What does sediment cores learn us about the climate ?

[Ulysse Mariette]

What does sediment cores learn us about the climate ?

Sediments are deposits left by the wind and the water. We can find them in lakes for example where rivers flow ends. Sediments are transported in suspension in the water, but when the river ends in a lake or the ocean the sediments sinks to the bottom of the lake where they stay.  With time, they are covered up with more recent sediments in fluctuation of the apports of rivers and winds. 

These sediments are used by scientists to study the evolution of the climate. The process to pick up the sediments is the following. Some steel tubes are put in the water and dipped to the sediments. The tubes gets into the many sedimentary layers. The more deep the tubes gets the older is the sedimentary layer. When tubes get pulled to the surface. They are cutted in several pieces, which correspond to a certain period of time and finally the tubes get cutted in the lenght and the two parts get analyzed. 

The sediments in lakes are different frome those in the ocean. In a lake, sediments contains dirt, sands and pollens which are highly useful to determine what was the climate on a specific period of time. After the identification of the pollen, scientists can reconstitute the ecosystem of a location and determinate the conditions of the climate at the time the pollen gets into the sedimentary layer. For example pollen of toundra is a sign of a cold climate. In the opposite, when oak pollen is found in the sediment, it’s a sign of warm climate. The lake of the Bourget in France is a good example. Scientist found some Toundra pollen in the sediments of this lake and dated it from 20 000 which correspond to the last little ice age Europe knew. 

Ocean sediments contains dead planton and other marine organisms. The varieties and the concentration of certain of these organims permit to know what was the conditions in the ocean, like temperature of the water. The sediment layers in the ocean started accumulated 55 million years ago. Since then, there was major modifications of the conditions in the ocean. There is pred-dominants colours in ocean sediments. Light-colored sediments and dark colored sediments. The difference between them is the quantity of shells inside. 

In a sediment core, when there is a boundary between dark and light sediments, it means that the quantity of shelled organism varied. The variation in shelled organism concentration illustrate the modification of the conditions of life in the ocean. Scientists put in evidence that a loss in shelled organism concentration result of a high concentration onf the CO² in the ocean. This CO² concentration can result of the melt of ice that contains methane. The methane reacted with oxygen forming CO². This CO² is absorbed by the ocean, increasing te acidification of water. More recently the anthropic rejects in CO² are increasing ocean acidification, that result in the modification of the species in the ocean. 

A great video to understand quickly the ocean acidification process and how it’s going to affect our lives : https://www.youtube.com/watch?v=6SMWGV-DBnk

Here is a link where you can read more about the extraction of sediments cores : https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sediment-core

[Throstur Thorsteinsson]

Dear Ulysse.

Good discussion about sediment cores.

Perhaps a figure or two would have helped, to break up the text a little also.

Perhaps also a reference to lake and ocean core papers.

You get 8.5 to 9.

Sincerely, Throstur.

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Throstur Thorsteinsson 
Professor

Environment and Natural Resources & Institute of Earth Sciences

Háskóli Íslands / University of Iceland
Askja, Sturlugata 7, 101 Reykjavik, Iceland
Beinn sími / Direct tel. +354 525 4940
Mobile +354 846 5429
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