Dry sedimentation processes in the high-elevation McMurdo Dry Valleys, Antarctica: A case study in University Valley

<p>The hyper-arid, cryotic, wind-dominated conditions in the high-elevation McMurdo Dry Valleys of Antarctica are among Earth’s most extreme environments and represent the closest terrestrial analog to the surface of Mars. These unique conditions result in complex surface processes that occur in the overall absence of liquid water. However, since water is typically believed to be required for these processes to occur, the mechanisms responsible for how these processes can persist in this environment are poorly understood. Previous studies that focused on individual processes of sedimentation in the Dry Valleys leave questions regarding the role of water in dry cryotic sedimentation as well as the rates at which these processes occur. This thesis addresses these questions by combining Optically Stimulated Luminescence (OSL) dating, meteoric Beryllium-10 (10Be) measurements, soil geochemistry analysis, and petrographic microscopy analysis on ice-cemented permafrost cores taken from University Valley, one of the high-elevation Dry Valleys, where the availability and effects of liquid water are minimal. These analyses were used to explore four main sedimentation processes that occur in the Dry Valleys: chemical weathering, fine particle translocation, eolian transport, and physical weathering. Analyzed together, findings from these analyses comprehensively describe the complex processes involved in dry cryotic sedimentation and determine the roles of different phases of water in this environment. Sediments in University Valley have accumulated at a rate of approximately 2.1 mm/ka for the last 200 ka, as dated by OSL, from erosion of the valley walls and deposition of windblown dust. Sediment accumulation is influenced by topography of the valley floor, depth of the ice table, aspect of the valley walls, wind direction, and mechanical breakdown of rocks due to solar heating. While persistent winds constantly remobilize fine particles and dust in the upper few cm of the dry ground, sediment grains that are sand-sized or larger do not undergo significant remobilization, and sediments in the ice-cemented ground are unaffected by remobilization and translocation processes. Rare clay bridges seen in thin section show that small, infrequent, transient surface wetting events have occurred over the last 200 ka. High anion concentrations associated with high surface meteoric 10Be measurements and clay bridges indicate that the source of these wetting events is the melting of wind-blown snow from coastal regions. Patterns in meteoric Be measurements show that these small transient wetting events are not sufficient to translocate fine particles through the soil profile, which suggests that the role of liquid water as a transporting agent is negligible in this environment. Chemical weathering in University Valley appears to be controlled by two main components: dolerite content of the sediments, and exposure to the atmosphere at the ground surface where condensation of water vapor onto grain surfaces readily leaches ions from dolerite grains under the oxidizing conditions of the Dry Valleys. In the absence of liquid water, chemical processes that occur in this environment rely on water vapor. Together, these results indicate that surfaces in University Valley are remarkably young and sedimentologically active. Because University Valley represents one of the closest terrestrial analogs to the surface of Mars, findings from this thesis may be applicable to understanding the timescales and the processes that control anhydrous sedimentation on the surface of Mars.</p>

Dry sedimentation processes in the high-elevation McMurdo Dry Valleys, Antarctica: A case study in University Valley

