A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration (2022) / Chapter Skim
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4 Artificial Upwelling and Downwelling
4 Artificial Upwelling and Downwelling
Pages 103-126
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From page 103... ...
The latter outcome (increased C sequestration) would require that the biological production of carbon exceed the delivery of dissolved inorganic carbon (DIC)
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From page 104... ...
(2010) conducted sea trials of a commercially available wave pump with the aim of stimulating a two-phased phytoplankton bloom (e.g., north of the Hawaiian Islands in the North Pacific subtropical gyre)
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From page 105... ...
; however, these methods come with added energy costs and so are less likely to be effective in CDR. Beyond direct ocean CDR, AU has been proposed as a means to support local aquaculture from fisheries to seaweed farms, which may have the cascading effect of enhancing ocean C sequestration (see Chapter 5)
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From page 106... ...
Expected biological and biogeochemical responses of sea trials Injects compressed gas in the pipe to High efficiency with an DOW uplift to air supply Air-lift pump (Liang and Peng, 2005) No sea trial data to date uplift DOW from deeper depths approximately 100 m3/min DOW a An air supply of 1 m3/min could uplift > 88 m3/min.
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From page 107... ...
. Although not directly related to ocean CDR, AU has also been proposed as a means of providing energy and cooling and hence reducing terrestrial C emissions (e.g., ocean thermal energy conversion [OTEC]
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From page 108... ...
If these were to be conducted, a determination of efficacy would be very similar to OIF in terms of cost and necessary components; however, the carbon potentially sequestered would need to be weighed relative to the upwelled carbon. Specifically, for AU to effectively sequester carbon from the atmosphere, we need to consider not only the C export ratios, that is, the ratio of inorganic carbon upwelled relative to the carbon sinking out of the upper ocean, but also the extent to which sinking organic carbon is attenuated with depth.
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From page 109... ...
ARTIFICIAL UPWELLING AND DOWNWELLING 109 FIGURE 4.2 Annual mean wave power density and direction (top) relative to the climatological mean WOA18 nitrate at 500-meter depth (bottom)
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From page 110... ...
Does AU need to be on the scale of millions of pumps deployed in the global ocean to be effective, as suggested by models? If so, this would have consequences for international shipping, fishing, and other unrelated activities at sea.
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From page 111... ...
Over a 10-year simulation, strong regional heterogeneity was observed, and changes in the air–sea flux as a result of AU were found to be both positive and negative across the global ocean. Reversibility is also an important consideration as the intentional upwelling of CO 2-rich deep water or downwelling of O2-rich surface waters has the potential to significantly alter ocean ecosystems from the epipelagic to the benthic.
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From page 112... ...
This is, of course, insufficient evidence of efficacy; verification cannot focus on evidence of enhanced growth of phytoplankton in the surface ocean because the fate of that material could be remineralized in the upper ocean. Rather changes in the sinking flux of particulate organic carbon into the deep ocean (below 1,000 meters)
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From page 113... ...
In summary, siting analyses will need to identify optimal nutrient, light, and wave conditions for growth and C sequestration potential as well as potential conflicts with other marine industries. The temporal scaling of AU deployments also needs to be considered relative to the timescale of biological responses.
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From page 114... ...
Model simulations of large-scale massive deployment (millions of pumps throughout the global ocean) suggest that subsurface waters may warm by a few degrees for a century-long deployment of AU (Oschlies et al., 2010b; Keller et al., 2014)
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From page 115... ...
Costs to do so will include materials for the pumps themselves, deployment costs, costs for development and maintenance of offshore monitoring and verification programs, any energy needed to power the pumps (e.g., ocean thermal energy conversion plants; Avery and Wu, 1994; Matsuda et al., 1998) , as well as any costs for removal of pumps at the end of their life cycle or after sustained damage and any necessary maintenance.
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From page 116... ...
For comparison, the mesocosm-based research on ecological impacts of AU was funded at €2.5M in 2017 by the European Research Council (Ocean artUp, 2021) , and the Advanced Research Projects Agency-Energy (ARPA-e)
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From page 117... ...
FIGURE 4.6 Calculations for salt-fountain pump networks where N is the number of pumps required to sustain a 10-acre kelp farm in (left) the Gulf of Mexico and (right)
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From page 118... ...
At the international level, the parties to the Convention on Biological Diversity (CBD) have adopted a series of decisions governing "geoengineering," the definition of which is likely to encompass AU and AD.3 The decisions recommend that parties to the CBD and other governments avoid geoengineering activities that may affect biodiversity, except for "small scale scientific research studies .
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From page 119... ...
4.7 RESEARCH AGENDA Proof-of-concept field experiments are needed in open-ocean conditions to assess technological readiness to monitor biological responses to upwelling, determine C sequestration potential relative to upwelled macronutrients and inorganic C, and monitor or model local and downstream environmental impacts of AU and potential concomitant downwelling. There are several natural oceanic analogs that can inform our understanding of the CDR potential of upwelling, including eastern boundary currents and the Southern Ocean.
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From page 120... ...
ocean's density field and sea-surface temperature and brings likely ecological shifts due to bringing colder, inorganic carbon and nutrient-rich waters to surface. Social considerations Potential conflicts with other uses (shipping, marine Encompass use conflicts, governance-readiness, protected areas, fishing, recreation)
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From page 121... ...
• Assessment of the CDR potential at a range of pumping frequencies including episodic versus continuous upwelling as well as any seasonal impacts on CDR potential and the optimal source-water horizons. • A monitoring plan that would be able to estimate the additionality of sequestration -- how much production and export would have occurred in natural phytoplankton communities in the absence of AU?
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From page 122... ...
Since AU would deliver remineralized DIC as well as potentially limiting nutritional resources, it is key to understand the nutrient-use stoichiometry of the local plankton populations relative to the stoichiometry of deep-source waters (which varies widely across the global ocean) ; simply, C export flux would need to exceed the upwelled carbon.
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From page 123... ...
surface to depth Should inform composite monitoring needed plan. 4.4 Modeling of C sequestration What is the CDR potential given 5 5 based upon achievable outcomes of sea trials and technological upwelling velocities and known advancement of pumps?
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From page 124... ...
Recent emphasis on co benefit of enhanced fisheries yet to be verified 4.6 Monitoring C and ecological What are the large-scale and downstream Low Low 10 10 shifts impacts and the timescales and depth New methods, Any method to New technologies are scales of sequestration? Development especially optical to measure C flow and quick to prototype but of autonomous and remote methods complement existing ecological shifts will expensive to bring to for assessment of biological carbon geochemical sensors have multiple uses for market at reliability pump (BCP)
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From page 125... ...
open-ocean CDR of research conduct needed) NOTE: Bold type identifies priorities for taking the next step to advance understanding of artificial upwelling and downwelling.
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From page 126... ...
Even if these predictions are correct and AU proves too costly or impractical for large-scale ocean CDR, AU may prove to be a valuable tool to promote aquaculture or fisheries (assuming the extraction costs do not exceed the C sequestration potential) or simply as a research tool to better understand the biological responses of microbial communities to nutrient perturbations.
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