Post-depositional processes visible in the integration of EGRIP high-resolution water isotope record and visual stratigraphy

With recent advances in analytical techniques, water stable isotope ratios can be measured in astounding detail in ice core records (~mm scale or equivalent to subannual resolution). While this has enabled the study of past climates across a vast range of timescales, the full set of processes driving the highest frequency variability in these water isotope records remains poorly understood. In the EastGRIP ice core, we observe a strong relationship between high-frequency water isotope anomalies (sharp transitions on the scale of cms) and variability in the visual stratigraphy of the ice. The water isotope timeseries reveals these anomalies that would otherwise be missed using traditional lower resolution discrete sampling methods (5-50 cm scale).&#160; A comparison with the dark-field imaging of stratigraphic layers (high-resolution line-scanning system; 50&#181;m/pix) from the EGRIP ice core indicates a correlation between bubble-free ice layers and the sharp transitions observed in the isotope record.&#160; Prior to this comparison, such anomalies in high-resolution isotope records were often dismissed as analytical artifacts. The striking correspondence to the bubble-free ice layers, which is a parameter measured independently from the isotopes, suggests the isotope variability is real. We are investigating a range of depositional and post-depositional processes that may may be able to explain the origin of this variability and its relationship to the physical properties of the ice. This study has implications for frequency analysis of the isotope data, and the related analysis of isotope diffusion and its effects on the recorded climate signal. Understanding these anomalies opens new doors to the interpretation of climate signals in ice cores.

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The Effect of Surface Sublimation on the Snow Isotope Signal

10.5194/egusphere-egu21-9701 ◽

2021 ◽

Author(s):

Sonja Wahl ◽

Alexandra Zuhr ◽

Maria Hörhold ◽

Anne-Katrine Faber ◽

Hans Christian Steen-Larsen

Keyword(s):

Isotopic Composition ◽

Climate Modeling ◽

Ice Core ◽

Greenland Ice Sheet ◽

Layer By Layer ◽

Climate Signal ◽

North East ◽

Depositional Processes ◽

Surface Snow ◽

Water Isotope

Post-depositional processes affect the stable water isotope signal of surface snow between precipitation events.&#160;Combined vapor-snow exchange processes and isotope diffusion influence the top layer of snow as well as buried layers below.&#160;This implies, that ice core isotope climate proxy records can not be interpreted as a precipitation weighted temperature signal alone.Here we present to what extend surface sublimation can explain in-situ observed changes of the stable water isotope signal in the snow. We use direct observations of the isotopic composition of the sublimation flux together with surface snow samples taken in the North-East of the Greenland Ice Sheet accumulation zone throughout the summer months of 2019 to demonstrate sublimation impacts. We show that, contrary to the understanding of effectless layer-by-layer removal of snow, sublimation involves fractionation and therefore influences the isotopic composition of the snow.&#160;Complementary measurements of humidity as well as isotope fluxes constrain the local vapor snow exchange and allow for the quantification of post-depositional influences while the snow is exposed to the atmosphere. This improved process understanding of the formation of the climate signal found in snow is important for merging climate modeling and ice core proxies.&#160;

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Local scale depositional processes of surface snow on the Greenland ice sheet

10.5194/tc-2021-36 ◽

2021 ◽

Author(s):

Alexandra M. Zuhr ◽

Thomas Münch ◽

Hans Christian Steen-Larsen ◽

Maria Hörhold ◽

Thomas Laepple

Keyword(s):

Spatial Scales ◽

Ice Core ◽

Negative Relationship ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Snow Accumulation ◽

Data Set ◽

Climate Signal ◽

Depositional Processes ◽

Snow Deposition

Abstract. Ice cores from polar ice sheets and glaciers are an important climate archive. Snow layers, consecutively deposited and buried, contain climatic information of the time of their formation. However, particularly low-accumulation areas are characterised by temporally intermittent precipitation, which can be further re-distributed after initial deposition. Therefore, the local conditions of accumulation at an ice core site influence the quantity and quality of the recorded climate signal in proxy records. Local surface features at different spatial scales further affect the signal imprint. This study therefore aims to characterise the local accumulation patterns and the evolution of the snow height to describe the contribution of snow (re-)deposition to noise in climate records from ice cores. By using a photogrammetry Structure-from-Motion approach, we generated near-daily elevation models of the snow surface for a 195 m2 area in the vicinity of the deep drilling site of the East Greenland Ice Core Project in northeast Greenland. Based on the snow height information we derived snow height changes on a day-to-day basis throughout our observation period from May to August 2018. Specifically, the average snow height increased by ~11 cm. The spatial and temporal data set allowed an investigation of snow deposition versus depositional modifications. We observed irregular snow deposition, erosion, and the re-distribution of snow, which caused uneven snow accumulation patterns, a removal of more than 60 % of the deposited snow, and a negative relationship between the initial snow height and the amount of accumulated snow. Furthermore, the surface roughness decreased from 4 to 2 cm throughout the spring and summer season at our study site. Finally, our study further shows that our method has several advantages over previous approaches, making it possible to demonstrate the importance of accumulation intermittency, and the potential influences of depositional processes on proxy signals in snow and ice.

