Teleconnections in the Climate System

1
Teleconnections in the Climate System

• North Atlantic and Monsoon connections

2
The Monsoon systems

• Asian Monsoon 2 subsystems
• Indian Monsoon
• East Asian Monsoon
• Australian Monsoon
• Orbital insolation, sea level, internal
  circulation changes

Hulu Cave North Bahia State, Brazil
3
East Asian Monsoon Record from Hulu Cave

• E. China
• d18O of 5 stalagmites, cover 74.87Ka to 10.93Ka
• 230 Th dating
• Eliminate processes other than precipitation and
  temperature by comparison of stalagmites growing
  at the same time
• No ve correlation between d13C and d18O

4
Temperature or precipitation?

• How to divide the effects on speleothem d18O?
• Current mean annual ppt1015mm, T15.4C
• Summer 80 ppt, d18O -9 to -13
• Winter 20 ppt, d18O -3 to 2
• Changes in past mean annual d18O likely due to
  changes in ratio of summer to winter
  precipitation
• Temp affects likely to be small (on fractionation
  during growth and on d18O of summer ppt)

5
Speleothem data
Long term looks like insolation effect, high
summer insolation increases continent-ocean T
contrast enhanced summer monsoons
6
Speleothem data Millennial Scale
7
Millennial Scale Variations

• Large d18O variation summer/winter ppt ratio
• Speleothem d18O resembles that of Greenland Ice
  core
• High Greenland T more intense East Asian summer
  monsoon
• Low Greenland T/Heinrich events weakened summer
  monsoon
• Some mismatch in detail
• Some correlation difficulties

8
Current System Brazilian drought

• Anomalous T gradient across equator warmer to
  the north
• Increase trade winds to the south
• Prevents southward migration of ICTZ no
  seasonal rains

9
Brazilian Speleothems and Travertines

• Brazil currently semi arid, can support
  speleothem/travertine deposits
• Past conditions must have been wetter
• Deposit U-Th dating links wet times in Brazil to
  cold Greenland T, Heinrich events and weakened
  East Asian monsoon
• tropical driver model as yet no convincing
  mechanism
• Climate model THC shutdown rearrangement of
  tropical rainfall
• Not clear how global connections are set up

10
Conclusions

• How are North Atlantic and Monsoon climates
  connected? Hulu Millennial scale - Strengthened
  summer East Asian monsoon when Greenland T
  higher. NE Brazil Wet period correspond to cold
  T in Greeland, Heinrich events and weakened
  summer East Asian monsoon
• What is the evidence for connections?
  Correspondence between Speleothem d18O data from
  East China (Hulu Cave) and Brazil with Greenland
  ice core d18O data
• What are the mechanisms that create the
  connection? Not really known, something to do
  with ocean-atmosphere circulation