The middle to late Eocene greenhouse climate modelled  using the CESM 1.0.5

Abstract. The early and late Eocene have both been the subject of many modelling studies, but few have focused on the middle Eocene. The latter still holds many challenges for climate modellers but is also key to understanding the events leading towards the conditions needed for Antarctic glaciation at the Eocene–Oligocene transition. Here, we present the results of CMIP5-like coupled climate simulations using the Community Earth System Model (CESM) version 1. Using a new detailed 38 Ma geography reconstruction and higher model resolution compared to most previous modelling studies and sufficiently long equilibration times, these simulations will help to further understand the middle to late Eocene climate. At realistic levels of atmospheric greenhouse gases, the model is able to show overall good agreement with proxy records and capture the important aspects of a warm greenhouse climate during the Eocene. With a quadrupling of pre-industrial concentrations of both CO2 and CH4 (i.e. 1120 ppm and ∼2700 ppb, respectively, or 4 × PIC; pre-industrial carbon), sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ∼ Bartonian) proxies. Being generally cooler, the simulated climate under 2 × PIC forcing is a good analogue for that of the late Eocene (38–34 Ma; ∼ Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, also indicate that the results presented here are in agreement with the available information. Our simulated middle to late Eocene climate has a reduced Equator-to-pole temperature gradient and a more symmetric meridional heat distribution compared to the pre-industrial reference. The collective effects of geography, vegetation, and ice account for a global average 5–7 ∘C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. This helps to explain Eocene warmth in general, without the need for greenhouse gas levels much higher than indicated by proxy estimates (i.e. ∼500–1200 ppm CO2) or low-latitude regions becoming unreasonably warm. High-latitude warmth supports the idea of mostly ice-free polar regions, even at 2 × PIC, with Antarctica experiencing particularly warm summers. An overall wet climate is seen in the simulated Eocene climate, which has a strongly monsoonal character. Equilibrium climate sensitivity is reduced (0.62 ∘C W−1 m2; 3.21 ∘C warming between 38 Ma 2 × PIC and 4 × PIC) compared to that of the present-day climate (0.80 ∘C W−1 m2; 3.17 ∘C per CO2 doubling). While the actual warming is similar, we see mainly a higher radiative forcing from the second PIC doubling. A more detailed analysis of energy fluxes shows that the regional radiative balance is mainly responsible for sustaining a low meridional temperature gradient in the Eocene climate, as well as the polar amplification seen towards even warmer conditions. These model results may be useful to reconsider the drivers of Eocene warmth and the Eocene–Oligocene transition (EOT) but can also be a base for more detailed comparisons to future proxy estimates.

Download Full-text

The middle-to-late Eocene greenhouse climate, modelled using the CESM 1.0.5

10.5194/cp-2020-29 ◽

2020 ◽

Cited By ~ 1

Author(s):

Michiel Baatsen ◽

Anna S. von der Heydt ◽

Matthew Huber ◽

Michael A. Kliphuis ◽

Peter K. Bijl ◽

...

Keyword(s):

Boundary Conditions ◽

Greenhouse Gas ◽

Radiative Forcing ◽

Middle Eocene ◽

Late Eocene ◽

Collective Effects ◽

Global Changes ◽

Radiative Balance ◽

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 get a better understanding of both Antarctic glaciation at the Eocene-Oligocene transition (~34 Ma) and late middle Eocene warmth, it is vital to have an adequate reconstruction of the middle-to-late Eocene climate. Results of higher (CMIP5-like) resolution coupled climate simulations are represented here using the Community Earth System Model (CESM) version 1. Two middle-to-late Eocene cases are considered with the same general boundary conditions but a different radiative forcing, using a new detailed 38 Ma geography reconstruction. Under 4× pre-industrial concentrations (PIC) of both CO2 (i.e. 1120 ppm) and CH4 (~2700 ppb), equilibrium sea surface temperatures correspond well to the available late middle Eocene (42–38 Ma; ~Bartonian) proxies. Being generally cooler, the simulated climate under 2× PIC forcing is a good analog for that of the late Eocene (38–34 Ma; ~Priabonian). Terrestrial temperature proxies, although their geographical coverage is sparse, 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. The collective effects of geography, vegetation and ice accounts for a global mean 5–7 °C difference between pre-industrial and 38 Ma Eocene boundary conditions, with important contributions from cloud and water vapour feedbacks. These 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 (i.e. ~500–1200 ppm CO2). Equilibrium climate sensitivity is reduced (0.62 °C/W m2; 3.2 °C warming between 38 Ma 2× PIC and 4× PIC) compared to that of the present-day climate (0.79 °C/W m2; 3.1 °C per CO2 doubling). Despite very limited sea ice and snow cover in both 38Ma cases, the model still shows a factor ~2 polar amplification in response to a further increase of atmospheric greenhouse gas concentrations. High latitudes in the modelled Eocene climate are mainly kept warm by an altered radiative balance in combination with global changes in geography and the absence of polar ice sheets compared to the pre-industrial reference.

