the role of the barents sea in the arctic climate system present global warming is amplified in the arctic and accompanied by unprecedented sea ice decline located along the main pathway of atlantic water entering the arctic the barents sea is the site of coupled feedback processes that are important for creating variability in the entire arctic air ice ocean system as warm atlantic water flows through the barents sea it loses heat to the arctic atmosphere warm periods like today are associated with high northward heat transport reduced arctic sea ice cover and high surface air temperatures the cooling of the atlantic inflow creates dense water sinking to great depths in the arctic basins and 60 of the arctic ocean carbon uptake is removed from the carbon saturated surface this way recently anomalously large ocean heat transport has reduced sea ice formation in the barents sea during winter the missing barents sea winter ice makes up a large part of observed winter arctic sea ice loss and in 2050 the barents sea is projected to be largely ice free throughout the year with 4 c summer warming in the formerly ice covered areas the heating of the barents atmosphere plays an important role both in arctic amplification and the arctic heat budget the heating also perturbs the large scale circulation through expansion of the siberian high northward with a possible link to recent continental wintertime cooling large air ice ocean variability is evident in proxy records of past climate conditions suggesting that the barents sea has had an important role in northern hemisphere climate for at least the last 2500 years

a 2000 year record of atlantic water temperature variability from the malangen fjord northeastern north atlantic a high resolution sedimentary record from the subarctic malangen fjord in northern norway northeastern north atlantic has been investigated in order to reconstruct variations in influx of atlantic water for the last 2000 years the fjord provides a regional oceanographic climatic signal reflecting changes in the north atlantic heat flux at this latitude because of its deep sill and the relatively narrow adjoining continental shelf the reconstructions are based on oxygen and carbon isotopic studies of benthic foraminifera from a high accumulation basin in the malangen fjord providing subdecadal time resolution a comparison between instrumental measurements of bottom water temperatures at the core location and the reconstructed temperatures from benthic foraminiferal 18o for the same time period demonstrates that the stable isotope values reflect the bottom water temperatures very well the reconstructed temperature record shows an overall decline in temperature of c 1 c from c 40 bc to ad 1350 this

reconstructing twentieth century sea surface temperature variability in the southwest pacific a replication study using multiple coral sr ca records from new caledonia 1 coral based climate reconstructions typically have not used multiple cores from a region to capture and replicate a climate signal largely because of concerns of coral conservation analytical expense and time constraints coral sr ca reproducibility through the twentieth century was investigated using three intracolony and three intercolony coral records from the reefs offshore of amedee island new caledonia different sampling resolutions were examined in coral sr ca fortnightly and monthly and 18o fortnightly monthly and seasonally as well as similar scale subsampling of the daily in situ sea surface temperature sst record the mean coral sr ca 18o and sst values do not change as a function of sampling resolution the coral sr ca signal is highly reproducible the average absolute offset between coeval monthly sr ca determinations between any two coral time series is 0 035 0 026 mmol mol 1 0 65 c which is less than twice the analytical precision of the coral sr ca measurements the stack average of the monthly coral sr ca variations and monthly anomalies are significantly correlated with monthly in situ sst 1967 1992 r 0 96 and 0 64 respectively p 0 05 and n 302 and 1 grid monthly sst data product 1900 1999 r 0 95 and 0 56 respectively p 0 05 and n 1198 the coral sr ca sst reconstruction exhibits interannual and decadal timescale fluctuations that exceed those observed in the gridded sst record which may reflect true differences between sst at a shallow reef site and those averaged over a 1 grid box or inadequacies in the methodology used to create the gridded sst product when few observations are available a warming trend of 0 6 c is observed in the twentieth century coral sr ca sst record

wind and buoyancy induced transport of the norwegian coastal current in the barents sea 1 the focus of this study is on the fluxes and forcing of the norwegian coastal current ncc at the entrance to the barents sea the structure and dynamics of the ncc which consists of a slope branch and an offshore branch are investigated using 1 a recent 1 year full depth current meter record in the core of the slope region 2 repeated hydrographic data at an inshore monitoring station 3 broader regional hydrographic surveys and 4 atmospheric reanalysis data the total fluxes are estimated to 1 8 sv for volume and 26 msv for freshwater relative to a reference salinity of 34 8 with the largest contributions from baroclinic offshore branch the heat flux calculated for the slope branch only is 34 tw these estimates are higher compared to earlier estimates but are based on more comprehensive data the major mode of variability in the slope branch is consistent with a continental shelf wave on time scales in the range of 3 16 days forced by the along coast component of the wind stress maximum along slope currents during fall winter corresponding to the stronger wind forcing during these seasons suggest that the observed seasonality in the ncc can be attributed to a similar mechanism

coupled north atlantic slope water forcing on gulf of maine temperatures over the past millennium to investigate ocean variability during the last millennium in the western gulf of maine gom we collected a 142 year old living bivalve arctica islandica l in 2004 and three fossil a islandica shells calibrated 14cams 1030 78 ad 1320 45 ad 1357 40 ad for stable isotope and growth increment analysis a statistically significant relationship exists between modern gom temperature records shell isotope derived 30 m r 0 79 p 0 007 prince 5 50 m r 0 72 p 0 019 boothbay harbor sst r 0 76 p 0 011 and labrador current lc transport data from the eastern newfoundland slope during 1993 2003 in all cases as lc transport increased gom water temperatures decreased the following year decadal trends in the north atlantic oscillation nao and the atlantic multidecadal oscillation amo influence gom water temperatures in the most recent period with water temperatures decreasing during nao and amo negative modes most likely linked to lc transport and gulf stream interaction mean shell derived isotopic changes 18oc during the last 1 000 years were 0 47 and likely reflect a 1 2 c cooling from 1000 ad to present based on these results we suggest that observed cooling in the gom during the last millennium was due to increased transport and or cooling of the lc and decreased gulf stream influence on the gom

