Ice Core Evidence Research Articles

Ice-core evidence of westerly and monsoon moisture contributions in the central Tibetan Plateau

AbstractStable isotopes are a primary tool for inferring past temperature changes and atmospheric moisture variability from ice cores. A 33 m ice core representing the period 1850–2004 was retrieved from the Tanggula Mountains, central Tibetan Plateau (5743 m a.s.l.), in August 2005. Annual average stable isotope (δ18O, δD) values generally increase during the period, while the second-order parameter of deuterium excess (d-excess) generally decreases. High annual average d-excess values (18.2‰) throughout the ice core suggest a significant contribution of continental recycled moisture. d-excess values shift from relatively higher values during 1850–1940 to lower values since the 1940s. Annual isotope values and reconstructed accumulation are compared with climate indices, local station temperature records and northern India monsoon precipitation. Significant correlation is observed between δ18O and the Southern Oscillation, NINO3.4 and Dipole Mode indices. Annual average d-excess values revealed a significant negative correlation with the Dipole Mode index. Results suggest a relatively greater contribution of westerly-dominated continental moisture prior to the 1940s and an increase in the contribution of moisture evaporated under more humid conditions since the 1940s.

Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation

The Greenland δ18O ice core record is used as a proxy for Greenland surface air temperatures and to interpret Atlantic Multidecadal Oscillation (AMO) variability. An analysis of annual δ18O data from six Arctic ice cores (five from Greenland and one from Canada's Ellesmere Island) suggests a significant AMO spatial and temporal variability within a recent period of 660 years. A dominant AMO periodicity near 20 years is clearly observed in the southern (Dye3 site) and the central (GISP2, Crete and Milcent) regions of Greenland. This 20‐year variability is, however, significantly reduced in the northern (Camp Century and Agassiz Ice Cap) region, likely due to a larger distance from the Atlantic Ocean, and a much lower snow accumulation. A longer time scale AMO component of 45–65 years, which has been seen clearly in the 20th century SST data, is detected only in central Greenland ice cores. We find a significant difference between the AMO cycles during the Little Ice Age (LIA) and the Medieval Warm Period (MWP). The LIA was dominated by a ∼20 year AMO cycle with no other decadal or multidecadal scale variability above the noise level. However, during the preceding MWP the 20 year cycle was replaced by a longer scale cycle centered near a period of 43 years with a further 11.5 year periodicity. An analysis of two coupled atmosphere‐ocean general circulation models control runs (UK Met Office HadCM3 and NOAA GFDL CM2.1) agree with the shorter and longer time‐scales of Atlantic Meridional Overturning Circulation (AMOC) and temperature fluctuations with periodicities close to those observed. However, the geographic variability of these periodicities indicated by ice core data is not captured in model simulations.

Paleometeorology: High resolution Northern Hemisphere wintertime mid-latitude dynamics during the Last Glacial Maximum

Hourly winter weather of the Last Glacial Maximum (LGM) is simulated using the Community Climate Model version 3 (CCM3) on a globally resolved T170 (75 km) grid. Results are compared to a longer LGM climatological run with the same boundary conditions and monthly saves. Hourly-scale animations are used to enhance interpretations. The purpose of the study is to explore whether additional insights into ice age conditions can be gleaned by going beyond the standard employment of monthly average model statistics to infer ice age weather and climate. Results for both LGM runs indicate a decrease in North Atlantic and increase in North Pacific cyclogenesis. Storm trajectories react to the mechanical forcing of the Laurentide Ice Sheet, with Pacific storms tracking over middle Alaska and northern Canada, terminating in the Labrador Sea. This result is coincident with other model results in also showing a significant reduction in Greenland wintertime precipitation – a response supported by ice core evidence. Higher-temporal resolution puts in sharper focus the close tracking of Pacific storms along the west coast of North America. This response is consistent with increased poleward heat transport in the LGM climatological run and could help explain “early” glacial warming inferred in this region from proxy climate records. Additional analyses shows a large increase in central Asian surface gustiness that support observational inferences that upper-level winds associated with Asian- Pacific storms transported Asian dust to Greenland during the LGM.

