(Table 1) Gas tie points used to correlate the ice cores NGRIP and EDML

Water isotope records from the EPICA Dronning Maud Land (EDML) and the NorthGRIP ice cores have revealed a one to one coupling between Antarctic Isotope Maxima (AIM) and Greenland Dansgaard-Oeschger (DO) events back to 50 kyr. In order to explore if this north-south coupling is persistent over Marine Isotopic Stage 5 (MIS 5), a common timescale must first be constructed. Here, we present new records of d18O of O2 (d18Oatm) and methane (CH4) measured in the air trapped in ice from the EDML (68-147 kyr) and NorthGRIP (70-123 kyr) ice cores. We demonstrate that, through the period of interest, CH4 records alone are not sufficient to construct a common gas timescale between the two cores. Millennial-scale variations of d18Oatm are evidenced over MIS 5 both on the Antarctic and Greenland ice cores and are coupled to CH4 profiles to synchronise the NorthGRIP and EDML records. They are shown to be a precious tool for ice core synchronisation. With this new dating strategy, we produce the first continuous and accurate sequence of the north-south climatic dynamics on a common ice timescale for the last glacial inception and the first DO events of MIS 5, reducing relative dating uncertainties to an accuracy of a few centuries at the onset of DO events 24 to 20. This EDML-NorthGRIP synchronisation provides new firm evidence that the bipolar seesaw is a pervasive pattern from the beginning of the glacial period. The relationship between Antarctic warming amplitudes and their concurrent Greenland stadial duration highlights the particularity of DO event 21 and its Antarctic counterpart. Our results suggest a smaller Southern Ocean warming rate for this long DO event compared to DO events of MIS 3.

Sea surafe temperture calculation for the Arabian Sea

Sea surface temperature (SST) and seawater d18O (d18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and d18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°-3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in d18Ow that are smaller than the d18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower d18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.

Data from the EPICA Dome C ice core EDC

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long - 28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

(Table 1) Micro-inclusion counts and ion concentrations in the five GRIP ice-core sections

We provide the first direct evidence that a number of water-soluble compounds, in particular calcium sulfate (CaSO4 2H2O) and calcium carbonate (CaCO3), are present as solid, micron-sized inclusions within the Greenland GRIP ice core. The compounds are detected by two independent methods: micro-Raman spectroscopy of a solid ice sample, and energy-dispersive X-ray spectroscopy of individual inclusions remaining after sublimation. CaSO4 2H2O is found in abundance throughout the Holocene and the last glacial period, while CaCO3 exists mainly in the glacial period ice. We also present size and spatial distributions of the micro-inclusions. These results suggest that water-soluble aerosols in the GRIP ice core are dependable proxies for past atmospheric conditions.