Date of Award
2025
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Natural Resources
First Advisor
Paul Bierman
Abstract
In 1966, the US Army retrieved the Camp Century sub-glacial core from northwestern Greenland. Prior work indicates that the 3.44 meter core contains 5 stratigraphic units. The geochemistry of the core, including the frozen porewater, has not yet been investigated. In this study, we performed geochemical and isotopic analysis on 26 sub-samples of pore water extracted from frozen sub-glacial material to further characterize these 5 units and investigate their paleoenvironmental significance. We measured pH and conductivity, water stable isotopes (δ18O and δD), and cation and anion concentrations.
Sample pH values ranged from 6.84 to 7.85. Conductivity values varied systematically with depth in the core, ranging from 52 uS to 1066 uS. The major cations in order of concentration were Ca2+>Mg2+>Na+>K+ with concentrations reaching >100 mg/L. In contrast, trace elements such as Mn, Mo, Sb, Ba, B, and As had concentrations around 0.1 mg/L. Formate, chloride, and sulfate were the most concentrated anions (>100 mg/L). Acetate and fluoride had moderate concentrations (~10 mg/L), and bromide, nitrite, nitrate, phosphate, and oxalate had low concentrations in all five units (< 5 mg/L). δ18O and deuterium excess measurements ranged from -29 ؉ to -19 ؉ and from 2 ؉ to 14 ؉, respectively. Differing elemental concentrations and stable isotope ratios in the porewater isolated from the core indicate at least three different weathering and temperature regimes.
Porewater chemistry indicated that the lowermost material in the core (129 cm of sediment-rich diamicton) is the most intensively weathered, as it has the lowest mean pH, highest mean conductivity, and the highest cation concentrations. This unit also has the highest δ18O, indicating relatively warmer climate. Porewater in the 103 cm overlying unit, which is ice-rich, has the most basic pH values and the lowest mean conductivity. It also has the lowest concentration of dissolved cations and anions as well as the lowest δ18O ratio indicating the coldest temperature regime. Porewater from well-sorted, sediment-rich material in the uppermost 112 cm of the sub-ice core has intermediate values of conductivity, pH, and water stable isotopes.
The porewater geochemistry results build on previous lithologic studies to suggest that the Camp Century sub-ice materials record at least one glacial and two interglacial times. The diamict at the bottom of the core is most likely a till, deposited during a cold period and weathered during an interglacial, during which higher temperatures and the movement of groundwater altered mineral grains, and resulted in porewater with a high concentration of dissolved elements. The ice-rich layer, with its low concentration of dissolved material and δ18O values, is consistent with colder temperatures. The uppermost material represents an interglacial period where porewater, because it is more dilute, was in contact for less time with the sediment than in the lowermost material. Together, these data indicate that the geochemistry of pore water, preserved frozen in subglacial materials, is a useful tool for interpreting paleoenvironmental conditions.
Language
en
Number of Pages
56 p.
Recommended Citation
Guimaraes Ribeiro de Souza, Juliana, "The Geochemistry of the Sub-Glacial Pore Ice at Camp Century, Northwestern Greenland" (2025). Graduate College Dissertations and Theses. 2056.
https://scholarworks.uvm.edu/graddis/2056