Biological Ocean Sequestration of CO2 Using Atmocean Upwelling


Our technology uses kinetic wave energy to bring up higher-nutrient deep water. In the presence of sunlight, and assuming appropriate ocean environmental conditions, the enhanced nutrients generate blooms of phytoplankton which absorb dissolved CO2 and generate oxygen through the process of photosynthesis. When the phytoplankton are consumed by higher trophic levels such as zooplankton and fish, or when the phytoplankton die, some of the absorbed CO2 as well as other biochemical contents sink. Some of this is remineralized and suspended in mid ocean depths, some sinks to the ocean floor, and some is sent back up to the surface by natural upwelling events (currents, storm-generated upwelling, heating/cooling cycles such as El Nino, etc.). This "biological pump" is the principle physical process responsible for the higher concentrations of nutrients, and CO2, which are found beneath the upper sunlit zone (typically 50 to 80 meters) of the ocean. Within the upper ocean's sunlit zone, however, the nutrients are quickly consumed, with the result that phytoplankton blooms diminish until upwelling brings up more nutrients.
Until recently, conventional wisdom regarding limits to phytoplankton productivity in the upper sunlit zone of the ocean cited the Redfield Ratio as the limiting factor to how much net benefit could accrue from wave-driven ocean pumps. The Redfield Ratio limits the amount of carbon that each phosphate atom can recycle. For the average of all the ocean is it 106 carbon atoms for every phosphate atom. If CO2 recycling efficiency is limited by phosphate, and deeper water contained proportional concentrations of nitrate, phosphate and dissolved CO2, then net additional absorption from upwelling of phosphate would be balanced by the higher concentrations of CO2 brought upward - at best a zero sum game.
But Professors David M. Karl from University of Hawaii, and Ricardo Letelier from Oregon State University have recently published a peer-reviewed paper which hypothesizes that upwelling of certain deeper waters (generally 300m or more) can result in a secondary bloom governed by nitrate as the limiting nutrient - with the result that several-fold greater net absorption of CO2 is possible. The absence of nitrate causes diazotrophic (nitrogen fixing) phytoplankton to dominate the second bloom, with super-Redfield C:P ratios of >200:1.  Click this link to read their paper.
Given this new Karl-Letelier hypothesis about potential net sequestration of CO2, if ocean biogeochemical conditions are suitable for generating primary and secondary blooms, and given the potential for a single Atmocean pump to produce nominal upwelling volume of 200,000 cubic meters per day (consistent with 3 meter wave height), initially we estimate precision upwelling could result in net additional sequestration of about 60 tons CO2 per pump per year, with the significant added benefit of 1.5 tonnes annual increase in fish biomass. Many elements of this process remain to be tested, including the multiple effects over many seasons and in different ocean environments, and how the upper, mid, and deep-ocean concentrations of nutrients and CO2 could transition over longer time periods.
To initiate testing of the Karl-Letelier Hypothesis, in May 2008 Atmocean participated in an ocean test of three pumps in the Pacific about 60nm north of Hawaii. This test is featured on the Discovery Channel Project Earth episode "Hungry Oceans". To order the DVD set of all eight Project Earth episodes, visit the Discovery Channel store, or contact Atmocean to purchase a DVD of just the "Hungry Oceans" episode. In brief, while not all the experimental goals were achieved (due to structural failures, and an inappropriate pump deployment method), the tests conclusively proved our capability to pump up nutrient-rich water from 300m deep in the open ocean, solely using wave energy. Since we learn more from failure than success, these tests prompted a new durable pump design for extreme ocean conditions. We expect this new design, which very closely mimics natural ocean mixing processes, can be produced and deployed at equal or lower cost than our "original" design. If comprehensive future testing demonstrates that the environmental consequences are manageable and achieves permanent, additional, net CO2 absorption in the oceans, this could lead to large-scale commercial implementation.

*U.S. and International Patents Pending

To discuss in more detail how Atmocean’s technology might accelerate the oceans’ uptake of CO2, please contact Philip W. Kithil, CEO, at [email protected]