Inflow Of Atlantic Water Research Articles

Footprints of Atlantification in the vertical distribution and diversity of gelatinous zooplankton in the Fram Strait (Arctic Ocean)

Gelatinous zooplankton (GZ), here understood as pelagic cnidarians and ctenophores, are an important component of marine ecosystems. Their diversity and distribution reflect local hydrological settings especially well, thus allowing the development of biotic indices for studying climate-mediated changes in the world’s oceans. The effects of global warming are most pronounced in the Arctic Ocean and have been further accelerated by the strengthening inflow of relatively warm Atlantic waters (AtW) via the Fram Strait, referred to as Atlantification. Here, we use the GZ distribution to describe the current state of Atlantic water inflow into the Arctic Ocean and to discuss the future of this fragile ecosystem. For this purpose, we characterized the abundance, diversity, and demography of the GZ identified from vertically stratified samples (down to 1000 m) collected in the Fram Strait along two latitudinally parallel transects of varying influence of AtW. Overall, we identified 17 taxa, with Aglantha digitale, Dimophyes arctica and Mertensia ovum being the most abundant. We then contrasted our jellyfish and ctenophore data with both biotic and environmental ecosystem characteristics and analysed the associations between the GZ community and water mass distribution. We showed that the more abundant GZ community was found along the southern transect; that the sampling depth and bathymetric zone played the most important roles in structuring the GZ diversity; that water mass distribution affected GZ demography; and that AtW was dominated by A. digitale, that constituted 66% of the total GZ abundance. Our results, although temporarily limited, suggest that the Atlantification will promote the expansion of boreal species into the Arctic, and could lead to a less diverse, but more abundant GZ community in the future. In addition, we compare in detail the GZ community found in different water masses, at different depths, and in different bathymetric zones, and supported with literature data, discuss the future of the European Arctic under the scenario of increasing inflow of Atlantic water.

Dynamics of Spontaneous (Multi) Centennial‐Scale Variations of the Atlantic Meridional Overturning Circulation Strength During the Last Interglacial

AbstractRecent reconstructions of bottom water δ13C during the last interglacial (LIG) suggest short‐lived variability in the Atlantic meridional overturning circulation (AMOC). Spontaneous (multi) centennial‐scale variability of the AMOC simulated in the Earth system model of intermediate complexity iLOVECLIM are investigated for that period. The model simulates abrupt AMOC transitions occurring at 300 years frequency and correspond to a switch of the AMOC vigor between a strong (∼17 Sv) and a weak (∼11 Sv) state. The onset of these abrupt transitions is associated with changes in orbital forcings resulting in the decline of summer insolation in the high latitudes of the North Atlantic and affecting the sea ice cover in two key deep convection regions: (1) the northern Nordic Seas (NNS) and (2) the northwest North Atlantic (NWNA). Northward inflow of Atlantic surface water increases the convection depth in (1) and strengthens the Greenland Iceland Norway (GIN) Seas overturning circulation. Subsequent ocean‐atmosphere interactions involving sea ice, ocean heat release, anomalies of evaporation‐precipitation, and wind stress over the Nordic Seas lead also to an increase in deep convection in (2), followed by increase in the AMOC strength.

Spatial Patterns of Particles and Plankton in the Warming Arctic Fjord (Isfjorden, West Spitsbergen) in Seven Consecutive Mid-Summers (2013–2019)

