The climate in Antarctica during the Middle Eocene: a modelling perspective

2020 ◽  
Author(s):  
Frederic Fluteau ◽  
Delphine Tardif ◽  
Guillaume Le Hir ◽  
Yannick Donnadieu ◽  
Pierre Sepulchre ◽  
...  
Keyword(s):  
General Circulation ◽  
Middle Eocene ◽  
Circulation Model ◽  
Late Eocene ◽  
Proxy Data ◽  
Polar Climate ◽  
Sedimentary Sequences ◽  
Orbital Configuration ◽  
Wet Climate ◽  
End Members

<p>The Middle Eocene represents the last ice-free period of the Cenozoic. Vegetation proxy data (wood, leaves, palynomorphs) discovered in the Antarctica peninsula and neighbouring islands or hosted in sedimentary sequences deposited on the continental margin reveal the presence of paratropical rain forests which thrived along the Antarctica coast during the Early Eocene. During the Middle and Late Eocene these flora have been progressively replaced by temperate <em>Nothofagus</em>-dominated rainforests (Contreras et al., 2013). Jacques et al. (2012) proposed, using a physiognomic approach (CLAMP), that a warm temperate and wet climate (with a marked summer rainy season) prevails until the middle Eocene (43±2 Ma) on the tip of the Antarctica Peninsula.</p><p>            To better constrain the climate in Antarctica and understand processes governing the polar climate during the Middle Eocene, we performed a set of experiments using the IPCC-like Earth System Model (IPSL-CM5A2-VLR) forced with a Middle Eocene (~40 Ma) paleogeography reconstruction and a 4 times pre-industrial atmospheric CO<sub>2</sub> level (1120ppm). To highlight the importance of the seasonality, we launched 6 orbital configurations exploring end-members situations. To complete the procedure, simulated sea surface temperatures and sea ice extents were then employed as boundary conditions to force the Atmospheric General circulation model LMDz6 (run at higher spatial resolution) coupled with a soil and vegetation model ORCHIDEE to simulate the corresponding vegetation over Antarctica. The 6 end-members Earth's orbital configuration allows exploring the full climatic spectrum which would have been recorded by proxy data. Simulated changes in atmospheric circulation will be discussed and the simulated climate and vegetation will be confronted to paleoclimatic indicators and vegetation data.</p>

scholarly journals Atmospheric dynamics on terrestrial planets with eccentric orbits

2020 ◽  
Author(s):  
Ilai Guendelman ◽  
Yohai Kaspi
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Balance Model ◽  
Maximum Temperature ◽  
Climate Response ◽  
Eccentric Orbits ◽  
Orbital Configuration ◽  
Main Engine ◽  
Atmospheric Moisture Content ◽  
Parent Star

<p>The insolation a planet receives from its parent star is the main engine of the climate and depends on the planet's orbital configuration. Planets with non-zero obliquity and eccentricity experience seasonal insolation variations. As a result, the climate exhibits a seasonal cycle, with its strength depending on the orbital configuration and atmospheric characteristics. In this study, using an idealized general circulation model, we examine the climate response to changes in eccentricity for both zero and non-zero obliquity planets. In the zero obliquity case, a comparison between the seasonal response to changes in eccentricity and perpetual changes in the solar constant shows that the seasonal response strongly depends on the orbital period and radiative timescale. More specifically, using a simple energy balance model, we show the importance of the latitudinal structure of the radiative timescale in the climate response. We also show that the response strongly depends on the atmospheric moisture content. The combination of an eccentric orbit with non-zero obliquity is complex, as the insolation also depends on the perihelion position. Although the detailed response of the climate to variations in eccentricity, obliquity, and perihelion is involved, the circulation is constrained mainly by the thermal Rossby number and the maximum temperature latitude. Finally, we discuss the importance of different planetary parameters that affect the climate response to orbital configuration variations.</p>

Model-data comparison in a strongly eddying Eocene ocean

2021 ◽  
Author(s):  
Peter Nooteboom ◽  
Michiel Baatsen ◽  
Peter Bijl ◽  
Erik van Sebille ◽  
Appy Sluijs ◽  
...  
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Late Eocene ◽  
Ocean Modeling ◽  
Equilibration Time ◽  
Model Data ◽  
Proxy Data ◽  
Biogeographic Patterns ◽  
Data Comparison

