Seafloor sampling...
Helping us to answer the big questions in the new millenium

Some of the biggest problems facing us in the new millennium will be caused by our 21st century lifestyle effecting the environment in which we live. We need to understand the causes of global warming and extreme weather conditions. Are these natural changes in the weather and climate? Or are they triggered and amplified as a result of the way we live today?

We know that the climate has changed in the past and we can see this if we look back through the geological record. What we see is that climate variation takes place over many different time scales of long and short duration.

Why collect cores?

To understand our influence on the climate now and in the future we must understand how the earth's climate has changed naturally in the past without the effects of modern mankind's lifestyle.

How do we do this?

One way is to study the sediments that have accumulated on the seafloor.

The oceans are very important in the way they influence, and are influenced by the climate. Changes in the climate are linked to changes in the oceans and this effects the sediments that slowly accumulate on the seafloor. If we collect samples (cores) down into the seafloor and examine the sediment layers, we can look back in time at previous changes in climatic conditions.

They can show us:

• How the sea temperature has changed
• How the climate has changed
• The effects of pollution on animals that feed on the seafloor
• Changes in ocean circulation
• Where there are stable areas of seafloor that can provide low environmental impact sites for communications cables and oil rigs

What is a core?

A core is a vertical cylinder or block of sediment, retrieved by forcing a metal tube, or a metal box, into the sediment, closing a lid at the bottom to trap the sediment inside, and then pulling it out again. This 'slice' will contain a section down through layers of sediment which have accumulated over time at that spot.

Right:
The gravity core is the most basic sampling device used to collect core samples from the seafloor, it penetrates less than 10 metres into the sediment

Sediment core collection

Collecting seafloor samples is an expensive process involving the use of complex sampling devices on research ships in remote ocean areas. It is very important that we extract the maximum amount of use from these samples. In 1997 the Natural Environment Research council decided to encourage the efficient use of these seafloor samples by setting up the British Ocean Sediment Core Repository Facility (BOSCORF) at National Oceanography Centre, Southampton.

Cores collected at sea are split into two halves and kept in individual sealed plastic boxes. When the cores are returned to Southampton Oceanography Centre they are stored inside a 4°C temperature controlled core repository, for use by others. As new measurement techniques become available and new concepts evolve, cores can be resampled to add to the knowledge base.

Collecting longer cores that have penetrated deeper into the seafloor sediment will provide us with sediments showing a more detailed record of climate variation from further back in time.

The NOCS Long Piston Corer

As we try to sample deeper and deeper into the mud on the seafloor the sampling devices become larger, more complex and more expensive. The LPC is the largest coring device used at NOCS and can penetrate. over 30 metres in to the seafloor.

The box corer (right)

Designed to take a sample of the sediment surface and bring it back to the ship intact. The box corer penetrates less than 100cm into the mud on the seafloor.

The open box corer (right)

Back on the ship, sub-sampling tubes have been pushed down into the sediment

Climate change

This picture (right) shows an equal area projection of the globe showing ice cover during the last ice age. The dark blue areas are land ice, the pale pink areas are sea ice, the yellow areas are land, and the blue areas are open sea. The British Isles are shown inside the red box.
As we can see, the UK and Ireland are at the same latitude as Siberia - between 50 and 60 degress north of the equator. Today, Siberia experiences temperatures as low as -40 degress Centigrade in winter, and the sea ports ice up, while Britain only experiences a few days of ice and snow each winter, with temperatures rarely getting below zero. This is because Britain benefits from the North Atlantic Drift, a warm current that gives up its heat to the atmosphere as it moves north to the Arctic, where it becomes cold enough to sink down and flow south again - part of the 'conveyor belt' of currents that help distribute heat around the globe.
Scientists looking at cores from the north Atlantic, such as those stored at our repository, are able to tell us about times when the 'conveyor belt' switched off and how that might have affected our climate.

When seafloor sediment moves

Sometimes sediments that accumulate on seafloor of the continental shelf and slope, reach a thickness where they become unstable. When this happens an earthquake can trigger the sediment into an giant mud slide that flows down the continental slope into deeper water. These mud slides and flows can be massive, involving hundreds of cubic kilometres of sediment. One large sediment flow studied in the North Atlantic covered an area larger than Wales.

Tsunami are giant waves generated by these underwater landslides, earthquakes or volcanoes. They travel very quickly over deep water, up to 600 km/hour, but may be only a metre or so high. Once they reach shallow water, however, they slow down and increase in height, up to as much as 30m or more. The city of Lisbon in Portugal was hit by an earthquake in 1755. The earthquake happened out at sea, and generated a tsunami which swept across the city, causing further damage and many deaths. Tsunami deposits have been found in Britain, resulting from a tsunami generated by the Storegga Slides, when a huge area off the coast of Norway collapsed several thousand years ago.