Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

Newman, Brent D.; Throckmorton, H.; Graham, David E.; Gu, Baohua; Hubbard, Susan S.; Liang, Liyuan; Wu, Yuxin; Heikoop, Jeffrey M.; Herndon, Elizabeth; Phelps, Tommy J.; Wilson, Cathy J.; Wullschleger, Stan D.

doi:10.1002/2014gl062804

Cited by 50 publications

(67 citation statements)

References 51 publications

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“…S3). Differences between geomorphic features were not evaluated in this study; however, Newman et al (2015) and Wainwright et al (2015) report greater geochemical differences amongst polygons rather than features at these sites.…”

Section: Depth Gradients In Water Chemistrymentioning

confidence: 93%

“…Water chemistry in the thaw season is characterized by vertical gradients with solute concentrations that (Brown 1969;Kokelj and Burn 2005;Newman et al 2015). Solute concentrations may increase near the permafrost boundary due to mineral dissolution or chemical weathering driven by increased water availability (e.g., Lacelle et al 2008), solute exclusion during downward freezing (e.g., Kokelj and Burn 2005), or inputs of ion-rich waters from depth during periodic thawing of the upper permafrost (Kokelj and Burn 2003).…”

Section: Depth Gradients In Water Chemistrymentioning

confidence: 99%

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Geochemical drivers of organic matter decomposition in arctic tundra soils

et al. 2015

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Climate change is warming tundra ecosystems in the Arctic, resulting in the decomposition of previously-frozen soil organic matter (SOM) and release of carbon (C) to the atmosphere; however, the processes that control SOM decomposition and C emissions remain highly uncertain. In this study, we evaluate geochemical factors that influence microbial production of carbon dioxide (CO 2 ) and methane (CH 4 ) in the seasonally-thawed active layer of interstitial polygonal tundra near Barrow, Alaska. We report spatial and seasonal patterns of dissolved gases in relation to the geochemical properties of Fe and organic C in soil and soil solution, as determined using spectroscopic and chromatographic techniques. The chemical composition of soil water collected during the annual thaw season varied significantly with depth. Soil water in the middle of the active layer contained abundant Fe(III), and aromatic-C and low-molecularweight organic acids derived from SOM decomposition. At these depths, CH 4 was positively correlated with the ratio of Fe(III) to total Fe in waterlogged transitional and low-centered polygons but negatively correlated in the drier flat-and high-centered polygons. These observations contradict the expectation Responsible Editor: Stephen Porder.Electronic supplementary material The online version of this article (

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Section: Depth Gradients In Water Chemistrymentioning

confidence: 93%

Section: Depth Gradients In Water Chemistrymentioning

confidence: 99%

Geochemical drivers of organic matter decomposition in arctic tundra soils

et al. 2015

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“…In conclusion, the hydrology of polygonal ground is a strong control on active layer biogeochemistry, nutrient availability and CO 2 and CH 4 production in arctic systems (e.g. Heikoop et al ., ; Newman et al ., ; Throckmorton et al ., ). These results provide additional insights into active layer water sources and cycling in a polygonal tundra landscape that will be critical to addressing uncertainties and building better regional or pan‐arctic hydrological and biogeochemical models.…”

Section: Discussionmentioning

confidence: 99%

“…Newman et al . () found that there was also development of strong geochemical depth gradients within the active layer at the study site in 2012. The presence of well‐developed isotope and geochemical gradients within these thin active layers suggests that advective mixing is likely minimal in polygonal ground near Barrow.…”

Section: Discussionmentioning

confidence: 99%

Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

Throckmorton

Newman

Heikoop

et al. 2016

Hydrological Processes

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Climate change and thawing permafrost in the arctic will significantly alter landscape hydro-geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO2 and CH4), and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques ( 2 H and  18 O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA) in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface active layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice-melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope ( 2 H versus  18 O). Freeze-out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze-out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of melt water, likely due to slow melting of seasonal ice. This research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process-based fine and intermediate scale hydrologic models.

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“…Previous studies at the BEO have established tight couplings between polygon types and features and spatial variations in chemistry, but temporal variations were not addressed (Heikoop et al, 2015;Newman et al, 2015;Wu et al, 2018). Previous studies at the BEO have established tight couplings between polygon types and features and spatial variations in chemistry, but temporal variations were not addressed (Heikoop et al, 2015;Newman et al, 2015;Wu et al, 2018).…”

Section: Biogeochemical Surveymentioning

confidence: 99%

Timing and duration of hydrological transitions in Arctic polygonal ground from stable isotopes

Conroy

Newman

Heikoop

et al. 2019

Hydrological Processes

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Land surface models and Earth system models that include Arctic landscapes must capture the abrupt hydrological transitions that occur during the annual thaw and deepening of the active layer. In this work, stable water isotopes (δ 2 H and δ 18 O) are used to appraise hydrologically significant transitions during annual landscape thaw at the Barrow Environmental Observatory (Utqiaġvik, Alaska). These hydrologically significant periods are then linked to annual shifts in the landscape energy balance, deduced from meteorological data and described by the microclimatic periods: Winter, Pre-Melt, Melt, Post-Melt, Summer, and Freeze-Up. The tight coupling of the microclimatic periods with the hydrological transitions supports the use of microclimatic periods as a means of linking polygonal surface water hydrology to meteorological datasets, which provides a mechanism for improving the representation of polygonal surface water hydrology in process-based models. Rayleigh process reconstruction of the isotopic changes revealed that 19% of winter precipitation was lost to sublimation prior to melting and that 23% of surface water was lost to evaporation during the first 10 days post-melt. This agrees with evaporation rates reported in a separate study using an eddy covariance flux tower located nearby. An additional 17% was lost to evaporation during the next 33 days. Stable water isotopes are also used to identify the dominant sources of surface water to various hydrogeomorphological features prevalent in polygonal terrain (a lake, a low centre polygon centre, troughs within the rims of low centre polygons, flat centre polygon troughs, a high centre polygon trough, and drainages). Hydrogeomorphologies that retained significant old water or acted as snow drifts are isotopically distinct during the Melt Period and therefore are easily distinguished. Biogeochemical changes related to the annual thaw are also reported and coupled to the hydrological transitions, which provides insight into the sources and sinks of these ions to and from the landscape. K E Y W O R D SArctic Coastal Plain, arctic hydrology, Barrow, hydrological transitions, polygonal ground, stable water isotopes, tundra, Utqiaġvik

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Microtopographic and depth controls on active layer chemistry in Arctic polygonal ground

Cited by 50 publications

References 51 publications

Geochemical drivers of organic matter decomposition in arctic tundra soils

Geochemical drivers of organic matter decomposition in arctic tundra soils

Active layer hydrology in an arctic tundra ecosystem: quantifying water sources and cycling using water stable isotopes

Timing and duration of hydrological transitions in Arctic polygonal ground from stable isotopes

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