Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities

On May 9-10th the Royal Society hosted the discussion meeting on: “Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities”.   This meeting was co-organised by ORCHESTRA and SONATA leads Andrew Meijers and Corinne Le Quéré, along with Pedro Monteiro of CSIR and Jean-Baptiste Sallée of LOCEAN.  The meeting served as a valuable community milestone seeking to assimilate and interpret insights and discoveries from observations and modelling of heat and carbon uptake, as well as identify future challenges and priorities for the coming five to ten years.  The meeting was attended by 100 people in person, with another 100+ online, with the ORCHESTRA/RoSES community well represented. Having so many of the international community together in person again at last, led to a very enthusiastic and engaged audience and each talk by the sixteen keynotes was discussed at length, as were the many posters provided by attendees.  Talks covered the outcomes of major programmes such as ORCHESTRA, physical processes, air-sea-ice interactions, biogeochemical and biological components of the carbon system, as well as global impacts of the Southern Ocean.  Recordings of presentations will become available at https://royalsociety.org/science-events-and-lectures/2022/05/southern-ocean/ and an issue of the Proceedings of the Royal Society A, with contributions by all speakers, will be released early in 2023.

ORCHESTRA and ENCORE: the highlights

After six years of ORCHESTRA and ENCORE research, and with ENCORE having officially ended on the 31st March, what have been the highlights and what foundations have been laid for future research from these projects? Andrew Meijers, who led the projects explains:

“ORCHESTRA (Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports) and its extension project ENCORE was a six year, ~11 million pound BAS led programme involving seven UK research centres. It sought to radically improve our ability to measure, understand and predict the circulation of the Southern Ocean through a series of milestone observational campaigns in combination with model development and analysis. Eleven cruises in the Weddell Sea and South Atlantic were undertaken, along with moorings, glider and profiler process studies and air-sea heat and carbon flux measurements from ships and aircraft. Numerous forward and adjoint model experiments, looking at ocean heat content sensitivities, were developed and supported by extensive analysis of coupled climate models and support for model development at the UK Met Office.

ORCHESTRA/ENCORE has resulted in almost 100 peer reviewed publications so far, innumerable talks and presentations, delivered public outreach and education and supported dozens of postdoctoral and PhD students.  As a National Capability programme its voyages, datasets and model development have provided a platform for the wider community to exploit.  It directly supported high impact policy relevant documents such as the IPCC Special Report on Oceans and Cryospheres, but also had impact beyond purely physical oceanography.  A great example of this were several high impact ecosystems papers supported by ORCHESTRA data, as well as explicit participation in the CCAMLR-ICED workshops and reports. 

There have been many research highlights coming out of ORCHESTRA, as well as the development of important community data tools; notably new mappings of hydrographic data and bulk formula code development by NOC partners.  Just a few examples of these highlights include:

  • Filling in huge gaps in air-sea flux observations through the installation of PML underway heat and carbon flux instrumentation on the RRS James Clark Ross (and soon on the RRS Sir David Attenborough too), and coordinating ship observations with complimentary BAS MASIN flights.  Novel results are already emerging showing the impacts that biological surfactants have in suppressing CO2 gas exchange between the ocean and atmosphere.
  • The discovery of declining trends in Weddell Sea Bottom Water volumes and export to the Scotia Sea, linked to changes in winds reducing formation rates in front of the Filchner-Ronne Ice Shelf. 
  • Observational and modelling efforts revealing new patterns in SubAntarctic Mode Water formation sites, and the discovery of strongly varying interannual ‘dipoles’ in formation in the Pacific and Indian basins, with potentially significant impact on our understanding of how the ocean responds to local and remote atmospheric changes and how heat and carbon are sequestered. 
  • Significant advances in understanding of how problematic Southern Ocean sea surface temperature biases in IPCC coupled climate models are formed (notably due to short wave radiation biases), and supporting the UK Met Office Southern Ocean group in addressing these issues in the HadGEM.
  • The completion of a milestone set of hydrographic sections, closing off the Weddell Sea and South Atlantic in two ‘boxes’, allowing the estimation of heat and carbon flux, storage and transports into and out of these key regions. 

While it is now formally finished, ORCHESTRA and ENCORE will continue to produce results and significantly influence the Southern Ocean communities thinking for many years to come.  It has been a great privilege and pleasure to lead this programme with such a motivated and talented group of scientists.

