*3.5. Stable Isotopes*

The distribution of δ13C within the water column varied between the different sampling times (Figure 7). In January 2017, δ13C decreased with depth. In April 2017, the water column was well mixed with respect to δ13C, and in May 2016, δ13C increased with depth. The <sup>δ</sup>13C value was generally higher at bank reefs (0.41‰ ± 0.06‰, depths 190–220 m) than at shallower wall reefs (0.37‰ ± 0.07‰, depths 80–220 m) (Table 3). <sup>δ</sup>18O increased with depth and had similar ranges for all sampling times. Therefore, δ18O was higher at bank reefs (0.39‰ ± 0.03‰) than at shallower wall reefs (0.34‰ ± 0.06‰) (Table 3). In May 2016, when samples were taken from most of the sites, δ18O had the largest range at ~150 m depth of Δδ18O = 0.12 ‰ (Figure 7). With a relatively low sample size (*n* = 37), these results are preliminary and only provide us the first look at the distribution of stable isotopes in Langenuen. Thus, these results have to be confirmed by future research.
