Romana Melis

Benthic biofacies to interpret Holocene environmental changes and human impact in Alexandria's Eastern Harbour, Egypt:

Holocene molluscan and foraminiferal faunas, sensitive ecological markers, are statistically treated to define their temporal and spatial distributions in radiocarbon-dated cores in Alexandrias Eastern Harbour. Up-core variations of these benthic biofacies record the evolution of depositional environments during the past 8000 years in this long-occupied Eastern Mediterranean port. The most important change occurred in the mid-Holocene between 6300 and 4300 yr ago, a time of lower sea level and minimal human activity. This faunal change, indicating a transition from a somewhat protected to a more open and higher-energy marine environment, resulted primarily from rise of sea level, lowering of the harbour floor and diminished shielding by Pleistocene coastal ridges and reefs near the bay mouth and within the harbour. Since that time, faunal assemblages have remained generally constant, except during the period from 2100 to 1800 yr ago when Greeks and Romans built the Heptastadion that connected Alexandria to Pharos Island; this construction effectively separated the Eastern from the Western Harbour. Absence of a well-marked faunal change during the past 18 centuries is unexpected, particularly in light of the much-increased population and associated human effects. The harbours overall large size, rise in relative sea level and continued exchange of marine water between the open shelf and port have maintained an active circulation pattern. The strong current regime and reworking of bottom sediments have generally masked short-term human effects and altered the harbours late-Holocene sediment stratigraphy. These factors help explain why benthic biofacies primarily record influences of natural processes that prevailed in this relatively unconfined, high-energy marine setting rather than those of a more constricted and anthropogenically impacted port.

r-Selected benthic foraminifera with associated bacterial colonies in Upper Pleistocene sediments of the Ross Sea (Antarctica): implications for calcium carbonate preservation

Investigations on foraminifera from Upper Pleistocene‐Holocene sediments cored in the continental slope of the western Ross Sea (2383 m water depth) revealed that the record of calcareous assemblages was restricted to a limited time interval (approximately 6 kyr) and characterized by a dominance of phytodetritus-exploiting taxa, such as Alabaminella weddellensis and Epistominella exigua. Rod-shaped calcified, fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces, either as clusters or as isolated cells, suggesting that significant changes (from underto oversaturated conditions with respect to calcium carbonate) in the chemistry of the seawater developed before the final burial of the foraminiferal tests. We postulate that bacterial activity on a microenvironmental scale (interface and pore water) in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities.

Holocene sea ice variability driven by wind and polynya efficiency in the Ross Sea

The causes of the recent increase in Antarctic sea ice extent, characterised by large regional contrasts and decadal variations, remain unclear. In the Ross Sea, where such a sea ice increase is reported, 50% of the sea ice is produced within wind-sustained latent-heat polynyas. Combining information from marine diatom records and sea salt sodium and water isotope ice core records, we here document contrasting patterns in sea ice variations between coastal and open sea areas in Western Ross Sea over the current interglacial period. Since about 3600 years before present, an increase in the efficiency of regional latent-heat polynyas resulted in more coastal sea ice, while sea ice extent decreased overall. These past changes coincide with remarkable optima or minima in the abundances of penguins, silverfish and seal remains, confirming the high sensitivity of marine ecosystems to environmental and especially coastal sea ice conditions.Strong regional heterogeneity prevents thorough understanding of the recent increase in Antarctic sea ice. Here, analysis of marine and ice cores in the Western Ross Sea shows that late Holocene contrasting sea ice patterns between open and coastal areas are related to katabatic winds and polynya efficiency.

Extreme depositional events on the NW-Barents Sea continental margin

Lucchi, Renata G. ... et. al.-- 87° Congresso della Societa Geologica Italiana e 90° Congresso della Societa Italiana di Mineralogia e Petrologia, The Future of the Italian Geosciences - The Italian Geosciences of the Future, 10-12 September 2014, Milan, Italy.-- 1 pageThe Montellina Spring (370 m a.s.l.) represents an example of groundwater resource in mountain region. It is a significant source of drinking water located in the right side of the Dora Baltea Valley (Northwestern Italy), SW of Quincinetto town. This spring shows a morphological location along a ridge, 400 m from the Renanchio Torrent in the lower sector of the slope. The spring was investigated using various methodologies as geological survey, supported by photo interpretation, structural reconstruction, NaCl and fluorescent tracer tests, discharge measurements. This multidisciplinary approach, necessary due to the complex geological setting, is required for the importance of the Montellina Spring. It is interesting in the hydrogeological context of Western Alps for its high discharge, relatively constant over time (average 150 l/s), and for its location outside a fluvial incision and suspended about 40 m above the Dora Baltea valley floor (Lasagna et al. 2013). According to the geological setting, the hydrogeological reconstruction of the area suggests that the large amount of groundwater in the basin is essentially favoured by a highly fractured bedrock, covered by wide and thick bodies of glacial and gravitational sediments. The emergence of the water along the slope, in the Montellina Spring, is essentially due to a change of permeability between the deep bedrock and the shallow bedrock and/or surficial sediments. The deep bedrock, showing closed fractures and/or fractures filled by glacial deposits, is slightly permeable. The shallow bedrock, strongly loosened as result of gravitational phenomena, and the local gravitational sediments are, on the contrary, highly permeable. The concentration of water at the spring is due to several reasons. a) The spring is immediately downward a detachment niche, dipping towards the spring, that essentially drains the water connected to the change of permeability in the bedrock. b) It is along an important fracture, that carries a part of the losses of the Renanchio Torrent. c) Finally, it is favored by the visible and buried morphology. Although it is located along a ridge, the spring occurs in a small depression between a moraine and a landslide body. It also can be favored by the likely concave trend of buried base of the landslide. At last, tracer tests of the Renanchio Torrent water with fluorescent tracer are performed, with a continuous monitoring in the Montellina Spring. The surveys permit to verify and quantify the spring and torrent hydrogeological relationship, suggesting that only a small fraction of stream losses feeds the spring.