Analysis of the mesoscale structure in the IMECOCAL region (off Baja California) from hydrographic, ADCP and altimetry data

[1] Six years of daily satellite data are used to quantify and map intraseasonal variability of chlorophyll and sea surface temperature (SST) in the California Current. We define intraseasonal variability as temporal variation remaining after removal of interannual variability and stationary seasonal cycles. Semivariograms are used to quantify the temporal structure of residual time series. Empirical orthogonal function (EOF) analyses of semivariograms calculated across the region isolate dominant scales and corresponding spatial patterns of intraseasonal variability. The mode 1 EOFs for both chlorophyll and SST semivariograms indicate a dominant timescale of $60 days. Spatial amplitudes and patterns of intraseasonal variance derived from mode 1 suggest dominant forcing of intraseasonal variability through distortion of large scale chlorophyll and SST gradients by mesoscale circulation. Intraseasonal SST variance is greatest off southern Baja and along southern Oregon and northern California. Chlorophyll variance is greatest over the shelf and slope, with elevated values closely confined to the Baja shelf and extending farthest from shore off California and the Pacific Northwest. Intraseasonal contributions to total SST variability are strongest near upwelling centers off southern Oregon and northern California, where seasonal contributions are weak. Intraseasonal variability accounts for the majority of total chlorophyll variance in most inshore areas save for southern Baja, where seasonal cycles dominate. Contributions of higher EOF modes to semivariogram structure indicate the degree to which intraseasonal variability is shifted to shorter timescales in certain areas. Comparisons of satellite-derived SST semivariograms to those calculated from co-located and concurrent buoy SST time series show similar features.Citation: Legaard, K. R., and A. C. Thomas (2007), Spatial patterns of intraseasonal variability of chlorophyll and sea surface temperature in the California Current,

Section: Dominant Patterns Of Intraseasonal Variabilitysupporting

confidence: 69%

Spatial patterns of intraseasonal variability of chlorophyll and sea surface temperature in the California Current

Legaard

Thomas

2007

“…EOF-3 and EOF-2 of ML salinity have common features. Both show centers of high variability, which might be associated with mesoscale surface eddies reported in the literature [Strub and James, 2000;Soto-Mardones et al, 2004;Espinosa-Carreon et al, 2004;Jeronimo and Gomez-Valdes, 2007]. 30°N, 27°N, and 24°N for the period 1997 -2007 were correlated with the PCs of ML temperature, ML salinity, and NHF, at interannual timescales.…”

Section: Discussionsupporting

confidence: 58%

Upper mixed layer temperature and salinity variability in the tropical boundary of the California Current, 1997–2007

Gómez-Valdés

Jerónimo

2009

Spatial and temporal interannual variability of mixed layer (ML) temperature and ML salinity off Baja California are examined using empirical orthogonal functions analysis. Conductivity‐temperature‐depth data collected from October 1997 through January 2007 over a grid based on Mexican Research of the California Current quarterly survey cruises are analyzed. Net heat flux (NHF) and sea surface height anomaly (SSH) from satellite products are also analyzed. The first leading mode of both ML temperature and ML salinity show a single‐signed loading pattern, in which the variability increases southward. Those patterns have been reported before, but they are lacking a quantitative explanation. ML temperature variability is mainly associated with NHF variability, while ML salinity variability is mainly associated with large‐scale SSH variability. The principal component (PC) of ML salinity is correlated with North Pacific Gyre Oscillation and Warm Water Volume climate indices, while the PC of ML temperature is only correlated with the latter index. Those results indicate that the principal mode of ML salinity variability is a diagnostic variable of basin‐scale process. An abrupt freshening (∼−0.7) and cooling (∼−4°C) event from January 1998 to January 1999 and an abrupt freshening (∼−0.5) event from January 2002 to January 2003 are conspicuous features in the mixed layer. The 1998–1999 events are associated with the major El Niño–La Niña cycle in the 10‐year period. The 2002–2003 freshening is related to an enhancement of subarctic water into the equatorward flow that started during the summer of 2002 off Oregon (49°N).

“…Figure 4 represents an 8-year mean, indicating that the features of the chl a signal which create the patchiness must be recurrent to be detected. Strong mesoscale variability, created by the interaction of the equatorward flowing coastal jet and the topography of Oregon/California coastline, is characteristic of the CCS [e.g., Strub and James, 2000;Soto-Mardones et al, 2004;Barth et al, 2005]. Many recurrent meanders and eddies form, for example, near the outflow of the Juan de Fuca strait, and in the lee of Cape Blanco, Cape Mendocino and Point Arena [Ikeda and Emery, 1984;Haidvogel et al, 1991;Barth et al, 2000;Marchesiello et al, 2003;MacFadyen et al, 2005].…”

Section: Timing Of Seasonal Chlorophyll Increasementioning

confidence: 99%

Interannual variability in timing of bloom initiation in the California Current System

Henson

Thomas

2007

[1] In the California Current System the spring transition from poleward to equatorward alongshore wind stress heralds the beginning of upwelling-favorable conditions. The phytoplankton response to this transition is investigated using 8 years (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) of daily, 4-km resolution, Sea-viewing Wide Field of view Sensor (SeaWiFS) chlorophyll a concentration data. Cluster analysis of the chlorophyll a time series at each location is used to separate the inshore upwelling region from offshore and oligotrophic areas. An objective method for estimating the timing of bloom initiation is used to construct a map of the mean bloom start date. Interannual variability in bloom timing and magnitude is investigated in four regions : 45°N-50°N, 40°N-45°N, 35°N-40°N and 20°N-35°N. Daily satellite derived wind data (QuikSCAT) allow the timing of the first episode of persistently upwelling favorable winds to be estimated. Bloom initiation generally coincides with the onset of upwelling winds (±15 days). South of $35°N, where winds are southward year-round, the timing of increased chlorophyll concentration corresponds closely to timing of the seasonal increase in upwelling intensity. A 1-D model and satellite derived photosynthetically available radiation data are used to estimate time series of depth-averaged irradiance. In the far north of the region (>46°N) light is shown to limit phytoplankton growth in early spring. In 2005 the spring bloom in the northern regions (>35°N) had a ''false start''. A sharp increase in chl a in February quickly receded, and a sustained increase in biomass was delayed until July. We hypothesize that this resulted in a mismatch in timing of food availability to higher trophic levels.