Impact of pulsed Atlantic water inflow into the Alboran Basin at the time of the Zanclean flooding

The study of more than 500 single- and multichannel seismic records enabled the generation of a detailed palaeo-bathymetric map of the Messinian surface over most of the Alboran Basin, Western Mediterranean. This regional surface is characterized by several erosional features (channels, terraces and canyons) and topographic highs (structural, volcanic and diapiric in origin). The most prominent feature is the incised Zanclean Channel crossing the entire basin, its entrenchment having been associated with the opening of the Strait of Gibraltar and subsequent inflow of Atlantic waters. The incision depth of the channel is variable, suggesting local variations in the erosive capacity of the Atlantic inflow, conditioned mainly by the regional basin topography and the local presence of topographic highs. Adjacent to this channel along the Spanish and Moroccan margins, and near the Strait of Gibraltar, several submarine terraces developed at different depths suggest a pulsed flooding of the Alboran Basin. There could have been two major inflow phases of Atlantic water, one shortly before and another during the Zanclean flooding, the latter accompanied by periods of relative sea-level stillstands that enabled terrace development. Alternatively, these features were all generated during the main flooding evident and subsequent pulsed infilling of the basin.     

Large warming and salinification of the Mediterranean outflow due to changes in its composition

The Mediterranean Sea transforms surface Atlantic Water (AW) into a set of cooler and saltier typical Mediterranean Waters (tMWs) that are formed in different subbasins within the sea and thus have distinct hydrological characteristics. Depending on the mixing conditions along their route and on their relative amounts, the tMWs are more or less differentiated at any given place, and some mix together up to forming new water masses. We emphasise the fact that any of these Mediterranean Waters (MWs) must outflow from the sea, even if more or less identifiable and/or in a more or less continuous way. Historical data from the 1960s–1980s showed that the densest MW outflowing through the Strait of Gibraltar at Camarinal Sill South (CSS) was a relatively cool and fresh tMW formed in the western basin, namely the Western Mediterranean Deep Water (WMDW). At these times, the sole other tMW identified in the strait was the Levantine Intermediate Water (LIW); no mention was made there of, in particular, the two densest tMWs formed in the eastern basin (in the Aegean and the Adriatic) that are now named Eastern Overflow Water (EOW) when they reach the Channel of Sicily (where they cannot be differentiated). A fortiori, no mention was made of the Tyrrhenian Dense Water (TDW) that results from the mixing of EOW with waters resident in the western basin (in particular WMDW) when it cascades down to ∼2000 m from the channel of Sicily. New measurements (essentially temperature and salinity time series) collected at CSS since the mid-1990s indicate that the densest MWs outflowing through the strait have been continuously changing; temperature and salinity there have been increasing, being actually (early 2000s) much warmer (∼0.3 °C) and saltier (0.06) than ∼20 years ago. These changes are one order of magnitude larger than the decadal trends shown for WMDW in particular. We thus demonstrate that, in the early 2000s, (i) the densest MW outflowing at Gibraltar is TDW and (ii) TDW is mainly composed of EOW (the percentage of MWs from the western basin, in particular WMDW, is lower): the densest part of the outflow is thus “more eastern than western”. This Mediterranean Sea Transient (a shift from the western basin to the eastern one) could be linked to the Eastern Mediterranean Transient (a shift from the Adriatic subbasin to the Aegean one). Whatever the case, we demonstrate that the proper functioning of the Mediterranean Sea leads to a variability in its outflow's composition that can have consequences for the mid-depth water characteristics in the North-Atlantic much more dramatic than previously thought.     

Mediterranean shelf-edge muddy contourites: examples from the Gela and South Adriatic basins

We present new evidence of shallow-water muddy contourite drifts at two distinct locations in the central Mediterranean characterized by a relatively deep shelf edge (between 170 and 300 m below sea level): the south-eastern Adriatic margin and the north-western Sicily Channel. The growth of these shelf-edge contourite drifts is ascribed to the long-term impact of the Mediterranean themohaline circulation. The Levantine Intermediate Water flows continuously, with annual or inter-annual variations, and affects the shelf edge and the upper slope in both study areas. In addition, the SW Adriatic margin is impinged by the seasonally modulated off-shelf cascading of North Adriatic Dense Water. This water mass has formed ever since the large Adriatic continental shelf was drowned by the post-glacial sea-level rise. It energetically sweeps the entire slope from the shelf edge to the deep basin. These bottom currents flow parallel or oblique to the depth contours, and are laterally constricted along markedly erosional moats aligned parallel to the shelf edge where they increase in flow velocity. The internal geometry and growth patterns of the shelf-edge contourites reflect changes in oceanographic setting affecting the whole Mediterranean Sea. In particular, seismic correlation with published sediment cores documents that these deposits are actively growing and migrating during the present interglacial, implying an enhancement in bottom-water formation during intervals of relative sea-level rise and highstand. Regardless of the specific mechanisms of formation, sediment drifts in both study areas have been affected by widespread thin-skinned mass-wasting events during post-glacial times. Repeated mass-transport processes have affected in particular the downslope flank of the shelf-edge contourite drifts, indicating that these muddy deposits are prone to failure during, or soon after, their deposition.     

Lago Mare and the Messinian Salinity Crisis: Evidence from the Alboran Sea (S. Spain)

This paper provides a new environmental, sedimentological and stratigraphic context of the Lago Mare deposits from the North Alboran region and clarifies their chronologic location with respect to the Messinian Salinity Crisis. We present new micropalaeontological data (dinoflagellate cysts, calcareous nannoplankton, planktonic foraminifers), correlated with field observations and offshore seismic interpretations. We show that the Lago Mare event known in three onshore localities (Río Mendelín near Malaga, Zorreras near Sorbas, Gafares near Níjar) follows the marine reflooding of the Mediterranean Basin which ended the Messinian Salinity Crisis. Chronologically, these Lago Mare deposits last from the latest Messinian to the early Zanclean. In fact, the first influx of Paratethyan organisms is revealed by the dinoflagellate cyst record from near Malaga within a Gilbert-type fan delta overlying the Messinian Erosional Surface. Invading molluscs and/or ostracods may have persisted in lagoonal coastal areas more or less affected by discontinuous marine influxes (Sorbas and Níjar). The Malaga area is convenient for a palaeogeographic and sedimentary reconstruction which shows the prevalent forcing of sea-level changes during the time-interval 5.600–5.332 Ma at the difference of the usually solicited prevalent tectonics. The studied Lago Mare event is the third episode resulting in such a palaeobiological assemblage in the Mediterranean region and corresponds to the final two-way water exchange at high sea level between the Mediterranean and the former Paratethys. It documents the onset of the modern marine circulation in the Mediterranean after the reflooding ending the Messinian Salinity Crisis.     

Oscillating Quaternary water levels of the Marmara Sea and vigorous outflow into the Aegean Sea from the Marmara Sea–Black Sea drainage corridor

