A new method for the measurement of biogenic silica in suspended matter of coastal waters: using Si:Al ratios to correct for the mineral interference
Measurement of biogenic silica (BSi) in the suspended matter of estuarine and coastal waters is not trivial because of the interference of lithogenic silica (LSi) that can represent up to 90% or more of the total particulate silica within the water column. Till date, no method has provided a satisfying way to correct this mineral interference when the most common wet-alkaline digestions are used. The most recently published method, Ragueneau and Tréguer (Mar. Chem., 45 (1994) 43–51), presents the disadvantage to be site-specific. In this paper, we present a robust method to measure BSi in all estuarine and coastal waters and correction for LSi interference. It consists of a double wet-alkaline digestion where the filter sample is submitted to a first digestion (0.2 M NaOH, pH 13.3) at 100 °C for 40 min. At the end of this first leach, all the BSi and part of the LSi have been converted into Si(OH)4. Si and Al concentrations ([Si]1 and [Al]1) in the supernatant are analyzed. After rinsing and drying, the filter is submitted to a second digestion, exactly identical to the first one, leading to the determination of the (Si:Al)2 ratio that is characteristic of the silicate minerals present in the sample. The corrected biogenic silica concentration is thus given by [BSi]=[Si]1–[Al]1(Si:Al)2. There are three basic assumptions behind the proposed method: (1) all the Al measured during the first leach is derived from silicate minerals, (2) all the biogenic silica has been digested during the first leach, so the second leach addresses the Si:Al ratio of silicate minerals only, and (3) silicate minerals dissolve during the second digestion exactly as during the first digestion, i.e. with a similar Si:Al ratio. Theoretical considerations and field experiments demonstrate that the above assumptions are accurate. Blanks and repeatability tests indicate that the detection limit ranges from 0.6 to 1.5 nmol of BSi present on the filter and that the uncertainty is close to 10%. This method was successfully applied to more than 200 samples from five different coastal areas, demonstrating the importance of this correction, which can represent up to 92% of the apparent BSi concentration determined after the first digestion.
(Continental Shelf Research. vol. 25, Issues (5-6), n° 0278-4343, pp. 697-710, 25/08/2026)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, VUB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS
Palynology of the northwestern Mediterranean shelf (Gulf of Lions): First vegetational record for the last climatic cycle
Palynology has been performed for the first time on Late Quaternary sediments of the Gulf of Lions. The aim is both to tighten the chronology of seismic profiles in the region, and to elucidate the vegetation of southern France during the Last Climatic Cycle. Four cores, taken on the shelf, mostly record Marine Isotope Stages (MIS) 1 and 2 and part of MIS 3 and MIS 5. The latter sediments might have been preserved in a paleodepression on the emergent shelf between the Rhône and the Hérault rivers. It would explain their preservation against transgression and regression erosions of more recent stages. This study also provides a synthesis of palynological continental data collected during the last 40 years in southern Europe. Preliminary comparisons made between the latter and new marine data demonstrate that refugia of Picea and Abies existed in southern France during MIS 3 and MIS 2. The dynamics of Artemisia, deciduous Quercus and Corylus, Abies and finally Fagus is also reconstructed for the last deglaciation. First results obtained in the Gulf of Lions confirm and complete that synthesis.
(Marine and Petroleum Geology. vol. 22, n° 0264-8172, pp. 845-863, 25/08/2026)
PEPS, UCBL, INSU - CNRS, CNRS, CBAE, UM2, EPHE, PSL, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS
Provenance of present-day eolian dust collected off NW Africa
Atmospheric dust samples collected along a transect off the West African coast have been investigated for their physical (grain-size distribution), mineralogical, and chemical (major elements) composition. On the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area. In addition, shipboard-collected atmospheric meteorological data, modeled 4-day back trajectories for each sampling day and location, and Total Ozone Mapping Spectrometer aerosol index data for the time period of dust collection (February-March 1998) were combined and used to reconstruct the sources of the groups of dust samples. On the basis of these data we were able to determine the provenance of the various dust samples. It appears that the bulk of the wind-blown sediments that are deposited in the proximal equatorial Atlantic Ocean are transported in the lower level (≳900 hPa) NE trade wind layer, which is a very dominant feature north of the Intertropical Convergence Zone (ITCZ). However, south of the surface expression of the ITCZ, down to 5°S, where surface winds are southwesterly, we still collected sediments that originated from the north and east, carried there by the NE trade wind layer, as well as by easterly winds from higher altitudes. The fact that the size of the wind-blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust's size distributions and measured wind strengths. However, a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of NW Africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial Atlantic.
