Isotope records in submarine speleothems from

Isotope records in submarine speleothems from

Séance spécialisée :
Climate changes : the karst record III
Montpellier, 11-14 mai 2003
Bull. Soc. géol. Fr., 2005, t. 176, no 4, pp. 363-373
Isotope records in submarine speleothems from the Adriatic coast, Croatia
MAÓA SURI‚1, NADA HORVATIN„I‚2, AXEL SUCKOW3, MLADEN JURA„I‚,4 and JADRANKA BAREÒI‚2
Keywords. – Karst, Submarine speleothem,
14 C
dating, d13 C, d18 O, Climate change, Adriatic Sea, Croatia
Abstract. – Isotope studies, using 14C dating, d13C and d18O measurements, were performed at eight speleothems taken
from three submerged caves situated along the eastern Adriatic coast, Croatia. The speleothems were taken from 17 m
to 38.5 m depth below mean sea level. The samples consist of four stalagmites and four stalactites in position of growth,
covered with marine biogenic overgrowth, and the length of speleothems ranges from ~80 mm to ~190 mm.
The youngest (surface) and the oldest (base) layers of speleothems were radiocarbon dated and the 14C ages range
from 21,600 cal B.P. to 37,000 yr B.P. During that period the global sea level was more than 40 m below the recent one,
so presently submerged objects were under the subaerial conditions necessary for speleothem deposition. 14C ages of the
youngest layer range from 21,600 to 32,200 cal B.P. for different submerged speleothems. This indicates the time when
the speleothem growth ceased, most probably due to flooding of the cave with either fresh or brackish water.
Speleothem growth during the Last Glacial Maximum (30-19 kyr ago) and different time of growth cessation for the different speleothem samples suggest that climate change was not the reason for cessation of deposition.
Samples for d13C and d18O measurements were taken from six submerged speleothems with sampling distances of
ca. 5-10 mm from the surface to the base of speleothems. Most of the d13C values are in the range from –10.5‰ to
–8.5‰, with few exceptions to –6‰. These values are typical for Dinaric karst, and very different values for marine
biogenic overgrowth indicate that no isotopic exchange took place during the submerged period. d18O values range from
–6.7‰ to –4.1‰. A weak correlation between d13C and d18O values indicates possible kinetic isotope fractionation during the calcite precipitation. If the d18O record is interpreted as climatic signal, it suggests similar climatic conditions
for the late Pleistocene and the Holocene, especially no significant differences in temperature and/or moisture transport.
Enregistrements isotopiques sur des spéleothèmes sous-marins de la côte adriatique, Croatie
Mots-clés. – Karst, Spéléothème sous-marin, Datation au
14 C,
⭸13 C, ⭸18 O, Changement climatique, Mer Adriatique, Croatie.
Abstract. – Des études isotopiques, consistant en datations au 14C ainsi qu'en mesures de ⭸13 et de ⭸18O, ont été effectuées sur huit spéléothèmes de trois grottes sous-marines situées en Croatie le long de la côte orientale de l'Adriatique.
Les spéléothèmes ont été échantillonnés entre 17 m et 38,5 m sous le niveau moyen de la mer. Les échantillons consistent en 4 stalagmites et 4 stalactites en position de croissance, recouverts d'une surcroissance biogénique marine. La
longueur des spéléothèmes échantillonnés est comprise entre 80 mm et 190 mm environ.
Les dépôts les plus récents (en surface) et les plus anciens (à la base) ont été datés au carbone 14. Les âges obtenus vont de 21 600 ans calendaires B.P. à plus de 37 000 ans B.P. A cette époque, le niveau moyen des mers se trouvait
à plus de 40 m sous son niveau actuel, de sorte que des objets actuellement submergés étaient soumis aux conditions subaériennes qui sont nécessaires pour le dépôt de spéléothèmes. Les âges 14 C de la couche la plus jeune vont de 21 600 à
32 200 années calendaires B.P. pour différents spéléothèmes submergés. Ce résultat donne une indication du moment
où la croissance de ces structures a cessé, très probablement à la suite d'une inondation de la grotte par de l'eau douce ou
saumâtre. La croissance des spéléothèmes au cours du dernier Maximum Glaciaire (de 30 à 19 ka B.P.), et le fait que la
croissance se soit arrêtée à des moments différents d'un échantillon à l'autre, suggèrent que cet arrêt n'est pas dû au
changement climatique.
Des échantillons pour les mesures de ⭸13C et ⭸18O ont été prélevés sur 6 spéléothèmes submergés à des distances
d'environ 5-10 mm entre la surface et la base. La plupart des valeurs de ⭸13C tombent dans la gamme – 10,5 ‰ à
– 8,5 ‰, avec quelques exceptions jusqu'à – 6‰. Ces valeurs sont typiques des karsts dinariques, et l'existence de valeurs très différentes pour les pellicules biogéniques démontre qu'il n'y a pas eu d'échange isotopique pendant la période
de submersion. Les valeurs de ⭸18O vont de – 6,7 ‰ à – 4 ‰. L'existence d'une faible corrélation entre les valeurs de 13C
et de ⭸18O indique la possibilité d'un fractionnement isotopique cinétique pendant la précipitation de calcite. Si l'on in18
terprète le ⭸ O comme un signal climatique, il suggère que les conditions climatiques ont été similaires au cours du
Pléistocène tardif et de l'Holocène, et notamment qu'il n'y a pas eu de différences significatives de température et/ou de
transport de l'humidité.
1
2
Department of Geography, University of Zadar, Tudmanova 24 i, 23000 Zadar, Croatia, [email protected]
Radiocarbon and Tritium Laboratory, Ruper BoÓkoviƒ Institute, Bijeni…ka 54, P.O. Box 180,10002 Zagreb, Croatia, [email protected],
[email protected]
3 Leibniz Institute for Applied Geosciences, Geochronology and Isotope Hydrology (S3), Stilleweg 2, D-30655 Hannover, Germany. Now at the Isotope
Hydrology Laboratory, International Atomic Energy Agency, Wagramer Strasse 5, A-1400 Vienna, Austria, [email protected].
4 Department of Geology, Faculty of Science, University of Zagreb, Zvonimirova 8, 10000 Zagreb, Croatia, [email protected]
Manuscrit déposé le 4 mai 2004; accepté après révision le 13 décembre 2004
Bull. Soc. géol. Fr., 2005, no 4
364
SURI‚ M. et al.
