scholarly journals Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics

2017 ◽  
Vol 13 (10) ◽  
pp. 1381-1401 ◽  
Author(s):  
Taraka Davies-Barnard ◽  
Andy Ridgwell ◽  
Joy Singarayer ◽  
Paul Valdes
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Climatic Variability ◽  
Circulation Model ◽  
Glacial Maximum ◽  
Minor Role ◽  
Terrestrial Biosphere ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The terrestrial biosphere is thought to be a key component in the climatic variability seen in the palaeo-record. It has a direct impact on surface temperature through changes in surface albedo and evapotranspiration (so-called biogeophysical effects) and, in addition, has an important indirect effect through changes in vegetation and soil carbon storage (biogeochemical effects) and hence modulates the concentrations of greenhouse gases in the atmosphere. The biogeochemical and biogeophysical effects generally have opposite signs, meaning that the terrestrial biosphere could potentially have played only a very minor role in the dynamics of the glacial–interglacial cycles of the late Quaternary. Here we use a fully coupled dynamic atmosphere–ocean–vegetation general circulation model (GCM) to generate a set of 62 equilibrium simulations spanning the last 120 kyr. The analysis of these simulations elucidates the relative importance of the biogeophysical versus biogeochemical terrestrial biosphere interactions with climate. We find that the biogeophysical effects of vegetation account for up to an additional −0.91 °C global mean cooling, with regional cooling as large as −5 °C, but with considerable variability across the glacial–interglacial cycle. By comparison, while opposite in sign, our model estimates of the biogeochemical impacts are substantially smaller in magnitude. Offline simulations show a maximum of +0.33 °C warming due to an increase of 25 ppm above our (pre-industrial) baseline atmospheric CO2 mixing ratio. In contrast to shorter (century) timescale projections of future terrestrial biosphere response where direct and indirect responses may at times cancel out, we find that the biogeophysical effects consistently and strongly dominate the biogeochemical effect over the inter-glacial cycle. On average across the period, the terrestrial biosphere has a −0.26 °C effect on temperature, with −0.58 °C at the Last Glacial Maximum. Depending on assumptions made about the destination of terrestrial carbon under ice sheets and where sea level has changed, the average terrestrial biosphere contribution over the last 120 kyr could be as much as −50 °C and −0.83 °C at the Last Glacial Maximum.

scholarly journals Impact of CO<sub>2</sub> and climate on the Last Glacial Maximum vegetation: results from the ORCHIDEE/IPSL models

2011 ◽  
Vol 7 (2) ◽  
pp. 557-577 ◽  
Author(s):  
M.-N. Woillez ◽  
M. Kageyama ◽  
G. Krinner ◽  
N. de Noblet-Ducoudré ◽  
N. Viovy ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Circulation Model ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Pollen Data ◽  
Last Glacial ◽  
Global Vegetation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Vegetation reconstructions from pollen data for the Last Glacial Maximum (LGM), 21 ky ago, reveal lanscapes radically different from the modern ones, with, in particular, a massive regression of forested areas in both hemispheres. Two main factors have to be taken into account to explain these changes in comparison to today's potential vegetation: a generally cooler and drier climate and a lower level of atmospheric CO2. In order to assess the relative impact of climate and atmospheric CO2 changes on the global vegetation, we simulate the potential modern vegetation and the glacial vegetation with the dynamical global vegetation model ORCHIDEE, driven by outputs from the IPSL_CM4_v1 atmosphere-ocean general circulation model, under modern or glacial CO2 levels for photosynthesis. ORCHIDEE correctly reproduces the broad features of the glacial vegetation. Our modelling results support the view that the physiological effect of glacial CO2 is a key factor to explain vegetation changes during glacial times. In our simulations, the low atmospheric CO2 is the only driver of the tropical forests regression, and explains half of the response of temperate and boreal forests to glacial conditions. Our study shows that the sensitivity to CO2 changes depends on the background climate over a region, and also depends on the vegetation type, needleleaf trees being much more sensitive than broadleaf trees in our model. This difference of sensitivity leads to a dominance of broadleaf types in the remaining simulated forests, which is not supported by pollen data, but nonetheless suggests a potential impact of CO2 on the glacial vegetation assemblages. It also modifies the competitivity between the trees and makes the amplitude of the response to CO2 dependent on the initial vegetation state.

scholarly journals Variations of oceanic oxygen isotopes at the present day and the LGM: equilibrium simulations with an oceanic general circulation model

2012 ◽  
Vol 8 (5) ◽  
pp. 4885-4922
Author(s):  
X. Xu ◽  
G. Lohmann ◽  
M. Werner ◽  
X. Zhang
Keyword(s):  
Oxygen Isotope ◽  
General Circulation Model ◽  
Last Glacial Maximum ◽  
General Circulation ◽  
Circulation Model ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Oceanic General Circulation Model ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. The isotope-enabled oceanic general circulation model, MPI-OM, is used to simulate the oxygen isotope compositions of sea waters in the oceans under preindustrial and last glacial maximum climate conditions. Simulated oceanic isotope distributions at the last glacial maximum (21 000 yr ago) show features similar to the preindustrial in most basins but the Northern North Atlantic. With the exception of the ice sheet impact, the oxygen-18 content variations at sea surface during the last glacial maximum are mainly controlled by the changes in boundary isotopic fluxes in most regions, while the changes from subsurface to bottom waters are mostly due to the differences in the water mass circulations. The changes in topography at the northern high latitudes have a remarkable influence on the isotopic composition in the Arctic Ocean. The pre-industrial and the last glacial maximum calcite oxygen isotope compositions in the surface water and their difference are also calculated. These results are compared with the observed values from different foraminifera species and are in agreement with the observations in most regions.

