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See detailPaleoenvironmental implications in the dried lake sediments (Amik Lake, Southern Turkey)
El Ouahabi, Meriam ULg; Hubert, Aurelia ULg; Vander Auwera, Jacqueline ULg et al

Poster (2016, July)

The Amik Basin in the Eastern Mediterranean region has been continuously inhabited since 6000 – 7000 BC. The study focuses on the sedimentary record of the Amik Lake located in the central part of the ... [more ▼]

The Amik Basin in the Eastern Mediterranean region has been continuously inhabited since 6000 – 7000 BC. The study focuses on the sedimentary record of the Amik Lake located in the central part of the basin. Our objective is to constrain major paleo-environmental changes in the area over the last 4000 years and to unravel possible human impacts on the sedimentation. A diverse array of complementary methods was applied on the 6 m long record. Mineralogical (XRD), and geochemical (XRF) analyses were performed. The age of the record is constrained combining radionuclide and radiocarbon dating. A high sedimentation rate of 0.12 cm/yr was inferred at the studied site. The 4000 years (since ~1800 BC) long record shows that significant fluctuations of the lake level and the riverine system inflow into the Amik Lake occurred. The Late Bronze lowstand led to punctual dryings of the lake at the end of the Bronze/Iron Age transition. At that time, the rivers yielded a large terrigenous input linked to strong soil erosion related mainly to deforestation and exploitation of mineral resources. During the Roman and later periods, upland soils were partly depleted and the riverine system completely transformed by channelization (anthropic) that led to a marshification of the Amik Basin [1]. Chemical and mineralogical composition of sediments is quite diversified reflecting the significant geological variation of drainage basins. Periods with strong aggradation linked to major increase in erosion were identified and characterized by high amount of Cr, Ni and Zr. Levels relatively rich in fluorite, richterite, enstatite, hornblende and chrysotile are a result of the erosion of the ophiolitic rocks from the surrounding Amanos Mountains. These levels are interpreted as periods of relatively high physical erosion, while more humid periods led to more intensive weathering. Consequently, the dominance of kaolinite, muscovite/illite and talc indicates a climate with contrasting seasons. During the most recent period a marked increase in terrigenous minerals associated with a rise in dolomite indicates ungoing erosion as well as the drying-out of the lake. [1] T.J. Wilkinson, L. Rayne, Water History, 2, 115-144 (2010). [less ▲]

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See detailThe last millenia sedimentary record of Lago Esponja from Northern Chilean Patagonia
Fagel, Nathalie ULg; Alvarez, Denisse; Araneda, Alberto et al

Poster (2016, April 20)

We evaluate the climate and environmental variability of Northern Chilean Patagonia during the Last Millennia, using a multi-proxy analysis of a sediment core from Lago Esponja (45°09’S, 72°08’W). The ... [more ▼]

We evaluate the climate and environmental variability of Northern Chilean Patagonia during the Last Millennia, using a multi-proxy analysis of a sediment core from Lago Esponja (45°09’S, 72°08’W). The lake is located in the region of Aysen del General Carlos Ibanez del Campo, in NW Patagonia. The study focuses on a multiproxy analysis of sedimentary records. The longest core (150 cm long) was collected in 2014 at 40 m depth. The sediment, which is composed of light brown organic-rich clayey silt, was analyzed for sedimentology (grain size, magnetic susceptibility organic matter and biogenic silica content), mineralogy (X-ray diffraction) and geochemistry (elemental and isotopic analyses of C and N, XRF core-scaner at 1 mm resolution). The radiocarbon ages, measured on 3 macro-remains, demonstrate that the core covers the last 6.700 years. The sedimentation rate ranges between 0.1 mm/yr in the lower section (100-150 cm) and 0.4 mm/yr in the upper meter. Visual descriptions and Scopix radiographies show that the sediment record is finely laminated except a massive decimetric coarser and darker layer corresponding to a tephra (estimated age 700AD±50). Magnetic susceptibility (confirmed by scopix radiographies) highlights the presence of 8 additional millimetric tephra layers. The biogenic silica content of the sediment is low (mean 5%). Diatom assemblage is dominated by benthic and acidophilous species, with high saprobic values. None marked changes were observed regarding the dynamic of the lake. The high organic matter content (mean 15%) and its high C/N ratio (12.7) throughout the core indicate inputs of allochtonous and terrestrial organic matter. Such parameters present high sediment variability also marked by changes in the chemical composition. The laminations reflect changes in the allochtonous sedimentary inputs, with high terrestrial inputs during wetter conditions in relation with the Westerlies. The sedimentary records of Lago Esponja will be compared with Eastern lacustrine record from the same latitude in order to confirm the climate-driven record. [less ▲]

