GRIP Ice Core Research Articles

Annually resolved events of Younger Dryas glaciation in Lochaber (Glen Roy and Glen Spean), western Scottish Highlands

AbstractThis paper presents the results of micromorphological analysis of laminated sediments that accumulated in ice‐dammed lakes in Lochaber (Glen Roy and vicinity) during the Younger Dryas (Loch Lomond) Stadial. These lakes were responsible for the formation of the famous ‘Parallel Roads of Glen Roy’ (Agassiz, 1840), prominent shorelines cut into the valley sides of Glen Roy and adjacent valleys. Annually deposited (varved) layers, which can be distinguished from other rhythmites by micromorphological examination, have enabled the construction of a varve chronology which underpins the glacial history of the region, the duration of the lake stands and rates of ice margin advance and retreat. The lake system existed for a total of 515 a. During a rise in lake levels, the lowermost (260 m), middle (325 m) and highest (350 m) lakes existed for minimal periods of 191, 112 and 116 a, respectively, and the fall of lake levels from 350 m to 260 m took 95 years. Ice advance rates of between 13.4 and 41.9 m a−1 are inferred, while ice retreat is estimated to have been ∼38.5 m a−1. A provisional correlation between the Lochaber varve and GRIP ice core records suggests that the lakes started to form at ca. 12 165 a BP, in turn implying that the Loch Lomond Readvance limits in this area were not achieved until late in the Younger Dryas interval, a conclusion which does not accord with that based on numerical model simulations. Copyright © 2010 John Wiley & Sons, Ltd.

Taking the pulse of the Sun during the Holocene by joint analysis of 14C and 10Be

We have studied solar variations during the Holocene (i.e., last ∼11,700 yr) by combining a new model of the Earth's dipole moment with 14C data from the IntCal04 record and 10Be data from the GRIP ice core. Joint spectral analysis of the two nuclide records suggests that the periodic behavior of the Sun was particularly pronounced between 6000–4500 yr BP and 3000–2000 yr BP, with dominating periodicities of ∼88, ∼150, ∼220, and ∼400 years, while this rhythmic behavior faded during other time intervals. The fact that the two reconstructions, based on radionuclides with distinct geochemical properties, agree with respect to both the frequency and timing of the periodic behavior, strongly suggests that they reflect the actual behavior of the Sun. Subtle but systematic differences between the amplitude spectra may point to an interplay between the climate system and the ∼220‐ and ∼400‐year solar cycles during intervals when these were particularly prominent.

40Ar/ 39Ar, K–Ar and 230Th– 238U dating of the Laschamp excursion: A radioisotopic tie-point for ice core and climate chronologies

A brief period of enhanced 10Be flux that straddles the interstadial warm period known as Dansgaard–Oeschger event 10 in Greenland and its counterpart in Antarctica, the Antarctic Isotope Maximum 10 is but one consequence of the weakening of Earth's magnetic field associated with the Laschamp excursion. This 10Be peak measured in the GRIP ice core is dated at 41,250 y b2k (= before year 2000 AD) in the most recent GICC05 age model obtained from the NorthGRIP core via multi-parameter counting of annual layers. Uncertainty in the age of the 10Be peak is, however, no better than ± 1630 y at the 95% confidence level, reflecting accumulated error in identifying annual layers. The age of the Laschamp excursion [Guillou, H., Singer, B.S., Laj, C., Kissel, C., Scaillet, S., Jicha, B., 2004. On the age of the Laschamp geomagnetic excursion. Earth Planet. Sci. Lett. 227, 331-343.] is revised on the basis of new 40Ar/ 39Ar, unspiked K–Ar and 238U– 230Th data from three lava flows in the Massif Central, France, together with the 40Ar/ 39Ar age of a transitionally magnetized lava flow at Auckland, New Zealand. Combined, these data yield an age of 40,700 ± 950 y b2k, where the uncertainty includes both analytical and systematic ( 40K and 230Th decay constant) errors. Taking the radioisotopic age as a calibration tie point suggests that the layer-counting chronologies for the NorthGRIP and GISP2 ice cores are more accurate and precise than previously thought at depths corresponding to the Laschamp excursion.

