A comparison of major chemical species seasonal concentration and accumulation at the South Pole and Summit, Greenland
Whitlow, S., P. A. Mayewski, and J. E. Dibb
Atmospheric Environment, Vol. 26A, No. 11, p. 2045-2054, 1992

High-resolution snow chemistry records have been recovered from a site close to the South Pole, covering the period 1955-1989, and from summit Greenland, for the periods 1979-1987 and 1259-1989. The seasonal variation of the major ions relative to delta 18-O and their average yearly fluxes are compared for the two sites. Comparisons are also made to limited available aerosol data. Gaseous species and some species with gaseous precursors (NO3, NH4, and excess Cl) have similar timings in South Pole and pre- 1900 Summit snow. Timing of non-sea-salt (nss) SO4 and species that are generated as marine and crustal aerosols (Na, nss Mg and nss Ca) differ between the two sites The timing or nss SO4 and NO3, is complicated in recent precipitation at Summit, Greenland, by the impact of anthropogenic emissions. Fluxes of sea-salt species, nss SO4 and NO3 (pre-1900 values for Summit) are less than a factor of 2 higher at Summit Species with a continental source nss K, nss Mg, nss Ca and NH4 are more than five- fold higher at Summit.

Inter-hemispheric transport of volcanic ash from a 1259 A.D. volcanic eruption to the Greenland and Antarctic ice sheets
Palais, J. M., M. S. Germani and G. A. Zielinski
Geophysical Research Letters, Vol. 19, No. 8, p. 801-804, April 24, 1992

A strong volcanic sulfuric acid signal corresponding to an age of 1259 A.D. has been reported in ice cores from Greenland, Antarctica, and Arctic Canada. Tiny (<5mm) volcanic glass shards were reported previously in samples from this layer in an ice core from the South Pole. Here we report the discover of volcanic glass shares from a contemporaneous layer in an ice core from Summit, Greenland. The major element composition of the glass shards in the Greenland sample are identical to those from the South Pole, confirming the assumption that has been made previously that the sulfuric acid signal in the ice cores is an inter-hemispheric time stratigraphic marker. The composition of these glass shards is similar to those produced by a 550-700 yrs. B.P. eruption of El Chichon volcano in Mexico, suggesting that it may be the source of the widely dispersed material.

Predicted time scales for GISP2 and GRIP boreholes at Summit, Greenland
Schott, C., E.D. Waddington and C.F. Raymond
Journal of Glaciology, Vol. 38, No. 128, p. 162-168, 1992

Two deep-drilling projects (GISP2 and GRIP) in central Greenland will provide ice cores for paleoclimate studies. Drilling decisions and preliminary interpretations require age-depth curves (time-scales). Using a finite-element momentum-balance model, we calculate the modern ice-flow pattern on the flow line through the two drill sites. Our model appears to require relatively soft ice either throughout the ice sheet or below the Wisconsinan-Holocene transition in order to match the modern geometry and mass balance. By scaling the ice velocity to an assumed mass-balance history throughout the past 200,000 years, we estimate the time-scales at both sites. At GISP2, a flank site, we place the 10,000 years BP isochrone (representing the Wisconsinan-Holocene transition) at 1535 m ice-equivalent depth. At GRIP, on the ice divide, the corresponding depth is 1377 m. Our calculations show ice older that 200,000 years at 100 m above the bed at both coring sites. The time-scale calculation can be used for drilling decisions and preliminary interpretations. It should be refined as more regional-survey and ice-core data become available.

Ice core sulfate from three Northern Hemisphere sites: Source and temperature forcing implications
Mayewski, P. A., Holdsworth, G., M. J. Spencer, S. Whitlow, M. Twickler, M. C. Morrison, K. K. Ferland, and L. D. Meeker
Atmospheric Environment, Vol. 27A, No. 17/18, p. 2915-2919, 1993

Comparison of ice core nss sulfate records (two sites in Greenland and one in the North Pacific) with temperature change records for the regions including these core sites (from Hansen and Lebedeff, 1987) provides further confirmation that change in the concentration of anthropogenic sulfate has had a significant effect on regional temperature during at least the period ~AD 1940-1970 over at least the Atlantic portion of the Arctic. Using the AD1880-1985 portion of our ice core records as an analog, we provide a test of the potential temperature depression caused by non-seasalt (nss) sulfate aerosols over Greenland during the period ~AD 700-1900 concluding that the anthropogenic era is unique by comparison. Statistical examination of this record allows a determination of the relative contributions for volcanic versus biogenic source nss sulfate during the period plus a characterization of the variability in these two sources.

Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores
Grootes, P. M., M. Stuiver, J. W. C. White, S. Johnsen, and J. Jouzel
Nature, Vol. 366, p. 552-554, 9 December 1993

Recent results from the Greenland Ice-core Project (GRIP) Summit ice core suggest that the climate in Greenland has been remarkably stable during the Holocene, but was extremely unstable for the time period represented by the rest of the core, spanning the last two glaciations and the intervening Eemian interglacial. Here we present the complete oxygen isotope record for the Greenland Ice Sheet Project 2 (GISP2) core, drilled 28 km west of the GRIP core. We observe large, rapid climate fluctuations throughout the last glacial period, which closely match those reported for the GRIP core. However, in the bottom 10% of the cores, spanning the Eemian interglacial and the previous glaciation, there are significant differences between the two records. It is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores. Considerable further work will be necessary to evaluate the likelihood of this, and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores.

Electrical conductivity measurements from the GISP2 and GRIP Greenland ice cores
Taylor, K. C., C.U. Hammer, R.B. Alley, H.B. Clausen, D. Dahl-Jensen, A.J. Gow, N.S. Gundestrup, J. Kipfstuhl, J.C. Moore, and E.D. Waddington
Nature, Vol. 366, p. 549-552, 9 December 1993

The direct-current electrical conductivity of glacial ice depends on its acidity, and can also indicate changes in climate, as ice formed in cold, dusty periods has a high concentration of alkaline dust, which significantly reduces the conductivity compared to warmer, less dusty periods. Here we present electrical conductivity records for the Greenland Ice Sheet Project 2 (GISP2) and Greenland Ice-core Project (GRIP) ice cores, drilled 28 km apart to enable direct comparison of the results. The upper parts of both records are consistent with previous evidence from other Greenland cores for a stable Greenland climate during the Holocene, and a series of warm events punctuating the last glacial period. However, there is a significant discrepancy between the two records in the bottom 10% of the cores, calling into question recent reports of climate variability in the last interglacial and the penultimate glaciation. At this stage, it is too early to say what exactly is causing the discrepancy, although ice flow may have introduced some discontinuities into the records. Further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores.

Climate correlations between Greenland and Antarctica during the past 100,000 years
Bender, M., T. Sowers, M.-L. Dickson, J. Orchardo, P. Grootes, P. Mayewski and D. Meese
Nature, Vol. 372, p. 663-666, 1994

The ice cores recovered from central Greenland by the GRIP and GISP2 projects record 22 interstadial (warm) events during the part of the last glaciation spanning 20-105 kyr before present. The ice core from Vostok, east Antarctica, records nine interstadials during this period. Here we explore links between Greenland and Antarctic climate during the last glaciation using a high-resolution chronology derived by correlating oxygen isotope data for trapped O2 in the GISP2 and Vostok cores. We find that interstadials occurred in east Antarctica whenever those in Greenland lasted longer than 2,000 years. Our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and Antarctica. Ice older than 115 kyr in the GISP2 core shows rapid variations in the 18O of O2 that have no counterpart in the Vostok record. The age-depth relationship, and thus the climate record, in this part of the GISP2 core appears to be significantly disturbed.

Climate records covering the last deglaciation
Sowers, T. and M. Bender
Science, Vol. 269, p. 210-214, 1995

Recent geochronological studies have shown that the sea level rise associated with the last glacial termination began about 19 kyr B. P.(calendar). Boreal regions began to warm about 14.7 kyr B.P. and other major deglacial events occurred at about 14 kyr B.P. (meltwater pulse 1A) and 11 kyr B.P. (meltwater pulse 1B). In this paper, we use the 18O of O2 trapped in ice cores as a time-stratigraphic marker for transferring the absolute chronology for the GISP II ice core to the Vostok and Byrd (Antarctic) ice cores. Our results suggest that, near the beginning of the last deglaciation, Antarctica began warming 2 - 6 kyr before Greenland. Atmospheric CO2 and CH4 concentrations began to rise 2-3 kyr before warming began in Greenland, and must have contributed to deglaciation and warming of temperate and boreal regions in the northern hemisphere.

