Continuous-depth analysis of soluble greenhouse gases in ice cores

点击翻译按钮获取中文摘要

Greenhouse gas levels in our atmosphere continue to rise steeply. Concentrations of carbon dioxide, methane and nitrous oxide are higher than at least the last 800,000 years of Earth's history. As our planet warms as a result, we face an uncertain future: how will our climate system respond? What feedbacks might be triggered, or tipping-points surpassed? And how quickly could abrupt changes occur? For answers to these questions, we can look to the past. Polar ice cores are particularly useful because they hold samples of ancient air, on which we can directly measure past changes in greenhouse gases. The current state-of-the-art in ice core analysis involves measuring the chemistry of water and air continuously as a stick of ice core is slowly melted. This method has proven highly effective for methane and has produced unprecedented records at centimetre-scale resolution. However, carbon dioxide, the most important greenhouse gas, and nitrous oxide, cannot yet be measured in this way, which limits the detail we can resolve. Crucially, our current methods make it difficult to resolve natural variability in carbon dioxide and nitrous oxide over human-relevant timescales of decades to centuries. The major challenge is that carbon dioxide and nitrous oxide are highly soluble gases. When ice sticks are melted, both gases quickly dissolve in the water and are difficult to recover. This project will develop a new method to efficiently extract carbon dioxide and nitrous oxide from a continuous stream of melted ice core. A range of factors impacting the degree of dissolution will be systematically tested and optimised. Gases will be measured with a suite of laser spectrometers specially adapted for the low gas flow rates obtained from ice. Parallel measurements on meltwater will be used to constrain the interaction between atmospheric carbon dioxide and carbonate-rich dust. Tests will be carried out on selected Antarctic ice core samples with different greenhouse gas levels to demonstrate the reliability of this innovative method relative to traditional techniques. This exploratory work pushes for a breakthrough in the way we measure greenhouse gases in ice cores. An online, continuous, method that enables high-resolution measurements of the three major greenhouse gases would revolutionise ice core science. Less than a decade ago, state-of-the-art discrete techniques for methane would require many years of analysis to produce a typical ice core record. Today, the same analysis can be done within a few months. This has shifted ice cores gas studies to a new, data-rich era. This work aims to enable a similarly significant scale-shift for scientific studies of carbon dioxide and nitrous oxide.