a new late holocene sea level record from the mississippi delta evidence for a climate sea level connection abstract a detailed relative sea level rsl record was constructed for the time interval 600 1600 ad using basal peat to track sea level and containing 16 sea level index points that capture 60 cm of rsl rise the study area is in the mississippi delta where the spring tidal range is 0 47 m the impact of ocean currents on sea surface topography is limited and crustal motions are well constrained age control was obtained by ams 14 c dating and most ages represent weighted means of two subsamples sample elevations were determined by combining differential gps measurements with optical surveying all index points were plotted as error boxes using 2 confidence intervals for the ages plus all vertical errors involved in sampling and surveying as well as the indicative range of the samples a striking clustering of sea level index points between 1000 and 1200 ad suggests a possible acceleration in the rate of rsl rise removal of the long term trend 0 60 mm yr 1 allows for the possibility of a sea level oscillation with a maximum amplitude of 55 cm however given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out comparison of the new rsl record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes including the medieval warm period and the little ice age however given the error margins associated with this reconstruction it is stressed that this causal mechanism is tentative and requires corroboration by high resolution sea level reconstructions elsewhere

coupling instrumental and geological records of sea level change evidence from southern new england of an increase in the rate of sea level rise in the late 19th century 1 we construct a high resolution relative sea level record for the past 700 years by dating basal salt marsh peat samples above a glacial erratic in an eastern connecticut salt marsh to test whether or not the apparent recent acceleration in the rate of sea level rise slr is coeval with climate warming the data reveal an average slr rate of 1 0 0 2 mm year from about 1300 to 1850 a d coupling of the regional tide gauge data 1856 to present with this marsh based record indicates that the nearly three fold increase in the regional rate of slr to modern levels likely occurred in the later half of the 19th century thus the timing of the observed slr rate increase is coincident with the onset of climate warming indicating a possible link between historic slr increases and recent temperature increases

atlantic multidecadal oscillation and northern hemisphere s climate variability proxy and instrumental records reflect a quasi cyclic 50 80 year climate signal across the northern hemisphere with particular presence in the north atlantic modeling studies rationalize this variability in terms of intrinsic dynamics of the atlantic meridional overturning circulation influencing distribution of sea surface temperature anomalies in the atlantic ocean hence the name atlantic multidecadal oscillation amo by analyzing a lagged covariance structure of a network of climate indices this study details the amo signal propagation throughout the northern hemisphere via a sequence of atmospheric and lagged oceanic teleconnections which the authors term the stadium wave initial changes in the north atlantic temperature anomaly associated with amo culminate in an oppositely signed hemispheric signal about 30 years later furthermore shorter term interannual to interdecadal climate variability alters character according to polarity of the stadium wave induced prevailing hemispheric climate regime ongoing research suggests mutual interaction between shorter term variability and the stadium wave with indication of ensuing modifications of multidecadal variability within the atlantic sector results presented here support the hypothesis that amo plays a significant role in hemispheric and by inference global climate variability with implications for climate change attribution and prediction

relative sea level rise and climate change over the last 1500 years we constructed a detailed relative sea level rise curve for the last 1500 years using a novel approach i e charting the rate of relative sea level rise using microfaunal and geochemical data from a coastal salt marsh sequence clinton ct usa the composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively the resulting sea level rise curve with age control from 14c dating and the onset of anthropogenic metal pollution shows strong increases in the rate of relative sea level rise during modern global warming since the late nineteenth century but not during the little climate optimum ad 1000 1300 there was virtually no rise in sea level during the little ice age ad 1400 1700 most of the relative sea level rise over the last 1200 years in clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years changes from slow to fast rates of relative sea level rise apparently occurred over periods of only a few decades we suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea level rise along the northeastern usa seaboard relative sea level rise in that area is currently faster than the worldwide average which may result partially from an ocean surface effect caused by hydrodynamics our data show no unequivocal correlation between warm periods on a decaal to centennial time scale and accelerated sea level rise one period of acclerated sea level rise may have occurred between about ad 1200 and 1450 which was the transition for the little climate optimum to the little ice age i e a period of cooling at least in northwestern europe local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea level however the second period of accelerated sea level rise occurred during the period of modern global warming that started at the end of the last century

trace metal behaviour in oxic and anoxic cacl brines of the wright valley drainage antarctica abstract geochemical speciation and reaction path models have been used to identify the major factors controlling mn fe cu pb zn ni and co concentrations in meltwaters and ca cl brines of the closed basin wright valley drainage system in antarctica the major aqueous features of this drainage system are a the onyx river a meltwater stream b lake vanda an ice covered stratified lake in which ca cl brines become more concentrated and ultimately anoxic with depth and c don juan pond a small highly saline ca cl brine pond trace metal concentrations in the groundwater have been estimated and used to derive hypothetical concentrations for trace metals in the ancient brine pool from which lake vanda was formed the results of this calculation support the premise that the trace metal distribution profiles observed in lake vanda are attributable to the influx of trace metals from the onyx river and to modern ongoing lake processes in the onyx river and in the oxic ca cl brines of lake vanda and don juan pond trace metal concentrations appear to be consistently controlled by adsorption and desorption from the surface of particulate fe oxides or fe hydroxides variations in the trace metal concentrations measured in the oxic brines can be directly related to the effect of changes in ph and major ion chemistry on the adsorption of each metal at the fe oxide surface for the onyx river and lake vanda this hypothesis is presented as modification to the currently accepted model green et al 1989 which postulates cu and ni adsorption onto particulate mn oxide in the anoxic h 2 s bearing ca cl brines at the base of lake vanda cu pb zn ni co and fe concentrations appear to be limited by precipitation of metal sulphide mineral phases and by the stability of metal bisulphide and polysulphide complex species mn is relatively mobile in the anoxic brine but mn concentrations may be limited by precipitation of a mn carbonate phase