A global perspective of nitrate flux in ice cores
Yang, Q., Mayewski, P.A., Whitlow, S., Twickler, M.S., Morrison, M.C., Talbot, R., Dibb, J.E. and Linder, E.
Journal of Geophysical Research, Vol. 100, No. D3, p. 5113-5121, 1995

The relationships between the concentration and flux of chemical species (Cl-, NO3-, SO42-, Na+, K+, NH4+, Mg2+, Ca2+) versus snow accumulation rate at GISP2, and 20D in Greenland, Mt. Logan from the St. Elias Range, Yukon Territory, Canada and Sentik Glacier from the northwest end of the Zanskar Range in the Indian Himalayas were examined. At all sites only nitrate flux and snow accumulation rate has a significant (a=0.05) linear relationship with high correlation coefficient. Nitrate concentration data are the only one of the chemical series that are normally distributed. Therefore we suggest that nitrate concentration in snow is affected by post depositional exchange with the atmosphere over a broad range of environmental conditions. The persistent summer maxima in nitrate observed in Greenland snow over the entire range of record studied (the last 800 years) may be mainly due to NOx released from PAN by thermal decomposition in the presence of higher OH concentrations in summer. The late winter/early spring nitrate peak observed in modern Greenland snow may be related to the build up of an anthropogenically derived NOy in the Arctic troposphere during the long polar winter.

Comparison of deep ice cores
Alley, R.B., A.J. Gow, S.J. Johnsen, J. Kipfstuhl, D.A. Meese and Th. Thorsteinsson.
Nature, Vol. 373, p. 393-394, 1995

Comparison of the GRIP and GISP2 deep ice cores from central Greenland has confirmed the occurence of exceptionally large, rapid changes in may climatic indicators over approximately the past 100,000 years. Similar rapid changes occur within deeper ice with a warm isotope signature (identified as the Eemian, Sangamonian, or stage 5e), but differences in their patterns between the two cores raise the possibility that at least one record was disturbed by ice-flow processes. Disturbances might include boudinage, open folding or similar processes that would distort the time depth relation but leave layers in stratigraphic order, o overturned folding that would disturb stratigraphic order. The GRIP and GISP2 steering bodies have initiated comparative studies of the two cores, including visible stratigraphy and crystal fabrics in selected sections of both cores, which are reported here. The most important results of these studies are reported.

Climate change during the last deglaciation in Antarctica
Mayewski, P.A., M.S. Twickler, S.I. Whitlow, L.D. Meeker, Q. Yang, J. Thomas, K. Kreutz, P. Grootes, D. Morse, E. Steig E.D. Waddington, E.S. Saltzman, P.-Y. Whung, K.C. Taylor
Science, Vol. 272, p. 1636-1638, 1996

Greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators. In this work, rapid climate change events in the Northern and southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores. High-resolution glaciochemical series, covering the period 10,000 to 16,000 years ago, from a central Greenland ice core and a new site in east Antarctica display similar variability. These findings suggest that rapid climate change events occur more frequently in Antarctica than previously demonstrated.

Major Changes in atmospheric circulation deduced from a Greenland ice core and comparison with an Antarctic ice core
Mayewski, P.A., L.D. Meeker, S. Whitlow, Q. Yang, K. Kreutz, and D. Reusch
Cryosphere, In Press

The GISP2, central Greenland, glaciochemical series (sodium, potassium, ammonium, calcium, magnesium, sulfate, nitrate and chloride) provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over much of the Northern Hemisphere. Interpretation of this record reveals the controls on both high and low frequency climate events of the last 110,000 years. Changes in insolation on the order of the major orbital cycles control the long-term behavior of atmospheric circulation patterns through changes in ice volume (sea level) and related positive feedbacks. Events such as the Heinrich events (massive discharges of icebergs first identified in the marine record) are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insulation and consequent glacier dynamics. Rapid climate change events (massive reorganizations of atmospheric circulation) are demonstrated to operate on 1450 year cycles possibly in response to internal oscillations in the ocean-atmosphere system or due to changes in solar output. Changes in insolation and associated positive feedbacks related to ice sheets assist in explaining favorable time periods and controls on the amplitude of these massive rapid climate change events. Comparison of the GISP2 glaciochemical series with an ice record from Taylor Dome in Antarctica indicates considerable similarity suggesting that both polar regions experience marked changes in climate. While preliminary evidence points to similar phasing of several major climate events in the two polar regions exact phasing can not as yet be determined, because dating of Antarctic ice core records is not as well-established as the dating for Greenland ice cores.

Abrupt Holocene climatic reorganizations registered in Greenland, East Africa and Antarctica
Stager, J.C., and P.A. Mayewski
In Press

Paleoclimatic records from equatorial East Africa, Antarctica, and Greenland reveal that atmospheric circulation changed abruptly at the early to mid-Holocene transition to full post-glacial conditions. A climatic reorganization occurred at all three sites between 8200 and 7800 years ago and lasted <200 years, and appears to have been related to abrupt transitions in both marine and terrestrial records around the world.