Page 5 - 31 antonioli PAG 55-56

Climex Maps - explanatory notes
SST from Serpulids overgrowths on Submerged
Speleothems
Sergio Silenzi
ICRAM - Central Institute for Marine Research, via Casalotti 300, 00166, Roma, Italy-s.silenzi@icram.org
Introduction
In this session are abstracted SST proxy data
for the Holocene Climatic Optimum (HCO ; 8 ka
BP) as deduced by oxygen isotope data from
Polychaeta serpulid overgrowths on
speleothems. The samples were collected in
three submerged caves located along the
Tyrrhenian coast in Italy:
1) Cape Palinuro (Lat. 40.02°N – Long.
15.16°EGw)
2) Argentarola Island (Lat. 42.26°N– Long.
11.07°EGw)
3) Marettimo Island (Lat. 37.58° N– Long.
12°03 EGw).
Speleothems were collected by means of scuba
diving to -21 m below sea level in the cave of
Argentarola, down to -48 m in the cave at
Palinuro and to –23 m in the cave at
Marettimo; discussion and complete references
on their using are available in Antonioli et al. any apparent growth hiatus.
(2001 and 2002).
Materials and methods
In the Tyrrhenian Sea, serpulids are typical
dwellers of submerged caves, which offer a dark
and sheltered environment, with restricted
water flow.
Holocene serpulid colonies grown on submerged
speleothems are typically 5 to 12 cm thick. At
the time of sampling, the outermost layer of
each colony was alive.
Optical microscopy observations coupled with
Scanning Electron Microscopy allowed us to rule
out diagenetic alteration of the Serpulid tubes
and recognize the absence of dissolution voids
and abiogenic cements. The growth patterns
were also recognized: commonly, new
individuals encrust the underlying dead
Policheta, thus forming a dense colony of
intertwined tubes. Serpulid colonies developed
on continental speleothems when the rising sea
level reached the speleothem tips. All the
colonies have been constructed by the
gregarious Serpula massiliensis, whose tubes
consist of 100% calcite (Milliman, 1976), as
confirmed by X-ray diffraction. Fossil Serpula
massiliensis tubes also consist of 100% calcite, from linear interpolation by assuming constant
as determined by X-ray diffraction.
For d18O reconstruction each subsample
analized (2 mm wide) was powdered (average 4
mg), roasted in vacuum at 350° for 30 minutes
to pyrolize organic matter and treated with
100% H3PO4 at 25°C for 6 hours. The CO2
released by the reaction and purified by using a
liquid nitrogen-ethyl alcohol slash at about -
80°C, was measured in a Finnigan Delta mass
spectrometer. Mean standard deviation of 18O
measurements was typically  0.1‰ (2 ).
Radiocarbon dating was carried out on 11
colonies. 18O series were based on 9 colonies:
6 at Argentarola cave, 2 at Cape Palinuro and 1
in Marettimo cave (Alessio et al 1996, Antonioli
and Oliverio 1996; Antonioli et al., 2001 and
2002).
The age at which serpulid colonies commenced
growing was calculated by 14C dating results and
by using a mathematical model that assumes
linear growth rates. The assumption is also
based on the fact that the colonies do not show
The model assumes that growth rates remained
constant during the Holocene. The sample used
for radiocarbon dating is a slab cut through the
whole colony, from the fossil bottom to the
living top. Conventional radiocarbon dating is
thus carried out on a sample encompassing the
whole time span through which the colony grew.
The model allowed us to obtain the age of the
bottom of the colony. The age thus obtained is
correct only if there was constant growth. The
mathematical method (Alessio et al., 1992)
was, therefore, tested by AMS 14C dating on the
skeletons of the first marine dwellers (table 1)
for the following samples: OS-2655 (Palinuro –
27 m) and OS-2656 (Palinuro –41.5 m). AMS
results yielded ages similar to those obtained
through the model on the samples R-2358
(Palinuro –27 m) and R-2377 (Palinuro –41.5
m). Our assumption that growth rates remained
constant, therefore, appears to be valid.
The validity of the model is supported by
another AMS date obtained for the outermost
layer of a stalactite (Argentarola cave, –18.5
m) in contact with the marine overgrowth.
The 18O data vs. time for each serpulid colony
have been reconstructed through extrapolation
growth rate.