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Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification (2020)

Rheuban, Jennie E. ; Doney, Scott C. ; McCorkle, Daniel C. ; [et al.]

American Geophysical Union

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Publication Date: 2022-05-26

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Rheuban, J. E., Doney, S. C., McCorkle, D. C., & Jakuba, R. W. Quantifying the effects of nutrient enrichment and freshwater mixing on coastal ocean acidification. Journal of Geophysical Research-Oceans, 124, (2019): 9085-9100, doi: 10.1029/2019JC015556.

Description: The U.S. Northeast is vulnerable to ocean and coastal acidification because of low alkalinity freshwater discharge that naturally acidifies the region, and high anthropogenic nutrient loads that lead to eutrophication in many estuaries. This study describes a combined nutrient and carbonate chemistry monitoring program in five embayments of Buzzards Bay, Massachusetts to quantify the effects of nutrient loading and freshwater discharge on aragonite saturation state (Ω). Monitoring occurred monthly from June 2015 to September 2017 with higher frequency at two embayments (Quissett and West Falmouth Harbors) and across nitrogen loading and freshwater discharge gradients. The more eutrophic stations experienced seasonal aragonite undersaturation, and at one site, nearly every measurement collected was undersaturated. We present an analytical framework to decompose variability in aragonite Ω into components driven by temperature, salinity, freshwater endmember mixing, and biogeochemical processes. We observed strong correlations between apparent oxygen utilization and the portion of aragonite Ω variation that we attribute to biogeochemistry. The regression slopes were consistent with Redfield ratios of dissolved inorganic carbon and total alkalinity to dissolved oxygen. Total nitrogen and the contribution of biogeochemical processes to aragonite Ω were highly correlated, and this relationship was used to estimate the likely effects of nitrogen loading improvements on aragonite Ω. Under nitrogen loading reduction scenarios, aragonite Ω in the most eutrophic estuaries could be raised by nearly 0.6 units, potentially increasing several stations above the critical threshold of 1. This analysis provides a quantitative framework for incorporating ocean and coastal acidification impacts into regulatory and management discussions.

Description: We thank Kelly Luis, Michaela Fendrock, Will Oesterich, Sheron Luk, Marti Jeglinksi, and Tony Williams for their help with field sample collection and logistical support and Chris Neill, Lindsay Scott, Rich McHorney, and Paul Henderson for laboratory sample analysis. We also thank the Waquoit Bay National Estuarine Research Reserve for loaning their handheld water quality meters and two anonymous reviewers for their feedback on this manuscript. Financial support for this work was provided by the John D. and Catherine T. MacArthur Foundation (grant no. 14‐106159‐000‐CFP), MIT Sea Grant (subaward 5710004045) and the West Wind Foundation. The data used in this analysis can be found in the NOAA NCEI repository for carbonate chemistry measurements, the Ocean Carbon Data System at the following link: https://www.nodc.noaa.gov/ocads/data/0206206.xml.

Keywords: Coastal Acidification ; Eutrophication

Repository Name: Woods Hole Open Access Server

Type: Article

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Modeling of the influence of sea ice cycle and Langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the West Antarctic Peninsula (2020)

Schultz, Cristina ; Doney, Scott C. ; Zhang, Weifeng G. ; [et al.]

American Geophysical Union

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Publication Date: 2022-05-26

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schultz, C., Doney, S. C., Zhang, W. G., Regan, H., Holland, P., Meredith, M. P., & Stammerjohn, S. Modeling of the influence of sea ice cycle and Langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the West Antarctic Peninsula. Journal of Geophysical Research: Oceans, 125(8), (2020): e2020JC016109, doi:10.1029/2020JC016109.

Description: The Southern Ocean is chronically undersampled due to its remoteness, harsh environment, and sea ice cover. Ocean circulation models yield significant insight into key processes and to some extent obviate the dearth of data; however, they often underestimate surface mixed layer depth (MLD), with consequences for surface water‐column temperature, salinity, and nutrient concentration. In this study, a coupled circulation and sea ice model was implemented for the region adjacent to the West Antarctic Peninsula, a climatically sensitive region which has exhibited decadal trends towards higher ocean temperature, shorter sea ice season, and increasing glacial freshwater input, overlain by strong interannual variability. Hindcast simulations were conducted with different air‐ice drag coefficients and Langmuir circulation parameterizations to determine the impact of these factors on MLD. Including Langmuir circulation deepened the surface mixed layer, with the deepening being more pronounced in the shelf and slope regions. Optimal selection of an air‐ice drag coefficient also increased modeled MLD by similar amounts and had a larger impact in improving the reliability of the simulated MLD interannual variability. This study highlights the importance of sea ice volume and redistribution to correctly reproduce the physics of the underlying ocean, and the potential of appropriately parameterizing Langmuir circulation to help correct for biases towards shallow MLD in the Southern Ocean. The model also reproduces observed freshwater patterns in the West Antarctic Peninsula during late summer and suggests that areas of intense summertime sea ice melt can still show net annual freezing due to high sea ice formation during the winter.