first cross matched floating chronology from the marine fossil record data from growth lines of the long lived bivalve mollusc arctica islandica integrated understanding of phasings within the climate system over the last glacial cycle and at higher frequencies is inhibited because no absolute timescale for the marine environment currently exists this precludes identification of forcings and feedbacks accurate temporal calibration of the marine radiocarbon reservoir effect and the application of radiocarbon as a proxy of short timescale ocean ventilation this has prompted a search for annually banded marine proxies in the hope of establishing an accurate marine chronometer we present annual growth band series from dead collected specimens of the long lived bivalve mollusc arctica islandica from the northern north sea and demonstrate their successful cross matching with the general timescale context independently verified by radiocarbon dating though at present limited to only a few statistically cross matched series this has already generated the longest arctica chronology and the first floating chronology constructed entirely from marine fossils the record covers the period from c ad 1000 to 1400 and integrates a 267 yr series from the longest lived arctica specimen yet recorded from the north sea this breakthrough in cross matching demonstrates that arctica islandica can fulfill its potential as the tree of the sea to provide an absolute timescale for the marine environment

impact of the atlantic meridional overturning circulation amoc on arctic surface air temperature and sea ice variability abstractthe simulated impact of the atlantic meridional overturning circulation amoc on the low frequency variability of the arctic surface air temperature sat and sea ice extent is studied with a 1000 year long segment of a control simulation of the geophysical fluid dynamics laboratory climate model version 2 1 the simulated amoc variations in the control simulation are found to be significantly anticorrelated with the arctic sea ice extent anomalies and significantly correlated with the arctic sat anomalies on decadal time scales in the atlantic sector of the arctic the maximum anticorrelation with the arctic sea ice extent and the maximum correlation with the arctic sat occur when the amoc index leads by one year an intensification of the amoc is associated with a sea ice decline in the labrador greenland and barents seas in the control simulation with the largest change occurring in winter the recent declining trend in the satellite observed sea ice extent also shows a similar pattern in t

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

reconstructing north atlantic marine climate variability using an absolutely dated sclerochronological network reconstructing regional to hemispheric scale climate variability requires the application of spatially representative and climatically sensitive proxy archives large spatial networks of dendrochronologies have facilitated the reconstruction of atmospheric variability and inferred variability in the atlantic ocean system however the marine environment has hitherto lacked the direct application of the spatial network approach because of the small number of individual absolutely dated marine archives in this study we present the first analyses of a network of absolutely dated annually resolved growth increment width chronologies from the marine bivalves glycymeris glycymeris and arctica islandica the network contains eight chronologies spanning 500 km along the western british continental shelf from the southern irish sea to north west scotland correlation analysis of the individual chronologies and a suite of climate indices including the atlantic multidecadal oscillation amo central england surface air temperature cet northeast atlantic sea surface temperatures sst s and the winter north atlantic oscillation wnao demonstrates that despite the large geographical distances been sites and the heterogeneous nature of the marine environment the increment width variability in these series contains an element of coherence likely driven by a common response to changing environmental forcing a nested principal component analysis pca was used to construct five composite series which explain between 31 and 74 of the variance across the individual chronologies linear regression analyses indicate that the composite series explain up to 41 of the variance in northeast atlantic ssts over the calibration period 1975 2000 calibration verification reduction of error re and coefficient of efficiency ce statistics indicate that the composite series contains significant skill at reconstructing multi decadal northeast atlantic sst variability over the past two centuries 1805 2010 these data suggest that composite series derived from sclerochronology networks can facilitate the robust reconstruction of marine climate over past centuries to millennia providing invaluable baseline records of natural oceanographic variability

evaluation of cmip5 models over the northern north atlantic in the context of forthcoming paleoclimatic reconstructions we evaluated 11 coupled climate model simulations regarding the spatial structures of sea surface temperature sst variability in the north atlantic during the second half of the twentieth century the subset of models includes ccsm4 csiro canesm and mpi esm participating in the fifth phase of the climate model intercomparison project the evaluation was performed to determine the potential of these models to be used at a later stage as test beds for the evaluation of climate field reconstruction methods that will use the extremely long lived bivalve mollusk arctica islandica an outstanding paleoclimate archive for the boreal and temperate north atlantic schone glob planet change 111 199 225 2013 several validation metrics such as the mean bias variance spatial and temporal co variability and trends of the north atlantic summer ssts showed that some of the models can be used to test paleoclimatic reconstructions however most models showed shortcomings in simulating the atlantic multidecadal oscillation concerning the co variability of summer ssts between proxy sites and the whole north atlantic sst field we found that these proxy locations contain a sst signal that might represent a basin wide signal for the north eastern north atlantic basin

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

simulated atlantic multidecadal oscillation during the holocene abstractthe atlantic multidecadal oscillation amo and its possible change during the holocene are examined in this study using long term simulations of the earth system model community earth system models cosmos a quasi persistent 55 80 yr cycle characterizing in the north atlantic sea surface temperature is highly associated with the multidecadal variability of the atlantic meridional overturning circulation amoc during the holocene this mode can be found throughout the holocene indicating that the amo is dominated by internal climate variability stronger than normal amoc results in warmer than normal surface temperature spreading over almost the whole north hemisphere in particular the north atlantic ocean during the warm phase of the amo more precipitation is detected in the north atlantic low and high latitudes it also generates a dipolar seesaw pattern in the sea ice anomaly the results reveal that the influence of the amo can be amplified by a more vigorous amoc variability during t

