Tyrrhenian Holocene Palaeoclimate Trends from Spelean Serpulids

Quaternary Science Reviews 20 (2001) 1661}1670

Tyrrhenian Holocene palaeoclimate trends from spelean serpulids Fabrizio Antonioli!*, Sergio Silenzi!", Silvia Frisia# !Environmental Department, ENEA-Casaccia, Via Anguillarese 301, 00060 S.Maria di Galeria Roma, Italy "ICRAM, Central Institute for Marine Research, Via Casalotti, 300, 00163 Roma, Italy #Museo Tridentino di Scienze Naturali, via Calepina 14, 38100 Trento, Italy

Abstract

In tropical regions, changes in sea level and sea surface temperature (SST) can be obtained from coral reefs. In temperate seas, such as the Mediterranean, where there are neither fossil nor actively growing coral reefs, palaeoclimatic trends and associated sea level rise can be reconstructed through radiocarbon ages and the geochemical properties of serpulid calcite tubes from colonies that dwell in submerged caves. In the present work, we reconstructed Holocene palaeoclimate trends for the Tyrrhenian Sea, through the oxygen isotopic composition of marine Polychaete serpulids that colonised continental speleothems when the sea invaded the caves which open along the Italian coast. The long term !#O trend extracted from multiple serpulid skeletons of &0.7 per mil increase over the last 8 kyr can be interpreted in terms of temperature change, but could also be due to long-term changes in the salinity balance of the Mediterranean. If the !#O trends recorded by serpulid calcite re#ected changes in Mediterranean SST starting at 8200 cal yr BP, it would coincide with the cooling trend recorded in the tropics and in Greenland ice cores. Spelean serpulids radiocarbon ages allowed us to reconstruct a Tyrrhenian sea level curve comparable to that recorded along the French Mediterranean coast. Spelean serpulid calcite, therefore, can be used as a useful tool to reconstruct paleoclimate and sea-level changes in temperate coastal karst regions. ! 2001 Elsevier Science Ltd. All rights reserved.

1. Introduction from carbonate !#O (Keigwin, 1996; Sabin and Pisias, 1996; Bond, 1997), alkenones (Bard et al., 1997), and A knowledge of mid latitude sensitivity to Holocene Sr/Ca ratio in corals (Guilderson et al., 1994; McCulloch global climate changes is essential for modelling how the et al., 1994; Beck et al., 1997) exhibit a marked mid- Earth's climate system responded during the deglaciation Holocene cooling trend interrupted by warm transients. and for simulating future climatic scenarios. Several Ice cores drilled in high mountain glaciers in the high-resolution palaeotemperature records have been Andes (Thompson et al., 1998) show large scale similarit- obtained from high latitude ice cores and tropical coral ies with tropical and polar records, but also regional reefs, foraminifers and glaciers. Climate change recon- di!erences, such as several warm transients in the late struction for the last deglaciation and Holocene, how- Holocene that are not recorded by GISP 2 (Greenland), ever, is still controversial because of di!erent timing and Byrd and Vostock (Antarctica) ice cores. Similarly, the amplitudes of climate variations at high and low latit- record of Holocene climate in the continental Mediterra- udes. For example, the GRIP ice core records are charac- nean region seems to di!er from both the high latitude terised by attenuated !#O trends in the middle and late ice cores and the low latitude marine records (Bar- Holocene that indicate slight cooling for the last 9000 yr Matthews et al., 1997; McDermott et al., 1999). Little is (Dansgard et al., 1993). For the same time slice, the known, as yet, about Holocene sea surface temperature Vostok ice core site in Antarctica records a more accen- (SST) trends in the Mediterranean, as few deposits can tuated cooling interrupted by several warm transients be reliably dated. Marine serpulid overgrowths on sub- (Jouzel et al., 1993). In the tropics, SST changes inferred merged speleothems (CaCO continental cave deposits) which formed in coastal karst regions provide a means of reconstructing the relative timings of sea level rise and paleoclimatic Holocene trends in temperate seas, * Corresponding author. Tel.: #39-6-3048-3955; fax: #39-6-3048- such as the Mediterranean, which are a crucial compon- 4029. ent in understanding the natural variability of climate E-mail address: [email protected] (F. Antonioli). (Bard et al., 1997).

