Were last glacial climate events simultaneous between Greenland and western Europe?

During the last glacial period, several large abrupt climate fluctuations took place on the Greenland ice cap and elsewhere. Often these Dansgaard/Oeschger events are assumed to have been synchronous, and then used as tie-points to link chronologies between the proxy archives. However, if temporally separate events are lumped into one illusionary event, climatic interpretations of the tuned events will obviously be flawed. Here, we compare Dansgaard/Oeschger-type events in a well-dated record from south-eastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties, that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, tuning of proxy archives should be avoided.

Stable oxygen isotopes of Globigerinoides ruber and biostratigraphic datums at ODP Site 165-1002

Ocean Drilling Program Site 1002 in the Cariaco Basin was drilled in the final two days of Leg 165 with only a short transit remaining to the final port of San Juan, Puerto Rico. Because of severe time constraints, cores from only the first of the three long replicate holes (Hole 1002C) were opened at sea for visual description, and the shipboard sampling was restricted to the biostratigraphic examination of core catchers. The limited sampling and general scarcity of biostratigraphic datums within the late Quaternary interval covered by this greatly expanded hemipelagic sequence resulted in a very poorly defined age model for Site 1002 as reported in the Leg 165 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Here, we present for the first time a new integrated stratigraphy for Site 1002 based on the standard of late Quaternary oxygen-isotope variations linked to a suite of refined biostratigraphic datums. These new data show that the sediment sequence recovered by Leg 165 in the Cariaco Basin is continuous and spans the time interval from 0 to ~580 ka, with a basal age roughly twice as old as initially suspected from the tentative shipboard identification of a single biostratigraphic datum. Lithologic subunits recognized at Site 1002 are here tied into this new stratigraphic framework, and temporal variations in major sediment components are reported. The biogenic carbonate, opal, and organic carbon contents of sediments in the Cariaco Basin tend to be high during interglacials, whereas the terrigenous contents of the sediments increase during glacials. Glacioeustatic variations in sea level are likely to exert a dominant control on these first-order variations in lithology, with glacial surface productivity and the nutrient content of waters in the Cariaco Basin affected by shoaling glacial sill depths, and glacial terrigenous inputs affected by narrowing of the inner shelf and increased proximity of direct riverine sources during sea-level lowstands.

Paleoceanography of sediment cores SO202-27-6 and MD01-2416

The glacial-to-Holocene evolution of subarctic Pacific surface water stratification and silicic acid (Si) dynamics is investigated based on new combined diatom oxygen (d18Odiat) and silicon (d30Sidiat) isotope records, along with new biogenic opal, subsurface foraminiferal d18O, alkenone-based sea surface temperature, sea ice, diatom, and core logging data from the NE Pacific. Our results suggest that d18Odiat values are primarily influenced by changes in freshwater discharge from the Cordilleran Ice Sheet (CIS), while corresponding d30Sidiat are primarily influenced by changes in Si supply to surface waters. Our data indicate enhanced glacial to mid Heinrich Stadial 1 (HS1) NE Pacific surface water stratification, generally limiting the Si supply to surface waters. However, we suggest that an increase in Si supply during early HS1, when surface waters were still stratified, is linked to increased North Pacific Intermediate Water formation. The coincidence between fresh surface waters during HS1 and enhanced ice-rafted debris sedimentation in the North Atlantic indicates a close link between CIS and Laurentide Ice Sheet dynamics and a dominant atmospheric control on CIS deglaciation. The Bølling/Allerød (B/A) is characterized by destratification in the subarctic Pacific and an increased supply of saline, Si-rich waters to surface waters. This change toward increased convection occurred prior to the Bølling warming and is likely triggered by a switch to sea ice-free conditions during late HS1. Our results furthermore indicate a decreased efficiency of the biological pump during late HS1 and the B/A (possibly also the Younger Dryas), suggesting that the subarctic Pacific has then been a source region of atmospheric CO2.