Seasonal and intraseasonal surface chlorophyll-a variability along the northwest African coast - art. no. C05007

Five years of SeaWiFS ocean color data are used to characterize the variability of surface chlorophyll (SCHL) over seasonal and intraseasonal timescales along the northwest African coast (between 10 degrees N and 33 degrees N). This variability is interpreted in regards of remotely sensed wind stress and sea surface temperature and of climatological surface nitrate concentration. Three regions with fairly different behaviors are identified: the region of the subtropical gyre (24 degrees N-33 degrees N) is characterized by a weak seasonality and chlorophyll confined at the coast. The inter-gyre region off Cape Blanc (19 degrees N-24 degrees N) is characterized by a weak seasonality and a persistent large offshore extension of chlorophyll. The region of the recirculation gyre (10 degrees N-19 degrees N) is characterized by a strong seasonality and a large offshore extension of chlorophyll from February to May followed by an abrupt chlorophyll drop that propagates northward from May to June. The seasonal variability is well explained by the seasonal variability in wind-forcing. Nutrient limitation is the key factor that explains the weak offshore extension of chlorophyll in the North. The chlorophyll drop in the South is attributed to the weakening of the wind-forcing and the simultaneous advection of warm water from the South by a coastal and seasonal branch of the North Equatorial Counter Current (NECC). Intraseasonal variability is present in all regions. The cases of good correlation between the intraseasonal variability of the chlorophyll and of the wind-forcing are found to be associated with weak chlorophyll offshore extension and large nutrient limitation

Coral-sponge-microencruster-microbialite associations in the Upper Jurassic reef: quantitative characterization of a case study from Eastern Sardinia (Italy)