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

a multiproxy reconstruction of hebridean nw scotland spring sea surface temperatures between ad 1805 and 2010 there is currently a deficiency of annually resolved temperature series from the marine environment we present a multiproxy reconstruction of hebridean shelf sea tiree passage nw scotland spring sea surface temperatures ssts for the period ad 1805 2010 the reconstruction is based on the growth increment series from the first absolutely dated annually resolved multi centennial glycymeris glycymeris bivalve mollusc sclerochronology coupled with previously published stable oxygen isotope data 18o from benthic foraminifera sampled from a dated sediment core from nearby loch sunart the independent series contain significant correlations with ssts across complementary frequency domains the low frequency component of the sedimentary archive was combined with the mid and high frequency components of the g glycymeris chronology indices to create a single multiproxy series split calibration verification statistics reduction of error re coefficient of efficiency ce and r2 indicate that the multiproxy record calibrated to local instrumental sea surface temperatures contains significant precision and skill at reconstructing spring ssts re 0 59 ce 0 26 r2 0 54 these data demonstrate that bivalve sclerochronologies when combined with low frequency proxies such as sediment archives can facilitate statistically robust reconstructions of palaeoceanographic variability during the late holocene for hydrographically significant regions of the temperate marine system previously void of annually resolved archives the reconstructed ssts contain a general warming trend of 0 60 0 14 c per century only four years in the reconstructed period 1999 2000 2002 and 2003 exceed temperatures greater than two standard deviations higher than the reconstructed mean sst 9 03 c whilst just three years in the first half of the 19th century 1835 1838 and 1840 fall more than 2 below the reconstructed mean 6 80 c

reprint of unexpected isotopic variability in biogenic aragonite a user issue or proxy problem abstract the present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive the marine bivalve arctica islandica with an emphasis on the potential of human induced variability arising from sampling techniques stable carbon 13ccarbonate and oxygen 18ocarbonate isotopes were analyzed for split intra sample and replicate intra and inter shell samples taken from a group of laboratory reared individuals a natural population from northern norway and a natural population from the gulf of maine usa compared to analytical uncertainty of 0 17 and 0 30 for 13c and 18o respectively among the natural populations the mean difference between shell splits and shell replicates ranged from 0 12 and 0 33 for 13c and 18o respectively our data suggest that heterogeneity of the carbonate material i e large range of isotopic composition within one sample due to seasonal environmental variability may contribute to unexpected variability more than human induced error from sampling imprecision when collecting whole annual increments furthermore 13c from juvenile shells were highly variable 2 standard deviation 0 65 approximately four times more variable than analytical precision high precision among 18o measurements of the laboratory reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater monte carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication substantial reduction in uncertainty occurs when increasing from two to three shells however replication using a total of four shells further decreased uncertainty to within the 99 confidence level published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual oftentimes however isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy derived noise furthermore population specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series

ocean quahogs arctica islandica and atlantic surfclams spisula solidissima on the mid atlantic bight continental shelf and georges bank the death assemblage as a recorder of climate change and the reorganization of the continental shelf benthos abstract the degree to which evidence of range shifts in shelf biomass dominants atlantic surfclams and ocean quahogs as a function of climate change is examined by comparing the dissimilarity in distribution of the living community and the record of habitation ensconced in the death assemblage comparison of the distribution of live animals and dead shells reveals for both species that live animals are rarely found where dead shells were not collected but dead shells were collected at a substantively larger number of sites than where live animals were found the geographic footprint resolved by the dead shells was much broader than that of live animals extensive spatially coherent regions exist inshore and offshore of the present day habitat of occupation where evidence of previous occupation exists sites where ocean quahog shells were found without live ocean quahogs included a portion of the continental shelf inshore of the present day habitable range an area only habitable under colder climatic conditions than observed today surfclam shells were found offshore of the present day habitable region in deeper water additional warming of bottom waters offshore would be necessary for surfclams to occupy the region now occupied solely by dead shells the death assemblage shows that these biomass dominants have repositioned themselves across the continental shelf during the past and this repositioning certainly is driven by changes in bottom water temperature moreover the distribution of surfclam shells indicates that the death assemblage may provide a possible window into the future as movement of the present day population is towards these deeper water previously occupied regions overall the death assemblage may provide an important source of information on range shifts sparing the need to carry out extensive and frequent benthic surveys and may permit reconstruction of ongoing shifts in community composition as a product of climate change when adequate survey data are not available

impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in porites corals restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive porites colony from the central great barrier reef australia secondary aragonite needles 20 m long cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10 dissolution is observed above this zone whereas older skeleton is pristine we investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary porites colonies collected at nearby reefs secondary aragonite overgrowth causes anomalies in skeletal density mg ca sr ca u ca o and c the secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature sst proxies o sst 1 6 c sr ca sst 1 7 c mg ca sst 1 9 c u ca sst 2 8 c dissolution through incongruent leaching also causes cool sst artifacts but only for trace element ratios mg ca sst 1 2 c sr ca sst 1 2 c u ca sst 2 1 c the sequence of preference with respect to dissolution of coral skeleton in seawater is mg ca sr u rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals the excellent agreement between apparent sst anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate proxy interpretations poor replication of records between different coral colonies however provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite copyright 2007 by the american geophysical union

barents sea multidecadal variability 1 we present area averaged time series of temperature for the 100 150 m depth layer of the barents sea from 1900 through 2006 this record is dominated by multidecadal variability on the order of 4 c which is correlated with the atlantic multidecadal oscillation index

a hemispheric mechanism for the atlantic multidecadal oscillation abstract the physical processes associated with the 70 yr period climate mode known as the atlantic multidecadal oscillation amo are examined based on analyses of observational data a deterministic mechanism relying on atmosphere ocean sea ice interactions is proposed for the amo variations in the thermohaline circulation are reflected as uniform sea surface temperature anomalies in the north atlantic these anomalies are associated with a hemispheric wavenumber 1 sea level pressure slp structure in the atmosphere that is amplified through atmosphere ocean interactions in the north pacific the slp pattern and its associated wind field affect the sea ice export through fram strait the freshwater balance in the northern north atlantic and consequently the strength of the large scale ocean circulation it generates sea surface temperature anomalies with opposite signs in the north atlantic and completes a negative feedback the authors find that the time scale of the cycle is associated with the

quantifying the influence of atlantic heat on barents sea ice variability and retreat abstractthe recent arctic winter sea ice retreat is most pronounced in the barents sea using available observations of the atlantic inflow to the barents sea and results from a regional ice ocean model the authors assess and quantify the role of inflowing heat anomalies on sea ice variability the interannual variability and longer term decrease in sea ice area reflect the variability of the atlantic inflow both in observations and model simulations during the last decade 1998 2008 the reduction in annual july june sea ice area was 218 103 km2 or close to 50 this reduction has occurred concurrent with an increase in observed atlantic heat transport due to both strengthening and warming of the inflow modeled interannual variations in sea ice area between 1948 and 2007 are associated with anomalous heat transport r 0 63 with a 70 103 km2 decrease per 10 tw input of heat based on the simulated ocean heat budget it is found that the heat transport into the western barents sea sets the bou

