Recent warming in central Greenland?
Alley, R. B. and B.R. Koci
Annals of Glaciology, Vol. 14, p. 6-8, 1990
Recent warming has occurred in near-surface firn in Central Greenland, as shown by analysis of a 217 m temperature profile from the GISP2 site. However, this warming falls within the range of natural variability and provides no clear evidence of a greenhouse signal.
Initial measurements of C02 concentrations (1530 to 1940 AD) in air occluded in the GISP2 ice core from
Wahlen, M., D. Allen, B. Deck and A. Herchenroder
Geophysical Research Letters, Vol. 18, No. 8, p. 1457-1460, August 1991
Initial measurements of CO2 in the air of bubbles in the GISP2 (Greenland Ice Sheet Project 2) ice core were performed using a dry extraction technique and tunable diode laser absorption spectroscopy. The record spans the years 1530 to 1940, and includes part of the little ice age. Absolute dating of the air was obtained from the location of the 14CO2 bomb peak in the bubble air, relative dating from the seasonal variations of d18O. The results for preindustrial times indicate constant atmospheric CO2 levels of 280±5 ppmv between 1530 and 1810 AD. Thereafter the concentrations rise rather abruptly. The record smoothly connects to the direct atmospheric observations from Mauna Loa.
Decade to century climate variability recorded in ice cores
Grootes, P. M.
Workshop on Climate Variability on Decade-to Century time scales. Irvine, CA, September 21-25, 1992. National Academy of Sciences.
Ice cores provide high-resolution, multi-parameter records of changes in climate and environmental conditions spanning two or more full glacial- interglacial cycles. Ice core records are mainly limited to polar regions, but detailed and long ice core records have also been obtained from the tropical Peruvian Andes and from the high mountains of China. The new ice core records being obtained from the summit of the Greenland ice sheet (GRIP, GISP2) show in unprecedented detail major climatic and environmental changes on both decadal and century time scales covering, so far, the last 40,000 years. Transitions between climate states appear to have been rapid; frequently of the order of a decade.
The "flickering switch" of late Pleistocene climate change
Taylor, K. C., G. W. Lamorey, G. A. Doyle, R. B. Alley, P. M. Grootes, P. A. Mayewski, J. W. C. White, and L. K. Barlow
Nature, Vol. 361, p. 432-436, 4 Feb. 1993
Polar ice contains a unique record of past climate variations; previous Greenland ice cores have documented relatively warm "interstadial" periods during the last glaciation and short (century-scale) returns to colder conditions during the glacial to interglacial warming. These climate features have also been observed to varying degrees in ocean sediment cores and terrestrial pollen and insect records. Here we report electrical conductivity measurements from a new Greenland ice core, which confirm these previous observations, and also reveal a hitherto unrecognized mode of rapid climate variation. Fluctuation in ice conductivity on the scales of <5-20 years reflect rapid oscillations in the dust content of the atmosphere. This "flickering" between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation.
Abrupt accumulation increase at the Younger Dryas termination in the GISP2 ice core
Alley, R. B., D. A. Meese, C. A. Shuman, A. J. Gow, K. C. Taylor, P. M. Grootes, J. W. C. White, M. Ram, E. D. Waddington, P. A. Mayewski, and G. A. Zielinski
Nature, Vol. 362, p. 527-529, 8 April 1993
The warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate, the best-known of which is the Younger Dryas event. Despite much study of the cause(s) of this event and the mechanism(s) by which it ended, large questions remain. Oxygen-isotopic data from Greenland ice cores suggest that the Younger Dryas ended abruptly, over a period of about 50 years. Moreover, ice-core dust concentrations suggest that the Younger Dryas may have ended in just 20 years or less. This extremely short timescale places severe constraints on the mechanism(s) of the transition. But dust concentration may respond to subtle changes in atmospheric circulation rather than to large changes in the major climate variables. Here we present results from a new Greenland ice core showing that snow accumulation doubled rapidly from the Younger Dryas episode to the subsequent Preboreal interval, possibly in one to three years. We also find that the accumulation-rate change from the Oldest Dryas to the Bolling/Allerod interstade was large and abrupt. The extreme rapidity of these changes in a direct climatic variable implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the North Atlantic climate system.
