The Southern Ocean plays a very important role in the global carbon-climate system Recent es
timates indicate that ~50% of all CO2 emitted by human activity (anthropogenic CO2) is stored in the Southern Ocean. The future trajectory of atmospheric CO2 concentrations – and thus the constraints on the minimum emissions reduction rates – thus depends critically on how the Southern Ocean carbon cycle will adjust to climate change.
Despite the importance of the Southern Ocean in ameliorating current increases in atmospheric CO2 and reducing the impact of man made climate change, the Southern Ocean remains under sampled and its carbon cycle is poorly understood.
South Africa has a comparative advantage through its geographical location to make a major impact in understanding and predicting the evolution of the Southern Hemisphere carbon-climate system.
CSIR research to understand the sensitivity of the Southern Ocean carbon cycle to climate change contributes to the global understanding of changes in Earth systems making South Africa a leading contributor to Southern Hemisphere ocean and climate science. In addition, we contribute to the development needs of South Africa by using these interesting global and regional challenges to attract and train a large number of post graduate students in advanced observations, numerical analysis and modelling. We are also developing the engineering and technological R&D skills needed to strengthen South Africa’s innovative capacity in the domains of ocean and coastal observational platforms and sensors.
The Southern Ocean plays three major roles in regulating the planet’s metabolism, all of which influence regional and global climate, ocean ecosystem productivity, ocean oxygen levels and global efforts to mitigate the effects of man-made CO2 on Earth’s systems.
Firstly, it is the only part of the ocean where CO2 rich deep waters (deeper than 2000 metres and pCO2 > 450µatm) upwell and exchange CO2 directly with the atmosphere south of the polar front. This means that despite it storing ~ 50% of industrial CO2 emissions, it also has the capacity, in response to anticipated climate change, of reversing its storage capacity and instead becoming a CO2 source posing potentially serious risks to the effectiveness of projected global emissions cuts. This mechanism, whereby the Southern Ocean becomes a source rather than a sink of CO2, is thought to be one of the explanations behind the long term cyclical response of atmospheric CO2 to glacial and inter-glacial climate cycles in the past million years, which suggests that over long periods, the ocean has been the most important regulator of atmospheric CO2.
Secondly, the physics of mode water and intermediate formation and flow into the low latitudes from the Southern Ocean are responsible for the supply of nutrients that drives more than 75% of ocean productivity, including South African coastal biodiversity and ecosystem services. Subantarctic mode water (SAMW) is an important water mass in the Earth’s oceans. It is formed near the Subantarctic Front on the northern flank of the Antarctic Circumpolar. These large scale processes are connected to surface ocean physics that respond sensitively to climate change impacts.
Thirdly, mode and intermediate waters not only supply nutrients and help store CO2 in the ocean interior, but are also responsible for the ventilation (oxygen concentrations) in the ocean interior which in turn play a role in the incidence and variability of coastal hypoxia.
Model data from the global science community as well as in situ observations over the past 30 years indicate that long term trends may be developing in surface mixed-layer characteristics of the Southern Ocean that are consistent with the expected outcomes of climate change driven by global warming. However, the impact of these changes on the carbon cycle and fluxes is likely to be highly non-linear.
A focus on the dynamical considerations (buoyancy forcing and wind-driven mixing) is a key step towards understanding the sensitivities of the system to change and its feedback to the planet’s warming as a result of changes in thermocline water formation, oceanic production and CO2 out gassing. The thermocline is the transition zone between the mixed layer at the surface and the deep ocean. The ocean mixed layer is primarily modulated by the seasonal cycle of heat and fresh water fluxes, which act to modulate the amount of nutrients and light available for primary production. Our recent work has highlighted that in very large areas of the Southern Ocean productivity and the biological carbon cycle are also modulated by sub-seasonal variability. This sensitivity to seasonal or sub-seasonal forcing is an important consideration in understanding the vulnerability of the Southern Hemisphere carbon cycle to climate change and reducing the uncertainty in predicting long term trends.
