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Warm Atlantic Water reaches the Arctic Ocean via two gateways: the Barents Sea Opening (BSO) and Fram Strait. Here, we study the near‐surface flow of the Atlantic Water in the Nordic Seas and its fractionation between these Arctic gateways, using simulated Lagrangian trajectories based on satellite altimetry for 1994–2018. Lagrangian particles are released in the eastern Nordic Seas, where Atlantic Water flows poleward in two current cores: an inner branch along the Norwegian Continental Slope and an outer sea ward branch. The trajectories toward Fram Strait and the BSO are, in an averaged sense, largely steered by the bottom topography, and on inter‐annual timescales we find an anticorrelation in the number of particles that reach the two gateways. Most of the particles released in the inner branch enter the Barents Sea and most of the particles seeded in the outer branch reach Fram Strait. However, there is a significant cross‐over of particles from the outer to the inner branch in the Lofoten Basin, and nearly half of the total number of particles entering the BSO originate in the outer branch. This cross‐over is accomplished solely by the time‐fluctuating part of the velocity field, and it becomes stronger when the eddy kinetic energy in the Lofoten Basin is anomalously high. Thus, the outer branch may, via processes in the Lofoten Basin, be important for Barents Sea climate variability. Plain Language Summary: Relatively warm water from the Atlantic Ocean flows northward in the eastern Nordic Seas and enters the Arctic Ocean through two passages: the Fram Strait and the western opening of the Barents Sea. The effect of this warm water inflow on the ice‐covered Arctic Ocean depends on how much of the flow enters through each passage. Here, we use satellite observations of surface currents to trace how parcels of warm Atlantic Waters move in the Nordic Seas. Our main finding is that Atlantic Water in the western, offshore branch can end up entering Barents Sea, a "hotspot" of the ongoing rapid high‐latitude climatic change. The amount of heat following this pathway into the Arctic depends on the strength and number of ocean eddies in the Lofoten Basin. We conclude that changes in the Arctic, including its sea ice cover, will partly depend on changes in the eddies in this sub‐Arctic basin. Key Points: We study the fractionation of Atlantic Water between the Barents Sea Opening and Fram Strait using a Lagrangian approach on altimetryAlmost 50% of the particles that reach the Barents Sea Opening originate in the western branch carrying Atlantic Water in the Nordic SeasThese particles cross the Lofoten Basin and their fate depends on the vigorous mesoscale eddy mixing in the region [ABSTRACT FROM AUTHOR]

A large amount of warm Atlantic water (AW) enters the Arctic as a boundary current through Fram Strait (West Spitsbergen Current [WSC]) and is the major oceanic heat source to the Arctic Ocean. Along the north‐western Svalbard shelf, the WSC splits into the shallow Svalbard Branch, the Yermak Branch that follows the slope of the Yermak Plateau, and the Yermak Pass Branch flowing across the plateau. The WSC has previously been studied using moorings, dedicated oceanographic transects, and models. In this study, we mapped the circulation patterns and AW flow around Svalbard using Vessel‐Mounted Acoustic Doppler Current Profiler data from multiple surveys during four consecutive summers (2014–2017). Despite the scattered nature of this compiled data set, persistent circulation patterns could be discerned. Spatial interpolation showed a meandering boundary current west of Svalbard and a more homogeneous AW flow, centered around the 1,000‐m isobath north of Svalbard. In all summers, we observed a northward jet between 79 and 80°N and the 1,000‐ and 500‐m isobaths, before the WSC divided into the three branches. North of Svalbard, the shallow Svalbard Branch reunited with the Yermak Pass Branch between 10 and 15°E and a part of the AW circulated within Hinlopen Trench. The calculated volume transport of 2 Sv in the upper 500 m compares well with model results and previous observations. Our results further show that the Yermak Pass Branch can be as important as the Svalbard Branch in transporting AW across the Yermak Plateau during summer. Plain Language Summary: We mapped how seawater flows from the Atlantic into the Arctic Ocean around the Svalbard archipelago. To know where and how much water flows from the Atlantic into the Arctic Ocean is important because Atlantic water is the major source of heat, nutrients, and plankton for the Arctic Ocean. Heat from Atlantic water plays a role in the increased melting of sea ice, and the nutrients and plankton drifting with the currents are a major food supply for the Arctic marine ecosystem. We mapped the ocean currents with acoustic current meters that are mounted to research vessels that surveyed the area west and north of the Svalbard archipelago. We found that the Atlantic water flowing around Svalbard can take three different pathways: the shallow Svalbard Branch close to the north‐western edge of Svalbard, the Yermak Branch that follows the slope of an underwater plateau north‐west of Svalbard, and the Yermak Pass Branch that flows across the plateau and which has not been observed in summer before. We also showed that Atlantic water circulates within Hinlopen trench, a large passage splitting the archipelago, which could create a local ecological hot spot due to the favorable nutrient and plankton supply. Key Points: Atlantic water transport west and north of Svalbard estimated from sparse VM‐ADCP data is 2 Sv in summerYermak Pass Branch was observed in summer and can be as important as the Svalbard Branch for Atlantic water transportAtlantic water circulates within Hinlopen trench and strait [ABSTRACT FROM AUTHOR]

