ABSTRACT: Sedimentological analysis of Holocene and glacial events in Central Baffin Bay, Labrador Sea: constraints from reflectance and elemental analysis.

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Abstract

A marine sediment core was taken in central Baffin Bay, a site sensitive to environmental change. The 155 cm long trigger core, 16TWC, and its associated piston core 16PC were taken during CCGS Hudson Expedition 2008-029 (70.46 deg. N; 64.66 deg. W; 2063 m-water depth). Shipboard DSR was measured on the core at 0.5 cm resolution with a Minolta CM-2600d (Ortiz, Arctic Workshop abstract, 2010). In the lab, instruments used to analyze the dried sediment at 1 cm resolution include a Minolta CM-2600d UV/VIS Spectrophotometer (400-700 nm wavelength range; 10 nm resolution; 3mm spot size) to measure Diffuse Spectral Reflectance (DSR) and an Innov-X Alpha series handheld XRF scanner to measure elemental analysis. Samples were freeze-dried, then wet sieved into <63, 63-150 and >150 um size classes using distilled water. The <63 um fractions were then air dried in a 1-liter beaker. Each sample was ground in a mortar and pestle to break up the grains. For the Minolta work each sample was placed on a single piece of weigh paper covered with Gladwrap™ plastic wrap to protect the instrument. The same individual ground sample was then tested with the XRF instrument. Each sample was placed in the individual SPEX™ XRF cup for measurement.We were able to construct a preliminary age model for the core by comparison with the GISP2 d18O record due to the close proximity of the two sites. The GISP2 d18O record was taken from the central Greenland ice sheet and our core was taken in nearby Central Baffin Bay. To form our preliminary age model we graphed the Minolta data L, a, and b* on depth and plotted them against the GISP2 record. We found that the a* data exhibited features that correlated best with the GISP2 record (Figure 1). We developed an age model by assigning ages to the peaks and troughs of the a* record based on their presumed analogs in the GISP2 d18O record. Plotting the wet shipboard DSR data against the dried lab-based DSR data indicates that the lab based measurements are approximately 1.5x brighter in terms of L*. This difference arises from water absorption in the shipboard samples, grain size differences and the higher resolution of the shipboard measurements. While the original core has a mixture of size fractions, homogenizing and sieving the samples in the lab to work on the <63 um yields results weighted toward the silt and clay size classes. Analysis of silt and clay particles should provide results that can be correlated over great distances because these size particles can be transported over a longer distance and are less influenced by rare, larger clasts. Depending on their composition, these size classes can be associated with glacial or non-glacial climate conditions and their delivery responds to sea level change (Wahsner et al. 1999). Separate Varimax Rotated Principal Component Analyses (V-PCA) were conducted on the reflectance and elemental data sets and three factors were pulled out from each instrumental data set. The DSR factors based on the dried samples from core 16TWC were compared with reflectance spectra from the combined shipboard DSR data set (Ortiz, Arctic Workshop abstract, 2010) and spectra for known minerals to evaluate which minerals were present. The first DSR factor from core 16TWC matches the first DSR factor from the shipboard data and is associated with Actinolite and Goethite. The second two factors bear some similarity to the shipboard DSR factors but do not match them exactly. This difference could be due to differences in geographic region and sample grainsize as noted above or the smaller size of the data set obtained from this single core. The first XRF factor exhibits large positive loadings (>0.90) on Ba, Zn, Ti, and Fe, and large negative loadings on Ca (-0.92). We interpret this as contrasting calcium and siliclastic terrigenous material. The second XRF component has strong positive loadings (>0.75) for Mn and Pb, and likely represents trace metal rich Mn oxides. The third XRF component exhibits a contrast between moderate positive loadings (0.56) for Co, and relatively strong negative loadings (-0.71) for Zr. This component represents terrigenous material, likely IRD, with a distinct provenance from the first XRF component. The reflectance factors can be correlated with the XRF factors and similarly with grain size factors associated with the transported components (Sadallah et al., Arctic Workshop abstract, 2010). The first DSR factor correlates with XRF factor 2, which corresponds to trace metal rich Magnesium Oxides. The second DSR factor is anti-correlated with the first XRF factor and relates to a contrast between carbonate and terrigenous sediment. The third DSR factor 3 is weakly correlated with the third XRF factor. The Central Baffin Bay is sensitive to the Greenland current where the silt and clay size particles can determine the extent of transport due to glacial and non-glacial conditions. The XRF and DSR factors allow us to differentiate the relative importance of sediment transport by sea ice, nepheloid flows, and iceberg IRD and provide a glimpse of local paleoclimate changes for the past 30,000 years in the Central Baffin Basin.

Bibliography of Canadian Geomorphology