Diatoms reveal climate changes

Knowledge of how the climate has varied in the past is necessary if we are to understand the causes and mechanisms behind today's climate changes and the impact of human activities on them. Using diatoms in sediment from Swedish mountain lakes, Christina Jonsson, Department of Physical Geography and Quaternary Geology at Stockholm University, has studied changes in atmospheric circulation.

Northern Sweden is sensitive to changes in atmospheric circulation since the region is affected by air masses of differing origin, from the North Atlantic, the Baltic, and the Arctic. Depending on which air mass dominates, the temperature and the amount of precipitation changes. The composition of the various oxygen isotopes 160 and 180 in precipitation is also impacted.

"Changes in precipitation influence in turn the oxygen content of lake water and are picked up by tiny diatoms living in the lakes. Shells from these algae are preserved in the sediment on the bottom of the lake and can be analyzed to reveal changes in circulation and variations in climate since the latest ice age, that is, during the last 10,000 years," says Christina Jonsson.

The dissertation uncovers both long-term changes in circulation and shorter periods of alte red circulation patterns. About 500 years ago a change in climate occur red when the amount of winter precipitation increased.

"This change in circulation probably marks the beginning of the so-called little ice age in this region," says Christina Jonsson.

The dissertation enhances our knowledge of how changes in atmospheric circulation have impacted the climate in Sweden over the last 10,000 years.