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Sea-level variations in coastal areas can differ significantly from those in the nearby open ocean. Monitoring coastal sea-level variations is therefore crucial to understand how climate variability can affect the densely populated coastal regions of the globe. In this paper, we study the sea-level variability along the coast of Norway by means of in situ records, satellite altimetry data, and a network of eight hydrographic stations over a period spanning 16 years (from 2003 to 2018). At first, we evaluate the performance of the ALES-reprocessed coastal altimetry dataset (1 Hz posting rate) by comparing it with the sea-level anomaly from tide gauges over a range of timescales, which include the long-term trend, the annual cycle, and the detrended and deseasoned sea-level anomaly. We find that coastal altimetry and conventional altimetry products perform similarly along the Norwegian coast. However, the agreement with tide gauges in terms of trends is on average 6 % better when we use the ALES coastal altimetry data. We later assess the steric contribution to the sea level along the Norwegian coast. While longer time series are necessary to evaluate the steric contribution to the sea-level trends, we find that the sea-level annual cycle is more affected by variations in temperature than in salinity and that both temperature and salinity give a comparable contribution to the detrended and deseasoned sea-level variability along the entire Norwegian coast. A conclusion from our study is that coastal regions poorly covered by tide gauges can benefit from our satellite-based approach to study and monitor sea-level change and variability.

Issue sup1: Copernicus Marine Service Ocean State Report, Issue 5 Supplement.-- Karina von Schuckmann (Editor), Pierre-Yves Le Traon (Editor), Neville Smith (Chair) (Review Editor), Ananda Pascual (Review Editor), Samuel Djavidnia (Review Editor), Jean-Pierre Gattuso (Review Editor), Marilaure Grégoire (Review Editor), The work was supported by the Copernicus Marine Environment Monitoring Service (CMEMS) LATEMAR project. CMEMS is implemented by Mercator Ocean in the framework of a delegation agreement with the European Union. This work has also been conducted as part of the bilateral project EOLO-1 (“Extreme Oceanic waves during tropical, tropical-like, and bomb cyclones”) between CNR-ISMAR and the University of Tokyo (Japan; Prof. Takuji Waseda). Antonio Ricchi funding have been provided via the PON “AIM” - Attraction and international mobility program AIM1858058. Joanna Staneva acknowledges H2020 IMMERSE Project, Arno Behrens was supported by CMEMS Waveflow project and G. Gayer by ESA Black Sea and Danube Regional Initiative (EO4BS).

Atmospheric forcing and climate modes of variability on various timescales are important drivers of sea level variability. However, the influence of such drivers on sea level variability along the South African east and south coast has not yet been adequately investigated. Here, we determine the timescales of sea level variability and their relationships with various drivers. Empirical Mode Decomposition (EMD) was applied to seven tide gauge records and potential forcing data for this purpose. The oscillatory modes identified by the EMD were summed to obtain physically more meaningful timescales—specifically, the sub-annual (less than 18 months) and interannual (greater than two years) scales. On the sub-annual scale, sea level responds to regional zonal and meridional winds associated with mesoscale and synoptic weather disturbances. Ekman dynamics resulting from variability in sea level pressure and alongshore winds are important for the coastal sea level on this timescale. On interannual timescales, there were connections with ENSO, the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM), although the results are not consistent across all the tide gauge stations and are not particularly strong. In general, El Niño and positive IOD events are coincident with high coastal sea levels and vice versa, whereas there appears to be an inverse relationship between SAM phase and sea level.

