Meryem Mojtahid

• University of Angers

The study of manganese (Mn) and iron (Fe) cycling in early diagenetic processes in estuaries is crucial for understanding the functioning of these vital ecosystems and predicting their responses to environmental change. The present study investigates the dynamic interplay of Mn and Fe in early diagenetic processes at highly contrasted hydrosediment...

The eastern Mediterranean Sea (EMS) sedimentary record is periodically interspersed with organic-rich ‘sapropel’ layers. Sapropels are characteristic of basin-wide anoxic events, triggered by precession-forced insolation maxima. Relatively subdued insolation maxima, however, are not always expressed as distinct sapropel events. The EMS sedimentary...

The Moroccan coasts are occasionally inundated by storm surges and tsunamis. Local historical archives recorded some of these events, such as the storm surge of 1913 CE and the tsunami of 1755 CE. The latter remains the most destructive event the country has ever faced, with major human and economic losses recorded mainly between the two cities of...

The present study aims at reconstructing mid-to late Holocene paleoenvironmental evolution of the Tahaddart lower estuary (NW of Morocco) and to find possible sedimentary evidence of past marine submersion events (storm surges and tsunamis). This is achieved through the study of four sedimentary cores and by using a multiproxy approach that combine...

The Moroccan coast is occasionally confronted with marine submersion events caused by storm surges and tsunamis. The Moroccan historical archives recorded some of these events, such as the storm surge of 2014 CE and the tsunami of 1755 CE. The latter remains the most destructive event the country has ever faced, with major human and economic losses...

The interaction between ocean circulation and ice‐sheet dynamics plays a key role in the Quaternary climate. Compared with the surface and deep regions of the Atlantic Meridional Overturning Circulation (AMOC), the study of intermediate depths during key time periods, such as Heinrich Stadials (HSs), remains poorly documented, especially for the no...

The recurrent latent‐heat polynya characterizing Storfjorden (Svalbard, Norway) triggers seasonal formation of thin first‐year sea ice. This leads to the production of dense, salty, and corrosive brines that cascade towards the sea floor and mix with shelf waters. The bottom topography of the fjord is responsible for the retention of these dense wa...

Kongsfjorden (Svalbard archipelago) is subjected to strong environmental gradients creating high physical and geochemical stress on benthic faunas. The present study aims at understanding the environmental drivers governing benthic foraminifera in the innermost part of the fjord. Surface sediments from 9 stations were sampled during August 2018 alo...

An unprecedented sampling effort on the Loire estuary allowed a multi scale approach to identify parameters controlling density variations of benthic foraminifera. Indeed, the distances between the samples analysed for this study vary from 1 cm to hundreds of kilometres. To catch this range of distance variations, a model called Scale Variance Anal...

Benthic foraminiferal assemblage data have been derived from a marine sediment core collected in a cold-water coral (CWC) site off northwest Scotland (near the Wyville Thomson Ridge - WTR). The record covers the last glacial period to the late Holocene. Our reconstructions enable to better constrain the paleoenvironmental changes that took place in...

Supplementary data set to "Deglacial to Holocene environmental changes in the northern Ligurian Sea: The dual influence of regional climate variability and large-scale intermediate Mediterranean circulation". https://doi.org/10.1016/j.palaeo.2021.110500

The sedimentary archives of the Mediterranean Sea record periodic deposits of organic-rich deposits, called sapropels in the eastern basin and organic-rich layers (ORL) in the western basin. Changes in both the Mediterranean circulation and inputs of fresh water through borderlands rivers under more humid climate, are important mechanisms to explai...

The upper branch of the Atlantic meridional overturning circulation (AMOC) plays a critical role in ocean circulation and climate change, yet its variability during the last glacial period is poorly documented. Here, we investigate the northward‐flowing Glacial Eastern Boundary Current (GEBC) in the North Atlantic, known today as the European Slope...

Despite covering only 0.82% of the ocean’s surface, the Mediterranean Sea supports up to 18% of all known marine species, with 21% being listed as vulnerable and 11% as endangered. The acceler- ated spread of tropical non-indigenous species is leading to the “tropicalization” of Mediterranean fauna and flora as a result of warming and extreme heat...

Mediterranean Ecosystem report on Climate and Global changes. Balzan MV, Hassoun AER, Aroua N, Baldy V, Bou Dagher M, Branquinho C, Dutay J-C, El Bour M, Médail F, Mojtahid M, Morán-Ordóñez A, Roggero PP, Rossi Heras S, Schatz B, Vogiatzakis IN, Zaimes GN, Ziveri P 2020 Ecosystems. In: Climate and Environmental Change in the Mediterranean Basin –...