holocene productivity changes off adelie land east antarctica 1 this study presents the first high resolution multiproxy investigation of primary productivity pp during the holocene from the antarctic continental margins micropaleontological and geochemical data from the sediment core md03 2601 associated to sea ice model outputs give unprecedented insights into the biological pump of the antarctic coastal area off adelie land in response to climatic changes plurimillennial and millennial changes of pp are observed in the study area in response to changes in nutrient availability stratification and growing season duration which are linked to sea ice upwelling wind and glacier dynamics the precessional cycle seems to be responsible in the pp long term variations while forcing factors involved at the millennial timescale remain more enigmatic our results emphasize enhanced biological pump during warmer and windier holocene phases because of a longer growing season and greater nutrient input antarctic coastal and continental shelf zones may therefore represent a more intense carbon sink in the future

unexpected isotopic variability in biogenic aragonite a user issue or proxy problem abstract the present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive the marine bivalve arctica islandica with an emphasis on the potential of human induced variability arising from sampling techniques stable carbon 13ccarbonate and oxygen 18ocarbonate isotopes were analyzed for split intra sample and replicate intra and inter shell samples taken from a group of laboratory reared individuals a natural population from northern norway and a natural population from the gulf of maine usa compared to analytical uncertainty of 0 17 and 0 30 for 13c and 18o respectively among the natural populations the mean difference between shell splits and shell replicates ranged from 0 12 and 0 33 for 13c and 18o respectively our data suggest that heterogeneity of the carbonate material i e large range of isotopic composition within one sample due to seasonal environmental variability may contribute to unexpected variability more than human induced error from sampling imprecision when collecting whole annual increments furthermore 13c from juvenile shells were highly variable 2 standard deviation 0 65 approximately four times more variable than analytical precision high precision among 18o measurements of the laboratory reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater monte carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication substantial reduction in uncertainty occurs when increasing from two to three shells however replication using a total of four shells further decreased uncertainty to within the 99 confidence level published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual oftentimes however isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy derived noise furthermore population specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series

north american central plains conductivity anomaly goes east the north american central plains electrical conductivity nacp anomaly has been known for almost two decades and its influence on palaeotectonic models of the north american continent has been significant magnetometer array studies have located the structure in a gross sense but there has not been until now a comprehensive magnetotelluric mt survey of it in this letter we report on the preliminary interpretation of data from thirty five mt sites recorded along a 400 km east west profile just north of the us canadian border we show that the anomaly at this latitude is 75 km farther east of the location previously mapped by the array studies modelling indicates that the conductive body has its top surface at about 10 km depth and appears to be anticlinal in shape the profile also extends sufficiently east that it traverses another previously known electrical structure referred to herein as the tobe anomaly we consider briefly other geophysical and geological data for the region and tentatively infer that the nacp structure is terminated to the east by the interpreted southern extension of the tabbernor fault fold system and that the tobe anomaly is an expression of the known southern extension of the thompson nickel belt both beneath phanerozoic sediments of the williston basin

is there a reliable taphonomic clock in the temperate north atlantic an example from a north sea population of the mollusc arctica islandica abstract two hundred and seventy seven shells of the long lived bivalve mollusc arctica islandica collected from the fladen ground northern north sea were radiocarbon dated and their taphonomic condition assessed in order to determine whether taphonomic condition might provide a reliable indication of time since the death of the animal with nine stations from across the fladen ground sampled some strong geographic biases in 14c ages were apparent with living and modern post bomb pulse material found in the northern part of the fladen ground while older material first half of the last millennium and early holocene lateglacial was concentrated in the central and western sites samples from the south and east fladen ground were sparse and were dominated by material from the second half of the last millennium this south north distribution is interpreted as the result of environmental change over millennial time scales in the north sea causing a gradual northward shift of living a islandica populations and is not thought to be related to post mortem transport of shells to the south and east taphonomic condition assessed using discriminant analysis and principal component analysis of five characteristics amount of remaining periostracum presence and condition of the ligament extent of erosion at the shell margin amount of bioerosion and condition of the inner shell layer appeared to be a generally unreliable indicator of time since the death of the animal based on these five taphonomic characteristics discriminant analysis placed 81 1 of post bomb shells 39 6 of shells from the period 0 500 yr bp 68 0 of shells from the period 500 1000 yr bp and 20 0 of shells from the early holocene lateglacial group into the correct radiocarbon age grouping providing no support for the idea that this method can be used to triage shells for chronology construction as an alternative to radiometric dating

a 250 year decadally resolved radiocarbon time history in the gulf of maine reveals a hydrographic regime shift at the end of the little ice age

wintertime warming of an arctic shelf in response to large scale atmospheric circulation 1 observations on the west spitsbergen shelf have shown that the dynamic response of the shelf to wind forcing has a profound effect on the heat content of the water hydrographic and atmospheric data have been analysed with respect to the relative importance of surface heat fluxes and advective processes on ocean temperature during the arctic winter of 2005 06 periods of sustained along shelf winds generated upwelling and cross shelf exchange causing extensive flooding of the coastal waters with warm atlantic water from the west spitsbergen current the winter temperature of the west spitsbergen shelf reverted to that typical of fall interrupting the normal cycle of sea ice formation in the region

