Loading of coloured dissolved organic matter in the Arctic Mediterranean Sea and its effects on the ocean heat budget

• Main Author: Pefanis, Vasileios
• Other Authors: Kanzow, Torsten, Walter, Maren
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2021
• Subjects: Arctic Ocean; CDOM; radiative heating; chlorophyll-a; Laptev Sea; Nordic Seas; coloured dissolved organic matter; sea ice; suspended material; phytoplankton; light; radiative transfer model; MITgcm; SCIATRAN; 550; 550 Earth sciences and geology; ddc:550; Arctic; Ice; laptev; permafrost; Phytoplankton; Sea ice
• Online Access: https://media.suub.uni-bremen.de/handle/elib/4849; https://doi.org/10.26092/elib/646; https://nbn-resolving.org/urn:nbn:de:gbv:46-elib48497

Currently, the most rapid increase in near-surface air temperature takes place in the Arctic, accompanied by a decline in sea ice cover. Consequently, the underwater shortwave radiation, and thus, the type and amount of phytoplankton are changing. In this context, the thawing permafrost, accompanied by increased precipitation and freshwater discharge, is expected to result in higher loads of coloured dissolved organic matter (CDOM) and total suspended matter (TSM) entering the Arctic Ocean. The amount of these optically active water constituents determines how much light is absorbed in the surface waters and how much can reach greater depths, affecting the vertical distribution of heat. In this thesis, I first examine the potential of CDOM and TSM in enhancing the radiative heating and sea ice melting in the shelf waters of the Laptev Sea, an area heavily influenced by one of the largest river systems in the Arctic region. By using in situ observations, I simulate the in-water radiative heating utilizing coupled atmosphere-ocean radiative transfer modelling (RTM). The results indicate that CDOM and TSM highly affect the energy budget of the Laptev Sea shelf waters, absorbing most of the solar energy in the first 2 meters of the water column. The increased absorbed energy leads to higher sea ice melt rates and changes in the heat exchange with the atmosphere. By using satellite remote sensing and RTM, I quantify the spatial distribution of radiative heating in the Laptev Sea for a typical summer day. The spatial patterns of radiative heating closely follow the distribution of the optically active water constituents, with the highest energy absorption occurring over river-influenced waters. As a next step, I upscale the previous one-dimensional and regional study by means of general circulation modelling for the entire Arctic Mediterranean Sea. By operating an ocean biogeochemical model coupled to a general circulation model with sea ice (Darwin-MITgcm), the effect of phytoplankton and CDOM is incorporated into ...