An ice core record of atmospheric response to anthropogenic sulfate and nitrate
Mayewski, P. A., W. B. Lyons, M. J. Spencer, M. S. Twickler, C. F. Buck, and S. Whitlow
Nature, Vol. 346, No. 6284, p. 554-556, 9 August, 1990

Records of sulfate and nitrate concentrations in ice cores show that these concentrations have increased recently because of the long-range transport of pollution from middle latitudes. But these records have been neither complete enough nor long enough to allow an assessment of their sensitivity to variations in the emissions of sulfate and nitrate precursors. We have now analyzed sections from an ice core in South and from GISP2 which have allowed us to extend the sulfate and nitrate record back from 1869 to 1767. This longer record has enabled us to determine the pre-industrial natural interannual variability of non- sea-salt sulfate and nitrate. We find that the background concentration in the remote atmosphere over Greenland is sensitive to changes in the anthropogenic emissions of sulfate and nitrate and responds to these variations on a timescale of the order of decades.

Volcanic ash from the 1362 A.D. Or¾fajokull eruption (Iceland) in the Greenland ice sheet
Palais, J. M., K. Taylor, P. A. Mayewski, and P. Grootes
Geophysical Research Letters, Vol. 18, No. 7, p. 1241-1244, July 1991

A continuous record of electrical conductivity measurements (ECM) was made on site during the drilling of a 200 m ice core at Summit, Greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions. In one detailed section that we studied a large peak in the number of particles, two orders of magnitude above the background, was measured. The particle peak was not associated with an ECM peak, however. The particles were identified as volcanic ash on the basis of both particle morphology and chemical composition. The ash composition suggests an explosive rhyolitic eruption and is believed to have originated from Or¾fajokull in Iceland in 1362 A.D.

Characteristics and possible source of 1479 A.D. volcanic ash layer in a Greenland ice core
Fiacco, J. R. Jr., J. M. Palais, M. S. Germani, G. A. Zielinski and P. A. Mayewski
Quaternary Research, Vol. 39, p. 267-273, 1993

A microparticle concentration peak in a GISP2 ice core contains volcanic glass shards of rhyolitic composition corresponding to the age of the 1479-1480 A.D. Mt. St. Helens Wn eruption. These glass shards are compositionally similar to the Wn tephra and comprise 83% of the total particle population. The shards are very coarse-grained (up to 40 µm diameter), suggesting rapid transport from their source to Greenland. A major sulfate peak in the ice occurs approximately 4 months after deposition for the glass shards. This difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol. Large-scale climatic perturbations following this eruption were evidently negligible. Glaciochemical seasonal indicators suggest a late-fall to early-winter 1479 A.D. eruption.

Lead variability in the western North Atlantic ocean and central Greenland ice: Implications for the search for decadal trends in anthropogenic emissions
Boyle, E. A. , R. M. Sherrell and M.P. Bacon
Geochimica et Cosmochimica Acta, Vol. 58, p. 3227-3238, 1994

Most of the lead in the modern ocean and atmosphere is of anthropogenic origin. Changes in the utilization of leaded gasoline should produce decadal-scale decreases in the total lead deposition from the atmosphere in remote locations. However, the search for decadal trends is confounded by large-amplitude short-term variability. Lead concentrations are highly variable in the surface waters of the western North Atlantic Ocean and in the snows deposited in central Greenland. In the western North Atlantic, 210Pb normalization minimizes this problem because 210Pb and Pb sources are spatially correlated and 210Pb emissions are constant, but this method does not work in the Arctic because sources of 210Pb and anthropogenic Pb to this region are poorly correlated. Because of the order-of-magnitude variability in Greenland snow Pb linked to annual cycles, any discontinuous time-series is likely to be affected by the phenomena of aliasing and reports of long-term trends should be regarded with reservation until confirmed by independent samplings.

