Laser assisted detection of past climate in ice cores

Around the poles, ice accumulated over millions of years can reach depths of several kilometers. The undisturbed deep ice preserves information about the past. The air bags and particles trapped in the ice tell scientists what the atmosphere used to be like. This has aroused great interest among paleoclimatologists in glacier ice cores.

By regularly sampling the ice core at its depth, they can reconstruct the past climate and its evolution over time. Like many other elements, hydrogen and oxygen have rarer and heavier variants or isotopes. Due to the fact that lighter variants are more prone to evaporation, the ratio of heavy to light isotopes of hydrogen and oxygen isotopes in the ice core can represent the temperature at which ice formed.

However, as researchers delve deeper, they discover older ice layers that are only a few millimeters thin each year. This type of ice is difficult to study using existing methods that provide centimeter level resolution. For example, a method based on laser ablation can violently shake the surface of an ice core. This is very similar to evaporation and can disrupt the ratio of isotopes, thereby limiting the resolution of laser ablation.

In a study published in the Journal of Glaciology, researchers at the Seiko Center of the Japanese Institute of Physics and Chemistry reported a laser melting method to study finer ice core slices. It can analyze stable water isotopes in ice cores as thin as three millimeters, "said Yuko Motizuki, the corresponding author of the study.

Motizuki and his team have developed a laser melting sampler that can emit lasers through optical fibers. When a laser hits a specific point on the ice core, it will melt the ice into water. The nozzle connected to the end of the optical fiber extracts molten water into a stainless steel vial. But then the researchers encountered another challenge - laser heating of the sample and changing isotope levels.
To avoid this situation, the research team carefully optimized the laser power, the speed at which the nozzle cuts through the ice layer, and the speed at which the melted sample is extracted by vacuum. The system achieves a delicate balance between speed and heat, allowing for rapid melting of ice below boiling point without interfering with isotopes, thereby achieving more accurate measurements.

Next, they validated the practicality of the laser melting method by conducting tests on ice cores at Dome Fuji, a Japanese research station in Antarctica. They recorded 51 observations at intervals of 3 millimeters at depths exceeding 90 meters. Although this depth was chosen to facilitate validation using other methods, with its higher resolution, the new method will enable paleoclimatologists to study past climates from deeper and older ice cores.

Imagine a dramatic, one-time event that quickly changed the temperature in the past. Although such an event may generate great interest, it is difficult to determine when it actually occurred without addressing past temperatures every year. The new method pushes back the time range until researchers are able to detect such events, and if the event occurred in the recent past, more accurately determines when it occurred.

In addition to unexpected events, this method will also enhance the understanding of natural solar changes. The heat radiated by the sun changes periodically, affecting the temperature on Earth. By determining the annual temperature in the distant past, scientists can better distinguish between temperature changes caused by solar activity and temperature changes caused by anthropogenic global warming.

Studying past climates also provides clues for the future. If we understand past natural changes, we can more accurately predict the future of global warming, "Motizuki said.

Source: Laser Network