The restructuring of planktonic communities towards an increasing share of small individuals is not only expected, but also already observed consequence of warming in the rapidly changing Arctic. Here we demonstrate a simultaneous study on the nano-, micro- and mesoplankton (divided into small and large), and corresponding size fractions of particles along a hydrographical gradient in the Isfjorden – the largest Spitsbergen fjord system. The sampling was performed in 7 following summers (2013-2019) from the main basin under the influence of Atlantic Waters (ISA station), up to Billefjorden – the innermost part affected by meltwaters from Nordenskioldbreen (BAB station). Our objective was to elucidate the composition and spatial patterns in distribution of plankton and particles (P&P) under various hydrographical regimes. Combining two laser-based measurements (LOPC and LISST) with standard plankton analysis allowed us to conclude that vertical hydrographical stratification and eddy activity were forcing either layered or patchy distribution of P&P. The concentrations of P&P measured by LISST (nano- and micro-) were lower than the abundance of the corresponding size fractions of protists, but they did not differ significantly among the stations due to different origin of P&P. Nevertheless, the decreasing trend in the abundance of both investigated mesoplankton fractions could be observed between the ISA and BAB stations, whereas the opposite tendency was noted for P&P. Moreover, the abundance of mesoplankton was equal to the concentrations of the corresponding size fractions of P&P at the ISA station and much lower than the LOPC counts at the BAB station, which points towards notable amount of marine aggregates in the glacial bay. Even if some observations alluded to P&P susceptibility to the local processes, the inter-annual variability in P&P distribution surpassed the differences between the sampling stations. It suggests that both the large-scale processes (i.e. intensified inflow of Atlantic Waters) and natural seasonal changes associated with subtle differences in sampling timing had a stronger influence on investigated plankton than local factors. This pioneering study, which links traditional and advanced methods, clearly demonstrated that such approach is convenient for tracking small-scale spatial patterns and inter-annual variability of P&P in the Arctic pelagial.

Variability and decadal trends in the Isfjorden (Svalbard) ocean climate and circulation – An indicator for climate change in the European Arctic

Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord’s climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SSTw/VTw: 0.7 ± 0.1/0.9 ± 0.3 °C 10 yr−1) and summer (SSTS/VTS: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr−1). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10 yr−1) and summer (0.7 ± 0.1 °C 10 yr−1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10 yr−1) and summer (0.07 ± 0.05 10 yr−1) suggest increased AW advection as a main reason for Isfjorden’s climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord’s impact on the local terrestrial climate.In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.

Reconstruction of Holocene oceanographic conditions in eastern Baffin Bay

Abstract. Baffin Bay is a semi-enclosed basin connecting the Arctic Ocean and the western North Atlantic, thus making out a significant pathway for heat exchange. Here we reconstruct the alternating advection of relatively warmer and saline Atlantic waters versus the incursion of colder Arctic water masses entering Baffin Bay through the multiple gateways in the Canadian Arctic Archipelago and the Nares Strait during the Holocene. We carried out benthic foraminiferal assemblage analyses, X-ray fluorescence scanning, and radiocarbon dating of a 738 cm long marine sediment core retrieved from eastern Baffin Bay near Upernavik, Greenland (Core AMD14-204C; 987 m water depth). Results reveal that eastern Baffin Bay was subjected to several oceanographic changes during the last 9.2 kyr. Waning deglacial conditions with enhanced meltwater influxes and an extensive sea-ice cover prevailed in eastern Baffin Bay from 9.2 to 7.9 ka. A transition towards bottom water amelioration is recorded at 7.9 ka by increased advection of Atlantic water masses, encompassing the Holocene Thermal Maximum. A cold period with growing sea-ice cover at 6.7 ka interrupts the overall warm subsurface water conditions, promoted by a weaker northward flow of Atlantic waters. The onset of the neoglaciation at ca. 2.9 ka is marked by an abrupt transition towards a benthic fauna dominated by agglutinated species, likely in part explained by a reduction of the influx of Atlantic Water, allowing an increased influx of the cold, corrosive Baffin Bay Deep Water originating from the Arctic Ocean to enter Baffin Bay through the Nares Strait. These cold subsurface water conditions persisted throughout the Late Holocene, only interrupted by short-lived warmings superimposed on this cooling trend.

Ventilation in the Arctic Ocean and the Role of Pacific Inflow Deduced From Transient Tracer Measurements

AbstractDuring the seventh Chinese National Arctic Research Expedition, measurements of CFC‐12 and SF6 were used to estimate ventilation time scales and anthropogenic CO2 (Cant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution (TTD) method. The profile distribution showed that there was a high CFC tongue entering through the Canada Basin in the intermediate layer (27.6 kg m−3 < σθ < 28 kg m−3), at latitudes between 75 and 85°N, related to the inflow of Atlantic water. The result shows that both intermediate and deep/bottom waters are better ventilated in the Arctic Ocean than in the Bering Sea. The mean age gradient of the Bering Sea Surface Water and Pacific water core of the southwest Canada Basin (24.7 < σθ < 26.2) could be a consequence of intensive mixing and entrainment of the inflow water from the Bering Sea. An expected difference in age between these areas was interpreted to reflect the transit time for the given water layers. Thus, a mean transit time from the Bering Sea (175.2–179.9°E, 59.7–61.6°N) to the western Arctic Ocean (151.6–158°W, 73.1–74.8°N) of 14.6 ± 4.6 years was estimated. The mean Cant column inventory in the upper 2,000 m was higher (~45 mol m−2) in the Arctic Ocean than in the Bering Sea (~25 mol m−2).

