A lacustrine carbonate record of Holocene seasonality and climate
Chad A. Wittkop et al., Dept. of Chemistry and Geology, Minnesota State University, Mankato, Minnesota 56001, USA. Pages 695-698.
Sediments from a small lake in Michigan contain millimeter-sized layers of organic matter and the mineral calcite, deposited in pairs each year for the past 9000 years. The amount of the mineral calcite in these layers varies through time, and Wittkop et al. show how these variations are linked to long-term changes in the Northern Hemisphere growing season as controlled by dynamics of Earth's orbit around the sun. Short-term variations in calcite abundance also occur on a scale of decades. While the cause of the short-term variations is more difficult to determine, comparison with other climate records from the same region and time period suggest changes in precipitation and temperature may be the cause. These short-term cycles share similarities with other records documenting the pattern of El Nio events over the past 5000 years, which suggest that such events have become more frequent and intense in this time.
Middle Miocene oxygen minimum zone expansion offshore West Africa: Evidence for global cooling precursor events
S. Kender et al., British Geological Survey, Keyworth, Nottingham NG12 5GG, UK. Pages 699-702.
The Middle Miocene Climatic Optimum (16 to 14 million years ago), considered genera
|Contact: Christa Stratton|
Geological Society of America