Viviane Bout-Roumazeilles

Elsa Cortijo

Laurent Labeyrie

Pierre Debrabant

Clay mineral evidence of nepheloid layer contributions to the Heinrich layers in the northwest Atlantic

Keywords: North Atlantic, clay minerals, nepheloid layer, Pleistocene

The clay fraction of four cores drilled in the north Atlantic Ocean was studied at a very high resolution over the last 150 ka in order to record the mineralogical signature of Heinrich events. Factor analysis of clay mineralogy establishes that three independent factors represent the main variations: a 'detrital factor' (illite C chlorite C kaolinite), a 'smectite factor', and a 'mixed-layer factor' (IVML: illite-vermiculite mixed-layered clay). The clay mineral fraction of core SU90-38 drilled in the northeastern Atlantic basin did not record any Heinrich event, whereas large changes in the clay mineral fraction occurred during Heinrich events H1, H2, H4, and H5 in the three cores from the northwestern Atlantic basin (cores SU90-08, SU90-11, and SU90-12). Heinrich layers are characterized by increases in the detrital factor in cores SU90-08 and SU90-11, and sharp increases in the mixed-layer factor in cores SU90-11 and SU90-12. The geographical setting of the cores, the pattern of surface, intermediate and deep water circulation, and the main sources of clay minerals allow recognition of two major mechanisms involved in the deposition of the Heinrich Layers: (1) an increased supply of detrital clay minerals by the icebergs; and (2) a specific input of illitevermiculite mixed-layer clay minerals by a nepheloid layer.

Introduction

High-resolution palaeoceanographic studies in the North Atlantic Ocean provide much evidence of massive fluxes of coarse detrital material that are interpreted as a consequence of abrupt climatic changes. The Heinrich layers corresponds to short periods of very high sedimentation rates These 'Heinrich layers' mainly occur within a preferential accumulation belt, between 40 and 50ºN, along the edge of the polar front [START_REF] Ruddiman | Late Quaternary deposition of ice-rafted sand in the sub-polar north Atlantic (lat. 40º to 65ºN)[END_REF][START_REF] Heinrich | Origin and consequences of cyclic ice-rafting in the northeast Atlantic Ocean during the past 130,000 years[END_REF][START_REF] Bond | Evidence for massive discharges of icebergs into the North Atlantic Ocean during the last glacial period[END_REF][START_REF] Broecker | Origin of the northern Atlantic's Heinrich events[END_REF][START_REF] Grousset | Patterns of ice-rafted detritus in the glacial north Atlantic (40º-55ºN)[END_REF]. These events are also characterized by decreases in the number of species and abundance of foraminifers, the resulting assemblages being dominated by the cold species N. pachyderma (left coiling) [START_REF] Bond | Evidence for massive discharges of icebergs into the North Atlantic Ocean during the last glacial period[END_REF]. A high content of detrital carbonate, especially dolomite, suggests that most of the terrigenous material originates from the eastern margin of the Laurentide ice-sheet [START_REF] Andrews | Detrital carbonate-rich sediments, northwestern Labrador Sea -implications for ice sheet dynamics and icebergs rafting (Heinrich) events in the north Atlantic[END_REF][START_REF] Huon | Mineralogical, K-Ar, and 86Sr/87Sr isotopes study of Holocene and late glacial sediment in a deep-sea core from northeast Atlantic Ocean[END_REF][START_REF] Andrews | Late Quaternary (stage 2 and 3) meltwater and Heinrich events, northwest Labrador Sea[END_REF]. Heinrich events are generally closely associated with instabilities of the Laurentide ice-sheet. MacAyeal (1993) suggested that the Heinrich events were caused by free oscillations of the Laurentide ice-sheet: when the frozen sediments, at the base of the ice-sheet, started to thaw, they formed a lubricant and the ice-sheet began to slip. Ice flow from Hudson Bay may have delivered coarse particles (between 150 µm and several millimetres), eroded from the calcareous Paleozoic bedrock, to the continental slope and to the deep oceanic basin. Debris flows, turbidity currents, and intermediate water masses may also be involved in producing the Heinrich layers. This is evident from the high accumulation rates observed in sediments sampled outside the main icebergs pathways [START_REF] Andrews | Detrital carbonate-rich sediments, northwestern Labrador Sea -implications for ice sheet dynamics and icebergs rafting (Heinrich) events in the north Atlantic[END_REF]). Here we used clay particles (<2 µm) which are easily transported by oceanic currents, to demonstrate the contribution of a nepheloid layer to the Heinrich layer deposits in the northwestern Atlantic basin.

Material and methods

Core settings

Four sediment cores from the cruise Paleocinat I in 1990 were studied: SU90-08, Fig. 1). Three cores were taken from the northwestern Atlantic basin: the southernmost core SU90-08 is located at 43ºN near the Azores, on the western flank of the mid-oceanic ridge at 3080 m depth, in a quiet deep environment; core SU90-11 (3645 m) and SU90-12 (2950 m) are situated on seamounts at 44 and 51ºN, respectively, near the entrance of the Labrador Sea. Cores SU90-11 and SU90-12 are situated on seamounts at 1000 m above the sea-floor: sedimentation at these sites is therefore only controlled by intermediate or/and surface water masses flowing out the Labrador sea. Core SU90-38 was sampled in the northeastern Atlantic basin, at 54ºN, near Rockall Plateau, at 2900-m water depth. This site is under the influence of the eastern drift of the North Atlantic Deep Water overflowing the Wyville-Thomson rise, and by surface water masses originating from the Greenland and Norwegian seas.

Correlation and chronology

The age model for each site is based on a comparison between the benthic and/or planktonic δ 18 O records and the spectral mapping SPECMAP stack [START_REF] Martinson | Age dating and the orbital theory of ice-ages: Development of high resolution 0 to 300 000year chronostratigraphy[END_REF] using the Analyseries software [START_REF] Paillard | Analyseries 1.0: a Macintosh software for the analysis of geographical time-series[END_REF]. A linear interpolation was applied between the stratigraphic levels identified (Table 2), assuming that the sedimentation rate was constant between these levels. The age-depth relations are given in Table 2 and shown in Fig. 2. The oxygen isotope analysis of foraminifers was measured on an automatic carbonate preparation line coupled to a Finnigan MAT 251 mass spectrometer (Centre des Faibles Radioactivités, Gif-sur-Yvette, France) Isotopic stages and their boundaries were deduced from isotopic curves, magnetic susceptibility, and reflectance [START_REF] Grousset | Patterns of ice-rafted detritus in the glacial north Atlantic (40º-55ºN)[END_REF][START_REF] Cortijo | Etude de la variabilité climatique à haute résolution dans des sédiments de l'Atlantique Nord[END_REF]. The mean sedimentation rate of core SU90-08 is about 4.2 cm/ka -1 and varies along the series (Fig. 2). The sedimentation rate is higher in the upper part of the core (0-107.6 ka), 5.3 cm/ ka -1 , and between 183.4 and 225.2 ka, where it reaches 6.2 cm/ ka -1 . Core SU90-11 records slower sedimentation rates than core SU90-08: the mean value is of 2.9 cm/ ka -1 (Fig. 3). The highest rates in this core are observed in the upper part (0-122.2 ka), 3.8 cm/ ka -1 . Core SU90-12 has the slowest and most regular sedimentation rate, with a mean value of 2.9 cm/ ka -1 (Fig. 3). The mean ages (Fig. 2) for the Heinrich layers (14.5 ka for H1, 22 ka for H2, 27 ka for H3, 40 ka for H4, 50 ka for H5, and 60 ka for H6) are deduced from the age model for core SU90-08 [START_REF] Grousset | Patterns of ice-rafted detritus in the glacial north Atlantic (40º-55ºN)[END_REF].

Method of clay analysis

All samples were first decalcified with 0.2 N hydrochloric acid. The excess acid was removed by repeated centrifugations. The clay-sized fraction (<2 µm) was isolated by settling, and oriented on glass slides (oriented mounts). Three XRD (X-ray diffraction) determinations were performed: (a) untreated sample; (b) glycolated sample (after saturation for 12 h in ethylene glycol); and (c) sample heated at 490ºC for two hours [START_REF] Holtzapffel | Les minéraux argileux. Préparation. Analyse diffractométrique et détermination[END_REF]. The analyses were run on a Philips PW 1710 X-ray diffractometer, between 2.49 and 32.5º2θ. Each clay mineral is then characterized by its layer plus interlayer interval as revealed by XRD analysis. Smectite is characterized by a peak at 14 Å on the untreated sample test, which expands to 17 Å after saturation in ethylene-glycol and retracts to 10 Å after heating.

Illite presents a basal peak at 10 Å on the three tests (natural, glycolated, and heated). The IVML (illite-vermiculite mixed-layered clay) is determined by a peak at 12 Å which does not expand after saturation in ethylene-glycol and retracts to 10 A° after heating. Chlorite is characterized by peaks at 14, 7, 4.72, and 3.53 Å on the three tests. Kaolinite is characterized by peaks at 7 and 3.57 Å on the untreated sample and after saturation in ethylene glycol. Both peaks disappear or are strongly reduced after heating. Semi-quantitative estimation of clay minerals abundances has been done according to the method detailed in [START_REF] Holtzapffel | Les minéraux argileux. Préparation. Analyse diffractométrique et détermination[END_REF].