Resolving climate change in the period 15–23 ka in Greenland ice cores: a new application of spectral trend analysis

AbstractNorthern Hemisphere climate history through and following the Last Glacial Maximum is recorded in detail in ice cores from Greenland. However, the period between Greenland Interstadials 1 and 2 (15–23 ka), i.e. the period of deglaciation following the last major glaciation, has been difficult to resolve in great detail. We here offer a new subdivision of this in the NGRIP, GRIP and GISP2 ice cores, by newly introducing spectral trend analysis to the study of climate‐related data series from ice cores. This analysis reveals patterns of change and discontinuity in the waveform properties of a data series, relating to the environmental (including climatic) history of accumulation of the rock or ice record. The application allows high‐resolution correlation between the ice cores, and a greatly improved subdivision of the study interval. Nine climatic phases are recognized, within which more identifiable events can also be correlated between the three locations.

Direct observation of salts as micro-inclusions in the Greenland GRIP ice core

AbstractWe provide the first direct evidence that a number of water-soluble compounds, in particular calcium sulfate (CaSO4·2H2O) and calcium carbonate (CaCO3), are present as solid, micron-sized inclusions within the Greenland GRIP ice core. The compounds are detected by two independent methods: micro-Raman spectroscopy of a solid ice sample, and energy-dispersive X-ray spectroscopy of individual inclusions remaining after sublimation. CaSO4·2H2O is found in abundance throughout the Holocene and the last glacial period, while CaCO3 exists mainly in the glacial period ice. We also present size and spatial distributions of the micro-inclusions. These results suggest that water-soluble aerosols in the GRIP ice core are dependable proxies for past atmospheric conditions.

Age–depth correlation, grain growth and dislocation-density evolution, for three ice cores

AbstractTwo previous theoretical analyses of data from the GRIP, Vostok and Byrd ice cores, presenting age–depth correlations, grain growth and dislocation-density evolution, are re-examined. It is found that the age–depth correlations are inconsistent with the idealized flow with unchanging history adopted, but that good correlations can be obtained by relaxing those restrictions. A modified grain-growth relation is proposed, consistent with the distinct growth profiles of the Vostok and other two cores, which can be solved simultaneously with the given dislocation-density evolution equation. These are solved for all three cores with the given parameters, and the depth profiles of grain diameter and dislocation density at the present time are determined with the new age–depth correlation and with that shown empirically in the papers. The varying flow history influences the age–depth correlation, and hence the depth profiles, which is important both for the interpretation of core data, and for the determination of constitutive variables at each depth at the present time.

For how long will the current grand maximum of solar activity persist?

Understanding the Sun's magnetic activity is important because of its impact on the Earth's environment. The sunspot record since 1610 shows irregular 11‐year cycles of activity; they are modulated on longer timescales and were interrupted by the Maunder minimum in the 17th century. Future behavior cannot easily be predicted – even in the short‐term. Recent activity has been abnormally high for at least 8 cycles: is this grand maximum likely to terminate soon or even to be followed by another (Maunder‐like) grand minimum? To answer these questions we use, as a measure of the Sun's open magnetic field, a composite record of the solar modulation function Φ, reconstructed principally from the proxy record of cosmogenic 10Be abundances in the GRIP icecore from Greenland. This Φ record extends back for almost 10,000 years, showing many grand maxima and grand minima (defined as intervals when Φ is within the top or bottom 20% of a Gaussian distribution). We carry out a statistical analysis of this record and calculate the life expectancy of the current grand maximum. We find that it is only expected to last for a further 15–36 years, with the more reliable methods yielding shorter expectancies, and we therefore predict a decline in solar activity within the next two or three cycles. We are not able, however, to predict the level of the ensuing minimum.

