Abstract
Abstract. The North Atlantic Ocean and northwest European shelf
experience intense low-pressure systems during the winter months. The effect
of strong winds on shelf circulation and water properties is poorly
understood as observations during these episodes are rare, and key flow
pathways have been poorly resolved by models up to now. We compare the
behaviour of a cross-shelf current in a quiescent period in late summer,
with the same current sampled during a stormy period in midwinter, using
drogued drifters. Concurrently, high-resolution time series of current speed
and salinity from a coastal mooring are analysed. A Lagrangian analysis of
modelled particle tracks is used to supplement the observations. Current
speeds at 70 m during the summer transit are 10–20 cm s−1, whereas
on-shelf flow reaches 60 cm s−1 during the winter storm. The onset of
high across-shelf flow is identified in the coastal mooring time series,
both as an increase in coastal current speed and as an abrupt increase in
salinity from 34.50 to 34.85, which lags the current by 8 d. We interpret
this as the wind-driven advection of outer-shelf (near-oceanic) water
towards the coastline, which represents a significant change from the
coastal water pathways which typically feed the inner shelf. The modelled
particle analysis supports this interpretation: particles which terminate in
coastal waters are recruited locally during the late summer, but recruitment
switches to the outer shelf during the winter storm. We estimate that during
intense storm periods, on-shelf transport may be up to 0.48 Sv, but
this is near the upper limit of transport based on the multi-year time
series of coastal current and salinity. The likelihood of storms capable of
producing these effects is much higher during positive North Atlantic Oscillation (NAO) winters.
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
Cited by
8 articles.
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