scholarly journals Estimation and calibration of the water isotope differential diffusion length in ice core records

2015 ◽  
Vol 9 (1) ◽  
pp. 927-973
Author(s):  
G. van der Wel ◽  
H. Fischer ◽  
H. Oerter ◽  
H. Meyer ◽  
H. A. J. Meijer
Keyword(s):  
Diffusion Length ◽  
Accumulation Rate ◽  
Pearson Correlation ◽  
Ice Core ◽  
Synthetic Data ◽  
Sampling Strategy ◽  
Good Alternative ◽  
Diffusion Method ◽  
Differential Diffusion ◽  
Water Isotope

Abstract. Paleoclimatic information can be retrieved from the diffusion of the stable water isotope signal during firnification of snow. The diffusion length, a measure for the amount of diffusion a layer has experienced, depends on the firn temperature and the accumulation rate. We show that the estimation of the diffusion length using Power Spectral Densities (PSD) of the record of a single isotope species can be biased and is therefore not a reliable proxy for past temperature reconstruction. Using a second water isotope and calculating the difference in diffusion lengths between the two isotopes this problem is circumvented. We study the PSD method applied to two isotopes in detail and additionally present a new forward diffusion method for retrieving the differential diffusion length based on the Pearson correlation between the two isotope signals. The two methods are discussed and extensively tested on synthetic data which are generated in a Monte Carlo manner. We show that calibration of the PSD method with this synthetic data is necessary to be able to objectively determine the differential diffusion length. The correlation based method proofs to be a good alternative for the PSD method as it yields equal or somewhat higher precision than the PSD method. The use of synthetic data also allows us to estimate the accuracy and precision of the two methods and to choose the best sampling strategy to obtain past temperatures with the required precision. Additional to application to synthetic data the two methods are tested on stable isotope records from the EPICA ice core drilled in Dronning Maud Land, Antarctica, showing that reliable firn temperatures can be reconstructed with a typical uncertainty of 1.5 and 2 °C for the Holocene period and 2 and 2.5 °C for the last glacial period for the correlation and PSD method, respectively.

scholarly journals Estimation and calibration of the water isotope differential diffusion length in ice core records

2015 ◽  
Vol 9 (4) ◽  
pp. 1601-1616 ◽  
Author(s):  
G. van der Wel ◽  
H. Fischer ◽  
H. Oerter ◽  
H. Meyer ◽  
H. A. J. Meijer
Keyword(s):  
Diffusion Length ◽  
Accumulation Rate ◽  
Pearson Correlation ◽  
Ice Core ◽  
Synthetic Data ◽  
Sampling Strategy ◽  
Good Alternative ◽  
Diffusion Method ◽  
Differential Diffusion ◽  
Water Isotope

Abstract. Palaeoclimatic information can be retrieved from the diffusion of the stable water isotope signal during firnification of snow. The diffusion length, a measure for the amount of diffusion a layer has experienced, depends on the firn temperature and the accumulation rate. We show that the estimation of the diffusion length using power spectral densities (PSDs) of the record of a single isotope species can be biased by uncertainties in spectral properties of the isotope signal prior to diffusion. By using a second water isotope and calculating the difference in diffusion lengths between the two isotopes, this problem is circumvented. We study the PSD method applied to two isotopes in detail and additionally present a new forward diffusion method for retrieving the differential diffusion length based on the Pearson correlation between the two isotope signals. The two methods are discussed and extensively tested on synthetic data which are generated in a Monte Carlo manner. We show that calibration of the PSD method with this synthetic data is necessary to be able to objectively determine the differential diffusion length. The correlation-based method proves to be a good alternative for the PSD method as it yields precision equal to or somewhat higher than the PSD method. The use of synthetic data also allows us to estimate the accuracy and precision of the two methods and to choose the best sampling strategy to obtain past temperatures with the required precision. In addition to application to synthetic data the two methods are tested on stable-isotope records from the EPICA (European Project for Ice Coring in Antarctica) ice core drilled in Dronning Maud Land, Antarctica, showing that reliable firn temperatures can be reconstructed with a typical uncertainty of 1.5 and 2 °C for the Holocene period and 2 and 2.5 °C for the last glacial period for the correlation and PSD method, respectively.

scholarly journals Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes

2011 ◽  
Vol 7 (2) ◽  
pp. 921-942
Author(s):  
S. B. Simonsen ◽  
S. J. Johnsen ◽  
T. J. Popp ◽  
B. M. Vinther ◽  
V. Gkinis ◽  
...  
Keyword(s):  
Diffusion Process ◽  
Surface Temperature ◽  
Diffusion Length ◽  
Ice Core ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
Differential Diffusion ◽  
Surface Temperatures ◽  
Temperature Reconstructions ◽  
The Difference

