South Africa in the Antarctic Circumnavigation Expedition: A multi-institutional and interdisciplinary scientific project

Abstract

The polar regions are more critically affected by climate change than any other region on our planet. On the Antarctic continent and in its surrounding oceans, the effects of climate change are likely to be dramatic, and include largescale catastrophic ice melt, loss of habitat and biodiversity, and global sea level rise. The 'Southern Ocean' refers to the region where Atlantic, Indian and Pacific Ocean waters come together to encircle Antarctica. These waters connect the different ocean basins by linking the shallow and deep limbs of the global ocean current system ('overturning circulation') and play a critical role in storing and distributing heat and carbon dioxide (CO2). The Southern Ocean thus regulates not only the climate of the Antarctic, but of the entire earth system. By extension, the capacity of the global ocean to ameliorate earth's changing climate is strongly controlled by the Southern Ocean. Marine phytoplankton (microscopic plants inhabiting the sunlit upper ocean) convert CO2 (an inorganic form of carbon) dissolved in surface waters into organic carbon through photosynthesis. This organic carbon fuels upper trophic levels such as fish, mammals and birds, and a portion sinks into the deep ocean where it remains stored for hundreds to thousands of years. This mechanism, which lowers the atmospheric concentration of CO2, is termed the 'biological pump'. The efficiency of the global ocean's biological pump is currently limited by the Southern Ocean, where the macronutrients (nitrate and phosphate) required for photosynthesis are never fully consumed in surface waters. In theory, increased consumption of these nutrients could drive higher organic carbon removal to the deep ocean, enhancing the oceanic uptake of atmospheric CO2. Indeed, more complete consumption of Southern Ocean nutrients is a leading hypothesis for the decrease in atmospheric CO2 that characterised the ice ages. Despite the global importance of the Southern Ocean, knowledge of the controls on and interactions among the physical, chemical and biological processes operating in Antarctic ecosystems is limited, largely because of a scarcity of in-situ observational data, compounded by the challenge of integrating siloed scientific fields. Given predictions that diverse aspects of Southern Ocean physics and carbon biogeochemistry are likely to change in the coming decades, a transdisciplinary approach to studying Antarctic systems is critical.