Liam Quinlan, Stellenbosch University, Earth Sciences, Stellenbosch, South Africa, Susanne Fietz, Stellenbosch University, Department of Earth Sciences, Faculty of Science, Stellenbosch, South Africa and Thomas James Ryan-Keogh, Council for Scientific and Industrial Research (CSIR), Southern Ocean Carbon-Climate Observatory (SOCCO), Cape Town, South Africa; National Oceanography Centre, Southampton, United Kingdom