Approximately 800,000 years ago something changed in the Earth’s climate system that led to the climate then following a series of approximately 100,000 year cycles. Small, predictable changes in the Earth’s orbit about the Sun act as triggers for the glacial and interglacial periods, but other factors such as ice sheet volume, CO2 concentration, and biological feedback mechanisms are also involved.
Oxygen is fundamental to oceanic biological processes and its decline can cause major changes in ocean productivity and biodiversity. Over the past 50 years low oxygen zones in the open oceans have expanded by an area equivalent to half the size of Canada and hundreds of coastal sites now have low oxygen concentrations that limit the distribution and abundance of animal populations.
Marine cores collected in the western tropical Pacific were used to compare the chronology of Southern Ocean warming near Antarctica and rising CO2 during the last deglaciation. The results provide evidence that the Southern Ocean off Antarctica warmed by ~2°C between 19,000 and 17,000 years before the present, about 1,000 years before the rise in atmospheric CO2.
Air bubbles in Greenland ice cores are analyzed to compare changes in Greenland surface temperature and atmospheric methane concentration during a rapid warming event lasting 200 years during the last deglaciation. It is found that changes in Greenland surface temperature and atmospheric methane emissions occurred essentially synchronously indicating that this warming event included the tropics.