Christophe Morhange

Changes of relative sea level during the past 5000 years in the ancient harbor of Marseilles, Southern France

In the ancient harbor of Marseilles, marine fauna fixed upon archaeological structures as well as bio-sedimentary units document a 1.5 m steady rise in relative sea level during the past 5000 years, followed by a near stable level at present datum from about 1500 years AD to the last century. This trend is similar to the one previously documented along the rocky coasts of the same region. Field observations inside and outside the harbor confirm that no sea level stand higher than the present ever occurred during the studied period in contradiction with the numerical model of Peltier but in agreement with the glacio-hydro-isostatic models of Lambeck and Johnston and Lambeck and Bard. q 2001 Elsevier Science B.V. All rights reserved.

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 Rhone, 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.

Rapid sea-level movements and noneruptive crustal deformations in the Phlegrean Fields caldera, Italy

The importance of Pozzuoli9s archaeological ruins in linking sea-level change and Earth deformation with volcanic activity has been recognized since the nineteenth century. The pillars of the Roman market were used as a paleotide gauge by pioneer geologists such as Lyell. For the first time, we have radiocarbon dated biological indicators on these remains, showing three 7 m relative sea-level highstands during the fifth century A.D., the early Middle Ages, and before the 1538 eruption of Monte Nuovo. These repeated uplift and subsidence cycles, not always followed by volcanic activity, have important implications for the evaluation of volcanic hazard.

Nile Delta’s sinking past: Quantifiable links with Holocene compaction and climate-driven changes in sediment supply?

The Nile Delta is a subsiding sedimentary basin that hosts ~66% of Egypt’s population and 60% of the country’s food production. Projected sea-level-rise scenarios for the coming decades have sharpened focus on the delta’s potential resilience to rapid changes in accommodation space. We use chronostratigraphic data from 194 organic-rich peat and lagoon points to quantitatively reevaluate the drivers of Nile Delta surface dynamics during the Holocene. Reconstructed subsidence rates range from 0.03 to 4.5 mm/yr, and are highest in the Manzala, Burullus, Idku, and Maryut lagoons, areas that correspond to deep late Pleistocene topography infi lled with compressible Holocene strata; 88% of the subsidence values are <2 mm/ yr. We suggest that during the Holocene two signifi cant but previously underestimated contributors to changes in Nile Delta mass balance have been sediment compaction and orbitally forced changes in sediment supply. Between 8000 and 4000 calibrated (cal) 14 C yr B.P., spatially averaged sedimentation rates were greater than subsidence, meaning that delta aggradation was the dominant geomorphological process at the regional scale. Since ca. 4000 cal yr B.P., a sharp climate-driven fall in Nile sediment supply, coupled with the human-induced drainage of deltaic wetlands, has rendered the depocenter more sensitive to degradation by sea-level rise and extreme fl ood events.

Geoscience rediscovers Phoenicia's buried harbors

After centuries of archaeological debate, the harbors of Phoenicia9s two most important city states, Tyre and Sidon, have been rediscovered, and including new geoarcheological results reveal how, where, and when they evolved after their Bronze Age foundations. The early ports lie beneath their present urban centers, and we have indentified four harbor phases. (1) During the Bronze Age, Tyre and Sidon were characterized by semi-open marine coves that served as protoharbors. (2) Biostratigraphic and lithostratigraphic data indicate the presence of early artificial basins after the first millennium B.C. (3) The harbors reached their apogees during the Greco-Roman and Byzantine periods. (4) Silting up and coastal progradation led to burial of the medieval basins, lost until now.

The Sea Peoples, from Cuneiform Tablets to Carbon Dating

The 13th century BC witnessed the zenith of the Aegean and Eastern Mediterranean civilizations which declined at the end of the Bronze Age, ∼3200 years ago. Weakening of this ancient flourishing Mediterranean world shifted the political and economic centres of gravity away from the Levant towards Classical Greece and Rome, and led, in the long term, to the emergence of the modern western civilizations. Textual evidence from cuneiform tablets and Egyptian reliefs from the New Kingdom relate that seafaring tribes, the Sea Peoples, were the final catalyst that put the fall of cities and states in motion. However, the lack of a stratified radiocarbon-based archaeology for the Sea People event has led to a floating historical chronology derived from a variety of sources spanning dispersed areas. Here, we report a stratified radiocarbon-based archaeology with anchor points in ancient epigraphic-literary sources, Hittite-Levantine-Egyptian kings and astronomical observations to precisely date the Sea People event. By confronting historical and science-based archaeology, we establish an absolute age range of 1192–1190 BC for terminal destructions and cultural collapse in the northern Levant. This radiocarbon-based archaeology has far-reaching implications for the wider Mediterranean, where an elaborate network of international relations and commercial activities are intertwined with the history of civilizations.

