Articles | Volume 15, issue 6
https://doi.org/10.5194/os-15-1801-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-15-1801-2019
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
20 Dec 2019
Research article |
| 20 Dec 2019
| 20 Dec 2019
Evaluation of nonidentical versus identical twin approaches for observation impact assessments: an ensemble-Kalman-filter-based ocean assimilation application for the Gulf of Mexico
Department of Oceanography, Dalhousie University, Halifax, Nova
Scotia, Canada
Department of Mathematics, The Hong Kong University of Science and
Technology, Hong Kong, China
Katja Fennel
Department of Oceanography, Dalhousie University, Halifax, Nova
Scotia, Canada
Bin Wang
Department of Oceanography, Dalhousie University, Halifax, Nova
Scotia, Canada
Arnaud Laurent
Department of Oceanography, Dalhousie University, Halifax, Nova
Scotia, Canada
Keith R. Thompson
Department of Oceanography, Dalhousie University, Halifax, Nova
Scotia, Canada
Lynn K. Shay
Rosenstiel School of Marine and Atmospheric Science, University of
Miami, Miami, Florida, USA
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Christopher Gordon, Katja Fennel, Clark Richards, Lynn K. Shay, and Jodi K. Brewster
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Bin Wang, Katja Fennel, Liuqian Yu, and Christopher Gordon
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We assess trade-offs between different types of biological observations, specifically satellite ocean color and BGC-Argo profiles and the benefits of combining both for optimizing a biogeochemical model of the Gulf of Mexico. Using all available observations leads to significant improvements in observed and unobserved variables (including primary production and C export). Our results highlight the significant benefits of BGC-Argo measurements for biogeochemical model optimization and validation.
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Katja Fennel, Simone Alin, Leticia Barbero, Wiley Evans, Timothée Bourgeois, Sarah Cooley, John Dunne, Richard A. Feely, Jose Martin Hernandez-Ayon, Xinping Hu, Steven Lohrenz, Frank Muller-Karger, Raymond Najjar, Lisa Robbins, Elizabeth Shadwick, Samantha Siedlecki, Nadja Steiner, Adrienne Sutton, Daniela Turk, Penny Vlahos, and Zhaohui Aleck Wang
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Angela M. Kuhn, Katja Fennel, and Ilana Berman-Frank
Biogeosciences, 15, 7379–7401, https://doi.org/10.5194/bg-15-7379-2018, https://doi.org/10.5194/bg-15-7379-2018, 2018
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Recent studies demonstrate that marine N2 fixation can be carried out without light. However, direct measurements of N2 fixation in dark environments are relatively scarce. This study uses a model that represents biogeochemical cycles at a deep-ocean location in the Gulf of Aqaba (Red Sea). Different model versions are used to test assumptions about N2 fixers. Relaxing light limitation for marine N2 fixers improved the similarity between model results and observations of deep nitrate and oxygen.
Bin Wang, Jiatang Hu, Shiyu Li, Liuqian Yu, and Jia Huang
Biogeosciences, 15, 6105–6125, https://doi.org/10.5194/bg-15-6105-2018, https://doi.org/10.5194/bg-15-6105-2018, 2018
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A physical–biogeochemical model was applied to study the response of hypoxia and oxygen dynamics to different riverine inputs. Results showed that the hypoxia in the Pearl River estuary was most sensitive to riverine inputs of POC, followed by DO and nutrients. This study also highlighted the significance of re-aeration for its buffering effects; i.e. the re-aeration responded rapidly to the perturbations of riverine inputs and in turn moderated the DO changes impacted by these perturbations.
Krysten Rutherford and Katja Fennel
Ocean Sci., 14, 1207–1221, https://doi.org/10.5194/os-14-1207-2018, https://doi.org/10.5194/os-14-1207-2018, 2018
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Using a regional model of the northwestern North Atlantic shelves, we calculate transport timescales and pathways in order to understand the transport processes that underlie the rapid oxygen loss, air–sea CO2 flux, and supply of plankton seed populations on the Scotian Shelf. Study results highlight the limited connectivity between the Scotian Shelf and adjacent slope waters; instead, the dominant southwestward currents bring Grand Banks and Gulf of St. Lawrence waters to the Scotian Shelf.
Katja Fennel and Arnaud Laurent
Biogeosciences, 15, 3121–3131, https://doi.org/10.5194/bg-15-3121-2018, https://doi.org/10.5194/bg-15-3121-2018, 2018
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Increasing human-derived nutrient inputs to coastal oceans lead to spreading dead zones around the world. Here a biogeochemical model for the northern Gulf of Mexico, where nutrients from the Mississippi River create the largest dead zone in North American coastal waters, is used for the first time to show the effects of single and dual nutrient reductions of nitrogen (N) and phosphorus (P). Significant reductions in N or N&P load would be required to significantly reduce hypoxia in this system.
