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Variability in the North Atlantic ocean heat transport at 26.5N on short (5-day) timescales is identified and contrasted with different behaviour at monthly intervals using a combination of RAPID/MOCHA/WBTS measurements and the NEMO-LIM2 1/12 ocean circulation/sea ice model. Wind forcing plays the leading role in establishing the heat transport variability through the Ekman transport response of the ocean and the associated driving atmospheric conditions vary significantly with timescale. We find that at 5-day timescales the largest changes in the heat transport across 26.5N coincide with north-westerly airflows originating over the American land mass that drive strong southward anomalies in the Ekman flow. During these events the northward heat transport reduces by 0.5-0.7 PW (i.e. about 50% of the mean). In contrast, the Ekman transport response at longer monthly timescales is smaller in magnitude (0.2-0.3 PW) and consistent with expected variations in the leading mode of North Atlantic atmospheric variability, the North Atlantic Oscillation. The north-westerly airflow mechanism can have a prolonged influence beyond the central 5-day timescale and on occasion can reduce the accumulated winter ocean heat transport into the north Atlantic by ~40%.

The North Atlantic and Europe experienced two extreme climate events in 2015: exceptionally cold ocean surface temperatures and a summer heat wave ranked in the top ten over the past 65 years. Here, we show that the cold ocean temperatures were the most extreme in the modern record over much of the mid-high latitude North-East Atlantic. Further, by considering surface heat loss, ocean heat content and wind driven upwelling we explain for the first time the genesis of this cold ocean anomaly. We find that it is primarily due to extreme ocean heat loss driven by atmospheric circulation changes in the preceding two winters combined with the re-emergence of cold ocean water masses. Furthermore, we reveal that a similar cold Atlantic anomaly was also present prior to the most extreme European heat waves since the 1980s indicating that it is a common factor in the development of these events. For the specific case of 2015, we show that the ocean anomaly is linked to a stationary position of the Jet Stream that favours the development of high surface temperatures over Central Europe during the heat wave. Our study calls for an urgent assessment of the impact of ocean drivers on major European summer temperature extremes in order to provide better advance warning measures of these high societal impact events.

Observations of the Atlantic meridional overturning circulation (AMOC) by the RAPID 26°N array show a pronounced minimum in the northward transport over the winter of 2009/10, substantially lower than any observed since the initial deployment in April 2004. It was followed by a second minimum in the winter of 2010/2011. We demonstrate that ocean models forced with observed surface fluxes reproduce the observed minima. Examining output from five ocean model simulations we identify several historical events which exhibit similar characteristics to those observed in the winter of 2009/10, including instances of individual events, and two clear examples of pairs of events which happened in consecutive years, one in 1969/70 and another in 1978/79. In all cases the absolute minimum, associated with a short, sharp reduction in the Ekman component, occurs in winter. AMOC anomalies are coherent between the Equator and 50°N and in some cases propagation attributable to the poleward movement of the anomaly in the wind field is observed. We also observe a low frequency (decadal) mode of variability in the anomalies, associated with the North Atlantic Oscillation (NAO). Where pairs of events have occurred in consecutive years we find that atmospheric conditions during the first winter correspond to a strongly negative Arctic Oscillation (AO) index. Atmospheric conditions during the second winter are indicative of a more regional negative NAO phase, and we suggest that this persistence is linked to re-emergence of sea surface temperature anomalies in the North Atlantic for the events of 1969/70 and 2009/10. The events of 1978/79 do not exhibit re-emergence, indicating that the atmospheric memory for this pair of events originates elsewhere. Observation of AO patterns associated with cold winters over northwest Europe may be indicative for the occurrence of a second extreme winter over northwest Europe.

Northern Europe experienced consecutive periods of extreme cold weather in the winter of 2009/2010 and in late 2010. These periods were characterised by a tripole pattern in North Atlantic sea surface temperature (SST) anomalies and exceptionally negative phases of the North Atlantic Oscillation (NAO). A global Ocean-Atmosphere General Circulation Model (OAGCM) is used to investigate the ocean’s role in influencing North Atlantic and European climate. Observed SST anomalies are used to force the atmospheric model and the resultant changes in atmospheric conditions over Northern Europe are examined. We observe differences between the atmospheric responses in the winter of 2009/2010 and the early winter of 2010. Our experiments suggest that North Atlantic SST anomalies did not significantly affect the development of the negative NAO phase in the cold winter of 2009/2010. However, in November and December 2010 the large-scale North Atlantic SST anomaly pattern leads to significant shift in the atmospheric circulation over the North Atlantic towards a NAO negative phase. Therefore, our results indicate that SST anomalies in November/December 2010 were particularly conducive to the development of a negative NAO phase which culminated in the extreme cold weather conditions experienced over Northern Europe in December 2010.

