Changing Spatial Patterns of Deep Convection in the Subpolar North Atlantic. Issue 7 (30th June 2021)

• Record Type: Journal Article
• Authors: Rühs, Siren; Oliver, Eric C. J.; Biastoch, Arne; Böning, Claus W.; Dowd, Michael; Getzlaff, Klaus; Martin, Torge; Myers, Paul G.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-30
• Subjects: ARGO -- deep convection -- greenland melting -- north atlantic subpolar gyre -- ocean modeling -- salinity anomaly; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017245
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Deep convection and associated deep water formation are key processes for climate variability, since they impact the oceanic uptake of heat and trace gases and alter the structure and strength of the global overturning circulation. For long, deep convection in the subpolar North Atlantic was thought to be confined to the central Labrador Sea in the western subpolar gyre (SPG). However, there is increasing observational evidence that deep convection also has occurred in the eastern SPG south of Cape Farewell and in the Irminger Sea, in particular, in 2015–2018. Here we assess this recent event in the context of the temporal evolution of spatial deep convection patterns in the SPG since the mid‐twentieth century, using realistic eddy‐rich ocean model simulations. These reveal a large interannual variability with changing contributions of the eastern SPG to the total deep convection volume. Notably, in the late 1980s to early 1990s, the period with highest deep convection intensity in the Labrador Sea related to a persistent positive phase of the North Atlantic Oscillation, the relative contribution of the eastern SPG was small. In contrast, in 2015–2018, deep convection occurred with an unprecedented large relative contribution of the eastern SPG. This is partly linked to a smaller north‐westward extent of deep convection in the Labrador Sea compared to previous periods of intensified deep convection, and may be a first fingerprint of freshening trends in the Labrador Sea potentially associated with enhanced Greenland melting and the oceanic advection of the 2012–2016 eastern North Atlantic fresh anomaly. Plain Language Summary: The subpolar North Atlantic is one of the few oceanic regions where deep convection occurs, a process by which surface waters become dense enough to mix downwards. Thereby, heat and carbon dioxide are transported into the deep ocean, helping to slow global warming. For long, deep convection in the subpolar North Atlantic was thought to be confined to the central Labrador Sea. However, recently, deep convection was also observed in the Irminger Sea. In this study, we use ocean model simulations to reconstruct when and where deep convection occurred since the mid‐twentieth century. Our simulations show a large variability in strength and spatial patterns of deep convection, with changing relative importance of the Labrador and Irminger Seas. Most notably, in the mid 2010's, deep convection shifted eastwards, so that the relative importance of the Irminger Sea and Labrador Sea were anomalously large and small, respectively. Freshening trends in the Labrador Sea suggest that this shift partially resulted from enhanced melting of Greenland's glaciers and changes in the North Atlantic circulation. Our results stress the need for monitoring and correctly modeling deep convection variability in the Labrador and Irminger Seas to better understand and predict the looming impact of future Greenland melting. Key Points: Eddy‐rich ocean model simulations (1958–2019) feature large variability of spatial deep convection patterns in subpolar North Atlantic In 2015–2018, deep convection showed exceptional large and small relative contributions of eastern and western subpolar gyre, respectively Small western contribution is potentially associated with enhanced Greenland melting and recent eastern North Atlantic fresh anomaly