Modeling Nutrient and Plankton Processes in the California Coastal Transition Zone: 2. A Three-Dimensional Physical-Bio-Optical Model

A three-dimensional (3-D) primitive equation model, developed to simulate the circulation features (filaments) observed in the California coastal transition zone (CTZ), was coupled to a nine-component food web model and a bio-optical model. The simulated flow fields from a 3-D primitive equation model are used to advect the constituents of the food web model, which include silicate, nitrate, ammonium, two phytoplankton size fractions, copepods, doliolids, euphausiids, and a detritus pool. The bio-optical model simulates the wavelength-dependent attenuation of the subsurface irradiance field. The overall objective of this modeling study was to understand and quantify the processes that contribute to the spatial and temporal development of nutrient and plankton distributions in the CTZ. The resulting simulated 3-D nutrient, plankton and submarine light fields agree well with those observed within the CTZ. Specifically, high nutrient and plankton biomass occur onshore and within the core of the simulated filament. Variations in the depth of the 1% light level, which result from the simulated plankton distributions, shallows to less than 30 m in regions of high phytoplankton biomass, and deepens to greater than 75 m in regions of low phytoplankton biomass. The onshore and offshore surface carbon flux patterns are similar in shape due to the meander-like flow patterns of the filament; however, the net across-shore area-integrated carbon flux is predominantly offshore. The total 20-day integrated carbon transport for the model domain varies with distance from shore and is highest (35 × 109 g C) in the region where the filament circulation pattern develops into an anticyclonic and cyclonic pair of eddies. The annual integrated carbon transport by filaments along the California coast is estimated to be 1.89 × 1012 g C

Recent Arctic climate change and its remote forcing of Northwest Atlantic shelf ecosystems

Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 3 (2012): 208-213, doi:10.5670/oceanog.2012.64.During recent decades, historically unprecedented changes have been observed in the Arctic as climate warming has increased precipitation, river discharge, and glacial as well as sea-ice melting. Additionally, shifts in the Arctic's atmospheric pressure field have altered surface winds, ocean circulation, and freshwater storage in the Beaufort Gyre. These processes have resulted in variable patterns of freshwater export from the Arctic Ocean, including the emergence of great salinity anomalies propagating throughout the North Atlantic. Here, we link these variable patterns of freshwater export from the Arctic Ocean to the regime shifts observed in Northwest Atlantic shelf ecosystems. Specifically, we hypothesize that the corresponding salinity anomalies, both negative and positive, alter the timing and extent of water-column stratification, thereby impacting the production and seasonal cycles of phytoplankton, zooplankton, and higher-trophic-level consumers. Should this hypothesis hold up to critical evaluation, it has the potential to fundamentally alter our current understanding of the processes forcing the dynamics of Northwest Atlantic shelf ecosystems.Funding for this research was provided by the National Science Foundation as part of the Regional and Pan-Regional Synthesis Phases of the US Global Ocean Ecosystem (GLOBEC) Program

Variability of Iberian upwelling implied by ERA-40 and ERA-Interim reanalyses

The Regional Ocean Modeling System ocean model is used to simulate the decadal evolution of the regional waters in offshore Iberia in response to atmospheric fields given by ECMWF ERA-40 (1961–2001) and ERA-Interim (1989–2008) reanalyses. The simulated sea surface temperature (SST) fields are verified against satellite AVHRR SST, and they are analysed to characterise the variability and trends of coastal upwelling in the region. Opposing trends in upwelling frequency are found at the northern limit, where upwelling has been decreasing in recent decades, and at its southern edge, where there is some evidence of increased upwelling. These results confirm previous observational studies and, more importantly, indicate that observed SST trends are not only due to changes in radiative or atmospheric heat fluxes alone but also due to changes in upwelling dynamics, suggesting that such a process may be relevant in climate change scenarios