These limitations will become even more critical with the advent of a new “Oldest Ice” ice core from East Antarctica (Beyond EPICA – Oldest Ice Core, BE-OIC) that aims to extend the ice core greenhouse gas records over the last 1.5 Myr.
MORTAL KOMBAT PROJECT 4.1 SEASON 2.9 RESOLUTION FULL
This is particularly pronounced for δ 13CO 2, where data are only available for selected time intervals during the last glacial cycle and often lack the required precision to make full use of this parameter ( Schmitt et al., 2012 Schneider et al., 2013 Eggleston et al., 2016 Bauska et al., 2018). However, due to the time-consuming and technically challenging nature of ice core analyses and the limited sample availability, the records are still restricted in precision and resolution. Reconstructing paleo-atmospheric changes in these gases and their isotopic composition has provided valuable insights into their biogeochemical cycles ( Blunier and Brook, 2001 Loulergue et al., 2008 Schilt et al., 2010 a Mitchell et al., 2011 Schmitt et al., 2012 Marcott et al., 2014 Bereiter et al., 2015 Bauska et al., 2018 Nehrbass-Ahles et al., 2020). Ice cores are unique natural archives preserving valuable information on atmospheric greenhouse gas concentrations ( CO 2, CH 4, and N 2O) in typically centennial resolution over hundreds of thousands of years. Moreover, Antarctic ice samples were measured to confirm the measurement performance, covering the range of variability expected in Pleistocene ice and highlighting the vertical resolution capabilities critical for its application within BE-OIC. The combined extraction and analysis system was extensively tested by sublimating gas-free ice with introduction of a standard gas to determine the accuracy and characterize potential artifacts. Besides the low sample volume requirements and the vertical resolution capabilities, the described method holds additional advantages over previous methods, including the immunity of the highly specific QCLAS analysis to drilling fluid contamination as well as the non-destructive nature of the spectroscopic gas analysis. This is accomplished by employing a directional and continuous laser-induced sublimation followed by analysis of the sample gas by a quantum cascade laser absorption spectrometer (QCLAS). We present a novel combined system for the extraction and the simultaneous measurement of CO 2, CH 4, and N 2O concentrations, as well as δ 13CO 2, which achieves a vertical resolution of 1–2 cm ( 3.5×3.5 cm cross section) with precisions of 0.4 ppm, 3 ppb, 1 ppb, and 0.04 ‰, respectively, in sublimation tests with standard gas over gas-free ice. Accordingly, for a century-scale resolution, the sample vertical extent must be reduced to a few centimeters containing only about 1–2 mL air STP. The ice from this period is expected to be close to bedrock and, due to glacier flow, extremely thinned with 15 000 years of climate history contained in only 1 m of ice. These aspects will become especially crucial for ice cores that aim to extend the ice core record to the last 1.5 Myr, i.e., across the Mid-Pleistocene Transition (as currently drilled within the European project Beyond EPICA – Oldest Ice Core (BE-OIC)). Precision, accuracy, and temporal resolution are key to making full use of atmospheric trace gas records in ice cores.
0 kommentar(er)
