scholarly journals Biogeochemical variability in the California Current System

2020 ◽  
Author(s):  
Curtis Deutsch ◽  
Hartmut Frenzel ◽  
James C. McWilliams ◽  
Lionel Renault ◽  
Faycal Kessouri ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Net Primary Productivity ◽  
Current System ◽  
California Current ◽  
Light Limitation ◽  
Biogeochemical Model ◽  
Past Century ◽  
Physical Analysis ◽  
California Current System ◽  
Mean State

AbstractThe biological productivity and diversity of the California Current System (CCS) is at the leading edge of major emerging climate trends, including hypoxia and acidification. We present results from a hindcast simulation (reanalysis) of an eddy-resolving oceanic physical-biogeochemical model of the CCS, to characterize its mean state and its patterns and drivers of variability in marine biogeochemical and ecosystem processes from 1995-2010. This is a companion paper to a physical analysis in Renault et al. (2019). The model reproduces long-term mean distributions of key ecosystem metrics, including surface nutrients and productivity and subsurface O2 and carbonate undersaturation. The spatial patterns of Net Primary Productivity (NPP) are broadly consistent with measured and remotely sensed rates, and they reflect a predominant limitation by nitrogen, with seasonal and episodic limitation by Fe nearshore in the central CCS, and in the open ocean northern CCS. The vertical distribution of NPP is governed by the trade-off between nutrient and light limitation, a balance that reproduces and explains the observed spatial variations in the depth of the deep Chl maximum. The seasonal to interannual variability of biogeochemical properties and rates is also well captured by model simulations. Because of the prevailing nutrient limitation, fluctuations in the depth of the pycnocline and associated nutricline are the leading single factor explaining interannual variability in the interior biogeochemical state, and the relationships between density and biogeochemical rates and tracers are consistent between model and observations. The magnitude and relationship between density structure and biogeochemical processes is illustrated by the 1997-98 El Niño event, which faithfully reproduces the single largest deviation from the mean state in the simulated period. A slower decadal shoaling of the pycnocline also accounts for the concomitant trends in hypoxic and corrosive conditions on the shelf. The resulting variability is key to understanding the vulnerability of marine species to oceanic change, and to the detection of such changes, soon projected to exceed the range of conditions in the past century.

Interannual variability in bottom-up processes in the upstream range of the California Current system: An isotopic approach

2012 ◽  
Vol 106 ◽  
pp. 16-27 ◽  
Author(s):  
Rana W. El-Sabaawi ◽  
Marc Trudel ◽  
David L. Mackas ◽  
John F. Dower ◽  
Asit Mazumder
Keyword(s):  
Interannual Variability ◽  
Current System ◽  
California Current ◽  
Bottom Up ◽  
California Current System

scholarly journals Annual and Interannual Variability in the California Current System: Comparison of an Ocean State Estimate with a Network of Underwater Gliders

2018 ◽  
Vol 48 (12) ◽  
pp. 2965-2988 ◽  
Author(s):  
Katherine D. Zaba ◽  
Daniel L. Rudnick ◽  
Bruce D. Cornuelle ◽  
Ganesh Gopalakrishnan ◽  
Matthew R. Mazloff
Keyword(s):  
Interannual Variability ◽  
Large Scale ◽  
Current System ◽  
Potential Temperature ◽  
California Current ◽  
Late Summer ◽  
Near Surface ◽  
State Estimate ◽  
California Current System ◽  
Annual Cycles

AbstractA data-constrained state estimate of the southern California Current System (CCS) is presented and compared with withheld California Cooperative Oceanic Fisheries Investigations (CalCOFI) data and assimilated glider data over 2007–17. The objective of this comparison is to assess the ability of the California State Estimate (CASE) to reproduce the key physical features of the CCS mean state, annual cycles, and interannual variability along the three sections of the California Underwater Glider Network (CUGN). The assessment focuses on several oceanic metrics deemed most important for characterizing physical variability in the CCS: 50-m potential temperature, 80-m salinity, and 26 kg m−3 isopycnal depth and salinity. In the time mean, the CASE reproduces large-scale thermohaline and circulation structures, including observed temperature gradients, shoaling isopycnals, and the locations and magnitudes of the equatorward California Current and poleward California Undercurrent. With respect to the annual cycle, the CASE captures the phase and, to a lesser extent, the magnitude of upper-ocean warming and stratification from late summer to early fall and of isopycnal heave during springtime upwelling. The CASE also realistically captures near-surface diapycnal mixing during upwelling season and the semiannual cycle of the California Undercurrent. In terms of interannual variability, the most pronounced signals are the persistent warming and downwelling anomalies of 2014–16 and a positive isopycnal salinity anomaly that peaked with the 2015–16 El Niño.

scholarly journals A Dynamically Downscaled Ensemble of Future Projections for the California Current System

2021 ◽  
Vol 8 ◽  
Author(s):  
Mercedes Pozo Buil ◽  
Michael G. Jacox ◽  
Jerome Fiechter ◽  
Michael A. Alexander ◽  
Steven J. Bograd ◽  
...  
Keyword(s):  
Current System ◽  
California Current ◽  
Nitrate Content ◽  
Biogeochemical Model ◽  
Climate Projections ◽  
Surface Mixed Layer ◽  
California Current System ◽  
The Future ◽  
The Mean ◽  
Source Waters

Given the ecological and economic importance of eastern boundary upwelling systems like the California Current System (CCS), their evolution under climate change is of considerable interest for resource management. However, the spatial resolution of global earth system models (ESMs) is typically too coarse to properly resolve coastal winds and upwelling dynamics that are key to structuring these ecosystems. Here we use a high-resolution (0.1°) regional ocean circulation model coupled with a biogeochemical model to dynamically downscale ESMs and produce climate projections for the CCS under the high emission scenario, Representative Concentration Pathway 8.5. To capture model uncertainty in the projections, we downscale three ESMs: GFDL-ESM2M, HadGEM2-ES, and IPSL-CM5A-MR, which span the CMIP5 range for future changes in both the mean and variance of physical and biogeochemical CCS properties. The forcing of the regional ocean model is constructed with a “time-varying delta” method, which removes the mean bias of the ESM forcing and resolves the full transient ocean response from 1980 to 2100. We found that all models agree in the direction of the future change in offshore waters: an intensification of upwelling favorable winds in the northern CCS, an overall surface warming, and an enrichment of nitrate and corresponding decrease in dissolved oxygen below the surface mixed layer. However, differences in projections of these properties arise in the coastal region, producing different responses of the future biogeochemical variables. Two of the models display an increase of surface chlorophyll in the northern CCS, consistent with a combination of higher nitrate content in source waters and an intensification of upwelling favorable winds. All three models display a decrease of chlorophyll in the southern CCS, which appears to be driven by decreased upwelling favorable winds and enhanced stratification, and, for the HadGEM2-ES forced run, decreased nitrate content in upwelling source waters in nearshore regions. While trends in the downscaled models reflect those in the ESMs that force them, the ESM and downscaled solutions differ more for biogeochemical than for physical variables.

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