Abstract. A new ice core paleothermometer is introduced based on the temperature dependent diffusion of the stable water isotopes in the firn. A new parameter called differential diffusion length is defined as the difference between the diffusion length of the two stable water isotopes 18O and deuterium. A model treatment of the diffusion process of the firn and the ice is presented along with a method of retrieving the diffusion signal from the ice core record of water isotopes using spectral methods. The model shows how the diffusion process is highly dependent on the inter-annual variations in the surface temperatures resulting in a longer diffusion length than by assuming an isothermal firn. The longer diffusion length can be explained by the strong non-linearly behavior of the saturation pressure over ice in the range of the surface temperature fluctuations. The method has been tested on δ18O and δD measurements, spanning the transition from the last glacial to the holocene, from the NorthGRIP ice core. The surface temperature reconstruction based on the differential diffusion resembles other temperature reconstructions for the NorthGRIP ice core. However, the Allerød warming is seen to be significantly warmer than observed in other ice core based temperature reconstructions. The mechanisms behind this behavior are not fully understood. The method shows the need of an expansion of high resolution stable water isotopes data sets from ice cores. However, the new ice core paleothermometer presented here will give valuable insight in past climate, through the physical process of isotope diffusion in the firn column of ice sheets.

scholarly journals Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes

2011 ◽  
Vol 7 (4) ◽  
pp. 1327-1335 ◽  
Author(s):  
S. B. Simonsen ◽  
S. J. Johnsen ◽  
T. J. Popp ◽  
B. M. Vinther ◽  
V. Gkinis ◽  
...  
Keyword(s):  
Diffusion Process ◽  
Surface Temperature ◽  
Diffusion Length ◽  
Ice Core ◽  
Ice Cores ◽  
Water Isotopes ◽  
Differential Diffusion ◽  
Surface Temperatures ◽  
Temperature Reconstructions ◽  
The Difference

Abstract. A new ice core paleothermometer is introduced based on the temperature dependent diffusion of the stable water isotopes in the firn. A new parameter called differential diffusion length is defined as the difference between the diffusion length of the two stable water isotopologues 2H1H16O and 1H218O. A model treatment of the diffusion process of the firn and the ice is presented along with a method of retrieving the diffusion signal from the ice core record of water isotopes using spectral methods. The model shows how the diffusion process is highly dependent on the inter-annual variations in the surface temperatures. It results in a diffusion length longer than if the firn was isothermal. The longer diffusion length can be explained by the strong nonlinearly behaviour of the saturation pressure over ice in the range of the surface temperature fluctuations. The method has been tested on δ18O and δD measurements, spanning the transition from the last glacial to the holocene, from the NorthGRIP ice core. The surface temperature reconstruction based on the differential diffusion resembles other temperature reconstructions for the NorthGRIP ice core. However, the Allerød warming is seen to be significantly warmer than observed in other ice core based temperature reconstructions. The mechanisms behind this behaviour are not fully understood. The method shows the need of an expansion of high resolution stable water isotope datasets from ice cores. However, the new ice core paleothermometer presented here will give valuable insight into past climate, through the physical process of isotope diffusion in the firn column of ice sheets.

scholarly journals Reconstruction of recent climate change in Alaska from the Aurora Peak ice core, central Alaska

2015 ◽  
Vol 11 (2) ◽  
pp. 217-226 ◽  
Author(s):  
A. Tsushima ◽  
S. Matoba ◽  
T. Shiraiwa ◽  
S. Okamoto ◽  
H. Sasaki ◽  
...  
Keyword(s):  
Climate Change ◽  
Accumulation Rate ◽  
Ice Core ◽  
Chemical Species ◽  
Volcanic Eruptions ◽  
Gulf Of Alaska ◽  
Temporal Variations ◽  
Storm Activity ◽  
Alaska Range ◽  
Recent Climate

Abstract. A 180.17 m ice core was drilled at Aurora Peak in the central part of the Alaska Range, Alaska, in 2008 to allow reconstruction of centennial-scale climate change in the northern North Pacific. The 10 m depth temperature in the borehole was −2.2 °C, which corresponded to the annual mean air temperature at the drilling site. In this ice core, there were many melt–refreeze layers due to high temperature and/or strong insolation during summer seasons. We analyzed stable hydrogen isotopes (δD) and chemical species in the ice core. The ice core age was determined by annual counts of δD and seasonal cycles of Na+, and we used reference horizons of tritium peaks in 1963 and 1964, major volcanic eruptions of Mount Spurr in 1992 and Mount Katmai in 1912, and a large forest fire in 2004 as age controls. Here, we show that the chronology of the Aurora Peak ice core from 95.61 m to the top corresponds to the period from 1900 to the summer season of 2008, with a dating error of ± 3 years. We estimated that the mean accumulation rate from 1997 to 2007 (except for 2004) was 2.04 m w.eq. yr-1. Our results suggest that temporal variations in δD and annual accumulation rates are strongly related to shifts in the Pacific Decadal Oscillation index (PDOI). The remarkable increase in annual precipitation since the 1970s has likely been the result of enhanced storm activity associated with shifts in the PDOI during winter in the Gulf of Alaska.