improving coral base paleoclimate reconstructions by replicating 350years of coral sr ca variations abstract coral based climate reconstructions are typically based on a single record and this lack of replication leads to questions in regards to chronology accuracy and reliability of the inclusive geochemical variations to record climate viability here we present two multi century coral sr ca records recovered from a porites lutea colony offshore of amedee island new caledonia 22 28 8 s 166 27 9 e the chronology was developed by cross dating the coral sr ca time series and verifying the chronology with high precision absolute 230th dating we identify chronological discrepancies of 2 3 and 3 7 years century 1 for reconstructions based on a single core with uncertainty increasing after 250 years we assess the impact of porites skeletal architecture on coral geochemistry by characterizing centimeter scale architectural structures with respect to sampling optimal sampling paths are those on the slab surface parallel to the growth direction of individual corallites along the central axis of an actively extending corallite fan coral sr ca time series extracted from optimal skeletal structures are highly reproducible with a mean absolute difference of 0 021 mmol mol 1 or 0 39 c for monthly determinations suboptimal skeletal architecture is characterized by corallites extending through the slab surface and the coral sr ca determinations derived from suboptimal paths tend to produce a warm bias that varies between 0 04 and 2 30 c disorganized skeletal architecture is characterized by small terminating or unclear corallite fans that produce a cold bias of 0 11 to 2 45 c in coral sr ca determinations these problematic architecture types also produce biases in coral 18o determinations but to a lesser extent we assess the impact of sampling a coral colony along paths that vary from vertical to horizontal in large and small porites colonies with extension rates 6 mm year 1 and we determine there is no significant difference in the coral sr ca records

a 1200 year multiproxy record of tree growth and summer temperature at the northern pine forest limit of europe combining nine tree growth proxies from four sites from the west coast of norway to the kola peninsula of nw russia provides a well replicated 100 annual measurements per year mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern fennoscandia the simple mean of the nine series z scored over their common period correlates strongly with mean june to august temperature averaged over this region r 0 81 allowing reconstructions of summer temperature based on regression and variance scaling the reconstructions correlate significantly with gridded summer temperatures across the whole of fennoscandia extending north across svalbard and south into denmark uncertainty in the reconstructions is estimated by combining the uncertainty in mean tree growth with the uncertainty in the regression models over the last seven centuries the uncertainty is 4 5 higher than in the 20th century and reaches a maximum of 12 ab

climate signatures on decadal to interdecadal time scales as obtained from mollusk shells arctica islandica from iceland pronounced decadal climate oscillations are detected in a multi centennial record based on shell growth rates of the marine bivalve mollusk arctica islandica from iceland the corresponding analysis of patterns in sea level pressure and temperature exhibit large scale teleconnections with north atlantic climate quantities we find that the record projects onto blocking situations in the northern north atlantic the associated circulation shows a low pressure signature over greenland and the labrador sea and a high pressure system over western europe associated with northeasterly flow towards iceland and weakening in the westerly zonal flow over europe it can be speculated that such circulation affects food availability controlling shell growth on multidecadal time scales the record shows a pronounced variability linked to north atlantic temperature in our record we find enhanced variability of the shell growth rates on multidecadal time scales and it appears that this oscillation has high amplitudes in the 16th to 18th century also consistent with marine alkenone data it is conceivable that these climate oscillations also linked to sea ice export and enhanced blocking are a more pronounced feature during times when the climate was relatively cold

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

strontium magnesium and barium incorporation in aragonitic shells of juvenile arctica islandica insights from temperature controlled experiments abstract in order to constrain spatial and temporal temperatures and environmental conditions in the north atlantic ocean during the holocene high resolution seasonal to annual marine proxies with excellent chronological constraints are needed the long lived ocean quahog arctica islandica which has the potential to provide a precise annually dated record via crossdating techniques is a fairly well developed and tested marine proxy archive in particular oxygen isotopes derived from a islandica shell carbonate have provided a wealth of information on marine climate and ocean circulation dynamics however shell derived oxygen isotopes are influenced by both the isotopic source water signature covarying with salinity and seawater temperature if seawater isotopic signature is not known temperature reconstructions become challenging thus an independent technique to estimate past seawater temperatures is highly desired however based on previous studies on adult and juvenile clams the utility of elemental ratios in a islandica shell material as environmental proxies remains questionable to further evaluate the influence of seawater temperature on elemental and isotopic incorporation during biomineralization a islandica shells were grown at constant temperatures under two regimes during a 16 week period from march 27 to july 21 2011 at the darling marine center in walpole maine individual juvenile clams were stained with calcein and cultured at 10 30 0 30 c for six weeks after this the clams were again stained with calcein and cultured at 15 00 0 40 c for an additional 9 5 weeks average salinity values were 30 20 0 70 and 30 70 0 70 in the first and second phases of the experiment respectively continuous sampling within and across the temperature conditions from 10 30 c to 15 00 c coupled with the calcein markings provided the ability to place each sample into a precise temporal framework and to establish exact average growth rates for the shells sampled after accounting for changes in the isotopic composition of seawater oxygen isotopes from one sampled shell effectively recorded seawater temperatures during the study and also gave confidence to the temporal fit of the data elemental ratios sr ca mg ca ba ca from five aragonitic shells were determined via laser ablation inductively coupled plasma mass spectrometry sr ca and mg ca data showed little coherence with temperature during the culture experiment including the rapid 5 c increase in seawater temperature however ba ca ratios showed an inverse relationship with seawater temperatures although this relationship was noisy additionally salinity interactions were present during the 15 00 c treatment further highlighting complex incorporation of elements during biomineralization incorporation of sr mg and ba were strongly and variably impacted by growth rates combined the results from these culture experiments demonstrate that sr ca mg ca ba ca ratios in juvenile a islandica shell material are dominated by physiological processes and thus not reliable as environmental proxies