Re-evaluation of the Last Glacial Maximum typesite at Dimlington, UK

Bateman, M. D., Buckland, P. C., Whyte, M. A., Ashurst, R. A., Boulter, C. & Panagiotakopulu, E. 2011: Re-evaluation of the Last Glacial Maximum typesite at Dimlington, UK. Boreas, 10.1111/j.1502-3885.2011.00204.x. ISSN 0300-9483. Recent erosion has allowed re-examination of the stratigraphy and sampling for both optically stimulated luminescence dating and palaeoecological analysis of the key sections in the Last Glacial Maximum deposits at Dimlington in East Yorkshire, England. Both stratigraphy and fossil insect evidence support a subaerial origin for laminated and cross-bedded sediments between two diamictons previously interpreted as synchronous. The fossil biota indicates conditions similar to those of a pond on sandur in the high Arctic, with little or no vegetation cover. The existence of distinct oscillations of the ice front is indicated. The first, within the period 21.7–16.2 ka, appears coincident with climate warming, as deduced from Greenland ice-core evidence, and is interpreted as an ice stream associated with changing flow patterns within the British–Irish Ice Sheet (BIIS). The second, dating between 16.2 and 15.5 ka, appears to coincide with a climatic cooling, although current models show that the BIIS had by this period already retreated back to ice centres. This new evidence supports the view that the eastern sector of the BIIS did not reach its maximal extent synchronously with other parts of the BIIS.

Ice core evidence for a 20th century decline of sea ice in the Bellingshausen Sea, Antarctica

This study uses ice core methanesulphonic acid (MSA) records from the Antarctic Peninsula, where temperatures have been warming faster than anywhere else in the Southern Hemisphere, to reconstruct the 20th century history of sea ice change in the adjacent Bellingshausen Sea. Using satellite‐derived sea ice and meteorological data, we show that ice core MSA records from this region are a reliable proxy for regional sea ice change, with years of increased winter sea ice extent recorded by increased ice core MSA concentrations. Our reconstruction suggests that the satellite‐observed sea ice decline in the Bellingshausen Sea during recent decades is part of a long‐term regional trend that has occurred throughout the 20th century. The long‐term perspective on sea ice in the Bellingshausen Sea is consistent with evidence of 20th century warming on the Antarctic Peninsula and may reflect a progressive deepening of the Amundsen Sea Low due to increasing greenhouse gas concentrations and, more recently, stratospheric ozone depletion. As a first‐order estimate, our MSA‐based reconstruction suggests that sea ice in the Bellingshausen Sea has retreated southward by ∼0.7° during the 20th century. Comparison with other 20th century sea ice observations, reconstructions, and model simulations provides a coherent picture of Antarctic sea ice decline during the 20th century, although with regional‐scale differences evident in the timing and magnitude of this sea ice decline. This longer‐term perspective contrasts with the small overall increase in Antarctic sea ice that is observed in post‐1979 satellite data.

Interhemispheric coupling, the West Antarctic Ice Sheet and warm Antarctic interglacials

Abstract. Ice core evidence indicates that even though atmospheric CO2 concentrations did not exceed ~300 ppm at any point during the last 800 000 years, East Antarctica was at least ~3–4 °C warmer than preindustrial (CO2~280 ppm) in each of the last four interglacials. During the previous three interglacials, this anomalous warming was short lived (~3000 years) and apparently occurred before the completion of Northern Hemisphere deglaciation. Hereafter, we refer to these periods as "Warmer than Present Transients" (WPTs). We present a series of experiments to investigate the impact of deglacial meltwater on the Atlantic Meridional Overturning Circulation (AMOC) and Antarctic temperature. It is well known that a slowed AMOC would increase southern sea surface temperature (SST) through the bipolar seesaw and observational data suggests that the AMOC remained weak throughout the terminations preceding WPTs, strengthening rapidly at a time which coincides closely with peak Antarctic temperature. We present two 800 kyr transient simulations using the Intermediate Complexity model GENIE-1 which demonstrate that meltwater forcing generates transient southern warming that is consistent with the timing of WPTs, but is not sufficient (in this single parameterisation) to reproduce the magnitude of observed warmth. In order to investigate model and boundary condition uncertainty, we present three ensembles of transient GENIE-1 simulations across Termination II (135 000 to 124 000 BP) and three snapshot HadCM3 simulations at 130 000 BP. Only with consideration of the possible feedback of West Antarctic Ice Sheet (WAIS) retreat does it become possible to simulate the magnitude of observed warming.

