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1. Ice-Tethered Profiler Biogeochemical Time-Series Data, Arctic Ocean, 2012-2021

   https://doi.org/10.18739/A2B853K2R  

   DeGrandpre, Michael ( January 2022 , NSF Arctic Data Center)

   The goal of the proposed study is to establish an Arctic Observing Network (AON) for sea surface partial pressure of carbon dioxide (pCO2) and pH in the perennially ice-covered portion of the Arctic Ocean. The carbon cycle is of particular concern in the Arctic because it is unknown how carbon sources and sinks will change in response to warming and the reduction of summer sea ice cover, and whether these changes will lead to increased greenhouse gas accumulation in the atmosphere. Furthermore, the penetration of anthropogenic caron dioxide (CO2) into the Arctic Ocean is leading to acidification with potentially serious consequences for organisms. Little is known about pCO2 and the inorganic carbon cycle in the central Arctic Ocean because most measurement programs to date have focused on the Arctic shelves during the accessible summer period. The investigators propose to use an existing component of the Arctic Observing Network, the Ice-Tethered Profilers (ITP), as platforms for deployment of in situ pCO2 and pH sensors. ITPs are automated profiling systems distributed throughout the perennial Arctic ice pack that telemeter data back to shore: 44 ITPs have been deployed since 2004 and the project is currently slated to continue through 2013. In the proposed work, a total of 6 ITPs will be equipped with CO2 sensors and four of these will also have pH sensors. The sensors will be fixed on the ITP cable ~2-4 meters below the ice. Each unit will include additional sensors for dissolved O2, salinity, and photosynthetically available radiation (and in some cases chlorophyll-a fluorescence) and will be capable of making 12 measurements per day for at least one year. These data, available in near real-time on the ITP web site (www.whoi.edu/itp/), will lead to a better understanding of the Arctic Ocean's role in regulating greenhouse gases and how the ecology of the Arctic will change with warming and acidification. The investigators will also engage in outreach programs including public presentations, podcasts, and school visits. A portion of the budget is also dedicated to the development of a climate-change/ocean acidification exhibit to be displayed in the University of Montana's science museum. The exhibit will reside at the museum for three months, then visit over 15 rural and tribal communities annually over a three year period. Undergraduate students will be recruited to assist with the sensor testing and data analysis, gaining a higher level of technical knowledge than possible through a traditional degree program. These data were collected using in situ sensors for the partial pressure of CO2 (pCO2), pH, dissolved oxygen (DO), photosynthetically available radiation (PAR), temperature, salinity and depth. Sensors were deployed at ~6 meter depth on ice-tethered profilers, in collaboration with Woods Hole Oceanographic Institution (Rick Krishfield and John Toole). Data are available at the website http://www.whoi.edu/page.do?pid=20781. 

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2. Autonomous seawater <i>p</i>CO₂ and pH time series from 40 surface buoys and the emergence of anthropogenic trends

   https://doi.org/10.5194/essd-11-421-2019  

   Sutton, Adrienne J. ; Feely, Richard A. ; Maenner-Jones, Stacy ; Musielwicz, Sylvia ; Osborne, John ; Dietrich, Colin ; Monacci, Natalie ; Cross, Jessica ; Bott, Randy ; Kozyr, Alex ; et al ( January 2019 , Earth System Science Data)

   Abstract. Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here, we present a data product of 40 individual autonomous moored surface ocean pCO2 (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterize a wide range of surface ocean carbonate conditions in different oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied to the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estimates for seawater pCO2 and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus in the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9±0.3 and 1.6±0.3 µatm yr−1, respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and https://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018). 

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3. Labrador Sea freshening linked to Beaufort Gyre freshwater release

   https://doi.org/10.1038/s41467-021-21470-3  

   Zhang, Jiaxu ; Weijer, Wilbert ; Steele, Michael ; Cheng, Wei ; Verma, Tarun ; Veneziani, Milena ( February 2021 , Nature Communications)

   The Beaufort Gyre (BG), the largest Arctic Ocean freshwater reservoir, has drastically increased its liquid freshwater content by 40% in the past two decades. If released within a short period, the excess freshwater could potentially impact the large-scale ocean circulation by freshening the upper subpolar North Atlantic. Here, we track BG-sourced freshwater using passive tracers in a global ocean sea-ice model and show that this freshwater exited the Arctic mostly through the Canadian Arctic Archipelago, rather than Fram Strait, during an historical release event in 1983–1995. The Labrador Sea is the most affected region in the subpolar North Atlantic, with a freshening of 0.2 psu on the western shelves and 0.4 psu in the Labrador Current. Given that the present BG freshwater content anomaly is twice the historical analog studied here, the impact of a future rapid release on Labrador Sea salinity could be significant, easily exceeding similar fluxes from Greenland meltwater.