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

characteristics of the recent eastward shift of interannual nao variability recent observational studies have shown that the centers of action of interannual variability of the north atlantic oscillation nao were located farther eastward during winters of the period 1978 97 compared to previous decades of the twentieth century in this study which focuses on the winter season december march new diagnostics characterizing this shift are presented further the importance of this shift for nao related interannual climate variability in the north atlantic region is discussed it is shown that an nao related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones near surface air temperature and turbulent surface heat flux throughout the north atlantic region by using a near surface air temperature dataset that is homogenous with respect to the kind of observations used it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s finally an eof based monte carlo test is developed to quantify the probability of changes in the spatial structure of interannual nao variability for a relatively short 20 yr time series given multivariate white noise it is estimated that the likelihood for differences in the spatial structure of the nao between two independent 20 yr periods which are similar as measured by the angle and pattern correlation between two nao patterns to the observed differences to occur just by chance is about 18 from the above results it is argued that care has to be taken when conclusions about long term properties of nao related climate variability are being drawn from relatively short recent observational data e g 1978 97

recirculation of atlantic water in the western barents sea 1 in this article the atlantic inflow with the north cape current to the barents sea and potential recirculation of this water in the bear island trough is investigated this is resolved by combining continuous current meter and repeated hydrographic section data in the barents sea opening the estimated annual mean net fluxes when excluding the contribution from the norwegian coastal current are 1 1 sv and 39 tw estimated relative to a reference temperature of 0 c the estimated heat flux associated with the outflow in the bear island trough is relatively large 12 tw long term current meter records do not show a close relationship between variations in the inflow and the outflow one year low pass filtered variations in temperature and salinity of the outflowing waters in the bear island trough are positively correlated with variations of the inflowing atlantic water with a lag of about seven months on the basis of a simple mixing model the outflow water consists of about 80 atlantic water that is additionally cooled by 2 0 2 5 c by heat loss to the atmosphere by considering the relative weak mean currents in this region it can be inferred that the fraction of the atlantic water that recirculates follows a relatively short pathway in the bear island trough before returning to the norwegian sea

linking large scale climate variability with arctica islandica shell growth and geochemistry in northern norway the lack of high resolution geographically diverse proxy records from the marine realm limits our understanding of climate dynamics in the north atlantic ocean and arctic during recent centuries we investigate the impact of large scale climate variability on the marine bivalve arctica islandica linnaeus 1767 from northern norway 71 n we evaluate the use of annual shell growth and geochemical records as proxies for north atlantic and arctic climate variability over centennial scales by developing a continuous 113 yr master shell growth chronology and an oxygen isotope record 18o from live caught shell material a relatively strong inverse relationship is observed between both the shell growth and isotopic proxies and large scale north atlantic sea surface temperatures in modern times r 0 54 to 0 90 p 0 05 this relationship is strengthened when using a combined shell growth oxygen isotope multiproxy index r 0 72 to 0 90 p 0 01 the regional spatial pattern of correlation resembles that of the north atlantic current as it bifurcates around 55 n indicating that large scale ocean surface current dynamics play an important role in regulating local ecosystem processes and thus shell growth in northern norway a combined proxy index created using multiple linear regression exhibits a relatively strong and time stable relationship with the atlantic multidecadal oscillation amo r 0 622 p 0 001 since ad 1900 variability in the relationship between the shell based records and the north atlantic oscillation coincide with variations in the amo index suggesting a complex relationship between atmospheric forcing on hydrographic variability and ecosystem dynamics in northern norway

a late holocene paleo productivity record in the western gulf of maine usa inferred from growth histories of the long lived ocean quahog arctica islandica to investigate environmental variability during the late holocene in the western gulf of maine usa we collected a 142 year old living bivalve arctica islandica in 2004 and three fossil a islandica shells of the medieval warm period mwp and late mwp little ice age lia period corrected 14cams 1030 78 ad 1320 45 ad 1357 40 ad in 1996 we compared the growth record of the modern shell with continuous plankton recorder cpr time series 1961 2003 from the gulf of maine a significant correlation r2 0 55 p 0 0001 exists between the standardized annual growth index sgi of the modern shell and the relative abundance of zooplankton species calanus finmarchicus we therefore propose that sgi data from a islandica is a valid proxy for paleo productivity of at least one major zooplankton taxa sgis from these shells reveal significant periods of 2 6 years nao like based on wavelet analysis multitaper method mtm analysis and singular spectrum analysis ssa during the late holocene based on established physical oceanographic observation in the gulf of maine we suggest that slope water variability coupled with north atlantic oscillation nao dynamics is primarily responsible for the observed sgi variability

mg ca ratios in coralline algae record northwest atlantic temperature variations and north atlantic oscillation relationships climate variability in the north atlantic has been linked in part to the north atlantic oscillation nao the nao influences marine ecosystems in the northwestern atlantic and transport variability of the cold labrador current understanding historic patterns of nao variability requires long term and high resolution climate records that are not available from instrumental data here we present the first century scale proxy record of sea surface temperature sst variability from the newfoundland shelf a region from which other annual resolution shallow marine proxies are unavailable the 116 year record was obtained from three sites along the eastern newfoundland shelf using laser ablation inductively coupled mass spectrometry determined mg ca ratios in the crustose coralline alga clathromorphum compactum the alga is characterized by a high mg calcite skeleton exhibiting annual growth increments and a century scale lifespan results indicate positive correlations between interannual variations in mg ca ratios and both station based and gridded instrumental sst in addition the record shows high spatial correlations to sst across the newfoundland shelf and the gulf of st lawrence before 1950 the mg ca proxy record reveals significant departures from gridded temperature records while the newfoundland shelf is generally considered a region of negative correlations to the nao the algal time series as well as a recent modeling study suggest a variable negative relationship with the nao which is strongest after 1960 and before the mid 1930s

accurate increment identification and the spatial extent of the common signal in five arctica islandica chronologies from the fladen ground northern north sea 1 the creation of networks of shell based chronologies which can provide regionally extensive high resolution proxies for the marine environment depends on the spatial extent of the common environmental signal preserved in the shell banding and on the reliability of the dating model here arctica islandica chronologies from five neighboring sites in the north sea are compared and the strength of the common environmental signal across distances up to 80 km is analyzed using statistical techniques derived from dendrochronology the signal is found to be coherent across these distances in a linked study chronologies based on one of the same sites but constructed by two different research teams are compared methodological differences in increment interpretation are found to lead to slippage in the dating models systematic inclusion or exclusion of intermittently occurring increments results in the two chronologies becoming misaligned by 4 years over a 70 year period comparisons with neighboring chronologies indicate that such increments can generally be regarded as genuine annual increments even if they are not visible in all shells

