Song, H., A. J. Miller, S. McClatchie, E. D. Weber, K. M. Nieto and D. M. Checkley, 2012:
Application of a data-assimilation model to
variability of Pacific sardine spawning and survivor
habitats with ENSO in the California Current System
Journal of Geophysical Research-Oceans, 117, C03009, doi:10.1029/2011JC007302.
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 Nina state
in April 2002 to a weak El Nino in April 2003. During another El Nino/Southern
Oscillation transition period in 2006/2007 when the El Nino state retreated
and the La Nina 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
Nina conditions, which extends the spawning habitat for sardine further
offshore. A statistical model of sardine spawning habitat shows better habitat
quality during the El Nino 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.
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