electrically conducting ca rich brines rather than water expected in the martian subsurface 1 if mars ever possessed a salty liquid hydrosphere which later partly evaporated and froze down then any aqueous fluids left near the surface could have evolved to become dense eutectic brines eutectic brines by definition are the last to freeze and the first to melt if cacl2 rich such brines can remain liquid until temperatures below 220 k close to the average surface temperature of mars in the martian subsurface in intimate contact with the ca rich basaltic regolith nacl rich early brines should have reacted to become ca rich fractional crystallization freezing and partial melting would also drive brines toward cacl2 rich compositions in other words eutectic brine compositions could be present in the shallow subsurface of mars for the same reasons that eutectic magma compositions are common on earth don juan pond antarctica a cacl2 rich eutectic brine provides a possible terrestrial analog particularly because it is fed from a basaltic aquifer owing to their relative density and fluid nature brines in the martian regolith should eventually become sandwiched between ice above and salts beneath a thawing brine sandwich provides one explanation among many for the young gullies recently attributed to seepage of liquid water on mars whether or not brine seepage explains the gullies phenomenon dense cacl2 rich brines are to be expected in the deep subsurface of mars although they might be somewhat diluted temperatures permitting and of variable salt composition in any case they should be good conductors of electricity

the formation of ca cl rich groundwaters in the dry valleys of antarctica field measurements and modeling of reactive transport abstract ca cl rich brines have been found in shallow subsurface flows groundwater systems lakes and ponds throughout the dry valleys of antarctica the apparent abundance of ca cl rich waters near the surface is unusual compared to global surface water compositions and a number of theories have been proposed to explain the genesis of these brines we show that an ice cemented soil developing on fluvial sediment in taylor valley also contains ca cl rich brine the distribution of soluble ions exchangeable cations and stable isotopes down to 2 1 m depth in the soil suggests that cacl2 was formed by cation exchange reactions during downward reactive transport of na cl rich brine from the soil surface to explore the implications of exchange reactions for the formation of ca cl rich brine ca na and ca mg exchange properties were measured in 1 mm 0 1 m and 4 75 m solutions low temperature reactions and brine transport were modeled in phreeqc by incorporating frezchem pitzer parameters and solubility products into phreeqc modeling shows that by freezing soils in equilibrium with dry valley surface waters a strong ca mg enrichment of the soil solution is caused by the exchange of aqueous na with exchangeable ca2 and mg2 ca mg enrichment also occurs as na cl rich brine from the soil surface advects into ice cemented soil by modeling this process in the borehole soil trends in ion distributions with depth can be predicted brine compositions from cation exchange reactions are consistent with ca cl rich brine compositions in the dry valleys although additional water rock interaction is proposed to account for the low mg2 concentrations in don juan pond furthermore the amount of cacl2 that can be produced by exchange reactions is consistent with estimated amounts of cacl2 in groundwaters beneath don juan pond this suggests that cation exchange reactions can explain the ca cl rich composition of the enigmatic don juan pond and other brines in the dry valleys

sea level rise spatially uneven and temporally unsteady why the u s east coast the global tide gauge record and the global altimeter data show different trends 1 impacts of ocean dynamics on spatial and temporal variations in sea level rise slr along the u s east coast are characterized by empirical mode decomposition analysis and compared with global slr the findings show a striking latitudinal slr pattern sea level acceleration consistent with a weakening gulf stream is maximum just north of cape hatteras and decreasing northward while slr driven by multidecadal variations possibly from climatic variations in subpolar regions is maximum in the north and decreasing southward the combined impact of sea level acceleration and multidecadal variations explains why the global mean slr obtained from 20 years of altimeter data is about twice the century long global slr obtained from tide gauge data the sea level difference between bermuda and the u s coast is highly correlated with the transport of the atlantic overturning circulation a result with implications for detecting past and future climatic changes using tide gauge data

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

soluble salt accumulations in taylor valley antarctica implications for paleolakes and ross sea ice sheet dynamics 1 soluble salt accumulations in soils of taylor valley antarctica provide a history of paleolakes and the advance of the ross sea ice sheet rsis in western taylor valley soluble salt accumulations are relatively high and are composed primarily of na ca2 cl and so42 in eastern taylor valley soluble salt accumulations are much lower and are composed primarily of na and hco3 na hco3 rich compositions in eastern taylor valley are formed through leaching calcite dissolution and cation exchange reactions and appear to influence the chemistry of nearby streams and lakes the data presented here support hypotheses that a lobe of the rsis expanded into eastern taylor valley and dammed proglacial paleolakes however in contrast to previous studies our findings indicate that the rsis advanced deeper into taylor valley and that paleolakes were less extensive by comparing soluble salt distributions across taylor valley we conclude that a lobe of the rsis filled all of eastern taylor valley and dammed paleolakes in western taylor valley up to approximately 300 m elevation following ice retreat smaller paleolakes formed in both western and eastern taylor valley up to about 120 m elevation with prominent still stands controlled by the elevation of major valley thresholds at higher elevations soluble salt accumulations are consistent with older soils that have not been affected by the most recent rsis advance

holocene sea level variability from chesapeake bay tidal marshes usa we reconstructed the last 10 000 years of holocene relative sea level rise rslr from sediment core records near chesapeake bay eastern united states including new marsh records from the potomac

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

an enhanced model of the contemporary and long term 200 ka sublimation of the massive subsurface ice in beacon valley antarctica a massive ice body buried under several decimeters of dry regolith in beacon valley antarctica is believed to be more than 1 ma old and perhaps over 8 1 ma however vapor diffusion models suggest that subsurface ice in this region is not stable under current climate conditions to better understand the controls on sublimation rates and stability of this massive ice we have modeled vapor diffusion using 12 years of climate and soil temperature data from 1999 to 2011 including field measurements of episodic snow cover and snowmelt events that have not been represented in previous models of ground ice sublimation the model is then extended to reconstruct the sublimation history over the last 200 ka using paleotemperatures estimated from ice core data from nearby taylor dome and a relationship between atmospheric temperature and humidity derived from our meteorological records the model quantifies the impact of episodic snow events they account for a nearly 30 reduction in the massive ice loss the sublimation rate of ground ice averages 0 11 mm a 1 between 1999 and 2011 in beacon valley parameterized with past environmental conditions and assuming the same regolith thickness the modeled sublimation rate of ground ice in beacon valley averages 0 09 mm a 1 for the last 200 ka comparable to the long term average rate estimated independently from various studies based on cosmogenic isotopes this study provides a realistic estimate of the long term sublimation history and supports the inference that the buried ice in beacon valley is older than 1 ma

