Controls on the spatial distribution of oceanic δ13CDIC

[摘要] We describe the design and evaluation of a large ensemble of coupledclimate–carbon cycle simulations with the Earth system model of intermediatecomplexity GENIE. This ensemble has been designed for application to a rangeof carbon cycle questions, including the causes of late-Quaternaryfluctuations in atmospheric CO₂. Here we evaluate the ensemble byapplying it to a transient experiment over the recent industrial era (1858 to2008 AD). We employ singular vector decomposition and principal componentemulation to investigate the spatial modes of ensemble variability of oceanicdissolved inorganic carbon (DIC) δ¹³C, considering both the spun-uppre-industrial state and the transient change. These analyses allow us toseparate the natural (pre-industrial) and anthropogenic controls on theδ¹³C_DIC distribution. We apply the samedimensionally-reduced emulation techniques to consider the drivers of thespatial uncertainty in anthropogenic DIC. We show that the sources ofuncertainty related to the uptake of anthropogenicδ¹³C_DIC and DIC are quite distinct. Uncertainty inanthropogenic δ¹³C uptake is controlled by air–sea gas exchange,which explains 63% of modelled variance. This mode of variability islargely absent from the ensemble variability in CO₂ uptake, which israther driven by uncertainties in thermocline ventilation rates. Although theneed to account for air–sea gas exchange is well known, these resultssuggest that, to leading order, uncertainties in the ocean uptake ofanthropogenic ¹³C and CO₂ are governed by very different processes.This illustrates the difficulties in reconstructing one from the other, andfurthermore highlights the need for careful targeting of bothδ¹³C_DIC and DIC observations to better constrain theocean sink of anthropogenic CO₂.

[学科分类] 地球化学与岩石