NEW FILM! The Ocean Driving the Climate

The Ocean Driving the Climate – Scientists are working to improve our understanding of the Southern Ocean and highlight its unique role in affecting Climate Change.

Watch the full film here: https://youtu.be/sUN2H7tsz3w

The Southern Ocean and our Climate

If you would like to know more about the Southern Ocean and the research carried out by the ORCHESTRA team, take a look at ‘The Southern Ocean and our Climate‘ publication. Find out how important the Southern Ocean is to the Earth’s climate system and see details about the huge operation involved in the research for this large-scale project. For example, you may not think of planes being involved in ocean science, but 94 aircraft flying hours have been accumulated over the last few years! ORCHESTRA research took to the skies using meteorological kit and measured things like how gases, such as carbon dioxide, transfer from the atmosphere to the ocean. Aircraft were just one of the many tools used in the research.

PhD studentship available

As part of the NERC-funded INSPIRE Doctoral Training Partnership (https://www.inspire-dtp.ac.uk/), we are seeking applicants for a competition-funded PhD studentship entitled: “The changing freshwater composition of the South Atlantic and Southern Ocean: causes and impacts“. This is a joint project between the British Antarctic Survey (in Cambridge) and the University of Southampton, with supervisors Povl Abrahamsen (BAS), Alberto Naveira Garabato (UoS), Mike Meredith (BAS), Robert Mulvaney (BAS), and Alex Brearley (BAS).

You can find more information about the project at: https://www.findaphd.com/phds/project/the-changing-freshwater-composition-of-the-south-atlantic-and-southern-ocean-causes-and-impacts/?p123752. Links to eligibility criteria and how to apply can be found at: https://www.inspire-dtp.ac.uk/how-apply. The deadline for applications is 4th January 2021, with interviews in the second half of February. The project will commence in late September 2021.

Please see the following brief project description:

The Southern Ocean exerts a disproportionate influence on our planet’s climate, via the strong drawdown of anthropogenic carbon and heat from the atmosphere that occurs there. This role is intimately connected to the Southern Ocean circulation; it is the key region globally where old waters are upwelled to the surface, and new waters created that sink back into the ocean interior. Freshwater inputs to the ocean can impact this circulation, by affecting density gradients and the stability of the upper ocean. Both sea ice meltwater and the melt of Antarctic glaciers exert such an influence, and both are known to be strongly variable, both in time and space. This project will use a tracer of freshwater inputs – the stable isotopes of oxygen in seawater – from the South Atlantic sector of the Southern Ocean to distinguish sea ice melt from other sources of freshwater in historical and recent ocean datasets. By linking these measurements with conventional oceanographic data, satellite data and the outputs of computer simulations, the student will determine the impact of known freshwater inputs on oceanographic circulation, the level to which variability in these sources impacts the ocean, and how such changes might influence climatically-important processes into the future.

When measured alongside salinity, the ratio of stable isotopes of oxygen in seawater is a key tracer for quantifying the input of sea ice melt separately from freshwater from other sources (glacial melt, precipitation). Substantial datasets of oxygen isotopes now exist, with many obtained recently from the NERC-funded ORCHESTRA programme (Ocean Regulation of Climate via Heat and Carbon Sequestration and Transport; https://www.orchestra.ac.uk). Ocean freshwater composition will be derived from these datasets using mass balance techniques, along with quantitative estimates of ocean circulation from inverse techniques applied to conventional oceanographic data, building on, and complementing, the inverse modelling that is being performed as part of ORCHESTRA. This will enable the ocean transports of different freshwater types to be determined, and their changes over time to be quantified. The availability of new datasets will enable these analyses to take place over larger spatial scales (i.e. basin scale) than has been done before. Relating these results to remotely-sensed quantifications of sea ice change and glacial ice change on Antarctica will reveal the impact on the ocean of the different freshwater inputs.

Please note that international students are eligible to apply; a limited number of studentships can be made available to international students. However, as things currently stand, the funding for these studentships will not cover the difference between UK and overseas tuition fees, leaving a shortfall of roughly £20k per year over the course of the 3.5-year PhD (~£70k in total). If you are not a UK citizen or permanent resident, you will need a plan for how you will cover these fees, e.g. through other grant sources. It is also possible that this situation might change before the start of the studentships, but this is not confirmed at present.

Other projects related to ocean/environment/climate are available from the INSPIRE Doctoral Training Partnership and details can be found at: https://noc.ac.uk/gsnocs/projects/inspire