An ice core based record of biomass burning in the Arctic and Subarctic, 1750 -1980
Whitlow, S. I., P. A. Mayewski, G. Holdsworth, M. S. Twickler, and J. E. Dibb
Tellus, Vol. 46B, p. 239-242, 1994

Ammonium records from three ice cores, 20D and GISP2 (Greenland) and Mt. Logan (Yukon ), covering the period from 1750 to the 1980s are analyzed. For each data set, samples with NH4+ concentrations greater than one standard deviation above the mean value also tend to be enriced in NO3- and K+, similar to the chemical composition of aerosols from aged biomass burning plumes. We believe the NH4+ spikes originate from biomass burning events. There is not a one to one correspondence between documented large fires and NH4+ spikes, nor are specific annual layers with elevated NH4+ concentrations often found in more than one core. However, frequency of NH4+ spikes increase during periods of more extensive and intensive biomass burning in the NH4+ source areas for the ice core sites. The 20D and GISP2 records are characterized by increased spike frequency from 1790 to 1810 and from 1830 to 1910. This latter time coincides with a period of increased biomass burning documented in the historical fire records for nothern North America. In contrast to both Greenland ice core records, the Mt. Logan NH4+ record shows periods of increased spike frequency from 1770-1790, 1810-1830, 1850-1870 and 1930- 1980. The poor agreement between the Mt. Logan record and athe records from Greenland suggests that another source area, perhaps Siberia, may be the dominant summertime souce area for NH4+ spikes in Mt. Logan snow.

Climatic impact of the A.D. 1783 Asama (Japan) eruption was minimal: Evidence from the GISP2 ice core
Zielinski, G. A., R.J. Fiacco, S. Whitlow, M.S. Twickler, M.S. Germani, K. Endo, M.Yasui
Geophysical Research Letters, Vol. 21, No. 22, p. 2365-2368, 1 November 1994

Assessing the climatic impact of the A.D. 1783 eruption of Mt. Asama, Japan, is complicated by the concurrent eruption of Laki, Iceland. Estimates of the stratospheric loading of H2SO4 for the A.D. 1108 eruption of Asama derived from the SO42- time series in the GISP2 Greenland ice core indicate a loading of about 10.4 x 1012g H2SO4 with a resulting stratospheric optical depth of 0.069. Assuming sulfur emissions from the A.D. 1783 eruption was only one-third of the 1108 event yields a H2SO4 loading value of 3.5 x 1012 g and a stratospheric optical depth of only 0.023. These results suggest minimal climatic effects in the Northern Hemisphere from the 1783 Asama eruption, thus any volcanically-induced cooling in the mid-1780s is probably due to the Laki eruption. Volcanic glass found in layers from early in 1783 could support the existence of an undocumented eruption prior to the Laki and Asama events as suggested by previous workers.

Atmospheric loading and transport due to the 1783-84 Laki eruption interpreted from ash particles and acidity in the GISP2 ice core
Fiacco, R. J. Jr., T. Thordarson, M. S. Germani, J. M. Palais, and S. Whitlow
Quaternary Research, Vol. 42, p. 231-240, 1994

Glass shards from the 1783 A.D. Laki, Iceland fissure eruptions were identified in a GISP2 ice core, preceding a major acidity/sulfate peak. Only 2% of the total particle load in the ice core for the summer of 1783 is Laki glass, reinforcing contemporary accounts that the predominant transport direction was to the east and southeast. Sulfate concentrations increase slightly during the fall of 1783 and remain steady through the winter due to slow oxidation rates during this season in the Arctic. The sulfate concentration then rises dramatically in the spring and summer of 1784 producing a massive sulfate peak, commonly used as a marker horizon in Greenland ice core studies. This suggests that a significant portion of the Laki eruption plume penetrated the tropopause and remained aloft for at least one year after the waning of the eruption. A "year without a summer" is noted at Summit, Greenland during the summer 1784 based on comparison of 18O with other glaciochemical seasonal indicators. This further supports the claim that a significant volume of sulfate aerosol remained in the upper Arctic atmosphere well after the eruption was complete.