The Atmosphere during the Younger Dryas
Mayewski, P. A., L. D. Meeker, S. Whitlow, M. S. Twickler, M. C. Morrison, R. B. Alley, P. Bloomfield, and K. Taylor
Science, Vol. 261, p. 195-197, 9 July 1993
One of the most dramatic climate events observed in marine and ice core records is the Younger Dryas (YD), a return to near-glacial conditions that punctuated the last deglaciation. High resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the Arctic atmosphere at this time. This record shows that both onset and termination of the YD occurred within 10-20 years and that massive, frequent and short-term (decadal or less) changes in atmospheric composition existed throughout this event. Changes in atmospheric composition are explained by changes in the size of the polar atmospheric cell and resultant changes in source regions plus growth and decay of continental biogenic source regions.
Greenland ice core "signal" characteristics :
An expanded view of climate change
Mayewski, P. A., L. D. Meeker, M. C. Morrison, M. S. Twickler, S. I. Whitlow, K. K. Ferland, D. A. Meese, M. R. Legrand, and J. P. Steffensen
Journal of Geophysical Research, Vol. 98, No. D7, p. 12,839-12,847, 20 July 1993
While there are several rich proxy records covering much of the last millennium, little is know about the composition of the soluble constituents of the atmosphere at this time. However, it is within the framework of the last millennium that the complexities of natural variability and the effects of anthropogenic forcing of the environment are interwoven. Inherent in this natural variability are properties of non-linearity, stationarity and non-stationarity all of which can be assessed by an innovative form of signal analysis that has been applied to glaciochemical time-series recently recovered from central Greenland.
The North Atlantic oscillation signature in deuterium and deuterium excess signals in the Greenland Ice
Sheet Project 2 ice core, 1840-1970
Barlow, L. K., White, J. W. C., Barry, R. G., Rogers, J. C., & Grootes, P. M.
Geophysical Research Letters, Vol. 20, No. 24, p. 2901-2904, December 23,1993
The Greenland Ice Sheet Project 2 (GISP2) core can enhance our understanding of the relationship between parameters measured in the ice in central Greenland and variability in the ocean, atmosphere, and cryosphere of the North Atlantic Ocean and adjacent land masses. Seasonal (summer, winter) to annual responses of D and deuterium excess isotopic signals in the GISP2 core to the seesaw in winter temperatures between West Greenland and northern Europe from A .D. 1840 to 1970 are investigated. This seesaw represents extreme modes of the North Atlantic Oscillation, which also influences sea surface temperatures (SSTs), atmospheric pressures, geostrophic wind strength, and sea ice extents beyond the winter season. Temperature excursions inferred from the D record during seesaw/extreme NAO mode years move in the same direction as the West Greenland side of the seesaw. Symmetry with the West Greenland side of the seesaw suggests a possible mechanism for damping in the ice core record of the lowest decadal temperatures experienced in Europe from A.D. 1500 to 1700. Seasonal and annual deuterium excess excursions during seesaw years show negative correlation with D. This suggests an isotopic response to a SST/ land temperature seesaw. The isotopic record from GISP2 may therefore give information on both ice sheet and sea surface temperature variability. Cross-plots of D and deuterium excess show a tendency for data to be grouped according to the prevailing mode of the seesaw, but do not provide unambiguous identification of individual seesaw years. A combination of ice core and tree ring data sets may allow more confident identification of GA and GB (extreme NAO mode) years prior to 1840.
