Abstract
The Deep Western Boundary Current (DWBC) along the western margin of the subpolar North Atlantic is an important component of the deep limb of the Meridional Overturning near its northern origins. A network of moored arrays from Denmark Strait to the tail of the Grand Banks has been installed for almost two decades to observe the boundary currents and transports of North Atlantic Deep Water as part of an internationally coordinated observatory for the Atlantic Meridional Overturning Circulation.The dominant variability in all of the moored velocity time series is in the week-to-month period range. While the temporal characteristics of this variability change only gradually between Denmark Strait and Flemish Cap, a broad band of longer term variability is present farther along the path of the DWBC at the Grand Banks and in the interior basins (Labrador and Irminger Seas). The vigorous intra-seasonal variability may well mask possible interannual to decadal variability that is typically an order of magnitude smaller than the high-frequency fluctuations. Here, the intra-seasonal variability is quantified at key positions along the DWBC path using both, observations and high resolution model data. The results are used to evaluate the model circulation, and in turn the model is used to relate the discrete measurements to the overall pattern of the subpolar circulation. Topographic waves are found to be trapped by the steep topography all around the western basins, the Labrador and Irminger Seas. In the Labrador Sea, the high intra-seasonal variability of the boundary current regime is separated by a region of extremely low variability in narrow recirculation cells from the basin interior. There, the variability is also on intra-seasonal time scales, but at much longer periods around 50days.
Highlights
Introduction and objectivesA joint observational and modeling effort coordinated and temporarily supported by the European Union (EU) named THOR (Thermohaline Overturning at Risk) and with additional17 support from other national projects with a focus on western boundary current intensity, variability, and change has been undertaken in the subpolar North Atlantic over most of the last two decades.The focus of this paper is on a comparative analysis of intra-seasonal variability along theDeep Western Boundary Current (DWBC) beginning shortly after exiting the subarctic24 regime at Denmark Strait (Macrander et al, 2007, Jochumsen et al, 2012)
We concentrated on the dominant variability of the DWBC in the subpolar North Atlantic
We investigated the intra-seasonal variability of the DWBC in mooring data from the overflow source at Denmark Strait, along East Greenland, from the interior Labrador Sea to its exit, around Flemish Cap toward the tip of the Grand Banks
Summary
Dear Editor of Progress in Oceanography, We re-submit the revised manuscript to be considered as a contribution to the collection of papers under SI: North Atlantic Polar. Page 9, §2.3.5: "This has immediate consequences for the investigation of longer term variability, as the number of degrees of freedom...": to emphasize this point and to add substance at the third point of the summary (§5), I suggest to summarize in a table the mean, the variance, the integral time scale, the number of degrees of freedom, and the statistic error on the mean, for all the current meters lying in the DWBC Right, this is a very valuable recommendation and we include such a table and discuss it near the end of the paper. 23 e Institut für Umweltphysik, Universität Bremen, Germany f CEFAS Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, UK
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