# Elevation and Mass Changes of the Southern Patagonia Icefield Derived from TanDEM-X and SRTM Data
## 3 Results
### Elevation Changes: Southern SPI on Multiple Timesteps  
In Figure 3 we compare different time periods for a subset of the southernmost SPI. The maps (a) and (b) reveal that the interval 2011/12-2015/16 shows positive dh/dt values in particular at higher elevations, but also on some of the glacier tongues such as at Perito Moreno. On the other hand, glacier tongues having shown negative elevation changes in 2000-2011/12 also exhibit a similar negative pattern in the 2011/12-2015/16 period. For the altitude range between 1000-2000 m the surface increased at maximum rates of 1.11 m\(\cdot\)a\({}^{-1}\) (2011/12-2015/16). As the area at this level is notably large it causes the overall mean elevation change of the studied southern part of the SPI to turn out positive for this period, with 0.128 \(\pm\) 1.1 m\(\cdot\)a\({}^{-1}\). The vertical and lateral co-registration accuracy is comparable for both time intervals. It has to be noted that the image differencing 2011/12-2015/16 is based, for both years, on summer acquisitions. The mean elevation changes of the TDX mosaics of 2011/12 to 2015/16 in reference to SRTM (2000) and 2011/12-2015/16 (TDX-TDX) are shown as hyposometric plots in Figure 3c. The range of values for each elevation bin of 50 m is indicated by the standard deviation (sd). As described in Section 3.1 the large variability at levels below 1300 m is caused by the heterogeneous change rates at the glacier tongues (cf. sd bars). At higher altitudes theses ranges get narrower, varying at \(\pm\)1 m\(\cdot\)a\({}^{-1}\) \begin{table}
\begin{tabular}{c c c c} \hline
**Scenarios** & **dh/dt (m\(\cdot\)a\({}^{-1}\))** & **dV/dt (km\({}^{3}\)\(\cdot\)a\({}^{-1}\))** & **dM/dt (Gt\(\cdot\)a\({}^{-1}\))** \\ \hline Scenario 1 & & & \(-\)10.34 \(\pm\) 2.2 \\ Scenario 2 & \(-\)1.06 \(\pm\) 0.21 & \(-\)11.5 \(\pm\) 2.3 & \(-\)9.77 \(\pm\) 2.1 \\ Scenario 3 & & & \(-\)7.97 \(\pm\) 1.7 \\ Scenario 1, (extrapolated) & \(-\)1.05 \(\pm\) 0.28 & \(-\)13.2 \(\pm\) 3.6 & \(-\)11.84 \(\pm\) 3.3 \\ \hline \end{tabular}
\end{table} 
Table 2: Volume and mass change computations for the SPI (10.772 km\({}^{2}\) of measured area corresponding to 85.7% of the SPI area) using different density scenarios for volume-to-mass conversion. last row: as Scenario 1 but including extrapolation for the missing 14.3 percent. The change rates for the lower elevation (\(\leq\)1300 m) vary less over time than higher up. Especially the areas at heights between 1300 and 2000 m show a big variance in the mean elevation change values. That is remarkable, as it represents 52% of the total glaciated area. The values for summer 2015/16 and winter 2016 delineate the upper and lower bound of the mean change rates in this elevation band. These values show seasonal differences with only about nine months temporal baseline. The two dates also reflect different surface conditions in winter and summer and hence not only elevation change, but also different signal penetration into the snow and fern cover. Figure 2: Elevation change maps of the SPI; names denote the major outlet glaciers. (**a**) pixel-based assessment 2000–2015/16; (**b**) averaged on catchment basis; (**c**–**h**) hypospmetry (cyan) and elevation changes (red) plotted for 50 m elevation bins for different glaciers. Pio XI glacier is known for its anomalous development at its two termini. As a singular exceptional case over the whole icefield it is attributed a neutral to slightly positive surface change rate on the plateau-like higher altitudes but experiencing lifted surface at the tongue, with rates increasing downstream to a maximum of 8 m\(\cdot\)a\({}^{-1}\) at its southern terminus. All graphs only refer to surveyed area which amounted for a total of 10772 km\({}^{2}\) for (**a**) and (**b**). Figure 3: Elevation changes of the southern SPI for different time periods.