Re-colonization of hostile environments by benthic foraminifera: an example from Montserrat, Lesser Antilles Volcanic Arc

Abstract

The Soufrière Hills Volcano, on the island of Montserrat, has an eruption history spanning over 2 million years. During this time the volcano has undergone multiple eruptions with intervening periods of low activity or dormancy. The most recent activity began in 1995 and has seen a series of major eruptive events. One of the most recent of these, and the focus of this study, occurred on the 20th May 2006. This major dome collapse produced 90 million m3 of volcanic material in only 3 hours, propelling ash clouds through the air and pyroclastic flows down the side of the volcano and into the sea. In this study of benthic foraminifera, cores from four sites off-shore Montserrat are analysed, including those collected from a location within the path of the 2006 ash cloud, around 10 km west of the Montserrat coast. In this area, one core contained 6-7 cm of ash overlying hemipelagic sediments. Volcanic ash is present in two distinct layers, one 3 cm layer produced by the 2006 eruption and the other, 3-4 cm layer, from an earlier eruption in 2003. Other cores were collected from areas unaffected by recent ash fall deposits and provide a base line for comparisons within the affected areas. To the east and south-east of Montserrat there is a different situation as this is the direction of travel of massive pyroclastic flows down the Tar Valley and the impact on the sea floor is more dramatic. There are also two extinct volcanic centres that allow the investigation of sea floor re-colonization on different time scales. The sites to the west of Montserrat record rapid colonization by benthic foraminifera of opportunistic taxa, comparable to that seen near Mt Pinatubo in the South China Sea while the sites to the east record a slower pattern of re-colonization by a wider spectrum of taxa, similar to that recorded at Deception Island in the Southern Ocean, with different benthic taxa performing the pioneering role.