Publication Date:
2020-12-01
Description:
We assessed the qualitative composition of fluorescent dissolved organic matter (FDOM) in Arctic Ocean surface
water and in sea ice north of the Svalbard Archipelago (in the Sophia Basin, the Yermak Plateau and the north
Spitsbergen shelf) in May and June 2015, during the “TRANSSIZ” expedition (Transitions in the Arctic Seasonal
Sea Ice Zone). Samples collected in open lead waters (OW), under-ice waters (UIW) and from the sea ice (ICE)
were analyzed by fluorescence spectroscopy and subsequently by multivariate statistical methods using Parallel
Factor Analysis (PARAFAC). Statistical analyses of all measured DOM fluorescence excitation and emission
matrices (EEMs) enabled four components to be identified and validated. The spectral characteristics of the first
component C1 (λEx/λEm 282(270)/335) corresponded to those of tryptophan. The spectral properties of the
other three components corresponded to those of humic-like substances: components two (C2 − λEx/λEm
315(252)/395) and three (C3 − λEx/λEm 357(258)/446) corresponded to humic-like substances of marine
origin, whereas component four (C4 − λEx/λEm 261(399)/492) resembled terrestrial humic-like substances.
Changes in FDOM composition were recorded in OW, in contrast to UIW and sea ice. In the OW the sum of
fluorescence intensities of humic-like components (C2, C3 and C4) was two times higher than the fluorescence
intensity of protein-like component (C1). Component C2 exhibited the highest fluorescence intensity. In the UIW
and particularly in the sea ice the fluorescence intensity of the protein-like component, IC1, was the highest. The
IC1 in the sea ice increased toward the sea ice bottom, reaching maximum values at the sea ice-water interface.
The calculated spectral indices (SUVA(254) and HIX) and ratios of fluorescence intensities of protein-like to
humic-like components, Ip/Ih, suggested that FDOM in water and sea ice was predominantly autochthonous,
characterized by low molecular weight organic compounds and low aromatic ring saturation. Enrichment factors
Dc, calculated from salinity-normalized values of the optical DOM properties and dissolved organic carbon
concentrations, indicated the significant fractionation of FDOM in the sea ice relative to the parent open waters.
The humic-like terrestrial component C4 was enriched the least, whereas the protein-like component C1 was
enriched the most. A statistically significant (p 〈 0.0001) and relatively strong (R = 63) correlation between IC1
and the total chlorophyll a concentration Tchla was found in the sea ice, which suggests that sympagic algal
communities were producers of the protein-like FDOM fraction.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
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