Greenland Ice Core Project Ice Core Research Articles

Greenland ice core evidence of the 79 AD Vesuvius eruption

Abstract. Volcanic tephra are independent age horizons and can synchronize strata of various paleoclimate records including ice and sediment cores. The Holocene section of the Greenland Ice Core Project (GRIP) ice core is dated by multi-parameter annual layer counting, and contains peaks in acidity, SO42− and microparticle concentrations at a depth of 429.1 to 429.3 m, which have not previously been definitively ascribed to a volcanic eruption. Here, we identify tephra particles and determine that volcanic shards extracted from a depth of 429.3 m in the GRIP ice core are likely due to the 79 AD Vesuvius eruption. The chemical composition of the tephra particles is consistent with the K-phonolitic composition of the Vesuvius juvenile ejecta and differs from the chemical composition of other major eruptions (≥ VEI 4) between 50–100 AD.

Determining the post-glacial evolution of a northeast Pacific coastal fjord using a multiproxy geochemical approachThis article is one of a series of papers published in this Special Issue on the theme Polar Climate Stability Network.

A 40.32 m piston core recovered from Effingham Inlet, on the west coast of Vancouver Island, provides the basis for a high-resolution geochemical study of the last deglaciation and the Holocene. Glacial retreat, basin isolation, sea-level rise, and productivity variations are determined using proxies for sediment composition (K/Al, Fe/Al, Mg/Al), grain size (Ti/Al, Zr/Al), sedimentary redox conditions (Mo/Al, U/Al), and productivity (wt.% organic carbon, wt.% opal). As local ice retreated and marine waters inundated the basin, coarse-grained glacimarine sediments were replaced by finer grained, laminated, opal-rich sediments. During meltwater pulse-1a, the dominance of local crustal rise over eustatic sea-level rise resulted in the progressive restriction of ocean circulation in Effingham Inlet and the formation of a temporary freshwater lake. The transition into stable Holocene conditions was initiated at ∼12 700 BP, which corresponds to the onset of the Younger Dryas, as identified by the Greenland Ice core Project (GRIP) ice core δ18O record and was completed by 10 700 BP, ∼800 years after the GRIP ice core record stabilized. Holocene Mo/Al and U/Al ratios range between 12–35 (×104) and 1–3.4 (×104), respectively, indicating that although large-amplitude, high-frequency fluctuations occur, the sediments of Effingham Inlet inner basin have remained organic rich and oxygen depleted for the entire Holocene period. The combination of anoxic bottom waters and a Holocene sedimentation rate of 217 cm/ka have preserved a high-resolution record of environmental change in the northeast Pacific over the last 11 000 years.

Evidence for stratigraphic distortion in the Greenland Ice Core Project (GRIP) ice core during Event 5e1 (120 kyr BP) from gas isotopes

The disturbed stratigraphy of the ice in the lowest 10% of the Greenland GRIP ice core has been previously demonstrated using gas measurements (δ18O of O2 and CH4) on a few meters depth scale. However, rapid ice isotopic variations (on the scale of 20 cm) are experienced in the bottom of the GRIP ice core with complex chemical signatures that make them difficult to reconcile with a disturbed stratigraphy of the ice. This is the case for event 5e1, first described as a dramatic cooling 120 kyr BP. We analyzed at a 5 cm resolution the isotopic composition of the air from 2 m of the GRIP bottom ice core covering event 5e1. The δ15N measurements, combined with a basic firn modeling, lead to the solid conclusion that the rapid event 5e1 is not a climatic event. Rapid variations of δ18O of O2 (δ18Oatm) are in agreement with a disturbed ice stratigraphy. However, the double peak shape of the δ18Oatm, recalling chemical data at the same depth, requires processes of diffusion after the mixing or even postcoring, placing limits to the interpretation of some classical paleoclimatic proxies in small scale mixed ice (<1 m).

A tentative reconstruction of the last interglacial and glacial inception in Greenland based on new gas measurements in the Greenland Ice Core Project (GRIP) ice core

The disturbed stratigraphy of the ice in the lowest 10% of the Greenland GRIP ice core prevents direct access to climatic information older than 110 kyr. This is especially regretful since this period covers the previous interglacial corresponding to marine isotopic stage 5e (MIS 5e, 130–120 kyr B.P.). Here we present a tentative reconstruction of the disturbed GRIP chronology based on the succession of globally well mixed gas parameters. The GRIP δ18Oice chronological sequence is obtained by comparing a new set of δ18O of atmospheric O2 and CH4 measurements from the bottom section of the GRIP core with their counterpart in the Vostok Antarctic profiles. This comparison clearly identifies ice from the penultimate glacial maximum (MIS 6, 190–130 kyr B.P.) in the GRIP core. Further it allows rough reconstruction of the last interglacial period and of the last glacial inception in Greenland which appears to lay its Antarctic counterpart. Our data suggest that while Antarctica is already entering into a glaciation, Greenland is still experiencing a warm maximum during MIS 5e.

