Date: 2014-05-01

Creator: Graham Harper Edwards

Access: Open access

Morainal and lacustrine sediments in Linnédalen, Spitsbergen, Svalbard, record the fluctuations of a glacier in a currently unglaciated mountain cirque during the Little Ice Age (LIA). This study attempts to reconstruct Late Holocene glacial activity within this cirque from geochemical, physical, and visual stratigraphic variation of the Linnévatnet lacustrine sediment record. A 57 cm lacustrine sediment core (D10.5) from Linnévatnet was analyzed at a high-resolution for variations in X-Ray Fluorescence (XRF)-measured elemental composition, spectral reflectance, and magnetic susceptibility. The visual stratigraphy was observed at a microscopic scale. An age-depth model for D10.5 is developed by extrapolating sedimentation rates from dated horizons, measured by 239+240Pu radionuclide fallout dating and chemostratigraphic enrichment of atmospheric anthropogenic pollutants. Visual stratigraphy of the sediment record indicates two periods of cirque glacier sediment delivery to Linnévatnet during the LIA (1329-1363 CE, 1816 CE-Present) and a third period of sediment delivery during the Medieval Climate Anomaly (MCA; 984-1082 CE). During non-glacial periods, stratigraphic variation in XRF-measured Ti and K appear to be associated with fluctuations in North Atlantic Oscillation (NAO)-regulated precipitation. Within the LIA glacial intervals, decadal-scale variations in sediment Ti and K geochemistry may result from advance and retreat of the cirque glacier ice-margin or fluctuations in precipitation. Stratigraphic variation in Fe content indicates complex erosional and hydrological processes associated with MCA precipitation and glacial meltwater. Stratigraphic and geochemical variations in the lacustrine record of Linnévatnet indicate that both cirque glacier activity and sediment transport in Linnédalen are more sensitive to climatological change than previously thought.

Date: 2020-01-01

Creator: Siena Brook Ballance

Access: Open access

Phytoplankton underpin marine trophic systems and biogeochemical cycles. Estuarine and coastal phytoplankton account for 40-50% of global ocean primary productivity and carbon flux making it critical to identify sources of variability. This project focuses on the Kennebec River and Harpswell Sound, a downstream, but hydrologically connected coastal estuary, as a case study of temperate river influence on estuarine nutrient regimes and phytoplankton communities. Phytoplankton pigments and nutrients were analyzed from water samples collected monthly at 8 main-stem rivers stations (2011-2013) and weekly in Harpswell Sound (2008-2017) during ice-free months. Spatial bedrock and land use impacts on river nutrients were investigated at sub-watershed scales using GIS. Spatial analysis reveals a 10-fold increase in measured phytoplankton biomass across the Kennebec River’s saltwater boundary, which demonstrates ocean-driven phytoplankton variability in the lower river. The biomass pattern is accompanied by a transition in phytoplankton community structure with respect to which groups co-occur (diatoms, chlorophytes, and cryptophytes) and which are unique (dinoflagellates in Harpswell). Upstream, the timing of each community depends on land-use proximity and seasonal discharge. In Harpswell Sound, the nutrient regime and phytoplankton community structure vary systematically: first diatoms strip silicate, then dinoflagellates utilize nitrate, followed by chlorophytes and cryptophytes that utilize available phosphate. These findings reveal, for the first time, patterns in phytoplankton communities and nutrient dynamics across the fresh to salt water interface. Ultimately the Kennebec River phytoplankton communities and nutrient regimes are distinct, and the river is only a source of silicate to Harpswell Sound.

Date: 2021-01-01

Creator: Eugen Florin Cotei

Access: Access restricted to the Bowdoin Community