Description: C. Schultz and S. Doney acknowledge support by the U.S. National Science Foundation (grant PLR‐1440435 to the Palmer Long Term Ecological Research program) and support from the University of Virginia. W. G. Zhang acknowledge support by the U.S. National Science Foundation (grant OPP‐1643901). The MITgcm model is an open source model (mitgcm.org). The version used in this study, with added parameterizations and specific configurations, is on C. Schultz’s github (https://github.com/crisoceano/WAP_MITgcm). A copy of the files with specific configurations for this study, the forcing files needed for the simulations, and a copy of the files used for the KPP package are in three separate records on zenodo.org, under DOIs 10.5281/zenodo.3627365, 10.5281/zenodo.3627564, and 10.5281/zenodo.3627742.

Keywords: West Antarctic Peninsula ; sea ice ; Langmuir circulation ; mixed layer depth ; glacial runoff

Repository Name: Woods Hole Open Access Server

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An atmospheric constraint on the seasonal Air-Sea exchange of oxygen and heat in the extratropics (2021)

Morgan, Eric J. ; Manizza, Manfredi ; Keeling, Ralph F. ; [et al.]

American Geophysical Union

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Publication Date: 2022-05-27

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(8), (2021): e2021JC017510, https://doi.org/10.1029/2021JC017510.

Description: The air-sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air-sea exchange of O2 has been shown to be closely related to the air-sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/heat ratio is both a fundamental biogeochemical property of air-sea exchange and a convenient metric for testing earth system models. Current estimates of the O2/heat flux ratio rely on sparse observations of dissolved O2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon-to-nitrogen ratio (Ar/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40–70°). The amplitude ratio, A APO/A ArN2, is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. A APO/A ArN2 is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of δAPO is compensated by similar variations in δ(Ar/N2). From the relationship between O2/heat and A APO/A ArN2 in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct O2/heat flux ratios of 3.3 ± 0.3 and 4.7 ± 0.8 nmol J-1 between 40 and 70° in the Northern and Southern Hemispheres respectively, providing a useful constraint for O2 and heat air-sea fluxes in earth system models and observation-based data products.

Description: The recent atmospheric measurements of the Scripps program have been supported via funding from the NSF and the National Oceanographic and Atmospheric Administration (NOAA) under grants 1304270 and OAR-CIPO-2015-2004269. M. Manizza and R. F. Keeling thank NSF for financial support via the OCE-1130976 grant. M. Manizza thanks additional financial support from NSF via the ARRA OCE-0850350 grant. S. C. Doney acknowledges support from NSF PLR-1440435. Keith Rodgers acknowledges support from IBS-R028-D1. Gael Forget and the ECCO group kindly provided the ECCOv4 heat fluxes.

Description: 2022-01-22

Repository Name: Woods Hole Open Access Server

Type: Article

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Modeling phytoplankton blooms and inorganic carbon responses to sea-ice variability in the West Antarctic Peninsula (2021)

Schultz, Cristina ; Doney, Scott C. ; Hauck, Judith ; [et al.]

American Geophysical Union

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Publication Date: 2022-10-26

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schultz, C., Doney, S. C., Hauck, J., Kavanaugh, M. T., & Schofield, O. Modeling phytoplankton blooms and inorganic carbon responses to sea-ice variability in the West Antarctic Peninsula. Journal of Geophysical Research: Biogeosciences, 126(4), (2021): e2020JG006227, https://doi.org/10.1029/2020JG006227.