INTRODUCTION
Ever since Hendy and Wilson [1968] introduced speleothems
as a relevant source of palaeoclimatic records, important advances concerning palaeoenvironmental conditions have
come out worldwide. Nevertheless, there are regions with
lack of speleothem growth during some time periods and
the following reasons are in discussion: climate change with
insufficient humidity (cessation of drip during periods of
aridity), lack of plant soil cover (not enough soil-CO2 for
carbonate dissolution), fissure blockage [Richards et al.,
1996], or change of subaerial, vadose conditions to phreatic
or marine ones in coastal areas. The latter refers to submerging of speleothems by rising sea level or simultaneously occurring rise of ground water as a consequence of
climate change.
A major part of Europe showed ceased or reduced
speleothem growth during the Last Glacial Maximum
(LGM). Data from Great Britain point to a growth cessation
from 26 kyr to 15 kyr B.P. [Gascoyne, 1992] and deposition
recommenced after 15 kyr B.P. [Lowe and Walker, 1998]. In
the Slovenian karst, an onset of more intensive speleothem
growth occurred 16 kyr B.P. but few sporadic samples are
found with speleothem growth during the glacial period
[Mihevc, 2001].
Records from the southern parts of Europe, especially
those under the marine influence show a different pattern.
Submerged speleothems along the Tyrrhenian Coast (Italy),
show uninterrupted speleothem deposition during the period
20,450 until 15,780 yr B.P. with an average growth rate of
1.4 mm/100 yr [Alessio et al., 1992]. Speleothems from Israel (Soreq Cave), are characterized by continuous growth
during the last 60 kyr with an average growth rate of more
than 1 mm/100 yr [Bar-Mathews et al., 1999], and the period
a
of the LGM from 25 kyr to 17 kyr B.P. shows different values for the stable isotopes 13C and 18O [Bar-Mathews et al.,
1996].
The Dinaric karst in Croatia is located between 43o and
o
46 N and includes a large karstic area presently below the
sea level within the Adriatic Sea basin. During the LGM
(30-19 kyr ago) considered as the timing of maximum
global ice volumes [Lambeck and Chappell, 2001; Lambeck
et al., 2002a, 2002b], this littoral part of Dinaric karst might
have been within the marine influenced temperate region at
the border of the European periglacial region.
GEOLOGICAL AND ENVIRONMENTAL SETTINGS
The Adriatic Sea is a semi-enclosed epicontinental basin
elongated in NW-SE direction between the Apennines and
the Dinaric mountain range, ca 800 km long and ca 200 km
wide. The northern part is characterized by a shelf area with
low gradient (0.02o) gradually deepening to –100 m. The
central part, called the Meso Adriatic Depression (MAD)
with the deepest point at Jabuka Pit (–280 m) has a maximum shelf gradient of 0.5o. The somewhat shallower
Palagruña (Pelagosa) Sill separates the MAD from the
South Adriatic Pit (–1233 m). This morphology caused considerable changes of the coast line and surface of the Adriatic Sea during the eustatic cycles. During the LGM period,
the Adriatic Sea was reduced to a semi-enclosed basin
within the MAD, whereas the last postglacial sea-level rise
generated an eight-fold widening of the shelf area of the
Adriatic Sea [Correggiari et al., 1996; Cattaneo et al., 2003]
(fig. 1).
The morphology of the eastern Adriatic coast remarkably differs from the western Adriatic coast as well as the
b
FIG. 1. – Land and sea distribution at the sea level a) 120 m lower than today (during LGM); b) 40 m lower than today (approx. 10 kyr B.P.) [modified after Correggiari et al., 1996].
FIG. 1. – Répartition terre-mer au niveau de la mer, a : 120 m sous le niveau actuel (durant le dernier maximum glaciaire) ; b : 40 m sous le niveau actuel
(à environ 10 ka B.P.) [modifié d'après Correggiari et al., 1996].
Bull. Soc. géol. Fr., 2005, no 4
ISOTOPE RECORDS IN SUBMARINE SPELEOTHEMS FROM THE ADRIATIC COAST, CROATIA
pattern of marine sedimentation along the coast. Unlike the
western Adriatic coast, the Croatian coast is highly indented
with 1246 islands, islets and rocks and indentedness coefficient of mainland coastline K = 3.4 [Duplan…iƒ Leder et al.,
2004]. The reasons for such distribution are specific tectonic and petrologic settings. Namely, the eastern Adriatic
coast presents a highly tectonically disturbed and additionally karstified complex of Mesozoic and Palaeogene limestones and dolomites up to 8000 m thick. Collision of the
Adriatic (Apulian) plate with the Hercynian (Variscan) European continent, by the end of the Cretaceous and in the
Palaeogene, disintegrated the Adriatic-Dinaric carbonate
platform and created a series of folds, overthrusts and reverse faults of Dinaric trend (NW-SE) [Jenkyns, 1991;
GuÓiƒ and Jelaska, 1993]. Processes of karstification within
the fractured bedrock took place downward to the former
erosional basis which is, in case of coastal caves, most often
sea level. Consequently, most of the karstic forms, erosional
and depositional, can be found up to 120 m below the present sea level due to the Pleistocene sea level fluctuations
[Lambeck et al. 2002a].
The high supply of suspended matter originating from
the rock weathering within the catchment areas of Po River
and Apennine rivers, remains along the Italian coast due to
cyclonic sea-current circulation [Orliƒ et al., 1992]. The
eastern Adriatic rivers carry predominantly dissolved matter
originating from weathering of soluble carbonate bedrock.
Due to scarcity of particulate riverborne material, dozens of
karstic phenomena (caves, pits, dolines, etc), can still be
recognized on the rocky bottom along the Croatian coast.
Analogous with the situation on the present coast and islands, the density of submerged caves is very high (e.g.
Bra… Island has one investigated speleological object every
1.8 km2), comprising a lot of relatively well preserved
speleothems that offer potential for reconstructing local
palaeoenvironmental conditions.
This survey encompassed three presently submerged
caves : the Cave in Tihovac Bay on Pag Island, Zmajevo
Uho Pit near Rogoznica and the Pit in Lu…ice Bay on Bra…
Island with speleothem samples down to depths of 31, 29.5,
and 40 m, respectively (fig. 2). According to one of the latest late Pleistocene-Holocene sea-level curves [Lambeck et
al., 2002b], the phase of emersion of the area above present
–40 m isobath, where the investigated objects are located,
lasted at least 70 ka, from marine isotope stage (MIS) 5a till
the beginning of MIS 1 (ca. 80-10 kyr B.P.) (fig. 3). Apparently, during that period, karstification, including
speleothem precipitation, could take place in case of appropriate climatic conditions.
According to Köppen’s climatic classification, the part
of the Croatian coast encompassed by this survey belongs to
Csa-type Mediterranean climate with temperate and rainy
winters and hot, dry summers. Mean annual air temperatures are between 14 and 16 oC, winter temperatures are between 6 and 9 oC and precipitation ranges from 750 to
1050 mm/yr. The relatively high Dinaric mountain range
that spreads along the present coast and the Alps on the
northwest forms the orographic barrier that protects the
Adriatic area from the continental influence. Even during
the cold phase with lower sea-level, while the studied caves
were inland, far from the sea, the marine influence should
have been dominant due to the flat terrain. The approximated temperatures of the Mediterranean region during the
365
°
FIG. 2. – Geographical position of the investigated objects : Cave in Tihovac Bay (1), Zmajevo Uho Pit (2) and Pit in Lu…ice Bay (3).
FIG. 2. – Situation géographique des sites étudiés : baie de Tihovac (1),
Zmajevo Uho (2), baie de Lu…ice (3).
last glacial were 5-10oC lower than present in winter and
1-3oC lower than present in summer [Prentice et al., 1992]
(tab. I). According to Peyron et al. [1998] south of the line
Pyrenees-Alps the mean annual temperature was 10 ± 5oC
lower and the temperature of the coldest month was
15 ± 5oC lower than today. The estimated shift of annual
precipitation in Italy and Greece during the LGM was
–600 ± 200 mm [Peyron et al., 1998]. Estimates by Miracle
[1995] suggest that, besides the lower mean temperatures,
the seasonal temperature variation was also larger than the
present one. The amount of precipitation was 10-20% lower
FIG. 3. – Cross section and position (elevation) of the investigated speleological objects in relation to the relative sea-level curve [replotted from
Lambeck et al., 2002a], A – Pit in Lu…ice Bay, B – Cave in Tihovac Bay,
C – Zmajevo Uho Pit. Locations of the speleological objects are not time
related. Dashed line – period of emersion during the sea level stand more
than 40 m lower than today.
FIG. 3. – Coupe et position (élévation) des spéléothèmes étudiés par rapport à la courbe du niveau marin [redessiné d'après Lambeck et al.,
2002a . A : cavité dans la baie de Lu…ice, B : grotte dans la baie de Tihovac, C : cavité de Zmajevo Uho. Les emplacements des objets spéléologiques ne sont pas reliés dans le temps. Tiretés : période d'émersion pendant
le stade de niveau marin à – 40 m par rapport à aujourd'hui.
Bull. Soc. géol. Fr., 2005, no 4
366
SURI‚ M. et al.
TABLE. I. – LGM temperature and precipitation estimations according to Prentice et al. [1992] and Peyron et al. [1998] for Mediterranean, and Miracle
[1995] for the eastern Adriatic region, compared with present values (Croatian Meteorological and Hydrological Service – CMHS).
TABL. I. – Températures et estimations des précipitations au cours du dernier maximum glaciaire, d'après Prentice et al. [1992] et Peyron et al. [1998]
pour la Méditerranée, et Miracle [1995] pour l'Adriatique oriental, comparées aux valeurs actuelles (Service météorologique et hydrologique de la
Croatie, CHMS).
Mean annual
temperature (°C)
Winter
temperature (°C)
Summer
temperature (°C)
Annual
precipitation (mm)
Reference
LGM
Prentice et al. (1992)
Miracle (1995)**
Peyron et al. (1998)
Present
CMHS
4.7 and 7.5
10 ± 5 l.t.p.
1-3 l.t.p.*
-10.4 and -8.2
15 ± 5 l.t.p.
14-16 (17)
6-9
5-10 l.t.p.
19.3 and 23.1
24-25
706 and 624
600 ± 200 l.t.p.
750-1050
* lower/less than present.
** values estimated for the regions northern (Pula) and southern (Hvar Island) from the investigated area.
* inférieur aux valeurs actuelles
** valeurs estimées pour les régions nord (Pula) et sud (île de Hvar) du domaine étudié.
than today but with pronounced seasonality – droughty
summers and rainy fall-winter periods. Owing to reduced
evaporation potential caused by decreased temperatures,
there was abundant precipitation runoff, even more than at
present [Miracle, 1995].
SITE DESCRIPTIONS AND SPELEOTHEM
SAMPLING
Speleothem samples were taken from three submarine caves
(fig. 2), all formed within Upper Cretaceous rudist limestones. Those are : the Cave in Tihovac Bay on Pag Island
(44° 23' 12'' N; 15° 03' 30'' E) with vertical entrance at present depth of 12 m, Zmajevo Uho Pit near Rogoznica
(43° 31' 48'' N; 15° 58' 00'' E) which entrance is at –2.5 m
and the Pit in Lu…ice Bay on Bra… Island (43° 18' 00'' N;
16° 27' 30'' E) with two entrances at 5 m depth. The caves
were investigated to the depths of 31, 29.5 and 40 m, respectively. The entrances of all three were formed by roof
collapsing.
Eight speleothems covered with marine biogenic overgrowth were collected by SCUBA divers in their growth position: stalactite P-23 from the depths of 23 m from the
Cave in Tihovac Bay, stalactites R-17 (fig. 4a) and R-21
(fig. 4b) from 17 and 21.4 m at Zmajevo Uho Pit and from
respective depths of 26, 28, 34, 36 and 38.5 m in the Pit in
Lu…ice Bay : stalactite B-26 (fig. 4c) and stalagmites B-28,
B-34 (fig. 4d), B-36 (fig. 4e) and B-38 (fig. 4f).
DESCRIPTION OF THE SPELEOTHEM SAMPLES
Speleothem sample lengths (together with marine overgrowth cover) ranged from 8.5 to 19 cm. They were longitudinally cut to enable insights into the growth layers and
continental-marine depositional margin. Marine biogenic
overgrowth consisted of remnants of the organisms belonging to biocenosis of cave and ducts in complete darkness
[Suriƒ, 2002]. The most abundant are the colonies of
spelean serpulids, similar as in submerged caves in
Tyrrhenian Sea [Antonioli et al., 2001; Bard et al., 2002].
