By Jess

My research is in paleoclimate, which involves looking for clues in the world around us and putting these clues together to investigate past climatic changes and build a picture of the way Earth used to be. It’s a bit like being a detective (well at least it is in my maybe slightly overactive imagination).

Slightly less glamorous is that all of the clues I am looking at for my research are found in mud that has been buried under the Mediterranean Sea for thousands if not millions of years.

Some sediment cores – who would have thought mud could be so colourful
Some sediment cores – who would have thought mud could be so colourful

So marine sediment cores might not look incredibly exciting at first glance, but it’s amazing how much information can be discovered in what would usually be dismissed as muck.

Sediment cores contain thousands of little microscopic shells. Tiny organisms called foraminifera which live in the water column, form these calcite shells as they grow, and when they die the shells sink to the sea floor and become preserved in sediments. As it is formed, the shell composition records information about the seawater around it, and if the sediment is dug up, this information can be retrieved.

Foraminifera shells, very close up. These are actually only about a quarter of a millimeter in size.
Foraminifera shells, very close up. In real life these are about the same size as a grain of sand.

For example, I measure stable oxygen isotope ratios of foraminifera shells, which are strongly influenced by global ice volumes. So from these tiny little shells, it is possible for me to reconstruct sea level changes going back millions of years in time.

Even leaf wax molecules from vegetation washed into the sea can become preserved in sediments. In January I visited the University of Manchester in the UK and learnt how to extract these from sediment samples. By measuring different isotopes from the leaf wax remains it is possible to track past changes in rainfall and vegetation type for the region.

These methods take a bit more effort, but you can learn things even by looking at the colour of the sediment cores. In the Mediterranean cores I work on, there are frequent intervals of black mud. These are ‘sapropels’ and form under anoxic conditions, when the deep sea is depleted of oxygen. This allows organic matter to be preserved, giving the sediments their distinct colour. These anoxic events occurred regularly in the Mediterranean’s history, when Earth’s orbit is such that there are warmer northern hemisphere summers (a minima in the precession cycle). We know how Earth’s orbits changed in history and therefore these sapropels can be used to accurately date the cores.

These are only a few of the things you can study in sediment cores to investigate past climatic and oceanic conditions, but there are lots, lots more. It is also possible to obtain records of temperature, ocean pH and levels of biological productivity, to name just a few.

So next time you’re swimming in the sea take a second to think of all the processes going on around you which are preserving clues about our world as it is today, all in the mud on the seafloor!