variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

influence of sea ice on the thermohaline circulation in the arctic north atlantic ocean a fully prognostic coupled ocean ice model is used to study the sensitivity of the overturning cell of the arctic north atlantic system to sea ice forcing the strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the arctic to the greenland sea and further to the subpolar gyre the model produces a 2 3 sv increase of the meridional circulation cell at 25n at the simulation year 15 corresponding to a decrease of 800 km in the sea ice export from the arctic previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic implying that sea ice induced variability in the overturning cell can reach 5 6 sv from peak to peak

detecting holocene changes in thermohaline circulation throughout the last glacial cycle reorganizations of deep ocean water masses were coincident with rapid millennial scale changes in climate climate changes have been less severe during the present interglacial but evidence for concurrent deep ocean circulation change is ambiguous

paleoceanography of the barents sea during the holocene 1 we measured the oxygen isotopic composition of planktonic and benthic foraminifera in three cores collected at key positions to reconstruct the paleoceanography of the barents sea core asv 880 on the path of the northern branch of atlantic water inflowing from the arctic ocean core asv 1200 in the central basin near the polar front and core asv 1157 in the main area of brine formation modern seawater 18o measurements show that far from the coast 18o variations are linearly linked to the salinity changes associated with sea ice melting the foraminifer 18o records are dated by 14c measurements performed on mollusk shells and they provide a detailed reconstruction of the paleoceanographic evolution of the barents sea during the holocene four main steps were recognized the terminal phase of the deglaciation with melting of the main glaciers which were located on the surrounding continent and islands the short thermal optimum from 7 8 ka b p to 6 8 ka b p a cold mid holocene phase with a large reduction of the inflow of atlantic water and the inception of the modern hydrological pattern by 4 7 ka b p brine water formation was active during the whole holocene the paleoclimatic evolution of the barents sea was driven by both high latitude summer insolation and the intensity of the atlantic water inflow

late holocene hydroclimate variability in costa rica signature of the terminal classic drought and the medieval climate anomaly in the northern tropical americas abstract in the northern tropical americas neotropics notable hydrological variability has been documented in multi proxy paleoclimate records between 600 and 1200 ce this interval generally overlaps with the maya terminal classic drought tcd 770 1100 ce and the medieval climate anomaly mca 950 1250 ce there is however limited paleoclimate data that provide reliable estimates of terrestrial thermal variability in southern central america during this time in this study we present chironomid based temperature reconstructions developed from sediment cores from two lakes 1 lago morrenas 3c a high elevation glacial lake located on the crest of the atlantic slope of the cordillera talamanca costa rica and 2 laguna zoncho a mid elevation lake located on the pacific slope in southern costa rica distinctive shifts in the chironomid assemblages occurred at both sites between 610 and 1230 ce these changes are inferred to reflect an 600 year interval characterized by depressed mean annual temperatures at lago morrenas 3c and dry conditions and lake level decline at laguna zoncho taken together the multi proxy paleoclimate records from these two lakes including stable carbon isotope 13c and charcoal data suggest that middle elevations on the pacific slope and high elevations on the atlantic slope of costa rica experienced sustained drought and possible cooling coeval with the tcd mca interval the timing of hydroclimate variability in these records provides support for the hypothesis that cooling and drought in the northern tropical americas during the tcd and early mca were linked to thermal changes in the tropical north atlantic

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

influence of ocean circulation and benthic exchange on deep northwest atlantic nd isotope records during the past 30 000 years neodymium nd isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance to better constrain the controls of water mass provenance and nonconservative effects on the archived nd isotope signal we present a new depth transect of nd isotope reconstructions from the blake bahama outer ridge along the north american continental margin covering the past 30 ka we investigated five sediment cores that lie directly within the main flow path of the deep western boundary current a major advection route of north atlantic deep water we found offsets between core tops and seawater nd isotopic compositions that are observed elsewhere in the northwest atlantic a possible explanation for this is the earlier suggested redistribution of sediment by nepheloid layers at intermediate as well as abyssal depths transporting material downslope and along the continental margin these processes potentially contributed to nd isotope excursions recorded in northwest atlantic sediment cores during the bolling allerod and early holocene an atlantic wide comparison of nd isotope records shows that the early holocene excursions had an additional contribution from conservative advection of unradiogenic dissolved nd nevertheless the trends of the nd isotope records are in general agreement with previous reconstructions of water mass provenance from the entire atlantic and also reveal millennial scale changes during the last deglaciation in temporal high resolution which have rarely been reported before further the new records confirm that during cold periods the northwest atlantic was bathed by an increased contribution of southern sourced water

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

multidecadal climate variability in the greenland sea and surrounding regions a coupled model simulation pronounced oscillations of ocean temperature and salinity occur in the greenland sea in a 2000 year integration of a coupled ocean atmosphere model the oscillations involving both the surface and subsurface ocean layers have a timescale of approximately 40 80 years and are associated with fluctuations in the inten sity of the east greenland current the greenland sea temperature and salinity variations are preceded by large scale changes in near surface salinity in the arctic which appear to propagate out of the arctic through the east greenland current these anomalies then propagate around the subpolar gyre into the labrador sea and the central north atlantic these oscillations are coherent with previously identified multi decadal fluctuations in the intensity of the north atlantic thermohaline circula tion the oscillations in the g eenland sea are related to atmospheric variability negative cold anomalies of surface air temperature are associated with negative cold sea surface temperature sst anomalies in the greenland sea with amplitudes up to 2oc near green land declining to several tenths of a degree c over north western europe the c01d sst anomalies and intensified east greenland current are also associated with enhanced northerly winds over the greenland sea