Mineralogical content, high Mg-calcite, aragonite and calcite, typical for skeletons of these organisms, was confirmed by X-ray diffraction analyses, as well as calcite as
the material of the speleothems [Suriƒ, 2002]. Speleothems
were composed of white to yellow-brownish detritus-poor
calcite (see fig. 4a-f). Stalagmites B-38 and B-36 were the
most suitable for sampling of individual layers for stable
isotope measurements because of clearly distinguished
growth layers, whereas the most damaged one (B-28) was
excluded from the detailed stable isotope measurements.
Two (R-21 and P-23) of four “stalactite” samples were stalactites with the axial initial duct in the center, while the
FIG. 4. – Longitudinal sections of sampled speleothems with marine overgrowth. Marked subsamples: lines (0-12) for stable isotope measurements and
parts (A, B, P) for 14C age determinations (A – the youngest part of the speleothem, B – the oldest part of speleothem samples, P – marine biogenic overgrowth). Scale bar 5 cm.
a – stalactite R-17 from Zmajevo Uho Pit, depth 17 m
b – stalactite R-21 from Zmajevo Uho Pit, depth 21.4 m
c – stalactite B-26 from the Pit in Lu…ice Bay, depth 26 m
d – stalagmite B-34 from the Pit in Lu…ice Bay, depth 34 m
e – stalagmite B-36 from the Pit in Lu…ice Bay, depth 36 m
f – stalagmite B-38 from the Pit in Lu…ice Bay, depth 38.5 m
FIG. 4. – Coupes longitudinales des spéléothèmes échantillonnés, avec leur pellicule biogénique marine. Sous-échantillons marqués : lignes (0-12) pour
les mesures d'isotopes stables et les parties A, B, P pour les déterminations d'âges 14C (A – partie la plus jeune du spéléothème, B – partie la plus âgée,
P – pellicule biogénique). Echelle graphique : 5 cm.
a – stalactite R-17 de Zmajevo Uho, profondeur 17 m
b – stalactite R-21 de Zmajevo Uho, profondeur 21,4 m
c – stalactite B-26 de Lu1ice, profondeur 26 m
d – stalagmite B-34 de Lu1ice, profondeur 34 m
e – stalagmite B-36 de Lu1uce, profondeur 36 m
f – stalagmite B-38 de Lu1ice, profondeur 38,5 m
Bull. Soc. géol. Fr., 2005, no 4
ISOTOPE RECORDS IN SUBMARINE SPELEOTHEMS FROM THE ADRIATIC COAST, CROATIA
a
b
c
d
e
f
367
Bull. Soc. géol. Fr., 2005, no 4
368
SURI‚ M. et al.
speleothems R-17 and B-26 grew in the form of drapery, so
the subsamples were taken laterally from the youngest to
the oldest part.
Some of the speleothems were partly damaged by boring marine organisms, thus, to avoid possible contamination, samples for analyses were taken from compact, not
damaged parts, where possible. However, d13C values
showed that there was no isotopical exchange of carbon between marine biogenic overgrowth and speleothem carbonates of terrestrial origin [Suri…, 2002].
METHODS
Speleothem sampling was performed by an electrical diamond-drill. Speleothem samples for 14C dating were taken
from the surface (below the marine biogenic layer) and
from the base (the oldest part). Samples for d13C and d18O
measurements (5-10 mg of carbonate) were separated from
the individual layer with distance of ca. 5-10 mm from the
surface to the base of the speleothem. They were taken so
that material for each single sample was always from within
one of the visually discernible growth layers (indicated by
black lines in figure 4). Different samples for stable isotope
analyses are distributed along the growth axis of the stalactites/stalagmites, as far as possible perpendicular to the
growth layers.
Radiocarbon measurements
The 14C age of the samples was determined by the gas proportional counter method [Srdo… et al., 1971; Horvatin…iƒ,
1980]. About 30 g of carbonate was necessary per sample for
these analyses, so it was not possible to measure several samples along the growth axis. The approximate areas used for
dating are indicated in figure 4. Carbonates for 14C analyses
were treated with dilute HCl to obtain CO2, which was subsequently converted to methane. For calculation of 14C values
the conventional protocol [Obeliƒ, 1989; Mook and van der
Plicht, 1999] was followed. The 14 C activity is expressed
as percent of modern carbon (pMC), which relates the 14 C
content of a sample to the 14C content of a modern standard
normalized for isotope fractionation. The accuracy is within
the range of ± 0.3 % and ± 1.4 %, depending on the 14C activity of a sample. The 14C age is expressed in conventional
14
C years B.P., adjusted to initial 14C activity, A0. Calibrated
age for 14C age < 22,000 yr B.P. is obtained as a mean of the
range obtained by OxCal calibration software [Bronk
Ramsey, 2003]. For 14C ages > 22,000 yr B.P. calibration age
is determined from the extended calibrated curve published
in Bard et al. [2004].
Stable isotope measurements
d13C and d18O values of the carbonate samples were determined by continuous flow isotope ratio mass spectrometry
(CF-IRMS) using a Finnigan GasBench and Delta-S mass
spectrometer. Approximately 120 µg of the powdered carbonate samples were filled in round-bottom borosilicate
glass exetainer vials closed with rubber septum screw caps
and flushed for 5 minutes at a flow rate of 50 ml/min with
pure helium gas using a CombiPal autosampler. During this
procedure and the subsequent measurements, the exetainers
were kept at a constant temperature of 70 oC in the
GasBench thermo block. Samples were dissolved in automatically dosed droplets of 98% phosphoric acid. The resulting helium-CO2 mixture in the headspace of the vials
was then flushed into the dedicated gas chromatograph of
the GasBench and the CO2 GC peak directly introduced into
the mass spectrometer via an open split. The IsodatNT software controlled the MS measurement process, autosampler
and acid pump.
Isotope ratios for carbon and oxygen in CO2 were calculated by IsodatNT from time integrals of the signal readings
of mass 44 (CO 2), 45 ( 13CO2) and 46 (C 18OO). The 76
Table II. – 14C ages, ␦18O and ␦13C values of the youngest (a) and oldest parts (b) of speleothem samples. pMC is 14C activity of sample expressed in percent of modern carbon. 14C age is expressed as conventional 14C age corrected for A0 (85%) with 1s error of measurement and as calibrated age in calendar yr B.P. Ages marked with (*) are calibrated according to the OxCal calibration software [Bronk Ramsey, 2003]; all other values according to the
proposed extension of the calibration curve [Bard et al, 2004]. (B – Pit in Lu…ice Bay, P – Cave in Tihovac Bay, R – Zmajevo Uho Pit).
