Low salinity intrusions in the western English Channel

Type Article
Date 2006-08
Language English
Author(s) Kelly Gerreyn B1, Hydes D1, Jegou Anne-Marie2, Lazure PascalORCID2, Fernand L3, Puillat I4, Garcia Soto C5
Affiliation(s) 1 : Univ Southampton, Natl Oceanog Ctr, Southampton SO14 3ZH, Hants, England.
2 : IFREMER, Dept Dynam Environm Cotier, F-29280 Plouzane, France.
3 : Ctr Environm Fisheries & Aquaculture Sci, Lowestoft NR33 0HT, Suffolk, England.
4 : Univ Paris 06, LOCEAN, F-75252 Paris 05, France.
5 : Inst Espanol Oceanog, Santander 39004, Spain.
Source Continental Shelf Research (0278-4343) (Elsevier), 2006-08 , Vol. 26 , N. 11 , P. 1241-1257
DOI 10.1016/j.csr.2006.03.007
WOS© Times Cited 39
Keyword(s) Bay of Biscay, English Channel, River plume, Ferrybox, Low salinity
Abstract Low salinity (< 35) surface waters (LSSW) at the southern entrance to the western English Channel (48.5 degrees N, 5.1 degrees W, near Ushant) were observed in late winter (March-April) in three successive years (2002-04) during near continuous ship of opportunity operations. The source of the LSSW is the northward spreading plumes from the Loire (47.5 degrees N, 2.5 degrees W) and Gironde (45.6 degrees N, 1.2 degrees W) along the French Atlantic coast. Fastest plume travel times were associated with northeasterly winds, consistent with Ekman theory. Differences between years in the mean winter (January-March) combined river discharges (D) was consistent with the minimum salinities (S-min) of the LSSW (2004: D = 4211 m(3) s(-1), S-min = 33.68; 2003: D = 3630 m(3) s(-1), S-min = 33.90; 2002: D = 1579 m(3) s(-1), S-min = 34.53). Winter mean (1905-74) salinity is otherwise 35.33 near Ushant.

The LSSW intruded into the western English Channel in each year, suggesting a common phenomenon. The low salinity intrusion was freshest (mean = 35.11 +/- 0.21) and most penetrative (reaching 50.7 degrees N, 1.0 degrees W by the end of the year) in 2003 on account of (1) entering on a spring tide giving greater tidal excursion into the western English Channel and (2) intrusion favourable winds (southwesterly/southeasterly) acting on the longer term residual flow. Less penetration occurred in 2004 when the arrival of the LSSW coincided with a neap tide followed by intrusion-resistant northwesterly winds, resulting in a less saline (mean = 35.20 +/- 0.23) intrusion. In 2004, transport tended to be offshore to at least 100km from the French Atlantic coast (47 degrees N, 4.8 degrees W-48 degrees N, 4.7 degrees W). In 2002, the lower volume of plume water relative to the other years produced a more saline intrusion (mean = 35.25 +/- 0.12). Prevailing westerly winds may have pushed this intrusion northwards beyond the route of the ferry, making it difficult to assess the true extent of the intrusion in 2002. A link of the LSSW to phases of the winter North Atlantic Oscillation index from a literature search of the last 84 years was inconclusive. (c) 2006 Elsevier Ltd. All rights reserved.
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