Scientific Basis

INTRODUCTION

Ocean Upwelling for mCDR

We welcome you to review the latest research on empirical data, scientific analysis, and conclusions that support the scientific basis for ocean upwelling (also known as artificial upwelling) for marine carbon dioxide removal (mCDR). Also, read our Frequently Asked Questions.

ARTIFICIAL UPWELLING – A REFINED NARRATIVE

Jürchott, M., Oschlies, A., & Koeve, W. (2023). Artificial upwelling—A refined narrative. Geophysical Research Letters, 50, e2022GL101870. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL101870

Summary of the study: The current story about artificial upwelling (AU) is that it brings nutrient-rich deep water to the ocean’s surface, which speeds up the biological carbon pump (BCP). The response of the solubility pump and the CO2 emission scenario is considered in our improved story. Using global ocean-atmosphere model experiments, we show that the effectiveness of a hypothetical maximum AU deployment in all ocean areas where AU is predicted to lower surface pCO2, the draw down of CO2 from the atmosphere during the years 2020–2100, strongly depends on the CO2 emission scenario and ranges from 1.01 Pg C/year (3.70 Pg CO2/year) under RCP 8.5 to 0.32 Pg C/year (1.17 Pg CO2/year) under RCP 2.6 Under the highest emission scenario (RCP 8.5), the solubility pump works just as well as the BCP. However, when CO2 emissions are low, the solubility pump responds by releasing CO2.

GEOMAR – ART-UP RESEARCH

A leading research effort in artificial upwelling (AU) is the EU Horizon funded program “Art-Up” under the direction of Professor Dr. Ulf Riebesell, Geomar-Kiel. The Art-Up links to their papers follow.

Baumann, Taucher, Paul, et al. “Effect of Intensity and Mode of Artificial Upwelling on Particle Flux and Carbon Export.” October, 27, 2021. https://www.frontiersin.org/articles/10.3389/fmars.2021.742142/full

Summary of study: Reducing CO2 emissions caused by people won’t be enough to stop global warming enough to meet the 1.5°C goal of the Paris agreement. To fight climate change effectively, we need to take steps to get rid of carbon dioxide from the air. One idea for getting rid of carbon dioxide is to create an artificial upwelling. By sending nutrient-rich deep water to the surface of the ocean to boost primary productivity, it might be possible to improve downward flows of particulate organic carbon (POC) and carbon sequestration. In this study, we looked at how different levels of artificial upwelling and two types of upwelling (repeated additions vs. a single addition) affect the export of POC, the stoichiometry of sinking matter, and the depth of remineralization. In the subtropical North Atlantic, we did a 39-day mesocosm experiment in which we added different amounts of deep water to oligotrophic surface water to make it grow. The total amount of nutrients went from 1.6 mol NO3– L–1 to 11.0 mol NO3– L–1. We found that, on the one hand, POC export under artificial upwelling more than doubled and the molar C:N ratios of sinking organic matter increased from values around Redfield (6.6) to 8–13, which is good for potential carbon dioxide removal. On the other hand, things that were sinking were remineralized faster and sank slower, which meant that they were remineralized at shallower depths. In the recurring upwelling mode, the properties of the particles were better for deep carbon export, while in the single mode, the C:N increase of sinking matter was stronger. In both ways that the water went up, about half of the organic carbon that was made stayed in the water column until the end of the experiment. This shows that the plankton communities were still getting used to each other. This could be because producers and consumers react at different rates. Because of this, there is a need for studies with longer experimental periods to measure the responses of communities that have fully adjusted. Lastly, our results showed that artificial upwelling changes many properties of sinking particles, and that the strength of the changes depends on how strong the upwelling is and how it is used.

Ortiz, Arístegui, Taucher, Riebesell. “Artificial Upwelling in Singular and Recurring Mode: Consequences for Net Community Production and Metabolic Balance.” January 12, 2022. https://www.frontiersin.org/articles/10.3389/fmars.2021.743105/full

Summary: The artificial upwelling of nutrient-rich waters and the increase in primary productivity that comes with it have the potential to increase the amount of fish caught in the ocean and strengthen the biological pump that pulls CO2 out of the air. Climate change and overfishing are two of the biggest problems of the 21st century. Understanding this technology as a “ocean-based solution” to these problems is becoming more and more important. Yet, not much is known about how well artificial upwelling works or what side effects it might have. We did a large off-shore mesocosm study (about 44 m3) in the oligotrophic waters of the Canary Islands to find out how artificial upwelling affects a natural oligotrophic plankton community at the community level. For 37 days, two different upwelling modes (a single deep-water pulse or a steady supply every 4 days) were used to simulate four different intensities of upwelling: 1.5, 3, 5, and 10 mol L–1 of nitrate, phosphate, and silicate. Here, we show what happened to net community production (NCP), metabolic balance, and the make-up of the phytoplankton community (250 m). When there was more upwelling, the cumulative NCP was higher. After the upwelling started, diatoms took over the phytoplankton community in all treatments, but other taxa, such as Coccolithophores, grew as the experiment went on. The amount of deep water added changed the metabolic balance, leading to I a balanced to net-heterotrophic system in the singular and (ii) a net-autotrophic system in the treatments with repeated upwelling. So, how nutrients are brought into an oligotrophic system is a key factor in how the ecosystem responds, with repeated upwelling leading to a higher long-term net community production (NCP) than a single upwelling. These results show how important it is to measure local responses to upwelling, like the structure and metabolism of communities. This has big implications for the possibility of using artificial upwelling as a way to increase primary production in the ocean.