The reproducibility of technical works and measurements was tested: 5 oriented mounts prepared from the same samples were submitted 3 times to XRD. The relative error is ±5%.

Method of factor analysis

Factor analysis has been performed on all clay abundance data. The method used the Principal Component Analysis (PCA) by the orthogonal transformation method [START_REF] Johnson | Applied Multivariate Statistical Analysis[END_REF][START_REF] Albarède | Introduction to Geochemical Modeling[END_REF]. The PCA explains the covariance structure of multivariate data through a reduction of the whole data to a smaller number of independent variables, called factors.

Results

General data and clay mineralogy

Core SU90-08

Sediments of core SU90-08 are mainly composed of gray to dark gray carbonate (foraminifera and nannofossil) oozes and muds interbedded with terrigenous muddy clay, silty mud and terrigenous mud (sand, silt and clay-sized particles mixed together). The clay mineral association is mainly composed of illite (37 7%) and smectite (33 ± 11%). Chlorite and kaolinite are less abundant with respectively 14% (±3%) and 11% (±3%) of the clay mineral association (Table 3). The random IVML constitutes less than 5% of clay minerals association [START_REF] Bout-Roumazeilles | Relations entre les variabilités minéralogiques et climatiques enregistrées dans les sédiments de l'Atlantique nord pendant les huit derniers stades glaciaires/interglaciaires[END_REF]. The Heinrich layers, which are characterized by their high coarse-size detrital content (calcite, dolomite, quartz, feldspars and amphiboles) are significantly enriched in illite (Table 4), which reaches 55% of the clay mineral association.

The content of chlorite (20%) and kaolinite (15%) also increases in these layers, whereas smectite sharply decreases (10%).

Core SU90-11

Sediments of core SU90-11 are composed of dark gray terrigenous muds interbedded with gray carbonate (nannofossils with foraminifera) muds. The clay mineral association is dominated by illite (average value of 34 ± 4%), with 17% (±7%) IVML and 20% (±4%) chlorite. Smectite and kaolinite represent 16% (±7%) and 12% (±2%) of the clay mineral association, respectively (Table 3). The Heinrich layers are characterized by high magnetic susceptibility, high detrital carbonate content, by a strong increase in IVML in the clay-size fraction, which reach 28% of the clay mineral association and absence of smectite. The percentages of chlorite and kaolinite remain stable.

Core SU90-12

The sediments of core SU90-12 are mainly composed of dark gray terrigenous muds, interbedded with minor levels of carbonate (nannofossils with foraminifera) muds. On the average, the clay fraction is dominated by mean values of 34% (±5%) illite and 21% (4%) chlorite (Table 3). The IVML represents 18% (±8%) of the clay mineral association.

Smectite (15 ± 8%) and kaolinite (12 ± 2%) are less abundant [START_REF] Bout-Roumazeilles | Relations entre les variabilités minéralogiques et climatiques enregistrées dans les sédiments de l'Atlantique nord pendant les huit derniers stades glaciaires/interglaciaires[END_REF]. The Heinrich layers are characterized by high contents of IVML, which reach 32% of the clay mineral association and by low contents of smectite (8%). The content of illite, chlorite, and kaolinite slightly decreases within the Heinrich layers.

Core SU90-38

Core SU90-38 is composed of dark gray terrigenous muddy clay, of gray carbonate mud, and of carbonate (foraminifera with nannofossils) oozes interbedded with minor beds of silt and fine sand. The clay mineral association mostly includes illite (39±7%) and smectite (35±11%). Chlorite (14±3%) and kaolinite (12±2%) are less abundant whereas the random illite-smectite mixed-layer minerals occur as trace amounts (Table 3). No significant modification of the clay association is observed in the Heinrich layers (Heinrich layers have been distinguished on the basis of their high detrital content). Illite (42 ± 5%) and smectite (32 ± 4%) still constitute the main part of the clay mineral association, and chlorite (14±2%) and kaolinite (12 ± 3%) are less abundant.

In summary, the mean percentages of illite, chlorite, and kaolinite are essentially constant in the four cores. Illite, chlorite, and kaolinite represent 62% (core SU90-08) to 67% (core SU90-12) of the clay mineral association. Abundant IVML characterizes the clay mineral association of the western cores SU90-11 (17%) and SU90-12 (18%), whereas it is absent from the two other cores. Low abundances of smectite characterized western cores SU90-11 and SU90-12 where it constitutes only 15% of the clay mineral association. In contrast smectite constitutes more than 30% of the clay mineral fraction in cores SU90-08 and SU90-38. In core SU90-08, the Heinrich layers are characterized by high contents of illite, chlorite, and kaolinite (up to 90% of the clay mineral association), whereas smectite strongly decreases. In cores SU90-11 and SU90-12, abundant IVML (up to 32%) characterizes the Heinrich layers. Smectite disappears in the Heinrich layers of core SU90-11, and is strongly reduced in core SU90-12. There is no coherent variation of illite, chlorite, and kaolinite within the Heinrich layers: illite, chlorite, and kaolinite increase in core SU90-11, decrease in core SU90-12, and strongly increase in core SU90-08. In core SU90-38, the clay mineralogy of the Heinrich layers is not different from the rest of the core.

Results of the correlation matrix

Core SU90-08

The correlation matrix of core SU90-08 (Table 5) indicates that the variations in chlorite, illite, and kaolinite abundances are very well correlated (0.7 < r < 0.8). Smectite abundances appear to be independent of the other minerals. The principal component analysis reveals that two factors represent the major variations (0.9<factor scores<1) in all four clay minerals (Table 6). One factor (the 'ICK factor') groups together illite, chlorite, and kaolinite, whereas the other one corresponds to smectite ('smectite factor'). The primary intercorrelation indicates that the two factors (r = 0) are independent.

Core SU90-11

In core SU90-11, the variations of chlorite, illite, and kaolinite are well correlated (r = 0.8). They are grouped (Table 6) together in the 'detrital factor' (factor scores = 0.9). The correlation matrix (Table 5) indicates that smectite and IVML are slightly anticorrelated (r = 0.6). Consequently, the primary intercorrelation reveals that the 'detrital factor' is not linked with the two others, whereas the 'smectite factor' and the 'mixed-layer factor' are not totally independent (r = 0.4).

Core SU90-12

The results of the factor analysis of core SU90-12 are approximately similar to those of core SU90-08. Once again, the variations of chlorite, of illite, and of kaolinite are well correlated and are represented by the 'detrital factor' (Tables 5 and6). The correlation indexes between smectite and the other mineral are higher than in the cores SU90-08 and SU90-11, but still below the confidence level. As a result, the intercorrelation reveals that the factors are not strictly independent even if the intercorrelation index remains below the confidence level (-0.5 < r < 0.5).

Core SU90-38

Correlation between the variations of chlorite, illite, and kaolinite for core SU90-38 is very high (0.8 < r < 0.9). The variations in smectite are not significantly correlated with those of the other clay minerals (Table 5). The 'detrital factor' represents the main variations of illite, of chlorite, and of kaolinite (factor scores = 0.9) and the 'smectite factor' represents the variations of smectite (factor score = 1).

Overall, the variations of illite, chlorite, and kaolinite in all the cores studied are represented by the 'detrital factor'. The variations in smectite are represented by the 'smectite factor' and these of the IVML by the 'mixed-layer factor'. Below we will discuss the variations of each factor before, during, and after the Heinrich events H1 to H6.

Results of the factor analysis

Core SU90-08

The 'detrital factor' is low from 130 to 70 ka and shows little variations except during the Heinrich events (Fig. 4). It increases very slightly during H6 and H3, whereas it increases sharply and reaches its maximum values during H5, H4, H2, and H1. The 'smectite factor' varies a lot during the last 130 ka. Its variations during all Heinrich events are not similar: in H6 and H3, the smectite factor increases, whereas it slightly decreases in H5, H4, H2, and H1.

Core SU90-11

The 'detrital factor' remains stable and low between 130 and 70 ka. An increase in the factor characterizes H5, H4, H2, and H1, whereas the factor does not change during H6 and H3 (Fig. 5). After H5, H4, H2, and H1, it returns to its mean level. There is no coherent variation of the 'smectite factor' during the Heinrich events. It remains stable during H6, H5, H3, and H2, increases in H1, and decreases in H4. The 'mixed-layer ' factor remains stable from 130 to 70 ka, and during H6 and H3, but shows very short increases during H5, H4, H2, and H1.

Core SU90-12

Major variations of the 'detrital factor' occur between 130 and 70 ka, whereas it remains relatively stable between 35 and 0 ka (Fig. 5). Heinrich events H6, H5, and H4 are characterized by increases of this factor, the most important variations being found in H5 and H4. Between 130 and 70 ka, the 'smectite factor' shows marked variations. Over the past 70 ka this factor is mostly characterized by decreases during H5, H4, and H2. The variations of the 'mixed layer factor' are similar to those of core SU90-11: the mixed-layer factor increases abruptly at the beginning of each Heinrich event, and then drops to below average values. This is especially obvious for H5 and H4.

Core SU90-38

The 'detrital factor' is significantly lower between 130 and 70 ka than between 70 and 10 ka. It remains stable in the upper part of the core even during Heinrich events. The 'smectite factor' records more variations than the 'detrital factor', but they are not correlated with Heinrich events: the factor decreases during H6, increases slightly during H5, H4, and H2, whereas it does not vary during H1 (Fig. 4).

