The Geological Society of America's 2020 Joint Meeting of the Southeastern Section and Northeastern Section has been canceled due to COVID-19. This is a virtual showcase of the work that was to be presented at the meeting in this space instead.
Caroline Moore, Sarah G. Evans, and Connor Miller
69-2 - MEASURING THE IMPACT OF GROUNDWATER ON BOG TURTLE THERMAL HABITAT IN SOUTHERN APPALACHIAN FENS
|Wetlands provide many ecosystem services such as improving water quality, helping to reduce flooding, and providing a habitat for many endangered species such as the federally threatened bog turtle. The bog turtle is a palm-sized, semi-aquatic turtle that is primarily found in fens, groundwater-fed alkaline wetlands. Since water has a higher specific heat than air, we hypothesize that the presence of groundwater in fens creates saturated soils that provides habitat for turtles to stay cool in the summer and warm during hibernation in the winter. Climate change may alter the thermal regime of fens, making it necessary to quantify baseline fen soil temperatures on seasonal timescales and understand thermal variability within fens so that we may anticipate future adverse impacts to the fen thermal habitat.|
In this study we assess soil water temperatures for two fens in the Appalachian Highlands of North Carolina, United States from August 2018 through November 2019. We record soil water temperature at 2.5, 5.0, and 10.0 cm below ground level including eight locations in an Ashe County fen (elevation: 1,573 m, area: 9,338 m2), and ten locations in a Wilkes County fen (elevation: 563 m, area: 18,500 m2).Preliminary results from the Ashe County fen confirm our hypothesis that soil water provides an important thermal buffer. In December 2018, the average daily air temperature was 3.0°C and the average daily magnitude (maximum-minimum) of air temperature was 9.3°C. At 2.5 cm below ground level, the average daily temperature was similar to the air temperature (2.5°C), but the average daily magnitude was only 1.6°C, suggesting that the soil was insulated from freezing temperatures. In June 2019, the average daily air temperature was 17.5±8.5°C. At 2.5 cm below ground level, the average daily temperature was 18.6±5.7°C, indicating that the soil was buffered from hotter summer temperatures. Forthcoming results will demonstrate how soil water temperatures vary within and between fens which will help enact more effective conservation strategies to protect bog turtle thermal habitats.
Virginia Brown and Sarah Carmichael
9-2 - EBSD AND TRACE ELEMENT ANALYSIS OF REPLACEMENT DOLOMITE IN THE LATEMAR PLATFORM
The Latemar carbonate platform in northern Italy contains bodies of replacement dolomite that have been altered via the infiltration of seawater mixed with hydrothermal fluids. These fluids travelled upwards and horizontally through the platform along fractures and bedding planes, and their flow path is documented by replacement dolomite containing significant amounts of Fe, Mn, and Zn. These zones of replacement dolomite are surrounded by unreacted limestone and the region has remained un-metamorphosed, allowing for detailed analysis of the replacement process. Although replacement dolomitization has long been studied on the regional or outcrop scale, it is still not well understood on the scale of individual crystals. Herein we investigate how trace element content in replacement dolomite is reflected in the zoning and the crystallographic orientation of the individual dolomite crystals. Scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) and energy dispersive X-ray spectrometry (EDS) was used to identify crystallographic orientation patterns and trace element distribution within replacement dolomite samples across a single outcrop. Analyses reflect a variety of intensities of fluid-rock reactions and are classified as heavy, moderate, minimal, and unreacted. Elevated Fe, Mn, and Zn in replacement dolomite resulted in a less ordered distribution of orientations in a sample, illustrated by weak pole figure patterns. This implies that the dolomite samples from areas with the heaviest fluid-rock reactions have a deformed chemical structure which has affected the replacement dolomitization process, creating an irregular spread of crystal orientations. These results will be compared with stable isotope signatures at the outcrop scale to refine existing heat flow models and time-integrated fluid flux estimates of dolomitization with the Latemar carbonate buildup.
Connor Stephens and Sarah G. Evans
59-13 - ANALYSIS OF INCREASED BASEFLOW ACROSS NORTHERN EURASIAN RIVERS UNDERLAIN BY PERMAFROST
The Arctic is currently warming at twice the rate of the global average, resulting in increased rates of Arctic river discharge and the thawing of perennially frozen ground known as permafrost. As permafrost thaws, the layer of soil above permafrost that thaws during the summer and refreezes in the winter known as the active layer, increases in depth. An increase in the depth of the active layer is postulated to be one of the main reasons why we have observed increased rates of river discharge in the Arctic. It is important to understand why and at what rate permafrost thaws, as the hydrology of permafrost is also intimately connected with the carbon cycle since thawing permafrost releases stored carbon as methane or carbon dioxide into the atmosphere more readily when soils are unsaturated, further accelerating climate warming. In this study we quantify how changes to Arctic permafrost relate to changes in Arctic river discharge by analyzing daily streamflow records across northern Eurasia for 139 different river discharge stations from 1913 to 2003. We perform a baseflow recession analysis for these stations for the low flow and snow-free months of September and October. We chose these low flow months when streamflow comes from groundwater storage or baseflow to minimize the influence of precipitation and snowmelt from higher elevations. Across all 139 river discharge stations we observe a positive recession flow intercept (a proxy for increasing active layer depth) for the majority of those stations underlain by continuous permafrost, while we see a negative recession flow intercept for stations underlain by less extensive permafrost including discontinuous, sporadic, isolated, and no permafrost regions. This may indicate that active layer is deepening in areas underlain by continuous permafrost which causes an increase in baseflow, while in areas without continuous permafrost, the increased baseflow may be caused by large scale permafrost thawing and an increase in regional hydraulic conductivity, or the ease at which water flows through the ground. The results from this work may help us to understand the changing hydrologic cycle in the Arctic which has implications for carbon cycling as the Arctic continues to warm.