Studies of the global sea-level budget (SLB) and the global ocean-mass budget (OMB) are essential to assess the reliability of our knowledge of sea-level change and its contributions. Here we present datasets for times series of the SLB and OMB elements developed in the framework of ESA's Climate Change Initiative. We use these datasets to assess the SLB and the OMB simultaneously, utilising a consistent framework of uncertainty characterisation. The time series, given at monthly sampling, include global mean sea-level (GMSL) anomalies from satellite altimetry; the global mean steric component from Argo drifter data with incorporation of sea surface temperature data; the ocean mass component from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry; the contribution from global glacier mass changes assessed by a global glacier model; the contribution from Greenland Ice Sheet and Antarctic Ice Sheet mass changes, assessed from satellite radar altimetry and from GRACE; and the contribution from land water storage anomalies assessed by the WaterGAP global hydrological model. Over the period Jan 1993–Dec 2016 (P1, covered by the satellite altimetry records), the mean rate (linear trend) of GMSL is 3.05 ± 0.24 mm yr−1. The steric component is 1.15 ± 0.12 mm yr−1 (38 % of the GMSL trend) and the mass component is 1.75 ± 0.12 mm yr−1 (57 %). The mass component includes 0.64 ± 0.03 mm yr−1 (21 % of the GMSL trend) from glaciers outside Greenland and Antarctica, 0.60 ± 0.04 mm yr−1 (20 %) from Greenland, 0.19 ± 0.04 mm yr−1 (6 %) from Antarctica, and 0.32 ± 0.10 mm yr−1 (10 %) from changes of land water storage. In the period Jan 2003–Aug 2016 (P2, covered by GRACE and the Argo drifter system), GMSL rise is higher than in P1 at 3.64 ± 0.26 mm yr−1. This is due to an increase of the mass contributions (now about 2.22 ± 0.15 mm yr−1, 61 % of the GMSL trend), with the largest increase contributed from Greenland. The SLB of linear trends is closed for P1 and P2, that is, the GMSL trend agrees with the sum of the steric and mass components within their combined uncertainties. The OMB budget, which can be evaluated only for P2, is also closed, that is, the GRACE-based ocean-mass trend agrees with the sum of assessed mass contributions within uncertainties. Combined uncertainties (1-sigma) of the elements involved in the budgets are between 0.26 and 0.40 mm yr−1, about 10 % of GMSL rise. Interannual variations that overlie the long-term trends are coherently represented by the elements of the SLB and the OMB. Even at the level of monthly anomalies the budgets are closed within uncertainties, while also indicating possible origins of remaining misclosures.

We present the in-situ biogeochemical data products distributed by the Copernicus Marine Service since 2018. The products offer available data of chlorophyll, oxygen, and nutrients (nitrate, silicate and phosphate), both in near-real time and as re-processed data, collected across the globe. The re-processing involves careful quality control utilizing tailored automated quality control procedures combined with visual inspection of questionable values by experts. Moreover, oxygen data are provided with uniform units for modelers (µmol/l) and other oceanic applications and monitoring purposes (µmol/kg) The products integrate observations aggregated from the Regional EuroGOOS consortium, as well as from SeaDataNet2, National Data Centers (NODCs) and JCOMM global systems, among others.We highlight some use cases, including a study showing an overall decline in the nutrient concentration (nitrate and silicate) of the Atlantic Water flowing though the Nordic Seas en-route to the Arctic Ocean, during the period 1990-2019. Moreover, the study shows indications of a delayed-response reduction further downstream in the Arctic Water exiting the Arctic Ocean through Fram Strait. Other use cases include the study of variability in the concentration of dissolved oxygen in the Mediterranean Sea, showing an association with dynamical processes.The in-situ near-real time biogeochemical product is updated every month whereas the re-processed product is updated two times per year. Products are delivered on NetCDF4 format compliant with the CF1.7 standard and well-documented quality control procedures.

