The late Holocene record of Lake Mareotis, Nile Delta, Egypt

Lake Maryut (northwestern Nile Delta, Egypt) was a key feature of Alexandria's hinterland and economy during Greco-Roman times. Its shores accommodated major economic centers, and the lake acted as a gateway between the Nile valley and the Mediterranean. It is suggested that lake-level changes, connections with the Nile and the sea, and possible high-energy events considerably shaped the human occupation history of the Maryut. To reconstruct Lake Maryut hydrology in historical times, we used faunal remains, geochemistry (Sr isotopic signature of ostracods) and geoarcheological indicators of relative lake-level changes. The data show both a rise in Nile inputs to the basin during the first millennia BCE and CE and a lake-level rise of ca. 1.5 m during the Roman period. A high-energy deposit, inferred from reworked radiocarbon dates, may explain an enigmatic sedimentary hiatus previously attested to in Maryut's chronostratigraphy

Late Holocene erosion of the Canopic promontory (Nile Delta, Egypt)

International audienceThe mouths of the Nile Delta are sensitive coastal areas, their geomorphology primarily being mediated by relative sea-level rise and sediment supply. To further document the Holocene evolution of the Nile's Canopic mouth, a core was taken from the southern shores of Abu Qir Bay, close to the ancient Canopic channel. Core bio-sedimentology and chronostratigraphy highlight four stages of marine incursion which are juxtaposed upon the general progradation trend of the Nile coast in this area. Compiled age-depth points from sediment cores taken in Abu Qir Bay underscore two phases of negative sediment budget at the Canopic mouth: (1) a first period, between 3.5 and 2 ka cal. yr BC, probably in relation to the well-documented mid-to-late Holocene decline in Nile flow; and (2) a second phase, after 0.5 ka cal. AD, linked to a decline in Canopic sediment supply to the coastal area, and concomitant with the development of the Rashid branch. The erosion and reworking of material flattened and lowered the promontory surface by up to 4 m. The submersion of the Canopic promontory was completed by relative sea-level rise, primarily controlled by the compaction and liquefaction of unconsolidated lagoonal muds. The lowering of the Canopic mouth led to the submersion of two ancient estuarine-harbor cities, known as East-Canopus and Herakleion, whose remains lie 4-7 m below present mean sea level. It is argued that the subsidence of the two cities cannot explain their abandonment during the late 7th early 8th century AD, taking into account the regional occupation pattern during Antiquity. Rather, the longevity of the two cities, spanning more than 13 centuries, shows that adaptation to coastal risks including erosion, subsidence and high-energy events like storms or tsunamis, was the rule. (C) 2016 Elsevier B.V. All rights reserved

« Kiln, sakieh and lake level change, Nile Delta, Egypt »

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Géoarchéologie des ports lagunaires en Méditerranée et en mer Noire

International audienc

Géoarchéologie des ports lagunaires en Méditerranée et en mer Noire

International audienc

Géoarchéologie des ports lagunaires en Méditerranée et en mer Noire

International audienc

Geoarchaeology of Portus Mareoticus: Ancient Alexandria's lake harbour (Nile Delta, Egypt)

International audienceAncient Alexandria possessed not only an important maritime front but also a long lake waterfront on its southern side. This dual waterfront was praised by the ancient geographer Strabo in the first century BCE, because its geomorphological configuration opened Alexandria to Mediterranean trade, and also the Nile delta and Egypt. While the city's maritime palaeogeography has been widely described and studied, Alexandria's lacustrine waterfront has largely been neglected and little is known about its palaeo-geography and archaeology. Here we report the chronostratigraphy of the southern edge of the modern city. Bio-sedimentological analyses of sediment archives allow us to reconstruct the evolution of the depositional environments and palaeogeographies for parts of ancient Alexandria's lacustrine waterfront. The chronological framework spans the last 2000 years. By marrying our data with ancient maps and historical sources, we propose a location for Portus Mareoticus. The lake's geomorphology suggests the presence of three ancient jetties, perpendicular to the shoreline and several hundreds meters long. The occupation of the investigated area began at the end of the first century BCE, linked to Roman domination and probably ended during late Roman times. The waterfront was then disconnected from the city during the 9th century CE, due to the desiccation of Maryut Lake, concomitant with the drying-up of the Canopic branch. Alexandria canal subsequently became the sole waterway linking the city to the Nile. The most western part of the canal, which extended freshwater supply and fluvial navigation down to the western marine harbour of Alexandria, was completed in the 16th century, probably in relation to the development of the marine harbours at the beginning of the Ottoman period. Our research sheds new light on the topography of ancient Alexandria

A physiological overview of the genetics of flowering time control.

Physiological studies on flowering time control have shown that plants integrate several environmental signals. Predictable factors, such as day length and vernalization, are regarded as 'primary', but clearly interfere with, or can even be substituted by, less predictable factors. All plant parts participate in the sensing of these interacting factors. In the case of floral induction by photoperiod, long-distance signalling is known to occur between the leaves and the shoot apical meristem (SAM) via the phloem. In the long-day plant, Sinapis alba, this long-distance signalling has also been shown to involve the root system and to include sucrose, nitrate, glutamine and cytokinins, but not gibberellins. In Arabidopsis thaliana, a number of genetic pathways controlling flowering time have been identified. Models now extend beyond 'primary' controlling factors and show an ever-increasing number of cross-talks between pathways triggered or influenced by various environmental factors and hormones (mainly gibberellins). Most of the genes involved are preferentially expressed in meristems (the SAM and the root tip), but, surprisingly, only a few are expressed preferentially or exclusively in leaves. However, long-distance signalling from leaves to SAM has been shown to occur in Arabidopsis during the induction of flowering by long days. In this review, we propose a model integrating physiological data and genes activated by the photoperiodic pathway controlling flowering time in early-flowering accessions of Arabidopsis. This model involves metabolites, hormones and gene products interacting as long- or short-distance signalling molecules