Abstract. River water is the main source of dissolved organic
carbon (DOC) in the Arctic Ocean. DOC plays an important role in the Arctic
carbon cycle, and its export from land to sea is expected to increase as
ongoing climate change accelerates permafrost thaw. However, transport
pathways and transformation of DOC in the land-to-ocean transition are
mostly unknown. We collected DOC and aCDOM(λ) samples
from 11 expeditions to river, coastal and offshore waters and present a new
DOC–aCDOM(λ) model for the fluvial–marine transition zone in
the Laptev Sea. The aCDOM(λ) characteristics revealed that the
dissolved organic matter (DOM) in samples of this dataset are primarily of
terrigenous origin. Observed changes in aCDOM(443) and its spectral
slopes indicate that DOM is modified by microbial and photo-degradation.
Ocean colour remote sensing (OCRS) provides the absorption coefficient of
coloured dissolved organic matter (aCDOM(λ)sat) at λ=440 or 443 nm, which can be used to estimate DOC concentration at high
temporal and spatial resolution over large regions. We tested the
statistical performance of five OCRS algorithms and evaluated the
plausibility of the spatial distribution of derived aCDOM(λ)sat. The OLCI
(Sentinel-3 Ocean and Land Colour Instrument) neural network swarm (ONNS) algorithm showed the best performance compared to in
situ aCDOM(440) (r2=0.72). Additionally, we found
ONNS-derived aCDOM(440), in contrast to other algorithms, to be partly
independent of sediment concentration, making ONNS the most suitable
aCDOM(λ)sat algorithm for the Laptev Sea region. The
DOC–aCDOM(λ) model was applied to ONNS-derived
aCDOM(440), and retrieved DOC concentration maps showed moderate
agreement to in situ data (r2=0.53). The in situ and
satellite-retrieved data were offset by up to several days, which may partly
explain the weak correlation for this dynamic region. Satellite-derived
surface water DOC concentration maps from Medium Resolution
Imaging Spectrometer (MERIS) satellite data demonstrate
rapid removal of DOC within short time periods in coastal waters of the
Laptev Sea, which is likely caused by physical mixing and different types of
degradation processes. Using samples from all occurring water types leads to
a more robust DOC–aCDOM(λ) model for the retrievals of DOC in
Arctic shelf and river waters.