reconstructing past seasonal to multi centennial scale variability in the ne atlantic ocean using the long lived marine bivalve mollusc glycymeris glycymeris the lack of long term highly resolved annual to sub annual and absolutely dated baseline records of marine variability extending beyond the instrumental period last 50 100 years hinders our ability to develop a comprehensive understanding of the role the ocean plays in the climate system specifically without such records it remains difficult to fully quantify the range of natural climate variability mediated by the ocean and to robustly attribute recent changes to anthropogenic or natural drivers here we present a 211 year 1799 2010 ce all dates hereafter are common era seawater temperature swt reconstruction from the northeast atlantic ocean derived from absolutely dated annually resolved oxygen isotope ratios recorded in the shell carbonate 18oshell of the long lived marine bivalve mollusc glycymeris glycymeris the annual record was calibrated using sub annually resolved 18oshell values drilled from multiple shells covering the instrumental period calibration verification statistics and spatial correlation analyses indicate that the 18oshell record contains significant skill at reconstructing northeast atlantic ocean mean summer swt variability associated with changes in sub polar gyre spg dynamics and the north atlantic current reconciling differences between the 18oshell data and corresponding growth increment width chronology demonstrates that 68 of the variability in g glycymeris shell growth can be explained by the combined influence of biological productivity and swt variability these data suggest g glycymeris can provide seasonal to multi centennial absolutely dated baseline records of past marine variability that will lead to the development of a quantitative understanding of the role the marine environment plays in the global climate system

marine climate in the irish sea analysis of a 489 year marine master chronology derived from growth increments in the shell of the clam arctica islandica abstract we demonstrate here that the growth increment variability in the shell of the long lived bivalve mollusc arctica islandica can be interpreted as an indicator of marine environmental change in the climatically important north atlantic shelf seas multi centennial up to 489 year chronologies were constructed using five detrending techniques and their characteristics compared the strength of the common environmental signal expressed in the chronologies was found to be fully comparable with equivalent statistics for tree ring chronologies the negative exponential function using truncated increment width series from which the first thirty years have been removed was chosen as the optimal detrending technique chronology indices were compared with the central england temperature record and with seawater temperature records from stations close to the study site in the irish sea statistically significant correlations were found between the chronology indices and a mean air temperature for the 14 month period beginning in the january preceding the year of growth b mean seawater temperatures for february october in the year preceding the year of growth c late summer and autumn air temperatures and sea surface temperatures for the year of growth and d the timing of the autumn decline in sst changes through time in the correlations with air and seawater temperatures and changes towards a deeper water origin for the shells in the chronology were interpreted as an indication that shell growth may respond to stratification dynamics

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

multi proxy reconstructions of northeastern pacific sea surface temperature data from trees and pacific geoduck abstract we demonstrate the potential for developing sea surface temperature sst reconstructions in the northeast pacific from combinations of tree ring and growth increment chronologies of the long lived marine bivalve the pacific geoduck six pacific geoduck chronologies developed from site along the washington british columbia coast are compared and combined with tree ring chronologies from california to alaska all chronologies are annually resolved and strongly relate to local to regional scale sst though differences in the response season as well as the spectral properties of the two proxies are observed both proxy types closely track sst and when used in combination yield a more robust sst reconstruction than tree ring or geoduck chronologies could provide alone in total variance explained in sst is 63 9 at the regional scale and 68 2 at a local scale providing sst estimates for more than 60 years prior to the start of continuous instrumental records in this region this study represents one of the few climate reconstructions where both proxies are annually resolved and is the first to integrate regional networks of geoduck chronologies and tree ring chronologies

unraveling environmental histories from skeletal diaries advances in sclerochronology high resolution proxy archives from aquatic settings are essential to better understand processes and mechanisms of global change during the last decade it has become increasingly evident that calcified tissues of bivalve mollusks and cold water corals in particular can significantly increase our knowledge of seasonal to multi decadal paleoclimate and paleoenvironmental variability in the extratropical oceans and coastal marine settings daily tidal fortnightly and annual growth patterns of periodically formed skeletal hard parts provide a means to place the proxy record in a precise temporal context their extreme longevity coupled with the running similarity between growth increment time series of contemporaneous bivalves opens the possibility of constructing stacked chronologies covering centuries to millennia which provide information on decadal climate and environmental variability and magnitudes of climate variability through time a current major research focus is on how to translate geochemical properties of the skeletons into quantifiable environmental proxy data and how to eliminate the adverse influence of vital effects on the proxy records this special issue presents the most recent advances in the field of sclerochronology specifically calcified tissues of bivalve mollusks cold water corals and tropical shallow water corals the majority of the contributions deal with the potential reconstruction of temperature ph and productivity through the analysis of variable growth rates sr ca mg ca ba ca u ca li ca 13c 18o and 44 40ca four papers present composite chronologies of two long lived bivalve species and discuss inherent decadal climate variability and one study demonstrates that sclerochronology can shed light on socioeconomic patterns of past human populations as well as resource use and resource management by people

coherent surface subsurface fingerprint of the atlantic meridional overturning circulation 1 satellite altimeter data shows a weakening of the north atlantic subpolar gyre during the 1990s which is thought as an indicator of a slowdown of the atlantic meridional overturning circulation amoc however whether the recent slowing subpolar gyre is a decadal variation or a long term trend remains unclear here i show that altimeter data is highly correlated with instrumental subsurface ocean temperature data in the north atlantic and both show opposite signs between the subpolar gyre and the gulf stream path such a dipole pattern is a distinctive fingerprint of amoc variability as shown for the first time by a 1000 year coupled ocean atmosphere model simulation the results suggest that contrary to previous interpretations the recent slowdown of the subpolar gyre is a part of a multidecadal variation and suggests a strengthening of the amoc the ongoing satellite and subsurface temperature measurements could be used to monitor future amoc variations sensitively