Wintertime sea level variability over the northern European continental shelf is largely wind-driven. Using daily gridded sea level anomaly from altimetry, we examine both the spatial and the temporal relationship between northern European sea level variability and large-scale atmospheric circulation patterns as represented by the jet cluster paradigm. The jet clusters represent different configurations of the eddy-driven jet stream and, therefore, provide a physical description of the atmospheric variability in the North Atlantic. We find that each of the four jet clusters is associated with a distinct northern European sea level anomaly pattern whose magnitudes are comparable to those of typical sea level variations on the shelf. In certain locations, such as the German Bight and the east coast of England, sea level anomalies are mainly associated with one single jet cluster. In other locations, such as the interior and the northern part of the North Sea, sea level anomalies are found to be sensitive to at least two jet configurations. Based on these regional sea level variations, we map out the locations on the shelf where each jet cluster or combination of clusters is most active before discussing the role of Ekman transport in inducing the resulting patterns. Through a multiple linear regression model, we also find that the jet clusters reconstruct up to 50% of the monthly mean sea level anomaly variance over the northern European continental shelf. The model best performs in the interior and the western part of the North Sea, suggesting that wind direction rather than wind speed plays a more prominent role over these regions. We conclude that the jet cluster approach gives valuable new insights compared to linear regression techniques for characterising wind-driven sea level variability over the northern European continental shelf. publishedVersion

Flooding events pose an ever increasing threat in a warming world. Safety standards for buildings and infrastructure are often based on past observations of local sea level, as measured by tide gauges and remote sensing systems. However, sea level at a given location is not an isolated property and is determined by a combination of factors. For extreme sea level events, there are two factors that of particular importance: the astronomical tide, and storm surges. In this work, we analysed measurements from 21 stations in the Norwegian tide gauge network, disentangling the factors contributing to the previously observed extreme events.By separating the observed sea level into a tidal component and a storm surge component, we found that in many cases the observed extreme sea level events were caused by an extreme storm surge coinciding with only a moderate tide, or an extreme tide coinciding with only a moderate storm surge. This raises the possibility of a ‘super-flooding’ event, where an extreme storm surge may occur with an extreme tide. Even in the short records examined in this study (less than 40 years), the combination of the highest observed tide with the highest observed storm surge would greatly exceed in the 1000-year return level event at many locations. This is often used as a national standard for critical infrastructure. We further complement the work by analysing the storm tracks close to Norway. By relating the storm surges with the individual storms giving rise to them, we found that many storm surges during extreme sea level events were related to cyclones of only moderate intensity. Combined with the previous findings, this work suggests the need to assess extreme sea level return values for future construction and infrastructure planning as the result of a multi-variable system. This is in contrast to basing such assessments on the single variable of observed sea level as it is done today.

The Copernicus Marine service is a “one-stop-shop” providing freely available operational data on the state of the marine environment for use by marine managers, advisors, and scientists, as well as intermediate and end users in marine businesses and operations. The Copernicus Marine service offers operationally updated and state-of-the-art products that are well documented and transparent. The European Commission’s long-term commitment to the Copernicus program offers long-term visibility and stability of the Copernicus Marine products. Furthermore, Copernicus Marine offers a dedicated service desk, in addition to training sessions and workshops.Here, we present the in situ biogeochemical data products distributed by the Copernicus Marine System since 2018. It offers available data of chlorophyll-a, oxygen, and nutrients collected across the globe. These products integrate observation aggregated from the Regional EuroGOOS consortium (Arctic-ROOS, BOOS, NOOS, IBI-ROOS, MONGOOS) and Black Sea GOOS as well as from SeaDataNet2 National Data Centers (NODCs) and JCOMM global systems (Argo, GOSUD, OceanSITES, GTSPP, DBCP) and the Global telecommunication system (GTS) used by the Met Offices.The in situ Near Real Time biogeochemical product is updated every month whereas the reprocessed product is updated two times per year. Products are delivered on NetCDF4 format compliant with the CF1.7 standard and well-documented quality control procedures.

