Changes in terrestrial carbon storage during interglacials: a comparison between Eemian and Holocene

International audienceA complex earth system model (atmosphere and ocean general circulation models, ocean biogeochemistry and terrestrial biosphere) was used to perform transient simulations of two interglacial sections (Eemian, 128?113 ky B.P., and Holocene, 9 ky B.P.-present). The changes in terrestrial carbon storage during these interglacials were studied with respect to changes in the earth's orbit. The effect of different climate factors for the changes in carbon storage were studied in offline experiments in which the vegetation model was forced with only temperature, hydrological parameters, radiation, or CO2 concentration from the transient runs. Although temperature caused the largest anomalies in terrestrial carbon storage, the increase in storage due to forest expansion and increased photosynthesis in the high latitudes was nearly balanced by the decrease due to increased respiration. Large positive effects on carbon storage came from an enhanced monsoon circulation in the subtropics between 128 and 121 ky B.P. and between 9 and 6 ky B.P., and from increases in incoming radiation during summer for 45° to 70° N compared to a control run with present-day insolation. Compared to this control run, the net effect of these changes was a positive carbon storage anomaly of about 200 Pg C for 125 ky B.P. and 7 ky B.P., and a negative anomaly around 150 Pg C for 116 ky B.P. Although the net increases for Eemian and Holocene were rather similar, the causes of this differ substantially. The decrease in terrestrial carbon storage during the experiments was the main driver of an increase in atmospheric CO2 concentration for both the Eemian and the Holocene

Dynamics of the terrestrial biosphere, climate and atmospheric CO₂ concentration during interglacials: a comparison between Eemian and Holocene

A complex earth system model (atmosphere and ocean general circulation models, ocean biogeochemistry and terrestrial biosphere) was used to perform transient simulations of two interglacial sections (Eemian, 128&ndash;113 ky B.P., and Holocene, 9 ky B.P.&ndash;present). The changes in terrestrial carbon storage during these interglacials were studied with respect to changes in the earth&apos;s orbit. The effects of different climate factors on changes in carbon storage were studied in offline experiments in which the vegetation model was forced only with temperature, hydrological parameters, radiation, or CO₂ concentration from the transient runs. <br><br> The largest anomalies in terrestrial carbon storage were caused by temperature changes. However, the increase in storage due to forest expansion and increased photosynthesis in the high latitudes was nearly balanced by the decrease due to increased respiration. Large positive effects on carbon storage were caused by an enhanced monsoon circulation in the subtropics between 128 and 121 ky B.P. and between 9 and 6 ky B.P., and by increases in incoming radiation during summer for 45&deg; to 70&deg; N compared to a control simulation with present-day insolation. <br><br> Compared to this control simulation, the net effect of these changes was a positive carbon storage anomaly in the terrestrial biosphere of about 200 Pg C for 125 ky B.P. and 7 ky B.P., and a negative anomaly around 150 Pg C for 116 ky B.P. Although the net increases for Eemian and Holocene were rather similar, the magnitudes of the processes causing these effects were different. The decrease in terrestrial carbon storage during the experiments was the main driver of an increase in atmospheric CO₂ concentration during both the Eemian and the Holocene

Uncertainties in the modelled CO2 threshold for Antarctic glaciation

A frequently cited atmospheric CO2 threshold for the onset of Antarctic glaciation of ∼780 ppmv is based on the study of DeConto and Pollard (2003) using an ice sheet model and the GENESIS climate model. Proxy records suggest that atmospheric CO2 concentrations passed through this threshold across the Eocene-Oligocene transition ∼34 Ma. However, atmospheric CO2 concentrations may have been close to this threshold earlier than this transition, which is used by some to suggest the possibility of Antarctic ice sheets during the Eocene. Here we investigate the climate model dependency of the threshold for Antarctic glaciation by performing offline ice sheet model simulations using the climate from 7 different climate models with Eocene boundary conditions (HadCM3L, CCSM3, CESM1.0, GENESIS, FAMOUS, ECHAM5 and GISS-ER). These climate simulations are sourced from a number of independent studies, and as such the boundary conditions, which are poorly constrained during the Eocene, are not identical between simulations. The results of this study suggest that the atmospheric CO2 threshold for Antarctic glaciation is highly dependent on the climate model used and the climate model configuration. A large discrepancy between the climate model and ice sheet model grids for some simulations leads to a strong sensitivity to the lapse rate parameter

Potential climatic transitions with profound impact on Europe

We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the ‘tipping’ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. <br/

Earliest Triassic microbialites in the South China Block and other areas; controls on their growth and distribution

