17:15 〜 18:45
[BBG01-P04] LATE HOLOCENE SEA LEVEL AND CLIMATE CHANGES RECORDED BY INTERTIDAL RED ALGAL RIMS
キーワード：Biogeoscience, Algal rim, Holocene, Lithphyllum Byssoides
The calcareous red algae Lithophyllum byssoides colonizes the intertidal zone of vertical cliffs, developing thick bioconstructions on the tidal notch base. Due to their high sensitivity to sea level change, these bioconstructions are powerful sea level marker frequently used to model precise eustatic curves. Two algal rims were sampled around the Capo Caccia Mesozoic limestone peninsula (NW Sardinia, Italy) to define late Holocene high-frequency Sea level fluctuations for Western Mediterranean Sea. The internal pattern of both rims is characterized by an in situ superposition of several generations of L. byssoides thalli binding sand-sized clasts composed of shell fragments along with quartz and feldspar grains. Thin sections and SEM analysis confirm L. byssoides is the dominant framework builder with minor Corallina elongate and Serpulidae worm encrusters, competing with bioeroders as L. lithophaga. The internal macrostructure combined with AMS radiocarbon ages selected along the algal growth directions reveal two accretion phases separated by a marked erosive surface. This analysis constrains the rims formation in the last 500 years and during two different sea level rises. The first accretion phase took place during the Little Ice Age between Maunder (1645–1715 AD) and Dalton (1790–1830 AD) solar Minima. The second occurred during the modern warming pulse (post 1850 AD). The erosive surface indicates a hiatus in rim growth related to a sea-level drop of, at least, 30 cm possibly associated to the latest stages of the LIA. This work estimates a growth rate for the L. byssoides build-ups of about 2 mm/yr and reveals the ability of intertidal red algal rims to record, also minimal, Sea level fluctuations occurred in the last centuries.