Methane is a potent greenhouse gas and large-scale rapid release of methane from hydrate may have contributed to past abrupt climate change inferred from the geological record. The discovery in 2008 of over 250 plumes of methane gas escaping from the seabed of the West Svalbard continental margin at ~400 m water depth (mwd) suggests that hydrate is dissociating in the present-day Arctic. Here we model the dynamic response of hydrate-bearing sediments over a period of 2300 years and investigate ocean warming as a possible cause for present-day and likely future dissociation of hydrate, within 350–800 mwd, west of Svalbard. Future temperatures are given by two climate models, HadGEM2 and CCSM4, and scenarios, Representative Concentration Pathways (RCPs) 8.5 and 2.6. Our results suggest that over the next three centuries 5.3–29 Gg yr−1 of methane may be released to the Arctic Ocean on the West Svalbard margin.

We use a new method based on point correlation maps and self-organising maps (SOMs) to identify teleconnection patterns in 60 yr of National Centres for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) sea level pressure (SLP) re-analysis data. The most prevalent patterns are the El Nino Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and the Southern Annular Mode (SAM). Asymmetries are found between base points in opposite centres of action of the NAO and the Pacific North America pattern (PNA). The SOM-based method is a powerful tool that allows us to efficiently assess how realistically teleconnections are reproduced in any climate model. The degree of agreement between modelled and re-analysis-based teleconnections (or between different models) can be summarised in a single plot. Here, we illustrate this by assessing the skill of the medium complexity climate model FORTE (Fast Ocean Rapid Troposphere Experiment). FORTE reproduces some realistic teleconnections, such as the Arctic Oscillation (AO), the NAO, the PNA, the SAM, the African Monsoon and ENSO, along with several other teleconnections, which resemble to varying degrees the corresponding NCEP patterns. However, FORTE tends to underestimate the strength of the correlation patterns and the patterns tend to be slightly too zonal. The accuracy of frequency of occurrence is variable between patterns. The Indian Ocean is a region where FORTE performs poorly, as it does not reproduce the teleconnection patterns linked to the Indian Monsoon. In contrast, the North and equatorial Pacific and North Atlantic are reasonably well reproduced.

Methane is a potent greenhouse gas and large-scale rapid release of methane from hydrate may have contributed to past abrupt climate change inferred from the geological record. The discovery in 2008 of over 250 plumes of methane gas escaping from the seabed of the West Svalbard continental margin at ~400 m water depth (mwd) suggests that hydrate is dissociating in the present-day Arctic. Here we model the dynamic response of hydrate-bearing sediments over a period of 2300 years and investigate ocean warming as a possible cause for present-day and likely future dissociation of hydrate, within 350–800 mwd, west of Svalbard. Future temperatures are given by two climate models, HadGEM2 and CCSM4, and scenarios, Representative Concentration Pathways (RCPs) 8.5 and 2.6. Our results suggest that over the next three centuries 5.3–29 Gg yr−1 of methane may be released to the Arctic Ocean on the West Svalbard margin.

We use a global Ocean-Atmosphere General Circulation Model (OAGCM) to show that the major mountain ranges of the world have a significant role in maintenance of the Atlantic Meridional Overturning Circulation (AMOC). A simulation with mountains has a maximum AMOC of 18 Sv (1 Sv = 106 m3 s−1) compared with ∼0 Sv for a simulation without mountains. Atlantic heat transport at 25°N is 1.1 PW with mountains compared to 0.2 PW without. The difference in AMOC is due to major changes in surface heat and freshwater (FW) fluxes over the Atlantic. In the Pacific changed surface fluxes lead to a meridional overturning circulation of 10 Sv. Our results suggest that the effects of mountains on the large-scale atmospheric circulation is to force the ocean towards a state with a vigorous AMOC and with no overturning in the Pacific.

Author Posting. © Inter-Research, 2005. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 287 (2005): 45-52, doi:10.3354/meps287045., An oceanographic cruise was carried out in the subtropical NE Atlantic in April 1999 with the aim of investigating the role of the Azores Current, the STORM (subtropical oceanic rings of magnitude) cyclonic eddies and the Great Meteor Tablemount in triggering phytoplankton production. This information combined with previous studies allowed us to determine the role of these features in the carbon budget of the photic layer in this oligotrophic region. The results suggest that mesoscale dynamics, although modifying hydrographic characteristics and phytoplankton spatial distribution, do not appear to significantly affect primary production in the NE subtropical Atlantic., This study was funded by the European Commission and the Spanish Ministerio de Educación y Cultura through the research programmes CANIGO (MAS3CT960060) and CARPOS (REN2003-09532-C03-01). B. Mouriño was supported by a PFPU fellowship from the Ministerio de Educación y Cultura (MEC, Spain) and a MECD/Fulbright postdoctoral fellowship.

