scholarly journals Global peatland initiation driven by regionally asynchronous warming

2018 ◽  
Vol 115 (19) ◽  
pp. 4851-4856 ◽  
Author(s):  
Paul J. Morris ◽  
Graeme T. Swindles ◽  
Paul J. Valdes ◽  
Ruza F. Ivanovic ◽  
Lauren J. Gregoire ◽  
...  
Keyword(s):  
General Circulation ◽  
Carbon Sink ◽  
Circulation Model ◽  
Ecological Change ◽  
Effective Precipitation ◽  
Last Glacial ◽  
Growing Seasons ◽  
Climate Space ◽  
The Tropics ◽  
The Last Glacial

Widespread establishment of peatlands since the Last Glacial Maximum represents the activation of a globally important carbon sink, but the drivers of peat initiation are unclear. The role of climate in peat initiation is particularly poorly understood. We used a general circulation model to simulate local changes in climate during the initiation of 1,097 peatlands around the world. We find that peat initiation in deglaciated landscapes in both hemispheres was driven primarily by warming growing seasons, likely through enhanced plant productivity, rather than by any increase in effective precipitation. In Western Siberia, which remained ice-free throughout the last glacial period, the initiation of the world’s largest peatland complex was globally unique in that it was triggered by an increase in effective precipitation that inhibited soil respiration and allowed wetland plant communities to establish. Peat initiation in the tropics was only weakly related to climate change, and appears to have been driven primarily by nonclimatic mechanisms such as waterlogging due to tectonic subsidence. Our findings shed light on the genesis and Holocene climate space of one of the world’s most carbon-dense ecosystem types, with implications for understanding trajectories of ecological change under changing future climates.

The Effect of a Large Freshwater Perturbation on the Glacial North Atlantic Ocean Using a Coupled General Circulation Model

2006 ◽  
Vol 19 (17) ◽  
pp. 4436-4447 ◽  
Author(s):  
C. D. Hewitt ◽  
A. J. Broccoli ◽  
M. Crucifix ◽  
J. M. Gregory ◽  
J. F. B. Mitchell ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Quasi Equilibrium ◽  
Last Glacial ◽  
Proxy Records ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial

Abstract The commonly held view of the conditions in the North Atlantic at the last glacial maximum, based on the interpretation of proxy records, is of large-scale cooling compared to today, limited deep convection, and extensive sea ice, all associated with a southward displaced and weakened overturning thermohaline circulation (THC) in the North Atlantic. Not all studies support that view; in particular, the “strength of the overturning circulation” is contentious and is a quantity that is difficult to determine even for the present day. Quasi-equilibrium simulations with coupled climate models forced by glacial boundary conditions have produced differing results, as have inferences made from proxy records. Most studies suggest the weaker circulation, some suggest little or no change, and a few suggest a stronger circulation. Here results are presented from a three-dimensional climate model, the Hadley Centre Coupled Model version 3 (HadCM3), of the coupled atmosphere–ocean–sea ice system suggesting, in a qualitative sense, that these diverging views could all have occurred at different times during the last glacial period, with different modes existing at different times. One mode might have been characterized by an active THC associated with moderate temperatures in the North Atlantic and a modest expanse of sea ice. The other mode, perhaps forced by large inputs of meltwater from the continental ice sheets into the northern North Atlantic, might have been characterized by a sluggish THC associated with very cold conditions around the North Atlantic and a large areal cover of sea ice. The authors’ model simulation of such a mode, forced by a large input of freshwater, bears several of the characteristics of the Climate: Long-range Investigation, Mapping, and Prediction (CLIMAP) Project’s reconstruction of glacial sea surface temperature and sea ice extent.

scholarly journals Ocean carbon cycling during the past 130,000 years – a pilot study on inverse paleoclimate record modelling

2016 ◽  
Author(s):  
Christoph Heinze ◽  
Babette Hoogakker ◽  
Arne Winguth
Keyword(s):  
Carbon Cycle ◽  
Sediment Core ◽  
Ocean Circulation ◽  
General Circulation ◽  
General Pattern ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Last Glacial ◽  
Modelling Studies ◽  
The Last Glacial

Abstract. What role did changes in marine carbon cycle processes and calcareous organisms play for glacial-interglacial variation in atmospheric pCO2? In order to answer this question, we explore results from an ocean biogeochemical ocean general circulation model. We make an attempt to systematically reconcile model results with time dependent sediment core data from the observations. For this purpose, simulated sensitivities of oceanic tracer concentrations to changes in governing carbon cycle parameters are fitted to measured sediment core data.We assume that the time variation of the governing carbon cycle parameters follows the general pattern of the glacial-interglacial deuterium anomaly. Our analysis provides an independent estimate of a maximum mean sea surface temperature drawdown of about 5 °C and a maximum outgassing of the land biosphere by about 430 PgC at the last glacial maximum as compared to preindustrial times. The overall fit of modelled paleoclimate tracers to observations, however, remains quite weak indicating the potential of more detailed modelling studies for full exploitation of the information as stored in the paleo-climatic archive. It can be confirmed, however, that a decline in ocean temperature and a more efficient biological carbon pump in combination with changes in ocean circulation are the key factors for explaining the glacial CO2 drawdown. The analysis suggests that potential changes in the export rain ratio POC:CaCO3 may not have a substantial imprint on the paleo-climatic archive. The use of the last glacial as an inverted analogue to potential ocean acidification impacts thus may be quite limited. A potential strong decrease in CaCO3 export production could contribute to the glacial CO2 decline in the atmosphere but remains hypothetical.

Thermal gradients in Europe during the last glacial-interglacial transition

2002 ◽  
Vol 81 (1) ◽  
pp. 113-122 ◽  
Author(s):  
H. Renssen ◽  
R.F.B. Isarin ◽  
J. Vandenberghe
Keyword(s):  
The Netherlands ◽  
General Circulation ◽  
Circulation Model ◽  
Polar Front ◽  
Temperature Gradients ◽  
Temperature Profiles ◽  
Last Glacial ◽  
Reconstructed Temperature ◽  
East West ◽  
The Last Glacial

AbstractTemperature profiles along east-west and north-south transects in Europe are presented for four time-slices covering the two most prominent warming phases of the last glacial-interglacial transition: Late Pleniglacial (LP), early Bøiling (BL), Younger Dryas (YD), and Preboreal (PB). These temperature profiles are based on two methods: 1) simulation experiments with an atmospheric general circulation model, 2) reconstructions based on terrestrial geological and palaeoecological data. The profiles have The Netherlands as intersection point (52°N, 5°E). During the cold phases (LP and YD), the simulated and reconstructed temperature gradients are very steep in a north-south direction, ranging in January from -25°C in northern Europe (56–60°N) to at least 5°C near the Mediterranean, and in July from 0°C to 20°C. The east-west profiles along 52°N for LP and YD show that temperatures in Eastern Europe were similar to the Atlantic coast (i.e. between ‒15°C and ‒25°C). During the warm phases (BL and PB), the temperature regimes resembled present-day thermal conditions, although steeper north-south and east-west temperature gradients were present during BL and PB. The model simulations suggest that continental Europe was a few degrees warmer during PB and BL than today in July under influence of the relatively high summer insolation. Considering the change of climate through time, the profiles show that in The Netherlands the warming during the two transitions (LP-BL, YD-PB) was relatively small compared to regions to the West and North, whereas in Eastern and Southern Europe the temperature increase is even smaller. This reflects the dominant influence of latitudinal movements of the North Atlantic polar front and associated sea-ice margin.

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.

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