Freshwater and polynya components of the shelf-derived Arctic Ocean halocline in summer 2007 identified by stable oxygen isotopes

• Main Authors: Bauch, Dorothea, Rutgers van der Loeff, Michiel, Andersen, Nils, Torres-Valdes, Sinhue, Bakker, Karel, Abrahamsen, E. Povl
• Format: Conference Object
• Language: English
• Published: 2011
• Subjects: Arctic; Arctic Ocean; Laptev Sea; Makarov Basin; Pacific; laptev; Lomonosov Ridge; makarov basin; Sea ice
• Online Access: https://oceanrep.geomar.de/id/eprint/12566/; https://oceanrep.geomar.de/id/eprint/12566/1/2011AGU-abstract-submitted.pdf

With the aim of determining the origin of freshwater in the halocline, fractions of river water and sea-ice meltwater (or brine influence from sea-ice formation) in the upper 150 m were quantified by a combination of salinity and _18O and nutrients in the Eurasian basins and the Makarov Basin. Our study indicates which layers of the Arctic Ocean halocline are primarily influenced by sea-ice formation in coastal polynyas and which are primarily influenced by sea-ice formation over the open ocean. With the ongoing changes in sea-ice coverage in the Arctic Ocean it can be expected that these processes will change in the immediate future and that the relative contributions to the halocline will change accordingly. Within the Eurasian Basin a west to east oriented front between net melting and production of sea-ice is observed. Outside the Atlantic regime dominated by net sea-ice melting, a pronounced layer influenced by brines released during sea-ice formation is present at about 30 to 50 m water depth with a maximum over the Lomonosov Ridge. The geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the Transpolar Drift. We use the ratio of sea-ice derived brine influence and river water to link the maximum in brine influence within the Transpolar Drift with a pulse of shelf waters from the Laptev Sea likely released in summer 2005. For a distinction of Atlantic and Pacific-derived contributions the initial phosphate corrected for mineralization with oxygen (PO*) and alternatively the nitrate to phosphate ratio (N/P) in each sample were used. While PO*-based assessments systematically underestimate the contribution of Pacific-derived waters, N/P-based calculations overestimate Pacific-derived waters within the Transpolar Drift due to denitrification in bottom sediments of the Laptev Sea. The extent of Pacific-derived water in the Arctic Ocean was approximately limited by the position of the Lomonosov Ridge in 2007. ...