“The Ekman Drain”: a conduit to the deep ocean for shelf material

Simpson, J.H. and McCandliss, R.R. (2013) “The Ekman Drain”: a conduit to the deep ocean for shelf material. Ocean Dynamics, 63 (9-10). pp. 1063-1072. DOI: 10.1007/s10236-013-0644-y

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A long (167 days) acoustic Doppler current profiler time series from the European continental slope west of Scotland has been analysed to investigate the influence of bathymetric steering on the slope current and the extent of down-slope transport in the bottom boundary layer. Within an interior region between the surface and bottom boundary layers, the direction of the flow is found to be remarkably consistent as required by the Taylor-Proudman theorem for geostrophic flow. The mean value of this interior flow direction is taken to be the effective direction of the bathymetry in controlling the geostrophic flow and so defines the rotation of coordinates required to determine along and cross-flow transports. Within a bottom boundary layer (BBL) of thickness ~100 m, the direction of the flow was deflected increasingly to the left with the mean veering angle ~12.5° at 12 mab and a down-slope speed of 2.6 cm s�1. The corresponding integrated transport (the �Ekman drain�) had an average value of ~1.6 m2 s�1 over the full observation period. This down-slope flow was significantly correlated (at 0.1 % level), with the stress applied by the along-slope flow although with considerable scatter (r.m.s. ~1 m2 s�1) which suggests the influence of other forcing mechanisms. Combining the BBL volume transport with an estimate of the mean concentration of suspended particulate material indicates an annual down-slope flux of 3.0�±�0.6 tonnes m�1 year�1, of which ~0.36�±�0.1 tonnes m�1 year�1 is carbon. Biogeochemical measurements indicate that the carbon flux in the Ekman drain predominates over settlement of organic material through the water column over the slope and provides for relatively rapid delivery of material to deep water.

Item Type: Article
Subjects: Research Publications
Departments: College of Natural Sciences > School of Ocean Sciences
Date Deposited: 09 Dec 2014 16:39
Last Modified: 23 Sep 2015 03:03
ISSN: 1616-7341
URI: http://e.bangor.ac.uk/id/eprint/658
Identification Number: DOI: 10.1007/s10236-013-0644-y
Publisher: Springer
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