanic concentrations and emissions of both gases on regional and, potentially, global scales

The Laptev and Eastern Siberian shelves are the world’s broadest shallow shelf systems. Large Siberian rivers and coastal erosion of up to meters per summer deliver large volumes of terrestrial matter into the Arctic shelf seas. In this chapter we investigate the applicability of Ocean Colour Remote Sensing during the ice-free summer season in the Siberian Laptev Sea region. We show that the early summer river peak discharge may be traced using remote sensing in years characterized by early sea-ice retreat. In the summer time after the peak discharge, the spreading of the main Lena River plume east and north-east of the Lena River Delta into the shelf system becomes hardly traceable using optical remote sensing methods. Measurements of suspended particulate matter (SPM) and coloured dissolved organic matter (cDOM) are of the same magnitude in the coastal waters of Buor Khaya Bay as in the Lena River. Match-up analyses of in situ chlorophyll-a (Chl-a) show that standard Medium Resolution Imaging Spectrometer (MERIS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-derived Chl-a is not a valid remote sensing product for the coastal waters and the inner shelf region of the Laptev Sea. All MERIS and MODIS-derived Chl-a products are overestimated by at least a factor of ten, probably due to absorption by the extraordinarily high amount of non-algal particles and cDOM in these coastal and inner-shelf waters. Instead, Ocean Colour remote sensing provides information on wide-spread resuspension over shallows and lateral advection visible in satellite-derived turbidity. Satellite Sea Surface Temperature (SST) data clearly show hydrodynamics and delineate the outflow of the Lena River for hundreds of kilometres out into the shelf seas.

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

The detection and prediction of changes in coastal ecosystems require a better understanding of the complex physical, chemical and biological interactions, which involves that observations should be performed continuously. For this reason, there is an increasing demand for small, simple and cost-effective in situ sensors to analyze complex coastal waters at a broad range of scales. In this context, this study seeks to explore the potential of beam attenuation spectra, c(λ), measured in situ with an advanced-technology optical transmissometer, for assessing temporal and spatial patterns in the complex estuarine waters of Alfacs Bay (NW Mediterranean) as a test site. In particular, the information contained in the spectral beam attenuation coefficient was assessed and linked with different biogeochemical variables. The attenuation at λ = 710 nm was used as a proxy for particle concentration, TSM, whereas a novel parameter was adopted as an optical indicator for chlorophyll a (Chl-a) concentration, based on the local maximum of c(λ) observed at the long-wavelength side of the red band Chl-a absorption peak. In addition, since coloured dissolved organic matter (CDOM) has an important influence on the beam attenuation spectral shape and complementary measurements of particle size distribution were available, the beam attenuation spectral slope was used to analyze the CDOM content. Results were successfully compared with optical and biogeochemical variables from laboratory analysis of collocated water samples, and statistically significant correlations were found between the attenuation proxies and the biogeochemical variables TSM, Chl-a and CDOM. This outcome depicted the potential of high-frequency beam attenuation measurements as a simple, continuous and cost-effective approach for rapid detection of changes and patterns in biogeochemical properties in complex coastal environments.

The Arctic Ocean plays an important role on the global hydrological and carbon cycles. It contributes 5–14% to the global balance of CO2 sinks and sources. Carbon is also cycled in the Arctic Ocean through the primary producers, with high primary production observed in the marginal ice zones, ice-free zones and melt ponds, with increased biogenic carbon export to the deep layers. Although being the smallest ocean basin, the Arctic Ocean receives ~11% of the global riverine runoff. Along with the freshwater, high loads of organic carbon are introduced in the Arctic Ocean. Most of it is observed in the fraction of dissolved organic matter (DOM). With the ongoing global warming, glacier melt and permafrost thaw are observed and pointed as the main drivers for increasing the freshwater discharge into the Arctic basin. Along side, permafrost thaw coupled with increased coastal erosion lead to an increase in mobilization of carbon from permafrost, which could have critical implications for microbial processes, primary production, terrestrial carbon fluxes to the shelf seas and, thus, carbon cycling in the Arctic. This thesis is focusing on tracing the mixing of DOM along the Siberian shelves and developing potential applications of DOM as an environmental tracer. Four main objectives have been pursed: (1) to quantify, characterize and assess the distribution and transformation of DOM across the river-shelf transition and provide insights into the fate of Arctic riverine DOM; (2) to assess the potential of DOM, especially its fluorescent fraction (FDOM), as a tracer of freshwater in the surface layers in the Arctic Ocean; (3) to characterize the non-water absorption in the surface central and eastern Arctic Ocean and further test whether bio-optical properties (such as absorption and reflectance) can reproduce hydrographical variability; (4) to evaluate the performance of ocean color algorithms frequently applied for studies in the Arctic Ocean using novel data from a cent

