Frédérique Eynaud

LONG TERM AND RECENT CLIMATE CHANGES RECORDED IN NORTH ATLANTIC OCEANIC ARCHIVES AROUND ICELAND

This contribution will compile paleoceanographic and paleoclimatic works which, over the last decades, provided major insights in our understanding of the Earth's climate natural variability and the underlying forcing mechanisms. A focus will be made on peri-icelandic marine records which document the climatic pace at different time-scales and are supported by multiproxy evidences. A special attention to the link in between the ocean and the cryosphere will be done.

Interest of the Icelandic sector 1.A "hot spot" for oceanographers!

The North Atlantic Ocean has always been the focus of extensive researches regarding modern and past oceanographic processes. This ocean is actually one of the world key areas to tackle the question of the thermohaline conveyor (THC) efficiency throughout time, as it houses important components of this major climatic artery (e.g. [START_REF] Broecker | Thermohaline Circulation, the Achilles Heel of Our Climate System: Will Man-Made CO2 Upset the Current Balance?[END_REF][START_REF] Rahmstorf | Risk of sea-change in the Atlantic[END_REF][START_REF] Broecker | What if the conveyor were to shut down?[END_REF]. Iceland represents a topographic barrier at the confluence of the Greenland, Iceland and Norwegian seas (GIN seas, also called the Nordic seas), and major surface and deep gateways thus bracket this domain. [START_REF] Blindheim | Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing[END_REF][START_REF] Mccartney | On the origin of the warm inflow to the Nordic Seas[END_REF] Tchernia, 1978 (SST annual mean). Dotted lines locate the major hydrographic fronts: PF: Polar Front, AF: Arctic Front, SAF: Sub-Arctic Front, after [START_REF] Dickson | The "Great Salinity Anomaly" in the Northern North Atlantic 1968-1982[END_REF]. Source: [START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF].

In the vicinity of Iceland, the duality of the cold currents originating from the Arctic basin versus the northward warm Atlantic inflow (Figure 1a) is plainly expressed at the surface and generates persistent hydrographic structures (Figure 1b) which constrain the distribution of the different water masses. This has direct repercussion on the planktonic living populations and, of course, on their fossil remains through sedimentary archives. Contrasted biological assemblages thus relay throughout time, from the seasonal time scale of the modern ocean, to the orbital scale of the Quaternary sediments. Deep currents aliment the deposit of giant edifices along the complex bathymetry and physiography of this area (Figure 2). In the South Icelandic basin, especially, the Gardar Drift has furnished high quality sedimentary sequences that helped to better constrain the long term and recent climatic changes of the north hemisphere. Sedimentary archives around Iceland furthermore benefit of invaluable chronostratigraphical indicators with the repetitive deposits of ash layers which constitute excellent age tiepoints for paleoceanographers. [START_REF] Faugères | Seismic features diagnostic of contourite drifts[END_REF]. SOURCE : Eynaud PhD thesis 1999

A "hot spot" for paleoclimatologists!

One of the major finding in Paleoclimatology over the last decades has been revealed both in ice cores and in sediment cores with the evidence of large variations of air temperature over millennial and submillennial periods, coupled to major North-Atlantic hydrological changes (Dansgaard et al., 1993, Figure 3). These rapid climatic oscillations, the so called Dansgaard-Oeschger (D-O) events, occur as cyclic but non-periodic phenomenon and represent abrupt and drastic flips of the climate system. They are major challenges regarding our comprehension of the Earth's climate variability and stability. The abrupt cold excursions, i.e. stadial events [START_REF] Dansgaard | Evidence for general instability of past climate from 250-kyr ice-core record[END_REF] or Heinrich events [START_REF] Heinrich | Origin and Consequences of Cyclic Ice Rafting in the Northeast Atlantic Ocean during the Past 130,000 Year[END_REF], which occurred during the last glacial period (Figure 3), provide excellent archives of Pleistocene rapid climatic transitions. They, furthermore, raised major questions about the pace of the natural system. The extreme Heinrich events result from a massive calving of icebergs in relation to the sudden collapse of the peri-arctic ice-sheets during the last glacial period (e.g. [START_REF] Heinrich | Origin and Consequences of Cyclic Ice Rafting in the Northeast Atlantic Ocean during the Past 130,000 Year[END_REF][START_REF] Bond | Correlations between climate records from North Atlantic sediments and Greenland ice[END_REF][START_REF] Hemming | Heinrich events: Massive late Pleistocene detritus layers of the North Atlantic and their global climate imprint[END_REF]. They took place at the end of a saw-tooth shaped cooling cycle of 4 successive stadials/interstadials (e.g. Bond cycles: [START_REF] Bond | Correlations between climate records from North Atlantic sediments and Greenland ice[END_REF]. However, the triggering of these events is still a matter of debate, as they imply complex mechanisms linking ice-sheet, atmosphere and ocean dynamics. Their impact was recognized worldwide (e.g. [START_REF] Leuschner | The low-latitude monsoon climate during Dansgaard-Oeschger cycles and Heinrich Events[END_REF][START_REF] Wang | A High-Resolution absolute-dated Late Pleistocene monsoon records from Hulu Cave[END_REF] and each of the Earth's surface reservoirs, i.e. the cryosphere, atmosphere, oceans, and biosphere, was affected. Some of the most severe Heinrich events impacted dramatically on the North Atlantic's overturning circulation (e.g. [START_REF] Zahn | Thermohaline instability in the North Atlantic during meltwater events: stable isotope and ice-rafted detritus records from core SO75-26KL, Portuguese margin[END_REF][START_REF] Curry | Millennial-scale changes in ventilation of the thermocline, intermediate, and deep waters of the Glacial North Atlantic, in Mechanisms of Global Climate Change at Millennial Time Scales[END_REF][START_REF] Roche | Constraints on the duration and freshwater release of Hein rich event 4 through isotope modelling[END_REF]. These events potentially constitute catastrophic analogues of modern or near-future ice-sheet (Antarctic especially) collapses in the context of global warming.

Regarding its geographical position, the Icelandic sector appears as a strategic sector to study this kind of climatic variability. This is also true regarding long term timescales (Figure 4), as Iceland is surrounded by major gateways which have played a crucial role in the evolution of the climate of the last million years. Several questions are raised on long term climate evolution, they are (1) the origin of the transition, approximately 4 million years ago, of Earth's climate into a state characterized by significant Northern Hemisphere (NH) continental glaciation; (2) the link in between the pace of Earth's climate and the orbital parameters (3) the shift at 900 ka from a 41-kyr obliquity cycle towards a 100 ka quasi-periodic cycle that has since dominated the Earth's climate history (e.g. [START_REF] Raymo | Glacial puzzles[END_REF]. All these questions can be treated from an "Icelandic point of view"!

some critical illustrations of the long term and recent climate changes around Iceland 2.1. about the THC variability

Thanks to the focus that has been put on giant contourite drifts, themselves built by the deep components of the THC, a significant number of sequences now exist in the south Icelandic basin, which furnish excellent documents of the THC variability throughout time. These sequences further served as supports of data compilation to better monitor paleoclimatic and paleoceanographic evolutions at the North Atlantic basin scale and thus represent excellent time -constrained records, tied to ice-core stratigraphies through regional climatic and ash layer tie-points and supported by traditional marine stratigraphic (δ 18 O) and dating techniques ( 14 C). This was the case, at suborbital time-scales, with the construction of the North Atlantic geomagnetic paleointensity stack (NAPIS, [START_REF] Laj | North Atlantic palaeointensity stack since 75 ka (NAPIS-75) and the duration of the Laschamp event[END_REF][START_REF] Laj | Geomagnetic field intensity, North Atlantic Deep Water circulation and atmospheric Δ14C during the last 50 kyr[END_REF]Stoner et al., 2002). In the same way, the "famous 'LR04'' stack of benthic δ 18 O Pliocene-Pleistocene records, compiled by [START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records[END_REF], also benefits for the North Atlantic sector from sequences retrieved in the south Icelandic basin.