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See detailChemical and mineralogical proxies of erosion episodes in the dried lake sediments (Amik Lake, Southern Turkey): paleoenvironmental implications
El Ouahabi, Meriam ULg; Hubert, Aurelia ULg; Lebeau, Héléne et al

Poster (2016, April 17)

The Amik Basin in the Eastern Mediterranean region has been continuously occupied since 6000-7000 BC. The landscape has sustained with highly variable anthropic pressure culminating during the Late Roman ... [more ▼]

The Amik Basin in the Eastern Mediterranean region has been continuously occupied since 6000-7000 BC. The landscape has sustained with highly variable anthropic pressure culminating during the Late Roman Period when the Antioch city reached its golden age. The basin also sustained a high seismic activity (M≥7) as it is a releasing step-over along the Dead Sea Fault. The study focuses on the sedimentary record of the Amik Lake occupying the central part of the Basin. Our objective is to constrain major paleo-environmental changes in the area over the last 4000 years and to unravel possible human impacts on the sedimentation. A diverse array of complementary methods was applied on the 6 m long record. High resolution of mineralogical (XRD) and geochemical (XRF) analyses were performed. Quantitative mineralogical phases of sediments by the Rietveld method were computed using Topaz software. The age of the record is constrained combining radionuclide and radiocarbon dating, and checked using the correlation between the earthquake history and rapidly deposited layer identified. A high sedimentation rate of 0.12 cm/yr was inferred at the coring site. The 4000 years old record shows that significant fluctuations of the lake level and the riverine system inflow into the Amik Lake occurred. The Late Bronze lowstand leaded to punctual dryings of the lake at the end of the Bronze/Iron transition marked by the collapse of the Hittite Empire and during the Dark ages. At that time, the riverine was carrying a large terrigenous input linked to strong soil erosion related to deforestation, exploitation of mineral resources and the beginning of upland cultivation. During the Roman Period and in the later periods, upland soils were partly depleted and the riverine system completely transformed by channelization that leaded to a mashification of the Amik Basin. Chemical and mineralogical composition of sediments is quite diversified reflecting the significant geological variation of drainage basins. Abundant calcareous minerals, especially calcite, aragonite, dolomite and small amount of wollastonite characterize the different sedimentary levels recorded in the lake. Levels relatively rich in fluorite, richerite, enstatite, and wollastonite are a result of the erosion of the ophiolitic rocks from the surrounding Amanos Mountains. These levels are interpreted as corresponding to relatively high erosive periods, while more humid periods lead to more intensive weathering and consequently to the dominance of kaolinite, muscovite/illite and talc more advanced in the relative stability scale, indicating a climate with contrasting seasons. During the most recent Period a marked increase in terrigeneous minerals associated with a rise in dolomite indicates ungoing erosion as well as the drying-out of the lake. [less ▲]

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See detailEarthquake imprints on a lacustrine deltaic system: the Kürk Delta along the East Anatolian Fault (Turkey)
Hubert, Aurelia ULg; El Ouahabi, Meriam ULg; Garcia-Moreno, David et al

in Sedimentology (2016)

Deltas contain sedimentary records that are not only indicative of water level changes, but also particularly sensitive to earthquake shaking typically resulting in soft-sediment-deformation structures ... [more ▼]

