Decadal-scale changes in shallow-infaunal foraminiferal assemblages at the Porcupine Abyssal Plain, NE Atlantic

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Gooday, Andrew, Malzone, M G, Bett, Brian, Lamont, Peter
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2010
• Subjects: SEASONAL DEPOSITION; INTERANNUAL VARIABILITY; TAXONOMIC COMPOSITION; SURFACE OCEAN PRODUCTIVITY; LONG-TERM CHANGE; ORGANIC-MATTER; DEEP-SEA; Oceanography; SEA BENTHIC FORAMINIFERA; NORTHEAST ATLANTIC; TEMPORAL VARIABILITY; North Atlantic; North Atlantic oscillation; Northeast Atlantic
• Online Access: https://pure.uhi.ac.uk/en/publications/1f3fc8cd-c812-43ac-9b63-3c6f25f80f4a; https://doi.org/10.1016/j.dsr2.2010.01.012

Trends in the abundance, diversity and taxonomic composition of 'live' (rose Bengal stained) foraminiferal assemblages (0-1 cm layer, >63-mu m fraction) were analysed in replicate multiple corer samples collected at the Porcupine Abyssal Plain (48 degrees 50' N, 16 degrees 30' W, 4850 m water depth) over a 13-yr period (1989-2002). Total densities were significantly higher in 1996-2002 compared to 1989-1994, a change coincident with a spectacular rise in the density of the holothurian Amperima. However, total densities exhibited no significant relation to seasons or any significant correlation with modelled organic matter flux, the North Atlantic Oscillation (NAO) index, Amperima densities, or megafaunal assemblage composition. Over the same period, species richness and diversity measures decreased and dominance increased, although not significantly. Multivariate analyses revealed three assemblages represented by samples collected in 1989-1994, 1996-July 1997 and October 1997-October 2002. These reflected temporal changes in the densities of higher taxa and species. Trochamminaceans, notably a small undescribed species, increased from 5-9% (1989-1994) to 29-40% (1996-2002) of the assemblage with a corresponding rise in absolute abundance. Species of Hormosinacea and Lagenammina also tended to increase in density from 1996/1997 onwards. Rotaliids, dominated by Alabaminella weddellensis and Epistominella exigua, showed a bimodal distribution over time with peak densities in May 1991 (32%) and September 1998 (28%) and lowest densities in 1996-1997. Responses by these species to seasonal phytodetritus inputs probably explain the relative abundance of E. exigua, and to a lesser extent A. weddellensis, in 1989 and 1991 when phytodetritus was present. A qualitative change in the phytodetrital food, repackaging of food by megafauna, increased megafaunal disturbance of the surficial sediment, or a combination of these factors, are possible explanations for the dominance of trochamminaceans from 1996 onwards. The ...