Kemper, Riebesell and Graf. Numerical Flow Modeling of Artificial Ocean Upwelling. January 3, 2022. https://www.frontiersin.org/articles/10.3389/fmars.2021.804875/full

Summary: Artificial Upwelling (AU) of nutrient-rich Deep Ocean Water (DOW) to the sunlit surface layer of the ocean has recently been suggested as a way to increase the ocean’s ability to store CO2 and produce fish. Climate change and food security for a growing human population have been looked at in terms of AU and its possible benefits. But a lot more research needs to be done on the safety, effectiveness, risks, and side effects of AU before we can make better predictions about its potential. Fluid dynamic modeling of the AU process and the transport of inorganic nutrients can give us the information we need to figure out how much damage certain AU devices do to the environment and is a useful tool for improving them. Yet, getting all flow phenomena that are important to the AU process right is still hard, and only a few models are able to do it. In this paper, the results of simulations made with a new numerical solution method are shown. The method is based on OpenFOAM, which is a free modeling environment. It solves the Reynolds-Averaged Navier-Stokes (RANS) equations with additional transport equations for energy, salinity, and inorganic nutrients. The method is meant to be useful for a wide range of ocean flow problems, such as density stratification caused by temperature and salinity and passive scalar transport. The studies in this paper are mostly about how the AU process affects the spread and concentration of nutrients in the mixed surface layer of the ocean. The new method does a good job of capturing the expected flow phenomena. Even though it is known that cold DOW that rises to the surface tends to sink back down due to its high density, the simulations in this paper show that the upwelled DOW settles at the lower boundary of the ocean’s mixed surface layer, keeping a lot of the nutrients available for primary production. Comparative studies of different design options are also shown and analyzed. The goal is to keep as many nutrients as possible in the mixed surface layer.

Ortiz, Joaquin et.al. (2022) Oligotrophic Phytoplankton Community Effectively Adjusts to Artificial Upwelling Regardless of Intensity, but Differently Among Upwelling Modes. Front. Mar. Sci., 20 June 2022 Sec.Marine Biogeochemistry. https://doi.org/10.3389/fmars.2022.880550

Summary: Artificial upwelling has been suggested as a way to increase CO2 sequestration in the ocean and/or increase fishery yields by increasing primary production in parts of the ocean that don’t produce much. But there isn’t much proof that it works, can be used, or has negative effects. Here, we show some of the results of a 37-day mesocosm study done in oligotrophic waters off the coast of Gran Canaria. The goal was to see how artificial upwelling affected the pelagic community in real-time. Upwelling was simulated in two ways: I with a single deep-water pulse and ii) with a steady supply every 4 days. Each way had four different intensities, which were set by the total amount of nitrate added: about 1.5, 3, 5.7, and 11 mol L-1. In this study, we focus on how the phytoplankton responds by looking at the 14C primary production rates (PP), Chlorophyll a, and biomass. We saw linear increases in PP, PP accumulation, Chlorophyll a, and biomass as the upwelling got stronger. Upwelling helped larger phytoplankton the most, so pico- and nano- to nano- and microphytoplankton changed places. When the upwelling was stronger, adding deep water on a regular basis produced more biomass than adding deep water in a single pulse. It also accumulated a lot more PP per unit of nutrients added and showed a stronger decrease in the percentage of extracellular release as the intensity of the upwelling increased. These results show that oligotrophic phytoplankton communities can adapt well to artificial upwelling, no matter how strong it is, but in different ways depending on the mode of upwelling. When there was a steady supply of upwelled waters, primary production and biomass growth were more efficient than when there was a single pulse of the same volume and nutrient load.

KOWEEK, OCEAN VISIONS

Koweek, David A. “Expected Limits on the Potential for Carbon Dioxide Removal From Artificial Upwelling (June 29, 2022). https://www.frontiersin.org/articles/10.3389/fmars.2022.841894/full

The Koweek study argues that field trials for ocean artificial upwelling are justified, pulling from a plethora of studies that have analyzed a variety of flow rates – which Ocean-based Climate Solutions’ ocean upwelling pump exceeds. Read Dr. Ian Walsh’s comments next regarding the Koweek study and its endorsement for further research.

Dr. Ian Walsh’s comments on David Koweek’s study on Expected Limits on the Potential for Carbon Dioxide Removal From Artificial Upwelling.

