| Summary: | Tesis con mención internacional Oceanic hydrography of the north-easternmost region of the North Atlantic subtropical gyre has been monitored since 2003 for the whole water column (>5000 m) by three sections extending zonally 200 nautical miles (nm) westwards of Cape Finisterre (43°N, western Iberia margin), and meridionally 100 nm off Cape Ortegal (8°W, southwestern Bay of Biscay) and 100 nm off Santander (3°47'W, southeastern Bay of Biscay), allowing for the analysis of the deep ocean variability from seasonal to interannual scales. Semiannual time series of the Finisterre oceanographic section from 2003 to 2010 have shown that all water masses down to the permanent thermocline (2000 dbar) exhibit a consistent seasonal signature in their thermohaline properties with notable asymmetry between the slope region and the outer ocean. 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 helped analyze 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, (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. Once signals were de-seasonalized, time ...
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