Deltas contain sedimentary records that are not only indicative of water level changes, but also particularly sensitive to earthquake shaking typically resulting in soft-sediment-deformation structures. The Kürk lacustrine delta lies at the south-western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault (EAF), which has generated earthquakes of magnitude 7. In this paper we have reevaluated water level changes and earthquake shaking that have affected the Kürk Delta combining geophysical data (seismic-reflection profiles and side-scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water level changes provides a temporal framework for the depositional record. In addition to the commonly soft-sediment-deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake-induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a paleoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the EAF. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (137Cs and 210Pb), two major sedimentary events were attributed to the 1874-1875 EAF earthquake sequence. Their sedimentological characteristics were determined by X-ray imagery, XRD, LOI, grain-size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post-seismic sediment reworking of earthquake-triggered landslides. [less ▲]

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See detailSubmarine Paleo-earthquake record of the Cinarcik segment of the North Anatolian Fault in the Marmara Sea (Turkey)
Drab, Laureen; Hubert, Aurelia ULg; Schmidt, Sabine et al

in Bulletin Seismological Society of America (2015), 105

The submarine part of the North Anatolian Fault (NAF) in the Marmara Sea is a significant hazard for the city of Istanbul (Turkey). The use of paleoseismological data to provide an accurate seismic risk ... [more ▼]

The submarine part of the North Anatolian Fault (NAF) in the Marmara Sea is a significant hazard for the city of Istanbul (Turkey). The use of paleoseismological data to provide an accurate seismic risk assessment for the area is constrained by the fact that the NAF system is submarine near Istanbul; thus a history of paleoearthquakes can be inferred only by using sediment cores. Here a record of turbidites was obtained in two cores and used to reconstruct the earthquake history along a main branch of the NAF, the Cinarcik Segment. Kullenberg core Klg04 (4 m long) was collected during Marmarascarps mission from a berm north of the fault and a second core (Klg03, 3.5 m long) was positioned in the Cinarcik Basin, 3 km south of the fault. Sedimentary sequences in the two cores were correlated using variations in Ca/Ti ratio, which reflect the local aquatic productivity compared with more terrigenous input. The turbidites between the two cores were then classified to distinguish the synchronous ones from the other ones. Radionuclide measurements suggest that the most recent turbidite recorded in both cores was triggered by the M=7.3 1894 earthquake. We conclude that the turbidites are earthquake-generated, based on: 1) their distinctive sedimentological and geochemical signatures, previously described and applied in the Marmara Sea; 2) the correlation of turbidites between cores at berm and basin sites; 3) the match of the most recent turbidites with a 19th century historical earthquake; and 4) the elimination of others processes. Because of its specific geomorphological location, core Klg04 likely records only mass wasting events related to the rupture on the Cinarcik Segment. To date older turbidites, we used 14C and paleomagnetic data to build an OxCal age model with a local reservoir correction (ΔR) of 400±50 yr. The Cinarcik Segment is found to have ruptured in AD1894, AD1509, sometime in the 14th century, AD989, AD740 and in the 5th century and have a mean recurrence interval of rupture between 243 and 396 years. Following the age model obtained we finally used the earthquake record history of the Cinarcik Segment to infer the rupture history of adjacent segments of the North Anatolian Fault during six earthquake cycles over the past 1500 years. [less ▲]

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See detailSeismically-triggered organic-rich layers in recent sediments from lake Gollukoy (North Anatolian Fault, Turkey
Avşar, Ulaş; Hubert, Aurelia ULg; De Batist, Marc et al

in Quaternary Science Reviews (2014), 103

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See detailThe earthquake sedimentary record in the the Sea of Marmara, Turkey
Hubert, Aurelia ULg; Drab, Loreen; Schmidt, Sabine et al

Conference (2012, October)

The submarine part of the North Anatolian Fault (NAF) is a very significant hazard for the 12 million people living in Istanbul (Turkey). An accurate seismic risk assessment necessitates ... [more ▼]