The SOCCO programme is a CSIR-led, multi-institutional South African initiative aiming to understand the link between climate and the carbon cycle in the Southern Ocean. The programme contributes a South African perspective to global concern around this potentially important positive feedback of the Earth climate system.
The programme comprises five active integrated projects, all focused on developing the integrated physical and biogeochemical understanding, through measurement and modelling, of the coupled carbon – climate system in the Southern Ocean.
Our research strategy comprises three focus areas:
- Earth system science research: understanding the scale sensitivities;
- Southern Hemisphere ocean – atmosphere CO2 fluxes; and
- Numerical model engineering and numerical analysis.
SOCCO partners are:
- University of Cape Town; Stellenbosch University; the Department of Environmental Affairs; the South African Weather Service; and the South African National Antarctic Programme
- Key international partners: Bjerknes Centre for Climate Research at the University of Bergen in Norway; and Princeton University
The programme contributes to the science and educational objectives of the Applied Centre for Climate and Earth Systems Science (ACCESS), a DST/NRF Centre of Excellence hosted by CSIR.
Focus area one: Earth System Science research
The development of global and regional scale Earth Systems Science is essential in making South Africa a recognised centre in Southern Hemisphere polar oceans and carbon – climate science
The first research objective is to address the question: how wrong are we getting the seasonal cycle of the carbon fluxes by not explicitly resolving the sub- mesoscale and sub-seasonal forcing in the Southern Ocean (regional and global models)?
The second research objective is to test and understand the sensitivity of the biogeochemical and upwelling elements of the Southern Ocean coupled carbon – climate system to changes in the large scale forcing characteristics of the Southern Annular Mode winds and fresh water fluxes. This activity is being developed through combining high resolution model and observational experiments. These comprise the South African Southern Ocean Seasonal Cycle Experiment in 2012, which also coincides with the launch of the new polar research ship, SA Agulhas II, and an international circumpolar equivalent that is still being planned possibly for 2014 – 2016. (www.subantarctic.net)
The Southern Ocean Seasonal Cycle Experiment (SOSCEx) to take place in 2012 incorporates ocean glider and CTD deployments supplemented by underway transects during the Gough and Good Hope line occupations. The gliders will be deployed south of Gough Island, then left to glide with the major ocean fronts (STF, SAF and APF), until the Good Hope line where they will be retrieved and redeployed to sample in mooring mode for three months at the Good Hope line.
Focus area two: Southern Hemisphere ocean – atmosphere CO2 fluxes, ocean physics and biogeochemistry
The focus of this research area is to contribute towards the global initiative to produce robust inter annual trends in the ocean – atmosphere CO2 fluxes, thereby enhancing South African science at global carbon budget scale.
To achieve this, we are in the process of establishing a long term observational programme in order to contribute high quality data to the global integrated carbon – climate observing network. The ship-based part of this plan has been in operation since 2008. Through the CSIR, the Department of Science and Technology funded the modernisation of the physics and biogeochemical observational capability of the SA Agulhas, South Africa’s polar research vessel since 1977. This project has now been extended to fund a new polar research ship as well as a number of new national facilities that provide advanced scientific and engineering training and research capabilities.
Figure illustrating SOCCO's oceanographic sampling strategy overlaid on the regions topography (in meters below sea level). Green line: Marion Island underway transect in April; red line: Gough Island underway transect in September; yellow line: GoodHope underway transect to Antarctica completed in December and February; magenta line: Buoy Run transect to South Georgia Island where underway and subsurface CTD measurements are taken.
Furthermore, to derive a seasonally unbiased estimate of CO2 ocean – atmosphere fluxes for the Southern Ocean – and reduce the present uncertainty from 25% and 40% to 10% – we are using a combination of empirical numerical analysis methods to relate in situ and remote sensing data and modelling platforms. These will then contribute to the international Surface Ocean CO2 Atlas (SOCAT) initiative (www.ioccp.org).
