quantitative mineralogy of surface sediments on the iceland shelf and application to down core studies of holocene ice rafted sediments abstract quantitative x ray diffraction analyses on the 2 mm sediment fraction from the iceland shelves are reported for subglacial diamictons seafloor surface sediments and the last 2000 cal yr bp from two cores the overall goal of the paper is to characterize the spatial variability of the mineralogy of the present day surface sediments 18 non clay minerals and 7 clay minerals compare that with largely in situ erosional products typified by the composition of subglacial diamictons and finally examine the late holocene temporal variability in mineral composition using multi mineral compositions the subglacial diamictons are dominated in the non clay mineral fraction by the plagioclase feldspars and pyroxene with 36 7 6 1 and 17 9 3 5 wt respectively with smectites being the dominant clay minerals the surface seafloor sediments have similar compositions although there are substantial amounts of calcite plus there is a distinct band of sites from nw to n central iceland that contain 1 6 wt of quartz this latter distribution mimics the modern and historic pattern of drift ice in iceland waters principal component analysis of the transformed wt log ratio non clay minerals is used to compare the subglacial surface and down core mineral compositions fifty eight percent of the variance is explained by the first two axes with dolomite microcline and quartz being important foreign species these analyses indicate that today the nw n central iceland shelf is affected by the import of exotic minerals which are transported and released from drift ice the down core mineralogy indicates that this is a process that has varied over the last 2000 cal yr bp

surface changes in the eastern labrador sea around the onset of the little ice age despite the relative climate stability of the present interglacial it has been punctuated by several centennial time scale climatic oscillations the latest of which are often colloquially referred to as the medieval climatic anomaly mca and the little ice age lia the most favored explanation for the cause of these anomalies is that they were triggered by variability in solar irradiance and or volcanic activity and amplified by ocean atmosphere sea ice feedbacks as such changes in the strength of the atlantic meridional overturning circulation amoc are widely believed to have been involved in the amplification of such climatic oscillations the labrador sea is a key area of deep water formation the waters produced here contribute approximately one third of the volume transport of the deep limb of the amoc and drive changes in the north atlantic surface hydrography and subpolar gyre circulation in this study we present multi proxy reconstructions from a high resolution marine sediment core located south of greenland that suggest an increase in the influence of polar waters reaching the labrador sea close to mca lia transition changes in freshwater forcing may have reduced the formation of labrador sea water and contributed towards the onset of the lia cooling

application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in holocene and late glacial shelf sediments off north iceland abstract the north icelandic shelf is partly distinguished by the tjornes fracture zone featuring numerous active basins in a mud dominated shelf environment late glacial and holocene high resolution sedimentary records from this area have been studied with tephrochronology as the main tool for correlation and for exact timing of palaeoceanographic events in the area data from three new piston cores from the shelf demonstrate the importance of tephra markers for the first chronological evaluation and correlation of the cores the correlation is extended with lithological logs and with magnetic susceptibility records a detailed multidisciplinary study including biostratigraphy and tephrochronology of a late holocene record of predominantly muddy sediments at the same location demonstrates that marked variations in the distribution of water masses occurred repeatedly through the last 4500 cal yr of special interest is the exact timing of a marked drop in sea surface temperature in the area indicated by ice rafting debris concentration to about 50 years before the hekla 3 eruption which occurred at 2980 cal yr bp this appears to predate most records of a general cooling event in nw europe by a couple of centuries two different possible age models one based on 14c dates combined with tephra markers and one based on tephra markers alone are discussed in context with the problem of different marine reservoir ages of the water masses in the area

multicentury scale records of carbonate hydrographic variability on the northern iceland margin over the last 5000 years the waters off northern iceland are subjected to extreme hydrographic variability on annual to decadal timescales in years when cold low salinity water moves coastward and sea ice is prevalent i e the late 1960s marine productivity of surface waters is low because the water column is well stratified in the opposite oceanographic mode warm salty atlantic water dominates the shelf and vertical mixing results in high productivity we track these two contrasting modes by measuring the carbonate content of marine sediments a proxy for productivity in three cores from northern iceland the fjord record b997 328pc is anchored by eleven 14c ams dates and has a resolution of one sample every 50 yr thirteen oscillations occurred over the last 4800 cal yr with an average length of 370 yr these are superimposed on a long term decrease in net carbonate accumulation the little ice age is marked by the largest decrease in carbonate content and in flux with smaller minima at 2300 and 3000 cal yr b p marked peaks in carbonate optima occurred at 2000 and 3800 cal yr b p the carbonate record from b997 328pc can be correlated with records on the inner shelf b997 330pc and midshelf b997 327pc indicating that significant regional changes in oceanography occurred at the southern margin of the norwegian greenland sea the marine carbonate fluctuations closely track temperature reconstructions from the greenland summit site for the last 2000 cal yr and show similar but slightly offset oscillations between 2000 and ca 4800 cal yr b p

early stage rifting of the northern tyrrhenian sea basin results from a combined wide angle and multichannel seismic study extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins the mechanisms that operate during the early stage of crustal extension are still intensely debated we present the results from coincident multichannel seismic and wide angle seismic profiles that transect across the northern tyrrhenian sea basin the profiles cross the corsica basin france to the latium margin italy where the early rift stage of the basin is well preserved we found two domains each with a distinct tectonic style heat flow and crustal thickness one domain is the corsica basin in the west that formed before the main rift phase of the northern tyrrhenian sea opening 8 4 ma the second domain is rifted continental crust characterized by tilted blocks and half graben structures in the central region and at the latium margin these two domains are separated by a deep 10 km sedimentary complex of the eastern portion of the corsica basin travel time tomography of wide angle seismic data reveals the crustal architecture and a subhorizontal 15 17 1 km deep moho discontinuity under the basin to estimate the amount of horizontal extension we have identified the pre syn and post tectonic sedimentary units and calculated the relative displacement of faults we found that major faults initiated at angles of 45 50 and that the rifted domain is horizontally stretched by a factor of 1 3 8 10 mm a the crust has been thinned from 24 to 17 km indicating a similar amount of extension 30 the transect represents one of the best imaged early rifts and implies that the formation of crustal scale detachments or long lived low angle normal faults is not a general feature that controls the rift initiation of continental crust other young rift basins like the gulf of corinth the suez rift or lake baikal display features resembling the northern tyrrhenian basin suggesting that half graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation

variability of the north atlantic current during the last 2000 years based on shelf bottom water and sea surface temperatures along an open ocean shallow marine transect in western europe marine localities on the west european shelf have been studied to reconstruct the nearshore palaeoceanography of the last two millennia the sites form a transect from the iberian margin northeastward via scotland to western norway and iceland proxies used for palaeoclimatic reconstructions include stable isotopes benthic and planktonic foraminfera diatoms dinoflagellates as well as geochemical and sedimentological parameters major changes as well as long term trends in oceanographic conditions are observed in the records including a general cooling trend through much of the last millennium there is a clear linkage between the atmospheric processes and the oceanic circulation and the ocean temperature variability in the records can be correlated with the so called mediaeval warm period and little ice age these oscillations are however by no means unique within the last two millennia as an example sea surface temperatures to the north of iceland and on the iberian margin were higher in the roman warm period than at any time during the mediaeval warm period however the palaeoceanographic record generally supports a distinct cooling at the transition between the mediaeval warm period and the little ice age while a number of records indicate a warming of coastal and shelf waters during the last 200 years the twentieth century does not appear to be unusual when the proxy records spanning the last two millennia are examined

