A 4000 year varve chronology and annual sedimentation rate record from Lago Argentino, Patagonia

Abstract:

Proglacial lakes provide valuable records of paleoclimate, volcanism, and glaciation. We present results from coring of Lago Argentino, a 1500 km² proglacial lake on the margin of the Southern Patagonian Icefield (SPI). Forty-seven sediment cores were recovered from water depths up to 600 meters, ranging up to 6 m in length (Shapley et al., EP010). Detailed analyses of this sediment reveal annual layering, or varves. In order to efficiently and reproducibly count these varves, we develop a new image autocorrelation-based varve counting tool, named countMYvarves (Van Wyk de Vries et al., U009). We use this toolbox to generate an annual resolution chronology and sedimentation rate record for all 47 Lago Argentino cores. We find that: 1) sedimentation rate versus distance from glacier front approximatively follows an exponential decay, although there is considerable variability due to lake bathymetry, sediment transport and non-glacial input, 2) sedimentation rate was higher in the little ice age (150-400 years ago) than in the last 100 years in 91.2% of cores, 3) a 100-150 year periodicity in sedimentation is found in many distal cores, and may reflect centennial timescale climate cyclicity in Southern Patagonia related to the Southern Annular Mode. These results provide new insight into century scale glacial change and sedimentation dynamics in a complex glacio-lacustrine system (Ito et al. EP010; Fedotova and Magnani, G004; Magnani et al. G004). The SPI is the largest Southern Hemisphere contributor to global sea level rise, and Lago Argentino provides key context to recent glacial changes.