The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early-21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming.

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[1] Dissolved organic carbon (DOC) and in situ fluorescence were measured along with hydrographic parameters in the Greenland, Iceland, and Norwegian Seas (Nordic Seas). Surface (<100 m) concentrations of DOC ranged from 60 to 118 mM with elevated values in the East Greenland Current (EGC) which transports water from the Arctic Ocean to the North Atlantic. EGC surface waters also showed a pronounced fluorescence maximum between 30 and 120 m depth in all EGC sections indicating the abundance of Arctic river derived DOC in this current. Based on fluorescence we estimated that 20-50% of the annual river discharge to the Arctic Ocean was exported in the EGC. The fluorescence maximum was typically associated with salinity around 33 and temperatures below À1°C which are characteristic of surface and upper halocline water in the Arctic Ocean. The elevated fluorescence in this water mass suggests a strong Eurasian shelf component and also suggests that in situ fluorescence could be used to trace Eurasian shelf water in the central Arctic Ocean. DOC concentrations in the Nordic Sea basins (>1000 m) were relatively high ($50 mM DOC) compared with other ocean basins indicating active vertical transport of DOC in this region on decadal timescales. Based on existing vertical transport estimates and 15 mM of semilabile DOC we calculated an annual vertical net DOC export of 3.5 Tg C yr À1 in the Greenland Sea and about 36 Tg C yr À1 for the entire Arctic Mediterranean Sea (AMS) including the Greenland-Scotland Ridge overflow. It appears that physical processes play a determining role for the distribution of DOC in the

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Water of Pacific origin, entering the Arctic Ocean through the Bering Strait, exits the Arctic Ocean through the Canadian Archipelago and the Fram Strait. The amount and timing of Pacific Water export through these gates depend on the upper circulation of the Arctic Ocean and react accordingly on changes. Nutrient and hydrographic data from four cruises to the area north of the Fram Strait in 1984, 1990, 1997, and 2004 show that substantial changes have occurred lately in the amount of Pacific Waters delivered to the Fram Strait and hence further to the Atlantic Ocean. While the data from 1984, 1990, and 1997 all showed considerable amounts of Pacific Water above the shelf and slope northeast of Greenland, this strong signal had completely vanished in 2004. The arrival of a previously not observed cold halocline layer at the area can be recognized in 1997.