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The Nordic Sea overflow, being a significant driver of the thermohaline circulation, exerts a substantial influence on environmental dynamics in the Arctic and globally. A better understanding about the trend of the storage volume of the Nordic Seas Overflows is of paramount importance to a realistic assessment of the North Atlantic circulation and variability. EN4.2.2 reanalysis data were utilized to acquire the monthly average time series of overflow water storage volume in the Nordic Sea from 1950 to 2022. The storage volume demonstrates seasonal variations, with fluctuations of approximately 10% around the average. Over the period from 1980 to 2022, the average volume per decade exhibited a consistent decrease. Linear fitting of the annual average data estimated the overall relative change trend in the last 43 years to be -7.2 ± 2.6%. However, the quality of the EN4.2.2 data brings the average error of about 12% in the calculation of the overflow storage volume, which implies that the downward trend requires further validation. From a spatial standpoint, the Norwegian Sea, particularly the Lofoten Basin, is the primary region where overflow water storage volume in the Nordic seas have decreased. This decrease corresponds to an increase in ocean temperatures within the upper layer (0-600m) of both the Lofoten Basin and the Norwegian Basin. The warming of these regions has directly impacted the overflow water storage volume, leading to its reduction. It is noteworthy that the ocean temperature rise in the upper layer is more influenced by the Atlantic inflow rather than air-sea flux, particularly in the Norwegian Basin. This is attributed to the substantial increase in SST in the North Atlantic, which aligns with the warm current regions in the Atlantic Ocean, and the lack of statistical significance in linear trend of the air-sea heat flux. Furthermore, there has been a more rapid reduction in the overflow storage volume in the Norwegian Sea from 2011 to 2022. Specifically, the annual average overflow volume from 2018 to 2022 dropped below the previous lowest value. Concurrently, the salinity of the upper Norwegian Sea and the Atlantic inflow decreased considerably, while there has been no significant change in ocean temperature. Therefore, this short-term fluctuation is predominantly attributed to the decrease in Atlantic inflow salinity. Interestingly, the decrease in overflow water volume in the Nordic Seas does not follow a linear pattern in relation to increasing ocean temperature; instead, it exhibits an accelerating trend. If the ocean temperature rises by 1°C, the overflow water volume in the Nordic Seas will decrease to 86% of the total volume. Overall, the overflow water storage in the Norwegian Sea undergoes complex interannual variations and is notably influenced by the influx from the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Trace metal contents and fluxes in downward particulate matter and dated sediment cores of the NW Alboran Sea are analysed in this study with the aim of assessing the role of the Atlantic inflow on their transport. Increases in Zn, Cu and Pb were detected in downward particulate matter collected by sediment traps after river flooding events and after the Aznalcollar mining spill. Their arrival coincided within the recently estimated time range for river particles discharged into the Gulf of Cádiz to reach the Alboran Sea, indicating that their transfer is enhanced during events of increased river inputs of contaminated particulate matter. This also suggests that the effects of potential tailing dam failures in the Gulf of Cádiz watersheds could reach the Alboran Sea. These trace metals also increased in the sediment cores from the continental rise since the second half of the 19th century, suggesting that contaminated particles have been continuously transferred towards the Mediterranean Sea since that time, when mining concessions and production increased in the SW Iberian Pyrite Belt. [Display omitted] • Contaminated sediment was transferred from the Gulf of Cádiz to the Alboran Sea. • The transfer of trace metal-enriched particles increased after major river flood events. • Trace metal enrichments were also detected after the Aznalcollar tailings dam failure. • Pyrite production and trace metals in Alboran Sea sediments have increased since the 1850s. • Potential tailing dam failures in the Gulf of Cádiz watersheds could affect the Alborán Sea. [ABSTRACT FROM AUTHOR]

