Benthic foraminiferal population dynamics at the Goban Spur off Southwest Ireland reveal glacial-interglacial bottom water ventilation and organic flux variability over the last 420,000 years

Abstract

Benthic foraminiferal assemblages from Deep Sea Drilling Project (DSDP) Site 548 on the Goban Spur off southwestern Ireland shed light on the changes in bottom water oxygenation and organic matter flux to the sea floor during the late Quaternary. Correlations of benthic foraminiferal δ¹⁸O values, the relative abundance of Neogloboquadrina pachyderma (%NP), and Ice Rafted Debris (IRD) concentration to global and regional and North Atlantic datasets suggest the upper 60 m of DSDP Site 548 extend to 420,000 years. Downcore variations of >63 μm benthic foraminifera assemblages, abundance, and diversity reveal changes in dissolved oxygen concentration and organic fluxes to the seafloor related to glacial-interglacial cyclicity. Cassidulina laevigata and low dissolved oxygen indicator taxa such as Bolivina spp. and Globobulimina spp. characterised colder climates associated with lighter benthic δ¹³C values, suggesting minimal organic flux and/or weaker bottom water ventilation. In contrast, warmer interglacials are typified by heavier benthic δ¹³C, increased %CaCO₃, common high dissolved oxygen indicator taxa such as Globocassidulina subglobosa and phytodetritus sensitive taxa such as Alabaminella weddellensis and Epistominella exigua, suggest a more ventilated bottom water and increased organic fluxes to the seafloor, possibly associated with the invigoration of the Mediterranean Outflow Water (MOW).