A multi-decadal meridional displacement of the Subpolar Front in the Newfoundland Basin

I Núñez-Riboni,J H Jungclaus,K Lohmann,M Bersch,H Haak

doi:10.5194/os-8-91-2012

I Núñez-Riboni, J H Jungclaus + Show 3 more

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https://doi.org/10.5194/os-8-91-2012

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Abstract

Abstract. Observations since the 1950s show a multi-decadal cycle of a meridional displacement of the Subpolar Front (SPF) in the Newfoundland Basin (NFB) in the North Atlantic. The SPF displacement is associated with corresponding variations in the path of the North Atlantic Current. We use the ocean general circulation model MPIOM with enhanced horizontal and vertical resolutions and forced with NCEP/NCAR reanalysis data to study the relation of the SPF displacement to atmospheric forcing, intensities of the subpolar gyre (SPG) and Meridional Overturning Circulation (MOC), and Labrador Sea Water (LSW) volume. The simulations indicate that the SPF displacement is associated with a circulation anomaly between the SPG and the subtropical gyre (STG), an inter-gyre gyre with a multi-decadal time scale. A sensitivity experiment indicates that both wind stress curl (WSC) and heat fluxes (which match LSW changes) contribute to the circulation anomalies in the frontal region and to the SPF displacement. An anticyclonic inter-gyre gyre is related to negative WSC and LSW anomalies and to a SPF north of its climatological position, indicating an expanding STG. A cyclonic inter-gyre gyre is related to positive WSC and LSW anomalies and a SPF south of its climatological position, indicating an expanding SPG. Therefore, the mean latitudinal position of the SPF in the NFB (a "SPF index") could be an indicator of the amount of LSW in the inter-gyre region. Spreading of LSW anomalies intensifies the MOC, suggesting our SPF index as predictor of the MOC intensity at multi-decadal time scales. The meridional displacement of the SPF has a pronounced influence on the meridional heat transport, both on its gyre and overturning components.

Highlights

The Subpolar Front (SPF) separates the cold and less saline waters of the subpolar gyre (SPG) from the subtropical waters
The simulations indicate that the SPF displacement is associated with a circulation anomaly between the SPG and the subtropical gyre (STG), an inter-gyre gyre with a multidecadal time scale
A novel data set (CliSAP data center) spanning 57 years of hydrographic observations in the North Atlantic evidences salinity anomalies related to a multi-decadal meridional displacement of the SPF in the Newfoundland Basin (NFB) (Fig. 3a)

Summary

Introduction

The Subpolar Front (SPF) separates the cold and less saline waters of the subpolar gyre (SPG) from the subtropical waters. At the decadal and longer time scales, the variability of the SPG has been found to be mainly driven by buoyancy fluxes modulated by the North Atlantic Oscillation (NAO; Eden and Jung, 2001): Changes from periods of lower to higher NAO index are associated with stronger westerlies and increase of latent and sensible heat fluxes from the ocean to the atmosphere over the SPG in winter (Cayan, 1992). This cooling intensifies the deep convection, forming LSW, and increasing the volume of intermediate water in the gyre’s interior.

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Conclusion