The fast climate fluctuations during the stadial and interstadial climate states

AbstractRapid climate changes during the last glacial period were first observed in ice-core records (Dansgaard and others, 1982). These shifts between interstadials, called Dansgaard–Oeschger (D-O) events, and stadials or deep glaciation were later seen in Atlantic sediment records (Bond and others, 1993), pointing to the ocean circulation as a strong component in the dynamics of these shifts (Wright and Stocker, 1991). the interstadial states are observed to have a characteristic ``sawtooth’’ shape, indicating a gradual drift of the stable interstadial state toward the stable stadial state. In order to contrast the two climate states, we have separated the δ18O signal from the Greenland Icecore Project ice core into periods corresponding to the two states. the climate variability in the two different climatic states is different (Johnsen and others, 1997). We find that the standard deviation is significantly larger in the stadial than in the interstadial state. Both states are found to have a larger standard deviation than the Holocene part of the record. the correlation times in the different states are difficult to obtain because of limited data resolution and diffusion of the isotopic signal. However, using a statistical technique, we have estimated the correlation times. We do not find significant differences in the correlation times, which are of the order of months, in the different climatic states. These findings are interpreted in the context of a simple linear stochastic model which provides information about the relative roles of the climatic forcing and the stability of the climate state governing the climate variability.

A comparison of radio-echo sounding data and electrical conductivity of the GRIP ice core

AbstractThe depth of reflecting layers in Arctic ice sheets has been determined by electromagnetic echo sounding, using a varying distance between transmitter and receiver to determine the radar wave velocity. The depth of the radar reflecting layers is compared with a profile of electrical conductivity measurements (ECMs) from the Greenland Ice Core Project (GRIP) ice core, in order to determine the velocity of the radar waves in the ice cap. By using several reflecting layers, it is possible to isolate the firn correction of the wave velocity and to estimate the accuracy of the calculated electromagnetic wave velocity. The measured firn correction is compared with the correction calculated from the density profile, and a comparison between the depth profiles of ECM and radar based on the corrected electromagnetic wave velocity is presented. This profile shows that acid layers, which originate from major volcanic eruptions, show up as reflecting radar horizons.

Intra-interglacial cold events: an Eemian-Holocene comparison

Abstract Rapid oscillations between warm and cold climates have been found in the oxygen isotope record of the Greenland Ice-core Project (GRIP) ice core during the Eemian/Marine oxygen Isotope Stage (MIS) 5e. In contrast, the variability in Greenland Ice Sheet Project 2 (GISP2) ice core is significantly different and some Atlantic deep-sea records suggest no such climate variations. We present here a high-resolution (50–300 years) set of marine proxies from the low-latitude east Atlantic margin (ODP Site 658), which suggest that in general the Eemian was climatically very similar to the Holocene. We, however, observe that the upwelling intensity off the West African coast was greatly reduced during the early Eemian, corresponding to the very mild climate observed in the European lake records. We observe that MIS 5e contains one significant short cold spell (<400 years), which is marked by a reduction of upper North Atlantic deep water ventilation. We suggest this cold event may correlate with the cold interval found in the European terrestrial records. The cause of the intra-Eemian event was likely to be the freshening and cooling observed in the Norwegian Sea. This brief cold spell, however, did not affect the overall stability of MIS 5e, and moreover it has an analogue event in the Holocene ‘Sub-Boreal’ period. Marine and terrestrial records thus seem to be incompatible with those of the GRIP ice core record, supporting the suggestion that the GRIP record has been altered by ice tectonics.

Modeling the signal transfer of sea water δ18O to the δ18O of atmospheric oxygen using a diagnostic box model for the terrestrial and marine biosphere

We make use of a simple diagnostic box model to determine the sensitivities of the influencing parameters for the isotopic signal transfer of seawater oxygen to atmospheric oxygen. We calculate the δ18O of atmospheric oxygen from prescribed oxygen fluxes of the living and dead biomes on land and in the ocean, respectively. The model is driven by an assumed (experiment 1) or measured (experiments 2 and 3) temporal seawater δ18O signal and a land biomass estimation. In experiment 1, we calculated the required changes of several model parameters in order to study fast variations of δ18O of atmospheric oxygen as seen in the Greenland Ice Core Project (GRIP) ice at depths assigned to the Eemian time period. Our calculations support evidence of stratigraphic problems at these depths in the GRIP ice core. In experiment 2, we adjusted the model output, which was driven by the benthic seawater δ18O record from V19‐30, to the measured Greenland Ice Sheet Project 2 δ18O record of atmospheric oxygen for the last 110,000 years, by varying the model parameter. Single and multi‐parameter matchings were performed. The results for single‐parameter runs exceed the uncertainty ranges for most of the parameters, while multiparameter variations are well within these ranges. The model calculations are most sensitive to the land respiration factor. Our results support the findings of Van de Water et al. [1994] that the fractionations associated with biomes activities were most probably lower during cold periods, which could point to a combination of fractionations with different temperature dependencies. The model results indicate periods of higher marine biological activity during the ice age than today. Temporal variations of the model parameters show a double peak around 10000 and 8000 years ago, which could be associated with meltwater pulses, as shown in experiment 3. However, they are hardly the well‐known Fairbanks [Fairbanks et al., 1992] pulses since these occur 3000 to 4000 years earlier.

