Southern Ocean dynamics, circulation and water mass formation

Project leader: Prof Matthew England (UNSW)

Staff and students: Dr Kathy Gunn, Dr Andrew Lenton (CSIRO); Mr Zhi Li (UNSW PhD student); and Dr Steve Rintoul (CSIRO).

[Music plays and animation waves appear moving up from the bottom of the screen and text appears above: The Centre for Southern Hemisphere Oceans Research]

[Image shows animation waves moving up the screen and over the text and then the image changes to show Professor Matthew England talking to the camera and text appears: Prof. Matthew England, CSHOR Project Leader, University of New South Wales]

Professor Matthew England: The key thing we’re trying to answer in this project is understanding the drivers of the warming in the Southern Ocean.

[Image changes to show a view looking out over a sunrise view of the ocean from the stern of a ship and then the image changes to show a view looking over the bow of the ship]

The Southern Ocean has warmed at the surface in certain sectors, at depths of the shelves and in the ocean abyss, and that warming could have profound implications for climate and we’re trying to understand exactly what is driving that warming and what we can expect into the future.

[Image changes to show Matthew talking to the camera]

The big reason this research is important is that we need to understand what’s happening with the oceans right at the Antarctic margin.

[Image changes to show a view of an ice shelf looking from the deck of a ship and then the image changes to show Matthew talking to the camera]

This is where the oceans sit right up against the ice shelves and ice sheets and the warming there in certain sectors has been very worrying recently. It’s at a rate that exceeds our expectations.

[Image changes to show a graph displaying the global sea level rise and text appears: Global mean sea level anomalies]

With warming there we’re going to see much greater rates of ice melt and that ice melt will drive global sea level rise. So, this is a profound question for humanity.

[Image changes to show a view of the Investigator moving through the water towards the camera]

The goal with this project in CSHOR is to have a comprehensive understanding of the drivers of warming of the oceans around Antarctica.

[Image changes to show Matthew talking to the camera]

Hundreds of millions of people live near the coast around the globe and are vulnerable to even just one metre of sea level rise. The warming around Antarctica at the moment is enough to melt ice at a rate that will contribute to that sea level rise into the future and that will displace people globally. Understanding this rate of warming at the Antarctic margin will help us understand future sea level rise which will help us plan for this inevitable relocation of communities around the world’s coastlines.

[Music plays and the image changes to show animation waves across the bottom of the screen and Qingdao National Laboratory for Marine Science and Technology, CSIRO, UNSW and University of Tasmania logos appear]

Prof Matthew England introduces the Southern Ocean dynamics, circulation and water mass formation project

Latest news

Interbasin and interhemispheric impacts of a collapsed Atlantic Overturning Circulation (June 2022)

A recent Nature Climate Change article, by Bryam Orihuela-Pinto, Matthew H. England & Andréa S. Taschetto (2022), shows that Atlantic Meridional Overturning Circulation collapse can accelerate the Pacific trade winds and Walker circulation by leaving an excess of heat in the tropical South Atlantic. This tropical warming drives anomalous atmospheric convection, resulting in enhanced subsidence over the east Pacific and a strengthened Walker circulation and trade winds. Further teleconnections include weakening of the Indian and South Atlantic subtropical highs and deepening of the Amundsen Sea Low. These findings have important implications for understanding the global climate response to ongoing greenhouse gas increases. The authors’ discuss the significance of their research in The Conversation.

Deep Argo Reveals Bottom Water Properties and Pathways in the Australian-Antarctic Basin (Feb. 2022)

A Journal of Geophysical Research: Oceans article by Foppert et al. (2021), on Antarctic Bottom Water changes and pathways revealed by Deep Argo floats, was selected as a Research Highlight in the AGU publication EOS. Twelve Deep Argo floats were deployed in the Australian-Antarctic Basin and have been continuously profiling for over two years, producing an unprecedented observational data set of AABW properties. Read the full article at this link.

Link to CSHOR science seminar project presentation, July 2021

Global changes in oceanic mesoscale currents (April 2021)

Prof Matthew England discussed results from work he published with colleagues at Australian National University that showed a significant increase in global eddy kinetic energy detected over the last 3 decades, with a particularly strong increasing trend signal over the Southern Ocean. The work, which appeared in Nature Climate Change, was profiled in the Sydney Morning Herald (Australia 22/04/2021), The Age (Australia 22/04/2021), and The Guardian (Australian Edition 23/04/2021). Read the journal article here.

