Oxygen Saturation Surrounding Deep Water Formation Events in the Labrador Sea From Argo-O-2 Data

Type Article
Date 2018-04
Language English
Author(s) Wolf Mitchell K.1, Hamme Roberta C.1, Gilbert DenisORCID2, Yashayaev IgorORCID3, Thierry VirginieORCID4
Affiliation(s) 1 : Univ Victoria, Sch Earth & Ocean Sci, Victoria, BC, Canada.
2 : Fisheries & Oceans Canada, Maurice Lamontagne Inst, Mont Joli, PQ, Canada.
3 : Fisheries & Oceans Canada, Bedford Inst Oceanog, Dartmouth, NS, Canada.
4 : IFREMER, Lab Oceanog Phys & Spatiale, Plouzane, France.
Source Global Biogeochemical Cycles (0886-6236) (Amer Geophysical Union), 2018-04 , Vol. 32 , N. 4 , P. 635-653
DOI 10.1002/2017GB005829
WOS© Times Cited 14
Keyword(s) oxygen saturation, convection, Argo, Labrador Sea, deep water formation
Abstract

Deep water formation supplies oxygen-rich water to the deep sea, spreading throughout the ocean by means of the global thermohaline circulation. Models suggest that dissolved gases in newly formed deep water do not come to equilibrium with the atmosphere. However, direct measurements during wintertime convection are scarce, and the controls over the extent of these disequilibria are poorly quantified. Here we show that, when convection reached deeper than 800 m, oxygen in the Labrador Sea was consistently undersaturated at -6.1% to -7.6% at the end of convection. Deeper convection resulted in greater undersaturation, while convection ending later in the year resulted in values closer to equilibrium, from which we produce a predictive relationship. We use dissolved oxygen data from six profiling Argo floats in the Labrador Sea between 2003 and 2016, allowing direct observations of wintertime convection. Three of the six optode oxygen sensors displayed substantial average in situ drift of -3.03 mu mol O-2 kg(-1)yr(-1) (-0.94% O-2 yr(-1)), which we corrected to stable deepwater oxygen values from repeat ship surveys. Observations of low oxygen intrusions during restratification and a simple mixing calculation demonstrate that lateral processes act to lower the oxygen inventory of the central Labrador Sea. This suggests that the Labrador Sea is a net sink for atmospheric oxygen, but uncertainties in parameterizing gas exchange limit our ability to quantify the net uptake. Our results constrain the oxygen concentration of newly formed Labrador Sea Water and allow more precise estimates of oxygen utilization and nutrient regeneration in this water mass.

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