In summary, the Heinrich events are not characterized by any significant variations of the 'detrital factor' and 'smectite factor' in core SU90-38, located in the northeastern Atlantic basin. By contrast, some of the Heinrich events -H5, H4, H2, and H1 -are characterized by the increase of the 'detrital factor' in cores SU90-08, SU90-11 and SU90-12, which were taken from the northwestern Atlantic basin. The variations of the 'detrital factor' associated with the Heinrich events are better developed in the southernmost cores SU90-08 (43ºN) and , than in the northernmost core SU90-12 (51ºN). The 'smectite factor' does not show a consistent pattern of variations. In core SU90-08, the 'smectite factor' decreases during the Heinrich events H5, H4, H2, and H1. In the other cores, the variations of the 'smectite factor' are not the same during all Heinrich events. Variations in the 'mixed-layer factor' characterize only the westernmost cores SU90-11 and SU90-12. Sharp increases to maximum value are followed by rapid drops below average values in the Heinrich events H5, H4, H2, and H1. In core SU90-12, the decrease of the 'mixed-layer factor ' is more drastic for H5 and H4.

Discussion

Clay mineral sources

Under present climatic conditions, the typical terrigenous clay minerals, illite and chlorite, mainly results from physical weathering of continental substrates at high latitudes [START_REF] Biscaye | Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans[END_REF][START_REF] Griffin | The distribution of clay minerals in the world ocean[END_REF][START_REF] Rateev | The distribution of the clay minerals in the oceans[END_REF][START_REF] Millot | Geology of Clays[END_REF][START_REF] Lisitzin | Sedimentation in the world ocean[END_REF][START_REF] Chamley | Remarque sur la sédimentation argileuse quaternaire en Mer de Norvege[END_REF][START_REF] Chamley | Clay Sedimentology[END_REF]. During glacial times or when climatic conditions were colder, physical weathering was intensified, leading to greater rock fragmentation and disintegration, and therefore increasing the terrigenous input to the ocean [START_REF] Chamley | Clay Sedimentology[END_REF]). In the northeastern Atlantic basin, the main sources of chlorite and illite are the Scandinavian shields, Scotland, Ireland and Greenland [START_REF] Moyes | Les sédiments profonds actuels et pléistocène récent de l'Atlantique nord-oriental et du sud de la Mer de Norvège[END_REF][START_REF] Biscaye | Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans[END_REF][START_REF] Griffin | The distribution of clay minerals in the world ocean[END_REF]). In the northwestern Atlantic basin, chlorite and illite derive from the Precambrian and Paleozoic igneous and sedimentary rocks of the North American continent, Baffin Island, and Greenland [START_REF] Piper | Late Quaternary clay mineral distribution along the eastern margin of Canada[END_REF][START_REF] Petersen | Mineralogical composition of the clay-size fraction of two fluvio-glacial sediments from east Greenland[END_REF][START_REF] Thiébault | Analysis of sedimentary facies, clay mineralogy, and geochemistry of the Neogene-Quaternary sediments in site 645, Baffin Bay[END_REF]. Kaolinite, in the northernmost Atlantic basin, is essentially inherited from adjacent land masses where it formed during pre-glacial times and is derived from pre-existing paleosols, sediments or sedimentary rocks on the continents [START_REF] Darby | Kaolinite and other clay minerals in Arctic Ocean sediments[END_REF][START_REF] Naidu | Clay mineral dispersal patterns in the north Bering and Chukchi Seas[END_REF][START_REF] Sancetta | Wisconsin-Holocene paleoenvironment of the Bering Sea: evidence from diatoms, pollen, oxygen isotopes and clay minerals[END_REF][START_REF] Chamley | Clay Sedimentology[END_REF][START_REF] Thiébault | Analysis of sedimentary facies, clay mineralogy, and geochemistry of the Neogene-Quaternary sediments in site 645, Baffin Bay[END_REF]. In the northeastern Atlantic basin, the sources of kaolinite are the Mesozoic areas around the Barents Sea [START_REF] Kuhlemann | Implications of a connection between clay mineral variations and coarse-grained debris and lithology in the central Norwegian-Greenland Sea[END_REF] and southeastern Svalbard [START_REF] Elverhøi | Sedimentological and mineralogical investigations of quaternary bottom currents off the Norwegian West Coast[END_REF]. In the northwestern Atlantic basin, kaolinite could derive from sedimentary formations of the North American continent [START_REF] Boyd | Baffin Bay continental shelf clay mineralogy[END_REF][START_REF] Piper | Late Quaternary clay mineral distribution along the eastern margin of Canada[END_REF] such as the black Cretaceous mudstones of Labrador [START_REF] Jennings | The Quaternary history of Cumberland Sound, southeastern Baffin Island: the marine evidence[END_REF]. The IVMLs are not commonly observed in sediments, and constitute a good discriminant for particle sources. They mainly result from moderate pedogenic processes during interglacial Quaternary conditions at mid-to high latitudes. They seem to result especially from the weathering of mica in an alkaline environment [START_REF] Millot | Geology of Clays[END_REF] or from pedogenic transformation in soils under temperate climatic conditions [START_REF] Berry | Mineralogy of the clay-size fractions of some north-Atlantic Arctic Ocean bottom current[END_REF]. IVML main sources are from Tertiary sediments in Virginia [START_REF] Mccartan | Mineralogy of the Haynesville, Virginia, cores[END_REF], the Canadian Appalachians Mountains [START_REF] Yang | Clay minerals as indicators of diagenetic and anchimetamorphic grade in an overthurst belt, external domain of southern Canadian Appalachians[END_REF] and in the Adirondack Mountains, NY State [START_REF] April | The nature of vermiculite in Adirondack soils and till[END_REF]. IVMLs form from pedogenic processes in the Canadian Appalachians Mountains and are transported by run-off to the Labrador shelf area.

IVML has been also identified as reworked material in fluvial sediments on the western coast of Greenland [START_REF] Petersen | Mineralogical composition of the clay-size fraction of two fluvio-glacial sediments from east Greenland[END_REF]. Recent work [START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF] in the Labrador basin demonstrates that IVMLs are abundant at shallow depth in Labrador shelf sediments (<300 m water depth). But their abundance decreases to traces at greater water depth and they have not been found yet in the deepest parts of the Labrador basin. At 2698 m off New Jersey (ODP Site 905A) IVML constitute 5-25% of the clay mineral association of Pleistocene sediments [START_REF] Deconinck | Eocene to Pleistocene clay mineral sedimentation off New-Jersey, western north Atlantic (ODP Leg 150, sites 903 and 905[END_REF]. IVMLs are assumed to be inherited from ancient soils developed on nearby mica-rich schists [START_REF] Rich | Muscovite weathering in a soil developed in the Virginia Piedmont[END_REF].

Smectite is common in North Atlantic sediments. It results from the chemical alteration of basalts, volcanic ashes and glasses, from pedogenic evolution of illite, or from erosion of old sediments formed during intervals when local climatic conditions (warm and hydrolyzing) allow pedogenic formation of smectite [START_REF] Desprairies | Relation entre la composition des smectites d'alteration sous-marine et leur cortège de terres rares[END_REF][START_REF] Chamley | Clay Sedimentology[END_REF]. Iceland, the Faeroe Islands [START_REF] Parra | Origin and evolution of smectites in recent marine sediments of the NE Atlantic[END_REF], and the North European continental Tertiary formations, constitute the main sources of smectite in the northeastern Atlantic basin. Smectite is less abundant in the northwestern Atlantic basin, because of greater distance from the main continental sources [START_REF] Berthois | Etude minéralogiques et géochimiques de quelques sédiments de la zone comprise entre les archipels Faeroes, Shetland, Orcades et Hébrides[END_REF][START_REF] Grousset | Sedimentogenèse d'un environnement de dorsale: la ride Açores-Islande au cours du dernier cycle climatique. Origines, vecteurs, flux des particules sédimentaires[END_REF][START_REF] Grousset | The Holocene sedimentary regime in the northern mid-Atlantic ridge region[END_REF], or because climatic conditions in adjacent continental areas were too cold to allow pedogenic formation of smectite during the Quaternary. Nevertheless, smectite represents 5-50% of the clay mineral association in the Labrador Sea [START_REF] Nielsen | Analysis of sedimentary facies, clay mineralogy, and geochemistry of the paleogene sediments of site 647, Labrador Sea[END_REF][START_REF] Thiébault | Analysis of sedimentary facies, clay mineralogy, and geochemistry of the Neogene-Quaternary sediments in site 645, Baffin Bay[END_REF][START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF]. The main sources of smectite in this area are the northeastern Canadian Tertiary formations and smectite is also a main component in sediments off Cumberland Sound and Baffin Island [START_REF] Jennings | The Quaternary history of Cumberland Sound, southeastern Baffin Island: the marine evidence[END_REF][START_REF] Andrews | Abrupt changes in marine conditions, Sunneshine fiord, eastern Baffin Island, NWT, during the last deglacial transition: Younger Dryas and H-0 events[END_REF][START_REF] Jennings | Shelf erosion and glacial ice proximity in the Labrador Sea during and after Heinrich events (H-3 or 4 to H-0) as shown by foraminifera[END_REF]. Higher abundances of smectite at the rise/slope boundary on the path of the Western Boundary Under-Current could result from the mixture of particles transported from the Northern Labrador Sea and from the Iceland-Reykjanes ridge [START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF].

