Southern Ocean observations and change
Project Leader: Dr Steve Rintoul
Staff and students: Dr Laura Herraiz-Borreguero (CSIRO); Dr Elizabeth Shadwick (CSIRO); Mr Saisai Hou (Ocean University of China PhD student).
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Steve Rintoul: My project is looking at the Southern Ocean with an emphasis on observations of the Southern Ocean and we’re targeting a few different things. One is changes in the deep ocean. We’ve found some of the strongest signals of change anywhere in the deep ocean in the waters around Antarctica and we really need to understand why. What does it mean? What are the implications of that and why is it happening?
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And one way we’ll do that is through ships, the traditional way that we have of measuring the deepest parts of the ocean, but we’ll also be deploying the first pilot arrays of something called deep Argo floats. These are profiling floats that can work through the whole ocean depth.
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Eighty percent of the Southern Hemisphere is covered by oceans and they’ve been largely unmeasured and poorly understood.
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That’s beginning to change, and we can use that new information to develop new insights into how the Southern Hemisphere oceans work and how they affect regional and global climate.
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This project will achieve two things.
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One it will allow us to better understand how and why the deep ocean is changing and two how changes in the Southern Ocean will affect the Antarctic ice sheet where the waters interact with the floating ice around the edge of Antarctica.
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Dr Steve Rintoul introduces the Southern Ocean observations and change project
The project will collect new physical and biogeochemical observations in the Southern Ocean and use them with the historical record to develop a better physical understanding of the sensitivity of circulation and water mass formation to changes in forcing.
The overall objective of the project is to quantify variability and trends in ocean circulation and water mass formation in the Australian sector of the Southern Ocean, using a combination of shipboard data, float observations and satellite data, and to identify the physical mechanisms driving change.
Specific objectives include:
- Quantify full-ocean depth changes along the SR3 repeat hydrographic section between Tasmania and Antarctica
- As part of a collaborative project with NZ and the USA, use profiling floats to obtain the first comprehensive, year-round measurements of the Ross Gyre and quantify the circulation
- Lead the design and implementation of the first international deep Argo pilot array in the Southern Ocean
- Assess the potential for warm ocean waters to reach ice shelf cavities in East Antarctica and drive enhanced basal melt, with potential focus areas including Prydz Bay and the Shackleton Ice Shelf
Antarctic floating ice walls protect against warming seas (Feb. 2020)
The Antarctic Ice Sheet contains enough ice, if melted, to raise global sea levels by tens of metres. A new study by Wåhlin et al., published in the journal Nature, shows that floating ice walls offer some protection to the ice sheet by deflecting warm ocean currents, that would otherwise penetrate cavities beneath the floating portions of the ice sheet.
In this paper, an international research group, including CSHOR’s Dr Herraiz-Borreguero, has explored the physics behind the warm ocean currents that surround the Antarctic coast. It is a step forward in understanding heat delivery to the Antarctic Ice Sheet.
Further detail is provided in the CSHOR post at this link. A link to the full article is listed with the reference at the end of this page.
The importance of Antarctica for the Earth’s climate (Jan. 2020)
A conversation between Dr Steve Rintoul and Robyn Williams on “The importance of Antarctica for the Earth’s climate” was broadcast on the ABC’s Science Show at this link. The talk was recorded at a public lecture during National Science Week.
Premier’s Tasmanian STEM Researcher of the Year (Nov. 2019)
Project Leader, Dr Steve Rintoul has been awarded the Premier’s Tasmanian STEM Researcher of the Year prize for his pioneering work on climate research in the Southern Ocean.
Sustained Antarctic Research (Sept. 2019)
A new paper published in One Earth presents a roadmap of future research imperatives in Antarctic and the Southern Ocean (Kennicutt et al., 2019). The volume of the journal was timed to coincide with the Climate Action Summit in New York. The paper provides a comprehensive summary of progress made on 80 high priority science questions identified in a “horizon scan” carried out in 2014 and outlines priorities for the future. A link to the article is provided below with the full reference.
2nd Deep Argo Workshop
CSHOR and CSIRO hosted the 2nd Deep Argo Workshop at CSIRO Marine Laboratories Hobart from 13 to 15 May 2019. Over 30 international and national scientists attended the workshop. A public seminar on the morning of day 1 was also well attended by Hobart-based ocean scientists.
Workshop outcomes include a plan to tackle several technical challenges experienced in deep Argo research, the co-ordination of national plans and improved communication between manufactures, scientists and funding agencies.
What we learnt from spending winter under Antarctic sea ice
Read the CSIRO Blog reporting on a new mission for our fleet of Argo floats at this link.
