Decoding last interglacial sea-level variations in the western Mediterranean using speleothem encrustations from coastal caves in Mallorca and Sardinia: A field data -- model comparison

Quaternary International 262 (2012) 56e64

Contents lists available at SciVerse ScienceDirect

Quaternary International journal homepage: www.elsevier.com/locate/quaint

Decoding last interglacial sea-level variations in the western Mediterranean using speleothem encrustations from coastal caves in Mallorca and Sardinia: A field data – model comparison Paola Tuccimei a, *, Bogdan P. Onac b, *, Jeffrey A. Dorale c, Joaquin Ginés d, Joan J. Fornós d, Angel Ginés d, Giorgio Spada e, Gabriella Ruggieri e, Mauro Mucedda f a

Dipartimento di Scienze Geologiche, “Roma Tre” University, Largo San Leonardo Murialdo 1, 00146 Roma, Italy Department of Geology, University of South Florida, 4202 E. Fowler Ave., SCA 528, Tampa, FL 33620, USA Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City, IA 52242, USA d Departament de Ciències de la Terra, Universitat de les Illes Balears, Ctra. Valldemossa km 7.5, 07122 Palma de Mallorca, Spain e Dipartimento di Scienze di Base e Fondamenti, Urbino University “Carlo Bo”, Via Santa Chiara, 27, I-61029 Urbino, Italy f Gruppo Speleologico Sassarese, Via G. Leopardi 1, 07100 Sassari, Italy b c

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 29 October 2011

UeTh ages of phreatic overgrowths on speleothems in coastal caves of the Western Mediterranean record high sea level positions during marine isotope stage (MIS) 5e of the last interglacial. While relative sea level (RSL) on the southeastern coast of Mallorca stood w2.6 m above present sea level (apsl) during MIS 5e, it stood w4.3 m apsl at this time in northwestern Sardinia. The difference between the two sites during MIS 5e and the deviation from the eustatic sea level trend during the Holocene was investigated using the numerical code SELEN. The offset between the eustatic curve and those pertaining to the two sites principally reflect the vertical deformations and geoidal variations in response to meltwater loading. As Sardinia is closer to the center of the Mediterranean basin, the hydro-isostatic component of RSL is enhanced here compared to Mallorca, which results in a modeled offset of w60 cm between the two sites. This result is qualitatively useful as it provides a partial reconciliation for the site differences. However, the need for refinement in the model is also recognized, as it does not match the observation based on UeTh dating of speleothem overgrowths in Mallorca that sea level there has remained stable for the past 2800 years. Overall, the results of the study first suggest that both sites largely track the eustatic sea level curve, and second suggest that glacial isostatic adjustment is a viable mechanism to reconcile some, if not most, of the relatively small elevation difference of MIS 5e sea level observed at Mallorca and Sardinia, although minor tectonic adjustments cannot be ruled out in explaining some low-amplitude local variations. Ó 2011 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction Among the many impacts associated with impending climate change, those related to rapid sea-level rise are of immediate concern to society (Alley et al., 2005). Sea level variations involve the transfer of water between ice sheets and oceans. To date, the primary evidence of a close link between ice-sheet growth/melt, sea level change, and insolation forcing (Milankovitch, 1941) comes from deep-sea sediments, U/Th dated coral terraces, and submerged speleothems (i.e., stalagmites, flowstones) (Shackleton, 2000; Gallup et al., 2002; Edwards et al., 2003; Antonioli et al., 2004; Alley et al., * Corresponding authors. Fax: þ1 8139742654. E-mail addresses: [email protected] (P. (B.P. Onac).

Tuccimei),

[email protected]

1040-6182/$ e see front matter Ó 2011 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2011.10.032

2005; Thomson and Goldstein, 2005, Cheng et al., 2009; Dutton et al., 2009; Siddall et al., 2009). The history of sea-level change contains valuable information on the possible magnitudes and rates of this transfer (Milne et al., 2009). Thus one approach for assessing future vulnerability to rapid sea level rise is to improve understanding of the forcing mechanism and responses of past events. Relative sea-level (RSL) change at a given site reflects not only changes in global ice volume, but also the response of the Earth to changes in surface loading in the form of surface deformation and geoid changes. This Earth response is referred to as “glacial isostatic adjustment” (GIA) (Lambeck and Chappell, 2001; Mitrovica and Milne, 2002), and has both glacio- and hydro- components (Milne and Mitrovica 2008; Pirazzoli, 2005). Eustatic (ice equivalent) sea-level reconstructions require accurate models of GIA, which require prescriptions of ice sheet history (including distribution,

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

volume, and duration) and Earth’s rheological properties (e.g., lithospheric and mantle heterogeneities, viscosity). Because uncertainties are inherent to all models (Spada et al., 2006), there is a continued need for additional, independent sources of sea-level data that might provide unique insight and cross-checks to the existing framework of past changes in sea-level. The coastal caves of Mallorca and Sardinia with their unique phreatic encrustations on speleothems provide one such source of additional sea level data (Tuccimei et al., 2006; Dorale et al., 2010) and can precisely document and potentially test the elevation and timing of various sea-level stands in the western Mediterranean region. This study examines the phreatic overgrowths on speleothems (POS) from several littoral caves in Mallorca and Sardinia that record the MIS 5e high stand. The numerical code SELEN, with

57

different scenarios for the chronology of the remote ice sheets, is used to evaluate the relative sea level (RSL) history of the region. 2. Background The islands of Mallorca (Spain) and Sardinia (Italy) sit in the microtidal western Mediterranean Sea (Fig. 1), an intermediatefield basin, moderately distant from the former major glaciation centers of the Northern Hemisphere (Stocchi and Spada, 2009). Further away from the ice sheets, regional differences in sea-level changes recorded in Mallorca and NW Sardinia are mainly controlled by the loading and unloading of the central basin of the western Mediterranean seafloor as ocean volumes change (Pirazzoli, 1996; Lambeck and Bard, 2000).

Fig. 1. Simplified tectonic map of the western Mediterranean and geological sketch maps of Sardinia and Mallorca islands.

