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Ocean circulation redistributes heat, freshwater, carbon, and nutrients all around the globe. Because of their importance in regulating climate, weather, extreme events, sea level, fisheries, and ecosystems, large-scale ocean currents should be monitored continuously. The Atlantic is unique as the only ocean basin where heat is, on average, transported northward in both hemispheres as part of the Atlantic Meridional Overturning Circulation (AMOC). The largely unrestricted connection with the Arctic and Southern Oceans allows ocean currents to exchange heat, freshwater, and other properties with polar latitudes.

Observational oceanographers are integral to the Blue‑Action consortium. The Blue-Action project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 727852. The consortium has provided coordinated feedback in the attached document, with inputs on the following: -Sustainability of Ocean observations; -Planning and sharing: planning of observations, data sharing and compliance with FAIR guidelines; -Maximising the Ocean Data.

This poster presents shortly how Blue-Action contributes tothe BluePrint for Ocean Observing in the Atlantic. The poster was presented at OceanObs'2019 by Steffen Olsen (DMI). Blue-Action contributes to defining the future Atlantic monitoring system by: optimizing the monitoring systems at the gateways to the Arctic, assessing and enhancing the usefulness of the North Atlantic ocean observations in decadal prediction systems, demonstrating the value of initialized decadal predictions in climate services &nbsp

About this document Deliverable: D6.1 First Joint workshop to (re)formulate open research questions of joint interest: “Tipping Elements in the Climate System, with a Focus on the North Atlantic” Work package in charge: WP6 Clustering Actual delivery date for this deliverable: Project-month 13 Dissemination level: The general public (PU) Lead author:Natural Environment Research Council, National Oceanography Centre (NOC): Gerard McCarthy Other contributing author:Danish Meteorological Institute (DMI): Chiara Bearzotti Summary for publication The first joint workshop on areas of common interest was held on 18-19 September 2017 at Wolfson College, Oxford (UK). The focus of the workshop was tipping elements in the climate system, with a focus on the North Atlantic. Blue-Action is focused on Arctic and high latitude changes. Therefore, the high number of tipping elements in this region and their potentially large impact on Northern Hemisphere climate is of particular interest and concern to Blue-Action scientists. The workshop was organised by the Blue-Action project to link Blue-Action scientists with experts outside the project. Key areas of research and actions for future collaboration were identified.

For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.

Presentation held at theClimate Science2Policy workshop on 17-18 November 2020. The event was organised by the Executive Agency for Small and Medium-sized enterprises (EASME), European Commission, in collaboration with a cluster of H2020 Earth System Science projects, like Blue-Action.

Poster presented at the Understanding Change and Variability in the North Atlantic Climate System, ACSIS - OSNAP - RAPID, Joint Science Meeting, 19-21 September 2017, Oxford, UK.

Overview of Work Package 2 of Blue-Action "Lower latitude drivers of Arctic change"

A novel ocean mixed layer heat budget analysis methodology is developed and used to investigate the physicalprocesses which determine Subpolar North Atlantic (SPNA) SST and OHC variability on decadal-multidecadaltimescales using the state-of-the-art coupled climate model HadGEM3-GC2. Contributions to OHC and SSTvariability from three sources are evaluated i) the net ocean-atmosphere heat flux, ii) divergence of the oceanichorizontal temperature transport and iii) entrainment between the ocean surface mixed layer and the layer beneath.Anomalies in OHC and SST tendency propagate anticlockwise around the SPNA on multidecadal timescaleswith a clear relationship to the Phase of the AMOC. AMOC anomalies lead SST tendencies which in turn leadOHC tendencies. This result is common to both eastern and western SPNA, although the primary driver of OHCvariability differs with surface fluxes dominant in the west and advection-diffusion in the east. The reciprocal ofthe mixed layer depth is found to be an important variable which causes SST to respond faster to AMOC changesthan OHC. The implications of these new results for interpretation of lower resolution coupled models, includingmany of those used in the CMIP6 assessment are discussed.