Detailed interpretation of single-channel air-gun and deep-tow boomer profiles demonstrates that the Marmara Sea, Turkey, experienced small-amplitude (∼70 m) fluctuations in sea level during the later Quaternary, limited in magnitude by the sill depth of the Strait of Dardanelles. Moderate subsidence along the southern shelf and Quaternary glacio-eustatic sea-level variations created several stacked deltaic successions, separated by major shelf-crossing unconformities, which developed during the transitions from global glacial to interglacial periods. Near the Strait of Dardanelles, a series of sand-prone deposits are identified beneath an uppermost (Holocene) transparent mud drape. The sandy deposits thicken into mounds with the morphology and cross-sectional geometries of barrier islands, sand waves, and current-generated marine bars. All cross-stratification indicates unidirectional flow towards the Dardanelles prior to the deposition of the transparent drape which began ∼7000 years BP, in strong support of the notion that the Marmara Sea flowed westwards into the Aegean Sea through the Dardanelles at times of deglaciation in northern Europe. The global sea-level curve shows that, at ∼11,000 and ∼9500 years BP, sea level rose to the sill depths of the Straits of Dardanelles and Bosphorus, respectively. The effect from ∼11,000 to ∼9500 years BP was seawater incursion into the Marmara Sea, drowning and formation of algal-serpulid bioherms atop lowstand barrier islands, and transgression of shelves and lowstand deltas. At ∼9500 years BP, glacial meltwater temporarily stored in the Black Sea lake, developed into a vigorous southward flow toward the Aegean Sea, forming west-directed sandy bedforms in the western Marmara Sea and initiating deposition of sapropel S1 in the Aegean Sea. This strong outflow persisted until ∼7000 years BP, after which a mud drape began to accumulate in the Marmara Sea and euryhaline Mediterranean mollusks successfully migrated into a progressively more saline Black Sea where sapropel deposition began. Most eastern Mediterranean sapropels from S1 to S11 appear to correlate with periods of rising sea level and breaching, or near-breaching, of the Bosphorus sill. These events are believed to coincide with times of vigorous outflow of low-salinity (?fresh) surface waters transiting the Black Sea–Marmara Sea corridor, and ultimately derived from melting of northern European ice sheets.     

Messinian pre-evaporite sapropels and precession-induced oscillations in western Mediterranean climate

Cyclical fluctuations in planktic foraminiferal assemblages have been recognized in the pre-evaporitic Messinian in a marginal basin of the western Mediterranean. The fluctuations coincide with a dominantly precession-controlled sedimentary cyclicity (sapropels). During sapropel deposition, high planktic foraminiferal diversities are indicative of relatively stable marine conditions, while during homogeneous marl deposition low diversities seem to indicate the presence of unfavourable, more saline surface water conditions. The dominance of a precession-related signal indicates that regional climate oscillations rather than (obliquity-related) glacio-eustatically controlled influxes of Atlantic and/or Mediterranean waters are responsible for the faunal fluctuations and sedimentary cyclicity. Our scenario links the persistence of normal marine conditions during sapropel formation with increased rainfall and run-off along the western Mediterranean at times that perihelion occurred in Northern Hemisphere summer. Less favourable, highly saline surface water conditions prevailed during periods of drier climate induced by opposite precessional extremes. The cyclical oceanographic fluctuations could also have governed periodic reef growth along the margins.     

Seasonal variability of water transport through the Straits of Gibraltar, Sicily and Corsica, derived from a high-resolution model of the Mediterranean circulation

The variability of the water transport through three major straits of the Mediterranean Sea (Gibraltar, Sicily and Corsica) was investigated using a high-resolution model. This model of the Mediterranean circulation was developed in the context of the Mercator project.The region of interest is the western Mediterranean between the Strait of Gibraltar and the Strait of Sicily. The major water masses and the winter convection in the Gulf of Lions were simulated. The model reproduced the meso-scale and large-scale patterns of the circulation in very good agreement with recent observations. The western and the eastern gyres of the Alboran Sea were observed but high interannual variability was noticed. The Algerian Current splits into several branches at the longitude of the Strait of Sicily level, forming the Tyrrhenian branch, and, the Atlantic Ionian Stream and the Atlantic Tunisian Current in the eastern Mediterranean. The North Current retroflexed north of the Balearic Islands and a dome structure was observed in the Gulf of Lions. The cyclonic barotropic Algerian gyre, which was recently observed during the MATER and ELISA experiment, was evidenced in the simulation.From time-series of 10-day mean transport, the three straits presented a high variability at short time-scales. The transport was generally maximum, in April for the Strait of Gibraltar, in November for the Strait of Sicily, and in January for the Strait of Corsica. The amplitudes of the transport through the Straits of Gibraltar (0.11 Sv) and Sicily (0.30 Sv) presented a weaker seasonal variability than that of the Strait of Corsica (0.70 Sv).The study of the relation between transport and wind forcing showed that the transport through the Strait of Gibraltar is dependent on local zonal wind over short time-scales (70%), which was not the case for the other straits (less than 30%). The maximum (minimum) of the transport occurred for an eastward (westward) wind stress in the strait. An interannual event was noticed in November–December 2001, which corresponded to a very low transport (0.3 Sv), which was characterised by a cyclonic circulation in the western Alboran Sea. That circulation was also reproduced by the model for other periods than winter during the interannual simulation.The transport through the Strait of Sicily is not influenced by local wind.The wind stress curl of the northwestern Mediterranean influenced the transport through the Strait of Corsica.     

