Schaap Allison

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Schaap
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Allison
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  • Article
    Advancing observation of ocean biogeochemistry, biology, and ecosystems with cost-effective in situ sensing technologies
    (Frontiers Media, 2019-09-12) Wang, Zhaohui Aleck ; Moustahfid, Hassan ; Mueller, Amy V. ; Michel, Anna P. M. ; Mowlem, Matthew ; Glazer, Brian T. ; Mooney, T. Aran ; Michaels, William ; McQuillan, Jonathan S. ; Robidart, Julie ; Churchill, James H. ; Sourisseau, Marc ; Daniel, Anne ; Schaap, Allison ; Monk, Sam ; Friedman, Kim ; Brehmer, Patrice
    Advancing our understanding of ocean biogeochemistry, biology, and ecosystems relies on the ability to make observations both in the ocean and at the critical boundaries between the ocean and other earth systems at relevant spatial and temporal scales. After decades of advancement in ocean observing technologies, one of the key remaining challenges is how to cost-effectively make measurements at the increased resolution necessary for illuminating complex system processes and rapidly evolving changes. In recent years, biogeochemical in situ sensors have been emerging that are threefold or more lower in cost than established technologies; the cost reduction for many biological in situ sensors has also been significant, although the absolute costs are still relatively high. Cost savings in these advancements has been driven by miniaturization, new methods of packaging, and lower-cost mass-produced components such as electronics and materials. Recently, field projects have demonstrated the potential for science-quality data collection via large-scale deployments using cost-effective sensors and deployment strategies. In the coming decade, it is envisioned that ocean biogeochemistry and biology observations will be revolutionized by continued innovation in sensors with increasingly low price points and the scale-up of deployments of these in situ sensor technologies. The goal of this study is therefore to: (1) provide a review of existing sensor technologies that are already achieving cost-effectiveness compared with traditional instrumentation, (2) present case studies of cost-effective in situ deployments that can provide insight into methods for bridging observational gaps, (3) identify key challenge areas where progress in cost reduction is lagging, and (4) present a number of potentially transformative directions for future ocean biogeochemical and biological studies using cost-effective technologies and deployment strategies.
  • Article
    Detection and quantification of a release of carbon dioxide gas at the seafloor using pH eddy covariance and measurements of plume advection
    (Elsevier, 2021-10-22) Koopmans, Dirk ; Meyer, Volker ; Schaap, Allison ; Dewar, Marius ; Färber, Paul ; Long, Matthew H. ; Gros, Jonas ; Connelly, Douglas P. ; Holtappels, Moritz
    We detected a controlled release of CO2 (g) with pH eddy covariance. We quantified CO2 emission using measurements of water velocity and pH in the plume of aqueous CO2 generated by the bubble streams, and using model predictions of vertical CO2 dissolution and its dispersion downstream. CO2 (g) was injected 3 m below the floor of the North Sea at rates of 5.7–143 kg d − 1. Instruments were 2.6 m from the center of the bubble streams. In the absence of injected CO2, pH eddy covariance quantified the proton flux due to naturally-occurring benthic organic matter mineralization (equivalent to a dissolved inorganic carbon flux of 7.6 ± 3.3 mmol m − 2 d − 1, s.e., n = 33). At the lowest injection rate, the proton flux due to CO2 dissolution was 20-fold greater than this. To accurately quantify emission, the kinetics of the carbonate system had to be accounted for. At the peak injection rate, 73 ± 13% (s.d.) of the injected CO2 was emitted, but when kinetics were neglected, the calculated CO2 emission was one-fifth of this. Our results demonstrate that geochemical techniques can detect and quantify very small seafloor sources of CO2 and attribute them to natural or abiotic origins.