Choosing the future of Antarctica
In a recent Nature article, Rintoul et al. present two narratives on the future of Antarctica and the Southern Ocean, from the perspective of an observer looking back from 2070. Read the CSHOR post, which includes a link to the full article, at this link.
The global influence of localised dynamics in the Southern Ocean
This Nature review by Dr Steve Rintoul evaluates the published research on Southern Ocean change: including changes in circulation, stronger winds, and increased freshwater input. The Southern Ocean exerts a disproportionate and profound influence on global ocean currents, climate, biogeochemical cycles, and sea level rise. The paper shows that substantial progress has been made in recent years in understanding the dynamics and global influence of the Southern Ocean. It is becoming clear that local scale processes play a fundamental part in shaping large-scale circulation. This is drive by the local topography which, of course, doesn’t change to a significant degree. Read the full article at this link.
Global warming is melting Antarctic ice from below
The results from a study published in Science Advances, and reported in a recent Guardian article, suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.
CSHOR is one of several organisations supporting the research and is duly acknowledged by the authors of the paper.
The figure below is an extract from the Science Advances paper.
Figure: Impact of glacial meltwater on dense water formation and shelf stratification.
On warm continental shelves, as those on the Sabrina Coast and in the Amundsen Sea (A), MCDW drives rapid ice shelf basal melt. The large volume of glacial meltwater prevents DSW formation in polynyas downstream of the meltwater outflow. MCDW remains in the bottom layer throughout the year in the polynya and further downstream, where it can access the ice shelf cavities. On cold continental shelves, the ice shelf cavities are filled by cold shelf waters, and basal melt rates are low. Glacial meltwater input is not sufficient to suppress winter convection in polynyas downstream of the meltwater outflow, as seen at Cape Darnley Polynya (B), allowing formation of DSW, the precursor to Antarctic Bottom Water.
Bestley, S., V. Andrews-Goff, E. van Wijk, S. R. Rintoul, M. C.Double and J. How (2019). New insights into prime forage grounds for thriving Western Australian humpback whales. Scientific Reports, 9, 13988. https://doi.org/10.1038/s41598-019-50497-2.
Castagno, P. V. Capozzi, G. R. DiTullio, P. Falco, G. Fusco, S. R. Rintoul, and G. Budillon (2019). Rebound of shelf water salinity in the Ross Sea. Nature Communications, 10, 1-6. https://doi.org/10.1038/s41467-019-13083-8.
Cougnon, E. A., Galton-Fenzi, B. K., Rintoul, S. R., Legrésy, B., Williams, G. D., Fraser, A. D., & Hunter, J. R. (2017). Regional Changes in Icescape Impact Shelf Circulation and Basal Melting. Geophysical Research Letters, 44(22), 11,519-11,527. https://doi.org/10.1002/2017GL074943.
Downes, S. M., Sloyan, B. M., Rintoul, S. R., & Lupton, J. E. (2019). Hydrothermal heat enhances abyssal mixing in the Antarctic Circumpolar Current. Geophysical Research Letters, 46, 812–821. https://doi.org/10.1029/2018GL080410.
Gao, L., Rintoul, S. R., & Yu, W. (2017). Recent wind-driven change in Subantarctic Mode Water and its impact on ocean heat storage. Nature Climate Change, 8, 58-63. https://doi.org/10.1038/s41558-017-0022-8.
Kennicutt II, M. C., D. Bromwich, D. Liggett, B. Nja ̊stad, L. Peck, S. R. Rintoul, C. Ritz, M. J. Siegert, A. Aitken, C. M. Brooks, J. Cassano, S. Chaturvedi, D. Chen, K. Dodds, N. R. Golledge, C. Le Bohec, M. Leppe, A. Murray, P. C. Nath, M. N. Raphael, M. Rogan-Finnemore, D. M. Schroeder, L. Talley, T. Travouillon, D. G. Vaughan, L. Wang, A. T. Weatherwax, H. Yang, and S. L. Chown (2019). Sustained Antarctic Research: a 21st Century Imperative. One Earth, 1, 95-113. https://doi.org/10.1016/j.oneear.2019.08.014.
Lambelet, M., Tina van de Flierdt, Edward C V Butler, Andrew R Bowie, Steve R Rintoul, Ros J Watson, Tom Remenyi, Delphine Lannuzel, Mark Warner, Laura F Robinson, Helen C Bostock and Louisa I Bradtmiller (2018). The Neodynium isotope fingerprint of Adélie Coast Bottom Water. Geophysical Research Letters, 45(20), 11,247-211,256. https://doi.org/10.1029/2018GL080074.