Tabl. II. – Ages 14C, valeurs de 18O et de 13C pour les parties les plus jeunes (a) et les plus anciennes (b) des échantillons de spéléothèmes. pMC est
l'activité 14C de l'échantillon exprimée en pourcentage de carbone moderne. L'âge au 14C est exprimé sous forme d'âge conventionnel 14C corrigé pour
Ao (85 %) avec 1 sigma d'erreur de mesure et d'âge calibré en années calendaires B.P. Les âges notés avec (*) sont calibrés en accord avec le logiciel de
calibration OxCal [Bronk Ramsey, 2003 ; toutes les autres valeurs le sont en accord avec l'extension proposée de la courbe de calibrage [Bard et al.,
2004 . B – cavité dans la baie de Lu1ice, P – grotte dans la baie de Tihovac, R – cavité de Zmajevo Uho).
Lab. No.
Sample
Z-3032
B-38-a
Z-3033
Z-3036
B-38-b
B-36-a
Z-3037
Z-3039
B-36-b
B-34-a
Z-3040
Z-3042
B-34-b
B-28-a
Z-3054
P-23-a
Z-3055
P-23-b
Z-3057
R-21-a
Z-3058
R-21-b
14
Location
Sampling depth
below sea level
(m)
38.5
Lu…ice Bay
(Bra… Island)
stalagmites
36.0
34.0
28.0
Tihovac Bay
(Pag Island)
stalactite
Zmajevo Uho
(Rogoznica)
stalactite
23.0
21.4
14
pMC
C age corrected for A0
(yr BP)
Calibrated C
age
(cal BP)
2,7 ± 0,5
27,550 ±1,600
0,0 ± 0,5
3,8 ± 0,5
> 37000
25,120 ±1,200
1,0 ± 0,5
8,5 ± 0,6
0,5 ± 0,5
8,9 ± 0,6
14
δ O
(PDB‰)
18
δ C
(PDB‰)
32,200
-4,2
-7,4
29,800
-4,9
-1,0
-9,5
-8,7
> 37000
18,500 ± 540
22,000*
-5,1
-5,4
-9,0
-8,8
> 37000
18,150 ± 520
21,600*
-5,8
-4,0
-9,7
-7,2
3,6 ± 0,5
25,480 ±1,230
30,300
-4,7
-7,5
2,1 ± 0,5
29,730 ±2,110
34,800
-5,3
-8,5
5,0 ± 0,5
22,750 ± 890
26,900
-4,1
-6,8
2,4 ± 0,4
28,505 ± 1320
33,500
-4,9
-6,2
* C ages calibrated according to the OxCal calibration software [Bronk Ramsey, 2003].
* Ages 14C calibrés en accord avec le logiciel de calibration OxCal [Bronk Ramsey, 2003].
Bull. Soc. géol. Fr., 2005, no 4
13
369
ISOTOPE RECORDS IN SUBMARINE SPELEOTHEMS FROM THE ADRIATIC COAST, CROATIA
measurements of each sequence run (14 NBS standards, 22
internal lab standards, 40 unknown samples) were corrected
to signal linearity, normalized to the international NBS19
and NBS20 standards of the same sequence with an Excel
spreadsheet and stored into the LabData database system
for quality assurance [Suckow and Dumke, 2001]. Each
sample was measured at least twice in independent sequence runs to control reproducibility. In case of deviation
of these two results of more than the defined precision, the
measurement was repeated. Overall precision of the quality
assurance standards during measurement of the carbonate
samples (3 months) was better than 0.2‰ for d13C and
0.3‰ for d18O. Results are given as per mil versus the international PDB standard.
Table III. – d13C and d18O values with distance from the surface of the speleothem for all speleothem samples. In the last column the 14C age of surface (A) and base (B) of speleothems is presented.
Tabl. III. – Valeurs de 13C et de 18O, et distance du spéléothème à la surface, pour tous les échantillons. Les âges 14C de la surface (A) et de la
base (B) des spéléothèmes sont présentés.
Sample
number
Distance
from
surface
(mm)
δ13C
(‰ PDB)
δ18O
(‰ PDB)
Calibrated
14
C age
(cal BP)
32,2
B-38-a
B-38/0
B-38/1
5.5
11.0
-7,4
-8,5
-9
-4,2
-5,1
-5,2
B-38/2
20.5
-8,9
-5,3
B-38/3
26.0
-8,9
-6,3
B-38/4
31.0
-9
-5,7
B-38/5
39.0
-8,7
-5
B-38/6
45.5
-9,2
-5
B-38/7
50.0
-9,4
-5,9
RESULTS AND DISCUSSION
B-38/8
55.5
-9,5
-5,5
B-38/9
61.0
-9,4
-5,3
Measured 14C ages, d18O and d13C values of the youngest
and the oldest parts of submerged speleothems are shown in
table II. For all speleothem samples we assumed an A0 of
85% as an average value determined earlier [Geyh, 1972;
Vogel, 1983; Genty and Massault, 1997, 1999; Genty et al.,
1998, 1999]. According to the measurements of 14C activity
of recent tufa in the Karst area of Croatia ranging from 80
to 90% [Horvatin…iƒ et al., 1989] the possible variations of
A0 value is ±5% that does not influence significantly the
14
C age of speleothem.
14
C ages of samples from the oldest parts of the
speleothems and from the youngest, surface layers, range
from > 37,000 yr B.P. to 21,600 cal B.P. Speleothems appear to be continuously deposited without any evident
depositional hiatus. However, it is hard to prove continuous
deposition of speleothems since no growth cessations could
be detected by radiocarbon dating. Excluding the results
falling beyond the dating range (> 37 kyr), most of the values are in or very close to the period of LGM (30-19 kyr
ago) according to Lambeck and Chappell [2001] and
Lambeck et al. [2002a, 2002b]. Such a distribution suggests
continuous speleothem precipitation from more than 37 kyr
throughout the whole LGM. Average axial growth rate of
the speleothems P-23 (34,800 – 30,300 cal B.P.) and R-21
(33,500 – 26,900 cal B.P.) were calculated to be 4 and
2 mm/100 yr, respectively.
14
C age of the youngest speleothem layers range from
32,200 to 21,600 cal B.P. They should indicate the time of
cessation of speleothem growth. Decreasing 14C ages of the
youngest speleothem layers in the stalagmites from the Pit
in Lu…ice Bay with decreasing depth below present sea level
(tab. II), suggest that the most probable reason for cessation
of their deposition was flooding by groundwater (change
from vadose conditions inside the cave to phreatic ones). If
the reasons of speleothem growth cessation were unfavourable climatic conditions with reduced humidity or lack of
vegetation, one could assume that at least in the same cave
the growth cessation of speleothems would have been simultaneous, which is obviously not the case.