0277-3791/01/$ - see front matter ! 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 3 7 9 1 ( 0 1 ) 0 0 0 1 2 - 9 1662 F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670

2. Methods tectonically quasi-stable areas of the Italian coast. In fact, the uplift rate following 125 kyr (isotope stage 5e) is In this study we present new C data and oxygen !0.038 mm/yr at Palinuro and !0.014 mm/yr at Ar- isotope time series from Polychaeta serpulid overgrowths gentarola (Antonioli and Oliverio, 1996; Alessio et al., on speleothems sampled in two submerged caves located 1992). Samples were collected by means of scuba diving along the Thyrrhenian coast in Italy at Cape Palinuro to !21 m below sea level in the cave of Argentarola, and (Lat. 40.023N}Long. 15.163E) and at the Island of Argen- down to !48 m in the cave at Palinuro (Fig. 2 ). In the tarola (Lat. 42.263N}Long. 11.073E) (Fig. 1). The two Tyrrhenian Sea, serpulids are typical dwellers of sub- cave sites were chosen on the basis of their location in merged caves, which o!er a dark and sheltered environment, with restricted water #ow. Holocene serpulid colonies grown on submerged speleothems are typically 5}12 cm thick. At the time of sampling, the outermost layer of each colony was alive. Maximum thickness was observed for colonies which grow at the centre of the cave, probably because of the low energy conditions and higher nutrient availability. Optical microscopy observations coupled with scann- ing electron microscopy allowed us to rule out diagenetic alteration of the serpulid tubes and recognise the absence of dissolution voids and abiogenic cements. The growth patterns were also recognized: commonly, new indi- viduals encrust the underlying dead Policheta, thus form- ing a dense colony of intertwined tubes (Fig. 3). 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 (Milli- man, 1976), as con"rmed by X-ray di!raction. Fossil

Fig. 1. The submerged Argentarola cave (Italy) at !18 m. Living serpulids form gregarious colonies on a submerged continental stalag- Fig. 2. Location of the submerged caves along the Thyrrenian coast mite. Maximum thickness of the fossils colonies is 12 cm. (Italy), where speleothems with serpulids overgrowth were sampled. F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670 1663

Fig. 4. Main steps of sampling procedure for !#O analysis. Spele- othems with marine overgrowth (A) found in submerged caves were sectioned following the growth lines (B) and analyzed (C).

bon dating and one for isotope analysis. A minimum of 6 to a maximum of 21 subsamples (2 mm wide and 2 mm long), were cut from each colony, depending on their growth thickness. Each subsample was powdered (average 4 mg), roasted in vacuum at 3503 for 30 min to pyro- lize organic matter and treated with 100% HPO at 253C for 6 h. The CO released by the reaction and puri"ed by using a liquid nitrogen-ethyl alcohol slash at about !803C, was measured in a Finnigan Delta mass spectrometer. Mean standard deviation of !#O measurements was typically $0.1" (2!). The outermost samples (2 mm), which contained the calcite secreted by living organisms, have a mean !#O value of 2.1$0.2" at both Argentarola and Cape Palinuro. Radiocarbon dating was carried out on 10 colonies, Fig. 3. Close view of a serpulid with inalterated tube (above). Surface 6 at Argentarola cave and 4 at Cape Palinuro in Scaletta layer of a speleothem in the Argentarola cave with serpulids over- cave (Figs. 5 and 6). !#O series were based on 8 colonies, growth (below). while the two colonies coming from Cape Palinuro (!47 and !48 m) were used to build the sea-level curve Serpula massiliensis tubes also consist of 100% calcite, as (Alessio et al., 1996; Antonioli and Oliverio, 1996). Bio- determined by X-ray di!raction. genic samples were not contaminated by speleothem Two-mm wide slabs were cut from 8 serpulid colonies material. The marine and continental deposits are com- perpendicular to the growth axis starting from the living monly separated by a smooth surface and can be easily outer layer down to the crust that "rstly colonised the recognised on the basis of a marked colour di!erence: the continental speleothem by using a diamond drill (Fig. 4). speleothem is translucent and dark brown, whereas the Each slab was then cut into two slices, one for radiocar- marine deposit is opaque and yellowish. 1664 F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670