These efforts contributed to the construction of a robust picture of the THC variability for the last 75 ka (Figure 5). Merged to the simulation works, they all showed its extreme sensitivity to freshwater inputs and challenged our understanding of abrupt climate changes, a major feature to prescribe its future evolution. This is on this dynamic component that we will focus part of the discussion. The THC variability, as deduced from peri-Icelandic marine archives, will then be documented at different time-scales (from the submillennial one to the orbital one), furthermore using the largest set of paleoceanographic proxies yet available.

migration of the polar front and its relation to icebergs surges : from glacial to modern features

Intimely coupled to the dynamic of the THC is the evolution of the latitudinal position of the Polar Front (PF). At Present, the PF closely follows the Greenland and eastern Canadian continental margins (Figure 1b). In the ocean it is defined as a physical oceanographic structure with high temperature and salinity gradients, which separates two different surface-water masses: the relatively warm, high-salinity Atlantic Water, and the cold low-salinity modified Polar Water carried southwards by the East and West Greenland and Labrador currents [START_REF] Holliday | Retroflection of part of the east Greenland current at Cape Farewell[END_REF]. This front constitutes a strong ecological barrier in the North Atlantic Ocean and also physically constrains sea-ice and iceberg drifting. The latitudinal migration of the Polar Front as south as 40°N during late Pleistocene cold events has been documented by numerous studies (e.g. [START_REF] Mcintyre | Glacial North Atlantic years ago: a CLIMAP reconstruction[END_REF][START_REF] Ruddiman | [END_REF][START_REF] Duprat | Les foraminifères planctoniques du Quaternaire terminal d'un domaine péricontinental (Golfe de Gascogne, Cote Ouest Ibérique, Mer d'Alboran) Ecologie-Biostratigraphie[END_REF][START_REF] Bard | Retreat velocity of the North Atlantic polar front during the last deglaciation determined by 14 C accelerator mass spectrometry[END_REF][START_REF] Abrantes | Sediment fluxes along the northeastern European Margin: Inferring hydrological changes between 20 and 8 kyr[END_REF]. We will build an inventory of its impact over Icelandic and peri-icelandic environments and paleoenvironments.

Figure 1 :

 1 Figure 1 : (a) Schematic view (after[START_REF] Blindheim | Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing[END_REF][START_REF] Mccartney | On the origin of the warm inflow to the Nordic Seas[END_REF] of the North Atlantic major surface currents (NAD, North Atlantic Drift; NAC, Norwegian Atlantic Current; IC, Irminger Current) and the intermediate Mediterranean Outflow Water current (MOW). Source: Eynaud et al. (2007) (b) Modern sea-surface hydrographic conditions of the North Atlantic Ocean. The SST isotherms are fromTchernia, 1978 (SST annual mean). Dotted lines locate the major hydrographic fronts: PF: Polar Front, AF: Arctic Front, SAF: Sub-Arctic Front, after[START_REF] Dickson | The "Great Salinity Anomaly" in the Northern North Atlantic 1968-1982[END_REF]. Source:[START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF].

  Figure 1 : (a) Schematic view (after[START_REF] Blindheim | Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing[END_REF][START_REF] Mccartney | On the origin of the warm inflow to the Nordic Seas[END_REF] of the North Atlantic major surface currents (NAD, North Atlantic Drift; NAC, Norwegian Atlantic Current; IC, Irminger Current) and the intermediate Mediterranean Outflow Water current (MOW). Source: Eynaud et al. (2007) (b) Modern sea-surface hydrographic conditions of the North Atlantic Ocean. The SST isotherms are fromTchernia, 1978 (SST annual mean). Dotted lines locate the major hydrographic fronts: PF: Polar Front, AF: Arctic Front, SAF: Sub-Arctic Front, after[START_REF] Dickson | The "Great Salinity Anomaly" in the Northern North Atlantic 1968-1982[END_REF]. Source:[START_REF] Eynaud | Position of the Polar Front along the western Iberian margin during key cold episodes of the last 45 ka[END_REF].

Figure 2 :

 2 Figure 2 : Major physiographic provinces around Iceland (after[START_REF] Faugères | Seismic features diagnostic of contourite drifts[END_REF]. SOURCE: Eynaud PhD thesis 1999

Figure 3 :

 3 Figure 3 : Climatic evolution of the last 50 ka as depicted by the Greenland ice core record ( 18 O NGRIP) compared to the summer insolation values at 65°N. Numbers on the Figure identify the Dansgaard-Oeschger warm interstadials. HEs : Heinrich events, B/A = Bölling-Alleröd oscillation, YD = Younger Dryas oscillation, TI = Terminaison I. SOURCE : Penaud, A. PhD thesis 2009.

Figure 4 :

 4 Figure 4 : Robert Rohde's Temperature Record Series over the last 5.5 millions years.

Figure 5 :

 5 Figure 5 : Schematic profile of North Atlantic deep-water (NADW) changes in the past 75 kyr (normalized to unity for modern times) based on ARM (anhysteretic remanent Magnetization) results from North Atlantic cores.[START_REF] Laj | Geomagnetic field intensity, North Atlantic Deep Water circulation and atmospheric Δ14C during the last 50 kyr[END_REF].


Jacques Giraudeau
email: j.giraudeau@epoc.u-bordeaux1.fr

THE HOLOCENE CLIMATIC HISTORY OF THE CIRCUM-ICELANDIC OCEANIC REALMS

One of the achievements of the IPY was to foster an unprecedented amount of research initiatives aiming at studying recent (Holocene) changes in ocean circulation and climate in the subarctic and arctic domains. Paleo-investigations offer invaluable information on natural environmental changes at decadal to millennial scale, as well as on the processes driving them. We hereby present some recent results based on proxy records from circum Icelandic areas.

Introduction

The northern North Atlantic and its subarctic and arctic seas have shown in recent decades unprecedented changes in physical and chemical conditions, which directly influence the ecosystem structure and processes. This region is extremely sensitive to the changes related to the humaninduced global warming (IPCC 2007) since there is an intricate connection of cryospheric (ice-sheets and sea-ice), atmospheric (winds related to strong gradients in sea-level pressures) and oceanic (through the opposition of northward flowing Atlantic water and southward flowing polar waters) processes. In particular, satellite observations have revealed a considerable decline in sea ice cover, mostly for the seasonal sea ice which constitutes approximately 50% of total ice coverage for the Arctic and the Antarctic [START_REF] Serreze | Perpsectives on the Arctic's shrinking sea-ice cover[END_REF]. The decline in seasonal ice extent is of particular concern since sea ice not only plays a central role in polar ecosystems but also has a great influence onto the Earth climate system itself. The sensibility of the marine biosphere to changes in local physico-chemical characteristics of the northern North Atlantic has been evidenced in the last decades by in-situ observations of biogeographical shifts of plankton biodiversity (e.g. [START_REF] Beaugrand | Reorganization of North Atlantic marine copepod biodiversity and climate[END_REF] or satellite observations showing drastic modifications in phytoplankton community (e.g. coccolithophore blooms in the Iceland Sea and the Barents Sea). Theses changes are thought to reflect modifications in the stratification and temperature of the water column linked with freshening of the northern ocean induced by sea-ice melting (Curry and Maulitzen, 2005) and increased surficial temperature due to increased northward inflow of Atlantic water [START_REF] Hatun | Influence of the Atlantic subpolar gyre on the thermohaline circulation[END_REF].

The instrumental record is far too short to document the full range of natural variability. In order to produce more reliable predictions of future change, data on longer time scales than the instrumental records, are needed. The climatic history of the past 2000 years with a succession of warm (Roman, Mediaeval) and cold (Little Ice Age) periods shows that rapid climate changes have occurred repeatedly in the recent past with major implications for human settlement throughout the Nordic seas (i.e. Inuit and Viking cultures). In addition, new evidences for optimal thermal conditions during the early part of the present interglacial (Holocene) suggest that the Arctic might have been seasonally ice-free around 9000 yrs before present [START_REF] Fisher | Natural variability of arctic sea-ice cover over the Holocene[END_REF] to an extent which might only be reached by the mid-21 st century [START_REF] Johannessen | Arctic climate change: observed and modelled temperature and seaice variability[END_REF]). However, discrepancies between observed and simulated sea ice distribution raises a need for improving our understanding of the sensitivity of the high latitude feedbacks. There is a crucial need to gain detailed information on the amplitude, the regional patterns, and the mechanisms of past environmental changes observed during the Holocene in order to predict the scale of current climate change. This information can be obtained using two complementary approaches, namely proxy records from marine sedimentary archives and paleoclimate modelling experiments. Proxy records are ideal to document regional ecosystem changes and to assess the physical-chemical processes which drove these ecological shifts.

The aim of this presentation is to question the view of a climatically stable Holocene period, and to provide, based on new proxy-based data, some tips on the regional complexity of both long and shortterm (millennial to centennial) climate and ocean circulation changes in the circum-Icelandic oceanic realms.