asynchronous little ice age glacier fluctuations in iceland and european alps linked to shifts in subpolar north atlantic circulation abstract records of past glacier fluctuations are an important source of paleoclimate data and provide context for future changes in global ice volume in the north atlantic region glacier chronologies can be used to track the response of terrestrial environments to variations in marine conditions including circulation patterns and sea ice cover however the majority of glacier records are discontinuous and temporally restricted owing in part to the extensive advance of northern hemisphere glaciers during the little ice age lia the most recent and severe climate anomaly of the neoglacial period here we combine an absolutely dated and continuous record of langjokull ice marginal fluctuations with new reconstructions of sediment flux through the past 1 2 ka using varved sediments from hvitarvatn a proglacial lake in iceland s central highlands large spatial and temporal variations in sediment flux related to changing ice cap dimensions are reconstructed from six sediment cores and seismic reflection profiles sediment data reveal two discrete phases of ice expansion occurring ca 1400 to 1550 ad and ca 1680 to 1890 ad these advances are separated by a persistent interval of ice retreat suggesting that a substantial period of warming interrupted lia cold the pattern of icelandic glacier activity contrasts with that of european glaciers but shows strong similarities to reconstructed changes in north atlantic oceanographic conditions indicating differing regional responses to coupled ocean atmosphere sea ice variations our data suggest that subpolar north atlantic circulation dynamics may have led to coherent asynchronous glacier fluctuations during the mid lia and highlight the importance of circulation variability in triggering and transmitting multidecadal scale climate changes to nearby terrestrial environments

late holocene ca 4 ka marine and terrestrial environmental change in reykjarfjordur north iceland climate and or settlement core b997 328pc is from the landward side of a 100 m deep basin in reykjarfjordur a small fjord on the north coast of the northwest peninsula of iceland this is an area that can be severely affected by incursions of polar sea ice but has not suffered marked land erosion during the settlement period the core is 422 cm in length and consists principally of fine grained muds with in situ molluscs eleven ams 14c dates on molluscs indicate a constant sediment accumulation rate of ca 1 cm 10 yr 1 for the last 4280 50 yr bp we measured and derived a variety of proxies for indications of changes in the nearshore environment these included physical properties and grain size mass accumulation rates micropalaeontology pollen and foraminifera multivariate analysis and constrained clustering were used to define major changes in the proxies in several parameters the major change in the fjord environment occurred close to 1000 14c yr ago thus approximately coincident with the onset of the settlement of iceland other changes are noted at around 1600 and 3400 14c yr ago betula pollen disappears from the record ca 1500 yr bp and there are peaks in marine productivity occurring ca 2 and 3 4 ka a major decline in carbonate accumulation and a sharp increase in the cold water benthic foraminifer elphidium excavatum forma clavata 400 yr ago represents the local marine signature of the little ice age none of the changes in our data can be explained adequately by a simple call to land use practices and an increase in land to sea transport but both the pollen and foraminiferal records indicate a decrease and even loss of warm elements in both flora and fauna over the past 4 kyr copyright 2001 john wiley sons ltd

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

reconstructing mid to high latitude marine climate and ocean variability using bivalves coralline algae and marine sediment cores from the northern hemisphere quantifying the role and contribution of the world s oceans in past present and future global change is an essential goal in climate paleoclimate and environmental studies although the global oceans interact and influence climate greatly the marine environment is substantially under represented in key climate assessment reports especially during the last millennium ipcc 2007 see palaeoclimate chapter 6 6 the last 2000 years the under representation of marine records in key climate documents likely results from the often imprecise chronologies associated with many marine based archives which greatly hinders singular climate comparisons lag lead phasing relationships with well dated and or annually resolved archives however several marine archive records have excellent chronological constraint in particular many marine bivalve taxa and coralline algae have annual increments that form within their carbonate framework that can be used to establish an absolutely dated chronology via cross dating techniques from the marine environment additionally in some cases where sedimentation rates are high and alternative chronological dating methods exist e g tephrochronology other than radiocarbon measurements often greater than 40 years uncertainty sediment archives can provide continuous sub decadal records of environmental change for centuries to millennia this brief introductory article and accompanying special issue will focus on the utilization of bivalves coralline algae and high resolution marine sediment cores in paleoclimate and environmental studies within the most recent millennium with a focus on the northern hemisphere

structure and tectonics of the erosional convergent margin off antofagasta north chile 23 30 s subduction erosion has dominated the evolution of the north chile convergent continental margin since at least the mesozoic we investigate the structure of the antofagasta 23 s sector of this margin along a transect using coincident wide angle and near vertical seismic profiling and gravity data a 2 d velocity field of the overriding and subducting plates was obtained using joint refraction and reflection travel time tomography a velocity derived density distribution was used to model marine gravity data and substantiate the velocity model the gravity and velocity models imply that the overriding plate is mainly made of arc type igneous basement the upper plate is constructed of two main rock bodies separated by a subhorizontal layer defined by a velocity inversion the top coincident with a reflection in near vertical seismic images the seismic boundary is interpreted as a detachment separating an upper extended domain with large scale normal faulting from a lower domain apparently undergoing a different type of deformation velocity derived porosity indicates that the front of the margin is probably fluid saturated and disaggregated by fracturation as a consequence of frontal subduction erosion fluids carried into the subduction channel within slope debris filling underthrusting grabens reduce basal friction and probably induce hydrofracturing and basal erosion along the underside of the overriding plate at depths greater than 20 km porosity and density values imply that most fluids have been exhausted and the lower part of the upper plate is structurally coherent and little fractured the change in physical properties leads to increased mechanical coupling along the plate boundary and occurs at the updip limit of the distribution of aftershocks of the 1995 antofagasta earthquake m w 8 0 defining the seismogenic zone

diatom surface sediment assemblages around iceland and their relationships to oceanic environmental variables canonical correspondence analysis of diatoms from surface sediment samples and oceanographic environmental variables shows that summer and winter sea surface temperatures water depth and winter sea surface salinity are the main environmental factors affecting diatom distribution around iceland of these summer sea surface temperature is the most important five diatom assemblages are distinguished and the distribution of these assemblages is clearly correlated with oceanic current patterns in the region the sea ice diatom assemblage is limited to the area where the east greenland current polar water has its strongest influence and the cold diatom assemblage is basically controlled by the less cold east icelandic current modified polar water the mixing diatom assemblage results from the interaction between the cold east greenland and east icelandic currents and the warm irminger current the warm diatom assemblage is located in the area dominated by the irminger current and may be used as an indicator of warm water masses atlantic water the coastal diatom assemblage is the only one strongly influenced by both water depth and summer water temperatures