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Using high-resolution tritium profiles to quantify the effects of melt on two Spitsbergen ice cores

Journal of Glaciology ◽

10.3189/002214311798843368 ◽

2011 ◽

Vol 57 (206) ◽

pp. 1087-1097 ◽

Cited By ~ 18

Author(s):

L.G. Van Der Wel ◽

H.J. Streurman ◽

E. Isaksson ◽

M.M. Helsen ◽

R.S.W. Van De Wal ◽

...

Keyword(s):

High Resolution ◽

Ice Core ◽

Radioactive Decay ◽

Ice Cores ◽

Density Profiles ◽

Ice Caps ◽

Depositional Processes ◽

Precipitation Record ◽

Main Effect ◽

Climatic Information

AbstractIce cores from small ice caps provide valuable climatic information, additional to that of Greenland and Antarctica. However, their integrity is usually compromised by summer meltwater percolation. To determine to what extent this can affect such ice cores, we performed high-resolution tritium measurements on samples from two ice cores from Spitsbergen covering the period AD1955–75. The very sharp and distinct peaks in the tritium precipitation record are subject to several post-depositional processes. We developed a model that uses the precipitation record as input and incorporates the three most important processes (radioactive decay, isotope diffusion and meltwater percolation). Results are compared with measured tritium and density profiles. Both ice-core records contain sharp bomb peaks in the pre-1963 period. It is shown that these peaks would be much smoother in the absence of melt. In this case the main effect of melt and the refreezing of percolation water is the formation of ice layers that form barriers for firn diffusion; thus melt paradoxically results in better preservation of the annual isotope signals. Conversely, for the period after 1963 the main effect of melt is a stronger smoothing of the tritium profiles.

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The role of sublimation as a driver of climate signals in the water isotope content of surface snow: Laboratory and field experimental results

10.5194/tc-2021-87 ◽

2021 ◽

Author(s):

Abigail G. Hughes ◽

Sonja Wahl ◽

Tyler R. Jones ◽

Alexandra Zuhr ◽

Maria Hörhold ◽

...

Keyword(s):

Isotopic Composition ◽

Laboratory Experiments ◽

Ice Core ◽

Water Isotopes ◽

Driving Mechanism ◽

Climate Signal ◽

Depositional Processes ◽

Surface Snow ◽

Isotope Content ◽

Water Isotope

Abstract. Ice core water isotope records from Greenland and Antarctica are a valuable proxy for paleoclimate reconstruction, yet the processes inﬂuencing the climate signal stored in the isotopic composition of the snow are being revisited. Apart from precipitation input, post-depositional processes such as wind-driven redistribution and vapor-snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal. Recent ﬁeld studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor- snow exchange is an important driving mechanism. Here we investigate how vapor-snow exchange and sublimation processes inﬂuence the isotopic composition of the snowpack. Controlled laboratory experiments under dry air ﬂow show an increase of snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer, with an attenuated signal down to 3 cm snow depth over the course of 4–6 days. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Using a simple mass-balance and diffusion box model in conjunction with our observed laboratory vapor isotope signals, we are able to reproduce the observed changes in the snow. This conﬁrms that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 day ﬁeld experiments at the East Greenland Ice Core Project site (Northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions, and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation play a role in creating the climate signal recorded in the water isotopes in surface snow. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such.