Oceanographic setting

The Iceland shelf and nearby oceanic realms bear essential components of the present surface, intermediate and deep circulation of the northern North Atlantic (Hopkins, 2001; Iceland separates an eastern (Iceland-Scotland) strait from a western (Denmark) strait, the passageways of surface Atlantic water inflow to the Nordic Seas and Arctic Ocean, and surface and bottom outflow to the mid-latitudes of the Atlantic Ocean. In terms of volume, the AW inflow to the Nordic Seas has been assessed through year-long instrumental measurements within both straits as ca. 8 Sv, most of this inflow being compensated by outflow from the bottom as ca. 6 Sv (surface outflow carried by the East Greenland Current being assessed at about 1.3 Sv [START_REF] Blindheim | Oceanography and climate[END_REF].

Holocene long-term trends

A zonal diachronism in long-term Holocene sea-surface temperature (SST) trends in the mid/high latitudes of the North Atlantic, equivalent to a ca. 3.5 kyr delay between the eastern and western North Atlantic has been documented from sediment cores in the Labrador, Irminger and Iceland Seas (as summarized by [START_REF] Solignac | Holocene sea surface conditions in the western North Atlantic: Spatial and temporal heterogeneities[END_REF] and the Norwegian Sea (as summarized by [START_REF] Jansen | The early to mid-Holocene thermal optimum in the North Atlantic[END_REF]. This zonal SST delay across the northern North Atlantic (Fig. 2; after [START_REF] Kaufman | Holocene thermal maximum in the western Arctic (0-180°W)[END_REF] corresponds to a similar zonal diachronism in long-term Holocene pattern of AW flow between the Denmark Strait and the Iceland-Scotland Strait [START_REF] Giraudeau | Millenial-scale variability in Atlantic water advection to the Nordic Seas derived from Holocene coccolith concentration records[END_REF]. [START_REF] Kaufman | Holocene thermal maximum in the western Arctic (0-180°W)[END_REF]. The horizontal blue arrow points to the area close to the remnant Laurentide ice-sheet, where the maximum delays are recorded.

Fig. 2: Proxy-based timing of the initiation of the Holocene altithermal across a longitudinal transect from the North-East Atlantic to the Barents sea (after

As suggested by [START_REF] Marchal | Apparent cooling of the sea surface in the northeast Atlantic and Mediterranean during the Holocene[END_REF], this delayed recovery of the circulation pattern close to Greenland might be related to the relative inertia of the remnant Laurentide ice sheet compared to the Fennoscandian following the last deglaciation. Surface circulation off north-west Iceland seems to follow this western Atlantic pattern, some biotic proxy-records indicating peak penetration of Irminger Current Water (in the form of Intermediate waters) between 3.5 and 5.5 cal kyr BP (Fig. 3; [START_REF] Giraudeau | Timing and mechanisms of surface and intermediate water circulation changes in the Nordic Seas over the last 10 000 cal. Years : A view from the North Iceland shelf[END_REF]. [START_REF] Giraudeau | Timing and mechanisms of surface and intermediate water circulation changes in the Nordic Seas over the last 10 000 cal. Years : A view from the North Iceland shelf[END_REF].

A potential influence of the more proximal Greenland ice cap as shown by [START_REF] Jennings | Freshwater forcing from the Greenland Ice Sheet during the Younger Dryas: Evidence from southeastern Greenland shelf cores[END_REF] for the last glaciations might also partly explain this diachronism, although the volume of fresh water released by this ice cap was much smaller than that from the Laurentide Ice Sheet. Foraminiferalbased SST estimates in the nearby Irminger Sea also provide evidence for maximum thermocline temperature centred at 4-5 cal kyr BP [START_REF] Came | Amplitude and timing of temperature and salinity variability in the subpolar North Atlantic over the past 10 k.y[END_REF], hereby confirming the circulation trend reconstructed off NW Iceland. A special point should however be raised on differences in reconstructed SSTs and circulation trends between the northwestern and the north central-eastern Icelandic shelf, this last area showing an Holocene climatic optimum 2 to 3000 years before its western counterpart. Such local disagreements might be explained by differences in environmental signature of the various proxies, and/or the influence of the local topography on circulation features.

Millenial-scale variability

Terrestrial and ice-core data from circum-North Atlantic locations point to millennial-scale anomalies of Holocene climate in relation with changes in the modes of atmospheric and oceanic circulation and transport of heat to high latitudes (e.g. [START_REF] Denton | Holocene climatic variations -Their pattern and possible cause[END_REF][START_REF] Magny | Holocene climatic variability as reflected by mid-European lake-level fluctuations, and its probable impact on prehistoric human settlements[END_REF][START_REF] Dahl | A new approach to calculating Holocene winter precipitation by combining glacier equilibrium-line altitudes and pine-tree limits: a case study from Hardangerjøkulen, central southern Norway[END_REF]. Although hardly temporarily consistent and reproducible, geochemical [START_REF] Came | Amplitude and timing of temperature and salinity variability in the subpolar North Atlantic over the past 10 k.y[END_REF][START_REF] Oppo | Deepwater variability in the Holocene epoch[END_REF] and sedimentological [START_REF] Andrews | Seeking a Holocene drift ice proxy: non clay mineral variations from the SW to Ncentral Iceland shelf: trends, regime shifts, and periodicities[END_REF][START_REF] Bianchi | Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland[END_REF][START_REF] Bond | A pervasive millenial-scale cycle in North Atlantic Holocene and Glacial Climates[END_REF]Hall et al., 2004[START_REF] Rousse | Holocene centennial to millennial-scale climatic variability: evidence from high-resolution magnetic analyses of the last 10 cal kyrs off North Iceland (core MD99-2275)[END_REF] records from the subpolar and polar North Atlantic, support the implication of the surface and deep ocean circulation patterns in the amplification of these recurrent recent climate anomalies and their transmission to distant areas. A major pitfall in this last assumption on Holocene times is the lack of firm, direct evidences for recurrent millennial-scale changes in the dynamics of the North Atlantic Drift (NAD) component of the meridional overturning circulation. While suggesting the existence of centennial to millennial-scale modulations of the surface circulation in the Nordic seas [START_REF] Risebrobakken | A high-resolution study of Holocene paleoclimatic and paleoceanographical changes in the Nordic Seas[END_REF][START_REF] Andersen | A highly unstable Holocene climate in the subpolar North Atlantic: evidence from diatoms[END_REF] and the subpolar gyre [START_REF] Giraudeau | Coccolith evidence for instabilities in surface circulation south of Iceland during Holocene times[END_REF][START_REF] Came | Amplitude and timing of temperature and salinity variability in the subpolar North Atlantic over the past 10 k.y[END_REF], biotic proxy-records available so-far often suffer from either subdued amplitude of changes or limited temporal resolution, and are therefore hardly conclusive.

Still, the most undisputable evidences for pervasive millennial-scale changes in Holocene climate are provided by terrestrial and ice-core records which all highlight recurrent changes in the modes of atmospheric circulation in the boreal Atlantic. The time series of sea-salt sodium (ssNa) flux in the Greenland Ice Sheet Project Two (GISP2) core [START_REF] O'brien | Complexity of Holocene climate reconstructed from a Greenland ice core[END_REF], believed to be an indicator of winter storminess and sea spray in the atmosphere of the high-latitude North Atlantic, strikingly exhibits peaks at times similar to the Holmsa loess record of windy, winter-like conditions over southern Iceland compiled by [START_REF] Jackson | Holocene loess deposition in Iceland: Evidence for millennial-scale atmosphere-ocean coupling, in the North Atlantic[END_REF]. The mean grain size of the loess from Holmsa, in turn shows a succession of peaks coeval with higher than average winter precipitation in the maritime climate-influenced southern Norway [START_REF] Bjune | Holocene mean July temperature and winter precipitation in western Norway inferred from palynological and glaciological lake sediment proxies[END_REF]. [START_REF] Giraudeau | Millenial-scale variability in Atlantic water advection to the Nordic Seas derived from Holocene coccolith concentration records[END_REF] compared with the detrended stacked record of IRD-based drift ice off Northern Iceland [START_REF] Andrews | Seeking a Holocene drift ice proxy: non clay mineral variations from the SW to Ncentral Iceland shelf: trends, regime shifts, and periodicities[END_REF]. Right -Winter mean sea level pressure regressed on standardized simulated inflows of Atlantic waters into the Nordic Seas. Isolines are drawn at 0.5 mb intervals, negative values with dashed lines (from [START_REF] Nilsen | Simulated North Atlantic -Nordic Seas water mass exchanges in an isopycnic coordinate OGCM[END_REF].

