During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events 1. Changes in Northern Hemisphere temperature, as recorded in Greenland 2-4 , are thought to have affected the location of the Atlantic intertropical convergence zone 5,6 and the strength of the Indian summer monsoon 7,8. Here we use high-resolution records of sediment colour-a measure of terrigenous versus biogenic content-from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system-in particular sea-ice extent-whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature. Ice-core records from Greenland 2,4 and sediment cores from the North Atlantic 1,9 demonstrate that, over the course of the last ice age, colder conditions (stadials) alternated with warmer periods (interstadials) on timescales of several millennia. Some of the stadial periods identified in Greenland and other records coincided with massive meltwater discharges (Heinrich events) 1 that originated from instabilities of the Northern Hemisphere ice sheets. Whereas the physical origin of Dansgaard-Oeschger oscillations still remains uncertain 10,11 , their global teleconnections have been identified using climate models 12,13 and palaeo-proxy data 5,7,14-16. However, previous proxy records have lacked the resolution to fully capture the effect of millennial-scale glacial variability on interannual to decadal tropical rainfall variability.

ABSTRACT. We present two new high-resolution sediment records from the southwestern Iceland and Norwegian Seas that were dated by numerous 14C ages up to 5414C ka BP. Based on various lines of evidence, the local 14C reservoir effect was restricted to 400-1600 yr. The planktic stable isotope records reveal several meltwater spikes that were sampled with an average time resolution of 50 yr in PS2644 and 130 yr in core 23071 during isotope stage 3. Most of the 6180 spikes correlate peak-by-peak to the stadials and cold rebounds of the Dansgaard-Oeschger cycles in the annual-layer counted GISP2 ice core, with the major spikes reflecting the Heinrich events 1-6. This correlation indicates large fluctuations in the calibration of 14C ages between 20 and 54 i4C ka BP. Generally the results confirm the 14C age shifts as predicted by the geomagnetic model of Laj, Mazaud and Duplessy (1996). However, the amplitude and speed of the abrupt decrease and subsequent major increase of our 14C shifts after 4514C ka BP clearly exceed the geomagnetic prediction near 40-43 and 32-34 calendar (cal) ka BP. At these times, the geomagnetic field intensity minima linked to the Laschamp and the Mono Lake excursions and confirmed by a local geomagnetic record, probably led to a sudden increase in cosmogenic 14C and 10Be production, giving rise to excess 14C in the atmosphere of up to 1200%o.

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An outstanding climate anomaly 8200 years before the present (B.P.) in the North Atlantic is commonly postulated to be the result of weakened overturning circulation triggered by a freshwater outburst. New stable isotopic and sedimentological records from a northwest Atlantic sediment core reveal that the most prominent Holocene anomaly in bottom-water chemistry and flow speed in the deep limb of the Atlantic overturning circulation begins at approximately 8.38 thousand years B.P., coeval with the catastrophic drainage of Lake Agassiz. The influence of Lower North Atlantic Deep Water was strongly reduced at our site for approximately 100 years after the outburst, confirming the ocean's sensitivity to freshwater forcing. The similarities between the timing and duration of the pronounced deep circulation changes and regional climate anomalies support a causal link.

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