1. High-resolution analysis of rapid climate change events from Greenland ice cores
E R Thomas, E W Wolff and R Mulvaney
British Antarctic Survey, Natural Environment Research Council, Madingley Road, Cambridge,CB3 OET
Jorgen P. Steffensen and Sigfus J. Johnsen
Department of Geophysics, The Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej. 30, DK-2100 Copenhagen, Denmark
A series of very large and rapid climate oscillations within the last glacial period were first observed in the Greenland ice core record as warmings of more than 10ºC occurring in timescales of decades or even years. Within these Dansgaard-Oeschger (D-O) events the climate remains latched in the warm period for several hundred years before returning to fully cold conditions in one final rapid step. Smaller, less extreme climate oscillations have also been observed in the present warm Holocene period, as isotope anomalies in the ice core record.
We present high-resolution chemical analysis of two rapid climate change events, one that occurred 8200 years ago (8.2 kyr event) during the Holocene with one 35,000 years (DO-8) ago during the last glacial. The sudden cooling event at 8.2 kyr, observed in the Greenland Ice Core Project (GRIP) equivalent to a drop of about 6C in Greenland, led to widespread cold, dry conditions lasting for just a few decades. We compare this with high-resolution chemical analysis of one of the longest and strongest Dansgaard-Oeschger events, D-O 8, that began 35.7 kyr BP and lasted approximately 1800 years. According to the GRIP record, the initial warming at the start of the event, and final cooling at the end appear to have occurred in less than 50 years.
Dansgaard-Oeschger event 8
A new cutting method and small volume ion chromatography (IC) technique was developed for this project to allow discrete samples to be taken every 2 mm to give sub-seasonal resolution.
The annual layers can be counted from the seasonal cycles to determine the duration of the transition into and out of Dansgaard-Oeschger event 8.
Figure 5
Stable isotope record from NGRIP during Dansgaard-Oeschger event 8
The initial results from the termination transition (indicated in figure 5) show good seasonal cycles in all nine species. Below is a comparison of the annual layer counting for the 8.2 kyr event, where the annual layer thickness is 11cms, and the layers from 1000 meters deeper at DO-8, where the annual layer thickness is just 1-2cms.
Figure 3 Defining the event from GRIP and GISP2 stable isotopes (zooming in from top to bottom)
Figure 1 Stable isotopes record from GRIP
Figure 2 Map of Greenland showing drill sites
We investigate a 20m section of the GRIP core spanning the full 8.2 kyr event and two 6 meter sections of the North Greenland Ice Core Project (NGRIP) ice core at both the transitions into and out of DO event 8.
Ion chromatography (IC) was used to measure nine major ions at a resolution of 1cm during the 8.2 kyr event and 2 mm during DO-8 using a new cutting technique and small volume IC method.
Figure 5 Annual layer counting
The 8.2 kyr event
The event has been defined, (figure3) using the stable isotope record from GRIP and GISP2.
Annual layer counting of nine species determined the length of the whole event to be ~ 179 years with the central event lasting 80 years
There is no significant change in any chemical species, and therefore deposition over Greenland, during the event. This would imply that unlike the larger Dansgaard-Oeschger events, no major change in atmospheric circulation occurred.
Figure 6 Annual layer counting for the 8.2 kyr event from GRIP (left) and D-O 8 from NGRIP (right)
Figure 4 Top: GRIP (red) and GISP2 (Blue) isotopes
Bottom: Chemistry for the 8.2 kyr event at 1 cm resolution
The results will show the true rate of change, accumulation rate and sequence of events for the most prominent event of the Holocene and the largest and strongest Dansgaard-Oeschger event of the glacial.
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