The ocean and atmosphere are major components of the Earth’s surface, with reactions within and between them controlling many of the properties of the Earth’s system. The atmosphere-ocean interface represents a vital link between the oceans and the atmosphere by acting as the conduit for the transfer of heat, momentum, aerosols, and gases. This means that understanding the pathways, sources, sinks and budgets of gases like carbon dioxide (CO2) and its impacts on Earth’s climate system is essential for monitoring and projecting future climate scenarios. The atmosphere-ocean exchange of CO2 has received the most attention amongst marine gases. Each year the oceans are considered to absorb about a third of the anthropogenic CO2 emissions. There is an increasing awareness that this net flux of CO2 into the oceans is reducing the pH (or increasing acidification) of the world’s surface oceans. The effect of this increasing acidification on marine life, productivity and possible feedbacks to the atmosphere are as yet unclear. Despite CO2 receiving the most attention other climatically important gases, for example nitrous oxide (N2O) and methane (CH4), also help to shape and control our climate.
In situ measurements of greenhouse gas fluxes and related forcing/control parameters of atmosphere-ocean fluxes remain sparse relative to the global ocean area. These measurements can provide sufficient information to develop regional relationships through process studies, and at some locations, long-term monitoring of key variables is ongoing. The flux of gases between the atmosphere and the ocean is controlled by wind speed, sea state, sea surface temperature, salinity, ice cover and surface processes including any biological activity and rainfall. Many of these processes can either be directly monitored from satellite Earth observation or proxies can be used to infer their existence and variability.
International initiatives are continuing to highlight the societal need for large scale global operational environmental and ecological monitoring (e.g. FutureEarth; Integrated Carbon Observing System, ICOS; Global Ocean Observing System, GOOS). Satellite based remote sensing, underpinned by modelling and in situ data have been identified as one key solution to this need for a global monitoring capability.
Atmosphere-ocean interaction and the exchange of greenhouse gases is a complex problem exacerbated by the size of the global ocean and the difficulty of making high quality measurements at the interface. Earth observation is well suited to this task as it can provide global coverage, quasi-synoptic, accurate and regular measurements of geophysical parameters at the ocean surface. Not all parameters relevant to the study of atmosphere-ocean interaction can be observed from space but historical satellite mission data and processing experience over 20 years has cumulated in several climate record quality data sets of ocean surface wind, sea surface temperature, sea surface waves and marine productivity. Today data from a variety of new missions are available (e.g., SMOS, Cryosat, GOSAT). In the near future the EU Copernicus Sentinel series and the development of nano satellite constellations will considerably enhance this capability. However, only a relatively small proportion of these space-derived datasets have been used to study atmosphere-ocean gas exchange in synergy and much more progress could be achieved (e.g. Land et al., 2015 has recently highlighted how satellite derived salinity measurements will help us study the salinity-alkalinity relationship).
This working group will build upon efforts, outputs, discussions and successes that have been achieved through the European Space Agency project “OceanFlux Greenhouse Gases” and three international workshops held in 2011, 2013 and 2014.
The purpose of this working group is to bring together key international researchers working in the field of atmosphere-ocean interaction and satellite Earth observation to i) identify and formulate new multi-satellite, model and in situ data synergies towards improving our understanding of the pathways, sources, sinks and budgets of greenhouse gases and ii) identify a roadmap for routine long-term space-asset-based monitoring of the oceanic sink of CO2.
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