Dr Kathy Gunn joins the project team (March 2021)

In early March 2021, Dr Kathy Gunn commenced a Postdoctoral Fellow position at CSIRO. Her research uses physical and acoustic observations to better understand water mass variability at a range of scales. She has worked on warm water transport in the west Antarctic Peninsula, mixing at fronts in the Southwest Atlantic, and small-scale to large-scale temperature and salinity variability in the Indian Ocean. As a member of the CSHOR team, Dr Gunn will use classic and state-of-the-art hydrographic observations to quantify the ventilation of bottom water over time and space. Dr Gunn replaces Dr Annie Foppert, who moved to a new role as Research Associate with the Australian Antarctic Partnership Program (AAPP).

AMOS Morton Medal 2020 (Dec. 2020)

Prof Matthew England has been awarded the Morton Medal in recognition of his leadership in oceanography and climate and related fields, particularly through education and the development of young scientists, and through the building of research environments in Australia. Prof England is Deputy Director (Research) and Scientia Professor – Climate Change Research Centre (CCRC) at The University of New South Wales, and a CSHOR Project Leader.

Publications

Belkin, I., A. Foppert, H. T. Rossby, T., S. Fontana, and C. Kincaid (2020). A Double-Thermostad Warm-Core Ring of the Gulf Stream. Journal of Physical Oceanography, 50, 2, 489–507. https://doi.org/10.1175/JPO-D-18-0275.1.

Devries, T., Le Quéré C., Andrews, O., Berthet, S, Hauck, J. Ilyina, T., Landschützer, P., Lenton, A., Lima. I., Nowicki, M. Schwinger, J., Séférian, R. (2019). Decadal trends in the ocean carbon sink. Proceedings of the National Academy of Sciences, 116(24), 11646-11651. https://doi.org/10.1073/pnas.1900371116.

Foppert, Annie (2019). Observed storm track dynamics in Drake Passage. Journal of Physical Oceanography, 3, 867-884. https://doi.org/10.1175/JPO-D-18-0150.1.

Foppert, A., Rintoul S. R., and England M. H. (2019). Along-slope variability of cross-slope eddy transport in East Antarctica. Geophysical Research Letters, 46(14), 8224-8233. https://doi.org/10.1029/2019GL082999.

Goyal, R., England, M. H., Jucker, M., & Sen Gupta, A. (2021). Response of Southern Hemisphere western boundary current regions to future zonally symmetric and asymmetric atmospheric changes. Journal of Geophysical Research: Oceans, 126, e2021JC017858. https://doi.org/10.1029/2021JC017858.

Goyal, R., Gupta, A. S., Jucker, M., & England, M. H. (2021). Historical and projected changes in the Southern Hemisphere surface westerlies. Geophysical Research Letters, 48, e2020GL090849. https://doi.org/10.1029/2020GL090849.

Goyal, R., Jucker, M., Sen Gupta, A., & England, M. H. (2021). Generation of the Amundsen Sea Low by Antarctic orography. Geophysical Research Letters, 48, e2020GL091487. https://doi.org/10.1029/2020GL091487.

Goyal, R., Jucker, M., Gupta, A. S., & England, M. H. (2022). A new zonal wave 3 index for the Southern Hemisphere. Journal of Climate. Early Online Release. https://journals.ametsoc.org/view/journals/clim/aop/JCLI-D-21-0927.1/JCLI-D-21-0927.1.xml.

Hauck, J., Lenton, A., Langlais, C, Matear, R. J. (2018). The fate of carbon and nutrients exported out of the Southern Ocean. Global Biogeochemical Cycles, 32(10), 1556-1573. https://doi.org/10.1029/2018GB005977.

Hauck, J., Zeising, M., Le Quéré, C., Gruber, N., Bakker, D. C. E., Bopp, L., Chau, T. T. T., Gürses, Ö., Ilyina, T., Landschützer, P., Lenton, A., Resplandy, L., Rödenbeck, C., Schwinger, J., and Séférian, R. (2020). Consistency and Challenges in the Ocean Carbon Sink Estimate for the Global Carbon Budget. Frontiers in Marine Science, 7, 1–33, https://doi.org/10.3389/fmars.2020.571720.

