TL;DR: In this paper, the isotope composition of snow in Greenland with meteorological and climatic parameters has been linked with the past few hundred years measured in ice cores using a new record of isotope values from the Greenland Ice Sheet Project 2 and Greenland Ice Core Project sites at Summit, Greenland.
Abstract: Recent efforts to link the isotopic composition of snow in Greenland with meteorological and climatic parameters have indicated that relatively local information such as observed annual temperatures from coastal Greenland sites, as well as more synoptic scale features such as the North Atlantic Oscillation (NAO) and the temperature seesaw between Jakobshaven, Greenland, and Oslo, Norway, are significantly correlated with δ18O and δD values from the past few hundred years measured in ice cores. In this study we review those efforts and then use a new record of isotope values from the Greenland Ice Sheet Project 2 and Greenland Ice Core Project sites at Summit, Greenland, to compare with meteorological and climatic parameters. This new record consists of six individual annually resolved isotopic records which have been average to produce a Summit stacked isotope record. The stacked record is significantly correlated with local Greenland temperatures over the past century (r=0.471), as well as a number of other records including temperatures and pressures from specific locations as well as temperature and pressure patterns such as the temperature seesaw and the North Atlantic Oscillation. A multiple linear regression of the stacked isotope record with a number of meteorological and climatic parameters in the North Atlantic region reveals that five variables contribute significantly to the variance in the isotope record: winter NAO, solar irradiance (as recorded by sunspot numbers), average Greenland coastal temperature, sea surface temperature in the moisture source region for Summit (30°–20°N), and the annual temperature seesaw between Jakobshaven and Oslo. Combined, these variables yield a correlation coefficient of r=0.71, explaining half of the variance in the stacked isotope record.
One of the great strengths of ice cores as proxies for past environmental conditions is that they can provide not only the long timescale necessary to view the large changes of the past glacial periods but also the high temporal resolution needed to look at socially relevant timescales, that is, subannual to decadal changes in climate and environmental conditions.
A total of six cores in the Summit region were drilled, sampled, and measured with sufficient temporal detail to calculate annual isotopic values.
The results of these studies are reviewed below.
3.2.1. Comparison with coastal temperatures. On the basis of both theoretical considerations and observations, stable
Isotope ratios of polar snows are commonly interpreted in terms of temperatures [Dansgaard, 1964] .
This approach depends on several key assumptions but is generally accepted as a very good first-order interpretation.
In all cases, except for the comparison with coastal temperatures mentioned earlier, the correlations with the stacked record were higher than the correlations with individual records.
Figure 6b shows the stacked isotopic record versus annual, winter (December-January-February.
TL;DR: The authors presented a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of re- gional Antarctic climate change during the last deglacia- tion using fast variations in global methane gas concen- trations as time markers.
Abstract: Precise information on the relative timing of north-south climate variations is a key to resolving ques- tions concerning the mechanisms that force and couple cli- mate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of re- gional Antarctic climate change during the last deglacia- tion. Using fast variations in global methane gas concen- trations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a de- tailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarc- tica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bolling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerod Cold Period, but with dating uncer- tainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric cou- pling mechanisms, including recently proposed bipolar at- mospheric teleconnections and/or rapid bipolar ocean tele- connections.
140 citations
Cites background from "The climate signal in the stable is..."
...Construction of compositeδ18Oice records from multiple ice cores has been demonstrated previously to reduce these local signals and produce reconstructions that more robustly represent regional climate trends (e.g. White et al., 1997; Andersen et al., 2006a)....
TL;DR: In this paper, the NEEM deep ice core isotope data was analyzed for their isotope composition to understand the processes affecting the climatic signal archived in the water stable isotope records from the deep core, showing that the intermittency of modern winter precipitation is responsible for the lack of strong NAO imprint.