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Local-scale deposition of surface snow on the Greenland ice sheet

The Cryosphere ◽

10.5194/tc-15-4873-2021 ◽

2021 ◽

Vol 15 (10) ◽

pp. 4873-4900

Author(s):

Alexandra M. Zuhr ◽

Thomas Münch ◽

Hans Christian Steen-Larsen ◽

Maria Hörhold ◽

Thomas Laepple

Keyword(s):

Structure From Motion ◽

Ice Core ◽

Ice Cores ◽

Snow Accumulation ◽

Data Set ◽

Simple Method ◽

Climate Signal ◽

Depositional Processes ◽

Surface Snow ◽

Snow Deposition

Abstract. Ice cores from polar ice sheets and glaciers are an important climate archive. Snow layers, consecutively deposited and buried, contain climatic information from the time of their formation. However, particularly low-accumulation areas are characterised by temporally intermittent precipitation, which can be further redistributed after initial deposition, depending on the local surface features at different spatial scales. Therefore, the accumulation conditions at an ice core site influence the quantity and quality of the recorded climate signal in proxy records. This study aims to characterise the local accumulation patterns and the evolution of the snow height to describe the contribution of the snow (re-)deposition to the overall noise level in climate records from ice cores. To this end, we applied a structure-from-motion photogrammetry approach to generate near-daily elevation models of the surface snow for a 195 m2 area in the vicinity of the deep drilling site of the East Greenland Ice-core Project in northeast Greenland. Based on the snow height information we derive snow height changes on a day-to-day basis throughout our observation period from May to August 2018 and find an average snow height increase of ∼ 11 cm. The spatial and temporal data set also allows an investigation of snow deposition versus depositional modifications. We observe irregular snow deposition and erosion causing uneven snow accumulation patterns, a removal of more than 60 % of the deposited snow, and a negative relationship between the initial snow height and the amount of accumulated snow. Furthermore, the surface roughness decreased by approximately a factor of 2 throughout the spring and summer season at our study site. Finally, our study shows that structure from motion is a relatively simple method to demonstrate the potential influences of depositional processes on proxy signals in snow and ice.

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Weighting alternative for water stable isotopes: Statical comparison between station- and firn/ice-records

Polish Polar Research ◽

10.1515/popore-2017-0006 ◽

2017 ◽

Vol 38 (2) ◽

pp. 105-124

Author(s):

István Gábor Hatvani ◽

Zoltán Kern

Keyword(s):

Stable Isotope ◽

Air Temperature ◽

Ice Core ◽

Precipitation Amount ◽

Ice Cores ◽

Arithmetic Means ◽

Depositional Processes ◽

Water Stable Isotope ◽

Annual Water ◽

Water Isotope

Abstract It is generally accepted that ice cores archive amount-weighted water stable isotope signals. In order to achieve an improved understanding of the nature of water stable isotope signals stored in ice cores annual δ18O and δ2H averages (i.e. amount-weighted) were calculated for two Antarctic meteorological stations, Vernadsky and Halley Bay, using monthly precipitation amount and monthly net accumulation as weights, respectively. These were then compared with the annual mean δ18O δ2H and records of the nearest available ice cores. In addition, at the stations, both arithmetic means (i.e. time-weighted) and amount-weighted (precipitation amount and net accumulation used as weights) annual air temperature averages were calculated and then compared to amount weighted annual mean δ18O and δ2H using correlation- and regression analyses. The main hypothesis was that amount weighted annual mean water isotope and temperature records from the stations would be able to replicate the annual water isotope signal stored in ice cores to a higher degree. Results showed that (i) amount weighting is incapable of ameliorating the signal replication between the stations and the ice cores, while arithmetic means gave the stronger linear relationships; (ii) post depositional processes may have a more determining effect on the isotopic composition of the firn than expected; and (iii) mean annual air temperature provided the closest match to ice core derived annual water isotope records. This latter conveys a similar message to that of recent findings, in as much as ambient temperature, via equilibrium isotope fractionation, is imprinted into the uppermost snow layer by vapor exchange even between precipitation events. Together, these observations imply that ice core stable water isotope records can be a more continuous archive of near-surface temperature changes than hitherto believed.

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Surface mass balance and water stable isotopes derived from firn cores on three ice rises, Fimbul Ice Shelf, Antarctica

The Cryosphere ◽

10.5194/tc-10-2763-2016 ◽

2016 ◽

Vol 10 (6) ◽

pp. 2763-2777 ◽

Cited By ~ 8

Author(s):

Carmen P. Vega ◽

Elisabeth Schlosser ◽

Dmitry V. Divine ◽

Jack Kohler ◽

Tõnu Martma ◽

...

