HOLOCENE MILLENNIAL-SCALE EFFECTIVE MOISTURE VARIATIONS IN THE CENTRAL NORTH ATLANTIC: EVIDENCE FROM LACUSTRINE AND PEAT CORES FROM THE AZORE ISLANDS

The North Atlantic has been identified as a critical region with regards to Northern Hemisphere climate change. Model and proxy records suggest that late Pleistocene and Holocene millennial-scale climate fluctuations are strongly linked to variations in thermohaline circulation, sea-surface temperature (SST), and atmospheric circulation in this region, possibly due to solar variability (Bond et al., 2001). Most records of North Atlantic oceanic/atmospheric dynamics have come from relatively low resolution marine records or from higher resolution terrestrial records peripheral to the North Atlantic itself, such as from the Greenland ice sheet and the surrounding mainlands. However, high-resolution climate records from within the North Atlantic region are largely lacking. Here we present a high-resolution mid- to late-Holocene lacustrine and peat record of changes in effective moisture from the Azore Islands in the central North Atlantic Ocean.

Cores were collected from Pico Bog and Lake Caveiro, located in two nearby small extinct volcanic craters on Pico Island, Azores (~30N, 28W and 870-900m asl). Proxy records from the alternating peat and gyttja record from Pico Bog and the Lake Caveiro core indicated alternating century to millennial-scale changes in effective moisture reflected in peat humification, testate amoebae, pollen, lake-level changes and C and N analysis. The position of the Azore Islands under the Azores High pressure dipole of the North Atlantic Oscillation (NAO) strongly influences the climate of the islands today. In the youngest part of the record (AD 1600–2000) shifts in effective moisture appear to correspond to shifts in the dominating NAO mode (Björck et a., 2006). Long-term precipitation changes (350–5100 cal yr BP) roughly correspond to the well-known North Atlantic drift-ice variations as well as other North Atlantic records; with low precipitation during drift-ice periods.