Presentation at the AGU Ocean Sciences Meeting, Portland Oregon, 11-16th February 2018. PL23A: Atlantic Meridional Overturning Circulation: Modeling and Observations

Presentation at: Blue-Action 2018 Annual Meeting, 19th January 2018, Bologna, Italy

The North Atlantic is notable for large decadal variability in sea surface temperature (SST) manifested as Atlantic Multi-decadal Variability (AMV). Whether the AMV is driven by external atmospheric or internal oceanic influences is an oft-disputed point. Long time series of atmospheric and ocean variables, in particular long timeseries of Gulf Stream position, reveal differing drivers of SST variability on quasi- and multi-decadal timescales. On quasi-decadal timescales an oscillatory signal identified in the North Atlantic Oscillation controls SST evolution directly via air-sea heat uxes. However, on multi-decadal timescales this relationship with SST changes, while remaining consistent in phase. and resonant in amplitude with Gulf Stream position. A recent reversal of the long term positive trend in Gulf Stream position coincides with a weakening and broadening in the Gulf Stream Extension indicating the onset of an AMV decline.

Presentation at: ACSIS Ocean-Ice Theme Science Day, 27th April, National Oceanography Centre, UK.

These four presentations have been the core of the side event to the All-Atlantic 2021 conference "Atlantic Pole to Pole: Climate Science 2 Policy" held on 2nd June 2021, as an online event. The side event was organised by four Horizon 2020 projects: Blue-Action, MISSION ATLANTIC, SO-CHIC and TRIATLAS. The recording of the entire event is also available here below. The policy briefing linked to this side event is available here: https://zenodo.org/record/4889819 We would like to thank once again all the participants!, The Blue-Action, MISSION ATLANTIC, SO-CHIC, and TRIATLAS projects have received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 727852, 862428, 821001, 817578 respectively.

Presentation at: Understanding Change and Variability in the North Atlantic Climate System, ACSIS - OSNAP - RAPID Joint Science Meeting,19-21 September 2017, Oxford, UK.

A novel ocean mixed layer heat budget analysis methodology is developed and used to investigate the physicalprocesses which determine Subpolar North Atlantic (SPNA) SST and OHC variability on decadal-multidecadaltimescales using the state-of-the-art coupled climate model HadGEM3-GC2. Contributions to OHC and SSTvariability from three sources are evaluated i) the net ocean-atmosphere heat flux, ii) divergence of the oceanichorizontal temperature transport and iii) entrainment between the ocean surface mixed layer and the layer beneath.Anomalies in OHC and SST tendency propagate anticlockwise around the SPNA on multidecadal timescaleswith a clear relationship to the Phase of the AMOC. AMOC anomalies lead SST tendencies which in turn leadOHC tendencies. This result is common to both eastern and western SPNA, although the primary driver of OHCvariability differs with surface fluxes dominant in the west and advection-diffusion in the east. The reciprocal ofthe mixed layer depth is found to be an important variable which causes SST to respond faster to AMOC changesthan OHC. The implications of these new results for interpretation of lower resolution coupled models, includingmany of those used in the CMIP6 assessment are discussed.

Presentation at: Understanding Change and Variability in the North Atlantic Climate System, ACSIS - OSNAP - RAPID Joint Science Meeting,19-21 September 2017, Oxford, UK.

Poster presented at the Understanding Change and Variability in the North Atlantic Climate System, ACSIS - OSNAP - RAPID, Joint Science Meeting, 19-21 September 2017, Oxford, UK.