scholarly journals Calculating uncertainty for the RICE ice core continuous flow analysis water isotope record

2018 ◽  
Vol 11 (8) ◽  
pp. 4725-4736 ◽  
Author(s):  
Elizabeth D. Keller ◽  
W. Troy Baisden ◽  
Nancy A. N. Bertler ◽  
B. Daniel Emanuelsson ◽  
Silvia Canessa ◽  
...  
Keyword(s):  
High Resolution ◽  
Continuous Flow ◽  
Ice Core ◽  
Flow Analysis ◽  
Calibration Error ◽  
Data Set ◽  
Total Uncertainty ◽  
Continuous Flow Analysis ◽  
Uncertainty Estimates ◽  
Water Isotope

Abstract. We describe a systematic approach to the calibration and uncertainty estimation of a high-resolution continuous flow analysis (CFA) water isotope (δ2H, δ18O) record from the Roosevelt Island Climate Evolution (RICE) Antarctic ice core. Our method establishes robust uncertainty estimates for CFA δ2H and δ18O measurements, comparable to those reported for discrete sample δ2H and δ18O analysis. Data were calibrated using a time-weighted two-point linear calibration with two standards measured both before and after continuously melting 3 or 4 m of ice core. The error at each data point was calculated as the quadrature sum of three factors: Allan variance error, scatter over our averaging interval (error of the variance) and calibration error (error of the mean). Final mean total uncertainty for the entire record is δ2H=0.74 ‰ and δ18O=0.21 ‰. Uncertainties vary through the data set and were exacerbated by a range of factors, which typically could not be isolated due to the requirements of the multi-instrument CFA campaign. These factors likely occurred in combination and included ice quality, ice breaks, upstream equipment failure, contamination with drill fluid and leaks or valve degradation. We demonstrate that our methodology for documenting uncertainty was effective across periods of uneven system performance and delivered a significant achievement in the precision of high-resolution CFA water isotope measurements.

scholarly journals At what depth is the Eemian layer expected to be found at NEEM?

2008 ◽  
Vol 48 ◽  
pp. 100-102 ◽  
Author(s):  
Susanne L. Buchardt ◽  
Dorthe Dahl-Jensen
Keyword(s):  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Monte Carlo Analysis ◽  
Interglacial Period ◽  
Ice Flow ◽  
North West ◽  
Flow Parameters ◽  
Drill Site ◽  
Radio Echo Sounding

AbstractNo continuous record from Greenland of the Eemian interglacial period (130–115 ka BP) currently exists. However, a new ice-core drill site has been suggested at 77.449˚ N, 51.056˚Win north-west Greenland (North Eemian or NEEM). Radio-echo sounding images and flow model investigations indicate that an undisturbed Eemian record may be obtained at NEEM. In this work, a two-dimensional ice flow model with time-dependent accumulation rate and ice thickness is used to estimate the location of the Eemian layer at the new drill site. The model is used to simulate the ice flow along the ice ridge leading to the drill site. Unknown flow parameters are found through a Monte Carlo analysis of the flow model constrained by observed isochrones in the ice. The results indicate that the Eemian layer is approximately 60m thick and that its base is located approximately 100m above bedrock.

scholarly journals A 2700-year annual timescale and accumulation history for an ice core from Roosevelt Island, West Antarctica

2017 ◽  
Author(s):  
Mai Winstrup ◽  
Paul Vallelonga ◽  
Helle A. Kjær ◽  
Tyler J. Fudge ◽  
James E. Lee ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Early Period ◽  
Volcanic Eruptions ◽  
Snow Accumulation ◽  
Atmospheric Methane ◽  
Accumulation Rates ◽  
West Antarctica ◽  
Ross Ice Shelf ◽  
Accumulation History

