A new study by an international group of researchers, including those at the University of Sheffield, has identified icebergs as being the ‘missing link’ that lead to an ice age.
Glaciations, which are extended periods of cold temperatures, are caused by a shift in the Earth’s orbit around the sun. These changes cause fluctuations in the amount of solar radiation reaching the Earth’s surface. However, how this leads to an ice age has been a mystery. This new study, led by scientists at Cardiff University, suggests that the change in orbit causes icebergs in the Antarctic to move further away from the South Pole and melt. The freshwater shifts away from the Southern Ocean to the Atlantic Ocean, causing the Southern Ocean to get saltier. This change in salinity disrupts large-scale ocean circulation patterns, resulting in more carbon dioxide being pulled from the atmosphere which reduces the greenhouse effect and plunges the earth into a time of lower temperatures: an ice age
The international group of scientists, including those from the University of Sheffield, reconstructed previous climatic conditions. One technique used small fragments of rock called Ice-Rafted Debris from melting icebergs which are reconstructed from the tiny deep-sea fossils, foraminifera. Representing 1.6 million years of geological history, these deposits collected by the International Ocean Discovery Program (IODP) Expedition 361 coincide with changes to deep ocean circulation which led to glaciation periods. Climate model simulations were also constructed which found icebergs had the capacity to move large volumes of freshwater.
Professor Grant Bigg, from the Department of Geography at the University of Sheffield, said: “The ground-breaking modelling of icebergs within the climate model is crucial for identifying and supporting the ice-rafted debris hypothesis of Antarctic iceberg meltwater impacts which are leading glacial cycle onsets.”
We are currently in a warm interglacial period however, the future of ice age cycles is uncertain, as temperatures rise due to anthropogenic carbon dioxide emissions. The warming of the Southern Ocean could prevent icebergs from travelling far enough north to disrupt the ocean circulation which starts the next glaciation period.
Co-author of the study and co-chief of the IODP expedition, Professor Ian Hall said, “Likewise as we observe an increase in the mass loss from the Antarctic continent and iceberg activity in the Southern Ocean, resulting from warming associated with current human greenhouse-gas emissions, our study emphasises the importance of understanding iceberg trajectories and melt patterns in developing the most robust predictions of their future impact on ocean circulation and climate.”
