A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration (2022) / Chapter Skim
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3 Nutrient Fertilization
3 Nutrient Fertilization
Pages 77-102
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From page 77... ...
According to criteria described in Chapter 1, the committee's assessment of the potential for ocean nutrient fertilization as a CDR approach is discussed in Sections 3.1–3.5 and summarized in Section 3.6. The research needed to fill gaps in understanding of ocean fertilization, as an approach to durably removing atmospheric CO2, is discussed and summarized in Section 3.7.
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From page 78... ...
due to steeper vertical gradients of inorganic carbon and enhanced vertical exchange at shallower depths. As an ocean CDR approach, the main goal would thus be to strengthen, or increase, the net transport of organic carbon out of the euphotic zone, and thereby increase the efficiency of the BCP, thus decreasing the carbon content of the surface waters in contact with the atmosphere while boosting the fraction of carbon that is transported to the deep sea where it can be sequestered on timescales >100 years.
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From page 79... ...
Consequently, it has also put this method at the forefront of public concerns regarding all forms of "geoengineering" and has led to many groups having already formed strong opinions for or against OIF. These social acceptance issues are often focused on OIF, yet this is only one ocean CDR approach, and many of the same acceptance issues would be common to at least all biotic ocean CDR approaches and in many cases abiotic ocean CDR as well, especially if deployed at scale (see Chapter 2)
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From page 80... ...
In addition to aOIF studies, natural systems with episodic or local high Fe delivery have improved the knowledge base for OIF. For example, a natural analog for natural nutrient fertilization is the atmospheric deposition of volcanic ash that leaches trace metals in seawater, generally promoting primary productivity (see Fisheries, below, and e.g., Duggen et al., 2007; Jones and Gislason, 2008; Hamme et al., 2010; Browning et al., 2014; Zhang et al., 2017)
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From page 81... ...
(2008) summarized several natural OIF studies where there was a nearby island source of natural iron in the Southern Ocean resulting in long-standing, yet locally variable bloom and export responses (Blain et al., 2008; Pollard et al., 2009)
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From page 82... ...
This flux attenuation is the result of combined processes that convert sinking forms of carbon to nonsinking forms, such as occurs with "sloppy feeding" by zooplankton on large organic aggregates, and by heterotrophic consumption of sinking particles and conversion to dissolved organic and inorganic carbon by resident zooplankton, microbes, and other animals in the mesopelagic. If attenuation efficiencies can be controlled or altered during purposeful additions at sites where the communities are more likely to sequester carbon, such as after the sinking of intact diatom cells, then the effectiveness of CDR would be directly affected, or at least the amount of iron needed greatly reduced.
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From page 83... ...
, but the response to aOIF has been the generation of diatom blooms that in the natural ocean are more often characterized by a lower b, hence the map showing b of 0.6 may be a better predictor of regional patterns of C sequestration for a surface source of fresh POC following aOIF. The issue of deliberately reducing or selecting for low POC attenuation efficiencies is an area of further research since the overall effectiveness of OF as a CDR approach will depend greatly on the fraction that reaches the deep ocean (see Export Efficiencies, above, and further discussion below)
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From page 84... ...
make satellite ocean color observations well suited to document the enhancement of surface ocean productivity created via OF (e.g., Westberry et al., 2013)
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From page 85... ...
However, satellite data only measure surface ocean properties and do not provide estimates of C export and other necessary biogeochemical determinations. The biogeochemical Argo profiling float network (which would continue to operate after the start of the treatment)
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From page 86... ...
The program is in development, so there is an opportunity to incorporate small sensors specific for OF monitoring, such as ocean MINIONS3 a small, inexpensive isopycnal float with onboard sensors and an upward-looking camera that quantifies POC export associated with sinking particles (Melissa Omand, University of Rhode Island, ongoing personal communication)
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From page 87... ...
These models have focused on a particular region (e.g., Southern Ocean) or HNLC regions globally and often use the complete drawdown of surface ocean macronutrients to simulate enhanced primary production and the amount of potential C removal.
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From page 88... ...