sea level climate correlation during the past 1400 yr we present a new mean high water curve for hammock river marsh clinton connecticut obtained by improving the age model for an existing record of relative marsh elevation based on foraminiferal analysis of a 1 8 m long peat core unlike the earlier curve the new curve confirms trend changes in mean high water rise during the past 1400 yr as noted for salt marshes 15 km farther west suggesting a regional cause these trend changes and century scale mean high water variations in the clinton record correlate positively with large scale regional variations in sea surface and summer air temperature indicating a link between sea level and the climate ocean system on the basis of the clinton mean high water curve we conclude that real sea level oscillated centimeters to decimeters on a century time scale over the past 1400 yr was 25 25 cm higher ca a d 1050 medieval warm period than ca a d 1650 little ice age and rose at a mean rate of 1 mm yr 1 over the past 350 yr there was little or no rise during the cool 1800s

late holocene sea level variability and atlantic meridional overturning circulation pre twentieth century sea level sl variability remains poorly understood due to limits of tide gauge records low temporal resolution of tidal marsh records and regional anomalies caused by dynamic ocean processes notably multidecadal changes in atlantic meridional overturning circulation amoc we examined sl and amoc variability along the eastern united states over the last 2000 years using a sl curve constructed from proxy sea surface temperature sst records from chesapeake bay and twentieth century sl sea surface temperature sst relations derived from tide gauges and instrumental sst the sl curve shows multidecadal scale variability 20 30 years during the medieval climate anomaly mca and little ice age lia as well as the twentieth century during these sl oscillations short term rates ranged from 2 to 4 mm yr 1 roughly similar to those of the last few decades these oscillations likely represent internal modes of climate variability related to amoc variability and originating at high latitudes although the exact mechanisms remain unclear results imply that dynamic ocean changes in addition to thermosteric glacio eustatic or glacio isostatic processes are an inherent part of sl variability in coastal regions even during millennial scale climate oscillations such as the mca and lia and should be factored into efforts that use tide gauges and tidal marsh sediments to understand global sea level rise

radiocarbon dating chronologic framework and changes in accumulation rates of holocene estuarine sediments from chesapeake bay abstract rapidly accumulating holocene sediments in estuaries commonly are difficult to sample and date in chesapeake bay we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of holocene sediment accumulation in the bay carbon in these sediments is a complex mixture of materials from a variety of sources analyses of different components of the sediments show that total organic carbon ages are largely unreliable because much of the carbon including coal has been transported to the bay from upstream sources and is older than sediments in which it was deposited mollusk shells clams oysters and foraminifera appear to give reliable results although reworking and burrowing are potential problems analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower chesapeake bay the biogenic carbonate radiocarbon ages are compatible with 210pb and 137cs data and pollen stratigraphy from the same sites post settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries including the chesapeake our data show that large variations in sediment mass accumulation rates occur among sites at shallow water sites local factors seem to control changes in accumulation rates with time our two relatively deep water sites in the axial channel of the bay have different long term average accumulation rates but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay mass accumulation rates at the two deep water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the chesapeake watershed

coherent multidecadal variability in north atlantic sea level 1 tide gauge records from around the north atlantic are examined and found to show variability on 20 30 year time scales sea surface height variability along the western boundary of the north atlantic shows a particularly strong and coherent signal similar variability is also found in an ensemble of runs using a state of the art climate model gfdl cm2 1 this sea surface height variability is linked to variability of temperatures in the upper layers of the ocean and thence to the atlantic multidecadal oscillation the variability is consistent with the excited internal ocean mode mechanism of multidecadal variability derived from idealised models and the timescale is consistent with that derived from observations of sub surface temperature variability

gulf stream density structure and transport during the past millennium the gulf stream transports approximately 31 sv 1 sv 10 6 m 3 s 1 of water and 1 3 10 15 w of heat into the north atlantic ocean the possibility of abrupt changes in gulf stream heat transport is one of the key uncertainties in predictions of climate change for the coming centuries given the limited length of the instrumental record our knowledge of gulf stream behaviour on long timescales must rely heavily on information from geologic archives here we use foraminifera from a suite of high resolution sediment cores in the florida straits to show that the cross current density gradient and vertical current shear of the gulf stream were systematically lower during the little ice age ad 1200 to 1850 we also estimate that little ice age volume transport was ten per cent weaker than today s the timing of reduced flow is consistent with temperature minima in several palaeoclimate records implying that diminished oceanic heat transport may have contributed to little ice age cooling in the north atlantic the interval of low flow also coincides with anomalously high gulf stream surface salinity suggesting a tight linkage between the atlantic ocean circulation and hydrologic cycle during the past millennium

a miocene polarity transition r n from the agno batholith luzon a geomagnetic reversal record has been obtained from the agno batholith 16 15 n 120 39 e in luzon island the philippines this body is a biotite hornblende quartz diorite dated at between 14 5 and 15 0 m y by the k ar whole rock method hysteresis properties show that the magnetic remanence is dominated by multidomain low titanium titanomagnetite a stable component of magnetization is isolated upon both thermal and alternating field demagnetization normal and reversed polarity zones within the batholith give tightly grouped results which when compared to other miocene poles from the baguio area allow a tilt correction to be made the resulting reversed to normal reversal sequence has a far sided vgp path and a decrease in intensity of magnetization of approximately a factor of 5 with a longer duration than the directional change the vgp path is confined in a longitudinal band 120 from the site and so differs from the characteristic reversed to normal transition paths in that it is not near sided intermediate field geometry cannot therefore always be the same for individual reversals the agno reversal record is consistent with a quadrupole field and reversal initiated in the northern hemisphere an octupolar intermediate field would require simultaneous flooding from both polar latitude bands

the geochemistry of don juan pond evidence for a deep groundwater flow system in wright valley antarctica abstract don juan pond djp antarctica is one of the most unusual surface waters on earth because of its cacl 2 rich composition to investigate the evolution of pond waters during closed basin evaporation and to understand the source of brines responsible for the chemistry of djp we apply a newly developed low temperature aqueous model in the na k ca mg cl system to djp by modeling the closed basin evaporation of djp and comparing ionic ratios between djp surface water deep groundwater shallow groundwater and other surface chemistries in wright valley we find that djp is best explained by upwelling deep groundwater as opposed to recent hypotheses proposing shallow groundwater sources the early closed basin evolution of brines in our model accurately predicts observed chemistries in djp however late stage closed basin evaporation produces mg k rich brines and salts that do not match the cacl 2 rich brine in djp based on groundwater inflow rates to djp we estimate that even the most concentrated brines in djp have undergone closed basin evaporation for less than a year to explain the observed lack of mg 2 and k accumulation in djp over time and the surprisingly young age for the brines we deduce that djp is a localized upwelling from a regional groundwater flow through system in which evaporated djp brines are recycled back into the subsurface over yearly timescales the existence of a regional groundwater flow system beneath djp has implications for water and solute budgets in cold desert ecosystems and may provide clues for the formation of groundwater and aqueous flows on mars

opposing decadal changes for the north atlantic meridional overturning circulation hydrographic properties of the north atlantic ocean have changed significantly over the past decades a combination of changes in seawater density calculated from observed properties of sea water and a numerical ocean model reveals that the strength of the meridional overturning circulation has changed in different directions in the subpolar and subtropical basins respectively

a sea level rise curve from guilford connecticut usa abstract high resolution stratigraphic studies based on sediment chemistry lithology macroflora and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at guilford connecticut show that coastal marshes are ephemeral environments marsh wide environmental variations were common and century long episodes of relative submergence alternated with emergence despite about 2 m of relative sea level rise rslr in connecticut over the last 1500 years the marshes have expanded both landwards and seawards and marsh accretion has been outpaced only marginally by rslr we used radiocarbon dating and the level of anthropogenic markers metal pollution as dated with 210 pb in the cores for age control for most of the last 1000 years the rate of rslr was between 1 3 and 1 8 mm yr but over the last 300 400 years it increased to 2 9 3 3 mm yr and has been faster than the accretion rate especially in the middle marsh the net submergence rate or submergence index ratio of the rate of rslr and marsh accretion rate averaged about 1 15 over the last 1000 years and increased to about 1 5 over the last 200 years the rate of rslr was very sluggish during the early part of the little ice age but we found a slightly higher rate during the little climate optimum this excursion is close to the noise level however the most significant observation is that rslr increased strongly around a d 1650 the onset of this acceleration falls in the middle to end of the little ice age and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases

is there a 60 year oscillation in global mean sea level 1 we examine long tide gauge records in every ocean basin to examine whether a quasi 60 year oscillation observed in global mean sea level gmsl reconstructions reflects a true global oscillation or an artifact associated with a small number of gauges we find that there is a significant oscillation with a period around 60 years in the majority of the tide gauges examined during the 20th century and that it appears in every ocean basin averaging of tide gauges over regions shows that the phase and amplitude of the fluctuations are similar in the north atlantic western north pacific and indian oceans while the signal is shifted by 10 years in the western south pacific the only sampled region with no apparent 60 year fluctuation is the central eastern north pacific the phase of the 60 year oscillation found in the tide gauge records is such that sea level in the north atlantic western north pacific indian ocean and western south pacific has been increasing since 1985 1990 although the tide gauge data are still too limited both in time and space to determine conclusively that there is a 60 year oscillation in gmsl the possibility should be considered when attempting to interpret the acceleration in the rate of global and regional mean sea level rise

rapid sea level rise abstract several global and regional factors contribute to observed sea level change along any particular coast global processes include changes in ocean mass glacio eustasy from ice melt ocean volume steric effects viscoelastic land movements glacioisostatic adjustment gia and changes in terrestrial water storage regional processes often connected to steric and glacial changes include changes in ocean circulation meridional overturning circulation moc glacial melting local gia regional subsidence and others paleoclimate instrumental and modeling studies show that combinations of these factors can cause relatively rapid rates of sea level rise exceeding 3 mm yr 1 over various timescales along particular coasts this paper discusses patterns and causes of sea level rise with emphasis on paleoclimatological records it then addresses the hypothesis of late holocene pre 20th century sea level stability in light of paleoclimatic evidence notably from reconstructions of sea surface temperature and glacial activity for significant climate and sea level variability during this time the practical difficulties of assessing regional sea level sl patterns at submillennial timescales will be discussed using an example from the eastern united states

does the mid atlantic united states sea level acceleration hot spot reflect ocean dynamic variability 1 to test a hypothesized faster than global sea level acceleration along the mid atlantic united states i construct a gaussian process model that decomposes tide gauge data into short term variability and longer term trends and into globally coherent regionally coherent and local components while tide gauge records indicate a faster than global increase in the rate of mid atlantic u s sea level rise beginning 1975 this acceleration could reflect either the start of a long term trend or ocean dynamic variability the acceleration will need to continue for 2 decades before the rate of increase of the sea level difference between the mid atlantic and southeastern u s can be judged as very likely unprecedented by 20th century standards however the difference is correlated with the atlantic multidecadal oscillation north atlantic oscillation and gulf stream north wall indices all of which are currently within the range of past variability

high precision three dimensional paleothermometry derived from paleomagnetic data in an alpine metamorphic unit in the dauphinoise zone of the french western alps a posttectonic thermoremanent magnetization carried by pyrrhotite has been isolated the paleomagnetic signature is interpreted as the record of successive partial thermoremanent magnetizations of opposite directions acquired during the early miocene slow cooling of the epimetamorphic marly limestones of the studied area a local vertical thermal gradient of 22 2 c km was derived from the unblocking temperature of a reversal recorded at different altitudes using this vertical gradient we have produced a paleotemperature map at the time of the reversal about 20 ma the map shows a horizontal regional thermal gradient of 7 c km the higher temperatures were toward the crystalline basement paleomagnetic directions demonstrate that this horizontal gradient was present during cooling its origin can be explained by large volume fluid circulation along the major fault that forms the boundary between the crystalline basement and its liassic cover