In this study 129I and 236U concentrations in seawater samples collected onboard R/V Polarstern during the PS100 expedition in the Fram Strait in 2016 are presented. The overall aim of the study was to investigate the distribution of these long‐lived radionuclides along the transect located at 79°N. The combination of both radionuclides was used for the first time in the Fram Strait to trace ocean circulation pathways of Atlantic waters. Results show that both 129I and 236U concentrations as well as 236U/238U ratios are about two times higher (> 600 × 107 at kg(−1), > 20 × 106 at kg(−1), and 2.8 × 10−9, respectively) in the cold and fresh outflowing surface waters from the Arctic Ocean (Polar Surface Water, PSW) compared to inflowing Atlantic origin waters (300 × 107 at kg(−1)129I, 12 × 106 at kg(−1)236U, and 1.4 × 10−9 236U/238U). A comparison with the different 129I and 236U input functions for the Atlantic branches entering the Arctic Ocean reveals that the middepth Atlantic origin waters outflowing the Arctic Ocean show more influence of the Barents Sea Branch Water than the Fram Strait Branch Water. The high radionuclide concentrations observed in the PSW indicate substantial influence of the Norwegian Coastal Current. This current carries a significantly larger proportion of 129I and 236U releases from European reprocessing plants than the aforementioned Atlantic branches. We estimate surface water transit times from the northern Norwegian Coast through the Arctic to the PSW of 12–19 years, less than for the middepth Barents Sea Branch Water (16–23 years). Plain Language Summary: In this work we reconstructed the circulation of Atlantic waters in‐ and outflowing the Arctic Ocean through one of the main gates connecting these two oceans: the Fram Strait, located between Greenland and Svalbard. We measured the long‐lived artificial radionuclides 129I and 236U to track the different water masses. These two radionuclides are present in the marine environment after the nuclear weapon tests (1950s‐1960s) and from two European nuclear reprocessing plants (from 1960's until today). In particular the input of 129I from these two reprocessing plants changed over time and can therefore also be used to estimate travel times of water masses. We collected 140 seawater samples at various depths from the Fram Strait in summer 2016. Our results depict higher concentrations of 129I and 236U in the waters outflowing the Arctic Ocean compared to those entering the polar region through the Fram Strait. The combination of 129I and 236U allowed us to distinguish between three main branches of Atlantic origin waters outflowing the Arctic Ocean having different travel times through the Arctic Ocean. We proved that 129I and 236U have a great potential as tracers to understand ocean circulation and travel times in the Arctic and North Atlantic oceans. Key Points: In 2016, inflowing Atlantic waters to the Arctic Ocean have lower 129I and 236U concentrations than outflowing Arctic watersHigh 129I and 236U in outflowing surface Arctic waters indicate substantial influence from the Norwegian Coastal CurrentCombination of 129I and 236U allowed for an estimation of transit times for Atlantic branches through the Arctic Ocean to the Fram Strait [ABSTRACT FROM AUTHOR]

