NSF OCE-0097316 05/01-04/04

We propose to carry out model sensitivity studies to examine several hypotheses for model differences. We further propose to make use of measurements from the JGOFS and WOCE surveys to determine which model gives a more realistic simulation, and to improve our estimates of the oceanic uptake and storage of anthropogenic CO2, bomb radiocarbon, and CFCs. Our goal is to advance both the development of reliable ocean models and the estimation of oceanic uptake of anthropogenic CO2 from observations with the aim of improving estimates of the oceanic carbon sink and our understanding of the ocean carbon cycle.
First, we will examine model simulated tracer-tracer relationships of anthropogenic CO2, bomb ¹⁴C, and CFCs to evaluate four specific aspects of model physics that we believe are important in determining tracer distributions. They are;

1. the relative magnitude of advective return flows of the North Atlantic Deep Water through the thermocline and the Southern Ocean;
2. the magnitude of convective exchange between surface and deep waters in the Southern Ocean;
3. bottom boundary layer advective pathways of newly formed deep waters; and
4. the magnitude and spatial distribution air-sea gas exchange.

Second, we will improve the estimates of anthropogenic CO2 inventories by making use of the model simulations in conjunction with observations to critically examine the C* methodology of separating the anthropogenic CO2 from the background total CO2 [Gruber et al., 1996] and by exploring alternative methods using the distributions of CFCs, bomb ¹⁴C, and CCl4. The potential to use these measurements to estimate anthropogenic CO2 inventory rests on theoretical arguments and supporting preliminary observations that these transient tracers would be good analogs of anthropogenic CO2 distributions in the ocean, given the similarities in their growth history of CFCs and CCl4 in the atmosphere and the time scale since the injection of bomb ¹⁴C into the ocean. The robustness of the relationship of anthropogenic CO2 with CFCs, bomb ¹⁴C, and CCl4 will be investigated using our new simulations in conjunction with simulations from the OCMIP. We will then use the survey tracer data to improve estimates of the oceanic uptake of anthropogenic carbon.

We have gathered a team that has expertise in ocean observations and ocean biogeochemical modeling. A coordinated examination of these tracers that historically have been examined in relative isolation promises a better understanding anthropogenic CO2, bomb ¹⁴C, CFCs, and CCl4 uptake in ocean models and in the real ocean.