The marine sediments as long-term climate archive:
The composition of marine sediments documents the environmental and climatic conditions that prevailed during their deposition. Thus, marine sediments are an excellent long-term archive of Earth´s climate.
In the following we will describe three recent examples of marine sediment investigations that significantly affected our insights into the development of the climate system and its most extreme states, both on a global scale and with emphasize on ocean regions most sensitive to climatic changes.
During recurring phases in Earth´s history, large lower parts of the oceans were oxygen-free (anoxic) over hundreds of thousands of years – these phases are referred to as Oceanic Anoxic Events (OAEs).
They represent environmental archives of times when Earth´s climate system was working profoundly different than today. A specific time interval affected by many OAEs was the Cretaceous period, around 135 to 85 million years before present, when wide-spread deposition of so-called »black shales« occurred. A specific region of high climatic relevance, the Arctic Ocean, was a »white spot« on the geological map of the Earth only a few years ago.
Its climate archives extended only several hundred thousand years into the past. Thus, the reconstruction of its environmental and climatic development over the past 60 Million years from sediment cores that were only recovered in 2004 is all the more exciting. But traces of extreme climate variations are also found in sediments deposited during the last ice age, i.e. the last hundred thousand years.
Understanding the global extent and impact of these so-called Dansgaard-Oeschger and Heinrich events, and unravelling their causal mechanism, is not only crucial to better understand the mode of operation of the climate system, but also its relation to modern climate changes.