Abstract: [1] Samples of precipitation and atmospheric water vapor were collected together with shallow firn/ice cores as part of the new deep drilling project in northwest Greenland: the NEEM project. These samples were analyzed for their isotope composition to understand the processes affecting the climatic signal archived in the water stable isotope records from the NEEM deep ice core. The dominant moisture source for the snow deposited at the NEEM-site may be originating as far south as 35°N from the western part of the Atlantic Ocean. The surface atmospheric water vapor appears in isotopic equilibrium with the snow surface indicating a large water exchange between the atmosphere and snowpack. The interannual variability of NEEM shallow firn/ice cores stable isotope data covering the last ∼40 years shows an unexpectedly weak NAO signal. Regional to global atmospheric models simulate a dominant summer precipitation in the NEEM area, suggesting that the intermittency of modern winter precipitation is responsible for the lack of a strong NAO imprint. The interannual variability of NEEM isotope data however shows a strong correlation with interannual variations of Baffin Bay sea ice cover, a relationship consistent with air mass trajectories. NEEM deep ice core isotopic records may therefore provide detailed information on past Baffin Bay sea ice extent. NEEM stable water isotope content increasing trend points to a local warming trend of ∼3.0°C over the last 40 years.
TL;DR: In this article, the authors reconstruct Greenland surface snow temperature variability over the past 4000 years at the GISP2 site (near the Summit of the Greenland ice sheet; hereafter referred to as Greenland temperature) with a new method that utilizes argon and nitrogen isotopic ratios from occluded air bubbles.
Abstract: [1] Greenland recently incurred record high temperatures and ice loss by melting, adding to concerns that anthropogenic warming is impacting the Greenland ice sheet and in turn accelerating global sea-level rise. Yet, it remains imprecisely known for Greenland how much warming is caused by increasing atmospheric greenhouse gases versus natural variability. To address this need, we reconstruct Greenland surface snow temperature variability over the past 4000 years at the GISP2 site (near the Summit of the Greenland ice sheet; hereafter referred to as Greenland temperature) with a new method that utilises argon and nitrogen isotopic ratios from occluded air bubbles. The estimated average Greenland snow temperature over the past 4000 years was −30.7°C with a standard deviation of 1.0°C and exhibited a long-term decrease of roughly 1.5°C, which is consistent with earlier studies. The current decadal average surface temperature (2001–2010) at the GISP2 site is −29.9°C. The record indicates that warmer temperatures were the norm in the earlier part of the past 4000 years, including century-long intervals nearly 1°C warmer than the present decade (2001–2010). Therefore, we conclude that the current decadal mean temperature in Greenland has not exceeded the envelope of natural variability over the past 4000 years, a period that seems to include part of the Holocene Thermal Maximum. Notwithstanding this conclusion, climate models project that if anthropogenic greenhouse gas emissions continue, the Greenland temperature would exceed the natural variability of the past 4000 years sometime before the year 2100.
TL;DR: In this paper, the authors examined why a conventional, or sea surface temperature, interpretation of the Greenland GRIP excess record seems inconsistent with inferred site and source temperature changes and assessed its geographic significance through a comparison with existing Dye 3 and North GRIP data.
129 citations
Additional excerpts
...Original data between 100 and 110 kaBP are presented, though the precise age of this section of the record is uncertain, due to the progressive deterioration of the comparison between GRIP and GISP2 isotopic profiles in this period (Grootes et al., 1993)....
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...Limited GISP2 excess data are also available for the last climatic transition (Taylor et al., 1997)....
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...Other published studies addressed surface samples (Fischer et al., 1998) as well as the GISP2 (White et al., 1997) and GRIP ice cores (Hoffmann et al., 1998a, 2001) extending through the last millenium....
[...]
...While a comparison between the d18O profiles measured along the two summit cores (GRIP and GISP2) shows that the records are basically undisturbed back to 100 ka BP, there is now ample evidence for stratigraphic disturbance of the lowest part of the two cores (Bender et al., 1994; Fuchs and Leuenberger, 1996; Chappellaz et al., 1997; Landais et al., 2004b)....
TL;DR: In this paper, a new Lagrangian moisture source diagnostic is applied to identify the atmospheric conditions relevant for the fractionation of stable water isotopes during evaporation over the ocean and subsequent transport to Greenland.
