Author

Kasey Legaard

Date of Award

12-2004

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Andrew Thomas

Second Committee Member

Mary Beard-Tisdale

Third Committee Member

Mary Jan Perry

Abstract

Physical forcing and biological response within the California Current coastal upwelling system are highly variable over a wide range of scales. Satellite remote sensing offers the only feasible means of quantifying this variability over the full extent of this current system. Here we quantify and compare patterns of physical and biological variability acting over seasonal, interannual and dominant intraseasonal time scales throughout the California Current System using more than five years (1997-2003) of daily SeaWiFS chlorophyll and NOAA/NASA AVHRR Oceans Pathfinder SST imagery. Mean seasonal cycles were modeled as the sum of annual and semiannual harmonics. Interannual variability was estimated by filtering non-seasonal time series. Dominant patterns of intraseasonal variability were determined using geostatistical semivariograms calculated from residual series following the removal of seasonal and interannual variability. We provide the first systematic and quantitative analysis of dominant temporal variability of chlorophyll and SST across the entire California Current System. Coastal upwelling circulation dictates the nature of seasonal variability along northern and central California, where weak seasonal cycles of SST fluctuate between spring minima and late summer maxima and chlorophyll concentrations peak in mid- to late summer. Off northern California, chlorophyll summer maxima are bounded by the seasonally recurrent meandering path of the upwelling fi-ont and jet. Seasonal cycles along South-central Baja appear to be more strongly affected by processes other than local upwelling, and mesoscale circulation plays a lesser role in determining seasonally recurrent spatial distributions of chlorophyll. Seasonal cycles differ notably across the Pacific Northwest and within the inner Southern California Bight. Interannual variation is generally dominated by El Niño and La Niña conditions. Relative levels of sensitivity to basin-scale forcing differ between SST and chlorophyll at most locations. Dominant patterns of intraseasonal variability are caused by the seasonally recurrent formation, intensification and westward migration of the upwelling jet and surrounding eddies. The distortion of large-scale SST and chlorophyll distributions by prominent eddies and meanders defines a dominant time scale of -60 days (equivalent to a dominant period of -120 days) throughout much of the region. SST variance is shifted toward a time scale of -40 days across much of the Pacific Northwest. Dominant chlorophyll variability is consistently shifted to 25-40 days inshore. Dominant scales of SST and chlorophyll variation deviate most markedly along the California coast between Point Conception (34.4' N) and Cape Mendocino (40.4" N), where major realignments of mesoscale currents may temporarily dissociate patterns of surface temperature and phytoplankton abundance.

Included in

Oceanography Commons

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