RATIONALE
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The Arctic world is experiencing unprecedented change under the double pressure of climate change and modernization. The current pace of Arctic warming now exceeds the most pessimistic scenarios of climate modellers. Rapid economic, social and political development coincides with this transformation of the Arctic environment. The exploration and exploitation of new mineral and oil resources accelerate. As they move towards self-governance, northern communities face critical health, education and economic issues. National frontiers in and around the central Arctic Ocean are being defined and negotiated. New sea-lanes are opening, facilitating access to resources. As a result, sovereignty issues multiply and magnify, and circum-Arctic nations increase their military presence in the region. Such on-going transformation poses environmental, socio-economic and strategic challenges that imperatively require a vastly improved understanding of the Arctic Ocean, its ecosys-tems, its resources, and its role in the global Earth system. Green Edge contributes to this challenge. A small number of research initiatives have been dedicated over the last decades to the study of the spring phytoplankton bloom (PSB) in the Arctic. They provided a valuable basic understanding of this phenomenon. Green Edge is the first study that addresses the Arctic PSB from the level of fundamental physical, chemical and biological processes to that of ecosystem (including Man), from small to pan-Arctic spatial scales, and from seasonal to multidecadal temporal scales in the past, present and future.

In Green Edge, we focus on primary productivity and on the fate of organic matter produced by phytoplankton during the most productive period of the year: spring. Green Edge is also partly motivated by the recent discovery that phytoplankton blooms may occur more extensively and more often under the ice-pack. Green Edge will contribute to the major societal challenge of efficient resource management and adaptation to climate change, through a better understanding and anticipation of environmental change. We will address significant knowledge gaps in Arctic marine biogeochemical cycles and the food web, and their linkages with local human populations. Green Edge is a large multidisciplinary project that brings together concepts extending from oceanography to whole-ecosystems, to impact on society. Green Edge will significantly contribute to the new French Arctic Initiative, which is currently being implemented (www.chantier-arctique.fr).