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles ocean drilling program legs 149 and 173 transect we present a wide angle seismic refraction study of an 80 40 km region of the southern iberia abyssal plain south of galicia bank an intersecting grid of two e w and four n s wide angle reflection refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean continent transition oct these structures can be systematically linked to variations in acoustic basement morphology and to results from ocean drilling program odp boreholes lateral changes in the velocity structure of the basement occur abruptly over distances of 20 km where complex variations may be found thinned upper continental crust 2 5 km thick with velocities of 5 0 6 6 km s is limited to a series of n s fault blocks immediately south of galicia bank this crust is underlain by a high velocity layer 7 3 7 9 km s of weakly serpentinized i e 0 25 peridotite which exists throughout the eastern part of the survey area basement within the oct appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally in the southeast sector of our survey where basement topography deepens and becomes subdued continental fault blocks are absent instead basement contains an upper layer of more pervasively serpentinized i e 25 45 peridotite that is 2 km thick this layer is characterized by low velocity at the top of basement 4 2 km s that increases rapidly with depth and it probably corresponds to a seismically unreflective layer previously identified in reflection profiles to the south of our survey in the western section of our survey beneath a series of elevated basement ridges velocities are reduced within both the upper basement layer 3 5 6 0 km s and lower layer 6 4 7 5 km s these changes suggest that both upper and lower layers have become more highly serpentinized with values of 60 100 in the upper layer and 25 45 in the lower layer probably during the last stages of rifting and immediately before formation of oceanic crust a normal or slow spreading oceanic crustal structure is not found within the survey region thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at odp site 897 and east of the j magnetic anomaly

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

late holocene summer sea surface temperatures based on a diatom record from the north icelandic shelf diatom assemblages from a high resolution core on the north icelandic shelf reveal a general late holocene cooling trend which is interrupted by three relatively warm periods diatom data from sur

sea surface temperature and sea ice variability in the subpolar north atlantic from explosive volcanism of the late thirteenth century 1 in this study we use ip25 and alkenone biomarker proxies to document the subdecadal variations of sea ice and sea surface temperature in the subpolar north atlantic induced by the decadally paced explosive tropical volcanic eruptions of the second half of the thirteenth century the short and long term evolutions of both variables were investigated by cross analysis with a simulation of the ipsl cm5a lr model our results show short term ocean cooling and sea ice expansion in response to each volcanic eruption they also highlight that the long response time of the ocean leads to cumulative surface cooling and subsurface heat buildup due to sea ice capping as volcanic forcing relaxes the surface ocean rapidly warms likely amplified by subsurface heat and remains almost ice free for several decades

holocene thermal maximum off north iceland evidence from benthic and planktonic foraminifera in the 8600 5200 cal year bp time slice abstract a high resolution study of palaeoceanographic changes off north iceland during the time period 8600 5200 cal year bp is based on benthic and planktonic foraminiferal assemblages the core material md99 2275 was obtained from about 440 m water depth on the eastern part of the north icelandic shelf changes in the faunal composition are interpreted to be mainly caused by variations in the strength of the relatively warm high salinity irminger current and the cold east icelandic current which have been shown to be linked to the climatic changes in the north atlantic region environmental proxies at that site are particularly sensitive to palaeoceanographic changes due to its position close to the marine polar front benthic assemblages show that relatively cold conditions prevailed at the base of the record an increase in the influence of atlantic water masses at the sea floor is seen at around 8400 cal year bp whereas the surface waters were relatively warm already at 8600 cal year bp the warming was interrupted by a cold event at around 8100 8000 cal year bp registered both in the bottom and surface waters and correlated with the so called 8 2 kyr cooling event both the benthic and the planktonic faunal compositions indicate that the irminger current had maximum influence in the area between 8000 and about 7300 cal year bp followed by a gradually decreasing influence through the remaining part of the studied time interval it is suggested that the contribution of atlantic water masses from the east and north east to the arctic surface waters off north iceland increased after around 7000 cal year bp and that this was further intensified after 6200 cal year bp at present the arctic surface water north of iceland consists of polar waters intermittently with direct influence from the east greenland current mixed with atlantic waters derived from the eastern part of the nordic seas a comparison of the mean values of selected environmental proxies in the interval 8600 5200 cal year bp with the upper part of the same core shows that the water masses north of iceland were considerably warmer during the holocene thermal maximum than during the last 2000 cal year in general results from core md99 2275 are in accordance with other marine records from the north icelandic shelf and the northern north atlantic region although a detailed comparison on a centennial time scale is hampered by problems with spatial as well as temporal changes in the marine reservoir ages in the region

holocene paleomagnetic secular variation psv near 80 n northwest spitsbergen svalbard implications for evaluating high arctic sediment chronologies abstract we present a paleomagnetic study of two holocene lake sediment sequences from northwest spitsbergen on svalbard norway core hap 212 from lake hajeren preserves a rare combination of a well defined characteristic remanent magnetization chrm and robust age control defined by 21 terrestrial macrofossil derived radiocarbon dates providing a unique opportunity to assess the stratigraphic potential of high arctic holocene paleomagnetic secular variation psv close to 80 n core amp 112 from hakluytvatnet which is also well dated is a poor magnetic recorder and cannot be used for geomagnetic reconstruction comparison of the hap 212 psv record with poorly dated regional records show similar directional features suggesting that psv can be used for chronological synchronization comparison of the hap 212 psv with well dated records 1800 km to the southwest and southeast show that these records are in phase at millennial timescales within dating and magnetic uncertainties indicating that a consistent geomagnetic signal is recorded at these temporal and spatial scales these findings support the notion that psv when optimally recorded can be used to import chronologies from lower latitudes to the high arctic where low organic content hard water effects lack of datable material and other difficulties often preclude more conventional radiocarbon dating

observed sources and variability of nordic seas overflow the overflows from the nordic seas maintain the deep branch of the north atlantic circulation that is an important part of the global climate system an analysis of observed ocean temperatures and salinities between 1950 and 2005 shows that the atlantic water circulating in the nordic seas is the main source for change in the overflow waters

palaeoceanography and climate changes off north iceland during the last millennium comparison of foraminifera diatoms and ice rafted debris with instrumental and documentary data planktonic and benthic foraminifera data as well as ice rafted debris data from a 210pb dated multicore b05 2006 mc04 covering the last ca 130 a on the north icelandic shelf 450 m water depth are compared with instrumental data and with the sea ice index for the area there is indication of a strong connection between atmospheric and oceanic changes a pronounced rise in the sea surface temperature is documented by the proxy data to occur at ad 1910 which is shortly before the rise in the air temperature in the region at ca ad 1920 but coinciding with the first rise in instrumentally measured annual sea surface temperature the great salinity anomaly in the 1960s and early 1970s is however not clearly expressed in the environmental proxies there has been a mean sedimentation rate of about 300 cm ka 1 at the core site based on a tephrochronological age model for the core md99 2275 the foraminifera and diatom assemblages show increased influence of atlantic water masses during the time interval ca ad 800 1300 the so called medieval warm period or medieval climatic anomaly whereas the interval ca ad 1300 1910 encompassing the little ice age was characterised by decreased sea surface temperatures due to intensified influence of arctic waters of the east icelandic current copyright 2009 john wiley sons ltd

