We know the past from a historical record of it written on paper, inscribed in stone, or from depictions of events entrapped in fossils. To understand past climates, scientists look for bubbles of past atmospheres trapped in ice cores as historical record of what happened. Typically, these ice cores could be obtained from three types of locations: (i) glaciers in the temperate region, (ii) glaciers on top of high mountains in the tropical and subtropical zones, and (iii) from the polar ice cap in Antarctica.
Each type of ice cores offers distinct information useful for climatologists to understand paleoclimate (i.e., past climates) over tens of thousands of years, and sometimes, hundreds of thousands of years. So far, the longest continuous time record of past climate extracted from bubbles in ice cores dates back 800000 years. One big differentiator of ice cores from glaciers in the temperate zone to those at ice caps and glaciers on tropical snowcapped mountains is location and their relation to trade winds. Specifically, besides containing a tiny pocket of past atmosphere in ice which reveals the composition of the atmosphere (e.g., the most relevant parameter for climate change research being carbon dioxide concentration), dust and other types of aerosols were also entrapped within compacted ice.
Having known the composition of the bubbles in ice cores, how do we know the year or time in history that corresponds to the atmospheric composition? The answer lies in oxygen isotope ratio analysis. Specifically, by channeling air in the gas bubbles into a mass spectrometer, the relative ratio of oxygen isotope 16 and oxygen isotope 18 (δ16O/δ18O) is determined, and when compared to the ratio present in the contemporary atmosphere, the age of the gas composition extracted could be estimated.
The cutting-edge frontier of paleoclimate research seeks to address two questions: (i) providing more understanding (through ice cores at glaciers of tropical mountains) of the effect of dust and aerosols on past climates, and (ii) determining atmospheric compositional changes far back into the past with a project seeking to drill a continuous ice core at Dome C or F of Antarctica for looking into past climates 1.5 million years ago. With an ice sheet of 3000 metres, the East Antarctic Ice Sheet holds the longest historical record of past atmospheres on Earth, allowing us to reconstruct changes in Earth’s atmosphere far back into time; thereby, yielding new understanding of how climatic changes arise from atmospheric compositional effects, and most importantly, providing a cornerstone to correlate other Earth’s geoscientific parameters to climate change.
Finally, with climate change unabating, the race is on to drill and collect as many ice cores from glaciers and ice caps on tropical mountains to chronologically archive changes in Earth’s trade winds patterns, and how dust and aerosols affect past Earth’s climate. Most of these ice cores are stored at American and European laboratories for further research.
Collectively, ice cores tell a story of how atmospheric composition evolved in relation to climatic parameters in a continuous trajectory limited by the depth of snow cover over a specific locale. Trapped in bubbles, analysis of atmospheric composition via gas chromatography and oxygen isotope ratio analysis would reveal patterns of fluctuations of key atmospheric gases such as carbon dioxide that correlates with temperature changes; thereby, allowing a lens into past climate. But, the enduring question remains our ability to obtain samples of past climate before they are released as gases as the ice caps protecting them melts under increasing temperature.
Category: atmospheric science, climate change,
Tags: climate change, atmospheric chemistry, ice cores, gas bubbles, isotopic analysis, mass spectrometry,