Download Full-text

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

10.5194/cp-2018-43 ◽

2018 ◽

Cited By ~ 9

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.

Download Full-text

Exploring the aerosol-cloud-radiation relationships in deep marine stratocumulus layers

10.5194/egusphere-egu2020-9470 ◽

2020 ◽

Author(s):

Anna Possner ◽

Ryan Eastman ◽

Frida Bender ◽

Franziska Glassmeier

Keyword(s):

High Resolution ◽

Boundary Layers ◽

Radiative Forcing ◽

Radiative Properties ◽

Radiative Balance ◽

Aerosol Cloud ◽

Modelling Studies ◽

Field Campaigns ◽

Ship Tracks ◽

Relative Change

Marine stratocumuli cover around a fifth of the worlds oceans and are a key contributor to Earth&#8217;s radiative balance at the surface. Their sensitivity to changes in anthropogenic aerosol concentrations remain a key uncertainty in the climate system. Our current understanding of their sensitivity and the plausible range of the aerosol-cloud radiative forcing is largely based on the process understanding obtained from field campaigns, high-resolution modelling, and satellite records of aerosol-induced phenomena such as volcano or ship tracks.Yet, a large fraction of these records is only applicable to relatively shallow planetary boundary layers (PBLs). Ship tracks are only found in boundary layers up to a depth of 800m. Field campaigns and high-resolution modelling studies of aerosol-cloud-radiation interactions in marine stratocumuli have been restricted to a similar range of PBL depths in the past. Meanwhile over 70% of marine boundary layers reside in deeper PBLs.The liquid water path (LWP) adjustment due to aerosol-cloud interactions in marine stratocumuli remains a considerable source of uncertainty for climate sensitivity estimates. An unequivocal attribution of LWP adjustments to changes in aerosol concentration from climatology remains difficult due to the considerable covariance between meteorological conditions alongside changes in aerosol concentrations.Here, we combine a range of space-born remote sensing retrievals to investigate the relationship of cloud-radiative properties for different boundary layer depths and aerosol concentrations. As done in previous studies we utilise the susceptibility framework, i.e. the relative change in LWP scaled by the relative change in cloud droplet number concentration, to quantify the change in LWP adjustment with PBL depth. We show that the susceptibility of LWP adjustments triples in magnitude from values of -0.1 in PBLs shallower than 0.5 km to -0.33 in PBLs deeper than 1 km.We further argue that LWP susceptibility estimates inferred from deep PBL climatologies are poorly constrained due to a lack of process-oriented observations. Meanwhile, susceptibilities inferred from climatology in shallow PBL regimes are consistent with estimates obtained from process modelling studies, but are overestimated as compared to pollution track estimates.

Download Full-text

Increase of upper troposphere/lower stratosphere wave baroclinicity during the second half of the 20th century

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-9143-2009 ◽

2009 ◽

Vol 9 (23) ◽

pp. 9143-9153 ◽

Cited By ~ 21

Author(s):

J. M. Castanheira ◽

J. A. Añel ◽

C. A. F. Marques ◽

J. C. Antuña ◽

M. L. R. Liberato ◽

...

Keyword(s):

Temperature Gradient ◽

20Th Century ◽

Radiative Forcing ◽

Lower Stratosphere ◽

Normal Modes ◽

Radiosonde Data ◽

Baroclinic Wave ◽

Meridional Temperature Gradient ◽

Upper Troposphere ◽

Modelling Studies

Abstract. A strengthening of the equatorward temperature gradient in the upper troposphere/lower stratosphere (UTLS), at subtropics and midlatitudes, is consistently reproduced in several modelling studies of the atmospheric response to the increase of greenhouse gas radiative forcing. Some of those studies suggest an increase of the baroclinicity in the UTLS region because of the enhanced meridional temperature gradient. This study presents observational evidence of an increase of the baroclinic wave components of UTLS circulation (UTLS wave baroclinicity), during the second half of the 20th century. The evidence is given by significant positive trends in the energy of baroclinic normal modes of the NCEP/NCAR reanalysis, and significant positive trends in the UTLS eddy available potential energy of the NCEP/NCAR, ERA-40, NCEP-2 and JRA-25 reanalyses. Significant positive trends in the frequency of double tropopause events in radiosonde data are also interpreted as a manifestation of an increase of the UTLS wave baroclinicity.

