ALBERT

Description: History helps us understand who we are and what we should become. This book demonstrates that primitivism is central to American religion. Primitivism is the dream of restoring religion to a purer order, as found in former times.

Description: Thermokarst (thaw) lakes emit methane (CH4) to the atmosphere, with the carbon (C) originating from terrestrial sources such as the Holocene soils of the lakes’ watersheds, thaw of Holocene- and Pleistoceneaged permafrost soil beneath and surrounding the lakes, and decomposition of contemporary organic matter (OM) in the lakes. However, the relative magnitude of CH4 production in surface lake sediments versus deeper thawed permafrost horizons is not well understood. We assessed anaerobic CH4 production potentials from 22 depths along a 590 cm long lake sediment core from the center of an interior Alaska thermokarst lake, Vault Lake, that captured the entire package of surface lake sediments, the talik (thaw bulb), and the top 40 cm of thawing permafrost beneath the talik. We also studied the adjacent Vault Creek permafrost tunnel that extends through icerich yedoma permafrost soils surrounding the lake and into underlying fluvial gravel. Our results show, in the center of a first generation thermokarst-lake, whole-column CH4 production is dominated by methanogenesis in the organic-rich surface lake sediments [151 cm thick; mean ± SD 5.95 ± 1.67 μg C-CH4 per g dry weight sediment per day (g dw−1 d−1); 125.9 ± 36.2 μg C-CH4 per g organic carbon per day (g Corg−1 d−1)]. The organic-rich surface sediments contribute the most (67%) to whole-column CH4 production despite occupying a lesser fraction (26%) of sediment column thickness. High CH4 production potentials were also observed in recently-thawed permafrost (1.18 ± 0.61 μg C-CH4 g dw−1 d−1; 59.60 ± 51.5 μg CCH4 g Corg−1 d−1) at the bottom of the talik, but the narrow thicknesses (43 cm) of this horizon limited its overall contribution to total sediment column CH4 production in the core. Lower rates of CH4 production were observed in sediment horizons representing permafrost that has been thawed in the talik for longer periods of time. The thickest sequence in the Vault Lake core, which consisted of combined Lacustrine silt and Taberite facies (60% of total core thickness), had low CH4 production potentials, contributing only 21% of whole sediment column CH4 production potential. No CH4 production was observed in samples obtained from the permafrost tunnel, whose sediments represent a non-lake environment. Our findings imply that CH4 production is highly variable in thermokarstlake systems and that both modern OM supplied to surface sediments and ancient OM supplied to both surface and deep lake sediments by in situ thaw, as well as shore erosion of yedoma permafrost, are important to lake CH4 production. Knowing where CH4 originates and what proportion of produced CH4 is emitted will aid in estimations of how C release and processing in a thermokarst-lake environment differs from other thawing permafrost and non-permafrost environments. References: Heslop, J.K.; Walter Anthony, K.M.; Sepulveda-Jauregui, A.; Martinez-Cruz, K.; Bondurant, A.; Grosse, G. and Jones, M.C. [2015]: Thermokarst lake methanogenesis along a complete talik profile. Biogeosciences, 12:4317–4331, doi:10.5194/bg-12-4317-2015.