Earliest Triassic microbialites (ETMs) and inorganic carbonate crystal fans formed after the end-Permian mass extinction (ca. 251.4 Ma) within the basal Triassic Hindeodus parvus conodont zone. ETMs are distinguished from rarer, and more regional, subsequent Triassic microbialites. Large differences in ETMs between northern and southern areas of the South China block suggest geographic provinces, and ETMs are most abundant throughout the equatorial Tethys Ocean with further geographic variation. ETMs occur in shallow-marine shelves in a superanoxic stratified ocean and form the only widespread Phanerozoic microbialites with structures similar to those of the Cambro-Ordovician, and briefly after the latest Ordovician, Late Silurian and Late Devonian extinctions. ETMs disappeared long before the mid-Triassic biotic recovery, but it is not clear why, if they are interpreted as disaster taxa. In general, ETM occurrence suggests that microbially mediated calcification occurred where upwelled carbonate-rich anoxic waters mixed with warm aerated surface waters, forming regional dysoxia, so that extreme carbonate supersaturation and dysoxic conditions were both required for their growth. Long-term oceanic and atmospheric changes may have contributed to a trigger for ETM formation. In equatorial western Pangea, the earliest microbialites are late Early Triassic, but it is possible that ETMs could exist in western Pangea, if well-preserved earliest Triassic facies are discovered in future work

Expanded oxygen minimum zones during the late Paleocene-early Eocene:Hints from multiproxy comparison and ocean modeling

Anthropogenic warming could well drive depletion of oceanic oxygen in the future. Important insight into the relationship between de-oxygenation and warming can be gleaned from the geological record, but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions. We use I/Ca in benthic foraminifera to reconstruct late Paleocene through early Eocene bottom and pore-water redox conditions in the South Atlantic and Southern Indian Oceans, and compare our results with those derived from Mn speciation and the Ce anomaly in fish teeth. We conclude that waters with lower oxygen concentrations were widespread at intermediate depths (1.5-2 km), whereas bottom waters were more oxygenated at the deepest site, in the Southeast Atlantic Ocean (>3 km). Epifaunal benthic foraminiferal I/Ca values were higher in the late Paleocene, especially at low oxygen sites, than at well-oxygenated modern sites, indicate higher seawater total iodine concentrations in the late Paleocene than today. The proxy-based bottom water oxygenation pattern agrees with the site-to-site O2 gradient as simulated in a comprehensive climate model (CCSM3), but the simulated absolute dissolved O2 values are low (<~35 µmol/kg), while higher O2 values (~60-100 µmol/kg) were obtained in an Earth system model (cGENIE). Multi-proxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved

Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery

The end-Permian mass extinction, ~252 million years ago, is notable for a complex recovery period of ~5 Myr. Widespread euxinic (anoxic and sulfidic) oceanic conditions have been proposed as both extinction mechanism and explanation for the protracted recovery period, yet the vertical distribution of anoxia in the water column and its temporal dynamics through this time period are poorly constrained. Here we utilize Fe–S–C systematics integrated with palaeontological observations to reconstruct a complete ocean redox history for the Late Permian to Early Triassic, using multiple sections across a shelf-to-basin transect on the Arabian Margin (Neo-Tethyan Ocean). In contrast to elsewhere, we show that anoxic non-sulfidic (ferruginous), rather than euxinic, conditions were prevalent in the Neo-Tethys. The Arabian Margin record demonstrates the repeated expansion of ferruginous conditions with the distal slope being the focus of anoxia at these times, as well as short-lived episodes of oxia that supported diverse biota

Dynamics of the terrestrial biosphere, climate and atmospheric CO₂ concentration during interglacials: a comparison between Eemian and Holocene

International audienceA complex earth system model (atmosphere and ocean general circulation models, ocean biogeochemistry and terrestrial biosphere) was used to perform transient simulations of two interglacial sections (Eemian, 128?113 ky B.P., and Holocene, 9 ky B.P.?present). The changes in terrestrial carbon storage during these interglacials were studied with respect to changes in the earth's orbit. The effects of different climate factors on changes in carbon storage were studied in offline experiments in which the vegetation model was forced only with temperature, hydrological parameters, radiation, or CO2 concentration from the transient runs. The largest anomalies in terrestrial carbon storage were caused by temperature changes. However, the increase in storage due to forest expansion and increased photosynthesis in the high latitudes was nearly balanced by the decrease due to increased respiration. Large positive effects on carbon storage were caused by an enhanced monsoon circulation in the subtropics between 128 and 121 ky B.P. and between 9 and 6 ky B.P., and by increases in incoming radiation during summer for 45° to 70° N compared to a control simulation with present-day insolation. Compared to this control simulation, the net effect of these changes was a positive carbon storage anomaly in the terrestrial biosphere of about 200 Pg C for 125 ky B.P. and 7 ky B.P., and a negative anomaly around 150 Pg C for 116 ky B.P. Although the net increases for Eemian and Holocene were rather similar, the magnitudes of the processes causing these effects were different. The decrease in terrestrial carbon storage during the experiments was the main driver of an increase in atmospheric CO2 concentration during both the Eemian and the Holocene