MARINE SEDIMENTOLOGICAL ANALYSIS FROM THE HUDSON STRAIGHT, LABRADOR SEA

During CCGS Hudson Expedition 2008-029, core 0004PC was raised from the Labrador Sea (61.46°N; 58.03°W; 2674 m water depth). Physical properties analysis of the core enables reconstruction of past sedimentological processes in the area. Analytical measurements were taken at 1 cm resolution for grain size spectra analysis by using a Malvern Mastersizer 2000, and diffuse spectral reflectance (DSR) using a Minolta CM2600D UV/VIS Spectrophotometer.

Varimax-rotated Principal Components Analysis (V-PCA) of the grain size spectra reveals four grain size modes. These modes, which related to different depositional processes, were identified by comparison with previously identified grain size modes following the methods of Darby et al., (2009). Grain size modes 1 and 4 are related to two distinct classes of nepheloid or gravity flows. Mode 1 contains more clay and fine silt, and less sand than mode 4. The differences observed between modes 1 and 4 indicate changes in bottom current energy levels within this area of the Labrador Sea at the times of deposition. Mode 1 was deposited at times of relatively low energy, as inferred from the finer sediment composition. Inversely, Mode 4 was deposited during times of relatively higher energy. Grain size Mode 2 relates to suspension freezing of sediment into sea ice, while grain size Mode 3 relates to sediment transported by anchor ice. Together, these four modes document changes in bottom water energy levels through time, and the interplay of sea ice transport and gravity flows on the depositional environment.

By applying V-PCA to the reflectance spectra, mineral composition was determined for each mode by comparing the observed mineral reflectance against a known mineral reflectance database. We infer reflectance Mode 1 is composed of smectite and dolomite, while Mode 2 is composed of illite. The mineral compositions of these two modes represent known clay mixtures associated with Arctic sediment, as well as the mineralogy of the surrounding landmasses. Mode 3 is composed of goethite and hematite, an iron oxide and oxyhydroxide which may indicate periods of increased bottom water oxygen levels. Mode 4 has high concentrations of calcite, possibly the result of the transport of detrital carbonate from the Laurentide Ice Sheet.