Western boundary circulation and coastal sea-level variability in Northern Hemisphere oceans

Samuel Tiéfolo Diabaté,Ivan D Haigh,Gerard D Mccarthy,Aurélie Duchez,Philip J Leadbitter,Joël Jean-Marie Hirschi,Didier Swingedouw

doi:10.5194/os-17-1449-2021

Abstract

Abstract. The northwest basins of the Atlantic and Pacific oceans are regions of intense western boundary currents (WBCs): the Gulf Stream and the Kuroshio. The variability of these poleward currents and their extensions in the open ocean is of major importance to the climate system. It is largely dominated by in-phase meridional shifts downstream of the points at which they separate from the coast. Tide gauges on the adjacent coastlines have measured the inshore sea level for many decades and provide a unique window on the past of the oceanic circulation. The relationship between coastal sea level and the variability of the western boundary currents has been previously studied in each basin separately, but comparison between the two basins is missing. Here we show for each basin that the inshore sea level upstream of the separation points is in sustained agreement with the meridional shifts of the western boundary current extension over the period studied, i.e. the past 7 (5) decades in the Atlantic (Pacific). Decomposition of the coastal sea level into principal components allows us to discriminate this variability in the upstream sea level from other sources of variability such as the influence of large meanders in the Pacific. Our result extends previous findings limited to the altimetry era and suggests that prediction of inshore sea-level changes could be improved by the inclusion of meridional shifts of the western boundary current extensions as predictors. Long-duration tide gauges, such as Key West, Fernandina Beach or Hosojima, could be used as proxies for the past meridional shifts of the western boundary current extensions.

Highlights

Western boundary currents (WBCs) are a major feature of global ocean circulation and play an important role in global climate by redistributing warm salty waters from the tropics to higher latitudes
The role of WBCs in the redistribution of heat and salt in the Atlantic is an integral part of the Atlantic Meridional Overturning Circulation (AMOC), resulting in heat transported towards the Equator in the South Atlantic and the largest heat transport of any ocean northwards in the North Atlantic (Bryden and Imawaki, 2001)
We propose scrutiny of the inshore sea level measured by tide gauges using cross-correlation and moving correlation analysis, as well as empirical orthogonal function (EOF) analysis

Summary

Introduction

Western boundary currents (WBCs) are a major feature of global ocean circulation and play an important role in global climate by redistributing warm salty waters from the tropics to higher latitudes. Diabaté et al.: Western boundary currents and coastal sea level either a stable and northern path or an unstable and southern path (Qiu et al, 2014; Imawaki et al, 2013; Kawabe, 1985). This variability is driven by the wind stress curl over the central North Pacific, which generates sea surface height (SSH) anomalies. When the KE is stable, it exhibits quasistationary meanders and a more northern mean position, and the Kuroshio south of Japan tends to follow either the typical large meander (tLM) or the nearshore non-large meander (nNLM) (Sugimoto and Hanawa, 2012; Qiu et al, 2014; Usui et al, 2013)

Results

Discussion

Conclusion