Presentation at: ACSIS Ocean-Ice Theme Science Day, 27th April, National Oceanography Centre, UK. &nbsp

Presentation at: Blue-Action 2018 Annual Meeting, 19th January 2018, Bologna, Italy

About this document Deliverable: D6.1 First Joint workshop to (re)formulate open research questions of joint interest: “Tipping Elements in the Climate System, with a Focus on the North Atlantic” Work package in charge: WP6 Clustering Actual delivery date for this deliverable: Project-month 13 Dissemination level: The general public (PU) Lead author: Natural Environment Research Council, National Oceanography Centre (NOC): Gerard McCarthy Other contributing author: Danish Meteorological Institute (DMI): Chiara Bearzotti Summary for publication The first joint workshop on areas of common interest was held on 18-19 September 2017 at Wolfson College, Oxford (UK). The focus of the workshop was tipping elements in the climate system, with a focus on the North Atlantic. Blue-Action is focused on Arctic and high latitude changes. Therefore, the high number of tipping elements in this region and their potentially large impact on Northern Hemisphere climate is of particular interest and concern to Blue-Action scientists. The workshop was organised by the Blue-Action project to link Blue-Action scientists with experts outside the project. Key areas of research and actions for future collaboration were identified., We support the Blue Growth! Visit us on: www.blue-action.eu Follow us on Twitter: @BG10Blueaction

A novel ocean mixed layer heat budget analysis methodology is developed and used to investigate the physicalprocesses which determine Subpolar North Atlantic (SPNA) SST and OHC variability on decadal-multidecadaltimescales using the state-of-the-art coupled climate model HadGEM3-GC2. Contributions to OHC and SSTvariability from three sources are evaluated i) the net ocean-atmosphere heat flux, ii) divergence of the oceanichorizontal temperature transport and iii) entrainment between the ocean surface mixed layer and the layer beneath.Anomalies in OHC and SST tendency propagate anticlockwise around the SPNA on multidecadal timescaleswith a clear relationship to the Phase of the AMOC. AMOC anomalies lead SST tendencies which in turn leadOHC tendencies. This result is common to both eastern and western SPNA, although the primary driver of OHCvariability differs with surface fluxes dominant in the west and advection-diffusion in the east. The reciprocal ofthe mixed layer depth is found to be an important variable which causes SST to respond faster to AMOC changesthan OHC. The implications of these new results for interpretation of lower resolution coupled models, includingmany of those used in the CMIP6 assessment are discussed.

Description of heat transport to the Arctic and work done by the Blue Action project, Work Package 2 in the first year.

The North Atlantic is notable for large decadal variability in sea surface temperature (SST) manifested as Atlantic Multi-decadal Variability (AMV). Whether the AMV is driven by external atmospheric or internal oceanic influences is an oft-disputed point. Long time series of atmospheric and ocean variables, in particular long timeseries of Gulf Stream position, reveal differing drivers of SST variability on quasi- and multi-decadal timescales. On quasi-decadal timescales an oscillatory signal identified in the North Atlantic Oscillation controls SST evolution directly via air-sea heat uxes. However, on multi-decadal timescales this relationship with SST changes, while remaining consistent in phase. and resonant in amplitude with Gulf Stream position. A recent reversal of the long term positive trend in Gulf Stream position coincides with a weakening and broadening in the Gulf Stream Extension indicating the onset of an AMV decline.

Presentation at: Evaluating climate and Earth System models at the process level. Modelling Workshop, 23-24 May 2017, Brussels.

These four presentations have beenthe core of the side event to the All-Atlantic 2021 conference "Atlantic Pole to Pole: Climate Science 2 Policy" held on 2nd June 2021, as an online event. The side event wasorganised by four Horizon 2020 projects:Blue-Action,MISSION ATLANTIC, SO-CHIC and TRIATLAS. The recording of the entire event is also available here below. The policy briefing linked to this side event is available here: https://zenodo.org/record/4889819 We would like to thank once again all the participants! &nbsp

This poster presents shortly how Blue-Action contributes to the BluePrint for Ocean Observing in the Atlantic. The poster was presented at OceanObs'2019 by Steffen Olsen (DMI). Blue-Action contributes to defining the future Atlantic monitoring system by: optimizing the monitoring systems at the gateways to the Arctic, assessing and enhancing the usefulness of the North Atlantic ocean observations in decadal prediction systems, demonstrating the value of initialized decadal predictions in climate services, Blue-Action received funding from the European Union's Horizon 2020 research and innovation programme Grant agreement no. 727852