Abstract: [1] A new Lagrangian moisture source diagnostic is applied to identify the atmospheric conditions relevant for the fractionation of stable water isotopes during evaporation over the ocean and subsequent transport to Greenland. Northern Hemisphere winter months with positive and negative North Atlantic Oscillation (NAO) index are studied on the basis of ERA-40 reanalysis data. Diagnosed moisture transport conditions are supplied to a Rayleigh-type isotope fractionation model to derive estimates for the isotopic composition of stable isotopes in winter precipitation on the Greenland plateau for the two NAO phases. Because of changes in atmospheric circulation, moisture source locations for precipitation in Greenland vary strongly for different phases of the NAO. The mean source SST is ∼5.0 K warmer during negative NAO months compared to the positive phase. This signal is considerably stronger than what would result from interannual SST variability at a spatially fixed moisture source. Furthermore, moisture transport takes place at warmer temperatures during NAO negative conditions. Simulated average isotopic depletion of Greenland precipitation is less negative by 3.8 ± 6.8‰ for δ18O during the negative compared to the positive NAO phase. Comparison with ice core data from central Greenland for three winters shows good agreement between observed and simulated variability. The synoptic interplay of the initial conditions at the moisture sources and of the atmospheric transport conditions leads to enhanced NAO-related interannual variability of stable isotopes. This could be important for understanding rapid shifts in stable isotopes during past climates. The isotope modeling applied here, however, considerably underestimates the absolute level of isotopic depletion. The offset is attributed to approximations in the model and uncertainties in the comparison with observational data. The high spatial resolution of the Lagrangian method reveals the nonhomogeneous structure of isotope NAO variability over the Greenland ice sheet. The results are therefore potentially useful for selecting new ice core drilling sites with maximum NAO variability.
126 citations
Cites background from "The climate signal in the stable is..."
...…is therefore apparent in the snow accumulation sequence of ice cores [Appenzeller et al., 1998a, 1998b; Mosley-Thompson et al., 2005], as well as to some extent in the (winter) stable isotope signals in firn and ice cores from central Greenland [Barlow et al., 1993, 1997; White et al., 1997]....
TL;DR: In this paper, the isotopic fractionation of water in simple condensation-evaporation processes is considered quantitatively on the basis of the fractionation factors given in section 1.2.
Abstract: In chapter 2 the isotopic fractionation of water in some simple condensation-evaporation processes are considered quantitatively on the basis of the fractionation factors given in section 1.2. The condensation temperature is an important parameter, which has got some glaciological applications. The temperature effect (the δ's decreasing with temperature) together with varying evaporation and exchange appear in the “amount effect” as high δ's in sparse rain. The relative deuterium-oxygen-18 fractionation is not quite simple. If the relative deviations from the standard water (S.M.O.W.) are called δ D and δ 18 , the best linear approximation is δ D = 8 δ 18 . Chapter 3 gives some qualitative considerations on non-equilibrium (fast) processes. Kinetic effects have heavy bearings upon the effective fractionation factors. Such effects have only been demonstrated clearly in evaporation processes, but may also influence condensation processes. The quantity d = δ D −8 δ 18 is used as an index for non-equilibrium conditions. The stable isotope data from the world wide I.A.E.A.-W.M.O. precipitation survey are discussed in chapter 4. The unweighted mean annual composition of rain at tropical island stations fits the line δ D = 4.6 δ 18 indicating a first stage equilibrium condensation from vapour evaporated in a non-equilibrium process. Regional characteristics appear in the weighted means. The Northern hemisphere continental stations, except African and Near East, fit the line δ D = 8.0 δ 18 + 10 as far as the weighted means are concerned (δ D = 8.1 δ 18 + 11 for the unweighted) corresponding to an equilibrium Rayleigh condensation from vapour, evaporated in a non-equilibrium process from S.M.O.W. The departure from equilibrium vapour seems even higher in the rest of the investigated part of the world. At most stations the δ D and varies linearily with δ 18 with a slope close to 8, only at two stations higher than 8, at several lower than 8 (mainly connected with relatively dry climates). Considerable variations in the isotopic composition of monthly precipitation occur at most stations. At low latitudes the amount effect accounts for the variations, whereas seasonal variation at high latitudes is ascribed to the temperature effect. Tokyo is an example of a mid latitude station influenced by both effects. Some possible hydrological applications are outlined in chapter 5. DOI: 10.1111/j.2153-3490.1964.tb00181.x
TL;DR: In this article, the authors present the complete oxygen isotope record for the Greenland Ice Sheet Project 2 (GISP2) core, drilled 28 km west of the GRIP core, and observe large, rapid climate fluctuations throughout the last glacial period.
