ALBERT

Description: A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of d18O and dD on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub µl amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1 per mil and 0.5 per mil for d18O and dD, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of d18O and dD, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

Description: A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of d18O and dD on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub µl amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1 per mil and 0.5 per mil for d18O and dD, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of d18O and dD, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

Description: Abstract: We present here a high resolution (0.11 m) dataset of the isotopic composition of the ice (δ¹⁸O) from the EPICA Dome-C ice core. The dataset covers the depth range 7.81-3189.89 m (0.05-802.427 ka). Analysis is performed in Copenhagen with a CO~2~ equilibration Mass Spectrometry system (Finnegan MAT 251). Samples of 5 ml are equilibrated with CO~2~ for 6 hours under vibrations, thereafter injected to the mass spectrometer where the ¹⁸O/¹⁶O ratio is obtained on masses 46 and 44. All measurements reported on the SMOW-SLAP scale using a 2-point linear calibration (standards used: Crete: -33.61 ‰ and DC02: -54.11 ‰ . The combined uncertainty of the record is 0.07 ‰. We interpolate the dataset on the AICC2012 chronology.

Description: A high resolution (0.05 m) water isotopic record (d18O) is available from the NorthGRIP ice core. In this study we look into the water isotope diffusion history as estimated by the spectral characteristics of the d18O time series covering the last 16,000 years. The diffusion of water vapor in the porous medium of the firn pack attenuates the initial isotopic signal, predominantly having an impact on the high frequency components of the power spectrum. Higher temperatures induce higher rates of smoothing and thus the signal can be used as a firn paleothermometer. We use a water isotope diffusion model coupled to a steady-state densification model in order to infer the temperature signal from the site, assuming the accumulation and strain rate history as estimated using the GICC05 layer counted chronology and a Dansgaard-Johnsen ice flow model. The temperature reconstruction accurately captures the timing and magnitude of the Bølling-Allerød and Younger Dryas transitions. A Holocene climatic optimum is seen between 7 and 9 ky b2k with an apparent cooling trend thereafter. Our temperature estimate for the Holocene climatic optimum, points to a necessary adjustment of the ice thinning function indicating that the ice flow model overestimates past accumulation rates by about 10% at 8 ky b2k. This result, is supported by recent gas isotopic fractionation studies proposing a similar reduction for glacial conditions. Finally, the record presents a climatic variability over the Holocene spanning millennial and centennial scales with a profound cooling occurring at approximately 4000 years b2k. The new reconstruction technique is able to provide past temperature estimates by overcoming the issues apparent in the use of the classical d18O slope method. It can at the same time resolve temperature signals at low and high frequencies.

Description: Polar precipitation archived in ice caps contains information on past temperature conditions. Such information can be retrieved by measuring the water isotopic signals of ?18O and ?D in ice cores. These signals have been attenuated during densification due to molecular diffusion in the firn column, where the magnitude of the diffusion is isotopologoue specific and temperature dependent. By utilizing the differential diffusion signal, dual isotope measurements of d18O and dD enable multiple temperature reconstruction techniques. This study assesses how well six different methods can be used to reconstruct past surface temperatures from the diffusion-based temperature proxies. Two of the methods are based on the single diffusion lengths of d18O and dD, three of the methods employ the differential diffusion signal, while the last uses the ratio between the single diffusion lengths. All techniques are tested on synthetic data in order to evaluate their accuracy and precision. We perform a benchmark test to thirteen high resolution Holocene data sets from Greenland and Antarctica, which represent a broad range of mean annual surface temperatures and accumulation rates. Based on the benchmark test, we comment on the accuracy and precision of the methods. Both the benchmark test and the synthetic data test demonstrate that the most precise reconstructions are obtained when using the single isotope diffusion lengths, with precisions of approximately 1.0°C. In the benchmark test, the single isotope diffusion lengths are also found to reconstruct consistent temperatures with a root mean-square-deviation of 0.7°C. The techniques employing the differential diffusion signals are more uncertain, where the most precise method has a precision of 1.9°C. The diffusion length ratio method is the least precise with a precision of 13.7°C. The absolute temperature estimates from this method are also shown to be highly sensitive to the choice of fractionation factor parameterization.

Description: This study examines the stable water isotope signal (δ18O) of three ice cores drilled on the Renland peninsula (East Greenland coast). While ice core δ18O measurements qualitatively are a measure of the local temperature history, the δ18O variability in precipitation actually reflects the integrated hydrological activity that the deposited ice experienced from the evaporation source to the condensation site. Thus, as Renland is located next to a fluctuating sea ice cover, the transfer function used to infer past temperatures from the δ18O variability is potentially influenced by variations in the local moisture conditions. The objective of this study is therefore to evaluate the δ18O variability of ice cores drilled on Renland and examine what amount of the signal that can be attributed to regional temperature variations. In the analysis, three ice cores are utilized to create stacked summer, winter and annually averaged δ18O signals (AD 1801-2014). The imprint of temperature on δ18O is first examined by correlating the δ18O stacks with instrumental temperature records from East Greenland (AD 1895-2014) and Iceland (AD 1830-2014) and with the regional climate model HIRHAM5 (AD 1980-2014). The results show that the δ18O variability correlates with regional temperatures on both a seasonal and an annual scale between 1910-2014 while δ18O is uncorrelated with Iceland temperatures between 1830-1909. Our analysis indicates that the unstable regional δ18O-temperature correlation does not result from changes in weather patterns through respectively strengthening and weakening of the North Atlantic Oscillation. Instead, the results imply that the varying δ18O-temperature relation is connected with the volume flux of sea ice exported through Fram Strait (and south along the coast of East Greenland). Notably, the δ18O variability only reflects the variations in regional temperature when the temperature anomaly is positive and the sea ice export anomaly is negative. It is hypothesized that this could be caused by a larger sea ice volume flux during cold years which suppresses the Iceland temperature signature in the Renland δ18O signal. However, more isotope-enabled modeling studies with emphasis on coastal ice caps are needed in order to quantify the mechanisms behind this observation. As the amount of Renland δ18O variability that reflects regional temperature varies with time, the results have implications for studies performing regression-based δ18O-temperature reconstructions based on ice cores drilled in the vicinity of a fluctuating sea ice cover.

Description: A first chronology for the East GReenland Ice core Project (EGRIP) over the Holocene and last glacial termination has been derived by transferring the annual layer counted Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP core to the EGRIP core using 381 matchpoints of mainly on volcanic events and common patterns (peaks and dips) recorded by electrical conductivity measurement (ECM) and dielectrical profiling (DEP) records.

Description: A first chronology for the East GReenland Ice core Project (EGRIP) over the Holocene and last glacial termination has been derived by transferring the annual layer counted Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP core to the EGRIP core using 381 matchpoints of mainly on volcanic events and common patterns (peaks and dips) recorded by electrical conductivity measurement (ECM) and dielectrical profiling (DEP) records.