Recent marine proxy-records (Fig. 4 left) such as drift ice abundances off Northern Iceland [START_REF] Andrews | Seeking a Holocene drift ice proxy: non clay mineral variations from the SW to Ncentral Iceland shelf: trends, regime shifts, and periodicities[END_REF] or the Holocene paleodynamics of AW flow through the Denmark and Iceland-Scotland Straits [START_REF] Giraudeau | Millenial-scale variability in Atlantic water advection to the Nordic Seas derived from Holocene coccolith concentration records[END_REF] suggest that the intensity of the southward polar and arctic water outflow carried by the East Greenland Current varied according to a millennial pacing, and in phase with the inflow of the North Atlantic Current to the Norwegian Sea. Such a pattern is consistent with dynamical considerations which relate the present tight link between the AW inflow in the Iceland Scotland Ridge and the polar outflow to the Denmark Strait to the winter-average cyclonic conditions over the Greenland, Iceland and Irminger seas (Fig. 4 right; [START_REF] Blindheim | Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing[END_REF][START_REF] Nilsen | Simulated North Atlantic -Nordic Seas water mass exchanges in an isopycnic coordinate OGCM[END_REF].

  Fig. 1). It is located close to the Arctic front which separates Arctic/Polar water masses carried by the southeastward East Iceland Current from Atlantic waters (AW). Atlantic waters bathing the western and north-central Iceland shelf originate from the North Iceland Irminger Current, a branch of the Irminger Current; whereas the eastern and north-eastern shelf are fed with warm waters from the main corridor of Atlantic waters toward the Nordic Seas (the North Atlantic Drift and Norwegian Atlantic Current).

Fig. 1 :

 1 Fig. 1: Main component of the surface circulation. Left: Solid and dashed arrows represent warm and cold currents, respectively (NAC-North Atlantic Current, NIIC-North Iceland Irminger Current). The dotted line refers to the present position of the Arctic Front (after Giraudeau et al., 2010). Right: surface circulation around Iceland (red to dark blue colors refer to the SST gradient from warm Atlantic to cold Polar waters).Together with the contour drifts moulded by the Norwegian Sea Overflow Water, and distributed along the eastern flank of the Reikjanes Ridge south of Iceland, the North Iceland Shelf stands as one the favourite play-ground for the late Quaternary/Holocene paleoceanographers. It owes it mainly because of the vertical distribution of key-elements of the surface and intermediate water masses of the Nordic Seas within a spatially restricted area.

Fig. 3 :

 3 Fig. 3: The overwhelming contributor to carbonate production and sedimentation off Iceland is the coccolithophore species C. pelagicus (central picture) who might occasionally bloom in arctic waters (right picture). Carbonate production off Iceland is tightly linked with input of nutrient-rich Irminger waters. The Holocene record of C. pelagicus concentration off NW Iceland suggest maximum input of Atlantic/Irminger water between 3.5 and 4.5 cal kyr BP[START_REF] Giraudeau | Timing and mechanisms of surface and intermediate water circulation changes in the Nordic Seas over the last 10 000 cal. Years : A view from the North Iceland shelf[END_REF].

Figure 4 :

 4 Figure 4: Left -Detrended and smotthed biotic record of AW flow into the Norwegian Sea[START_REF] Giraudeau | Millenial-scale variability in Atlantic water advection to the Nordic Seas derived from Holocene coccolith concentration records[END_REF] compared with the detrended stacked record of IRD-based drift ice off Northern Iceland[START_REF] Andrews | Seeking a Holocene drift ice proxy: non clay mineral variations from the SW to Ncentral Iceland shelf: trends, regime shifts, and periodicities[END_REF]. Right -Winter mean sea level pressure regressed on standardized simulated inflows of Atlantic waters into the Nordic Seas. Isolines are drawn at 0.5 mb intervals, negative values with dashed lines (from[START_REF] Nilsen | Simulated North Atlantic -Nordic Seas water mass exchanges in an isopycnic coordinate OGCM[END_REF].


Gudmundsson Agust
email: iceland.email.jardis@geoice.net

ROCK GLACIERS AND RELICT DEBRIS BODIES IN CENTRAL NORTH ICELAND

Active rock glaciers exist in the mountains of north and east Iceland and are also found very scattered in the south and west Iceland. They are normally found below N and NE facing cirques at altitudes higher than 800m but are occasionally detected at elevation down to 600m. In the mountainous costal areas of west, north west, north and east Iceland exist numerous debris bodies fulfilling all criteria requested for relict rock glaciers. In some cases we have continuous sequence from active rock glaciers at the top, changing over to relict debris bodies at lower altitudes. Spatial distribution of these debris formations in central north Iceland has been analysed and are discussed.

Introduction

Rock glaciers (RG) are tongue shaped bodies or lobate features generally composed of angular boulders. Their form resembles usually the form of a small outlet glaciers, in active state often with steep 20-40m high fronts and normally showing well defined surface relief. Rock glaciers are normally devised into three stages of activity; active, inactive and relict. Active RG are considered to show the most expressive indication of permafrost in alpine topography and relict RG are considered to show expression of former cooler climate (permafrost). Rock glaciers are found at various cool climate conditions, both in dry continental mountains as well as in maritime regions. At the present, they are frequently found in mountains or costal areas adjacent to present glaciers (Humlum 1996). Definition and mapping of rock glaciers has not been extensive in Iceland as well as (until recently) in other Nordic countries [START_REF] Svenson | The Rock Glacier, A New Feature in Scandinavian Geomorphology[END_REF].

Topography and bedrock

Tröllaskagi is a mountainous peninsula between the glacially eroded fjords, Skagafjörður and Eyjafjörður in central north Iceland, see figures 3 and 10. The bedrock of Tröllaskagi is what remains of an old plateau where mountain-tops rise frequently above 1200-1300m peaking up to 1536m in the highest mountain Kerling. The bedrock consists of late tertiary (8-13 M.y.) basalt lavas, frequently 5-15m thick, intercalated with scattered relatively thin sediments. Several relict central volcanoes exist buried in the basalt plateau, consisting of various volcanic and sedimentary rock types and tectonic structures, resulting in higher susceptibility to rock weathering than the "average" plateau basalt.

Present climatic conditions in the Tröllaskagi peninsula show annual mean temperature of 3-4 °C at sea level and precipitation of 1500-1700 mm in the upper part of the mountains. The Tröllaskagi has been more or less ice-free during at least the last 10 ka (or even longer), as supported by dated shell remains, (11,2 ka C 14 BP uncorrected) in costal sediments at the Sauðárkrókur town in Skagafjörður and 12,7 ka (C 14 BP uncorrected) in Héðinsfjörður and 42 ka at Almenningar west from Siglufjörður).

Mapping, definition and distribution

Rock glaciers in the mountains of Tröllaskagi, have been mapped discontinuously by the present author during the last 25 years, both in the field and by interpretation of aerial photos. The definition criteria used for active, inactive and relict rock glaciers has been described in various papers (e.g.: Warhaftig and Cox 1959;[START_REF] Corte | a. Rock glacier taxonomy, in Rock glaciers[END_REF]Barsch, 1996, Humlum;[START_REF] Humlum | The climatic significance of rockglaciers[END_REF].

Activity and spatial distribution

All activity stages of rock glaciers are found in the Tröllaskagi mountains, active, inactive and relict. The active RG are considered to have formed during the Holocene, and the inactive RG are possibly also mainly from the Holocene time (some of them could possibly be older). Approx 570 rock glaciers have been defined, but the number might increase considerably, depending on how to define composed small lobate RG and various composite bodies of relict RG. Of the rock glaciers 165 (approx 30%) are defined active and 402 (approx. 70%) inactive and relict (most of them relict). A similar ratio of activity has been described in the Disco area W-Greenland [START_REF] Humlum | The climatic significance of rockglaciers[END_REF] in Alaska and middle west USA [START_REF] Wahrhaftig | Rock glaciers in the Alaska Range[END_REF].

