CHRONOLOGY AND EXTENT OF OUTERMOST CIRQUE MORAINES IN THE SOUTHERNMOST FUEGIAN ANDES AND CANADIAN CORDILLERA

PONCE, J.F.; MENOUNOS, B.; FERNÁNDEZ, M.; SCHAEFER, J.

Ushuaia

Congreso; VI Congreso Argentino de Cuaternario y Geomorfología; 2015

CADIC-CONICET

Most alpine glaciers in southernmost Patagonia and in the Canadian Cordillera achieved their maximum Holocene extents in the last 1000 years, but the synchronicity of century-scale advances between these regions remains uncertain. In the Canadian Cordillera glaciers began their climatic advances as early as the 11th century and reached their maximum Holocene positions during the early 18th or mid-19th century. Several glaciers began to expand during the 13th and 14th centuries and many likewise advanced during the mid-15th, 16th, and 17th centuries. In South America, the timing and spatial pattern of glacier expansion over the last millennium is less certain. In Patagonia some studies indicate three advances during the last 1000 years at about 1220-1380 AD, 1600-1630 AD and 1860-1950 AD. Dating uncertainties, however, hinder a robust comparison between the hemispheres. Advances in the measurement of terrestrial cosmogenic nuclides (TCN) now allow young samples to be dated with low measurement errors (5-10% of the sample age). TCN provides new opportunities to constrain the timing of late-Holocene advances in both hemispheres, and thus provides one method to test inter-hemispheric climate variability. To assess hemispheric synchronicity of late-Holocene glacier expansion, we visited 14 glaciers in the Fuegian Andes (TdF, 54º 40ʹ S 68º 30ʹ W, Tierra del Fuego, Argentina), Mackenzie Mountains (MM, 62º 00ʹ N; 127º 50ʹ W, Yukon and Northwest Territories) and Northern Coast Mountains (NCM, 59º 50ʹ N; 136º 00ʹ W, British Columbia and Yukon, Canada). These glaciers exist at high latitude and all occur in rain shadow positions. We targeted end moraines composed of quartz-bearing rock, and we obtained 49 samples from stable boulders atop prominent terminal moraines. Our work also mapped the magnitude of retreat from outermost moraines for 71 glaciers in the study area (26 in TDF, 23 in MM and 22 in NCM). We identified one and occasionally two closely-spaced terminal moraines front glaciers in the study area and up to four recessional moraines lie upvalley from the terminal moraines. The terminal moraines descend to 680±131; 1771±109 m and 1270 ± 185 m a. s. l. for the TDF, MM and NCM regions respectively. Average glacier retreat for these three regions is 778±432 m (41±23%), 1138±373 m (39±13%) and 1341 ± 618 m (36±16%). Topographic factors likely explain the more variable length change for the small cirque glaciers in TDF. We await the 10Be results that will allow us to assess the synchronicity of last millennium century-scale advances between northwestern Canada and southernmost Patagonia.