Topological Constraints by the Greenland–Scotland Ridge on AMOC and Climate

AbstractChanges in the geometry of ocean basins have been influential in driving climate change throughout Earth’s history. Here, we focus on the emergence of the Greenland–Scotland Ridge (GSR) and its influence on the ocean state, including large-scale circulation, heat transport, water mass properties, and global climate. Using a coupled atmosphere–ocean–sea ice model, we consider the impact of introducing the GSR in an idealized Earth-like geometry, comprising a narrow Atlantic-like basin and a wide Pacific-like basin. Without the GSR, deep-water formation occurs near the North Pole in the Atlantic basin, associated with a deep meridional overturning circulation (MOC). By introducing the GSR, the volume transport across the sill decreases by 64% and deep convection shifts south of the GSR, dramatically altering the structure of the high-latitude MOC. Due to compensation by the subpolar gyre, the northward ocean heat transport across the GSR only decreases by ~30%. As in the modern Atlantic Ocean, a bidirectional circulation regime is established with warm Atlantic water inflow and a cold dense overflow across the GSR. In sharp contrast to the large changes north of the GSR, the strength of the Atlantic MOC south of the GSR is unaffected. Outside the high latitudes of the Atlantic basin, the surface climate response is surprisingly small, suggesting that the GSR has little impact on global climate. Our results suggest that caution is required when interpreting paleoproxy and ocean records, which may record large local changes, as indicators of basin-scale changes in the overturning circulation and global climate.

Variations in eastern Mediterranean hydrology during the last climatic cycle as inferred from neodymium isotopes in foraminifera

The Nd isotopic compositions (εNd) of mixed planktonic foraminifera have been analyzed in two sediment cores collected in the Nile deep-sea fan in order to reconstruct past εNd of the Eastern Mediterranean Deep Water (EMDW) and to assess the relative contributions of Nile discharge and Modified Atlantic Water (MAW) inflow to the Eastern Mediterranean Sea hydrology, as well as their potential control on anoxic events over the last climatic cycle. The two foraminiferal εNd records are similar and display an increase in εNd values during the African Humid Periods. Superimposed on this precession-forced variability (insolation received by the Earth at low latitudes), the record of variations in foraminiferal εNd indicates a 2-unit decrease in εNd during the interglacial Marine Isotope Stages (MIS) 5 and 1 compared to glacial MIS6, 4, 3 and 2. The εNd results suggest that the long-term glacial to interglacial changes in Nd isotopic composition of EMDW were not entirely induced by variations in Nile River discharge and Saharan dust inputs. Decreases in εNd during MIS5 and MIS1 interglacials indicate an increase in the contribution of unradiogenic MAW to the eastern Mediterranean Sea related to high sea-level stands and greater seawater exchange between the North Atlantic and Mediterranean basins. In addition, radiogenic seawater εNd values observed during African Humid Periods (and sapropel events) are associated with an intensification of Nile discharge and an increase in residence time of deep-water masses in the eastern Mediterranean Sea, which induces an increase in the interaction between deep-water masses and radiogenic sediments along the margin of the eastern Mediterranean Sea. Results confirm that an intensification of the hydrological exchanges between the western and eastern Mediterranean basins during high sea-level stand and the subsequent higher proportion of Atlantic Water in the Levantine Basin may have preconditioned the eastern Mediterranean Sea to sapropel depositions during the last climatic cycle.

