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The Southern Ocean is a critical component of Earth's climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, and ocean biogeochemistry and microbiology. This circumpolar cruise included visits to 12 remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter-term variations, geographic setting of environmental processes, and interactions between them over the duration of 90 d. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable we applied an unsupervised machine learning method, the sparse principal component analysis (sPCA), which describes environmental processes through 14 latent variables. To derive a robust statistical perspective on these processes and to estimate the uncertainty in the sPCA decomposition, we have developed a bootstrap approach. Our results provide a proof of concept that sPCA with uncertainty analysis is able to identify temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and "hotspots" of interaction between environmental compartments. While confirming many well known processes, our analysis provides novel insights into the Southern Ocean water cycle (freshwater fluxes), trace gases (interplay between seasonality, sources, and sinks), and microbial communities (nutrient limitation and island mass effects at the largest scale ever reported). More specifically, we identify the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity; the fact that sea ice controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilisation and reduced light limitation; and the clear regional patterns of aerosol characteristics that have emerged, stressing the role of the sea state, atmospheric chemical processing, and source processes near hotspots for the availability of cloud condensation nuclei and hence cloud formation. A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper-ocean layer light intensity, surface wind speed and relative humidity played an important role in our analysis, highlighting the necessity for Earth system models to represent them adequately. In conclusion, our study highlights the use of sPCA to identify key ocean-atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. It thereby fills an important gap between simple correlation analyses and complex Earth system models. The sPCA processing code is available as open-access from the following link: https://renkulab.io/gitlab/ACE-ASAID/spca-decomposition (last access: 29 March 2021). As we show here, it can be used for an exploration of environmental data that is less prone to cognitive biases (and confirmation biases in particular) compared to traditional regression analysis that might be affected by the underlying research question., Earth System Dynamics, 12 (4), ISSN:2190-4987, ISSN:2190-4979

POLAR 2018 - XXXV SCAR Meetings and SCAR/IASC Open Science Conference, 19-23 June 2018, Davos, Switzerland, Climate warming affects the development and distribution of sea ice south of the Polar Front around Antarctica and its associated ecosystems, but at present the evidence of feedbacks on climate through ecosystem-derived changes in the atmosphere is sparse. The PEGASO cruise visited the Antarctic region of the South Orkney Islands at the northern edge of the Weddell Sea, and the Subantarctic region of the South Georgia Island, in summer 2015. Each region was studied intensively in lagrangian mode over a few days and diel cycles. Oceanic measurements of plankton abundance, diversity, activity and physiology, plus organic matter characteristics, organic volatile compounds (dimethylsulfide, isoprene, halomethanes) and nutrient concentrations, were compared with simultaneous atmospheric measurements of aerosol numbers, size and composition. Samples of surface seawater and melted sea ice were bubbled in an aerosol-generation tank and the characteristics of the sprayed aerosol were monitored. This integrated study allowed to link phytoplankton bloom stages and the emission of aerosol-forming particulate and gaseous substances. For instance, we observed that the microbiota of sea ice and sea ice-influenced ocean are a previously unknown significant source of atmospheric organic nitrogen, including low molecular weight alkyl-amines. Given the keystone role of nitrogen, sulfur, carbon and iodine compounds in aerosol formation, growth and neutralization, our findings call for greater chemical and source diversity in the modeling efforts linking the marine ecosystem to aerosol-mediated climate effects in the Southern Ocean