Download Full-text

Increase of upper troposphere/lower stratosphere wave baroclinicity during the second half of the 20th century

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-18597-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 18597-18619 ◽

Cited By ~ 1

Author(s):

J. M. Castanheira ◽

J. A. Añel ◽

C. A. F. Marques ◽

J. C. Antuña ◽

M. L. R. Liberato ◽

...

Keyword(s):

Temperature Gradient ◽

Potential Energy ◽

20Th Century ◽

Radiative Forcing ◽

Lower Stratosphere ◽

Normal Modes ◽

Radiosonde Data ◽

Upper Troposphere ◽

Available Potential Energy ◽

Modelling Studies

Abstract. A strengthening of the equatorward temperature gradient in the upper troposphere/lower stratosphere (UTLS), at subtropics and midlatitudes, is consistently reproduced in several modelling studies of the atmospheric response to the increase of greenhouse gas radiative forcing. Some of those studies suggest an increase of the baroclinicity in the UTLS region because of the enhanced meridional temperature gradient. This study presents observational evidence of an increase of UTLS wave baroclinicity, during the second half of the 20th century. The evidence is given by significant positive trends in the energy of baroclinic normal modes of the NCEP/NCAR reanalysis, and significant positive trends in the eddy available potential energy of the ERA-40 reanalysis as well as in the eddy available potential energy of the JRA-25 reanalysis. Significant positive trends in the frequency of double tropopause events in radiosonde data are also interpreted as a manifestation of an increase of the UTLS wave baroclinicity.

Download Full-text

Monitoring of long-range transported smoke in polar regions with remote sensing instruments

10.5194/egusphere-egu21-15699 ◽

2021 ◽

Author(s):

Ramiro González Catón ◽

Carlos Toledano ◽

Roberto Román Diez ◽

David Mateos ◽

Eija Asmi ◽

...

Keyword(s):

Particle Size ◽

Long Range ◽

Biomass Burning ◽

Radiative Forcing ◽

Single Scattering ◽

The Arctic ◽

Polar Regions ◽

Intergovernmental Panel ◽

Radiative Balance ◽

The Impact

Long range transported aerosol from biomass burning affects polar regions, especially the Arctic. The frequency and intensity of bushfires in the context of a warming climate has been pointed out in the last report of the Intergovernmental Panel on Climate Change. In high latitudes, these events impact large areas through long-range transport of the smoke particles in the troposphere or even the stratosphere. The lifetime and radiative impact are related with the height of the plumes and the processes that modify particle size and absorptive properties during the transport. Several recent publications have shown the impact of the Australian smoke in the southern hemisphere, including Antarctica, in January-March 2020. The tools that were used to monitor that extraordinary event can be used in the Arctic to investigate similar effects in the frequent biomass burning events that generate smoke plumes in boreal regions. In this work, we present the results derived from ground-based instrumentation as well as satellite and model data. The change of the smoke properties after several days of transport is also provided, namely an increase in the fine mode particle size and the single scattering albedo, as well as a decrease in the coarse mode particle concentration. These features are relevant for radiative forcing calculations and therefore the impact of long range transported smoke in the radiative balance over polar regions.

