We investigated the stable isotope hydrology of Sable Island, NS, Canada over a four
year period from September, 2017 until August, 2021. The δ 2 H and δ 18 O values of inte-
grated monthly precipitation were weakly seasonal and ranged from -66 to -17 per mil
and from -9.7 to -3.1 per mil, respectively. Fitting these monthly precipitation data
resulted in a Local Meteoric Water Line (LMWL) defined by: δ 2 H = 7.28 ± 0.22×δ 18 O
+ 7.95 ± 1.38 per mil. Amount weighted annual precipitation had δ 2 H and δ 18 O values
of -37 ± 12 per mil and -6.1 ± 1.6 per mil, respectively. Deep groundwater had more
negative δ 2 H and δ 18 O values than mean annual precipitation, suggesting recharge oc-
curs mainly in the winter, while shallow groundwater had δ 2 H and δ 18 O values more
consistent with mean annual precipitation or mixing of freshwater with local seawater.
Surface waters had more positive values and showed evidence of isolation from the
groundwater system. The stable isotopic compositions of plant(leaf) water, on the
other hand, indicate plants use groundwater as their source. Fog had δ 2 H and δ 18 O
values that were significantly more positive than those of local precipitation, yet had
similar 17 O-excess values. Our results establish an important framework for ongoing
isotopic studies of feral horses and other wildlife on Sable Island.