Biomass burning record and black carbon concentration in the GISP2 ice core
Chylek, P., B. Johnson, P. A. Damiano, K. C. Taylor, and P. Clement
Geophysical Research Letters, Vol. 22, No. 2, p. 89-92, 1995

We have determined the black carbon concentration in three sets of ice core samples from the GISP2 ice core. The peaks in black carbon concentration between 330 and 340 A. D. correlate well with peaks in ammonium concentration and dips in electrical conductivity, which allows us to identify extensive forest fires in this time period. The average black carbon concentration is found to be 2.1 µg of black carbon per 1kg of snow melt water. Black carbon concentration is considerably lower in three samples from the early Holocene and the last glacial maximum (two samples are consistent with no carbon present). The ice from the current industrial epoch shows an average black carbon concentration of about 2.0 µg/kg suggesting that anthropogenic activities did not increase significantly the rate of black carbon deposition at the GISP2 Greenland site.

Evidence of the Eldgj‡ (Iceland) eruption in the GISP2 Greenland ice core: Relationship to eruption processes and climatic conditions in the tenth century
Zielinski, G.A., M.S. Germani, G. Larsen, M.G.L. Baillie, S. Whitlow, M.S. Twickler and K. Taylor
The Holocene, Vol. 5, p. 129-140, 1995

Glaciochemical studies and the evaluation of tephra in the GISP2 ice core provide information on the characteristics and potential environmental and climatic effects of the mid- to late 930s AD voluminous fissure eruption of Eldgj‡, Iceland. The similarity in the chemical composition of basaltic glass shards found in a section of core dated at 938 + 4 AD compared to proximal glass from the Eldgj‡ eruption verifies the presence of Eldgj‡ debris. A dacitic glass present in the same layer probably originated from Eldgj‡ as well, in which case Eldgj‡ was the primary contributor of sulfur-rich aerosols to the atmosphere in the late 930's AD. We can not completely exclude the possibility of another explosive eruption in the 930's AD that produced this dacitic glass. Estimated maximum stratospheric loading is 100 x 1012 g H4SO4 over a three to six year period following the eruption, but loading could be as low as half of that value. A search of historical and proxy records for the late 930's - early 940's AD fail to consistently show a period of climatic cooling especially considering the lack of an absolute date for the Eldgj‡ eruption. This inconsistent response is similar to that observed after the equally voluminous 1783 AD fissure eruption of Laki, Iceland, using the same proxy data sets. However, a marked drop in surface temperatures in the Northern Hemisphere follows the Laki eruption.

Stratospheric loading and optical depth estimates of explosive volcanism over the last 2100 years derived from the Greenland Ice Sheet Project 2 ice core
Zielinski, G.A.
Journal of Geophysical Research-Atmospheres, Vol. 100, No. D10, p. 20,937-20,955, October 20, 1995

The high-resolution and lengthy records of volcanic aerosol deposition in ice cores allow the assessment of the atmospheric impact of different styles and magnitudes of past eruptions and the impact of volcanism during periods of different climatic conditions. The 2100-year long volcanic SO42- time series in the Greenland Ice Sheet Project 2 (GISP2) ice core was used to calculate the mass stratospheric loading (MD) of H4SO4 and resulting optical depth values (tD=MD/1.5 x 1014 g) for individual and multiple closely spaced eruptions. Calibration of the calculated optical depth values with other compilations spanning the last 150 years provides a range of values for each eruption or set of eruptions essential to quantifying the climate forcing capabilities of each of these events. Limitations on the use of the results exist because this is only a single ice core, sampling was biannual and transport, and deposition of aerosols is not consistent among individual eruptions. The record of volcanic optical depth estimates is characterized by distinct trends within three consecutive 700-year time periods. The period from 100 B.C. to A.D. 600 is characterized by the fewest eruptions, and optical depth values are lower than those in the rest of the record. The exception is an extremely large signal of three years duration that is probably associated with an unknown Icelandic eruption around 53 B.C., with the possible contribution of another high-latitude eruption. The presence another signal at 43 B.C. suggests that at least two eruptions impacted climate in the middle decade of the first century B.C. The period from A.D. 600 to 1300 has intermediate numbers and magnitudes of volcanic events except for the very large 1259 event. Stratospheric loading and optical depths values for the 1259 event are twice that for Tambora (A.D. 1815). The state of the climate system in the middle of the 13th century A.D. may not have been sensitive enough to the atmospheric perturbation the 1259 eruption, thus the apparent lack of abundant proxy evidence of climatic cooling around A.D. 1260. The most recent 700 years (A.D. 1400-1985) are characterized by the greatest number of eruptions (half of those recorded over the 2100 years of record) and, in general, the highest stratospheric loading and optical depth values for individual and the combined effects of multiple eruptions. The large Kuwae eruption (A.D. 1450s) may have perturbed the atmosphere at least as much as Krakatau and possibly of a magnitude similar to Tambora. Multiple eruptions in the 50- to 60-year periods from A.D. 1580s-1640s and A.D. 1780s-1830s may have had a significant impact on enhancing the already cool climatic conditions in those time periods, particularly around A.D. 1601 and 1641. These findings imply that multiple eruptions closely spaced in time are more likely to have a major impact on a decadal time scale when existing climatic conditions are in a more sensitive or transitional state. The GISP2 ice core record also indicates that several relatively unknown eruptions may have been large sulfur producers during the 17th and 19th centuries A.D., thereby warranting further studies of those particular events.