The Barents Sea is a key region in the Earth System and is home to highly productive marine resources. An integrated approach for strategic sustainable management of marine resources in such shelf-sea marine ecosystems requires, among many other aspects, a robust understanding of the impact of climate on local oceanic conditions. Here, using a combined observational and modelling approach, we show that decadal climatic trends associated with the North Atlantic Subpolar Gyre (SPG), within the period 1960–2019, have an impact on oceanic conditions in the Barents Sea. We relate hydrographic conditions in the Barents Sea to the decadal variability of the SPG through its impact on the Atlantic Inflow via the Faroe-Shetland Channel and the Barents Sea Opening. When the SPG warms, an increase in the throughput of subtropical waters across the Greenland-Scotland Ridge is followed by an increase in the volume of Atlantic Water entering the Barents Sea. These changes are reflected in pronounced decadal trends in the sea-ice concentration and primary production in the Barents Sea, which follow the SPG after an advective delay of 4–5 years. This impact of the SPG on sea-ice and primary production provides a dynamical explanation of the recently reported 7-year lagged statistical relationship between SPG and cod (Gadus morhua) biomass in the Barents Sea. Overall, these results highlight a potential for decadal ecosystem predictions in the Barents Sea.

The development of larger and longer lasting northern hemisphere ice sheets during the mid‐Pleistocene Transition (MPT) coincided with global cooling. Here, we show that surface waters of the north‐eastern Atlantic actually warmed across this interval (∼1.2–0.8 Ma), which we argue reflects an increase in the north‐eastward transport of heat and moisture via the North Atlantic Current (NAC) into the Nordic Seas (the Atlantic Inflow). We suggest that simultaneous cooling and warming along the north‐western and south‐eastern margins (respectively) of the NAC during Marine Isotope Stage 28 (∼995 ka) reflected the increasing persistence of northern ice sheets as Atlantic Inflow increased. This resulted in a diachronous shift from ∼40 to ∼100 kyr cyclicity across the North East (NE) Atlantic as the growing influence of northern ice sheets spread southwards; to the north‐west of the NAC the first "100 kyr" cycle preceded Termination 12 (∼960 ka), while on the south‐eastern margin of the NAC the transition occurred ∼100 kyr later. Exploratory climate model simulations suggest that increasing Atlantic Inflow at this time could have accelerated ice sheet growth because pre‐existing moderately sized ice sheets allowed the positive effect of increasing precipitation to outpace melting. In addition, we propose that the dependence of post‐MPT ice sheets on moisture transport via the Atlantic Inflow may ultimately contribute to their apparent vulnerability to insolation forcing once a critical size threshold is crossed and high latitude ice sheets become starved of a vital moisture source. Key Points: Warming of interglacial surface northeast Atlantic across the mid‐Pleistocene TransitionFirst "100 kyr" glacial cycle preceded Marine Isotope Stage 25 (∼0.95 Ma)Increasing Atlantic Inflow could promote ice sheet growth given pre‐existence of moderately sized ice sheets [ABSTRACT FROM AUTHOR]

While the influence of the subpolar gyre (SPG) on thermohaline variability in the eastern North Atlantic is well documented, the extent and timescale of the influence of the SPG on North Sea is not well understood. This is primarily because earlier investigations on the causes of variability in the North Sea water properties mostly focused on the role of atmosphere and deployed regional models. Here using a historical simulation with the Max Planck Institute Earth System Model (MPI‐ESM), we investigate circulation and water mass variability in key regions, namely, the Rockall Trough and the Faroe‐Scotland Channel, which link the North Atlantic to the North Sea. We find that salinity covaries with advective lags in these three regions and that the northern North Sea salinity follows the Rockall Trough with a lag of 1 year. We show that recurring and persistent excursions of salinity anomalies into the northern North Sea are related to the SPG strength and not to the local acceleration of the inflow. Furthermore, we illustrate that the SPG signal is more pronounced in salinity than in temperature and that this simulated SPG signal has a period of 30–40 years. Overall, our study suggests that, at low frequency, water mass variability originating in the North Atlantic dominates changes in the North Sea water properties over those due to local wind‐driven volume transport. Plain Language Summary: Earlier investigations on the causes of variability in the North Sea water properties have mostly focused on the role of the atmosphere. This follows from the general idea that shallowness of the North Sea makes it more responsive to wind speed and direction than the deeper ocean. In the present contribution, we identify variability in North Sea water properties other than that induced by the atmosphere. For our analysis, we use a historical simulation with a global coupled model for two reasons: (a) In the model, the connections between North Atlantic and North Sea are represented, which would not be the case in a regional model, and (b) the model provides a long continuous time series of water properties, which is not available from spatially and temporally scarce observations. We find that the strength of subpolar gyre (SPG) has an impact on the salinity of the North Sea. When the SPG is weak (strong), water from the subtropical (subpolar) North Atlantic dominates the inflow into the North Sea and thus increasing (decreasing) the salinity. This modulation of inflow properties happens at decadal periods and beyond and is largely independent of the amount of Atlantic water entering the North Sea. Key Points: Low frequency open ocean impact on the North Sea is revealed in a global coupled modelThe properties of Atlantic inflow to the North Sea follow changes in subpolar gyre strength, while the total inflow is wind drivenThe subpolar gyre signal in the Faroe‐Shetland Channel and the North Sea is more pronounced in salinity than in temperature [ABSTRACT FROM AUTHOR]

