MAJOR FEATURES OF GLACIOCHEMISTRY OVER THE LAST 110,000 YEARS IN THE GREENLAND ICE SHEET PROJECT 2 ICE CORE

摘要

Major chemical species (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, Ca2+) and delta(18)O covering the last 110,000 years from the Greenland Ice Sheet Project 2 (GISP2) ice core were utilized in this study in order to reconstruct the soluble chemistry of the atmosphere over Greenland and interpret major climate events that have affected the region. During the Holocene the major chemical species and delta(18)O do not display any significant relationship. However, a strong inverse correlation was found between concentrations of the major chemical species and delta(18)O (a proxy for temperature) during the last glacial period, suggesting that in general during periods of decreased temperature, there is an increase in atmospheric chemical loading. Examination of changes in major chemical composition over the last 110,000 years of the GISP2 ice core reveals that during the Holocene, the atmosphere was acidic; during interstadials the atmosphere was neutral or alkalescent; and during stadials the atmosphere was alkaline. In addition, the relative abundance of major chemical species varied during the Holocene, stadials, and interstadials. During the Holocene, NH4+ and NO3- are the dominant cations and anions; while Ca2+ and SO42- are the dominant cations and anions during the stadials and interstadials, This suggests that source regions or types differed between the Holocene and the last glacial period. In addition, changes in chemical composition and changes in chemical ratios also indicate that source regions differed during the Holocene, stadials, and interstadials. Twenty-four previously identified Dansgaard-Oeschger (stadial/interstadial) events [Dansgaard: et al., 1993] were in the GISP2 chemical series. The duration of the stadials is inversely correlated with variations in sea level over the last glacial period (i.e., the more extensive the northern hemisphere ice sheet, the longer the duration of the stadial). There is also a close correspondence between the duration of interstadials and the timing of Heinrich events (massive icebergs discharged into the ocean) in the GISP2 ice core. Long. (up to 2000 years) warm periods follow each Heinrich event, suggesting perhaps that enhanced deep-water circulation is re-initiated following Heinrich events. [References: 51]