geochemistry of the onyx river wright valley antarctica and its role in the chemical evolution of lake vanda the onyx river wright valley antarctica is a dilute meltwater stream originating in the vicinity of the wright lower glacier it acquires a significant fraction of its salt content when glacial meltwaters contact wright valley soils at lake brownworth and the concentrations of all ions increase with distance along the 28 km channel down to lake vanda average millimolar concentrations of major ions at the vanda weir during the 1980 1981 flow season were ca 0 119 mg 0 061 na 0 212 k 0 033 q 0 212 so4 0 045 hco3 0 295 and sio2 0 049 based on the flow measurements of chinn 1982 this amounts to an annual flux in moles to lake vanda of ca 0 238 106 mg 0 122 106 na 0 424 106 k 0 066 106 cl 0 424 106 so4 0 09 106 hco3 0 59 106 sio2 0 098 106 in spite of the large salt input from this source equilibrium evaporation of onyx river water would have resulted in early calcite deposition and in the formation of a na mg cl hco3 brine rather than in the ca na mg cl waters observed in lake vanda the river alone could not have produced a brine having the qualitative geochemical features of the lower saline waters of lake vanda it is proposed that the vanda brine is instead the result of past 1200 yrs bp mixing events between onyx river inflows and calcium chloride rich deep groundwaters derived from the don juan basin the mixing model presented here shows that the onyx river is the major contributor of k hco3 so4 and possibly mg found in the lake and a significant contributor approximately one half of the observed na calcium and cl on the other hand came largely from deep groundwater sources in the don juan basin all concentrations except mg are well predicted by this model the chemical composition of the geologically recent upper lake is explained in terms of ionic diffusion from the pre formed brine coupled with onyx river inflow ionic ratios calculated from this latter model are in very good agreement with those observed in the lake at 35 meters

recent global sea level acceleration started over 200 years ago 1 we present a reconstruction of global sea level gsl since 1700 calculated from tide gauge records and analyse the evolution of global sea level acceleration during the past 300 years we provide observational evidence that sea level acceleration up to the present has been about 0 01 mm yr2 and appears to have started at the end of the 18th century sea level rose by 6 cm during the 19th century and 19 cm in the 20th century superimposed on the long term acceleration are quasi periodic fluctuations with a period of about 60 years if the conditions that established the acceleration continue then sea level will rise 34 cm over the 21st century long time constants in oceanic heat content and increased ice sheet melting imply that the latest intergovernmental panel on climate change ipcc estimates of sea level are probably too low

experimental evaluation of thermal recording of successive polarities during uplift of metasediments summary the discovery of a post tectonic natural remanent magnetization nrm carried by pyrrhotite in the dauphinoise zone of the western alps allows us to test the ability of these rocks to record a sequence of magnetic polarity versus temperature acquired during their slow cooling several laboratory experiments composite partial thermal remanent magnetizations ptrms thellier thellier experiments trm thermal demagnetization as well as nrm demagnetization were performed this shows that the pyrrhotite grains are single domain sized and that they are able to record successive independent ptrms the nrm thermal demagnetization analysis demonstrates the occurrence of several antiparallel components a comparison between nrm and trm thermal demagnetizations is attempted in order to highlight small ptrms naturally recorded in a temperature interval of only a few degrees we attempt to retrieve the temperature at which each reversal occurs during the post metamorphic cooling this method called thermopalaeomagnetism is discussed and developed in order to delineate the sequence of polarity chrons recorded versus temperature

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

transient response of the moc and climate to potential melting of the greenland ice sheet in the 21st century 1 the potential effects of greenland ice sheet gris melting on the atlantic meridional overturning circulation moc and global climate in the 21st century are assessed using the community climate system model version 3 with prescribed rates of gris melting only when gris melting flux is strong enough to be able to produce net freshwater gain in upper subpolar north atlantic does the moc weaken further in the 21st century otherwise this additional melting flux does not alter the moc much relative to the simulation without this added flux the weakened moc doesn t make the late 21st century global climate cooler than the late 20th century but does reduce the magnitude of the warming in the northern high latitudes by a few degrees moreover the additional dynamic sea level rise due to this weakened moc could potentially aggravate the sea level problem near the northeast north america coast

sea level changes since the last glacial maximum an appraisal of the ipcc fourth assessment report the ipcc fourth assessment report ar4 stated that global sea level rose by about 120 m between the last glacial maximum lgm and 3 2 ka and did not rise again until the late 19th century a review of relevant literature demonstrates that the rise may have been larger by 10 15 m that the timing of stabilisation is poorly constrained within the last 7 ka bp and that the onset of modern rates of sea level rise is not synchronous and uniform across the globe the lgm lowstand as defined in the ar4 is based on the classic barbados sea level history but the sea level curve from this island may not be an accurate eustatic approximation if glacial isostatic adjustment gia processes were significant as suggested by various authors the barbados sea level curve revealed the existence of meltwater pulse mwp 1a at around 14 000 cal a bp questions about the source and causal mechanism of mwp 1a are still being explored by field scientists and gia modellers these problems have direct relevance for contemporary measurements of ice mass changes because space geodetic measurements rely on information provided by gia models to separate land motion from ice mass changes global patterns of holocene sea level change are controlled by regional sea level variability not only through isostatic and tectonic processes but also through steric effects longer wavelength gravitational changes produced by changing ice ocean mass flux and hemispheric scale perturbations in the earth s rotation eustasy is therefore merely a concept not a measurable quantity constraining the late holocene ice melt contribution to global sea level rise and determining regional sea level rise patterns in the 18th and 19th centuries are important future tasks for sea level scientists these will establish the baseline contributions to 20th and 21st century sea level rise and will help to determine the causes of modern rates of sea level rise constraining historical sea level accelerations and short term ice mass flux will aid models of ice sheet dynamics and help to reduce current uncertainties in future sea level predictions the ar4 shows that regional sea level variability is clearly present in sea level change patterns for the past 50 a and an important challenge for the next ipcc assessment is to incorporate this variability into regional future sea level rise scenarios copyright 2009 john wiley sons ltd

hydrological characteristics of recurrent slope lineae on mars evidence for liquid flow through regolith and comparisons with antarctic terrestrial analogs abstract on the basis of their morphology and seasonal thermal characteristics recurrent slope lineae rsl on mars have been inferred to be a possible result of the flow of a liquid likely a saline brine through the upper portions of the martian regolith in this note we analyze repeat hirise imaging of rsl to show that the downslope growth rate of recurrent slope lineae is well fit by an elementary groundwater flow model that also describes the downslope propagation of antarctic water tracks terrestrial analogs to rsl and that the apparent permeability of rsl bearing slopes is consistent with the observed sandy regolith substrate