Marine ecosystems: Despite covering only 0.82% of the ocean’s surface, the Mediterranean Sea supports up to 18% of all known marine species, with 21% being listed as vulnerable and 11% as endangered. The accelerated spread of tropical non-indigenous species is leading to the “tropicalization” of Mediterranean fauna and flora as a result of warming...

We present fossil benthic foraminiferal assemblage data from marine sediment core SS02/06-GC2 located in the abyssal plain of the Murray Canyon Group (offshore South Australia). The sedimentological characteristics indicate the presence of turbidite deposits showing classical Bouma-like sequences, dated between ~40 and 12 cal ka BP. These results c...

The rapid response of benthic foraminifera to environmental factors (e.g. organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such an approach, however, requires a thorough knowledge of their modern ecology in...

We present a high‐resolution study covering the past 19 ka from the southeastern Mediterranean Sea, based on benthic foraminiferal faunas and their stable oxygen and carbon isotopes. These data are integrated with previously published and newly acquired planktic foraminiferal data from the same sediment core in order to investigate the benthic‐plan...

We discuss paleoenvironments of north-western France over the last 7 kyrs in terms of: i) long-term changes (relative sea-level rise and boreal summer insolation), ii) rapid climate changes (millennial-scale Bond events and multi-decadal regimes of the North Atlantic Oscillation: NAO) and iii) growing human impacts in watersheds. Our study focuses...

The high-time resolution (∼70 years in average) multi-proxy analysis conducted on the mid-shelf core CBT-CS11 (47°46.429'N; 4°25.308'W; 73 m depth; 3.96 m long; NW France, S Brittany) revealed the complexity of the palaeohydrological and palaeoclimatic signals recorded over the last 7 kyrs in the recently published paper: "Oceanic versus continenta...

Abstract. The rapid response of benthic foraminifera to environmental factors (e.g., organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such approach, however, requires a thorough knowledge of their modern ec...

Paleostudies often rely on foraminiferal calcite chemistry, which reflect past sea water condition through so-called proxy relationships. One way to evaluate robustness of these proxy relationships is to test them in well-studied and during well-constrained climate transitions. The southeastern (SE) Mediterranean is a perfect natural laboratory wit...

A mid- to late-Holocene paleohydrological reconstruction from the northeast Atlantic is proposed through the study of a high-resolution sedimentary record from the northern continental shelf of the Bay of Biscay (BoB). Three foraminiferal species dominate the assemblages with Rosalina globularis showing an overall decrease in absolute and relative...

Sediment core KV14bis was retrieved from the Fosse du Croisic, a Loire River incised paleovalley located in the inner shelf of the Bay of Biscay. This core (5.4 m length) covers the past 2.6 cal kyr BP with high sedimentation rate. A multiproxy approach (X-ray imagery, XRF data, grain size analyses, and benthic foraminiferal assemblages) was applie...

Nowadays, the Storfjorden (Svalbard) is a first-year sea-ice production zone characterized by intense production of brine and cascading of brine-enriched shelf waters (BSW). Brine formation, and the consequent injection of salty and relatively acid dense water into the deepest ocean, was likely more important during the cold climatic periods of Hol...

Three hundred thirty Van Veen grab samples were collected from surface sediments along the Loire estuary, from the upstream of Nantes to the estuary mouth (80 km long). The main objective of this work is to study the spatial distributional patterns of grain size characteristics and their link to environmental parameters (e.g., transport processes,...

Using benthic foraminiferal-based proxies in sediments from the Celtic margin, we provide a well-dated record across the last deglaciation of the Channel River dynamics and its potential impact on the hy-drology of intermediate water masses along the European margin. Our results describe three main periods: 1) During the Last Glacial Maximum, and b...

This paper documents the evolution over the last 10 kyr of one of the key parameters of climate: sea-surface temperatures (SSTs) in the North Atlantic. We focus on the southern Bay of Biscay, a highly sensitive oceanographic area regarding the dynamics of the North Atlantic subpolar and subtropical gyres (SPG and STG respectively). This site furthe...

Estuaries are dynamic systems that collect terrestrial, aerial, fluvial, and marine inputs, including organic microfossils, which, when fossilized and observed on palynological slides, are also referred to as palynomorphs (pollen and non-pollen palynomorphs including dinoflagellate cysts or dinocysts). To understand these organic microfossil deposi...

Assessing the extent of metal contamination in estuarine surface sediments is hampered by the high heterogeneity of sediment characteristics, the spatial variability of trace element sources, sedimentary dynamics and geochemical processes in addition to the need of accurate reference values for deciphering natural to anthropogenic contribution. Bas...

