The Arctic Ocean exports a large amount of terrestrial dissolved organic matter (tDOM) to the Nordic seas. Climate change is projected to increase the supply of tDOM but sea ice retreat might lead to a simultaneous loss of tDOM due to intensifying photodegradation. While the DOM abundance can be estimated quickly via optical properties, quantifying DOM photodegradation requires experiments that last between one and ten days. Here, we simulated sunlight exposures of samples from the Siberian Shelf, Central Arctic Ocean, and Fram Strait. On average, 51 % of peak C fluorescence and 33 % of absorbance (350 nm) was lost due to photobleaching while no photomineralization was detectable. A N-way partial least squares model was trained to predict the proportion of photodegradable DOM fluorescence (“photosensitivity index”, PI) from the unexposed fluorescence landscapes. The prediction root mean squared error was 0.03 (4.8 % of the average PI). We then applied the model to > 1500 samples spanning from the Lena River plume to the East Greenland Shelf and observed an accumulation of photosensitive DOM (high PI) at depth. DOM in the mixed layer was often distinctly photobleached (low PI). The photosensitivity of tDOM in polar surface water did not change significantly until the material was exported to Fram Strait. Our findings indicate that fluorescence-based estimates of photobleaching offer valuable insights into the occurrence of photodegradation.

Primary Presenter: Urban Wuensch, Technical University of Denmark (urbw@aqua.dtu.dk)

Authors:

Urban Wünsch, Technical University of Denmark  (urbw@aqua.dtu.dk)

Rafael Gonçalves-Araujo, Technical University of Denmark  (rafgo@aqua.dtu.dk)

Mats Granskog, Norwegian Polar Institute  (mats.granskog@npolar.no)

Linea Gry Ebbesen, Technical University of Denmark  ()

Maria Papadimitraki, Technical University of Denmark  (mapap@aqua.dtu.dk)

Colin Stedmon, Technical University of Denmark  (cost@aqua.dtu.dk)