Showing papers by "Sigfus J Johnsen published in 2014"

A continuous stream flash evaporator for the calibration of an IR cavity ring down spectrometer for isotopic analysis of water

Abstract: A new technique for high resolution simultaneous isotopic analysis of $\delta^{18}\mathrm{O}$ and $\delta\mathrm{D}$ in liquid water is presented. A continuous stream flash evaporator has been designed that is able to vaporise a stream of liquid water in a continuous mode and deliver a stable and finely controlled water vapour sample to a commercially available Infra Red Cavity Ring Down Spectrometer. Injection of sub $\mu l$ amounts of the liquid water is achieved by pumping liquid water sample through a fused silica capillary and instantaneously vaporising it with a 100% efficiency in a home made oven at a temperature of $170 ^{o}$C. The system's simplicity, low power consumption and low dead volume together with the possibility for automated unattended operation, provides a solution for the calibration of laser instruments performing isotopic analysis of water vapour. Our work is mainly driven by the possibility to perform high resolution on line water isotopic analysis on Continuous Flow Analysis systems typically used to analyze the chemical composition of ice cores drilled in polar regions. In the following we describe the system's precision and stability, sensitivity to varying levels of sample size and we assess the observed memory effects. A test run with standard waters of different isotopic composition is presented, demonstrating the ability to calibrate the spectrometer's measurements on a VSMOW scale with a relatively simple and fast procedure.

The investigation and experience of using ESTISOL™ 240 and COASOL™ for ice-core drilling

Abstract: Continuous good-quality deep ice cores provide excellent scientific data with which to reconstruct a past climate record for >800 ka. At depths starting from ∼100m using an electromechanical drill, a drilling liquid is essential for successful recovery of the very high-quality ice cores demanded by modern scientific analysis techniques (e.g. continuous flow analysis). Finding a suitable drill fluid for use at deep ice-coring drill sites is not an easy task. Temperatures vary greatly not just from site to site, but also at a site where the average mean temperature from surface to bedrock can vary from –55°C to –2.75°C. In the past 60 years, many fluids have been used, with varying degrees of success, but for various reasons are either unavailable, are now considered unsafe and dangerous or are too environmentally damaging to be permitted. Here we report on our pre-season investigation into possible candidate drill fluids, with specific information concerning ESTISOL™ 240 and COASOL™, the rationale behind the redesign of our drill successfully used at NorthGRIP, Greenland, and EPICA DML, Antarctica, the knock-on effect of those changes, and our field experience in Greenland at Flade Isblink in 2006 and at NEEM in 2009–10.

Modelling the response of stable water isotopes in Greenland precipitation to orbital configurations of the previous interglacial

Abstract: The relation between δ 18 O of precipitation and temperature has been used in numerous studies to reconstruct past temperatures at ice core sites in Greenland and Antarctica. During the past two decades, it has become clear that the slope between δ 18 O and temperature varies in both space and time. Here, we use a general circulation model driven by changes in orbital parameters to investigate the Greenland δ 18 O–temperature relation for the previous interglacial, the Eemian. In our analysis, we focus on changes in the moisture source regions, and the results underline the importance of taking the seasonality of climate change into account. The orbitally driven experiments show that continental evaporation over North America increases during summer in the warm parts of the Eemian, while marine evaporation decreases. This likely flattens the Greenland δ 18 O response to temperature during summer. Since the main climate change in the experiments occurs during summer this adds to a limited response of δ 18 O, which is more strongly tied to temperature during winter than during summer. A south–west to north–east gradient in the δ 18 O–temperature slope is also evident for Greenland, with low slopes in the south–west and steeper slopes in the north–east. This probably reflects the proportion of continental moisture and Arctic moisture arriving in Greenland, with more continental moisture in the south–west and less in the north–east, and vice versa for the Arctic moisture. Keywords: stable water isotopes, modelling, moisture source, seasonality, previous interglacial (Published: 9 September 2014) Citation: Tellus B 2014, 66 , 22872, http://dx.doi.org/10.3402/tellusb.v66.22872 To access the supplementary material to this article, please see Supplementary files under Article Tools online.