58

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

Along the coast of Mallorca and Sardinia, the interaction between freshwater and seawater produces a geochemical environment that allows caves and speleothems to develop in a unique manner when compared to caves formed in more common inland settings. Most of the littoral caves at these two sites are well-decorated with vadose speleothems that formed during early Quaternary time when the caves were air-filled chambers. Throughout the middle and late Pleistocene, the caves were repeatedly flooded due to glacio-eustatic sea level oscillations. The water level of each flooding event left a clear mark as a distinct POS (encrustation of calcite or aragonite over existing speleothems or along cave walls; Ginés et al., 1981; Vesica et al., 2000; Fornós et al., 2002). Several well-defined carbonate overgrowth horizons below, at, and above the presentday sea level (corresponding to modern and older sea-level high and low stands) have been recognized (Fig. 2). Over the past several decades speleothems (i.e., stalagmites and flowstones) have emerged as powerful proxy records for long periods of Quaternary paleoclimate history. There are at least two reasons for this. First, speleothems are well suited for U-series dating, so that a very precise chronology can be tied to their stratigraphy (Richards and Dorale, 2003). Second, the growth of speleothems is linked to the Earth’s atmosphere and hydrosphere in a number of ways, making them sensitive natural archives of climatic and environmental changes (Dorale et al., 1992, 1998; Lauritzen, 1993; Fairchild et al., 2006; Onac et al., 2006; Lachniet, 2009). The use of ordinary submerged speleothems as proxies for sealevel reconstruction was first explored by Spalding and Matthews (1972) in the Bahamas and subsequently by others in different regions of the world (Harmon et al., 1978; Li et al., 1989; Richards et al., 1994; Antonioli et al., 2004; Dutton et al., 2009; Suric et al., 2009). While the U/Th dating of the materials can be very robust using this technique, it really only documents the “moment” when a particular elevation within the cave became flooded or air-filled, not precisely when and where the water level was actually located throughout the bulk of the rise-fall cycle (Richards et al., 1994; Bard et al., 2002; Dutton et al., 2009). Particularly in the case of sea level drop, the “moment” may be significantly compromised by unknown lags between the timing of sub-aerial exposure and the initiation of speleothem deposition. Submerged speleothems that contain biogenic overgrowth crusts (e.g., serpulid worm tubes) refine this basic technique. Such studies have been undertaken on the Tyrrhenian Sea (Bard et al., 2002; Antonioli et al., 2004; Dutton et al., 2009), Bermuda (Harmon et al., 1981), Bahamas (Lundberg and Ford, 1994; Richards et al., 1994), and the eastern seaboard of the Adriatic Sea (Suri c et al., 2009). In

comparison, the phreatic carbonate encrustations featured here, arguably provide a more precise and less ambiguous indicator of the timing and the absolute elevation of any given low and high sea level stand throughout the late Quaternary (Ginés and Ginés 1995; Vesica et al., 2000; Tuccimei et al., 2006, 2010; Dorale et al., 2010). 3. Geological setting The Western Mediterranean (Fig. 1), where the islands of Mallorca (Balearic Archipelago) and Sardinia are located, shows a complex geological structure which results from the interaction of the European and the African plates with a set of small plates (Iberian and Apulian) trapped in between them (Sàbat and Gelabert, 2003). The NEeSW convergence between the plates of Africa and Europe originated the opening of the Valencia trough-Gulf of Lyon basin (30e20 Ma) and led (20e10 Ma) to an eastward migration of Corsica and Sardinia (Gueguen et al., 1997; Séranne, 1999). 3.1. Mallorca (Balearic archipelago) The Balearic archipelago represents the emerged part of the prolongation into the Western Mediterranean of the Southeast Iberian Betic Range, which is separated from the Spanish coast by a submarine trough (Valencia trough). The carbonate lithologies, occurring almost continuously since the Middle Triassic to the present (Fornós and Gelabert, 1995; Gibbons and Moreno, 2002), feature a variety of karst landscapes. The structural evolution occurred during Mesozoic and Tertiary time and caused a very complex sequence of mainly extensional and short compressive events (Banda and Santanach, 1992; Dañobeitia et al., 1992). The last two phases of these tectonic events affected the island of Mallorca (the biggest island of the archipelago) and shaped it to its present geomorphologic configuration. The first corresponds to a compressive phase, active from the Paleogene to Middle Miocene; the second, an extensional phase Upper Miocene in age, which generated a structure composed of horsts and grabens bounded by Upper Miocene normal faults (Gelabert et al., 1992). The horsts correspond to the mountain ranges (Serra de Tramuntana and Serres de Llevant) and consist of an imbricate thrust sheet system facing NW. The grabens correspond to basins (Pla and Migjorn) that are now filled with sediments (Upper Miocene to Quaternary). These sediments are generally considered post-orogenic and compressive structures are not evident. Consequently, Mallorca could be considered tectonically stable since the Upper Miocene. However, there is evidence of

tide amplitude mean paleo-sea levels

POS present sea-level

mean paleo-sea levels

Fig. 2. Schematic cross-section through a coastal cave in Mallorca and Sardinia showing multiple levels of phreatic overgrowths on speleothems (POS).

