Late‐summer peak in sediment accumulation in two lakes with contrasting watersheds, alaska

Abstract

The timing of clastic sedimentation in two glacial‐fed lakes with contrasting watersheds was monitored using sequencing sediment traps for two consecutive years at Allison Lake (Chugach Range, Alaska) and four months at Shainin Lake (Brooks Range, Alaska). Shainin Lake is a weakly stratified lake fed by distant glaciers, whereas Allison Lake is more strongly stratified and fed predominantly by proximal glaciers. At Shainin Lake, sediment accumulation started in late June and reached its maximum in mid‐August, just before lake mixing and during a period of low river discharge. The grain size of the sediment reaching the sediment trap in Shainin Lake was homogenous throughout the summer. At Allison Lake, pulsed sedimentation of coarse particles during late summer and early fall storms were superimposed on the fine‐grained sedimentation pattern similar to that observed at Shainin Lake. These storms triggered underflows that were observed in the thermal structure of the lake and deposited abundant sediment. The sequencing sediment traps reveal a lag between fluvial discharge and sediment deposition at both lakes, implying limitations to interpreting intra‐annual sedimentary features in terms of inflow discharge.

Key words:

• lake sedimentation
• glacier‐fed lake
• Alaska

Acknowledgements

Jason Briner, Elizabeth Ceperley, William D'Andrea, Anne Krawiec, Barney Peterson, Heidi Roop, Caleb Schiff and David Vaillencourt assisted in the field, and Katherine Whitacre and Megan Saalfeld assisted in the laboratory. CH2MHill Polar Services and Toolik Field Station provided logistical support. Access to Shainin Lake was by permission of the Arctic Slope Regional Corporation. We are grateful to them for allowing access to their land. Copper Valley Electric Association commissioned the discharge data from Allison Lake. The Flagstaff office of the US Geological Survey allowed access to their grain‐size analyzer. This study was funded by NSF awards ARC‐1107662 (Shainin Lake), and EAR‐0823522 and ARC‐0909332 (Allison Lake). DF was supported by a postdoctoral scholar award through Northern Arizona University. Datasets were provided by the Toolik Field Station Environmental Data Center with support from NSF grants 455541 and 1048361. This is GLERL contribution # 1769.

Additional information

Notes on contributors

Megan Arnold

David Fortin, Darrell Kaufman, Megan Arnold, School of Earth Sciences & Environmental Sustainability, Northern Arizona University, 625 S Knoles Drive, bldg. 12, Flagstaff, AZ 860111 E‐mail: [email protected], [email protected], [email protected]

Erik Schiefer

Nathan Hawley, NOAA / GLERL, 4840 S. State Rd., Ann Arbor, MI 48108‐9719 E‐mail: [email protected]

Nathan Hawley

Erik Schiefer, Geography, Planning and Recreation, Northern Arizona University, 19 W McConnell Drive, PO Box 15016, Flagstaff, AZ 86011‐5016 E‐mail: [email protected]