The Mediterranean calcareous red alga Lithophyllum byssoides forms thick bioconstructions in the intertidal zone, developing in a very narrow vertical range (ca. 20 cm), making it an exceptionally precise indicator of past sea-level positions. This high sensitivity to even minimal sea-level fluctuations enables the detection of high-frequency, low-amplitude changes that occurred over the last 1000 years. The Late-Holocene relative sea-level curve presented here, is based on L. byssoides rims extensively encrusting the swell-exposed rocky shores of the Mesozoic limestone cliffs of northwestern Sardinia (NW Mediterranean). The rim accretion structures reveal the in situ superposition of multiple generations of L. byssoides thalli, which bind sand-sized clasts. Combined AMS radiocarbon dating identifies four main growth phases, each bounded by distinct erosional surfaces. These phases correlate with stages of relative sea-level rise and coincide with the warmest periods of the last millenium. In contrast, erosional surfaces frequently draped by a reddish muddy matrix indicate sea-level drops associated with the coldest phases of the Little Ice Age. Our findings indicate decimetric relative sea-level fluctuations on sub-centennial timescales, which significantly exceed the average magnitude of sea-level change documented over the last millenium, implying major shifts in coastal dynamics and ecosystems. These results support a strong link between sub-centennial climate variability and sea-level fluctuations and underscore the value of L. byssoides rims as high-resolution archives of past sea-level oscillations.
Fantini et al. (Fri,) studied this question.
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