Abstract. We present a 2700-year annually resolved timescale for the Roosevelt Island Climate Evolution (RICE) ice core, and reconstruct a past snow accumulation history for the coastal sector of the Ross Ice Shelf in West Antarctica. The timescale was constructed by identifying annual layers in multiple ice-core impurity records, employing both manual and automated counting approaches, and constitutes the top part of the Roosevelt Island Ice Core Chronology 2017 (RICE17). The maritime setting of Roosevelt Island results in high sulfate influx from sea salts and marine biogenic emissions, which prohibits a routine detection of volcanic eruptions in the ice-core records. This led to the use of non-traditional chronological techniques for validating the timescale: RICE was synchronized to the WAIS Divide ice core, on the WD2014 timescale, using volcanic attribution based on direct measurements of ice-core acidity, as well as records of globally-synchronous, centennial-scale variability in atmospheric methane concentrations. The RICE accumulation history suggests stable values of 0.25 m water equivalent (w.e.) per year until around 1260 CE. Uncertainties in the correction for ice flow thinning of annual layers with depth do not allow a firm conclusion about long-term trends in accumulation rates during this early period but from 1260 CE to the present, accumulation rate trends have been consistently negative. The decrease in accumulation rates has been increasingly rapid over the last centuries, with the decrease since 1950 CE being more than 7 times greater than the average over the last 300 years. The current accumulation rate of 0.22 ± 0.06 m w.e. yr−1 (average since 1950 CE, ±1σ) is 1.49 standard deviations (86th percentile) below the mean of 50-year average accumulation rates observed over the last 2700 years.

scholarly journals Climatic Records from the Dunde Ice Cap, China

1988 ◽  
Vol 10 ◽  
pp. 178-182 ◽  
Author(s):  
Lonnie G. Thompson ◽  
Wu Xiaoling ◽  
Ellen Mosley-Thompson ◽  
Xie Zichu
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Average Thickness ◽  
The Past ◽  
Bedrock Topography ◽  
Ice Cap ◽  
Pulse Radar ◽  
Oxygen Isotope Ratios ◽  
Ice Core Record ◽  
Climatic Record

Results from the first glaciological investigation of the Dunde ice cap demonstrate that a long, highly temporally resolvable climatic ice-core record is preserved in this ice cap. Measurements of stratigraphy, microparticle concentrations, liquid conductivity, and oxygen-isotope ratios from three snow pits in 1984 suggest that the annual accumulation is approximately 200 mm (water equivalent). Measurement of microparticle concentrations and conductivities of pit samples collected in 1986 confirm the existence of annual dust layers and an annual accumulation rate of ∼200 mm/year over the past 5 years. Bore-hole temperatures of –5.4°C at 30 m indicate that the ice cap is polar. Mono-pulse radar depth determinations yield an average thickness of 140 m, which (coupled with the smooth bedrock topography and the current accumulation rate) suggest that the Dunde ice cap should contain at least a 3000 year climatic record. A drilling program to recover that record from this subtropical location is planned for 1987.

scholarly journals Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

2013 ◽  
Vol 9 (3) ◽  
pp. 983-999 ◽  
Author(s):  
E. Capron ◽  
A. Landais ◽  
D. Buiron ◽  
A. Cauquoin ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Detailed Comparison ◽  
Last Deglaciation ◽  
Depth Study ◽  
Dronning Maud Land ◽  
The Last Deglaciation ◽  
Correct Estimation ◽  
Lock In

Abstract. Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

Estimating the diffusion length in the deepest section of ice cores; A case study for MIS19 in Dome-C

2021 ◽  
Author(s):  
Thomas Laepple ◽  
Thomas Münch ◽  
Torben Kunz ◽  
Mathieu Casado ◽  
Maria Hoerhold
Keyword(s):  
Diffusion Length ◽  
Ice Core ◽  
Ice Cores ◽  
Climate Information ◽  
Climate Signal ◽  
A Value ◽  
Recovery Strategies ◽  
Length Estimate ◽  
And Diffusion

&lt;p&gt;To recover very old climate information from ice core records, one needs to interpret the deepest part of an ice core. As the oldest record, the Dome-C ice core can serve as an analogue for the Beyond EPICA Oldest Ice Core that is currently being drilled.&lt;br&gt;&lt;br&gt;Pol et al., EPSL 2010 analyzed high resolution water isotope data from the Dome-C ice core and found evidence for a limited preservation of climate variability in the deep section of the core due to mixing and diffusion. For instance, for Marine Isotope Stage 19, the study estimated a mixing/diffusion length between 40 and 60 cm, a value more than double than&amp;#160;what is&amp;#160;predicted by current firn and&amp;#160;ice diffusion&amp;#160;models. Knowing the diffusion length is important to interpret the isotope signal and is the basis to deconvolve climate records. As a result, it is key to bridge the gap in the estimation of the diffusion length between potentially biased statistical methods and firn and ice diffusion models.&lt;br&gt;We review this diffusion length estimate for MIS19, and also outline a new&amp;#160;general&amp;#160;method how to estimate the diffusion length in&amp;#160;highly thinned deep ice.&amp;#160; This approach presents&amp;#160;an important tool for better characterizing the preservation of the climate signal in old ice&amp;#160;and thus&amp;#160;for&amp;#160;designing optimal sampling and recovery strategies.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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