Historical biomass burning: Late 19th century agriculture revolution in northern hemisphere ice core data and its atmospheric interpretation
Holdsworth, G., P. Chylek, P. Damiano, B. Deck, K. Higuchi, B. Johnson, P.A. Mayewski, M. Wahlen and G.A. Zielinski
Journal of Geophysical Research- Atmospheres, Vol. 101(D18), p. 23,317-23,334, 1996

Ice core data from Yukon and Greenland spanning from 1750 to 1950, indicate that between ca 1850 and ca 1910, a clear atmospheric signal exists of the Pioneer Agriculture Revolution. This is best seen in NH4+ ion and particulate concentrations, but also in some limited soot concentration data. Tree cellulose 13C data and some early (controversial) air CO2 data, provide other independent evidence for mainly north American, late 19th century biomass burning. Some northern hemisphere ice core derived CO2 concentration data seem to contain a biomass burning signal and are interpreted in view of all the other results. A global carbon cycle model simulation of atmospheric CO2 mixing ratios suggests that some of the ice core carbon dioxide values do not represent fully mixed atmospheric values but it tends to support these data as suggesting that transient inter-hemispheric, CO2 gradients of similar magnitude to the present one, could have existed late last century.

Volcanic ash from Icelandic ~57,300 yr BP eruption found in GISP2 (Greenland) ice core
Ram, M., J. Donarummo Jr., M. Sheridan
Geophysical Research Letters, Vol. 23(22), p. 3167-3169, 1996

We have found volcanic ash in Wisconsinan ice from the GISP2 ice core retrieved from the Summit location in Central Greenland. The ash consists predominately, of large rhyolitic glass shards similar to the ones found in Wisconsinan Dye 3 ice from Southern Greenland. We give the results of our analysis of the ash and present evidence that correlates this ash with the Z2 ash layer found in Atlantic sediment cores, with the Dye 3 ash, with ash recently found in the GRIP ice core from Central Greenland and with ash associated with the Icelandic Thorsmšrk ignimbrite. The mineralogy of the ash is very similar to that of ash from the Icelandic Tindfjallajškull volcano that is also present in the Thorsmšrk ignimbrite and we suggest that this is the source volcano. Tindfjallajškull has also been suggested as the source of the Z2 ash. Based on the excellent dating of the GISP2 ice core, we determined that the eruptions that produced the GISP2 ash occurred 57,300 ± 1,300 yr. BP of the Z2 ash based on the SPPECMAP chronology. This provides us with a reliable revision of the Dye 3 ice core dating at a depth of ~1950 m. This ice was originally dated at ~ 70,000 yr. BP.

