Evolution of the Asian monsoon from the Cretaceous to the modern

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Evolution of the Asian monsoon from the
Cretaceous to the modern a modelling
study.Dan Lunt, Alex Farnsworth, Claire
Loptson, Paul Markwick
How has palaeogeography, greenhouse gases, solar
output, and evolving ice, controlled the Asian
monsoon system over the last 150 million years
?
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(1) Introduction
Last 150 Ma Major climate trends, variability
events
Data from Friedrich et al (2012)
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(2) Previous modelling work

• Previous work on a limited number of time
  periods (mostly focussed on the role of Tibetan
  uplift)
• Previously coarse (mostly idealised)
  palaeogeographies.

Hahn and Manabe, JAS, 1975
Zhisheng et al, Nature, 2001
Park et al, J.Clim, 2012
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(3) Experimental Design
Palaeogeographies provided by Getech and Paul
Markwick
Created using similar techniques to those
outlined in Markwick (2007), based on published
lithologic, tectonic and fossil studies, the
lithologic databases of the Paleogeographic Atlas
Project (University of Chicago), and deep sea
(DSDP/ODP) data. Extensively updated from
Markwick (2007), e.g. bathymetry, new rotations,
more underlying data.
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(3) Experimental Design
CO2 forcing
Solar forcing
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(3) Experimental Design
The model HadCM3L (with vegetation) state-of-the
-art for long simulations
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(3) Experimental Design
The model HadCM3L
How good is it for the palaeo?
Lunt et al, Clim. Past (2012) Data compiled by
Tom Dunkley Jones.
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(3) Experimental Design (consistent across all
simulations)
Phase 1
Phase 2
Phase 3
Phase 4
50-years
400-years
500-1000 years
57-years
Deep ocean temperature
Pre-industrial CO2 Pre-industrial
SSTs Paleogeography's Uniform Veg
Lakes
4xCO2 TRIFFID Solar constants Ozone
concentrations
No Ice 2 x CO2
Creation of islands Baratropic stremfunction
Ice 2 x CO2
Ice 4 x CO2
Simulation spinup from Alex Farnsworth
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(4) Results
Global means...
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(4) Results
SSTs...
e.g. Maximum warmth shifts from W. Pacific to E.
Indian ocean in Late Eocene. Zonal mean
relatively constant. ENSO is a constant
feature. Winter Arctic and Southern Ocean seaice
for all time periods.
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(4) Results
Precipitation...
e.g. ITCZ is constant feature High
precipitation does not penetrate into East Asian
continent until later Cenozoic
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(4) Results
Vegetation...
e.g. Expansive N and S American deserts in early
Cretaceous. Green Sahara develops in late
Eocene. Maximum East Asian desert extent in Late
Cretaceous
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(4) Results
Fixed(red) and roving (blue) East Asian
monsoon regions (EAMR)
Precipitation trends...
Global
EAMR roving
EAMR fixed
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(4) Results
Seasonality...
Cretaceous
Paleogene
Neogene
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(4) Results
Model-data comparisons...
Data trends are given here over the Duration of
the period (length of line) Red Trend
disagreement Black Trend agreement
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Summary

• Global precipitation decrease over the last 150
  million years.
• East Asian monsoon regions shows a decrease in
  the Cretaceous followed by increase in the
  Paleogene and early Neogene, then a decrease in
  the Pliocene.
• Associated vegetation shifts, such as maximum
  desert extent in the late Cretaceous.
• Shifts in seasonality, with maximum
  precipitation moving progressively earlier in the
  year.
• Some support for some trends from data.

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(5) Future work

• More data
• Mechanistic understanding of modelled monsoon
  trends
• Role of orbital forcing
• Separate factors (paleogeography vs. CO2 vs. ice
  vs. solar)
• Role of orbital forcing
• Model internal parameter sensitivity studies.
• CESM simulations of the Cretaceous (Chris Poulsen
  and Clay Tabour)
• PMIP working group on pre-Pliocene climates
• Joint venture between data and modelling
  communities

Model output available. Email d.j.lunt_at_bristol.ac
.uk