(Journal of Geophysical Research: Atmospheres. vol. 110, n° 2169-897X, 25/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Fluorescence fingerprint of fulvic and humic acids from varied origins as viewed by single-scan and excitation/emission matrix techniques
Excitation/emission matrix (EEM), single-scan excitation and synchronous fluorescence spectra of a series of FA and HA from distinct environments are presented. The EEM plots show at least four spectral features whose corresponding Ex/Em pairs relate to the α', α, β and γ (or δ) fluorophores previously found in natural waters spectra. The α' and α peaks, which identify typical humic-like components, are present in all samples, independently of the organic matter (OM) source. In FA, their Ex/Em pairs are ~260 nm/460 nm and ~310 nm/440 nm, respectively. In HA their excitation and emission maxima are red-shifted, the corresponding Ex/Em pairs being located at ~265 nm/525 nm and ~360 nm/520 nm, respectively. The appearance of β and γ (or δ) peaks is dependent both on the OM origin and on HS aging. The former (Ex/Em ~ 320 nm/430 nm), that has been associated with the incidence of marine humic-like material, is present only in a few marine and estuarine HA. It emerges as a shoulder on the α peak and its detection is dependent on a balance between its magnitude and the magnitude and emission maxima location of the α peak. The γ (or δ) peak (Ex/Em ~ 275 nm/315 nm in FA, and ~275 nm/330 nm in HA), on the other hand, is better visualized in FA than in HA diagrams. It has typical protein-, mainly tryptophan-like, fluorescence properties and appears with varied significance in a few marine and estuarine samples being hardly detected in samples from exclusively terrestrial environments. It is also shown in this study that with selected λex, λem and Δλ values, regular emission, excitation and synchronous spectra can, together, provide a good picture of the OM sources and aging for extracted HS. \textcopyright 2004 Elsevier Ltd. All rights reserved.
(Chemosphere. vol. 58, n° 0045-6535, pp. 715--733, 25/08/2026)
UCS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Relationship between land-use in the agro-forestry system of les Landes, nitrogen loading to and risk of macro-algal blooming in the Bassin d`Arcachon coastal lagoon (SW France)
Nitrogen loading to the Bassin d`Arcachon coastal lagoon (SW France) was evaluated by studying land-use and nitrogen output in its 3001 km2 catchment. At present, the catchment is dominated by forestry (79%), while intensive agriculture occupies 9% of the surface. The N-output of two hydrological subunits, i.e. the Tagon subunit dominated by pine forestry and the Arriou II subunit comprising both forestry and intensive agriculture, were monitored for a seven year period (1996-2002). From these observations it was calculated that forestry contributes on average 1.6 kg total N ha-1 yr-1, which is dominated by organic nitrogen (DONCPON are 70% of N). On an areal basis, intensive agriculture contributes 26 times more than forestry, i.e. 41.6 kg total N ha-1 yr-1, which is mainly in the form of nitrate (65% of N). These data were upscaled to the catchment and the upscaling was validated by comparison to gauged nitrogen throughputs for the catchment of the Leyre river that is the major tributary to the system. Taking into account the other known N sources and the interannual variability in the catchment it was estimated that nitrogen loading to the lagoon was on average 90 kg ha-1 yr-1 (range from 54 to 126 kg ha-1 yr-1). The sandy soils of the catchment have a clear potential for denitrification, but anoxic conditions (waterlogged) and input of organic matter to fuel this process are required. Currently, agricultural practices and spatial planning do not make use of this potential. Nitrogen loading in the Bassin d`Arcachon is reflected by 10-40 µM nitrate concentrations in winter, which became depleted during spring as a result of uptake by vegetation. Short-term uptake experiments showed that the macroalga Monostroma obscurum is well adapted to temperatures between 10 to 20°C and competitive with respect to the seagrass Zostera noltii when the nitrate concentrations are above 10 µM. Spring conditions with high nitrate and high insolation are therefore favourable for M. obscurum and this species presents a high risk for algal blooming. In contrast, the macroalga Enteromorpha clathrata well adapted to summertime temperatures around 25°C, forms occasionally blooms in the lagoon. This phenomenon is limited due to the low DIN concentrations in summer.
(Estuarine, Coastal and Shelf Science. vol. 62, n° 0272-7714, pp. 453-465, 25/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR ADBX, CEMAGREF, UR REBX, CEMAGREF, IFREMER
The biogeography of major diatom taxa in Southern Ocean surface sediments: 3. Tropical/Subtropical species
This paper gives a modern circumscription of Tropical/Subtropical diatoms regarding their relationship with sea-surface temperatures (SST) and sea ice cover. Diatoms from 228 core-top sediment samples collected from the Southern Ocean were studied to determine the geographic distribution of eight major diatom species/taxa preserved in surface sediments generally located north of the Subantarctic Front. The comparison of the relative contribution of diatom species with modern February SST and sea-ice cover reveals species-specific sedimentary distributions regulated both by water temperatures and sea ice conditions. Although selective preservation might have played some role, their presence in surface and downcore sediments from the Southern Ocean are reliable indicators of high SST and poleward transport of waters from the Tropical/Subtropical Atlantic. Our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches. D
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 223, n° 0031-0182, pp. 49-65, 25/08/2026)
UTAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Gas transfer velocities in a tropical reservoir and its river downstream. Wind speed and rainfall effect
We have measured simultaneously the methane (CH4) and carbon dioxide (CO2) surface concentrations and fluxes in the Petit-Saut reservoir (French Guiana) and its tidal river (Sinnamary River) downstream the dam, during two field experiments in wet (May 2003) and dry season (December 2003). Gas fluxes were measured with floating chambers (FC) on the artificial lake and on the river, and with the eddy covariance (EC) technique for CO2 during a 24h experiment on the lake. For each chamber measurement, wind speed was measured at 1m above the water surface and recalculated at 10 m using the formulation proposed by Amorocho et DeVrie (1980). During the 24h EC experiment the wind speed at 10m (U10) and the rainfall rates were recorded by a meteorological station. For each flux measurement the gas transfer velocity normalized for a Schmidt Number of 600 was computed.