Keyword(s):

High Resolution ◽

Stable Isotope ◽

Mass Balance ◽

Temporal Variability ◽

Ice Cores ◽

Surface Mass Balance ◽

Ice Shelf ◽

Climate Signal ◽

Surface Mass ◽

Water Stable Isotope

Abstract. Three shallow firn cores were retrieved in the austral summers of 2011/12 and 2013/14 on the ice rises Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blåskimen Island (BI), all part of Fimbul Ice Shelf (FIS) in western Dronning Maud Land (DML), Antarctica. The cores were dated back to 1958 (KC), 1995 (KM), and 1996 (BI) by annual layer counting using high-resolution oxygen isotope (δ18O) data, and by identifying volcanic horizons using non-sea-salt sulfate (nssSO42−) data. The water stable isotope records show that the atmospheric signature of the annual snow accumulation cycle is well preserved in the firn column, especially at KM and BI. We are able to determine the annual surface mass balance (SMB), as well as the mean SMB values between identified volcanic horizons. Average SMB at the KM and BI sites (0.68 and 0.70 mw. e. yr−1) was higher than at the KC site (0.24 mw. e. yr−1), and there was greater temporal variability as well. Trends in the SMB and δ18O records from the KC core over the period of 1958–2012 agree well with other previously investigated cores in the area, thus the KC site could be considered the most representative of the climate of the region. Cores from KM and BI appear to be more affected by local meteorological conditions and surface topography. Our results suggest that the ice rises are suitable sites for the retrieval of longer firn and ice cores, but that BI has the best preserved seasonal cycles of the three records and is thus the most optimal site for high-resolution studies of temporal variability of the climate signal. Deuterium excess data suggest a possible effect of seasonal moisture transport changes on the annual isotopic signal. In agreement with previous studies, large-scale atmospheric circulation patterns most likely provide the dominant influence on water stable isotope ratios preserved at the core sites.

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

Atmospheric Measurement Techniques ◽

10.5194/amt-11-4725-2018 ◽

2018 ◽

Vol 11 (8) ◽

pp. 4725-4736 ◽

Cited By ~ 2

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.

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

10.5194/egusphere-egu21-14089 ◽

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

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. 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&#160;what is&#160;predicted by current firn and&#160;ice diffusion&#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. We review this diffusion length estimate for MIS19, and also outline a new&#160;general&#160;method how to estimate the diffusion length in&#160;highly thinned deep ice.&#160; This approach presents&#160;an important tool for better characterizing the preservation of the climate signal in old ice&#160;and thus&#160;for&#160;designing optimal sampling and recovery strategies.&#160;

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Tephra in the Greenland Ice cores: Insights into Icelandic volcano-climate impacts

10.5194/egusphere-egu21-9187 ◽

2021 ◽

Author(s):

Imogen Gabriel ◽

Gill Plunkett ◽

Peter Abbott ◽

Bergrún Óladóttir ◽

Joseph McConnell ◽

...

Keyword(s):

High Resolution ◽

Ice Core ◽

Ice Cores ◽

Volcanic Eruptions ◽

Climate Impacts ◽

Geochemical Analysis ◽

Volcanic Events ◽

Societal Impacts ◽

The Impact ◽

Ice Core Records

Volcanic eruptions are considered as one of the primary natural drivers for changes in the global climate system and understanding the impact of past eruptions on the climate is integral to adopt appropriate responses towards future volcanic eruptions.The Greenland ice core records are dominated by Icelandic eruptions, with several volcanic systems (Katla, Hekla, B&#225;r&#240;arbunga-Vei&#240;iv&#246;tn and Grimsv&#246;tn) being highly active throughout the Holocene. A notable period of increased Icelandic volcanic activity occurred between 500-1250 AD and coincided with climatic changes in the North Atlantic region which may have facilitated the Viking settlement of Greenland and Iceland. However, a number of these volcanic events are poorly constrained (duration and magnitude). Consequently, the Greenland ice cores offer the opportunity to reliably reconstruct past Icelandic volcanism (duration, magnitude and frequency) due to their high-resolution, the proximity of Iceland to Greenland and subsequent increased likelihood of volcanic fallout deposits (tephra particles and sulphur aerosols) being preserved. However, both the high frequency of eruptions between 500-1250 AD and the geochemical similarity of Iceland&#8217;s volcanic centres present challenges in making the required robust geochemical correlations between the source volcano and the ice core records and ultimately reliably assessing the climatic-societal impacts of these eruptions.To address this, we use two Greenland ice core records (TUNU2013 and B19) and undertake geochemical analysis on tephra from the volcanic events in the selected time window which have been detected and sampled using novel techniques (insoluble particle peaks and sulphur acidity peaks). Further geochemical analysis of proximal material enables robust correlations to be made between the events in the ice core records and their volcanic centres. The high-resolution of these polar archives provides a precise age for the event and when utilised alongside other proxies (i.e. sulphur aerosols), both the duration and magnitude of these eruptions can be constrained, and the climatic-societal impacts of these eruptions reliably assessed.

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