The submarine part of the North Anatolian Fault (NAF) is a very significant hazard for the 12 million people living in Istanbul (Turkey). An accurate seismic risk assessment necessitates paleoseismological data, which can be retrieved in the Marmara Sea by using sedimentary cores. We present here a record of turbidites obtained in cores spanning the Tekirdag ̆ Basin, the Western High, the Central Basin, and the Cinarcik Basin. In the Tekirdag and Western High the turbidites are synchronous pointing to shaking by earthquakes as a triggering mechanism. Generally seismoturbidites in the Marmara Sea are distinguished from other turbidites based in their large extension, their particular granulometric and their particular geochemical characteristics. The 210Pb and 137Cs radionucleides measurements have also shown that the M=7.4 1912 Mürefte earthquake and the M=7.3 1894 Prince's Island earthquake have left a distinctive sedimentary imprint at the top of the studied cores. The chronology of other seismoturbidites is built combining radiocarbon dating and secular variation patterns of paleo-declination and paleo-inclination. Finally the obtained record is compared to the historical seismicity record. [less ▲]

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See detailLast millenium environmental changes in Lake Bertrand sediments, Chilean Patagonia
Sacré, Vincent ULg; Fagel, Nathalie ULg; Schmidt, Sabine et al

Poster (2012, April 23)

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See detailThe earthquake sedimentary record in marine sediment from cores in the western part of the Marmara Sea, Turkey
Drab, Laureen; Hubert, Aurelia ULg; Schmidt, Sabine et al

Conference (2012, April)

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See detailThe earthquake sedimentary record in the Western part of the Sea of Marmara, Turkey
Drab, Laureen; Hubert, Aurelia ULg; Schmidt, Sabine et al

in Natural Hazards & Earth System Sciences (2012)

The submarine part of the North Anatolian Fault (NAF) is a very significant hazard for the 12 million people living in Istanbul (Turkey). An accurate seismic risk assess- ment necessitates ... [more ▼]

The submarine part of the North Anatolian Fault (NAF) is a very significant hazard for the 12 million people living in Istanbul (Turkey). An accurate seismic risk assess- ment necessitates paleoseismological data, which can be re- trieved in the Sea of Marmara only using sedimentary cores. Here a record of turbidites was obtained in five cores span- ning the Tekirdag ̆ Basin, the Western High and the Central Basin linked by the Tekirdag ̆ Fault Segment. The turbidites are synchronous at different sites across basins and structural highs. The only possible triggering mechanism is thus shak- ing related to major earthquakes. In particular the M=7.4 1912 Mu ̈refte earthquake has let a distinctive sedimentary imprint in all the studied cores. Radiocarbon dating implies a turbidite recurrence interval of about 300 years. In addi- tion the low number of turbidites documented in the Central Basinsuggestsquasi-synchronousrupturesoftheTekirdag ̆ Segment and the adjacent Central Segment of the NAF or a partial seismic slip on the Central Segment. Both scenarii have implications regarding seismic hazard. Finally through we obtained a reliable paleoseismological record of the rup- tures along the Tekirdag ̆ Segment, further chronological con- straints are needed to accurately date the events and correlate them with known historical earthquakes. [less ▲]

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See detailTurbiditic sedimentary record in the different basins of the Sea of Marmara
Hubert, Aurelia ULg; Drab, Laureen; Schmidt, Sabine et al

Conference (2011, June 13)

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See detailParticulate carbon export during a bloom of Emiliania huxleyi in the Northwest European continental margin (northern Bay of Biscay)
Schmidt, Sabine; Harlay, Jérôme ULg; Borges, Alberto ULg et al

Poster (2011, April 03)

Coccolithophores, the dominant pelagic calcifiers in the oceans, play a key role in the marine carbon cycle through calcification, primary production and carbon export, the main drivers of the biological ... [more ▼]