<p>The hyper-arid, cryotic, wind-dominated conditions in the high-elevation McMurdo Dry Valleys of Antarctica are among Earth’s most extreme environments and represent the closest terrestrial analog to the surface of Mars. These unique conditions result in complex surface processes that occur in the overall absence of liquid water. However, since water is typically believed to be required for these processes to occur, the mechanisms responsible for how these processes can persist in this environment are poorly understood. Previous studies that focused on individual processes of sedimentation in the Dry Valleys leave questions regarding the role of water in dry cryotic sedimentation as well as the rates at which these processes occur. This thesis addresses these questions by combining Optically Stimulated Luminescence (OSL) dating, meteoric Beryllium-10 (10Be) measurements, soil geochemistry analysis, and petrographic microscopy analysis on ice-cemented permafrost cores taken from University Valley, one of the high-elevation Dry Valleys, where the availability and effects of liquid water are minimal. These analyses were used to explore four main sedimentation processes that occur in the Dry Valleys: chemical weathering, fine particle translocation, eolian transport, and physical weathering. Analyzed together, findings from these analyses comprehensively describe the complex processes involved in dry cryotic sedimentation and determine the roles of different phases of water in this environment. Sediments in University Valley have accumulated at a rate of approximately 2.1 mm/ka for the last 200 ka, as dated by OSL, from erosion of the valley walls and deposition of windblown dust. Sediment accumulation is influenced by topography of the valley floor, depth of the ice table, aspect of the valley walls, wind direction, and mechanical breakdown of rocks due to solar heating. While persistent winds constantly remobilize fine particles and dust in the upper few cm of the dry ground, sediment grains that are sand-sized or larger do not undergo significant remobilization, and sediments in the ice-cemented ground are unaffected by remobilization and translocation processes. Rare clay bridges seen in thin section show that small, infrequent, transient surface wetting events have occurred over the last 200 ka. High anion concentrations associated with high surface meteoric 10Be measurements and clay bridges indicate that the source of these wetting events is the melting of wind-blown snow from coastal regions. Patterns in meteoric Be measurements show that these small transient wetting events are not sufficient to translocate fine particles through the soil profile, which suggests that the role of liquid water as a transporting agent is negligible in this environment. Chemical weathering in University Valley appears to be controlled by two main components: dolerite content of the sediments, and exposure to the atmosphere at the ground surface where condensation of water vapor onto grain surfaces readily leaches ions from dolerite grains under the oxidizing conditions of the Dry Valleys. In the absence of liquid water, chemical processes that occur in this environment rely on water vapor. Together, these results indicate that surfaces in University Valley are remarkably young and sedimentologically active. Because University Valley represents one of the closest terrestrial analogs to the surface of Mars, findings from this thesis may be applicable to understanding the timescales and the processes that control anhydrous sedimentation on the surface of Mars.</p>

Research sites get closer to field camps over time: Informing environmental management through a geospatial analysis of science in the McMurdo Dry Valleys, Antarctica

As in many parts of the world, the management of environmental science research in Antarctica relies on cost-benefit analysis of negative environmental impact versus positive scientific gain. Several studies have examined the environmental impact of Antarctic field camps, but very little work looks at how the placement of these camps influences scientific research. In this study, we integrate bibliometrics, geospatial analysis, and historical research to understand the relationship between field camp placement and scientific production in the McMurdo Dry Valleys of East Antarctica. Our analysis of the scientific corpus from 1907–2016 shows that, on average, research sites have become less dispersed and closer to field camps over time. Scientific output does not necessarily correspond to the number of field camps, and constructing a field camp does not always lead to a subsequent increase in research in the local area. Our results underscore the need to consider the complex historical and spatial relationships between field camps and research sites in environmental management decision-making in Antarctica and other protected areas.

Meteoric Beryllium-10 in Miocene permafrost and the onset of persistent polar aridity in East Antarctica

Continental scale ice sheets have occupied Antarctica since the major global cooling across the Eocene/Oligocene boundary (~33.9 Ma). However, the timing and nature of the transition to a relatively stable and persistent terrestrial East Antarctic Ice Sheet that characterizes the modern environment remains disputed. Although proxy data show global surface temperatures remained significantly warmer through the late Miocene than today, the hypothesis that the upper elevations of the McMurdo Dry Valleys remained under a hyper-arid polar climate since the mid-Miocene has persisted. Here, we constrain the onset of polar aridity in the McMurdo Dry Valleys region using meteoric Beryllium-10 as a tracer of water infiltration in mid-Miocene and late Quaternary-age soils at three sites situated >1000 m a.s.l.. Our results show that meteoric Beryllium-10 infiltrated the soils for a period after sediment emplacement ~15.0 – 14.0 Ma, terminating at ~6.0 Ma. Reconstruction of climate from paleo-active layer thickness and threshold of mobility of meteoric Beryllium-10 suggests that at 6.0 Ma, summer temperatures were 7 – 10°C with annual precipitation >10 mm. Polar aridity at high elevations has persisted since ~6.0 Ma, well after previous reconstructions (13.8 – 12.5 Ma). Together, our findings indicate that high elevations of the McMurdo Dry Valleys experienced interval(s) of warm-wet climate between ~14.0 – 6.0 Ma which reconciles observations of coastal warmth and reduced ice in the Ross Embayment.

