Sarmiento, Jorge: Princeton University (Project Lead)
Project Funding:
2014 - 2016
NRA: 2013 NASA: Carbon Cycle Science
Funded by NASA
Abstract:
Motivation - The ocean is the largest dynamic carbon reservoir at the Earth's surface, containing around 98% of the carbon in the atmosphere-ocean system as dissolved inorganic carbon (DIC), a result of oceanic carbon 'pumps' driven by a combination of physical and biological processes. Understanding the ocean's role in taking up and storing atmospheric CO2 requires an analysis of the manner in which ocean circulation interacts with photosynthesizing organisms at its sunlit surface to transport DIC, together with the inorganic nutrients that fuel photosynthesis, into and out of the ocean's surface mixed layer, where CO2 is exchanged with the atmosphere. The circumpolar Southern Ocean plays a particularly important role in the ocean's carbon pumps. This importance is a result of its unique physical circulation, which upwells DIC and nutrients from the deep ocean, transports them across the energetic fronts of the Antarctic Circumpolar Current (ACC), and subducts them into the ocean interior, both in the Subantarctic and the high Antarctic. Each of these physical processes is known to be strongly influenced by the effect of mesoscale eddies, vortices of order 10-100 km that represent the most energetic portion of the ocean's circulation. However, whilst it is to be expected that mesoscale eddies impose a strong influence on the transport of DIC and nutrients in the Southern Ocean, and thus on the dynamics of carbon cycling and ocean-atmosphere CO2 exchange, assessing this influence quantitatively has posed a formidable challenge, since mesoscale eddies have been both undersampled in observations and unresolved in the global models used to study climate and biogeochemistry.
Objective - The advent of the satellite observations of sea surface height and temperature, along with recent ultra-high resolution modeling developments, provide the opportunity for fundamental breakthroughs in our understanding of the role of mesoscale phenomena in both physical climate and biogeochemical cycles. The work proposed herein is uniquely poised to investigate the role of mesoscale eddies in cross-frontal transport and subduction of nutrients and carbon, by capitalizing on the recent development of new methodologies of eddy-tracking from satellite observations, and on a new set of model simulations including prognostic biogeochemistry and novel model diagnostic tools.
Contribution - We propose to use a combination of satellite-observation-derived analyses and a unique hierarchy of model simulations coupled to prognostic biogeochemistry, with spatial resolutions chosen to produce circulation that range from non-eddying to highly eddying. An eddy-tracking method will be applied to both satellite products and simulations to census and categorize eddies, allowing a detailed comparison of observed and simulated eddies as well as observational and model-based estimates of eddy-induced tracer transport, allowing inference of the importance of the portion of the eddy field not resolved by current satellite missions. A detailed identification and quantification of processes involved in cross-frontal transport and subduction of DIC and nutrients will be carried out using novel online model diagnostics. The hierarchy of models will allow an evaluation of the importance of explicitly resolving eddies in models, thus enabling assessment of current climate model skills. Sensitivity experiments to atmospheric CO2
increase will permit the investigation of the response of the biogeochemical tracer transport mediated by mesoscale eddies to climate change.
By addressing the role of mesoscale eddies in the cross-frontal transport and subduction of DIC and nutrients in the Southern Ocean, this work responds directly to the NASA ROSES-13 solicitation on Carbon Research in Critical Regions, helping to understand the processes that drive carbon storage in high-latitude oceans, and their response to increasing atmospheric CO2 and attendant climate warming.
More details may be found in the following project profile(s):
