Southern Ocean Carbon and Climate Observatory, CSIR, P.O. Box 320, Stellenbosch, 7599, South Africa

Department of Oceanography, University of Cape Town, Cape Town, 7701, South Africa

Southern Ocean Carbon and Climate Observatory, CSIR, P.O. Box 320, Stellenbosch, 7599, South Africa

Department of Earth Sciences, Stellenbosch University, Stellenbosch, 7602, South Africa

Laboratoire de Physique des Océans, Centre IRD de Bretagne, 29280 Plouzané, France

Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), University of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia

NIOZ, Dutch Institute for Sea Research, Den Burg, Texel, The Netherlands

now at: Centre for Assessment of Pesticides and Biocides, Wageningen, The Netherlands

Department of Earth Sciences, Stellenbosch University, Stellenbosch, 7602, South Africa

Southern Ocean Carbon and Climate Observatory, CSIR, P.O. Box 320, Stellenbosch, 7599, South Africa

Department of Oceanography, University of Cape Town, Cape Town, 7701, South Africa