Dynamics of the Heinrich events

Clay minerals allow recognition of temporal variations in the characteristics of the Heinrich events in the following ways:

-In the northeastern Atlantic basin, Heinrich layers, which are otherwise characterized by an increased coarse fraction, are not characterized by any variation of the clay mineral association. By contrast, in the northwestern Atlantic basin, most of the Heinrich layers are also characterized by important modifications in the clay mineral associations.

-The Heinrich layers of the North West Atlantic are enriched in 'detrital' clay minerals (i.e. illite C chlorite C kaolinite) especially in the southern cores SU90-08 (43ºN) and . However, the more recent Heinrich layers (H1 and H2) of the northernmost core SU90-12 do not show any enrichment in detrital clay minerals.

-Increased supply of detrital clay minerals is especially obvious in H1 (14.5 ka), H2 (22 ka), H4 (40 ka), and H5 (50 ka). Only slight increases are observed in H3 (27 ka) and H6 (60 ka) (the 'detrital factor' slightly increases).

Since illite, chlorite, and kaolinite all increase simultaneously during the Heinrich events, their input probably result from the same mechanism. This mechanism starts abruptly as shown by the rapid increase of the 'detrital factor' at the beginning of the Heinrich events.

Chlorite, illite, and kaolinite, in the northwestern Atlantic basin, derive from the erosion of Precambrian/Paleozoic igneous rocks [START_REF] Piper | Late Quaternary clay mineral distribution along the eastern margin of Canada[END_REF][START_REF] Thiébault | Analysis of sedimentary facies, clay mineralogy, and geochemistry of the Neogene-Quaternary sediments in site 645, Baffin Bay[END_REF] and Paleozoic/Cretaceous sedimentary rocks of the north American continent, especially in the Labrador and Baffin Bay area [START_REF] Boyd | Baffin Bay continental shelf clay mineralogy[END_REF][START_REF] Jennings | The Quaternary history of Cumberland Sound, southeastern Baffin Island: the marine evidence[END_REF]. According to the main actual surface-water circulation pattern in the western basin (Fig. 1), an ice-rafting mechanism is then assumed to be responsible for the enhanced supply of detrital clay minerals as for detrital carbonates [START_REF] Andrews | Detrital carbonate-rich sediments, northwestern Labrador Sea -implications for ice sheet dynamics and icebergs rafting (Heinrich) events in the north Atlantic[END_REF][START_REF] Bond | Evidence for massive discharges of icebergs into the North Atlantic Ocean during the last glacial period[END_REF][START_REF] Grousset | Patterns of ice-rafted detritus in the glacial north Atlantic (40º-55ºN)[END_REF]. A logical model is as follows: during the growth of the Laurentide ice-sheet, its base eroded the sedimentary formations and bedrock of the Canadian Shield, and consequently glacially reworked detrital carbonates (calcite and dolomite) and detrital clay minerals were transported into the ice to the shelf area. There, fragmentation of the ice-sheet released icebergs containing detrital clay minerals, which followed the main surface circulation pattern (Labrador Current) to the North Atlantic ocean (Fig. 1). During their southern transfer, the icebergs began to melt and progressively discharged their detrital load. The northernmost cores (SU90-11 and SU90-12) are located on seamounts, 1000 m above the sea floor, so bottom currents cannot be involved in particle transport to these sites. Close association of increased detrital clays with sand-sized ice-rafted particles at site SU90-11 suggest that sedimentation processes involved ice melting. Melting accelerated when icebergs reached warmer waters near the polar front, and changed direction to follow the North Atlantic Drift, increasing the incorporation of ice-rafted particles (including detrital clays) to the sediment.

The Heinrich events are also characterized by: -An increased supply of IVML supply in (39ºW), whereas IVMLs are absent from the eastern Atlantic basin and in the eastern part of the northwestern Atlantic basin (core SU90-08, 30ºW). The comparison between the variations of both 'detrital' and 'mixed-layer' factors in cores SU90-11 and SU90-12 indicates that increased supply of mixed-layer supply precedes deposition of typically detrital clay minerals.

Moreover, IVML supply stops before detrital clays began to decrease. It suggests (1) that two different mechanisms are involved, and (2) that the IVML supply results from a mechanism more rapid than those responsible for the supply of illite, chlorite, and kaolinite.

-Increased supply of IVML also occurs in the two more recent Heinrich events (H1 and H2) of core SU90-12 where there is no evidence of any increased detrital ice-rafted clays.

All this evidence indicates that IVMLs have not been transported by ice like detrital carbonates and detrital clay minerals. Moreover, the specific location of the cores SU90-11 and SU90-12 (on seamounts, 1000 m above the sea floor) prevents particle transport to these sites by bottom currents. These minerals may be carried either by deep to intermediate water masses or by eolian circulation. Comparison of the distribution of the IVML in the northwestern Atlantic basin and of the main atmospheric circulation pattern is not consistent with an eolian supply [START_REF] Bout-Roumazeilles | Relations entre les variabilités minéralogiques et climatiques enregistrées dans les sédiments de l'Atlantique nord pendant les huit derniers stades glaciaires/interglaciaires[END_REF]. Therefore, intermediate to deep watercirculation may be responsible for the supply of the mixed-layer clays during the Heinrich events. This supply could be associated to the mechanism of the Labrador nepheloid layer [START_REF] Eittreim | Suspended matter along the continental margin of the North American basin[END_REF][START_REF] Eittreim | Turbidity distribution in the deep waters of the western Atlantic trough[END_REF][START_REF] Biscaye | Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans[END_REF]Eittreim, 1974, 1977) or to iceshelf flow [START_REF] Hulbe | An ice shelf mechanism for Heinrich layer production[END_REF]. Ice-flow during fragmentation of ice caps and release of icebergs eroded surface sediments of the continental shelves. In the Labrador Sea, these shallow sediments are enriched in IVML [START_REF] Bout-Roumazeilles | Relations entre les variabilités minéralogiques et climatiques enregistrées dans les sédiments de l'Atlantique nord pendant les huit derniers stades glaciaires/interglaciaires[END_REF][START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF], formed through pedogenic processes and transported to the shelf area by run-off during interglacials (Fig. 7). These particles contribute to the formation of a nepheloid layer which flows at intermediate depth because of relatively high density. Increased fragmentation of the Labrador ice sheet during some Heinrich events (H1, H2, H4 and H5) may have resulted in intensified erosion of IVML-rich surface sediments on the shelf. Increased IVML appears directly linked to ice-sheet dynamics. Increases of both ice-rafted detritus and IVML characterizes the Heinrich events but they are not closely dependent (Fig. 6). This suggests variations of ice-sheet dynamics in relation to climate, which need further investigations.

Spatial distribution of the nepheloid layer

Extension of the nepheloid layer can be estimated by comparison of mineralogical data from subsurface sediments at various depths, latitudes and longitudes of the northwestern Atlantic (Table 7). The database includes the Paleocinat I cruise mineralogical data [START_REF] Bout-Roumazeilles | Relations entre les variabilités minéralogiques et climatiques enregistrées dans les sédiments de l'Atlantique nord pendant les huit derniers stades glaciaires/interglaciaires[END_REF], and mineralogical results [START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF] from the Labrador Sea and the North Atlantic Ocean (cruises Hudson 90 and 91).

The IVMLs are abundant at shallow water depth (301 to 530 m) of the southern Labrador shelf (cores 1, 2, and 3, Table 7). They decrease at deeper water depth: 5% in core 4 (1364 m), trace amounts in cores 5 (1984 m) and 6 (2648 m). These results indicate that the nepheloid layer formed in shallow areas, especially off southern Labrador. The presence of IVML in subsurface sediments from seamounts east of the shelf (cores provides evidence of the main southeastward direction of the nepheloid layer (Fig. 7).

However, it is surprising not to find IVML in core 7 nor in cores 25, 27, and 28 [START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF]. This could result from the deep location of these cores (between 3378 and 3992 mbsf), but in this case it is difficult to explain the presence of IVML in core SU90-11 (3645 mbsf).

Nevertheless the northern edge of the nepheloid layer is roughly situated near 57ºN. This edge is related to the position of the intermediate-to deep-water current, which flows from the Irminger basin to the Labrador basin off southern Greenland. IVMLs have not been reported from the northeastern Atlantic basin. The analysis of the clay mineral fraction from cores 9003,9005,9006,9009,9010, does not reveal any traces of IVML in subsurface sediments. This indicates that the eastern edge of the nepheloid layer (Fig. 7) is situated somewhere between 39ºW (core SU90-12) and 34ºW (core 9010). Hence it appears that the mid-oceanic ridge acts as a barrier to prevent the extension of the nepheloid layer into the northeastern Atlantic basin. The nepheloid layer flows southward, following the pattern of deep circulation (Fig. 7) and carrying IVML to the latitude of New Jersey at least [START_REF] Deconinck | Eocene to Pleistocene clay mineral sedimentation off New-Jersey, western north Atlantic (ODP Leg 150, sites 903 and 905[END_REF].

Conclusions

(1) Most Heinrich events of the northwest Atlantic Ocean are characterized by major modifications of the clay minerals association and incorporation of clay-size ice-rafted particles to the sediments: (a) Heinrich events H1, H2, H4, and H5 are enriched in illite, chlorite, and kaolinite.

