Long-term vs short-term subsite erosion rates on microtidal shore platforms (Southern Mallorca, Balearic Islands, Western Mediterranean)

Abstract

We address changes in microtopography of a supratidal rocky surface on calcareous rocks in the shore platform of s'Alavern (S de Mallorca) by means of a TMEM monitoring device. TMEM site was installed in 2004 and subsequent microtopographies were obtained in 2005, 2008 and 2021; as well as a bi-hourly monitoring in 2005. When comparing subsite short-term erosion rates against long-term erosion rates, the results indicate that the erosion rates obtained during time intervals of less than 5 years show higher erosion rates (0.45 vs. 0.22 mm year−1) and with greater variance than those obtained for monitoring intervals greater than a decade. When comparing the variability of the value of the microtopographical altitude in hourly intervals with the behaviour of those same points on a long-time scale, it is evident that, in the short term, those points that experience negative displacements show higher long-term erosion rates than those that experience positive shifts on an hourly scale. However, this pattern is not statistically significant, which suggests that the magnitude and trend of the microtopography change is reflecting the role of different processes and agents that are operating at different temporal scales.