Report: New ice-dating technology gives insight on past climate



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Why use ice cores? How do ice cores work? Layers in the ice Information from ice cores Further reading References Comments. Current period is at right. From bottom to top: Milankovitch cycles connected to 18O. From top to bottom: Ice sheets have one particularly special property. They allow us to go back in time and to sample accumulation, air temperature and air chemistry from another time[1].

Ice core records allow us to generate continuous reconstructions of past climate, going back at leastyears[2]. By looking at past concentrations of greenhouse gasses in layers in ice cores, antarctic ice core dating sites can calculate how modern amounts of carbon dioxide and methane compare to those of the past, and, essentially, compare past antarctic ice core dating sites of greenhouse gasses to temperature. Ice coring has been around since the s. Ice cores have been drilled in ice sheets worldwide, but notably in Greenland[3] and Antarctica[4, 5].

Through analysis of ice cores, scientists learn about glacial-interglacial cycles, changing atmospheric carbon dioxide levels, and climate stability over the last 10, years. Many ice cores have been drilled in Antarctica. This schematic cross section of an ice sheet shows an ideal drilling site at the centre of the polar plateau near the ice divide, with ice flowing away from the ice divide in all direction.

The large Greenland and Antarctic ice sheets have huge, high plateaux where snow accumulates in an ordered fashion. Slow ice flow at the centre of these ice sheets near the ice divide means that the stratigraphy of the snow and ice is preserved. Drilling a vertical hole through this ice involves a serious effort involving many scientists and technicians, and usually involves a static field camp for a prolonged period of time. Shallow ice cores m long are easier to collect and can cover up to a few hundred years antarctic ice core dating sites accumulation, depending on accumulation rates.

Deeper cores require more equipment, and the borehole must be antarctic ice core dating sites with drill fluid to keep it open. The drill fluid used is normally a petroleum-derived liquid like kerosene. It must have a suitable freezing point and viscosity. Collecting the antarctic ice core dating sites ice cores up to m requires a semi permanent scientific camp and a long, multi-year campaign[6]. 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. Seasonal differences in the snow properties create layers — just like rings in trees. Unfortunately, annual layers become harder to see deeper in the ice core. Other ways of dating ice cores include geochemisty, layers of ash tephraelectrical conductivity, and using numerical flow models to understand age-depth relationships.

This 19 cm long of GISP2 ice core from m depth shows annual layers in the ice. 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. Although radiometric dating of ice cores has been difficult, Uranium has been used to date the Dome C ice core from Antarctica. Dust is present in ice cores, and it contains Uranium. The decay of U to U from dust in the ice matrix can antarctic ice core dating sites used to provide an additional core chronology[7].

The thickness of the annual layers in ice cores can be used to derive a precipitation rate after correcting for thinning by glacier flow. Ice cores provide us with lots of information beyond bubbles of gas in the ice. For example, melt layers are related to summer temperatures. More melt layers indicate warmer summer air temperatures. 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. The distribution of melt layers through time is a function of the past climate, and has been used, for example, to show increased melting in the Twentieth Century around the NE Antarctic Peninsula[8]. It is possible to discern past air temperatures from ice cores. This can be related directly to concentrations of carbon dioxide, methane and other greenhouse gasses preserved in the ice.

Snow precipitation over Antarctica is made mostly of H 2 16 O molecules There are also rarer stable isotopes: Past precipitation can be used to reconstruct past palaeoclimatic temperatures. The relationship is consistent and linear over Antarctica[9]. Snow falls over Antarctica and is slowly converted to ice.

The stable isotopes are measured in ice through a mass spectrometer. The figure above shows changes in ice temperature during the last several glacial-interglacial cycles and comparison to changes in global ice volume. The local temperature changes are from two sites in Antarctica and are derived from deuterium isotopic measurements.

An example of using stable isotopes to reconstruct past air temperatures is a shallow ice core drilled in East Antarctica[10]. Disparate records often provide conflicting evidence. This ice core attempted to investigate the evidence for cooler temperatures during this period. The top 50 m of the ice core was analysed at 2. Ice core antarctic ice core dating sites were analysed for stable isotope ratios, major ions and trace elements. An age model was extrapolated to the ice core using a firm decompaction model[10].

The study showed that there were three distinct periods: The area was cooler and stormier. This photograph shows me Bethan Davies visiting Nancy Bertler and antarctic ice core dating sites in her ice core laboratory at GNS, Antarctic ice core dating sites Zealand. The ice core is continuously melted and analysed by numerous automatic machines. The most important property of ice cores is that they are a direct archive of past atmospheric gasses.

Air is trapped at the base of the firn layer, and when the compacted snow turns to ice, the air is trapped in bubbles. This transition normally occurs m below the surface[6]. The offset between the age of the air and the age of the ice is accounted for with well-understood models of firn densification and gas trapping.


Antarctic ice core research at USGS National Ice Core Lab