Download Full-text

Geographic contingency, not species sorting, dominates macroevolutionary dynamics in an extinct clade of neogastropods (Volutospina; Volutidae)

Paleobiology ◽

10.1017/pab.2020.60 ◽

2021 ◽

pp. 1-15

Author(s):

Dana S. Friend ◽

Brendan M. Anderson ◽

Warren D. Allmon

Keyword(s):

Middle Eocene ◽

Ecological Factors ◽

Geographic Range ◽

Late Eocene ◽

Range Size ◽

Species Sorting ◽

Extinction Rates ◽

Geographic Range Size ◽

Speciation Rates ◽

Planktotrophic Larvae

Abstract Rates of speciation and extinction are often linked to many ecological factors, traits (emergent and nonemergent) such as environmental tolerance, body size, feeding type, and geographic range. Marine gastropods in particular have been used to examine the role of larval dispersal in speciation. However, relatively few studies have been conducted placing larval modes in species-level phylogenetic context. Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades have not considered both phylogenetic context and net speciation (speciation–extinction) rates. This study utilizes Eocene volutid Volutospina species from the U.S. Gulf Coastal Plain and the Hampshire Basin, U.K., to explore the relationships among larval mode, geographic range, and duration. Based on the phylogeny of these Volutospina, we calculated speciation and extinction rates in order to compare the macroevolutionary effects of larval mode. Species with planktotrophic larvae had a median duration of 9.7 Myr, which compared significantly to 4.7 Myr for those with non-planktotrophic larvae. Larval mode did not significantly factor into geographic-range size, but U.S. and U.K. species do differ, indicating a locality-specific component to maximum geographic-range size. Non-planktotrophs (NPTs)were absent among the Volutospina species during the Paleocene–early Eocene. The relative proportions of NPTs increased in the early middle Eocene, and the late Eocene was characterized by disappearance of planktotrophs (PTs). The pattern of observed lineage diversity shows an increasing preponderance of NPTs; however, this is clearly driven by a dramatic extinction of PTs, rather than higher NPT speciation rates during the late Eocene. This study adds nuance to paleontology's understanding of the macroevolutionary consequences of larval mode.

Download Full-text

Impact of mid Eocene greenhouse warming on America’s southernmost floras

Communications Biology ◽

10.1038/s42003-021-01701-5 ◽

2021 ◽

Vol 4 (1) ◽

Cited By ~ 1

Author(s):

Damián A. Fernández ◽

Luis Palazzesi ◽

M. Sol González Estebenet ◽

M. Cristina Tellería ◽

Viviana D. Barreda

Keyword(s):

Middle Eocene ◽

Pollen Grains ◽

Late Eocene ◽

Significant Rise ◽

Spores And Pollen ◽

Deep Time ◽

Nonparametric Estimators ◽

Southern Patagonia ◽

Marine Realm ◽

High Diversity

AbstractA major climate shift took place about 40 Myr ago—the Middle Eocene Climatic Optimum or MECO—triggered by a significant rise of atmospheric CO2 concentrations. The biotic response to this MECO is well documented in the marine realm, but poorly explored in adjacent landmasses. Here, we quantify the response of the floras from America’s southernmost latitudes based on the analysis of terrestrially derived spores and pollen grains from the mid-late Eocene (~46–34 Myr) of southern Patagonia. Robust nonparametric estimators indicate that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The high atmospheric CO2 and increasing temperatures may have favored the combination of neotropical migrants with Gondwanan species, explaining in part the high diversity that we observed during the MECO. Our reconstructed biota reflects a greenhouse world and offers a climatic and ecological deep time scenario of an ice-free sub-Antarctic realm.

Download Full-text

Falcatifolium (Podocarpaceae) macrofossils from paleogene sediments in south-eastern Australia: a reassessment

Australian Systematic Botany ◽

10.1071/sb97014 ◽

1998 ◽

Vol 11 (6) ◽

pp. 711 ◽

Cited By ~ 5

Author(s):

Robert S. Hill ◽

Leonie J. Scriven

Keyword(s):

Leaf Morphology ◽

Middle Eocene ◽

Late Eocene ◽

South Eastern ◽

Early Oligocene ◽

Extant Species ◽

Eastern Australia ◽

South Eastern Australia

A re-investigation of macrofossils previously referred to the extantpodocarpaceous genus Falcatifolium Laubenfels shows thatno records can be sustained. Falcatifolium australisD.R.Greenwood from Middle Eocene sediments in Victoria bears littleresemblance to extant species in the genus and is transferred to the newfossil genus Sigmaphyllum R.S.Hill & L.J.Scriven.Specimens from Early Oligocene sediments in Tasmania previously assigned toFalcatifolium are described as a second species ofSigmaphyllum, S. tasmanensisR.S.Hill & L.J.Scriven, and specimens from mid to late Eocene sediments inTasmania previously assigned to Falcatifolium do notbelong to that genus, although their true generic affinities are uncertain.Dispersed cuticle specimens from Late Eocene–Oligocene sediments inSouth Australia referred to Falcatifolium are notreliable records of the genus and require further investigation. However,Dacrycarpus eocenica D.R.Greenwood, from Middle Eocenesediments in Victoria is transferred to Falcatifolium,and is similar to the extant species F. angustumLaubenfels, which has a leaf morphology unusual for the genus.Falcatifolium eocenica (D.R.Greenwood) R.S.Hill & L.J.Scriven is the only reliable record of the genus in the Australian fossilrecord to date.