<p>Simulations of the geological past using General Circulation Models (GCMs) are computationally expensive. Mainly because of the long equilibration time scales, most of these GCMs have ocean components with a horizontal resolution of 1° or coarser. Such models are non-eddying and the effects of mesoscale ocean eddies on the transport of heat and salt are parameterized. However, from present-day ocean modeling studies, it is known that eddying ocean models better represent regional and time-mean ocean flows compared to non-eddying models. At the same time, proxy data from sediment sample sites represent climate at specific locations. Hence, the coarse ocean resolution of typical palaeo-GCMs lead to a challenge for model-data comparison in past climates.</p><p>Here we present the first simulations of a global eddying Eocene ocean with a 0.1° (horizontal) resolution model, which are initialized and forced with data from a coarser resolution (1° horizontally) equilibrated coupled ocean-atmosphere GCM. We investigate the response of the model equilibrium state to the change in ocean resolution and the consequences this has for model-data comparison in the middle-late Eocene (38Ma). We find that, compared to the non-eddying model, the eddying ocean resolution of palaeomodels reduce the biases in both sea surface temperatures and biogeographic patterns which are derived from proxy data.</p>

The middle Eocene to early Miocene integrated sedimentary record in the Qaidam Basin and its implications for paleoclimate and early Tibetan Plateau uplift

2013 ◽  
Vol 50 (2) ◽  
pp. 183-196 ◽  
Author(s):  
Bowen Song ◽  
Kexin Zhang ◽  
Jingfang Lu ◽  
Chaowen Wang ◽  
Yadong Xu
Keyword(s):  
Chemical Weathering ◽  
Middle Eocene ◽  
Qaidam Basin ◽  
Source Area ◽  
Late Eocene ◽  
Sedimentary Sequences ◽  
Humid Condition ◽  
Southern Central ◽  
Central Tibet ◽  
High Elevations

Detailed analysis of whole-rock geochemistry, clay minerals, sedimentary color, and pollen in the Dahonggou section, northeast of the Qaidam Basin, are investigated, and the results suggest an intense weathering in the source area during the middle Eocene (∼48.5–40.5 Ma), indicating a warm and humid condition. The distinct decrease of chemical weathering degree in source regions began at ∼40.5 Ma, which is in agreement with the distinct decrease in redness of sedimentary sequences and the disappearance of thermophilic elements in pollen records. This 40.5 Ma cooling event extent demonstrated evidence for an intensification of central Asian aridification, which could be attributed to attainment of high elevations in southern-central Tibet and retreat of the Paratethys from central Asia in the late Eocene, reducing moisture transport to the Qaidam Basin.

scholarly journals Atmospheric multidecadal variations in the North Atlantic realm: proxy data, observations, and atmospheric circulation model studies

2006 ◽  
Vol 2 (4) ◽  
pp. 633-656
Author(s):  
K. Grosfeld ◽  
G. Lohmann ◽  
N. Rimbu ◽  
K. Fraedrich ◽  
F. Lunkeit
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
General Circulation Models ◽  
Proxy Data ◽  
Model Studies ◽  
The North ◽  
The North Atlantic

Abstract. We investigate the spatial and temporal characteristics of multidecadal climate variability in the North Atlantic realm, using observational data, proxy data and model results. The dominant pattern of multidecadal variability of SST depicts a monopolar structure in the North Atlantic during the instrumental period with cold (warm) phases during 1900–1925 and 1970–1990 (1870–1890 and 1940–1960). Two atmospheric general circulation models of different complexity forced with global SST over the last century show SLP anomaly patterns from the warm and cold phases of the North Atlantic similar to the corresponding observed patterns. The analysis of a sediment core from Cariaco Basin, a coral record from the northern Red Sea, and a long-term sea level pressure (SLP) reconstruction reveals that the multidecadal mode of the atmospheric circulation characterizes climate variability also in the pre-industrial era. The analyses of SLP reconstruction and proxy data depict a persistent atmospheric mode at least over the last 300 years, where SLP shows a dipolar structure in response to monopolar North Atlantic SST, in a similar way as the models' responses do. The combined analysis of observational and proxy data with model experiments provides an understanding of multidecadal climate modes during the late Holocene. The related patterns are useful for the interpretation of proxy data in the North Atlantic realm.

scholarly journals Insights into the early Eocene hydrological cycle from an ensemble of atmosphere–ocean GCM simulations