The Late Jurassic records one of the largest reefal expansions of the Phanerozoic, with major diffusion and differentiation in the Tethys realm (WOOD, 1999; KIESSLING, 2002; CECCA et al., 2005). Several depositional and compositional models about Upper Jurassic reef types (see INSALACO et al.,1997; LEINFELDER et al., 2002, 2005; RUSCIADELLI et al., 2011 for a revision) have been published but little knowledge is available about the Eastern Sardinian reefs. This study focuses on the compositional and sedimentological characterization of the Upper Tithonian reef complex presently exposed in the area of Cala Gonone (Orosei Gulf) (Fig.1). The Upper Jurassic carbonate succession of Eastern Sardinia consists of three Bathonian-Callovian to Berriasian (DIENI & MASSARI, 1985; JADOUL et al., 2010 and references therein) carbonate depositional systems developed on the southern Europe passive margin (Fig.1): 1) the first (Dorgali Fm.) is characterized by ooidal grainstone, accumulated above wave base on structural highs (Variscan basement), capped by an Upper Bathonian-Callovian condensed succession with a few Fe-phosphatic hardgrounds; 2) a low-angle Oxfordian-upper Tithonian depositional system: the shallow ramp deposition (Tului Fm.) is characterized by basal oolitic facies overlain by prograding coral-stromatoporoid reefs, interfingering with outer ramp-basinal peloidal packstone-wackestone (S\u2019Adde and Baunei Fms.); 3) the third depositional carbonate system (Bardia Fm.) developed after an Early Tithonian regressive trend, locally marked by carbonate breccias indicative of subaerial exposure. The lower part of the Bardia Fm. (upper Tithonian) is locally characterized by gentle slopes (3-15\ub0) with bioclastic-coral-sponge facies associations (LANFRANCHI et al., 2011). This progradational unit is followed by up to 400-500 m of back reef and inner platform shallow water carbonates.REEF COMPONENTS AND FACIES Compositional and sedimentological analysis of the Bardia reef has been carried out through the combination of \u201cmacroscopic\u201d (outcrop-scale) and \u201cmicroscopic\u201d (microfacies-scale) observations on exceptionally exposed saw-cut quarry walls, over a surface of a few hundreds square metres in three different locations. The external surface of each macroscopically detectable component has been emphasized on the quarry walls (Fig.2). The areal distribution of each portion has been stored as vector images, defining frequency, density and area occupied by the reef components. Microfacies and paleontological analyses have been performed on 280 thin sections. Reef components were grouped into three broad categories: 1) macroscopically detectable organisms (mainly corals, sponges, bivalves, gastropods, echinoderms); 2) microscopically detectable components (microencrusters and microbialites); 3) fine- to coarse bioclastic debris and mud-supported facies. Corals show different degree of reworking, from in life-position skeletons more than 2.5 m2 in size to centimetre-sized rubble. The 49 recognized genera of corals have been classified according to external morphology and corallite type. Calcified sponges (Stromatoporoids) are a few centimetres to tens of centimetres in size, occurring as isolated specimens and in densely-packed assemblages. Siliceous sponges and spiculae are replaced respectively by precipitated automicrite and calcite spar. Microbialite and microencruster organisms form domal, columnar or irregular accretionary crusts, few millimetres to several centimetres in thickness. Frequently, crusts bind neighbouring skeletons of large biota, developing metre-scale bioconstructions. These components combine in various proportions within and among quarries, reflecting abrupt lateral and vertical changes of environmental conditions. Quarry 1 is characterized by large branched and massive coral colonies partially or totally encrusted by centimetre thick microencruster crusts and well-washed bioclastic facies, indicating sediment reworking in a high\u2013energy environment. This facies abruptly passes laterally into a densely packed massive microsolenid coral and calcareous sponge assemblage and microbialite and microencruster (Tubiphytes. and other nubeculariids) boundstone. Microsolenid assemblages are commonly interpreted to have formed in deeper water (LATHULI\uc8RE & GILL, 1995; GILL et al., 2004) or alternatively related to poorly illuminated shallow-water cave environments, and adapted to low-sedimentation, low-energy and nutrient-rich conditions (INSALACO, 1996; DUPRAZ & STRASSER, 2002). Quarry 2 is characterized by progressive vertical variations from facies dominated by densely packed platy and flat coral colonies (microsolenids and others) to facies dominated by calcareous sponges and loosely packed phaceloid coral colonies. Microbialite and microencrusters (Tubiphytes and other nubeculariids) envelope and bind large biota. Platy growth forms are generally interpreted as a response to poor illumination (INSALACO, 1996). Consequently the whole association seems to be compatible with poorly illuminated water, low sedimentation rate in a low energy environment. Quarry 3 records large scale bedding (from 1 m to several metres) defined by six intervals dominated respectively by 1) bivalves; 2) dasycladacean algae; 3) reworked massive thamnasterioid coral colonies; 4) thin phaceloid corals and calcareous sponges in growth position; 5) branched ramose coral colonies and calcareous sponges; 6) reworked massive plocoid coral colonies and gastropods. Large biota within intervals 3, 4 and 5 are largely encrusted by different microencrusters such as Koskinobulina, Thaumatoporella, light-dependent Lithocodium-Bacinella, and microbial accrectionary crust. Coral assemblages and microencruster association reveal a progressive increasing of the energy regime and sediment reworking in well-lit waters (INSALCO, 1996; SCHIMD & LEINFELDER, 2002), while the presence of bivalve, algae and gastropod floatstone represents the temporary shifting to \u201cperi-reefal\u201d environments. Despite variability of facies associations in the three quarries, a paleoecological evolution from quarry 1 to quarry 3 emerges, reflecting the change from moderate energy environment with more protected, poorly illuminated cave environment (quarry 1), through a low energy, poorly illuminated environment characterized by low sedimentation rate (quarry 2), to a high energy, well illuminated environment, characterized by high sedimentation rate and reworking (quarry 3). The relative position of the studied quarries along an ideal depositional profile remains speculative, although a medium-scale progradational trend, from distal to proximal setting, seems to be compatible with the long-scale stratigraphic trend of the Bardia Fm. Spectacular outcrop conditions, amount of data collected, biota taxonomic classifications and the observed stratigraphic evolution provide the solid base for paleo-biogeographical comparisons with other Upper Jurassic Tethyan reef complexes. REFERENCES CECCA F., GARIN M., MARCHAND D., LATHUILIERE B. & BARTOLINI A. (2005). Paleoclimatic control of biogeographic and sedimentary events in Tethyan and peri-Tethyan areas during the Oxfordian (Late Jurassic). Pal.Pal.Pal., 222, 10\u201332. DIENI I. & MASSARI F. (1985). Mesozoic of Eastern Sardinia. In: Cherchi A. (ed.), 19th European Micropaleontological Colloquium. Sardinia, October 1-10. Micropaleontological researches in Sardinia. Guidebook, 66-77. DUPRAZ C. & STRASSER A. (2002) Nutritional modes in coral-microbialite reefs (Jurassic, Oxfordian, Switzerland): evolution of trophic structure as a response to environmental change. Palaios 17, 449-471. GILL G., SANTANTONIO M. & LATHUILI\uc8RE B. (2004). The depth of pelagic deposits in the Tethyan Jurassic and the use of corals: an example from the Apennines. Sedimentary Geology, 166, (3-4), 311\u2013334. INSALACO E. (1996) Upper Jurassic microsolenids biostromes of northern and central Europe: facies and depositional environment. Pal. Pal. Pal., 121, 169\u2013194. INSALACO E., HALLAM A. & ROSEN B.R. (1997). Oxfordian (Upper Jurassic) coral reefs in western Europe: reef types and conceptual depositional model. Sedimentology 44, 707\u2013734. JADOUL F., LANFRANCHI A., CASELLATO C.E., BERRA F. & ERBA E. (2010). I sistemi carbonatici giurassici della Sardegna orientale (Golfo di Orosei). In Geol.F.Trips of ISPRA and Societ\ue0 Geologica Italiana Vol. 2, 122 pp. KIESSLING,W. (2002). Secular variations in the Phanerozoic reef systems. In: Kiessling,W., Fl\ufcgel, E., Golonka, J. (Eds.), Phanerozoic Reef Patterns: SEPM, Spec. Publ., 72, 625\u2013690. LATHULI\uc8RE B. & GILL G. (1995). Some new suggestions on functional morphology in pennular corals. In: B Lathuili\ue8re, J Geister (Eds.), Coral Reefs in Past, Present and Future. Proceeding of the 2nd European Meeting of the International Society for Reef Studies, Publications du Service G\ue9ologique du Luxembourg, 29, 259\u2013264 LANFRANCHI A., BERRA F. & JADOUL F. (2011). Compositional changes in sigmoidal carbonate clinoforms (Late Tithonian, eastern Sardinia, Italy): insights from quantitative microfacies analyses. Sedimentology 58, 2039\u20132060 LEINFELDERR.R., SCHLAGINTWEIT F., WERNER W., EBLI O., NOSE,M., SCHMID D.U. & HUGHES G.W. (2005). Signi\ufb01cance of stromatoporoids in Jurassic reefs and carbonate platforms\u2014concepts and implications. Facies 51, 287\u2013325. LEINFELDER R.R., SCHMID D.U., NOSE M. & WERNER W. (2002). Jurassic reef patterns. The expression of a changing globe. In: Kiessling, W., Fl\ufcgel, E., Golonka, J. (Eds.), Phanerozoic Reef Patterns: SEPM Spec Publ, 72,. 465\u2013520. RUSCIADELLI G., RICCI C., LATHUILI\uc8RE B. (2011) The Ellipsactinia Limestones of the Marsica area (Central Apennines): A reference zonation model for Upper Jurassic Intra-Tethys reef complexes. Sed. Geol., 233, 69\u201387 WOOD, R.A. (1999). Reef Evolution. Oxford University Press