Atmospheric soluble dust records from a Tibetan ice core: Possible climate proxies and teleconnection with the Pacific Decadal Oscillation

In autumn 2005, a joint expedition between the University of Maine and the Institute of Tibetan Plateau Research recovered three ice cores from Guoqu Glacier (33°34′37.8″N, 91°10′35.3″E, 5720 m above sea level) on the northern side of Mt. Geladaindong, central Tibetan Plateau. Isotopes (δ18O), major soluble ions (Na+, K+, Mg2+, Ca2+, Cl−, NO3−, SO42−), and radionuclide (β‐activity) measurements from one of the cores revealed a 70‐year record (1935–2005). Statistical analysis of major ion time series suggests that atmospheric soluble dust species dominate the chemical signature and that background dust levels conceal marine ion species deposition. The soluble dust time series have interspecies relations and common structure (empirical orthogonal function (EOF) 1), suggesting a similar soluble dust source or transport route. Annual and seasonal correlations between the EOF 1 time series and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis climate variables (1948–2004) suggest that the Mt. Geladaindong ice core record provides a proxy for local and regional surface pressure. An approximately threefold decrease of soluble dust concentrations in the middle to late 1970s, accompanied by regional increases in pressure and temperature and decreases in wind velocity, coincides with the major 1976–1977 shift of the Pacific Decadal Oscillation (PDO) from a negative to a positive state. This is the first ice core evidence of a potential teleconnection between central Asian atmospheric soluble dust loading and the PDO. Analysis of temporally longer ice cores from Mt. Geladaindong may enhance understanding of the relationship between the PDO and central Asian atmospheric circulation and subsequent atmospheric soluble dust loading.

Ice core evidence for significant 100‐year regional warming on the Antarctic Peninsula

We present a new 150‐year, high‐resolution, stable isotope record (δ18O) from the Gomez ice core, drilled on the data sparse south western Antarctic Peninsula, revealing a ∼2.7°C rise in surface temperatures since the 1950s. The record is highly correlated with satellite‐derived temperature reconstructions and instrumental records from Faraday station on the north west coast, thus making it a robust proxy for local and regional temperatures since the 1850s. We conclude that the exceptional 50‐year warming, previously only observed in the northern Peninsula, is not just a local phenomena but part of a statistically significant 100‐year regional warming trend that began around 1900. A suite of coupled climate models are employed to demonstrate that the 50 and 100 year temperature trends are outside of the expected range of variability from pre‐industrial control runs, indicating that the warming is likely the result of external climate forcing.

Antarctic sea ice extent during the Holocene reconstructed from inland ice core evidence

Interannual fluctuations in the Antarctic sea ice extent (SIE) affect the global albedo and heat balance, and they may affect global CO2 levels. We found that the annual trend of sodium ion fluxes in the snowpack in the Dome Fuji region of East Antarctica can serve as a proxy for the present‐day SIE in the southern Indian Ocean and Weddell Sea sectors. We then used sodium ion profiles obtained from the Dome Fuji ice core to reconstruct the SIE during the Holocene. We observed that (1) the beginnings of both the climatic optimum (12.0 ka BP) and neoglaciation (5.4 ka BP) in the Southern Ocean, indicated by siliceous microfossil records, are consistent with decreases (11.8 ka BP) and increases (5.4 ka BP) in the sodium ion fluxes in the Dome Fuji ice core, and (2) the interannual fluctuation in the SIE during some periods of the neoglaciation was greater than the interannual fluctuation during the climatic optimum.