Illite and chlorite are typically detrital clay minerals resulting from glacial erosion. In the northwestern Atlantic basin, they mainly derive from the Precambrian and Paleozoic igneous and sedimentary rocks of the North American continent [START_REF] Piper | Late Quaternary clay mineral distribution along the eastern margin of Canada[END_REF][START_REF] Thiébault | Analysis of sedimentary facies, clay mineralogy, and geochemistry of the Neogene-Quaternary sediments in site 645, Baffin Bay[END_REF]. In the northwestern Atlantic basin, kaolinite is derived from adjacent landmasses where it formed during pre-glacial or interglacial periods, and from old sedimentary formations (such as the black Cretaceous mudstones of Labrador [START_REF] Boyd | Baffin Bay continental shelf clay mineralogy[END_REF][START_REF] Jennings | The Quaternary history of Cumberland Sound, southeastern Baffin Island: the marine evidence[END_REF].

(b) The Heinrich layers are also enriched in IVML, which formed during interglacial periods through pedogenic processes [START_REF] Berry | Mineralogy of the clay-size fractions of some north-Atlantic Arctic Ocean bottom current[END_REF]. In the northwestern Atlantic basin, these minerals have been transported by run-off during interglacial periods from the Canadian Appalachian Mountains [START_REF] Yang | Clay minerals as indicators of diagenetic and anchimetamorphic grade in an overthurst belt, external domain of southern Canadian Appalachians[END_REF] to the Labrador shelf [START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF].

(2) Clay mineral studies show that the Heinrich layers do not only result from an icerafting mechanism, and the dynamic of their formation is complex and results from at least two important mechanisms: [START_REF] Eittreim | Suspended matter along the continental margin of the North American basin[END_REF][START_REF] Eittreim | Turbidity distribution in the deep waters of the western Atlantic trough[END_REF][START_REF] Biscaye | Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans[END_REF]Eittreim, 1974, 1977). [START_REF] Andrews | Detrital carbonate-rich sediments, northwestern Labrador Sea -implications for ice sheet dynamics and icebergs rafting (Heinrich) events in the north Atlantic[END_REF] first proposed its contribution to the Heinrich deposits on the basis of high sedimentation rates. This mechanism is more rapid, and at least as important as ice-rafting discharges, because of the huge amounts of particles transported in a very short time. The extension of the nepheloid layer is determined by comparison of mineralogical analyses of subsurface sediments from different cores. The nepheloid layer forms in shallow areas and flows eastward along the slope and in the basin at intermediate water depth, to the mid-oceanic ridge which prevents penetration of the nepheloid layer into the northeastern Atlantic basin. The current flows principally southward, following the main pattern of deep-water circulation.

(3) Comparison between the variations of IVML and of illite C chlorite C kaolinite, indicates that increased mixed-layer supply by the nepheloid precedes the detrital clay supply by ice-rafting processes. The nepheloid layer formation and ice-rafting processes do not depend directly from each other. Nevertheless, ice-sheet dynamics are assumed to be responsible for both mechanisms. This implies that ice-sheet dynamics are more complex than previously thought, and that they strongly control the transport of fine particles to the ocean. Therefore, clay minerals could be used as markers for further investigations of the dynamics of ice-sheets. [START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF].

Figure captions

Table 1 Core characteristics Table 2 Age-depth relation for the studied cores Table 3 Mean clay mineral composition (%) and standard deviation (Sd) of sediments from the studied cores without Heinrich layers data Table 4 Mean clay mineral composition (%) and standard deviation (Sd) of Heinrich layers sediments from the studied cores Table 5 Correlation matrix between clay minerals species for the studied cores Table 6 Scores of the orthogonal transformation varimax solution (factor analysis) for the detrital, smectite, and mixed-layer factors for the studied cores Table 7 Core characteristics, and 10-14v percentages in subsurface sediments

  (a) Detrital carbonates and typically detrital clay minerals (illite C chlorite C kaolinite) are carried and discharged by icebergs during disintegration of the Laurentide ice-sheet. (b) The enhanced supply in IVML results from the erosion of the shelf during formation of a dense nepheloid layer flowing at an intermediate water depth, and following the general pattern of intermediate and deep-water circulation. Such a nepheloid layer is seasonally documented in the modern Labrador Sea

Fig. 1 .

 1 Fig. 1. Study area, cores location and main deep and surface circulation patterns modified from McCave and Tucholke (1986), Dickson and Brown (1994) and Lucotte and Hillaire-Marcel (1994).

Fig. 2 .

 2 Fig. 2. Age-depth relation for the studied cores.

Fig. 3 .

 3 Fig. 3. δ 18 O on benthic and planktonic foraminifera of cores SU90-08, SU90-11, SU90-12 and SU90-38. The Heinrich layers are indicated by gray rectangles.

Fig. 4 .

 4 Fig. 4. Variations of the detrital (gray line) and smectite factors (dashed line), and δ 18 O on benthic foraminifera over the last 130 kyr for cores SU90-08 (lower). Variations of the detrital and smectite factors over the last 130 kyr for core SU90-38 (upper). Heinrich Events H1 to H6 are indicated by gray rectangles.

Fig. 5 .

 5 Fig. 5. Variations of the detrital (gray line), smectite (dashed line), and mixed-layer (solid line) over the last 130 kyr for cores SU90-11 (lower) and SU90-12 (upper). Heinrich Events H1 to H6 are indicated by gray rectangles.

Fig. 6 .

 6 Fig. 6. Nepheloid layer and Ice-Rafted-Detritus transportation mechanisms since the Labrador continental shelf area toward the open ocean during the Heinrich events, in relation with the vertical and horizontal growth of the Laurentide ice-sheet. ICK = detrital minerals: illite, chlorite, and kaolinite. IVML = illite-vermiculite mixed-layer red clay.

Fig. 7 .

 7 Fig. 7. Main sub-actual extension of the nepheloid layer main surface and IRD transportation patterns according to clay mineral analyses from Paleocinat I cores 9003 to 9020 (Bout-Roumazeilles, 1995) and from Hudson 90-91 cores[START_REF] Fagel | Clay mineral signature of the NW Atlantic Boundary Undercurrent[END_REF].

Acknowledgements

We are grateful to Philippe Récourt for technical assistance. Review and constructive comments by C. Robert and K.T. Pickering are gratefully acknowledged. The coring cruise Paleocinat I of the French R/V Le Suroît was supported by Genavir and IFREMER. This work was financially supported by PNEDC from INSU, by the EEC program Environment and Climate (EV5V-CT92-0117) and by the URA 719 CNRS 'Sédimentologie et Géodynamique', Université de Lille 1.


E Geulin

B Pégourié

M Goto

G Motojima

R Sakamoto

A Matsuyama

Link between ablation and line emission for hydrogen fuelling pellet in LHD

Ablation rate ∝ Line emission H 𝜶 • Volume averaged cloudlets parameters determined

→•

  Cloudlet physical and geometrical characteristics as initial conditions of the drift phase Fuel the plasma core after ablation and homogenization (drift phase) Fueling → Depends mainly on the ablation profile Local pressure perturbation in the plasma edge ELM Pacing → Depends on ablation profile of multiple fragments in rapidly evolving plasma used : • High speed imaging spectroscopy ○ multibranch fiberscope + fast camera ○ 1 image every 20 μs, exposure time: 2 μs. ○ Each objective lens is equipped with a band filter (H β with two filter widths: 5 and 20 nm, and the continuum close to λ = 576 nm) used : • High speed imaging spectroscopy • Fast diodes • Absolutely calibrated high-resolution spectrometer Experimental apparatus -LHD 2/10 The LHD stellarator : • R = 3.6 m, • a = 0.6m, • B = 3 T 3 diagnostics were used : • High speed imaging spectroscopy • Fast diodes • Absolutely calibrated high-resolution spectrometer ○ 1 spectrum every 16 μs, time resolution 84 μs ○ domain λ = 370 -710 nm : • R = 3.6 m, • a = 0.6m, • B = 3 T 3 diagnostics were used : • High speed imaging spectroscopy • Fast diodes • Absolutely calibrated high-resolution spectrometer ⇒ Accurate time cross calibration of the 3 diagnostics ⇒ Camera image + Diode + each cloudlet determine: density(n), temperature(T), radius(R), length(Z) II. Get the local ablation rate III. Determine its link with the different line emission Model: Radiation model coupled to a 3-D radiative transfer calculation ❏ Local thermodynamic equilibrium assumed ❏ Line Emission / Bremsstrahlung / Radiative attachment / Recombination taken into account ❏ Cloudlet assumed cylindrically symmetric The only cloudlet spectrum can be fitted by severals (n,T,R,Z) 𝑍 = 2.22 m , 𝑅 = 0.13 cm 𝑍 = 0.05 m, 𝑅 = 1are composed of A. A : (≈ 10 25 m -3 ) and cold (≈1 eV) core B. A thin less dense ( ≈10 24 m -3 ) and hotter (≈ 2 eV) external layer II. The contribution of the thin layer to the spectrum is small but its presence is required for an accurate fit of the images Result 3 / 5: Cloudlet parameters along pellet path 7/10 I. Ablation rate is calculated as N𝝂, → cloudlets particle contents N (i.e. the ablation rate multiplied by the time for building a cloudlet) → cloudlet ejection frequency 𝝂 (i.e. the inverse of the time for building a cloudlet) II. 𝝂 is determined from the oscillations of the diode signals (from 50 to 100 kHz, increasing along the pellet path). and emission dependence with time shows although the general trend of the ablation rate and line emissions are similar, ⇒ no clear proportionality can be established between them ⇒ one cannot accurately infer the ablation profile from line emission. unambiguous determination of ablation cloudlet characteristics requires the knowledge of calibrated images and spectrum. II. The model and procedure described here allows to evaluate: -The cloudlet geometry, density and temperature distributions, -The local (i.e. instantaneous) ablation rate, -The relation between line emission (H 𝞪 , H 𝞫 …) and the ablation rate ⇒ No strict proportionality is observed between them. each cloudlet determine : density(n), temperature(T), radius(R), length(Z) II. Get the local ablation rate III. Determine its link with the different line emission Model : Radiation model coupled to a 3-D radiative transfer calculation ❏ Local thermodynamic equilibrium assumed ❏ Line Emission / Bremsstrahlung / Radiative attachment / Recombination taken into account ❏ Cloudlet assumed cylindrically symmetric Camera


