Abstract. Glaciar Jorge Montt (48 • 20 S/73• 30 W), one of the main tidewater glaciers of the Southern Patagonian Icefield (SPI), has experienced the greatest terminal retreat observed in Patagonia during the past century, with a recession of 19.5 km between 1898 and 2011. This retreat has revealed trees laying subglacially until 2003. These trees were dated using radiocarbon, yielding burial ages between 460 and 250 cal yrs BP. The presence of old growth forest during those dates indicates that Glaciar Jorge Montt was upvalley of its present position before the commonly recognized Little Ice Age (LIA) period in Patagonia. The post-LIA retreat was most likely triggered by climatically induced changes during the 20th century; however, Glaciar Jorge Montt has responded more dramatically than its neighbours. The retreat of Jorge Montt opened a 19.5 km long fjord since 1898, which reaches depths in excess of 390 m. The bathymetry is well correlated with glacier retreat rates, suggesting that dynamic responses of the glacier are at least partially connected to near buoyancy conditions at the ice front, resulting in high calving fluxes, accelerating thinning rates and rapid ice velocities.

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13Patagonia, located in southern South America, is a vast and remote region 14 holding a rich variety of past environmental records but a small number of 15 meteorological stations. Precipitation over this region is mostly produced by 16 disturbances embedded in the westerly flow and is strongly modified by the 17 austral Andes. Uplift in the windward side leads to hyper-humid conditions 18 along the Pacific coast and the western slope of the Andes; in contrast, 19 downslope subsidence dries the eastern plains leading to arid, highly 20 evaporative conditions. 21Here we investigate the dependence of Patagonia's local climate (precipitation 22 and near surface air temperature) year-to-year variability on large-scale 23 circulation anomalies using results from a 30-year long high-resolution 24 numerical simulation. Variations of the low-level zonal wind account for a large 25 fraction of the rainfall variability at synoptic and interannual timescales. Zonal 26 wind also controls the amplitude of the air temperature annual cycle by 27 changing the intensity of the seasonally varying temperature advection. 28We also investigate the main modes of year-to-year variability of the zonal flow 29 over southern South America. Year round there is a dipole between mid and 30 high latitudes. The node separating wind anomalies of opposite sign migrates 31 through the seasons, leading to a dipole over Patagonia during austral summer 32 and a monopole during winter. Reanalysis data also suggests that westerly flow 33 has mostly decreased over north-central Patagonia during the last four decades, 34 causing a drying trend to the west of the Andes, but exhibit a modest increase 35 over the southern tip of the continent. 36 3

Tidewater calving glaciers can undergo large fluctuations not necessarily in direct response to climate, but rather owing to complex ice–water interactions at the glacier termini. One example of this process in Chilean Patagonia is Glaciar Jorge Montt, where two cameras were installed in February 2010, collecting up to four glacier photographs per day, until they were recovered on 22 January 2011. Ice velocities were derived from feature tracking of the geo-referenced photos, yielding a mean value of 13 ±4 md–1 for the whole lower part of the glacier. These velocities were compared to satellite-imagery-derived feature tracking obtained in February 2010, resulting in similar values. During the operational period of the cameras, the glacier continued to retreat (1 km), experiencing one of the highest calving fluxes ever recorded in Patagonia (2.4 km3 a–1). Comparison with previous data also revealed ice acceleration in recent years. These very high velocities are clearly a response to enhanced glacier calving activity into a deep water fjord.

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