risk and resilience in the late glacial a case study from the western mediterranean abstract the period spanning the last glacial maximum through early holocene encompasses dramatic and rapid environmental changes that offered both increased risk and new opportunities to human populations of the mediterranean zone the regional effects of global climate change varied spatially with latitude topography and distance from a shifting coastline and human adaptations to these changes played out at these regional scales to better understand the spatial and temporal dynamics of climate change and human social ecological technological systems or sets during the transition from full glacial to interglacial we carried out a meta analysis of archaeological and paleoenvironmental datasets across the western mediterranean region we compiled information on prehistoric technology land use and hunting strategies from 291 archaeological assemblages recovered from 122 sites extending from southern spain through mediterranean france to northern and peninsular italy as well as 2 386 radiocarbon dates from across this region we combine these data on human ecological dynamics with paleoenvironmental information derived from global climate models proxy data and estimates of coastlines modeled from sea level estimates and digital terrain the lgm represents an ecologically predictable period for over much of the western mediterranean while the remainder of the pleistocene was increasingly unpredictable making it a period of increased ecological risk for hunter gatherers in response to increasing spatial and temporal uncertainty hunter gatherers reorganized different constituents of their sets allowing regional populations to adapt to these conditions up to a point beyond this threshold rapid environmental change resulted in significant demographic change in mediterranean hunter gatherer populations

influence of paleotopography base level and sedimentation rate on estuarine system response to the holocene sea level rise the example of the marais vernier seine estuary france the response of coastal systems to allogenic forcing factors is of interest to diverse research communities including those interested in global change sequence stratigraphy and modelling quaternary systems are of particular interest because they provide analogues for ancient rock records to understand the processes responsible for the sedimentary evolution of estuarine systems it is necessary to study as many fluvial systems as possible the objective of this review of the sedimentary evolution of a coastal marsh is to describe the influence of glacial paleotopography on the record of climatic and sea level changes the marais vernier located at the interface between the marine and fluvial parts of the estuary is a part of the lower seine valley wetland network which formed after the last glacial maximum previous studies have described the holocene filling which is composed of peat and detrital material deposited following climatic and sea level changes to understand the sedimentary evolution a paleotopographical based on drillings and electromagnetic surveys and a chronological framework based on radiocarbon dates for the southern peat marsh were defined the peat marsh paleotopography has three erosional surfaces the s1 surface is the oldest and also the highest topographically the s2 surface is younger wider and incised below the s1 surface the s3 surface the youngest of the three is narrow and deeply incised radiometric ages were considered on the basis of their geographical position in relation to the s3 surface prior to 7 5 ka cal bp sediments accumulated only above the narrow area described by the s3 surface at a rate of 5 5 mm yr 1 after 7 5 ka cal bp shortly after the flooding of the seine estuary sediments accumulated as peat deposits over the entire peat marsh at a rate of 3 mm yr 1 in response to the sea level rise the paleotopography delimits the area of deposition during the holocene and thus plays a critical role in determining the vertical accretion rate expressed as a thickness prior to 7 5 ka cal bp the vertical accretion rate 5 5 mm yr 1 was less than that observed for the seine estuary 6 8 mm yr 1 however rate of sea level rise and sediment supply which also affects sediment accumulation rates vary in northwestern europe during the holocene therefore although the marais vernier is a good illustration of paleotopographic influence the effects of autocompaction sea level and sediment supply complicate efforts to quantify the degree to which it controls sediment accumulation

cold event at 8200 yr b p recorded in annually laminated lake sediments in eastern europe a quantitative annual mean temperature reconstruction from an annually laminated lake sediment sequence in estonia eastern europe shows a distinct cold period at 8400 8080 yr b p before a d 2000 the timing is consistent with that seen in the greenland ice core data and various high resolution records from western europe during maximal cooling at 8250 8150 yr b p the annual mean temperature in estonia was 2 0 c colder than prior to and 3 0 c colder than after the cooling the pollen stratigraphic and sedimentological data suggest especially cold and snowy winter conditions the duration and amplitude of the cold event agree with the modeled impact of a sudden freshening of the north atlantic surface water and subsequent perturbation of the thermohaline circulation provided that the cold event was caused by a pulse of freshwater from the melting laurentide ice sheet to the north atlantic the results indicate a strong teleconnection between the north atlantic oceanic forcing and the east european climate at least up to long 26 e mediated probably by the changing intensity of the zonal atmospheric circulation

model data comparison for the 8 2 ka bp event confirmation of a forcing mechanism by catastrophic drainage of laurentide lakes abstract to improve our understanding of the mechanism behind the 8 2 ka bp cooling event we compare proxy evidence with climate model simulations in which the thermohaline ocean circulation is perturbed by a freshwater pulse into the labrador sea both the proxy data and model results show a cooling that is mainly concentrated in the north atlantic region ranging from more than 5 c cooling in the nordic seas to about 0 5 1 c over europe and less than 0 5 c over the subtropical north atlantic data and model also indicate a weakening of the summer monsoon and generally a drier circum north atlantic over the south atlantic ocean the model simulates a slight warming mostly less than 0 5 c which falls within the uncertainty of proxy data and thus could not be confirmed to examine in detail the structure of the 8 2 ka bp event we also compare the modeled climatological evolution at two locations with high quality records revealing a generally consistent picture the good model data agreement confirms the hypothesis that the 8 2 ka bp event was forced by a freshwater induced weakening of the thermohaline circulation other forcings are unlikely since they would result in an alternative geographical distribution and expression of the climate response

millennial scale climatic cycles in the early pliocene pollen record of ptolemais northern greece early pliocene lacustrine sediments from the ptolemais basin northern greece exhibit a climatically induced cyclicity which can be correlated with the orbital cycle of precession superimposed on precession controlled cycles palynological time series data reveal a higher order climatic cyclicity with periodicities of 10 2 5 and 1 5 ka these millennial scale vegetation changes are likely to reflect changes of the soil moisture gradient on mountain slopes caused by fluctuations in orographic winter precipitation such fluctuations corroborate the concept of a nao like north atlantic climatic teleconnection during early pliocene times the periodicities are similar to those of climate oscillations inferred from quaternary records the occurrence of millennial scale cyclicity in a time interval when the northern hemisphere was essentially ice free implies an ultimate forcing mechanism that operated independently of changes in the thermohaline circulation in the atlantic ocean the cycles are likely to be related to long period variations in solar activity

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

little ice age cold interval in west antarctica evidence from borehole temperature at the west antarctic ice sheet wais divide 1 the largest climate anomaly of the last 1000 years in the northern hemisphere was the little ice age lia from 1400 1850 c e but little is known about the signature of this event in the southern hemisphere especially in antarctica we present temperature data from a 300 m borehole at the west antarctic ice sheet wais divide results show that wais divide was colder than the last 1000 year average from 1300 to 1800 c e the temperature in the time period 1400 1800 c e was on average 0 52 0 28 c colder than the last 100 year average this amplitude is about half of that seen at greenland summit grip this result is consistent with the idea that the lia was a global event probably caused by a change in solar and volcanic forcing and was not simply a seesaw type redistribution of heat between the hemispheres as would be predicted by some ocean circulation hypotheses the difference in the magnitude of the lia between greenland and west antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions

the holocene labrador current changing linkages to atmospheric and oceanographic forcing factors the role of labrador current lc in providing freshwater to the north atlantic and hence modulating the atlantic meridional overturning circulation amoc has been debated with very few data this study provides the first data on the relative speed of the lc for the past 9 2 ka using mean size of the sortable silt of sediments as a proxy from a mid shelf basin in the western labrador sea lc speed progressively intensified from 9 2 5 ka during which two meltwater events had minor influence the lc was fastest between 5 ka and 3 1 ka and gradually weakened after 3 1 ka the mean size of the sortable silt data shows overall co variations with similar existing data from deep water areas of the greater north atlantic suggesting an overarching link that modulates changes in both the near surface and deep north atlantic a dynamical link between the lc and amoc vigor is hypothesized in which high meltwater discharge in the labrador sea oriented the subpolar gyre spg more north south meridional weakening the spg and thus decelerating the upper limb of the amoc conversely reduction in lc transport during the late holocene due to the greater export of sea ice oriented the spg more east west

insights on the events surrounding the final drainage of lake ojibway based on james bay stratigraphic sequences abstract deglaciation of the james bay region was highly dynamic with the occurrence of ice cochrane readvances into glacial lake ojibway around final deglaciation time which culminated with the drainage of ojibway waters into hudson bay and subsequent incursion of the tyrrell sea at 8 ka renewed interest on these events comes from the possible link between the drainage of the ice dammed lake agassiz ojibway and a major climate deterioration known as the 8 2 ka cooling event recent glaciological modeling suggests that this drainage may have occurred subglacially a mechanism that can accommodate more than one lake discharge as suggested by marine records the exact number and timing of drainage events as well as location of the lake discharge pathway s remain however largely unconstrained here we focus on the events that led to the drainage of lake ojibway by documenting late glacial sedimentary sequences located east of james bay our investigations indicate that the deglacial sequence consists of a readvance till extensive ojibway rhythmites and thick marine sediments the glaciolacustrine and marine units are separated by a 60 cm thick horizon composed of laminated silt beds containing rounded clay balls and disseminated clasts resulting from the abrupt drainage of the lake radiocarbon dating of marine fossils lying above the drainage horizon indicates that the glaciolacustrine episode ended around 8128 8282 cal yr bp micropaleontological analyses reveal that freshwater ostracods candona sp and marine microfossils foraminifers dinocysts occur together in the upper part of the ojibway sediments analysis of oxygen isotopes 18 o of ostracods and foraminifers originating from the same stratigraphic position show highly contrasting values that suggest possible subglacial exchanges between lake ojibway and tyrrell sea waters prior to the final drainage event the complexity of the deglacial events is further indicated by radiocarbon dating of marine shells retrieved from a cochrane till that suggests that the last ice readvance occurred almost simultaneously with the final lake discharge these results bring additional constraints on the drainage mechanism of the coalesced lake agassiz ojibway and indicate that the james bay region formed an important drainage pathway for meltwaters at the end of the last deglaciation

late holocene variability of upper north atlantic deep water temperature and salinity 1 magnesium calcium ratios in benthic foraminifera cibicidoides pachyderma from a sediment core on the laurentian slope 1854 m exhibit strong millennial scale fluctuations during the past 4000 years we convert these data to seawater paleotemperatures using a new monospecific linear equation results suggest that the temperature of upper north atlantic deep water dominated by labrador seawater today has varied by at least 2 c during the late holocene millennial scale coolings coincide with previously identified periods of increased drift ice and regional glacier advances including the little ice age paired oxygen isotope measurements indicate that salinity and perhaps density were reduced during the cold periods we discuss possible mechanisms for transmitting this cold fresh signal from surface waters to intermediate depths our reconstructed late holocene ranges in upper north atlantic deep water properties greatly exceed those of the instrumental record and imply that large changes may be yet to come

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

variability in temperature and geometry of the norwegian current over the past 600 yr stable isotope and grain size evidence from the norwegian margin core p1 003mc was retrieved from 851 m water depth on the southern norwegian continental margin close to the boundary between the norwegian current nc and the underlying cold norwegian sea deep water the core chronology was established by using 210pb measurements and 14c dates suggesting a sampling resolution of between 2 and 9 yr sea surface temperature sst variations in the nc are reconstructed from stable oxygen isotope measurements in two planktonic foraminifera species neogloboquadrina pachyderma d and globigerina bulloides the high temporal resolution of the sst proxy records allows direct comparison with instrumental ocean temperature measurements from ocean weather ship ows mike in the norwegian sea and an air temperature record from the coastal island ona western norway the comparison of the instrumental and the proxy sst data suggests that n pachyderma d calcify during summer whereas g bulloides calcify during spring the 18o records of both species suggest that the past 70 yr have been the warmest throughout the past 600 yr the spring and summer proxy temperature data suggest differences in the duration of the cold period of the little ice age the spring temperature was 1 3 c colder throughout most of the period between ca ad 1400 and 1700 and the summer temperature was 1 2 c colder throughout most of the period between ca ad 1400 and 1920 fluctuations in the depth of the lower boundary of the nc have been investigated by examining grain size data and benthic foraminiferal assemblages the data show that the transition depth of the lower boundary of the nc was deeper between ca ad 1400 and 1650 than after ca ad 1750 until present copyright 2003 john wiley sons ltd