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

minor tectonic activity in the center of the island (Giménez, 2003), related to the Neogene NEeSW normal fault structures (Gelabert, 1998) and fault-propagation folds trending NWeSE, perpendicular to the normal faults (Rohdenburg and Sabelberg, 1973). Fornós et al. (2002) point out a general tectonic tilting with a progressive lowering of the southwest part of the island at a rate of 0.02 mm/ year. A wide range of karst features (Ginés, 1995) in the form of solutional voids and caves develop in the Upper Miocene carbonate platform limestones and calcarenite deposits (Pomar et al., 1990). Most littoral caves preserve the complex Pleistocene sea level history (Ginés and Ginés, 1995) in both vadose and phreatic speleothems precipitated during successive periods of rising and lowering of the water level inside these caves, and also in their sedimentary infillings, collapse, and breccia formation. 3.2. Capo Caccia area (NW Sardinia) The Capo Caccia region is located along the northwestern edge of Sardinia where extensive outcrops of the Hercynian basement rocks are covered by Mesozoic carbonates (Fig. 1; Carmignani et al., 1992). Sardinia is tectonically stable to locally slowly subsiding (due to cooling of lithosphere; Burrus and Audebert, 1990), and forms a block almost coherent with mainland Europe (Gueguen et al., 1998). Within this generally stable setting, small vertical motions are recognizable in areas were the MIS 5e sea high stand is accurately positioned and excellent lateral exposure of the upper tidal notch are also available (Ulzega and Hearty, 1986; Kindler et al., 1997; Antonioli et al., 2006, 2007). The elevation of this marker decreases from east to west across different rock promontories from 5.5 to 3.5 m apsl (Ferranti et al., 2006). The westward subsidence may record minor block motion, likely linked to the fault system occurring along the western continental margin of the Mediterranean Sea (Carminati et al., in press). In addition, the MIS 5e double notch is morphologically similar to the Late Holocene notch at the observed sites, suggesting that the history of Holocene sea-level changes might be applied to the last interglacial high stand. If these data are evaluated in the light of global sea-level history during the last interglacial period when sea level stood higher than the modern one (Shackleton, 2000; Waelbroeck et al., 2002; Siddall et al., 2003) and, in particular focusing on the NW Mediterranean coasts, where the average level attained by the sea during MIS 5e is inferred to be w6  3 m, relative to modern sea level (Lambeck et al., 2004), it can be assumed that sea level changes at the Capo Caccia region nearly follow the eustatic curve. Along the limestone cliffs of the Capo Caccia promontory a large number of littoral caves occur. Speleothem encrustations develop along cave walls or pre-existing supports. At Grotta di Nettuno (a very well-known show cave), a particular level of POS and a black oxidation marks (consisting of iron and manganese oxides) along

59

the cave walls are evident and positioned at the same elevation with the MIS 5e upper tidal notch (4.3 m apsl; Tuccimei et al., 2007), and a similar alignment of overgrowths form at the present sea level. 4. Material and methods 4.1. Speleothem encrustations The littoral limestone areas of Mallorca and Sardinia host numerous caves, now partially drowned by brackish waters as a result of post-glacial sea level rise. Most caves formed by dissolution in the mixing zone between fresh water and marine water. Subsequently, extensive collapse processes led to their volumetric enlargement (Ginés, 1995; Ginés and Ginés, 2007). The passages of all investigated caves are within 250 m from the coast. One of the most distinctive features of these coastal caves is the presence of large pools, occupying their lower parts in connection with the present-day Mediterranean Sea level. The height of the water in these pools is tightly controlled by sea level and undergoes daily fluctuations as a result of minor sea oscillations, tidal, and/or barometric pressure. At present, in such a microenvironment, at or a few centimeters below and above the water table where CO2 escapes the brackish water, precipitation of calcite or/and aragonite takes place as horizontal encrustations that overgrow existing speleothems or cave walls (Ginés et al., 1981). In general terms, the investigated encrustations are crystalline overgrowths that define strictly horizontal bands some decimeters in width. These belt-like phreatic overgrowths on speleothems (POS) are formed at present-day sea level and are clearly postglacial in age, as documented by UeTh and 14C dating (Tuccimei et al., 2010, 2011). Usually, the thickest part of these encrustations is located in the middle of the crystallization band, then gradually decreasing upward and downward. The maximum thickness of the overgrowth relates to the statistically most frequent position of the water table (i.e., the mean sea level during the deposition of the crystalline overgrowth). From a mineralogical and crystallographical point of view, highmagnesium calcite and (to a lesser extent) aragonite are dominant in these phreatic overgrowths. Calcite deposits form encrustations with rough or even macrocrystalline surfaces, whereas acicular aragonite deposits are characterized by smooth surfaces. Although less abundant, aragonite encrustations are reported from Mallorca both as post-glacial deposits or recording ancient high sea-stands (Dorale et al., 2010; Tuccimei et al., 2010). A total of 4 samples from POS were collected at þ2.5 and þ2.6 m apsl, respectively in two different caves of southern Mallorca. From Sardinia, the only studied cave (Grotta di Nettuno) provided 2 samples corresponding to POS alignments located at þ4.3 m apsl (Table 1).

Table 1 Sample information and UeTh ages of speleothem encrustation formed during MIS 5e high stand in Mallorca and NW Sardinia. Cave Cova Cova Cova Cova

des Pas de Vallgornera, Mallorca d Pas de Vallgornera, Mallorca del Dimoni, Mallorca del Dimoni, Mallorca

Grotta di Nettuno, NW Sardinia Grotta di Nettuno, NW Sardinia

Sample code

Elevation (m apsl)

Age (yr)

Reference

CPV-B6 CPV-B9 DI-D1-2 DI-D3

2.60 2.60 2.50 2.50

120.6  0.9a 116.2  0.6a 118.4  0.9b 114.2  0.9b

Dorale et al. (2010) Dorale et al. (2010) Tuccimei et al. (2006) Tuccimei et al. (2006)

GN-D3-2 GN-D4

4.30 4.30

117  2.0a 120  2.0a

Tuccimei et al. (2007) Tuccimei et al. (2007)

Errors are 2s of the mean and are based on the analytical precision. m apsl, metres above present sea level. a Measured by Thermal Ionization Mass Spectrometry. b Measured by Inductively Coupled Plasma Mass Spectrometry.

60

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

4.2. UeTh dating method Speleothem encrustations were dated using the UeTh method. This is the most widely used dating technique applied to speleothems and is based on the extreme fractionation of the parent isotopes (238U and 234U) from their long-lived daughter 230Th in the hydrosphere. Uranium, markedly more soluble than Th in the surface and nearsurface environments, is readily mobilized as highly soluble uranyl ion (UO2þ 2 ) and its complexes, whereas Th is readily precipitated or adsorbed on detrital particles. Uranium is co-precipitated with CaCO3 in the crystal lattice, while incorporation of Th is generally negligible. In the absence of detrital Th, 230Th only forms by in-situ radioactive decay of co-precipitated U. If the crystal lattice remains a closed system with respect to the loss or gain of U and Th, the age of a speleothem can be calculated through measurement of radioactive production and decay of their isotopes in the system (Edwards et al., 1987; Richards and Dorale, 2003). Specific information on sample preparation and measurement are reported in Tuccimei et al. (2006, 2007) and Dorale et al. (2010). 4.3. Sea level modeling Sea level variations driven by the melting of continental ice sheets are modeled using the public-domain program SELEN (Spada and Stocchi, 2007), which solves the “Sea Level Equation” (SLE) in the form given by Farrell and Clark (1976) according to a pseudo-spectral iterative numerical scheme. All the phenomena associated with glacial isostatic adjustment (GIA), which include relative sea level (RSL) variations, vertical movements and gravity changes, can be modeled by means of the SLE. SELEN assumes a radially stratified, incompressible Earth and a linear Maxwell visco-elastic rheology for the mantle (i.e., lateral viscosity variations are not included in modeling). The reader is referred to Spada and Stocchi (2007) for a detailed review of the theory background of the SLE and to the home page of SELEN (http://www.fis.uniurb.it/ spada/SELEN_minipage.html) for information about the numerical method and examples of applications. In its basic form, the SLE reads:

