Transcript Closing of Drake Passage and Antarctic climate

Timing and Climatic
Consequences of the Opening of
Drake Passage
H.D. Sher E.E. Martin, Nature. 2006
Evidence
• Abrupt climate reversal
– 34Ma: Permanent glaciation of Antarctica
• Increased biological productivity
Hypotheses
• Opening of Drake Passage
• Increased inter-basin exchange
• This leads to upwelling induced
productivity in the Ocean
• Reduced poleward heat transport to
Antarctica
Method
• Neodymium isotope ratio Nd143/Nd144
– Ratio is high (more radiogenic) on the Pacific
sector of Antarctica. Due to the presence of
young volcanic rock in this sector. ND=-3
– In the Atlantic sector, the terrain is much older
and have much lower ND ratio. ND=-9
• Ferro-Manganese ocean crust and fossil
fish teeth preserves the Nd signal.
– Fossil fish teeth have a better resolution than
ocean crust
Neodymium record
46Ma to present
Interpretation
• Atlantic sector water mixes with Pacific sector
waters (radiogenic).
• OR
• Pacific water enters the Atlantic sector (Indian
Ocean)  90 east ridge forms a barrier
between east-west of the ridge
• Pacific water enters the Atlantic through the
Panama passage  Romanche Fracture zone
and Walvis ridge show no signs of Pacific water
intrusions.
Problems
• Why is the signal at Maud Rise less
significant?
– Ocean stratified, and the Pacific signal
remained at depth
– Proto Polar Front at Maude rise which would
have isolated the water at Maude rise from
the influence from the Pacific sector. This front
is apparent in paleo productivity across that
front from one side to the other
Hypothesis
• Opening of Drake Passage  increase
mixing in the southern ocean  more
nutrient upwelling  more productivity 
more carbon sequestration  less CO2 in
the atmosphere
• And possibly less poleward heat transport
associated with the opening of the Drake
Passage
Delta O18 record
70Ma to present