Sediment distribution and evolution of sedimentary processes in a small sandy turbidite system (Golo system, Mediterranean Sea): implications for various geometries based on core framework

The Golo Margin in eastern Corsica is dissected by four canyons and two gullies which fed turbidite systems. Study of the dispersal of surficial sediments and flow dynamic in the Golo system is based on Kullenberg and interface cores interpreted in relation to a previously published seismic dataset. Cores were described in detail and interpreted within a sedimentary and stratigraphic framework. During the last 42,000 years, gravity processes which occurred in the large systems with a canyon source were mainly slide-induced, differentiated turbulent surges and hyperpycnal flows. Processes occurring in the small system with a gully source are mainly hyperconcentrated and concentrated flows. Deposits from the Corsican Margin can intercalate with products of processes triggered on the Pianosa Ridge located in the eastern part of the basin. During relative sea-level lowstands or during periods of rapid or high-amplitude sea-level fall, only large canyons (South and North Golo) are supplied by carbonate-rich hyperconcentrated and concentrated flows which are channelled in incised valleys on the shelf. During periods of slow or low-amplitude sea-level fall and during sea-level rise, sediments are trapped on a shelf delta and intensely winnowed by shelf hydrodynamic processes. Sand-rich hyperconcentrated and concentrated flows occur. All the systems fed by a canyon are active simultaneously. Gullies form and are active only during periods of sea-level rise. During relative highstands of sea level (Holocene), all the system is draped by hemipelagic sediments. Relative sea-level changes and canyon location relative to river mouths have a strong influence on the nature of sediment input, and the initiation and type of gravity flows which, in turn, control morphology and geometry.     

On the presence of a coastal current of Levantine intermediate water in the central Tyrrhenian sea

The hydrological structure and the seasonal variability of marine currents in the Tyrrhenian Sea, off the coasts of Latium, are analysed using a data set obtained during several cruises between February 1988 and August 1990. Of particular interest is the fact that the hydrological surveys show the intermittent presence of a current of Levantine Intermediate Water (LIW) flowing anticlockwise along the Italian slope, at 250–700 m. This current is of particular importance in inferring the pathways of the Levantine Intermediate Water in the western Mediterranean Sea and in particular in the Tyrrhenian basin, downstream of the Strait of Sicily. These phenomena remain an open problem: our observations give support to the Millot's proposed general scheme, on the existence of a general cyclonic circulation of the LIW from the Strait of Sicily to the western Mediterranean, as opposed to a direct injection of LIW towards the Algerian basin.     

Estimation of the transports through the Strait of Gibraltar

An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the M_sf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference.     

Anoxic basins of the eastern Mediterranean: geological framework

A brief review of the geological knowledge on the anoxic basins of the eastern Mediterranean is presented. Anoxic basins have been discovered in two different geological settings in the eastern Mediterranean. Bannock Basin belongs to the compressional style of the Mediterranean Ridge, and Tyro and Poseidon Basins belong to the transcurrent tectonic style of the Strabo Trench. The origin of the basins is subsurface salt dissolution triggered by tectonic deformation of the sediments on the Mediterranean Ridge, and tectonic subsidence (pull-apart mechanism) in the Strabo Trench. The onset of a deep-sea brine lake is always related to the outcrop of Messinian salts on the side-walls of the basin. The rate of basin subsidence controls the evolution of the brine lakes, which can also be completely diluted by bottom water circulation.     