2010a <1 Decadal to centennial timescale Southern Ocean OIF only, but global impacts considered, including downstream impacts and CO2 backflux -- Table 1 Keller et al. 2014 1 to 5 Southern Ocean only south of 30°, decreasing quickly from 5 to 1 if measured on centennial scales Natural BCP Various 5 to 12 Natural BCP for reference of euphotic zone C loss (e.g., Siegel et al., 2014)
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From page 89... ...
(2010) measured DA in stored cells from two natural settings and two aOIF studies (Southern Ocean Iron Experiment–South and FeExII)
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From page 90... ...
(2010) noted that "neurotoxin impacts at higher trophic levels, well known in shelf and coastal regions, have not yet been reported in open ocean systems.'' They conclude that caution is warranted, but as with any ocean CDR approach, there will be unintended consequences that will be important to study, and thus be able to predict, if one were to move from aOIF research to large-scale implementation.
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From page 91... ...
Lacking longer or larger-scale aOIF studies to directly examine deep-ocean impacts, studies of natural OF systems may provide another line of evidence regarding the impacts of OIF on deepsea biota. When comparing a naturally Fe-enriched setting versus nearby controls off the Crozet Plateau in the Southern Ocean, the Fe-induced increased supply of organic carbon to the seafloor led to greater densities and biomass of deep-sea animals (Wolff et al., 2011)
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From page 92... ...
It is clear that for macronutrient fertilization (N, Si, P) , the amount of macronutrient added would be much greater than OIF, and hence the raw material costs are greater as reflected in the cost per ton of CO2 removed.
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From page 93... ...
SOURCE: Boyd, 2008. set largely by both the bioavailability of the added iron and the extent of shallow remineralization of sinking POC flux that is stimulated in response to the Fe addition.
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From page 94... ...
Specifically: • In 2008, the parties to the Convention on Biological Diversity (CBD) adopted a nonbind ing decision recommending that governments take a "precautionary approach" and refrain from engaging in nutrient fertilization, except for "small scale research studies within coastal waters" (Para.
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From page 95... ...
Finally, if research activities are funded by commercial interests, there is even a greater need for a clear and transparent code of conduct to ensure that results are considered unbiased and accepted by the public. 3.6 SUMMARY OF CARBON DIOXIDE REMOVAL POTENTIAL The criteria for assessing the potential for ocean nutrient fertilization as a feasible approach to ocean CDR, described in Sections 3.2–3.5, is summarized in Table 3.3.
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From page 96... ...
at shallower ocean depths; however, some carbon will reach the deep ocean with >100-year horizons for return of excess CO2 to surface ocean. Scalability Medium–High What is the potential scalability at some future date Potential C removal >0.1–1.0 Gt CO2/yr with global-scale implementation (low, <0.1 Gt CO2/ (medium confidence)
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From page 97... ...
and confidence in estimate scale (low, medium, high) Cost and challenges of carbon accounting Medium Relative cost and scientific challenge associated with Challenges tracking additional local carbon transparent and quantifiable carbon tracking (low, sequestration and impacts on carbon fluxes outside of medium, high)
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From page 98... ...
? What is the best code of conduct that should be followed for research on OF (and other CDR approaches)
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From page 99... ...
Future projects could be 10–100 times larger than prior aOIF experiments, adding hundreds to thousands of tons of iron and resulting in blooms of 105–106 km2 that could be tracked and studied for longer than a single annual growth cycle. The potential for net C sequestration of OIF is large enough (Gt C sequestered for >100 yr)
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From page 100... ...
iron from surface to depth are needed 3.3 In field experiments using more What are CDR efficiencies Modest Modest/High 25 10 than 100 t Fe over a 1,000 km2 at scale and what are the Regional impacts during Early public concern Research needs to or greater initial patch size, intended and unintended Fe addition period and with OIF for ocean measure all possible followed over annual cycles ecological impacts? some concerns beyond geoengineering due geochemical, test boundaries.
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From page 101... ...
NOTE: Bold type identifies priorities for taking the next step to advance understanding of ocean fertilization as an ocean CDR approach.
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