    

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4. Harmonization of global surface ocean pCO2 mapped products and their flux calculations; an improved estimate of the ocean carbon sink

   https://doi.org/10.5194/essd-2021-16  

   Fay, A. R. ; Gregor, L. ; Landschützer, P. ; McKinley, G. A. ; Gruber, N. ; Gehlen, M. ; Iida, Y. ; Laruelle, G. G. ; Rödenbeck, C. ; Zeng, J.: ( December 2021 , Earth system science data)

   Elger, Kirsten ; Carlson, David ; Klump, Jens ; Peng, Ge (Ed.)

   Air-sea flux of carbon dioxide (CO2) is a critical component of the global carbon cycle and the climate system with the ocean removing about a quarter of the CO2 emitted into the atmosphere by human activities over the last decade. A common approach to estimate this net flux of CO2 across the air-sea interface is the use of surface ocean CO2 observations and the computation of the flux through a bulk parameterization approach. Yet, the details for how this is done in order to arrive at a global ocean CO2 uptake estimate varies greatly, unnecessarily enhancing the uncertainties. Here we reduce some of these uncertainties by harmonizing an ensemble of products that interpolate surface ocean CO2 bservations to near global coverage. We propose a common methodology to fill in missing areas in the products and to calculate fluxes and present a new estimate of the net flux. The ensemble data product, SeaFlux (Gregor & Fay (2021), doi.org/10.5281/zenodo.4133802, https://github.com/luke-gregor/SeaFlux), accounts for the diversity of the underlying mapping methodologies. Utilizing six 30 global observation-based mapping products (CMEMS-FFNN, CSIR-ML6, JENA-MLS, JMA-MLR, MPI-SOMFFN, NIESFNN), the SeaFlux ensemble approach adjusts for methodological inconsistencies in flux calculations that can result in an average error of 15% in global mean flux estimates. We address differences in spatial coverage of the surface ocean CO2 between the mapping products which ultimately yields an increase in CO2 uptake of up to 19% for some products. Fluxes are calculated using three wind products (CCMPv2, ERA5, and JRA55). Application of an appropriately scaled gas exchange 35 coefficient has a greater impact on the resulting flux than solely the choice of wind product. With these adjustments, we derive an improved ensemble of surface ocean pCO2 and air-sea carbon flux estimates. The SeaFlux ensemble suggests a global mean uptake of CO2 from the atmosphere of 1.92 +/- 0.35 PgC yr-1. This work aims to support the community effort to perform model-data intercomparisons which will help to identify missing fluxes as we strive to close the global carbon budget. 

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5. When “evaporites” are not formed by evaporation: The role of temperature and pCO2 on saline deposits of the Eocene Green River Formation, Colorado, USA

   https://doi.org/10.1130/B35303.1  

   Demicco, Robert V. ; Lowenstein, Tim K. ( November 2019 , GSA Bulletin)

   null (Ed.)

   Abstract Halite precipitates in the Dead Sea during winter but re-dissolves above the thermocline upon summer warming, “focusing” halite deposition below the thermocline (Sirota et al., 2016, 2017, 2018). Here we develop an “evaporite focusing” model for evaporites (nahcolite + halite) preserved in a restricted area of the Eocene Green River Formation in the Piceance Creek Basin of Colorado, USA. Nahcolite solubility is dependent on partial pressure of carbon dioxide (pCO2) as well as temperature (T), so these models covary with both T and pCO2. In the lake that filled the Piceance Creek Basin, halite, nahcolite or mixtures of both could have precipitated during winter cooling, depending on the CO2 content in different parts of the lake. Preservation of these minerals occurs below the thermocline (>∼25 m) in deeper portions of the basin. Our modeling addresses both: (1) the restriction of evaporites in the Piceance Creek Basin to the center of the basin without recourse to later dissolution and (2) the variable mineralogy of the evaporites without recourse to changes in lake water chemistry. T from 20 to 30 °C and pCO2 between 1800 and 2800 ppm are reasonable estimates for the conditions in the Piceance Creek Basin paleolake. Other evaporites occur in the center of basins but do not extend out to the edges of the basin. Evaporite focusing caused by summer-winter T changes in the solubility of the minerals should be considered for such deposits and variable pCO2 within the evaporating brines also needs to be considered if pCO2 sensitive minerals are found. 

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