Satellite‐derived variability in chlorophyll, wind stress, sea surface height, and temperature in the northern California Current System

Abstract

Satellite‐derived data provide the temporal means and seasonal and nonseasonal variability of four physical and biological parameters off Oregon and Washington (41°–48.5°N). Eight years of data (1998–2005) are available for surface chlorophyll concentrations, sea surface temperature (SST), and sea surface height, while six years of data (2000–2005) are available for surface wind stress. Strong cross‐shelf and alongshore variability is apparent in the temporal mean and seasonal climatology of all four variables. Two latitudinal regions are identified and separated at 44°–46°N, where the coastal ocean experiences a change in the direction of the mean alongshore wind stress, is influenced by topographic features, and has differing exposure to the Columbia River Plume. All these factors may play a part in defining the distinct regimes in the northern and southern regions. Nonseasonal signals account for ∼60–75% of the dynamical variables. An empirical orthogonal function analysis shows stronger intra‐annual variability for alongshore wind, coastal SST, and surface chlorophyll, with stronger interannual variability for surface height. Interannual variability can be caused by distant forcing from equatorial and basin‐scale changes in circulation, or by more localized changes in regional winds, all of which can be found in the time series. Correlations are mostly as expected for upwelling systems on intra‐annual timescales. Correlations of the interannual timescales are complicated by residual quasi‐annual signals created by changes in the timing and strength of the seasonal cycles. Examination of the interannual time series, however, provides a convincing picture of the covariability of chlorophyll, surface temperature, and surface height, with some evidence of regional wind forcing.

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“…Dentro de escalas intra-anuales, el ciclo estacional es una de las escalas de mayor influencia en las variaciones de la biomasa del fitoplancton (Venegas et al, 2008). La variabilidad de CLO asociada con el ciclo estacional demuestra alta actividad durante invierno y primavera, que se refleja con altas concentraciones de CLO en toda la plataforma continental de Nayarit.…”

“…Within the intraannual scales, the seasonal cycle is one of the scales of higher influence in the variations of the biomass of the phytoplankton (Venegas et al, 2008). concentraciones de CLO dentro de Bahía de Matanchén y en sus inmediaciones, lo cual debe estar asociado a procesos locales y la dinámica costera.…”

Time-Space Variability of Chlorophyll-a and Associated Physical Variables within the Region off Central-Southern Chile

“…In the northern section, mean WS is equatorward (favorable to offshore Ekman transport) and more intense whereas it is weaker and mostly eastward (towards the coast and upwelling neutral) in the southern section. In comparison with the region of the California Current System, where the band of transition in the mean direction of WS is located at ~45°N [15], in the HCS this band is located around 41-42°S. Furthermore, mean WSC is cyclonic (negative) and favorable to upwelling (Ekman pumping) in a band (~25-70 km width) close to the coast and more intense in the northern section.…”

“…These differences arise from latitudinal variation in large scale wind systems and/or from local variations in wind forcing linked to coastal topography, coastline orientation, and/or bathymetry; in addition, variations in large-scale circulation and mesoscale activity, and continental runoff can have a significant influence [11][12][13][14][15]. Geographical and/or local changes in the distribution of phytoplankton biomass and/or biological production rates have been positively related to spatial variability in wind-driven coastal upwelling [7,15,16] but, in some cases, this association has been found to be weak or negative [17,18]. The level of mesoscale activity (in terms of eddy kinetic energy) has been identified as an additional forcing factor causing cross-shore differences in the distribution of nutrients and/or phytoplankton (biomass and primary production rates) between and within EBCs [12,19,20].…”

Relationships among upwelling, phytoplankton blooms, and phycotoxins in coastal Oregon shellfish

“…There was no difference between the start of upwelling calculated from yearly dates and wind climatology in Region E. This was due to the more steady southward direction of the winds in this area throughout the spring and summer. There is a change in wind, and hence upwelling, climatology around Cape Blanco (42.84°N, between the coastal Regions D and E; Samelson et al 2002, Huyer et al 2005, Venegas et al 2008. North of Cape Blanco there was no significant difference in the timing of the upwelling season, but south of Cape Blanco upwelling favorable winds started significantly earlier and finished significantly later.…”