Fig. 5. Section of Argentarola cave showing the location of the sampled speleothems.

Fig. 6. Cape Palinuro, section of Scaletta cave with the location of sampled speleothems.

The age at which Serpulid colonies commenced grow- bon dating is a slab cut through the whole colony, from ing was calculated by C dating results (Table 1) and by the fossil bottom to the living top. Conventional using a mathematical model that assumes linear growth radiocarbon dating is thus carried out on a sample en- rates. The assumption is also based on the fact that the compassing the whole time span through which the col- colonies do not show any apparent growth hiatus. ony grew. The model allowed us to obtain the age of the The model assumes that growth rates remained con- bottom of the colony. The age thus obtained is correct stant during the Holocene. The sample used for radiocar- only if there was constant growth. The mathematical F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670 1665

Table 1 Age of samples. Calibration after Stuiver and Reimer, 1993. The sample Argentarola }3.5 m was only used for the sea level curve shown in Alessio et al., 1996

Altitude (m) Lab. number Conventional age !C Age cal BP 1! calculated Age cal BP 1! (BP 1!) through the model

Palinuro C ages !27 R-2358 4285$50 2.90 8430$150 !27 OS-2655 7810$45 3.09 8223$71 !41.5 R-2377 4015$50 3.00 8680$130 !41.5 OS-2656 8150$45 3.56 8560$63 !41.5 R-2382 13237$104! !1.03 13915$167! !47 R-2523 4448$50 3.82 9865$155 !48 OS-3533 9580$35 3.58 10253$72

Argentarola C ages !3.5 R-2144 3270$110 1.39 6500$285 !6 R-2134 3330$80 1.39 6590$110 !9.5 R-2135 3405$80 2.77 6770$190 !14 R-2386 3507$76 3.50 7360$200 !16 R-2396 3865$55 3.70 8300$150 !21.5 R-2250 4290$60 3.33 9430$170 !18.5 R-2352 4384$81 3.14 9590$120 !18.5 OS-3535 10050$50! !3.00 9724$135