Sðw; l; tÞ ¼



 F U ;

F  U þ SE þ g g

(1)

where Sðw; l; tÞ is sea level change at a point of co-latitude w and longitude l, t is time, g is the reference gravity acceleration, F ¼ Fðw; l; tÞ and U ¼ Uðw; l; tÞ are the total incremental gravitational potential and the vertical displacement of the solid surface of the Earth, respectively, the symbol h/i represents an average over the surface of the oceans that ensures mass conservation, and

SE ¼ SE ðtÞ;

(2)

is the eustatic component of S, which represents the sea level variation that would be observed assuming F ¼ 0 and U ¼ 0, i.e., completely neglecting the gravity variations and assuming a rigid Earth. From Equation (1), the spatially uniform eustatic component simply represents the ocean-average of the actual sea level variations, namely SE ¼ hSi. The explicit form of SE is

SE ¼ 

DmðtÞ ; rw Aoc

(3)

where Dm(t) is the variation of the mass of the ice sheets with respect to a previous reference configuration, rw is the density of water and Aoc is the area of the surface of the oceans. Since here the horizontal migration of shorelines is not modeled, Aoc is constant in Equation (3). However, F and U account for rotational effects

according to the formulation described by Milne and Mitrovica (1998). In the following, the RSL curve at a site of coordinates ðw; lÞ is obtained computing the difference


RSLðw; l; tBP Þ ¼ Sðw; l; tBP Þ  S w; l; tp ;

(4)

where S is the solution of the SLE obtained from Equation (1), tBP is time before present (BP) and tp is present time. To explicitly solve Equation (1), the history of the continental ice sheets and the mantle rheology must be specified. These two fundamental inputs of the SLE are required to evaluate the incremental gravitational potential F and vertical displacement U globally by means of spatio-temporal convolutions that describe for the delayed response of the Earth to surface loading and account self-consistently for the associated gravity field variations (details are available in Spada and Stocchi, 2006). This work employs model ICE-5G, which describes the melting of the global continental ice masses during the last glacial-interglacial period, assuming a specific viscosity profile of the mantle (VM2) (see Peltier, 2004). ICE-5G does not include information about the details of the global ice history during the marine isotopic stages MIS5e. Because a detailed reconstruction of the global distribution of the thickness of continental ice sheets during these periods is not available to date, the RSL variations at the sites of interest during the melting and the postglacial phases that have followed the Last Glacial Maximum are utilized as analogues, according to model ICE-5G. This allows for an evaluation of the deviations of the RSL curves from the eustatic response, and enlightens differences in the histories of sea level in the Sardinian and Mallorcan sites. A precise assessment of the history of RSL at these sites could be possible only by a detailed knowledge of the amplitude of the hydro-isostatic component during the whole time span since MIS 5e, but unfortunately this knowledge does not exist. 5. Results and discussion 5.1. Elevation of MIS 5e in Mallorca and NW Sardinia Geomorphological and morphostratigraphical studies combined with ages obtained through U/Th, amino-acid, and optically stimulated luminescence dating on emerged coastal deposits from southern Mallorca documented two high stands during MIS 5e; one occurred at the beginning of the last interglacial period at w135 ka, and one centered around 117 ka (Hearty, 1987; Cuerda, 1989; Hillaire-Marcel et al., 1996; Zazo et al., 2003; Bardají et al., 2009). The elevation of the 117 ka sea stand is well documented by available U-series ages of carbonate encrustations collected at elevations between 2 and 3 m in the coastal caves of Mallorca (Table 1; Tuccimei et al., 2006; Dorale et al., 2010). Coastal deposits of MIS 5a age were recorded in Mallorca by Butzer and Cuerda (1962), Hearty (1987), and Cuerda (1989), and are present w1.5 m above present sea level. The ages obtained for carbonate encrustations collected from five caves on eastern and southern part of the island cluster around 81 ka (Dorale et al., 2010). The elevations of MIS 5e coeval POS slightly increase northwards, along the eastern coast of the island (Fornós et al., 2002). Between 120 and 117 ka, in Capo Caccia area, the Mediterranean sea level stood at w þ4.3 m relative to present sea level (Table 1; Tuccimei et al., 2007), slightly less than 2 m higher than coeval records in Mallorca. 5.2. Modeling of regional deviations from the eustatic relative sea level trend The RSL curves associated with GIA deviate from the eustatic curve of an amount that strongly depends upon the site location

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

61

Fig. 3. Contour plot of RSL (m) at 4 ka BP generated using the ICE5-G(VM2) model.

(Clark et al., 1978). The magnitude of these deviations is mainly determined by the combined effects of glacio and hydro-isostasy, which are associated with the response of the Earth to the ice and melt water loads, respectively. Both processes are responsible for vertical deformations of the solid surface of the Earth and variations of the geoid height. These effects, which are simultaneously described by the SLE (see Equation (1)), have a complex geographical pattern that is also determined by the timedepending ocean-continents distribution (Milne, 1998). The amplitude of glacio- and hydro-isostatic contributions to RSL depends on the location of the site with respect to the former ice sheets. In the near-field sites, the glacio-isostatic component directly associated with ice loading and unloading is dominant, while far field sites are mostly affected by deformations associated with hydro-isostasy (Milne and Mitrovica, 2008). As discussed by Stocchi and Spada (2007), sea level variations associated with GIA during the last glacialeinterglacial period in the Mediterranean has a strong hydro-isostatic component that shapes the deformation pattern across the whole basin both during the melting phase that followed the Last Glacial Maximum and during the post-glacial period. In this region, RSL curves are thus mainly controlled by the amount of melt-water that filled the basin and by the delayed response of the visco-elastic mantle to this process. Due to the proximity with the former Northern Europe ice sheets, direct glacio-isostatic effects play a significant role in the northern Adriatic region and in southern France (Lambeck and Purcell, 2005). The pattern of RSL across the Mediterranean is illustrated using the contour lines of RSL at time 4 ka BP (Fig. 3), which according to model ICE-5G corresponds to the end of the melting phase and to the beginning of the post-glacial period. Fig. 3 shows that RSL has been increasing during the last 4 ka across the bulk of the basin. Fig. 4 shows the RSL curves predicted for the considered cave in Mallorca (circles) and Sardinia (diamonds) during the last 8 ka, according to the computations based on model ICE-5G(VM2). The two curves show a similar trend, characterized by a sea level rise of about 10 m during the considered time period. Their small offset is the consequence of the vicinity, the two sites being located approximately 450 km apart. The two curves are offset by w20 cm during the post-glacial rebound phase (i.e., during the last 4 ka), and by w60 cm during the melting phase. The eustatic RSL curve, which is the same for the two sites, is also shown. This curve describes the history of sea-level that would be observed for a rigid, non-gravitating Earth (see discussion of Section 4.2). Hence, the