(Journal of Marine Systems, n° 0924-7963, 25/08/2026)
LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Palynology of the northwestern Mediterranean shelf (Gulf of Lions): First vegetational record for the last climatic cycle
Palynology has been performed for the first time on Late Quaternary sediments of the Gulf of Lions. The aim is both to tighten the chronology of seismic profiles in the region, and to elucidate the vegetation of southern France during the Last Climatic Cycle. Four cores, taken on the shelf, mostly record Marine Isotope Stages (MIS) 1 and 2 and part of MIS 3 and MIS 5. The latter sediments might have been preserved in a paleodepression on the emergent shelf between the Rhône and the Hérault rivers. It would explain their preservation against transgression and regression erosions of more recent stages. This study also provides a synthesis of palynological continental data collected during the last 40 years in southern Europe. Preliminary comparisons made between the latter and new marine data demonstrate that refugia of Picea and Abies existed in southern France during MIS 3 and MIS 2. The dynamics of Artemisia, deciduous Quercus and Corylus, Abies and finally Fagus is also reconstructed for the last deglaciation. First results obtained in the Gulf of Lions confirm and complete that synthesis.
(Marine and Petroleum Geology. vol. 22 (6-7), n° 0264-8172, pp. 845-863, 25/08/2026)
PEPS, UCBL, INSU - CNRS, CNRS, CBAE, UM2, EPHE, PSL, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS, UL2, UCBL, CNRS
Carbon dioxide and methane emissions and the carbon budget of a 10-year old tropical reservoir (Petit Saut, French Guiana)
The emissions of carbon dioxide (CO2) and methane (CH4) from the Petit Saut hydroelectric reservoir (Sinnamary River, French Guiana) to the atmosphere were quantified for 10 years since impounding in 1994. Diffusive emissions from the reservoir surface were computed from direct flux measurements in 1994, 1995, and 2003 and from surface concentrations monitoring. Bubbling emissions, which occur only at water depths lower than 10 m, were interpolated from funnel measurements in 1994, 1997, and 2003. Degassing at the outlet of the dam downstream of the turbines was calculated from the difference in gas concentrations upstream and downstream of the dam and the turbined discharge. Diffusive emissions from the Sinnamary tidal river and estuary were quantified from direct flux measurements in 2003 and concentrations monitoring. Total carbon emissions were 0.37 ± 0.01 Mt yr-1 C (CO2 emissions, 0.30 ± 0.02; CH4 emissions, 0.07 ± 0.01) the first 3 years after impounding (1994-1996) and then decreased to 0.12 ± 0.01 Mt yr-1 C (CO2, 0.10 ± 0.01; CH4, 0.016 ± 0.006) since 2000. On average over the 10 years, 61% of the CO2 emissions occurred by diffusion from the reservoir surface, 31% from the estuary, 7% by degassing at the outlet of the dam, and a negligible fraction by bubbling. CH4 diffusion and bubbling from the reservoir surface were predominant (40% and 44%, respectively) only the first year after impounding. Since 1995, degassing at an aerating weir downstream of the turbines has become the major pathway for CH4 emissions, reaching 70% of the total CH4 flux. In 2003, river carbon inputs were balanced by carbon outputs to the ocean and were about 3 times lower than the atmospheric flux, which suggests that 10 years after impounding, the flooded terrestrial carbon is still the predominant contributor to the gaseous emissions. In 10 years, about 22% of the 10 Mt C flooded was lost to the atmosphere. Our results confirm the significance of greenhouse gas emissions from tropical reservoir but stress the importance of: (1) considering all the gas pathways upstream and downstream of the dams and (2) taking into account the reservoir age when upscaling emissions rates at the global scale.
(Global Biogeochemical Cycles. vol. 19, n° 0886-6236, pp. GB4007, 25/08/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, EDF R&D, EDF [E.D.F.], UFF, USP
Live foraminiferal faunas from a 2800 m deep lower canyon station from the Bay of Biscay : Faunal response to focusing of refractory organic matter
(Deep Sea Research. vol. 52, n° 0146-6291, pp. 1189-1227, 25/08/2026)
UA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOBB, OOB, UPMC, CNRS, UPMC, INSU - CNRS, CNRS