Atlantic-Origin Overflow Water in the East Greenland Current

Lisbeth Håvik,Thomas W N Haine,Kjetil Våge,Mattia Almansi

doi:10.1175/jpo-d-18-0216.1

Lisbeth Håvik, Thomas W N Haine + Show 2 more

Open Access

https://doi.org/10.1175/jpo-d-18-0216.1

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Abstract

AbstractDense water masses transported southward along the east coast of Greenland in the East Greenland Current (EGC) form the largest contribution to the Denmark Strait Overflow. When exiting Denmark Strait these dense water masses sink to depth and feed the deep circulation in the North Atlantic. Based on one year of mooring observations upstream of Denmark Strait and historical hydrographic profiles between Fram Strait and Denmark Strait, we find that a large part (75%) of the overflow water ( ≥ 27.8 kg m−3) transported by the EGC is of Atlantic origin (potential temperature θ > 0°C). The along-stream changes in temperature of the Atlantic-origin Water are moderate north of 69°N at the northern end of Blosseville basin, but southward from this point the temperature decreases more rapidly. We hypothesize that this enhanced modification is related to the bifurcation of the EGC taking place close to 69°N into the shelfbreak EGC and the separated EGC. This is associated with enhanced eddy activity and strong water mass modification reducing the intermediate temperature and salinity maxima of the Atlantic-origin Water. During periods with a large (small) degree of modification the separated current is strong (weak). Output from a high-resolution numerical model supports our hypothesis and reveals that large eddy activity is associated with an offshore shift of the surface freshwater layer that characterizes the Greenland shelf. The intensity of the eddy activity regulates the density and the hydrographic properties of the Denmark Strait Overflow Water transported by the EGC system.

Highlights

The circulation in and north of Denmark Strait is complex and exhibits high temporal and spatial variability (e.g., Våge et al 2013; Harden et al 2016; Behrens et al 2017; von Appen et al 2017; Håvik et al 2017b; Almansi et al 2017)
The strongest current flowing into Denmark Strait is the shelfbreak East Greenland Current
Near the Kögur transect (Fig. 1) the separated East Greenland Current (EGC) partly merges with the North Icelandic Jet (NIJ) flowing southwestward from the Iceland Sea, and the combined flow follows the deep part of the

Summary

Introduction

The circulation in and north of Denmark Strait is complex and exhibits high temporal and spatial variability (e.g., Våge et al 2013; Harden et al 2016; Behrens et al 2017; von Appen et al 2017; Håvik et al 2017b; Almansi et al 2017). We focus on the modification of the Atlantic-origin Water in the EGC based on historical hydrographic profiles of temperature and salinity between Fram Strait and Denmark Strait as well as a year of hydrographic and velocity measurements obtained from moorings along the Kögur transect (Fig. 1) in 2011–12. We use a selection of historical conductivity, temperature, and depth (CTD) data from the western Nordic Seas between 678 and 788N from 1980 to 2014 (Våge et al 2015), to investigate the hydrographic properties of the Atlantic-origin Water in the shelfbreak EGC upstream of Denmark Strait. A few profiles with spurious salinity data were removed manually Based on these criteria we obtained 380 CTD profiles sampling the Atlantic-origin layer along the east Greenland shelf between Fram Strait and Denmark Strait. We note that the model simulated one year, whereas the observations along the Greenland shelf break were biased toward late summer and spread over 35 years

Atlantic-origin Water in the shelfbreak East Greenland Current at Kögur

Structure of the East Greenland Current branches at Kögur

Eddy activity in East Greenland Current

Findings

Discussion and conclusions