Holmes, R. M., J. D. Zika, and M. H. England (2019). Diathermal Heat Transport in a Global Ocean Model. Journal of Physical Oceanography, 49, 141-161. https://doi.org/10.1175/JPO-D-18-0098.1.

Holmes, R. M., J. D. Zika, R. Ferrari, A. F. Thompson, E. R. Newsom and M. H. England (2019). Atlantic Ocean heat transport enabled by Indo-Pacific heat uptake and mixing, Geophysical Research Letters, 46, 13,939-13,949. https://doi.org/10.1029/2019GL085160.

Lago, V., and M. H. England (2019). Projected slowdown of Antarctic Bottom Water formation in response to amplified meltwater contributions, Journal of Climate, 32(19), 6319-6335. https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0622.1.

Li, Q., & England, M. H. (2020). Tropical Indo‐Pacific teleconnections to Southern Ocean mixed layer variability. Geophysical Research Letters, 47, e2020GL088466. https://doi.org/10.1029/2020GL088466.

Li, Q., England, M. H., & McC. Hogg, A. (2021). Transient Response of the Southern Ocean to Idealized Wind and Thermal Forcing across Different Model Resolutions, Journal of Climate, 34(13), 5477-5496, https://doi.org/10.1175/JCLI-D-20-0981.1.

Li, Q., S. Lee, M. H. England, and J. L. McClean (2019). Seasonal-to-interannual response of Southern Ocean mixed layer depth to the Southern Annular Mode from a global 1/10° ocean model. Journal of Climate, 32(18), 6177-6195. https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0159.1.

Li, Z., M. H. England; S. Groeskamp; I. Cerovečki; Y. Luo (2021). The origin and fate of Subantarctic Mode Water in the Southern Ocean, Journal of Physical Oceanography, 51(9), 2951–2972. https://journals.ametsoc.org/view/journals/phoc/51/9/JPO-D-20-0174.1.xml.

Martínez-Moreno, J., Hogg, A.M., England, M.H. Constantinou, N. C., Kiss, A. E., and Morrison, A. K. (2021). Global changes in oceanic mesoscale currents over the satellite altimetry record. Nature Climate Change, 11, 397–403, https://doi.org/10.1038/s41558-021-01006-9.

Meijers, A. J. S., Cerovečki, I., King, B. A., & Tamsitt, V. M. (2019). A see‐saw in Pacific Subantarctic Mode Water formation driven by atmospheric modes. Geophysical Research Letters. https://doi.org/10.1029/2019GL085280.

Orihuela-Pinto, B., England, M.H. & Taschetto, A.S. (2022). Interbasin and interhemispheric impacts of a collapsed Atlantic Overturning Circulation. Nature Climate Change. https://doi.org/10.1038/s41558-022-01380-y.

Orihuela-Pinto, B., Santoso, A., England, M. H., & Taschetto, A. S. (2022). Reduced ENSO Variability due to a Collapsed Atlantic Meridional Overturning Circulation. Journal of Climate, 35(16), 5307-5320. https://journals.ametsoc.org/view/journals/clim/35/16/JCLI-D-21-0293.1.xml.

Patel, R. S., Llort, J., Strutton, P. G., Phillips, H. E., Moreau, S., Conde Pardo, P., & Lenton, A. (2020). The biogeochemical structure of Southern Ocean mesoscale eddies. Journal of Geophysical Research: Oceans, 125, e2020JC016115. https://doi.org/10.1029/2020JC016115.

Purich, A., England, M. H., Cai, W., Sullivan, A., & Durack, P. J. (2018). Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model. Journal of Climate, 31(7), 2613-2632. https://doi.org/10.1175/JCLI-D-17-0092.1

Shimura, T., Hemer, M., Lenton, A., Chamberlain, M. A., & Monselesan, D. (2020). Impacts of ocean wave‐dependent momentum flux on global ocean climate. Geophysical Research Letters, 47, e2020GL089296. https://doi.org/10.1029/2020GL089296.

