Greenland Ice Sheet Project 2 Ice Core Research Articles

Post-bubble close-off fractionation of gases in polar firn and ice cores: effects of accumulation rate on permeation through overloading pressure

Abstract. Gases in ice cores are invaluable archives of past environmental changes (e.g., the past atmosphere). However, gas fractionation processes after bubble closure in the firn are poorly understood, although increasing evidence indicates preferential leakages of smaller molecules (e.g., neon, oxygen, and argon) from the closed bubbles through the ice matrix. These fractionation processes are believed to be responsible for the observed millennial δO2/N2 variations in ice cores, linking ice core chronologies with orbital parameters. In this study, we investigated high-resolution δAr/N2 of the GISP2 (Greenland Ice Sheet Project 2), NGRIP (North Greenland Ice Core Project), and Dome Fuji ice cores for the past few thousand years. We find that δAr/N2 at multidecadal resolution on the "gas-age scale" in the GISP2 ice core has a significant negative correlation with accumulation rate and a positive correlation with air contents over the past 6000 years, indicating that changes in overloading pressure induced δAr/N2 fractionation in the firn. Furthermore, the GISP2 temperature and accumulation rate for the last 4000 years have nearly equal effects on δAr/N2 with sensitivities of 0.72 ± 0.1 ‰ °C−1 and −0.58 ± 0.09 ‰ (0.01 m ice year−1)−1, respectively. To understand the fractionation processes, we applied a permeation model for two different processes of bubble pressure build-up in the firn, "pressure sensitive process" (e.g., microbubbles: 0.3–3 % of air contents) with a greater sensitivity to overloading pressures and "normal bubble process". The model indicates that δAr/N2 in the bubbles under the pressure sensitive process are negatively correlated with the accumulation rate due to changes in overloading pressure. On the other hand, the normal bubbles experience only limited depletion (< 0.5 ‰) in the firn. Colder temperatures in the firn induce more depletion in δAr/N2 through thicker firn. The pressure sensitive bubbles are so depleted in δAr/N2 at the bubble close-off depth that they dominate the total δAr/N2 changes in spite of their smaller air contents. The model also indicates that δAr/N2 of ice cores should have experienced several per mil of depletion during the storage 14–18 years after coring. Further understanding of the δAr/N2 fractionation processes in the firn, combined with nitrogen and argon isotope data, may lead to a new proxy for the past temperature and accumulation rate.

Variation in the Indian summer monsoon intensity during the Bølling‐Ållerød and Holocene

Variations in the Indian summer monsoon (ISM) intensity during the last 16.7 ka have been studied using organic carbon (Corg), δ15N of sedimentary organic matter, CaCO3, sediment texture, δ18OC, and Mg/Ca‐derived sea surface temperature, δ18O of sea water and sea surface salinity, in a 14C‐dated sediment core from the eastern Arabian Sea. The δ18O in water and planktonic foraminifera shells off the central west coast of India may be controlled by the ISM intensity as this area receives high precipitation and land runoff. Also, the Corg and CaCO3 contents of sediments and δ15N of sedimentary organic matter may be linked to ISM‐induced productivity and denitrification. The results of the present study reveal that between 16 and 15.2 ka BP, the ISM was weak with minor fluctuations and started intensifying around 15.2 ka BP, at the onset of the Bølling‐Ållerød (B‐A) event. The B‐A event is characterized by higher water column denitrification rates comparable to the present day. The ISM signatures observed in the δ18OC record of B‐A event compare well with those from Timta cave of the western Himalayas and also the Asian summer monsoon signatures from the Hulu caves in China and warming signatures in Greenland Ice Sheet Project 2 (GISP2) suggesting atmospheric teleconnections through Intertropical Convergence Zone. The boundary between the Younger Dryas and the Holocene is discernible with small episodes of abrupt events of increased ISM intensity. This decrease in δ18OC values at ~11.8 ka BP is contemporary with June solar insolation maximum at 30° north and the increase in methane in the GISP2 ice core supporting episodes of warmer climate and increase in ISM intensity. The ISM seems to have been most stable between 7 and 5.6 ka BP. The core exhibits periodicity of 500 years that is comparable to the Atlantic water formation and the Chinese monsoon.

Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas

One explanation of the abrupt cooling episode known as the Younger Dryas (YD) is a cosmic impact or airburst at the YD boundary (YDB) that triggered cooling and resulted in other calamities, including the disappearance of the Clovis culture and the extinction of many large mammal species. We tested the YDB impact hypothesis by analyzing ice samples from the Greenland Ice Sheet Project 2 (GISP2) ice core across the Bølling-Allerød/YD boundary for major and trace elements. We found a large Pt anomaly at the YDB, not accompanied by a prominent Ir anomaly, with the Pt/Ir ratios at the Pt peak exceeding those in known terrestrial and extraterrestrial materials. Whereas the highly fractionated Pt/Ir ratio rules out mantle or chondritic sources of the Pt anomaly, it does not allow positive identification of the source. Circumstantial evidence such as very high, superchondritic Pt/Al ratios associated with the Pt anomaly and its timing, different from other major events recorded on the GISP2 ice core such as well-understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction, hints for an extraterrestrial source of Pt. Such a source could have been a highly differentiated object like an Ir-poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis.

Dating the Siple Dome (Antarctica) ice core by manual and computer interpretation of annual layering

AbstractThe Holocene portion of the Siple Dome (Antarctica) ice core was dated by interpreting the electrical, visual and chemical properties of the core. The data were interpreted manually and with a computer algorithm. The algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the GISP2 (Greenland Ice Sheet Project 2) ice core, 10Be stratigraphic ties to the dendrochronology 14 C record and the dated volcanic stratigraphy. The algorithm interpretation is more consistent and better quantified than the tedious and subjective manual interpretation.

Extraterrestrial accretion from the GISP2 ice core

The rate of extraterrestrial accretion for particles in the size range 0.45 μm to ∼20 μm was determined from dust concentrates extracted from Greenland Ice Sheet Project 2 (GISP2) ice core samples. Using instrumental neutron activation analysis (INAA), we determined the iridium (Ir) content of the dust. Following a core-specific correction for terrestrial Ir and assuming a chondritic Ir abundance of 500 ppb, we measure an average accretion rate for 0.45 μm to ∼20 μm particles over the entire Earth of 0.22 (± 0.11) × 10 9 g/yr (kton/yr) for 317 years of ice through the interval 6 to 20 ka. This is consistent with the interplanetary dust accretion rate of 0.17 (± 0.08) x 10 9 g/yr that we derive from published 3He data for the GISP2 core. Accounting for particles that are larger and smaller than those detected by or experiment, our best estimate of the total accretion rate (including particle sizes up to about 4 cm in diameter) is 2.5 × 10 9 g/yr. The uncertainty in this estimate is dominated by statistical fluctuations in the number of particles expected to end up in the ice core and not by measurement error. Based on Monte Carlo simulations, we estimate the upper limit for total extraterrestrial accretion to Earth of 6.25 × 10 9 g/yr (95% confidence level). This accretion rate is consistent with some estimates from micrometeorite concentrations in polar ice, estimates from ground-based radar studies, and with accretion estimates of 3He-bearing interplanetary dust particles, assuming that 3He is correlated with particle surface area. It is, however, lower than estimates based on platinum group element studies of marine sediments. The conflict may indicate systematic errors with either the marine or the non-marine samples, departures from the assumed particle spectrum of Grün and coauthors, or time-variable accretion rates, with the early Holocene period being characterized by low levels of accretion.