Episodic basin-scale soil moisture anomalies associated with high relative humidity events in the McMurdo Dry Valleys, Antarctica

Outside of hydrologically wetted active layer soils and humidity-sensitive soil brines, low soil moisture is a limiting factor controlling biogeochemical processes in the McMurdo Dry Valleys. But anecdotal field observations suggest that episodic wetting and darkening of surface soils in the absence of snowmelt occurs during high humidity conditions. Here, I analyse long-term meteorological station data to determine whether soil-darkening episodes are present in the instrumental record and whether they are, in fact, correlated with relative humidity. A strong linear correlation is found between relative humidity and soil reflectance at the Lake Bonney long-term autonomous weather station. Soil reflectance is found to decrease annually by a median of 27.7% in response to high humidity conditions. This magnitude of darkening is consistent with soil moisture rising from typical background values of < 0.5 wt.% to 2–3 wt.%, suggesting that regional atmospheric processes may result in widespread soil moisture generation in otherwise dry surface soils. Temperature and relative humidity conditions under which darkening is observed occur for hundreds of hours per year, but are dominated by episodes occurring between midnight and 07h00 local time, suggesting that wetting events may be common, but are not widely observed during typical diel science operations.

Reconstructing 15 Myr of environmental change in the McMurdo Dry Valleys through permafrost geochemistry

<p><b>The McMurdo Dry Valleys of Antarctica are the largest ice-free region in Antarctica. Valley downcutting by major outlet glaciers and post-glacial uplift since the mid-Miocene have resulted in predominantly younger surficial sediments in the low elevation, coastal areas and significantly older sediments in high elevation, inland areas. The hyper-arid conditions that prevail in the high elevations (> 1000 m a.s.l.) of the McMurdo Dry Valleys have protected these surfaces from alteration and weathering, and provide important sediment records of paleoenvironments dating back to the early Miocene. The Friis Hills (77°45’S, 161°30’E, 1200–1500 m a.s.l.) are a 12 km-wide inselberg situated at the head of Taylor Valley. This unique location allowed Miocene-age sediments to be preserved and protected from subsequent ice sheet expansions. Permafrost within these sediments is potentially the oldest on Earth. </b></p><p>As sediments accumulate in periglacial environments, permafrost aggrades with minimal lag time and potentially preserves sediments, organic material and ground ice. The 2016 Friis Hills Drilling Project retrieved a ∼50 m thick permafrost sequence, which not only consists of an archive of Antarctic environmental changes from approximately 14–15 Ma but also records the paleoenvironmental changes of the Neogene and provides insight on the modern hyper-arid environment. The main objective of this project is to understand the unique geochemical characteristics of these permafrost cores and document 15 Myr of change in the upper elevations of the McMurdo Dry Valleys. </p><p>Paleoenvironmental reconstructions of interglacial periods suggest a tundra-like environment in the high elevations of continental Antarctica through the mid-Miocene. Plants such as lichens, liverworts, mosses, grasses and sedges, dicots and Nothofagaceae occupied the Friis Hills during the mid-Miocene. The δ13C signal of C3 plants (-25.5 ± 0.7 ‰ VPDB) corresponds to a semi-arid environment with a mean annual precipitation ranging from 300 to 850 mm yr-1. The unusually high δ15N reflects an ecosystem with up to three trophic levels, supported by the presence of insect fragments, feathers barbs (birds) and tardigrades fragments within the sediment. The deep ice lenses and their meteoric signature suggest a near-saturated active layer during the mid-Miocene. Temperature reconstructions based on the corrected δ18O value of the deep ground ice and change in paleogeography imply that the mid-Miocene (11.1–13.9 Ma) was ∼6 to 12°C warmer. These paleoenvironmental conditions are comparable to those found in the modern Arctic, such as in west Greenland. </p><p>A dominant trend of literature suggests that the high elevations of the McMurdo Dry Valleys have remained under a hyper-arid polar climate since ∼13.8 Ma. However, the presence of 10Bemet in the upper section of the Friis Hills and Table Mountain cores provides evidence for the translocation of clays, which is only possible under a warmer and wetter climate. The 10Bemet concentrations imply that these conditions were present until ∼6.0 Ma at Friis Hills and Table Mountain, consequently challenging the idea that the upper McMurdo Dry Valleys have remained frozen under hyper-arid climate since the mid-Miocene climate transition. Hence, this finding supports the hypothesis that the Miocene has undergone progressive cooling with onset of polar aridity between 7 and 5.4 Ma. The erosion-corrected paleo-active layer depth suggests mean annual air temperatures ranging from -12 to -9°C ∼6.0 Ma. In other words, this thesis shows that the upper McMurdo Dry Valleys have been frozen under hyperarid conditions only since ∼6 Ma and not for 14 Myr as previously thought. </p><p>The ground ice in the uppermost 1 m originates from the modern freezing of evaporated snowmelt and the presence of high salt content which allows unfrozen water in the near-surface. The conformity of dry permafrost samples to biological ratios suggests that the modern environment is regulated by biochemical processes and the current pool of organic carbon in the dry permafrost appears to be in equilibrium with a modern climate and ecosystem. These findings not only characterize the paleoenvironmental changes of continental Antarctica through the late Miocene but also provide a better understanding of the modern ultraxerous conditions of the McMurdo Dry Valleys.</p>