scholarly journals Impact of CO<sub>2</sub> and climate on the Last Glacial Maximum vegetation

2011 ◽  
Vol 7 (1) ◽  
pp. 1-46 ◽  
Author(s):  
M.-N. Woillez ◽  
M. Kageyama ◽  
G. Krinner ◽  
N. de Noblet-Ducoudré ◽  
N. Viovy ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Circulation Model ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Pollen Data ◽  
Last Glacial ◽  
Global Vegetation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Vegetation reconstructions from pollen data for the Last Glacial Maximum (LGM), 21 kyr ago, reveal lanscapes radically different from the modern ones, with, in particular, a massive regression of forested areas in both hemispheres. Two main factors have to be taken into account to explain these changes in comparison to today's potential vegetation: a generally cooler and drier climate and a lower level of atmospheric CO2. In order to assess the relative impact of climate and atmospheric CO2 changes on the global vegetation, we simulate the potential modern vegetation and the glacial vegetation with the dynamical global vegetation model ORCHIDEE, driven by outputs from the IPSL_CM4_v1 atmosphere-ocean general circulation model, under modern or glacial CO2 levels for photosynthesis. ORCHIDEE correctly reproduces the broad features of the glacial vegetation. Our modelling results support the view that the physiological effect of glacial CO2 is a key factor to explain vegetation changes during glacial times. In our simulations, the low atmospheric CO2 is the only driver of the tropical forests regression, and explains half of the response of temperate and boreal forests to glacial conditions. Our study shows that the sensitivity to CO2 changes depends on the background climate over a region, and also depends on the vegetation type, needleleaf trees being much more sensitive than broadleaf trees in our model. This difference of sensitivity leads to a dominance of broadleaf types in the remaining simulated forests, which is not supported by pollen data, but nonetheless suggests a potential impact of CO2 on the glacial vegetation assemblages. It also modifies the competitivity between the trees and makes the amplitude of the response to CO2 dependent on the initial vegetation state.

scholarly journals Modeling Mediterranean ocean climate of the Last Glacial Maximum

2010 ◽  
Vol 6 (5) ◽  
pp. 2005-2054
Author(s):  
U. Mikolajewicz
Keyword(s):  
General Circulation Model ◽  
Last Glacial Maximum ◽  
General Circulation ◽  
Circulation Model ◽  
Glacial Maximum ◽  
Strong Increase ◽  
Last Glacial ◽  
The Mediterranean ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. A regional ocean general circulation model of the Mediterranean is used to study the climate of the last glacial maximum. The atmospheric forcing for these simulations has been derived from simulations with an atmospheric general circulation model, which in turn was forced with surface conditions from a coarse resolution earth system model. The model is successful in reproducing the general patterns of reconstructed sea surface temperature anomalies with the strongest cooling in summer in the northwestern Mediterranean and weak cooling in the Levantine, although the model underestimates the extent of the summer cooling in the western Mediterranean. However, there is a strong vertical gradient associated with this pattern of summer cooling, which makes the comparison with reconstructions nontrivial. The exchange with the Atlantic is decreased to roughly one half of its present value, which can be explained by the shallower Strait of Gibraltar as a consequence of lower global sea level. This reduced exchange causes a strong increase of the salinity in the Mediterranean in spite of reduced net evaporation.

scholarly journals Modeling Mediterranean Ocean climate of the Last Glacial Maximum

2011 ◽  
Vol 7 (1) ◽  
pp. 161-180 ◽  
Author(s):  
U. Mikolajewicz
Keyword(s):  
General Circulation Model ◽  
Last Glacial Maximum ◽  
General Circulation ◽  
Circulation Model ◽  
Glacial Maximum ◽  
Strong Increase ◽  
Last Glacial ◽  
The Mediterranean ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. A regional ocean general circulation model of the Mediterranean is used to study the climate of the Last Glacial Maximum. The atmospheric forcing for these simulations has been derived from simulations with an atmospheric general circulation model, which in turn was forced with surface conditions from a coarse resolution earth system model. The model is successful in reproducing the general patterns of reconstructed sea surface temperature anomalies with the strongest cooling in summer in the northwestern Mediterranean and weak cooling in the Levantine, although the model underestimates the extent of the summer cooling in the western Mediterranean. However, there is a strong vertical gradient associated with this pattern of summer cooling, which makes the comparison with reconstructions complicated. The exchange with the Atlantic is decreased to roughly one half of its present value, which can be explained by the shallower Strait of Gibraltar as a consequence of lower global sea level. This reduced exchange causes a strong increase of salinity in the Mediterranean in spite of reduced net evaporation.

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