Monika Zabłocka

Bio‐optical properties of Arctic drift ice and surface waters north of Svalbard from winter to spring

We have quantified absorption by CDOM, aCDOM(k), particulate matter, ap(k), algal pigments, aph(k), and detrital material, aNAP(k), coincident with chlorophyll a in sea ice and surface waters in winter and spring 2015 in the Arctic Ocean north of Svalbard. The aCDOM(k) was low in contrast to other regions of the Arctic Ocean, while ap(k) has the largest contribution to absorption variability in sea ice and surface waters. ap(443) was 1.4–2.8 times and 1.3–1.8 times higher than aCDOM(443) in surface water and sea ice, respectively. aph(k) contributed 90% and 81% to ap(k), in open leads and under-ice waters column, and much less (53%–74%) in sea ice, respectively. Both aCDOM(k) and ap(k) followed closely the vertical distribution of chlorophyll a in sea ice and the water column. We observed a tenfold increase of the chlorophyll a concentration and nearly twofold increase in absorption at 443 nm in sea ice from winter to spring. The aCDOM(k) dominated the absorption budget in the UV both in sea ice and surface waters. In the visible range, absorption was dominated by aph(k), which contributed more than 50% and aCDOM(k), which contributed 43% to total absorption in water column. Detrital absorption contributed significantly (33%) only in surface ice layer. Algae dynamics explained more than 90% variability in ap(k) and aph(k) in water column, but less than 70% in the sea ice. This study presents detailed absorption budget that is relevant for modeling of radiative transfer and primary production.

Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

Optical properties of chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM) were characterized in the Nordic Seas including the West Spitsbergen Shelf during June–July 2013, 2014, and 2015. The CDOM absorption coefficient at 350 nm, aCDOM(350) showed significant interannual variation (T test, p< 0.00001). In 2013, the highest average aCDOM(350) values (aCDOM(350)= 0.30± 0.12 m−1) were observed due to the influence of cold and low-salinity water from the Sørkapp Current (SC) in the southern part of the West Spitsbergen Shelf. In 2014, aCDOM(350) values were significantly lower (T test, p< 0.00001) than in 2013 (average aCDOM(350)= 0.14± 0.06 m−1), which was associated with the dominance of warm and saline Atlantic Water (AW) in the region, while in 2015 intermediate CDOM absorption (average aCDOM(350)= 0.19± 0.05 m−1) was observed. In situ measurements of three FDOM components revealed that fluorescence intensity of protein-like FDOM dominated in the surface layer of the Nordic Seas. Concentrations of marine and terrestrial humic-like DOM were very low and distribution of those components was generally vertically homogenous in the upper ocean (0–100 m). Fluorescence of terrestrial and marine humic-like DOM decreased in surface waters (0–15 m) near the sea ice edge due to dilution of oceanic waters by sea ice meltwater. The vertical distribution of protein-like FDOM was characterized by a prominent subsurface maximum that matched the subsurface chlorophyll a maximum and was observed across the study area. The highest protein-like FDOM fluorescence was observed in the Norwegian Sea in the core of warm AW. There was a significant relationship between the proteinlike fluorescence and chlorophyll a fluorescence (R2= 0.65, p< 0.0001, n= 24 490), which suggests that phytoplankton was the primary source of protein-like DOM in the Nordic Seas and West Spitsbergen Shelf waters. Observed variability in selected spectral indices (spectral slope coefficient, S300–600, carbon-specific CDOM absorption coefficient at 254 and 350 nm, SUVA254, a CDOM(350)) and the nonlinear relationship between CDOM absorption and the spectral slope coefficient also indicate a dominant marine (autochthonous) source of CDOM and FDOM in the study area. Further, our data suggest that aCDOM(350) cannot be used to predict dissolved organic carbon (DOC) concentrations in the study region; however the slope coefficient (S300–600) shows some promise in being used.