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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/bg-2020-70
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-70
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Mar 2020

Submitted as: research article | 05 Mar 2020

Review status
A revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

A regional hindcast model simulating ecosystem dynamics, inorganic carbon chemistry and ocean acidification in the Gulf of Alaska

Claudine Hauri1, Cristina Schultz2, Katherine Hedstrom3, Seth Danielson3, Brita Irving1, Scott C. Doney2, Raphael Dussin4, Enrique N. Curchitser5, David F. Hill6, and Charles A. Stock4 Claudine Hauri et al.
  • 1University of Alaska Fairbanks, International Arctic Research Center, Fairbanks, AK, USA
  • 2University of Virginia, Department of Environmental Sciences, Charlottesville, VA, USA
  • 3University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Fairbanks, AK, USA
  • 4Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 5Department of Environmental Sciences, Rutgers University, New Brunswick, NJ, USA
  • 6Oregon State University, OR, USA

Abstract. The coastal ecosystem of the Gulf of Alaska (GOA) is especially vulnerable to the effects of ocean acidification and climate change that can only be understood within the context of the natural variability of physical and chemical conditions. Controlled by its complex bathymetry, iron enriched freshwater discharge, and wind and solar radiation, the GOA is a highly dynamic system that exhibits large inorganic carbon variability from subseasonal to interannual timescales. This variability is poorly understood due to the lack of observations in this expansive and remote region. To improve our conceptual understanding of the system, we developed a new model set-up for the GOA that couples the three-dimensional Regional Oceanic Model System (ROMS), the Carbon, Ocean Biogeochemistry and Lower Trophic (COBALT) ecosystem model, and a high resolution terrestrial hydrological model. Here, we evaluate the model on seasonal to interannual timescales using the best available inorganic carbon observations. The model was particularly successful in reproducing observed aragonite oversaturation and undersaturation of near-bottom water in May and September, respectively. The largest deficiency of the model is perhaps its inability to adequately simulate spring time surface inorganic carbon chemistry, as it overestimates surface dissolved inorganic carbon, which translates into an underestimation of the surface aragonite saturation state at this time. We also use the model to describe the seasonal cycle and drivers of inorganic carbon parameters along the Seward Line transect in under-sampled months. As such, model output suggests that a majority of the near-bottom water along the Seward Line is seasonally under-saturated with regard to aragonite between June and January, as a result of upwelling and remineralization. Such an extensive period of reoccurring aragonite undersaturation may be harmful to CO2 sensitive organisms. Furthermore, the influence of freshwater not only decreases aragonite saturation state in coastal surface waters in summer and fall, but simultaneously also decreases surface pCO2, thereby decoupling the aragonite saturation state from pCO2. The full seasonal cycle and geographic extent of the GOA region is undersampled, and our model results give new and important insights for months of the year and areas that lack in situ inorganic carbon observations.

Claudine Hauri et al.

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Interactive discussion

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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Claudine Hauri et al.

Data sets

Gulf of Alaska ROMS-COBALT Hindcast Simulation 1980 - 2013 C. Hauri, K. Hedstrom, and S. Danielson https://doi.org/10.24431/rw1k43t

Model code and software

Master branch with COBALT early 2020 K. Hedstrom, S. Mack, M. Hadfield, and R. Hetland https://doi.org/10.5281/zenodo.3647609

For use with v3.8_cobalt of ROMS K. Hedstrom https://doi.org/10.5281/zenodo.3647663

Master branch with COBALT mid 2019 K. Hedstrom, S. Mack, M. Hadfield, and R. Hetland https://doi.org/10.5281/zenodo.3661518

Claudine Hauri et al.

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Short summary
The coastal ecosystem of the Gulf of Alaska (GOA) is especially vulnerable to the effects of ocean acidification and climate change. To improve our conceptual understanding of the system, we developed a new regional biogeochemical model set-up for the GOA. Model output suggests that bottom water is seasonally high in CO2 between June and January. Such extensive periods of reoccurring high CO2 may be harmful to sensitive organisms. Our results give insights to where and when data gaps exist.
The coastal ecosystem of the Gulf of Alaska (GOA) is especially vulnerable to the effects of...
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