Project Hypotheses

Thomas Kreamer

Uranium Activity Ratios as an indicator of melting permafrost

Water draining from basins containing permafrost comes from the melting of the permafrost to some varying degree. The permafrost is composed of frozen water mixed with sediment, and this ice has been there for 100's to 1000's of years. Thus, the ice accumulates the decay products of the contained sediment and integrates it over a long time. One of the longer lived decay products is 234U, which can accumulate in the ice by decay and physical ejection from the sediment of the 238U decay product. When old permafrost melts it releases the uranium, which is high in 234U (high UAR, Uranium Activity Ratio). Water draining ordinary clastic terrain doesn't "accumulate" any 234U in this way, and reflects much more closely the ratio found in rock or sediment, which is much closer to 1.0.

Assuming this is a process occurring in permafrost terrains, there may be some climatic significance to UAR values of water in the Yukon River. That is, if the UAR of the Yukon goes up over time, it may indicate increased melting of old permafrost (as opposed to some kind of yearly melting-refreezing-melting of shallow or surficial permafrost), which could not accumulate much 'new' 234U during this time.

Preliminary results show that the rivers draining permafrost regions have high UAR's. The Porcupine River (draining clarge areas of continuous permafrost) has consistently been around 2.00, a very high value for surface waters. The Sheenjek (1.73 for the June sample) and Chandalar (1.60 for the June sample) are also higher than rivers draining non-permafrost regions, such as the Tanana (average around 1.20) and the Charley (1.19 for the June sample).

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U.S. Department of the Interior \| U.S. Geological Survey URL: http://ak.water.usgs.gov/yukon/hypothesis/Kreamer.php Page Contact Information: E-mail comments or questions to Bob Ourso Last modified: April 25 2005 14:20:29.