Tracking Nile Delta vulnerability to Holocene change.

Understanding deltaic resilience in the face of Holocene climate change and human impacts is an important challenge for the earth sciences in characterizing the full range of present and future wetland responses to global warming. Here, we report an 8000-year mass balance record from the Nile Delta to reconstruct when and how this sedimentary basin has responded to past hydrological shifts. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the ‘monsoon pacemaker’, attested throughout the mid-latitude tropics. Following the early to mid-Holocene growth of the Nile’s deltaic plain, sediment losses and pronounced erosion are first recorded after ~4000 years ago, the corollaries of falling sediment supply and an intensification of anthropogenic impacts from the Pharaonic period onwards. Against the backcloth of the Saharan ‘depeopling’, reduced river flow underpinned by a weakening of monsoonal precipitation appears to have been particularly conducive to the expansion of human activities on the delta by exposing productive floodplain lands for occupation and irrigation agriculture. The reconstruction suggests that the Nile Delta has a particularly long history of vulnerability to extreme events (e.g. floods and storms) and sea-level rise, although the present sediment-starved system does not have a direct Holocene analogue. This study highlights the importance of the world’s deltas as sensitive archives to investigate Holocene geosystem responses to climate change, risks and hazards, and societal interaction.

Solar pacing of storm surges, coastal flooding and agricultural losses in the Central Mediterranean

Storm surges, leading to catastrophic coastal flooding, are amongst the most feared natural hazards due to the high population densities and economic importance of littoral areas. Using the Central Mediterranean Sea as a model system, we provide strong evidence for enhanced periods of storminess leading to coastal flooding during the last 4500 years. We show that long-term correlations can be drawn between storminess and solar activity, acting on cycles of around 2200-yr and 230-yr. We also find that phases of increased storms and coastal flooding have impacted upon mid- to late Holocene agricultural activity on the Adriatic coast. Based on the general trend observed during the second half of the 20th century, climate models are predicting a weakening of Mediterranean storminess. By contrast, our new data suggest that a decrease in solar activity will increase and intensify the risk of frequent flooding in coastal areas.

Holocene morphogenesis of Alexander the Great's isthmus at Tyre in Lebanon.

In 332 B.C., Alexander the Great constructed an ≈1,000-m-long causeway to seize the offshore island of Tyre. The logistics behind this engineering feat have long troubled archaeologists. Using the Holocene sedimentary record, we demonstrate that Alexanders engineers cleverly exploited a shallow proto-tombolo, or sublittoral sand spit, to breach the offshore citys defensive impregnability. We elucidate a three-phase geomorphological model for the spits evolution. Settled since the Bronze Age, the areas geological record manifests a long history of natural and anthropogenic forcings. (i) Leeward of the island breakwater, the maximum flooding surface (e.g., drowning of the subaerial land surfaces by seawater) is dated ≈8000 B.P. Fine-grained sediments and brackish and marine-lagoonal faunas translate shallow, low-energy water bodies at this time. Shelter was afforded by Tyres elongated sandstone reefs, which acted as a 6-km natural breakwater. (ii) By 6000 B.P., sea-level rise had reduced the dimensions of the island from 6 to 4 km. The leeward wave shadow generated by this island, allied with high sediment supply after 3000 B.P., culminated in a natural wave-dominated proto-tombolo within 1–2 m of mean sea level by the time of Alexander the Great (4th century B.C.). (iii) After 332 B.C., construction of Alexanders causeway entrained a complete anthropogenic metamorphosis of the Tyrian coastal system.

Vulnerability of Mediterranean Ecosystems to Long-Term Changes along the Coast of Israel

Although human activity is considered to be a major driving force affecting the distribution and dynamics of Mediterranean ecosystems, the full consequences of projected climate variability and relative sea-level changes on fragile coastal ecosystems for the next century are still unknown. It is unclear how these waterfront ecosystems can be sustained, as well as the services they provide, when relative sea-level rise and global warming are expected to exert even greater pressures in the near future (drought, habitat degradation and accelerated shoreline retreat). Haifa Bay, northern Israel, has recorded a landward sea invasion, with a maximum sea penetration 4,000 years ago, during an important period of urban development and climate instability. Here, we examine the cumulative pressure of climate shifts and relative sea-level changes in order to investigate the patterns and mechanisms behind forest replacement by an open-steppe. We provide a first comprehensive and integrative study for the southern Levant that shows that (i) human impact, through urbanization, has been the main driver behind ecological erosion in the past 4,000 years; (ii) climate pressures have reinforced this impact; and (iii) local coastal changes have played a decisive role in eroding ecosystem resilience. These three parameters, which have closely interacted during the last 4,000 years in Haifa Bay, clearly indicate that for an efficient management of the coastal habitats, anthropogenic pressures linked to urban development must be reduced in order to mitigate the predicted effects of Global Change.