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