The MarQUEST (Marine Biogeochemistry and Ecosystem Modelling Initiative in QUEST) project was established to develop improved descriptions of marine biogeochemistry, suited for the next generation of Earth system models. We review progress in these areas providing insight on the advances that have been made as well as identifying remaining key outstanding gaps for the development of the marine component of next generation Earth system models. The following issues are discussed and where appropriate results are presented; the choice of model structure, scaling processes from physiology to functional types, the ecosystem model sensitivity to changes in the physical environment, the role of the coastal ocean and new methods for the evaluation and comparison of ecosystem and biogeochemistry models. We make recommendations as to where future investment in marine ecosystem modelling should be focused, highlighting a generic software framework for model development, improved hydrodynamic models, and better parameterisation of new and existing models, reanalysis tools and ensemble simulations. The final challenge is to ensure that experimental/observational scientists are stakeholders in the models and vice versa

The control of atmospheric storm tracks by ocean dynamics, orography, and their interaction is investigated using idealized experiments with a simplified coupled atmosphere-ocean climate model. The study focuses on the quasi-steady state for the storm tracks in the Northern Hemisphere winter mean. The experiments start with a background state without mountains and ocean dynamics, and in separate stages include orography and a dynamic ocean to obtain a more realistic control simulation. The separate effects of ocean dynamics, orography, and their nonlinear interaction are identified for the storm tracks and the surface thermodynamic forcing over the ocean. The model study suggests that atmospheric storm tracks are a robust feature of the climate system, occurring at midlatitudes even if there is no orographic forcing or ocean heat transport. Ocean dynamics generally lead to a poleward shift in both the storm track and the maximum in atmospheric northward heat transport and induce a northeastward tilt over the Atlantic. This poleward shift is linked to the extra heat transport by the ocean and the tightening of sea surface temperature gradients on the western side of ocean basins. Orographic forcing causes along-track variability with a weakening of the storm track over the continents and induces a northeastward tilt over the western Pacific, which is associated with a stationary planetary wave train generated by the Tibetan Plateau. The interaction between ocean dynamics and orographic forcing plays a localized role, enhancing the contrast between the Atlantic and Pacific. Much of the response to the forcing is eddy mediated and transient eddies help to spread the influence of orographic and ocean forcing.

The impact of extreme Nordic Seas heat loss on Denmark Strait (DS) dense water transport is examined in (1) control runs of the Hadley Centre HadCM3 and HadGEM1 coupled climate models and (2) perturbation experiments with the fast coupled model FORTE that allow heat flux effects to be isolated from wind stress. All three models show an approximately linear increase in southward DS transport of cold dense water with increasing Nordic Seas winter heat loss in the range −80 to −250 Wm−2. The propagation of the cold anomaly from the Nordic Seas source along a trajectory through the DS and into the Irminger Basin is also examined. A common response time is found with the strongest decrease in DS temperature occurring within 8–12 months of the heat loss signal. Our results show that Nordic Seas heat loss must be considered in addition to other processes in understanding DS variability.

The physical context for ocean margin exchange at Goban Spur is described. Observations adjacent to, prior to and during the Ocean Margin EXchange (OMEX) project of 1993-1996 are used. They include currents measured on moorings, drogued-buoy tracks; temperature and other data from CTD profiles, especially as indicators of vertical mixing; evidence from models, particularly for turbulence causing vertical mixing. These data are combined in estimates of (seasonally dependent) mean flow, tidal currents, other current variability, exchange and mixing over the main cross-slope section studied in OMEX and in nearby and contrasted locations (aided by the use of earlier and adjacent measurements). Causative physical processes are discussed: potentially northward flow along the continental slope, effects of Goban Spur topography, eddies, wind-driven transport, cascading, tides, fronts, internal tides, internal waves, surface waves. Among these, there is evidence thatthe along-slope flow, typically O(0.05ms(-1)), is reduced or even reversed in spring, is generally weaker than at some other margin sectors owing to the non-meridional alignment and indentations in the Celtic Sea slope, and may sometimes overshoot rather than follow the depth contours around Goban Spur;tidal currents are O(0.2ms(-1)) on the adjacent shelf but O(0.1ms(-1)) or less over most of Goban Spur; they increase to the southeast;other (wind- and eddy-forced) contributions to the currents are typically O(0.1ms(-1)) or less, except on the shelf, and decrease with depth;wind-, tide- and wave-forced currents are probably the most consistent agents of cross-slope exchange O(1m(2)s(-1)), with topographic effects being important locally (canyons, spurs);stratification starts intermittently until early June, becomes shallower through June and deepens by September. In 1995, one storm on 5-8 September roughly doubled the upper mixed-layer depth to > 40m and reinstated maximal primary production in the upper mixed lay

Recent studies claim that useful predictability of the North Atlantic Oscillation (NAO) up to several years in advance may be possible using atmospheric models in which the sea surface temperature (SST) is specified from observations. Achieving this goal requires that such models adequately capture the observed variation in the NAO at interannual as well as interdecadal timescales. We investigate whether this is the case by comparing interannual variability in the HadAM3 atmospheric model with observations in the SOC air-sea flux dataset for 1980-1995. We find that the model NAO time variation does not correspond to that observed, thus claims of multiannual predictability need to be viewed with caution. In addition, analysis of the observations reveals that NAO related SST anomalies do not exert a significant heat flux feedback on the atmosphere at seasonal to interannual timescales.