On the origin and timing of rapid changes in atmospheric methane during the Last Glacial Period

We present high resolution records of atmospheric methane from the GISP2 (Greenland Ice Sheet Project 2) ice core for four rapid climate transitions that occurred during the past 50 ka: the end of the Younger Dryas at 11.8 ka, the beginning of the Bølling‐Allerød period at 14.8 ka, the beginning of interstadial 8 at 38.2 ka, and the beginning of interstadial 12 at 45.5 ka. During these events, atmospheric methane concentrations increased by 200–300 ppb over time periods of 100–300 years, significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record. We suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change. We find no evidence for rapid, massive methane emissions that might be associated with large‐scale decomposition of methane hydrates in sediments. With additional results from the Taylor Dome Ice Core (Antarctica) we also reconstruct changes in the interpolar methane gradient (an indicator of the geographical distribution of methane sources) associated with some of the rapid changes in atmospheric methane. The results indicate that the rise in methane at the beginning of the Bølling‐Allerød period and the later rise at the end of the Younger Dryas were driven by increases in both tropical and boreal methane sources. During the Younger Dryas (a 1.3 ka cold period during the last deglaciation) the relative contribution from boreal sources was reduced relative to the early and middle Holocene periods.

Possible solar influences on the dust profile of the GISP2 Ice Core from central Greenland

The Greenland Ice Sheet Project 2 (GISP2) ice core dust profile in glacial (Wisconsinan) ice from Central Greenland has been measured using Laser‐Light Scattering (LLS) from ice. This data exhibits considerable high frequency variability. By applying appropriate running averages to the data, certain regularities emerge. Thus, for example, when the data was smoothed with rectangular 4 and 5 year running averages, ∼11 year dust modulations of considerable amplitude were revealed. In this paper, we show how further smoothing of the data causes very large, longer period dust modulations centered at ∼91 years in a Gaussian distribution to emerge. We believe that this corresponds to the 80–90 year modulation of the 11 year sunspot cycle first suggested by Gleissberg. We also show how adjacent 11 year dust periods can combine in a unique way to generate a 22 year (Hale) period of dust modulation. The way this occurs is similar to that by which a 22 year modulation of the measured terrestrial neutron flux is generated from two 11 year periods. Taken together with our observation of a ∼200 year (Suess) dust modulation period, these observations strengthen our claim that the dust modulations we measured in GISP2 ice are solar induced and suggest a mechanism for their production.

Interdisciplinary investigations of the end of the Norse Western Settlement in Greenland

The loss of the Norse Western Settlement in Greenland around the mid-fourteenth century has long been taken as a prime example of the impact of changing climate on human populations. This study employs an interdisciplinary approach combining historical documents, detailed archaeological investigations, and a high-resolution proxy climate record from the Greenland Ice Sheet Project 2 (GISP2) to investigate possible causes for the end of this settlement. Historical climate records, mainly from Iceland, contain evidence for lowered temperatures and severe weather in the north Atlantic region around the mid-fourteenth century. Archaeological, palaeoecological and historical data specifically concerning the Western Settlement suggest that Norse living conditions left little buffer for unseasonable climate, and provide evidence for a sudden and catastrophic end around the mid-fourteenth century. Isotopic data from the GISP2 ice core provide annual- and seasonal-scale proxy-temperature signals which suggest multiyear intervals of lowered temperatures in the early and mid-fourteenth century. The research synthesized here suggests that, while periods of unfavourable climatic fluctuations are likely to have played a role in the end of the Western Settlement, it was their cultural vulnerabilities to environmental change that left the Norse far more subject to disaster than their Inuit neigh bours.

An interlaboratory comparison of techniques for extracting and analyzing trapped gases in ice cores

We undertook an interlaboratory comparison of techniques used to extract and analyze trapped gases in ice cores. The intercomparison included analyses of standard reference gases and samples of ice from the Greenland Ice Sheet Project 2 (GISP2) site. Concentrations of CO2, CH4, the δ;18O of O2, the δ15N of N2, and the O2/N2, and Ar/N2 ratios were measured in air standards and ice core samples. The standard reference scales for CO2 and CH4 were consistent at the ±2% level. The δO2/N2 and δ18O of O2 measurements showed substantial deviations between the two laboratories able to measure these ratios. The deviations are probably related to errors associated with calibration of the working standards. The δArN2 and δ15N of N2 measurements were consistent. Five laboratories analyzed the CH4 concentration in a 4.2‐m section of the GISP2 ice core. The average of 20 discrete CH4 measurements was 748±10 parts per billion by volume (ppbv). The standard deviation of these measurements was close to the total analytical uncertainty associated with the measurements. In all cases, those laboratories employing a dry extraction technique determined higher CH4 values than laboratories using a wet extraction technique. The origin of this difference is unclear but may involve uncertainties associated with blank corrections. Analyses of the CO2 concentration of trapped gases showed extreme variations which cannot be explained by analytical uncertainties alone. Three laboratories measured the [CO2] on 21 discrete depths yielding an average value of 283±13 parts per million by volume (ppmv). In this case, the standard deviation was roughly a factor of 2 greater than the analytical uncertainties. We believe the variability in the measured [CO2] results from impurities in the ice which may have compromised the [CO2] of trapped gases in Greenland ice.

