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Chemistry and Ecology 125

Downloaded by [Weizmann Institute of Science] at 03:22 26 June 2013 upper infralittoral, and are mostly found in place (and not reworked by marine erosion). Because of
their continuous growth and the possibility of dating the fossil portion using AMS 14C, vermetids

represent unique archives which retain palaeoclimatic information at high-resolution, spanning
the last ∼2000 years. All these reasons make them ideal biological sea-level indicators [25].

In the central Mediterranean region, for example, the study of vermetids can provide an accurate

reconstruction of the sea level of the late Holocene, based on precise knowledge of the vertical

position of the living portion with respect to reef mean sea level and longevity [26]. Along

Levantine coasts, tectonic vertical displacement values were extracted from tens of sites using

D. petraeum as a bioindicator of past sea level [27].

Current knowledge of past sea-level variations in the Mediterranean Sea results mainly from

beachrock deposits [28], submerged speleothems [29,30], and archaeological remains [31,32]

and other biological markers [33] which, however, do not cover the last 2000 years. The interval

between the fifteenth and nineteenth centuries, which includes the end of the Medieval Warm

Period and the Little Ice Age (LIA) is crucial to understanding the link between sea-level changes

and rapid climatic fluctuations, and can only be studied using fossil vermetid reefs.

A portion of vermetid reef collected in a tectonically stable area in northwest Sicily and radio-
carbon dated at 430 ± 30 yr cal BP revealed that the sea level was −40 ± 8 cm below present
mean sea level [4]. The same portion was analysed for stable isotopes (δ18O) by Silenzi et al. [6],

who identified a colder phase during the LIA (between the seventeenth and nineteenth cen-
turies), with a sea-surface temperature 1.99 ± 0.37◦C lower than today, consistent with literature
data [34]. Recently, data by Silenzi et al. [5] have been revised based on the aragonitic structure

of D. petraeum [26], by applying the fractionation equation of biogenic aragonite and sea-
surface temperature [T = 20.6 − 4.34 × (δ18Oaragonite − δ18Oseawater)]. Conversion of the δ18O
time series into temperature resulted in an average annual temperature for the LIA ranging
from 17.6 to 21.1◦C. The period after the LIA is characterised by a warming trend which is

briefly interrupted by a colder phase between 1930 and 1940, which lasted until the mid-1990s

(Figure 3(a)).

Following these promising results, Sisma-Ventura et al. [7] reconstructed the sea-surface tem-
perature, hydrology and productivity along the Israeli coast using the δ18O and δ13C signatures

of seven cores. The isotopic data span the last 500 years with an average resolution of 6 years.
The authors showed that the δ18O signature of the living D. petraeum corresponds precisely

to the range of values for inorganic carbonates precipitated at equilibrium with seawater for a
temperature range of 23–28◦C (Figure 3(b)).

The LIA in the Israeli coast is characterised by two cold anomalies (around 1590 and
1700 yr cal BP) separated by an intermediate warm period (∼1580–1680 yr cal BP). According
to the authors, the Levantine Basin was probably 1◦C colder than the present during the LIA
maximum. However, due to the poor chronological constrain, based on only a single 14C dating

obtained by Antonioli et al. [4] in Sicily, care should be taken in interpreting the results presented

by Sisma-Venturi et al. [7].

Recently, Silenzi et al. [26] presented new data on sea-level variation in the western Mediter-
ranean, covering two specific time periods (between 2380 ± 40 and 1520 ± 45 yr cal BP, and
over the last three centuries). These data were obtained from two tectonically quasistable areas:

S. Vito Lo Capo (northern Sicily) and Cabo de Gata (southeast Spain). Preliminary results show
that the sea level in Sicily rose from −27.5 ± 1.6 cm (2385 ± 40 yr cal BP) to −10.5 ± 1.6 cm
(1520 ± 40 yr cal BP), with an average rate of 0.20 ± 0.02 mm · yr−1.

New studies are currently being performed along a west–east megatransect in the Mediterranean
Sea: 14C AMS dating, δ18O and trace element ratios on 16 new cores from southeast Spain,

northwest Sicily, west Apulia, north Tunisia and several locations on the coasts of Lebanon and

Crete. All these data will be combined with the aim of reconstructing the Mediterranean sea-level

and sea-surface temperature variations during the last two millennia.