!Sample coming from the outermost layer of the stalactite. Samples with Lab number R*are from C Lab of Physics, at University La Sapienza, Rome. Sample with Lab number OS*are from AMS C Lab at Woods Hole (USA) method (Alessio et al., 1992) was, therefore, tested by Following Bard (1988), a correction of !400 yr for the AMS C dating on the skeletons of the "rst marine Mediterranean Sea water was adopted, and the corrected dwellers (Table 1) for the following samples. The C dates were converted to calendar ages by using the AMS C age of sample OS-2656 (Palinuro, !41.5 m, revised CALIB 3.0 calibration program (Stuiver and Table 1), obtained from the "rst marine dwellers, is Reimer, 1993). 8560$63 yr, while the age of sample R-2358 (same speleothem) is 8680$130 yr. The latter calculation comes from the application of the model to the entire fossil 3. Results portion of the speleothem. Since there is a di!erence of 120 yr, the dates are comparable and overlap, consider- The six serpulid colonies sampled at Argentarola coming the margin of error. The AMS C age of sample OS- menced growth at 6590$185 cal yr BP at !6 m, 2655 (Palinuro }27 m, Table 1), obtained from the "rst 6770$190 cal yr BP at !9.5 m, 7360$200 cal yr BP at marine dwellers, is 8223$71 yr, and sample R-2358 !14.5 m, 8300$150 cal yr BP at !16 m, 9590$120 (same speleothem) is 8430$150 yr (from the entire fossil cal yr BP at !18.5 m, 9430$170 cal yr BP at !21.5 m. portion). Again, the datations of the two samples are The four serpulid colonies of Palinuro commenced comparable and overlap, because of the 207 yr di!erence. growth at 8223$71 cal yr BP at !27 m and 8680$65 AMS results yielded ages similar to those obtained cal yr BP at !41.5 m, 9865$155 cal yr BP at }47 m and through the model and our assumption that growth rates 10,253$72 cal yr BP at }48 m. Fig. 7 shows the Tyr- remained constant, therefore, appears to be valid. rhenian Sea level rise curve reconstructed by Alessio et al. The validity of the model is supported by another (1996) using the mentioned data. This curve correlates AMS date (sample OS-3535; age 9724$135 yr BP) ob- well with the sea-level curve predicted for the French tained for the outermost continental layer of a stalactite Mediterranean coast, reconstructed by Lambeck and (Argentarola cave, }18.5 m) in contact with the marine Bard (2000) from a variety of data sources, such as overgrowth. The age obtained through the model for the shell fragments, Bryozoans, terrestrial and marine cave bottom of the serpulid colony which encrusted the stalac- deposits. tite is 9590$120 yr BP: the bottom part is younger than The !#O trends vs. time for each serpulid colony have the outer layer of the speleothem, and that is consistent been reconstructed through linear interpolation by as- with the stratigraphic setting of the two deposits. We, suming constant growth rate (Fig. 8). Seasonal growth therefore, infer that the model provides a reliable esti- rate for many marine invertebrates is not correlated mate of the age of commencement of Serpulid colony with temperature (Coma et al., 2000). We, therefore, hy- growth. pothesize that growth rate was constant throughout the 1666 F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670

