For example, melt layers are related to summer temperatures. More melt layers indicate warmer summer air temperatures. If we want to reconstruct past air temperatures, one of the most critical parameters is the age of the ice being analysed. Fortunately, ice cores preserve annual layers, making it simple to date the ice. Deeper cores require more equipment, and the borehole must be filled with drill fluid to keep it open. The drill fluid used is normally a petroleum-derived liquid like kerosene. The bottom plot shows global ice volume derived from δ18O measurements on marine microfossils (benthic foraminifera) from a composite of globally distributed marine sediment cores. An example of using stable isotopes to reconstruct past air temperatures is a shallow ice core drilled in East Antarctica. The presence of a “Little Ice Age”, a cooler period ending ~100 to 150 years ago, is contested in Antarctica.
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The thickness of the annual layers in ice cores can be used to derive a precipitation rate (after correcting for thinning by glacier flow). Melt layers are formed when the surface snow melts, releasing water to percolate down through the snow pack. They form bubble-free ice layers, visible in the ice core. This section contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers.
From the US National Oceanic and Atmospheric Administration, Wikimedia Commons.
Past precipitation rates are an important palaeoenvironmental indicator, often correlated to climate change, and it’s an essential parameter for many past climate studies or numerical glacier simulations.