1. The paper demonstrates that a flow rate approximately equal to that observed with published AU flow rates is unlikely to support a production and export response sufficient to reach an mCDR removal rate of 1 gigatonne of CO2atmo/year with pumps deployed uniformly over the world ocean. [N.B. I use tonne to refer to the SI measurement while the paper refers to the imperial ton at least in the text. The difference is immaterial to this review, but I’m presuming the text should use the SI unit spelling as SI units are used in the rest of the text.]
2.  The model takes into account DIC and TA upwelling and potential outgassing
3. The model uses a single flow rate (0.05 m3 s-1)
4. The model uses a variety of C:N:P stoichiometries
   1. C:N:P fixed through primary productivity
   2. Micro and macro algae cases
5. No explicit export function
   1. No regeneration scaling
      1. Time
      2. Depth
6. Photoperiod modulation is included in the model
7. The model uses a 1 AUP km-2 density over most of the world ocean

The nice thing about David Koweek’s study is that it couples gas exchange and DIC and TA upwelling kinetics with a reasonable range of nutrient stoichiometry and results in a positive net carbon sequestration potential. Along with Wu et al., 2022 currently under review (https://doi.org/10.5194/esd-2021-104), the Koweek model demonstrates that artificial upwelling has the potential to impact CO2atmo.

This is important as I consider the primary unknown in terms of impact on AU sequestration potential is the scaling of nutrient stimulated production uptake of pCO2 relative to the carbonate system kinetics. There is still much to learn about this interaction, but at the least, we see that models that include carbonate system dynamics show positive sequestration potential.

Relevant to Ocean-Based:

1. The flow rate for Ocean-Based’s AUP is estimated to be 5000 m3/hour
2. This is 27.8 times the Koweek model flow rate
3. Using the Ocean-Based flow rate to scale the Koweek model results generates a rate of mCDR of 1.39 gigatonnes/year
   1. This is above the 1 gigatonne/year
4. From an enterprise perspective, the mCDR potential is not based on a basin or ocean scale uniform deployment but on maximizing mCDR income relative to enterprise costs.
   1. AU pump (AUP) density will be a function of maximizing pump efficiency on an mCDR basis per pump per expected pump lifetime. A uniform deployment scenario, while attractive to modeling, is not likely to be efficient from the standpoint of resource allocation or cash flow relative to enterprise costs (capital, operations, maintenance, and MRV costs) and income.
   2. The operative scaling for an enterprise is mCDR/AUP/ocean area/time: moles CO2atmo AUP-1 km-2 time-1
      1. Time: day (diel cycle), monthly (seasonal), annual (seasonal), decadal (life of the pump, ENSO)
   3. The operative scaling for the economic potential includes the cost of mCDR production (pump capital + operations + maintenance + MRV) over the time scale relative to mCDR payments.
5. The upshot of taking the perspective of the enterprise is that the scaling of the enterprise will result in the selection of the most advantageous milieus for the placement of the marginal (next) pump. ASIDE: This is entirely different from the testing phase, in which experiential concerns and data gathering are the most important considerations. [running a Test, Fail, Advance loop]
6. If we run the Koweek model as an optimization tool:
   1. What conditions need to be met to generate a global integrated value that is significant?
      1. Sensitivity analysis concerning volume transport
      2. Force depths with optimal PO4ex input values
      3. K&L 2008 & White et al. 2007 papers
   2. Use the HOT data set as input?
   3. Include the annual cycle relative to the wave energy and upwelling volume relative to the dispersion ratio
      1. There is probably an annual cycle in wave energy that begets a dispersion ratio that goes above and below the diatom bloom point (Ulf et al., mesocosm results)
      2. What does that look like on an annual basis?
      3. Determine the seasonal and annual export cycle using multiple modes based on dispersion ratio and volume pumped:
         1. If we look at three modes:
            1. Diatom bloom
            2. Top-down (1% export of primary productivity)
            3. K&L/White et al., diazotroph bloom
         2. Derive the modal export function
            1. Sum over the annual cycle
   4. Derive the future productivity decrease in the central gyres due to increased SST for future additionality
      1. Do a basin match up, e.g., find the warmer temperature data from BGC Argo and calculate areal differences based on projected future temperatures
      2. Look at Behrenfeld et al., 2006 and subsequent papers (where referenced) for a general relationship
7. The model does not consider export and fractionation
   1. This is an upper limit model
   2. Use the tri-modal export model to refine export and sequestration
   3. Define other benefits from AU
      1. Temperature/stratification feedback
         1. Especially relative to marine heat waves
         2. Especially relative to trophic level restoration and or impact minimization
            1. Highest value might be as a way of creating pockets of ecological stabilization to retain significant populations through the warmer ocean

Striking coherence between maximum chlorophyll maps (e.g. Feldman maps) and the microalgae potential, with perhaps the exceptions of the eastern edges of the South Pacific and South Atlantic which look offset higher in the upwelling potential.

A more recent paper with similar mapping:

Behrenfeld., M., O’Malley, R., Siegel, D., McClain, C., Sarmiento, J., Feldman, G., Milligan, A., Falkowski, P., Letelier, R., and Boss, E. (2006). Climate-driven trends in contemporary ocean productivity. Nature, 444, 752-755.

Philip Kithil’s graph of pumping rate, and pump diameter (as a valid product) whereas Koweek uses pumping rate and depth)

As stated above, Ocean-based Climate Solutions, Inc’s ocean upwelling pump flow rate is significantly higher than the models analyzed in the Koweek paper. This is because flow rate is directly correlated to pipe diameter and less to pipe length (depth of the inlet) as shown in Koweeks’ Figure 1.