monitoring the atlantic meridional overturning circulation the rapid climate change programme rapid has established a prototype system to continuously observe the strength and structure of the atlantic meridional overturning circulation moc at 26 5 n here we provide a detailed description of the rapid moc monitoring array and how it has evolved during the first four deployment years as well as an overview of the main findings so far the rapid moc monitoring array measures 1 gulf stream transport through florida strait by cable and repeat direct velocity measurements 2 ekman transports by satellite scatterometer measurements 3 deep western boundary currents by direct velocity measurements 4 the basin wide interior baroclinic circulation from moorings measuring vertical profiles of density at the boundaries and on either side of the mid atlantic ridge and 5 barotropic fluctuations using bottom pressure recorders the array became operational in late march 2004 and is expected to continue until at least 2014 the first 4 years of observations april 2004 april 2008 have provided an unprecedented insight into the moc structure and variability we show that the zonally integrated meridional flow tends to conserve mass with the fluctuations of the different transport components largely compensating at periods longer than 10 days we take this as experimental confirmation of the monitoring strategy which was initially tested in numerical models the moc at 26 5 n is characterised by a large variability even on timescales as short as weeks to months the mean maximum moc transport for the first 4 years of observations is 18 7 sv with a standard deviation of 4 8 sv the mechanisms causing the moc variability are not yet fully understood part of the observed moc variability consists of a seasonal cycle which can be linked to the seasonal variability of the wind stress curl close to the african coast close to the western boundary fluctuations in the gulf stream and in the north atlantic deep water nadw coincide with bottom pressure variations at the western margin thus suggesting a barotropic compensation ongoing and future research will put these local transport variations into a wider spatial and climatic context

kinematics of the crust around the ama drime massif southern tibet constraints from paleomagnetic results abstract secondary magnetic remanences are used to study late orogenic rotation and tilting on a e w transect in southern tibet at 28 5 n sampling was performed on both sides of the ama drime massif adm remanent magnetization resides in pyrrhotite formed during metamorphism and is related to the last cooling event through 325 c curie temperature of pyrrhotite the existence of antipodal ptrms demonstrates that the chrm is of thermoremanent origin and was acquired during cooling of the tethyan metasediments penetrative deformation was still going on in ronghbuk area until ca 250 c whereas it was already completed in dinggye area significant departures from the expected field direction during the age of remanence acquisition cannot be interpreted by consistent vertical axis rotation of blocks antagonist deviations on both sides of the adm are explained as tiltings around an horizontal axis striking n20 these tiltings are estimated to be younger than 13 12 ma and they are related to the adm exhumation initiated since 33 ma

florida current surface temperature and salinity variability during the last millennium surface water d 18 ow near dry tortugas increased 0 4 during the course of the little ice age lia 1200 1850 a d equivalent to a salinity increase of 0 8 1 5 on the great bahama bank where surface waters are influenced by the north atlantic subtropical gyre d 18 ow increased by 0 3 during the last 200 years although a portion 0 1 of this shift may be an artifact of anthropogenically driven changes in surface water sco2 the remaining d 18 ow signal implies a 0 4 1 increase in salinity after 200 years b p the simplest explanation of the d 18 ow data is southward migration of the atlantic hadley circulation during the lia scaling of the d 18 ow records to salinity using the modern low latitude d 18 ow s slope produces an unrealistic reversal in the salinity gradient between the two sites only if d 18 ow is scaled to salinity using a high latitude d 18 ow s slope can the records be reconciled variable atmospheric 14 c paralleled dry tortugas d 18 ow suggesting that solar irradiance paced centennial scale migration of the inter tropical convergence zone and changes in florida current salinity during the last millennium citation lund d c and w curry 2006 florida current surface temperature and salinity variability during the last millennium paleoceanography 21 pa2009 doi 10 1029 2005pa001218

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

spectral evidence for hydrated salts in recurring slope lineae on mars transient streaks that appear seasonally on martian slopes are consistent with brine flows but evidence of water or salts has been lacking analysis of spectral data reveals hydrated salts associated with the streaks confirming a briny origin

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

formation of recurring slope lineae by liquid brines on present day mars 1 recurring slope lineae rsl are small scale seasonal flow features identified by mars reconnaissance orbiter that present several interesting characteristics such as an albedo contrast seasonal dependence and a strong preference for equator facing slopes all of these characteristics strongly suggest a thermally driven mechanism such as a liquid triggered or dominated flow here we investigate the possibility that these features are formed by melting of brines of various compositions via a combination of thermodynamic and kinetic numerical models results suggest that a solution with a freezing temperature of 223 k can best reproduce the observed seasonality relatively high surface evaporation rates at the rsl locations make the flows quickly disappear over a single season our model reproduces well the seasonality of rsl and can explain the preference for equator facing slopes suggesting that brine flows and therefore liquids are possible on a small time and space scale today on mars however if the rsl are indeed formed by brines it may indicate that a recharge mechanism is active in order to maintain a source of brine over even short geological timescales which would have important implications for the martian water cycle

sea level change during the last 2500 years in new jersey usa relative sea level changes during the last w2500 years in new jersey usa were reconstructed to test if late holocene sea level was stable or included persistent and distinctive phases of variability foraminifera and bulk sediment d 13 c values were combined to reconstruct paleomarsh elevation with decimeter precision from sequences of salt marsh sediment at two sites using a multi proxy approach the additional paleoenvironmental information provided by bulk sediment d 13 c values reduced vertical uncertainty in the sea level reconstruction by about one third of that estimated from foraminifera alone using a transfer function the history of sediment deposition was constrained by a composite chronology an ageedepth model developed for each core enabled reconstruction of sea level with multi decadal resolution following correction for land level change 1 4 mm yr four successive and sustained multi centennial sea level trends were objectively identified and quantified 95 confidence interval using error in variables change point analysis to account for age and sea level uncertainties from at least 500 bc to 250 ad sea level fell at 0 11 mm yr the second period saw sea level rise at 0 62 mm yr from 250 ad to 733 ad between 733 ad and 1850 ad sea level fell at 0 12 mm yr the reconstructed rate of sea level rise since w1850 ad was 3 1 mm yr and represents the most rapid period of change for at least 2500 years this trend began between 1830 ad and 1873 ad since this change point reconstructed sea level rise is in agreement with regional tide gauge records and exceeds the global average estimate for the 20th century these positive and negative departures from background rates demonstrate that the late holocene sea level was not stable in new jersey