Inter-basin movements of Mediterranean sperm whales provide insight into their population structure and conservation

The sperm whale is one of the very few deep diving mammal species in the Mediterranean Sea. Following a rare mass stranding of male sperm whales in the Adriatic Sea in December 2009, photo-identification methods were used in order to investigate previous sightings of the stranded whales in the region. Fluke photos of the stranded whales were compared with those of 153 and 128 free-ranging individuals photographed in the western and eastern Mediterranean basins, respectively. Three out of the seven stranded whales had been previously photo-identified and some of them more than once. To reach the stranding place, two of these re-identified whales performed long-range inter-basin movements of about 1600-2100 km (in a straight line) either through the Strait of Sicily or the Strait of Messina. In addition, comparisons among all whales photographed in the two Mediterranean basins revealed that one more individual first photographed in the western basin (1991) was re-identified 13 years later in the eastern basin (2004). These three cases provide the first conclusive evidence of inter-basin movement of sperm whales in the Mediterranean Sea. Inter-basin gene flow is important for the survival of the small and endangered Mediterranean sperm whale population. Mitigating the disturbance created by human activities in the straits area is crucial for its conservation.     

Late Neogene evolution of the Taza–Guercif Basin (Rifian Corridor,Morocco) and implications for the Messinian salinity crisis

Magnetostratigraphic and biostratigraphic results are presented from Neogene deposits in the Taza–Guercif Basin, located at the southern margin of the Rifian Corridor in Morocco. This corridor was the main marine passageway which connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza–Guercif composite section to the astronomical time scale, allows an accurate dating of three subsequent events in the Rifian Corridor. (1) The oldest marine sediments marking the opening of the Rifian Corridor were deposited at 8 Ma. At this age, a deep (600 m) marine basin developed in the Taza–Guercif area, marked by deposition of precession-controlled turbidite–marl cycles. (2) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of the marine corridor took place at the Tortonian/Messinian boundary, at an age of 7.2 Ma. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. (3) The Taza–Guercif Basin was emergent at an age of 6.0 Ma and, subsequently, continental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Rifian Corridor actually initiated the Messinian salinity crisis, well before the deposition of the Messinian evaporites in the Mediterranean.     

Late Miocene–early Pliocene planktonic foraminifer event-stratigraphy of the Bajo Segura basin: A complete record of the western Mediterranean

The Bajo Segura basin (eastern Betic Cordillera) has one of the most complete late Miocene–early Pliocene marine records of the western Mediterranean. An updated planktonic foraminifer zonal scheme based on recent astronomically tuned biozones is presented for this interval, documenting a complete succession of biostratigraphic markers, from biozone MMi9 (earliest Tortonian) to MPl3 (latest early Pliocene), of likely significance for regional-scale correlation throughout the Mediterranean. The findings reveal a series of intrazonal events (some unreported until now in the Mediterranean Neogene basin), including the particularly interesting two influxes of the Globorotalia miotumida group during the Tortonian. These biostratigraphic findings are the basis for a framework of the major allostratigraphic units in the basin based on planktonic foraminifer event-stratigraphy: synthems Tortonian I, Tortonian II, Tortonian-Messinian I, Messinian II, and Pliocene. In addition, the timing of the main tectono-sedimentary and palaeogeographic events throughout the basin's evolution has been further constrained. Our results suggest that, at least in the Bajo Segura basin, the late-Messinian barren interval (non-distinctive zone) can be considered an ecobiostratigraphic zone (cenozone) characterized by dwarf fauna of planktonic foraminifera. Consequently, the Bajo Segura composite section can be regarded as a biostratigraphic reference section for Neogene basins in the Betic Cordillera and hence also in the Western Mediterranean.     

