On the spatial structure and temporal variability of poleward transport between Scotland and Greenland

Abstract

The flow north of warm subtropical water though the northeastern Atlantic is known to have many pathways that vary over time. Here we use a combination of upper ocean current measurements between Greenland and Scotland near 60 N and satellite altimetry to examine the space-time variability of poleward transport. The high-resolution scans of currents in the top 400 m show that the Reykjanes Ridge serves as a very effective separator of flow toward the Nordic and Labrador Seas, respectively. Whereas the Labrador Sea branch exhibits two mean flows to the north on the western slope of the Reykjanes Ridge, the eastern branch flows north in roughly equal amounts over the deep Maury channel and east of Hatton Bank including the Slope Current. There is also a well-defined southward flow along the eastern slope of the Reykjanes Ridge. The satellite altimetric sea surface height (SSH) data show good overall agreement with geostrophically determined -level difference from the repeat ADCP sections (1999)(2000)(2001)(2002), but are unable to resolve the fine structure of the topographically defined mean circulation. The altimetric data show that variations in poleward flow west and east of the Reykjanes Ridge are strongly anticorrelated. They further reveal that the two eastern subbranches also exhibit anticorrelated variability, but offset in time with respect to the Labrador Sea branch. Remarkably, all these variations cancel out for the entire Greenland-Scotland section leaving a gradual decrease in sea-level difference of about 0.06 m over the 1993 to the end of 2010 observation period.

Directly measured currents and estimated transport pathways of Atlantic Water between 59.5°N and the Iceland–Faroes–Scotland Ridge

“…The western rather well-defined branch is ultimately bound for the Labrador Sea where it contributes to the production of intermediate depth Labrador Sea water (e.g. Chafik et al, 2014). The eastern branch becomes the major source of all water entering the Nordic Seas (Orvik and Niiler, 2002), but the pathways by which the water reaches the IcelandÁFaroesÁScotland ridge (IFSR) are clearly influenced by the complex banks topography west of Scotland (Fig.…”

“…By combining the high resolution ( Â5 km), repeat scans of currents along four routes, we seek to construct a detailed representation of the major pathways of AW through the Iceland Basin and banks region from 59.58N to the IFSR. Chafik et al (2014) use the Nuka Arctica C route ADCP data and satellite altimetry to describe the spatial and temporal characteristics of poleward flows between Greenland and Scotland over the top 400 m. Of particular note in the Chafik et al (2014) study is the strong role of the RR in separating topographically bound flows towards the Nordic and Labrador Seas. We focus here on the flow east of the RR as the principal source of water entering the Nordic Seas across the IFSR.…”

“…We focus here on the flow east of the RR as the principal source of water entering the Nordic Seas across the IFSR. According to Chafik et al (2014), the total transport across the C route can be decomposed into three primary flows, from west to east, they are a 4.5 Sv flow over the Maury Channel, a 1.2 Sv flow just east of George Bligh Bank and 1.7 Sv flow along the Scottish slope. They propose that these two latter currents combine at the entrance to the FaroesÁShetland Channel as the Slope Current.…”

“…Expanding upon the findings of Chafik et al (2014), we include here the Nuka Arctica data along its great circle (G) and diagonal (D) routes. The G route runs rather parallel to the Chafik et al (2014) (C) route and as such serves as valuable independent measure of how well transport can be estimated by ship-mounted ADCPs over these great distances.…”

“…The G route runs rather parallel to the Chafik et al (2014) (C) route and as such serves as valuable independent measure of how well transport can be estimated by ship-mounted ADCPs over these great distances. The diagonal route (D) is central to this study, for it helps delineate the flow patterns between the C and G transects to the south and the Norro¨na route along the IFSR.…”