The Atlantic inflow in the Fram Strait (78°50'N) has synoptic scale variability based on an array of moorings over the period of 1998-2010. The synoptic scale variability of Atlantic inflow, whose significant cycle is 3-16 d, occurs mainly in winter and spring (from January to April) and is related with polar lows in the Barents Sea. On the synoptic scale, the enhancement (weakening) of Atlantic inflow in the Fram Strait is accompanied by less (more) polar lows in the Barents Sea. Wind stress curl induced by polar lows in the Barents Sea causes Ekman-transport, leads to decrease of sea surface height in the Barents Sea, due to geostrophic adjustment, further induces a cyclonic circulation anomaly around the Barents Sea, and causes the weakening of the Atlantic inflow in the Fram Strait. Our results highlight the importance of polar lows in forcing the Atlantic inflow in the Fram Strait and can help us to further understand the effect of Atlantic warm water on the change of the Arctic Ocean. [ABSTRACT FROM AUTHOR]

The Norwegian Atlantic Current represents the northernmost reaches of the (sub)surface limb of the Atlantic Meridional Overturning Circulation. Its shelf-edge branch, the Norwegian Atlantic Slope Current (NwASC), is of particular interest as it seems to be the main conduit for advected heat towards the Arctic. The objective of this study was to investigate northward oceanic heat transport in the NwASC on longer, geologically meaningful time scales. To this end, we reconstructed variations in the strength of the NwASC over the late Holocene using the sortable-silt method. We then analysed the statistical relationship between our palaeo-flow reconstructions and published upper-ocean hydrography proxy records from the same location on the mid-Norwegian Margin. Our sortable-silt time series show prominent multi-decadal to multi-centennial variability, but no clear long-term trend over the past 4200 years. These records we thus interpret to represent perturbations in a relatively stable late-Holocene mean flow. Our in-depth statistical analysis indicates that upper-ocean temperatures at the mid-Norwegian Margin may have varied independently from the strength of the NwASC on multi-decadal to multi-centennial time scales over the past few millennia. [ABSTRACT FROM AUTHOR]

Atlantic Water, with its origin in the western Atlantic, enters the Nordic Seas partly as a barotropic current following the continental slope. This water mass is carried across the Atlantic by the baroclinic North Atlantic Current (NAC). When the NAC meets the continental slope at the east side of the Atlantic, some of the transport is converted to barotropic transport over the slope before continuing northward. Here, we show that this baroclinic to barotropic conversion is in agreement with geostrophic theory. Historical observations show that the transport of the slope current increases significantly from the Rockall Channel (RC) to the Faroe–Shetland Channel (FSC). Geostrophy predicts that with a northward decreasing buoyancy, baroclinic currents from the west will be transferred into northward topographically steered barotropic flow. We use hydrographic data from two sections crossing the continental slope, one located in the RC and another in the FSC, to estimate baroclinic and barotropic transport changes over the slope, within the framework of geostrophic dynamics. Our results indicate that ~1 Sv of the cross-slope baroclinic flow is mainly converted to northward barotropic transport above the 200–500m isobaths, which is consistent with observed transport changes between the RC and the FSC. Similar processes are also likely to occur further south, along the eastern Atlantic margin. This shows that AW within the slope current in the FSC is derived from both the eastern and the western Atlantic, in agreement with earlier studies of AW inflow to the Nordic Seas.

