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    ABSTRACT: The variability of the mixed layer depth (MLD) is examined over a decade (1997-2007) for the tropical boundary of the California Current (24-32°N), using conductivity-temperature-depth observations collected by quarterly survey cruises. Results indicate that salinity gradients control MLD rather than temperature gradients. The mean state of the upper ocean indicates that contours of constant MLD are parallel to the coast, with mixed layer thickness decreasing toward the coastal zone. The deepest (˜70 m) thickness is reached in January and the shallowest (˜15 m) occurs in July. The warmer conditions (summer) are reproduced for a simple thermal energy equation. The rest of the seasons are reproduced for a one-dimensional momentum balance for the upper ocean, which includes Ekman dynamics and stratification. This comparison indicates that the variability of MLD is mainly due to wind-driven phenomena except during the heating period. In particular, seasonal and interannual variability of the MLD are correlated with offshore Ekman transport. An abrupt MLD change occurs between January 1998 and January 2000 associated with the strong El Niño-La Niña cycle shift that occurred in this period.
    Journal of Geophysical Research Atmospheres 01/2010; 115. · 3.44 Impact Factor
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    ABSTRACT: We document interannual changes in the species composition of euphausiids inhabiting the waters off Baja California during the period of 1997–2005. Thirty-two euphausiid species were identified from sev-enteen cruises, with the dominant species being Euphausia eximia, Euphausia gibboides, Nyctiphanes simplex, Thysanoessa gregaria, Nematoscelis difficilis, and Stylocheiron affine (present in 74–92% of the samples). Species composition had the strongest difference between coastal (Vizcaino Bay and the Ulloa Gulf) and oceanic waters. The coastal shelf was dominated almost exclusively by N. simplex while the oce-anic regions showed a high diversity. In oceanic waters the most abundant species was N. difficilis off both the northern (32–30°N) and the central (30–24°N) Baja California peninsula. The highest krill biomass, however, was recorded in the central region in January 1998 during an El Niño and consisted principally of abundant larvae of E. eximia. La Niña was characterized by an increase of the 'transition zone' species (E. gibboides, N. difficilis, T. gregaria) and the subarctic Euphausia pacifica. This last even entered in Vizcaino Bay but was not apparent in the central region compared to the north. High abundance of E. pacifica was also observed in July 2002 and was linked to subarctic water intrusion and July 2005. Some swarms of Thysanoessa spinifera were observed during April and July of 2005. The presence of subarctic species E. pacifica and T. spinifera in Baja California waters contrasted with their strong decrease in northern sec-tors of the California Current System during 2005. This biological information, joined with high upwelling activity (compared to delayed upwelling off Oregon and northern California), reinforces the importance of regional studies in eastern boundary currents.
    Progress In Oceanography 11/2012; · 3.99 Impact Factor

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