Sergio Silenzi

Chapter 1 Mediterranean climate variability over the last centuries: A review

Publisher Summary This chapter discusses a necessary task for assessing to which degree the industrial period is unusual against the background of pre-industrial climate variability. It is the reconstruction and interpretation of temporal and spatial patterns of climate in earlier centuries. There are distinct differences in the temporal resolution among the various proxies. Some of the proxy records are annually or even higher resolved and hence record year-by-year patterns of climate in past centuries. Several of the temperature reconstructions reveal that the late twentieth century warmth is unprecedented at hemispheric scales and is explained by anthropogenic, greenhouse gas (GHG) forcing. The chapter discusses the availability and potential of long, homogenized instrumental data, documentary, and natural proxies to reconstruct aspects of past climate at local- to regional-scales within the larger Mediterranean area, which includes climate extremes and the incidence of natural disasters. The chapter describes the role of external forcing, including natural and anthropogenic influences, and natural, internal variability in the coupled ocean–atmosphere system at subcontinental scale.

Sea-level during the penultimate interglacial period based on a submerged stalagmite from Argentarola Cave (Italy)

Accurate constraints are presented for the absolute age, duration and sea-level for the highstand corresponding to marine isotope stage (MIS) 7.1. Our work is based on a stalagmite collected in a currently submerged cave from Italy (Argentarola Cave). Flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms. Precise uranium^thorium (U^Th) ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during MIS 7.2 and MIS 6, the penultimate glacial period. In addition, the period of marine transgression is bracketed between 202 and 190 kyr BP, defining a MIS 7.1 duration of 11 ˛ 2 kyr. Comparison with previous studies provides a new constraint on the sea-level during MIS 7.1 that has approximately remained between 318 and 39 m relative to present sea-level. The timing of the MIS 7.1 highstand is in full agreement with the SPECMAP chronology which contrasts with the growing body of evidence showing a significant phase difference for MIS 5.5. A tempting conclusion is that second order sea-level highstands such as MIS 7.1 may be purely driven by astronomical changes, in contrast with major terminations such as Termination II. Atmospheric CO2 levels may partly explain this contrast since the two sea-level transitions, (MIS 7.2^7.1 and MIS 6^5.5) are characterized by very different CO2 rises (20 vs 100 ppm). fl 2002 Elsevier Science B.V. All rights reserved.

Hydrological conditions over the western Mediterranean basin during the deposition of the cold Sapropel 6 (ca. 175 kyr BP)

A new oxygen isotope record is reported from a stalagmite collected in the Argentarola Cave located on the Tyrrhenian coast of Italy. As shown from observations and numerical modeling of N 18 O in modern precipitation, the recorded N 18 O variability for this zone is dominated by the amount of precipitation (so-called ‘amount effect’). The N 18 O profile measured in the stalagmite is characterized by a prominent negative excursion (ca. 2^3x) between 180 and 170 kyr BP. This paleoclimatic feature is interpreted as being due to a relatively wet period which occurred during the penultimate glacial period, more precisely, during Marine Isotope Stage 6.5. This pluvial phase is shown to correspond chronologically to the deposition of the sapropel event 6 (S6). Although this particular sapropel event occurred during a cold phase, the N 18 O excursion is similar to those corresponding to other sapropels (S4, S3 and S2). The evidence for humid conditions during S6 in the western Mediterranean basin agrees with previous studies based on deep-sea sediment cores. Taken collectively, the data suggest that during sapropel events dilution of ocean surface waters was not restricted to the output of the river Nile but was rather widespread over the entire Mediterranean Sea due to increased rainfall. < 2002 Elsevier Science B.V. All rights reserved.

A Review of 2000 Years of Paleoclimatic Evidence in the Mediterranean

The integration of climate information from instrumental data and documentary and natural archives; evidence of past human activity derived from historical, paleoecological, and archaeological records; and new climate modeling techniques promises major breakthroughs for our understanding of climate sensitivity, ecological processes, environmental response, and human impact. In this chapter, we review the availability and potential of instrumental data, less well-known written records, and terrestrial and marine natural proxy archives for climate in the Mediterranean region over the last 2000 years. We highlight the need to integrate these different proxy archives and the importance for multiproxy studies of disentangling complex relationships among climate, sea-level changes, fire, vegetation, and forests, as well as land use and other human impacts. Focusing on dating uncertainties, we address seasonality effects and other uncertainties in the different proxy records. We describe known and anticipated challenges posed by integrating multiple diverse proxies in high-resolution climate-variation reconstructions, including proxy limitations to robust reconstruction of the natural range of climate variability and problems specific to temporal scales from interannual to multicentennial. Finally, we highlight the potential of paleo models to contribute to climate reconstructions in the Mediterranean, by narrowing the range of climate-sensitivity estimates and by assimilating multiple proxies.