The d13C and d18O values, as well as the distance of
taken samples from the surface for all measured
speleothems are shown in table III. Samples for stable isotopes are marked with numbers in figure 4a-f for each individual speleothem. The plot of d13C versus d18O for all
samples is shown in figure 5a. In figure 5b examples of
B-38/10
69.5
-9,4
-5,3
B-38/11
74.5
-9,7
-5,4
B-38-b
-9,5
-4,9
B-36-a
-8,7
-4,7
>37,000
29,8
B-36/1
22.5
-9,7
-5,9
B-36/2
27.5
-9,6
-5,6
B-36/3
32.5
-8,6
-4,8
B-36/4
39.5
-9
-4,7
B-36/5
47.5
-9,1
-4,8
B-36/6
55.5
-8,8
-4,1
B-36/7
71.5
-9,8
-5,5
B-36/8
81.5
-10,3
-6
B-36/9
88.5
-10,4
-6,3
B-36/10
94.5
-9,6
-5,7
B-36/11
104.3
-8,7
-5,4
B-36/12
123.5
-9
-4,8
-9
-5,1
>37,000
22
B-36-b
B-34-a
-8,8
-5,4
B-34/1
16.0
-9,7
-6,3
B-34/2
29.0
-9,2
-6
B-34/3
49.0
-9,9
-6,7
B-34/4
60.0
-9,7
-5,8
B-34/5
70.5
-9,9
-6,5
B-34/6
80.0
-9,8
-5,7
B-34-b
-9,7
-5,8
>37,000
B-28-a
-7.2
-4.0
21,6
-6
B-26/2
14.5
-8,1
B-26/3
25.0
-9,6
-6
B-26/4
36.0
-9,7
-6,6
B-26/5
45.0
-9,2
-6
B-26/6
53.0
-9,4
-6,2
B-26/7
62.0
-9,4
-5,5
B-26/8
74.0
-7,8
-5,6
R-21-a
R-21/1
2.0
-6,8
-4,1
-6,2
-4,2
R-21/2
6.0
-7,6
-4,7
R-21/3
13.5
-6,9
-5,9
-6,2
-4,9
R-17/1
8.0
-8,6
-5,7
R-17/2
13.0
-9,8
-6,5
R-17/3
25.0
-9,2
-6,2
R-17/4
34.0
-8,2
-4,5
R-17/5
43.0
-9,1
-5
-7.5
-8.5
-4.7
-5.3
R-21-b
P-23-a
P-23-b
26,9
33,5
30,3
34,8
d13C and d18O distribution vs. the distance from the surface
are presented for speleothems B-34, B-36 and B-38.
The d 13 C and d 18 O values of speleothem samples range
from –10.4‰ to –6.2‰ and from –6.7‰ to –4.1‰,
Bull. Soc. géol. Fr., 2005, no 4
370
SURI‚ M. et al.
-5.0
B-38
B-36
B-34
B-28
B-26
R-21
R-17
P-23
-7.0
-8.0
13
C (‰)
-6.0
-9.0
-10.0
-11.0
-7.0
-6.5
-6.0
a
-5.5
18
-5.0
-4.5
-4.0
-3.5
O (‰)
b
FIG. 5. – a – d13C vs. d18O values of submerged speleothems collected in Pit in Lu…ice Bay (B-38, B-36, B-34, B-28, B-26), in Zmajevo Uho Pit (R-21,
R-17) and in Cave in Tihovac Bay (P-23);
b – Distribution of d13C and d18O values according to the distance from the surface of the individual speleothems from the Pit in Lu…ice Bay (B-34, B-36,
B-38).
FIG. 5. – a – 13C en fonction de 18C pour les spéléothèmes submergés des sites de Lu1ice (B-38, B-36, B-34, B-34, B-28, B-26), de Zmajvo Uho (R-21,
R-17) et de Tihovac (P-23).
b – Répartition des valeurs de 13C et de 18O en fonction de la distance de chaque spéléothème du site de Lu1ice à partir de la surface (B-34, B-36,
B-38).
respectively (fig. 5a). The most reliable data for temporal
d 18 O and d 13 C distributions would be achieved from a single speleothem [Gascoyne, 1992; Lowe and Walker, 1998;
Bar-Matthews et al., 1997, 1999]. Since none of our
speleothems covers the whole age range of interest, we
have to assume that all five samples taken from a limited
area such as the Pit in Lu…ice Bay, can be regarded as the
same system, since they were precipitated at the small distance of a few meters and from drip water with, most probably, very similar or same 18 O/ 16 O and 13 C/ 12 C ratios.
The d13C values of speleothems range mostly from
–10.5‰ to –8.5‰, with few exceptions to –6‰. These values are typical for Dinaric karst speleothems [Horvatin…iƒ et
al, 2003]. The d13C values indicate that the origin of carbon, e.g. dissolution of CO2 in soil air, dissolution of carbonates from the rocks and the process of speleothem
precipitation was similar for all measured speleothems. Five
of six speleothems have mean d13C values between –9‰
and –9.6‰. The exception is R-21 with mean d13C of
–6.7‰ (tab. III) indicating lower soil carbon and/or vegetation impact on the process of calcite precipitation. The remarkable difference between the d13C values of
speleothems and those of the marine biogenic overgrowth
which range from –2.6‰ to 2.5‰ [Suriƒ, 2002], suggests
that there were no significant isotopic exchange processes
between the continental, speleothem carbon and marine carbon incorporated into the carbonate skeletons of
encrustrated organisms.
Figure 5a indicates a weak correlation between d13C
and d18O for some of the samples, e.g. B-36, which could
indicate kinetic isotope fractionation during the calcite precipitation. According to the theory and the early suggestions of Hendy [1971] this is an indication that the climate
signal of d18O might be masked, since only when calcite
precipitation occurs under equilibrium conditions the d18O
values are directly related to the cave temperature. On the
other hand there are well established palaeoclimatic records
Bull. Soc. géol. Fr., 2005, no 4
from speleothems where the d13C and d18O values are obviously correlated [Bar-Mathews et al., 1996, 1997, 1999;
Winograd et al., 1992; Coplen et al., 1994]. We therefore
treat our speleothem data as a palaeoclimate proxy although
we are aware of the fact that neither the d13C nor the d18O
necessarily correlate in a direct manner to temperature, precipitation or plant cover.