In this study the variability of Atlantic Water (AW) entering the Nordic Seas from the North Atlantic through the passage between Iceland, the Faroe Islands and Scotland has been investigated. The poleward transport of this warm AW is a key component in maintaining a relatively mild climate in the northwestern Europe. Satellite remote sensing datasets from altimetry and the Gravity field and steady state Ocean Circulation Explorer (GOCE) mission, in combination with surface drifters, fixed current meter, and hydrographic data are used. The high-resolution mean dynamic topography (MDT) is shown to resolve the time-invariant surface currents in the inflow region. In addition to the improved MDT, we take benefit of the new reprocessed sea level anomaly data in the estimation of absolute dynamic topography. Analysis of the monthly surface velocities from 1993 to 2016 demonstrates significant influence of the large scale atmospheric forcing associated with the North Atlantic Oscillation (NAO). Furthermore, a significant increase in surface velocities along the slope current, front current and the Norwegian Coastal Current are found during winter. Finally, combining altimetry with hydrographic data, we demonstrate that the variability in surface velocities of the inflow region is also reflected in the deeper layers, and that altimetry therefore can be used to monitor the variability of the poleward transport of AW in this region.

The Lofoten Basin is the most eddy rich region in the Norwegian Sea. In this paper, the characteristics of these eddies are investigated from a comprehensive database of nearly two decades of satellite altimeter data (1995–2013) together with Argo profiling floats and surface drifter data. An automated method identified 1695/1666 individual anticyclonic/cyclonic eddies in the Lofoten Basin from more than 10,000 altimeter-based eddy observations. The eddies are found to be predominantly generated and residing locally. The spatial distributions of lifetime, occurrence, generation sites, size, intensity, and drift of the eddies are studied in detail. The anticyclonic eddies in the Lofoten Basin are the most long-lived eddies (>60 days), especially in the western part of the basin. We reveal two hotspots of eddy occurrence on either side of the Lofoten Basin. Furthermore, we infer a cyclonic drift of eddies in the western Lofoten Basin. Barotropic energy conversion rates reveals energy transfer from the slope current to the eddies during winter. An automated colocation of surface drifters trapped inside the altimeter-based eddies are used to corroborate the orbital speed of the anticyclonic and cyclonic eddies. Moreover, the vertical structure of the altimeter-based eddies is examined using colocated Argo profiling float profiles. Combination of altimetry, Argo floats, and surface drifter data is therefore considered to be a promising observation-based approach for further studies of the role of eddies in transport of heat and biomass from the slope current to the Lofoten Basin.

ExcerptSea-level rise (SLR) poses a great threat to approximately 10% of the world’s population residing in low-elevation coastal zones (i.e., land located up to 10 m of present-day mean sea-level (MSL))[...]

During the Last Interglacial (LIG) period, between 130 and 116 thousand years before present (ka BP), the Greenland Ice Sheet (GrIS) was considerably reduced in size, contributing to a global mean sea-level (MSL) rise of 0.5–4.2 m relative to the present. This is not sufficient to explain the 6–9 m MSL rise estimated for the LIG, which implies that a significant contribution to the LIG highstand came from Antarctica. Following the LIG the GrIS grew and attained its maximum volume of about 12 m global sea-level equivalents (SLEs) between 18 and 16 ka BP. Since then the GrIS margins have retreated on an order of several hundred km, following a general pattern of lagged response to changes in high-latitude summer insolation and global greenhouse gas concentrations. On shorter timescales and over smaller spatial scales the combination of internal ice-sheet dynamics and external climate dynamics has often resulted in a more complex and asynchronous behaviour of the ice-sheet margin. The GrIS probably reached its minimum Holocene extent around 4 ka BP, and modelling studies suggest that it contributed to a rise in global MSL of less than 0.2 m relative to the present at this time. A period of steady growth followed the Holocene minimum and in many areas the ice sheet advanced beyond its present limits during the ‘Little Ice Age’ (i.e. the last few centuries). Currently the GrIS occupies an area of ~ 1.7 × 106 km2 and features a volume of ~ 2.96 × 106 km3, which amounts to ~ 7.4 m SLE. Observations show that the rate of mass loss from the GrIS has been accelerating over the past few decades, and ice sheet modelling indicates that we have to go back to the last deglaciation (around 10 ka BP) in order to find sustained melt rates that were higher than those experienced over the last decade. The future development of the GrIS will have a profound influence on sea level, both globally and regionally, but there are large uncertainties related to how the GrIS will respond to future global warming. Based on a range of modelling studies employing different emission scenarios, the GrIS is expected to contribute about 0.1–0.3 m to global MSL rise by the end of the 21st century. In a longer time perspective, modelling suggests that melting of the GrIS may replace ocean thermal expansion as the most important factor in future sea-level rise, potentially contributing with 0.7–2.6 m SLE within the next 500 years. Multi-millennial simulations show that the entire ice sheet (~ 7.4 m SLE) might disappear completely within less than three thousand years under high-emission scenarios, i.e. with atmospheric CO2 reaching four times preindustrial levels.