Langlais, C. E., Lenton, A., Matear, R., Monselesan, D., Legrésy, B., Cougnon, E., & Rintoul, S. (2017). Stationary Rossby waves dominate subduction of anthropogenic carbon in the Southern Ocean. Scientific Reports, 7(1), 17076. https://doi.org/10.1038/s41598-017-17292-3.
Moreau, S., D. Lannuzel, J. Janssens, M. Arroyo, M. Corkill, E. Cougnon, C. Genovese, B. Legresy, A. Lenton, V. Puigcorbe, L. Ratnarajah, S. Rintoul, M. Rocca-Marti, M. Rosenberg, E. Shadwick, A. Silvano, P.G. Strutton, B. Tilbrook (2019). Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas. Journal of Geophysical Research: Oceans, 124(5), 2943-2968. https://doi.org/10.1029/2019JC015071.
Newman, L., P. Heil, R. Trebilco, K. Katsumata, A. Constable, E. van Wijk, K. Assmann, J. Beja, P. Bricher, R.Coleman, Daniel Costa, S. Diggs, R. Farneti, S. Fawcett, S.T Gille, Katharine R Hendry, S. Henley, E. Hofmann, Ted Maksym, Matthew Mazloff, A. Meijers, M. M Meredith, S. Moreau, B. Ozsoy, R. Robertson, I. Schloss, O. Schofield, J. Shi, E. Sikes, I. J Smith, S. Swart, A. Wahlin, Guy Williams, Michael JM Williams, L. Herraiz-Borreguero, Stefan Kern, J. Lieser, R. A Massom, J. Melbourne-Thomas, P.Miloslavich, G.Spreen (2019). Delivering sustained, coordinated, and integrated observations of the Southern Ocean for global impact. Frontiers in Marine Science 6(433). https://doi.org/10.3389/fmars.2019.00433.
Pardo, P. C., Tilbrook, B., Langlais, C., Trull, T. W., & Rintoul, S. R. (2017). Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania. Biogeosciences, 14(22), 5217-5237. https://www.biogeosciences.net/14/5217/2017/.
Rintoul, S. R. (2018). The global influence of localized dynamics in the Southern Ocean. Nature, 558(7709), 209-218. https://doi.org/10.1038/s41586-018-0182-3.
Rintoul, S. R., Chown, S. L., DeConto, R. M., England, M. H., Fricker, H. A., Masson-Delmotte, V., Naish, T. R., Siegert, M. J., & Xavier, J. C. (2018). Choosing the future of Antarctica. Nature, 558(7709), 233-241. https://doi.org/10.1038/s41586-018-0173-4.
Schlitzer, R. et al. (2018). The GEOTRACES Intermediate Data Product 2017. Chemical Geology, 493, 210-223 (Rintoul one of 238 authors) https://doi.org/10.1016/j.chemgeo.2018.05.040.
Snow, K., Rintoul, S. R., Sloyan, B. M., & Hogg, A. M. (2018). Change in Dense Shelf Water and Adélie Land Bottom Water Precipitated by Iceberg Calving. Geophysical Research Letters, 45(5), 2380-2387. https://doi.org/10.1002/2017GL076195.
Silvano, A., Rintoul, S. R., Kusahara, K., Peña-Molino, B., van Wijk, E., Gwyther, D. E., & Williams, G. D. (2019). Seasonality of Warm Water Intrusions Onto the Continental Shelf Near the Totten Glacier. Journal of Geophysical Research: Oceans, 124(6), 4272-4289. https://doi.org/10.1029/2018JC014634.
Silvano, A., Rintoul, S. R., Peña-Molino, B., Hobbs, W. R., van Wijk, E., Aoki, S., Tamura, T., & Williams, G. D. (2018). Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water. Science Advances, 4(4). https://advances.sciencemag.org/content/4/4/eaap9467.
Wallace, L.O., E.M. van Wijk, S.R. Rintoul and B. Hally (2020). Bathymetry-constrained navigation of Argo floats under sea ice on the Antarctic continental shelf. Geophysical Research Letters, 47, e2020GL087019. https://doi.org/10.1029/2020GL087019.
Wåhlin, A. K., N. Steiger, E. Darelius, K. M. Assmann, M. S. Glessmer, H. K. Ha, L. C. Herraiz-Borreguero, C. Heuzé, A. Jenkins, T. W. Kim, A. K. Mazur, J. Sommeria, and S. Viboud, (2020) Ice front blocking of ocean heat transport to an Antarctic ice shelf. Nature, 578, 568–571. https://doi.org/10.1038/s41586-020-2014-5.