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

wobbly ocean conveyor circulation during the holocene abstract compared to the last glacial period the climate of the holocene has been quite stable however the record does suggest that at high latitudes in the north temperatures have cooled at least since the middle holocene and that this cooling has been modulated by millennial duration fluctuations that culminated in the medieval warm little ice age oscillation in this paper we explore the possibility that these variations were associated with concurrent changes in the strength of the atlantic s conveyor circulation three lines of evidence are considered one involves records that relate directly to ocean operation a second involves the tie between sea ice extent in the northern atlantic and the extent of mountain glaciers in the european alps and in the cordillera of western north america and a third involves evidence for a bipolarity in climate changes in the northern and southern polar regions in addition we look into clues provided by the atlantic multidecadal oscillation amo although at this point no firm conclusion can be drawn the case for ocean involvement is sufficiently strong to merit further attention

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

evidence for solar forcing of sea surface temperature on the north icelandic shelf during the late holocene diatom proxies from the modern position of the oceanographic polar front north of iceland record variability in sea surface temperatures ssts during the past 2 k y the sedimentary record is dated with tephrochronology alleviating marine 14c reservoir age uncertainties comparison of changes in ssts on the north icelandic shelf with variations in the atmospheric circulation above greenland north american atlantic coastal ssts and mean temperature anomalies for the northern hemisphere suggests synchronous north atlantic wide fluctuations which would seem to imply a common forcing factor a positive and significant correlation between our sst record from the north icelandic shelf and reconstructed solar irradiance together with modeling results supports the hypothesis that solar forcing is an important constituent of natural climate variability in the northern north atlantic region

holocene shifts in sub surface water circulation of the north east atlantic inferred from nd isotopic composition in cold water corals abstract variations of the sub polar gyre spg and the sub tropical gyre stg circulation during the holocene are believed to be related to regional and global climate over this time period to improve our understanding of these phenomena we provide new constraints on variations in surface circulation patterns using neodymium isotopes end on precisely u th dated coral fragments of l pertusa the fragments were retrieved from two sediment cores taken from cold water coral cwc mounds at 127 134 m water depth in the mingulay reef complex located on the western british continental shelf the results have been combined with end analyzed on seawater samples from two stations located on the continental shelf and margin in order to establish whether end is a reliable proxy of the ocean circulation variations and notably of the relative contribution of water originating from the spg and stg end values in cwcs from the mingulay reef complex range from 14 5 0 4 to 11 8 0 3 highlighting two major variations unradiogenic end values 14 5 0 4 indicate a higher contribution of water from the spg around 2 8 ka conversely more radiogenic values at 3 4 ka 11 8 0 3 point to a declining spg strength accompanied by stronger northward penetration of stg water along the western european margin transported by the shelf edge current sec and or cooler and fresher waters from the interior seas the eastward extension of the spg at 2 8 ka is associated with lower 14c reservoir age 200 yrs compared to periods associated with a higher contribution of stg waters this indicates that 14c reservoir ages are mainly a function of vertical mixing of the sub surface of the ocean as stronger vertical ventilation is not associated with a higher proportion of local radiogenic surface water we hypothesize it could represent vertical ventilation in the north eastern atlantic active spg is associated with a better ventilation of the water masses within the spg and warmer climatic conditions in northern europe and in the eastern norwegian sea linked to an intensification of the surface limb of the amoc

reconstructions of surface ocean conditions from the northeast atlantic and nordic seas during the last millennium we undertake the first comprehensive effort to integrate north atlantic marine climate records for the last millennium highlighting some key components common within this system at a range of temporal and spatial scales in such an approach careful consideration needs to be given to the complexities inherent to the marine system composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three dimensional ocean dynamics this study focuses on the northeast ne north atlantic ocean particularly sites influenced by the north atlantic current a composite plus regression approach is used to create an inter regional ne north atlantic reconstruction of sea surface temperature sst for the last 1000 years we highlight the loss of spatial information associated with large scale composite reconstructions of the marine environment regional reconstructions of ssts off the norwegian and icelandic margins are presented along with a larger scale reconstruction spanning the ne north atlantic the latter indicates that the medieval climate anomaly warming was most pronounced before ad 1200 with a long term cooling trend apparent after ad 1250 this trend persisted until the early 20th century while in recent decades temperatures have been similar to those inferred for the medieval climate anomaly the reconstructions are consistent with other independent records of sea surface and surface air temperatures from the region indicating that they are adequately capturing the climate dynamics of the last millennium consequently this method could potentially be used to develop large scale reconstructions of ssts for other hydrographically constrained regions

revised age estimate of the mjauvotn tephra a on the faroe islands based on bayesian modelling of c 14 dates from two lake sequences tephra horizons are potentially perfect time markers for dating and cross correlation among diverse holocene palaeoenvironmental records such as ice cores and marine and terrestrial sequences but we need to trust their age here we present a new age estimate of the holocene mjauvotn tephra a using accelerator mass spectrometry c 14 dates from two lakes on the faroe islands with bayesian age modelling it is dated to 6668 6533 cal a bp 68 2 confidence interval significantly older and better constrained than the previous age copyright c 2010 john wiley sons ltd

identification and definition of primary and reworked tephra in late glacial and holocene marine shelf sediments off north iceland nine tephra layers in marine sediment cores md99 2271 and md99 2275 from the north icelandic shelf spanning the late glacial and the holocene have been investigated to evaluate the effectiveness of methods to detect tephra layers in marine environments to pinpoint the stratigraphic level of the time signal the tephra layers provide and to discriminate between primary and reworked tephra layers in a marine environment these nine tephra layers are the borrobol like tephra vedde ash askja s tephra saksunarvatn ash and hekla 5 hekla 4 hekla 3 hekla 1104 and v1477 tephras the methods used were visual inspection magnetic susceptibility x ray photography mineralogical counts grain size and morphological measurements and microprobe analysis the results demonstrate that grain size measurements and mineralogical counts are the most effective methods to detect tephra layers in this environment revealing all nine tephra layers in question definition of the tephra layers revealed a 2 3 cm diffuse upper boundary in eight of the nine tephra layers and 2 3 cm diffuse lower boundary in two tephra layers using a multi parameter approach the stratigraphic position of a tephra layer was determined where the rate of change of the parameters tested was the greatest compared with background values below the tephra the first attempt to use grain morphology to distinguish between primary and reworked tephra in a marine environment suggests that this method can be effective in verifying whether a tephra layer is primary or reworked morphological measurements and microprobe analyses in combination with other methods can be used to identify primary tephra layers securely the study shows that there is a need to apply a combination of methods to detect define the time signal and discriminate between primary and reworked tephra in marine environments copyright 2011 john wiley sons ltd

landslide tsunamis propagating along a plane beach a forced two horizontal dimension analytical model is developed to investigate the distinguishing physical features of landslide induced tsunamis generated and propagating on a plane beach the analytical solution is employed to study the wave field at small times after the landslide motion starts at larger times the occurrence of transient edge waves travelling along the shoreline is demonstrated showing the differences with the transient waves propagating over a bottom of constant depth results are satisfactorily compared with available experimental data finally the validity of non forced numerical models is discussed

