Preprints
https://doi.org/10.5194/bg-2021-185
https://doi.org/10.5194/bg-2021-185

  03 Aug 2021

03 Aug 2021

Review status: this preprint is currently under review for the journal BG.

Oxygen export to the deep ocean following Labrador Sea Water formation

Jannes Koelling1, Dariia Atamanchuk1, Johannes Karstensen2, Patricia Handmann2, and Douglas W. R. Wallace1 Jannes Koelling et al.
  • 1Dalhousie University, Halifax, Nova Scotia, Canada
  • 2GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany

Abstract. The Labrador Sea in the North Atlantic Ocean is one of the few regions globally where oxygen from the atmosphere can reach the deep ocean directly. This is the result of wintertime convection, which homogenizes the water column to a depth of up to 2000 m, and brings deep water undersaturated in oxygen into contact with the atmosphere. In this study, we analyze how the intense oxygen uptake during Labrador Sea Water (LSW) formation affects the properties of the outflowing deep western boundary current, which ultimately feeds the upper part of the North Atlantic Deep Water layer in much of the Atlantic Ocean.

Seasonal cycles of oxygen concentration, temperature, and salinity from a two-year time series collected by sensors moored at 600 m nominal depth in the outflowing boundary current at 53° N show that LSW is primarily exported in the months following the onset of convection, from March to August. During the rest of the year, properties of the outflow resemble those of Irminger Water, which enters the basin with the boundary current from the Irminger Sea. The input of newly ventilated LSW increases the oxygen concentration from 298 μmol L−1 in January to a maximum of 306 μmol L−1 in April. As a result of this LSW input, 1.57 × 1012 mol year−1 of oxygen are added to the outflowing boundary current, mostly during summer, equivalent to 49 % of the wintertime uptake from the atmosphere in the interior of the basin. The export of oxygen from the subpolar gyre associated with this direct southward pathway of LSW is estimated to supply about 71 % of the oxygen consumed annually in the upper North Atlantic Deep Water layer in the Atlantic Ocean between the equator and 50° N. Our results show that the formation of LSW is important for replenishing oxygen to the deep oceans, meaning that possible changes in its formation rate and ventilation due to climate change could have wide-reaching impacts on marine life.

Jannes Koelling et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Oxygen export to the deep ocean following Labrador Sea Water formation by Koelling et al.', Ilaria Stendardo, 26 Aug 2021
  • RC2: 'Comment on bg-2021-185', Anonymous Referee #2, 30 Aug 2021
  • RC3: 'Review of Koelling et al. “Oxygen export to the deep ocean following Labrador Sea Water formation”', Graeme MacGilchrist, 30 Aug 2021
  • RC4: 'Review: `Oxygen export to the deep ocean following Labrador Sea Water formation’ by Koelling et al.', Anonymous Referee #4, 01 Sep 2021
  • RC5: 'Comment on bg-2021-185', Anonymous Referee #5, 14 Sep 2021

Jannes Koelling et al.

Jannes Koelling et al.

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Short summary
In this study, we investigate oxygen variability in the deep western boundary current in the Labrador Sea from multiyear moored records. We estimate that about half of the oxygen taken up in the interior Labrador Sea by air-sea gas exchange during deep water formation is exported southward the same year. Our results underline the complexity of the oxygen uptake and export in the Labrador Sea, and highlight the important role this region plays in supplying oxygen to the deep ocean.
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