WAIS Divide ice coring


Ice sticks and isotopes: The Continuous Flow Melt System

We have developed a new technique for extracting a very high-resolution paleoclimate record from ice cores.

Previous methods for gaining isotopic measurements from ice cores involved carefully sawing the core into half-inch slices. Each slice was analyzed, yielding approximately 24 to 50 samples per meter of ice. The new method yields more than 2,400 isotopic values per meter, an improvement of two orders of magnitude. Virtually any isotopic signal preserved in the ice can be captured.

How it works

INSTAAR Valerie Morris attends to the system she helped develop to make continuous isotopic measurements on 1-meter sticks of ice that are slowly melted (~2 cm/min) and analyzed in a laser-based cavity ring down spectrometer (CRDS), yielding over 2,400 measurement points per meter. The small video screen at top shows a closeup of the vertical ice stick being slowly melted on the melt head in the freezer at right, then carried by peristaltic pumps to the rest of the system.

A 1-meter stick of ice is slowly melted on a melt head in a freezer at a rate of about 2 centimeters per minute. The resulting water is carried by peristaltic pumps to the rest of the system, where it is analyzed in a Picarro laser-based cavity ring down spectrometer (CRDS).

A schematic diagram of the continuous flow Melt System. A Picarro L2130 laser spectrometer is used. Diagram by Bruce Vaughn.

An ice stick is delivered to the melter by the square acrylic tube held by the carousel. Photo by Bruce Vaughn.

The parts of the system that are outside the freezer include the pumps, standards, open split, nebulizer, furnace, and Picarro instrument. The small box is the display for the infrared water detector. Photo by Bruce Vaughn.

A one-meter section of ice core from West Antarctica shows a dramatic ash layer found at approximately 2,570-meter depth as it was in the field. Photo by Heidi Roop.

The same ash layer as it appeared in the smaller stick of ice in the INSTAAR melter system. Photo by Valerie Morris, INSTAAR.

Stable isotopes of water are a proxy for temperature in ice cores. The above is the detailed isotopic signal extracted by the new system over a 20-meter section of ice, centered on a depth of 1665 meters (estimated age ~8,800 ybp). The top panel shows dD in blue; the middle panel shows d18O in red; and the lower panel shows Deuterium-Excess in black. The small dots of either green or yellow show comparison with independent measurement by another lab (Steig et al., University of Washington) on 1/2 meter averaged samples. Positive peaks in dD and d18O represent the warmer summers, and negative peaks are the colder winters.

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