The climate of southern Chile during the last 16,000 years

The fluctuations of temperature and rainfall over the last 16,000 years at 43° S in southern Chile have been deduced from the types of pollen at various depths in sediment from the bottom of a lake there (1). The age of each pollen type was determined by radio-carbon dating, and it was assumed that the pollens existed in temperature & precipitation regimes like those where they are now found in Chile. In particular, January mean temperatures were shown to have risen from about 11° C at about 16,000 BP (i.e. 16 kBP) at the end of the last Ice Age to reach a peak of about 21° C around 11 kBP, a minimum of 9° C at 10 kBP, and a maximum of 20° C at 9 kBP. Thereafter temperatures fell irregularly towards the present 15° C, apart from a maximum of 17° C around the year 1400 AD, and a minimum of 11° C near the turn of this century.

At the same time, annual rainfalls fluctuated from 2 metres in 16 kBP, 5 m at 10.5 kBP, 1.2 m at 8 kBP, 5.1 m at 4.5 kBP, 3 m at 3 kBP, 4.5 m around 1,000 AD, 2.5 m at about 1400 AD, 4 m in 1650 AD or thereabouts, and 2 m nowadays.

These figures show a remarkably large range of conditions, however it should be noted that some pollen types grow in a range of climate regimes, and that in southern Chile the meridional variations of temperature and rainfall are not independent - for instance, it is likely that during a colder period a different temperature/precipitation relation existed than the current one.

In any event, the apparent climate variations match fluctuations of the length of a glacier in the region, which was short in 6.9 kBP (when precipitation was low) and increased three times, at around 4.5 kBP, 2 kBP, and during the 19th century, when conditions were cool and moist. The dates resemble those for glacial advances in New Zealand, Australia and New Guinea.

(1) Heussler, C.J. & S.S. Streeter 1980. A temperature and precipitation record of the past 16,000 years in southern Chile. Science, 210, 1345-7.