The Deep Western Boundary Current at Cape Farewell: Results from a Moored Current Meter Array

Abstract

An analysis is made of data from 30 Aanderaa recording current meters (RCMs) set on nine moorings located east of Cape Farewell, the southern tip of Greenland. The purpose of the measurements was to allow for the estimation of transport in the deep western boundary current (DWBC) below a depth of about 1500 m. The records commenced in September 2005 and lasted from 9.5 to 11.5 months. After calibration of the raw data, 12-h averages of temperature and current were derived and the latter employed to estimate the flow across and along the array direction. The 9.5-month average transport of water colder than 38C was found to be 7.8 Sv (1 Sv [ 1 3 10 6 m 3 s 21 ) with a standard error of 0.8 Sv. For water denser than s u 5 27.85 kg m 23 , the transport is calculated as 4.5 Sv. Whether either of these values is significantly different from comparable measurements made 500 km upstream cannot be determined. In marked contrast, for s u . 27.8 kg m 23 , the transport is estimated as only 9.0 Sv, smaller than the widely accepted value of 13 Sv for nearby measurements made in 1978. A reevaluation of the calculations and assumptions made then allows one to determine the uncertainty of the earlier estimate and thereby conclude that the difference between the previous and present measurements is significant, that is, that the transport has decreased between 1978 and 2005-06. A weakening of the transport during the 9.5-month period is also observed, along with a warming and an increase in salinity in the core of the DWBC. These latter changes are shown to be consistent with interannual variability rather than a long-term trend.

Transport of Nordic Seas overflow water into and within the Irminger Sea: An eddy‐resolving simulation and observations

“…At the SECF section, these two values are 9.4 and 5.6 Sv from the model results, in comparison to 9.0 and 4.5 Sv based on data [Bacon and Saunders, 2010]. At this point, we summarize the model-determined circulation in terms of a transport budget.…”

Moored observations of shelfbreak processes at the inflow to and outflow from the Arctic Ocean

“…Intriguingly, there is no indication of the presence of the Spill Jet or the DSOW cyclones at Cape Farewell, the southern tip of Greenland (Bacon and Saunders, 2010;Daniault et al, 2011a). This indicates that they spin down or get significantly transformed along the East Greenland slope.…”

“…This is significantly less than the estimate presented by Dickson and Brown (1994) at this location. Bacon and Saunders (2010) also elucidated the magnitude of the variability in the DWBC. Its overall standard deviation is 2.9 Sv with a de-correlation timescale of 4-10 days, and the majority of the variability is in the 10-50 day band.…”

“…Finally, the Deep Western Boundary Current is the near-bottom southward flow that transports the densest part of the NADW (Dickson and Brown, 1994). Interestingly, mooring observations at Cape Farewell (the southern tip of Greenland) have found no sign of mesoscale variability similar to that of DSOW cyclones (Daniault et al, 2011a;Bacon and Saunders, 2010). This suggests that the DSOW cyclones spin-down and break up during their transit along the East Greenland slope.…”

Sustaining observations of the unsteady ocean circulation

“…A new basin-wide observational array is set to be deployed in 2014 to observe the overturning in the subpolar North Atlantic (Overturning in the Subpolar North Atlantic Programme, OSNAP) [54]. The UK-contribution to OSNAP builds both on the expertise developed through RAPID and from previous array deployments at Cape Farewell, Greenland, where the deep western boundary current was measured [55,56]. The aim of the programme is to quantify heat and freshwater fluxes around the subpolar gyre, from the Labrador Sea to Cape Farewell, to Scotland.…”