Review of Artificial Downwelling for Mitigating Hypoxia in Coastal Waters

Liu, Shuo; Zhao, Lige; Xiao, Canbo; Fan, Wei; Cai, Yong; Pan, Yiwen; Chen, Ying

doi:10.3390/w12102846

Cited by 13 publications

(4 citation statements)

References 72 publications

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“…Even though there is consensus regarding the underlying processes, the numerical quantitative simulation of hypoxic conditions remains challenging because it is, essentially, the quest to simulate extreme (low) values that are determined by the difference of relatively large and uncertain numbers. This introduces high uncertainty to both the open ocean model applications (e.g., Cocco et al, 2013;Dietze and Löptien, 2013;Löptien and Dietze, 2017) and Baltic Sea model applications (Meier et al, 2011(Meier et al, , 2012, which limits their contribution to management or geoengineering decisions of stakeholders. For example, it has been illustrated in a global model that deficiencies in biogeochemical model components may be compensated for by deficiencies in circulation model components (Löptien and Dietze, 2019), thereby obscuring even the sign of the sensitivity of the (global) warming to come.…”

Section: Introductionmentioning

confidence: 99%

Retracing hypoxia in Eckernförde Bight (Baltic Sea)

Dietze

Löptien

2021

Biogeosciences

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Abstract. An increasing number of dead zoning (hypoxia) has been reported as a consequence of declining levels of dissolved oxygen in coastal oceans all over the globe. Despite substantial efforts a quantitative description of hypoxia up to a level enabling reliable predictions has not been achieved yet for most regions of societal interest. This does also apply to Eckernförde Bight (EB) situated in the Baltic Sea, Germany. The aim of this study is to dissect underlying mechanisms of hypoxia in EB, to identify key sources of uncertainties, and to explore the potential of existing monitoring programs to predict hypoxia by developing and documenting a workflow that may be applicable to other regions facing similar challenges. Our main tool is an ultra-high spatially resolved general ocean circulation model based on a code framework of proven versatility in that it has been applied to various regional and even global simulations in the past. Our model configuration features a spacial horizontal resolution of 100 m (unprecedented in the underlying framework which is used in both global and regional applications) and includes an elementary representation of the biogeochemical dynamics of dissolved oxygen. In addition, we integrate artificial “clocks” that measure the residence time of the water in EB along with timescales of (surface) ventilation. Our approach relies on an ensemble of hindcast model simulations, covering the period from 2000 to 2018, designed to cover a range of poorly known model parameters for vertical background mixing (diffusivity) and local oxygen consumption within EB. Feed-forward artificial neural networks are used to identify predictors of hypoxia deep in EB based on data at a monitoring site at the entrance of EB. Our results consistently show that the dynamics of low (hypoxic) oxygen concentrations in bottom waters deep inside EB is, to first order, determined by the following antagonistic processes: (1) the inflow of low-oxygenated water from the Kiel Bight (KB) – especially from July to October – and (2) the local ventilation of bottom waters by local (within EB) subduction and vertical mixing. Biogeochemical processes that consume oxygen locally are apparently of minor importance for the development of hypoxic events. Reverse reasoning suggests that subduction and mixing processes in EB contribute, under certain environmental conditions, to the ventilation of the KB by exporting recently ventilated waters enriched in oxygen. A detailed analysis of the 2017 fish-kill incident highlights the interplay between westerly winds importing hypoxia from KB and ventilating easterly winds which subduct oxygenated water.

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Section: Introductionmentioning

confidence: 99%

Retracing hypoxia in Eckernförde Bight (Baltic Sea)

Dietze

Löptien

2021

Biogeosciences

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“…Along with the intentional transport of CO 2 , installed pipes may transport surface heat, fertilising nutrients, as well as oxygen into subsurface waters (Stigebrandt et al, 2015). Artificial downwelling may concurrently improve upon ocean cycling and be utilised to mitigate hypoxia (Liu et al, 2020), but impact assessments have thus far not been undertaken to conclude the extent of such impacts for artificial downwelling for the purpose of CO 2 removal (GESAMP, 2019). The scale of space and infrastructure needed to deploy the technology would reflect that of artificial upwelling, and similar impacts on marine ES can be expected (National Academies of Sciences, Engineering, and Medicine, 2022).…”

Section: Artificial Downwellingmentioning

confidence: 99%

Ocean-based negative emissions technologies: a governance framework review

Röschel,

Neumann

2023

Front. Mar. Sci.

