Southern Ocean phytoplankton community characteristics, primary production, CO2 flux and the effects of climate change

New oceanographic data and knowledge from the coast and ice edge of Kong Håkon VII Hav, Antarctica, Southern Ocean. Today, there are gaps in knowledge and observations from the ocean around Antarctica, and of the consequences for marine life due to climate change. Rapid changes in the Antarctic marine environment have caused an urgency to protect habitats that are essential for the ecosystem., particulairy near the coast and ice edge off the coast of Dronning Maud Land/Kong Håkon VII Hav. The project research is a collaboration between South African and Norwegian researchers in physical, chemical, and biological topics, with the goal to increase the knowledge about the relatively unknown Kong Håkon VII Hav. Using observations and data from the research vessels RV «Kronprins Haakon» and SA «Agulhas», new fundamental data and knowledge have been provided, in a highly under-sampled area in Antarctica. The research is highly related to climate and environmental changes, with the focus on phytoplankton primary production and community characteristics, the oceanic carbon dioxide (CO2) uptake, and progressing ocean acidification and changes in marine ecosystem. The first Norwegian 7-week long joint research cruise was successfully performed in 2019 on RV «Kronprins Haakon» to Antarctica, where Norwegian and South African scientists, post-doctoral students and PhD students participated, collected unique autumn data, jointly analysed data, and later worked on joint manuscripts. The exchange of knowledge involved scientists, postdoctoral students, and students from both countries, and we have used joint instrumentation/laboratory and visits of South-Africans in Norway, and Norwegians in South Africa to contribute with joint publications. In October 2019, a joint workshop was arranged by the Norwegian scientists in Tromsø, Norway, where all participants were invited, and several South African and Norwegian members actively took part. In September-October 2019, two South African PhD students visited Norway for one month for knowledge exchange and to work with data, learn new methods and joint publications, and two Norwegian scientists visited South Africa in January-February 2020 for further collaboration, knowledge exchange and co-supervision of PoD students. During covid restrictions in 2020-2021, most meetings were carried out digitally (on-line). Both South-African PhD students contributed to all activities and results in the project, delivered their thesis, defended it on-line, and passed the examination in 2021 and 2022. Results from the project show the strengths of ocean CO2 uptake in different regions in the Kong Håkon VII Hav, depending on different processes during autumn, such as sea-ice formation, vertical mixing of water masses, wind stress and previous or present blooms. The seasonal ice-covered area south of 60°S was found to be a significant CO2 sink of atmospheric CO2 in autumn, which has not previously been reported. This CO2 sink coincided with the remnants of large blooms, lowering the surface water CO2 content. Results showed that the evolution of sea-ice extent plays a role for bloom initiation but not termination, where grazing by zooplankton is important to finish the bloom. Bloom magnitude in autumn is controlled by current interaction with topography for supply of nutrients and iron. An unexpectedly large bloom in the open ocean was observed in autumn which was explained by unusually strong easterly winds and upwelling of iron- and nutrient-rich deep water, derived from hydrothermal vents at the bottom. Experiments performed also conclude that the autumn bloom in the sea-ice edge was not iron limited due to excess iron supply from the sea ice to the surface water. Long-term observations using satellite images of chlorophyll a showed that trends in the length and amplitude of the blooms increased more than previously reported, from 10 days per decade to 50 days per decade due to changes in nutrient and light availability. The ocean blooms likely facilitate enhanced carbon export and sustains high standing stocks of Antarctic krill, supporting feeding hotspots for fish, marine birds, and baleen whales. The results were presented at meetings and conferences (both in person and digitally due to covid-19). Several scientific manuscripts have been published in 2020-2023. Data has been published for open access in data bases in Norway and South Africa to be available for the international scientific community and contributes to UN Ocean Decade SDG variables. Data and findings will contribute to capacity building, education and new insights of the relatively unknown region and have high relevance for the carbon cycle, the vulnerable marine ecosystem, climate change and management. New findings have been presented in social media, to bring increased awareness to the society about climate change. Understanding will have impacts on climate predictions, mitigation and cost of adaptation and management.

SOPHY-CO2 has successfully been carried out including research cruises to Southern Ocean/Antarctica/Kong Håkon VII Hav and sample collection, new unique data, manuscripts published in peer-reviewed and high-impact journals and social media, exchange of knowledge, resources and facilites, graduations of two PhD students and one master student within the project, and contributing to capacity building in the two countries. Findings contribute to new insights and understanding of the region and have high relevance for the carbon cycle, the marine ecosystem, climate change, and spatial management. The new findings have been published (e.g. Nature communications, Frontiers in Marine Science, Biogeosciences and Nature Climate Change) and presentated at international conferences (e.g. Southern Ocean Observing System (SOOS), Ocean in a High CO2 world) and webinars (e.g GOA-ON) but also published in social media and institutes webpages, and during school visits. These outcome will bring the international research forward to improve data coverage, contribute to global and carbon modeling, future predictions and will lead to further international and interdisciplinary collaboration. Data from SOPHY-CO2 contribute to UN Ocean Decade SDG variables, to the international scientific community, and to a base line and background environment status to observe changes in the marine system. Collaboration between the two countries has improved research and the understanding of climate change and effects on the Southern Ocean ecosystem, which is sensitive to changes such as warming, sea-ice melting and surface freshening, which will impact primary (phytoplankton, ice algae) and seconday production, (e.g krill, fish). The ocean blooms likely facilitates enhanced carbon export and sustain high standing stocks of Antarctic krill, supporting feeding hotspots for fish, marine birds and baleens whales. Awareness of changes in the Southern Ocean and ecosystem among society and importance of the ocean and marine system will help to protect and manage a sensitive marine environment. It may also contribute with backgound knowledge for an establishment of marine protected areas (MPA). Understanding will have significant impacts on climate predictions, effectiveness of mitigation measures and economic cost of adaptation plans and environmental managements strategies. The project contributes to strategic plans such as research and education plans and has contributed to capacity building in both countries, educated and contributed to several young research scientists, that have gained substantial knowledge of the Southern Ocean and will continue with marine research and contribute to a future sustainable ocean. Data is already in use by other students in 2023 and will be used by new students in future in both countries for further capacity building.

Climate change is a big challenge to society, and preparation of new national and international strategies for society to adapt to these changes depend on the ability to make realistic future climate scenarios. Using physical, chemical and biological oceanographic data from SA Agulhas and RV Kronprins Haakon will enhance the transfer knowledge between South Africa and Norway, and will contribute with increased knowledge in establishing a Marine Protected Area in the Dronning Maud Land (DML), Antarctica. The applied project will provide new, unique and fundamental data and knowledge to fill the gaps in a highly under-sampled area, related to climate and environmental change focusing on the phytoplankton primary production and community characteristics, the oceanic carbon dioxide (CO2) uptake, progressing ocean acidification and changes in marine ecosystem. Changes in the Antarctic marine environment have caused an urgency to protect habitats that are essential for the ecosystem. A new Marine Protected Area near the coast and ice edge of DML is a Norwegian priority. Interdisciplinary Norway-South Africa collaboration, will strengthen the goal for the project, including joint cruises, data analysis, instrumentation/laboratory, exchange and visit of students, joint workshop and publications that will improve the success of the outcome of the projects. South Africa students will participate in all aspects of the project. Researchers from both countries will actively take part in the project and collaborate for the success of the project as well as planning for future collaborative research joint proposals. Sharing knowledge, cruises, technology, laboratory facilities and students will lead to enhanced collaboration and competence building, which will result in enhanced expertise in marine science for future job opportunities in South Africa.