Climate and ocean changes in Arctic-subarctic environments

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The research program concerns the variability of climate, ocean and environments at high latitudes of the Northern Hemisphere, and their recording by sedimentary archives. It will address fundamental questions about i) the resilience of Arctic sea ice under "warm" climates of the past, ii) the ocean circulation patterns in response to the opening/closure of the Arctic gateways and iii) the pre-Anthropogenic baseline conditions in the Arctic-subarctic realm. Some focus will be put on the sea ice cover, which is a critical climate parameter through ice-albedo feedback responsible for Arctic amplification. The possible disappearance or resilience of Arctic sea ice and their impact on the biota and global climate are critical issues that need to be urgently examined. Whereas the recent decline of Arctic sea ice led to hypothesize the disappearance of perennial ice within 30 years, the rarity of sea ice data prior to satellite observations prevents assessing its natural variability. Moreover, paradoxical indication for multi-year sea ice in the Arctic during warm episodes of the last millions of years, suggests that Arctic sea ice might be a resilient feature in the Late Cenozoic climate system. Similarly, the ocean response to the ongoing warming is not unequivocal, especially in the subarctic basins as the freshwater budget of the Arctic Ocean and its exchanges with the North Atlantic control heat fluxes, salinity, density and convection, i.e., the North Atlantic thermohaline circulation. As a contribution to international initiatives, I intend to reconstruct climate and ocean conditions in the Arctic-subarctic realm, notably for documenting the Earth’s system response under extreme conditions. Special attention will be given to the early Holocene (~10-6 ka), and warm interglacial stages of the Quaternary marked by high insolation, and to the Pliocene (~5.3-2.5 Ma) when forest extended into the Canadian Arctic and atmospheric carbon dioxide peaked at about 400 ppmv. To meet these objectives, access to marine sedimentary archives from Arctic and subarctic seas are needed. Sediments to analyze include cores from ODP (Ocean Drilling Program) and IODP (Integrated ODP) in addition to cores to be collected within the frame of international expeditions. From a methodological point of view, the reconstruction of climate and ocean parameters will be based on the analysis of organic-walled microfossils, notably dinoflagellate cysts, as tracers of planktonic production and sea-surface conditions, and pollen and spores, as proxies for land-sea correlation and terrestrial climate reconstructions, in addition to complementary sedimentological, isotopic and geochemical analyses. Aside the main stream of research, some attention will be paid to ocean and environmental changes over the last centuries, with the aim to fill the gap between instrumental and sedimentary records and to better calibrate quantitative reconstructions from proxies. This work is needed to determine pre-Anthropocene baseline conditions (i.e., prior to instrumental records) and thus improve estimates of anthropogenic trends. It will also permit to assess life-threatening environmental changes (eutrophication, hypoxia, red tides) in coastal settings and will provide a clue on their natural vs human-driven causes. The research program is tightly linked to national and international initiatives (VITALS, ArcTrain, PMIP, IODP) aiming at the monitoring and forecasting of ocean and climate changes in Arctic-subarctic environments, which is indispensable for sustainable development of high latitude regions. It will contribute to the training of students of all levels to address complex issues related to Arctic-subarctic climate change and/or coastal processes.