do paleoclimate proxies agree a test comparing 19 late holocene climate and sea ice reconstructions from icelandic marine and lake sediments geochemical mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments modern spatial calibrations or down core comparisons with instrumental climate data multi proxy studies provide another means of evaluating interpretations of proxies this paper presents a multi proxy assessment comparing 19 sub centennially resolved late holocene proxy records covering the period 300 1900 ad from seven icelandic marine and lacustrine core sites we employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and ultimately their utility as proxies for regional climate proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera abundance of the sea ice biomarker ip25 allochthonous quartz in marine sediments a proxy for drift ice around iceland marine carbonate abundance total organic carbon concentration chironomid assemblages lacustrine biogenic silica and carbon nitrogen ratios in lake sediments most of the examined proxy records including temperature and sea ice proxies correlate strongly with each other over multi centennial timescales and thus do appear to record changes in regional climate copyright 2011 john wiley sons ltd

millennial scale variations of the holocene north atlantic mid depth gyre inferred from radiocarbon and neodymium isotopes in cold water corals abstract variations in north atlantic ocean mid depth circulation during the holocene are poorly understood it is believed that they had a significant influence on the properties of water entering the nordic sea by redistributing heat and freshwater potentially affecting deep water formation and climate to improve our knowledge of the ne atlantic mid depth circulation radiocarbon and neodymium isotope analyses have been then carried out on precisely dated u th l pertusa and m oculata coral fragments from two sediment cores taken at 750 m water depth on the sw rockall trough margin cold water coral cwc end values vary between 12 2 0 3 and 16 6 0 4 and result from variable contributions of unradiogenic mid depth subpolar gyre mid spg water 15 and more radiogenic eastern north atlantic water enaw 11 which is transported northward to the rockall trough by boundary currents along the european margin increased coral end reflects a westward contraction of the mid spg water and a higher proportion of enaw the mid holocene from 8 8 to 6 8 ka bp is marked by unradiogenic coral end from 16 6 0 4 to 14 6 0 5 indicating a greater eastward extension of the mid spg this is followed by a shift from 6 8 to 5 ka bp toward more radiogenic end values from 15 4 0 3 to 13 3 0 2 suggesting a westward contraction of the mid spg and a higher proportion of enaw the mid holocene long term change in end is characterized by millennial variations of up to 2 5 epsilon units well marked during the late holocene indicating that eastward extension of the mid spg coeval with warm periods in northern europe e g the medieval climatic anomaly and the roman warm period most of the cwc derived 14c values match the global ocean values indicating that the water masses bathing the corals were generally well ventilated the exceptions are a few short intervals of eastward extension of the mid spg which are characterized by lower 14c during the late holocene we propose that these minor 14c fluctuations in the rockall trough may be related to local changes in the mixed layer depth or to variability in the advection of water from the labrador sea where deep convection gives rise to thermocline waters that are relatively depleted in terms of 14c the eastward extension of the mid spg between 8 8 and 6 8 ka bp is associated with the holocene climatic optimum concurrent with a maximum strength of the iceland scotland overflow water isow which is indicative of an increase in the atlantic meridional overturning circulation amoc this period is followed by a transition in the north atlantic circulation which occurred around 6 8 ka bp and coincides with the onset of labrador sea water formation a decrease of the isow strength and a contraction of the mid spg leading to a greater intrusion of saline subtropical water into the subpolar atlantic

vavilov seamount a mildly alkaline quaternary volcano in the tyrrhenian basin vavilov seamount emerges from the central tyrrhenian plain at 3600 m depth and reaches 684 m below sea level four dives in the cyana submersible showed that this voluminous volcanic edifice 350 400 km3 can be divided into two parts 1 from its base to 1500 m deep a pile of thick submarine basaltic flows and 2 an upper part above 1500 m consisting of smaller radial lava flows related to a major central volcano vavilov s s and other minor vents aligned north south the basal series is affected by normal faults directed north to n40 and strongly tilted westward like the neighbouring sardinian continental block radiometric ages of upper lavas range from 0 1 to 0 4 ma other observations suggest that the late phase of construction has been subaerial and lead to estimate the upper quaternary subsidence of the basin to at least 500 m 4 5 mm yr 1 although vavilov is located at the supposed centre of oceanic accretion the characteristics of its lavas strongly differ from those of the underlying crust the basalts fall into the mildly alkaline series and are strongly enriched in light ree among the products of passive margin volcanism they may be compared with intermediate basalts between the olivine tholeiite of the continental flood basalts and the p type oceanic basalts in terms of oceanic volcanism they are very close to oceanic island basalts oib vavilov appears as a structure independent of the oceanic crust which supports it and does not represent a ridge related to the oceanic accretion as one might suppose

north atlantic ecosystem sensitivity to holocene shifts in meridional overturning circulation rapid changes in north atlantic climate over the last millennia were driven by coupled sea surface atmospheric processes and rates of deep water formation holocene climate changes however remain poorly documented due to a lack of high resolution paleoclimate records and their impacts on marine ecosystems remain unknown we present a 4500 years absolute dated sea surface radiocarbon record from northeast atlantic cold water corals in contrast to the current view that surface ocean changes occurred on millennial scale cycles our record shows more abrupt changes in surface circulation changes were centered at 3 4 2 7 1 7 and 1 2 ky bp and associated with atmospheric re organization solar irradiance may have influenced these anomalies but changes in north atlantic deep water convection are likely to have amplified these signals critically we provide the first evidence that these perturbations in atlantic meridional overturning circulation led to the decline of cold water coral ecosystems from 1 2 to 0 1 ky bp

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

decadal variability of sea surface temperatures off north iceland over the last 2000 years abstract ocean variability at decadal time scales remains poorly described partly because of the scarcity of high temporal resolution marine records here we present a reconstruction of sea surface temperatures ssts over the past two millennia at unprecedented temporal resolution 2 to 5 years from a marine core located off north iceland alkenone paleothermometry was used to infer sst variability and tephrochronology to build the age model spectral analyses of the sst signal indicate intermittent 20 25 year oscillations with periods of strong and weak power that are likely reflecting the ocean response to wind forcing presumably the north atlantic oscillation nao warmer ssts and paleo magnetic proxy data between 1000 and 1350 year a d overlapping the medieval warm period mwp suggest enhanced heat transport across the denmark strait by the north icelandic irminger current niic this is in contrast with the subsequent period which includes the little ice age lia showing continuous cooling towards the 20th century reduced niic flow through the denmark strait likely resulting from higher freshwater and sea ice export from the arctic would account for the observed colder conditions

palaeoceanographic changes off north iceland through the last 1200 years foraminifera stable isotopes diatoms and ice rafted debris abstract palaeoclimatic changes through the last 1200 calibrated years have been documented by high resolution multi proxy studies of three cores from about 400 m water depth on the north icelandic shelf benthic and planktonic foraminiferal assemblages and stable isotope values as well as ice rafted debris ird concentrations are compared with diatom based sea surface water temperatures and the reconstructed mean temperature for the northern hemisphere changes in surface and bottom water characteristics are mainly due to variations in the strength of the relatively warm high salinity irminger current and the cold east icelandic current the time period between 1200 and around 7 800 cal years bp including the medieval warm period was characterized by relatively high bottom and surface water temperatures due to the inflow of atlantic water masses after that a general temperature decrease in the area marks the transition to a period with increased influence of the east icelandic current and at the sea floor the norwegian sea deep water this corresponds to the transition to the little ice age after about 3 400 cal bp the inflow of cold east icelandic current was further enhanced in particular this had a strong influence on the surface waters while the sea floor was under some influence of atlantic water masses resulting in stratification of the water masses there is no clear indication of any warming in the area during the last decades