offset between the eustatic curve and those pertaining to the two sites principally reflect the vertical deformations and geoidal variations in response to melt water loading. Fig. 4 shows that deviations from eustasy are considerable during the melting phase while during the post-glacial period the visco-elastic readjustment is the only mechanism of RSL variation. A regional view of the RSL across the western Mediterranean is shown in Fig. 5, where frames (a) and (b) correspond to the scenarios of 2 and 6 ka BP, respectively. The two contour plots have a similar shape, with maximum RSL variations expected in the Sea of Sardinia. Their amplitudes vary between w 5.50 and 0.65 m in the two time periods. Since the site of Grotta di Nettuno is closer to the center of the Mediterranean basin, the hydro-isostatic component of RSL is enhanced here compared to Mallorca, and accounts for a simulated RSL difference of about w60 cm (Fig. 5b), and provides a partial explanation for the RSL difference between Mallorca and Sardinia. The simulated RSL difference of w60 cm, in fact, accounts for about one third of the observed difference between Mallorca and Sardinia, and leaves about 1 m for further reconciliation. Uncertainties in the field data could plausibly account for some of this (perhaps w20e30 cm), and uncertainties in the modeling parameters and results could easily account for the remainder.

Fig. 4. RSL curves (m) predicted for Mallorca (circles) and Sardinia (diamonds) over the last 8 ka based upon the ICE-5G(VM2) model.

62

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

Fig. 5. Contour lines of RSL (m) at 2 ka BP (a) and 6 ka BP (b) across the western Mediterranean according to model ICE5-G(VM2).

An important field observation at Mallorca against which the simulation can be compared is that RSL appears to have been approximately stable for the past 2800 years. This observation is based on UeTh dating of “modern” POS associated with current water levels, which routinely yield dates of w2800 BP in their interior-most parts (Tuccimei et al., 2010, 2011). This remark strongly suggests that RSL has not moved appreciably in the past 2800 years, which does not agree with the simulated RSL curves for Mallorca, which indicates a RSL rise of w60 cm. Therefore, it is likely that the model has overestimated RSL change for Mallorca, and that the difference between RSL at Mallorca and Sardinia is probably greater than that indicated by the model results. More accurate results might come from model refinements including improved spatial resolution that could incorporate the regional structure around Mallorca. The history of Holocene sea-level changes applied here can only be partially accurate in their representation of the real conditions during the last interglacial highstand (Lambeck et al., 2002; Antonioli et al., 2006; Kopp et al., 2009). Finally, some of the elevation difference that is observed and not entirely justified by the modeling could be plausibly attributed to minor local tectonic processes: a progressive subsidence towards the south west possibly linked to a strike-slip field in

Mallorca (Fornós et al., 2002; Giménez, 2003) and a local westward subsidence in NW Sardinia, possibly accommodated by faults associated with the continental margin of the Western Mediterranean Sea (Tuccimei et al., 2007). Looking at the whole picture, the estimated total effect of such tectonic movements is at most a metre, and possibly significantly less. 6. Conclusions The regional deviations from the eustatic relative sea level trend in the western Mediterranean were investigated using the numerical code SELEN. The modeling shows that the hydroisostatic component of relative sea level in Sardinia, located closer to the center of the Mediterranean basin, is enhanced with respect to Mallorca. However, data from late Holocene speleothem overgrowths forming at present-day sea level in Mallorca seemingly conflict with the predicted present-day rate of relative sea level change due to glacial isostatic adjustment (Mitrovica and Milne, 2002), indicating that isostatic adjustment effects have been somewhat overestimated for this region. Finally, minor tectonic adjustments cannot be ruled out in explaining some low-amplitude local variations.