the regime shift of the 1920s and 1930s in the north atlantic abstract during the 1920s and 1930s there was a dramatic warming of the northern north atlantic ocean warmer than normal sea temperatures reduced sea ice conditions and enhanced atlantic inflow in northern regions continued through to the 1950s and 1960s with the timing of the decline to colder temperatures varying with location ecosystem changes associated with the warm period included a general northward movement of fish boreal species of fish such as cod haddock and herring expanded farther north while colder water species such as capelin and polar cod retreated northward the maximum recorded movement involved cod which spread approximately 1200 km northward along west greenland migration patterns of warmer water species also changed with earlier arrivals and later departures new spawning sites were observed farther north for several species or stocks while for others the relative contribution from northern spawning sites increased some southern species of fish that were unknown in northern areas prior to the warming event became occasional and in some cases frequent visitors higher recruitment and growth led to increased biomass of important commercial species such as cod and herring in many regions of the northern north atlantic benthos associated with atlantic waters spread northward off western svalbard and eastward into the eastern barents sea based on increased phytoplankton and zooplankton production in several areas it is argued that bottom up processes were the primary cause of these changes the warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the north atlantic in the 20th century

reproducibility of trace element time series na ca mg ca mn ca sr ca and ba ca within and between specimens of the bivalve arctica islandica a la icp ms line scan study abstract trace element time series in bivalve mollusk shells and other biogenic materials can potentially serve as environmental proxies yet the applicability of element to calcium ratios is often challenging because non environmental factors such as vital effects distort or mask environmental signals if a trace element time series is driven by an environmental factor it should be reproducible within and between coeval specimens of the same species in the present study we tested whether time series of trace element to calcium ratios can be reproduced within and between coeval specimens of the bivalve arctica islandica and thus whether an external signal is encoded in the temporal variations of trace elements along the shells we determined the concentration of sodium magnesium manganese strontium and barium by means of la icp ms in line scan mode in the hinge area of seven specimens from the isle of man the gulf of maine and iceland in each specimen the element composition was determined along two replicate line scans to gauge intra specimen reproducibility the degree to which trace element time series can be reproduced was inferred from linear regression analysis and equaled on average 95 4 for ba ca 82 27 for mg ca 83 18 for sr ca 74 23 for mn ca and 22 4 for na ca ratios values correspond to coefficients of determination of the linear regression analysis expressed in percent the synchrony of ba ca time series between contemporaneous specimens from the same habitat has already been demonstrated in previous studies here we observed common high frequency variations i e peaks among coeval a islandica from the same site for mg ca sr ca mn ca and na ca ratios especially among specimens of similar ontogenetic age and with similar shell growth patterns the results of the present study should be considered in interpretations of trace element time series in bivalve shells as they can help to improve environmental and climate reconstructions

north atlantic oscillation dynamics recorded in shells of a long lived bivalve mollusk existing reconstructions of the winter north atlantic oscillation wnao are based on terrestrial proxies and historical documents no direct high resolution long term rec ords from marine settings are available for this major climate dictating phenomenon which severely affects a variety of economic aspects of our society here we present a 245 yr proxy wnao index based on shells of the long lived marine bivalve mollusk arctica islandica variations in annual rates of shell growth are positively correlated with wnao related changes in the food supply maximum amplitudes in frequency bands of 7 9 and 5 7 yr fall exactly within the range of instrumental and other proxy wnao indices these estimates were obtained for specimens collected live 2000 km apart in the central north sea and on the norwegian shelf hence the wnao influences hydrographic regimes of large regions of the ocean our study demonstrates that a islandica can reliably reconstruct wnao dynamics for time intervals and regions without instrumental records our new tool functions as a proxy for the wnao index prior to the twentieth century greenhouse forcing and has the potential to further validate other proxy based wnao records

proteinaceous corals as proxy archives of paleo environmental change abstract high resolution marine data are critical to evaluating anthropogenic impacts on our environment considering the spatial and temporal limitations of direct instrumental measurements proxy data extracted from marine environmental archives are necessary to separate anthropogenic changes from those that would occur naturally the majority of late holocene high resolution environmental reconstructions are derived from marine carbonates including tropical scleractinian corals bivalves crustose coralline algae and sclerosponges however these archives are restricted to the top hundreds of meters of the water column and only preserve environmental variability that is captured by calcium carbonate skeletons at a very few select locations marine sediments archive annual environmental variability in organic and inorganic materials recently additional types of corals are proving to yield information complimentary to these traditional marine archives including cold water scleractinian corals and proteinaceous corals a taxonomically diverse group the proteinaceous corals are broadly defined as those having a branching gross morphology with skeleton comprised at least partly of protein rich organic material they encode characteristics of their food and ambient environment into the chemical and physical composition of their skeleton this environmental encoding combined with their banded skeleton and significant longevity means that proteinaceous corals hold information in their skeleton that helps fill the spatial and temporal gaps in our knowledge of past and present ocean conditions here i review the environmental reconstructions derived from geochemical measurements of the proteinaceous coral skeletons this information is grouped into the mesopelagic environmental variability captured in the skeleton of bamboo corals surface processes captured in the organic skeletons of corals across all ocean depths and environmental variability documented by skeletal radiometric isotopes we include animals from two separate subclasses within the class anthozoa including the parasitic zoanthids that secrete a sclero proteic skeleton since the proteinaceous corals are taxonomically diverse we consider the unique features that define this group of corals including their distribution morphology nutrition and longevity we find that uncertainty surrounding biological parameters limits the precision of reconstructions derived from the calcitic skeleton in contrast analytical effort and cost constrain the number of reconstructions from the organic skeleton through this discussion we provide insights into the uses challenges and directions for future research for this important environmental archive

gulf of maine shells reveal changes in seawater temperature seasonality during the medieval climate anomaly and the little ice age article i nfo in this study we use subannually resolved oxygen isotope values of fossil dead collected and modern live caught bivalve shells arctica islandica l from the northwestern atlantic gulf of maine usa to reconstruct past seasonal changes in seawater temperature our results indicate decreased seasonal temperature amplitude of about 1 6 c or 21 during medieval times ca ad 1033 1062 compared to shells from the early little ice age ca ad 1321 1391 and during the late 19th century ad 1864 1886 additionally seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the gulf of maine during the 11th century compared to summers and winters in the 14th century and the late 19th century the inferred decreased seasonality during medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures as seawater cooled during the little ice age we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle