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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.12.014 Byline: Julie Deshayes (a), Claude Frankignoul (a), Helge Drange (b)(c)(d)(e) Abstract: The influence of changes in the rate of deep water formation in the North Atlantic subpolar gyre on the variability of the transport in the Deep Western Boundary Current is investigated in a realistic hind cast simulation of the North Atlantic during the 1953-2003 period. In the simulation, deep water formation takes place in the Irminger Sea, in the interior of the Labrador Sea and in the Labrador Current. In the Irminger Sea, deep water is formed close to the boundary currents. It is rapidly exported out of the Irminger Sea via an intensified East Greenland Current, and out of the Labrador Sea via increased southeastward transports. The newly formed deep water, which is advected to Flemish Cap in approximately one year, is preceded by fast propagating topographic waves. Deep water formed in the Labrador Sea interior tends to accumulate and recirculate within the basin, with a residence time of a few years in the Labrador Sea. Hence, it is only slowly exported northeastward to the Irminger Sea and southeastward to the subtropical North Atlantic, reaching Flemish Cap in 1-5 years. As a result, the transport in the Deep Western Boundary Current is mostly correlated with convection in the Irminger Sea. Finally, the deep water produced in the Labrador Current is lighter and is rapidly exported out of the Labrador Basin, reaching Flemish Cap in a few months. As the production of deep-water along the western periphery of the Labrador Sea is maximum when convection in the interior is minimum, there is some compensation between the deep water formed along the boundary and in the interior of the basin, which reduces the variability of its net transport. These mechanisms which have been suggested from hydrographic and tracer observations, help one to understand the variability of the transport in the Deep Western Boundary Current at the exit of the subpolar gyre. Author Affiliation: (a) LOCEAN, IPSL, Universite Pierre et Marie Curie - Paris 6, Paris, France (b) Nansen Environmental and Remote Sensing Centre, Bergen, Norway (c) Bjerknes Centre for Climate Research, University of Bergen, Bergen, Norway (d) Geophysical Institute, University of Bergen, Bergen, Norway (e) Nansen-Zhu International Research Centre, Beijing, China Article History: Received 21 March 2006; Revised 14 December 2006; Accepted 29 December 2006

Poleward ocean heat transport is a key process in the earth system. We detail and review the northward Atlantic Water (AW) flow, Arctic Ocean heat transport, and heat loss to the atmosphere since 1900 in relation to sea ice cover. Our synthesis is largely based on a sea ice-ocean model forced by a reanalysis atmosphere (1900–2018) corroborated by a comprehensive hydrographic database (1950–), AW inflow observations (1996–), and other long-term time series of sea ice extent (1900–), glacier retreat (1984–), and Barents Sea hydrography (1900–). The Arctic Ocean, including the Nordic and Barents Seas, has warmed since the 1970s. This warming is congruent with increased ocean heat transport and sea ice loss and has contributed to the retreat of marine-terminating glaciers on Greenland. Heat loss to the atmosphere is largest in the Nordic Seas (60% of total) with large variability linked to the frequency of Cold Air Outbreaks and cyclones in the region, but there is no long-term statistically significant trend. Heat loss from the Barents Sea (∼30%) and Arctic seas farther north (∼10%) is overall smaller, but exhibit large positive trends. The AW inflow, total heat loss to the atmosphere, and dense outflow have all increased since 1900. These are consistently related through theoretical scaling, but the AW inflow increase is also wind-driven. The Arctic Ocean CO2 uptake has increased by ∼30% over the last century—consistent with Arctic sea ice loss allowing stronger air-sea interaction and is ∼8% of the global uptake. [ABSTRACT FROM AUTHOR]

