Abstract There is clear evidence that rapid warming has been fuelling significant changes in the ocean and cryosphere in the Antarctic Peninsula region. Less is known about how terrestrial biological ecosystems, particularly plants, are responding to warming and hydroclimatic change. We show that high evaporative environmental conditions and microclimate associated with topography lead to humidity-dependent evaporative effects on the oxygen isotope ratios (δ 18 O) of moss waters and α-cellulose in the northern Antarctic Peninsula, based on a spatial (> 400 km) isotopic survey at 14 sites over 24 days during summer 2020. The δ 18 O of moss waters define a water line of δ 2 H = 4 × δ 18 O + 37 for Polytrichum strictum and δ 2 H = 3.8 × δ 18 O + 38.9 for Chorisodontium aciphyllum , indicating enrichment compared to line slopes ranging from 6.7 to 8.5 for snow, standing water, previous published snapshots of moss waters and the long-term local meteoric water lines along the Antarctic Peninsula. The δ 18 O of moss waters negatively correlated with relative humidity (which ranged from ~50% to 100%) and not with temperature or latitude, where a higher δ 18 O indicates increased evaporative enrichment or dry conditions. A positive correlation between the δ 18 O of moss waters and α-cellulose (ρ = 0.397, P = 0.011) for P. strictum (ρ = 0.533, P = 0.007) but not C. aciphyllum suggests that the high evaporative conditions from the season imprinted on the cellulose. Lastly, we found significant positive correlations between topographic aspect (north-exposedness) and the δ 18 O of moss waters (ρ = 0.569, P < 0.001) and α-cellulose (ρ = 0.579, P < 0.001), indicating that irradiance on north-facing slopes promotes drier conditions and evaporative enrichment. Topographic aspect (and resulting microclimate) is an important and predictable determinant of the δ 18 O of moss waters and α-cellulose. This study highlights that mosses are sensitive recorders of climatic and non-climatic conditions in polar terrestrial ecosystems.
Groff et al. (Fri,) studied this question.