In the way of more background, the following 2013 reference makes it clear that both calving rates and basal ice melting rates are high for the PIIS (PI in the images); in part due to the frequent advection of warm CDW.
The linked reference better quantifies the ice mass loss from both calving and basal melting for the major Antarctic ice shelves.
The first attached image shows: Calving fluxes (green) and basal mass loss (−BMB; red). Pie chart shows numbers for surveyed ice shelves only. Errors, 1 s.d. b, Ratio between calving flux (green) and BMB (red), in per cent of total flux.
The second attached figure shows a significant correlation (R2 = 0.84 (coefficient of determination); P = 3.13 × 10−5; F-test) between surface lowering rates8 and our mean basal mass-loss rates (−SBMB) for thinning ice shelves.
M. A. Depoorter, J. L. Bamber, J. A. Griggs, J. T. M. Lenaerts, S. R. M. Ligtenberg, M. R. van den Broeke & G. Moholdt, (2013),"Calving fluxes and basal melt rates of Antarctic ice shelves," Nature, doi:10.1038/nature12567
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12567.html?WT.ec_id=NATURE-20130919Abstract: "Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321 ± 144 gigatonnes per year and a total basal mass balance of −1,454 ± 174 gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing."