Sedimentological and benthic foraminiferal data pertaining to ODP Holes 208-1262A and 208-1263C

Eocene Thermal Maximum 2 (ETM2) occurred ~1.8 Myr after the Paleocene Eocene Thermal Maximum (PETM) and, like the PETM, was characterized by a negative carbon isotope excursion coupled with warming. We combined benthic foraminiferal and sedimentological records for Southeast Atlantic Sites 1263 (1500 m paleodepth) and 1262 (3600 m paleodepth) to show that benthic foraminiferal diversity and accumulation rates declined more precipitously and severely at the shallower site during peak ETM2. The sites are in close proximity, so differences in surface productivity cannot have caused this differential effect. Instead, on the basis of an analysis of climate modelling experiments, we infer that changes in ocean circulation pattern across ETM2 may have resulted in more pronounced warming at intermediate depths (Site 1263). The effects of more pronounced warming include increased metabolic rates, leading to a decrease in effective food supply and increased deoxygenation, thus potentially explaining the more severe benthic impacts at Site 1263. In response to more severe benthic disturbance, bioturbation may have decreased at Site 1263 as compared to Site 1262, hence differentially affecting the bulk carbonate record. We use a sediment-enabled Earth system model to test whether a reduction in bioturbation and/or the likely reduced carbonate saturation of more poorly ventilated waters can explain the more extreme excursion in bulk d13C and sharper transition in wt% CaCO3 at Site 1263. We find that both enhanced acidification and reduced bioturbation during peak ELMO conditions are needed to account for the observed features. Our combined ecological and modelling analysis illustrates the potential role of ocean circulation changes in amplifying local environmental changes and driving temporary, but drastic, loss of benthic biodiversity and abundance.

Abundances and ebridian skeleton contents from IODP Exp302

Abundant and diversified ebridians recovered during IODP Expedition 302 (ACEX) have been identified and counted in order to establish their taxonomy and to decipher the biostratigraphic potential of ebridians in the central Arctic Ocean. In the ACEX samples these fossils are preserved in Lithologic Units 1/6 and 2, which consist mainly of dark silty clay and biosiliceous ooze, respectively. Thirty taxa have been distinguished, three of which are described as new species (Ammmodochium lomonosovense, Pseudammodochium karyon, and pseudammodochium psichion). The most dominant ebridian species is Pseudammodochium dictyoides throughout the biosiliceous section. The second dominant species varies alternately throughout the section. Based on the characteristic occurrences of major ebridian taxa, the ebridian assemblageswere divided into GroupsAtoDin stratigraphic order. The ebridian assemblages in piston core USGS Fl-422 from the Alpha Ridge probably correlate to our assemblage Group A of early middle Eocene age, although rare younger taxa are irregularly included.

Planktic foraminifera across the Cretaceous-Tertiary transition in the Antarctic Ocean

Three Antarctic Ocean K/T boundary sequences from ODP Site 738C on the Kerguelen Plateau, ODP Site, 752B on Broken Ridge and ODP Site 690C on Maud Rise, Weddell Sea, have been analyzed for stratigraphic completeness and faunal turnover based on quantitative planktic foraminiferal studies. Results show that Site 738C, which has a laminated clay layer spanning the K/T boundary, is biostratigraphically complete with the earliest Tertiary Zones P0 and P1a present, but with short intrazonal hiatuses. Site 752B may be biostratigraphically complete and Site 690C has a hiatus at the K/T boundary with Zones P0 and P1a missing. Latest Cretaceous to earliest Tertiary planktic foraminiferal faunas from the Antarctic Ocean are cosmopolitan and similar to coeval faunas dominating in low, middle and northern high latitudes, although a few endemic species are present. This allows application of the current low and middle latitude zonation to Antarctic K/T boundary sequences. The most abundant endemic species is Chiloguembelina waiparaensis, which was believed to have evolved in the early Tertiary, but which apparently evolved as early as Chron 30N at Site 738C. Since this species is only rare in sediments of Site 690C in the Weddell Sea, this suggests that a watermass oceanographic barner may have existed between the Indian and Atlantic Antarctic Oceans. The cosmopolitan nature of the dominant fauna began during the last 200,000 to 300,000 years of the Cretaceous and continued at least 300,000 years into the Tertiary. This indicates a long-term environmental crisis that led to gradual elimination of specialized forms and takeover by generalists tolerant of wide ranging temperature, oxygen, salinity and nutrient conditions. A few thousand years before the K/T boundary these generalists gradually declined in abundance and species became generally dwarfed due to increased environmental stress. There is no evidence of a sudden mass killing of the Cretaceous fauna associated with a bolide impact at the K/T boundary. Instead, the already declining Cretaceous taxa gradually disappear in the early Danian and the opportunistic survivor taxa (Ch. waiparaensis and Guembelitria cretacea) increase in relative abundance coincident with the evolution of the first new Tertiary species.