A geological sampling program to investigate the nature of the sea bed sediments around Heard Island and McDonald Islands (HIMI) was conducted from the RV Aurora Australis during the summer of 2003/04.
Sampling was conducted with a Shipek grab at a number of shallow near shore sites, as well as sites on the surrounding undersea plateau below waters with depths from 200 to 2500 metres.
Given the volcanic nature of Heard Island and the McDonald Islands it was not surprising to find an abundance of volcanic material in the samples closer to the island.
Typically this volcanic material comprised fresh or weathered basalt and some pumice. Pumice is formed as lava ejected from a volcanic vent cools and solidifies, leaving air pockets where the trapped gases escape. Some types of pumice will float on water depending on the amount of air bubbles present in the rock.
Shell material consisting of bivalves, barnacles, gastropods, corals and worm tubes was found in shallow samples from the plateau. Both live and skeletal foraminifera were recovered. These are tiny, single-celled organisms known as protists, with shells that are commonly divided into chambers.
Exotic rocks that you would not expect to find in a volcanic region were also found in some of the samples. These rocks were probably carried to Heard Island within icebergs, a process known as ‘ice rafting’, and were deposited to the sediment as the ice melted.