Submerged terraces in the Laccadive Islands,India

The Laccadive atolls have recently been surveyed in detail (1:5,000 and 1:10,000). These surveys indicated the occurrence of a number of terraces on the seaward reefs of these islands at 7–12, 15, 21–36 (prominent) and 43–47 m depths. The first break in the profile of the seaward reefs occurs at depths of 3–5 m and on the windward side this extends down to about 12 m, the break at this shallow depth represents a wave-cut platform. The deeper terraces (>12 m) appear to have been formed during periods of lowered sea level. The most prominent terrace at 21–36 m is correlable with similar terraces recorded on other atolls. The terraces at Bangaram Island are covered by sediment while those at Kadmat do not have any sediment. In some of the atolls, surfaces at depths comparable to the seaward terraces are found in the lagoons also indicating extensive effects of lowered sea levels.     

Growth and demise of the Jurassic carbonate platform in the intracratonic Paris Basin (France): Interplay of climate change,eustasy and tectonics

It is usually very difficult to identify and quantify the relative influence of tectonics, eustasy and climate on carbonate system evolution from sedimentary records. In order to improve our understanding of these mechanisms, we have traced for the first time, the evolution of the eastern Paris Basin platform throughout the entire Jurassic period. This carbonate platform underwent eight successive growth and demise phases, with different depositional profiles ranging from ramps to flat-topped geometries. The eight carbonate growth periods are compared with the standard sea-level curves, local tectonic regimes and recently published oxygen-isotope and/or clay mineralogy databases. Prograding heterozoan facies along ramp profiles mark periods dominated by second-order eustatic sea-level rise, relatively cool sea surface temperatures, and mesotrophic and humid conditions (Hettangian, Pliensbachian, late Oxfordian, Tithonian). During these periods, variable detrital contents in the sedimentary succession hampered the efficiency of shallow-marine carbonate factories. Higher sea surface temperatures, oligotrophic and humid conditions associated with either eustatic sea-level rise or very high local subsidence occurred during the early Bajocian and the mid-Oxfordian. These seawater properties seem to have favoured the aggradation of scleractinian corals forming dome-shaped bioherm buildups. An oolitic and lime-mud carbonate system, deposited during the Bathonian second-order eustatic sea-level fall, is characterised by miliolid-rich micritic facies on a rimmed-ramp under stable, cooler and drier conditions. The second-order maximum flooding associated with a sea surface temperature decline and/or a seawater eutrophication caused at least five carbonate demise periods (i.e. Toarcian, earliest late Bajocian, Callovian/Oxfordian transition, earliest late Oxfordian and Kimmeridgian).     

Late Miocene stable isotope stratigraphy of SE Atlantic ODP Site 1085: Relation to Messinian events

High-resolution benthic oxygen isotope and XRF (Fe and Ca) records from Site 1085 drilled in the Mid-Cape basin (ODP Leg 175) are used to investigate global climate changes during the Late Miocene in relation to Messinian geological events. The cyclic fluctuations of the time series at Site 1085 enable us to establish a reliable chronology for the time interval 7.3–4.7 Ma. Spectral analysis of the δ¹⁸O record indicates that the 41-kyr period of orbital obliquity dominates the Late Miocene record. A global climate record was extracted from the oxygen isotopic composition of benthic foraminifera. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The time interval 7.3–6.25 Ma characterized by low-amplitude δ¹⁸O variations is followed by a period marked by maximum in the δ¹⁸O values (6.25–5.57 Ma). At about 5.56 Ma, a rapid decrease in δ¹⁸O values is documented that may reflect a warming of deep-water temperature associated with a global warming period. Comparison between the timing of the oceanic isotope events and the chronology of the Mediterranean Salinity Crisis suggest that global eustatic processes were not essential in the Mediterranean Salinity Crisis history. From our data, we infer that the global warmth documented in the Early/mid-Pliocene probably started during the Late Miocene (at 5.55 Ma). At the same time, the onset of evaporite deposition in the central basin of the Mediterranean Sea took place. Sharp changes in the sedimentation rates, mainly driven by terrigenous input at this site, are observed during the Messinian Stage.     