A critical consideration found in the Liu and Jin reference cited by Koweek in this Figure 1, and confirmed by us, is that the water column inside the pipe gains momentum, delivering far more volume than a simple wave height x period calculation.  Liu and Jin determined the simple calculated flow rate was 0.45 m/s, whereas the measured flow rate was 0.95 m/s – greater by a factor of 111%! Our own data found a 60% greater measured vs. calculated flow rate.

RELATED RESEARCH ON MARINE CARBON DIOXIDE REMOVAL

Siegel David A., et al. (2021) Assessing The Sequestration Time Scales Of Some Ocean-Based Carbon Dioxide Reduction Strategies. 2021 Environ. Res. Lett. (In Press) https://doi.org/10.1088/1748-9326/Ac0be0

Summary of the study: Carbon dioxide (CO2) removal (CDR) strategies that use the ocean are an important part of the set of steps needed to get negative greenhouse gas emissions. Many ocean-based CDR strategies depend on putting CO2 or organic carbon (which will eventually turn into CO2) into the deep ocean or making the biological pump of the ocean work better. These methods won’t lead to permanent sequestration because ocean currents will eventually bring the CO2 back to the surface, bringing it back into balance with the atmosphere. Here, a model of steady state global ocean circulation and mixing is used to figure out how long CO2 that has been put into the deep ocean stays out of the air. Because there are an infinite number of ways to get from a place at depth to the surface of the water, there will be a range of sequestration times for any single discharge location. The result is that the probability distribution is very skewed, with a long tail of very long transit times. This makes the mean sequestration times much longer than normal time scales. Deeper discharge sites will store CO2 for a much longer time than shallower ones. The average time to store CO2 is between a few decades and a few centuries, but in the deep North Pacific, it takes close to a thousand years. There are big differences in how long it takes for carbon to be stored within and between the major ocean basins. In general, the Pacific and Indian Oceans take longer to store carbon than the Atlantic and Southern Oceans. Assessments done over a 50-year period show that most of the carbon injected at depths greater than 1000 m will stay there, with a few places like the Western North Atlantic being an exception. Ocean CDR strategies that aim to increase the productivity of upper ocean ecosystems so that more carbon can be exported to depth will have a short-term effect on CO2 levels in the air because about 70 percent of the carbon will be brought back to the surface ocean within 50 years. The results shown here will help plan ocean CDR strategies that can help limit the damage to the climate caused by CO2 emissions from fossil fuels.

Dittmar Thorsten, et al. (2021) Enigmatic Persistence Of Dissolved Organic Matter In The Ocean. June 2021 Nature Reviews Earth & Environment. https://www.nature.com/articles/s43017-021-00183-7

Summary: Marine dissolved organic matter (DOM) has more carbon than all the Earth’s living things put together. Organisms in the ocean constantly release a wide variety of molecules that become food for microheterotrophs. However, for reasons that aren’t clear, some of these molecules stay in the ocean as DOM for thousands of years. In this Perspective, we look at two ideas that could explain this persistence and compare them. The “intrinsic recalcitrance” paradigm, which has been around for a long time, says that the stability of DOM comes from the way molecules are made. In the “emergent recalcitrance” theory, marine microheterotrophs change DOM all the time, and recalcitrance develops on an ecosystem level. Both ideas make sense based on what we know about the ocean today, but they predict very different responses of the DOM pool to changes in the climate. To learn more about how DOM stays around, we propose a new research strategy called “the ecology of molecules.” This strategy combines the ideas of “intrinsic” and “emergent” recalcitrance with the ecological and environmental context.

Baklouti M., Pagès R., Alekseenko E., Guyennon A., Grégori G. (2021). On the Benefits of Using Cell Quotas in Addition to Intracellular Elemental Ratios in Flexible-Stoichiometry Plankton Functional Type Models. Application to the Mediterranean Sea. Prog. Oceanogr. 197, 102634. https://www.sciencedirect.com/science/article/abs/pii/S0079661121001191

Summary: In the last few decades, there have been a growing number of marine Plankton Functional Type (PFT) models. Since the NPZD models that came before them, the general trend has been toward making models that are more and more complicated, either in terms of the number of variables they include or the level of detail they consider. In this way, flexible-stoichiometry models have been an important step in the history of this type of models. Since then, new developments have been written about in the literature, and this paper focuses on one of them: the addition of abundance to biomass to describe PFTs. With the growing number of studies and data sets from flow cytometry, this new feature makes it possible to test the model. It also makes it possible to get cell quotas (expressed as the amount of a given biogenic element per unit cell) for each PFT of the model. Cell quotas and intracellular ratios are used to control the speed of the different biogeochemical processes in the model. It is suggested here that their role may be crucial for accurately representing some processes, such as mineralization by heterotrophic bacteria. In this paper, we talk about some of the other benefits of cell quotas, such as how they help us understand how the trophic web works and how well organisms are eating. Lastly, the seasonal changes in the number of cells in the PFT that represent large phytoplankton can be used to explain why the NW Mediterranean spring bloom happens from an internal status point of view.

Boyd, P.W., Claustre, H., Levy, M. et al. Multi-faceted particle pumps drive carbon sequestration in the ocean. Nature 568, 327–335 (2019). https://doi.org/10.1038/s41586-019-1098-2

Summary: The ocean’s ability to take carbon out of the atmosphere and store it has a big effect on the climate of the whole planet. The biological pump stores carbon in the deep ocean and scientists think it works by letting organic particles from the surface waters sink down into the deep ocean. But the settling flux alone is usually not enough to balance mesopelagic carbon budgets or meet the needs of subsurface biota. Here, we look at some other physical and biological processes that send particles that are in the air or that are sinking to deeper levels. We think that these “particle injection pumps” probably sequester as much carbon as the gravitational pump, helping to close the carbon budget and encouraging more research into their environmental control.

Dymond, Jack R; Lyle, Mitchell W (1985). Flux comparisons between sediments and sediment traps in the eastern tropical Pacific: Implications for atmospheric CO2 variations during the Pleistocene. Limnology and Oceanography, 30(4), 699-712, https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.1985.30.4.0699

Summary: At two sites in the Guatemala Basin, the regeneration rates of unstable elements and biogenic components were measured by comparing the fluxes of material caught in sediment traps to the fluxes of material that stayed in the sediments. From 95 to 99% of the N, P, organic C, CaCO3, opal, and Br that reach the sea floor are made again at the two sites. For elements that are mostly bound in refractory phases (like Al, Sc, Ti, and Fe), the particle-associated flux to the bottom is within 20% of the rate of accumulation in the sediment.

Summary: At two sites in the Guatemala Basin, the regeneration rates of unstable elements and biogenic components were measured by comparing the fluxes of material caught in sediment traps to the fluxes of material that stayed in the sediments. From 95 to 99% of the N, P, organic C, CaCO3, opal, and Br that reach the sea floor are made again at the two sites. For elements that are mostly bound in refractory phases (like Al, Sc, Ti, and Fe), the particle-associated flux to the bottom is within 20% of the rate of accumulation in the sediment.

Karl, David & Letelier, Ricardo. (2008). Karl, D. M. & Letelier, R. M. Nitrogen fixation-enhanced carbon sequestration in low nitrate, low chlorophyll seascapes. Mar. Ecol. Prog. Ser. 364, 257-268. Marine Ecology-progress Series – MAR ECOL-PROGR SER. 364. 257-268. 10.3354/meps07547. https://doi.org/10.4319/lo.1985.30.4.0699

Summary: The amount of fluxes in the carbon cycle of subtropical and tropical marine habitats is determined by the amount of inorganic nutrients. These habitats have low levels of nitrate (NO3-) and chlorophyll (LNLC regions) at the sea surface. They also have low rates of organic matter production and export, and they have the least potential to store carbon in the world’s oceans. The low NO3- resupply should favor bacteria that fix nitrogen (N2), called diazotrophs, as long as all other growth-limiting nutrients are available. Several recent field studies have tried to improve N2 fixation in LNLC regions by fertilizing mesoscale areas with iron, phosphorus, or both. We hypothesize that controlled upwelling of nutrient-rich deep water may also be effective. Based on a quantitative analysis of the vertical distribution of NO3-, phosphate (PO4 3-), and dissolved inorganic carbon (DIC) at Station ALOHA (22° 45′ N, 158° W), we think that controlled upwelling of low NO3-:PO4 3- seawater may increase N2 fixation, organic matter production, and net carbon sequestration. Also, a long-term (20-year) set of data from Station ALOHA leads us to believe that the upwelling of water from a depth of 300 to 350 m during the summer months will cause a two-stage phytoplankton bloom. The first stage will be marked by a diatom bloom with a NO3-supported Redfield ratio (e.g. C106:N16:P by atoms). After removing NO3- in the right amount, the remaining PO4 3- from the low N:P.

Lampitt, R.S. (1985) Evidence for the seasonal deposition of detritus to the deep-sea floor and its subsequent resuspension, Deep Sea Research Part A. Oceanographic Research Papers, Volume 32, Issue 8, Pages 885-897, ISSN 0198-0149, https://doi.org/10.1016/0198-0149(85)90034-2

Summary:

A free-fall benthic time-lapse camera and current meter system were used to look at how the seabed in the Porcupine Seabight (50°N, 13W, northeast Atlantic) changes over time. Changes in the benthic environment happen down to 4000 m because of how quickly phytodetritus falls to the bottom. Photos taken every 8 hours from May 1 to the middle of August showed that the seabed changed significantly between June and July. From the time of the spring bloom until it reached the sea floor, the rate at which the trash sank was calculated. In 1982 and 1983, when spring bloomed, was very different from year to year, the sinking rates were likely between 100 and 150 m d1. Individual aggregates up to 12 mm in diameter and up to 50 mm at 4000 m came between the frames at all depths. Over the next few days after they fell to the sea floor, their breakup was watched. Some of these things were taken from the sea floor and used in an experiment to measure how fast they sink.

Once on the sea floor, the detrital carpet moves over the surface of the sediment because of bottom currents. When bottom currents are faster than about 7 cm s1 (at the height of 1 m), the material is resuspended. At the same time that the amount in suspension goes up, the amount that can be seen on the sea bed goes down. Because the current changes with the tides, the changes in the particles in the water near the sea floor have a strong tide component.

It discusses how the structure of benthic and benthopelagic communities is affected by a detrital critical erosion threshold.

Walsh, I.D., W.D. Gardner, M.J. Richardson, S.P. Chung, C.A. Plattner, V.L. Asper (1997) Particle dynamics as controlled by the flow field of the eastern equatorial Pacific, Deep Sea Research Part II: Topical Studies in Oceanography, Volume 44, Issues 9–10, Pages 2025-2047, ISSN 0967-0645, https://doi.org/10.1016/S0967-0645(97)00079-9

Summary: During the JGOFS EgPac October 1992 time series cruise to the equator, a Large Aggregate Profiling System (LAPS) was used to record the concentration and size distribution of particles in the marine snow size range (> 0.5 mm diameter). During the twenty days that the time series station was on the equator, profiles were always made at local midnight. When the LAPS data set is put together with the CTD/transmissometer data set from the EgPac program’s intensive profiling operation, it shows that the equatorial flow field drives a complex process of particle production and aggregation.

During the cruise, a Tropical Instability Wave (TIW) was seen to have an effect on the transmissometer/aggregate and temperature/salinity data sets. At the same time that the thermocline sank the most, and the aggregate volume concentration was at its lowest, the rate of particle production peaked. After that, the number of particles in the surface water went up, and then the number of aggregates went up. Near the end of the time series, conditions on the equator became “quasi-oligotrophic,” which means that there were more subsurface particles and aggregates and fewer new particles being made. This is similar to what happens in more northerly places.

When a TIW moves through, it causes changes in the temperature and salinity fields. These changes are caused by, in order, the trailing edge, the cool cusp water moving northwest, and the convergent front. Current meters at the equator recorded a rotating flow at 80 m, with the flow changing from southeast to northeast. A simple model of the meridional flow field is shown. In this model, the upwelled water from the equator moves away from the poles and then returns at shallow depths to mix with the EUC. This return flow is shown by the fact that the vertical gradients of nutrients and oxygen at the equator are less than those at the poles and that there is a maximum of subsurface particles below the EUC. The effect of the flow field on how particles are spread out can be seen in the meridional pattern of the sediment accumulation rate (Murray and Leinen, 1996). The flow of particles back to the equator is shown by the fact that the rate of buildup is highest near the equator. Murray and Leinen (1996) wrote that the long-term effects of TIWs can be seen in the uneven accumulation rates across the equator, with the highest rate of accumulation south of the equator, the lowest rate near 2°N, and the highest rate near 4°N.

Walsh, Ian, Jack Dymond, Robert Collier (1988). Rates of recycling of biogenic components of settling particles in the ocean derived from sediment trap experiments, Deep Sea Research Part A. Oceanographic Research Papers, Volume 35, Issue 1, Pages 43-58, ISSN 0198-0149, https://doi.org/10.1016/0198-0149(88)90056-8

Summary: At three sites in the North Equatorial Pacific, the rates of recycling of the main parts of the biologically produced particulate flux (organic carbon, calcium carbonate, and opal) were measured. The biogenic fluxes measured in sediment traps were normalized to the particulate aluminum flux, and reaction rate constants were calculated based on the assumption that first-order processes happen when particles settle between two sediment traps that are next to each other. At each site, the most water was moving through the middle. Assuming that particles settle at a rate of 100 m per day, the rate constants for organic carbon, calcium carbonate, and opal below the mid-water flux maxima were, respectively, 3.7–13 y1, 2.3–4.5 y1, and 1.0–7.9 y1. For organic carbon, the rate constants ranged from 15 to 32 years per year, for calcium carbonate from 11 to 20 years per year, and for opal from 6.4 to 27 years per year.

White, A., Björkman, K., Grabowski, E., Letelier, R., Poulos, S., Watkins, B., & Karl, D. (2010). An Open Ocean Trial of Controlled Upwelling Using Wave Pump Technology, Journal of Atmospheric and Oceanic Technology, 27(2), 385-396. https://doi.org/10.1175/2009JTECHO679.1

Summary: In 1976, John D. Isaacs came up with the idea of using wave energy to change the density structure of the ocean and pump deep, nutrient-rich water to the surface layers where the sun shines. The basic idea is simple: a length of tubing with a surface buoy at the top and a one-way valve at the bottom can be extended below the euphotic zone to act as a pipe for deep water. The vertical movement of the ocean causes the attached valve to open when a wave is going down and close when it is going up. This causes deep water to rise to the surface of the ocean. Isaacs’ wave-powered pump has been used in many different ways, like to make energy or for aquaculture. More recently, it has been suggested that artificial upwelling could be used to boost primary productivity and carbon sequestration. However, the basic engineering idea behind the pump hasn’t changed. In June 2008, the authors tested a commercially available wave pump (called Atmocean) north of Oahu, Hawaii, to figure out how to set it up at sea and how long it would last in the open ocean. As part of an experiment to test a recently published theory, this test was done to see if upwelling water with more phosphate (P) than nitrogen (N) compared to the “Redfield” molar ratio of 16N:1P would cause a two-phased phytoplankton bloom. The end result of this field experiment was that deep water was quickly brought to the surface of the ocean (in less than two hours for a 300-m distance), but the materials in the pump broke apart under the dynamic stresses of the ocean environment. Wave-driven upwelling of cold water was recorded for about 17 hours, with a volumetric upwelling rate of about 45 m3 h1 and an estimated total input of 765 m3 of nutrient-rich deep water. The authors talk about how they set up a 300-m wave pump, how they got samples of a biogeochemical response, the engineering challenges they faced, and what these results mean for future experiments that try to make phytoplankton grow faster.

Chikamoto, M., DiNezio, P. (2021).  Multi-Century Changes in the Ocean Carbon Cycle Controlled by the Tropical Oceans and the Southern Ocean, https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GB007090

Summary: It is expected that the oceans will continue to take in carbon dioxide (CO2) from human activities over the next few hundred years, but it is still unclear what is causing these changes. We looked at these processes in a simulation of how the climate and carbon cycle will change in the future if the RCP8.5 high emission scenario comes true. The simulation shows that the oceans will take in more and more CO2 from human activities, reaching a peak around the year 2080. After that, they will slow down but still take in a lot of CO2 until the year 2300. Changes in sea-air CO2 fluxes in the tropical and southern oceans are the main cause of these long-term changes in uptake. In the tropics, if upwelling and vertical gradients of dissolved carbon go down, carbon-rich thermocline waters won’t move up and down as much, stopping CO2 from escaping naturally. In the Southern Ocean, waters that have less carbon dissolved in them rise to the surface. This keeps the surface carbon level low, which makes it easier for CO2 to be taken in over the next few hundred years. In the centuries that followed, CO2 uptake slowed down because the warming of the ocean and changes in carbon chemistry made CO2 less soluble and less able to be stored in the ocean. When the Atlantic Meridional Overturning Circulation (AMOC) breaks down, as is expected to happen in the next century, a lot less CO2 is taken up by the oceans. So, figuring out how the global carbon cycle will change over the next few hundred years depends on changes in the chemistry of carbon, how water and air move through the Southern and Tropical Oceans, and the possibility that the AMOC will break down.

Ilyina, T., Li, H., Spring, A., Müller, W. A., Bopp, L., Chikamoto, M. O., et al. (2021). Predictable variations of the carbon sinks and atmospheric CO₂ growth in a multi-model framework. Geophysical Research Letters, 48, e2020GL090695. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL090695

Summary: The strength of the land and ocean carbon sinks can change from year to year or decade to decade, which makes it hard to predict the growth rate of carbon dioxide (CO2) in the atmosphere from year to year. This kind of information is very important to make sure that measures to reduce fossil fuel emissions are working. Using a multi-model framework with prediction systems that are set up based on the observed state of the physical climate, we find that some models can predict the global ocean carbon sink with a skill of up to 6 years. Single models tend to have longer time horizons for predicting what will happen in a region. On land, the ability to predict the weather for up to two years is mostly kept in the tropics and extra-tropics, which is made possible by how the physical climate is set up. We also show that natural changes in the land and ocean carbon sinks can be used to predict the growth rate of CO2 in the atmosphere with a lead time of 2 years. The accuracy of this prediction is limited by the length of time that land carbon sinks can be predicted.

MRV: MODELING AND MEASURING EXPORT & SEQUESTRATION

By Dr. Ian Walsh, Consulting Chief Scientist @ Ocean-based Climate Solutions, Inc

In the ocean we have challenges to measuring the impact of ocean upwelling and deriving time weighted sequestration fluxes.

But these are entirely tractable challenges: we have tools and experience through generations of oceanographers in measuring carbon flux through the ocean where we can and estimating where we don’t have data. We have local process studies and global models that provide bounds to carbon fluxes from diel to annual and greater time scales. Global models typically use well structured physical models (get the physics right first!) overlayed with biogeochemical models with more or less stocks and pathways to apportion energy and variability over significant time scales.

The challenge with ocean upwelling is that along with nutrients, the dissolved inorganic carbon (DIC) concentration also has a regeneration profile, with low concentrations at the surface relatively monotonically increasing with depth, with the gradient controlled mostly by water mass.

So we have to measure both the nutrients and the carbonate chemistry of the upwelled water. What we want with the upwelled water source is a source water for upwelling where there is an ‘excess’ of nutrients relative to the DIC such that there is a net uptake and fixing of atmoCO₂ into the particle pool via phytoplankton rather than simply a quick shunting of upwelled CO₂ as DIC into the fixed carbon pool. The presence of ‘excess’ nutrients, particularly phosphate, relative to DIC in the twilight zone is a steady state result of nutrients having higher first order remineralization rates than particulate organic carbon. This dynamic operates over long periods of time and space driving the linkage of atmoCO2 to ocean upwelling on a global scale through recent geological time has been long established (Dymond and Lyle, 1985)

There are many ways to define the ‘excess’ relative nutrient load relative to the carbon load. Karl and Letelier (2008) used the phosphate concentration relative to nitrate and DIC to define a sequestration potential for a given depth profile. The attraction for using this method is that temporal and spatial variability of dissolved constituents in the ocean decreases with depth and particularly in the central gyres a relative sparsity of data still yields volumetric/depth/time relationships that are reasonably stable, and hence the initial conditions of the setting of a particular pump deployment in a central gyre can be reasonably assumed to be the conditions over annual time scales.