Preliminary depth-age scale of the GISP2 ice core
Meese, D.A., R.B. Alley, A.J. Gow, P. Grootes, P.A. Mayewski, M. Ram, K.C. Taylor, E. Waddington and G. Zielinski
CRREL Special Report 94-01, February 1994
This report contains a preliminary depth-age scale for the GISP2 core. An accurate depth-age scale is a prerequisite for comparison of this record to other climatic records and for the interpretation of other measurements from the core. An essentially continuous depth-age scale was obtained using parameters that yield characteristic annual layer signals, including visual stratigraphy electrical conductivity measurements (ecm), stable isotopes and laser light scattering of dust. Additionally, known historical volcanic signals were identified in the core and used for tie-points throughout the Holocene and in some cases deeper in the core. This report is for limited distribution until the data become available to the World Data Center.
Changes in atmospheric circulation and ocean ice cover over the North Atlantic during the last 41,000
Mayewski, P.A., L. D. Meeker, S.I. Whitlow, M. S. Twickler, M. C. Morrison, P. Bloomfield, G. C. Bond, R. B. Alley, A. J. Gow, P. M. Grootes, D. A. Meese, M. Ram, K. C. Taylor, W. Wumkes
Science, Vol. 263, p. 1747-1751, 25 March 1994
High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PCI)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.
Record of volcanism since 7000 B.C. from the GISP2 Greenland ice core and implications for the
Zielinski, G.A., P.A. Mayewski, L.D. Meeker, S. Whitlow, M.S. Twickler, M. Morrison, D.A. Meese, A.J. Gow and R.B. Alley
Science, Vol. 264, p. 948-952, 13 May 1994
Sulfate concentrations from continuous bi-yearly sampling of the GISP2 Greenland ice core provide a record of potential climate-forcing volcanism since 7000 B.C. We matched 85% of the events recorded over the last 2000 years to documented volcanic eruptions, but only about 30% of the events from 1 to 7000 B.C. Several historic eruptions were possibly greater sulfur producers than previously thought. There are three times as many events from 5000 to 7000 B.C. as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions. This increased volcanism in the early Holocene may have contributed to climatic cooling.
The accumulation record from the GISP2 core as an indicator of climate change throughout the Holocene
Meese, D. A., A. J. Gow, P. Grootes, P. A. Mayewski, M. Ram, M. Stuiver, K. C. Taylor, E. D. Waddington and G. A. Zielinski
Science, Vol. 266, p. 1680-1682, 9 December 1994
A depth/age scale and accumulation history for the Holocene have been established on the GISP2 core providing the most accurate and continuous record currently available. The depth/age scale was obtained by counting annual layers in the core using various independent techniques. An annual record of surface accumulation during the Holocene was obtained by correcting the observed layer thickness for flow- thinning. Fluctuations in accumulation provide a continuous and detailed record of climate variability over central Greenland during the Holocene. Climate events, including "Little Ice Age" type events are examined.
The GISP2 ice core record - paleoclimate highlights
Mayewski, P.A. and M. Bender
Reviews of Geophysics Supplement, p. 1287-1296. July 1995 (US National Report to the IUGG 1991-1994)
Understanding the Earth system and, in particular, its climate, remains one of the major intellectual challenges faced by science. The processes influencing climate, the mechanisms through which they act, and the responses they generate are, in general, as complex and poorly understood as they are important. Because observational records of climate processes span only the most recent years of Earth's history and, in many instances, are known to be markedly affected by anthropogenic influences, paleorecords of past climates are exceedingly important to the development of scientific understanding of local, regional and global climate systems. Of the various paleorecords available to science, ice cores from polar ice sheets provide the most direct and highest resolution view of the paleoatmosphere.
Resolved: The Arctic controls global climate change. In Arctic Oceanography: Marginal ice zone and
R. B. Alley
American Geophysical Union Coastal and Estuarine Studies. W.O. Smith, Jr. and J.M. Grebmeier (eds.), p. 263-283, 1995
Paleoclimatic records of the most recent million years show strong variability in the Arctic, and nearly synchronous variability of similar or smaller magnitude elsewhere. The timing of climate variability relative to changes in the seasonality and strength of sunlight reaching the Earth (Milankovitch forcing) shows that much of the global response is controlled by conditions at high northern latitudes. Physical modeling of this system requires some important climatic element with a slow time constant, and Arctic or subarctic continental ice sheets are the only viable candidates at the present time. Shorter-period (Heinrich/Bond and Dansgaard/Oeschger) oscillations are strongest in the North Atlantic region but appear elsewhere. Internal oscillations of ice sheets and of the North Atlantic ocean are the leading hypotheses for controlling mechanisms. The global climate system is probably linked to Arctic forcing and oscillations through the deepwater formation in the North Atlantic, and its effects on global atmospheric circulation, sea ice, carbon dioxide, methane and dust.
