VARVE DEPOSITION AND THE SEDIMENT YIELD RECORD AT 3 SMALL LAKES OF THE SOUTHERN CANADIAN CORDILLERA

Lacustrine sediments deposited in three small glacier-fed lakes of the southern Canadian Cordillera are derived primarily from subglacial er osion and delivered via short proglacial streams or by direct melting and calving of cirque glaciers. Sediment transport and deposition duri ng early summer is controlled by runoff-generated bottom currents and in the late summer through winter by settling from suspension. This fo rms distinct rhythmic laminations of silt and clay in distal lake area s. Cesium-137 content in all three lakes indicates that these are varv e sediments. Time series of varve thickness covering the interval 1863 to present show distinct declines in sediment yield from 310 to less than 150 t km-2 a-1. The decline is related to sediment exhaustion fol lowing glacier retreat from Little Ice Age maxima and the opening of i ntervening sediment storage sites. Annual varve thickness is significa ntly related to fluctuations in summer or late summer temperature high lighting the importance of ice ablation, melt-water runoff, and sub-gl acial sediment sources in controlling deposition rates. Singular clima te events, such as autumn storms provide distinctive sedimentary signa tures in the varve record. Reconstructed sediment yield for the Little Ice Age is as much as 100% greater than the average Holocene rate.