Biological evidence of sea-level rise during the last 4500 years on the rocky coasts of continental southwestern France and Corsica

On the rocky coasts of the northwestern Mediterranean basin, biogenic littoral rims built by the coralline rhodophyte Lithophyllum lichenoides develop, whose remains may be preserved for millennia when submerged in a rising sea environment. These remains can be used as biological indicators of recent sea-level variations. Our survey of the continental coasts of Var and Bouches du Rhône, west of Marseilles (southern France) and of northern Corsica shows that relative sea level rose about 1.6 m in the study area during the last 4500 years without exceeding the present datum. The rate of sea-level rise was 0.4 mm per year between 4500 and 1500 yr B.P. and slowed down to 0.2 mm per year from 1500 yr B.P. to present time. There are also morphological indications of an acceleration of the rate of sea-level rise during the last century, supporting the evidence of tide gauges. Regions at the periphery of the above zone (Alpes Maritimes, Italian border zone, and the French and Spanish Catalonia regions) were also surveyed, but a weaker development of Lithophyllum rims and bad preservation of algal remains led to unconvincing dates which could also be linked to regional tectonic trends.     

Variability of the Kuroshio deduced from sea level data from the Izu Islands

Flow patterns and positions of the Kuroshio in the vicinity of the Izu Ridge are clarified by analyzing hydrographic observations and daily mean sea levels at Hachijo-jima, Miyake-jima and Oshima in the period from 1964 to 1981.Correlations are calculated between differences of dynamic depth anomaly at the surface refered to 1,000 db and differences of daily mean sea level between the two islands. The datum line of the tidal station at Hachijo-jima is about 90 cm higher than that at Miyake-jima, and about 20 cm higher than that at Oshima. A clear correlation is found between the cross-section transport of the Kuroshio and the mean sea-level difference between Hachijo-jima and Miyake-jima. The sea-level difference of the flow pattern without meander off Enshu-nada (type N) tends to be larger than that of the flow patterns with meander (type A and type B). This seems to indicate that the volume transport of the Kuroshio in the meandering period is smaller than that during the straight path period. Large sudden increases or decreases in the mean sea-level difference occur when the flow pattern changes and the Kuroshio axis shifts. The frequency of occurrence of quiet periods in the sea-level difference reflect the flow pattern of the Kuroshio.     

Seismic and sequence stratigraphy of the central western continental margin of India: late-Quaternary evolution

Seismic and sequence stratigraphic architecture of the central western continental margin of India (between Coondapur and south of Mangalore) has been investigated with shallow seismic data. Seismic stratigraphic analysis defined nine seismic units, that are configured in a major type-1 depositional sequence possibly related to fourth-order eustatic sea-level changes, comprising regressive, lowstand, transgressive and highstand systems tracts. The late-Quaternary evolution of the continental margin took place under the influence of an asymmetric relative fourth-order sea-level cycle punctuated by higher frequency cycles. These cycles of minor order were characterised by rapid sea-level rises and gradual sea-level falls that generated depositional sequences spanning different time scales. During the regressive periods, dipping strata were developed, while erosional surfaces and incised valleys were formed during the lowstands of sea level. Terraces, v-shaped depressions, lagoon-like structures observed on the outer continental shelf are the result of the transgressive period. In the study area we have recognised a complex erosional surface that records a long time span during the relative sea-level fall (regressive period) and the following sea-level lowstand and has been reworked during the last transgression. We also infer that sedimentation processes changed from siliciclastic sedimentation to carbonate sedimentation and again to siliciclastic sedimentation, marking an important phase in the late-Quaternary evolution of the western continental shelf of India. We attribute this to an abrupt climate change at the end of the oxygen isotope stage 2, between the Last Glacial Maximum and the Bølling-Allerod event (14?000 yr BP). This sensitive climate change (warming) favoured the formation of reefs at various depths on the shelf, besides the development of Fifty Fathom Flat, a carbonate platform on the outer shelf off Bombay developed prior to 8300 yr BP. The highstand systems tracts were deposited after the sea level reached its present position.