Northward ocean heat transport and its variability influence the Arctic sea ice cover, contribute to surface warming or cooling, or simply warm or cool the Arctic Ocean interior. A simulation with the forced global ocean model NorESM20CR, aided by hydrographic observations since 1900, show large decadal fluctuations in the ocean heat transport, with the largest variations in the Atlantic sector. The simulated net poleward ocean heat transport over the last century is about 68 TW, and 88% of this occurs in the Barents Sea Opening (45 TW) and the Fram Strait (15 TW). Typical variations are 40 TW over time scales between 5 and 10 years, related to thermohaline and wind stress forcings. The mean heat transport in the Davis Strait is about 10 TW, and less than 5 TW flows north in the Bering Strait. The core temperature of the Atlantic Water (AW) entering the Arctic Ocean has increased in recent decades, consistent with an ongoing expansion of the Atlantic domain (Atlantification), but earlier warm events are also documented. The temperature of the northward‐flowing AW thus plays a vital role, with decadal variations of around 0.5 ∘C. The Nordic Seas atmosphere contributes with thermodynamic forcing, dampening the advected heat anomalies. In the Barents Sea, variations in the inflow volume flux dominate, while variations in temperature dominate the heat transport in the Fram Strait. There are significant trends over recent decades, also dominated by the Barents Sea that presently has 1 Sv higher volume transport and +1.0 ∘C warmer AW than the long‐term mean. Plain Language Summary: Ocean currents bring heat northward into the Arctic Ocean. This ocean heat influences the sea ice cover regionally and warms the Arctic Ocean surface and interior. Warm and salty Atlantic Water that enters the Arctic Ocean through the Fram Strait and the Barents Sea dominates the oceanic heat contribution to the Arctic Ocean in the 20th century. In this study, we have investigated how this ocean heat transport has varied over time and which physical mechanisms that influence these variations. Understanding these natural variations is important for explaining ongoing Arctic change today. Our main tool for investigation is a global ocean model driven by observed atmospheric variations, and we compare this model with observations of temperature and salinity in the Nordic Seas. We find that the ocean heat transport has varied on different time scales and that these variations are linked to changes in the wind systems in the Nordic Seas, atmosphere‐ocean heat exchanges, and, to some extent, local winds in the straits. Overall, the ocean heat transports and Atlantic Water temperatures have increased during recent decades. These changes are especially large at the Barents Sea entrance where the water has warmed about 1 ∘C. Key Points: Atlantic Ocean heat transport variability dominates in the Northern Hemisphere and on centennial scaleVolume transport changes due to wind stress curl and temperature due to advection and local forcingOcean heat transport in the Fram Strait is dominated by temperature variability but in the Barents Sea Opening by volume variability [ABSTRACT FROM AUTHOR]

The Ocean Model Intercomparison Project (OMIP) is an endorsed project in the Coupled Model Intercomparison Project Phase 6 (CMIP6). OMIP addresses CMIP6 science questions, investigating the origins and consequences of systematic model biases. It does so by providing a framework for evaluating (including assessment of systematic biases), understanding, and improving ocean, seaice, tracer, and biogeochemical components of climate and earth system models contributing to CMIP6. Among the WCRP Grand Challenges in climate science (GCs), OMIP primarily contributes to the regional sea level change and near-term (climate/decadal) prediction GCs. OMIP provides (a) an experimental protocol for global ocean/sea-ice models run with a prescribed atmospheric forcing; and (b) a protocol for ocean diagnostics to be saved as part of CMIP6. We focus here on the physical component of OMIP, with a companion paper (Orr et al., 2016) detailing methods for the inert chemistry and interactive biogeochemistry. The physical portion of the OMIP experimental protocol follows the interannual Coordinated Ocean-ice Reference Experiments (CORE-II). Since 2009, CORE-I (Normal Year Forcing) and CORE-II (Interannual Forcing) have become the standard methods to evaluate global ocean/seaice simulations and to examine mechanisms for forced ocean climate variability. The OMIP diagnostic protocol is relevant for any ocean model component of CMIP6, including the DECK (Diagnostic, Evaluation and Characterization of Klima experiments), historical simulations, FAFMIP (Flux Anomaly Forced MIP), C4MIP (Coupled Carbon Cycle Climate MIP), DAMIP (Detection and Attribution MIP), DCPP (Decadal Climate Prediction Project), ScenarioMIP, High- ResMIP (High Resolution MIP), as well as the ocean/sea-ice OMIP simulations. [ABSTRACT FROM AUTHOR]

Instrumental temperature records show that the global climate may experience decadal-scale periods without warming despite a long-term warming trend. We analysed 17 global climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5), identifying the likelihood and duration of periods without warming in the four Representative Concentration Pathway (RCP) scenarios RCP2.6, RCP4.5, RCP6.0 and RCP8.5, together with the preindustrial control and historical simulations. We find that non-warming periods may last 10, 15 and 30 years for RCP8.5, RCP6.0 and RCP4.5, respectively. In the models, anomalous ocean heat uptake and storage are the main factors explaining the decadal-scale surface temperature hiatus periods. The low-latitude East Pacific Ocean is a key region for these variations, acting in tandem with basin-scale anomalies in the sea level pressure. During anomalously cold decades, roughly 35-50 % of the heat anomalies in the upper 700 m of the ocean are located in the Pacific Ocean, and 25 % in the Atlantic Ocean. Decadal-scale ocean heat anomalies, integrated over the upper 700 m, have a magnitude of about 7.5 × 10 J. This is comparable to the ocean heat uptake needed to maintain a 10 year period without increasing surface temperature under global warming. On sub-decadal time scales the Atlantic, Pacific and Southern Oceans all have the ability to store large amounts of heat, contributing to variations in global surface temperature. The likelihood of decadal-scale non-warming periods decrease with global warming, firstly at the low latitude region stretching eastward from the tropical Atlantic towards the western Pacific. The North Atlantic and Southern Oceans have largest likelihood of non-warming decades in a warming world. [ABSTRACT FROM AUTHOR]

The proposed disposal of sulphur dioxide (SO2) from flue gases by pumping it into the ocean is problematic both for environmental and economic reasons. Environmentally, using seawater to scrub the SO2 out of the flue gases would result in the outgassing of carbon dioxide (CO2) that would worsen the greenhouse effect. Economically, the use of seawater scrubbing would force power stations to use 10% of their power just for disposal of SO2. On the other hand, all research conducted so far indicates that the ocean is a suitable and economical place for disposing of SO2 pollution.

A coupled climate model is used to explore the response of the tropical sea surface temperature (SST) to positive SST anomalies in the global extratropics. The main model results here are consistent with previous numerical studies. In response to prescribed SST anomalies in the extratropics, the tropical SSTs rise rapidly and reach a quasi-equilibrium state within several years, and the tropical subsurface temperatures show a slow response. The annual-mean Hadley cell, as well as the surface trades, are weakened. The weakened trades reduce the poleward Ekman transports in the tropical ocean and, furthermore, lead to anomalous positive convergences of heat transport, which is the main mechanism for maintaining the tropical Pacific SST warming. The process of an extratropical influence on the tropics is related to both the atmospheric and oceanic circulations. The intertropical convergence zone (ITCZ) moves southward and eastward in the Pacific, corresponding to a reduction of the Hadley circulation and Walker circulation. At the same time, convective precipitation anomalies are formed on the boundary of the climatological ITCZ, while the climatological mean convections centered in the Southeast Asia region are suppressed. The largely delayed response of the tropical subsurface temperature cannot be explained only by the strength change of the subtropical cells (STCs), but can be traced back to the slow changing of subsurface temperature in the extratropics. In the extratropical oceans, warming and freshening reduce the surface water density, and the outcropping lines of certain isopycnal layers are moved poleward. This poleward movement of outcropping lines can weaken the positive temperature anomalies, or even lead to negative anomalies, on given isopycnal layers. Displayed on time-dependent isopycnal layers, positive subsurface temperature anomalies are present only in the region after subduction, and are subsequently replaced by negative temperature anomalies in the deep tropics regions. The noticeable features of the density compensation of temperature and salinity indicate that diapycnal processes play an important role in the equatorward transport of the temperature and salinity anomalies from the midlatitude. [ABSTRACT FROM AUTHOR]

Abstract: A three-box model of the Atlantic Ocean is used to examine the influence different parameterisations of the diapycnal mixing may have on the large scale dynamics of the ocean circulation. Special emphasis is given to the northward volume and heat transports. The vertical diffusivity is taken in the general form , where N is the buoyancy frequency, and the parameter space is explored. An imposed freshwater forcing of the northern high latitude box is used as a test case to investigate the behaviour of the model compared to similar types of sensitivity experiments carried out with, for instance, General Circulation Models. Four different solution states are identified, separated by three critical values of . For small values of , both heat and volume fluxes decrease with increasing freshwater flux. Increasing leads first into a parameter domain where the transport of heat increases with increasing freshwater forcing, then at even higher also the volume transport increases. Finally, a fourth state is found where strong advection of warm water leads to an increase of the northern box temperature, as opposed to cooling for small . The behaviour of the critical values of is discussed with respect to model dynamics and parameters. A subtle interplay between changes in the thermocline depth and the advective fluxes from the thermocline box into northern box, which both are modulated by diapycnal mixing, is found to be the key process in determining the behaviour of the model. Finally, the implications for modelling and understanding of basic features of the ocean circulation are discussed. [Copyright &y& Elsevier]

The spatial-temporal distribution of the anthropogenic radionuclide 137Cs originating from nuclear bomb testing and the Sellafield reprocessing plant in the Irish Sea is simulated using a global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The physical model has a horizontal resolution of about 40 km, and it is forced with daily atmospheric reanalysed fields for the period 1948 to 2002. A comparison of the temporal evolution of observed and simulated concentrations of 137Cs has been conducted for the regions east of Scotland, west of central Norway and at the entrance of the Barents Sea. It follows that the annual mean 137Cs concentration signal from the Sellafield discharge reaches the southwestern Barents Sea region in 5 yr, in accordance with available observations. To more accurately assess the age of the caesium-tagged water masses, three additional experiments were performed with an Eulerian age coupled to the evolution of the tracer concentration. It is demonstrated that the transit time depends on the duration of the tracer release history, on the dynamical ocean state and on whether the transit time is derived from the time difference between the release history and the concentration evolution downstream of the release, or as an explicit Eulerian age tracer. The Eulerian age tracer gives a transit time for a Sellafield-like discharge to reach the Barents Sea of 56 months in the 1970s, 52 months in the 1960s and 51 months in the 1980s, and that this difference is strongly governed by the ocean dynamics in the Faeroe–Scotland region. [ABSTRACT FROM AUTHOR]

The transient response of the climate system to anomalously large freshwater input to the high latitude seas is examined using the newly developed Bergen Climate Model. A 150-yr twin-experiment has been carried out, consisting of a control and a freshwater integration. In the freshwater integration, the freshwater input to the Arctic Ocean and the Nordic Seas is artificially increased by a factor of 3, or to levels comparable to those found during the last deglaciation. The obtained response shows a reduced maximum strength of the Atlantic Meridional Overturning Circulation (AMOC) over the first 50 yr of about , followed by a gradual recovery to a level comparable to the control integration at the end of the period. The weakened AMOC in the freshwater integration is caused by reduced deep-water formation rates in the North Atlantic subpolar gyre and in the Nordic Seas, and by a reduced southward flow of intermediate water masses through the Fram Strait. The recovery of the AMOC is caused by an increased basin-scale upwelling in the Atlantic Ocean of about 1 Sv, northward transport of saline waters originating from the western tropical North Atlantic, and a surface wind field maintaining the inflow of Atlantic Water to the Nordic Seas between the Faroes and Scotland. Associated with the build-up of more saline waters in the western tropical North Atlantic, a warming of ∼0.6 °C over the uppermost 1000 m of the water column is obtained in this region. This finding is consistent with paleo records during the last deglaciation showing that the tropics warmed when the high latitudes cooled in periods with reduced AMOC. Furthermore, the results support the presence of a coupled North-Atlantic-Oscillation-like atmosphere–sea-ice–ocean response mode triggered by the anomalous freshwater input. Throughout most of the freshwater integration, the atmospheric circulation is characterized by anomalously low sea level pressure in the Nordic Seas and anomalously high sea level pressure over Spain. This forces the North Atlantic Drift to follow a more easterly path in the freshwater integration than in the control integration, giving an asymmetric sea surface temperature response in the northern North Atlantic, and thereby maintaining the properties of the Atlantic Water entering the Nordic Seas between the Faroes and Scotland throughout the freshwater integration. [ABSTRACT FROM AUTHOR]