Download Full-text

Late Paleogene paleotopographic evolution of the northern Cordilleran orogenic front: Implications for demise of the orogen

Geological Society of America Bulletin ◽

10.1130/b35919.1 ◽

2021 ◽

Author(s):

Majie Fan ◽

Kurt N. Constenius ◽

Rachel F. Phillips ◽

David L. Dettman

Keyword(s):

Initial Phase ◽

Middle Eocene ◽

High Elevation ◽

Late Eocene ◽

Crustal Extension ◽

Late Oligocene ◽

Slab Rollback ◽

Basin Floor ◽

Climate Cooling ◽

High Range

The paleotopographic history of the North American Cordilleran orogen holds the key to understanding mechanisms of orogenesis and subsequent orogenic collapse. It has been suggested that the orogenic front in western Montana (USA) and Alberta (Canada) was more than 4 km high during Late Cretaceous−early Eocene contractional deformation and during the initial phase of extension in the middle Eocene; however, the late Eocene−Oligocene topographic evolution during continued extensional collapse remains poorly constrained. Here we extend the paleotopographic record in the Kishenehn Basin in northwestern Montana and southeastern British Columbia (Canada) to the late Oligocene by studying δ18O values of fossil mollusks and cement and paleosol carbonates. The molluscan taxa changed from three sympatric groups with preferred habitats ranging from tropical wet, semi-arid subtropical, and temperate during the middle and late Eocene, to mainly a single group associated with temperate environment during the Oligocene, reflecting a decline in molluscan biodiversity induced by climate cooling across the Eocene−Oligocene transition. Reconstructed δ18O values of alpine snowmelt and basinal precipitation decreased by 1.4‰ and 3.8‰, respectively, from the middle to late Eocene, reflecting climate cooling and ∼1 km surface uplift of the basin floor. The reconstructed alpine snowmelt δ18O values then increased by 2.9‰ in the Oligocene suggesting a ∼0.5 km drop in elevation of the orogenic front. Collectively, the results of our new and previously published δ18O data chronicle the paleotopographic response to the change from flat-slab subduction to slab rollback over a 45 m.y. period. These data suggest that the orogenic front was characterized by high elevation (>4 km) in the ancestral Lewis-Clark-Livingston ranges during latest Cretaceous−early Eocene (ca. 75−52 Ma) contraction. The initial phase of extension related to the Kishenehn Basin created a lowland basin with a surface elevation of only ∼1.5 km during the early middle Eocene (ca. 46−44 Ma) whereas the ranges remained >4 km high. The high range elevations were sustained for at least 12 m.y. in the middle to late Eocene concurrent with extension, while the basin floor elevation was uplifted to ∼2.5 km by the latest Eocene (ca. 36−34 Ma). Basin aggradation can explain at most half of the 1 km basin floor uplift. The remaining amount (at least 0.5 km) and sustained high range elevation suggest that range denudation and crustal extension was compensated by the isostatic and thermal effects of slab rollback and/or passage of a slab window and infusion of hot asthenosphere beneath the continent. The range elevation in the orogenic front decreased ∼0.5 km by the late Oligocene (ca. 28 Ma), associated with a decrease in rock uplift rate associated with extension. A post-Oligocene elevation drop of ∼1 km resulted in both the ranges and basin floor reaching modern topography in the Kishenehn Basin drainage, likely due to the regional effect of Neogene Basin and Range extension. This study, along with the previous investigation of the Kishenehn Basin by Fan et al. (2017), are the first studies that systematically investigate paleorelief of the orogenic belt by reconstructing paleoelevations of the mountains and the basin at the same time. The results highlight that the Cordilleran orogenic front of northern Montana and southern British Columbia sustained its high elevation edifice for at least 12 m.y. after the start of extension. We suggest that initial crustal extension did not result in orogenic demise because of concurrent thermal and isostatic uplift.

Download Full-text