Northern European sea levels show a non-stationary link to the North Atlantic Oscillation (NAO). The location of the centers of the NAO dipole, however, can be affected through the interplay with the East Atlantic (EAP) and the Scandinavian (SCAN) teleconnection patterns. Our results indicate the importance of accounting for the binary combination of the NAO with the EAP/SCAN for better understanding the non-stationary drivers inducing sea level variations along the European coasts. By combining altimetry and tide gauges, we find that anomalously high monthly sea levels along the Norwegian (North Sea) coast are predominantly governed by same positive phase NAO+/EAP+ (NAO+/SCAN+) type of atmospheric circulation, while the Newlyn and Brest tide gauges respond markedly to the opposite phase NAO−/EAP+ combination. Despite these regional differences, we find that coherent European sea level changes project onto a pattern resembling NAO+/SCAN+, which is signified by pressure anomalies over Scandinavia and southern Europe forcing winds to trace the continental slope, resulting in a pile-up of water along the European coasts through Ekman transport. We conclude that taking into consideration the interaction between these atmospheric circulation regimes is valuable and may help to understand the time-varying relationship between the NAO and European mean sea level.

The Atlantic Ocean's thermohaline circulation is an important modulator of global climate. Its northern branch extends through the Nordic Seas to the cold Arctic, a region that appears to be particularly influenced by climate change. A thermohaline circulation is fundamentally concerned with two degrees of freedom. This is in particular the case for the inflow of warm and saline Atlantic Water through the Nordic Seas toward the Arctic that is balanced by two branches of outflow. The authors present an analytical model, rooted in observations, that constrains the strength and structure of this Arctic–Atlantic thermohaline circulation. It is found, maybe surprisingly, that the strength of Atlantic inflow is relatively insensitive to anomalous freshwater input; it mainly reflects changes in northern heat loss. Freshwater anomalies are predominantly balanced by the inflow's partition into estuarine and overturning circulation with southward polar outflow in the surface and dense overflow at depth, respectively. More quantitatively, the approach presented herein provides a relatively simple framework for making closed and consistent inference on the thermohaline circulation's response to observed or estimated past and future change in the northern seas.

The circulation and water mass transports north of the Denmark Strait are investigated using recently collected and historical in situ data along with an idealized numerical model and atmospheric reanalysis fields. Emphasis is placed on the pathways of dense water feeding the Denmark Strait Overflow Water plume as well as the upper-layer circulation of freshwater. It is found that the East Greenland Current (EGC) bifurcates at the northern end of the Blosseville Basin, some 450 km upstream of the Denmark Strait, advecting overflow water and surface freshwater away from the boundary. This “separated EGC” flows southward adjacent to the previously identified North Icelandic Jet, indicating that approximately 70% of the Denmark Strait Overflow Water approaches the sill along the Iceland continental slope. Roughly a quarter of the freshwater transport of the EGC is diverted offshore via the bifurcation. Two hypotheses are examined to explain the existence of the separated EGC. The atmospheric fields demonstrate that flow distortion due to the orography of Greenland imparts significant vorticity into the ocean in this region. The negative wind stress curl, together with the closed bathymetric contours of the Blosseville Basin, is conducive for spinning up an anti-cyclonic gyre whose offshore branch could represent the separated EGC. An idealized numerical simulation suggests instead that the current is primarily eddy-forced. In particular, baroclinic instability of the model EGC spawns large anti-cyclones that migrate offshore and coalesce upon reaching the Iceland continental slope, resulting in the separated EGC. Regardless of the formation mechanism, the recently obtained shipboard data and historical hydrography both indicate that the separated EGC is a permanent feature of the circulation north of the Denmark Strait.

The overflows from the Nordic seas maintain the deep branch of the North Atlantic circulation that is an important part of the global climate system. An analysis of observed ocean temperatures and salinities between 1950 and 2005 shows that the Atlantic water circulating in the Nordic seas is the main source for change in the overflow waters.

Changes to mean sea level and/or sea level extremes (e.g., storm surges) will lead to changes in coastal impacts. These changes represent a changing exposure or risk to our society. Here, we present 21st century sea-level projections for Norway largely based on the Fifth Assessment Report from the Intergovernmental Panel for Climate Change (IPCC AR5). An important component of past and present sea-level change in Norway is glacial isostatic adjustment. We therefore pay special attention to vertical land motion, which is constrained using new geodetic observations with improved spatial coverage and accuracies, and modelling work. Projected ensemble mean 21st century relative sea-level changes for Norway are, depending on location, from −0.10 to 0.30 m for emission scenario RCP2.6; 0.00 to 0.35 m for RCP 4.5; and 0.15 to 0.55 m for RCP8.5. For all RCPs, the projected ensemble mean indicates that the vast majority of the Norwegian coast will experience a rise in sea level. Norway’s official return heights for extreme sea levels are estimated using the average conditional exceedance rate (ACER) method. We adapt an approach for calculating sea level allowances for use with the ACER method. All the allowances calculated give values above the projected ensemble mean Relative Sea Level (RSL) rise, i.e., to preserve the likelihood of flooding from extreme sea levels, a height increase above the most likely RSL rise should be used in planning. We also show that the likelihood of exceeding present-day return heights will dramatically increase with sea-level rise.

The Arctic plays a fundamental role in the climate system and shows significant sensitivity to anthropogenic climate forcing and the ongoing climate change. Accelerated changes in the Arctic are already observed, including elevated air and ocean temperatures, declines of the summer sea ice extent and sea ice thickness influencing the albedo and CO2 exchange, melting of the Greenland Ice Sheet and increased thawing of surrounding permafrost regions. In turn, the hydrological cycle in the high latitude and Arctic is expected to undergo changes although to date it is challenging to accurately quantify this. Moreover, changes in the temperature and salinity of surface waters in the Arctic Ocean and Nordic Seas may also influence the flow of dense water through the Denmark Strait, which are found to be a precursor for changes in the Atlantic meridional overturning circulation with a lead time of around 10 years (Hawkins and Sutton in Geophys Res Lett 35:L11603, 2008). Evidently changes in the Arctic and surrounding seas have far reaching influences on regional and global environment and climate variability, thus emphasizing the need for advanced quantitative understanding of the ocean circulation and transport variability in the high latitude and Arctic Ocean. In this respect, this study combines in situ hydrographical data, surface drifter data and direct current meter measurements, with coupled sea ice–ocean models, radar altimeter data and the latest GOCE-based geoid in order to estimate and assess the quality, usefulness and validity of the new GOCE-derived mean dynamic topography for studies of the ocean circulation and transport estimates in the Nordic Seas and Arctic Ocean.

[1] The variable oceanic exchanges between the Nordic seas and the Atlantic proper have been investigated using an isopycnic coordinate ocean model for the period 1948–2007. Observed and simulated time series of volume transports in the Denmark Strait (DS), between Iceland and the Faroe Islands, and in the Faroe-Shetland Channel (FSC) are used to evaluate the model, and the model captures much of the variability. The inflow of Atlantic Water in the FSC and the outflow of light Polar Water in the DS and of dense Overflow Water in both FSC and DS are all found to covary with an atmospheric pattern resembling the North Atlantic Oscillation. An increase in the FSC inflow is associated with a decrease in the FSC overflow and an increase in the DS overflow. The exchanges' response to the atmospheric forcing is mainly of a barotropic nature, but they are also influenced by baroclinic processes. The modeled antiphase between FSC inflow and overflow is connected to a vertical displacement of the isopycnal separating the two water masses in the channel and along the path of the Norwegian Atlantic Slope Current, consistent with hydraulic control of the FSC exchanges.

[1] Global sea level has been rising by about 20 cm during the last century and is expected to continue to rise in the 21st century. The rise and variability is not spatially uniform. To be able to project local changes in relative sea level (RSL), it is important to identify the processes that govern regional RSL variability. In this study, we assess the importance of different contributions to RSL variability along the coast of Norway in the period 1960–2010. By using hydrographic station data at the coast, sea level pressure, and observed vertical land uplift, we compute RSL changes due to thermal expansion, haline contraction, the inverted barometer effect, and land uplift caused by glacial isostatic adjustment. The combination of these contributions is compared to RSL variability observed with tide gauges. For all but the two southernmost stations, the reconstructed RSL explains 70–85% of the observed variability of the monthly sampled time series. The inverted barometer effect is responsible for more than half of the explained variability, while thermosteric height represents the largest contribution to the linear trend. Due to land uplift, the local RSL rise is weaker and partly negative along the Norwegian coast. The residual (observed minus reconstructed) shows a positive trend ranging from 1.3 mm yr−1 to 2.3 mm yr−1. It is speculated that the reason for this is an increase of mass in the ocean due to melting of land-based ice and, to a lesser degree, the combined thermohaline expansion in the deep Nordic seas.

[1] A carbon budget for the Nordic Seas is derived by combining recent inorganic carbon data from the CARINA database with relevant volume transports. Values of organic carbon in the Nordic Seas’ water masses, the amount of carbon input from river runoff, and the removal through sediment burial are taken from the literature. The largest source of carbon to the Nordic Seas is the Atlantic Water that enters the area across the Greenland-Scotland Ridge; this is in particular true for the anthropogenic CO2. The dense overflows into the deep North Atlantic are the main sinks of carbon from the Nordic Seas. The budget show that presently 12.3 ± 1.4 Gt C yr −1 is transported into the Nordic Seas and that 12.5 ± 0.9 Gt C yr −1 is transported out, resulting in a net advective carbon transport out of the Nordic Seas of 0.17 ± 0.06 Gt C yr −1 . Taking storage into account, this implies a net air-to-sea CO2 transfer of 0.19 ± 0.06 Gt C yr −1 into the Nordic Seas. The horizontal transport of carbon through the Nordic Seas is thus approximately two orders of magnitude larger than the CO2 uptake from the atmosphere. No difference in CO2 uptake was found between 2002 and the preindustrial period, but the net advective export of carbon from the Nordic Seas is smaller at present due to the accumulation of anthropogenic CO2.

©2011. American Geophysical Union. All Rights Reserved. An isopycnic coordinate ocean model has been used to investigate the importance of different mechanisms on the Barents Sea climate variability for the period 1948–2006 Observed and simulated time series from the Kola Section are used to evaluate the model, and the model captures both the temperature and its variability. Based on lagged correlations between different climatological time series, it is shown here that heat transport through the Barents Sea Opening and solar heat flux are about equally important to the climate variability in the Barents Sea. The heat transport has greater potential of predictability due to a relatively long time lag. Furthermore, the non-solar and the net heat flux variability is governed by fluctuations in the oceanic heat content. All time series considered important for the Barents Sea climate variability show significant correlation to the North Atlantic Oscillation (NAO) pattern on a decadal time scale. As the associated low pressure system in the Nordic Seas moves eastward from 1948–1977 to 1978–2006, the correlation between NAO and heat transports into the Barents Sea becomes higher.