Depletion of nitrate and chloride as a consequence of the Toba volcanic eruption
Yang, Q., P. A. Mayewski, M. Twickler, S.I. Whitlow
Geophysical Research Letters, Vol. 23(18), p. 2513-2516, 1996

Continuous measurements of SO42- and electrical conductivity (ECM) along the GISP2 ice core record the Toba mega-eruption at a depth 2590.95 to 2091.25 m (71,000±5000 years ago). Major chemical species were analyzed at a resolution of 1 cm per sample for this section. Am ~6-year long period with extremely high volcanic SO42 coincident with a 94% depletion of nitrate and 63% depletion of chloride is observed at the depth of the Toba horizon. Such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies. The nearly complete depletion of nitrate (to 5 ppb) encountered at the Toba level is the lowest value in the entire ~250,000 years of the GISP2 ice core record. We propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this mega-eruption.

Potential Atmospheric impact of the Toba mega-eruption ~71,000 years ago
Zielinski, G.A., P.A. Mayewski, L.D. Meeker, S. Whitlow, M. Twickler, and K. Taylor
Geophysical Research Letters, Vol. 23, p. 837-840, 1996

A decade-long period of volcanic sulfate recorded in the GISP2 ice core about 71,100±5000 years ago provides detailed information on the atmospheric and climatic impact of the Toba mega-eruption. Deposition of these aerosols occur at the beginning of an ~1000-year long stadial event, but not before the longer glacial period beginning ~67,500 years ago. Stratospheric loading estimates are only about 250 x 1012 g H2SO4 possibly from enhanced scavenging within the aerosol cloud of mega-eruptions. Optical depths of ~0.2 still would have occurred throughout the entire 10-year period. These values are large enough to have cooled global surface temperatures by ~1¡C per year for ten years, and thus enhanced the amount of cooling during the initial two centuries of this millennium-long cold period.

A 110,000-year record of explosive volcanism from the GISP2 (Greenland) ice core
Zielinski, G.A., P.A. Mayewski, L.D. Meeker, S. Whitlow and M. Twickler
Quat. Res., Vol. 45, p. 109-118, 1996

The time series of volcanically-produced sulfate from the GISP2 ice core is used to develop a continuous record of explosive volcanism over the past 110,000 yr. We identified ~850 volcanic signals (700 of these from 110,000 to 9000 years ago) with sulfate concentrations greater than that associated with historical eruptions from either equatorial or mid-latitude regions that are known to have perturbed global or Northern Hemisphere climate, respectively. This number is a minimum because decreasing sampling resolution with depth, source volcano location, variable circulation patterns at the time of the eruption, and post-depositional modification of the signal can result in an incomplete record. The largest and most abundant volcanic signals over the past 110,000 yr, even after accounting for lower sampling resolution in the earlier part of the record, occur between 17,000 and 6000 yr. ago, during and following the last deglaciation. A second period of enhanced volcanism occurs 35,000-22,000 yr. ago, leading up to and during the last glacial maximum. These findings further support a possible climate-forcing component in volcanism. Increased volcanism often occurs during stadial interstadial transitions within the last glaciation, but this is not consistent over the entire cycle. Ages for some of the largest known eruptions 100,000-9000 yr. ago closely correspond to individual sulfate peaks or groups of peaks in our record.

An assessment of the record of the 1982 El Chich—n eruption as preserved in Greenland snow
Zielinski, G.A., J.E. Dibb, S. Whitlow, M.S. Twickler, Q. Yang, and M.S. Germani
Journal of Geophysical Research, 1997