Tamsitt, V. (2018). Moving windows to the deep ocean (News and Views), Nature Climate Change, 8, 941-942. https://doi.org/10.1038/s41558-018-0324-5

Tamsitt, V., Cerovečki, I., Josey, S., Gille, S., and Schulz, E. (2020). Mooring Observations of Air–Sea Heat Fluxes in Two Subantarctic Mode Water Formation Regions. Journal of Climate, 33(7), 2757-2777. https://journals.ametsoc.org/view/journals/clim/33/7/jcli-d-19-0653.1.xml

Tamsitt, V., M. H. England, S. R. Rintoul, A. K. Morrison, 2021: Residence time of warm Circumpolar Deep Water on the Antarctic continental shelf, Geophysical Research Letters, 48, e2021GL096092. https://doi.org/10.1029/2021GL096092

Tamsitt, V., L. D. Talley and M. R. Mazloff (2019). A Deep Eastern Boundary Current carrying Indian Deep Water south of Australia. Journal of Geophysical Research: Oceans. https://doi.org/10.1029/2018JC014569.

Webb, D. J., R. M. Holmes, P. Spence, and M. H. England (2019). Barotropic Kelvin wave-induced bottom boundary layer warming along the West Antarctic Peninsula. Journal of Geophysical Research: Oceans. https://doi.org/10.1029/2018JC014227.

Webb, D. J., R. M. Holmes, P. Spence, and M. H. England (2022). Propagation of barotropic Kelvin waves around Antarctica. Ocean Dynamics 72, 405–419. https://doi.org/10.1007/s10236-022-01506-y.

Webb, D. J., P. Spence, R. M. Holmes, and M. H. England (2021). Planetary-wave induced strengthening of the AMOC forced by poleward intensified Southern Hemisphere westerly winds, Journal of Climate, 34(17), 7073–7090. https://doi.org/10.1175/JCLI-D-20-0858.1.

Wei, Y., Gille, S. T., Mazloff, M. R., Tamsitt, V., Swart, S., Chen, D., & Newman, L. (2020). Optimizing Mooring Placement to Constrain Southern Ocean Air–Sea Fluxes, Journal of Atmospheric and Oceanic Technology, 37(8), 1365-1385. https://journals.ametsoc.org/view/journals/atot/37/8/jtechD190203.xml.

Project objectives

1. Warming in the surface Southern Ocean

Explore the drivers of the Amundsen-Bellingshausen Sea warming, including warming driven by changes in the pathway / temperatures of the Antarctic Circumpolar Current (ACC), atmospheric teleconnections from the tropics, and coupled ice-ocean feedbacks. A high-resolution ocean model will be used to examine the role of westerly wind anomalies and associated changes in the upwelling and poleward transport of Circumpolar Deep Water. Observations will be used to test and improve the model simulations.

2. Warming in the abyssal ocean

Configure a hierarchy of model experiments to investigate the sensitivity of the lower cell of the Southern Ocean overturning circulation to changes in forcing (wind, heat flux and freshwater fluxes from sea ice melt and melting ice shelves).

3. Warming over the Antarctic continental shelf

Explore what controls the delivery of ocean heat to Antarctic ice shelves. Simulations using global coupled models, high resolution regional models, and idealised process models will be used to assess the sensitivity of ocean – ice shelf interaction to changes in forcing.

4. Carbon uptake in the Southern Ocean

Explore the sensitivity of ocean carbon uptake to changes in the upper cell over the Southern Ocean. A high-resolution biogeochemical model will be used to determine the physical mechanisms responsible for exchange of carbon between the atmosphere and the Southern Ocean (both uptake of anthropogenic carbon and outgassing of natural carbon).

5. Dynamics of the Antarctic Circumpolar Current

Use high resolution models to explore Antarctic Circumpolar Current (ACC) dynamics, with a focus on interaction across scales. The momentum and vorticity budgets of the ACC have long been known to depend on interaction of the current with sea floor bathymetry, but exactly how the large-scale balances are maintained is not understood. Internal waves, sub-mesoscale filaments and mesoscale eddies all likely play a role in determining the response of the current to changes in forcing. High-resolution model studies will be used to explore the impact of local dynamics on the response of the ACC to anomalies in forcing.