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| Titel |
Dispersal of fluvial sediment in two sub-arctic fjords on the Labrador Coast: Nachvak Fjord and Saglek Fjord, Canada |
| VerfasserIn |
Elisabeth Kahlmeyer, Samuel J. Bentley |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047781
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| Zusammenfassung |
| Recent marine records of fluvial sediment supply to two sub-arctic fjords in northern
Labrador (Eastern Canada) have been studied in order to determine fluvial transfer of
terrestrial material to the fjords, and to develop baseline knowledge for future studies.
Multibeam and sub-bottom acoustic data and sediment cores (box and gravity) were
collected in Nachvak and Saglek fjords in Northern Labrador, within Canada’s Torngat
Mountains National Park, as part of the most extensive study of the park’s marine
resources to date. In order to assess sediment discharge and the fjord’s sediment
dispersal system, data collection was concentrated on marine basins fed by the
largest fluvial catchments associated with each fjord. Each core was sub-sampled for
X-radiography, grain size, and radiochemical analysis, and was analyzed for sedimentary
structures and sediment accumulation rates. Radiochemical analysis is based on the
particle-bound radioisotopes 210Pb and 137Cs, which have been used to determine sediment
accumulation rates (SAR), and 210Pb inventories and flux over decadal to centennial
time scales. Sediment thickness and extent in the fjord basins were studied from
sub-bottom profiles and bathymetry data. Results show that in both fjords sediment is
accumulating in depocenters in the center of each basin. In Nachvak Fjord, which is fed
primarily by small rivers with very steep, small, presently glaciated catchments, the
thickness of postglacial sediment observed in sub-bottom profiles compares well
with thicknesses projected from recent sediment accumulation rates and implies
that postglacial sedimentation was on average constant. In Saglek Fjord, which is
fed by larger rivers with more extensive catchments that lack glaciers, postglacial
sediment thickness is on average 40 % less than that projected from recent sediment
accumulation rates, suggesting more rapid sediment accumulation for the past ~100 y than
for that averaged over post-glacial time. Present mass accumulation rates for the
Nachvak fjord basin are on average 1200 t km-2 y-1, and 39,000 t/y for the entire
basin, and for Saglek, 1100 t km-2 y-1, and 43,000 t y-1 for the entire basin.
Comparison between MAR values and results from a previously published statistical
model estimating fluvial sediment supply from catchment properties shows that
the model overestimates fluvial measured sediment flux by a factor of 5-25, with
marginally closer results for Nachvak Fjord than for Saglek Fjord. This suggests
that either the fjord’s marine basins are less efficient sediment traps than we had
hypothesized, or that the model is significantly overestimating the fluvial sediment flux. |
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