4. Discussion

4.1. Thyrrhenian !18O record

Polychaete serpulids are believed to secrete calcium carbonate close to !#O equilibrium with sea water and do not show metabolic e!ects on oxygen isotope fractionation (Videtich, 1986) . The !#O value of serpulid tube calcite, therefore, should be a function of the !#O value of sea water and of the ambient temperature (e.g. O'Neil et al., 1969). The three variables which should be accounted for when interpreting the !#O signal of Thy- rrhenian Serpulids are (1) changes in !#O composition of sea water; (2) salinity #uctuations due to the delicate hydrologic balance of the Mediterranean Sea; and (3) changes in sea surface temperature. In practice, serpulid calcite !#O re#ect the sum of global variations of the ocean water !#O due to changes in continental ice volume, the Thyrrhenian sea surface !#O variations due to changes in marine and freshwater budget, and the isotopic fractionation between calcite and water, which depends upon the temperature at which serpulids formed Fig. 7. Upper and lower limits of predicted sea level change along the their tubes. Cote d'Azur, France (from Lambeck and Bard 2000, black lines, replot- The hydrologic balance of the Mediterranean Sea has ted). The curve reports maximum and minimum sea-level rise as esti- probably remained similar to the present day balance for mated by the model used by the authors for their study area. In this the past 18 kyr (Kallel et al., 1997). Nevertheless, between curve are placed our sea-level rise data reconstructed from C ages (circle), calculated for the "rst layer of marine overgrowths on continen- 9000 and 6000 years BP, the sea level rose by about 40 m tal deposits; the analytical error for dating and sea level data is within as a consequence of a global sea level change. The !#O the circles. The points seem to show a good concordance. The di!erence of the Mediterranean water, therefore, was in#uenced by between predicted sea level change and some spelean serpulids data can the !#O of the Atlantic Sea water. Conversely, for the be due to the fact that the predicted curve was calibrated for a Mediter- last 6000 yr the Tyrrhenian sea-level rise amounts to only ranean region with glacio-isostatic characteristics di!erent from those of our investigated areas. 3 m (Alessio et al., 1996) and, therefore, the Mediterra- nean Sea water !#O should have been little in#uenced by the Atlantic water signal. The !#O values of surface water are also in#uenced by salinity changes. At present, the Mediterranean salinity Holocene. This hypothesis is supported by the validation varies from 36.15" at Gibraltar to 39" in the Western of the model which was used to date the bottom of the Mediterranean (Pierre, 1999). These values have changed colonies. The outermost layers (active serpulids) from through time. On the basis of foraminifera assemblages, di!erent colonies sampled in di!erent caves and at di!er- Kallel et al. (1997) indicates that the salinity of the ent depths have a similar mean !#O value (2.1", Fig. 9). Thyrrhenian Sea surface decreased between 8000 and Statistical treatment of the data relative to living ser- 4500 yr BP During this time span, there was a #uctuation pulids indicated that the 12 values measured fall within in sea surface salinity from 39 to about 35 per mil (Kallel the 2! interval and thus the data set can be considered et al., 1997) as a consequence of humid climate conditions. homogeneous. In fact, the living serpulid values fall with- The lower !#O values of Thyrrhenian spelean ser- in the interval 1.96637}2.40697 (2.18667$0.2203), which pulids between 8000 and 7000 cal yr BP could also re#ect corresponds to the range XM $2SD, while the mean stan- a Thyrrhenian !#O decrease due to freshwater in#ux, dard deviation of analytical uncertainty was typically which was put to evidence by Kallel et al. (1997). The shift $0.1 (2!). Even by treating separately the means of to heavier !#O values coincides with a decrease in the living serpulid values from Argentarola Island and Palin- rate of Mediterranean sea-level rise and, therefore, with uro Cape, the XM di!erences are not signi"cant. The stat- a reduced #ow of Atlantic Sea water within the Mediter- istical values obtained are the following: ranean. If the !#O of Thyrrhenian spelean serpulids preliminary test on Argentarola Island/Palinuro Cape were to record salinity changes, the !#O trend illus- variance: Variance ratio"4.85149. Test on the mean: trated in Fig. 8 would indicate that the Thyrrhenian Pooled variance"0.09901; t-Test Statistic (ABS Value)" salinity increased considerably in the last 9000 yr 1.13942; nonsigni"cant at the 1% level. (increase exceeding 2,3"). We, therefore, believe that F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670 1667

Fig. 8. The !#O(" PDB) vs. time series for each colony sampled at Argentarola and Cape Palinuro (typical analytical error is $0.1"). serpulid calcite !#O record could be mainly related to The measured present-day !#O value of sea water SST trend rather than to salinity changes, in agreement both within and outside the submerged caves is constant, with other studies (Bard et al., 1997; Beck et al., 1997; and is 0.9" (SMOW). However, the SST measured with- Bond et al., 1997). in the submerged caves ranges from 173 in winter to 243C in summer, and the SST outside the caves ranges from 4.2. Temperature trends 143 in winter to 253 in summer. Cave waters are therefore less subjected to seasonal temperature variations, and If we assume that Thyrrhenian Sea water !#O com- can be considered as representative of average mean position mainly re#ects the SST variation, time changes annual temperature. In the submerged caves at both in !#O of serpulid tube calcite could re#ect SST trends Palinuro and Argentarola we did not record the presence (cooling vs. warming) averaged over about 200 yr, which of a thermocline. This physical characteristic of the is the mean time span encompassed by a 2 mm sample. coastal caves makes it possible to compare the !#O 1668 F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670