Active rock glaciers

Most of the active rock glaciers are glacially derived, showing ice on the surface in the upper part [START_REF] Corte | a. Rock glacier taxonomy, in Rock glaciers[END_REF]). The lobate rock glaciers are normally talus derived, much smaller or especially shorter and relatively thicker (thickness/length) than the others. these are often located side by side under steep walls or in north heading cirques (see figure 1). Both the glacial-and talus derived genetic types of rock glaciers occur in composite various stages where one tongue is overridden by a younger one sometimes forming layered pile of ice cored debris bodies consisting of up to 4-5 layers (see figure 1). The average size of active rock glaciers in Tröllaskagi peninsula is approx. 0.5 km 2 forming a total area of almost 82 km 2 .

Highest frequency of the active debris bodies is heading towards N and NNE with the average inclination of 17°. The average altitude of RILA (rock glacier initiation altitude (see definitions by [START_REF] Humlum | Rock glacier appearance level and rock glacier initiation line altitude: A methodological approach to the study of rockglaciers[END_REF] for explanations of RILA, RAL, RSA) is 986 m a.s.l. and average RSA (rock glacier snout altitude) is at 853 m a.s.l., thus covering an average altitude difference of 133 m. The glacially derived rock glaciers extend over considerably greater altitude difference compared to the talus derived. The creep rate of several active RG has been measured as 0,2-1m / year.

Relict and inactive rock glaciers

Over 400 debris bodies in the Tröllaskagi area. have been defined as relict or inactive rock glaciers. The definition criteria for relict RG and the recognition of individual bodies is mainly based on surface appearance and relief (frequently defined by using aerial photos as well as in the field). The definition is also based on internal structure, layering and on grain size distribution, compared to grain sizes of other kind of sedimentations. The material and grain size distribution resembles the internal character of active rock glaciers, described in such literature (e.g. [START_REF] Evin | Lithology and fracturing control of rock glaciers in southwestern Alps of France, in Rock glaciers[END_REF]) and often also have grain distribution like Icelandic glacial moraines.

The average size of the debris bodies in the area, defined relict rock glaciers is approx. 0.8 km 2 forming a total area of 320 km 2 . Highest frequency of the inactive and relict debris bodies are facing towards N-NNW and less frequency is facing E-SES. The average inclination of these bodies is 13°. Less frequently the relict rock glaciers is facing north and south. The average altitude of RILA is 629 m a.s.l. and average RSA 403 m a.s.l., thus covering a height difference of 226 m.

The RILA of both the active and relict rock glaciers is generally about 200 m lower altitude in the northern part of the peninsula compared to the southern part. Also there is a great increase in number and average size of debris bodies towards north, with high frequency of relict RG and lower ratio of the active ones. On the other hand, the relict debris bodies almost disappear in the innermost part of the deep walleyes in the middle part of the Tröllaskagi but increase in number and size towards the costal mountains of Skagafjörður and Eyjafjörður (fig. 1). Stratified debris bodies at the sea shore west of Siglufjörður. Layers of very coarse grained subangular and angular rock fragments inbetween more fine grained and silty sediments On the other hand the greatest number of the active rock glaciers is found in the central part of the Tröllaskagi peninsula. The creep rate of several debris bodies or relict RG has been measured as 0,1-0,6m / year. Traditionally these debris bodies in the Tröllaskagi area as well as elsewhere in Iceland have previously been described as sedimentations formed by bergsturz [START_REF] Jónsson | Berghlaup. Raektunarfélag Norðurlands[END_REF][START_REF] Sigurðsson | Möðrufellshraun, berghlaup eða Jökulruðningur?[END_REF][START_REF] Hjartarson | Berghlaup á Íslandi[END_REF][START_REF] Humlum | The climatic significance of rockglaciers[END_REF], and this seems to be consistent to what is widely cited or referred to as misinterpretation in papers on rock glaciers (Barsch 1996, Giardino, Shroder and[START_REF] Giardino | Rock Glaciers[END_REF].

Rock glaciers in other areas of Iceland

Although active RG and ice cored moraines are most frequent and best developed in the Tröllaskagi area, central north Iceland, such RG features also exist, almost up to the same degree in the peninsula east of Eyjafjörður as well in the mountains south of Vopnafjörður and in the mountains of east Iceland south from Héraðsflói. Scattered active RG and ice cored moraines exist in the highest mountains of east Iceland. Additionally scattered active RG are found in the surrounding mountains of Vatnajökull and a few near Langjökull, see figure 9 for brief locations.. Debris bodies classified as relict rock glaciers (and formerly ice cored moraines and debris covered glaciers) are very frequent in the peripheral range of the Vestfirðir (north west peninsula). They exist in the Snaefellsnes peninsula and in the alpine mountains of Faxaflói (Esja -Skarðsheiði). In northern Iceland the debris bodies are frequent in the high-and costal mountains of Húnaflói and Skagafjörður area, culminating around Eyjafjörður (both sides). In east Iceland the relict debris bodies are frequent in the mountains south of Héraðsflói, gradually decreasing south to the Djúpivogur area. From there (Djúpivogur) such relict debris bodies are very rare in south Iceland, along the inland and the south coast to Faxaflói.

Conclusion

Rock glaciers of all stages of activity (active, inactive and relict) exist in the mountains of Tröllaskagi middle north Iceland. The active RG are formed during the Holocene time with some periods of varying production activity resulting in layered or stratified rock glaciers.

The formation of relict rock glaciers probably took place during the Weichselian glaciation and late glacial time. At the northernmost coast of Tröllaskagi, sea shore sediments are encountered, containing shell remains expressing with dated carbon figures of over 42 ka (conventional 14 C BP). Directly on the top of these sea shore sediment exist relict debris bodies of relict RG presently creeping slowly towards the cost (Figs. 7 and8). Numerous debris bodies, defined as relict rock glaciers, designate no major glaciers in the northern part of Tröllaskagi area during last glaciation.

Figure 1 .

 1 Figure 1. Composite talus derived and glacial derived rock glaciers near Holar in Tröllaskagi.

Figure 2 .

 2 Figure 2. Map of the Tröllaskagi peninsula showing distribution of rock glaciers / debris covered glaciers

Figure 4a .

 4a Figure 4a. Rose diagram showing directional trend of active rock glaciers and relict debris bodies defined as relict rock glaciers. Figure 4b. Diagram showing average elevation and direction of RILA and RSA for active rock glaciers and relict debris bodies defined as relict rock glaciers.

Figure 5 .

 5 Figure 5. Direction and elevation of individual active rock glaciers and relict debris bodies.

Figure 6 .

 6 Figure 6. Debris bodies most probably of relict rockglaciers in Eyjafjörður.

Figure 7 .

 7 Figure 7. Debris bodies of relict/inactive stratified rockglaciers at the sea shore west of Siglufjörður. The debris bodies are resting on stratified gravel containing shell remains C 14 42 ky. old.

  Figure 8.Stratified debris bodies at the sea shore west of Siglufjörður. Layers of very coarse grained subangular and angular rock fragments inbetween more fine grained and silty sediments

Figure 9 .

 9 Figure 9. Iceland, distribution of rock glaciers areas and possible outer limits of the ice cap during considerable part of last glaciation.

  Glacial moraines in the Skagafjörður district in addition to dated shell remains from the town Sauðárkrókur and Héðinsfjörður, indicate limited glaciers and no major glaciers in the Tröllaskagi area in lateglacial time. Distribution of debris bodies defined as relict rock glaciers in the peripheral range of the peninsula, and the low frequencies of these in the middle part of Tröllaskagi indicate valley glaciers of limited extent in the area at least during and since late glacial time. Dated shell remains from the Reykjanes peninsula (SW Iceland) show measured dating figures in the range of 20-35 thousand years and dated volcanic rock formed over 40 thousand years ago from the same area, indicate limited glaciers in SW Iceland during the later part of last glaciation. (No dated shells have been found in Iceland from the period 13-20 thousand years ago, probably as a result of relatively low sea level during that period. The dated shell remains and rock from the Reykjanes-Faxaflói area support limited extent of the inland ice cap during Weichselian glaciation, making possibilities for growth of rockglaciers in the peripheral mountains of Iceland.


Minh Tuan Ho

Sylvain Roche
email: sylvain.roche@irisa.fr

Frédéric Weis
email: frederic.weis@irisa.fr

Design of a Smart Information Diffusion Service using RFID-based Location System

Keywords: Pervasive computing, context-awareness, location service, RFID, WLAN Informatique diffuse, sensibilité au contexte, service de localisation, étiquette électronique, réseaux locaux sans fil Les

In this paper, we present the design and the implementation of a contextual and multimodal information diffusion system for museums. We propose a proactive service (1) with the ability to sense the profile of nearby visitors, using RFID and WLAN connectivity, (2) that adapts the information content to the target user, and finally (3) that distributes automatically the information to several devices, collective devices like large wall panels disseminated in museum or directly to digital guide carried by visitors.

