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Meijers AJS, Meredith MP, Shuckburgh EF, Kent EC, Munday DR, Firing YL, King B, Smyth TJ, Leng MJ, George Nurser AJ, Hewitt HT, Povl Abrahamsen E, Weiss A, Yang M, Bell TG, Alexander Brearley J, Boland EJD, Jones DC, Josey SA, Owen RP, Grist JP, Blaker AT, Biri S, Yelland MJ, Pimm C, Zhou S, Harle J, Cornes RC. Finale: impact of the ORCHESTRA/ENCORE programmes on Southern Ocean heat and carbon understanding. Philos Trans A Math Phys Eng Sci 2023; 381:20220070. [PMID: 37150199 PMCID: PMC10164468 DOI: 10.1098/rsta.2022.0070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Accepted: 01/24/2023] [Indexed: 05/09/2023]
Abstract
The 5-year Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA) programme and its 1-year extension ENCORE (ENCORE is the National Capability ORCHESTRA Extension) was an approximately 11-million-pound programme involving seven UK research centres that finished in March 2022. The project sought to radically improve our ability to measure, understand and predict the exchange, storage and export of heat and carbon by the Southern Ocean. It achieved this through a series of milestone observational campaigns in combination with model development and analysis. Twelve cruises in the Weddell Sea and South Atlantic were undertaken, along with mooring, glider and profiler deployments and aircraft missions, all contributing to measurements of internal ocean and air-sea heat and carbon fluxes. Numerous forward and adjoint numerical experiments were developed and supported by the analysis of coupled climate models. The programme has resulted in over 100 peer-reviewed publications to date as well as significant impacts on climate assessments and policy and science coordination groups. Here, we summarize the research highlights of the programme and assess the progress achieved by ORCHESTRA/ENCORE and the questions it raises for the future. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.
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Affiliation(s)
| | | | - Emily F. Shuckburgh
- Department of Computer Science and Technology, University of Cambridge, William Gates Building 15 JJ Thomson Avenue, Cambridge CB3 0FD, UK
| | - Elizabeth C. Kent
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - David R. Munday
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
| | - Yvonne L. Firing
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Brian King
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Tim J. Smyth
- Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK
| | - Melanie J. Leng
- British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
| | | | | | - E. Povl Abrahamsen
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
| | - Alexandra Weiss
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
| | - Mingxi Yang
- Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK
| | - Thomas G. Bell
- Plymouth Marine Laboratory, Prospect Place, Plymouth PL1 3DH, UK
| | | | - Emma J. D. Boland
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
| | - Daniel C. Jones
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
| | - Simon A. Josey
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Robyn P. Owen
- National Oceanography Centre, Joseph Proudman Building, 6 Brownlow Street, Liverpool L3 5DA, UK
| | - Jeremy P. Grist
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Adam T. Blaker
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Stavroula Biri
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | | | - Ciara Pimm
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
- Department of Earth, Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool, UK
| | - Shenjie Zhou
- British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK
| | - James Harle
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Richard C. Cornes
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
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Sauermilch I, Whittaker JM, Klocker A, Munday DR, Hochmuth K, Bijl PK, LaCasce JH. Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling. Nat Commun 2021; 12:6465. [PMID: 34753912 PMCID: PMC8578591 DOI: 10.1038/s41467-021-26658-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 09/08/2021] [Indexed: 11/09/2022] Open
Abstract
Declining atmospheric CO2 concentrations are considered the primary driver for the Cenozoic Greenhouse-Icehouse transition, ~34 million years ago. A role for tectonically opening Southern Ocean gateways, initiating the onset of a thermally isolating Antarctic Circumpolar Current, has been disputed as ocean models have not reproduced expected heat transport to the Antarctic coast. Here we use high-resolution ocean simulations with detailed paleobathymetry to demonstrate that tectonics did play a fundamental role in reorganising Southern Ocean circulation patterns and heat transport, consistent with available proxy data. When at least one gateway (Tasmanian or Drake) is shallow (300 m), gyres transport warm waters towards Antarctica. When the second gateway subsides below 300 m, these gyres weaken and cause a dramatic cooling (average of 2–4 °C, up to 5 °C) of Antarctic surface waters whilst the ACC remains weak. Our results demonstrate that tectonic changes are crucial for Southern Ocean climate change and should be carefully considered in constraining long-term climate sensitivity to CO2. The role of Southern Ocean gateways contributing to the Eocene-Oligocene climate transition is still debated. Here, the authors present high-resolution ocean simulations to show that gateways opening led to a reorganization of ocean circulation, heat transport and Antarctic surface water cooling.
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Affiliation(s)
- Isabel Sauermilch
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia. .,Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.
| | - Joanne M Whittaker
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
| | - Andreas Klocker
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia.,Australian Research Council Centre of Excellence for Climate Extremes, University of Tasmania, Hobart, Australia
| | | | - Katharina Hochmuth
- Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany.,School of Geography, Geology and the Environment, University of Leicester, Leicester, UK
| | - Peter K Bijl
- Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands
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Hogg AM, Munday DR. Does the sensitivity of Southern Ocean circulation depend upon bathymetric details? Philos Trans A Math Phys Eng Sci 2014; 372:20130050. [PMID: 24891390 DOI: 10.1098/rsta.2013.0050] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change.
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Affiliation(s)
- Andrew McC Hogg
- Research School of Earth Sciences and ARC Centre of Excellence for Climate System Science, The Australian National University, Canberra, Australian Capital Territory 0200, Australia
| | - David R Munday
- Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK
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