Poleward along-shore current pulses on the inner shelf of the Bay of Biscay

We analyzed strong events of coastal poleward along-shore currents above 10 cm s−1 and up to more than 50 cm s−1 on the inner shelf (50-80 m depth) of the Bay of Biscay (BoB) from the Spanish coast to the Brittany coast. We used data from four acoustic Doppler current profilers (ADCPs) deployed from July 2009 to August 2011. The goal of this study was to analyze current variability at meso- and subinertial scales and their generation mechanisms. These currents occurred all year long and were classified into three types. Events occurring principally in the southern part of the BoB were classified as southern events. Bay-scale events were defined when strong poleward currents were detected over all the shelf, typically stronger on the Spanish and the southern Brittany shelves. Strong events were characterized by depth averaged current velocities over 40 cm s−1 in the southern part of the BoB. At short time lags, the along-shore currents were clearly related to along-shore wind stress at upstream locations. An explanation is provided for longer time lags in terms of coastal trapped wave (CTW) dynamics. The first CTW mode phase speeds were in agreement with the propagation speeds of the fastest events (> 5 m s−1), while inner shelf modes could explain the slowest events (∼ 1-3 m s−1). The cross-shelf density gradient and the extension of the IPC were also associated with strong coastal poleward along-shore currents. The duration of the events, the vertical structure of the currents and the associated coastal trapped waves were studied in relation with the stratification

Regulation of tau internalization, degradation, and seeding by LRP1 reveals multiple pathways for tau catabolism

In Alzheimer's disease (AD), pathological forms of tau are transferred from cell to cell and "seed" aggregation of cytoplasmic tau. Phosphorylation of tau plays a key role in neurodegenerative tauopathies. In addition, apolipoprotein E (apoE), a major component of lipoproteins in the brain, is a genetic risk determinant for AD. The identification of the apoE receptor, low-density lipoprotein receptor-related protein 1 (LRP1), as an endocytic receptor for tau raises several questions about the role of LRP1 in tauopathies: is internalized tau, like other LRP1 ligands, delivered to lysosomes for degradation, and does LRP1 internalize pathological tau leading to cytosolic seeding? We found that LRP1 rapidly internalizes 125I-labeled tau, which is then efficiently degraded in lysosomal compartments. Surface plasmon resonance experiments confirm high affinity binding of tau and the tau microtubule-binding domain to LRP1. Interestingly, phosphorylated forms of recombinant tau bind weakly to LRP1 and are less efficiently internalized by LRP1. LRP1-mediated uptake of tau is inhibited by apoE, with the apoE4 isoform being the most potent inhibitor, likely because of its higher affinity for LRP1. Employing post-translationally-modified tau derived from brain lysates of human AD brain tissue, we found that LRP1-expressing cells, but not LRP1-deficient cells, promote cytosolic tau seeding in a process enhanced by apoE. These studies identify LRP1 as an endocytic receptor that binds and processes monomeric forms of tau leading to its degradation and promotes seeding by pathological forms of tau. The balance of these processes may be fundamental to the spread of neuropathology across the brain in AD

Designer exosomes produced by implanted cells intracerebrally deliver therapeutic cargo for Parkinson’s disease treatment

Exosomes function as intercellular information transmitters and are candidates for delivery of therapeutic agents. Here the authors present EXOtic, a synthetic biology device for in-situ production of designer exosomes and demonstrate in vivo application in models of Parkinson's disease