We present the first full water column Nd isotope ( ε Nd ) and concentration data for Caribbean seawater, as well as for stations close to the Orinoco River mouth and in the Florida Straits. The surface inflow into the southeastern Caribbean via the Guyana Current is characterized by an ε Nd signature of −10.9, which is a consequence of the mixing of relatively unradiogenic ε Nd signatures (−13.6) supplied by the Orinoco River with contributions from the Amazon River (∼−10). Despite the proximity to land, sub-surface and intermediate waters within the Caribbean largely retain the ε Nd signatures of their source water masses in the Atlantic. In contrast, the deep waters of the Caribbean show ε Nd signatures at least 3 ε Nd units more radiogenic than the inflowing Upper North Atlantic Deep Water (UNADW). A ε Nd shift from −13 to −9.7 can be explained by addition of radiogenic Nd to the deep Caribbean through weathering inputs from land. However, in order to balance such large shifts in ε Nd with at the same time modest increases in Nd concentrations, Nd must also be removed from seawater within the basin. It is suggested that the long residence time of deep waters in the Caribbean allows significant interaction of seawater with sinking particles and seafloor sediments resulting in more radiogenic values. These findings have implications for the use of ε Nd as a proxy for paleocirculation in restricted basins, in which the residence times of the deep waters are long. [ABSTRACT FROM AUTHOR]

A physical-biological coupled model was used to estimate the effect of the physical processes at the Strait of Gibraltar over the biogeochemical features of the Atlantic Inflow (AI) towards the Mediterranean Sea. This work was focused on the seasonal variation of the biogeochemical patterns in the AI and the role of the Strait; including primary production and phytoplankton features. As the physical model is 1D (horizontal) and two-layer, different integration methods for the primary production in the Biogeochemical Fluxes Model (BFM) have been evaluated. An approach based on the integration of a production-irradiance function was the chosen method. Using this Plankton Functional Type model (BFM), a simplified phytoplankton seasonal cycle in the AI was simulated. Main results included a principal bloom in spring dominated by nanoflagellates, whereas minimum biomass (mostly picophytoplankton) was simulated during summer. Physical processes occurring in the Strait could trigger primary production and raise phytoplankton biomass (during spring and autumn), mainly due to two combined effects. First, in the Strait a strong interfacial mixing (causing nutrient supply to the upper layer) is produced, and, second, a shoaling of the surface Atlantic layer occurs eastward. Our results show that these phenomena caused an integrated production of 105 g C m − 2 year − 1 in the eastern side of the Strait, and would also modify the proportion of the different phytoplankton groups. Nanoflagellates were favored during spring/autumn while picophytoplankton is more abundant in summer. Finally, AI could represent a relevant source of nutrients and biomass to Alboran Sea, fertilizing the upper layer of this area with 4.95 megatons nitrate year − 1 (79.83 gigamol year − 1 ) and 0.44 megatons C year − 1 . A main advantage of this coupled model is the capability of solving relevant high-resolution processes as the tidal forcing without expensive computing requirements, allowing to assess the effect of these phenomena on the biogeochemical patterns at longer time scales. [ABSTRACT FROM AUTHOR]

