Glacial and Interglacial Cycles in the Mediterranean

Climate change occurs on range of different scales and magnitudes - need to understand large scale changes to understand smaller scale variations

In  Med, glacial/interglacial cycles reflected by changes in precip - in N Hemisphere by ice sheet expansion

• Largest control on climate - effects ecology
• only slight change in temps

Affect of changing temperature - example from global climate models for Last Glacial Maximum (20kyrs BP) (Kageyma et al 2006):

• Worst case scenario (from this model);
  • Winter temperatures 3oC (modern = 9oC)
  •  Summer temperatures 13oC (modern = 25oC)

Geomorphic records show changes in lake levels, and changes to activeness of river systems Palaeoecological records display shift to semi-arid/arid veg

In Turkey, Greece and North Africa:

• Modern lakes are surrounded by old lake levels
•  Represent more extensive and deeper lake levels than at present
•  These relict shorelines dated to L.G.M. (18 to 20 kyrs)

Used to suggest that glacial climates were much wetter than present  Many researchers suggested term Pluvial episodes to correlate with Glacial episodes in northern Europe

Example - Lake Ioannina, Western Greece

• Dated by radiocarbon technique
• Lake levels were 3.2m higher than they are today dated to between 24,500 and 19,000 years B.P. = GLACIAL PERIOD
• Dominance of Artimesia
• Lowering of lake levels occurred after 16,500 and 14,000 years B.P.
• Supported by other geomorphic records - sed deposition and stream power
• Good record for pollen - seds are kept water logged where water levels are still high preventing decay 

Palaeoecology from the Med

Contrasts with geomorphological records Cores taken from lakes for pollen analysis Radiocarbon dating of organic material shows semi-arid/ arid climate

Pollen sequence from Padul (Near Granada, southern Spain)

• Last Glacial Maximum characterised by treeless landscape
• Grass pollen makes up ca 50% of pollen
• Artemisia shrubs make up 20 to 30% of pollen
• Artemisia genus of shrubs that are adapted to semi-arid/arid climates

Pollen records from across Med record consistent glacial veg - Artemisia steppe veg form Spain to Turkey -> lake basins also record high water levels at the time

Disagreement - (see Prentice et al, 1992)

Vegetation and lake levels both driven by rainfall but reflect different aspects of hydrological system:

• In Med lake levels and river activity reflect amount of available surface runoff
•  Vegetation reflects amount of available moisture throughout the year

Proposed Model of Glacial Climate 

Precipitation became much more seasonal:

• Higher rainfall in winter
• Longer period of spring summer drought
• Runoff during winter was intense = lake levels became greater
• Lower temperatures meant lower levels of evapotranspiration = high water levelspersisted for longer

Longer period of summer drought:

• Ecosystems adapted to lower moisture availability
•  Species must be capable of surviving long periods of drought
•  Woodland replaced by Artemisia dominated steppe - only for a small part of the LGM
•  Reduced vegetation density (lower biomass) causes increased runoff, feeding lake systems

Problems with reconstructing pollen records as many don't extend far back enough and increased errors seen in older dates

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