Carbon isotopes in lake sediments and peats of last glacial age: implications for the global carbon cycle

Vegetation reconstructions based on pollen and plant macrofossils show that there was a global reduction in forest at the last glacial maximum compared with preindustrial times. Open vegetation types including tundra, steppe and grassland expanded. The loss of land through encroachment by ice was roughly compensated by the exposure of the continental shelves due to lower sea level. Significant controversy surrounds vegetation changes in specific areas, notably in the tropics, where the implications for estimates of carbon storage are particularly great. Many rainforest plants and animals have highly disjunct distributions, which were attributed by biogeographers to the restriction of tropical rainforest to isolated enclaves, or ‘refugia’, during glacial times. The combination of generally harsher climate and lower atmospheric CO2 resulted in net decreases in primary production and in carbon storage in terrestrial vegetation and soils. Since the total atmospheric CO2 content was also lower, the carbon lost from the continents must have been transferred to the oceans.