New ice core evidence for a volcanic cause of the A.D. 536 dust veil

New and well‐dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533–534 ± 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree‐ring data to have occurred in A.D. 536. Tree‐ring data suggest that this was the most severe and protracted short‐term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.

Paleoclimatic implications of an 850‐year oxygen‐isotope record from the northern Tibetan Plateau

Oxygen‐isotope records from the sediments of hydrologically‐closed lakes are commonly interpreted in terms of changing effective precipitation. We compare an 850‐year‐long oxygen‐isotope record derived from ostracode carbonate from the sediments of Sugan Lake, in the northern Tibetan Plateau, with tree‐ring and ice core evidence for changing temperature, precipitation and isotopic composition of the lake's inflow. Taking into account all of these independent records, we show that variations in the carbonate δ18O values could not have been the result of varying effective precipitation alone: changes in water temperature and in the δ18O of source waters also played a significant role. Where independent records of temperature, precipitation or the isotopic composition of input waters are unavailable, care should be taken to avoid simplistic interpretations of carbonate stable isotope records, as these may contribute to incorrect paleoclimatic reconstructions.

Glacial/interglacial changes in mineral dust and sea‐salt records in polar ice cores: Sources, transport, and deposition

Sea‐salt and mineral dust records as represented by Na+ and Ca2+ concentrations, respectively, in Greenland and Antarctic ice cores show pronounced glacial/interglacial variations. For the Last Glacial Maximum (LGM), mineral dust (sea salt) concentrations in Greenland show an increase of a factor of approximately 80 (15) compared to the Holocene and significant shifts by a factor of 15 (5) during Dansgaard‐Oeschger events. In Antarctica the dust (sea salt) flux is enhanced by a factor of 15 (3) during the LGM compared to the Holocene, and variations by approximately a factor of 8 (1–2) exist in parallel to Antarctic warm events. Primary glacial dust sources are the Asian deserts for Greenland and Patagonia for Antarctica. Ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in Greenland ice cores. In Antarctica, changes in ice core fluxes are in large parts related to source variations both for sea salt and dust, where the formation of sea‐salt aerosol from sea ice may play a pivotal role. Summarizing our latest estimates on changes in sources, transport, and deposition, these processes are roughly able to explain the glacial increase in sea salt in both polar regions, while they fall short by at least a factor of 4–7 for mineral dust. Future improvements in model resolution and in the formulation of source and transport processes together with new ice core records, e.g., on dust size distributions, will eventually allow convergence of models and observations.

Ice core evidence for a very tight link between North Atlantic and east Asian glacial climate

Corresponding millennial‐scale climate changes have been reported from the North Atlantic region and from east Asia for the last glacial period on independent timescales only. To assess their degree of synchrony we suggest interpreting Greenland ice core dust parameters as proxies for the east Asian monsoon systems. This allows comparing North Atlantic and east Asian climate on the same timescale in high resolution ice core data without relative dating uncertainties. We find that during Dansgaard‐Oeschger events North Atlantic region temperature and east Asian storminess were tightly coupled and changed synchronously within 5–10 years with no systematic lead or lag, thus providing instantaneous climatic feedback. The tight link between North Atlantic and east Asian glacial climate could have amplified changes in the northern polar cell to larger scales. We further find evidence for an early onset of a Younger Dryas‐like event in continental Asia, which gives evidence for heterogeneous climate change within east Asia during the last deglaciation.

DROUGHT AND THE MAYA COLLAPSE

AbstractBetween a.d. 760 and 930, millions of Maya disappeared from the Earth. We examine changes in the physical environment in which the Maya lived. The ice-core evidence from Greenland indicates that around the time of the Maya Collapse, a minimum in solar insolation and a low in solar activity occurred, accompanied by severe cold and dryness over Greenland, indicating hemispheric climatic conditions propitious for drought in the Maya Lowlands. In the northeastern Caribbean, sea-surface salinity (SSS) was lowered. The most severe drought of the past 7,000 years devastated the Yucatan Peninsula. Large Maya cities collapsed in four phases of abandonment spaced about fifty years apart around a.d. 760, 810, 860, and 910. A new core taken from Lake Chichancanab in Quintana Roo shows three peak episodes of brutal drought within a 150- to 200-year drought. A marine core from the Cariaco Basin off Venezuela precisely dates four severe drought episodes to 760, 810, 860, and 910, coincident with the four phases of abandonment of cities. The long-term drought appears to have lasted from 760 to 930 in the Cariaco Basin. The climatic changes were the most drastic the Maya had faced in the preceding 1,500 years and the most severe of the preceding 7,000 years.

Ice core evidence for asynchronous glaciation on the Tibetan Plateau

Over the last two decades, ice core records have been systematically recovered from low-latitude, high-elevation ice fields from across the Tibetan Plateau (TP) and each core has provided new information about regional climate and environmental change. When viewed collectively, these ice core histories provide compelling evidence that the growth (glaciation) and decay (deglaciation) of large ice fields in the lower latitudes are often asynchronous with high-latitude glaciation and deglaciation that occur on Milankovitch time scales. Here, we examine the evidence for asynchronous glaciation on the TP as recorded in ice cores from the Guliya ice cap on the northwestern margin, and the Puruogangri ice cap and Dasuopu glacier in central Tibet and along the southern margin of the TP, respectively. We contend that although stable isotopic records from Antarctica, Greenland, Tanzania, Peru, and Bolivia suggest global-scale cooling during the last glacial stage, over much of the TP precipitation is a stronger driver of glaciation. Here, we present evidence suggesting that glacier expansion on the southern and central TP is driven mainly by variations in monsoonal precipitation that is modulated by precession-driven insolation changes. The basal (oldest) ice in the Puruograngri and Dasuopu ice fields was deposited in the early to mid-Holocene, while ice near the base of Guliya is more than 500,000 yr old.

Ice core evidence for a second volcanic eruption around 1809 in the Northern Hemisphere

[1] A volcanic signal observed in ice cores from both polar regions six years prior to Tambora is attributed to an unknown tropical eruption in 1809. Recovery of dacitic tephra from the 1809 horizon in a Yukon ice core (Eclipse) that is chemically distinct from andesitic 1809 tephra found in Antarctic ice cores indicates a second eruption in the Northern Hemisphere at this time. Together with the similar magnitude and timing of the 1809 volcanic signal in the Arctic and Antarctic, this could suggest a large tropical eruption produced the sulfate and Antarctic tephra and a minor Northern Hemisphere eruption produced the Eclipse tephra. Nonetheless, the possibility that there were coincidental eruptions of similar magnitude in both hemispheres, rather than a single tropical eruption, should not be discounted. Correctly attributing the source of the 1809 volcanic signal has important implications for modeling the magnitude and latitudinal distribution of volcanic radiative forcing.

Late Quaternary climate-driven environmental change in the Larsemann Hills, East Antarctica, multi-proxy evidence from a lake sediment core

Little is known about the response of terrestrial East Antarctica to climate changes during the last glacial–interglacial cycle. Here we present a continuous sediment record from a lake in the Larsemann Hills, situated on a peninsula believed to have been ice-free for at least 40,000 yr. A mutli-proxy data set including geochronology, diatoms, pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record. We interpret this as Marine Isotope Stage 5e after application of a chronological age-depth model and similar ice core evidence. Dry and cold conditions are inferred during the last glacial, with lake-level minima, floristic changes towards a shallow water algal community, and a greater biological receipt of ultraviolet radiation. During the Last Glacial Maximum and Termination I the lake was perennially ice-covered, with minimal snowmelt in the catchment. After ca. 10,500 cal yr B.P., the lake became seasonally moated or ice-free during summer. Despite a low accumulation rate, the sediments document some Holocene environmental changes including neoglacial cooling after ca. 2450 cal yr B.P., and a gradual increase in aridity and salinity to the present.

Ice core evidence for secular variability and 200-year dipolar oscillations in atmospheric circulation over East Antarctica during the Holocene

Two Holocene ice core records from East Antarctica (Vostok and EPICA-Dome C) were analysed for dust concentration and size distribution at a temporal resolution of 1 sample per ~50 years. A series of volcanic markers randomly distributed over the common part of the ice cores (from 9.8 to 3.5 kyear BP) ensures accurate relative dating (±33 years). Dust-size records from the two sites display oscillations structured in cycles with sub-millennial and secular scale frequencies that are apparently asynchronous. The power spectra of the composite sum (Σ) of the two dust-size records display spectral energy mostly for 150- to 500-year periodicities. On the other hand, the 200-year band is common to both records and the 200 year components of the two sites are out-of-phase (100-year lead or lag) over ~5.5 kyear, a phenomenon also reflected by a significant (>99% conf. lev.) band in the power spectra of the composite difference (Δ) of the two size records. During long-range transport, mineral dust originating from the Southern Hemisphere continents is graded to a variable extent depending on the altitude and duration of atmospheric transport. Relatively coarse dust is associated with air mass penetration from the middle–lower troposphere and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the Antarctic plateau, a hypothesis already proposed for the changes that occurred during the Last Glacial Maximum to Holocene transition (Delmonte et al. 2004b). Moreover, we assume that the overall fluctuation of air mass advection over Antarctica depends on the meridional pressure gradient with respect to low latitudes, i.e. the Antarctic Oscillation (AAO). We therefore suggest a regional variability in atmospheric circulation over East Antarctica. The 150–500 year power spectrum of the composite (Σ) parameter represents the long term variability of the AAO, imprinted by secular internal oscillations probably related to the southern ocean-climatic system. On the other hand, the Δ dust composite parameter suggests a persistent atmospheric dipole over East Antarctica delivering coarser (finer) dust particles alternatively to Vostok and Dome C regions with a bi-centennial periodicity. Indeed, a seesaw phenomenon in dust size distribution was already observed at three East Antarctic sites during the last deglaciation (Delmonte et al. 2004b) and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south pole. Interestingly, the Δ parameter shows a pronounced 200-year oscillation mode, throwing new light on the unresolved question of a possible relationship between climate and solar activity.

Ice core evidence for the extent of past atmospheric CO2 change due to iron fertilisation

An extended high‐resolution ice core record of dust deposition over the past 60 ka from Dome C, Antarctica, is presented. The data are in conflict with the idea that changes in aeolian iron input into the Southern Ocean were the major cause for the 80 ppm glacial‐interglacial CO2 increase. During the deglaciation, the CO2 increase shows a linear relationship with the fall of the logarithm of the nss‐Ca2+ flux, a proxy for dust deposition. However, the very large variations in the nss‐Ca2+ flux related to the glacial Antarctic warm events A1 to A4 were accompanied by small CO2 variations only. Our data‐based analysis suggests that decreased Southern Ocean dust deposition caused at most a 20 ppm increase in CO2 at the last glacial‐interglacial transition. Rapid decreases in dust deposition to the northern Pacific could have been responsible for a maximum of 8 ppm in addition.

Ice core evidence for Antarctic sea ice decline since the 1950s.

The instrumental record of Antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal Antarctica. Here we report a significant correlation (P < 0.002) between methanesulphonic acid (MSA) concentrations from a Law Dome ice core and 22 years of satellite-derived sea ice extent (SIE) for the 80 degrees E to 140 degrees E sector. Applying this instrumental calibration to longer term MSA data (1841 to 1995 A.D.) suggests that there has been a 20% decline in SIE since about 1950. The decline is not uniform, showing large cyclical variations, with periods of about 11 years, that confuse trend detection over the relatively short satellite era.