Abstract: Atlantic Water (AW) transported from the Nordic Seas is the major source of oceanic heat to the Arctic Ocean. Based on results from the TOPAZ reanalysis, a regional coupled ice‐ocean data assimilation system, we show that interannual variability of AW temperature in the Fram Strait (FS) is associated with the strength of the Greenland Sea gyre (GSG) circulation. The response of the GSG to the anomalous wind stress curl over the Nordic Seas modifies the AW inflow and thus influences the variability of AW temperature in the FS. A stronger (weaker) GSG circulation increases (decreases) the AW flow speed toward FS, leading to increased (decreased) oceanic heat content and higher (lower) AW temperature therein. This implies that the Nordic Seas circulation is not only a passive conduit of AW, but its response to overlying atmospheric variability can also largely influence the AW temperature in the FS by modifying the transport of AW. [ABSTRACT FROM AUTHOR]

The circulation and water mass properties in the Eurasian Basin are discussed based on a review of previous research and an examination of observations made in recent years within, or parallel to, DAMOCLES (Developing Arctic Modeling and Observational Capabilities for Long-term Environmental Studies). The discussion is strongly biased towards observations made from icebreakers and particularly from the cruise with R/V Polarstern 2007 during the International Polar Year (IPY). Focus is on the Barents Sea inflow branch and its mixing with the Fram Strait inflow branch. It is proposed that the Barents Sea branch contributes not just intermediate water but also most of the water to the At lantic layer in the Amundsen Basin and also in the Makarov and Canada basins. Only occasionally would high temperature pulses originating from the Fram Strait branch penetrate along the Laptev Sea slope across the Gakkel Ridge into the Amundsen Basin. Interactions between the Barents Sea and the Fram Strait branches lead to formation of intrusive layers, in the Atlantic layer and in the intermediate waters. The intrusion characteristics found downstream, north of the Laptev Sea are similar to those observed in the northern Nansen Basin and over the Gakkel Ridge, suggesting a flow from the Laptev Sea towards Fram Strait. The formation mechanisms for the intrusions at the continental slope, or in the interior of the basins if they are reformed there, have not been identified. The temperature of the deep water of the Eurasian Basin has increased in the last 10 yr rather more than expected from geothermal heating. That geothermal heating does influence the deep water column was obvious from 2007 Polarstern observations made close to a hydrothermal vent in the Gakkel Ridge, where the temperature minimum usually found above the 600-800m thick homogenous bottom layer was absent. However, heat entrained from the Atlantic water into descending, saline boundary plumes may also contribute to the warming of the deeper layers. [ABSTRACT FROM AUTHOR]

The circulation and water mass properties in the Eurasian Basin are discussed based on a review of previous research and an examination of observations made in recent years within, or parallel to, DAMOCLES (Developing Arctic Modelling and Observational Capabilities for Long-term Environmental Studies). The discussion is strongly biased towards observations made from icebreakers and particularly from the cruise with R/V Polarstern 2007 during the International Polar Year (IPY). Focus is on the Barents Sea inflow branch and its mixing with the Fram Strait inflow branch. It is proposed that the Barents Sea branch contributes not just intermediate water but also most of the Atlantic layer that is found in the Amundsen Basin and also in the Makarov and Canada basins. Only occasionally would high temperature pulses originating from the Fram Strait branch penetrate along the Laptev Sea slope across the Gakkel Ridge into the Amundsen Basin. Interactions between the Barents Sea and the Fram Strait branches lead to formation of intrusive layers, in the Atlantic layer and in the intermediate waters. The intrusion characteristics found downstream north of the Laptev Sea are similar to those observed in the Northern Nansen Basin and over the Gakkel Ridge, implying a flow from the Laptev Sea towards Fram Strait. The formation mechanisms for the intrusions at the continental slope, or in the interior of the basins if they are reformed there, have not been identified. The temperature of the deep water of the Eurasian Basin has increased in the last 10 yr rather more than expected from geothermal heating. That geothermal heating does influence the deep water column was obvious from 2007 Polarstern observations made close to a hydrothermal vent in the Gakkel Ridge, where the temperature minimum usually found above the 600- 800m thick homogenous bottom layer was absent. However, heat entrained from the Atlantic water into descending boundary plumes may also contribute to the warming of the deeper layers. [ABSTRACT FROM AUTHOR]