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. HaywoodI.C. Rutt Slide 2 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 Slide 3 EGU 2007, CR140 Dan Lunt Hypothesis to
test Closure 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, Earths Climate The closure of the
Panama Seaway and the onset of Northern Hemisphere Glaciation:
Cause or Coincidence? Slide 4 EGU 2007, CR140 Dan Lunt ~ 370 m
depth Closed 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. Slide 5 EGU 2007, CR140 Dan Lunt Surface air temperature,
closed Seaway open Seaway Bi-polar response. Max 7 o C warming in
North Atlantic following closure. Global average: +0.25 o C The
closure of the Panama Seaway and the onset of Northern Hemisphere
Glaciation: Cause or Coincidence? Slide 6 EGU 2007, CR140 Dan Lunt
Atlantic Circulation [Sv] Atlantic circulation, Pliocene closed
SeawayAtlantic circulation, Pliocene open Seaway The closure of the
Panama Seaway and the onset of Northern Hemisphere Glaciation:
Cause or Coincidence? Slide 7 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? Slide 8 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? Slide 9 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] 1.161.21 The closure of
the Panama Seaway and the onset of Northern Hemisphere Glaciation:
Cause or Coincidence? Slide 10 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!
Slide 11 EGU 2007, CR140 Dan Lunt Other mechanisms for inception
Atmospheric composition changes (e.g. CO 2 ). Orbital fluctuations.
Open Seaway CO 2 = 400ppmv Modern orbit Closed Seaway CO 2 =
400ppmv Modern orbit Closed Seaway CO 2 = 280ppmv Modern orbit
Closed Seaway CO 2 = 280ppmv Glacial Inception orbit Slide 12 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 studies e.g. Solely orbital forcing. Slide 13
EGU 2007, CR140 Dan Lunt