Seasonality of intermediate waters hydrography west of the Iberian Peninsula from an 8 yr semiannual time series of an oceanographic section

Abstract

Abstract. Seasonality of hydrographical properties at depth in the western Iberian margin (eastern North Atlantic) is analysed from a 2003-2010 time series of a semiannual oceanographic section extending ∼ 200 nm off Cape Finisterre (43 • N). All water masses down to the permanent thermocline (2000 dbar) show a consistent seasonal signature in their thermohaline properties and there is a notable asymmetry between the slope region and the outer ocean (in the surroundings of the Galicia Bank). There is overall cooling and freshening of eastern North Atlantic central waters in summertime, which is larger and deeper-reaching on the slope. In summertime, Mediterranean Water (MW) gets tightly attached against the slope and is uplifted, reinforcing its thermohaline signature and diminishing its presence at the outer ocean. In wintertime the situation reverses, MW seems to detach from the slope and spreads out to the open ocean, even being observed a secondary branch around the Galicia Bank. Thermohaline seasonality at depth shows values up to 0.4 • C and 0.08 in salinity at the lower MW, of the order of 20 % of the overall interannual variability observed during the whole period. Decomposition of thermohaline changes at isobaric levels to changes along isoneutral surfaces and changes due to vertical displacements help analyse the physical processes behind the observed seasonality in terms of (1) the large-scale seasonality of the subtropical gyre in response to the seasonal migration of the subtropical high pressure system and subsequent anomalies in Ekman transport and wind stress curl, (2) the continental slope dynamics, characterized by summer upwelling, winter development of the Iberian Poleward Current and Mediterranean water spreading, and (3) the possible influence of seasonal changes of water mass properties at their formation sources.

Oceanic density fronts steering bottom-current induced sedimentation deduced from a 50 ka contourite-drift record and numerical modeling (off NW Spain)

“…Also, internal-wave trains which migrate against the continental slope might have such an effect (Cacchione and Southard, 1974;Pomar et al, 2012;Shanmugan, 2012). Internal waves are described for all water depths and at various time scales (daily to seasonal) for the Galician margin (Apel, 2002;Krahmann et al, 2008;Prieto et al, 2012). An upslope transport of denser LSW would be induced if internal waves approach from western directions and break on the drift.…”

The vertical structure of upper ocean variability at the Porcupine Abyssal Plain during 2012–2013

“…[]; Prieto et al . []) or on moorings with instruments at a limited number of depths [ Chidichimo et al ., ; Machin et al ., ; Hartman et al ., ]. Even studies which combine ships, moorings, Argo floats and satellite observations [ Hartman et al ., ; Ullgren and White , ], do not obtain coverage of a full year with sufficient temporal and vertical resolution to capture many ocean processes.…”

IEOOS: the Spanish Institute of Oceanography Observing System

“…All the RadMed oceanographic stations are included in the Mediterranean Operational Network for the Global Observing System (MonGOOS) and in the IBAMar database . Along the Iberian Basin and NW slope, seasonality signals in the vein of Mediterranean Water have been detected in the area, with the vein constrained to the shelf break in the summer and widely distributed in winter (Prieto et al, 2013). Complete deep section coverage in the Cantabrian Sea has been discontinued recently although some deep stations have been included for monthly sampling.…”