Friday, 20 July 2012

Day 16 - The tiny, tiny details

Foraminifera - they may be tiny, but if you look carefully…

H. elegans
Forams are single-celled organisms, which can be found living in deep-sea sediments. Benthic forams, which live in the seabed, are among the most common organisms living in today’s oceanic environments. Forams come in many different shapes and sizes and their structure can be quite elaborate. They have a test (shell), which is made either of calcium carbonate that they secrete, or from agglutinated sediment: bits of fine sand and sediment particles that the forams find on the sea floor.

Foraminifera are being collected on this cruise using the megacorer. This device takes sediment core samples from the ocean floor. The megacorer is lowered off the side of the ship to the sea floor to depths of around 4800m where the cylinders are pushed into the seabed.

Epistominella exigua
The megacorer is used to collect both macrofauna (organisms retained on a 300 μm mesh) and meiofauna (organisms that pass through meshes of 500 μm but are retained on a 40-69 μm mesh). The foraminifera fall into the group meiofauna because of their size. Macrofauna samples are collected in 100mm diameter cylinders, whereas meiofauna, (because they are smaller) are collected in 70mm diameter cylinders. Once back at the surface, the cores are taken off the megacorer and into the laboratory on the ship where they are sliced horizontally into twelve depth layers. Hundreds of forams can be found just in the top one cm layer of a megacore slice.

Bulimina aculeata

The samples collected during the cruise will be taken back to Southampton and used to understand the vertical distribution of forams throughout the sediment layers. Also, the relationship of foram distribution to the topography of the sea floor at the Porcupine Abyssal Plain will be investigated.

Trumpet Lagenammina

Laetitia Gunton PhD student at National Oceanography Centre Southampton and Natural History Museum, London

Images: A variety of deep-sea benthic foraminifera