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HOW DYNAMIC ARE FLUVIAL-DELTAIC SYSTEMS DRAINING LAND-ICE? A CASE-STUDY OF CLYDE RIVER, BAFFIN ISLAND
OVEREEM, IRINA INSTAAR.
Briner, Jason P. INSTAAR.
Kettner, Albert J. INSTAAR.
Global Circulation Models predict that future climate change due to antropogenic forcing will be amplified at high latitude and have important feedback on global climate (e.g. Dickson, 1999; PARCS, 1999). Sedimentary modeling studies indicate that climate change could have a profound impact on the sediment flux transported into the coastal zone (Syvitski and Andrews, 1994; Syvitski, 2002). Such model predictions are still uncertain. On the one hand this is because the present 2D sedimentary simulation models do not properly address sediment storage in the fluvial domain. On the other hand there is a strong component of temporal uncertainty, which is due to the short measurement records in the Arctic. Little is known of the natural environmental variability in Arctic fluvial-deltaic systems. Extreme events, e.g. peak floods or even glacial lake outbursts, are of low-frequency (and thus rarely monitored), but may have a high impact. We selected Clyde River on Northern Baffin Island to improve model concepts and test them against a real-world example.
Our numerical hydrological model, HydroTrend, requires drainage basin characteristics and climate data as input parameters to predict daily discharge (Q) and sediment load (Qs) records. Clyde River basin has been delineated from Canadian Topographic Survey DEM data and was found to comprise 2526 km2. Clyde River is about 66km long, drains the SE part of the Barnes Ice Cap and includes a large pro-glacial lake, Generator Lake. The maximum elevation in the drainage basin is 1450m and the estimated glacier equilibrium line is 1000m. Daily temperature (T) and precipitation (P) data have been measured at the town of Clyde River (Fig 1). Mean annual T is -12°C, average monthly temperatures are above 0°C in June, July and August and mean annual P is 21cm. Based on these data HydroTrend shows a typical short melting season of less than 100 days between end of June and the beginning of September. The bulk of the water and sediment load discharge occurs in on average 45 days of the year. The mean Q over the melt season is rather low at 28m3/sec. HydroTrend predicts a modest total sediment load of ~0.1million ton per year. However, the simulated peak event over a 50 year run drains 484m3/sec and the sediment concentration for that event is estimated to be 38kg/m3, which means that most probably a hyperpycnal plume develops for a few hours at the river mouth. Sensitivity tests, mostly focused on varying melt water discharge from the Barnes Ice Cap, show a larger range of Q and Qs predictions. This will especially be relevant if increased melting of the Barnes Ice Cap due to global warming continues.
Field observations in the Clyde River indicate that the present-day main river probably does not exceed its incised channel system and floods only the lowermost terraces occasionally. In addition, we compared the mapped channel and bar geometry in the summer of 2003 and the 1967 aerial photo; the analysis revealed only moderate changes.
The system response of the near-coastal part of the modern Clyde River is apparently subdued by the incised nature of the river.
The deglaciation history of Clyde Fjord is known in detail based on mapped moraines, cosmogenic and radiocarbon dates (Briner et al., 2003). We collected additional shell samples for dating and related them to sedimentary section in the delta deposits close to the present fjord head. The dates are merged with the previously existing dates, and show that the withdrawal of the main ice flows from the fjordhead area occurred between roughly 8000 C14 yrs (very close to the fjord head) and 6600 C14 yrs more land inward. Sedimentation rates must have been very high: two shell samples in marine muds which are ~12m apart have ages of 7470 +/- 40 and 7620 +/-40 C14 yrs, a time span of only 150 years. Volumetric reconstructions in a GIS of the mapped terrace surfaces and available dates corroborate the rapid sedimentation. In addition, a terrace surface is observed 21.6m above m.s.l., of which 60% is covered with boulders ranging from ~30cm to 1m. We interpret these deposits to be deposited by a catastrophic event for example a glacial lake outburst, possibly related to a phase of ice-cap reorganization. System dynamics appear much more pronounced proximal to the ice stream. The comparison between the modern-day Clyde River and the deposition during ice retreat indicates that the proximity of the ice margin is a strong factor determining the sediment flux dynamics.
For ungauged basins numerical models form a tool to predict water and sediment fluxes under changing climatic conditions. However, models will still need to incorporate new concepts to capture glacio-fluvial system dynamics, which can vary a great deal over time.
Briner J.P., Miller G.H., Davis P.T., Bierman P.R., Caffeed, M. 2003. Last Glacial Maximum ice sheet dynamics in Arctic Canada inferred from young erratics perched on ancient tors, Quaternary Science Reviews, v. 22, p.437-444.
Church, M., 1972. Baffin Island Sandurs: a study of Arctic fluvial processes. Bulletin 216, Geological Survey of Canada, Department of Energy, Mines and Resources.
Dickson, B., 1999. Oceanography: all change in the Arctic. Nature 397, 04 February 1999, p.389-391.
PARCS, 1999. The Arctic PaleoSciences in the Context of Global Change research. PARCS, Paleoenvironmental ARCtic Sciences, ESH Secretariat, AGU, Washington, D.C..
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Syvitski, J.P.M., 2002. Sediment transport variability in Arctic Rivers: implications for a warmer future. Polar Research, v. 22,2,p. 323-330.
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