Introduction

Providing pertinent and accessible information to people in a museum has always been a challenge. Broad availability of fast mobile Internet through WLAN and cellular networks enables unlimited access to cultural digital content. The amount of cultural information targeting mobile users is rapidly increasing and a huge number of web repositories for tens of museums is now available. Therefore the main problem for a visitor is not any more to find information, but to retrieve pertinent information depending on the context of the visit (duration of the visit, user's location, user's interest etc.).

The SmartMuseum1 European project aims to address efficient on-site cultural heritage content access by monitoring user's activities. Mobile device is one of the two main subsystems in the SmartMuseum architecture, the other one is the profile matching / recommendation server. The latter is able to assist the user to find contents that are likely of interest for the user [START_REF] Ruotsalo | Smartmuseum: Personalized Context-aware Access to Digital Cultural Heritage[END_REF]. It reduces the need of interaction with the device. That is particularly important in ubiquitous scenarios, where the usability of the mobile devices often limits the user's willingness to perform complicated search queries.

The mobile device is the main interaction point to the system for the visitor. In a SmartMuseum scenario, a visitor explicitly requests information from an item among a list proposed by the recommender system, or read a RFID, associated with the local area or an object of this area. In that case, a URI stored into the RFID, allows to retrieve information. These interactions can be seen as "pull" type. The visitor carries a PDA, offering him access to web-type information system in a contextual manner: requests include context descriptors such as current position or user profile that can influence the available information or its presentation. This approach is presented in [START_REF] Kuusik | SMARTMUSEUM: Cultural Content Recommendation System for Mobile Users[END_REF].

A recommender system combined with an explicit selection of the information by the visitor (touching an object in a recommendation list and/or reading a RFID a in given area) offers a good solution but also has limitation. First it assumes that the selection interface can be easily used by the visitor, which may not always the case. For example, the user with visual disability will not be aware of the availability of a short-lifetime information (announcement of the beginning of a conference in the museum). Second this approach is limited to provide information proposed by the recommender system and requested by visitors, not unsolicited information.

Our idea is to provide a proactive service that senses the environment and spontaneously adapts its behavior to the local context. Typical sensing involves determining the profiles of near by visitors, allowing the dynamic computation of group profiles and enabling global adaptation of the environment to the context. For example, if a room in the museum uses vocal explanations or shows short documentation movies, environment sensing enables automatic selection of the dominant language (and appropriate selection of subtitles in the case of a movie) accordingly to the current visitors in the area.

The objective here is to offer the possibility to mobile device to receive automatically contextual information. A proactive service senses the environment and spontaneously adapts its behavior to the local context. The interactions between the mobile device and the SmartMuseum server can be seen as "push" type. The notion of "context" considered here refers to a description of a physical situation in the museum; a physical situation may be described by low descriptors such as raw sensor values (GPS position, RFID, etc.), but these one are usually not directly relevant for an application. Here we propose to use RFID disseminated in the museum in combination with WLAN connectivity for designing a location service in the museum. And context-awareness requires higher level description that can be used easily by service. For example, an application shouldn't have to do only position computation if the goal is to determine what is the language spoken by nearby people. So we use existing parameters (mainly the spoken language) extracted from the existing user's profile used by the initial pull mode. Of course, monitoring the environment to identify people and using user's profile parameters raises a strong privacy concern. This problem is addressed in this paper.

The purpose of this paper is to present our results with the design and the implementation of such a service. This work is an extension of the initial SmartMuseum architecture [START_REF] Kuusik | SMARTMUSEUM: Cultural Content Recommendation System for Mobile Users[END_REF], and of an ambient service we initially designed for transportation systems [START_REF] Couderc | Ubi-board: A smart information diffusion system[END_REF]. The rest of the paper is organized as follows: in the second section we present the principle of the diffusion service for museum. Then the third section describes the system architecture and its implementation. The underlying location service is presented in the fourth section. Finally in the last section, we present related work and the conclusion.

Motivation for a diffusion service in a museum

In a museum, visitors may speak different languages, have a disability, and can be interested by different information. A classical strategy is to deliver variants of the same information, for example versions of different languages. The problem with this approach is that all variants cannot be delivered to all mobile devices, (1) due to the limited size of the screen of a mobile device and (2) because it tends to flood underlying wireless communication infrastructure.

Our objective is to design a context-sensing information diffusion system to detect and identify group of users (co-located in a given area of the museum), and to provide them with unsolicited messages like "conference invitation at 1pm, room leonardo", with a multi-language support, and multi-modal support. For example, Text To Speech (TTS) functionality will be automatically activated for people with visual disability. Two aspects must be addressed for implementing such a service. First the service requires determining visitor's context in a given spatial area of the museum. For that, two kinds of information are required: visitor's localization and personal parameters like "spoken language" and "ability to see". Localization can be accessed using RFID reading, combined with WLAN connectivity. Personal parameters can be extracted directly from SmartMuseum profile stored in mobile device. Of course collecting these data (localization and parameters of the profile) in museum environment is a privacy concern, as it potentially enables visitor tracking when associated with SmartMuseum user's account. So we only use "anonymous attributes" of the user's profile such as "language spoken", and information sent by mobile device application is not associated with SmartMuseum user's account.

Second a provisioning strategy is decided to target visitors in an efficient way. By efficient, we mean allocating the collective resources to larger groups (the "major" spoken language), and using mobile device for smaller groups. For that, we use the majority rule: the collective devices (or example large wall panels) are allocated to display message in "major" language, while messages in "minor" languages and messages "compliant with Text To Speech engine" for users with visual disability, are forwarded to mobile devices. These both aspects are summarized in Figure 1.

Presentation of the system architecture

Context sensing generally involves two types of operation:

• Getting on context attribute, which is basically a "read" operation on context-derived data.

• Triggering an operation when a context-specific condition is met.

A simple and efficient abstraction that provides both functionalities is a tuple space model, such as SPREAD [START_REF] Couderc | SPREADing the web[END_REF]. In the following, we describe briefly how the tuple space model can be used as a context-aware abstraction.

Tuple space as a context-aware abstraction

Tuple spaces use a shared data structure for enabling dynamic cooperation between applications. Data are structures made of sequences of basic data types, such as < "f rench", 1 > which describes a visitor who speaks French, the last field is set to 1 to indicate that the Text To Speech (TTS) functionality must be used. In the case of pervasive computing, the tuple space is typically shared between objects in the same physical context, allowing implicit spatial addressing of data provided in the same "memory bubble" (i.e in our approach, the bubble corresponds to WLAN communication range). For example, collecting all the French users in the room could be expressed by a request pattern like read < "f rench", ?id >. Such a request can wait until a matching tuple is found (which means a French user enters the room in the museum), providing a way to control the flow of a program according to environment events.

Context sensing and location service

The goal of profile sensing modules (on mobile device and Manager) is to determine the visitor's context in a given spatial area of the museum. For that, two kind of information are required: visitor's localization and two personal parameters extracted from local user's profile ("language" and "ability to see"). When using SmartMuseum application, a visitor reads an RFID storing an object URI (for example urn:imss:instrument:4040). With this information, mobile device retrieves automatically the main object information page, associated with (1) the object room location, (2) content URLs provided by the museum and (3) external content URLs (for example wikipedia links related to the museum object).

We made the assumption that if the Manager knows the tag read by a visitor, it could localize him in the museum. So when a device reads a RFID, it publishes automatically the associated room location using a SPREAD function. Then if this device can be seen by the Manager (using capture function), the latter can deduce that (1) the mobile device is connected to WiFi network of museum and (2) it is near the tag. Using combined RFID reading / WLAN connectivity, the Manager can obtain a good approximation of user's localization. Finally, a tuple is published by the mobile device just after RFID reading using the call Out < room, age, language, T T S, Hash@M AC > where • age is a counter indicating if the user's location is still valid or not (see more explanations below).

• T T S is a boolean value defining if the Text To Speech functionality must be used.

• Hash@M AC is a hashed value of WiFi physical address of the device. Hash function is used to guarantee user's anonymity (login is not used), and is used by the Manager for identifying mobile device.