The sensitivity of the ocean circulation to changes in solar irradiance is examined using an isopycnic coordinate, global ocean general circulation model (OGCM) coupled to a thermodynamic/dynamic sea-ice model. In the experiments, changes in the surface radiation forcing are calculated based on orbital data assuming that the atmospheric conditions are otherwise unchanged. Two sensitivity experiments are run with the ocean–sea-ice model: one with high and one with low solar irradiance representative of the last interglacial and glacial periods, respectively. The results show that the Atlantic merdional overturning circulation (AMOC) is increased (reduced) in response to lower (higher) summer solar irradiance. It is found that changes in the Arctic sea-ice volume and area are the main reason for the response. For the low solar irradiance case, less sea-ice is melted in summer leading to a saltier Arctic Ocean. This saltier water is then advected into the sinking regions in the winter, enhancing the intermediate and deep water formation. For the high solar irradiance case, a similar, but opposite, response occurs. The results thus confirm that the AMOC is very sensitive to external forcing. It is suggested that the scheme used for calculating changes in solar irradiance could prove useful when conducting glacial inception studies with fully coupled atmosphere–ocean models. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the ventilation of chlorofluorocarbons (CFC) in the North Atlantic Ocean. Background on the introduction of CFC trace gas in the atmosphere; Zonal distribution of CFC; Influence of North Atlantic deep waters on CFC concentration.

Multidimensional advection schemes based on the forward-upstream discretization are presented that with only one corrective step produce solutions comparable to the most accurate solutions produced by the multi-dimensional positive definite advection transport algorithm (MPDATA) family of schemes. The proposed schemes are not positive definite by structure, in contrast to the family of MPDATA schemes. A monotonicity-preserving algorithm is therefore an integral part of the schemes. Based on linear von Neumann analysis and numerical advection experiments in uniform, rotational, and deformational flows, it has been shown that all of the monotone versions of the schemes are stable for Σ[sup M] [sub 1] ¦α[sup 1]¦, where a I and M are the advective Courant number and the M SI dimensionality of the problem, respectively. Five of the proposed schemes have an amplification error close to, or slightly less than, that of the most accurate versions of the MPDATA scheme. The monotone second-order version of the most accurate scheme is 60% more expensive than the basic second-order MPDATA scheme with one antidiffusive correction step, but 70% cheaper than the corresponding monotone version of MPDATA. In addition, the most accurate of the proposed schemes is more cost efficient than any of the MPDATA schemes. All of the second-order versions of the schemes have a phase error similar to the first-order forward-upstream scheme. The phase error can be reduced by compensating for the second-order forward-upstream discretization error term. If the uniform version of the second-order forward-upstream discretization error term is applied to the schemes, the most accurate scheme becomes up to five times as efficient as the most accurate MPDATA scheme. [ABSTRACT FROM AUTHOR]

This corrects the article DOI: 10.1038/ncomms15875 [ABSTRACT FROM AUTHOR]