Continuous dust concentration profile of pre‐Holocene ice from the Greenland Ice Sheet Project 2 ice core: Dust stadials, interstadials, and the Eemian

In this paper, we present and discuss the pre‐Holocene dust profile of the Greenland Ice Sheet Project 2 (GISP2) ice core retrieved from central Greenland measured using laser/light scattering (LLS) from ice and compare it with the electrical conductivity method and oxygen isotope profiles. We describe how we dated the pre/Holocene ice using the annual dust peaks observed with LLS (starting from the accepted chronology to 2250 m) and obtained a chronology in substantial accord with the gas‐age dating of the ice. We also show that the GISP2 ice core penetrated the Eemian and that a record of a 10.2‐kyr penultimate glaciation is present in the GISP2 core.

Is There Evidence for Solar Forcing of Climate in the GISP2 Oxygen Isotope Record?

Changes in solar constant over an 11 yr cycle suggest a certain, but limited, degree of solar forcing of climate. The high-resolution climate (oxygen isotope) record of the Greenland GISP2 (Greenland Ice Sheet Project 2) ice core has been analyzed for solar (and volcanic) influences. The atmospheric14C record is used as a proxy of solar change and compared to the oxygen isotope profile in the GISP2 ice core. An annual oxygen isotope profile is derived from centimeter-scale isotope measurements available for the post-A.D. 818 interval. Associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium. The detailed record of volcanic aerosols, converted to optical depth and volcanic explosivity change, was also compared to the isotope record and the oxygen isotope response calibrated to short-term volcanic influences on climate. This calibration shows that century-scale volcanic modulation of the GISP2 oxygen isotope record can be neglected in our analysis of solar forcing. The timing, estimated order of temperature change, and phase lag of several maxima in14C and minima in18O are suggestive of a solar component to the forcing of Greenland climate over the current millennium. The fractional climate response of the cold interval associated with the Maunder sunspot minimum (and14C maximum), as well as the Medieval Warm Period and Little Ice Age temperature trend of the past millennium, are compatible with solar climate forcing, with an order of magnitude of solar constant change of ∼0.3%. Even though solar forcing of climate for the current millennium is a reasonable hypothesis, for the rest of the Holocene the century-scale events are more frequent in the oxygen isotope record than in the14C record and a significant correlation is absent. For this interval, oceanic/atmospheric circulation forcing of climate may dominate. Solar forcing during the surprisingly strong 1470 yr climate cycle of the 11,000–75,000 yr B.P. interval is rather hypothetical.

Major features of glaciochemistry over the last 110,000 years in the Greenland Ice Sheet Project 2 ice core

Major chemical species (Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+, Ca2+) and δ18O 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 δ18O do not display any significant relationship. However, a strong inverse correlation was found between concentrations of the major chemical species and δ18O (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 inters t adials 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 inters t adials. 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.

