Ancient Temperature Record Found in Deep Ocean Sediment

Researchers have developed a new method that lets them draw on natural temperature records. In the past there have been difficulties in interpreting what the Earths ancient climate was like. Scientists have relied on measuring the Earths temperature and amount of water held in glaciers and ice caps. The new technique gives a much more detailed view of fluctuations during warm and cold periods in the climate. The Mid-Pleistocene is an important turning point in climate history. Between 1.25 million and 60,000 years ago the planets ice age cycle changed from 40,000 to 100,000 year cycles. This was due to recurrent changes in the planets orbit around the Sun. The changes were small changes, but little was known about what happened during this transition. The new technique works by analyzing variations in the ratio of magnesium to calcium contained in the fossilized shells of tiny microorganisms called foraminifera trapped in successive layers of sediment on the seabed. As the foraminifera were growing, they absorbed calcium and magnesium in proportions that depended on the temperature of the water around them. Previous methods instead used the ratio between two forms of oxygen, known as isotopes - one slightly heavier than the other. Oxygen isotope analysis was originally conceived as a proxy for past temperatures. But later scientists pointed out that the ratio was more heavily influenced by how much ice there was at the time the foraminifera were alive than by the temperature per se - more of the lighter isotope tends to get locked up in ice as it formed, so the water left in the oceans has more of the heavier one, and foraminifera shells preserve this difference. So in recent years scientists have seen oxygen isotopes as an indicator of the total volume of ice on Earth, ignoring the temperature component. Scientists discovered the prevailing view was wrong and that temperature does effect the results of oxygen isotope analysis. The international project was carried out over several years and recovered sediment samples from deep-water locations from all around the world.