New data on the Holocenic sea-level rise in NW Sicily (Central Mediterranean Sea)

The emerged and submerged coastal tracts of selected areas in NW Sicily (San Vito Lo Capo Promontory and Marettimo Island in the Egadi Archipelago) have been studied by means of an interdisciplinary approach (geomorphological and neotectonic surveys, palaeontological, depositional and petrographical observations) with the aim to characterize the coastal evolution of the sector over a wide time frame (Late Pleistocene and Holocene) and to recognize the geological indicators of relative sea-level fluctuations. Neotectonic studies performed all along the coastal sector through the check of the present-day height of marine notches and of the inner margin of marine terraces of Eutyrrhenian age allowed to assess the entity of post-Tyrrhenian differential crustal movements in the area. The calculated rates of uplift confirm the relative stability of the area in the last 125 ka and that the relative corrections introduced can be considered negligible in the reconstruction of sea-level rise in the last thousand years. On the base of these considerations, the sea-level rise curve which has been drawn for the Holocene through the radiometric dating (14C and U/Th) of submerged speleothems and Vermetid reefs is assumed to gain a regional significance and to represent a good reference datum for the Central–Southern Mediterranean Sea. In addition, the sea-level rise data are in good agreement with the predicted sea-level curves based on geophysical models previously applied to the same study areas.

A new marker for sea surface temperature trend during the last centuries in temperate areas: Vermetid reef

The presence of Vermetid reefs in temperate waters, their diffusion in the Mediterranean Sea, and the possibility of performing 14 C ages allowed the use of Vermetids as an indicator of sea level changes. We present new data on sea climate trend fluctuations that could be interpreted as Sea Surface Temperature (SST) variations, recorded on Vermetid (Dendropoma petraeum) reefs, by means of isotopic analysis. The isotopic records show positive values of the d 18 O relative to present-day values in the period between 1600 and 1850 AD; this deviation occurs in association with the climatic cooling event known as Little Ice Age (LIA). Subsequently, we can observe the warming trend that characterized the last century. These preliminary results indicate that Vermetids could be considered a new SST proxy-data for the Mediterranean Sea and, more generally, for temperate areas. D 2003 Elsevier B.V. All rights reserved.

Vermetid reefs in the Mediterranean Sea as archives of sea-level and surface temperature changes

Vermetid reefs are among the most important bioconstructions in the Mediterranean Sea, with a distribution restricted to the warmest part of the basin. Their structure, and vertical and geographical distribution make them good biological indicators of changes in sea level and sea-surface temperature over the last two millennia.

Sea level changes and tectonic mobility: Precise measurements in three coastlines of Italy considered stable during the last 125 ky

Abstract Fast uplift or subsidence rates, related to intense tectonic-seismic activity, affect the Mediterranean coasts, especially in its eastern sector and Calabria, whereas other areas appear relatively stable. Along the southern Italian coast, the most widely distributed and therefore useful reference datum is the paleo sea level related to isotopic substage 5e (125 ky). In the present study, this marker (inner edge of marine terrace or notch) has been safely identified along three sectors of the Italian coast generally considered tectonically stable: eastern Sardinia, southern Latium and northwestern Sicily. In Latium the top of the Eutyrrhenian transgression was found to vary between −5 and +9.8 m a.s.l. along a 100 km long coast. A well carved Eutyrrhenian notch can be followed for ca. 35 km along the coast of Orosei in Sardinia, gradually varying in elevation between 7.7 and 10.5 m a.s.l., thus indicating a regional tilt. In Sicily, the inner edges of the Eutyrrhenian terrace and marine notches are at elevations between 8 and 13.9 m a.s.l. In all these areas the stage 5e marker has shown a significant local mobility demonstrating its utility for detailing either areal or linear tectonic activity during the last 125 ky along the Tyrrhenian Sea coasts.

Quantitative assessment of post tyrrhenian differential crustal movements in a mediterranean coastal area (S. Vito-Sicily-Italy)

Abstract Aim of the present study, which is part of the E.U. Commission SELF II Research Project, is the reconstruction of the Pleistocene and Holocene tectonic trends in a Mediterranean coastal area. The study is focused on the upper Pleistocene to Holocene tectonic history of NW Sicily. The emerged and submerged coastal zone of a selected area (St. Vito lo Capo, NW Sicily) was studied, by using jointly different sectoral approaches and carrying out geological and geomorphological surveys. The studied area shows morphological evidence of a succession of marine terraces, which is uncommon for the Mediterranean region. These evidences of the coastal evolution, which are currently located both above and below the present sea level, were ascribed to the Middle and Upper Pleistocene, by using morphological (notches and terraces) and stratigraphical criteria, supported by radiometric dating. A detailed study of the longitudinal profiles of the most recently emerged marine terraces, ascribed to isotope stage 5e, revealed the presence of six sectors characterized by different rates of crustal uplift during the post Tyrrhenian age. The rates of uplift calculated for each of these post-Tyrrhenian age sectors allowed to recognize that the error related to tectonic uplift, in the reconstruction of eustatic fluctuations relative to the last 10 kyr from submerged speleothems and vermetid reefs, is negligible.