The rapid deglaciation of the Arctic increases the flux of terrestrial
organic matter into the marine carbon cycle. The proportions, mixing,
and turnover rates of organic matter from deglaciated terrestrial and
glacial watershed sources are poorly understood in Arctic fjords. We
characterized the mixing and flux of dissolved organic matter (DOM) in
two Arctic fjords, Kongsfjorden and Scoresby Sund. DOM was sampled and
analyzed along the natural mixing gradient from glacial meltwater to the
marine waterbody to reveal chemical proxies for glacier-derived organic
matter utilizing (ultra)high-resolution mass spectrometry of
solid-phase extracted DOM. The molecular composition of DOM in
Kongsfjorden was homogenous in elemental ratios of O/C, H/C, and N/C and
aromaticity due to high mixing and low glacial run-off. In Scoresby
Sund, a strong correlation between DOM composition and salinity was
observed. The freshwater proportion of DOM was characterized by a low
N/C ratio, unsaturated molecules, and a high terrestrial index. The
surface stratification in Scoresby Sund prevented vertical mixing of
glacier-derived and marine DOM with denser water masses. Glacial
meltwater DOM in Scoresby Sund was similar to terrestrial DOM,
suggesting either an unknown source of additional DOM or selective DOM
removal processes. In summary, the high proportion of terrestrial DOM
proxies suggests a strong imprint of deglaciation on the Arctic carbon
cycle.
FörderungenOpen Access publication fund of the AWI Helmholtz Centre for Polar and Marine Research Alfred Wegener Institute (AWI) Helmholtz research program "Changing Earth, Sustaining our Future" Ministry of Foreign Affairs, Business and Trade German Federal Ministry of Education and Research German Research Foundation Bundesministerium fr Bildung und Forschung