CArbon Production of under-ICE phytoplankton blooms in a changing Arctic Ocean

Periodic Reporting for period 2 - CAP-ICE (CArbon Production of under-ICE phytoplankton blooms in a changing Arctic Ocean)

Okres sprawozdawczy: 2020-01-15 do 2021-01-14

Over the last decades, sea-ice in the Arctic Ocean (AO) has undergone unprecedented changes, with drastic decline in its extent, thickness and duration. Modern climate models are unable to simulate these changes, leading to large uncertainties in Arctic and Global Change predictions. Sea-ice strongly attenuates solar radiation and it is generally thought that phytoplankton, which drives Arctic marine CO2 sequestration, only grow in open waters once sea-ice retreats in spring. However, the discovery of large under-ice phytoplankton blooms (UIBs) growing beneath sea-ice contradicts this paradigm. UIB productivity in ice-covered regions has been suggested to be ten-fold larger than presently modeled. By initiating an international network (USA, France, Canada, Germany, Norway), the CAP-ICE project will acquire knowledge on the occurrence of UIBs, the physical mechanisms that control their initiation and productivity, and will quantify how UIBs affect the Arctic carbon cycle and climate.

CAP-ICE will equally combine observational, modeling and novel technology approaches. Multiple pan-Arctic expeditions will provide new field observations on the environmental conditions controlling UIBs. Since UIBs are invisible to ocean color satellite sensors, developing a novel model adapted to under-ice environments will allow quantifying the contribution of UIBs to the Arctic carbon cycle. Finally, the recent launch of autonomous robotic platforms (Bio-Argo floats) will support the first assessment of UIB primary production and carbon export in AO and the implementation of a Bio-Argo Arctic network.

By the end of this fellowship, CAP-ICE has made substantial contributions to the understanding of under-ice biogeochemical cycles through a combination of approaches. CAP-ICE has helped to provide the scientific community with needed knowledge and future directions for Arctic science. In addition, CAP-ICE has revealed new discoveries, not only in the Arctic, through the expansion of modern autonomous platforms. We are just at the beginning of a new era of rapid deployment of new autonomous systems in the Arctic, and CAP-ICE has contributed to this international effort.

"The overarching hypothesis of CAP-ICE is that in the present warming climate, UIBs are more prevalent and productive than open water blooms across the AO due to high pre-bloom nutrient concentrations beneath the sea-ice and increased light transmission through thin sea-ice and melt ponds. To test this hypothesis, the main objectives of the CAP-ICE project was to examine three specific objectives:
• Characterize the optimal environmental conditions controlling the initiation and magnitude of UIBs;
• Design a coupled satellite-derived sea-ice/biogeochemical model adapted to under-ice Arctic waters;
• Integrate the carbon contribution of UIBs to the marine Arctic carbon cycle.

Environmental conditions controlling UIBs. The researcher has proposed to write a review on the recent main changes in phytoplankton dynamics in the Arctic Ocean for Nature Climate Change. Such review is currently lacking for the Arctic scientific community and more broadly for scientists actively involved in the science of climate change. Based on our Arctic expertise and knowledge (with the host researcher, i.e. Kevin Arrigo), we gathered the latest breakthroughs in our field and our understanding of Arctic marine ecosystems in the context of rapid environmental change. This review brings together updated satellite-derived trends in Arctic primary production, new discoveries based on ""traditional"" expeditions and novel ""autonomous"" platforms. More importantly, by achieving this prospective, we attempt to outline the main scientific challenges that the community will have to tackle in the short- and long-term.
In a second paper (in Elementa), based on an international consortium, the fellow compiled a comprehensive dataset from a large number of Arctic Ocean expeditions to identify the environmental drivers responsible for initiating and shaping the magnitude and assemblage structure of UIBs. The main finding was that two main types of UIBs bloom were identified, dominated by either diatoms or the prymnesiophyte, Phaeocystis pouchetii. The implications of such dichotomy in UIBs could have important ramifications for Arctic biogeochemical cycles, and ultimately impact carbon flow to higher trophic levels and the deep ocean.

Satellite-derived sea-ice/biogeochemical model. Designing a coupled satellite-derived sea-ice/biogeochemical model adapted to under-ice Arctic waters is a complex task. This second objective was addressed in an article summarizing everything we know about UIBs and highlighting their impact on marine Arctic carbon cycle for a special issue of Frontiers in Marine Science. By running a unique simulation, we were able to determine the magnitude and extent of the UIBs in the past and present. During the period (1850-1900), UIBs were restricted at low latitude in the Arctic Ocean and only for one month. But today, during the period (2010-2014), UIBs occur for at least 3 months in summer and throughout the Arctic Ocean. Such findings suggest the relevance of these UIBs on Arctic biogeochemical cycles (and in particular the carbon cycle) and marine ecosystems (temporal asynchrony, species diversity, migrations) in the context of climate change.

New autonomous technologies in the Arctic Ocean. In the same article in Frontiers in Marine Science, the novelty of this work and its scope of application, also in line with the objective 3, is to gather all the information obtained by autonomous platforms. Not only BGC-Argo floats were discussed, but also other autonomous platforms (e.g. ITPs ""Ice-tethered profilers"", ROVs ""Remotely Operated Vehicle""). This initiative will be useful for the Arctic scientific community by showing the potential and the progress we can make in understanding under sea-ice phytoplankton dynamics using these new technologies.

At this end of the fellowship, the direct and indirect outcomes of the MSCA Fellowship are, four peer reviewed articles as first author (in Nature Climate Change, Nature Communications, Frontiers in Marine Science and Elementa: Science of the Anthropocene), 7 peer reviewed articles as co-authors (in Cell, Nature Communications, Frontiers in Marine Science, Global Biogeochemical Cycles, Journal of Geophysical Research: Oceans, Scientific Report and Deep-Sea Research Pt. II), and finally 1 peer reviewed article on disseminating data (in Earth System Science Data)."

In terms of dissemination, the researcher published a dataset, related to the paper in Elementa (in Zenodo). Regarding the communication, the societal implications of the project and public engagement, the researcher continues to be involved with the press and local media (in particular with the outcome of several papers in Nature Communications, Nature Climate Change and Frontiers in Marine Science). I have been in contact with many international journalists to describe my research and by participating in a radio show (a local show in California; Goggles Optional). Finally, through several invitations to international conferences (e.g. Gordon Conference; OCB meeting at WHOI in the Maine, FAABulous workshop) or collaborations/seminars (e.g. U. Laval, Canada; SCRIPPS, California; IMAS, Tasmania), I have been able to enthusiastically promote my research, as well as the Marie Curie program.

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Periodic Reporting for period 2 - CAP-ICE (CArbon Production of under-ICE phytoplankton blooms in a changing Arctic Ocean)

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