caves where there is freshwater percolation (Belloni and Bianchi, 1982). The curve shown in Fig. 10a was obtained by combin- ing the 8 curves of !#O variation with time presented in Fig. 8. This curve shows that serpulid calcite !#O increased over the last 8200 cal yr BP, although only two !#O values show such a marked response and three of them show little evidence of peak at all, which is, therefore, indicative of mid and late Holocene Mediterranean summer SST cooling. The regression line obtained through interpolation of the data reported in Fig. 10a has a positive angular coe$cient di!erent from zero. The Fig. 9. The !#O(" PDB) vs. depth trend. The !#O were extracted from the outermost layer of living serpulid colonies that dwell onto 12 slope of the line does not fall within the statistical error. di!erent submerged speleothems from !9.5 to !48 m. We considered The observed !#O variation through time is signi"cant 3 di!erent sites: black circle: Palinuro Cape; white circle: Argentarola and, therefore, we infer that the cooling trend thus identi- Island; gray circle: Marettimo Island (Southern Tyrrhenian Sea). Note "ed is signi"cant (Regression coe$cient B"}0.8756; In- that the !#O values (2.19$0.2" PDB) are similar and, therefore, are tercept A"2.11980; Variance error"0.07106; t-Student not in#uenced by water depth. value of B"8.44829; t-Student value of A"1.39788). The cooling trend that begins at 8200 cal yr BP is signals extracted from colonies sampled at di!erent recorded always in the Thyrrhenian Sea by the !#O of depths, and permits the assumption that serpulids long- G. Bulloides (Kallel et al., 1997 Fig. 10c), although the term records of mean annual temperature changes of curve obtained from foraminifera has a smoother pro"le near-surface sea water averaged over 200 yr. with respect to that obtained from serpulids. Information on serpulid growth rates is available for The serpulid !#O record for the Holocene (Fig. 10a) is harbour and brackish-water species (Bianchi and Morri, characterised by maximum deglacial warming that co- 1996), for which maximum tube growth occurs in sum- incided with the maximum rate of sea-level rise mer. Faster growth rates during warm seasons were also (20 mm/yr between 9000 and 8200 cal yr BP) (Fig. 10b). documented for aragonite serpulids from a submarine The warming was followed by a progressive fall in SST, cave o! the coast of Belize (Videtich, 1986). Serpulids of which was synchronous with a deceleration in the rate of tropical origin, such as Serpula massiliensis put most of sea-level rise to 6 mm/yr between 8200 and 7000 cal yr their energy into reproduction in autumn and winter. BP The Mediterranean SST warming, therefore, co- They spend their energies to grow in summer, following incided with the highest rates of sea-level rise. their biological rhythm. Their annual growth rate is Data on peri-Mediterranean continental speleothems considered, however, constant as for other Mediterra- indicate that the latest portion of the Holocene was nean invertebrates, and independent from temperature. characterised by a complex substructure with a decrease Coma et al. (2000) for example write `2The fact that in temperature starting from 7500 yr BP, interrupted by many taxa are not correlated with temperature makes the warm transients between 6400 and 3500 cal yr BP Mediterranean environment a convenient ecosystem in (McDermott et al., 1999). Taking into account dating which to distinguish the e!ects of secondary production uncertainties, the Tyrrhenian SST cooling recorded by from those of temperature. Environmental factors, such spelean serpulids is in phase with a mid-Holocene tem- as photoperiod, food availability, oxygen, salinity and perature decrease recorded by other proxy data, such temperature, all in#uence energy expenditure in marine as the !#O of marine foraminifera and continental organism. Generally, Mediterranean organism react to speleothems. their total environment rather than to a single factor2a. So we infer that serpulids commonly grew in summer throughout the Holocene, and that their growth rate was 5. Comparison with tropical and high latitude records season-dependent, not temperature dependent, and that their calcite !#O signal records summer sea surface In our opinion, the !#O trends recorded by Thyr- temperature trends within and outside the caves. rhenian spelean serpulids seem to re#ect SST trends. We, If the assumptions that Serpula massiliensis secretes its therefore, attempted a comparison among the Holocene tube close to oxygen isotopic equilibrium and its growth paleoclimatic record preserved in serpulids from rate is maximum in summer are correct, a net shift to Thyrrhenian caves (Fig. 10a) and the Holocene sea level higher !#O should be the result of decreasing summer rise in the Thyrrhenian (Fig. 10b), and other climate SST. We exclude the possibility that !#O changes re#ect proxy data series, such as the Thyrrhenian SST record the in#uence of karstic freshwater on the basis of the reconstructed from G. Bulloides (Fig. 10c ) and the Indian observation that Serpula massiliensis are not present in Ocean alkenone series (Fig. 10d). F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670 1669