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

climate connections between the hemisphere revealed by deep sea sediment core ice core correlations abstract correlation of southern ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean s thermohaline circulation over the last 80 000 years our observations suggest that while north atlantic deep water variability manifests itself clearly in southern ocean nutrient proxy records over periods as short as 500 yr this deep water variability did not promote a direct link between climate variability in the high latitudes of the two hemispheres on millennial timescales in particular the proxy records indicate that on average northern hemisphere climate fluctuations lagged those of the southern hemisphere by 1500 yr

early middle pleistocene deep circulation in the western subtropical atlantic southern hemisphere modulation of the north atlantic ocean early middle pleistocene climate and deep ocean hydrography have been reconstructed using oxygen and carbon isotope ratio measurements in planktonic and benthic foraminifera from a high deposition rate sedimentary succession recovered at the bermuda rise in the northern sargasso sea ocean drilling program leg 172 site 1063 the site s water depth makes it sensitive to changes in the balance between north atlantic deep water nadw and antarctic bottom water aabw in the deep north atlantic allowing the evaluation of perturbations in deep water production at different timescales millennial scale fluctuations superimposed on the longer period oscillations of orbital origin occurred during all the observed climate states the highest amplitude sub milankovitch fluctuations were mainly associated with interglacials particularly after the intensification of the glacial regime at c 900 ka using the benthic carbon isotope signal as a water mass tracer and by comparing the delta 13c record to a suite of drill sites in the north atlantic and pacific oceans it has been possible to infer that the relative strength of aabw production varied through time as did that of nadw a scenario in which the two different source components of deep water can undergo dramatic changes in their circulation regime through time should be taken into consideration when evaluating the role of thermohaline circulation in global climate change

solar forcing of climatic change during the mid holocene indications from raised bogs in the netherlands two cores of mid holocene raised bog deposits from the netherlands were 14 c wiggle match dated 14 c as a proxy for changes in solar activity is validated this paper adds to the increasing body of evidence that solar variability forced climatic changes during the holocene 14 c wiggle match dating mid holocene wet shifts

sea level variability in the northwest atlantic during the past 1500 years a delayed response to solar forcing 1 numerical experiments with a coupled oceanatmosphere model ecbilt have shown that centennial variations in sea level sl in the northwest atlantic may be associated with deep ocean salinity anomalies generated by solar forced variations in the north atlantic overturning circulation here we compare simulated sl curves for the gulf stream region with reconstructed late holocene sl records from connecticut usa simulated sl variations lag the solar forcing record by ca 120 year this lag is found to be robust over a small number of different experiments the reconstructed sl curves visually match the solar forcing optimally when lagging it by ca 125 yr a quantitative test shows that the correlation is significant while this result is not sensitive to dating uncertainties the temporal response pattern of the simulated sl curves compares reasonably well with the reconstructions index terms 4556 oceanography physical sea level variations 1650 global change solar variability 4255 oceanography general numerical modeling 4267 oceanography general paleoceanography 3030 marine geology and geophysics micropaleontology citation van de plassche o g van der schrier s l weber w r gehrels and a j wright sea level variability in the northwest atlantic during the past 1500 years a delayed response to solar forcing geophys res lett 30 18 1921 doi 10 1029 2003gl017558 2003

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

bipolar changes in atmospheric circulation during the little ice age annually dated ice cores from siple dome west antarctica and central greenland indicate that meridional atmospheric circulation intensity increased in the polar south pacific and north atlantic at the beginning 1400 a d of the most recent holocene rapid climate change event the little ice age lia as deduced from chemical concentrations at these core sites the lia was characterized by substantial meridional circulation strength variability and this variability persists today despite strong evidence for an end to lia cooling thus increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

testing the 231pa 230th paleocirculation proxy a data versus 2d model comparison 1 variations of the atlantic meridional overturning circulation amoc are believed to have crucially influenced earth s climate due to its key role in the inter hemispheric redistribution of heat and carbon to assess its past strength the sedimentary 231pa 230th proxy has been developed and improved but also contested due to its sensitivity to other factors beyond ocean circulation in order to provide a better basis for the understanding of the atlantic 231pa 230th system and therefore to shed light on the controversy we compare new measurements of holocene sediments from the north brazilian margin to water column data and the output of a two dimensional scavenging circulation model based on modern circulation patterns and reversible scavenging parameters we show that sedimentary 231pa 230th data from one specific area of the atlantic are in very good agreement with model results suggesting that sedimentary 231pa 230th is predominantly driven by the amoc therefore 231pa 230th represents an appropriate method to reconstruct past amoc at least qualitatively along the western margin

radiocarbon and stable isotope constraints on last glacial maximum and younger dryas ventilation in the western north atlantic 1 foraminiferal abundance 14c ventilation ages and stable isotope ratios in cores from high deposition rate locations in the western subtropical north atlantic are used to infer changes in ocean and climate during the younger dryas yd and last glacial maximum lgm the 18o of the surface dwelling planktonic foram globigerinoides ruber records the present day decrease in surface temperature sst of 4 c from gulf stream waters to the northeastern bermuda rise if during the lgm the modern 18o salinity relationship was maintained this sst contrast was reduced to 2 c with lgm to interglacial 18o changes of at least 2 2 ssts in the western subtropical gyre may have been as much as 5 c colder above 2 3 km glacial 13c was higher than today consistent with nutrient depleted younger bottom waters as identified previously below that 13c decreased continually to 0 5 about equal to the lowest lgm 13c in the north pacific ocean seven pairs of benthic and planktonic foraminiferal 14c dates from cores 2 5 km deep differ by 1100 340 years with a maximum apparent ventilation age of 1500 years at 4250 m and at 4700 m apparent ventilation ages are presently unavailable for the lgm 2 5 km because of problems with reworking on the continental slope when sea level was low because lgm 13c is about the same in the deep north atlantic and the deep north pacific and because the oldest apparent ventilation ages in the lgm north atlantic are the same as the north pacific today it is possible that the same water mass probably of southern origin flowed deep within each basin during the lgm very early in the yd dated here at 11 25 0 25 n 10 conventional 14c kyr bp equal to 12 9 calendar kyr bp apparent ventilation ages 2 3 km water depth were about the same as north atlantic deep water today below 2 3 km four yd pairs average 1030 400 years the oldest apparent ventilation age for the yd is 1600 years at 4250 m this strong contrast in ventilation which indicates a front between water masses of very different origin is similar to glacial profiles of nutrient like proxies this suggests that the lgm and yd modes of ocean circulation were the same

