Dysaerobic conditions during Heinrich events 4 and 5: Evidence from phosphorus distribution in a North Atlantic deep-sea core
Reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments. The degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions, which may be linked to larger scale phenomena, such as bottom water circulation, water column ventilation, and organic carbon flux. Phosphorus phases of the <50-μm-sized fraction of deep-sea sediments from core SU 90-09 (North Atlantic, 43°31'N, 30°24'W, 3375 m below sea level) have been analyzed using a sequential extraction technique (SEDEX method) to reconstruct phosphorus geochemistry during Heinrich events 4 and 5. Comparison with Holocene samples from the same site indicates that postdeposition diagenetic transformation has not affected phosphorus distribution in the deep part of the sediments. Total and reactive phosphorus average 0.40 ± 0.04 mg/g and 0.30 ± 0.05 mg/g, respectively, and are comparable to values found in analog deep-sea environments in the North Atlantic. Detrital phosphorus, the phase linked to igneous- and metamorphic-derived material, sharply increases during Heinrich events and covaries with the ice-rafted debris record, whereas authigenic and Fe-bound phosphorus phases, both influenced by redox conditions, decrease or even disappear. These findings suggest that during the deposition of Heinrich layers (HLs), environmental parameters hampered the precipitation of these phases. Large freshwater discharges in relation to iceberg surges may have provoked a temporary stratification of the water column. Accordingly, dysaerobic conditions in the sediments may have fostered the loss of dissolved phosphorus from the sediments to the water column, in a direct and rapid response to the changed conditions. Decreasing trends in organic matter elemental ratios (total organic carbon/organic phosphorus) and Rock-Eval oxygen index values, along with the presence of partly authigenic dolomite and ankerite within HLs, also support this assumption.
(Geochimica et Cosmochimica Acta. vol. 66, n° 0016-7037, pp. 4069-4083, 21/02/2026)
iEES, INRA, UPMC, UPEC UP12, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Behaviour of Organic Carbon in Nine Contrasting European Estuaries
A cross-system comparison of organic carbon origin and behaviour in nine European estuaries is presented. The study sites display a very large range of hydrological and environmental conditions. The watershed of the respective estuaries were characterized by plotting the total organic carbon (TOC) in the rivers versus the inhabitants/discharge ratio. This allows to distinguish four types of watershed with regard to anthropogenic forcing and organic carbon levels: polluted by sewage inputs (Scheldt and to a much lesser extent, Ems, Sado and Thames), decontaminated (Elbe and Rhine), pristine (Gironde and Douro) and eutrophized (Loire and Scheldt). In the estuarine zone, dissolved organic carbon (DOC) almost always decreased linearly with increasing salinity. Exceptions were: the Scheldt, where a net consumption of sewage-derived DOC was observed, the Gironde, where a net production of DOC occurred in the maximum turbidity zone (MTZ) and the Sado and Ems, where DOC was supplied from large intertidal areas. By contrast, a large fraction of the riverine particulate organic carbon (POC) was mineralized in all the estuaries, except the Douro, where residence time of waters is only a few days. A fraction of POC appeared however refractory and accumulated in the MTZs, where terrestrial soil-derived material dominates (Elbe, Ems, Loire, Gironde and Sado). In the marine regions of most estuaries, autochthonous POC was present during spring and summer. The analysis of all river and estuarine data allows estimation of the loss of continental POC occurring in each estuary. It decreases in the following order: Scheldt≫Thames>Ems=Sado=Loire>Gironde>Elbe>Rhine>Douro, which almost corresponds to the anthropogenic pressure in the respective watersheds. Two major variables appear to control the intensity of this mineralization: the origin of the POC, the lability increasing with pollution, and the residence time of particles in the estuarine zone.
(Estuarine, Coastal and Shelf Science. vol. 54, pp. 241-262, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Winter dynamics on the northern Portuguese shelf. Part 1: physical processes
Results of a program of observations carried out on the northern Portuguese shelf and slope, between July 1996 and June 1999 are used to characterise the main physical processes of the winter regime. The data set includes time series of waves and currents at mid-shelf (86 m depth) and of winds, atmospheric pressure and sea level at the coast, as well as hydrographic and suspended particle matter (SPM) observations carried during three multidisciplinary surveys. The wave regime was found to be characterised by highly energetic conditions during the winter, with storm events leading to waves of significant heights exceeding 5 m with mean periods of over 10 s. Prevailing southerly winds force a downwelling regime over the shelf with poleward flow at mid-shelf (~10-20 cm/s) and offshore transport in the bottom Ekman layer. Episodic strong upwelling events can occur during this period, leading to important changes in the near bottom stratification at mid-shelf. Tidal currents at mid-shelf are dominated by the contribution of the M 2 tide (~3 cm/s) and are polarised in the cross-shelf direction, reflecting the guiding effect of the Porto Canyon.