Variability in the SO42- and Cl- signal from the 1982 El Chich—n eruption in a series of 12 shallow snow pits across the Greenland ice sheet is used to evaluate the potential for recording a moderate northern equatorial eruption in a single Greenland ice core. Composition of volcanic glass found in spring 1983 snow in one of the pits in the Summit region matches that from El Chich—n glass thereby verifying the deposition of material from the eruption. High Na+ and Cl- concentrations in this same layer probably represent deposition of the reaction products of halite and H2SO4 as observed in the stratosphere following the eruption. These finding and the presence of a Cl- signal in five of the other pits indicate that the Cl- aerosol component of an eruption has the potential to remain aloft for at least one year after the eruption. Distinct SO42- peaks that can be confidently linked to El Chich—n were only found in 50% of the records developed through sub-seasonal sampling. However, in several other pits broad, but more subdued peaks that are thought to represent more lengthy periods of El Chich—n aerosol deposition as opposed to deposition from a single snowfall event, also were observed. Smoothing of the original data by the calculation of annual SO42- flux resulted in the presence of maximum flux values between 1982 and 1984 (years thought to be affected by El Chich—n aerosol deposition) in 9 of the 12 pits. These results suggest that a single ice core from anywhere in Greenland may record a signal from a northern equatorial eruption of similar magnitude to El Chich—n about 75% of the time despite the overall high levels of SO42- deposition from anthropogenic sources that make identification and quantification of the volcanic SO42- portion of the record more difficult than obtaining the same data for pre-industrial volcanism. Nevertheless, composite records from all the pits sampled yielded stratospheric loading (~20 Mt) and optical depth (t= 0.13) estimates similar to stratospheric and satellite-based measurements following the eruption. Equally high SO42- concentration and flux values in snow from 1980-1982 reflect deposition from the many volcanic eruptions 1979-1981.

Biomass burning recorded in the GISP2 Ice Core: A record from eastern Canada?
Taylor, K., P.A. Mayewski, M.S. Twickler, S. Whitlow
The Holocene, Vol. 6, No. 1, In Press

Combustion byproducts from biomass burning are preserved in annually stratified layers in the Greenland ice sheet. Electrical conductivity and ammonium records from the GISP2 ice core in central Greenland have been used to develop a 6,000 year record of biomass burning. Although there is some uncertainty regarding the source area for the combustion byproducts, it is likely that the majority of the material originates in eastern Canada. Time periods of high biomass burning activity occurred in 0 to 150 BP, 350 BP to 750 BP, and 5,000 BP to > 6,000 BP. The period 1,150 BP to 3,250 BP is characterized by moderately elevated levels of biomass burning activity. These periods are associated with drier conditions. The 5,000 BP to > 6,000 BP period of high biomass burning activity may also be related to forest successional sequences following the removal of the Laurentide ice sheet. This paper explains how ice cores can be used to develop records of biomass burning and offers suggestions for future studies.

Temporal variability of Pb, Cd and Pb isotope deposition in central Greenland
Sherrell, R. M., and E. Boyle
In Review

A subseasonally resolved record of Pb and Cd concentrations in central Greenland snow reveals 35-fold and 20-fold variations, respectively. The dominant feature of the record is an annual spring peak for both metals, coincident with anthropogenic sulfate. No secular trend in Pb or Cd deposition flux for the decade can be distinguished against intra- and interannual variability. Lead isotopic composition in the spring concentration peaks indicates a mixture of Eurasian Pb sources, consistent with a factor of two or smaller concentration trend over the 1980's. Similar high-resolution studies of older sequences may be important for discerning long-term anthropogenic and climate-related trends from natural short-term variability in records of trace metals in recent and ancient polar ice and snow. Initial results from older samples indicate that Pb and Cd concentrations increased roughly in parallel over the last 300 years; concentrations of both metals show 2-fold increases between 1699 and ~1780, and a second doubling by the 1980's. This change is broadly consistent with a published history of Pb evolution in northern Greenland, and suggests linked pre-automotive anthropogenic sources for Pb and Cd.

Holocene climatic instability: A large event 8000-8400 years ago
Alley, R.B., P.A. Mayewski, T. Sowers, M. Stuiver, K.C. Taylor,
In Review

The largest Holocene climate event in Greenland ice-core proxies, with approximately half the amplitude of the Younger Dryas, occurred ~8000 to 8400 years ago. This Holocene event affected regions well beyond the North Atlantic basin, as shown by synchronous increases in windblown chemical indicators together with a large decrease in methane. Widespread proxy records from the tropics to the north polar regions show a short-lived cool, dry, or windy event of similar age. The spatial pattern of terrestrial and marine changes is similar to that of the Younger Dryas event, suggesting a role for the North Atlantic thermohaline circulation. Possible forcings identified thus far for this Holocene event are small, consistent with recent models results of high sensitivity and strong linkages in the climate system.