Climate change impact on primary production and phytoplankton taxonomy in Western Spitsbergen fjords based on pigments in sediments

Abstract Arctic climate changes are of global significance. This work investigates the influence of climate change on primary production and phytoplankton taxonomic composition in the western Spitsbergen fjords over the last century, using pigments in sediments. Nine sediment cores were analysed for chloropigment and carotenoid contents, and the five found to be richest in pigments were dated (210Pb, 137Cs) and analysed for additional parameters (Corg, Ntot, δ13C, grain size). The three well-dated cores, representing the last 70–130 y, were selected for tracking primary production and phytoplankton taxonomy changes in the past. The sum of chloropigments-a (∑Chlns-a) in the undisturbed sediments is a good marker of primary production in the adjacent Spitsbergen fjord waters. The sum of 19′-hexanoyloxyfucoxanthin and 19′-hexanoyloxy-4-ketofucoxanthin to diatoxanthin ratio (∑Hexcs/Diato) in sediments is proposed as a proxy of changes in haptophytes to diatom and dinoflagellate proportions, connected with climate variability. ∑Chlns-a and ∑Hexcs/Diato ratio sediment profiles have shown that the impact of global warming on primary production and phytoplankton taxonomic composition is observed even in the north of Spitsbergen. In the most northern studied site, Raudfjorden, visible effects of warming started about a decade later than in Kongsfjorden. Recent high primary production in Kongsfjorden and Raudfjorden is related to a high proportion of haptophytes compared to diatoms and dinoflagellates, linked to warm Atlantic Water inflow. In Hornsund, primary production was also observed to have increased, but not as rapidly as at other sites, probably due to a greater influence of cold Arctic Water.

Multiproxy evidence of the Neoglacial expansion of Atlantic Water to eastern Svalbard

Abstract. The main goal of this study is to reconstruct the paleoceanographic development of Storfjorden during the Neoglacial (∼4 cal ka BP). Storfjorden is one of the most important brine factories in the European Arctic and is responsible for deepwater production. Moreover, it is a climate-sensitive area influenced by two contrasting water masses: warm and saline Atlantic Water (AW) and cold and fresh Arctic Water (ArW). Herein, a multiproxy approach was applied to provide evidence for existing interactions between the inflow of AW and sea ice coverage, which are the major drivers of environmental changes in Storfjorden. The sedimentary and microfossil records indicate that a major reorganization of oceanographic conditions in Storfjorden occurred at ∼2.7 cal ka BP. The cold conditions and the less pronounced presence of AW in Storfjorden during the early phase of the Neoglacial were the prerequisite conditions for the formation of extensive sea ice cover. The period after ∼2.7 cal ka BP was characterized by alternating short-term cooling and warming intervals. Warming was associated with pulsed inflows of AW and sea ice melting that stimulated phytoplankton blooms and organic matter supply to the bottom. The cold phases were characterized by heavy and densely packed sea ice, resulting in decreased productivity. The ancient environmental DNA (aDNA) records of foraminifera and diatoms support the occurrence of the major pulses of AW (∼2.3 and ∼1.7 cal ka BP) and the variations in sea ice cover. The episodes of enhanced AW inflow were marked by an increase in the percentage of DNA sequences of monothalamous foraminifera associated with the presence of fresh phytodetritus. Cold and less productive intervals were marked by an increased proportion of monothalamous taxa known only from environmental sequencing. The diatom aDNA record indicates that primary production was continuous during the Neoglacial, regardless of the sea ice conditions. However, the colder periods were characterized by the presence of diatom taxa associated with sea ice, whereas the present-day diatom assemblage is dominated by open-water taxa.

Bathymetry constrains ocean heat supply to Greenland’s largest glacier tongue

Mass loss from the Greenland ice sheet has increased over the past two decades, currently accounting for 25% of global sea-level rise. This is due to increased surface melt driven by atmospheric warming and the retreat and acceleration of marine-terminating glaciers forced by oceanic heat transport. We use ship-based profiles, bathymetric data and moored time series from 2016 to 2017 of temperature, salinity and water velocity collected in front of the floating tongue of the 79 North Glacier in Northeast Greenland. These observations indicate that a year-round bottom-intensified inflow of warm Atlantic Water through a narrow channel is constrained by a sill. The associated heat transport leads to a mean melt rate of 10.4 ± 3.1 m yr–1 on the bottom of the floating glacier tongue. The interface height between warm Atlantic Water and colder overlying water above the sill controls the ocean heat transport’s temporal variability. Historical hydrographic data show that the interface height has risen over the past two decades, implying an increase in the basal melt rate. Additional temperature profiles at the neighbouring Zachariae Isstrom suggest that ocean heat transport here is similarly controlled by a near-glacier sill. We conclude that near-glacier, sill-controlled ocean heat transport plays a crucial role for glacier stability. Ocean heat transport underneath the floating tongue of 79 North Glacier, Greenland, is controlled by a sill in the inflow channel, according to ship-based and mooring data as well as bathymetric data.

