Sediments

What are sediments? Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice, and/or by the force of gravity acting on the particles. Sediment can consist of rocks and minerals, as well as the remains of plants and animals. It can be as small as a grain of sand or as large as a boulder.

A sediment story Sediments cored from the ocean bottom serve as a timeline of events: each year's sediments are stacked on top of the ones from the year before. The deeper the sediment, the older it is. Cores from sediment on the sea floor can provide information about past climate. Unlike ice cores, which supply direct information, sediment cores give indirect evidence. For example, to determine temperature, scientists painstakingly pick out and count plankton shells, which twist in different directions depending on the temperature of the water they grew in.

Antarctica’s Rock Cores

Lake sediments Composition and sedimentation rates change in response to environmental conditions. Pollen in the sediments can indicate the type of vegetation present, and plankton biota indicate physical and chemical conditions in the lake water.

Ocean sediments Ocean sediment cores contain primitive shelled animals (foraminifera) whose abundance in the surface layers of the ocean depends on surface water temperature and other conditions.

Foramniferas Foraminifera, also known as forams, and diatoms are commonly used climate proxies. Forams and diatoms are shelled organisms found in aquatic and marine environments. There are both planktonic, or floating in the water column, and benthic, or bottom dwelling, forms.

It’s all in the shells… Foram shells are made up of calcium carbonate (CaCO3) while diatom shells are composed of silicon dioxide (SiO2). The chemical make up of these shells reflect water chemistry at the time of shell formation.

It’s also a numbers game… Relative abundance as well as species composition in particular areas may indicate environmental conditions. Typically, warmer weather will cause organisms to proliferate. In addition, since each species has a particular set of ideal growing conditions, species composition at a particular site at a particular time may indicate past environmental conditions. Forams

So…what can sediments tell us about past climates?