Short Term Climate Change in the Mediterranean during the last Glacial

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  • Created by: nicola
  • Created on: 12-04-11 10:14

Marine core records - show gradual transitions in ice volume = L/T changes related to orbital forcing (Milankovitch)

Ice core records - show changing temps but on much shorter timescales - ice accumulation is recorded on an annual basis (high resolution)

The broad patterns seen in marine cores are reflected in ice cores however ice shows more climatic instability due to it recording at shorter timescales - very responsive, easily illustrates fluctuations in temps

Marine environs have slower sedimentation records therefore only record L/T changes - recording global ice volume therefore S/T changes in temps e.g. increase in glacial period, may not be recorded as glaciers may not respond

Compaction of seds in both marine and ice cores can distort records - increase in distortion with age of sed (at base of core)

Ice cores - darker layers show summer season = increase temps cause snow melt leaving behind an increase in concentration of dust and impurities

Characteristics of S/T climate forcing

Warming/ cooling lasts 00's/000's of yrs

Transition from peak cooling to peak warming can occur in decades

Interstadials/ Stadials = Sub-Milankovitch events -  mainly from changes in salinity which affect THC from glacier meltwater

  • e.g. Younger Dryas - meltwater from Laurentide ice sheet initially flows into gulf of Mexico, redirected into N Atlantic which switches of THC and causes cooling - lasted for approx 1000 yrs

Causes changes mainly to N Hemisphere but also to Med

S/T warming and cooling events in Glacial periods are known as Dansgaard-Oeschger insterstadials or stadials (also appear to be driven by changes in THC)

Last glacial - characterised by large climate fluctuations related to iceberg release = Henrich events

  • D/O cycles correlate to vast amounts of sea ice being released into N Atlantic, which upon melting releases fresh, cold water switching off the THC
  • Shown by large amounts of ice rafted detritus in marine cores
  • Henrich events trigger multiple D/O cycles - these cycles are recorded in ice core records
  • Caused by climate warming

S/T changes in Mediterranean

Often a link between rainfall and temp but not always a clear cut trend

In Med, changes shown by variations in precipitation

Changes in temp gradients across the N Atlantic affect wind movements into the Mediterranean

  • In present day - N Atlantic region of Africa and Spain warmed by THC as is Britain and Iceland = no major pressure difference so moist NW winds can flow into Med - temp differences between regions due to insolation factors
  • Reduced THC activity (glacials) - Spain and N Africa still warmed by THC but Britain and Ireland cool from reduced heat transfer = major pressure difference between N and S Europe (from temp diff) so moist NW winds are diverted north leaving Med dry

Vegetation studies from 70s and 80s show evidence for changes in veg (from glacial to interglacial periods) but sampled at low resolution so too difficult for interpretation to be precise for S/T changes

Med during D/O cycles (Moreno at al, 2004)

  • D/O interstadials - moist westerlies can flow into Med
  • D/O stadials - moist westerlies pushed further…

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