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

coherent deep flow variation in the iceland and american basins during the last interglacial the first direct evidence that the deepflow speed of north atlantic deep water nadw in the south iceland and north americanbasins declined dramatically over a period of a few hundred years at about 120 000 years ago is presented the flow rate inferred from silt grain size then rose into the subsequent cool period stage 5d these changes are clear and synchronous in records from both locations these circulation events are recorded less markedly in chemical and isotopic proxies for the nutrient status of water masses the congruence of flowvariation and hydrography at the two separated sites suggests they are primarily controlled by variation in the deep thermohaline circulation

combining benthic foraminiferal ecology and shell mn ca to deconvolve past bottom water oxygenation and paleoproductivity the mn ca of carbonate tests of living deep sea foraminifera hoeglundina elegans bulimina aculeata uvigerina peregrina and melonis barleeanus were determined together with pore water manganese along a bottom water oxygen gradient across the lower boundary of the arabian sea oxygen minimum zone although mn has long been considered an indicator for contamination new cleaning protocols and high resolution laser ablation icp ms now allow the reliable analyses of test associated mn within locations mn incorporation between species varies as a function of their in sediment depth preferences and associated pore water chemistry under well oxygenated bottom water conditions shallow infaunal species incorporate little mn in their test whereas the species collected from deeper habitats show elevated mn concentrations with decreasing oxygen contents pore water mn concentrations and benthic foraminiferal in sediment distribution change whereas mn ca in shallow infaunal species responds moderately to bottom water oxygenation mn ca of the infaunal species m barleeanus correlates well to oxygenation although high productivity results in a shallower redox cline within the sediment pore water mn is retained as long as the bottom water remains oxygenated under reduced bottom water oxygen conditions mn escapes to the overlying water column and test associated mn ca decreases also in the infaunal species by combining pore water chemistry of mn calcitic mn ca and foraminiferal ecology a new conceptual model is presented troxchem3 that provides a framework for deconvolving past organic matter input and bottom water oxygenation

the last 3000 years in the ria de vigo nw iberian margin climatic and hydrographic signals the hydrographic evolution of the r o a de vigo nw spain during the last 3000 years has been reconstructed using benthic foraminiferal assemblages stable oxygen isotopes molecular biomarkers and sea surface temperatures sst reconstructed from the u k9 37 index benthic oxygen isotopes and sst records provide evidence of episodic salinity contrasts between surface and bottom waters the comparison of ssts with other climate records for the northern hemisphere has allowed the inference of oceanographic and climatic signals which describe the changes in hydrographic conditions of the r oa in general two different periods can be recognized from 975 cal bc to cal ad 1000 the organic carbon is mainly of continental origin benthic foraminiferal assemblages are typical of environments that are poorly oxygenated rich in organic matter and dominated by eurihaline taxa percentages of planktonic foraminifera are low and ssts are warmer than today these data suggest a restricted environment where the exchange with open ocean waters was diminished at cal ad 1000 an important hydrographic change in the r oa circulation involved an intensie cation of coastal upwelling processes as ree ected in colder ssts and increases in the contribution of marine organic carbon and planktonic and opportunistic benthic foraminifera in these conditions the sediments of the r oa recorded not only local factors but also several well known northern hemisphere climate signals

a regional 8200 cal yr bp cooling event in northwest europe induced by final stages of the laurentide ice sheet deglaciation the most notable change in 18o in greenland ice cores during the holocene occurs at 8200 cal yr bp here we present a new high resolution marine record from the northern north sea along with tree ring data from germany which contain evidence of a pronounced temperature drop 2 c contemporaneous with that of the greenland ice core records the synchronous timing of the cooling event in the greenland ice cores marine record and tree ring data from northwest europe reflects a regional influence on the north atlantic ocean atmospheric system suggesting a prominent role of the north atlantic thermohaline circulation the operation of the north atlantic ocean circulation is sensitive to variation in the freshwater budget implying that any change in freshwater flux is capable of altering the north atlantic circulation system we hypothesise minor but long term freshwater fluxes in the final stages of the deglaciation of the laurentide ice sheet as a forcing mechanism 1998 john wiley sons ltd

late pleistocene and early holocene glaciations in taiwanese mountains abstract the high mountain range of taiwan is unglaciated at present but numerous glacial landforms and sediments in three mountain massifs the nanhuta shan the hsueh shan and the yushan support the concept of repeated glaciations of these areas during the pleistocene and early holocene optically stimulated luminescence osl data derived from glacial and glacier related sediments suggests a glaciation about 8 9 0 5 ka called the nanhuta glacier advance which could be correlated either to the younger dryas or the global 8 2 ka cooling event alley et al 1997 holocene climatic instability a prominent widespread event 8200 yr ago geology 25 6 483 486 absolute data from pre holocene sediments are still rare although glacial evidence valley shape erratic boulders glacial trimlines and sediments indicates a larger extent of valley glaciers during the pleistocene

a possible 20th century slowdown of southern ocean deep water formation chlorofluorocarbon 11 inventories for the deep southern ocean appear to confirm physical oceanographic and geochemical studies in the southern ocean which suggest that no more than 5 x 10 6 cubic meters per second of ventilated deep water is currently being produced this result conflicts with conclusions based on the distributions of the carbon 14 carbon ratio and a quasi conservative property po 4 in the deep sea which seem to require an average of about 15 x 10 6 cubic meters per second of southern ocean deep ventilation over about the past 800 years a major reduction in southern ocean deep water production during the 20th century from high rates during the little ice age may explain this apparent discordance if this is true a seesawing of deep water production between the northern atlantic and southern oceans may lie at the heart of the 1500 year ice rafting cycle