The impact of Dansgaard–Oeschger cycles on the loessic environment and malacofauna of Nussloch (Germany) during the Upper Weichselian

AbstractA loess sequence has been sampled continuously at high resolution in Nussloch (Rhine Valley, Germany) for malacological and grain-size analyses between ca. 34 and 20 ka. Molluscan abundance and richness, percentage in hygrophilous species and grain-size index show cyclical variations related to the lithological loess–gley alternation. Major molluscan abundance maxima were triggered by temperature increases through an enhancement of the reproduction cycle, whereas cyclical richness fluctuations and percentage in hygrophilous species reflect variations in local humidity and changes in the environmental mosaic. Malacological parameters allow the distinction of four environmental phases organised in cyclical successions correlated with most of the loess–gley doublets. The correlation of the grain-size index of the Nussloch loess sequence with the dust content of the GRIP ice core demonstrates the synchronicity of major molluscan abundance maxima and δ18O increases characterising temperature increases during Dansgaard–Oeschger interstades. A schematic model is proposed to link the North Atlantic Dansgaard–Oeschger climatic oscillations with local environmental changes indicated by both malacofauna and pedostratigraphy. This malacological study of the Nussloch loess sequence thus provides new information about the response of terrestrial loessic palaeoenvironments to millennial-timescale climatic fluctuations during the Upper Weichselian (∼ marine isotope stage 2 (MIS 2) and end of MIS 3).

A Holocene tephra record from the Lofoten Islands, Arctic Norway

Pilcher, J., Bradley, R. S., Francus, P. & Anderson, L. 2005 (May): A Holocene tephra record from the Lofoten Islands, Arctic Norway. Boreas, Vol. 34, pp. 136–156. Oslo. ISSN 0300–9483. A tephrochronology has been established for a peat bog in the Lofoten Islands that provides a dating framework for future lake and bog studies of climate variation in this climatically sensitive area. Twenty-three tephra layers were identified, all apparently of Icelandic origin. These included the historically dated tephras of AD 1875 (Askja), AD 1362 (Öraefajökull), AD 1158 (Hekla), AD 1104 (Hekla) and the Landnam tephra identified at AD 875 in the GRIP ice core. Other layers, previously radiocarbon dated in Ireland and elsewhere, include the Hekla eruptions of c. 2310 BC and c. 5990 BC. The basal clays below the peat contain tephra of both the Askja eruption of c. 9500 BC (10 000 radiocarbon years BP) and the well-known Vedde Ash of c. 12 000 BP (10 030 80 BC in GRIP ice core).

Synchronizing ice cores from the Renland and Agassiz ice caps to the Greenland Ice Core Chronology

Four ice cores from the Agassiz ice cap in the Canadian high arctic and one ice core from the Renland ice cap in eastern Greenland have been synchronized to the Greenland Ice Core Chronology 2005 (GICC05) which is based on annual layer counts in the DYE‐3, GRIP and NGRIP ice cores. Volcanic reference horizons, seen in electrical conductivity measurements (ECM) have been used to carry out the synchronization throughout the Holocene. The Agassiz ice cores have been matched to the NGRIP ice core ECM signal, while the Renland core has been matched to the GRIP ice core ECM signal, thus tying the cores to GICC05. Furthermore, it has been possible to synchronize the Renland ice core to NGRIP‐GICC05 in the glacial period back to 60,000 years b2k (years before A.D. 2000), on the basis of a matching of transitions between stadials and interstadials. This work brings the total number of ice core records that have been rigorously tied to the GICC05 timescale up to nine. Renland annual layer thicknesses are increasing with depth during the period from 7 to 8.5 ka b2k, a highly unusual observation only matched by a similar thickness increase in the glacial section of the Renland core some 60 ka ago. Annual layer thicknesses in the Agassiz ice cores point to a well‐developed Raymond bump in the Agassiz ice cap.

A relationship between ion balance and the chemical compounds of salt inclusions found in the Greenland Ice Core Project and Dome Fuji ice cores

We have proposed a method of deducing the chemical compounds found in deep polar ice cores by analyzing the balance between six major ions (Cl−, NO3−, SO42−, Na+, Mg2+, and Ca2+). The method is demonstrated for the Holocene and last glacial maximum regions of the Dome Fuji and GRIP ice cores. The dominant compounds depend only on the ion balance and the sequence of chemical reactions. In priority order, the principle salts are calcium sulfate, other sulfates, nitrate, chloride, and carbonate. The chemical abundances deduced by this method agree well with the results of Raman spectroscopy on individual salt inclusions. The abundances in the ice cores are shown to reflect differences in climatic periods (the acidic environment of the Holocene versus the reductive environment of the last glacial maximum) and regional conditions (the marine environment of Antarctica versus the continental environment of Greenland).