Jonathan Lemay, Helmuth Thomas, Susanne E. Craig, William J. Burt, Katja Fennel, and Blair J. W. Greenan
Biogeosciences, 15, 2111–2123, https://doi.org/10.5194/bg-15-2111-2018, https://doi.org/10.5194/bg-15-2111-2018, 2018
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We report a detailed mechanistic investigation of the impact of Hurricane Arthur on the CO2 cycling on the Scotian Shelf. We can show that in contrast to common thinking, the deepening of the surface during the summer months can lead to increased CO2 uptake as carbon-poor waters from subsurface water are brought up to the surface. Only during prolonged storm events is the deepening of the mixed layer strong enough to bring the (expected) carbon-rich water to the surface.
Julia M. Moriarty, Courtney K. Harris, Katja Fennel, Marjorie A. M. Friedrichs, Kehui Xu, and Christophe Rabouille
Biogeosciences, 14, 1919–1946, https://doi.org/10.5194/bg-14-1919-2017, https://doi.org/10.5194/bg-14-1919-2017, 2017
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In coastal aquatic environments, resuspension of sediment and organic material from the seabed into the overlying water can impact biogeochemistry. Here, we used a novel modeling approach to quantify this impact for the Rhône River delta. In the model, resuspension increased oxygen consumption during individual resuspension events, and when results were averaged over 2 months. This implies that observations and models that only represent calm conditions may underestimate net oxygen consumption.
Zuo Xue, Ruoying He, Katja Fennel, Wei-Jun Cai, Steven Lohrenz, Wei-Jen Huang, Hanqin Tian, Wei Ren, and Zhengchen Zang
Biogeosciences, 13, 4359–4377, https://doi.org/10.5194/bg-13-4359-2016, https://doi.org/10.5194/bg-13-4359-2016, 2016
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In this study we used a state-of-the-science coupled physical–biogeochemical model to simulate and examine temporal and spatial variability of sea surface CO2 concentration in the Gulf of Mexico. Our model revealed the Gulf was a net CO2 sink with a flux of 1.11 ± 0.84 × 1012 mol C yr−1. We also found that biological uptake was the primary driver making the Gulf an overall CO2 sink and that the carbon flux in the northern Gulf was very susceptible to changes in river inputs.
A. Laurent, K. Fennel, R. Wilson, J. Lehrter, and R. Devereux
Biogeosciences, 13, 77–94, https://doi.org/10.5194/bg-13-77-2016, https://doi.org/10.5194/bg-13-77-2016, 2016
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In low oxygen environments, the lack of oxygen influences sediment biogeochemistry and in turn sediment-water fluxes. These nonlinear interactions are often missing from biogeochemical circulation models because sediment models are computationally expensive. A method for parameterizing realistic sediment-water fluxes is presented and applied to the Mississippi River Dead Zone where high primary production, stimulated by excess nutrient loads, promotes low bottom water conditions in summer.
L. Yu, K. Fennel, A. Laurent, M. C. Murrell, and J. C. Lehrter
Biogeosciences, 12, 2063–2076, https://doi.org/10.5194/bg-12-2063-2015, https://doi.org/10.5194/bg-12-2063-2015, 2015
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Our study suggests that a combination of physical processes and sediment oxygen consumption determine the spatial extent and temporal dynamics of hypoxia on the Louisiana shelf. In summer, stratification isolates oxygen-rich surface waters from hypoxic bottom waters; oxygen outgasses to the atmosphere at this time. A large fraction of primary production occurs below the pycnocline in summer, but this primary production does not strongly affect the spatial extent of hypoxic bottom waters.
K.-K. Liu, C.-K. Kang, T. Kobari, H. Liu, C. Rabouille, and K. Fennel
Biogeosciences, 11, 7061–7075, https://doi.org/10.5194/bg-11-7061-2014, https://doi.org/10.5194/bg-11-7061-2014, 2014
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This paper provides background info on the East China Sea, Japan/East Sea and South China Sea and highlights major findings in the special issue on their biogeochemical conditions and ecosystem functions. The three seas are subject to strong impacts from human activities and/or climate forcing. Because these continental margins sustain arguably some of the most productive marine ecosystems in the world, changes in these stressed ecosystems may threaten the livelihood of a large human population.
Z. Xue, R. He, K. Fennel, W.-J. Cai, S. Lohrenz, and C. Hopkinson
Biogeosciences, 10, 7219–7234, https://doi.org/10.5194/bg-10-7219-2013, https://doi.org/10.5194/bg-10-7219-2013, 2013
W. J. Burt, H. Thomas, K. Fennel, and E. Horne
Biogeosciences, 10, 53–66, https://doi.org/10.5194/bg-10-53-2013, https://doi.org/10.5194/bg-10-53-2013, 2013
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Short summary
We present a first direct comparison of nonidentical versus identical twin approaches for an ocean data assimilation system. We show that the identical twin approach overestimates the value of assimilating satellite observations and undervalues the benefit of assimilating temperature and salinity profiles. Misleading assessments such as undervaluing the impact of observational assets are problematic and can lead to misguided decisions on balancing investments among different observing assets.
We present a first direct comparison of nonidentical versus identical twin approaches for an...