Atlantic Water, with its origin in the western Atlantic, enters the Nordic Seas partly as a barotropic current following the continental slope. This water mass is carried across the Atlantic by the baroclinic North Atlantic Current (NAC). When the NAC meets the continental slope at the east side of the Atlantic, some of the transport is converted to barotropic transport over the slope before continuing northward. Here, we show that this baroclinic to barotropic conversion is in agreement with geostrophic theory. Historical observations show that the transport of the slope current increases significantly from the Rockall Channel (RC) to the Faroe-Shetland Channel (FSC). Geostrophy predicts that with a northward decreasing buoyancy, baroclinic currents from the west will be transferred into northward topographically steered barotropic flow. We use hydrographic data from two sections crossing the continental slope, one located in the RC and another in the FSC, to estimate baroclinic and barotropic transport changes over the slope, within the framework of geostrophic dynamics. Our results indicate that ~1 Sv of the cross-slope baroclinic flow is mainly converted to northward barotropic transport above the 200-500m isobaths, which is consistent with observed transport changes between the RC and the FSC. Similar processes are also likely to occur further south, along the eastern Atlantic margin. This shows that AW within the slope current in the FSC is derived from both the eastern and the western Atlantic, in agreement with earlier studies of AW inflow to the Nordic Seas. [ABSTRACT FROM AUTHOR]

Larsen, K. M. H., Hátún, H., Hansen, B., and Kristiansen, R. 2012. Atlantic water in the Faroe area: sources and variability. – ICES Journal of Marine Science, 69: 802–808.The inflow of Atlantic water (AW) across the Greenland–Scotland Ridge and into the Nordic Seas controls both physical and biological conditions in the northeastern Atlantic through its transport of heat, salt, and other properties. The two main branches of this flow pass through the Iceland–Faroe Gap and the Faroe–Shetland Channel, respectively. Regular monitoring along four standard sections crossing these flows provides time-series of the AW temperature and salinity variability since the late 1980s. The analysis of these series presented shows a persistent increasing trend in both temperature and salinity, modulated by smaller subdecadal oscillations. Using supplementary data sources, the previously established link between the large-scale circulation in the North Atlantic and Atlantic inflow properties is supported. Salinity is also impacted by large changes in the Bay of Biscay source waters, and upstream air–sea heat fluxes modulate temperature. Relationships between changes in transport and associated residence time, and the modifying strength of the air–sea interaction and mixing, are also discussed. [ABSTRACT FROM PUBLISHER]

Abstract: The variability of the ice and freshwater transports through the main openings of the Nordic Seas is studied based on a 200-year simulation with a sea ice–ocean model forced by stochastic surface wind stress anomalies representative of Northern annular mode (NAM). The spectrum of the ice export through Fram Strait (FS), which constitutes the main contribution to the total freshwater export anomaly from the Arctic, shows no significant peak though half of the variance is concentrated at periods longer than a year. The standard deviation of the freshwater export to the subpolar gyre through Denmark Strait only amounts to 40% of the standard deviation of the total (ice+liquid) freshwater export through FS, with a comparatively larger variance in the low-frequency range, suggesting that the Greenland Sea could act as a low-pass filter. In the upper layer of the Iceland–Scotland Passage, positive phases of the NAM lead to a fast increase of the northward volume and salt transports. Within 2 years, the salt transport anomaly, however, changes sign due to advection of negative salinity anomalies which originate in the subpolar gyre and can be traced up to the Barents Sea. [Copyright &y& Elsevier]

Three hydrographic sections running east from the coast of Shetland into the central northern North Sea have been surveyed since 1989. These sections cross the East Shetland Atlantic Inflow, which is one of the three northerly oceanic inflows to the North Sea. The East Shetland Atlantic Inflow has previously been discounted as of great importance to the hydrography and ecology of the North Sea. However, results from the hydrographic sections, current meter deployments and acoustic Doppler current profiler surveys reveal that the current is a persistent feature of North Sea circulation during the summer months. This inflow may form the western boundary of a cyclonic gyre in the bottom waters east of Shetland. When considering the ecological significance of the inflow it is evident that there have been substantial changes in the salinity of the northern North Sea, and of the adjacent oceanic waters during the past decades. A 20-year record of hydrographic parameters along the standard JONSIS section (59°17′N) suggests that these changes are related to decadal variability of the two western North Sea inflows; the Fair Isle Current and the ESAI. These changes are in turn related to changes in the oceanic waters at the entrance to the North Sea, as demonstrated by long-term time series generated from two standard sections in the Faroe–Shetland Channel. It is directly via the ESAI, and indirectly via the Fair Isle Current, that oceanic variability is communicated to the North Sea. [ABSTRACT FROM PUBLISHER]