Search

Integrated Ocean Drilling Program (IODP) Expedition 310 to the reef terraces around Tahiti, French Polynesia, was the second expedition to utilize a mission-specific platform and was conducted by the European Consortium for Ocean Research Drilling (ECORD) Science Operator (ESO). The objectives of Expedition 310 are to establish the course of last deglacial sea level rise at Tahiti, to define sea-surface temperature variations for the region over the period 20,000–10,000 cal. y BP, and to analyze the impact of sea level changes on reef growth and geometry. To meet these objectives, the last deglacial reef sequence, which consists of successive reef terraces seaward of the living barrier reef, was cored from a dynamically positioned vessel during October and November 2005. A total of 37 boreholes at 22 sites were cored in water depths ranging from 41.65 to 117.54 m. Borehole logging operations in ten boreholes at seven sites provided continuous geophysical information about the drilled strata. Cores were described during the Onshore Science Party at the IODP Bremen Core Repository during February and March 2006, where minimum and some standard measurements were made. Further postcruise research on samples taken during the Onshore Science Party is expected to fulfill the objectives of the expedition.

The Cenozoic history (0 to 65 million years, Myr, ago) of the Arctic Ocean is largely unknown from direct evidence. Here we present the first Cenozoic palaeoceanographic record constructed from > 400 m of core from a recent drilling expedition to the Lomonosov Ridge. Our record shows a palaeoenvironmental transition from a warm greenhouse world, of the latest Palaeocene and early Eocene, to an icehouse world influenced by sea ice and icebergs from the middle Eocene to the present. We show: 1-2 cm per thousand years (ka) sedimentation rates occurred from the middle Miocene - Holocene (~18-0 Myr) in stark contrast to rates proposed in earlier studies; the first occurrence of ice-rafted debris (IRD) is in the middle Eocene (~45 Myr), ~35 Myr earlier than previously thought; prior to the IRD, fresh surface waters were present at ~49 Myr; and warm surface waters, ~10° warmer than previous estimates, occurred during the Palaeocene Eocene Thermal Maximum (PETM). The revised timing of Arctic cooling events coincides with those from Antarctica, supporting arguments for bi-polar symmetry in climate change.

It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions that characterized the early Palaeogene period (55-45 Myr ago) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (∼50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an ∼800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from ∼10°C to 13°C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas. © 2006 Nature Publishing Group.