A review of Pine Island Glacier, West Antarctica: hypotheses of instability vs. observations of change

The Pine Island Glacier ice-drainage basin has been cited as the part of the West Antarctic ice sheet most prone to substantial retreat on human time-scales. Here we review the literature and present new analyses showing that this ice-drainage basin is glaciologically unusual. Due to high precipitation rates near the coast, Pine Island Glacier basin has the second highest balance flux of any extant ice stream or glacier. Well-defined tributaries flow at intermediate velocities through the interior of the basin and have no regions of rapid velocity increase. The tributaries coalesce to form Pine Island Glacier which has characteristics of outlet glaciers (e.g. high driving stress) and of ice streams (e.g. shear margins bordering slow-moving ice). The glacier flows across a complex grounding zone into an ice shelf. There, it comes into contact with warm Circumpolar Deep Water which fuels the highest basal melt-rates yet measured beneath an ice shelf. The ice front position may have retreated within the past few millennia but during the last few decades it appears to have shifted around a mean position. Mass balance calculations of the ice-drainage basin as a whole show that there is currently no measurable imbalance, although there is evidence that some specific areas within the basin are significantly out of balance. The grounding line has been shown to have retreated in recent years. The Pine Island Glacier basin is clearly important in the context of the future evolution of the West Antarctic ice sheet because theoretically, it has a high potential for change and because observations already show change occurring. There is, however, no clear evidence to indicate sustained retreat or collapse over the last few decades.

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