Comment on “A synchronized dating of three Greenland ice cores throughout the Holocene” by B. M. Vinther et al.: No Minoan tephra in the 1642 B.C. layer of the GRIP ice core

Denton, J. S., Pearce, N. J. G. (2008). Comment on “A synchronized dating of three Greenland ice cores throughout the Holocene” by B. M. Vinther et al.: No Minoan tephra in the 1642 B.C. layer of the GRIP ice core. Journal of Geophysical Research, 113, D04303, 7 PP

Synchronization of the NGRIP, GRIP, and GISP2 ice cores across MIS 2 and palaeoclimatic implications

We here present a synchronization of the NGRIP, GRIP, and GISP2 ice cores based mainly on volcanic events over the period 14.9–32.45 ka b2k (before AD 2000), corresponding to Marine Isotope Stage 2 (MIS 2) and the end of MIS 3. The matching provides a basis for applying the recent NGRIP-based Greenland Ice Core Chronology 2005 (GICC05) time scale to the GRIP and GISP2 ice cores, thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores. Based on the matching, a period of anomalous high accumulation rates in the GISP2 ice core is detected within the period 16.5–18.3 ka b2k. The δ 18 O and [ Ca 2 + ] profiles of the three cores are presented on the common GICC05 time scale and generally show excellent agreement across the stadial–interstadial transitions and across the two characteristic dust events in Greenland Stadial 3. However, large differences between the δ 18 O and [ Ca 2 + ] profiles of the three cores are seen in the same period as the 7–9% increase in the GISP2 accumulation rate. We conclude that changes of the atmospheric circulation are likely to have occurred in this period, altering the spatial gradients in Greenland and resulting in larger variations between the records.

Modelling binge–purge oscillations of the Laurentide ice sheet using a plastic ice sheet

AbstractA simple combined heat and ice-sheet model has been used to calculate temperatures at the base of the Laurentide ice sheet. We let the ice sheet surge when the basal temperature reaches the pressure-melting temperature. Driving the system with the observed accumulation and temperature records from the GRIP ice core, Greenland, produces surges corresponding to the observed Heinrich events. This suggests that the mechanism of basal sliding, initiated when the basal temperature reaches the melting point, can explain the surges of the Laurentide ice sheet. This study highlights the importance of the surface temperature and accumulation rate as a means of forcing the timing and strength of the Heinrich events, thus implying important ice-sheet climate feedbacks.

Recycling of cosmogenic nuclides after their removal from the atmosphere; special case of appreciable transport of 10Be to polar regions by aeolian dust

In this paper we discuss the general problem of recirculation of atmospheric cosmogenic isotopes after their initial removal from the atmosphere. Practically all nuclides are recycled after their removal from the atmosphere. The noble gas radio-nuclides re-circulate between the atmosphere and the hydrosphere; the fraction of time spent in these reservoirs depends on their solubility and half-lives. Radiocarbon atoms spend most of their life-time in the oceans before being removed to the sediments. All cosmogenic nuclides which are removed from the atmosphere by wet precipitations spend most of their life-time in the hydrosphere or in sediments. A special exception arises in the case of nuclides such as 10Be and 26Al, which are particle-active and adhere to aerosols and top soils in the lithosphere. Strong winds dislodge surface particles and transport the smaller particles to great distances. We discuss the special case of the transport of particle reactive 10Be via aeolian dust, which can result in appreciable 10Be fluxes in polar regions in cold climates, vis-à-vis its direct deposition from the atmosphere. We compare estimated concentrations of dust transported 10Be with the measured total 10Be concentrations in Antarctica in the Vostok and Taylor Dome ice cores, and atmospheric 10Be concentrations in Greenland in the GISP and GRIP ice cores. During certain epochs, high aeolian dust concentrations contribute significantly to 10Be fluxes in Greenland, comparable to or greater than atmospheric 10Be fluxes. In the Antarctica, however, even during epochs of high dust fluxes, the aeolian 10Be contributions are < 10% of the atmospheric 10Be fluxes. These results imply that great care should be taken in analyzing 10Be concentrations in Greenland especially!