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The model pathways of the Intergovernmental Panel for Climate Change (IPCC) for the timely achievement of global climate targets, especially the target of limiting global warming to 1.5°C compared to pre-industrial levels, suggest the need for safeguarding and enhancing the global carbon sink. Experts argue that the deployment of so-called negative emissions technologies for large-scale carbon dioxide removal holds potential for keeping the temperature in line with limits set by the Paris Agreement. Ocean-based negative emissions technologies (ONETs) intend to enhance carbon sequestration and storage in the ocean, e.g., by changing the ocean’s physical or biogeochemical properties. But in addition to these intended effects, ONETs may also cause unintentional impacts on the ocean’s condition and on related coastal and marine ecosystem services that are relevant for the attainment of a range of global policy goals. This article links potential direct and indirect, intentional and unintentional impacts of eight ONETs on the marine environment to the regulations and policy goals of international environmental agreements of the current global ocean governance regime. The results thereof outline a direct, implicit and indirect governance framework of ONETs. Hereby, a broader perspective of the concept of (global) ocean governance is adopted to outline a wider network that goes beyond the explicit regulation of ONETs within the realm of ocean governance. This first-order assessment derives gaps and challenges in the existing governance framework, as well as needs and opportunities for comprehensive governance of the technologies. It is determined that while the inclusion of ONETs in the global climate strategy may be deemed necessary for reaching net zero emission targets in the future, a range of potential trade-offs with other policy goals may need to be considered or dealt with when deploying ONETS for climate mitigation. Further, foresight-oriented and adaptive governance mechanisms appear imperative to bridge gaps resulting from extensive uncertainties and unknowns linked to ONET deployment in a changing ocean and. The identified ONET governance framework reiterates current challenges in ocean governance, for instance related to fragmentation, but also represents an opportunity for a synergistic and integrated approach to future governance.

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“…Hypoxia is one of the common problems in aquatic environments [ 18 , 19 ] that can have major impacts on populations of some crayfish species due to their high oxygen demands [ 20 – 22 ]. Other crayfish species have been documented as withstanding oxygen depletion for long periods [ 23 , 24 ], and empiric observations suggest that even species that are considered sensitive to hypoxia may persist in poorly oxygenated waters [ 25 ].…”

Section: Introductionmentioning

confidence: 99%

Living on the edge: Crayfish as drivers to anoxification of their own shelter microenvironment

Neculae,

Barnett,

Miok

et al. 2024

PLoS ONE

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Burrowing is a common trait among crayfish thought to help species deal with adverse environmental challenges. However, little is known about the microhabitat ecology of crayfish taxa in relation to their burrows. To fill this knowledge gap, we assessed the availability of oxygen inside the crayfish shelter by series of in-vivo and in-silico modelling experiments. Under modeled condition, we found that, except for the entrance region of the 200 mm, a flooded burrow microenvironment became anoxic within 8 h, on average. Multiple 12-hour day-night cycles, with burrows occupied by crayfish for 12 h and empty for 12 h, were not sufficient for refreshing the burrow microenvironment. We then examined the degree to which crayfish species with different propensities for burrowing are tolerant of self-created anoxia. From these experiments, primary and secondary burrowers showed best and most consistent tolerance—exhibiting ≥ 64% survival to anoxia and 25–91% survival of ≥ 9 h at anoxia, respectively. Tertiary burrowers exhibited little to no tolerance of anoxia with 0–50% survival to anoxia and only one species exhibiting survival (2%) of ≥ 9 h at anoxia. Results suggest that moderate to strongly burrowing crayfish can quickly draw down the dissolved oxygen in burrow water but appear to have conserved a legacy of strong tolerance of anoxia from their monophyletic ancestors–the lobsters–whereas tertiary burrowers have lost (or never evolved) this ability.

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Review of Artificial Downwelling for Mitigating Hypoxia in Coastal Waters

Cited by 13 publications

References 72 publications

Retracing hypoxia in Eckernförde Bight (Baltic Sea)

Retracing hypoxia in Eckernförde Bight (Baltic Sea)

Ocean-based negative emissions technologies: a governance framework review

Living on the edge: Crayfish as drivers to anoxification of their own shelter microenvironment

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