(Progress in Oceanography. vol. 52, n° 0079-6611, pp. 129-153, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Oligocene reefal deposits in the Pisang Ridge and the origin of the Lucipara Block (Banda Sea, eastern Indonesia)
In 1998 we dredged early Oligocene/late Oligocene boundary, shallow-water reefal deposits and pelagic, early Pliocene muds in the submerged Pisang Ridge. The shallow-water deposits were identified as moderate- to low-energy coral-reef depositional environments, which confirms that the PisangRidg e belonged to the continental to continental-arc Lucipara Block which also includes the TukangBesi, Lucipara and Rama ridges. On the basis of these findings, it was possible to reconstruct parts of the general geological evolution of the Lucipara Block, which drifted away from northern Irian Jaya duringmid- Miocene times and collided with the Kolonodale Block during the late Miocene. A late-early Oligocene calc alkaline volcanic arc developed in the Weber Trough area, then uplifted to a shallow-water position at the early–late Oligocene boundary in the Pisang Ridge. Late Oligocene–early Miocene metamorphism subsequently developed, prior to the deposition of early Miocene coral reefs in the Rama Ridge. Locally, late Miocene metamorphism was identified in the Lucipara Ridge, prior to the latest Miocene–Pliocene general drowning and the splitting of the Lucipara Block into several small blocks throughout the Banda Sea region.
(Geo-Marine Letters. vol. 22, n° 0276-0460, pp. 66-74, 21/02/2026)
CNRS, SPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS
Enhanced aridity and atmospheric high-pressure stability over the western Mediterranean during the North Atlantic cold events of the past 50 k.y.
(Geology. vol. 30, n° 0091-7613, pp. 863, 21/02/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ICREA, ISMAR, ISMAR, CNR
Nepheloid layer dynamics in the northern Portuguese shelf
A general hydrographic and nephelometric survey of the NW Portuguese continental shelf and upper slope was undertaken, under winter and spring conditions. The nepheloid layer dynamics along the shelf during three cruises were controlled, principally by the following factors: (a) the hydrography of the shelf-slope waters, i.e. the nepheloid layers followed isopycnals and water masses; (b) prevalence of upwelling or downwelling circulation over the shelf; (c) dispersion of material by river discharge (mainly the Douro river); (d) resuspension of mid-shelf fine deposits induced by swell; (e) peculiar morphology with the presence of Porto Canyon and outer shelf rock outcrops. The general circulation controls the seaward extension of the nepheloid layers. In winter, under dominant downwelling conditions, an intense bottom nepheloid layer (BNL) was observed on the shelf, due to river borne particle supply and remobilization of mid-shelf muddy sediments (depth ≈100 m). In this period the BNL increased in thickness to the top of the slope, following the isopycnals. Near the shelf-break the BNL detached to form intermediate nepheloid layers (INL). Small INLs appear deeper in some areas of the slope. A surface nepheloid layer (SNL) appears in the surface water over the shelf and slope. In spring, biological particles mainly contribute to the SNL, which is separated from the BNL by a zone of clear water. In winter the SNL is restricted to the inner shelf where there are high inputs of fluvial particles. Downwelling circulation probably induces transport of shelf particles to deeper waters in the BNL. In spring, the predominant circulation was southward (upwelling), the water column was highly stratified, and dispersion of particles in the SNL was offshore.
(Progress in Oceanography. vol. 52, n° 0079-6611, pp. 195-213, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Reconciling down core anticorrelation of diatom carbon and nitrogen isotopic ratios from the Southern Ocean
Oceanic nutrient cycling in the Southern Ocean is supposed to have an important impact on glacial-interglacial atmospheric CO 2 changes and global climate. In order to characterize such nutrient cycling over the last two climatic cycles we investigated carbon and nitrogen isotopic ratios of diatom-bound organic matter (d 13 C diat and d 15 N diat , respectively) in two cores retrieved form the Atlantic and Indian sectors of the Antarctic Ocean. The two cores show the same isotopic patterns. The d 13 C diat values are depleted during glacial periods and enriched during interglacial periods, indicating lower productivity during cold times. The d 15 N diat values are enriched during glacial periods and depleted during interglacial periods, arguing for greater nitrate utilization during cold times. Taken at face value, this apparent contradiction leads to opposite conclusions on the role of the Southern Ocean biological pump on the atmospheric CO 2 changes. However, the two sets of data can be reconciled by a ''sea ice plus mixing rate scenario'' that calls upon a balance between the effect of cutting off gas transfer at the ocean-atmosphere boundary and the effect of reducing vertical transport of nutrients through the pycnocline.
