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://doi.org/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://www.researchgate.net/publication/238005444_Karl_D_M_Letelier_R_M_Nitrogen_fixation-enhanced_carbon_sequestration_in_low_nitrate_low_chlorophyll_seascapes_Mar_Ecol_Prog_Ser_364_257-268

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://doi.org/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://doi.org/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.