With rising global pollution, characterizing the processes of a previously unpolluted world is becoming ever more challenging. In the Antarctic and the surrounding Southern Ocean, we still find the cleanest seas and atmosphere on Earth. This makes it a particularly suitable place to investigate fundamental processes of ocean-atmosphere interactions in an almost pristine place. However, existing research in the Southern Ocean is mostly regional, making it difficult to generalize across the whole area.
The Antarctic Circumnavigation Expedition (ACE), organized in 2016–2017 by the Swiss Polar Institute, represents the first foray into linking the islands, the surrounding ocean, and the Antarctic continent. The wide range of marine, terrestrial, and atmospheric measurements collected by the 22 projects on board is helping to establish baselines for many variables across the different regions. The data also provide valuable input for Earth system models.
The ACE–Delivering Added Value to Antarctica (ACE-DATA) project is a joint effort of domain scientists and the Swiss Data Science Center aiming to exploit this cross-disciplinary data set. As part of this effort, scientists involved with seven ACE projects met in Lausanne, Switzerland, in November 2018 to discuss the Southern Ocean’s complex interactions between sea state, phytoplankton, trace gases, aerosols, and clouds. This is of particular importance because global climate models still fail to reproduce the cloud coverage over the Southern Ocean, resulting in a poor representation of the energy balance. This effect, in turn, has repercussions for simulations of sea ice extent, latitudinal energy transport, and sea surface temperature.
The discussions among the ACE-DATA projects focused on the continuous data recordings, which were obtained all around Antarctica (Figure 1). These are, for example, observations of net community production and identification of microbial physiology, which allow assessment of phytoplankton density and diversity; measurements of the wavefield and precipitation patterns; and cloud condensation nuclei (CCN) and cloud droplet concentrations across the Southern Ocean. The data set allows understanding regional differences by ocean (Indian, Pacific, Atlantic), latitude, and topography.
Meeting participants also reported that elevated nutrient concentrations and biological activity were observed near subantarctic islands, albeit with limited influence on the CCN and cloud droplet population. They also pointed out “hot spots” of biological activity near Mertz Glacier and Siple Island. The latter was unexpectedly accessible due to ice-free conditions.
Attendees discussed in detail the coupling between calm seas, nutrient availability, high biological activity, and unusually high CCN at these hot spots. For example, one project reported high concentrations of dimethyl sulfide (DMS)—a metabolic product of microbes—in the seawater around these sites, while scientists from a second project found elevated levels of DMS oxidation products not only in the air but also condensed onto aerosol particles.
Participants agreed that the heterogeneity of the Southern Ocean and the large variety of parameters make it challenging to connect the dots beyond specific hot spot observations. They resolved to share their results and refined data sets so that ACE-DATA can fulfill its aim to leverage advanced spatial and temporal correlation techniques to produce understanding of regional processes that modulate the properties of clouds. Identifying these processes will help us to estimate the impact of climate change on the future energy balance of the Southern Ocean.
We acknowledge the efforts of all ACE members. ACE and Julia Schmale received funding from École Polytechnique Fédérale de Lausanne, the Swiss Polar Institute, and Ferring Pharmaceuticals Inc. ACE-DATA is funded by the Swiss Data Science Center.
Julia Schmale and Sebastian Landwehr express their gratitude and respect for Professor David Walton, chief scientist of the Antarctic Circumnavigation Expedition, who passed away on 12 February 2019. They remain deeply inspired by his enthusiasm and broad knowledge of polar science.
—Sebastian Landwehr ([email protected]) and Julia Schmale, Paul Scherrer Institute, Villigen, Switzerland; and David W. H. Walton, British Antarctic Survey, Cambridge, U.K.