Coccolithophores, the dominant pelagic calcifiers in the oceans, play a key role in the marine carbon cycle through calcification, primary production and carbon export, the main drivers of the biological CO2 pump. Massive blooms of Emiliania huxleyi are observed each year at the continental margin of the Bay of Biscay. The BG02/11 cruise (RV Belgica), supported by near-real time remote sensing data, was conducted in early May 2002, along a transect on the outer shelf of the Northern Bay of Biscay between the La Chapelle Bank (southern region of the transect) and Goban Spur (northern region of the transect) (47.0°-50.5°N, 5.0°-11.0°W). Biogeochemical variables including primary production, calcification, partial pressure of CO2 (pCO2), chlorophyll-a (Chl-a), particle load, particulate organic and inorganic carbon (POC, PIC), Th-234 were measured in surface waters to assess particle dynamics, and carbon export in relation to the development of a coccolithophore bloom. We observed a marked northward decrease in water irradiance, Chl-a concentration and calcification rates: the bloom exhibited lower values and may have been less well developed in the Goban Spur area. There was also a large northward decrease in particulate 234Th settling fluxes along the transect from La Chapelle Bank to Goban Spur. The export fluxes of POC and PIC from the top 80 m, determined using the ratios of POC and PIC to Th-234 of particles, ranged from 81 to 323 mgC m-2 d-1 and from 30 to 128 mgC m-2 d-1, respectively. The highest fluxes were observed in waters presenting a well-developed coccolithophore bloom, as shown by high reflectance of surface waters. Despite the high calcification rates at the southernmost stations, surface waters were a net sink of atmospheric CO2 during this cruise. These results tend to demonstrate the enhancement of coccolithophore blooms on the efficiency of the surface community to export carbon to deep ocean. However, improvements in the estimation of POC and PIC export during coccolithophore blooms are needed to not only understand the present calcification to primary production (C:P) ratio, but also to help understand future sequestration of organic and inorganic carbon to the deep ocean. [less ▲]

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See detailBenthic remineralization in the northwest European continental margin (northern Bay of Biscay)
Suykens, Kim; Schmidt, Sabine; Delille, Bruno ULg et al

in Continental Shelf Research (2011), 31

We report a dataset of sediment characteristics and biogeochemical fluxes at the watersediment interface at the northwest European continental margin (northern Bay of Biscay). Cores were obtained in June ... [more ▼]

We report a dataset of sediment characteristics and biogeochemical fluxes at the watersediment interface at the northwest European continental margin (northern Bay of Biscay). Cores were obtained in June 2006, May 2007 and 2008, at 18 stations on the shelf break (120 to 180 m), and at 2 stations on the continental slope (520 m and 680 m). Water-sediment fluxes of dissolved oxygen (O2), total alkalinity (TA), nitrate (NO3-), and dissolved silicate (DSi) were measured at a total of 20 stations. Sediment characteristics include: grain size, chlorophyll-a (Chl-a) and phaeopigment (Phaeo) content, particulate organic (POC) and inorganic (PIC) carbon content, and lead-210 (210Pb) and thorium-234 (234Th) activities. Sediments were sandy (fine to coarse) with organic matter (OM) (1.0 - 4.0 %) and Chl-a (0.01 - 0.95 μg g-1) contents comparable to previous investigations in the same region, and a relatively high PIC fraction (0.8 - 10.2 %). Water-sediment O2 fluxes (-2.4 to -8.4 mmol O2 m-2 d-1) were low compared to other coastal environments and correlated well with OM and Chl-a content. 234Th activity profiles indicated that Chl-a sediment content was mainly controlled by physical mixing processes related to local hydrodynamics. The correlation between water-sediment fluxes of O2 and NO3- indicated a close coupling of nitrification/denitrification and total benthic organic carbon degradation. Dissolution of biogenic silica (0.05 to 0.95 mmol m-2 d-1) seemed uncoupled from organic carbon degradation, as characterized by water-sediment O2 fluxes. The link between water-sediment fluxes of TA and O2 indicated the occurrence of metabolic driven dissolution of calcium carbonates (CaCO3) in the sediments (~ 0.33 ± 0.47 mmol m-2 d-1) which represented ~ 1 % of the pelagic calcification rates due to coccolithophores measured during the cruises. These CaCO3 dissolution rates were below those reported in sediments of continental slopes and of the deep ocean, probably due to the high over-saturation with respect to CaCO3 of the water column overlying the continental shelf sediments of the northern Bay of Biscay. Rates of total benthic organic carbon degradation were low compared to water column rates of primary production and aphotic community respiration obtained during the cruises. [less ▲]

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See detailSedimentological fingerprints of paleoseimic activity revealed from lake sediments: a case study from the North Anatolian Fault (NAF), Turkey
Avsar, Ulas; Hubert, Aurelia ULg; Fagel, Nathalie ULg et al

in Abstracts with Programs - Geological Society of America (2010, October)