Impact of Atlantic water inflow on winter cyclone activity in the Barents Sea: insights from coupled regional climate model simulations

The impact of the Atlantic water inflow (AW inflow) into the Barents Sea on the regional cyclone activity in winter is analyzed in 10 ensemble simulations with the coupled Arctic atmosphere-ocean-sea ice model HIRHAM-NAOSIM for the 1979–2016 period. The model shows a statistically robust connection between AW inflow and climate variability in the Barents Sea. The analysis reveals that anomalously high AW inflow leads to changes in static stability and wind shear in the lower troposphere, and thus favorable conditions for cyclogenesis in the Barents/Kara Seas. The frequency of occurrence of cyclones, but particularly of intense cyclones, is increased over the Barents Sea. Furthermore, the cyclones in the Barents Sea become larger (increased radius) and stronger (increased intensity) in response to an increased AW inflow into the Barents Sea, compared to years of anomalously low AW inflow.

Pelagic occurrences of the ice amphipod Apherusa glacialis throughout the Arctic.

Apherusa glacialis is a common, sea ice-associated amphipod found throughout the Arctic Ocean and has long been considered permanently associated with the sea ice habitat. However, pelagic occurrences of A. glacialis have also been reported. It was recently suggested that A. glacialis overwinters at depth within the Atlantic-water inflow near Svalbard, to avoid being exported out of the Arctic Ocean through the Fram Strait. This study collated pelagic occurrence records over a 71-year period and found that A. glacialis was consistently found away from its presumed sea ice habitat on a pan-Arctic scale, in different depths and water masses. In the Svalbard region, A. glacialis was found in Atlantic Water both in winter and summer. Additionally, we analyzed A. glacialis size distributions throughout the year, collected mostly from sea ice, in order to elucidate potential life cycle strategies. The majority of young-of-the-year A. glacialis was found in the sea ice habitat during spring, supporting previous findings. Data on size distributions and sex ratios suggest a semelparous lifestyle. A synchronous seasonal vertical migration was not evident, but our data imply a more complex life history than previously assumed. We provide evidence that A. glacialis can no longer be regarded as an autochthonous sympagic species.

Foraminiferal and dinocyst associations as indicators of the Holocene environmental changes at the Cambridge Strait, Franz Josef Land

Herein we report the first decadal to centennial–scale resolution data on foraminiferal and dinocyst assemblages from core AMK-5454 collected in the hard-to-reach Cambridge Strait, Franz Josef Land, and on corresponding paleoenvironments over the last 9.2 ka. The dinocyst and foraminiferal assemblages from the core are rather diverse through the Holocene and represented by 24 and 33 taxa, respectively. The most active hydrodynamics and probably Atlantic Water (AW) inflow are suggested by the enhanced values of autotrophic dinocysts and epibenthic species, as well as Melonis barleeanus, from 9.2 to 6.3 cal ka BP. Specific benthic assemblages indicate high-productivity frontal conditions at site location from 6.3 to 4.1 cal ka BP. AW influx from the Franz Victoria Trough to the Cambridge Strait in subsurface to bottom layer, below the very cold Arctic Water and dense sea ice, is documented by enhanced % Cassidulina teretis over the last 4.5 ka.

