Observed variability of the North Atlantic Current in the Rockall Trough
from four years of mooring measurements.
Abstract
The Rockall Trough is one of the main conduits for warm Atlantic Water
to the Nordic Seas. Ocean heat anomalies, originating from the eastern
subpolar gyre, are known to influence Arctic sea ice extent, marine
ecosystems, and continental climate. Knowledge of the transport through
this basin has previously been limited to estimates from hydrographic
sections which cannot characterise the intra‐annual and multi‐annual
variability. As part of the Overturning in the Subpolar North Atlantic
Programme (OSNAP), a mooring array was deployed in the Rockall Trough in
order to obtain the first continuous measurements of transport. Here, we
define the methodology and the errors associated with estimating these
transports. Results show a 4‐year mean northward transport of 6.6 Sv (1
Sv = 106 m3/s) by the North Atlantic Current (NAC) in the east and
interior of the Rockall Trough (2014‐2018). A mean transport of ‐2.0 Sv
(southward) is observed in the west of the basin, which could be part of
a recirculation around the Rockall Plateau. The 90‐day low‐pass filtered
transport shows large sub‐annual and inter‐annual variability (‐1.6 Sv
to 9.1 Sv), mostly resulting from changes in the mid‐basin geostrophic
transport. Satellite altimetry reveals the periods of low and high
transport are associated with significant changes in the Rockall Trough
circulation. There is a detectable seasonal signal, with the greatest
transport in spring and autumn.