Coastal phytoplankton blooms in the Southern California BightIntroductionData and methodsScripps Pier time seriesBloom characteristicsConstant threshold: major and minor bloomVarying thresholdCalCOFI time seriesNDBC buoyClimate indicesResultsLong-term mean chlorophyllSeasonality and the spring bloomQuantifying phytoplankton bloomsConstant thresholdVarying thresholdCorrelations between the Pier data and physical variablesLong-term trend of surface chlorophyllDiscussion and conclusionsAcknowledgmentsReferencesCoastal phytoplankton blooms in the Southern California BightHey-Jin Kima,b,*, Arthur J. Millera, John McGowana, Melissa L. CarteraaScripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United StatesbMonterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, United Statesarticle infoArticle history:Received 19 December 2007Received in revised form 6 May 2009Accepted 8 May 2009Available online 19 May 2009abstractSurface chlorophyll (CHL) measured at the Scripps Pier in the Southern California Bight (SCB) for 18 years(1983–2000) reveals that the spring bloom occurs with irregular timing and intensity each year, unlikesea-surface temperature (SST), which is dominated by a regular seasonal cycle. In the 1990s, the springbloom occurred earlier in the year and with larger amplitudes compared to those of the 1980s. Seasonalanomalies of the Pier CHL have no significant correlation with local winds, local SST, or upwelling index,which implies that classical coastal upwelling is not directly responsible for driving chlorophyll varia-tions in nearshore SCB.The annual mean Pier CHL exhibits an increasing trend, whereas the Pier SST has no evident concom-itant trend during the CHL observation period. The interannual variation of the Pier CHL is not correlatedwith tropical El Niño or La Niña conditions over the entire observing period. However, the Pier CHL wassignificantly influenced by El Nino/Southern Oscillation during the 1997/1998 El Niño and 1998/1999 LaNiña transition period. The Pier CHL is highly coherent at long periods (3–7 years) with nearby offshorein situ surface CHL at the CalCOFI (California Cooperative Fisheries Investigations) station 93.27.Ó 2009 Elsevier Ltd. All rights reserved.1. IntroductionCoastal algal blooms have been reported in the Southern Cali-fornia Bight (SCB) for over 100 years (Torrey, 1902). Beginningaround 1918, W.E. Allen began a 20-year program of monitoringphytoplankton populations by daily counts of cell numbers fromwater samples taken at the end of the Scripps Pier (32° 52.00N,117° 15.40W, Fig. 1)(Allen, 1938, 1941). In his summary paper hediscussed the frequency of what he called ‘‘red waters” (six in30 years) but without really defining that term. He emphasizedinterannual variations of the unusually large blooms he measuredand attempted to determine their longshore and offshore extent.He could find no convincing relationship to local temperaturechanges.High primary production in coastal waters in the SCB is sea-sonal and has an inshore–offshore gradient. Sverdrup and Allen(1939) noted this spatial gradient by counting the number of dia-toms per liter in the SCB. They showed that recently upwelled‘‘new” inshore surface water contains many diatoms whereas ‘‘old”offshore water has few diatoms.Since the pioneering research of Sverdrup and Allen (1939),physical and biochemical variables have been measured to betterunderstand the link between physical processes and biological re-sponses in the SCB. For instance, the California Cooperative Fisher-ies Investigations (CalCOFI) program has conducted routinemeasurements of chlorophyll and major nutrients, in addition tohydrographic surveys, since 1984 (Hayward and Venrick, 1998).However, very nearshore waters adjacent to the coastline werenot regularly observed until Southern California Coastal OceanObserving System (SCCOOS) stations were added to the currentCalCOFI grid in 2004. Therefore the magnitude and variability ofprimary productivity in nearshore waters of the SCB is not yet wellknown.Remote sensing data of surface chlorophyll also show the con-trast of productive coastal water and oligotrophic offshore waterin the California Current (Strub et al., 1990; Eppley, 1992; Thomaset al., 1994; Legaard and Thomas, 2006). However, satellite chloro-phyll data from very nearshore waters have systematic and ran-dom errors due to the optical complexity of nearshore watercaused by organic and inorganic suspended particles and bottomreflectance (Kahru and Mitchell, 1999; Darecki and Stramski,2004). The discrepancy between SeaWiFS satellite chlorophylland water-sampled chlorophyll at the Pier is larger than that be-tween SeaWiFS chlorophyll and CalCOFI shipboard chlorophyllmeasurement in offshore water (Kim, 2008). Thus the satellite-de-rived chlorophyll has not been suitable for study of chlorophyllvariability over the inner shelf close to the coastline in the SCB.Surface chlorophyll was measured at the end of Scripps Piertwice a week from 1983 to 2000. This 18-year time series is a rarelong-term ecosystem monitoring record that provides an unprec-edented view of the variability and nature of coastal phytoplank-ton blooms in the nearshore SCB. Surface chlorophyll in the0079-6611/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.pocean.2009.05.002* Corresponding author. Present address: Monterey Bay Aquarium ResearchInstitute, 7700 Sandholdt Road, Moss Landing, CA 95039, United States.E-mail address: [email protected] (H.-J. Kim).Progress in Oceanography 82 (2009) 137–147Contents lists available at ScienceDirectProgress in Oceanographyjournal homepage: www.elsevier.com/locate/poceansouthern California Current is significantly correlated with depth-integrated chlorophyll and depth-integrated primary production(Hayward and Venrick, 1982; Mantyla et al., 1995; Millan-Nunezet al., 1996). In this paper, we will characterize the seasonal cycle,interannual variability and long-term trends of surface phyto-plankton bloom events using the Scripps Pier time series and Cal-COFI dataset. We will then examine the Pier chlorophyllvariability with respect to both local and remote physical ocean-ographic variability.2. Data and methodsTwo independent data sets of surface chlorophyll (CHL) wereused to analyze spatial and temporal variability: the Scripps Piertime series and