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EGU 2007, CR140 Dan Lunt
Introduction. GCM and ice sheet simulations. Conclusions. Other mechanisms for inception. Future plans.
The closure of the Panama Seaway and the onset of Northern Hemisphere glaciation: Cause or Coincidence?
D.J. Lunt, P.J. Valdes
A. Haywood I.C. Rutt
EGU 2007, CR140 Dan Lunt
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
Zachos et al, 2001
CAUSE OR COINCIDENCE?Bartoli et al, 2005
EGU 2007, CR140 Dan Lunt
Hypothesis to testClosure of the Seaway
enhancement of Atlantic circulation
warmer SSTs
increased evaporation at high latitudes.
increase in precipitation
inception of Northern Hemisphere Glaciation
+ increase understanding of climate / ice sheet interactions for future climate change!
Ruddiman, Earth’s Climate
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
EGU 2007, CR140 Dan Lunt
~ 370 m depthClosed Seaway (late Pliocene) Open Seaway (early Pliocene)
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
2 experiments with a fully-coupled atmosphere-ocean General Circulation Model (AOGCM), HadCM3.
EGU 2007, CR140 Dan Lunt
Surface air temperature, closed Seaway – open Seaway
Bi-polar response.
Max 7oC warming in North Atlantic following closure.
Global average: +0.25oC
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
EGU 2007, CR140 Dan Lunt
Atlantic Circulation [Sv]
Atlantic circulation, Pliocene closed Seaway Atlantic circulation, Pliocene open Seaway
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
EGU 2007, CR140 Dan Lunt
Precipitation change, Closed-Open
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
EGU 2007, CR140 Dan Lunt
Ice-sheet model – GLIMMER. Based on Payne (1999).
Predicts evolution of ice-sheet geometry (extent, elevation), given a driving climate (temp and precip).
Annual PDD scheme for surface mass-balance
Temperature downscaled using high-resolution (40 km) orography and a constant lapse rate.
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
EGU 2007, CR140 Dan Lunt
Modelled Pliocene (closed)Modelled Pliocene (open) Closed - open
Modelled Pliocene (open)
Modelled Pliocene (closed)
Ice sheet volume [m of sea level]
1.16 1.21
The closure of the Panama Seaway and the onset of Northern Hemisphere Glaciation: Cause or Coincidence?
EGU 2007, CR140 Dan Lunt
Conclusions
Model results indicate that the closure of the Panama Seaway did not directly cause Northern Hemisphere Glaciation during the Pliocene.
The process for the slight enhancement of glaciation following closure of the seaway is as proposed in the original hypothesis, i.e. mixing of Atlantic and Pacific waters leading to a massive enhancement of the Atlantic MOC, increased evaporation and precipitation over Greenland, which leads to enhanced glaciation.
Climate Dynamics, in press.
CAUSE OR COINCIDENCE?
Given caveats!
EGU 2007, CR140 Dan Lunt
Other mechanisms for inceptionAtmospheric composition changes (e.g. CO2).
Orbital fluctuations.
Open Seaway
CO2 = 400ppmv
Modern orbit
Closed Seaway
CO2 = 400ppmv
Modern orbit
Closed Seaway
CO2 = 280ppmv
Modern orbit
Closed Seaway
CO2 = 280ppmv
Glacial Inception orbit
EGU 2007, CR140 Dan Lunt
Future work
Validation with paleodata:Daniela Schmidt, Richard Pancost, Bristol Earth Sciences and Bristol Chemistry
Other effects?? Rockies uplift….Gavin Foster, Bristol Earth Sciences
Effect of the closure on the Antarctic ice sheet
Complete sensitivity studiese.g. Solely orbital forcing.
EGU 2007, CR140 Dan Lunt