Ninth Year Annual Report:
Carbon Science: Future Plans
Temporal Shifts in the Sources and Sinks of Atmospheric CO2
In order to be able to identify the mechanisms that are driving changes in the net land uptake of CO2, the Sarmiento Group plans to implement a statistical technique that is able to detect changes in the dependence between several variables using copulas.
Copulas are multivariate statistical distributions widely used to represent multidimensional phenomenon such as observed in hydrology and climatology, for example. The advantage of copulas is that they allow one to represent the dependence (without assuming a specific form for the relation) between several variables that do not necessarily belong to the same distribution. For example, a copula can represent the dependence between a variable that has an asymmetric shape (e.g. precipitation totals) with another variable whose distribution has a symmetric shape (e.g. mean temperature). New efforts will be made with the goal of being able to detect a change in the copula parameters. These parameters express the dependence relation. This new approach will be used to study the dependence between the terrestrial uptake, the intensification in the hydrological cycle and/or the increase in shortwave radiation.
Temporal Changes in Air-Sea CO2 Fluxes
To better quantify air-sea fluxes of CO2, the Sarmiento Group plans to continue working with the differences between reanalysis forcings and their impact on how gas exchange calculations and carbon budgeting are performed. The motivation for this continuing work is to make the modeling methodologies more robust to dynamical changes in forcing, which the group seeks to study using long-term studies with earth system models. This is particularly important for studies of climate change using coupled ocean-atmosphere models.
Impacts of Ocean Acidification
The Morel Group's ongoing work on the effect of ocean acidification on phytoplankton will continue during 2010 through: 1) laboratory studies of the effect of high CO2 on the iron requirement of phytoplankton; 2) laboratory experiments designed to elucidate the mechanisms by which high CO2 accelerates the growth rate of phytoplankton; and 3) field experiments to test the effect of low pH on the bioavailability of organic phosphate.
In addition, future experiments will investigate the question of the effect of high CO2 concentrations on the composition of marine phytoplankton. The working hypothesis is that the carbon to nitrogen ratio in the biomass of N-limited phytoplankton may increase at high CO2 due to the diminished requirements for key proteins. This work will involve the use of continuous cultures of model phytoplankton species in the laboratory and incubation experiments with natural phytoplankton populations in N-limited regions of the oceans.
Southern Ocean Biogeochemistry
The Bender Group plans to continue its studies of Southern Ocean biogeochemistry. This work is done on scientific ships of opportunity as a collaboration with oceanographers from Australia and South Africa. The researchers will continue to measure net community production of the upper ocean ecosystems and carbon export (sinking), and analyze the results to understand controls on the fertility of ocean ecosystems. The work will comprise three new thrusts. First, continued work on an instrument to make continuous measurements of dissolved inorganic carbon in surface seawater along cruise tracks. If, as expected, it is ready for deployment next fall, the instrument will be added to a suite of measurements on one ship operating in the Southern Ocean, in order to determine rates of productivity over the entire spring and summer growing season.
Second, Bender and colleagues will compare measured rates of net community production and carbon export with rates simulated by models of ocean circulation and ocean biology/chemistry. Third, encouraged by preliminary results, they will examine the possibility of using the concentration of particulate organic carbon in ocean surface water, accessed by global satellite measurements, to extrapolate ship-based measurements of net community production to the entire Southern Ocean and beyond. The product would be maps of carbon export that would reveal, in great detail, the progression of carbon fluxes over the sea surface during the course of the growing season in the Southern Ocean, and would strongly reflect the underlying processes governing those fluxes.
The Bender Group's research in paleoclimatology for the coming year will focus on the dating of ice cores from Mullins Valley and the Allan Hills, Antarctica. If ages greater than 1 million years are confirmed, the group will begin analyzing greenhouse gas concentrations in the trapped air of these samples, thereby extending back in time the record of the relationship between greenhouse gas concentrations and global climate.