Reconstructing 15 Myr of environmental change in the McMurdo Dry Valleys through permafrost geochemistry

<p><b>The McMurdo Dry Valleys of Antarctica are the largest ice-free region in Antarctica. Valley downcutting by major outlet glaciers and post-glacial uplift since the mid-Miocene have resulted in predominantly younger surficial sediments in the low elevation, coastal areas and significantly older sediments in high elevation, inland areas. The hyper-arid conditions that prevail in the high elevations (> 1000 m a.s.l.) of the McMurdo Dry Valleys have protected these surfaces from alteration and weathering, and provide important sediment records of paleoenvironments dating back to the early Miocene. The Friis Hills (77°45’S, 161°30’E, 1200–1500 m a.s.l.) are a 12 km-wide inselberg situated at the head of Taylor Valley. This unique location allowed Miocene-age sediments to be preserved and protected from subsequent ice sheet expansions. Permafrost within these sediments is potentially the oldest on Earth. </b></p><p>As sediments accumulate in periglacial environments, permafrost aggrades with minimal lag time and potentially preserves sediments, organic material and ground ice. The 2016 Friis Hills Drilling Project retrieved a ∼50 m thick permafrost sequence, which not only consists of an archive of Antarctic environmental changes from approximately 14–15 Ma but also records the paleoenvironmental changes of the Neogene and provides insight on the modern hyper-arid environment. The main objective of this project is to understand the unique geochemical characteristics of these permafrost cores and document 15 Myr of change in the upper elevations of the McMurdo Dry Valleys. </p><p>Paleoenvironmental reconstructions of interglacial periods suggest a tundra-like environment in the high elevations of continental Antarctica through the mid-Miocene. Plants such as lichens, liverworts, mosses, grasses and sedges, dicots and Nothofagaceae occupied the Friis Hills during the mid-Miocene. The δ13C signal of C3 plants (-25.5 ± 0.7 ‰ VPDB) corresponds to a semi-arid environment with a mean annual precipitation ranging from 300 to 850 mm yr-1. The unusually high δ15N reflects an ecosystem with up to three trophic levels, supported by the presence of insect fragments, feathers barbs (birds) and tardigrades fragments within the sediment. The deep ice lenses and their meteoric signature suggest a near-saturated active layer during the mid-Miocene. Temperature reconstructions based on the corrected δ18O value of the deep ground ice and change in paleogeography imply that the mid-Miocene (11.1–13.9 Ma) was ∼6 to 12°C warmer. These paleoenvironmental conditions are comparable to those found in the modern Arctic, such as in west Greenland. </p><p>A dominant trend of literature suggests that the high elevations of the McMurdo Dry Valleys have remained under a hyper-arid polar climate since ∼13.8 Ma. However, the presence of 10Bemet in the upper section of the Friis Hills and Table Mountain cores provides evidence for the translocation of clays, which is only possible under a warmer and wetter climate. The 10Bemet concentrations imply that these conditions were present until ∼6.0 Ma at Friis Hills and Table Mountain, consequently challenging the idea that the upper McMurdo Dry Valleys have remained frozen under hyper-arid climate since the mid-Miocene climate transition. Hence, this finding supports the hypothesis that the Miocene has undergone progressive cooling with onset of polar aridity between 7 and 5.4 Ma. The erosion-corrected paleo-active layer depth suggests mean annual air temperatures ranging from -12 to -9°C ∼6.0 Ma. In other words, this thesis shows that the upper McMurdo Dry Valleys have been frozen under hyperarid conditions only since ∼6 Ma and not for 14 Myr as previously thought. </p><p>The ground ice in the uppermost 1 m originates from the modern freezing of evaporated snowmelt and the presence of high salt content which allows unfrozen water in the near-surface. The conformity of dry permafrost samples to biological ratios suggests that the modern environment is regulated by biochemical processes and the current pool of organic carbon in the dry permafrost appears to be in equilibrium with a modern climate and ecosystem. These findings not only characterize the paleoenvironmental changes of continental Antarctica through the late Miocene but also provide a better understanding of the modern ultraxerous conditions of the McMurdo Dry Valleys.</p>