Large Arctic temperature change at the Wisconsin-Holocene glacial transition
Cuffey, K.M., G.D. Clow, R.B. Alley, M. Stuiver, E.D. Waddington, and R.W. Saltus
Science, Vol. 270, p. 455-458, 1995
Analysis of borehole temperature and GISP2 ice-core isotopic composition reveals that the warming from average glacial conditions to the Holocene in central Greenland was large, approximately 15¡C. This is at least a three- fold amplification of the coincident temperature change in the Tropics and mid-latitudes. The coldest periods of the last glacial were probably 21¡C colder than the present over the Greenland ice sheet.
The effect of ice sheet thickness changes on the accumulation history inferred from GISP2 layer
Cutler, N.A., C.F. Raymond, E.D. Waddington, D.A. Meese, and R.B. Alley,
Annals of Glaciology, Vol. 21, p. 26-32, 1995
In order to infer past net accumulation rates at the Greenland summit using layer thickness data from the GISP2 ice core, we have developed a non-linear, one-dimensional flow model of an ice sheet that allows for thickness change in response to mass balance variations. The model is used to investigate how net accumulation rate changes affect the time evolution of: (1) the ice sheet thickness, (2) the vertical strain rate pattern, and (3) the corresponding internal annual layer structure. The model is parameterized to fit the present net accumulation rate and thickness of the Greenland ice sheet summit. This parameterization results in a characteristic time constant for adjustment to accumulation changes of about 6000 years and yields an ice sheet about 400 meters thinner than its present thickness during the last glacial period. Accumulation rate histories inferred from GISP2 layer thickness data using both a constant and variable thickness model are compared. In general, the variable thickness model predicts lower accumulation rates for the last glacial maximum to the present. However, sensitivity analyses indicate that the inferred accumulation history cannot be precisely determined by this model. Our analysis defines an envelope of likely accumulation histories bounded above by the accumulation history inferred by the constant thickness model and bounded below by a calculation from this new model where the ice sheet thickness is most sensitive to mass balance changes. General features of this envelope include: (1) minimum accumulation rates during the last glacial period range from about 1/3 to 1/4 the present rate (0.24 m/yr. ice equivalent),(2) the maximum accumulation rate during the B¿lling-Aller¿d warm period (13-15 ky bp) ranges from 0.16 to 0.20 m/yr. ice equivalent, and (3) the lower bound predicts a more gradual increase in accumulation since the end of the Younger Dryas than the constant thickness model upper bound.
Variations in melt-layer frequency in the GISP2 ice core: Implications for Holocene summer temperatures
in central Greenland
Alley, R.B. and S. Anandakrishnan
Annals of Glaciology, Vol. 21, p. 64-70, 1995
The rare melt features in the GISP2, central Greenland deep ice core have decreased in frequency over the most recent 7000 years. Calibration of this change in melt frequency against modern spatial variation of melt frequency and temperature in central Greenland, and against modern temporal variability of temperatures in central Greenland, indicates that mean mid-summer temperatures have cooled over the most recent 7000 years, probably by slightly more than 1¡C if variability of summer temperatures has not changed. Comparison to GRIP isotopic records from central Greenland and to the melt record from the Agassiz ice cap, Arctic Canada, suggests some seasonal and regional coherence for this cooling signal, as well as for a cold event about 8000-8500 years ago.
