Dominant Iceberg Transport of Terrigenous Coarse Sand at Site 918, Southeastern Greenland Margin, with Increases in the Relative Importance of Sea Ice During Low IRD Times
Abstract
ODP Site 918 is 130 km from the SE Greenland margin, within the present limit of iceberg discharge. Its off-shelf location allowed for a continuous record of ice-rafted debris (IRD) deposition in distal to proximal glaciomarine facies from the late Miocene to present. Prior research shows 5 episodes of large ice-rafting events since 4.7 Ma; these occurred at times of climatic transition, presumably triggered by major calving events from the SE to central-east Greenland coast. Here we aim to determine the contribution of iceberg vs. sea ice-rafted sediment at peak and background times of IRD input at Site 918. SEM analysis of 19 samples ( 20 quartz grains each) from IRD peak and background horizons were studied to observe textural features that can serve as indicators of glacial ice or sea ice activity. Results show that both background and peak IRD events are dominated by grains that are subangular, with medium relief, breakage blocks, fractures, and some degree of dissolution and microlayering. However, peak vs. background differences also exist: 78% of the grains from peak IRD events are subangular to very angular; this decreases to 65% at times of background levels of IRD input. Discriminant analysis showed a significant difference (p<0.01) between these two populations; 64% of the samples were correctly reclassified to their original groups (background or peak IRD events). Peak IRD events show high loadings on features that tend to be associated with mechanical weathering, i.e., iceberg transported (angular grains, high relief, breakage blocks, fractures, cusps, and low dissolution), whereas background events show high loadings on features associated with chemical weathering, i.e., sea ice transported (rounded grains, medium-low relief, dissolution, striations, and micro-layering). Ongoing work on the percent classification of individual grains will give further insight into the variability in the two IRD transport processes. Results suggests that iceberg transport dominated along the SE Greenland margin since the late Miocene, with relative increases in sea ice transport during periods of low IRD abundance. This environment appears better suited to capture the paleo-glacial record rather than the sea ice record, with calving overwhelming most of the sea ice processes at the time of deposition.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP23E1531H
- Keywords:
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- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICSDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4926 Glacial;
- PALEOCEANOGRAPHYDE: 4954 Sea surface temperature;
- PALEOCEANOGRAPHY