Abstract: RECENT results1,2 from the Greenland Ice-core Project (GRIP) Summit ice core suggest that the climate in Greenland has been remarkably stable during the Holocene, but was extremely unstable for the time period represented by the rest of the core, spanning the last two glaciations and the intervening Eemian inter-glacial. Here we present the complete oxygen isotope record for the Greenland Ice Sheet Project 2 (GISP2) core, drilled 28 km west of the GRIP core. We observe large, rapid climate fluctuations throughout the last glacial period, which closely match those reported for the GRIP core. However, in the bottom 10% of the cores, spanning the Eemian interglacial and the previous glacia-tion, there are significant differences between the two records. It is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores. Considerable further work will be necessary to evaluate the likelihood of this, and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores.
TL;DR: Measured 18O/16O ratios from the Greenland Ice Sheet Project 2 (GISP2) ice core extending back to 16,500 cal yr B.P. provide a continuous record of climate change since the last glaciation as discussed by the authors.
TL;DR: In this paper, the authors investigated the well-known tendency for winter temperatures to be low over northern Europe when they are high over Greenland and the Canadian Arctic, and conversely, they found that these pressure anomalies are so distributed that the pressure in the region of the Icelandic low is negatively correlated with the pressure over the North Pacific Ocean and over the area south of 50°N in the North Atlantic Ocean, Mediterranean and Middle East.
Abstract: We have investigated the well-known tendency for winter temperatures to be low over northern Europe when they are high over Greenland and the Canadian Arctic, and conversely. Well-defined pressure anomalies over most of the Northern Hemisphere are associated with this regional seesaw in temperature, and these pressure anomalies are so distributed that the pressure in the region of the Icelandic low is negatively correlated with the pressure over the North Pacific Ocean and over the area south of 50°N in the North Atlantic Ocean, Mediterranean and Middle East, but positively correlated with the pressure over the Rocky Mountains. The composite patterns of pressure anomalies in the seesaw are almost identical to the fist eigenvector in the monthly mean pressure, but the standard deviations of pressure anomalies in seesaw mouths are as large as the standard deviations of monthly means in general. Since 1840 the seesaw, as defined by temperatures in Scandinavia and Greenland, occurred in more than 40%...
TL;DR: In this paper, the authors compared the North Atlantic Oscillation (NAO) and Southern Oscillations (SO) from the standpoint of their association with Northern Hemisphere winter mean distributions of sea-level pressure (SLP) and 500 mb height.
Abstract: The North Atlantic Oscillation (NAO) and Southern Oscillation (SO) are compared from the standpoint of their association with Northern Hemisphere winter mean distributions of sea-level pressure (SLP) and 500 mb height. The NAO and SO are associated with significant SLP differences over much of the hemisphere except for Siberia and western North America. Significant SLP and 500 mb height differences occur in the NAO over the Atlantic Ocean and near Baja California, while in the SO they occur over the Pacific Ocean, India and the western Atlantic. Only over the latter region do large pressure and height variations consistently occur in the extremes of both oscillations; these are also associated with winter temperature variability over the southeastern United States. For example, during winter 1982–83, when the two oscillations simultaneously reached extremes, the NAO was associated with record December warmth east of the Mississippi River, but during January and February the SO dominated the heigh...