reconstructing palaeoprecipitation from an active cave flowstone several drill cores were obtained from a laminated actively forming flowstone from a shallow cave in austria highly resolved petrographic and geochemical analyses combined with multi annual cave monitoring reveal a distinct sensitivity of flowstone growth and composition to late holocene meteoric precipitation the regular sub millimetre scale lamination consists of thicker translucent laminae and thinner organic inclusion rich laminae there is also a macroscopic millimetre scale banding of darker and lighter bands comprising several laminae stable isotope analyses of drill cores and modern calcite precipitates show a pronounced positive covariation of 13c and 18o values indicative of kinetic isotope effects comparing the isotope values with petrography shows gradual changes across several of the annual laminae i e changes of several per mille on a multi annual to decadal timescale the stable isotope and trace element composition as well as the flowstone petrography are mainly controlled by the variable drip water discharge controlling the water film thickness and water residence time on the flowstone surface and consequently the intensity of co2 degassing kinetic isotope enrichment and concomitant calcite precipitation drill core pfu6 provides an isotope record of the last ca 3000 years at near annual resolution a distinct phase of low c and o isotope values interpreted as increased discharge and hence higher meteoric precipitation occurred from ca 300 to 140 a b2k second half of the little ice age and another wet interval occurred around 700 a corresponding to reported medieval glacier advances the roman warm period was also dominated by relatively wet conditions although significant decadal variability prevailed increased precipitation further characterized the intervals from ca 2480 to 2430 and 2950 to 2770 a dry conditions persisted during the medieval climate anomaly although this trend towards reduced precipitation started earlier the highest c isotope values of the last 2 ka are recorded around 750 a and another dry phase is centred at 1480 a this new record shows that inter annual to decadal oscillations are a dominant mode of variation during the last 3 ka in the alps copyright 2011 john wiley sons ltd

nd isotope signature of holocene baltic mn fe precipitates as monitor of climate change during the little ice age neodymium nd isotope profiles were analyzed on two baltic mn fe precipitates 99 2 and tl1 from shallow water 20 m of the mecklenburg bay the age range of these mn fe precipitates determined by 226raex ba dating reaches from recent growth back to 4300 and 1000 yr bp respectively over this time range the nd isotope composition varies from end 0 13 1 to 17 5 in the selected baltic precipitates indicating substantial changes in the nd isotope composition of the baltic sea the lowest end values were recorded during the time interval of the little ice age lia ad 1350 to 1850 these minimum values indicate either an increase of the input of less radiogenic nd from scandinavian archean proterozoic sources end about 22 to the baltic sea or a decrease of the input of more radiogenic nd from continental european sources end about 12 and or north sea water end about 10 variations of both erosive continental input and north sea inflow may indicate a direct response of the nd isotope signal in the baltic sea to climate changes during the lia and be related to cyclic shifts in the atmospheric circulation triggered by the north atlantic oscillation nao another aspect that possibly influenced the input of trace elements and nd isotopes into the baltic sea is the population development in the circum baltic area during the lia the lowest end values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland the reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the baltic sea by rivers which in turn may have resulted in a change of the nd isotope composition of baltic sea water

the past climate change heats up research during the past decade has provided a shocking new assessment of the speed with which major climate changes can sweep across our planet the most precise evidence of rapid climate change comes from cores extracted from mountain glaciers and from the larger ice sheets of greenland and antarctica annual layers in the glacial ice provide the chronology and key data on snowfall temperature influx of dust and trace gases from the ancient atmosphere trapped in air bubbles there is ominous evidence that during the past few thousand years earth s climate has been anomalously tranquil compared to its behavior during the preceding hundred thousand years we still live within a glacial interval albeit at a time of glacial recession for more than 3 million years continental glaciers have been expanding and contracting and in a few tens of thousands of years if not stifled by human induced global warming they will once again spread southward to new jersey and the alps

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

late holocene variability in florida current surface density patterns and possible causes 1 planktonic foraminiferal 18o time series from three well dated high sedimentation rate cores near the florida keys 24 4 n 83 3 w exhibit repeated centennial to millennial scale oscillations during the late holocene isotopic shifts of 0 2 0 3 over the past 5200 years represent changes in sea surface temperature sst of 1 0 1 5 c or salinity variability of 1 2 psu the largest significant isotopic events are centered at approximately 200 2000 3200 and prior to 4000 calendar years bp high florida current 18o during the little ice age lia correlates with published records of high 18o in the sargasso sea and low sst off the coast of west africa an interval of generally low 18o in the florida straits from 1800 to 500 years bp is synchronous with the medieval warm period off west africa but leads low 18o in the sargasso sea by several hundred years synchronous cooling across the subtropical gyre during the lia is difficult to explain using interannual north atlantic oscillation patterns but may be consistent with the simulated effects of reduced solar irradiance at frequencies between 1 1000 and 1 300 years during the late holocene florida current 18o is coherent with a published estimate of 14c production rate radiocarbon production seems to lead 18o at these frequencies but uncertainty in the phase calculation precludes a clear lead lag relationship at frequencies lower than 1 300 years florida current 18o is coherent and in phase with atmospheric 14c the coherence of 14c and 18o at periods 1000 years implies oceanic circulation may play a role in modulating atmospheric radiocarbon on millennial timescales

