Inter-annual Variability of the Current System off the West Greenland Coast from a very high-resolution numerical model

Abstract

Analyzing a high-resolution (1/60°) numerical model over 2008 to 2018, the inter-annual variability of the West Greenland Coastal Current (WGCC) on the shelf and West Greenland Current (WGC) at shelf break is presented. Both currents flow from Cape Farewell and extend to Davis Strait, with their model speeds and transports corresponding well with observations. The inter-annual variability of the WGCC and WGC near southwest Greenland are opposite, with the former declining while the latter strengthened, both by a speed change above 0.1 m/s. Both currents are predominantly buoyancy forced, but wind forcing becomes more dominant towards Davis Strait. The main exchanges from the two currents to interior occur between Cape Desolation and Fylla Bank, with net volume, freshwater, heat transport decreases of 1.4 Sv, 13 mSv, 36.7 TW. The freshwater transport of the WGC itself does not drop in between these sections, receiving freshwater from the WGCC to compensate for the losses to the basin interior. Thus, we see significant freshwater (83.1 mSv) and heat transports (70.7 TW) of the WGC remaining at Fylla Bank that reach the northern basin instead of being fluxed into the interior pof the Labrador Sea. This suggests that the exchange between the current system and the interior is more limited than previously thought, and most of the Greenland and Arctic melt reaches the northern Labrador Sea. Our results highlight the importance of resolving the WGCC and shelf processes.

Emerging impacts of enhanced Greenland melting on Labrador Sea dynamics

“…The slope current (Figure 3b, orange lines) has greater annual mean velocities from 2002-2021 on average than the WGCC (blue lines) and appears to increase while the WGCC shows stronger interannual variability. At OSNAP West, slope current speed has an increasing trend over the last two decades, also found by (Gou et al, 2022) south of Fylla Bank. Both the mean WGCC and slope current velocities are greater in REF (solid lines) than in SENS, particularly in 2011 where the speeds deviate more (Figure 3b).…”

“…The density decrease on the shelf intensifies the horizontal gradient towards the denser interior LAB and strengthens the WGC via thermal wind balance (Gou et al, 2022;Katsman et al, 2004). To investigate these changes in the boundary current system, we take an exemplary cross section at OSNAP West (Lozier et al, 2019) to obtain the velocity structure of the WGC in REF (Figure 3a).…”

“…The boundary current consists of two current cores both reaching velocity magnitudes up to 0.5 m/s: the West Greenland coastal current (WGCC) and just off the shelfbreak, the slope current. The WGCC contains the most polar water along with traces of Greenland meltwater (Lin et al, 2018;Pacini et al, 2020;Gou et al, 2022). The slope current is adjacent and lies above the saltier and warmer Irminger Current (Fratantoni & Pickart, 2007;Myers et al, 2009).…”

“…Along southeast Greenland at Cape Farewell, tip jets, northeasterly winds, and a retroflection can export freshwater into the central Irminger Sea (Duyck et al, 2022;Holliday et al, 2007). The WGC consists of near surface buoyant and fresh -2-manuscript submitted to Geophysical Research Letters waters with warmer and salty Irminger water at depth (Gou et al, 2022;Myers et al, 2007;Fratantoni & Pickart, 2007;Pacini et al, 2020). There are differing pathways freshwater is transported by the WGC, it can flow northward into Baffin Bay or cyclonically around the Labrador basin (Pacini et al, 2021;Gou et al, 2021).…”