Most of the Holocene speleothems from the Dinaric karst
with prevailing continental climate recorded d18O values from
–8‰ to –5‰, while those from the marine influenced regions
(Mediterranean) show d18O values from –6‰ to –3.5‰
[Horvatin…iƒ et al., 2003]. The d18O values recorded in the
speleothems of the present investigation, deposited during the
LGM, range from –6.7‰ to –4.1‰. The similarity between
late Pleistocene and Holocene d18O values suggest similar climatic conditions during these two periods. This is in contrast
to the differences in estimated mean annual temperatures during the LGM period being down to 10 oC lower than today.
However one should keep in mind that the d18O signal in
speleothems is not directly connected to the temperature. d18O
values in speleothems originate from the drip water. The 18O
signal in precipitation water is influenced not only by temperature but e.g. also by the transport pathway of the water
vapour, the amount of rain falling and the distance from the
coast. Temperature, air exchange and humidity within the cave
where the speleothem precipitates further influence the isotopic values in the resulting carbonate. Therefore, neither the
similarity between late Pleistocene and Holocene d18O values
from the eastern Adriatic coast, nor the difference between the
values measured in our samples and from recent speleothems
from Slovenia with a mean value of –6.7‰ in d18O [Genty et
al., 1998] should directly be interpreted as palaeoclimatic signal. Especially the changes in water vapour pathways due to
the changed coastline between LGM and Holocene can have a
similar magnitude in the isotope effect on d18O as compared to
the temperature. Therefore, further studies on continuous stable isotope records on dated speleothems between the LGM
ISOTOPE RECORDS IN SUBMARINE SPELEOTHEMS FROM THE ADRIATIC COAST, CROATIA
and the Holocene are necessary before a reliable interpretation
as palaeoclimatic proxy is possible. Also dating with a geochronological method reaching beyond the 14C timescale like
luminescence or with a combination of methods able to detect
geochemical alterations of the samples like 234U/230Th/231Pa
would be desirable.
CONCLUSIONS
Although not of high resolution, this palaeoenvironmental
study gives a hint that global abrupt late Pleistocene-Holocene climatic changes were not as severe in the eastern Adriatic region as in the other parts of Europe. ␦ 13 C and ␦ 18 O
values of our records indicate that during the LGM the climate in the eastern Adriatic region was warmer than north of
the Alps, probably due to the influence of the Mediterranean
371
Sea from the south and due to the Dinarides and Alps acting
as orographic barriers from north and north-east.
Speleothem records from 21,000 cal B.P. to > 37,000 yr
B.P. suggest that the palaeoenvironmental conditions (appropriate temperature, sufficient rainfall, vegetation cover)
were adequate for speleothem precipitation during the LGM
although not as favourable as in the Holocene. The ␦13C and
␦18O records, which do not show significant isotopic differences between LGM and Holocene values, additionally support the conclusion that climatic conditions were adequate
for speleothem deposition during the LGM. According to
the obtained results speleothem growth cessation was not
directly connected to climate influence but to the position
of speleothems relative to the rising sea-level at the end of
the last glaciation. Namely, successive growth termination
occurred because of flooding of the caves either by fresh or
brackish groundwater and not due to climatic reasons.
References
ALESSIO M., ALLEGRI L., ANTONIOLI F., BELLUOMINI G., FERRANTI L.,
IMPORTA S., MANFRA L. & PROPOSITO A. (1992). – Risultati preliminari relativi alla datazione di speleotemi sommersi nelle fasce
costiere del Tirreno centrale. – Giorn. Geol., s3., 54/2, 165-193.
ANTONIOLI F., SILENZI S. & FRISIA S. (2001). – Tyrrhenian Holocene paleoclimate trends from spelean serpulids. – Quat. Sci. Rev., 20/15,
1661-1670.
BAR-MATHEWS M., AYALON A. & KAUFMAN A. (1996). – Late Quaternary paleoclimate in the eastern Mediterranean isotope systematics of
Soreq Cave speleothems. In : S.E. LAURITZEN, Ed., Extended abstracts of a Conference Climate Change : The Karst Record, 1-4th
August 1996. – Department of Geology, University of Bergen,
10-11.
BAR-MATTHEWS M., AYALON A. & KAUFMAN A. (1997). – Late Quaternary
paleoclimate in the eastern Mediterranean region from stable
isotope analysis of speleothems at Soreq Cave, Israel. – Quat.
Res. 47, 155-168.
BAR-MATTHEWS M., AYALON A., KAUFMAN A. & WASSERBURG G. (1999). –
The eastern Mediterranean paleoclimate as a reflection of regional events : Soreq Cave, Israel. – Earth Planet. Sci. Lett., 166,
85-95.
BARD E., ANTONIOLI F. & SILENZI S. (2002). – Sea-level during the penultimate interglacial period based on a submerged stalagmite from
Argentarola Cave (Italy). – Earth Planet. Sci. Lett., 196, (3-4),
135-146.
BARD E., ROSTEK F. & MÉNOT-COMBER G. (2004). – A better radiocarbon
clock. – Science, 303, 178-179.
BRONK RAMSEY C. (2003). – The OxCal Program Manual, v.3.9. – Submitted on WWW, http : //www.rlaha.ox.ac.uk/oxcal/oxcal.htm
CATTANEO A., CORREGGIARI A., LANGONE L. & TRINCARDI F. (2003). – The
late-Holocene Gargano subaqueous delta, Adriatic shelf : sediment pathways and supply fluctuations. – Mar. Geol., 193,
61-91.
COPLEN T.B., WINOGRAD I.J., LANDWEHR J.M. & RIGGS A.C. (1994). –
500,000-year stable carbon isotopic record from Devils Hole,
Nevada. – Science, 263, 361-365.
CORREGGIARI A., ROVERI M. & TRINCARDI F. (1996). – Late Pleistocene and
Holocene evolution of the North Adriatic Sea. – Il Quaternario,
9(2), 697-704.
DUPLAN…Iƒ LEDER T., UJEVIƒ T. & …ALA M. (2004). – Coastline lengths of
islands in the Croatian part of the Adriatic Sea determined from
the topographic maps at the scale of 1/25 000. – Geoadria, 9/1,
5-32.
GASCOYNE M. (1992). – Paleoclimate determination from cave calcite deposits. – Quat. Sci. Rev., 11, 609-632.
GENTY D. & MASSAULT M. (1997). – Bomb 14C recorded in laminated speleothems : calculation of dead carbon proportion. – Radiocarbon, 39, 33-48.