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

catastrophic 1638 earthquakes in calabria southern italy new insights from paleoseismological investigation the reanalyses of all the primary historical sources of the catastrophic march june 1638 calabrian earthquakes permitted to split up the seismic sequence in different events that occurred in conterminous areas and to direct our geological surveys of the june shock inside the sila massif northern calabria we carried out paleoseismological analyses along the lakes fault lf a previously unknown fault lf trending nw se cuts the eastern sector of the sila massif and dips southwestward damming the drainage network that runs toward the ionian sea we opened four trenches close to or inside some of the small marshes and ponds created by the footwall uplift finding evidence of several displacement events the last one being the june 1638 earthquake m 6 7 the fault location fits with the historical description of a long fracture opened during the event our trenching area being still named by the natives the earthquake sag the young geomorphic expression of lf recalls that of the 1980 irpinia fault suggesting its relatively recent activation within the extensional regime characterizing the calabrian arc conversely the northern continuation of lf cecita lake fault which we argue to be active too is not associated to any historical earthquake of the italian seismic catalogue this fact evidencing a long at least 1000 years elapsed time our study permits 1 the relocation of the june 1638 earthquake inside the sila massif the epicenter being shifted with respect to the macroseismically derived one 2 the revision of the whole 1638 sequence 3 the discovery of the lf 4 the recognition of the evidence of the june 1638 surface faulting plus four previous paleoearthquakes and 5 the evaluation of its slip rates and return interval finally the relationship of lf with the neighboring faults casts light to the seismotectonic of the region providing a new insight to the seismic hazard analysis

low frequency and high frequency changes in temperature and effective humidity during the holocene in south central sweden implications for atmospheric and oceanic forcings of climate an integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes here we report a 10 000 year quantitative record of annual mean temperature tann based on pollen climate transfer functions and pollen stratigraphical data from lake flarken south central sweden the pollen based temperature reconstruction is compared with a reconstruction of effective humidity as reflected by a 18o record obtained on stratigraphy of lacustrine carbonates from lake igelsjon c 10 km from lake flarken which gives evidence of pronounced changes in effective humidity the relatively low tann and high effective humidity as reflected by a low evaporation inflow ratio suggest a maritime early holocene climate 10 000 8 300 cal year bp seemingly incompatible with the highly seasonal solar insolation configuration we argue that the maritime climate was due to the stronger than present zonal flow enhanced by the high early holocene sea surface temperatures in the north atlantic the maritime climate mode was disrupted by the abrupt cold event at 8 200 cal year bp followed at 8 000 cal year bp by a stable holocene thermal maximum the latter was characterized by tann values about 2 5 c higher than at present and markedly dry conditions indicative of stable summer time anti cyclonic circulation possibly corresponding with modern blocking anticyclonic conditions the last 4 300 year period is characterized by an increasingly cold moist and unstable climate the results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability generality and interpretability of the palaeoclimatic results further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial scale climate dynamics

surface and deep ocean variability in the northern sargasso sea during marine isotope stage 3 new geochemical proxy data from bermuda rise piston cores reveal ocean and climate conditions in the northern sargasso sea during marine isotope stage 3 using 18o on the planktonic foraminifer globigerinoides ruber we can correlate explicitly with every stadial interstadial change in greenland ice between 32 and 58 ka these data suggest repetitive changes of 4 c in the annual average sea surface temperature sst with maximum cooling comparable to or greater than sst during glacial maximum conditions the extent of sst depression is about the same for typical stadial events and for heinrich events 4 and 5 which we have identified on the bermuda rise by traces of ice rafting benthic foraminiferal 13c decreases during every stadial event consistent with reduced production of the deepest component of north atlantic deep water and shoaling of its interface with antarctic bottom water this interpretation is supported by benthic cd ca data from the climate cycle associated with interstadial 8

depth of activation of sediment by plunging breakers on a steep sand beach abstract field data were collected over a lunar tidal cycle on a meso tidal medium sand estuarine beach in delaware bay usa to document the relationship between wave height and depth of sediment activation in a low wave energy environment dominant energy was at the frequencies of locally generated waves and ocean swell significant wave heights ranged from 0 06 m to 0 52 m periods of locally generated waves averaged 4 0 s during strong onshore winds and 2 6 s during low speed winds waves on the foreshore were always plunging the foreshore maintained a slope of approximately 6 0 throughout the study period mean grain size at mid foreshore was 0 46 mm the greatest net surface elevation change in response to storm erosion and post storm recovery was 0 26 m results confirm previous observations that depths of sediment activation are greater for steeper beaches the spatial variability in depths of activation across the foreshore is comparable to results of tidal cycle studies where the ratio of depth of activation to wave height is great because a large percentage of the foreshore comes under the influence of the breakers the ratio of depth of activation to wave height on the portion of the foreshore that is not transgressed by the breakers is lower and comparable to results of short term investigations provided that the influence of beach slope is considered in the calculation of breaking wave height

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

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

holocene millennial scale productivity variations in the sicily channel mediterranean sea 1 the calcareous nannofossil assemblages of ocean drilling program hole 963d from the central mediterranean sea have been investigated to document oceanographic changes in surface waters the studied site is located in an area sensitive to large scale atmospheric and climatic systems and to high and low latitude climate connection it is characterized by a high sedimentation rate the achieved mean sampling resolution is 70 years that allowed the sicily channel environmental changes to be examined in great detail over the last 12 ka bp we focused on the species florisphaera profunda that lives in the lower photic zone its distribution pattern shows repeated abundance fluctuations of about 10 15 such variations could be related to different primary production levels given that the study of the distribution of this species on the sicily channel seafloor demonstrates the significant correlation to productivity changes as provided by satellite imagery productivity variations were quantitatively estimated and were interpreted on the basis of the relocation of the nutricline within the photic zone led by the dynamics of the summer thermocline productivity changes were compared with oceanographic atmospheric and cosmogenic nuclide proxies the good match with holocene master records as with ice rafted detritus in the subpolar north atlantic and the near 1500 year periodicity suggest that the sicily channel environment responded to worldwide climate anomalies enhanced northern hemisphere atmospheric circulation which has been reported as one of the most important forcing mechanisms for holocene coolings in previous mediterranean studies had a remarkable impact on the water column dynamics of the sicily channel