Complexity of Holocene climate as reconstructed from a Greenland ice core
O'Brien, S.M., P.A. Mayewski, L.D. Meeker, D.A. Meese, M.S. Twickler, S.I. Whitlow
Science, Vol. 270, p. 1962-1964, 1995
Glaciochemical time series developed from the GISP2 ice core indicate that several periods of air flow reorganization occurred during the Holocene, likely related to changes in the magnitude and extent of the northern polar vortex (NPV). The greatest NPV expansions, and potentially the coldest temperatures since the Younger Dryas event peaked at Å 200 and 5,500 yBP. These events are separated by several cooling events of lesser magnitude, the most significant of which peak at Å 2900 and 8400 yBP. We suggest that a major ~5,500-6,000 year cycle and a minor ~2,500-2,700 year cycle of climate changes exists in our record. The latter is similar to the spacing of cold events measured in a variety of other proxy records.
The GISP2 18O climate record of the past 16,500 years and the role of the sun, ocean and volcanoes
Stuiver, M., P.M. Grootes and T.F. Braziunas
Quaternary Research, Vol. 44, p. 341-354, 1995
Measured 18O/16O ratios from the Greenland Ice Sheet Project (GISP2) ice core extending back to 16,500 ca yr. B.P. provide a continuous record of climate change since the last glaciation. High- resolution annual 18O/16O results were obtained for most of the current millennium (A.D. 818 - 1985) which record the Medieval Warm Period, the Little Ice Age, and a distinct 11 year 18O/16O cycle. Volcanic aerosols depress central Greenland annual temperature (~l.5oC maximally) and annual 18O/16O for about 4 yr. after each major eruptive event. On a bi-decadal to millennial time scale, the contribution of solar variability to Holocene Greenlandic temperature change is ~0.4oC. The role of thermohaline circulation change on climate, problematic during the Holocene, is more distinct for the 10,000-16,500 cal yr1 B.P. interval. The Oldest Dryas - Bolling-Allerod - Younger Dryas sequence appears in great detail. Bi-decadal variance in 18O/16O, but not necessarily in temperature, is enhanced during the last phase of the late-Glacial, and the Younger Dryas, suggesting switches of air mass transport between jet stream branches. The branched system is nearly instantaneously replaced at the beginning of the Bolling and Holocene (at ~14,670 and ~11,650 cal yr. B.P., respectively) by an atmospheric circulation system in which 18O/16O and annual accumulation initially track each other closely. Thermodynamic considerations of the accumulation rate-temperature relationship can be used to evaluate the 18O/16O- temperature relationship. The GISP2 ice layer count years of major GISP2 climate transitions also support the use of coral 14C ages for age calibration.
Rapid Variation in Atmospheric Methane Concentration During the Past 110,000 Years
Brook, Edward J., T. Sowers, J. Orchardo
Science, Vol. 273, p. 1087-1091, 1996
A methane record from the GISP2 ice core reveals that millennial-scale variations in atmospheric methane concentration characterized much of the past 110,000 years. As previously observed in a shorter record from central Greenland, abrupt concentration shifts of about 50 to 300 parts per billion by volume were coeval with most of the interstadial warming events (better known as Dansgaard-Oeschger events) recorded in the GISP2 ice core throughout the last glacial period. The magnitude of the rapid concentration shifts varied on a longer time scale in a manner consistent with variations in Northern Hemisphere summer insolation, which suggests that insolation may have modulated the effects of interstadial climate change on the terrestrial biosphere.
The Younger Dryas termination and North Atlantic Deep Water formation: Insights from climate model
simulations and Greenland ice cores
Fawcett, Peter J., A.M. Ëgœstsd—ttir, R.B. Alley, C.A. Shuman
Paleoceanography, Vol. 12, p. 23-38, February 1997
Results from the GISP2 and GRIP ice cores show that the termination of the Younger Dryas (YD) climate event in Greenland was a large and extremely fast climate change. A reinitiation of North Atlantic Deep Water formation following a shutdown, and its associated winter release of heat to the atmosphere, has been suggested as the most likely cause of this climate transition. To test this idea, two general circulation model experiments using GENESIS have been completed for YD time (12,000 calendar years ago): one with low heat flux in the Nordic Seas (10 W/m2, deep water shutdown) and one with high Nordic Sea heat flux (300 W/m2, active deep water formation). Comparison of Greenland climate differences between these experiments with the ice core records shows that when deep water is turned on, much of the YD termination warming is achieved. The increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation, which obscures the dominantly wintertime response to the specified forcing. The winter storm track shift toward Greenland contributes much of the climate change at the YD termination.
