Application of a data‐assimilation model to variability of Pacific sardine spawning and survivor habitats with ENSO in the California Current System

Abstract

The Pacific sardine (Sardinops sagax) showed significant differences in spawning habitat area, spawning habitat quality and availability of survivor habitat as the Pacific Ocean went through the La Niña state in April 2002 to a weak El Niño in April 2003. During another El Niño/Southern Oscillation transition period in 2006–2007 when the El Niño state retreated and the La Niña returned, a similar pattern in spawning habitat quality was seen. The coupling between the atmospheric forcing, the physical ocean states and the properties of the sardine egg spawning are investigated using dynamically consistent data‐assimilation fits of the available physical oceanographic observations during these months. Fits were executed using the Regional Ocean Modeling System four‐dimensional variational assimilation platform along with adjoint model runs using a passive tracer to deduce source waters for the areas of interest. Analysis using the data‐assimilation model runs reveals that unusually strong equatorward wind‐forcing drives offshore transport during the La Niña conditions, which extends the spawning habitat for sardine further offshore. A statistical model of sardine spawning habitat shows better habitat quality during the El Niño conditions, which is associated with higher egg densities and corresponded to higher daily egg production. Concentration of eggs is also increased by convergence of water. The results of the source waters analysis using the adjoint data assimilation model support the idea that offshore transport extends the spawning habitat, and show that higher levels of nutrient are brought into the spawning habitat with high concentration of sardine eggs.

Multi-Scale Sampling to Evaluate Assemblage Dynamics in an Oceanic Marine Reserve

“…In 2002 stations with high PC1 scores (i.e., oceanic species) clustered in the southwest portion of the sample domain. In addition, stations west of the shelf in the northern part of the CalCOFI domain contained coastal species, suggesting offshelf transport in 2002, a pattern also identified for S. sagax in spring of that year [13]. In 2003, by contrast, oceanic species impinged upon the shelf and into the CCA together with warmer water.…”

“…This study occurred during a transition from La Niña (2002) to El Niño (2003, 2004) conditions [13] which enabled us to assess how fluctuating ocean conditions affected within- and between-year assemblage structure at both spatial scales.…”

Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction

“…To further investigate and quantify the export flux from subduction, we used a dynamically consistent, data-assimilating ROMS model (29,30). Consistent with observational interpretations, modeled vertical velocities confirmed relatively strong subduction over most of E-Front during transect 1 and weak upwelling during transect 2 (Fig.…”

“…We then calculated flux using the equations J = [POC] × w or J = [ΔTOC] × w, where J is flux (milligrams C per square meter per day) and w is the vertical velocity (meters per day) derived from a dynamically consistent data-assimilative model. Data assimilation was conducted within the ROMS with a 9-km grid resolution using a four-dimensional variational approach that repeatedly adjusted initial and boundary conditions to minimize the mismatch between the model and physical measurements (e.g., temperature, salinity) measured on our cruise (30).…”

The role of subduction and gravitational sinking in particle export, carbon sequestration, and the remineralization length scale in the California Current Ecosystem

“…The reductions by fitting the observations are 52%, 47%, and 55% for 2006, 2007, and 2008 cruises, respectively. For detailed information, readers are referred to Song et al () and Miller et al ().…”