Seasonality of the transitional region of the California Current System off Baja California

Abstract

Hydrographic data collected over the period 1997-2013 are analyzed to investigate the seasonality of hydrographic features and associated geostrophic flows off the Baja California peninsula. The upper ocean in the region was found to be homogeneous in winter and spring but subdivided into two regions in the summer and autumn. In the first case, the system typically shows relatively low-temperature and salinity waters, which give it a subarctic character. In the second, only the region north of Punta Eugenia (28 N) maintains subarctic characteristics, while the southern region receives an inflow of tropical and subtropical waters that results from the weakening of northwesterly winds, which allows the poleward advection of surface waters. Also during this period, a positive wind stress curl promotes the zonal advection of North Pacific's eastern edge waters into the coast and to the north as a surface coastal flow. Average seasonal patterns of geostrophic flow at 200 dbar revealed that the differentiation into provinces is also evident at that depth, with two clearly defined cyclonic structures in summer and autumn, both separated at the latitude of Punta Eugenia. The analyses conducted also showed a clear continuity of the California undercurrent along the shelf break, with more diffuse currents in the winter. Poleward flows were observed throughout the water column, especially in summer and autumn, although the origin of the surface flow does not necessarily involve a surfacing of the California Undercurrent.

Water Masses and Circulation in the Tropical Pacific off Central Mexico and Surrounding Areas

“…3); their mixing strongly characterizes this area. Although Durazo (2015) suggested the presence of the warm and salty Subtropical Surface Water near the Pacific coast of Baja California, we did not find any clear signature of this water either in the transition area or in the CCS, but it is possible that it occurs during strong interannual events like El Niño when poleward flow along the eastern boundary is enhanced (Strub and James 2002). Instead, the net evaporation throughout the year in the Transition area would explain the saltier nature of its waters in the surface, compared with their source areas.…”

“…5. The coast of the Baja California Peninsula is a region of permanent upwelling (Durazo 2015) that reaches its maximum in spring (Kurczyn et al 2012). It is reflected in the presence of a sharp gradient of the 25 kg m 23 isopycnal depth in the across-shore direction in the CCS.…”

“…Nevertheless, the large spatial scale considered in their study missed important features of subbasin scale like the tropical Pacific off central Mexico (TPCM). Smaller-scale studies in this region used hydrographic data that covered only restricted areas (Roden 1972;Castro et al 2000Castro et al , 2006Godínez et al 2010;León-Chávez et al 2010Durazo 2015) or are not focused on water masses (Cepeda-Morales et al 2013). The scarcity of data in the TPCM, in comparison with the available amount of historical data in surrounding areas like the California Current System or the Gulf of California, has hindered the characterization of the circulation and the water masses in this region.…”

Seasonal changes in paralarval cephalopod communities on the southwest coast of Baja California Sur (spring and autumn 2003)

“…In autumn this flow weakens and tends to form sinuous meanders (Durazo 2015). The oceanic region off the southwestern coast of Baja California Sur En términos ambientales, durante la primavera, en el área oceánica desde Ensenada hasta punta Abreojos, la corriente de California se presenta como un flujo intenso paralelo a la costa con dirección al ecuador.…”

“…The oceanic region off the southwestern coast of Baja California Sur En términos ambientales, durante la primavera, en el área oceánica desde Ensenada hasta punta Abreojos, la corriente de California se presenta como un flujo intenso paralelo a la costa con dirección al ecuador. En otoño este flujo se debilita y tiende a la formación de meandros sinuosos (Durazo 2015). La región oceánica frente a la costa suroccidental de Baja California Sur (CSO) (Fig.…”