First results of on-line water isotope measurements – University of Copenhagen

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06 July 2009

First results of on-line water isotope measurements

First results.

(Click on figure for higher resolution.) First results from the new online water isotope instrument. The measurement covers 15 meters of ice from about 800 AD. The blue curve shows delta-18O and the red is delta-D. The results are preliminary and uncalibrated, but they show that the measurement is feasible. Further data analysis and comparison to conventional water isotope measurements will reveal the quality of the new results.

The isotopic composition of the ice is one of the most important climate proxies provided by ice cores. Conventionally, the water isotopic composition is obtained from discrete samples that are cut from the ice core in the field, send to laboratories and measured on a mass spectrometer. For the NEEM core we do for example cut about 1 cm2 of the ice core into 2.5 or 5.0 cm long samples, in total more than 50000 samples all along the ice core, each packed in individual plastic bags. Back in the labs it takes several years to carry out the measurements and obtain the valuable high resolution climate profile. A new generation of mass spectrometers based on laser absorption in a multi-pass cavity enables fast water isotope measurements on very small water quantities. For the first time in Greenland, we have one of those instruments in the science trench at NEEM. The instrument is connected to the CFA laboratory that provides a continuous melt water stream from a melt head. In principle, this setup allows to obtain online high resolution profiles of water isotopes directly here at the site. Since the setup is now tested for the first time there are many difficulties and the new measurements cannot replace conventional measurements, but they have the potential to do so in the future. We are therefore very proud of being able to show the first results from the new instrument here.

What we have done today:

  1. Drilling with the NEEM long drill: 37.28 m. Drillers depth: 941.76 m.
  2. Logging brittle zone ice. Final depth: 623.70 m.
  3. Ice core processing: 19.80 m. Depth: 601.70 m.
  4. CFA analysis: 23.10 m. Depth: 275.55 m.

Ad.1: Drillers Report July 5: ‘We finished the weekend with another good day recovering 24.5m of core finishing at 904.48 m depth. The first run of the day was used to clean the hole and recovered a short core but part dropped off on the way up and was recovered in the subsequent run although a bit worse for the extra trip down and back.’

Weather: In the morning wind picked up and we got up to 30 knots from SW at noon. During the afternoon wind dropped again and in the evening we have below 10 knots. Temperatures around -11°C all day; down to -17°C at night with clear blue sky. Pressure has been rising during the day. There has been quite some snow drift. It has not been possible to groom the skyway today, but Timothy will go out with the beam tomorrow.

FL, Anders Svensson

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