The physical oceanographic environment during the CCE-LTER Years: Changes in climate and concepts

Abstract

The California Current System (CCS) has been studied by the California Cooperative Oceanic Fisheries Investigations program for many decades. Since 2004, the Southern California Bight (SCB) and the oceanic region offshore has also been the site for the California Current Ecosystem (CCE) Long-Term Ecological Research (LTER) program, which has established long-term observational time series and executed several Process Cruises to better understand physical–biological variations, fluxes and interactions. Since the inception of the CCE-LTER, many new ideas have emerged about what physical processes are the key controls on CCS dynamics. These new perspectives include obtaining a better understanding of what climate patterns exert influences on CCS physical variations and what physical controls are most important in driving CCE ecological changes.Physical oceanographic and climatological conditions in the CCS varied widely since the inception of the CCE-LTER observational time series, including unusual climate events and persistently anomalous states. Although the CCE-LTER project commenced in 2004 in the midst of normal ocean conditions near the climatological means, over the following decade, El Nino/Southern Oscillation conditions flickered weakly from warm to cold, with the Pacific Decadal Oscillation (PDO) generally tracking that behavior, while the North Pacific Gyre Oscillation (NPGO) evolved to persistent and strong positive conditions after 2007, indicative of enhanced upwelling from 2007 to 2012. Together the combined impact of the negative PDO state (La Nina conditions) and positive NPGO state (increased upwelling conditions) yielded remarkably persistent cool conditions in the CCS from late 2007 to early 2009 and from mid-2010 through 2012.The broad-scale climate variations that occurred over the North Pacific and CCS during this time period are discussed here to provide physical context for the CCE-LTER time series observations and the CCE-LTER Process Cruises. Data assimilation fits, using the Regional Ocean Modeling System four-dimensional data assimilation framework, were successfully executed for the 1-month time period surrounding each of the Process Cruises. The fits provide additional information about how the physical flows evolve during the course of the multi-week Process Cruises. Relating these physical states to the numerous biological measurements gathered by the CCE-LTER time series observations and during the Process Cruises will yield vital long-term perspective of how changing climate conditions control the ocean ecosystem in this region and information on how this important ecosystem can be expected to evolve over the coming decades.