Publication Date:
2022-05-26
Description:
Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 53 (2006): 1483-1516, doi:10.1016/j.dsr.2006.06.005.
Description:
We study the dynamics of the planktonic ecosystem in the coastal upwelling zone
within the California Current System using a three-dimensional, eddy-resolving circulation model coupled to an ecosystem/biogeochemistry model. The physical model
is based on the Regional Oceanic Modeling System (ROMS), configured at a resolution of 15 km for a domain covering the entire U.S. West Coast, with an embedded
child grid covering the central California upwelling region at a resolution of 5 km.
The model is forced with monthly mean boundary conditions at the open lateral
boundaries as well as at the surface. The ecological/biogeochemical model is nitrogen based, includes single classes for phytoplankton and zooplankton, and considers
two detrital pools with different sinking speeds. The model also explicitly simulates
a variable chlorophyll-to-carbon ratio. Comparisons of model results with either remote sensing observations (AVHRR, SeaWiFS) or in situ measurements from the
CalCOFI program indicate that our model is capable of replicating many of the
large-scale, time averaged features of the coastal upwelling system. An exception is
the underestimation of the chlorophyll levels in the northern part of the domain,
perhaps because of the lack of short-term variations in the forcing from the atmosphere. Another shortcoming is that the modeled thermocline is too diffuse, and that
the upward slope of the isolines toward the coast is too small. Detailed time-series
comparisons with observations from Monterey Bay reveal similar agreements and
discrepancies. We attribute the good agreement between the modeled and observed
ecological properties in large part to the accuracy of the physical fields. In turn,
many of the discrepancies can be traced back to our use of monthly mean forcing.
Analysis of the ecosystem structure and dynamics reveal that the magnitude and
pattern of phytoplankton biomass in the nearshore region are determined largely
by the balance of growth and zooplankton grazing, while in the offshore region,
growth is balanced by mortality. The latter appears to be inconsistent with in situ
observations and is a result of our consideration of only one zooplankton size class
(mesozooplankton), neglecting the importance of microzooplankton grazing in the
offshore region. A comparison of the allocation of nitrogen into the different pools
of the ecosystem in the 3-D results with those obtained from a box model configuration of the same ecosystem model reveals that only a few components of the
ecosystem reach a local steady-state, i.e. where biological sources and sinks balance
each other. The balances for the majority of the components are achieved by local
biological source and sink terms balancing the net physical divergence, confirming
the importance of the 3-D nature of circulation and mixing in a coastal upwelling
system.
Description:
Most of this work has been made possible by two grants from NASA. Additional support is acknowledged from NSF’s ITR program.
Keywords:
Phytoplankton dynamics
;
Nutrient cycling
;
Coastal biogeochemistry
;
California Current
;
Upwelling
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
171098 bytes
Format:
7070311 bytes
Format:
application/pdf
Format:
application/pdf
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