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

Acknowledgements These investigations are integrated within the research projects CGL2010-18616 and CGL2009-07392 of the Spanish Government Ministerio de Ciencia e Innovación e FEDER. Part of this work was supported by COST Action ES0701 “Improved Constraints on Models of Glacial Isostatic Adjustment” and is a contribution to #0911 INQUA-CMP Project.BPO and JAD were supported by NSF grants AGS-1103108 and AGS-1102947, respectively. References Alley, R.B., Clark, P.U., Huybrechts, P., Joughin, I., 2005. Ice-sheet and sea-level changes. Science 310, 456e460. Antonioli, F., Bard, E., Potter, E.K., Silenzi, S., Improta, S., 2004. 215-ka history of sea-level oscillations from marine and continental layers in Argentarola Cave speleothems (Italy). Global and Planetary Change 43, 57e78. Antonioli, F., Ferranti, L., Kershaw, S., 2006. A glacial isostatic adjustment origin for double MIS 5.5 and Holocene marine notches in the coastline of Italy. Quaternary International 145-146, 19e29. Antonioli, F., Anzidei, M., Lambeck, K., Auriemma, R., Gaddi, D., Furlani, S., Orrù, P., Solinas, E., Gaspari, A., Karinja, S., Kovacic c, V., Surace, L., 2007. Sea level change during the Holocene in Sardinia and in the North-eastern Adriatic (Central Mediterranean sea) from archaeological and geomorphological data. Quaternary Science Reviews 26, 2463e2486. Banda, E., Santanach, P., 1992. The Valencia trough (western Mediterranean): an overview. Tectonophysics 208, 183e202. Bard, E., Antonioli, F., Silenzi, S., 2002. Sea-level during the penultimate interglacial period based on a submerged stalagmite from Argentarola Cave (Italy). Earth and Planetary Science Letters 196, 135e146. Bardají, T., Goy, J.L., Zazo, C., Hillaire-Marcel, C., Dabrio, C.J., Cabero, A., Ghaleb, B., Silva, P.G., Lario, J., 2009. Sea level and climate changes during OIS 5e in the Western Mediterranean. Geomorphology 104, 22e37. Burrus, J., Audebert, F., 1990. Thermal and compaction processes in a young rifted basin containing evaporites e Gulf of Lions, France. American Association of Petroleum Geologists Bulletin 74, 1420e1440. Butzer, K.W., Cuerda, J., 1962. Coastal stratigraphy of southern Mallorca and its implications for the Pleistocene chronology of the Mediterranean Sea. Journal of Geology 70, 398e416. Carmignani, L., Barca, S., Cappelli, B., di Pisa, A., Gattiglio, M., Oggiano, G., Pertusati, P.C., 1992. A tentative geodynamic model for the Hercynian basement of Sardinia. In: Carmignani, L., Sassi, F.P. (Eds.), Contribution to the Geology of Italy with Special Regard to the Paleozoic Basement. IGCP 276, Newsletter, vol. 5, pp. 61e82. Carminati, E., Doglioni, C., Gelabert, B., Panza, G., Raykova, R.B., Roca, E., Sabat, F., Scrocca, D. Evolution of the Western Mediterranean. In: Bally, A.W., Roberts, D. (Eds.), Phanerozoic Regional Geology of the World (vol. 1), Elsevier, in press. Clark, J.A., Farrell, W.E., Peltier, W.R., 1978. Global changes in postglacial sea-level: a numerical calculation. Quaternary Research 9, 265e287. Cheng, H., Edwards, R.L., Broecker, W.S., Denton, G.H., Kong, X., Wang, Y., Zhang, R., Wang, X., 2009. Ice age terminations. Science 326, 248e252. Cuerda, J., 1989. Los tiempos cuaternarios en Baleares (2nd ed.), Conselleria de Cultura, Educació i Esports, Govern Balear, Palma de Mallorca, 310 pp. Dañobeitia, J.J., Arguedas, M., Gallart, F., Banda, E., Makris, J., 1992. Deep crustal configuration of the Valencia trough and its Iberian and Balearic borders from extensive refraction and wide-angle reflection profiling. Tectonophysics 203, 37e55. Dorale, J.A., González, L.A., Reagan, M.K., Pickett, D.A., Murrell, M.T., Baker, R.G., 1992. A high-resolution record of holocene climate change in speleothem calcite from Cold Water Cave, Northeast Iowa. Science 258, 1626e1630. Dorale, J.A., Edwards, R.L., Ito, M., González, L.A., 1998. Climate and vegetation history of the midcontinent from 75 to 25 ka: a speleothem record from Crevice Cave, Missouri, USA. Science 282, 1871e1874. Dorale, J.A., Onac, B.P., Fornós, J.J., Ginés, J., Ginés, A., Tuccimei, P., Peate, D.W., 2010. Sea-level 81,000 years ago in Mallorca. Science 327, 860e863. Dutton, A., Bard, E., Antonioli, F., Esat, T.M., Lambeck, K., McCulloch, T., 2009. Phasing and amplitude of sea-level and climate change during the penultimate interglacial. Nature Geoscience 2, 355e359. Edwards, R.L., Cheng, J.H., Wasserburg, G.J., 1987. 238Ue234Ue230The232Th systematics and the precise measurement of time over the past 500,000 years. Earth and Planetary Science Letters 81, 75e192. Edwards, R.L., Cutler, K.B., Cheng, H., Gallup, C.D., 2003. Geochemical evidence for Quaternary sea-level changes. In: Elderfield, H. (Ed.), Treatise of Geochemistry, vol. 6. Elsevier-Pergamon, Oxford, pp. 343e364. Fairchild, I.J., Smith, C.L., Baker, A., Fuller, L., Spotl, C., Mattey, D., McDermott, F., 2006. Modification and preservation of environmental signals in speleothems. Earth Science Reviews 75, 105e153. Farrell, W.E., Clark, J.A., 1976. On postglacial sea level. Geophysical Journal of the Royal Astronomical Society 46, 647e667. Ferranti, L., Antonioli, F., Mauz, B., Amorosi, A., Dai Pra, G., Mastronuzzi, G., Monaco, C., Orrù, P., Pappalardo, M., Radtke, U., Renda, P., Romano, P., Sansò, P.,

63

Verrubbi, V., 2006. Markers of the last interglacial sea-level high stand along the coast of Italy: tectonic implications. Quaternary International 145-146, 30e54. Fornós, J.J., Gelabert, B., 1995. Lithology and tectonics of the Majorcan karst. In: Ginés, A., Ginés, J. (Eds.), Karst and caves in Mallorca, Endins, 20 & Monografies de la Societat d’Història Natural de les Balears, vol. 3, pp. 27e43. Fornós, J.J., Gelabert, B., Ginés, A., Ginés, J., Tuccimei, P., Vesica, P.L., 2002. Phreatic overgrowths on speleothems: a useful tool in structural geology in littoral karstic landscapes. The example of Eastern Mallorca (Balearic Islands). Geodinamica Acta 15, 113e125. Gallup, C.D., Cheng, H., Taylor, F.W., Edwards, R.L., 2002. Direct determination of the timing of sea level change during Termination II. Science 295, 310e313. Gelabert, B., 1998. La estructura geológica de la mitad occidental de la Isla de Mallorca, ITGE. Colección Memorias, Madrid, pp. 1e129. Gelabert, B., Sàbat, F., Rodríguez-Perea, A., 1992. An structural outline of the Serra de Tramuntana of Mallorca (Balearic Islands). Tectonophysics 203, 167e183. Gibbons, W., Moreno, T (Eds.), 2002. The Geology of Spain, The Geological Society London, 649 pp. Giménez, J., 2003. Nuevos datos sobre la actividad post-Neógena de la Isla de Mallorca. Geogaceta 33, 79e82. Ginés, A., Ginés, J., 2007. Eogenetic karst, glacioeustatic cave pools and anchialine environments on Mallorca Island: a discussion of coastal speleogenesis. International Journal of Speleology 36 (2), 57e67. Ginés, J., 1995. Mallorca’s endokarst: the speleogenetic mechanisms. In: Ginés, A., Ginés, J. (Eds.), Karst and caves in Mallorca. Endins, 20 & Monografies de la Societat d’Història Natural de les Balears, vol. 3, pp. 71e86. Ginés, J., Ginés, A., 1995. Speleochronological aspects of karst in Mallorca. In: Ginés, A., Ginés, J. (Eds.), Karst and caves in Mallorca. Endins, 20 & Monografies de la Societat d’Història Natural de les Balears, vol. 3, pp. 99e112. Ginés, J., Ginés, A., Pomar, L., 1981. Morphological and mineralogical features of phreatic speleothems occurring in coastal caves of Majorca (Spain). In: Proceedings of the 8th International Congress of Speleology, Bowling Green, vol. 2, pp. 529e532. Gueguen, E., Doglioni, C., Fernández, M., 1997. Lithospheric boudinage in Western Mediterranean back-arc basins. Terra Nova 9, 184e187. Gueguen, E., Doglioni, C., Fernández, M., 1998. On the post-25 Ma geodynamic evolution of the western Mediterranean. Tectonophysics 298, 259e269. Harmon, R.S., Schwarcz, H.P., Ford, D.C., 1978. Late Pleistocene sea level history of Bermuda. Quaternary Research 9, 205e218. Harmon, R.S., Land, L.S., Mitterer, R.M., Garrett, P., Schwarcz, H.P., Larson, G.J., 1981. Bermuda sea level during the last interglacial. Nature 289, 481e483. Hearty, P.J., 1987. New data on the Pleistocene of Mallorca. Quaternary Science Reviews 6, 245e257. Hillaire-Marcel, C., Gariépy, C., Ghaleb, B., Goy, J.L., Zazo, C., Cuerda Barcelo, J., 1996. U-series measurements in Tyrrhenian deposits from Mallorca e further evidence for two last-interglacial high sea levels in the Balearic islands. Quaternary Science Reviews 15, 53e62. Kindler, P., Davaud, E., Strasser, A., 1997. Tyrrhenian coastal deposits from Sardinia (Italy): a petrographic record of high sea levels and shifting climate belts during the last interglacial (isotopic substage 5e). Palaeogeography, Palaeoclimatology, Palaeoecology 133, 1e25. Kopp, R.E., Simons, F.J., Mitrovica, J.X., Maloof, A.C., Oppenheimer, M., 2009. Probabilistic assessment of sea level during the last interglacial stage. Nature 462, 863e867. Lachniet, M.S., 2009. Climatic and environmental controls on speleothem oxygenisotope values. Quaternary Science Reviews 28, 412e432. Lambeck, K., Bard, E., 2000. Sea-level change along the French Mediterranean coast for the past 30000 years. Earth and Planetary Science Letters 175 (3e4), 203e222. Lambeck, K., Chappell, J., 2001. Sea level change through the last glacial cycle. Science 29, 679e686. Lambeck, K., Purcell, A., 2005. Sea-level change in the Mediterranean Sea since the LGM: model predictions for tectonically stable areas. Quaternary Science Reviews 24, 1969e1988. Lambeck, K., Esat, T.M., Potter, E.K., 2002. Links between climate and sea levels for the past three million years. Nature 419, 199e206. Lambeck, K., Antonioli, F., Purcell, A., Silenzi, S., 2004. Sea level change along the Italian coast for the past 10,000 yrs. Quaternary Science Reviews 23, 1567e1598. Lauritzen, S.E., 1993. Natural environmental change in karst: the Quaternary record. Catena supplement 25, 21e40. Li, W.X., Lundberg, J., Dickin, A.P., Ford, D.C., Schwarcz, H.P., McNutt, R., Williams, D., 1989. High-precision mass-spectrometric uranium-series dating of cave deposits and implications for palaeoclimate studies. Nature 339, 534e536. Lundberg, J., Ford, D.C., 1994. Late Pleistocene sea level change in the Bahamas from mass spectrometric U-series dating of submerged speleothem. Quaternary Science Reviews 13, 1e14. Milankovitch, M., 1941. Canon of Insolation and the Ice-age Problem. Royal Serbian Academy, Belgrade, Yugoslavia. Milne, G.A., 1998. Refining models of the glacial isostatic adjustment process, PhD thesis, University of Toronto, CA, 126 pp. Milne, G.A., Mitrovica, J.X., 1998. Postglacial sea-level change on a rotating Earth. Geophysical Journal International 133, 1e19. Milne, G.A., Mitrovica, J.X., 2008. Searching for eustasy in deglacial sea-level histories. Quaternary Science Reviews 27, 2292e2302.