Julien Abadji
email: julien.abadji@inria.fr

Pedro Javier Ortiz Suárez

Laurent Romary
email: laurent.romary@inria.fr

Benoît Sagot

Ungoliant: An Optimized Pipeline for the Generation of a Very Large-Scale Multilingual Web Corpus

Since the introduction of large language models in Natural Language Processing, large raw corpora have played a crucial role in Computational Linguistics. However, most of these large raw corpora are either available only for English or not available to the general public due to copyright issues. Nevertheless, there are some examples of freely available multilingual corpora for training Deep Learning NLP models, such as the OSCAR and Paracrawl corpora. However, they have quality issues, especially for low-resource languages. Moreover, recreating or updating these corpora is very complex. In this work, we try to reproduce and improve the goclassy pipeline used to create the OSCAR corpus. We propose a new pipeline that is faster, modular, parameterizable, and well documented. We use it to create a corpus similar to OSCAR but larger and based on recent data.Also, unlike OSCAR, the metadata information is at the document level.

Introduction

With the increasing interest in language modeling in recent years in Natural Language Processing (NLP) [START_REF] Rogers | A primer in BERTology: What we know about how BERT works[END_REF], particularly concerning contextualized word representations1 [START_REF] Peters | Deep contextualized word representations[END_REF][START_REF] Devlin | BERT: Pre-training of deep bidirectional transformers for language understanding[END_REF], there has also been an explosion in interest for large raw corpora, as some of these latest models require almost 1TiB of raw text for pre-training [START_REF] Raffel | Exploring the limits of transfer learning with a unified text-to-text transformer[END_REF][START_REF] Tom | Language models are few-shot learners[END_REF].

While most of these language models were initially trained in English [START_REF] Devlin | BERT: Pre-training of deep bidirectional transformers for language understanding[END_REF][START_REF] Yang | Xlnet: Generalized autoregressive pretraining for language understanding[END_REF][START_REF] Clark | ELECTRA: pretraining text encoders as discriminators rather than generators[END_REF][START_REF] Zaheer | Big bird: Transformers for longer sequences[END_REF][START_REF] Xiong | Nyströmformer: A nyström-based algorithm for approximating selfattention[END_REF] and consequently most of the large corpora used to pre-train them were in English, there has been a recent push to produce larger high quality corpora for other languages, namely those of [START_REF] Grave | Learning word vectors for 157 languages[END_REF], CCNet [START_REF] Wenzek | CCNet: Extracting high quality monolingual datasets from web crawl data[END_REF], Multilingual C4 (mC4) [START_REF] Xue | mt5: A massively multilingual pre-trained text-to-text transformer[END_REF] and OSCAR [START_REF] Javier | Asynchronous pipelines for processing huge corpora on medium to low resource infrastructures[END_REF], 2020) for pre-training language models, as well as, Paracrawl [START_REF] Esplà | ParaCrawl: Web-scale parallel corpora for the languages of the EU[END_REF][START_REF] Bañón | ParaCrawl: Web-scale acquisition of parallel corpora[END_REF], CCAligned [START_REF] El-Kishky | CCAligned: A massive collection of cross-lingual web-document pairs[END_REF] and WikiMatrix [START_REF] Schwenk | Wiki-Matrix: Mining 135M parallel sentences in 1620 language pairs from Wikipedia[END_REF] which are parallel corpora for training Machine Translation (MT) models. Of these, only OSCAR, Paracrawl, CCaligned and WikiMatrix are freely available and easily downloadable.

In this paper we propose a new multilingual corpus for language modeling, and for that we take inspiration in the OSCAR corpus and its pipeline goclassy2 [START_REF] Javier | Asynchronous pipelines for processing huge corpora on medium to low resource infrastructures[END_REF], 2020), but we propose a new pipeline Ungoliant3 that is faster, modular, parametrizable and well-documented. We then use it to produce a new corpus similar to OS-CAR, yet larger, based on recent data containing mentions of last years' events such as the COVID-19 pandemic, the 2020-2021 United States racial unrest, the Australian wildfires, the Beirut explosion and Brexit among others. Moreover, contrarily to OSCAR, our corpus retains metadata information at the document level. We release our pipeline under an Apache 2.0 open source license and we publish the corpus under a research-only use license following the licensing schemes proposed by OSCAR [START_REF] Javier | Asynchronous pipelines for processing huge corpora on medium to low resource infrastructures[END_REF], 2020) and Paracrawl [START_REF] Esplà | ParaCrawl: Web-scale parallel corpora for the languages of the EU[END_REF][START_REF] Bañón | ParaCrawl: Web-scale acquisition of parallel corpora[END_REF]. its Generation Pipeline

OSCAR

OSCAR is a multilingual corpus derived from Com-monCrawl4 , a project that provides web crawl data for everyone on a periodic manner, usually each month. CommonCrawl provides data in several formats, from raw HTML source code to pure text. OSCAR was generated from the pure text data version (WET files) of the November 2018 crawl, distributed in the form of 56,000 shards, that were then filtered and classified by language (Ortiz [START_REF] Javier | Asynchronous pipelines for processing huge corpora on medium to low resource infrastructures[END_REF][START_REF] Javier | A monolingual approach to contextualized word embeddings for mid-resource languages[END_REF]. OSCAR is available through several means, and has been used in numerous projects [START_REF] Javier | Asynchronous pipelines for processing huge corpora on medium to low resource infrastructures[END_REF]. OSCAR's generation pipeline also suffers from numerous issues, which we plan to address simultaneously with the release of a new, more powerful, stable, and higher quality pipeline Simply put, OSCAR is composed of single language files that contain textual data (ta.txt for the Tamil language, for example). However, due to the often huge sizes of these files, and subsequently the impracticality of storage and distribution, OS-CAR files are split and compressed in equally sized parts.

OSCAR comes in four different versions, each suited differently for different tasks, and allows less limited ways of sharing the corpus more widely. These versions are either unshuffled or shuffled (that is, for each language, lines have been shuffled, destroying records integrity), and non-deduplicated or deduplicated (since duplicate lines account for more than half of the total data5 generated by the pipeline). For the unshuffled versions, each language file contains paragraphs that come from the same record, and each paragraph is separated by a newline.

OSCAR is inherently linked to its generation pipeline, and as such its quality partly depends on the pipeline's quality. While OSCAR is considered to be one of the cleanest multilingual corpora available [START_REF] Caswell | Language ID in the wild: Unexpected challenges on the path to a thousandlanguage web text corpus[END_REF][START_REF] Caswell | Quality at a Glance: An Audit of Web-Crawled Multilingual Datasets[END_REF], several problems have been described, and the state of the publicly available code raises questions about maintenance and maintenability of the pipeline itself.

Apart from the fact that its content dates back to 2018, the current OSCAR corpus suffers from quality issues discussed in [START_REF] Caswell | Language ID in the wild: Unexpected challenges on the path to a thousandlanguage web text corpus[END_REF][START_REF] Caswell | Quality at a Glance: An Audit of Web-Crawled Multilingual Datasets[END_REF], including:

• Language label mismatches and inconsistencies, which occurs earlier in the pipeline and would be fixable downstream,

• Representation washing as defined by [START_REF] Caswell | Quality at a Glance: An Audit of Web-Crawled Multilingual Datasets[END_REF], whereby low resource languages, while present in the corpus, are of a significantly lower quality than higher resource languages without any quality metric available publicly.

The most recent Common Crawl dump contains 64,000 shards. Each shard is composed of numerous records, and each record holds textual content along with metadata. While CommonCrawl shards hold document-level metadata that could be useful downstream, they were discarded and do not appear in OSCAR, whereas other corpora generated from the same source include them, e.g. CCNet [START_REF] Wenzek | CCNet: Extracting high quality monolingual datasets from web crawl data[END_REF]. This limits OSCAR users to the textual content only, whereas metadata could have been distributed along with the corpus itself.

goclassy

OSCAR was built using goclassy, a highperformance asynchronous pipeline written in Go [START_REF] Javier | Asynchronous pipelines for processing huge corpora on medium to low resource infrastructures[END_REF]. However, it suffers from several caveats that makes the re-generation and update of the corpus relatively complex in practice.

While goclassy's source code is easily readable thanks to the choice of an uncluttered language and a pragmatic approach, the lack of structure in both the source and the project itself makes goclassy difficult to extend and maintain.

