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Geochemical and biological research offers academics a window into earth history, enabling them to piece together events that occurred before records began. Much of our understanding of past climate change is based on geology, in particular the study of sedimentary rocks deposited in the oceans.

April Neander

The paper that first recognised and defined Oceanic Anoxic Events (OAEs), written by Oxford professor Hugh Jenkyns and an American colleague, is considered a seminal contribution to geological history, that led the way to numerous studies on the effects of oxygen starvation in the oceans.

The discovery of organic-rich sediments, often described as black shales, at numerous deep-sea drilling sites during the early 1970s, led to the wider acknowledgement of the oceanic impact of climate change. At certain intervals during the Jurassic era, huge bouts of volcanic activity triggered increased concentrations of atmospheric carbon dioxide. This then caused a knock-on greenhouse effect, raising the sea-surface temperature and reducing oxygen levels in large parts of the ocean.

At the same, oceans benefited from increased nutrient levels, and as a result marine algae and bacteria bloomed. As they died, these organisms were preserved in sediments that formed on the sea floor and over time changed into source rocks for oil. It is these phenomena that illustrate the causes and effects of OAEs.

New research, published in Nature Geoscience, has for the first time examined the impact of this type of sediment deposition in lakes. The study demonstrates that lake environments responded in a similar way to climate change, developing the same anoxic conditions as in the oceans.

Led by Earth Sciences post-graduate student Weimu Xu, the work offers insight into how environmental factors have affected lake formation throughout the ages. Weimu and the  team studied sediments from one of the largest lakes in Earth history - double the size of England and three times the size of Lake Superior - the largest lake (in surface area) in the world today. This ancient lake formed rapidly in the Sichuan Basin, China, as a result of Toarcian (Early Jurassic) climate change, about 183 million years ago.

Weimu spoke with the University of Oxford's Science Blog about the study’s key findings and what they can tell us about climate change today.

Click here to see the full interview on the Science Blog.