Description: The interaction and feedbacks between surface water and permafrost are fundamental processes shaping the surface of continuous permafrost landscapes. Lake-rich regions of Arctic lowlands, such as coastal plains of northern Alaska, Siberia, and Northwest Canada, where shallow thermokarst lakes often cover 20-40% of the land surface are a pronounced example of these permafrost processes. In these same Arctic coastal regions, current rates of near-surface atmospheric warming are extremely high, 0.8 °C / decade for example in Barrow, Alaska, primarily due to reductions in sea ice extent (Wendler et al., 2014). The thermal response of permafrost over recent decades is also rapid, warming approximately 0.6°C / decade for example at Deadhorse, Alaska, yet this permafrost is still very cold, less than -6°C (Romanovsky et al., 2015). The temperature departure created by water in lakes set in permafrost is well recognized and where mean annual bed temperatures (MABT) are above 0 °C, a talik develops (Brewer, 1958). The critical depth of water in lakes where taliks form is generally in excess of maximum ice thickness, which has historically been around 2 m in northern Alaska. Thus, lakes that are shallower than the maximum ice thickness, which are the majority of water bodies in many Arctic coastal lowlands, should maintain sublake permafrost and have a shallow active layer if MABT’s are below freezing. Recent analysis, however, suggests a lake ice thinning trend of 0.15 m / decade for lakes on the Barrow Peninsula, such that the maximum ice thickness has shifted to less than 1.5 m since the early 2000’s. We hypothesized that the surface areas most sensitive to Arctic climate warming are below lakes with depths that are near or just below this critical maximum ice thickness threshold primarily because of changing winter climate and reduced ice growth. This hypothesis was tested using field observations of MABT, ice thickness, and water depth collected from lakes of varying depths and climatic zones on the coastal plain and foothills of northern Alaska. A model was developed to explain variation in lake MABT by partitioning the controlling processes between ice-covered and open-water periods. As expected, variation in air temperature explained a high amount of variation in bed temperature (72%) and this was improved to 80% by including lake depth in this model. Bed temperature during the much longer ice-covered period, however, was controlled by lake depth relative to regional maximum ice thickness, termed the Effective Depth Ratio (EDR). A piecewise linear regression model of EDR explained 96% of the variation in bed temperature with key EDR breaks identified at 0.75 and 1.9. These breaks may be physically meaningful towards understanding the processes linking lake ice to bed temperatures and sublake permafrost thaw. For example if regional lake ice grows to 1.5 m thick, the first break is at lake depth of 1.1 m, which will freeze by mid-winter and may separate lakes with active-layers from lakes with shallow taliks. The second EDR break for the same ice thickness is at a lake depth of 2.9 m, which may represent the depth where winter thermal stratification becomes notable (greater than 1 °C) and possibly indicative of lakes that have well developed taliks that store and release more heat. We then combined these ice-covered and open-water models to evaluate the sensitivity of MABT to varying lake and climate forcing scenarios and hindcast longer-term patterns of lake bed warming. This analysis showed that MABT in shallow lakes were most sensitive to changes in ice thickness, whereas ice thickness had minimal impact on deeper lakes and variation in summer air temperature had a very small impact on MABT across all lake depths. Using this model, forced with Barrow climate data, suggests that shallow lake beds (1-m depth) have warmed substantially over the last 30 years (0.8 °C / decade) and more importantly now have an MABT that exceeds 0 °C. Deeper lake beds (3-m depth), however, are suggested to be warming at a much slower rate (0.3 °C / decade), compared to both air temperature (0.8 °C/ decade) and permafrost (0.6 °C/ decade). This contrasting sensitivity and responses of lake thermal regimes relative to surrounding permafrost thermal regimes paint a dramatic and dynamic picture of an evolving Arctic land surface as climate change progresses. We suggest that the most rapid areas of permafrost degradation in Arctic coastal lowlands are below shallow lakes and this response is driven primarily by changing winter conditions. References: Brewer, M. C. (1958), The thermal regime of an arctic lake, Transactions of the American Geophysical Union, 39, 278-284. Romanovsky, V. E., S. L. Smith, H. H. Christiansen, N. I. Shiklomanov, D. A. Streletskiy, D. S. Drozdov, G. V. Malkova, N. G. Oberman, A. L. Kholodov, and S. S. Marchenko, (2015). The Arctic Terrestrial Permafrost in “State of the Climate in 2014” . Bulletin of the American Meteorological Society, 96, 7, 139-S141, 2015 Wendler, G., B. Moore, and K. Galloway (2014), Strong temperature increase and shrinking sea ice in Arctic Alaska, The Open Atmospheric Science Journal, 8, 7-15.