holocene history of drift ice in the northern north atlantic evidence for different spatial and temporal modes 1 we present new high resolution proxy data for the holocene history of drift ice off iceland based on the mineralogy of the 2 mm sediment fraction using quantitative x ray diffraction these new data bolstered by a comparison with published proxy records point to a long term increasing trend in drift ice input into the north atlantic from 6 to 5 ka toward the present day at sites influenced by the cold east greenland current this feature reflects the late holocene neoglacial or cooling period recorded in ice cores and further terrestrial archives on greenland in contrast a decrease in drift ice during the same period is recorded at sites underlying the north atlantic drift which may reflect a warming of this region the results document that holocene changes in iceberg rafting and sea ice advection did not occur uniformly across the north atlantic centennial scale climate variability in the north atlantic region over the last 4 kyr is linked to the observed changes in drift ice input increased drift ice may have played a role in the increase of cold intervals during the late holocene e g the little ice age cooling

coupling of palaeoceanographic shifts and changes in marine reservoir ages off north iceland through the last millennium abstract our study of spatial and temporal marine reservoir age changes on the north icelandic shelf is based on two high resolution 1000 year sedimentary records from images core sites md99 2273 and md99 2275 located at 650 m and 470 water depths respectively the sedimentary and fossil record is extremely sensitive to past oceanographic and climatic changes in this region it has been demonstrated that the position of the polar front across the shelf has been very dynamic through the last millennium and our results show that deviations in the marine reservoir ages can be used as a palaeoceanographic tool for tracing changes in the water masses the presence of historically and terrestrially dated tephra markers from icelandic volcanoes makes it possible to construct a reliable tephrochronological age depth model for each of the marine sediment cores a comparison of these age models with age models based on calibrated ams radiocarbon age determinations of marine molluscs displays major deviations through the last 1000 years the discrepancy between the two types of age models shows that there was an average reservoir age of about 650 years at md99 2273 and 590 years at site md99 2275 with considerable changes through time this is suggested to be related to a generally high but fluctuating inflow of apparently old polar waters to the area a comparison with the distribution of two benthic foraminiferal indicator species in the cores one for polar and arctic water masses islandiella norcrossi and one for atlantic water cassidulina neoteretis as well as with different proxies for sea ice cover in the area shows that there was an increase in the penetration of cold polar and arctic water masses after ad 1300 i e during the little ice age at both sites resulting in an increase in the reservoir ages relatively high reservoir ages throughout the last millennium at the deepest core site md99 2273 can be attributed to a continuously high polar water influence at the sea floor the location of this site to the west of the kolbeinsey ridge which has acted as a submarine barrier throughout the holocene may have contributed to a relatively high influence of cold denmark strait overflow water in this area

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

exceptional ocean surface conditions on the se greenland shelf during the medieval climate anomaly diatom inferred 2900 year long records of august sea surface temperature asst and april sea ice concentration asic are generated from a marine sediment core from the se greenland shelf with a special focus on the interval ca 870 1910 common era c e reconstructed in subdecadal temporal resolution the medieval climate anomaly mca between 1000 and 1200 c e represents the warmest ocean surface conditions of the se greenland shelf over the late holocene 880 b c e before the common era to 1910 c e it was characterized by abrupt decadal to multidecadal changes such as an abrupt warming of 2 4 c in 55 years around 1000 c e temperature changes of these magnitudes are rare on the north atlantic proxy data compared to regional air temperature reconstructions our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the greenland ice sheet or intensified sea ice export from the arctic as a response to atmospheric warming at the beginning of the mca a cool phase from 1200 1890 c e associated with the little ice age ends with the rapid warming of asst and diminished asic in the early twentieth century the results show that the periods of warm asst and asic minima are coupled with solar minima suggesting that solar forcing possibly amplified by atmospheric forcing have been behind the variability of surface conditions on the se greenland over the last millennium the results indicate that the se greenland shelf is a climatologically sensitive area where extremely rapid changes are possible and highlights the importance of the area under the present warming conditions

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

amincissement de la croute et accretion au centre du bassin tyrrhenien d apres la sismique refraction seismic refraction lines were carried out in the deep central area of the tyrrhenian basin and near the foot of adjacent margins using air guns as seismic source and pop up bottom seismographs pubs valuable correlations between refraction and reflection data enable us to identify messinian and pre messinian series beneath plio quaternary series on stretched margins toward the middle of the basin detritic to volcanodetritic series overlay the acoustic basement the p wave velocity depth distributions inferred from synthetic seismograms on most of the profiles are similar to those computed for oceanic areas especially for spreading zones such as the atlantic ridge the east indian ridge the reykjanes ridge progressive velocity increasing with depth velocity inversions within the crust moho depth of 10 11 km low pn velocity of 7 73 km s 1 suggesting the existence of an abnormal mantle layer 3 is 7 km deep probably including a 2 km thick layer 3b 7 44 km s 1 our data are in good agreement with the assumption of a recent accretion beneath the central basin of the tyrrhenian sea along a cross section at 40 n latitude running from the sardinian to the apenninic margins the moho discontinuity rapidly rises from 27 km to 11 km depth beneath the central tyrrhenian basin the 6 0 km s 1 granitic layer beneath sardinia disappears east of the central fault and reappears again along the facing apenninic margin

biological and climate controls on north atlantic marine carbon dynamics over the last millennium insights from an absolutely dated shell based record from the north icelandic shelf given the rapid increase in atmospheric carbon dioxide concentrations pco2 over the industrial era there is a pressing need to construct long term records of natural carbon cycling prior to this perturbation and to develop a more robust understanding of the role the oceans play in the sequestration of atmospheric carbon here we reconstruct the past biological and climate controls on the carbon isotopic 13cshell composition of the north icelandic shelf waters over the last millennium derived from the shells of the long lived marine bivalve mollusk arctica islandica variability in the annually resolved 13cshell record is dominated by multidecadal variability with a negative trend 0 003 0 002 yr 1 over the industrial era 1800 2000 common era this trend is consistent with the marine suess effect brought about by the sequestration of isotopically light carbon 13c of co2 derived from the burning of fossil fuels comparison of the 13cshell record with contemporaneous proxy archives over the last millennium and instrumental data over the twentieth century highlights that both biological primary production and physical environmental factors such as relative shifts in the proportion of subpolar mode waters and arctic intermediate waters entrained onto the north icelandic shelf atmospheric circulation patterns associated with the winter north atlantic oscillation and sea surface temperature and salinity of the subpolar gyre are the likely mechanisms that contribute to natural variations in seawater 13c variability on the north icelandic shelf contrasting 13c fractionation processes associated with these biological and physical mechanisms likely cause the attenuated marine suess effect signal at this locality

