Periodic Reporting for period 4 - Ocean artUp (Ocean Artificial Upwelling)
Berichtszeitraum: 2021-07-01 bis 2021-12-31
The human population is projected to rise from 7 billion today to close to 10 billion by 2050. Providing food to this many people will be one of the greatest challenges of the 21st century. Due to competing interests in land use from various societal sectors, the potential for expanding farmland is limited. This turns the focus on the ocean, which covers more than two thirds of our Earth’s surface. However, marine fish stocks for the most part are already fully exploited or even over-exploited. And even aquaculture, the fastest growing food sector worldwide, requires animal feed, either from wild fish or land farming. Ocean artificial upwelling could help increase marine productivity and raise fish production. If powered by renewable energy, this could be achieved at a low carbon footprint. In contrast to the high water demand of livestock production on land, it would come free of freshwater usage, and by tapping into the huge deep ocean nutrient reservoir, it would be independent of crop fertilizers. If applied off-shore out of range of shipping routes and fishing grounds, there would be no competing interests for space.
The productivity of the ocean is limited by the transport of nutrient-rich deep waters to the sun-lit surface layer. In large parts of the global ocean this transport is blocked by a temperature-induced density gradient, with warm light waters residing on top of heavier cold waters. These regions, which are referred to by scientists as ocean deserts, are presently expanding due to global warming. Enhancing the upward transport of nutrient-rich deep waters through artificial upwelling can break this blockade and make these waters more productive. To what extent this raises fish production and whether it can strengthen oceanic CO2 sequestration is still an open question. Importantly, the potential risks and side effects of this approach are largely unknown.
Ocean artUp aims to study the feasibility and effectiveness of artificial upwelling in fertilizing ocean productivity and enhancing energy transfer to higher trophic levels with the potential of raising fish production. Ocean artUp further investigates the impacts of artificial upwelling on biogeochemical cycling, including carbon export potential, and air-sea gas exchange of climate relevant gases. A particular emphasis is laid on elucidating the associated risks and potential side effects in terms of changing ocean ecosystems structure and functioning and modifying nutrient inventories and fluxes.
The productivity of the ocean is limited by the transport of nutrient-rich deep waters to the sun-lit surface layer. In large parts of the global ocean this transport is blocked by a temperature-induced density gradient, with warm light waters residing on top of heavier cold waters. These regions, which are referred to by scientists as ocean deserts, are presently expanding due to global warming. Enhancing the upward transport of nutrient-rich deep waters through artificial upwelling can break this blockade and make these waters more productive. To what extent this raises fish production and whether it can strengthen oceanic CO2 sequestration is still an open question. Importantly, the potential risks and side effects of this approach are largely unknown.
Ocean artUp aims to study the feasibility and effectiveness of artificial upwelling in fertilizing ocean productivity and enhancing energy transfer to higher trophic levels with the potential of raising fish production. Ocean artUp further investigates the impacts of artificial upwelling on biogeochemical cycling, including carbon export potential, and air-sea gas exchange of climate relevant gases. A particular emphasis is laid on elucidating the associated risks and potential side effects in terms of changing ocean ecosystems structure and functioning and modifying nutrient inventories and fluxes.
To achieves the objectives we have (i) designed, constructed and tested a 1:5 scale wave pump, (i) carried out an in-shore pilot experiment simulating artificial upwelling in a wide range of nutrient enrichments, (iii) conducted an in situ mesocosm study off Gran Canaria simulating artificial upwelling with pulsed and continuous addition of nutrient-rich deep water in four different mixing ratios, and (iv) are performing hydromechanical modelling to identify feasible pump designs and dimensions, quantify and optimize the volume transport of forced upwelling for a given electrical power. Although still preliminary, the results of these investigations revealed that (a) a minimum mixing ratio of 10% of nutrient-rich deep water with oligotrophic surface water is needed to achieve a detectable change in plankton community structure, productivity and trophic transfer, (b) mixing ratios of this magnitude are difficult to achieve with wave pump systems, pointing at electrically powered pumps or propellers as a more promising approach for artificial upwelling, and (c) continuous deep water supply yields a plankton community with a more efficient trophic transfer than a single deep water pulse of the same total volume addition. In-depth analysis of the experimental and modelling data is presently on-going, the results of which will guide the ecosystem-biogeochemical modelling, the technical design and construction of an upwelling system as well as further experimental activities, ultimately leading up to a field validation.
Ocean artUp is the first project to examine the effects of forced upwelling of nutrient-rich deep water on plankton ecology and pelagic biogeochemistry in oligotrophic open ocean waters. As part of this Ocean artUp has for the first time determined the relationship between upwelling intensity and the trophic transfer efficiency in natural plankton communities. This will allow to optimize the implementation of forced upwelling in terms of maximizing fish production. Ocean artUp is also the first project to assess the effects of forced upwelling on the biological carbon pump, from carbon uptake through primary production, the consumption of primary produced organic matter in the pelagic food web, to the sinking of particulate organic carbon and its remineralisation on the way to depth. In combination, these measurements will allow to quantify the export efficiency and ultimately the CO2 sequestration potential of artificial upwelling. The results obtain through Ocean artUp will thus provide a basis to quantify the cost-benefit relationship of artificial upwelling both in raising food production and as a means for CO2 removal.