We used sedimentological and foraminiferal characteristics of four sedimentary cores, supported by paleogeographical and historical data, to reconstruct the depositional history of the inner Loire estuary (Near Saint-Nazaire, France) and the response of benthic foraminifera to the mid- to late-Holocene marine flooding of the incised valley. These w...

This paper documents the last 10 ka evolution of one of the key parameters of climate: sea-surface temperatures (SST) in the subpolar North Atlantic. We focus on the southern Bay of Biscay, a highly sensitive oceanographic area because of its strategic and nodal position regarding the dynamics of the North Atlantic subpolar and subtropical gyres. T...

Ninety-seven surface sediment samples were collected in September 2012 from intertidal and subtidal areas along the Loire estuary (western France). The main objective of this work is to study the spatial distributional patterns of living benthic foraminifera and their link to the environmental parameters (distance to sea, elevation, grain size, tot...

La compréhension du fonctionnement climatique par le passé sans l’intervention de l’homme et après son installation est indispensable pour écrire les scénarii possibles de l’évolution future du climat. En ce sens, l’Holocène est une période d’un grand intérêt puisque les variations climatiques qui l’ont ponctué sont autant d’analogues au changement...

Rose-Bengal-stained foraminiferal assemblages (> 150 μm) were analysed along a five-station bathymetric transect across the core and the lower part of the oxygen minimum zone (OMZ) on the Indian margin of the Arabian Sea. Sediment cores were collected using the manned submersible Shinkai 6500 during the RV Yokosuka cruise YK08-11 in the post-monsoo...

Over the past 13 ka, the hydrology for the southeastern Mediterranean wasmainly regulated by Nile River runoff, which in turn was controlled by climate forcing. Being affected by orbital forcing, and the position of the Intertropical Convergence Zone (ITCZ), planktic foraminiferal data (assemblages, stable isotopes, and size properties) indicate th...

Rose Bengal stained foraminiferal assemblages were analysed along a five-station bathymetric transect across the core and the lower part of the oxygen minimum zone (OMZ) on the Indian margin of the Arabian Sea. Sediment cores were collected using the manned submersible Shinkai 6500 during RV Yokosuka cruise YK08-11 in the post-monsoon season (Octob...

A unique high-resolution record from the Nile prodelta has been investigated in order to study past hydrological and climatic changes in the southeastern Levantine region over the last 13 cal ka BP. To this end, we used planktic foraminifera (accumulation rates, diversity, assemblages and size properties) as bioindicators of the ecological characte...

Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea oxygen minimum zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom water oxygenation (BWO), pore water chemistry and organic matter (organic carbon and phytopigment) distribution. A series o...

Dead (sub-fossil) benthic foraminiferal faunas (>150 µm) were investigated at 39 stations sampled in the Rhône prodelta (Gulf of Lions, NW Mediterranean) in June 2005 and September 2006 (MINERCOT 2 and BEHEMOTH cruises). Cluster analyses based on these foraminiferal assemblages divide our study area into four main thanatofacies directly related to...

Live (Rose Bengal stained) benthic foraminifera from the Murray Ridge, within and below the northern Arabian Sea Oxygen Minimum Zone (OMZ), were studied in order to determine the relationship between faunal composition, bottom-water oxygenation (BWO), pore-water chemistry and organic matter (organic carbon and phytopigment) distribution. A series o...

Benthic and planktic foraminiferal assemblages from two sediment cores (2,000 m depth, 44°33′N, 2°45′W) were analyzed to first compare modern and dead faunas and next to study changes in the hydrology of the southeastern Bay of Biscay (SE BoB) over the last 12.8 cal ka BP. Considering benthic ecosystem characteristics, the first part of the paleore...

The southeastern part of the Bay of Biscay is under the combined influence of the eastern branch of the North Atlantic Current (NAC) and coastal river plumes. The objective of this study is to use foraminiferal distribution from a 3 m high resolution record (SE Bay of Biscay; 550 m water depth) as proxies to evaluate the hydrological pattern of the...

Although foraminifera are a dominant component of many marine benthic communities, quantification of their predation on prokaryotes remains an experimental challenge. We have developed an approach that allows us to study grazing by adult specimens of the calcareous species Haynesina germanica and Ammonia beccarii, and the single-chambered agglutina...

Whether eustatic sea-level rise through the Holocene has been punctuated or continuous has remained controversial for almost two decades. Resolving this debate has implications for predicting future responses of remaining ice sheets to climate change and also for understanding the drivers of human settlement and dispersal patterns through prehistor...