Textures and fabrics in the GRIP ice core

A comprehensive study of textures and fabrics has been carried out on the Greenland Ice Core Project (GRIP) ice core. Crystal sizes and c axis orientations have been measured on thin sections with conventional techniques, yielding new information on the growth, rotation and recrystallization of ice crystals in the Greenland Ice Sheet. Normal grain growth is found to persist to a depth of 700 m in the core, where the onset of polygonization due to increasing strain prevents a further increase in grain size in the Holocene ice. Smaller crystals are observed in the Wisconsin ice, larger crystals are found in the Eemian ice, and the crystal size is found to vary with climatic parameters in these periods. This dependence, which probably results from variable impurity content in the ice, persists to a depth of 2930 m. Coarse‐grained ice, probably resulting from rapid growth of crystals at comparatively high temperatures, is found in the lowest 100 m of the core. The data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet. A significant strengthening is not observed at the Holocene‐Wisconsin transition. The fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m. The evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear. Evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth. Stretched fabrics in coarse‐grained ice in the lowest 100 m could be due to tensional stresses; this ice is unlikely to be undergoing any significant horizontal deformation at the present time.

Flow properties of the ice from the Greenland Ice Core Project ice core: The reason for folds?

Long‐term deformation tests on ice from the Greenland Ice Core Project (GRIP) deep ice core show that ice from the different climate zones in the ice core has flow properties correlated with the concentrations of impurities in the sample. The deformation tests are performed by uniaxial unconfined compression at −16°C with an octahedral compression stress of 3 bars. The ice samples are compressed for ½ to 3 years until the tertiary strain rate is reached. It is believed that by the end all downhole flow conditions are forgotten and that the ice sample has settled in a state determined by the applied stress and temperature conditions. All samples are tested under the same stress and temperature conditions so the resulting deformation rates and final ice crystal size and fabrics can only differ due to varying impurity concentrations. The results show that ice from cold climatic periods with high concentrations of impurities deforms more slowly than ice from warm climatic periods in compression. When tertiary creep is reached, the crystal size is smaller in the cold ice than in the warm. The ice from warmer climatic periods with lower concentrations of impurities deforms at a factor of 2–3 times more rapidly in compression. The tertiary steady state crystal size is increased by 50% and the ice crystals have oriented more favorably for the applied compression in the warm ice, which is believed to be the reason why the strain rates are greater here than in the cold ice. In the bottom 200 m of the GRIP ice core, zones are observed with folds on the scale of 1–8 cm. An investigation of the ice layers in and around the folds shows that the layers are composed of ice from different climatic zones. The folding is believed to result from the different flow and rheological properties of the layers involved in the folding structures.

Raman spectroscopic study on the nitrogen/oxygen ratio in natural ice clathrates in the GRIP Ice Core

We have carried out Raman spectroscopic experiments on air clathrates in the GReenland Ice Core Project (GRIP) deep ice core. We present new N2/O2 measurements that markedly differ from previous measurements of the Dye‐3 ice core: the N2/O2 ratio we observe is much closer to atmospheric. This has new implications for the interpretation of gas distributions in ice sheets and the reconstruction of past atmospheric conditions.

The Eem Stable Isotope Record along the GRIP Ice Core and Its Interpretation

A 3029-m-long deep ice core extending nearly to bedrock has been drilled at the very top of the Greenland ice sheet (Summit) by the Greenland Ice-core Project (GRIP), an international European joint effort organized by the European Science Foundation. The ice core reaches back to 250,000 yr B.P. according to dating based partly on stratigraphic methods and partly on ice-flow modeling. A continuous and detailed stable isotope (δ18O) profile along the entire core depicts dramatic temperature changes in Greenland through the last two glacial cycles, including abrupt climatic shifts during the Eem/Sangamon Interglaciation, which is elsewhere recorded as a warm and stable period. The stratigraphic continuity of the Eemian layers has therefore been scrutinized. New ice core studies, comprising cloudy band observations, deconvolution, and frequency analyses, lead to the conclusion that the climate instability suggested during the Eem Interglaciation in Greenland is likely to be real, though no conclusive evidence is available. Whereas latitudinal displacements of the North Atlantic Ocean current are considered the immediate cause of the glacial climate instability, longitudinal displacements may be the immediate cause of the Eemian instability. If so, the Eemian climate changes will be much subdued outside the Arctic region and will probably only be recognizable in sedimentary sequences of high sensitivity and temporal resolution.