2015 ◽  
Vol 11 (4) ◽  
pp. 3277-3339 ◽  
Author(s):  
M. J. Carmichael ◽  
D. J. Lunt ◽  
M. Huber ◽  
M. Heinemann ◽  
J. Kiehl ◽  
...  
Keyword(s):  
General Circulation ◽  
Hydrological Cycle ◽  
Middle Eocene ◽  
Circulation Model ◽  
Large Error ◽  
Early Eocene ◽  
Air Temperatures ◽  
Simulated Precipitation ◽  
Precipitation Estimates ◽  
Simulated Surface

Abstract. Recent studies, utilising a range of proxies, indicate that a significant perturbation to global hydrology occurred at the Paleocene–Eocene Thermal Maximum (PETM; ~56 Ma). An enhanced hydrological cycle for the warm early Eocene is also suggested to have played a key role in maintaining high-latitude warmth during this interval. However, comparisons of proxy data to General Circulation Model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised, despite significant differences in simulated surface temperatures. In this work, we undertake an intercomparison of GCM-derived precipitation and P-E distributions within the EoMIP ensemble (Lunt et al., 2012), which includes previously-published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure and precipitation relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to preindustrial. This is primarily due to elevated atmospheric paleo-CO2, although the effects of differences in paleogeography/ice sheets are also of importance in some models. For a given CO2 level, globally-averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP/dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that a number of GCMs underestimate precipitation rates at high latitudes. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences apparent between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.

scholarly journals Atmospheric multidecadal variations in the North Atlantic realm: proxy data, observations, and atmospheric circulation model studies

2007 ◽  
Vol 3 (1) ◽  
pp. 39-50 ◽  
Author(s):  
K. Grosfeld ◽  
G. Lohmann ◽  
N. Rimbu ◽  
K. Fraedrich ◽  
F. Lunkeit
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
General Circulation Models ◽  
Proxy Data ◽  
Model Studies ◽  
The North ◽  
The North Atlantic

Abstract. We investigate the spatial and temporal characteristics of multidecadal climate variability in the North Atlantic realm, using observational data, proxy data and model results. The dominant pattern of multidecadal variability of SST depicts a monopolar structure in the North Atlantic during the instrumental period with cold (warm) phases during 1900–1925 and 1970–1990 (1870–1890 and 1940–1960). Two atmospheric general circulation models of different complexity forced with global SST over the last century show SLP anomaly patterns from the warm and cold phases of the North Atlantic similar to the corresponding observed patterns. The analysis of a sediment core from Cariaco Basin, a coral record from the northern Red Sea, and a long-term sea level pressure (SLP) reconstruction reveals that the multidecadal mode of the atmospheric circulation characterizes climate variability also in the pre-industrial era. The analyses of SLP reconstruction and proxy data depict a persistent atmospheric mode at least over the last 300 years, where SLP shows a dipolar structure in response to monopolar North Atlantic SST, in a similar way as the models' responses do. The combined analysis of observational and proxy data with model experiments provides an understanding of multidecadal climate modes during the late Holocene. The related patterns are useful for the interpretation of proxy data in the North Atlantic realm.

scholarly journals A model–model and data–model comparison for the early Eocene hydrological cycle

2016 ◽  
Vol 12 (2) ◽  
pp. 455-481 ◽  
Author(s):  
Matthew J. Carmichael ◽  
Daniel J. Lunt ◽  
Matthew Huber ◽  
Malte Heinemann ◽  
Jeffrey Kiehl ◽  
...  
Keyword(s):  
General Circulation ◽  
Model Comparison ◽  
Elevated Temperatures ◽  
Hydrological Cycle ◽  
Middle Eocene ◽  
Circulation Model ◽  
Large Error ◽  
Early Eocene ◽  
Air Temperatures ◽  
Simulated Precipitation

Abstract. A range of proxy observations have recently provided constraints on how Earth's hydrological cycle responded to early Eocene climatic changes. However, comparisons of proxy data to general circulation model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised. In this work, we undertake an intercomparison of GCM-derived precipitation and P − E distributions within the extended EoMIP ensemble (Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes previously published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure, and precipitation-relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to the preindustrial conditions. This is primarily due to elevated atmospheric paleo-CO2, resulting in elevated temperatures, although the effects of differences in paleogeography and ice sheets are also important in some models. For a given CO2 level, globally averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP∕dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa, and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that GCMs generally underestimate precipitation rates at high latitudes, although a possible seasonal bias of the proxies cannot be excluded. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.