In a 10-stations bathymetrical transect in the Bay of Biscay, we observed important changes in the density, composition and microhabitats of live foraminiferal faunas from the outer continental shelf to the abyssal plain. Four zones are recognised: (1) at the upper continental shelf (140m water depth), foraminiferal densities are very high and the...

The microhabitats and the composition of living benthic foraminiferal faunas in the sediments deposited off the Rhône River mouth are directly influenced by the Rhône River input. In this shallow-water environment (20-98 m water depth), the vertical distribution of the species is not well defined, probably due to the low penetration of oxygen into...

Benthic foraminifera were collected in the Rhône prodelta (Gulf of Lions, Mediterranean Sea), an enriched zone with high organic matter content. In June 2005, sediment cores were sampled at depths ranging from 20 to 100 m. Four distinct foraminiferal assemblages were determined in the study area, reflecting the geographical distribution of the impa...

Living (rose-Bengal stained) benthic foraminifera were investigated at 20 stations sampled in September 2006 in the prodelta of the Rhône river (Gulf of Lions, NW Mediterranean, BEHEMOTH cruise). The depth of these stations ranges between 15 and 100 m depth. An important dataset of environmental parameters (temperature, salinity, granulometry, pore...

By comparing benthic foraminiferal and macrofaunal responses to sewage sludge disposal in the Firth of Clyde (Scotland), we wanted to investigate the possibility of using foraminifera as bio-indicators of marine environmental degradation. Both groups present a similar distributional pattern, with poor faunas composed of species tolerant to strong o...

Since 2003 we have tested the use of benthic foraminiferal faunas as bio-indicators of highly biodegradable oil-based drill fluids and cuttings. In this paper we present data for 4 sites off western Africa (Angola, Congo and Gabon), with water depths varying from 30 to 670 m. A very similar faunal response to environmental perturbation is found in...

The aim of this work is to evaluate the potential utilisation of benthic foraminifera as bioindicators of eutrophication phenomena in open marine environments. More precisely, we have compared different types of eutrophicated environments, in natural (sediments of the Rhône prodelta) and anthropogenic conditions (oil drill cuttings off Congo and Ga...

[1] We have compiled results obtained from four high sedimentation rate hemipelagic sequences from the Celtic sector of the NW European margin ( NE Atlantic) to investigate the paleoceanographic and paleoclimatic evolution of the area over the last few climatic cycles. We focus on periods characteristic of deglacial transitions. We adopt a multipro...

Deglacial laminated facies on the NW European continental margin: The hydrographic significance of British-Irish Ice Sheet deglaciation and Fleuve Manche paleoriver discharges F. Eynaud and S. Zaragosi

We have compiled results obtained from four high sedimentation rate hemipelagic sequences from the Celtic sector of the NW European margin (NE Atlantic) to investigate the paleoceanographic and paleoclimatic evolution of the area over the last few climatic cycles. We focus on periods characteristic of deglacial transitions. We adopt a multiproxy se...

We present a study of benthic foraminiferal. faunas from the outer continental shelf off Congo (tropical West Africa), with the aim to determine the impact of the discharge of oily drill cuttings on the sea floor environment, to judge the regenerating capacity of the benthic ecosystem, and to investigate the possibility to develop an environmental...

During E&P offshore activities, and in particular during drilling operations, the living conditions of the flora and fauna on the seabed may be disturbed. The paper describes the study made for assessing the actual impact of the discharged cuttings, the regenerating capacity of the ecosystem and the medium and long-term recolonization processes, ba...

Core MD03-2692 was retrieved in a water-depth of 4064 m on the Celtic margin (Bay of Biscay) during the SEDICAR cruise onboard the RV Marion Dufresne II. It covers the last 360 ka in a total length of 39 m. Multidisciplinary analyses have been applied to this sequence with the aim of studying the palaeoclimatic and palaeoenvironmental signals of th...

High resolution paleoclimatic and paleoceanographic studies have shown that the orbital forcing may not have been the only control on ice sheet growth and decay (e.g. Heinrich events), then suggesting major feedback mechanisms implying both the atmosphere, the cryosphere, the oceans and the biosphere. Global climate modeling is one of the best meth...

Ce travail de thèse a pour objectif d'évaluer la possibilité d'utilisation des foraminifères benthiques comme bio-indicateurs des phénomènes d'eutrophisation en milieu marin ouvert. Le but de notre étude est de comparer différents types d'environnements eutrophiés, sous des conditions naturelles (sédiments du prodelta du Rhône) et anthropiques (déb...