Description: Interactions and feedbacks between abundant surface waters and permafrost fundamentally shape lowland Arctic landscapes. Sublake permafrost is maintained when the maximum ice thickness (MIT) exceeds lake depth and mean annual bed temperatures (MABTs) remain below freezing. However, declining MIT since the 1970s is likely causing talik development below shallow lakes. Here we show high-temperature sensitivity to winter ice growth at the water-sediment interface of shallow lakes based on year-round lake sensor data. Empirical model experiments suggest that shallow (1m depth) lakes have warmed substantially over the last 30years (2.4°C), withMABT above freezing5 of the last 7years.This is incomparison to slower ratesofwarming in deeper (3 m) lakes (0.9°C), with already well-developed taliks. Our findings indicate that permafrost below shallow lakes has already begun crossing a critical thawing threshold approximately 70 years prior to predicted terrestrial permafrost thaw in northern Alaska.

Description: Thermokarst lakes are prevalent in Arctic coastal lowland regions and sublake permafrost degradation and talik development contributes to greenhouse gas emissions by tapping the large permafrost carbon pool. Whereas lateral thermokarst lake expansion is readily apparent through remote sensing and shoreline measurements, sublake thawed sediment conditions and talik growth are difficult to measure. Here we combine transient electromagnetic surveys with thermal modeling, backed up by measured permafrost properties and radiocarbon ages, to reveal closed‐talik geometry associated with a thermokarst lake in continuous permafrost. To improve access to talik geometry data, we conducted surveys along three transient electromagnetic transects perpendicular to lakeshores with different decadal‐scale expansion rates of 0.16, 0.38, and 0.58 m/year. We modeled thermal development of the talik using boundary conditions based on field data from the lake, surrounding permafrost and a borehole, independent of the transient electromagnetics. A talik depth of 91 m was determined from analysis of the transient electromagnetic surveys. Using a lake initiation age of 1400 years before present and available subsurface properties the results from thermal modeling of the lake center arrived at a best estimate talk depth of 80 m, which is on the same order of magnitude as the results from the transient electromagnetic survey. Our approach has provided a noninvasive estimate of talik geometry suitable for comparable settings throughout circum‐Arctic coastal lowland regions.

Description: Little is known about temperature sensitivity of permafrost organic carbon (OC) mineralization over time scales of years to centuries following thaw. Due to their formation and thaw histories, taliks (thaw bulbs) beneath thermokarst lakes provide a unique natural laboratory from which to examine how permafrost thawed in saturated anaerobic conditions responds to changes in temperature following long periods of time since thaw. We anaerobically incubated samples from a 590 cm thermokarst lake sediment core near Fairbanks, Alaska at four temperatures (0, 3, 10, and 25 ºC) bracketing observed talik temperatures. We show that since initial thaw ~400 yr BP CH4 production shifts from being most sensitive to at lower (0-3 ºC; Q10-EC=1.15E7) temperatures to being most sensitive at higher (10-25 ºC; Q10-EC=67) temperatures. Frozen sediments collected from beneath the talik, thawed at the commencement of the incubation, had significant (p ≤ 0.05) increases in CH4 production rates at lower temperatures but did not show significant CH4 production rate increases at higher temperatures (10-25 ºC). We hypothesize the thawing of sediments removed a major barrier to C mineralization, leading to rapid initial permafrost C mineralization and preferential mineralization of the most biolabile OC compounds. In contrast, sediments which had been thawed beneath the lake for longer periods of time did not experience statistically significant increases in CH4 production at lower temperatures (0-10 ºC), but had high temperature sensitivities at higher temperatures (10-25 ºC). We believe these rate increases are due to warmer temperatures in the experimental incubations crossing activation energy thresholds, allowing previously recalcitrant fractions of OC to be utilized, and/or the presence of different microbial communities adapted to thawed sediments. Recently-deposited sediments at shallow depths in the lake core experienced increases in CH4 production across all incubation temperatures (Q10-ST=4.4).