Rodgers, Keith: Princeton University (Project Lead)
Project Funding:
2009 - 2012
NRA: 2008 NASA: Ocean Biology and Biogeochemistry
Funded by NASA
Abstract:
How is the ocean carbon cycle responding to human activity? Recently a number of studies have argued that the rate of carbon uptake by the ocean has slowed over the last decade. Schuster and Watson [2007] have argued using surface pCO2 measurements from the North Atlantic that there has been a dramatic decrease (more than 50%) of the flux of carbon into the subtropical North Atlantic over the last decade. A similar argument was made using pCO2 measurements from the western subpolar gyre of the North Atlantic by Corbiere et al. [2007]. If the observations used in these studies are indeed representative of this basin-scale, this implies a significant departure from the pattern of uptake of anthropogenic CO2 by the North Atlantic identified in the GLODAP [Sabine et al., 2004; Key et al., 2004] analysis, where the North Atlantic was unambiguously a region of globally maximum anthropogenic CO2 uptake. Similarly, Le Quéré et al. [2007] have used ocean carbon model simulations and atmospheric inverse model calculations to argue that carbon uptake over the Southern Ocean may have “saturated” over the last decade due to changes in the ocean/atmosphere system. Taken together, these results raise the question as to whether climate-induced changes in the ocean/atmosphere system are leading to dramatic changes in the exchange of carbon between the atmospheric and oceanic reservoirs.
The question naturally arises as to whether such changes are reflected in the rate of change of ocean carbon inventories being measured through the Repeat Hydrography program. Preliminary analyses of repeat ocean carbon and biogeochemistry measurements have to date not been able to answer this question conclusively. Simple differences in carbon measurements along repeated WOCE lines tend to reveal patchy structures that are difficult to interpret. This patchiness stems from the fact that there is an elevated level of natural variability of carbon in the ocean. Empirical methods have been developed to detect change against the background of this variability, but the skill of such methods has not been demonstrated quantitatively. An important stumbling block is that the mechanisms controlling the natural variability in the carbon cycle are not well understood.
It is imperative that this knowledge be developed in order to facilitate an estimate of how the ocean uptake of anthropogenic carbon changes in time, and this constitutes the main objective of the proposed work. The project will proceed in two stages. First, it is our intention to make combined use of observations and models to characterize the spatial and temporal scales of variability of DIC, O2, and PO4 in the ocean, and to relate them to in the dynamics of circulation. To what extent does variability in these tracers project onto the dominant structures of variability in circulation? And what processes may contribute to decouple these different tracers from dynamical variations, as well as from each other?
The second objective of this work is to use satellite data to aid in the detection of anthropogenic DIC in the ocean. Commonly used multiple linear regression (MLR) methods are empirical methods and simplistic for detecting changes in the natural carbon cycle. In particular they don’t adequately account for carbon changes associated with dynamical variability. Frontal shifts, planetary waves, and eddies are known to be reflected in remotely sensed products such as sea surface height (SSH) and sea surface temperature (SST), and we will develop methods which incorporate this high-resolution information into the detection framework.
The two main deliverables of the proposed work will be a new detection algorithm for anthropogenic carbon along repeat sections and an estimate of the rate of global uptake.
More details may be found in the following project profile(s):