The pipeline is not functional out-of-the-box, as the user has to provide the compressed shards from CommonCrawl, manually install fasttext [START_REF] Joulin | Fasttext.zip: Compressing text classification models[END_REF][START_REF] Joulin | Bag of tricks for efficient text classification[END_REF] and create specific directories by themselves, since only partial instructions are given in the supplied README file.

goclassy also makes heavy use of I/O, as data is saved and loaded repeatedly between steps; as an example, the identification step stores language identification data and individual sentences in two files, before generating the final files (one per language). Despite these limitations, goclassy's performance is good due to Go's emphasis on easy and efficient parallelization and inherent speed. The pipeline uses clever handling of file descriptors, limiting I/O calls cost in some parts.

Building a new OSCAR-like corpus

We introduce Ungoliant, a new corpus generation pipeline that, like goclassy, creates a large-scale multilingual text corpus from a CommonCrawl dump. Contrarily to goclassy, Ungoliant is fully modular, better structured, and highly parametrizable; thereby allowing comparisons between several parallelization strategies. A specific effort was put in testing and documentation. Parts of Ungoliant are heavily inspired by goclassy, although it is implemented in Rust rather than in Go, which is sometimes faster. 6Additionally, we use Ungoliant to generate a new corpus from a recent Common Crawl dump. The new corpus includes metadata information while retaining backward compatibility with the OSCAR corpus.

Ungoliant

Rationale and scope

While Ungoliant is heavily inspired by goclassy, it provides a better set of tools to download, process, filter and aggregate textual and contextual data from CommonCrawl. These operations can be sequential, parallel or both, depending on contexts and performance requirements.

We provide both batch and streaming processing, so that the whole pipeline could be run either online, with every step running on streams of data, or offline, with every step running on tangible files, or a mix of both, using already downloaded Common-Crawl dumps but streaming the rest of the process. Moreover, we embed numerous filtering and deduplication utilities directly inside Ungoliant, making these features available for pipeline composition and post-processing.

Ungoliant features a loosely defined pipeline interface, on which we re-implement goclassy's one, while improving performance by threading more aggressively and avoiding I/O where it is not necessary: While goclassy uses intermediate files for tags and sentences, we try to keep everything in memory in order to avoid losing time loading or writing files. The Rust language provides constructs that helps us build complex abstractions and pipelines while limiting proactive file I/O or computing, since nearly all the reimplemented pipeline is built around lazy evaluation. File I/O is only used when loading shards, and when writing sentences in language files. Through benchmarking we found that the best parallelization strategy is to use rayon7 , a workstealing [START_REF] Blumofe | Scheduling multithreaded computations by work stealing[END_REF] parallel and concurrent library enabling massive parallelization. We parallelize on shard-, record-and sentence-level processing.

To evaluate Ungoliant performance, we run both goclassy and Ungoliant's implementation on 1, 10, 25 and 100 Common Crawl shards both on a middle-range laptop computer (i5-7200u, 8GB RAM, NVMe SSD) and a HPC node (Xeon 5218 (64 Threads), 180GB RAM). Results are shown in Table 1.

Ungoliant performs better than goclassy on all tasks, independently of the platform or number of shards processed. However, we can note that Ungoliant's speedup is higher on short tasks, which is explained by its aggressive multithreading strategy, while goclassy uses a record-scope multithreading at its finest granularity.

Iterating on the goclassy pipeline

CommonCrawl dumps contain metadata that hold useful information such as related records, recognized language(s), or origin URLs. Since OSCAR pipeline discards metadata and sentences can be shuffled, we lose the ability to investigate those metadata themselves, as well as working on potentially multilingual documents, since we separate text from metadata.

The new pipeline (and the resulting new corpus schema) aims to establish a first link between textual data and metadata from CommonCrawl, while staying backward compatible with the existing OS-CAR schema.

In other words, switching from the original OS-CAR corpus and the newly generated one should be a drop-in operation.

Metadata extraction and linking

Our choice of keeping the corpus backward compatible with the original OSCAR introduces changes in the way the corpus is generated, namely regarding metadata: a record's body is composed of sentences that aren't guaranteed to be of the same language. Since OSCAR merges sentences from multiple records into a single file, special attention has to be paid to the metadata dispatch too.

Approaches to tackle this problem range from (1) storing all metadata in a single location to (2) having language-specific metadata files that contain the metadata for each line in the language file.

Both (1) and ( 2) have their strengths and weaknesses, namely:

1. Having all metadata at the same place may facilitate wide queries about whole metadata, but at a cost of a very large size (which harms both accessibility and performance).

2. Getting the metadata for a given line is fast since line numbers are synchronized, but there is repeated information and a potentially important increase in size.

We choose a hybrid approach which keeps metadata local to each language, while trying to limit the information repetition by keeping an entry by group of chunks rather than by line, where a chunk is a series of contiguous sentences that share the same language from the same document.

An overview of the pipeline can be seen in Figure 1, with a more precise view on record processing and metadata extraction in Figure 2.

Metadata are distributed via JSON-encoded files holding an ordered list of metadata entries, along with offsets (o) and paragraph lengths (l), enabling any user to get the content of a said metadata by querying for lines (o, o + l] in the content file.

This approach still has drawbacks, in particular when looking for the corresponding metadata of a given sentence/paragraph, where one has to perform a search on the metadata file, or when working with multilingual documents. Another drawback is the resulting cost of potentially merging back numerous language parts: Since metadata query is offset-based, merging back metadata files implies updating those offsets.

Having paragraphs and metadata linked by offsets in a highly parallelized pipeline implies to take special care at the offset level. The solution is to use shard-scoped offsets (starting from 0 for each language), and to keep global offsets protected by a mutex guard. This way, when a given shard is done processing and is ready to be written on disk, we convert shard-scoped offsets to global-scoped ones, update the global-scoped ones and then write text and metadata on disk. We compare running times for the reimplementation of the goclassy pipeline, and our new pipeline adding metadata extraction, using both desktop and HPC contexts. The results are reported in Table 2.

Metadata generation does not seem to influence generation time dramatically. However, we can notice a slight performance difference between HPC and Desktop contexts. These differences may lie in the storage medium differences, I/O layout, or algorithmic peculiarities benefiting desktop contexts because of other bottlenecks.

Characteristics of our new backward compatible OSCAR-like corpus

We evaluate the newly generated corpus, assessing its ability to reflect events that occurred after the publication of OSCAR 2018 and detail the metadata format and potential use.

Comparison with OSCAR

While it is expected that our new corpus has a larger file size than OSCAR since CommonCrawl itself grew from 7.42TB to 8.06TB, metadata quickly adds up and take for nearly 15% of the whole uncompressed data. The size augmentation is not the same for each language, and while the whole corpus is bigger now, some languages are smaller than they were before. Results show that already largely represented languages gain more and more data (like the English language, which constitutes more than a third of the original OSCAR), except for the Russian language which loses approximately 100Gb of textual content. These results are summarized in Figure 3.

• • • • • • • •
However, in a context where the number of languages is very high (higher than 150) and of varying sizes, evolution can't be analyzed via a mere size evaluation. By computing, for each language, the relative size difference between the 2018 and 2021 releases of OSCAR, less resourced languages do appear, hinting at a better representation of some of them. These results can be found in Figure 4.

Numerous languages have been omitted from Figure 4, either:

• because they were present in the original OS-CAR and are now absent (Central Bikol and Cantonese)

• because they were absent in the original OS-CAR and are now present (Manx, Rusyn, Scots and West Flemish)

Precautions have to be taken when using these corpora and further work has to be done to correctly assess the quality of low-to-mid resource languages in order to better reflect the quality of each corpus to the OSCAR users. Some languages exhibited either a particularly low number of sentences or a very low quality, and as such couldn't be usable, while still accounting for a language in the total language count of the original OSCAR.

Metadata

Metadata provides new contextual data that is useful to evaluate the corpus and draw metrics. The total size of metadata is 1.2TB, ranging from 4Kb to 500Gb, depending on the number of lines. Relative size varies from 100% to 20%, diminishing with the textual data size, which is expected.

Metadata are provided in single files for now, but split versions of both textual and contextual data will be released soon after the release of the corpus, enabling easy access.

Our choice of keeping metadata aside from the main content adds some complexity when working with both textual and contextual data: • Looking for lines corresponding to a particular metadata entry is easier: one has to read the textual file, skipping until the o-th line, then read l lines.

Presence of events

Using a sample of an English part of our corpus, we perform a simple search of terms in order to assess and compare the presence of pre-and post-2018 events and persons in both corpora. Terms and frequency are grouped in Table 4.

Our corpus keeps around the same number of occurrences for pre-2018 events or public figures such as Barack Obama, while increasing the occurrence of people linked to more recent events (Joe Biden). We include search terms linked to post-2018 events in French and Arabic which are smaller corpora (resp. 200 and 80 GB), and in Burmese, a mid-resource language (approximately 2GB). We observe a term occurrences evolution that reflects the linked events' timing and importance.

License

This new corpus will be released under a researchonly license that is compliant with the EU's exceptions for research in text and data mining. Contrarily to the original OSCAR, no shuffled version of the corpus will be distributed, instead we will put in place an authentication system that will allow us to verify that requests for the corpus come from research institutions. A contact form will be also provided for independent researchers so that we can study their particular cases and determine if the utilization of the corpus corresponds to a legitimate research use.