Of course, when no new RFID is read, localization information can become obsolete. In order to characterize the validity of the information of localization, we introduce a counter date into the tuple published by the device. This counter is initialized to 0 when a RFID is read, and maintained at this value as long as the visitor browses among information (URLs and external links) related to the RFID. On the other hand if no activity is detected in the terminal, the counter is incremented every 30 seconds, and the terminal is considered as "non localized" when date is equal to 3. This principle is presented in Figure 3.

On server side, the Manager retrieves all "localization tuples" published by mobile devices using capture function.

Content provisioning

According to information provided by context sensing module, content provisioning module is able to identify a specific group of visitors in the museum (for example people in a room), and to calculate a "major group" and a set of "minor groups". When a message must be sent to this group, content provisioning module publishes a tuple in the museum : Out < room, validity, ID_msg, message, majority, T T S >, where

• room is the room number. This parameter is equal to -1 if the message must be sent to all visitors in the museum.

• validity corresponds to the time of validity of message sent in the tuple.

• ID_msg is used to identify the message sent by the Manager. Information is transmitted over an unreliable channel (802.11/IP/UDP). So it is sent several times by the Manager as message remains valid. In case of multiple reception, the terminal takes into account only once a given identifier.

• majority is a boolean indicating whether the language used in the tuple is dominant. If the majority language is the language of the visitor, the contents of the message is not displayed by the terminal, a simple sound signal returns the visitor towards the collective screen.

• T T S is a boolean indicating whether the message sent in the tuple is the version to be played by the Text To Speech engine implemented in the terminal.

Implementation

Mobile device. The mobile application (context sensing, tuple engine, GUI) has been implemented on a PDA HP Ipaq 214, running under Windows Mobile. TTS (Text To Speech) functionality is based on the integration of an external Text To Speech engine [START_REF]AcapelaTTS for windows mobile[END_REF]. RFID reading. For SmartMuseum experimentations, the objects have been equipped with 13,56MHz (ISO14443A) RFID tags used for content triggering and user's positioning. At now PDA and Smartphones do not support natively tag reading. So we used an SDIO HF RFID reader (SDID 1020 from Wireless Dynamics). But in a near future this functionality will be largely implemented on several mobile phones using NFC standard. So we stored information on tag so that SmartMuseum RFID can be also read (without any specific application) by NFC phone. For that goal memory of tags contains (see Figure 4) "MIFARE Application Directory" an index of all applications stored in the tag, "Application 1" using NFC Smart Poster format.

The Smart Poster content is used to display on the PDA screen information corresponding to the museum object. Two areas are used, just after the application header (see Figure 4): (1) the header stores the type of application and the payload size, (2) the Title record contains generally a common name for the object or service referenced by the URI (it can be the bookmark name if a URL is provided in the following record; in our application, it is used as object URI), and (3) the URI The use of two distinct fields for PDA and NFC phones allows to take benefit from both device types. Our tests showed that this "SmartMuseum tag format" allows a NFC phone to read object tag and to automatically retrieve information on SmartMuseum server.

Manager. The server (location service and content provisioning) is a .NET application allowing museum's administrator to monitor "major" and "minor" user's groups in the museum and to manage through a simple graphical user interface all variants of SPREAD messages (see Figure 5).

Analysis of our results

Our architecture is able to provide pertinent and accessible information for visitors in a museum. An other important feature of our system is that context sensing is based on a very simple location service. In many museums, RFIDs are already used for object referencing. Our system can be easily deployed, just by using existing tags and WLAN communications. The main weakness of our approach is that localization parameter calculated by the location service is false if a visitor does not read any RFID. In the next section, we propose a simple solution to improve visitor's localization: our approach is to allow mobile device to detect a "neighbor terminal" that has recently read a RFID. For evaluating this proximity, we use the similarity of radio conditions: two terminals are considered as neighbors if (1) the measured radio signal strengths are close to each other and (2) the both devices are attached to the same WiFi Access Points.

Extension of the location service

As illustrated in Figure 3, a visitor is localized whenever he reads a RFID and he uses related data on its PDA. But afterwards if no RFID is read in the museum, the visitor is not taken into account when "major" and "minor" groups are calculated.

We propose two new steps in order to improve existing location service:

1. Whenever a user reads a RFID, the PDA evaluates its radio conditions, and sends them to the server. These data are kept in the server until user's localization becomes too old (e.g. age ≥ 3).

2. When a user is no more localized, PDA evaluates its radio conditions, and sends them to the server. Then the server compares these values to other local values associated with nodes that are still localized.

Two parameters have been considered to evaluate radio conditions: RSSI (Received Signal Strengh Indication) and SNR (Signal to Noice Ratio). To the common knowledge, both parameters are equally suitable for developing WLAN positioning service [START_REF] Borenovic | Comparative Analysis Of RSSI, SNR And Noise Level Parameters Applicability For Wlan Positioning Purposes[END_REF]. We chose finally the SNR, because it can be easily measured on many WLAN interfaces. The configurations of the WLAN nodes and APs are described in Table 1.

In the area of museum, user's movements are simulated using two models: (1) a mobility model with predefined trajectories and (2) the Random Way Point (RWP) model.

For the mobility model with predefined trajectories, we determine the paths whose stops are specific points that correspond to the positions of RFID tags. The nodes of this model move with velocity v = 0.5m/s and take a pause of 10 seconds at each stop. We select 100 points in the simulation area corresponding to the positions of RFID tags. At each stop, a node using this model of mobility captures SNR values for each AP. An example of data captures on these 100 positions is given by Figure 8. With the RWP model, mobile nodes are initially uniformly distributed in the range of simulation. Then, nodes move in a direction randomly chosen with a constant speed v = 0.5m/s. Upon arrival, the mobile node pauses for 60 seconds before making another move. We use this second model of mobility to have a realistic simulation environment. Indeed, the radio conditions (SNR or RSSI) of a node can vary in the presence of other nodes in the physical neighborhood. Thus nodes using RWP model are injected into simulations, in order to test the location algorithm under realistic radio conditions. For example, Figure 9 presents SNR values of two close nodes for a given AP. The two curves are quite similar, the difference does not exceed a few dB. These small variations reflect changes in the vicinity, they are induced by other mobile nodes. During simulations, we varied two parameters: the number of nodes, and the duration during which an information of localization (parameters SN R RF ID ) remains valid. In the solution presented in 4.1, this duration was fixed at 90 seconds (age < 3). It seemed interesting to increase this duration, in order to evaluate the impact on the results of our algorithm.

Through simulations, we generated SNR logs, to which we applied the location algorithm. Figure 10 presents the results for two numbers of visitors (72 and 102). The x-axis represents the validity of information of localization SN R RF ID (30sec, 60sec, . . . ). The y-axis indicates the percentage of correct localizations. Below threshold of validity (90 seconds), the algorithm gives good results: at least 70% of calculated positions are exact. One can also note the number of users does not have impact on quality of the results. The chosen period of validity is suited to the targeted application. These results are degraded beyond 90 seconds, the percentage of good evaluations do not exceed 50%, and the lower the density of the nodes is, the more the effectiveness of the algorithm decreases.

Related work

We propose a simple architecture for providing pertinent and accessible information to visitors in a museum. Defining smarter ways to deliver information in cultural areas is not new. Since the concepts of context-awareness was introduced by Weiser in [START_REF] Weiser | Some Computer Science Issues in Ubiquitous Computing[END_REF], many prototypes of ambient information systems appeared such [START_REF] Schilit | Context-aware computing applications[END_REF], [START_REF] Cheverst | Experiences of developing and deploying a context-aware tourist guide: The guide project[END_REF] and [START_REF] Fink | User Modeling for Personalized City Tours[END_REF]. In these systems, the user carries a mobile device that is the main interface with the information system. Considering existing systems, the main feature of our system is its ability to push automatically information towards several devices, collective devices are used for the "major" spoken language, and individual devices can be targeted for "minor" groups.

An other important feature of our system is that context sensing is based on a very simple location service. In many museums, RFIDs are already used for object referencing. Our system can be easily deployed, just by using existing tags and WLAN communications.

The research in the area of determining user location is in broad categories: the cellular communication system, the ultra sound, infrared based systems or RFID based system... However, each solution has different advantages and disadvantages.

