Exceptional 20th Century Ocean Circulation in the Northeast Atlantic

Peter T. Spooner,Svetlana Radionovskaya,Alan D. Fox,Neil L. Rose,Robbie Mallett,Delia W. Oppo,Emma Cooper,David J. R. Thornalley,J. Murray Roberts

doi:10.1029/2020gl087577

Abstract

AbstractThe North Atlantic subpolar gyre (SPG) connects tropical and high‐latitude waters, playing a leading role in deep‐water formation, propagation of Atlantic water into the Arctic, and as habitat for many ecosystems. Instrumental records spanning recent decades document significant decadal variability in SPG circulation, with associated hydrographic and ecological changes. Emerging longer‐term records provide circumstantial evidence that the North Atlantic also experienced centennial trends during the 20th century. Here, we use marine sediment records to show that there has been a long‐term change in SPG circulation during the industrial era, largely during the 20th century. Moreover, we show that the shift and late 20th century SPG configuration were unprecedented in the last 10,000 years. Recent SPG dynamics resulted in an expansion of subtropical ecosystems into new habitats and likely also altered the transport of heat to high latitudes.

Highlights

The North Atlantic is a critical region in the climate system
We present the first evidence that 20th century Northeast Atlantic surface ocean circulation was unusual compared to the last 10,000 years
The North Atlantic Current (NAC) and subpolar front (SPF) separate the cold, fresh subpolar gyre (SPG) waters from the warmer, saltier waters originating in the subtropical gyre

Summary

Introduction

The subpolar gyre (SPG) provides the connection between the tropical Atlantic and the deep‐water formation regions of the Iceland Basin, Nordic and Labrador Seas, and the Arctic Ocean (Lozier et al, 2019; Tiedje et al, 2012). It is characterized by cyclonic flow in the Iceland Basin and Irminger and Labrador Seas (Figure 1). The North Atlantic Current (NAC) and subpolar front (SPF) separate the cold, fresh SPG waters from the warmer, saltier waters originating in the subtropical gyre. Changes in SPG dynamics influence the Atlantic Meridional Overturning Circulation (AMOC), Arctic ocean temperature, stratification and sea ice cover, and economically important ecosystems (Årthun et al, 2012; Hátún et al, 2009; Jansen et al, 2016; Østerhus et al, 2005; Rhein et al, 2011)

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