Direct north-south synchronization of abrupt climate change record in ice cores using Beryllium 10

Abstract. A new, decadally resolved record of the 10Be peak at 41 kyr from the EPICA Dome C ice core (Antarctica) is used to match it with the same peak in the GRIP ice core (Greenland). This permits a direct synchronisation of the climatic variations around this time period, independent of uncertainties related to the ice age-gas age difference in ice cores. Dansgaard-Oeschger event 10 is in the period of best synchronisation and is found to be coeval with an Antarctic temperature maximum. Simulations using a thermal bipolar seesaw model agree reasonably well with the observed relative climate chronology in these two cores. They also reproduce three Antarctic warming events observed between A1 and A2.

Early Holocene climate oscillations recorded in three Greenland ice cores

A new ice core chronology for the Greenland DYE-3, GRIP, and NGRIP ice cores has been constructed, making it possible to compare the δ 18 O and accumulation signals recorded in the three cores on an almost annual scale throughout the Holocene. We here introduce the new time scale and investigate δ 18 O and accumulation anomalies that are common to the three cores in the Early Holocene (7.9–11.7 ka before present). Three time periods with significant and synchronous anomalies in the δ 18 O and accumulation signals stand out: the well-known 8.2 ka event, an event of shorter duration but of almost similar amplitude around 9.3 ka before present, and the Preboreal Oscillation during the first centuries of the Holocene. For each of these sections, we present a δ 18 O anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the Greenland ice cap.

Methane gas release from the Storegga submarine landslide linked to earlyHolocene climate change: a speculative hypothesis

The 3000 km3 Storegga submarine landslide occurred c. 8150 years ago from an area rich in gas hydrates off the western coast of Norway. A synchronous increase of 80—100 ppb in atmospheric methane concentrations is recorded in the Greenland GRIP ice core. This increase is hypothesized to reflect methane releases from the Storegga slide debris at an estimated rate of 20—25 Tg/yr for several hundred years following the slide. Methane is a powerful greenhouse gas, and methane release from the Storegga submarine landslide may have contributed to the rapid termination of the brief but intense 8200 yr cold event and the subsequent evolution of Holocene climate.

Variable 10Be fluxes in lacustrine sediments from Tristan da Cunha, South Atlantic: a solar record?

A 650-yr-long sediment sequence from a crater lake on Tristan da Cunha, South Atlantic, was analysed for its 10Be content. Based on 14C dating, and sedimentary, geochemical, magnetic and palynological records, the period between 900 and 1450 AD appears to have been unusually stable in terms of sedimentation and vegetation and therefore this period was chosen for analysis of the 10Be content. During this period of highly organic sedimentation and closed vegetation, the pattern of 10Be flux variations follows the 10Be fluctuations from the GRIP ice core and estimated 14C production rates well. However, before and after this stable period, variable sedimentation rates have to be accounted for to obtain results that are comparable to the established 10Be/ 14C records. Our data show not only the possibility of obtaining detailed enough 10Be flux data from sedimentary sequences to reconstruct past solar forcing but also how sensitive this type of record is to sedimentary and environmental changes. If suitable archives can be found, they have the potential to improve reconstructions of solar activity far back in time.

Gas isotopes in ice reveal a vegetated central Greenland during ice sheet invasion

Environmental conditions prevailing during build‐up of the Greenland Ice Sheet (GIS) are not yet established. Here we use results from gas isotopes from basal ice of the GRIP ice core to show that central Greenland was vegetated during invasion by the ice sheet. The δ13CCH4 and δ18O of O2 values obtained were never encountered before in ice core studies. Such values are indeed the signature of a significant biological activity.