2018 Ocean Sciences Meeting, 11-16 February, in Portland, Oregon, Climate warming affects the development and distribution of sea ice south of the Polar Front around Antarctica and its associated ecosystems, but at present the evidence of feedbacks on climate through ecosystem-derived changes in the atmosphere is sparse. The PEGASO cruise visited the Antarctic region of the South Orkney Islands at the northern edge of the Weddell Sea, and the Subantarctic region of the South Georgia Island, in summer 2015. Each region was studied intensively in lagrangian mode over a few days and diel cycles. Oceanic measurements of plankton abundance, diversity, activity and physiology, plus organic matter characteristics, organic volatile compounds (dimethylsulfide, isoprene, halomethanes) and nutrient concentrations, were compared with simultaneous atmospheric measurements of aerosol numbers, size and composition. Samples of surface seawater and melted sea ice were bubbled in an aerosol-generation tank and the characteristics of the sprayed aerosol were monitored. This integrated study allowed to link phytoplankton bloom stages and the emission of aerosol-forming particulate and gaseous substances. For instance, we observed that the microbiota of sea ice and sea ice-influenced ocean are a previously unknown significant source of atmospheric organic nitrogen, including low molecular weight alkyl-amines. Given the keystone role of nitrogen, sulfur, carbon and iodine compounds in aerosol formation, growth and neutralization, our findings call for greater chemical and source diversity in the modeling efforts linking the marine ecosystem to aerosol-mediated climate effects in the Southern Ocean

POLAR 2018 - XXXV SCAR Meetings and SCAR/IASC Open Science Conference, 19-23 June 2018, Davos, Switzerland.-- 1 page, Climate warming affects the development and distribution of sea ice around Antarctica and its associated ecosystems, but at present the evidence of feedbacks on climate through ecosystem-derived changes in the atmosphere is sparse. The PEGASO cruise visited the Antarctic region of the South Orkney Islands at the northern edge of the Weddell Sea, and the Subantarctic region of the South Georgia Island, in summer 2015. Each region was studied intensively in lagrangian mode over a few days and diel cycles. Oceanic measurements of plankton abundance, diversity, activity and physiology, plus organic matter characteristics, aerosol-forming organic volatile compounds (dimethylsulfide, methylamines, isoprene, halomethanes) and nutrient concentrations, were compared with simultaneous atmospheric measurements of aerosol numbers, size and composition. Samples of surface seawater and melted sea ice were bubbled in an aerosol-generation tank and the characteristics of the sprayed aerosol were monitored. This integrated study allowed to link phytoplankton bloom stages and the emission of aerosol-forming particulate and gaseous substances. Our findings call for greater chemical and source diversity in the modeling efforts linking the marine ecosystem to aerosol-mediated climate effects in the Southern Ocean

4th Interlab Meeting, 22-23 May 2017, Banyuls-sur-Mer, France, Marine viruses, together with other planktonic microorganisms, play an important role on the marine ecosystem functioning, and their activity can contribute on the marine aerosol composition. During the interdisciplinary PEGASO expedition, we visit four contrasting areas of the Southern Ocean (Antarctic and sub-antarctic), with high (South Giorgia Island) to low degree (Orkney Islands) of microplanktonic biomass and activity and derived secondary compounds concentration. In this study we aimed to (I) describe different viral community abundance and structures (distribution and diversity) among four contrasted areas; (II) relate them with their main hosts (bacteria and phytoplankton) as well as with physicochemical variables and (III) uncover their relation with metabolic secondary compounds generated by marine microbiological activity, which in turn, can be related with the marine aerosol composition

9 pages, Since the publication of 47 key phytoplankton pigment data sheets in the volume by Jeffrey et al. (1997b), several new algal groups and pigments have been reported. To reflect this and the increased use of mass spectrometry for phytoplankton pigment characterisation we have compiled revised and expanded data sheets documenting 47 carotenoids and 21 chlorophylls. These new data sheets complement the ones produced for the 1997 volume. They are also available online, at www.cambridge.org/phytoplankton, for ease of consultation. We do not include data sheets for the many chlorophyll transformation products found particularly in sediments; for information on these pigments readers should refer to the comprehensive review by Keely (2006). Similarly, our coverage of pigments contained in phototrophic bacteria is limited mostly to cyanobacteria found in the water column of freshwater and marine environments (see Chapter 1, this volume), hence we exclude the newly discovered chlorophyll f in stromatolites (Chen et al., 2010). Readers interested in anoxygenic phototrophic bacteria should consult the reviews by Takaichi (1999) and Scheer (2006)