Description: The ocean coastal-shelf-slope ecosystem west of the Antarctic Peninsula (WAP) is a biologically productive region that could potentially act as a large sink of atmospheric carbon dioxide. The duration of the sea-ice season in the WAP shows large interannual variability. However, quantifying the mechanisms by which sea ice impacts biological productivity and surface dissolved inorganic carbon (DIC) remains a challenge due to the lack of data early in the phytoplankton growth season. In this study, we implemented a circulation, sea-ice, and biogeochemistry model (MITgcm-REcoM2) to study the effect of sea ice on phytoplankton blooms and surface DIC. Results were compared with satellite sea-ice and ocean color, and research ship surveys from the Palmer Long-Term Ecological Research (LTER) program. The simulations suggest that the annual sea-ice cycle has an important role in the seasonal DIC drawdown. In years of early sea-ice retreat, there is a longer growth season leading to larger seasonally integrated net primary production (NPP). Part of the biological uptake of DIC by phytoplankton, however, is counteracted by increased oceanic uptake of atmospheric CO2. Despite lower seasonal NPP, years of late sea-ice retreat show larger DIC drawdown, attributed to lower air-sea CO2 fluxes and increased dilution by sea-ice melt. The role of dissolved iron and iron limitation on WAP phytoplankton also remains a challenge due to the lack of data. The model results suggest sediments and glacial meltwater are the main sources in the coastal and shelf regions, with sediments being more influential in the northern coast.

Description: C. Schultz, S. C. Doney, M. T. Kavanaugh, and O. Schofield acknowledge support by the US National Science Foundation (Grant no. PLR-1440435), and C. Schultz and S. C. Doney acknowledge support from the University of Virginia. This research has also received funding from the Helmholtz Young Investigator Group Marine Carbon and Ecosystem Feedbacks in the Earth System (MarESys), Grant number VH-NG-1301.

Keywords: Air-sea fluxes ; Biogeochemical modeling ; Inorganic carbon cycle ; Phytoplankton bloom ; Sea ice ; West Antarctic Peninsula

Repository Name: Woods Hole Open Access Server

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A geostatistical framework for quantifying the imprint of mesoscale atmospheric transport on satellite trace gas retrievals (2020)

Torres, Anthony D. ; Keppel-Aleks, Gretchen ; Doney, Scott C. ; [et al.]

American Geophysical Union

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Publication Date: 2022-10-26

Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Atmospheres 124 (17-18), (2019): 9773-9795, doi: 10.1029/2018JD029933.

Description: National Aeronautics and Space Administration's Orbiting Carbon Observatory‐2 (OCO‐2) satellite provides observations of total column‐averaged CO2 mole fractions (XCO2 ) at high spatial resolution that may enable novel constraints on surface‐atmosphere carbon fluxes. Atmospheric inverse modeling provides an approach to optimize surface fluxes at regional scales, but the accuracy of the fluxes from inversion frameworks depends on key inputs, including spatially and temporally dense CO2 observations and reliable representations of atmospheric transport. Since XCO2 observations are sensitive to both synoptic and mesoscale variations within the free troposphere, horizontal atmospheric transport imparts substantial variations in these data and must be either resolved explicitly by the atmospheric transport model or accounted for within the error covariance budget provided to inverse frameworks. Here, we used geostatistical techniques to quantify the imprint of atmospheric transport in along‐track OCO‐2 soundings. We compare high‐pass‐filtered (〈250 km, spatial scales that primarily isolate mesoscale or finer‐scale variations) along‐track spatial variability in XCO2 and XH2O from OCO‐2 tracks to temporal synoptic and mesoscale variability from ground‐based XCO2 and XH2O observed by nearby Total Carbon Column Observing Network sites. Mesoscale atmospheric transport is found to be the primary driver of along‐track, high‐frequency variability for OCO‐2 XH2O. For XCO2 , both mesoscale transport variability and spatially coherent bias associated with other elements of the OCO‐2 retrieval state vector are important drivers of the along‐track variance budget.

Description: The authors thank the leadership and participants of the NASA OCO‐2 mission and acknowledge financial support from NASA Award NNX15AH13G. A.D. Torres also acknowledges support from the NASA Earth and Space Science Fellowship Award 80NSSC17K0382. We thank TCCON for providing observations. We thank A. Jacobson and the National Oceanographic and Atmospheric Administration Earth System Research Laboratory in Boulder, CO, for providing CarbonTracker CT2017 data, available online (http://carbontracker.noaa.gov). We thank S. Wofsy for providing HIPPO data, funded by the National Science Foundation and NOAA and available online (https://www.eol.ucar.edu/field_projects/hippo). The TCCON Principal Investigators acknowledge funding from their national funding organizations. TCCON data were obtained from the archive at the https://tccondata.org Web site. NARR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site (https://www.esrl.noaa.gov/psd/).

Keywords: Atmospheric transport ; Greenhouse gases ; CO2 ; Mesoscale ; OCO‐2 ; TCCON

Repository Name: Woods Hole Open Access Server

Type: Article

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