GENTY D., VOKAL B., OBELIC B. & MASSAULT M. (1998). – Bomb 14C time
history recorded in two modern stalagmites – importance for
soil organic matter dynamics and bomb 14C distributions over
continents. – Earth Planet. Sci. Lett., 160, 795-809.
GENTY D. & MASSAULT M. (1999). – Carbon transfer dynamics from bomb
14 C and ␦ 13 C time series of a laminated stalagmite from SW
France. Modelling and comparison with other stalagmite records. – Geochim. Cosmochim. Acta, 63, 1537-1548.
GENTY D., MASSAULT M., GILMOUR M., BAKER A., VERHEYDEN S. & KEPENS E. (1999). – Calculation of past dead carbon proportion
and variability by the comparison of AMS 14C and TIMS ages
on the Holocene stalagmites. – Radiocarbon, 41, 251-270.
GEYH M. A. (1972). – On the determination of the initial 14C content in
ground water. In : T.A. RAFTER and T. GRANT-TAYLOR, Eds.,
Proc. 8th Int. 14C Conf., Wellington, NZ – R. Soc NZ, Wellington, New Zeland, 434-472.
GUÓIƒ I. & JELASKA V. (1993). – Upper Cenomanian-Lower Turonian
sea-level rise and its consequences on the Adriatic-Dinaric carbonate platform. – Geol. Rundsch, 82, 676-686.
HENDY C.H. (1971). – The isotope chemistry of speleothems I. The calculation of the effects of different modes of formation on the isotopic composition of speleothems and their applicability as
paleoclimatic indicators. – Geochim. Cosmochim. Acta, 35,
801-824.
HENDY C. H. & WILSON A. T. (1968). – Palaeoclimatic data from speleothems. – Nature, 219, 48-51.
HORVATIN…Iƒ N. (1980). – Radiocarbon and tritium measurements in water
samples and application of isotopic analyses in hydrology. – Fizika, 12, 201-218.
HORVATIN…Iƒ N., SRDO… D., ÒILAR J. & TVRDIKOVA H. (1989). – Comparison
of the 14C activity of groundwater and recent tufa from karst
areas in Yugoslavia and Czechoslovakia. – Radiocarbon, 31,
884-892.
HORVATIN…Iƒ N., KRAJCAR BRONIƒ I. & OBELIƒ B. (2003). – Differences in
the 14C age, ␦13c and ␦18O of Holocene tufa and speleothem in
the Dinaric Karst. – Palaeogeogr., Palaeoclimatol., Palaeoecol.,
193, 139-157.
JENKYNS H. (1991). – Impact of Cretaceous sea level rise and anoxic events
on the Mesozoic carbonate platform of Yugoslavia. – AAPG
Bull., 75, 1007-1017.
LAMBECK K. & CHAPPELL J. (2001). – Sea level change through the Last
Glacial Cycle. – Science, 292, 679-686.
Bull. Soc. géol. Fr., 2005, no 4
372
SURI‚ M. et al.
LAMBECK K., ESAT T. M. & POTTER E. K. (2002a). – Links between climate
and sea level for the past three million years. – Nature, 419,
199-206.
LAMBECK K., YOKOYAMA Y. & PURCELL T. (2002b). – Into and out of the
Last Glacial Maximum : sea level change during Oxygen Isotope Stages 3 and 2. – Quat. Sci. Rev., 21, 343-360.
LOWE J.J. & WALKER M.J.C. (1998). – Reconstructing Quaternary environments. – Longman, Essex, 2nd ed., 434 p.
MIHEVC A. (2001). – Speleogeneza DivaÓkega krasa. – Zaloñba ZRC,
Ljubljana, 180 p.
MIRACLE P. T. (1995). – Broad-spectrum adaptations re-examined : hunter-gatherer responses to late Glacial environmental changes in
the eastern Adriatic. – Ph.D. Thesis, University of Michigan,
USA.
MOOK W. G. & VAN DER PLICHT J. (1999). – Reporting 14C activities and
concentrations. – Radiocarbon, 41, 227-239.
OBELIƒ B. (1989). – The radiocarbon data base at Rudjer BoÓkoviƒ Institute
Radiocarbon Laboratory. – Radiocarbon, 31, 1057-1062.
ORLIƒ M., GA…Iƒ M. & LA VIOLETTE P.E. (1992). – The currents and circulation of the Adriatic Sea. – Oceanol. Acta, 15, (2), 109-124.
PEYRON O., GUIOT J., CHEDDADI R., TARASOV P., REILLE M., DEBEAULIEU
J.-L., BOTTEMA S. & ANDRIEU V. (1998). – Climatic reconstruction in Europe for 18,000 yr B.P. from pollen data. – Quat. Res.,
49, (2), 183-196.
Bull. Soc. géol. Fr., 2005, no 4
PRENTICE I. C., GUIOT J. & HARISON S. P. (1992). – Mediterranean vegetation, lake levels and palaeoclimate at the Last Glacial Maximum. – Nature, 360, 658-660.
RICHARDS D.A., BORTON C.J., SMART P.L. & EDWARDS R.L. (1996). – Submerged speleothems from the Bahamas : sea levels, paleoclimate and uranium-series disequilibria. In : S.E. LAURITZEN, Ed.,
Extended Abstracts of a Conference Climate Change : The Karst
Record, 1-4th August 1996. – Department of Geology, University of Bergen, 134-135.
SRDOƒ D., BRAYER B. & SLIEP…EVICƒ A. (1971). – Ruper BoÓkoviƒ Institute
radiocarbon measurements I. – Radiocarbon, 13, 135-140.
SUCKOW A. & DUMKE I. (2001). – A database system for geochemical, isotope hydrological and geochronological laboratories. – Radiocarbon, 43, (2), 305-317.
SURIƒ M. (2002). – Gornjopleistocensko-holocensko kolebanje morske razine na istoƒnoj obali Jadrana. – Master of Science Thesis, Faculty of Science, University of Zagreb, 102 p.
VOGEL J.C. (1983). – 14C variations during the Upper Pleistocene. – Radiocarbon, 25, 213-218.
WINOGRAD I.J., COPLEN T.B., LANDWEHR J.M., RIGGS A.C., LUDWIG K.R.,
SZABO B.J., KOLESAR P.T. & REVESZ K.M. (1992). – Continuous
500,000-year climate record from Vein Calcite in Devils Hole,
Nevada. – Science, 258, 255-260.