Linking French Atlantic rivers to low salinity intrusions in the western English Channel: highly resolved monitoring from the EU FerryBox project

Abstract

Low salinity surface waters at the southern entrance (Ushant) to the western English Channel have been monitored from a near-continuous record of data collected on a ferry operating between Portsmouth (UK) and Bilbao (Spain) since April 2002. These fresh waters originate from poleward flowing plumes from French Atlantic rivers (e.g. Loire). Winter river outflows were above average in 2004 and 2003 and average in 2002 which is consistent with the minimum salinities observed near Ushant in late winter (33.68, 33.90, 34.53 in 2004, 2003, 2002, respectively). These surface water masses intrude into the western English Channel in all three years of monitoring, suggesting a frequent phenomena. The extent of the intrusion is linked to prevailing winds, with southerly winds favourable to intrusion. In contrast, northerly winds force the plume waters offshore. It is hypothesised that the more intense of these low salinity intrusions (in 2003) can enhance summer blooms of the red tide forming dinoflagellate Karenia mikimotoi through both increased stability of the upper water column and nutrient supply