Moreover, the introduction of metadata makes our corpus far more queryable, thus simplifying and speeding up the handling of take-down GDPR requests. this reason, we will be releasing the complete set of metadata under a CC0 public domain license, so that any individual can check if their personal or even copyrighted data is in our new corpus and make a request accordingly.

Conclusion

We show that our solution is able to generate an OSCAR-like corpus that is augmented with metadata without breaking compatibility, while being faster, better tested and thoroughly documented. We believe our new pipeline and corpus will be useful for applications in computational linguistics as well as in corpus linguistics in general.

The generated corpus is of a larger size when including metadata and without deduplication. How-ever, deduplicated textual content is of the same magnitude between OSCAR 2018 and OSCAR 2021, while reflecting topic changes from all over the world. This fact suggests that old data may be lost with the time passing, and could be resolved by using CommonCrawl releases to build an incremental corpus, with every version augmenting the corpus size.

Metadata enables queries and statistics on the generated data, and we believe that it can be used to filter OSCAR to generate corpora that respond to certain criteria.

We plan to make this new version of OSCAR available under research constraints, with split versions of both textual content and metadata along with tools to operate on the corpus, enabling fast and easy operation on the corpus for researchers.

Figure 1 :Figure 2 :

 12 Figure 1: Scheme of the Ungoliant pipeline. The red square represents CommonCrawl content hosting, where the compressed shards are fetched. The Process Shard steps hold shard processing, paragraph creation and merging (see Figure 2), and are internally parallelized. • : CommonCrawl compressed shard. • : Uncompressed shard, containing records. • : Record Metadata • : Language identification • ¶: Paragraph, composed of sentences identified as

Figure 3 :

 3 Figure 3: Comparison of language size (in bytes) between OSCAR 2018 and OSCAR 2021 (top/bottom 5 only).

Figure 4 :

 4 Figure 4: Comparison of language percentage between OSCAR 2018 and OSCAR 2021 (top/bottom 5 only).

•

  When trying to get the metadata of given sentence, one has to get the line number k, then sequentially (or use a search algorithm since offsets are sorted) look for the record (with offset o and length l), where k ∈ [o, o + l].

Table 1 :

 1 Comparison of approximate generation times depending on platform and number of shards.

	Platform #shards goclassy Ungoliant Approx. speedup
		1	30s	13s	×2.3
	Desktop	10	3m6s	2m12s	×1.3
		25	9m10s	5m47s	×1.5
		1	40s	6s	×6.6
	HPC	25	2m40s	1m6s	×2.4
		100	7m59s	4m14s	×1.8

Table 3 :

 3 Comparison of CommonCrawl and OSCAR sizes between 2018 and 2021 versions. Compressed (CommonCrawl) sources are from November 2018 and February 2021. Total is Textual + Metadata without deduplication.

Table 4 :

 4 Comparison of occurrences of news-related terms between OSCAR and our corpus in a sample of 100 CommonCrawl shards. For the Burmese language, we use the whole 2018 and 2021 corpus since it is a low resource language. Terms are translated in the corpus language.

	Language	Term	2018	2021
	Arabic	Beirut port explosion	0	31
	Burmese*	Min Aung Hlaing	387	3439
	English	Obama 30039 27639
	English	Biden	990 19299
	French	Yellow Vests	2	96

In which one takes a unnanotated large textual corpus in a particular language and tries to predict a missing word in order to learn a vector space representation for it.

https://github.com/oscar-corpus/ goclassy

https://github.com/oscar-corpus/ ungoliant

https://commoncrawl.org

OSCAR-orig:

6.3TB, OSCAR-dedup: 3.2TB

https://benchmarksgame-team.pages. debian.net/benchmarksgame/fastest/ rust-go.html

https://github.com/rayon-rs/rayon


G L Falchetto

P Tamain

H Bufferand

G Ciraolo

N Fedorczak

Ph Ghendrih

E Laribi

B Luce

E Serre

R Tatali

la diffusion de documents scientifiques

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The formation of a strongly reversed radial electric field in the pedestal region of a tokamak plasma is considered to play a key role in the generation of improved confinement regimes, as the related sheared flow is suspected to strongly impact turbulence, by stabilizing it [1] and leading to the formation of an edge transport barrier and to the transition to highconfinement "H-mode" [2]. However, the mechanisms underlying its formation and interplay with turbulent transport are not yet elucidated.

Here, the dynamics of a self-generated reversed radial electric field, Er and its interplay with edge/SOL turbulence are investigated via global flux-driven simulations in 3D geometry with the fluid electrostatic code TOKAM3X [3][4][5][6], in response to increasing injected heating power.

 Systematic spontaneous generation of a reversed radial electric field E r in the proximity of the separatrix is found in TOKAM3X electrostatic non-isothermal turbulence simulations in a limited circular plasma, encompassing CFR and SOL.  E r well strongly increases with increasing injected power, consistently with experimental observations.  Global steepening of the density profile with increasing power.

  Self-generated reversed radial electric field in 3D global flux-driven fluid edge plasma turbulence simulations Gloria L. Falchetto, Patrick Tamain, Hugo Bufferand, G. Ciraolo, Nicolas Fedorczak, P Ghendrih, Elias Laribi, Benjamin Luce, Eric Serre, Raffaele Tatali To cite this version: Gloria L. Falchetto, Patrick Tamain, Hugo Bufferand, G. Ciraolo, Nicolas Fedorczak, et al.. Selfgenerated reversed radial electric field in 3D global flux-driven fluid edge plasma turbulence simulations. EPS 2021 -47th EPS Conference on Plasma Physics, Jun 2021, Virtual conference, France. 45A, pp.P1.1065, Europhysics conference abstracts -ISBN: 979-10-96389-13-1. cea-03301601  Self-consistent 3D electrostatic drift-reduced Braginskii model, 6 fields: 𝑁, Γ 𝑢 ∥ , 𝐸 𝑒 𝑇 𝑒 , 𝐸 𝑖 𝑇 𝑖 , 𝑊 𝜙 , 𝐽 ∥  Non-isothermal turbulence [Baudoin CPP 58 2018; Tatali NF 61, 2021]  Flux-driven global approach: no scale separation  Bohm-Chodura boundary conditions in parallel direction at the limiter [Stangeby, 2000]  Verified via MMS/PoPe/iPoPe (independent Projection on Proper elements) [Cartier-Michaud et al., PoP 23, 2016; PoP 27, 2020]  Versatile geometry (slab/limiter/divertor/different plasma shapes/RMP) [Galassi et al. NF 57, 2017; Nespoli et al. NF 59, 2019; Luce et al., PPCF 63, 2021]  Neutrals via coupling to EIRENE [Fan et al. Nucl. Mat. Energy 18, 2019 ]

 2 TOKAM3X

 2 Plasma temperature profiles steepen, with the creation of a strong gradient in the near SOL, reminiscent of the narrow  q feature. Interplay of the self-generated reversed E r with turbulence: -particle and energy transport fluxes in the CFR from turbulent to diffusive, -dominantly conducted energy fluxes in the SOL -turbulence stabilization in the closed field lines region mainly resulting from reduced collisionality due to the increased T Particle and energy fluxes: from turbulent to diffusive Self-generated reversed radial electric field in 3D global flux-driven fluid edge plasma turbulence simulations 3D global flux-driven model [Tamain et al., JCP 321, 2016] Circular limited case, encompassing closed field lines region (CFR) and Scrape-Off-Layer (SOL) r/a=0.8-1.2 (including buffers) COMPASS-like tokamak plasma parameters: Injected heating increased in two steps from baseline simulation: [P, Px1.5, Px2] Runs > 10 6 t ( ci -1 ) up to quasi-stationary state ~ [5, 3.8, 1] ms Mesh resolution on ½ torus : (,,) 64 x 512 x 64 Upcoming, simulations in more realistic edge plasma conditions • particle source at the limiter • recycling neutrals • divertor geometry • neoclassical viscosity • realistic collisionality  Recently released SOLEDGE3X code [8] cfr Bufferand IAEA 2021  Recently released SOLEDGE3X code [8] cfr Bufferand IAEA 2021 Self-consistent reversed E r generation & profile steepening This work was supported by the EUROfusion -Theory and Advanced Simulation Coordination (E-TASC).

Flux-driven

  simulation, with constant particle flux incoming from the core  radial particle flux constant. The radial particle and electron energy fluxes can be decomposed as: Increased power affects the particle and energy fluxes:  transport from turbulent to diffusive in the CFR : no evident impact of Er shear on the turbulence stabilization  interplay with Er shear in the pedestal  Slight reduction of fluctuation level in CFR increase in near SOL  E r shear max in TOKAM3X simulations (w/o recycling) systematically @ few Larmor radii outside separatrix, in near SOL region similar to [Chankin PPCF 2017]  Reversed E r peak @separatrix, strongly increases with increasing injected power  Global density profile steepening with increasing power and formation of a pedestal in temperature interplay with turbulence: fluctuation level &  N  <E r > t,, Baseline Px1.5 Px2  E r oscillation ~ f GAM [Sugama JPP 2006] -similarity to LCO/I-phase? to be further investigated Cfr in AUG [Cavedon NF 2017 Medvedeva PPCF 2017] in WEST Vermare P4.1078 EPS 2021 <E r > , Density radial decay length  N decreases with power [Falchetto PRL 2004; Tatali NF 2021] r/a=1.1 Energy ExB flux dominantly conducted in SOL