The CO2 concentration of air trapped in GISP2 ice from the Last Glacial Maximum-Holocene transition
Smith, H.J., M. Wahlen, D. Mastroianni, and K.C. Taylor
Geophys. Res. lett., Vol. 24(1), p. 1-4, 1997
Measurements of the CO2 concentration of air trapped in Greenland Ice Sheet Project Two ice show an increase from approximately 190 ppm to 270 ppm during the 8000 years between the end of the last glacial maximum and the beginning of the Holocene. This increase is in agreement with other parallel records from both Greenland and Antarctica, although the GISP2 data exhibit considerable variability over periods as small as 50-100 years and show that CO2 can be affected by processes occurring within the ice after bubble formation. The in-situ reactions which contribute to the modification of the concentrations of paleoatmospheric CO2 may include both CO2 uptake as well as CO2 production. The existence of two major episodes of CO2 enrichment, in addition to the variability of the data, prevents a precise determination of the progression of the increase in atmospheric CO2, although the 80 ppm rise between 18.0 kyBP and 10.4 kyBP is evident. These results strongly suggest that some intervals of the GISP2 CO2 record must be interpreted in the context of the chemical composition of the ice, and that records of atmospheric CO2 in polar ice can be considered accurate only if the ice is either (essentially ) carbonate-free or contains abundant carbonate.
Paleoenvironmental implications of the insoluble microparticle record in the GISP2 (Greenland) ice core
during periods of rapidly changing climate of the Pleistocene-Holocene transition
Zielinski, G.A. and G.R. Mershon
Geol. Soc. Amer. Bull., In Press
Oscillations in the time series of insoluble microparticles characteristics between 0.7 and 11.0 mm in the GISP2 ice core reflect changes in environmental conditions in the northern hemisphere from 10,500 to 14,000 years ago. Elevated values in microparticle numbers and mass, especially during the Younger Dryas (YD), 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 (MND) are a proxy for increased strength in zonal winds (westerlies). Highs in MND 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 grains size based on mass (MMD) 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 MMD often lead these other parameters by 100-200 years 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 MND trends (strengthening zonal winds) following the maxima in the early YD suggest an expansion of mid-latitude circulation systems (sub-tropical highs), thereby maintaining latitudinal temperature and pressure gradients. Increased variability in MMD during the warm Preboreal, compared to the colder YD, may be a function of 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 inter-annual variability in climate.
Major chemical species fluctuations over the last 110,000 years in the GISP2 ice core
Yang, Q., P.A. Mayewski, M. Twickler, S. Whitlow, P. Grootes and M. Stuiver
Major chemical species (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, Ca2+) covering the last 110,000
years BP were compared with the oxygen isotope record from the GISP2 ice core. Highly inverse
correlation coefficients were found between concentrations of Cl-, SO42-, Na+, K+, Mg2+, Ca2+ and
d18O during the last glacial period. These six ions also display high correlation coefficients related to
each other during the same period. Twenty-four well defined stadial/interstadial cycles were found using
the GISP2 chemical series. Although these six ions have the same timing of onset and decay for each
stadial/interstadial, four different types of species variation were identified within stadial/interstadial
events. Changes in major chemical composition suggest that during the Holocene, the atmosphere was
characterized by acidic environment; during interstadials the atmosphere was characterized by neutral or
alkalescent environment; during stadials the atmosphere was characterized by alkaline environment.
Chemical composition and ratios also indicates hat source regions differ during the Holocene, stadials and
interstadials for terrestrial related species, such as Ca2+, SO42- hat source regions differ during the
Holocene, stadials and interstadials for terrestrial related species, such as Ca2+, SO42- and CO32-.