SO-CHIC has already provided significant advances in at least five main themes:
O1. To initiate a sustained monitoring of budgets of heat and carbon in the Southern Ocean, by quantifying their fluxes at the air-sea-ice interface and estimating interannual variability of heat and carbon storage in the Southern Ocean.
Large-scale net air-sea carbon and heat fluxes are effectively evaluated through the monitoring of ocean heat and carbon content, which are easier to monitor than air-sea fluxes.
Air-sea flux are monitored by air-sea flux mooring has been envisioned, as part of a multiplatform observing system to be used alongside satellite data and observations from autonomous platforms and ships. But many gaps remain on such observing systems and monitoring air-sea fluxes from these observations or from reanalysis ingesting these observations remain dubious. To overcome the remaining gaps, a long-term monitoring can also be achieved, and we made important progress in describing past changes and their causes, linking to change in circulation and ocean stability.
O2. To improve understanding of the spatial distribution and variability of heat and carbon exchanges between the atmosphere and the deep ocean, focusing on the dynamics of the ocean mixed-layer, its relation to sea ice distribution, and on assessing what has caused the opening of the open-ocean Weddell Polynya in 2016 and 2017 (i.e. a large-scale ice-free area within closed sea-ice cover), more than 40 years after its previous occurrence.
Research from the past two decades has now clearly demonstrated that the Southern Ocean circulation plays a first-order role in global climate by absorbing large amounts of carbon dioxide and heat from the atmosphere, which slow down the rate of global warming. Unfortunately, the processes at play are unclear, and the fundamental consequences of these processes are not even captured by the most sophisticated climate models. As part of SO-CHIC we have started great progress in providing new understanding of the mixed-layer processes controlling air-sea fluxes, as well as deep mixing process undermining the opening of open ocean polynya. In particular, we investigated novel observation of upper ocean turbulence, combined with air-sea fluxes observation to link fluxes to their root causes.
O3. To improve understanding of the formation and export of bottom waters in the Bottom Boundary Layer, which ventilate the world’s abyssal oceans, and to propose new strategies to represent such key processes, which are major shortcomings of current state of the art climate models.
Carbon and Heat can enter the Southern Ocean through the formation, export, and consumption of bottom waters. The Weddell Gyre is one of the key formation regions for Antarctic Bottom Water (AABW) and ventilates much of the Atlantic Ocean. SO-CHIC was already able to make a big step forward by investigating the deep ocean processes controlling the consumption of bottom water. Current work investigates the long term observed change of bottom water to link them to observed changes at formation sites.
O4. To identify critical sensitivities in the Southern Ocean climate system that must be correctly represented in models in order to significantly reduce uncertainties in future projections of oceanic heat and carbon content.
The surface climate of Earth is determined by a complex set of interactions among the atmosphere, the ocean, the cryosphere, and the land. In the Southern Ocean, these interactions involve physical, chemical, and biological processes, many of which are poorly understood, which blur our understanding on what are the key critical sensitivities of the Southern Ocean climate system. An important endeavour of SO-CHIC has been to delineate how observed and future change of ocean characteristics (e.g. heat, carbon content) depends on the sum of processes that can themselves feedback on air-sea fluxes. We were also able to explore sensitivity of the Southern Ocean to self-reinforcing changes associated with atmosphere-cryosphere-ocean interactions.
O5. To enable free and open access to all data and to maximise impact on the climate report (IPCC), climate services, and climate-model groups.
A key objective of SO-CHIC is that it should lead to the exploitation of results, beyond the project itself, which goes one step further than the mere production and dissemination of new scientific knowledge. The project is closely linked with major European climate services to support data delivery and development of expertise. SO-CHIC has made major advances in the dissemination platforms that has already been adopted by the wider community. SO-CHIC already had important impact in the 6th assessment cycle of the IPCC, through the reports themselves but also the dissemination activities around them, including high-level policy events.
