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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - CAP-ICE (CArbon Production of under-ICE phytoplankton blooms in a changing Arctic Ocean)

Teaser

Summary

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.

Work performed

\"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 will be achieved by examining three specific objectives:
â€¢ Characterize the optimal environmental conditions controlling the initiation and magnitude of UIBs;
â€¢ Design a coupled satellite-derived sea-ice/biogeochemical model adapted to under-ice Arctic waters;
â€¢ Integrate the carbon contribution of UIBs to the marine Arctic carbon cycle.

Objective 1: This objective has been fully addressed and have been published in two peer-reviewed papers. The researcher has proposed to write a review on the recent main changes in phytoplankton dynamics in the Arctic Ocean (including under-ice phytoplankton dynamics) 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. Prof Kevin Robert 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 the international consortium (as proposed in the MSCA), the fellow compiled a comprehensive dataset from a large number of Arctic Ocean expeditions (i.e. covering the spring sea-ice covered period to summer sea-ice free conditions) 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.

Objective 2: Designing a coupled satellite-derived sea-ice/biogeochemical model adapted to under-ice Arctic waters is a complex task. This second objective is still in progress and will hopefully be operational before the end of the MSCA fellowship. Two major steps must be taken to succeed; to examine what might be available from satellite-derived sea-ice products and more importantly, relevant to biogeochemical cycles. Unfortunately, the first idea of using a 1D model will not be appropriate to incorporate the complexity of the environmental factors highlighted in the objective 1. The researcher will have to use a more complex 3D model and initiate collaborations with groups already having such models and expertise. Due to their complexity, these 3D models cannot be developed within the framework of the MSCA fellowship, so the researcher is in the process of contacting potential collaborators.

Objective 3: The fellow is currently leading an article summarizing everything we know about IUBs and highlighting their impact on marine Arctic carbon cycle for a special issue of Frontiers in Marine Science: \"\"Towards a Unifying Pan-Arctic Perspective of the Contemporary and Future Arctic Ocean\"\". The novelty of this work and its scope of application, which is perfectly in line with this objective 3, is to gather all the information obtained by autonomous platforms. Not only BGC-Argo floats will be discussed, as proposed in the proposal, but also other autonomous platforms (e.g., ITPs \"\"Ice-tethe\"

Final results

In terms of dissemination, the researcher will publish a dataset, which will be linked to the submitted paper in Elementa. Regarding the communication and my public engagement, the researcher continues to be involved with the press and local media (in particular with the outcome of one of a paper in Nature Communications). 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) 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.