spatial variability of late holocene and 20th century sea level rise along the atlantic coast of the united states accurate estimates of global sea level rise in the pre satellite era provide a context for 21 st century sea level predictions but the use of tide gauge records is complicated by the contributions from changes in land level due to glacial isostatic adjustment gia we have constructed a rigorous quality controlled database of late holocene sea level indices from the u s atlantic coast exhibiting subsidence rates of 0 8 mm a 1 in maine increasing to rates of 1 7 mm a 1 in delaware and a return to rates 0 9 mm a 1 in the carolinas this pattern can be attributed to ongoing gia due to the demise of the laurentide ice sheet our data allow us to defi ne the geometry of the associated collapsing proglacial forebulge with a level of resolution unmatched by any other currently available method the corresponding rates of relative sea level rise serve as background rates on which future sea level rise must be superimposed we further employ the geological data to remove the gia component from tide gauge records to estimate a mean 20 th century sea level rise rate for the u s atlantic coast of 1 8 0 2 mm a 1 similar to the global average however we fia distinct spatial trend in the rate of 20 th century sea level rise increasing from maine to south carolina this is the fi rst evidence of this phenomenon from observational data alone we suggest this may be related to the melting of the greenland ice sheet and or ocean steric effects

signature of the atlantic meridional overturning circulation in sea level along the east coast of north america in this letter we examine the relationship between the north atlantic meridional overturning circulation moc and sea level sl along the east coast of north america in the eddy permitting ocean model occam we find a distinctive topography following pattern of sl variability in the western north atlantic that is closely linked with the changing strength of the moc with a 2 cm drop in sl along the us east coast corresponding to a 1sv increase in the moc we find a similar pattern of sl variability in the altimetry record and show that this meridionally coherent sl mode dominates interannual sl variability at tide gauges along the north american east coast between 40 50n hence we conclude that north american coastal sea level may indeed be a useful indicator of moc variability on interannual timescales allowing an observationally based estimate of the likely range of interannual moc fluctuations to be determined citation bingham r j and c w hughes 2009 signature of the atlantic meridional overturning circulation in sea level along the east coast of north america geophys res lett 36 l02603 doi 10 1029 2008gl036215

reconciling two alternative mechanisms behind bi decadal variability in the north atlantic understanding the preferential timescales of variability in the north atlantic usually associated with the atlantic meridional overturning circulation amoc is essential for the prospects for decadal prediction however the wide variety of mechanisms proposed from the analysis of climate simulations potentially dependent on the models themselves has stimulated the debate of which processes take place in reality one mechanism receiving increasing attention identified both in idealized models and observations is a westward propagation of subsurface buoyancy anomalies that impact the amoc through a basin scale intensification of the zonal density gradient enhancing the northward transport via thermal wind balance in this study we revisit a control simulation from the institut pierre simon laplace coupled model 5a ipsl cm5a characterized by a strong amoc periodicity at 20 years previously explained by an upper ocean atmosphere sea ice coupled mode driving convection activity south of iceland our study shows that this mechanism interacts constructively with the basin wide propagation in the subsurface this constructive feedback may explain why bi decadal variability is so intense in this coupled model as compared to others

post middle miocene rotations recorded in the bourg d oisans area western alps france by paleomagnetism abstract in order to test the occurrence of post metamorphic rotations or tiltings a paleomagnetic study was undertaken in 44 sites from the inverted half graben of bourg d oisans zone dauphinoise western alps the magnetization carried by pyrrhotite was acquired after metamorphic culmination around the oligo miocene limit no obvious rotations around a vertical axis are recorded instead the dispersion of paleomagnetic data is interpreted as due to a variable tilting around a horizontal n20e axis consistent with structural observations this gentle folding in the sedimentary cover is probably associated with thrusting of the belledonne external crystalline massif over the foreland basement the age of the tiltings reported in this paper is estimated as being younger than 9 13 ma

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

observed interannual variability of the atlantic meridional overturning circulation at 26 5 n the atlantic meridional overturning circulation moc plays a critical role in the climate system and is responsible for much of the heat transported by the ocean a mooring array nomianally at 26 circ n between the bahamas and the canary islands deployed in apr 2004 provides continuous measurements of the strength and variability of this circulation with seven full years of measurements we now examine the interannual variability of the moc while earlier results highlighted substantial seasonal and shorter timescale variability there had not been significant interannual variability the mean moc from 1 apr 2004 to the 31 march 2009 was 18 5 sv with the annual means having a standard deviation of only 1 0 sv from 1 april 2009 to 31 march 2010 the annually averaged moc strength was just 12 8 sv representing a 30 decline this downturn persisted from early 2009 to mid 2010 we show that the cause of the decline was not only an anomalous wind driven event from dec 2009 mar 2010 but also a strengthening of the geostrophic flow in particular the southward flow in the top 1100 m intensified while the deep southward return transport particularly in the deepest layer from 3000 5000 m weakened this rebalancing of the transport from the deep overturning to the upper gyre has implications for the heat transported by the atlantic

modeling ocean heat content changes during the last millennium 1 observational studies show a significant increase in ocean heat content over the last half century herein we estimate heat content changes during the last millennium with a climate model whose forcing terms have been best fit to surface proxy data the model simulates the observed late 20th century ocean heat content increase and a comparable little ice age minimum when glacial advances are factored in these results imply a sea level fall after the middle ages that is consistent with some geologic data the present ocean heat content increase can be traced back to the mid 19th century with a near linear rate of change during the 20th century

time temperature relations for the remagnetization of pyrrhotite fe7s8 and their use in estimating paleotemperatures abstract paleotemperature controls the maturation of coal and hydrocarbons in sedimentary basins and is also important in determining paleogeothermal gradient and hence tectonic style in exhumed metamorphic terrains one method of estimating paleotemperature analyses the partial remagnetization of a rock due to heating in thick volcanic or sedimentary sequences over subcrustal heat sources such as plumes or at convergent plate margins the overprinted natural remanent magnetization nrm of a rock records both the age and the paleotemperature of remagnetization but a temperature correction from laboratory to geological time scales is required using theoretical time temperature relations time temperature relations are well known for magnetite fe 3 o 4 but are reported here for the first time for pyrrhotite fe 7 s 8 another common nrm carrier data for each mineral separately yield independent estimates of paleotemperature if geologically reasonable estimates of heating time can be made paleotemperature can be estimated without geological input if data for both minerals are combined together with the age of remagnetization determined from the paleomagnetic pole of the nrm overprint these paleotemperature estimates can be used to infer the history of heating and uplift following burial as a test case we examine thermally acquired nrm overprints carried by pyrrhotite fe 7 s 8 and magnetite fe 3 o 4 in the milton monzonite of southeastern australia these overprints record a heating event about 100 ma ago probably thermal doming prior to rifting of the tasman sea that upgraded coal rank in the sydney basin extrapolating from laboratory to geological times using the new time temperature contours for pyrrhotite we estimate that the presently exposed sydney basin in the vicinity of the milton monzonite was remagnetized by heating to 165 30 c for 100 ka assuming a paleogeothermal gradient of 70 c km appropriate for young or incipient rifts the depth of burial at the time of remagnetization is estimated to have been 2 3 0 4 km this figure is in excellent agreement with independent estimates based on reflectance data for the coal accessory mineral vitrinite

