News & Events

September 10th, 2006

No pervasive Holocene ice-rafted debris (IRD) signal in northern North Atlantic?

John Andrews, Anne Jennings, and colleagues have assembled marine core records of ice-rafted debris (IRD) off North Iceland, East Greenland, and Labrador that are at odds with an earlier and oft-cited study showing a pervasive ~1.5 thousand year periodicity of IRD delivery during the Holocene (last ~11,400 years). Andrews et al. used quantitative X-ray diffraction on the < 2 mm sediment fraction of four well-dated cores from different ice-dominated regions. There were significant differences in the trends of the IRD as well as an absence of a pervasive millennial signal. These results suggest that IRD delivery to the northern North Atlantic is not synchronized regionally nor is periodic. Moreover, the results should make researchers question the underlying environmental forcing behind the earlier studies' data (hematite-stained quartz sands). Although the ~1.5 thousand year cycles in this and other records may be associated with solar forcing, the specific link to ice rafting appears ambiguous. The varying trends in the new data suggest that the Holocene oceanographic/climate evolution of each region should be considered individually. Preliminary results were published in a special August 2006 issue of the PAGES Newsletter about the National Science Foundation's Earth System History (ESH) program. More publications are underway.