Climate's astronomical sensors

摘要

Earth's climate 'feels' the slow changes in the parameters of our orbit around the Sun. The great ice sheets of the Northern Hemisphere are one sensor, in that they are sensitive to the amount of solar energy they receive in summer. Lisiecki et al. (page 85 of this issue) provide evidence that ocean dynamics also responds to orbital changes, and not just in the north. Much of our life is controlled by the rhythms of days and seasons - not surprisingly, given that the Sun is our ultimate source of energy. Earth's atmosphere senses the rhythms of days and seasons, too, but both atmosphere and oceans may respond to the much longer astronomical cycles that affect incoming solar radiation. In 1976, Hays et al. described how they tackled this problem. They collected deep-sea sediments in the Southern Ocean, dated them according to depth, and analysed the oxygen-isotope composition of the calcium carbonate remains of foraminifera preserved in the sediments.