multiproxy evidence of holocene climate variability from estuarine sediments eastern north america water temperature estimated from ostracode mg ca ratios the results indicate a much drier early holocene in which mean paleosalinity was 28 ppt in the northern bay falling 25 to 20 ppt during the late holocene early holocene mg ca derived temperatures varied in a relatively narrow range of 13 to 16 c with a mean temperature of 14 2 c and excursions above 16 c the late holocene was on average cooler mean temperature of 12 8 c in addition to the large contrast between early and late holocene regional climate conditions multidecadal 20 40 years salinity and temperature variability is an inherent part of the region s climate during both the early and late holocene including the medieval warm period and little ice age these patterns are similar to those observed during the twentieth century caused by nao related processes comparison of the midlatitude chesapeake bay salinity record with tropical climate records of intertropical convergence zone fluctuations inferred from the cariaco basin titanium record suggests an anticorrelation between precipitation in the two regions at both millennial and centennial timescales

metamorphic control of the magnetic mineralogy of black shales in the swiss alps toward the use of magnetic isogrades abstract the magnetic susceptibility of the helvetic jurassic black shales sampled around the aar and gothard massifs in the swiss alps is due to iron bearing silicates magnetite or pyrrhotite it exhibits a clear correlation with the alpine metamorphism from zeolite to amphibolite facies it firstly decreases due to the breakdown of original magnetite then sharply increases when pyrite is transformed into magnetic pyrrhotite using numerous field measurements of the susceptibility it was possible to carry out a fast and precise mapping of the pyrrhotite in isograde which appears to correspond closely to the stilpnomelane out isograde the matrix susceptibility obtained by means of high field measurements with a cryogenic magnetometer is due to iron bearing silicates and shows only smooth variations with metamorphism both monoclinic and hexagonal pyrrhotites are observed in the high grade area

the medieval climate anomaly and little ice age in chesapeake bay and the north atlantic ocean abstract a new 2400 year paleoclimate reconstruction from chesapeake bay cb eastern us was compared to other paleoclimate records in the north atlantic region to evaluate climate variability during the medieval climate anomaly mca and little ice age lia using mg ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation driven estuarine hydrography results show that warmest temperatures in cb reached 16 17 c between 600 and 950 ce common era centuries before the classic european medieval warm period 950 1100 ce and peak warming in the nordic seas 1000 1400 ce a series of centennial warm cool cycles began about 1000 ce with temperature minima of 8 to 9 c about 1150 1350 and 1650 1800 ce and intervening warm periods 14 15 c centered at 1200 1400 1500 and 1600 ce precipitation variability in the eastern us included multiple dry intervals from 600 to 1200 ce which contrasts with wet medieval conditions in the caribbean the eastern us experienced a wet lia between 1650 and 1800 ce when the caribbean was relatively dry comparison of the cb record with other records shows that the mca and lia were characterized by regionally asynchronous warming and complex spatial patterns of precipitation possibly related to ocean atmosphere processes

an aerial view of 80 years of climate related glacier fluctuations in southeast greenland both marine and land terminating glaciers in southeast greenland have experienced dramatic recent retreat an 80 year record of historical aerial photographs and satellite imagery shows that many land terminating glaciers in this region retreated more rapidly in the 1930s than today whereas marine terminating glaciers have retreated faster in the 2000s

salt marsh erosion associated with hurricane landfall in southern new england in the fifteenth and seventeenth centuries lithostratigraphic and radiocarbon data from the inland section of pattagansett river marsh connecticut show that this sheltered part of the salt marsh underwent significant erosion twice during the past 600 yr each time followed by rapid and complete infilling of the eroded space with tidal mud and low marsh and high marsh peat we argue that the erosion cannot be attributed to increases in tidal prism or to lateral migration of tidal channels the 2 age range a d 1390 1470 for the first low marsh growth in the older regressive sequence agrees well with the age range a d 1400 1440 for a hurricane deposit 60 km to the east the younger regressive sequence is dated with the greatest probability to the period a d 1640 1670 i e shortly after the hurricanes of a d 1635 and 1638 our conclusion that the most likely cause of the erosion was hurricane activity is relevant to paleostorm research and the study of marsh sensitivity to and recovery from storm erosion

thermochronometry and cooling rates deduced from single sample records of successive magnetic polarities during uplift of metamorphic rocks in the alps france summary pyrrhotite bearing metamorphic calcschists from the western alps very probably carry a trm acquired during slow cooling of the unit during the late tertiary sequences of successive polarities have been recorded and can be unravelled by very detailed thermal demagnetization polarity versus temperature profiles on single samples are compared to the polarity time scale allowing on a statistical basis the estimation of a cooling rate of soocmyr at the time of trm acquisition 20 25 ma low apparent palaeointensities i0 pt are estimated by comparison with artificial trm

using foraminiferal transfer functions to produce high resolution sea level records from salt marsh deposits maine usa quantitative analyses of foraminiferal distributions along the coast of maine are used to provide transfer functions for reconstruction of sea level changes from fossil foraminiferal assemblages the indicative meaning of fossil assemblages is most accurately predicted by a training set that incorporates live and dead foraminifera and that uses flooding duration not height as the predictor variable sea level records are produced for two sites in maine usa a middle marsh site in scarboro and a high marsh site in machiasport these records offer temporal resolution of five to seven years and span the past century they are compared with instrumental data from a nearby tidal station to assess their accuracy strong correlations are found between the geologic records and the observational data in particular between the foraminiferal record from machiasport and the tide gauge record from eastport r2 0 83 p 0 005 thus a foraminifera based transfer function approach offers great potential for reso