The impact of the 1991 Mt. Pinatubo eruption on deep-sea foraminiferal communities: A model for the Cretaceous-Tertiary (K/T) boundary?

The ash layer from the 1991 Mt. Pinatubo eruption provided a natural laboratory to assess mass mortality and the rates of recovery of deep marine ecosystems after a catastrophic event and to draw a parallel with the environmental impact of the K/T boundary event on deep-sea foraminiferal communities. The first recolonization assemblages of benthic foraminifers after the Mt. Pinatubo ash fall exhibit surprising similarities with benthic foraminiferal communities established following the K/T boundary event, i.e., comparatively low abundance and diversity, absence of suspension feeders, dominance of mobile infaunal taxa and a high proportion of agglutinated foraminifers. The first foraminifers to recolonize the deep sea after both catastrophic events were opportunistic forms with high capability for rapid dispersal. However, major differences are evident in the timing and duration of the faunal transitions. Post-eruption assemblages with high proportions of epibenthic suspension feeders became established after a short initial recolonization phase of approx. 6-7 years on the Mt. Pinatubo ash layer. In the K/T sections, comparatively stable new benthic foraminiferal assemblages, including suspension feeders, only became established several thousand years after the event. Delayed recovery of the pelagic ecosystem and poor deep-water ventilation probably slowed down the recovery of the benthic community structure after the K/T boundary.