The ability to forecast sea ice (both extent and thickness) and weather conditions are the major factors when it comes to safe marine transportation in the Arctic Ocean. This paper presents findings focusing on sea ice and weather prediction in the Arctic Ocean for navigation purposes, in particular along the Northeast Passage. Based on comparison with the observed sea ice concentrations for validation, the best performing Earth system models from the Intergovernmental Panel on Climate Change (IPCC) program (CMIP5—Coupled Model Intercomparison Project phase 5) were selected to provide ranges of potential future sea ice conditions. Our results showed that, despite a general tendency toward less sea ice cover in summer, internal variability will still be large and shipping along the Northeast Passage might still be hampered by sea ice blocking narrow passages. This will make sea ice forecasts on shorter time and space scales and Arctic weather prediction even more important.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-017-0951-5) contains supplementary material, which is available to authorized users.

International audienceThe suitability of the colorimetric method in a custom-made instrumental set-up and the commercial potentiometric SeaFET®electrode sensor to measure pH in surface oceanic water in the Arctic was investigated during the Chinese Arctic Research Expedition (CHINARE) in summer 2014. The instruments were set up in parallel on the on-board underway seawater supply for 65 days, enabling comparison in various conditions in the Arctic Ocean from the Chukchi Sea to the ice-covered high latitudes (81°N) and the open-water North-western Pacific Ocean. Overall, the instruments yielded pH datasets of similar high quality (method uncertainty ≤0.01

Abstract. The drastic reduction of the Arctic sea ice over the past 40 years is the most glaring evidence of climate change on Planet Earth. Among all the variables characterizing sea ice, the sea ice volume is by far the most sensitive one for climate change since it is decaying at the highest rate compared to sea ice extent and sea ice thickness. In 40 years the Arctic Ocean has lost about 3/4 of its sea ice volume at the end of the summer season corresponding to a reduction of both sea ice extent and sea ice thickness by half on average. From more than 16 000 km3, 40 years ago, the Arctic sea ice summer minimum dropped down to less than 4000 km3 during the most recent summers. Being a combination of Arctic sea ice extent and sea ice thickness, the Arctic sea ice volume is difficult to observe directly and accurately. We estimated cumulative Freezing-Degree Days (FDD) over a 9 month freezing time period (September to May each year) based on ERA Interim surface air temperature reanalysis over the whole Arctic Ocean and for the past 38 years. Then we compared the Arctic sea ice volume based on sea ice thickness deduced from cumulative FDD with Arctic sea ice volume estimated from PIOMAS (Pan Arctic Ice Ocean Modeling and Assimilation System) and from the ESA CRYOSAT-2 satellite. The results are strikingly similar. The warming of the atmosphere is playing an important role in contributing to the Arctic sea ice volume decrease during the whole freezing season (September to May). In addition, the FDD spatial distribution exhibiting a sharp double peak-like feature is reflecting the Multi Y ear Ice (MYI) versus First Year Ice (FYI) dual disposition typical of the Arctic sea ice cover. This is indicative of a significant contribution from the vertical ocean heat fluxes throughout the ice depending on MYI versus FYI distribution and the snow layer on top of it influencing the surface air temperature accordingly. In 2018 the Arctic MYI vanished almost completely for the first time ever over the past 40 years. The quasi complete disappearance of the Arctic sea ice is more likely to happen in summer within the next 15 years with broad consequences for Arctic marine and terrestrial ecosystems, climate and weather patterns on a planetary scale and globally on human activities.

A drastic ice decline in the Arctic Ocean, triggered by global warming, could generate rapid changes in the upper ocean layers. The ice retreat is particularly intense over the Canadian Basin where large ice free areas were observed since 2007. The CHINARE 2008 expedition was conducted in the Western Arctic (WA) ocean during a year of exceptional ice retreat (August–September 2008). This study investigates whether a significant reorganization of the primary producers in terms of species, biomass and productivity has to be observed in the WA as a result of the intense ice melting. Both pigments (HPLC) and taxonomy (microscopy) acquired in 2008 allowed to determine the phytoplanktonic distribution from Bering Strait (65° N) to extreme high latitudes over the Alpha Ridge (86° N) encompassing the Chukchi shelf, the Chukchi Borderland and the Canadian Basin. <br><br> Two different types of phytoplankton communities were observed. Over the ice-free Chukchi shelf, relatively high chl-<i>a</i> concentrations (1–5 mg m^&minus;3) dominated by 80 % of diatoms. In the Canadian Basin, surface waters are oligotrophic (<0.1 mg m^&minus;3) and algal assemblages were dominated by haptophytes and diatoms while higher biomasses (~0.4 mg m^&minus;3) related to a deep Subsurface Chlorophyll Maximum (SCM) are associated to small-sized (nano and pico) phytoplankton. The ice melting onset allows to point out three different zones over the open basin: (i) the ice free condition characterized by deep and unproductive phytoplankton communities dominated by nanoplankton, (ii) an extended (78°–83° N) Active Melting Zone (AMZ) where light penetration associated to the stratification start off and enough nutrient availability drives to the highest biomass and primary production due to both diatoms and large flagellates, (iii) heavy ice conditions found north to 83° N allowing light limitation and consequently low biomass and primary production associated to pico and nanoplankton. <br><br> To explain the poverty (Canadian Basin) and the richness (Chukchi shelf) of the WA, we explore the role of the nutrient-rich Pacific Waters, the bathymetry and two characteristics linked to the intense ice retreat: the stratification and the Surface Freshwater Layer (SFL). The freshwater accumulation induced a strong stratification limiting the nutrient input from the subsurface Pacific waters. This results in a biomass impoverishment of the well-lit layer and compels the phytoplankton to grow in subsurface. <br><br> The phytoplankton distribution in the Chukchi Borderland and north Canadian Basin, during the summer of exceptional ice retreat (2008), suggested when compared to in-situ data from a more ice covered year (1994), recent changes with a decrease of the phytoplankton abundance while averaged biomass was similar. The 2008 obtained phytoplankton data in the WA provided a state of the ecosystem which will be useful to determi...