64

P. Tuccimei et al. / Quaternary International 262 (2012) 56e64

Milne, G.A., Gehrels, W.R., Hughes, C.W., Tamisiea, M.E., 2009. Identifying the causes of sea-level change. Nature Geoscience 2, 471e478. Mitrovica, J.X., Milne, G.A., 2002. On the origin of late Holocene sea-level highstands within equatorial ocean basins. Quaternary Science Reviews 21, 2179e2190. Onac, B.P., T amas¸, T., Constantin, S., Pers¸oiu, A., 2006. Archives of Climate Change in Karst. In: Karst Waters Institute Special Publications, vol. 10 Charles Town WV. Peltier, W.R., 2004. Global glacial isostasy and the surface of the Ice-Age Earth: the ICE-5G(VM2) model and GRACE. Annual Review of Earth and Planetary Sciences 32, 111e149. Pirazzoli, P.A.,1996. Sea-Level Changes: the Last 20,000 Years. Wiley, Chichester, 211 pp. Pirazzoli, P.A., 2005. A review of possible eustatic, isostatic and tectonic contributions in eight late-Holocene relative sea-level histories from the Mediterranean area. Quaternary Science Reviews 24, 1989e2001. Pomar, L., Rodríguez-Perea, A., Sàbat, F., Fornós, J.J., 1990. Neogene stratigraphy of Mallorca Island. In: Agustí, J., Domènec, R., Julià, R., Martinell, J. (Eds.), Iberian Neogene Basins, Field Guidebook. Paleontología i Evolució (Mem. Esp.), vol. 2, pp. 271e320. Richards, D.A., Dorale, J.A., 2003. Uranium-series chronology and environmental applications of speleothems. In: Bourdon, B., Henderson, G.M., Lundstrom, C.C., Turner, S.P. (Eds.), Uranium-series Geochemistry. Reviews in Mineralogy & Geochemistry, vol. 52. Geochemical Society/Mineralogical Society of America, Washington, pp. 407e460. Richards, D.A., Smart, P.L., Edwards, R.L., 1994. Maximum sea level for the last glacial period from U-series ages of submerged speleothems. Nature 367, 357e360. Rohdenburg, H., Sabelberg, U., 1973. Quartäre Klimazyklen im Westlichen Mediterraneangebiet und ihre Auswirkungen auf die Relief und Bodenentwicklung. Catena 1, 71e180. Sàbat, F., Gelabert, B., 2003. Late Cenozoic Geodynamic evolution of the Western Mediterranean. A.A.P.G. Int. Conf., Barcelona, pp. A83. Séranne, M., 1999. The Gulf of Lyon continental margin (NW Mediterranean) revisited by IBS: an overview. In: Geological Society, London, Special Publications, vol. 156, pp. 15e36. Shackleton, N.J., 2000. The 100,000-year ice-age cycle identified and found to lag temperature, carbon dioxide, and orbital eccentricity. Science 289, 1897e1902. Siddall, M., Rohling, E.J., Almogi-Labin, A., Hemleben, C.H., Meischner, D., Schmelzer, I., Smeed, D.A., 2003. Sea levelfluctuations during the last glacial cycle. Nature 423, 853e858. Siddall, M., Stocker, T.F., Clark, P.U., 2009. Constraints on future sea-level rise from past sea-level change. Nature Geoscience 2, 571e575. Spada, G., Antonioli, A., Cianetti, S., Giunchi, C., 2006. Glacial isostatic adjustment and relative sea-level changes: the role of lithospheric and upper mantle heterogeneities in a 3-D spherical Earth. Geophysical Journal International 165, 692e702. Spada, G., Stocchi, P., 2006. The Sea Level Equation, Theory and Numerical Examples. Aracne, Roma, 96 pp. Spada, G., Stocchi, P., 2007. SELEN: a Fortran 90 program for solving the “Sea Level Equation”. Computers & Geosciences 33. doi:10.1016/j.cageo.2006.08.006.

Spalding, R.F., Matthews, T.D., 1972. Submerged stalagmites from caves in the Bahamas: indicators of low sea level stand. Quaternary Research 2, 470e472. Stocchi, P., Spada, G., 2007. Post-glacial sea-level in the Mediterranean Sea: Clark’s zones and role of remote ice sheets. Annals of Geophysics 50 (6), 741e761. Stocchi, P., Spada, G., 2009. Influence of glacial isostatic adjustment upon current sea level variations in the Mediterranean. Tectonophysics 474 (1e2), 56e68. Suri c, M., Richards, D.A., Hoffmann, D.L., Tibljas, D., Juracic, M., 2009. Sea-level change during MIS 5a based on submerged speleothems from the eastern Adriatic Sea (Croatia). Marine Geology 262 (1e4), 62e67. Thomson, W.G., Goldstein, S.L., 2005. Open-system coral ages reveal persistent suborbital sea-level cycles. Science 308, 401e404. Tuccimei, P., Ginés, J., Ginés, A., Gracía, F., Fornós, J.J., 2006. Last interglacial sea level changes in Mallorca island (Western Mediterranean). High precision U-series data from phreatic overgrowths on speleothems. Zeitschrift für Geomorphologie 50, 1e21. Tuccimei, P., Fornós, J., Ginés, A., Ginés, J., Gràcia, F., Mucedda, M., 2007. Sea level change at Capo Caccia (NW Sardinia) and Mallorca (Balearic Islands) during oxygen isotope substage 5e, based on Th/U datings of phreatic overgrowths on speleothems. In: Pons, G.X., Vicens, D. (Eds.), Geomorfologia Litoral i Quaternari. Homenatge a Joan Cuerda Barcelo. Monografies de la Societat d’Historia Natural de les Balears, vol. 14, pp. 121e136. Tuccimei, P., Soligo, M., Ginés, J., Ginés, A., Fornós, J., Kramers, J., Villa, I.G., 2010. Constraining Holocene sea levels using UeTh ages of phreatic overgrowths on speleothems from coastal caves in Mallorca (Western Mediterranean). Earth Surface Processes and Landforms 35 (7), 782e790. Tuccimei, P., Van Strydonck, M., Ginés, A., Ginés, J., Soligo, M., Villa, I.M., Fornós, J.J., 2011. Comparison of 14C and UeTh ages on two Holocene phreatic overgrowths on speleothems from Mallorca (Western Mediterranean) Mediterranean): environmental implications. International Journal of Speleology 40 (1), 1e7. Available online at: www.ijs.speleo.it. Ulzega, A., Hearty, P.J., 1986. Geomorphology, stratigraphy and geochronology of Late Quaternary marine deposits in Sardinia. Zietschrift fur Geomorphologie, Suppl. Bd. 62, 119e129. Vesica, P., Tuccimei, P., Turi, B., Fornós, J., Ginés, J., Ginés, A., 2000. Late Pleistocene paleoclimates and sea-level change in the Mediterranean as inferred from stable isotope and U-series studies of overgrowths on speleothems, Mallorca (Spain). Quaternary Science Reviews 19, 865e879. Waelbroeck, C., Labeyrie, L., Michel, E., Duplessy, J.C., Lambeck, K., McManus, J.F., Balbon, E., Labracherie, M., 2002. Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records. Quaternary Science Reviews 21, 295e305. Zazo, C., Goy, J.L., Dabrio, C.J., Bardaji, T., Hillaire-Marcel, C., Ghaleb, B., GonzalezDelgado, J.A., Soler, V., 2003. Pleistocene raised marine terraces of the Spanish Mediterranean and Atlantic coasts: records of coastal uplift, sea-level highstands and climate changes. Marine Geology 194, 103e133.