A novel ocean mixed layer heat budget analysis methodology is developed and used to investigate the physicalprocesses which determine Subpolar North Atlantic (SPNA) SST and OHC variability on decadal-multidecadaltimescales using the state-of-the-art coupled climate model HadGEM3-GC2. Contributions to OHC and SSTvariability from three sources are evaluated i) the net ocean-atmosphere heat flux, ii) divergence of the oceanichorizontal temperature transport and iii) entrainment between the ocean surface mixed layer and the layer beneath.Anomalies in OHC and SST tendency propagate anticlockwise around the SPNA on multidecadal timescaleswith a clear relationship to the Phase of the AMOC. AMOC anomalies lead SST tendencies which in turn leadOHC tendencies. This result is common to both eastern and western SPNA, although the primary driver of OHCvariability differs with surface fluxes dominant in the west and advection-diffusion in the east. The reciprocal ofthe mixed layer depth is found to be an important variable which causes SST to respond faster to AMOC changesthan OHC. The implications of these new results for interpretation of lower resolution coupled models, includingmany of those used in the CMIP6 assessment are discussed

Presentation at: Evaluating climate and Earth System models at the process level. Modelling Workshop, 23-24 May 2017, Brussels.

Observational oceanographers are integral to the Blue‑Action consortium. The Blue-Action project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 727852. The consortium has provided coordinated feedback in the attached document, with inputs on the following: -Sustainability of Ocean observations; -Planning and sharing: planning of observations, data sharing and compliance with FAIR guidelines; -Maximising the Ocean Data., The Blue-Action project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 727852

A novel ocean mixed layer heat budget analysis methodology is developed and used to investigate the physicalprocesses which determine Subpolar North Atlantic (SPNA) SST and OHC variability on decadal-multidecadaltimescales using the state-of-the-art coupled climate model HadGEM3-GC2. Contributions to OHC and SSTvariability from three sources are evaluated i) the net ocean-atmosphere heat flux, ii) divergence of the oceanichorizontal temperature transport and iii) entrainment between the ocean surface mixed layer and the layer beneath.Anomalies in OHC and SST tendency propagate anticlockwise around the SPNA on multidecadal timescaleswith a clear relationship to the Phase of the AMOC. AMOC anomalies lead SST tendencies which in turn leadOHC tendencies. This result is common to both eastern and western SPNA, although the primary driver of OHCvariability differs with surface fluxes dominant in the west and advection-diffusion in the east. The reciprocal ofthe mixed layer depth is found to be an important variable which causes SST to respond faster to AMOC changesthan OHC. The implications of these new results for interpretation of lower resolution coupled models, includingmany of those used in the CMIP6 assessment are discussed.

This workshop brought together groups from 9 European institutions and 6 European countries to promote closer collaboration between the groups making moored and other observations along the eastern boundary of the subpolar North Atlantic. This workshop was timely and fruitful as a clustering activity between European funded Blue-Action, Atlas and the recently funded A4 project in Ireland, with extended funding for NOAC and OSNAP recently secured, and new announcements of opportunity associated with OSNAP in the UK. We successfully described the observations that are ongoing on the eastern margin of the subpolar North Atlantic. Problems, sustainability, and opportunities were all discussed. Scientific problems that straddle the region were discussed. In particular, focus on the European Slope Current highlighted open scientific questions that can be addressed with co-ordinated analysis of the existing arrays and co-ordinated observations in the future. The workshop was held on 14 October 2019 in Edinburgh (UK), at the Hudson Beare Building, King’s Buildings, Edinburgh University. The workshop was organised by Gerard McCarthy (NUIM) and Stuart Cunnigham (SAMS), with the support of the project management of Blue-Action (DMI) and Atlas (University of Edinburgh). The workshop is a collaboration of three EU-funded projects, Blue-Action and ATLAS, funded by the European Union’s Horizon 2020 research and innovation programme under grant agreements No 727852 (Blue-Action) and No 678760 (ATLAS) and the A4 project (Aigéin, Aeráid, Agus athrú Atlantaigh—Oceans, Climate, and Atlantic Change), funded by the Irish Marine Institute and the European Regional Development fund (grant: PBA/CC/18/01)., Blue-Action and Atlas have received funding from the European Union's Horizon 2020 research and innovation programme under grant agreements No 727852 (Blue-Action) and No 678760 (ATLAS). A4 (Aigéin, Aeráid, agus athrú Atlantaigh) is funded by the Marine Institute and the European Regional Development fund (grant: PBA/CC/18/01)