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophorid blooms in the Northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

Poster (2010, May 03)

Balch et al. (2007) evaluated global pelagic contemporary calcification from remote sensing data (mainly associated to coccolithophores) to 1.6 ± 0.3 Pg PIC yr-1 (1 Pg = 1015 g; PIC = particulate ... [more ▼]

Balch et al. (2007) evaluated global pelagic contemporary calcification from remote sensing data (mainly associated to coccolithophores) to 1.6 ± 0.3 Pg PIC yr-1 (1 Pg = 1015 g; PIC = particulate inorganic carbon). This would imply that coccolithophores would be the most important pelagic calcifier in the oceans, since other estimates of contemporary global pelagic calcification range between 0.7 Pg PIC yr-1 based on accumulation rates and sediment trap data (Milliman et al. 1999), and 1.4 Pg PIC yr-1, based on the seasonal cycle of total alkalinity (TA) in the euphotic zone (Lee 2001). The development of coccolithophorid blooms affects the seawater carbonate chemistry, and air-sea CO2 fluxes, through the organic carbon pump and the carbonate counter-pump. The ratio between calcification (carbonate counter-pump), and organic carbon production (organic carbon pump), the C:P ratio, depends on the life cycle (bloom development), and growth conditions of coccolithophores. At the onset of the coccolithophorid bloom, when nutrients are available for growth, organic carbon production dominates over calcification (C:P << 1, the so-called organic phase). At the end of the bloom, in nutrient depleted conditions, and high irradiances (due to stronger stratification), organic carbon production decreases and calcification increases (C:P ≤ 1, the so-called inorganic phase). Several manipulative experiments to test the effect of ocean acidification on coccolithophores have shown that while calcification would decrease, the export of organic carbon would increase mainly through increasing transparent exopolymer particles (TEP) production. For a credible implementation in mathematical models of such feed-back mechanisms to allow the projection of a future evolution of carbon biogeochemistry under global change, it is required to understand present day biogeochemistry and ecology of naturally occurring pelagic calcifying communities. In particular, the overall effect of phytoplankton communities on the C:P ratio, and the net effect on carbonate chemistry, and related air-sea CO2 fluxes. [less ▲]

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See detailParticle export with coccolithophorid Emiliania huxleyi blooms in the Bay of Biscay. XII International Symposium on Oceanography of the Bay of Biscay
Schmidt, Sabine; Harlay, Jérôme ULg; Roevros, Nathalie et al

Conference (2010, May 03)

Coccolithophores, one of the most productive calcifying phytoplanktonic groups, often form massive blooms in the temperate and sub-polar oceans, and in particular at continental margins and in shelf seas ... [more ▼]

Coccolithophores, one of the most productive calcifying phytoplanktonic groups, often form massive blooms in the temperate and sub-polar oceans, and in particular at continental margins and in shelf seas. Export of organic carbon and calcification are the main drivers of the biological CO2 pump and are expected to change with oceanic acidification. Coccolithophores are also a major producer of dimethyl sulphide (DMS), whose oxidation products of DMS affect the number and size distribution of tropospheric cloud condensation nuclei, with possible consequences for cloud albedo and heat balance. Coccolithophores are further known to produce transparent exopolymer particles (TEP) that promote particle aggregation and sinking. Coccolithophores play thus key roles in the global carbon, carbonate and sulphur cycles, and, in turn, in climate regulation. The objectives of the Belgian CCCC project (Role of Oceanic Production and Dissolution of Calcium Carbonate in Climate Change) was to evaluate the role in climate regulation of calcification, primary production and export processes during coccolithophorid blooms. Field investigations, supported by remote sensing data, were conducted in the Northern Gulf of Biscay on the continental shelf and slope region (47°- 50°30'N, 5°-11°W) where coccolithophorid blooms are frequently and recurrently observed. During the cruises in May 2002 and 2003 on board the r/v Belgica, fundamental variables (temperature, salinity, primary production, Chl. a, particulate organic carbon) were measured in the water column. To estimate the spatial variability of particle dynamics in surface waters in relation with the coccolithophorid bloom development, we had employed the natural radionuclide 234Th. The preferential scavenging of the particle-reactive daughter 234Th (t1/2= 24.1 days) while its soluble parent, 238U, remains nearly constant, provides an appropriate tool for assessing temporal variations of the removal of particles from surface waters, at a time scale of weeks. The two cruises have permitted to sample two different situations; in particular in May 2002, it was possible to sample a well-developed bloom. As a result, 234Th present contrasted profiles in the upper 0-80 m during the two investigations. In May 2003, 234Th was nearly in equilibrium with 238U (its radioactive parent) along with high particulate activities: this seems to indicate an early bloom situation with low grazing fluxes. On the opposite, in May 2002, deficits of 234Th toward 238U were indicating more efficient particle export from upper waters. Synthesis of the acquired data will be discussed to compare particle dynamics and the magnitude of particulate carbon export using 234Th and POC data at different states of coccolithophorid bloom in the Northern Gulf of Biscay. [less ▲]