A column model is set up for the Barents Sea to explore sensitivity of surface fluxes and heat storage from varying ocean heat transport. Mean monthly ocean transport and atmospheric forcing are synthesised and force the simulations. Results show that by using updated ocean transports of heat and freshwater the vertical mean hydrographic seasonal cycle can be reproduced fairly well. Our results indicate that the ~70 TW of heat transported to the Barents Sea by ocean currents is lost in the southern Barents Sea as latent, sensible, and long wave radiation, each contributing 23–39 TW to the total heat loss. Solar radiation adds 26 TW in the south, as there is no significant ice production. The northern Barents Sea receives little ocean heat transport. This leads to a mixed layer at the freezing point during winter and significant ice production. There is little net surface heat loss annually in the north. The balance is achieved by a heat loss through long wave radiation all year, removing most of the summer solar heating. During the last decade the Barents Sea has experienced an atmospheric warming and an increased ocean heat transport. The Barents Sea responds to such large changes by adjusting temperature and heat loss. Decreasing the ocean heat transport below 50 TW starts a transition towards Arctic conditions. The heat loss in the Barents Sea depend on the effective area for cooling, and an increased heat transport leads to a spreading of warm water further north.

[1] The variability in the volume exchanges between the North Atlantic and the Nordic Seas during the last 50 years is investigated using a synoptic forced, global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The simulated volume fluxes agree with the existing observations. The net volume flux across the FaroeShetland Channel (FSC) is positively correlated with the net flux through the Denmark Strait (DS; R = 0.74 for 3 years low pass filtering), but negatively correlated with the net flux across the Iceland-Faroe Ridge (IFR; R = 0.80). For the Atlantic inflow across the FSC and IFR, the correlation is R = 0.59. For the transports through the FSC and DS, the simulation suggests that an atmospheric pattern resembling the North Atlantic Oscillation is the main driving force for the variations, involving Ekman fluxes and barotropic adjustment. The model also shows a 0.7 Sv reduction of the Atlantic inflow to the Nordic Seas since the late 50’s. INDEX TERMS: 4215 Oceanography: General: Climate and interannual variability (3309); 4255 Oceanography: General: Numerical modeling; 9315 Information Related to Geographic Region: Arctic region; 1635 Global Change: Oceans

The understanding of climate and climate change is fundamentally concerned with two things: a welldefined and sufficiently complete climate record to be explained, for example of observed temperature, and a relevant mechanistic framework for making closed and consistent inferences concerning causeand-effect. This is the case for understanding observed climate, as it is the case for historical climate as reconstructed from proxy data and future climate as projected by models. The present study offers a holistic description of northern maritime climate e from the Last Glacial Maximum through to the projected global warming of the 21st century e in this context. It includes the compilation of the most complete temperature record for Norway and the Norwegian Sea to date based on the synthesis of available terrestrial and marine paleoclimate reconstructions into continuous times series, and their continuation into modern and future climate with the instrumental record and a model projection. The scientific literature on a variable northern climate is reviewed against this background, and with a particular emphasis on the role of the Norwegian Atlantic Current e the Gulf Stream's extension towards the Arctic. This includes the introduction of an explicit and relatively simple diagnostic relation to quantify the change in ocean circulation consistent with reconstructed ocean temperatures. It is found that maritime climate and the strength of the Norwegian Atlantic Current are closely related throughout the record. The nature of the relation is however qualitatively different as one progresses from the past, through the present, and into the future. © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

International Altimetry Team., In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion., At the forefront of this support, we must obviously mention the space agencies CNES, ESA and NASA which have played and still play a decisive role in the development and launch of several prominent altimetry missions from the outset. Other agencies such as DLR, EUMETSAT, ISRO, NOAA, NSOAS and organizations such as CMEMS, also contribute significantly to developments in all forms of altimetry.