Organic carbon and nutrients are increasingly mobilized from permafrost coasts due to accelerated coastal erosion in response to Arctic warming. We present dissolved organic matter (DOM) quantities in surface water in the nearshore zone of the southern Beaufort Sea from three consecutive summer seasons under different meteorological conditions. Colored and fluorescent dissolved organic matter (cDOM, fDOM) properties are used to differentiate the terrestrial from the marine DOM component. Dissolved organic carbon (DOC) concentrations in the nearshore zone of the southern Beaufort Sea vary between about 1.5 and 5 mg C L-1. In low salinity conditions between 8 and 15, high DOC concentrations of 3.5 to 5 mg C L-1 prevail. Storm events can lead to strongly decreased DOC concentration and increasing salinity (14 to 28) in surface water, probably due to upwelling. In windy and wavy conditions throughout the season, the water column is well-mixed and DOC-poor because saline waters are transported from the offshore to the nearshore. We recognized a significant negative correlation between DOC and salinity, independent from varying meteorological conditions. This suggests conservative mixing between DOC derived from permafrost coasts and marine primary production. Stable stratification in the nearshore zone and calm weather conditions will increase the influence of terrestrial-derived DOM and the potential turnover time for biogeochemical cycling in coastal ecosystems. The strength of the terrestrial influence can be estimated by salinity and stable water isotope measures as they directly correlate with DOC concentrations; the lower the salinity the stronger the terrestrial influence. We conclude that the terrestrial footprint of coastal erosion on DOM concentrations in the nearshore zone is significant and may increase with future climate warming. Meteorological conditions play a major role for the strength of the terrestrial DOM signal, which can vary on short timescales.

Climate change affects the Arctic with regards to permafrost thaw, sea-ice melt, alterations to the freshwater budget and increased export of terrestrial material to the Arctic Ocean. The Fram and Davis Straits represent the major gateways connecting the Arctic and Atlantic. Oceanographic surveys were performed in the Fram and Davis Straits, and on the east Greenland Shelf (EGS), in late summer 2012/2013. Meteoric (fmw), sea-ice melt, Atlantic and Pacific water fractions were determined and the fluorescence properties of dissolved organic matter (FDOM) were characterized. In Fram Strait and EGS, a robust correlation between visible wavelength fluorescence and fmw was apparent, suggesting it as a reliable tracer of polar waters. However, a pattern was observed which linked the organic matter characteristics to the origin of polar waters. At depth in Davis Strait, visible wavelength FDOM was correlated to apparent oxygen utilization (AOU) and traced deep-water DOM turnover. In surface waters FDOM characteristics could distinguish between surface waters from eastern (Atlantic + modified polar waters) and western (Canada-basin polar waters) Arctic sectors. The findings highlight the potential of designing in situ multi-channel DOM fluorometers to trace the freshwater origins and decipher water mass mixing dynamics in the region without laborious samples analyses.

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets, and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased toward the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation.

The Lena is one of the largest rivers in the world and is responsible, through its outflow to the Laptev Sea, for a significant fraction of the total fresh water and organic matter discharge into the Arctic Ocean. With the known effects of climate change in the Arctic and associated increase of permafrost thaw rates, the Lena River discharge and consequent export of terrigenous dissolved organic matter (DOM) into the Arctic Ocean tends to increase. Such variations may affect the nutrients and carbon dynamics in the region with consequences for the primary production and the CO2 exchanges in the ocean-atmosphere boundary layer. Understanding the dynamics and optical properties of colored DOM (CDOM) is of great value for carbon cycle modelling since CDOM is the fraction of the DOM which interacts with light and can be detected by satellite ocean color remote sensing. In this context, this study aims to investigate the dynamics of CDOM regarding the hydrographical forcing in the Lena Delta region based on in situ data collected during the late summer 2013. Water column structure was assessed through temperature and salinity profiles acquired with CTD casts and the CDOM characterization and quantification were determined based on both absorption and fluorescence spectra obtained with a HORIBA© Aqualog spectrofluorometer. The CDOM absorption at 443nm (a443; used as a CDOM amount index) and the terrestrial and marine absorption slopes of CDOM [STER (275-295nm) and SMAR (350-400nm), respectively] were obtained based on the absorption spectra. The CDOM components were identified by analysis of the excitation-emission-matrices and based on the literature. a443 was directly (inversely) related with temperature (salinity), denoting the strong modulation of CDOM by the hydrographical forcing: the highest CDOM amounts with riverine compounds were related to the Lena River Plume, while the salty waters from Laptev Sea presented lower a443 and associated with marine compounds.

Colored dissolved organic matter (CDOM) absorption and fluorescence spectra were analyzed from samples collected in the Lena River Delta region (Siberia, Russia; summer-2013) and in the Alfacs Bay (Ebro River Delta, Spain; summer-2013/winter-2014) in order to use optical measurements to infer loading and origin of CDOM. Absorbance spectra and Excitation-Emission matrices (EEMs) were obtained with a HORIBA Aqualog® spectrofluorometer. CDOM absorption at 443nm (a443) and terrestrial absorption slope (STER, 275–295nm) were inversely related (r2=0.49; p<0.05) and differed significantly (p<0.05) among the campaigns. The highest a443 values were presented by the Lena (1.28±0.81m-1) followed by Alfacs summer (0.53±0.33m-1) and Alfacs winter (0.32±0.27m-1) samples. A significant vertical decrease of a443 over the water column was observed within the Lena samples, with the highest values in the surface samples (2.10±0.7m-1) and the lowest values within the bottom (5–25m; 0.71±0.25m-1) (p<0.05). No differences between surface and bottom samples were found for the Alfacs samples (p>0.05). The slope ratio between STER and the marine absorption slope (SMAR, 350–400nm) showed that surface Lena waters were under influence of terrigenous CDOM while the deeper layer was characterized by marine CDOM content. Traditional “peak-picking” method for EEM analysis detected four components: UVA and UVC humic-like (peaks C and A, respectively; allochthonous; detected in all samples) and tyrosine- and UVA marine humic-like (peaks B and M; autochthnous). However, peaks B and M were characteristic from bottom Lena samples and few Alfacs samples presented peak B. Parallel-Factorial-Analysis will be further applied on EEMs to precisely detect the CDOM components.