Locations and mechanisms of ocean ventilation in the high-latitude North Atlantic in an eddy-permitting ocean model

Type Article
Date 2020-12
Language English
Author(s) Macgilchrist Graeme A.1, Johnson Helen L.1, Marshall David P.2, Lique CamilleORCID3, Thomas Matthew4, 5, Jackson Laura C.6, Wood Richard A.6
Affiliation(s) 1 : Department of Earth Sciences, University of Oxford, Oxford, U.K.
2 : Department of Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, U.K.
3 : Univ. Brest, CNRS, IRD, Ifremer, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Brest, France
4 : National Oceanic and Atmospheric Administration, Geophysical Fluid Dynamics Laboratory, Princeton, U.S.A
5 : University Corporation for Atmospheric Research, Boulder, Colorado, USA
6 : Hadley Centre, Met Office, Exeter, U.K.
Source Journal Of Climate (0894-8755) (American Meteorological Society), 2020-12 , Vol. 33 , N. 23 , P. 10113-10131
DOI 10.1175/JCLI-D-20-0191.1
WOS© Times Cited 6
Keyword(s) North Atlantic Ocean, Atmosphere-ocean interaction, Lagrangian circulation/transport, Ocean circulation, Boundary currents, Diapycnal mixing
Abstract

A substantial fraction of the deep ocean is ventilated in the high-latitude North Atlantic. Consequently, the region plays a crucial role in transient climate change through the uptake of carbon dioxide and heat. However, owing to the Lagrangian nature of the process, many aspects of deep Atlantic Ocean ventilation and its representation in climate simulations remain obscure. We investigate the nature of ventilation in the high latitude North Atlantic in an eddy-permitting numerical ocean circulation model using a comprehensive set of Lagrangian trajectory experiments. Backwards-in-time trajectories from a model-defined ‘North Atlantic DeepWater’ (NADW) reveal the locations of subduction from the surface mixed layer at high spatial resolution. The major fraction of NADW ventilation results from subduction in the Labrador Sea, predominantly within the boundary current (̴ 60% of ventilated NADW volume) and a smaller fraction arising from open ocean deep convection (̴ 25%). Subsurface transformations — due in part to the model’s parameterization of bottom-intensified mixing—facilitate NADWventilation, such that water subducted in the boundary current ventilates all of NADW, not just the lighter density classes. There is a notable absence of ventilation arising from subduction in the Greenland-Iceland-Norwegian Seas, due to the re-entrainment of those waters as they move southward. Taken together, our results emphasize an important distinction between ventilation and dense water formation in terms of the location where each takes place, and their concurrent sensitivities. These features of NADW ventilation are explored to understand how the representation of high-latitude processes impacts properties of the deep ocean in a state-of-the-science numerical simulation.

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Macgilchrist Graeme A., Johnson Helen L., Marshall David P., Lique Camille, Thomas Matthew, Jackson Laura C., Wood Richard A. (2020). Locations and mechanisms of ocean ventilation in the high-latitude North Atlantic in an eddy-permitting ocean model. Journal Of Climate, 33(23), 10113-10131. Publisher's official version : https://doi.org/10.1175/JCLI-D-20-0191.1 , Open Access version : https://archimer.ifremer.fr/doc/00646/75833/