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

holocene annual mean temperature changes in estonia and their relationship to solar insolation and atmospheric circulation patterns abstract we reconstructed annual mean temperature tann trends from three radiocarbon dated holocene pollen stratigraphies from lake sediments in estonia northern europe the reconstructions were carried out using a north european pollen climate calibration model based on weighted averaging partial least squares regression the cross validated prediction error of the model is 0 89 c and the coefficient of determination between observed modern tann values and those predicted by the model is 0 88 in the reconstruction the holocene thermal maximum htm is distinguishable at 8000 4500 cal yr b p with the expansion of thermophilous tree species and tann on average 2 5 c higher than at present the pollen stratigraphical data reflect progressively warmer and drier summers during the htm analogously with the modern decadal scale climatic variability in north europe we interpret this as an indication of increasing climatic continentality due to the intensification of anticyclonic circulation and meridional air flow post htm cooling started abruptly at around 4500 cal yr b p all three reconstructions show a transient ca 300 years cooling of 1 5 2 0 c at 8600 8000 cal yr b p we tentatively correlate this cold event with the north atlantic 8 2 ka event at 8400 8000 cal yr b p provided that the 8 2 ka event was caused by freshening of the north atlantic surface water our data provide evidence of the climatic and vegetational responsiveness of the boundary of the temperate and boreal zones to the weakening of the north atlantic thermohaline circulation and the zonal energy transport over europe no other cold events of comparable magnitude are indicated during the last 8000 years

regional climate variability in the western subtropical north atlantic during the past two millennia 1 western subtropical north atlantic oceanic and atmospheric circulations connect tropical and subpolar climates variations in these circulations can generate regional climate anomalies that are not reflected in northern hemisphere averages assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long term regional variability we present reconstructions of gulf stream sea surface temperature sst and hydrographic variability during the past two millennia based on the magnesium calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical north atlantic sediment cores reconstructed sst suggests low frequency variability of 1 c during an interval that includes the medieval climate anomaly mca and the little ice age lia a warm interval near 1250 a d is distinct from regional and hemispheric temperature possibly reflecting regional variations in ocean atmosphere heat flux associated with changes in atmospheric circulation e g the north atlantic oscillation or the atlantic meridional overturning circulation seawater d 18 o which is marked by a fresher mca and a more saline lia covaries with meridional migrations of the atlantic intertropical convergence zone the northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking carolina slope and tropical atlantic hydrology

constraining the variability of the atlantic meridional overturning circulation during the holocene there is a converging body of evidence supporting a measurable slowdown of the atlantic meridional overturning circulation amoc as climate warms and northern hemisphere ice sheets inexorably shrink within this context we assess the variability of the amoc during the holocene based on a marine sediment core retrieved from the deep northwest atlantic which sensitively recorded large scale deglacial transitions in deep water circulation while there is a diffuse notion of holocene variability in labrador and nordic seas overturning we report a largely invariable deep water circulation for the last 11 000 years even during the meltwater pulse associated with the 8 2 ka event sensitivity tests along with high resolution 231pa 230th data constrain the duration and the magnitude of possible holocene amoc variations the generally constant baseline during the holocene suggests attenuated natural variability of the large scale amoc on submillennial timescales and calls for compensating effects involving the upstream components of north atlantic deep water

relative sea level change in newfoundland canada during the past 3000 years abstract several processes contributing to coastal relative sea level rsl change in the north atlantic ocean are observed and or predicted to have distinctive spatial expressions that vary by latitude to expand the latitudinal range of rsl records spanning the past 3000 years and the likelihood of recognizing the characteristic fingerprints of these processes we reconstructed rsl at two sites big river and placentia in newfoundland from salt marsh sediment bayesian transfer functions established the height of former sea level from preserved assemblages of foraminifera and testate amoebae age depth models constrained by radiocarbon dates and chronohorizons estimated the timing of sediment deposition during the past 3000 years rsl rose by 3 0 m at big river and by 1 5 m at placentia a locally calibrated geotechnical model showed that post depositional lowering through sediment compaction was minimal to isolate and quantify contributions to rsl from global regional linear regional non linear and local scale processes we decomposed the new reconstructions and those in an expanded global database using a spatio temporal statistical model the global component confirms that 20th century sea level rise occurred at the fastest century scale rate in over 3000 years p 0 999 distinguishing the contributions from local and regional non linear processes is made challenging by a sparse network of reconstructions however only a small contribution from local scale processes is necessary to reconcile rsl reconstructions and modeled rsl trends we identified three latitudinally organized groups of sites that share coherent regional non linear trends and indicate that dynamic redistribution of ocean mass by currents and or winds was likely an important driver of sea level change in the north atlantic ocean during the past 3000 years

palaeo oceanography deepwater variability in the holocene epoch the conversion of surface water to deep water in the north atlantic results in the release of heat from the ocean to the atmosphere which may have amplified millennial scale climate variability during glacial times1 and could even have contributed to the past 11 700 years of relatively mild climate known as the holocene epoch 2 3 4 here we investigate changes in the carbon isotope composition of benthic foraminifera throughout the holocene and find that deep water production varied on a centennial millennial timescale these variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

the 8200 year b p event in the slope water system western subpolar north atlantic 1 stable isotope trace metal alkenone paleothermometry and radiocarbon methods have been applied to sediment cores in the western subpolar north atlantic between hudson strait and cape hatteras to reveal the history of climate in that region over the past 11 kyr we focus on cores from the laurentian fan which is known to have rapid and continuous accumulation of hemipelagic sediment although results among our various proxy data are not always in agreement the weight of the evidence alkenone sea surface temperature sst 18o and abundance of globigerinoides ruber indicates a continual cooling of surface waters over laurentian fan from about 18 c in the early holocene to about 8 c today alternatively mg ca data on planktonic foraminifera indicate no systematic change in holocene sst the inferred long term decrease in sst was probably driven by decreasing seasonality of northern hemisphere insolation two series of proxy data show the gradual cooling was interrupted by a two step cold pulse that began 8500 years ago and lasted about 700 years although this event is associated with the final deglaciation of hudson bay there is no 18o minimum anywhere in the labrador sea yet there is some evidence for it as far south as cape hatteras finally although the 8200 year b p event has been implicated in decreasing north atlantic ventilation and hence widespread temperature depression on land and at sea we find inconsistent evidence for a change at that time in deep ocean nutrient content at 4 km water depth