Weekly variability of hydrography and transport of northwestern inflows into the northern North Sea

Abstract Quantifying the variability of North Sea inflows and understanding the temporal variability of their physical properties are essential for understanding, modelling and managing the ecosystems of the North Sea. The Joint North Sea Information System (JONSIS) line hydrographic section crosses the path of the main inflows of Atlantic water into the northwestern North Sea. We use observations from an autonomous underwater glider to observe the inflows at high spatial and temporal resolutions. The glider completed 10 partial sections of the JONSIS line in October and November of 2013. Key water masses of the inflow are identified; their spatial distribution varies greatly from section to section. This is not apparent from long-running ship surveys of the JONSIS line, which are generally several months apart. In particular, the distribution of water of most recent Atlantic origin varies as summer stratification decays throughout autumn: at the start of the deployment it is present as a thin layer beneath the thermocline; at the end of the deployment, it occupies the full depth of the water column. Thermohaline flow, i.e. that which is driven by horizontal density gradients, is focused into three or four jets (approximately 10 km wide). Jets as narrow as these have not previously been observed in the region. We also observe baroclinic eddies. The thermohaline transport of the inflows is compared with the absolute transport that is derived by referencing geostrophic shear to the glider's dive-average current. Thermohaline transport (approximately 0.2 Sv) is consistently smaller than absolute transport (approximately 0.5 Sv). The week-to-week variability in hydrography and flow structure identified in this study is relevant to on-going efforts to define a background state against which the nature of anthropogenic changes can be assessed, and future modelling efforts should represent the spatial and temporal variability that we have identified.

Vertical Structure and Seasonal Variability of the Inflow to the Lofoten Basin Inferred From High‐Resolution Lagrangian Simulations

AbstractThe Lofoten Basin in the eastern Nordic Seas plays a central role in modifying the warm Atlantic Water inflow toward the Arctic Ocean. Here, the Atlantic Water experiences increased residence times, cooling, and substantial transformation. In this study, we investigate the Atlantic Water inflow pathways to the Lofoten Basin and their vertical and seasonal variations using 2‐D and 3‐D Lagrangian simulations forced by a high‐resolution ocean model. Atlantic Water enters the basin from all directions, but we find two main inflow pathways at all vertical levels, one close to the Lofoten Escarpment in the southeast, associated with the Slope Current, and another close to the Helgeland Ridge in the southwest, associated with the Front Current. The surface inflow exhibits a stronger seasonal forcing than the inflow at depth as well as a stronger heat loss that is dominated by water masses entering the basin from the south. At deeper levels, the warm inflow from the east cools, while the relatively colder inflow from the west warms. The 2‐D and 3‐D synthetic trajectories show similar pathways. However, they are affected differently by the seasonal signal, giving different heat exchange patterns. Our results have implications for how results from Lagrangian observations in the region should be interpreted.

Mean Structure and Seasonality of the Norwegian Atlantic Front Current Along the Mohn Ridge From Repeated Glider Transects

AbstractThe poleward flow of Atlantic Water in the Nordic Seas forms the upper limb of the meridional overturning circulation driving an important heat transport. The Norwegian Atlantic Front Current along the Mohn Ridge between the Greenland and Norwegian Seas is characterized for the first time, using repeated sections over 14 months from autonomous underwater gliders and two research cruises. The Norwegian Atlantic Front Current follows the 2,550‐m isobath with a width of 38 ± 2 km and absolute geostrophic velocities peaking at 0.56 ± 0.03 m s−1. The mean transport of Atlantic Water is 3.2 ± 0.2 Sv (equivalent to temperature transport of 71 ± 5 TW). Seasonal variability was observed with a magnitude of 0.8 Sv and maximum values in the fall. The deep currents at 1,000 m explained most of this seasonal variation and were anticorrelated with time‐integrated wind stress curl over the Lofoten Basin. Part of this flow might recirculate within the Lofoten Basin, while the rest continues toward the Arctic.

Postglacial paleoceanography of the western Barents Sea: Implications for alkenone-based sea surface temperatures and primary productivity

