Inorganic Carbon
Data on CaCO3 contents, accumulation rates, foraminiferal fluxes, dissolution susceptibility have been collected for many hundreds of marine cores. Estimates of calcium carbonate accumulation have been compiled for specific intervals or locations and Archer has carried out a synthesis of CCD. Based on existing compilations and literature we will synthesize this data. There are a number of ancillary issues that also need to be addressed. One is the uncertainty as to glacial-interglacial changes in deep sea inorganic carbon system from different proxies we will summarise this evidence for comparison with model runs.
Desorption of nutrients (Fe and P) from fine-grained sediment will be incorporated within the sediment module. Having accurately described modern water-column and core-top CaCO3 patterns, we will test concepts which have been proposed to explain glacial-interglacial cycles in atmospheric CO2 based on compensation mechanisms. Such hypothesis testing will be performed by both (i) a forward modelling approach, and (ii) through data assimilation. For (i), specific model features will be altered and model proxy response tested against observations. This approach will allow un-realistic past changes to be rejected and the effect of other changes on the carbon cycle to be assessed. Automated filtering and assimilation techniques developed in GENIEfy will also be used to tune the model to optimally reproduce past data, and if possible, complete time series. This process will refine prior estimates of uncertainty in model parameters, and will be intricately linked with the process of the testing of physical hypotheses.
It has been proposed, based on d13C of ice core CO2, that the 20 ppm increase in CO2 since the mid-Holocene (ca. 8000 years ago) was caused by a ca. 200 Gt decrease in the terrestrial biomass over this period . However, this is very large, equivalent to ca. 30 years of fossil fuel CO2 increase at the current rate. An alternative explanation is a long-term response of the oceanic carbonate system to a ca. 500 Gt increase in terrestrial biomass during the Early Holocene. Recently it has been claimed that the Holocene rise in atmospheric CO2 is anthropogenic rather than natural, based on comparison with the three preceding glacial terminations, but this is contradicted by its similarity to MIS 11. GENIE is well equipped to test this in that it has interactive sediments and a choice of vegetation/soil components.
Marine records from around the globe reveal a period of carbonate dissolution beginning roughly 600 kyr ago and lasting approximately 400 kyr, with a maximum intensity at around 400 ka during MIS 11. Increased carbonate dissolution during the Mid-Brunhes Dissolution Interval (MBDI) has been identified throughout the Atlantic. The event was not limited to abyssal depths but is also seen in waters shallower than 1000m. Intriguingly, atmospheric CO2 varied very little during the event yet it represents a major perturbation to the global carbon system. Simply increasing the relative production of CaCO3 to Corg in the surface ocean, while inducing the desired effect of enhanced CaCO3 dissolution, causes an increase in atmospheric CO2. Indeed all mechanisms so far put forward to explain the MBDI demand a corresponding increase in CO2. Major growth of coral reefs occurred at this time. The proliferation of Gephyrocapsa coccolithophore also occurred. Changes in ballasting by increasing CaCO3 flux may have occurred. These and other hypotheses will be tested.