The tropical Indian Ocean alkenone record for latest portion of Holocene is characterised by a cooling trend between 7000 and 1000 cal yr BP (Bard et al., 1997) (the record for the last 1000 yr is lacking from the cores). mid-Holocene SST cooling initiated in the tropical Paci"c Ocean 8800 cal yr BP (Guilderson et al., 1994, Mc Culloch et al., 1996). The tropical Indian Ocean and Paci"c SST records show warm transients superimposed on the cooling trend at 4500 cal yr BP and between 6000 and 4500 cal yr BP (Bard et al., 1997; Guilderson et al., 1994; Mc Culloch et al., 1996), respectively. These warm SST transients appears to be attenuated both in the serpulids and foraminifera !#O records. If we agree with the hypothesis that the !#O pro"les from alchenones, corals and foraminifera identify a late Holocene SST cooling trend, it would then seem prob- able that the !#O temporal trends in Thyrrhenian serpulid calcite do indeed re#ect SST changes rather than salinity changes. In particular, the Mediterranean cooling trend seems to coincide with the Greenland Holocene 8.2 cooling event (e.g. Walker et al., 1999). The 8.2 event, appears to be the only clearly-de"ned event in the GRIP oxygen isotope pro"le for the Last Termination. Walker et al. (1999) stress that the climatic signi"cance of the 8.2 stratigraphic event in the GRIP !#O record cannot be fully exploited until the of GRIP oxygen isotope ratio is better understood and correlated with the marine and terrestrial records.

6. Conclusions

The !#O values of serpulid tube calcite from submerged caves and C dating of the "rst marine organisms that colonised the continental speleothems that were being submerged by sea water entering the cave during the Holocene sea level rise, have the potential to allow the reconstruction of Holocene environmental changes and the synchronous sea level rise in temperate seas, such as the Mediterranean Sea. By assuming that salinity and !#O of the sea water reservoir #uctuations had little in#uence on the serpulid !#O signal, the radiocarbon dated !#O time series extracted from marine Serpula massiliensis colonies which grew on submerged caves on

!&&&&&&&&&&&&&&&&&&&&&&&&& Fig. 10. Comparison beetween: (a) Tyrrhenian Sea serpulid !#O(" pdb) time-series with regression line (in black); (b) Tyrrhenian Sea level rise curve (black circle: Serpulids; white circle: Vermetid reefs and Archeological data) (from Antonioli and Leoni, 1998, Antonioli et al., 1999); (c) the foraminifera !#O time-series from a sediment core drilled in the Tyrrhenian Sea; (d) the alkenone temperature record from the Indian Ocean (SST 3C). The reversal to cooling is recorded 7}8 kyr BP in the marine records. The cooling trend appears to be a global phenomenon, but amplitudes and delays of temperature reversal are indicative of regional e!ects. The dashed gray line shows the beginning (8200 yr cal BP) of the supposed cooling trend in the Mediterranean. 1670 F. Antonioli et al. / Quaternary Science Reviews 20 (2001) 1661}1670 tectonically stable coasts of the Thyrrhenian Sea indicate Bianchi, C.N., Morri, C., 1996. 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