The Messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years (refs 1±3). Earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated Mediterranean basin that had been repeatedly isolated from the Atlantic Ocean 1,2 , but elucidation of the causes of the isolationÐwhether driven largely by glacio-eustatic or tectonic processesÐhave been hampered by the absence of an accurate time frame. Here we present an astronomically calibrated chronology for the Mediterranean Messinian age based on an integrated high-resolution stratigraphy and`tuning' of sedimentary cycle patterns to variations in the Earth's orbital parameters. We show that the onset of the Messinian salinity crisis is synchronous over the entire Mediterranean basin, dated at 5:96 6 0:02 million years ago. Isolation from the Atlantic Ocean was established between 5.59 and 5.33 million years ago, causing a large fall in Mediterranean water level followed by erosion (5.59±5.50 million years ago) and deposition (5.50±5.33 million years ago) of non-marine sediments in a large`Lago Mare' (Lake Sea) basin. Cyclic evaporite deposition is almost entirely related to circum-Mediterranean climate changes driven by changes in the Earth's precession, and not to obliquity-induced glacio-eustatic sea-level changes. We argue in favour of a dominantly tectonic origin for the Messinian salinity crisis, although its exact timing may well have been controlled by the ,400-kyr component of the Earth's eccentricity cycle.Most hypotheses about the initiation of the Messinian salinity crisis (MSC) agree that it resulted from a complex combination of tectonic and glacio-eustatic processes which progressively restricted and ®nally isolated the Mediterranean Sea from the open ocean 1±8 . The gradual modi®cation of water exchange with the Atlantic caused important palaeoceanographic changes in the Mediterranean. This is re¯ected in the classic Messinian sequence of Sicily 9 which starts at 7.24 Myr ago (ref.3) with alternations of open marine marls and sapropels, passes via diatomites into the Lower Evaporites (gypsum, evaporitic limestone and halite), and ends, above an erosional surface, with the Upper Evaporites (gypsum, marls) and fresh to brackish water deposits of Lago Mare facies.Here we de®ne the MSC as the interval of evaporite deposition and Lago Mare sedimentation in the Mediterranean before the Pliocenē ooding 5.33 Myr ago 10 . Controversies still exist, however, over the timing and duration of the MSC; these range from a synchronous event 1 (that is, onset of the MSC in all basins at the same time) to a two-step event 4 (onset of MSC ®rst in marginal basins and later in deep basins) to a completely diachronous evolution 5 (onset of MSC totally dependent on local basinal setting). Equally large controversies exist over the cause, and the effects, of the isolation of the Mediterranean; the two basic explanations are (1) a large glacio-eustatic sea-level drop, r...

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Abstract. Past sea surface temperature (SST) evolution in the Alboran Sea (western Mediterranean) during the last 50,000 years has been inferred from the study of C37 alkenones in International Marine Global Change Studies MD952043 core. This record has a time resolution of~200 years allowing the study of millennial-scale and even shorter climatic changes. The observed SST curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period. Comparison of this Alboran record with b180 from Greenland ice (Greenland Ice Sheet Project 2 core) shows a strong parallelism between these SST oscillations and the Dansgaard-Oeschger events. Five prominent cooling episodes standing out in the SST profile are accompanied by an anomalous high abundance of Neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals. These features and the isotopic record reflect drastic changes in the surface hydrography of the Alboran Sea in association with Heinrich events H1-5.

A continuous high-resolution Western Mediterranean sea surface temperature (SST) alkenone record spanning the past 250,000 years shows that abrupt changes were more common at warming than at cooling. During marine isotope stage (MIS) 6, SST oscillated following a stadial-interstadial pattern but at lower intensities and rates of change than in the Dansgaard/Oeschger events of MIS 3. Some of the most prominent events occurred over MISs 5 and 7, after prolonged warm periods of high stability. Climate during the whole period was predominantly maintained in interglacial-interstadial conditions, whereas the duration of stadials was much shorter.

We propose a revised age calibration of the onset of the Messinian salinity crisis (MSC) in the Mediterranean based on re-analysis of two “classical” sections: Perales (Sorbas basin, Spain) and Monticino (Vena del Gesso basin, Italy). The main novelties are recognition of an extra gypsum cycle in the transitional interval of the Perales section and the revision of the magnetostratigraphy in the Monticino section. We show that the first primary gypsum bed is located three precessional cycles above the C3r/C3An magnetic reversal, correlating to the summer insolation peak at 5.969 Ma; consequently we place the MSC onset in the preceding flexural point in the insolation curve at 5.971 Ma. Accordingly, we suggest that the MSC onset was preconditioned by the reduction of the hydrological exchanges with the Atlantic ocean and was finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern Africa

[1] Down-core samples of planktonic and benthic foraminifera were analyzed for oxygen and carbon isotopes in International Marine Past Global Changes Study (IMAGES) core MD99-2343 in order to study the interactions between climate change in the Northern Hemisphere and the western Mediterranean thermohaline circulation at times of Heinrich events (HE). Our results confirm the antiphase correlation between enhanced North Atlantic Deep Water formation and low ventilation in the Mediterranean. However, this study reveals that this antiphase relationship in deepwater formation between the North Atlantic and Mediterranean was interrupted during times of HE when the injection of large volumes of water from melting icebergs reached the entrance to the Mediterranean. These events, which lasted less than 1000 years, are represented by pronounced decreases in both planktonic d18 O and benthic d 13 C signals. Lower salinities of Mediterranean surface water resulted in a slowdown of western Mediterranean deepwater overturn even though cold sea surface temperatures and drier climate should have resulted in enhanced deepwater formation.

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A high-resolution integrated stratigraphy is presented for the Abad marls of the Sorbas and Nijar basins in SE Spain (preevaporitic Messinian of the Western Mediterranean). Detailed cyclostratigraphic and biostratigraphic analyses of partially overlapping subsections were needed to overcome stratigraphic problems in particular encountered at the complex transition from the Lower to the Upper Abad. The resulting Abad composite section contains a continuous stratigraphic record from the Tortonian/Messinian boundary up to the transition to the Messinian evaporites of the Yesares Member. All together, 18 calcareous plankton events were recognized which were shown to be synchronous throughout the Mediterranean by means of detailed (bed-to-bed) cyclostratigraphic correlations. The magnetostratigraphy allowed the identi®cation of the four magnetic reversals of chron C3An in the Upper Abad. Details in the sedimentary cycle patterns allowed the Abad composite to be astronomically calibrated. This calibration to the 658N summer insolation curve of solution La90 (1,1) yielded astronomical ages for all sedimentary cycles, calcareous plankton bioevents, ash layers and paleomagnetic reversals. Up to now, the Abad composite is the only astronomically well-calibrated section that provided a reliable cyclostratigraphy, magnetostratigraphy and calcareous plankton biostratigraphy. As such it will serve as a reference section both for the pre-evaporite Messinian in the Mediterranean as well as for the Messinian interval in the Astronomical Polarity Time Scale. q