The task then is to gauge the actual delivered seawater. For that we can use a mixing model over the volume addition:

Temperature_z,plume = A * Temperature_z,ambient + D * Temperature_intake

PO_4ex plume = A * PO_4z,ambient + D * PO_4intake

And

A + D = 1

Since for the oligotrophic ocean we can assume that the available dissolved nutrient concentration in the mixed layer is non detectable, i.e.:

PO_4ML,ambient = 0

Where z here is replaced by the mixed layer depth.

If we assume that the upwelled volume is dispersed into the plume, and that the plume is entirely within the mixed layer, and the mixed layer is equal to or less than the euphotic depth, then we can presume that all upwelled water that enters at the intake is dispersed within the mixed layer and is taken up over time into the biological system.

Since we know that the ambient excess phosphate is zero, then the additional phosphate added to the system will also devolve to zero and that this will occur on the order of days. Hence, the simplest measurement of the net sequestration effect of a given artificial upwelling pump can be based on the temperature and nutrient load relationship at the intake depth range and the measured temperature anomaly at the surface.

SCALING OCEAN CARBON SEQUESTRATION & VERIFICATION

The following is by Ian D. Walsh; ianwalsh@comcast.net; @iandavidwalsh; adapted from Ian’s WHOI OCB Summer Workshop Presentation at Woods Hole, MA, 20-23 June 2022 for website form by Salvador Garcia. Acknowledgments: IDW consults for Ocean-Based Climate Solutions Inc. (Ocean-Based) which has developed and built artificial upwelling pumps and is testing the systems. Ocean-Based did not directly pay for or have editorial control of the research presented here.

INTRODUCTION

The idea of artificial upwelling using vertical tubes in the ocean open has been around for a long time (Stommel et al., 1956). Similarly, the linkage of atmoCO2 to ocean upwelling on a global scale through recent geological time has been long established (Dymond and Lyle, 1985). Current considerations of the potential impact of artificial upwelling have outlined an uncertainty matrix and a research strategy for artificial upwelling within a broader review of ocean-based carbon dioxide removal (CDR) (NASEM, 2021). Meanwhile, the carbon offset ‘market’ is booming (your favorite news source), including ocean CDR.

Here I present some considerations and calculations on the scalability of artificial upwelling and verification pathways to hopefully advance the discussion and spark interest in the OCB community.

OLIGOTROPHIC OCEAN: HAWAII OCEAN TIME SERIES NUTRIENT DATA

The oligotrophic ocean is an attractive deployment location or artificial upwelling at least through the testing phase because the generally low abundance of nutrients in the absence of upwelling provides an excellent background to track the impact of artificial upwelling and a source of excess phosphate at depth to test Karl and Letelier’s hypothesis that net sequestration CO2 is driven by excess phosphate.

Data obtained via the Hawaii Ocean Time-series HOT-DOGS application; the University of Hawai’i at Mānoa. National Science Foundation Award # 1756517

PARTNERSHIPS TO DRIVE VERIFICATION

Verification of sequestration should be independent from the deployment and operation of sequestration technologies, though these should be tightly linked to drive the system towards increase effectiveness.

Continuation of public strategies to measure and model ocean carbon dynamics will contribute to ocean CDR measurements and verification.

Local modeling for additionally and effectiveness of ocean CDR technologies should couple with wider scale public modeling efforts.

Costs for verification relative to ocean CDR will then be spread between the operators of ocean CDR and the wider public and reduce conflict of interest uncertainties.

ARTIFICIAL UPWELLING – WAVE ENERGY DRIVES THE SYSTEM

SENSITIVITY AND DETECTION

SCALING: IS ONE GIGATON CO2 PER YEAR POSSIBLE?

REFERENCES

Stommel, H., Arons. A.B., and Blanchard, D., 1956: An oceanographical curiosity: the perpetual salt fountain. Deep Sea Research, Vol. 3, pp. 152-153. https://www.sciencedirect.com/science/article/abs/pii/0146631356900958?via%3Dihub

Dymond, J. and Lyle, M. 1985. Flux comparisons between sediments and sediment traps in the Eastern Tropical Pacific: Implications for atmospheric CO2 variations during the Pleistocene. Limnology and Oceanography, 30(4), pp. 699-712. http://dx.doi.org/10.4319/lo.1985.30.4.0699

Karl, David & Letelier, Ricardo. 2008. Nitrogen fixation-enhanced carbon sequestration in low nitrate, low chlorophyll seascapes. Mar. Ecol. Prog. Ser. 364, 257-268. http://dx.doi.org/10.3354/meps07547

National Academies of Sciences, Engineering, and Medicine. 2021. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278

Kithil, P., Garcia, S., and Walsh, I., 2022. Ocean Carbon Dioxide Removal using Wave-powered Artificial Upwelling Pumps. The Journal of Ocean Technology, Vol. 17, No. 1, 2022. https://issuu.com/journaloceantechnology/docs/e-jot_vol17n1_interactive_book_lr_flipbook