The increasing influence of Atlantic Water (AW) in the Barents Sea, a process known as “Atlantification”, is gradually decreasing sea ice cover in the region. Ongoing global climate warming is likely to be one of its drivers, but to further understand the role of natural variability and the biogeochemical impacts of the inflow of AW into the western Barents Sea, we reconstructed sea surface temperatures (SSTs) and primary productivity in Storfjordrenna, a climatically sensitive area south of Spitsbergen, between approximately 13,950 cal yr BP and 1300 cal yr BP. The alkenone U37K* proxy has been applied to reconstruct SSTs, and the alkenone accumulation rate in marine sediments has been used to infer changes in primary productivity. Our data show that the SST increase was concomitant with the progressive loss of sea ice cover and an increase in primary productivity in the western Barents Sea. We interpret these changes as reflecting the increasing influence of AW in the area as the ice sheets retreated in Svalbard. The transition from the Arctic to the Atlantic domain first occurred after 11,500 cal yr BP, as the Arctic Front moved eastward of the study site but with considerable variability in surface ocean conditions. High SSTs at approximately 6400 cal yr BP may have led to limited winter surface cooling, likely inhibiting convective mixing and the return of nutrients to the euphotic zone and/or enhanced organic matter consumption by zooplankton due to an earlier light signal in the ice-free Storfjordrenna. During the late Holocene (3600-1300 cal yr BP), low insolation facilitated sea ice formation and thus brine production. The former may have launched convective water mixing and increased nutrient resupply to the sea surface, consequently enhancing primary productivity in Storfjordrenna. We propose that, on the basis of the paleoceanographic evidence, the modern increasing inflow of warm AW and the disappearance of pack ice on the Eurasian continental shelf are likely to weaken convective water mixing and decrease primary production in the region.

Influence of Phytoplankton Advection on the Productivity Along the Atlantic Water Inflow to the Arctic Ocean

Northwards flowing Atlantic waters transport heat, nutrients, and organic carbon in the form of zooplankton into the eastern Greenland Sea and Fram Strait. Less is known of the contribution of phytoplankton advection in this current, the Atlantic Water Inflow (AWI) spanning from the North Atlantic to the Arctic Ocean. The in situ and advected primary production was estimated by using the physical-biological coupled SINMOD model, from northern Norway coast (along the Norwegian Atlantic Current, NAC), the West Spitsbergen Current (WSC) and the entrance to the Arctic Ocean in northern Fram Strait. The simulation results show that changes in phytoplankton biomass at any one location along the AWI are supported primarily by advection. This advection is 5-50 times higher than the biomass photosynthesized in situ, seasonally variable, with minimum contribution in June, at the time of maximum in situ primary production. Advection in the NAC transports phytoplankton biomass from areas of higher production in the south, contributing to the maintenance of phytoplankton productivity further north. In situ productivity further decreases north of Svalbard Archipelago, at the entrance to the Arctic Ocean. Excess in situ annual production in northern WSC is exported to the Arctic Ocean during the growth season (April to September). The balance between in situ and advected primary production defines three main regions along the AWI, presumably modulated by the spatial and temporal variability of copepod grazing. As the sea ice reduces its annual extent and warmer waters enter the Arctic Ocean, ecological characteristics of the ice-free WSC with its AWI signature could extend north and east of Svalbard and into the central Arctic. Advection thus constitutes an important link connecting marine ecosystems of the Arctic and Atlantic Ocean, mainly at the gateways.

Holocene environmental changes in Dicksonfjorden, west Spitsbergen, Svalbard

Multi-proxy analyses of two sediment cores from Dicksonfjorden were performed to reconstruct Holocene environmental conditions in this northern branch of Isfjorden, the largest fjord system in Svalbard. Factors affecting the depositional processes include shifts in sources of sediments, ice rafting and regional glacio-isostatic rebound. Sediments were derived from Palaeozoic siliciclastics and carbonates occurring at the fjord head and sides, respectively. Their relative contributions were controlled by falling relative sea level and the resulting progradation of the major stream and delta systems closer to the core sites. Deposition of clasts from sea-ice rafting persisted throughout most of the Holocene. Following a period of low, but continuous, clast fluxes (ca. 11 000–7000 calibrated years before the present), ice rafting was most intensive between ca. 7000 and 3000 calibrated years before the present. It can be related to extensive seasonal sea-ice formation caused by regional cooling. The prograding deltas also provided coarse sediments. Reduced ice rafting from ca. 3000 calibrated years before the present suggests enhanced formation of shorefast and/or permanent sea ice, suppressing sea-ice rafting in the fjord, in response to the cool climate and reduced heat flux from Atlantic Water. Episodic inflow of Atlantic Water and low turbidity of surface water can, however, account for a larger amount of marine organic matter produced in the outer fjord. The sedimentary record in Dicksonfjorden, where tidewater glaciers are absent, reflects similar climate and oceanographic variations as reconstructed in fjords on western Spitsbergen that are influenced by tidewater glaciers.