Can changes in redox sensitive dissolved trace elements be used as indicators of changes in carbon cycling?
An important focus of the USGS effort is to understand how climate warming will affect carbon cycling in the Yukon Basin. Climate change will also affect redox cycling within the basin by altering process such as soil flushing, wetlands hydrology, and stratification and overturning of lakes. If concentrations or seasonal variability of redox sensitive trace elements (such as Mn, Fe, Mo, and V) can be linked with carbon cycling in various Yukon Basin environments, then monitoring of dissolved trace elements may provide a useful early indicator of carbon system changes. An advantage of working in concert with the USGS program is that we can compare our results on concentrations and cycling of trace elements with their carbon results.
What are the differences in trace element mobilization in the different environments of the Yukon Basin? Are rivers draining glacial terrains more dilute than others and with fractionated ratios (relative to rock ratios) of trace elements (due to greater physical weathering relative to chemical weathering; e.g., Stallard, 1985) or is there extreme fractionation between more soluble elements and more strongly sorbed elements due to the high suspended loads? Do rivers draining wetlands show the greatest effects of redox processes due to their wet organic soils (e.g., Shotyk, 1988)? Do watersheds underlain by continuous permafrost have low dissolved metal concentrations due to low mineral interactions or is there enhanced transport of organic-bound metals due to their high DOC (MacLean et al., 1999; Buttle & Fraser, 1992)? And finally, what do the results in differing environments tell us about how these concentrations will change in response to the projected effects of climate warming (e.g., thawing of permafrost, drying of wetlands) or have changed in the past due to glacial cycles (e.g., increased glaciation)?
There are few reliable dissolved trace element data available for arctic environments. Do the extreme temperatures, glacial processes, and/or permafrost lead to significant differences (as compared, for example, to the Mississippi or Amazon Rivers) in trace element mobilization? If so, then what are the implications for interpreting changes in trace element paleoceanographic proxies across glacial-interglacial boundaries?
What are the geological source effects on dissolved trace element concentrations in the Yukon Basin?
Geological effects on dissolved trace element concentrations are most pronounced for less strongly sorbed elements such as U (Palmer & Edmond, 1993) and V (Shiller & Mao, 2000). Because of the complex geology of Alaska, it is possible that the physiographic factors (glaciation, permafrost, etc.) will have more of an impact on the spatial variability of dissolved trace element concentrations in the Yukon Basin than will geology. Nonetheless, there is the opportunity to sample low order streams draining one predominant lithology as a means of examining source rock effects (e.g., Shiller & Frilot, 1996; Shiller & Mao, 2000). Comparing small watersheds with similar physiography but differing lithology will help resolve the relative effects of geological source versus physiographic factors.
