Oxygen-18 of O 2 Records the Impact of Abrupt Climate Change on the Terrestrial Biosphere

Planted Evidence To understand the spatial patterns and consequences of past climate change requires the identification of reliable proxies that reflect specific aspects of those changes, such as temperature or rainfall in a given location. Also of interest are proxies for broader categories of change, such as methane production or the sources of carbon dioxide. Severinghaus et al. (p. 1431 ) present a 100,000-year-long record of the oxygen isotopic composition of atmospheric O 2 (δ 18 O atm ) extracted from air from polar ice cores. δ 18 O atm is a general measure of the strength of low-latitude terrestrial photosynthesis and thus of local rainfall because plant metabolism is controlled in large part by water availability. δ 18 O atm changes were related to Heinrich and Dansgaard-Oeschger events, two modes of abrupt climate change common over that interval, and δ 18 O atm was controlled mostly by the strength of the Asian and North African monsoons. The rapid changes observed should also help to synchronize ice core records.