Mid-Pleistocene (800-400 ka) records of benthic and planktic foraminfer d18O and d13C, planktic foraminifer based SST, and IRD of IODP Site 306-U1314

Stable carbon and oxygen isotopes from benthic and planktic foraminifers, planktic foraminifer assemblages and ice rafted debris from the North Atlantic Site U1314 (Integrated Ocean Drilling Program Expedition 306) were examined to investigate orbital and millennial-scale climate variability in the North Atlantic and its impact on global circulation focusing on the development of glacial periods during the mid-Pleistocene (ca 800-400 ka). Glacial initiations were characterized by a rapid cooling (6-10 °C in less than 7 kyr) in the mean annual sea surface temperature (SST), increasing benthic d18O values and high benthic d13C values. The continuous increase in benthic d18O suggests a continuous ice sheet growth whereas the positive benthic d13C values indicate that the flow of the Iceland Scotland Overflow water (ISOW) was vigorous. Strong deep water formation in the Norwegian Greenland Sea promoted a high transfer of freshwater from the ocean to the continents. However, low SSTs at Site U1314 suggest a subpolar gyre cooling and freshening that may have reduced deep water formation in the Labrador Sea during glacial initiations. Once the 3.5 per mil threshold in the benthic d18O record was exceeded, ice rafting started and ice sheet growth was punctuated by millennial-scale waning events which returned to the ocean part of the freshwater accumulated on the continents. Ice-rafting events were associated with a rapid reduction in the ISOW (benthic d13C values dropped 0.5-1 per mil) and followed by millennial-scale warmings. The first two millennial-scale warm intervals of each glacial period reached interglacial temperatures and were particularly abrupt (6-10 °C in ~3 kyr). Subsequent millennial-scale warm events were cooler probably because the AMOC was rather reduced as suggested by the low benthic d13C values. These two abrupt warming events that occurred at early glacial periods were also observed in the Antarctic temperature and CO2 records, suggesting a close correlation between both Hemispheres. The comparison of the sea surface proxies with the benthic d18O record (as the Southern sign) indicates the presence of a millennial-scale seesaw pattern similar to that seen during the Last Glacial period.

(Table 1) Benthic foraminifera at DSDP Site 72-516

DSDP Site 516 contains a complete middle Eocene to lower Miocene interval with a well-developed Oligocene sequence that is more than 300 m thick. In this paper, the most important and characteristic benthic foraminiferal species from this interval are described and illustrated, and their quantitative and biostratigraphic distribution is given. Middle Eocene benthic assemblages, derived from pelagic intercalations in a partly turbiditic sequence, are low in diversity. Benthic assemblages of fairly high diversity occur in limestones, chalks, and oozes of the upper Eocene to lower Miocene. The consistently high rate of new species appearances at Site 516 during late Eocene and Oligocene contrasted greatly with the very slow rate of change in abyssal faunas at that time; there were no significant faunal changes at the Eocene/Oligocene boundary. The assemblages are dominated by Cibicidoides (mostly C. ungerianus or C. kullenbergi) and Lenticulina. Buliminids were also important during the Eocene and early Oligocene. Faunal comparison with other Atlantic DSDP sites and drill holes in the Gulf of Mexico suggest an approximately mid-bathyal (500-1500 m) depth of deposition during late Eocene and Oligocene.

Distribution of benthic abyssal gastropods in the Iberian Deep-Sea Basin (Table 2)

During the cruises 3 and 15 of R.V. "Meteor", representatives of 7 families of benthic abyssal gastropods were collected. The prevalent group was the Turridae; the Naticidae are represented by 2 species, the remaining families by a single species each. A survey of the frequency and distribution of the species within the study area is given. A systematic part deals with the individual species in detail, including notes on taxonomy, material and distribution. Concerning the composition of the abyssal gastropod fauna of the present material, Neogastropoda are 4 times as many as Archaeogastropoda and 6 times as many as Mesogastropoda and Opisthobranchia. 89 % of all specimens are Neogastropoda. Usually deep-sea organisms have a non-pelagic development, but many of the Iberian deep-sea Turrids have a planktotrophic protoconch, that means a long pelagic larval period. Among the 19 species, 2 are cosmopolitan, 9 show a transatlantic distribution and 8 are confined to East-Atlantic basins.