scholarly journals Interannual Variability of Land–Atmosphere Coupling Strength

2013 ◽  
Vol 14 (5) ◽  
pp. 1636-1646 ◽  
Author(s):  
Zhichang Guo ◽  
Paul A. Dirmeyer
Keyword(s):  
Soil Moisture ◽  
Interannual Variability ◽  
Coupling Strength ◽  
Land Surface ◽  
General Circulation ◽  
Circulation Model ◽  
Turbulent Fluxes ◽  
Near Surface ◽  
Soil Wetness ◽  
Wet Climate

Abstract Recent studies in the Global Land–Atmosphere Coupling Experiment (GLACE) established a framework to estimate the extent to which anomalies in the land surface state (e.g., soil moisture) can affect rainfall generation and other atmospheric processes. Within this framework, a multiyear GLACE-type experiment is carried out with a coupled land–atmosphere general circulation model to examine the interannual variability of land–atmosphere coupling strength. Soil wetness with intermediate values are in the range at which rainfall generation, near-surface air temperature, and surface turbulent fluxes are most sensitive to soil moisture anomalies, and thus, land–atmosphere coupling strength peaks in this range. As a result, the “hot spots” with strong land–atmosphere coupling strength appear in regions with intermediate climatological soil wetness (e.g., transition zones between dry and wet climates), consistent with previous studies. Land–atmosphere coupling strength experiences significant year-to-year variation because of interannual variability of soil moisture and the local spatiotemporal evolution of hydrologic regime. Coupling strength over areas with dry (wet) climate is enhanced during wet (dry) years since the resultant soil wetness enters into the sensitive range from a relatively insensitive range, and soil moisture can have stronger potential impact on surface turbulent fluxes and convection. On the other hand, land–atmosphere coupling strength over areas with wet (dry) climate is weakened during wet (dry) years since the soil wetness moves further away from the sensitive range. This results in a positive correlation between the land–atmosphere coupling strength and soil moisture anomalies over areas with dry climate and a negative correlation over areas with wet climate.

scholarly journals Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

2018 ◽  
Author(s):  
Michiel Baatsen ◽  
Anna S. von der Heydt ◽  
Matthew Huber ◽  
Michael A. Kliphuis ◽  
Peter K. Bijl ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Radiative Forcing ◽  
General Circulation ◽  
Middle Eocene ◽  
Late Eocene ◽  
Global Changes ◽  
The North ◽  
South Pacific Ocean ◽  
Polar Ice Sheets ◽  
Modelling Studies

Abstract. While the early Eocene has been considered in many modelling studies, detailed simulations of the middle and late Eocene climate are currently scarce. To understand Antarctic glaciation at the Eocene-Oligocene Transition (~ 34 Ma) as well as middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Here, we present a set of high resolution coupled climate simulations using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with new detailed 38 Ma geographical boundary conditions with a different radiative forcing. With 4 × pre-industrial concentrations of CO2 (i.e. 1120 ppm) and CH4 (~ 2700 ppb), the equilibrium sea surface temperatures correspond well to available late middle Eocene (42–38 Ma) proxies. Being generally cooler, the simulated climate with 2 × pre-industrial values is a good analog for that of the late Eocene (38–34 Ma). Deep water formation occurs in the South Pacific Ocean, while the North Atlantic is strongly stratified and virtually stagnant. A shallow and weak circumpolar current is present in the Southern Ocean with only minor effects on southward oceanic heat transport within wind-driven gyres. Terrestrial temperature proxies, although limited in coverage, also indicate that the results presented here are realistic. The reconstructed 38 Ma climate has a reduced equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. Climate sensitivity is similar (~ 0.7 °C/Wm2) to that of the present-day climate (~ 0.8 °C/Wm2; 3 °C per CO2 doubling), with significant polar amplification despite very limited sea ice and snow cover. High latitudes are mainly kept warm by albedo and cloud feedbacks in combination with global changes in geography and the absence of polar ice sheets. The integrated effect of geography, vegetation and ice accounts for a 6–7 °C offset between pre-industrial and 38 Ma Eocene boundary conditions. These 38 Ma simulations effectively show that a realistic middle-to-late Eocene climate can be reconstructed without the need for greenhouse gas concentrations much higher than proxy estimates. The general circulation and radiative budget allow for mild high-latitude regions and little to no snow and ice cover, without making equatorial regions extremely warm.

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