Paleoenvironmental implications of the insoluble microparticle record in the GISP2 (Greenland) ice core during the rapidly changing climate of the Pleistocene–Holocene transition

Research Article| May 01, 1997 Paleoenvironmental implications of the insoluble microparticle record in the GISP2 (Greenland) ice core during the rapidly changing climate of the Pleistocene–Holocene transition Gregory A. Zielinski; Gregory A. Zielinski 1Climate Change Research Center, Institute for the Study of Earth, Oceans and Space and Department of Earth Science, University of New Hampshire, Durham, New Hampshire 03824 Search for other works by this author on: GSW Google Scholar Grant R. Mershon Grant R. Mershon 1Climate Change Research Center, Institute for the Study of Earth, Oceans and Space and Department of Earth Science, University of New Hampshire, Durham, New Hampshire 03824 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1997) 109 (5): 547–559. https://doi.org/10.1130/0016-7606(1997)109<0547:PIOTIM>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gregory A. Zielinski, Grant R. Mershon; Paleoenvironmental implications of the insoluble microparticle record in the GISP2 (Greenland) ice core during the rapidly changing climate of the Pleistocene–Holocene transition. GSA Bulletin 1997;; 109 (5): 547–559. doi: https://doi.org/10.1130/0016-7606(1997)109<0547:PIOTIM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Oscillations in the time series of insoluble microparticle characteristics between 0.7 and 11.0 μm in the Greenland Ice Sheet Project 2 (GISP2) ice core reflect changes in environmental conditions in the Northern Hemisphere from 10 500 to 14 000 yr ago. Elevated values in microparticle number and mass, especially during the Younger Dryas, are related to Northern Hemisphere aridity and the subsequent increase in dust available for long-range transport to Greenland. This scenario occurs with the colder climatic conditions that result from a more expanded (spatially and temporally) polar vortex. Peaks in mean grain size based on number (mean number diameter) are a proxy for increased strength in zonal winds (westerlies). Highs in mean number diameter in the earlier part of the record often coincide with number and mass peaks reflecting the increased temperature and pressure gradients with an expanded polar vortex. Highs in mean grain size based on mass (mean mass diameter) reflect greater deposition of the coarser size fraction, and thus are a proxy for increased storminess associated with better developed synoptic-scale pressure systems in the northernmost Atlantic region. Peaks in mean mass diameter often lead these other parameters by 100–200 yr, suggesting an increase in storminess with the initial southward migration of the mean position of the polar front prior to full development of a more expanded polar vortex. The general decline in number and mass trends (decreased aridity with a contracting polar vortex) together with increasing mean number diameter trends (strengthening zonal winds) following the maxima in the early Younger Dryas suggest an expansion of mid-latitude circulation systems (subtropical highs), thereby maintaining latitudinal temperature and pressure gradients. Increased variability in mean mass diameter during the warm Preboreal, compared to the colder Younger Dryas, may be a function of the greater seasonality during warmer climatic periods, and thus more frequent storms associated with higher frequency oscillations in the position of the polar front with changing seasons and increased interannual variability in climate. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Stratospheric loading and optical depth estimates of explosive volcanism over the last 2100 years derived from the Greenland Ice Sheet Project 2 ice core

The high‐resolution and lengthy records of volcanic aerosol deposition in ice cores allow assessment of the atmospheric impact of different styles and magnitudes of past eruptions and the impact of volcanism during periods of varied 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 H2SO4 and resulting optical depth values (τD = MD/1.5 × 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 3 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 of another signal at 43 B.C. suggests that at least two eruptions impacted climate in the middle decade of the 1st 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 thirteenth century A.D. may not have been sensitive enough to the atmospheric perturbation of 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.

Biomass burning record and black carbon in the GISP2 Ice Core

We have determined the black carbon concentration in three sets of ice core samples from the GISP2 (Greenland Ice Sheet Project 2) ice core. The major peaks in black carbon concentration between 320 and 330 A.D. correlate well with peaks in ammonium concentration and with the dips in electrical conductivity measurements (ECM), which allows us to identify extensive forest fires in this time period. The average black carbon concentration during the 320 to 330 A.D. decade is found to be 2.1 µg of black carbon per 1 kg of snow melt water. The current snow (1989 and 1990) from the GISP2 site shows an average black carbon concentration of about 2.0 µ/kg suggesting that the rate of black carbon deposition at the GISP2 Greenland site during 1989–1990 was about the same as 1670 years ago.