Geochemistry of streams, soils, and permafrost and the geochemical effects of climate change in a continuous permafrost region, Arctic Alaska, United States.

다국어 초록 (Multilingual Abstract)

Climate warming can impact arctic ecosystems by altering watershed geochemistry through permafrost degradation and increased mineral weathering. This dissertation evaluated the importance of these changes in arctic Alaska by examining permafrost and soil geochemistry, mineral weathering, and changes in stream geochemistry.
Elemental and 87Sr/86Sr geochemistry of streams and soils, permafrost, and soil parent materials from glacial deposit surfaces of varying ages were evaluated. Carbonate content increases with soil depth across all surfaces, and exchangeable P, K, and Ca concentrations are significantly (p<0.05) greater in permafrost than in active-layer mineral soil. These results suggest that increasing thaw depth will increase carbonate alkalinity, Ca, K, and P supply to soils and streams across the region. Elemental depletion factors for a subset of these soils forming a chronosequence indicate that carbonate weathering is the dominant weathering process, and long-term weathering rates are 0.5-11 meq m-2 yr-2.
Based on increasing Ca/Na and Ca/Ba and decreasing 87Sr/ 86Sr with depth in soils and permafrost, elemental ratios and 87Sr/86Sr in an arctic stream were used as tracers of the maximum depth of soil water flow and therefore changes in integrated thaw depth across the watershed. From 1994 to 2004, mean 87Sr/ 86Sr values in low-discharge late summer stream water decreased from 0.7122 to 0.7119 (R2=0.62, p=0.012), and Ca/Na and Ca/Ba showed significant increasing trends that were consistent with increasing depth of soil water flowpaths. These trends provide new evidence for increasing thaw depth, despite the lack of measured increases using traditional thaw probe techniques.
The effects of an in-stream thermokarst feature on stream chemistry were also investigated. Solute concentrations, alkalinity, and conductivity were elevated downstream from the thermokarst. Estimates suggest geochemical changes may be detectable downstream in rivers up to 100 times the size of the original affected stream. These data further support the use of stream geochemistry as an indicator of spatially heterogeneous permafrost degradation.
This research suggests that permafrost degradation on the Alaskan North Slope is exposing previously frozen carbonate minerals to weathering, thereby influencing stream geochemistry. These geochemical changes are an important consideration when examining the overall impact of climate change on arctic ecosystems.