IGBP-SCOR FTI background

The atmospheric concentration of carbon dioxide is now higher than experienced on Earth for at least the last 650,000 years, and presumably the last several million years. Moreover, the current rate of CO2 rise of 1.1 ppm/year exceeds even the relatively rapid increases at transitions from glacial to interglacial periods by about two orders of magnitude. As a direct effect of rising CO2, global temperatures are predicted to increase by several degrees during this century. Another less-highlighted consequence will be increased surface ocean pCO2 and a lowering of the pH of the surface ocean. For example, as atmospheric CO2 levels double over their pre-industrial values by the middle of this century, the accompanying surface ocean pH changes are expected to be three times greater than those experienced during glacial to interglacial transitions.

Many questions on the effect of increasing atmospheric CO2 on ocean chemistry and marine life remain unanswered or cannot be answered quantitatively. These include a robust prediction of changes in ocean carbonate chemistry, the buffering effect of carbonate sediments, the effect of weathering rates and fluvial input, feedback with the plankton community, in particular carbonate producers, the effect on overall marine production, including fish, tolerance of corals to changing water chemistry, and others. There have been initiatives (e.g. SCOR-IOC symposium “The ocean in a high CO2 world”, a Royal Society study on surface ocean acidification, and an NSF/NOAA/USGS-sponsored workshop on impacts of increasing CO2 on marine calcifiers) to approach these questions, mainly on the basis of oceanographic observations and modeling. However, modern-day observations are fundamentally limited by the small range of CO2 variations that can be observed naturally. On the other hand, laboratory experiments and model simulations are limited by the requirement to simplify the complexity of the atmosphere-ocean-biosphere system.

reef2585One way around this dilemma is to complement modern observations and modeling results with paleoenvironmental reconstructions from historic periods of major atmospheric CO2 changes. It is clear that there is no perfect paleo-analog to the greenhouse scenario predicted for the next decades and centuries in terms of absolute CO2 level and rate and magnitude of CO2 rise.
Nevertheless, the record of Earth’s history contains periods of rapidly rising and/or persistently high atmospheric CO2 levels, which provide opportunities to observe Earth system responses in a range of scenarios.

Therefore, the proposed FTI could address long- and short-term changes in past ocean biogeochemistry over the last 100 million years, with a focus on particular periods in Earth's history, for example:

(i) The seven glacial-interglacial transitions of the last 650,000 years, when atmospheric CO2 repeatedly increased by up to 100 ppm (40%), accompanied by a surface ocean pH decrease of the order of 0.15 units.

(ii) The Eocene change in carbonate compensation depth.

(iii) The Paleocene Eocene Thermal Maximum 55 million years ago, where abrupt processes (e.g. massive release and oxidation of methane hydrates) resulted in a transient CO2 increase of the order of several hundred ppm, presumably at a high rate that approximates the present situation. This event also provides the opportunity to observe recovery times of the Earth system to a CO2 perturbation.

(iv) The middle Cretaceous ~100-80 million years ago, as an example of an extreme and lasting greenhouse world, with estimated atmospheric CO2 concentrations three to ten times higher than present.