Bio‐optical Properties of Surface Waters in the Atlantic Water Inflow Region off Spitsbergen (Arctic Ocean)

Abstract

Bio‐optical properties of surface waters were characterized off western and northern Spitsbergen in the summers of 2013, 2014, and 2015. We observed statistically significant year‐to‐year differences in spatial distribution of spectral absorption (a(λ)) and beam attenuation (c(λ)). Highest a(λ) and c(λ) were located in the frontal zone between water masses and co‐varied strongly with chlorophyll a fluorescence. Phytoplankton pigments dominated the absorption budget at 443 nm (50%). The contribution of chromophoric dissolved organic matter to total nonwater absorption was highest at 412 nm (42%), and detrital absorption contributed most at 550 nm (37%). Almost all inherent optical properties, except chromophoric dissolved organic matter, were highly correlated with the chlorophyll a concentration (Chla, R2 > 0.81). Relationships between Chla and the particulate and phytoplankton pigments absorption coefficients at 443 and 676 nm were characterized by significant determination coefficients (R2 > 0.73). The phytoplankton pigments line height absorption aLH(676) was found to be the most reliable optical proxy for determination of Chla, compared to total nonwater absorption, apg(676), and stimulated in situ chlorophyll a fluorescence intensity, IChla. In the presence of sea ice melt the water column was stratified and the vertical distribution of inherent optical properties was characterized by a surface minimum followed by a distinct subsurface maximum, aligned with a subsurface chlorophyll a maximum. We surmise that prevailing regional wind patterns affect sea ice and surface drift in central Fram Strait, and thus the location of sea ice meltwater, which affects the vertical stratification and occurrence of subsurface chlorophyll a maximum.

Inherent optical properties and optical characteristics of dissolved organic and particulate matter in an Arctic fjord (Storfjorden, Svalbard) in early summer

“…Sample-based values of aphy(440) and aNAP(440) (Figure 8, middle and bottom) and their distribution with depth were in similar range as reported in WSC waters by (Kowalczuk et al, 2017(Kowalczuk et al, , 2019, further pointing to the presence of AW dominated waters. Although not targeting the subsurface chl-a maxima at time of sampling (since in situ data was not available to guide the water sampling), the sample-based phytoplankton absorption at 440 nm (Figure 8, middle) indicates increased absorption by phytoplankton in the subsurface, and at deeper depth in the southern fjord compared to the central part of the fjord.…”

“…As it could also be assessed qualitatively from Figure 10, this also highlights the strong dependence of the absorption budget to the wavelength of the radiation, the CDOM contribution dramatically decreasing with increasing wavelength. The relative CDOM contribution was thus higher than what has been found in the Atlantic water in the West Spitsbergen Current (WSC) with average CDOM contribution of 42% at 412nm (Kowalczuk et al, 2019), as well as in AW north of Svalbard with CDOM contribution of 43% at 443nm (Kowalczuk et al, 2017)…”

“…While we are not aware of any existing optical surveys in the Storfjorden, there have been a few studies examining the optical characteristics of waters in the Barents Sea proper (Aas & Berge, 1976;Aas & Høkedal, 1996;Falk-Petersen et al, 2000;Hancke et al, 2014;Hovland et al, 2014;Kostakis et al, 2020;Orkney et al, 2020). Further, a number of other studies have been conducted in the region of AW inflow west and north of Svalbard (Kowalczuk et al, 2019;Makarewicz et al, 2018;Pavlov et al, 2015Pavlov et al, 2017. All these studies point toward a significant contribution of phytoplankton to light attenuation in the open Barents Sea both north and south of the polar front, since the concentration of coloured dissolved organic matter (CDOM) in water masses of AW origin is relatively low, compared to 'true' polar waters with a distinctly higher CDOM signal (Pavlov et al, 2015).…”

CDOM Optical Properties and DOC Content in the Largest Mixing Zones of the Siberian Shelf Seas

“…CDOM represents an essential constituent affecting ocean color. Thus, in the Arctic Ocean, the contribution of a CDOM (443) to the total non-water absorption can reach~50% [73]. It was shown that systematic differences in chlorophyll retrievals resulting from different ocean color models are related to each model's ability to account for the absorption of light by CDOM [14].…”

Planktonic Protists of the Eastern Nordic Seas and the Fram Strait: Spatial Changes Related to Hydrography During Early Summer

“…To better understand these dependencies, future protist studies should relate to mesoscale phenomena, be supplemented by at least mesozooplankton data and water chemistry, and have an equivalent in springtime. Because recent satellite-derived and bio-optical in situ surveys suggested rapid expansion of temperate phototrophic protists (mainly coccolithophores) in the Arctic (e.g., Dylmer et al, 2015;Neukermans et al, 2018;Kowalczuk et al, 2019), it would also be reasonable to confirm these suppositions by microscopic studies. Our research does not support these findings.…”