chronology of late holocene climatic events in the northern north atlantic based on ams 14c dates and tephra markers from the volcano hekla iceland a combination of ams14c dating and tephrochronology has been used to date late holocene oceanographic events in a 335 cm marine record covering about 4600 cal yr with sedimentation rates exceeding 80 cm 1000 yr 1 the core site is located 50 km offshore on the northern icelandic shelf tephra markers from iceland serve to correlate the marine and terrestrial records especially notable is the presence of three geochemically correlated tephra markers from the icelandic volcano hekla hekla 4 hekla 3 and hekla 1104 benthic and planktonic foraminiferal abundance and distribution as well as the petrography of the sand fraction of the muddy shelf sediments are used as palaeoceanographic proxies the foraminiferal assemblages reflect a general cooling trend during the last 4600 yr a marked drop in sea surface temperatures is registered at about 3000 cal yr bp corresponding to the level of the hekla 3 tephra there is faunal indication of temperature amelioration during the medieval warm period and a cooling again during the little ice age periods of ice rafting events are indicated by ice rafted debris ird concentrations e g at around 3000 cal yr bp and during the little ice age the former event occurred just prior to the deposition of the hekla 3 tephra marker the largest holocene hekla eruption a correlation with terrestrial climatic events in iceland is presented a standard marine reservoir correction of 400 14c yr appears to be reasonable at least during periods with high influence of water masses from the irminger current on the northern icelandic shelf an increase to ca 530 14c yr may have occurred however when water masses derived from the east greenland current were dominant in the area copyright 2000 john wiley sons ltd

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

variability of marine climate on the north icelandic shelf in a 1357 year proxy archive based on growth increments in the bivalve arctica islandica a multicentennial and absolutely dated shell based chronology for the marine environment of the north icelandic shelf has been constructed using annual growth increments in the shell of the long lived bivalve clam arctica islandica the region from which the shells were collected is close to the north atlantic polar front and is highly sensitive to the varying influences of atlantic and arctic water masses a strong common environmental signal is apparent in the increment widths and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95 confidence level they are low r 0 2 indicating that a more complex combination of environmental forcings is driving growth remarkable longevities of individual animals are apparent in the increment width series used in the chronology with several animals having lifetimes in excess of 300 years and one at 507 years being the longest lived non colonial animal so far reported whose age at death can be accurately determined the sample depth is at least three shells after ad 1175 and the time series has been extended back to ad 649 with a sample depth of one or two by the addition of two further series thus providing a 1357 year archive of dated shell material the statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age related trend in shell growth comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales particularly during the period surrounding the transition from the medieval climate anomaly to the little ice age

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

crustal types and tertiary tectonic evolution of the alboran sea western mediterranean multichannel seismic reflection images across the transition between the east alboran and the algero balearic basins show how crustal thickness decreases from about 5 s two way traveltime twtt 15 km thick in the west east alboran basin to 2 s twtt typical of oceanic crust 6 km thick in the east algero balearic basin we have differentiated three different crustal domains in this transition mainly on the basis of crustal thickness and seismic signature boundaries between the three crustal domains are transitional and lack evidence for major faults tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic suggesting a strong relationship between magmatism and crustal structure stratigraphic correlation of lithoseismic units with sedimentary units of southeastern betic basins indicates that sediments onlap igneous basement approximately at 12 ma in the eastern area and at 8 ma in the western area linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent from west to east thin continental crust modified by arc magmatism magmatic arc crust and oceanic crust middle to late miocene arc and oceanic crust formation in the east alboran and algero balearic basins respectively occurred during westward migration of the gibraltar accretionary wedge and shortening in the betic rif foreland basins arc magmatism and associated backarc oceanic crust formation were related to early to middle miocene subduction and rollback of the flysch trough oceanic basement subduction of this narrow slab beneath the alboran basin was coeval with collision of the alboran domain with the iberian and african passive margins and subsequent subcontinental lithosphere edge delamination along the betic rif margins

a 4500 year reconstruction of sea surface temperature variability at decadal time scales off north iceland marine paleo records acquired at high temporal resolution provide critical data for testing numerical climate models and help to understand processes underlying ocean variability this study presents a unique 4500 year reconstruction of sea surface temperature sst obtained from alkenones in the north atlantic polar front area off north iceland at an average temporal resolution of 4 5 years spectral analysis of this signal shows dominant multidecadal oscillations which occurred with a stronger amplitude between 2500 and 4200 years bp hand in hand with fluctuations of bottom currents indicated by paleomagnetic proxies contemporaneous large excursions of the inter tropical convergence zone itcz are also recorded by the distant cariaco titanium time series suggesting a link with low latitude atlantic climate we speculate that the oscillations reflect changes of the meridional overturning circulation moc induced by increased enso activity

radiocarbon based circulation age of the world oceans 1 the distributions of deep ocean 14c data are often used to illustrate the rate of deep ocean circulation the associated conventional 14c ages show a difference of 1000 years between the north atlantic and the southern ocean and a difference of another 1000 years between the southern ocean and the north pacific these differences may be interpreted directly and mistakenly as the timescale of circulation the characterization of the deep ocean circulation being millennial is common using objectively gridded natural 14c data of key et al 2004 i recast 14c in terms of circulation by accounting for 1 long surface ocean reservoir 14c ages and 2 two sources of deep water formed in the north atlantic and around antarctica the new distribution of circulation 14c ages is more consistent with the deep ocean being characterized by a centennial timescale than a millennial timescale also the role of the southern sourced deep water is now made more obvious by accounting for the two important controls on oceanic 14c that are not well known outside the field of chemical oceanography the new map will be useful as an illustration of global deep ocean circulation to the wider scientific community and as a pedagogical tool to new students in earth sciences and oceanography

a new path for the denmark strait overflow water from the iceland sea to denmark strait 1 denmark strait overflow water dsow is one of the main components of the thermohaline circulation there has been no consensus on where it is formed and by which way it is brought to the denmark strait it is shown here that it is brought to the sill by a hitherto unknown current that is traced from the sill back into the iceland sea north of iceland the transport of this current is sufficient to account for a major part of the transport of dsow as it has been measured at the sill if some entrainment of ambient water is assumed this supports theories suggesting that the iceland sea is the main source for the dsow and this has consequences for the way in which climate change affects the thermohaline circulation

overriding plate structure of the nicaragua convergent margin relationship to the seismogenic zone of the 1992 tsunami earthquake we present 2 d seismic velocity models and coincident multichannel seismic reflection images of the overriding plate and the inter plate boundary of the nicaragua convergent margin along two wide angle seismic profiles parallel and normal to the trench acquired in the rupture area of the 1992 tsunami earthquake the trench perpendicular profile runs over a seamount subducting under the margin slope at the location where seismological observations predict large coseismic slip along this profile the igneous basement shows increasing velocity both with depth and away from the trench reflecting a progressive decrease in upper plate rock degree of fracturing upper mantle like velocities are obtained at approximate to 10 km depth beneath the fore arc sandino basin indicating a shallow mantle wedge a mismatch of the inter plate reflector in the velocity models and along coincident multichannel seismic profiles under the slope is best explained by approximate to 15 velocity anisotropy probably caused by subvertical open fractures that may be related to fluid paths feeding known seafloor seepage sites the presence of a shallow partially serpentinized mantle wedge and the fracture related anisotropy are supported by gravity analysis of velocity derived density models the downdip limit of inter plate seismicity occurs near the tip of the inferred mantle wedge suggesting that seismicity could be controlled by the presence of serpentinite group minerals at the fault gouge near the trench the inferred local increase of normal stress produced by the subducting seamount in the plate boundary may have made this fault segment unstable during earthquake rupture which could explain its tsunamigenic character

marine reservoir age variability and water mass distribution in the iceland sea abstract lateglacial and holocene tephra markers from icelandic source volcanoes have been identified in five sediment cores from the north icelandic shelf and correlated with tephra layers in reference soil sections in north iceland and the grip ice core land sea correlation of tephra markers that have been radiocarbon dated with terrestrial material or dated by documentary evidence provides a tool for monitoring reservoir age variability in the region age models developed for the shelf sediments north of iceland based on offshore tephrochronology on one hand and on calibrated ams 14c datings of marine molluscs on the other display major deviations during the last 4500 years the inferred temporal variability in the reservoir age of the regional water masses exceeds by far the variability expected from the marine model calculations the observed reservoir ages are generally considerably higher by up to 450 years than the standard model ocean it is postulated that the intervals with increased and variable marine reservoir age reflect incursions of arctic water masses derived from the east greenland current to the iceland sea and the north icelandic shelf

three dimensional moho topography in italy new constraints from receiver functions and controlled source seismology in complex tectonics regions seismological geophysical and geodynamic modeling require accurate definition of the moho geometry various active and passive seismic experiments performed in the central mediterranean region revealed local information on the moho depth in some cases used to produce interpolated maps in this paper we present a new and original map of the 3 d moho geometry obtained by integrating selected high quality controlled source seismic and teleseismic receiver function data the very small cell size makes the retrieved model suitable for detailed regional studies crustal corrections in teleseismic tomography advanced 3 d ray tracing in regional earthquake location and local earthquake tomography our results show the geometry of three different moho interfaces the european adriatic ionian and tyrrhenian the three distinct moho are fashioned following the alpine and apennines subduction collision and back arc spreading and show medium to high frequency topographic undulations reflecting the complexity of the geodynamic evolution

abrupt climate changes for iceland during the last millennium evidence from high resolution sea ice reconstructions a high resolution account of icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker ip25 produced by sea ice algae comparison with historical sea ice records demonstrates a strong correlation between documented sea ice occurrences and the ip25 proxy an excellent agreement is also observed between the ip25 record and a diatom based sea surface temperature reconstruction obtained from the same core and the crowley and lowery northern hemisphere temperature reconstruction using this approach we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and or climate conditions around iceland during the little ice age

oceanographic changes through the last millennium off north iceland temperature and salinity reconstructions based on foraminifera and stable isotopes abstract temperature and salinity reconstructions for two 1000 year high resolution sedimentary records located at the boundary between atlantic and arctic surface waters on the north icelandic shelf are based on transfer functions and oxygen isotopes for planktonic and benthic foraminifera there is a general increase of arctic water indicator species at the transition from the medieval warm period into the little ice age lia and a subsequent return of atlantic water indicator species towards the end of the lia and in the 20th century the timing of the reconstructed temperature changes both at the beginning and at the end of the lia appears to be slightly different for the different water masses the earliest temperature change is seen in the bottom and subsurface waters where a cooling is reconstructed as early as ad 1150 1200 at both locations whereas previously published diatom based and alkenone based sea surface temperature reconstructions show a change at ad 1300 coinciding with the air temperature shift in the area our results show the need of a thorough understanding of the oceanography in the study area as well as the different living habitat for the biological proxies used for the temperature estimates

diatom based reconstruction of palaeoceanographic changes on the north icelandic shelf during the last millennium abstract pronounced palaeoceanographic changes during the last millennium are revealed by high resolution diatom records from site md99 2275 on the north icelandic shelf there is a high degree of consistency between the reconstructed summer sea surface temperature sst record based on diatoms and the instrumental and documentary data during the last 100 years this confirms the reliability of this proxy for the study of palaeoceanographic and palaeoclimatic changes on the north icelandic shelf the present diatom based summer sst reconstruction shows that the last millennium was characterized by a general cooling trend but with some fluctuations warm and stable conditions with relatively strong influence of the irminger current on the north icelandic shelf are indicated during the interval ad 940 1300 corresponding in time to the medieval warm period mwp a considerable cooling at ad 1300 indicates the transition to the little ice age lia with increased influence of polar and arctic water masses deriving from the east greenland and east icelandic currents an extended cooling period between ad 1300 and 1910 is characterized by approximately century scale oscillations with marked cold intervals at ad 1325 1375 ad 1460 1500 ad 1610 1670 and ad 1810 1910 separated by relatively mild spells a two step warming during the last 100 years is interrupted by three cool events around ad 1920 in the ad 1960s and in the late ad 1990s in general the diatom based indication of palaeoceanographic changes on the north icelandic shelf during the last millennium corresponds to other proxy based palaeoclimatic and palaeoceanographic records in the north atlantic region

sea surface temperature variability in the subpolar atlantic over the last two millennia 1 a decadal resolution time series of sea surface temperature sst spanning the last two millennia is reconstructed by combining a proxy record from a new sediment sequence with previously published data from core md99 2275 north of iceland the alkenone based sst reconstruction is validated with historic observational data and compared to a new similar temporal resolution reconstruction obtained from sediment core rapid21 3k in the subpolar north atlantic the two sst paleorecords show consistent multidecadal scale coolings throughout the interval and similar expressions during the contrasted climatic periods colloquially known as the medieval climatic anomaly mca and little ice age lia in order to further understand the temporal and spatial sst variations and investigate the influence of natural forcings on the observed sst changes during the last millennium we compare our time series to simulations using the institut pierre simon laplace ipslcm4 v2 climate model this comparison highlights the potential importance of volcanism as a natural forcing driving coherent abrupt cooling events captured in the subpolar north atlantic records

seismic structure of the central tyrrhenian basin geophysical constraints on the nature of the main crustal domains in this work we investigate the crustal and tectonic structures of the central tyrrhenian back arc basin combining refraction and wide angle reflection seismic was gravity and multichannel seismic mcs reflection data acquired during the medoc mediterraneo occidental 2010 survey along a transect crossing the entire basin from sardinia to campania at 40 n the results presented include a 450 km long 2 d p wave velocity model obtained by the traveltime inversion of the was data a coincident density model and a mcs poststack time migrated profile we interpret three basement domains with different petrological affinity along the transect based on the comparison of velocity and velocity derived density models with existing compilations for continental crust oceanic crust and exhumed mantle the first domain includes the continental crust of sardinia and the conjugate campania margin in the sardinia margin extension has thinned the crust from 20 km under the coastline to 13 km 60 km seaward similarly the campania margin is also affected by strong extensional deformation the second domain under the cornaglia terrace and its conjugate campania terrace appears to be oceanic in nature however it shows differences with respect to the reference atlantic oceanic crust and agrees with that generated in back arc oceanic settings the velocities depth relationships and lack of moho reflections in seismic records of the third domain i e the magnaghi and vavilov basins support a basement fundamentally made of mantle rocks the large seamounts of the third domain e g vavilov are underlain by 10 20 km wide relatively low velocity anomalies interpreted as magmatic bodies locally intruding the mantle

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research