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Interactive Carbon Studies AK Water Office Overview Hypotheses Hydrology Site Qualification Sites Sample Collection Crew Rosters Personnel Training 2004 Summary 6/04 Log/Photos 8/04 Log/Photos 2003 Summary 6/03 Log/Photos 8/03 Log/Photos 2002 Summary 6/02 Log/Photos 8/02 Log/Photos Products/Biblio Related Links |
Project Hypotheses
Denny EberlAre carbonates (calcite + dolomite) dissolving in the Yukon River?The Yukon River is one of the few large rivers in the world that carries large quantities of carbonate minerals (calcite + dolomite). Quantitative X-ray diffraction analyses of bottom and suspended sediments shows that these minerals originate as glacial flour derived from the St. Elias Range, where they then travel down the Donjek and White Rivers to enter the Yukon River in the Yukon Territory north of Whitehorse. In the graph below it can be seen that Yukon River bottom sediments (collected by kayakers) near Whitehorse contain about 2 weight percent carbonates. When the White River tributary enters the Yukon river, this value jumps to about 14%. (Is the White River made white by the carbonates it carries?) Thereafter the carbonates decrease to about 2 % near the end of the river at Pilot Station. Is this decreasing trend related to the progressive dissolution downstream of carbonates in the Yukon River, or is the decrease related to dilution of carbonates by tributary sediments? In order to understand the movement of carbon in the river, which we want to do to know in order to determine whether or not permafrost is melting in the basin, it is necessary to account for the possible addition of inorganic carbon to the system by carbonate dissolution. An approximate mass balance calculation, using average percentages for the minerals in suspended sediments at the fixed stations (data for three years were used in the simple averages) and sediment flow data indicates that approximately 1.2 x 106 metric tons of suspended carbonate, roughly 1/4 of that carried by the river, may dissolve between Eagle and Pilot Station each year, a river distance of about 2500 km. This total includes about 30% of the suspended calcite and 15% of the suspended dolomite. Similarly, roughly 3 x 106 metric tons of feldspar dissolve. This includes approximately 1% of the alkali feldspar carried by the river between Eagle and Pilot Station, and 25% of the plagioclase. Roughly 6 x 106 metric tons of quartz dissolves over the same reach, or 3% of that carried. It is estimated that 10% of the yearly calcium ion load for the river comes from the dissolution of carbonates and plagioclase between Eagle and Pilot Station. |
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