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Title: Water masses and circulation in the S.E. Pacific and the 'El Nino' event
Author: Robles, F. L. E.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1980
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Data from 80 oceanographic cruises, carried out between 1931 and 1973, were analysed to describe the upper water masses, general circulation, coastal upwelling and "E1 Nino" events along the S.E. Meridional Pacific. Four main water masses were found to be present in the upper 1000 metres of the zone: (a) Subtropical surface water - found at the northern part characterized by a salinity maxima of 34.8-35.0"/oo. (b) Sub-antarctic water - the dominant feature in the surface layers, characterized by low salinities fluctuating between 32.0°/oo and 34.8°/oo, at depths of between 20 metres and 130 metres. Oceanic spreading of these waters varies seasonally, in accordance with the S.E. Pacific anticyclonic gyre; similarly, coastal spreading is seasonally controlled by the fresh-water input in the south. (c) Equatorial subsurface water - present at depths of 300 to 350 metres at the northeastern half of the zone with salinity maxima ranging from 34.5 to 34.9°/oo; in the north this maxima appears associated to an oxygen minimum layer. In the N.E. corner (the Arica-Mejillones region), interaction between "fiords waters" coming from the south and surface and sub-surface waters with high salinities, defines a different water mass - the Arica-Mejillones water, characterized by a higher subsurface salinity maxima (34.7-34.0°/oo) which, coastally, spread_ towards the south at depths of 100 metres. (d) Antarctic Intermediate water - defined by a (lower) salinity minima of 34.2°/oo to 34.6°/oo; its spreading takes place at depths between <500 to >600 metres and it is apparently associated with an oxygen maxima decreasing towards the north. The horizontal circulation follows, in general, the spreading path of the water masses listed above: (a) On the western side, around 1000km offshore, a sluggish northerly motion dominates with velocities (relative) ti 4cm/sec; (b) Further to the east, a flow enters the zone at about 79°W and spreads southerly, at about 5OOkm offshore, with velocities ti 6cm/sec; (c) Nearer to the shore, a somewhat faster northerly flow is found (velocities ti l8cm/sec) at 300-400km offshore; (d) Within the remaining coastal region, three other currents may be found: a coastal counter current, flowing southerly at 200km offshore, with velocities ti l2cm/sec; the "fiords current", which spreads northerly at about 100km offshore with velocities fluctuating between 6 and l6cm/sec; and, a third current, flowing south and very close to the coastline, with velocities ti 20cm/sec (mainly corresponding to the spreading of the Arica-Mejillones water). Coastal upwelling is mainly observed during Spring-Summer, along the northern and central regions. The main source for upwelling is provided by the coastal (fiord) salinity minima. The expressions, in the SE Meridional Pacific, of the air-sea phenomena known as "El Nino", may be summarized as follows: (a) Oceanic Subtropical and Equatorial Subsurface southerly penetrations are reinforced and extended towards the west; (b) The oceanic part of the Subantarctic System progressively weakens; (c) The Iumboldt-Fiords coastal part of the Subantarctic System is reinforced, in the southern regions, and further north is split into the "proper" Humboldt current and a coastal "Fiords Current"; (d) In the N.E. corner, high salinity surface waters (> 35.0°/oo) approach the coastline and, from there, extend south; (e) Waters in the Arica-Mejillones Area stabilizes and further develop the strong Spring Summer thermocline; this, in time, extends to the coastline. Coastal upwelling, on these occasions, ceases and downwelling is observed in areas close to the shore.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available