Description of heat transport to the Arctic and work done by the Blue Action project, Work Package 2 in the first year.

This workshop brought together groups from 9 European institutions and 6 European countries to promote closer collaboration between the groups making moored and other observations along the eastern boundary of the subpolar North Atlantic. This workshop was timely and fruitful as a clustering activity between European funded Blue-Action, Atlas and the recently funded A4 project in Ireland, with extended funding for NOAC and OSNAP recently secured, and new announcements of opportunity associated with OSNAP in the UK. We successfully described the observations that are ongoing on the eastern margin of the subpolar North Atlantic.Problems, sustainability, and opportunities were all discussed. Scientific problems that straddle the region were discussed. In particular, focus on the European Slope Current highlighted open scientific questions that can be addressed with co-ordinated analysis of the existing arrays and co-ordinated observations in the future. The workshop was held on 14 October 2019 in Edinburgh (UK), at the Hudson Beare Building, King’s Buildings, Edinburgh University. The workshop was organised by Gerard McCarthy (NUIM) and Stuart Cunnigham (SAMS), with the support of the project management of Blue-Action (DMI) and Atlas (University of Edinburgh). The workshop is a collaboration of three EU-funded projects, Blue-Action and ATLAS, funded by the European Union’s Horizon 2020 research and innovation programme under grant agreements No 727852 (Blue-Action) and No 678760 (ATLAS) and the A4 project (Aigéin, Aeráid, Agus athrú Atlantaigh—Oceans, Climate, and Atlantic Change), funded by the Irish Marine Institute and the European Regional Development fund (grant: PBA/CC/18/01).

Overview of Work Package 2 of Blue-Action "Lower latitude drivers of Arctic change"

Presentation at the AGU Ocean Sciences Meeting, Portland Oregon,11-16th February 2018. PL23A: Atlantic Meridional Overturning Circulation: Modeling and Observations

Presentation held at the Climate Science2Policy workshop on 17-18 November 2020. The event was organised by the Executive Agency for Small and Medium-sized enterprises (EASME), European Commission, in collaboration with a cluster of H2020 Earth System Science projects, like Blue-Action., The Blue-Action project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 727852

A novel ocean mixed layer heat budget analysis methodology is developed and used to investigate the physicalprocesses which determine Subpolar North Atlantic (SPNA) SST and OHC variability on decadal-multidecadaltimescales using the state-of-the-art coupled climate model HadGEM3-GC2. Contributions to OHC and SSTvariability from three sources are evaluated i) the net ocean-atmosphere heat flux, ii) divergence of the oceanichorizontal temperature transport and iii) entrainment between the ocean surface mixed layer and the layer beneath.Anomalies in OHC and SST tendency propagate anticlockwise around the SPNA on multidecadal timescaleswith a clear relationship to the Phase of the AMOC. AMOC anomalies lead SST tendencies which in turn leadOHC tendencies. This result is common to both eastern and western SPNA, although the primary driver of OHCvariability differs with surface fluxes dominant in the west and advection-diffusion in the east. The reciprocal ofthe mixed layer depth is found to be an important variable which causes SST to respond faster to AMOC changesthan OHC. The implications of these new results for interpretation of lower resolution coupled models, includingmany of those used in the CMIP6 assessment are discussed