The two positioning technologies most know in the cellular communication system is Time Difference Of Arrival (TDOA) and Angle Of Arrival (AOA). TDOA systems use the principle that the position transmitter can be estimated by the function of the difference in arrival times of signals at two or more base stations. However, a very small de-synchronization may cause a positioning error in several tens of meters. The AOA system uses simple triangulation based on the estimated angle of arrival of a signal to two or more base stations to estimate the location of the transmitter. This system requires special antenna to determine the exact angle of reception. Furthermore, because these systems are promising for outdoor environments, then their effectiveness in indoor environments is limited by the multiple reflections of the radio signal frequency (RF). This leads to an inaccurate estimate of the TDOA or AOA, and a very expensive material for a synchronization time.

The infrared based systems have been proposed in many recent applications for user's location. In the Active Badge system [START_REF] Want | The Active Badge Location System[END_REF] and [START_REF] Azuma | Tracking requirements for augmented reality[END_REF], a badge worn by a person emits a unique infrared signal. The IR fixed receivers catch this signal and relays it to the location center. The characteristic of an IR signal is to not broadcast for long distance, it is then locked in a room with walls. This will properly position the user in a room. The technique based on the IR signal proposes several disadvantages such as limited scope, the cost of installation, and sensitivity to interference in the presence of direct sunlight. Similarly, Criket [START_REF] Priyantha | The Cricket location-support system[END_REF] combines the technology of RF and ultrasound for location-aware services. The transmitter on the ceiling broadcasts the frames of radio frequency (RF). After receiving a few bits of these frames RF, the receiver switches to the communication mode ultrasound and begins to capture the ultrasonic pulses that arrive just after the frames RF a few moments. The receiver measures the time difference in receiving between the first bit of RF and ultrasonic signal and uses the maximum likelihood to estimate the distance. The disadvantage of this approach is overloading treatment on the side of receiver and the installation cost.

A positioning system on the active RFID LANDMARC [START_REF] Ni | LANDMARC: Indoor Location Sensing Using Active RFID[END_REF] uses RFID tags fixed to serve as reference points. This approach requires the signal strength of each tag for readers in the detectable range. Each reader has a preset power threshold to limit the radius for detecting RFID tags. He then compares the received power level of the detected tag with a preliminary power measure to know what distance is. The advantage of LANDMARC is that power information is updated regularly and to correctly locate at a distance of 1 meter with 50% error. However, this approach should suffer an important interference of a large number of tags and readers, the movement of people within range of application and the cost.

The closest related work to our solution of indoor localization is the RADAR system [START_REF] Bahl | RADAR: An In-Building RF-based User Location and Tracking System[END_REF] which uses the RF signal strength to estimate the distance between the receiver and the transmitter. During the first phase (offline stage) RSSI vectors corresponding to each location (fingerprint) are measured and stored in a database server as a map of RSSI. During the second phase (online stage), thanks to information from the user's signal strength RSSI, the server uses the approach of the K nearest neighbors to determine the position of the user on the map of RSSI.

Our solution does not require the deployment of specific technologies (like a specific antenna) or the use of a first phase to generate radio conditions fingerprint. We use instead a simple and effective technology of Wireless LAN and RFID to obtain a correct location of users in museum. SNR information is updated on the server side whenever the user reads an RFID tag. And finally the installation cost is low and has a small impact on server side.

Conclusion

In this paper, we present the design of a context-sensing service for providing pertinent information to visitors in a museum. This service has the ability to detect and identify groups of users co-located in a given area of the museum, and to provide them with unsolicited messages. Two aspects are treated by this service. First a provisioning strategy allows to target visitors according to their spoken language, collective resources are allocated to the larger group, and PDA carried by visitors are used for smaller groups. And second, visitor's context, based on visitor's localization and visitor's "spoken language", is calculated using a simple location service. The latter uses RFIDs disseminated in the museum in combination with WLAN connectivity. It does not require any off-line phase for recording radio conditions, and it just uses the similarity of radio conditions between close visitors. Considering the targeted service, our simulations show that visitor's localizations are estimated with a good degree of accuracy.

Figure 1 :

 1 Figure 1: Overview of the diffusion system

  +2(<:7%A)+16@(BC%D'E9%D:%56''2FG% H:79'79%6&'1'79(<:7% H:79'E9%1'71+78% 41'&I1% %6&:J@'%!"#"$%&'H:79'E9%1'71+78% H:79'79%6&:K+1+:7+78% 3&'1'79(<:7%/(7(8'/'79% H://07+2(<:7%1:=>(&'% !"#$%&'#()%&& #*+,+-.%'&

Figure 2 :

 2 Figure 2: System architecture

!!Figure 3 :

 3 Figure 3: Location mechanism

Figure 4 :Figure 5 :

 45 Figure 4: RFID tag format

Figure 6 :Figure 7 :

 67 Figure 6: Capture of the radio conditions !"#$%&'()'"* !)$+)$*

Figure 8 :

 8 Figure 8: SNR values for a node with predefined trajectory

Figure 9 :

 9 Figure 9: SNR values of two neighbor nodes

Figure 10 :

 10 Figure 10: Simulation results

Table 1 :

 1 4. Simulation time is 30 min. Parameters of the WLAN APs and nodes

	Date Rate (Mbps)	54
	Physical characteristics	Extended Rate PHY
		(802.11g)
	Channel	1 ; 6 ; 11
	Transmit Power (W)	0.2 (AP) -0.005 (node)
	Packet Reception-Power
	Threshold (dBm)	-95

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Acknowledgment

SmartMuseum (Cultural Heritage Knowledge Exchange Platform)15 is a Research and Development project sponsored under the Europeans Commission's 7th Framework (FP7-216923).

Principle

Whenever a user reads a RF ID tag, it captures not only information from the RF ID tag, but also the SNR value of each WLAN Access Points (AP) in its communication range. Finally, the radio conditions are represented by the set SN R RF ID = {SN R 1 RF ID , SN R 2 RF ID , ..., SN R M RF ID }, where M is the number of AP deployed in the museum. Of course when an AP is out of range, the corresponding SNR value is set to 0 (see Figure 6).

After that, the PDA publishes a SPREAD message to the server as in Figure 7. The initial message defined in Figure 3 is extended with two new parameters: id RF ID and SN R RF ID . The triplet {room, id RF ID , SN R RF ID } is stored on the server while user's localization remains valid (e.g. age < 3, see Figure 7).

When a user is no more localized, it sends its radio conditions SN R

After receiving the published SPREAD message, the server performs algorithm 1 based on location information stored in its database. This algorithm calculates the best position where the user is likely to be. This step is described in Figure 7.

The server performs the location algorithm by combining user's information (SN R U ) and valid positions in its database (set of SN R RF ID ). It collects N valid positions whose values SN R RF IDi are close to SN R U with an acceptable error equal to δ SN R (e.g. ∀k,

In our study, δ SN R = 1dB. Then two methods can be used to estimate user's location:

1. Among the N valid positions, if there are n positions that are in the same room Room and if n is greater than a half of N , then the server might conclude that the user is in the room Room.

2. Otherwise, the server will determine the user's position that has a minimal standard deviation σ i (i= 1,2,...,N). The latter is calculated using the formula:

M is the number of access points in the museum. Finally the user has a second possible position with a standard deviation little greater than the previous one.

If the server does not yet find a position, it announces that the location is unknown. All these steps are presented in the following algorithm:

Simulation and evaluation

Our goal is to study the efficiency of our location algorithm. For that, we proceed by simulating the museum environment. We use the OPNET Academic edition simulator. The features of the topology configuration is as following:

1. The wireless infrastructure spans an area of 100 x 100 meters.

2. There are one server and three APs.

3. WLAN technology is Wifi IEEE 802.11g [START_REF]IEEE Standard for Information technology -Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications[END_REF].

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Susana Maria Da Silva

Agostinho Bernardino

Pedro Fernandes

Luís Fonseca

Susana ; Bernardino

A new biocatalyst: Penicillin G Acylase immobilized in sol-gel micro-particles with magnetic properties

Keywords: cephalexin, immobilization, penicillin G acylase, sol-gel

Figure 1 -Figure 2 -Figure 3 -Figure 4 -Figure 5 -Figure 6 -Figure 7 -Figure 8 -Figure 9 -Figure 10 -Figure 11 -

 1234567891011 Figure 1 -SEM micrograph of sol-gel micro-particles with encapsulated magnetite and PGA (bar match 10 µm). 254x190mm (96 x 96 DPI)

Wiley-VCH Biotechnology Journal