(Paleoceanography. vol. 17, n° 0883-8305, pp. 10-1-10-8, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Present day sedimentary processes on the northern Iberian shelf
The Galicia-Minho Shelf features two large mud patches, the Douro and the Galicia Mud patches. These are recent sediment bodies that have accumulated under a combination of conditions including: (1) abundant supplies of sediment; (2) morphological barriers that act as sediment traps; and (3) hydrographic conditions that favour the accumulation of fine sediment in these sinks. This paper describes the mechanisms controlling the deposition of the fine-grained sediment depositions and the processes that result in resuspension processes on the Galicia-Minho Shelf. Fine-grained sediments are provided from discharges from the river basins on the southern sector of the shelf, mainly the Douro and Minho rivers. Sediments are exported from river estuaries onto the shelf during episodic flood events. In contrast, most of the sediments originating from the Galician hinterland fail to contribute significantly to sedimentation on the shelf, because they are retained in the Galician Rías, which function as sediment traps. Sediments deposited on the shelf are frequently remobilized, particularly during southwesterly storms that coincide with downwelling conditions. Once in suspension the fine-grained sediments are transported northwards by the poleward flowing bottom currents and are eventually deposited on the Douro and Galicia Mud patches after a series of resuspension events. The locations of the two mud patches are strongly influenced by the shelf morphology. Fines already deposited on the mud patches are occasionally reintroduced into the system by large storm events. Some material from the Douro Mud patch and adjacent areas is re-deposited in the Galicia Mud patch. It is probable that sediments re-suspended from the Galicia Mud patch are carried off the shelf when storm events coincide with downwelling conditions.
(Progress in Oceanography. vol. 52, n° 0079-6611, pp. 249-259, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Winter dynamics on the northern Portuguese shelf. Part 2: bottom boundary layers and sediment dispersal
The northern Portuguese shelf, between 41°N and 42°N, is characterised by the presence of a mid-shelf mud deposit, the Douro Mud Patch (DMP). Observations conducted between July 1996 and June 1999 under the framework of project OMEX II-II, are used to examine the impact of the dynamic processes in the lower water column, particularly on the DMP. The typical wave conditions observed during the winter maintain a highly energetic environment, capable of promoting the erosion of fine sediments at mid-shelf depths. However, the bottom nepheloid layers generated beneath these waves only extend a few meters above the bottom and are contained within rocky outcrops with similar heights that fringe the outer shelf. Each year there are about ten storms, mostly associated with southerly winds that create downwelling conditions over the shelf. The waves associated with these storms produce shear velocities over 3 cm/s at mid-shelf and bottom nepheloid layers which extend a few tens of meters above the bottom and spread offshore, over the outer shelf and upper slope. A rough estimate suggests that these events account for an offshore export of about 20×10 6 kg of fine sediments each year (equivalent to 1-2% of sediments trapped at DMP).
(Progress in Oceanography. vol. 52, n° 0079-6611, pp. 155-170, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Late quaternary variations of elemental ratios (C/Si and N/Si) in diatom-bound organic matter from the Southern Ocean
The carbon cycle in the Southern Ocean is considered as a major factor controlling past atmospheric CO 2 concentration variations. However, accumulation rates of biogenic opal are not linearly related to carbon burial rates. Here, we show that it is possible to measure the carbon and nitrogen content of diatom-bound organic matter (%C diat and %N diat , respectively) and that the signals recorded do not appear to be analytical artifacts. Analyses of two cores from the Atlantic and Indian sectors of the Southern Ocean show that %C diat and %N diat change on glacial-interglacial cycles by 30-40% and 120-175%, respectively. Accordingly, C/N ratios vary between 3 and 7 on glacial-interglacial timescales. If changes recorded in the occluded organic matter are representative of the changes in the diatom bulk organic matter, this provides a new tool to document the carbon cycle in the Southern Ocean and to determine its role on past atmospheric pCO 2 variations. Laboratory experiments on diatom cultures are needed to validate the use of diatom organic bound C and N as a tracer of diatom physiology and of carbon export from surface waters. r 2002 Elsevier Science Ltd. All rights reserved. Re´sume´LeRe´sume´ Re´sume´Le cycle du carbone de l'Oc! ean Austral est certainement un des facteurs majeurs contr # olant les concentrations atmosph! eriques pass! ees en CO 2. Cependant, les taux d'accumulation de l'opale biog" ene ne sont pas lin! eairement li! es aux taux d'accumulation du carbone organique et ne peuvent donc pas # etre directement utilis! es en tant que traceur de la pal! eoproductivit! e. Nous montrons ici qu'il est possible de mesurer les teneurs en carbone et azote dans la mati" ere organique intrins" eque des diatom! ees (%C diat and %N diat respectivement), et que les signaux fossiles ne sont pas le r! esultat d'artefacts analytiques. L'analyse de deux carottes provenant des secteurs Atlantique et Indien de l'Oc! ean Austral indique que les %C diat and %N diat ont respectivement vari! e de 30-40% et de 120-175% au cours des cycles glaciaires-interglaciaires. Les rapports C/N ont en cons! equence vari! e de 3 " a 7 au cours des cycles glaciaires-interglaciaires. Si les variations enregistr! ees dans la mati" ere organique intrins" eque sont repr! esentatives des changements du bulk des diatom! ees, nous aurons un nouvel outil pour documenter le cycle oc! eanique du carbone et pour d! eterminer son r # ole dans les variations pass! ees de pCO 2 atmosph! eriques. Des exp! eriences en laboratoire sur des cultures de diatom! ees sont cependant n! ecessaires afin de valider l'outil %C diat and %N diat comme traceur des conditions physiologiques des diatom! ees et des flux de carbone export! es depuis la couche euphotique.
(Deep Sea Research Part II: Topical Studies in Oceanography. vol. 49, n° 0967-0645, pp. 1939 - 1952, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS