Recent glacier variations in the Southern Patagonia Icefield, South America

The area variations of 48 outlet glaciers of the Southern Patagonia Icefield, South America, were elucidated for a period between 1944/45 and 1985/86, utilizing various remotely-sensed data. All but two of these glaciers are currently calving into a proglacial lake or a fiord. During the 41-yr period, most glaciers retreated, while a few glaciers remained almost stagnant and two glaciers had a net advance. The largest rate of area loss was 1.21 km(2) yr(-1) (or a distance of 484 m) at O'Higgins Glacier, which is by far the largest loss in Patagonia. On the other hand, Pio XI Glacier, the largest glacier in South America, advanced at a rate of 1.45 km(2) yr(-1) (or a distance of 288 m) during the same period. Moreno Glacier oscillated frequently, with a net gain of 4.1 km(2) in area in 39 yr; however, it is regarded to be currently in equilibrium. Some locational contrasts in the retreating rates can be recognized. For example, those on the northern half and on the east retreated at greater rates than those on the southern half and on the west, respectively. Possible causes for such variation patterns include temperature warming, although weak, in this century in the area south of latitude 46 degrees S. On top of such climatic forcing, glacier dynamics affected by the size of the glacier, surface gradient around the equilibrium line (EL), and calving status and channel ge ometry exerted influence, causing a wide variety of the changing rates. The volume of ice loss due to snout retreats during the 41-yr period is estimated to be on the order of 40 to 80 km(3). The volume loss in the ablation area due to thinning is roughly estimated at about 100 to 300 km(3) for the same period.