Focus area three: Numerical model engineering and numerical analysis
To achieve the above objectives, we need to develop advanced skills in numerical modelling development and engineering over the next decade. This will be crucial if we want to maintain sustainable research and innovation capacity. This is an area that is already a recognised strength of the CSIR and SOCCO plans to enhance this in the field of climate and Earth systems science. The plan to achieve this is twofold:
- Firstly, by addressing interesting and challenging questions about the coupled carbon-climate system, we are stimulating the development of a local community of model engineers that can contribute to wider needs in science and outside; and
- Secondly, the SOCCO programme is used to attract graduate students, especially from higher education institutions, to Earth Systems Science and the ocean-carbon cycle, with a specific focus on the polar Southern Hemisphere oceans.
ACCESS funding currently partially supports three post doc and three post-graduate students. Additional funding from the National Research Foundation covers research costs and travel, as well as a number of studentships.
South Africa is in a unique geographic position to play a significant role in expanding this understanding, and in doing so, make a difference to both global and regional climate observations. Our strategic advantage is considerable because of our proximity to the relatively poorly understood Southern Ocean compared to northern hemisphere oceans.
Key to gaining new knowledge depends on enhancing our observational skills, including computer modelling. A number of these research and specialised skills training facilities are operational and linked to existing educational programmes:
- Water column profiling (CTDs and underway CTDs and long range ocean gliders), hosted by the Department of Environmental Affairs and the CSIR
- High precision CO2 and pCO2 measuring facility at the CSIR
- Bio-optics facility, CSIR
- High precision nutrient and oxygen measuring facility, University of Cape Town
- Ocean productivity facility at the University of Cape Town, with plans to include Carbon Export Flux-Thorium and Traps
- Iron (Fe) clean analytical experimental facility, University of Stellenbosch
SOCCO researchers are closely involved with a LEAP Science and Maths school in Cape Town, where they are working with the science and maths teachers to encourage interest and excitement about these subjects and Earth Systems Science. For more information, contact Dr Sandy Thomalla and Warren Joubert.
Dr Pedro Monteiro - Ocean Biogeochemistry, CSIR and programme head
Dr Nicolas Fauchereau - Climatology and Numerical Analysis, CSIR
Dr Thato Mtshali - Iron Biogeochemistry, CSIR
Dr Nicolette Chang - Oceanography and Modelling, CSIR
Dr Sandy Thomalla - Ocean Productivity and Bio-optics, CSIR
Dr Sebastiaan Swart - Physical Oceanography (Post Doc), CSIR/UCT
Dr Alessandro Tagliabue - Biogeochemistry and Modelling (Post Doc), CSIR/UCT
Mr Warren Joubert - Carbon and Nitrogen Biogeochemistry, CSIR
Leletu Nohayi - CO2 Laboratory, CSIR
Local Partners (joint funding)
Prof Alakendra Roychoudhury, Stellenbosch University
Assoc Prof. Mike Lucas, University of Cape Town
Dr Howard Waldron, University of Cape Town
Dr Onno Ubbink, CSIR Modelling and Digital Science
Dr Sonali Das, CSIR Built Environment (Statistical Modelling)
Prof Peter Witbooi, University of Western Cape
International Partners (joint funding)
Prof Michael Bender, Princeton University, USA
Prof. Richard Bellerby, Bjerknes Centre for Climate Research
Post Graduate Students (funded by SOCCO)
Warren Joubert, PhD
Nomkwezane Kobo, MSc
Luke Gregor, MSc
Nicolas Pringle, MSc
Ceinwen Smith, MSc
Stephanie Rainier, MSc
Marizelle van der Walt, MSc (Genetic Algorithms)
Wesley Pretorius, MSc (Empirical methods for reduced CO₂ flux uncertainties)
Gert Wessels, Developing PhD proposal
Mutshutshu Tsanwani, Developing PhD proposal
Dr Pedro Monteiro
Head: Oceans Systems and Climate
CSIR Natural Resources and the Environment
P.O. Box 320
Tel: +27 _21 888 2437
Fax: +27 _21 888 2693
Mobile: +27 _82 448 8844