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See detailBenthic remineralization in the northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Schmidt, Sabine; Delille, Bruno ULg et al

Poster (2010, May 02)

We report a data-set of sediment characteristics and biogeochemical fluxes at the water-sediment interface at the northeast European continental margin (northern Bay of Biscay). Cores were obtained in ... [more ▼]

We report a data-set of sediment characteristics and biogeochemical fluxes at the water-sediment interface at the northeast European continental margin (northern Bay of Biscay). Cores were obtained in June 2006, May 2007 and 2008, at 8 stations on the shelf break (120 to 180 m), and at 2 stations on the continental slope (520 m and 680 m). Sediment-water fluxes of dissolved oxygen (O2), total alkalinity (TA), nitrate (NO3-), and dissolved silicate (DSi) were measured at a total of 20 stations. Sediment characteristics include: grain size, chlorophyll-a (Chl-a) and phaeopigment (Phaeo) content, particulate organic (POC) and inorganic (PIC) carbon content, and 234Th and 210Pb activities. Sediments were sandy (fine to coarse) with organic matter (OM) (1.0 - 4.0 %) and Chl-a (0.01 - 0.95 µg g-1) contents comparable to previous publications in the same region, and a relatively high PIC fraction (0.8 - 10.2 %). Sediment-water O2 fluxes (-2.4 to -8.4 mmol O2 m-2 d-1) were low compared to other coastal environments and correlated well with OM and Chl-a content. 234Th activity profiles indicated that Chl-a sediment content (apparently the main driver of total benthic organic carbon degradation) was mainly controlled by physical mixing processes related to local hydrodynamics. The correlation between sediment-water fluxes of O2 and NO3- indicated a close coupling of nitrification/denitrification and total benthic organic carbon degradation. Dissolution of biogenic silica (0.05 to 0.95 mmol m-2 d-1) was uncoupled from organic carbon degradation, characterized by sediment-water O2 fluxes. The link between sediment-water fluxes of TA and O2 indicated metabolic driven dissolution ( 0.33 +/- 0.47 mmol m-2 d-1) of calcium carbonates (CaCO3) in the sediments which represented ~1 % of the pelagic calcification rates due to coccolithophores. These rates were below those reported in sediments of continental slopes and of the deep ocean, probably due to the high over-saturation with respect to CaCO3 of the water column overlying the continental shelf sediments of the northern Bay of Biscay. Rates of total benthic organic carbon degradation and CaCO3 dissolution were low compared to water column rates of primary production, aphotic community respiration and CaCO3 production obtained during the cruises. [less ▲]

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See detailThe earthquake sedimentary record of the Marmara Sea, Turkey
Drab, Laureen; Hubert, Aurelia ULg; Schmidt, Sabine et al

in Geophysical Research Abstracts (2010, May)

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See detailPaleolimnological and Sedimentological Traces of the 1943 (Ms=7.3) Earthquake in the sediments of Ladik Lake, Samsun/Turkey
Ulas, Avsar; Hubert, Aurelia ULg; Fagel, Nathalie ULg et al

in Geophysical Research Abstracts (2009, April), 11(EGU2009-12641-1),

Detailed reference viewed: 51 (2 ULg)