holocene paleoceanography of the northwest passage canadian arctic archipelago abstract a series of cores box and piston were collected at 2 key locations in lancaster sound cores 2004 804 009 bc and pc and barrow strait cores 2005 804 004 bc and pc in the canadian arctic archipelago to document the evolution of sea surface conditions in the main axis of the northwest passage during the holocene time period reconstruction of sea surface parameters summer temperature and salinity duration of sea ice cover were estimated based on transfer functions using dinoflagellate cyst assemblages as proxy indicators the chronology of these cores is based on calibrated ams 14c dates 210pb analyses and correlations between paleomagnetic secular variations of the geomagnetic field and a predicted spherical harmonic model of the geomagnetic field cals7 k 2 our age models for both cores indicate that 009 pc spans the last 11 100 cal bp while 004 pc encompasses the last 10 800 cal bp calculated sedimentation rates are in the range of 43 140 cm kyr for core 009 pc and 15 118 cm kyr for core 004 pc allowing for a millennial time scale resolution in each core our results indicate relatively harsh conditions in lancaster sound between 10 800 and 9000 cal bp summer temperatures 2 c cooler than at present which we associate with the presence of active ice streams in northernmost baffin bay and a weak west greenland current this is followed by a warming trend up to 3 c higher than present that took place between 8500 and 5500 cal bp which we associate with the holocene thermal maximum and to a large scale atmospheric pattern such as the arctic oscillation operating at the millennial time scale this is concomitant with an increase in the relative abundance of phototrophic dinoflagellate cyst taxa a gradual cooling of sea surface temperature and increased sea ice follow this from 5500 cal bp until the modern period in barrow strait harsh sea surface conditions prevailed from 11 100 to 5500 cal bp with summer temperatures as low as 4 c cooler than at present the warming trend occurred later in this region between 5500 and 1000 cal bp after which a gradual cooling is observed until the modern period the apparent shift or opposite warming trends between lancaster sound and barrow strait after 5500 cal bp could be the result of a change in atmospheric circulation patterns related to a possible shift in the ao mode from ao to ao comparison of ice core 18o record from devon island ice cap and the reconstructed sea surface temperature from core 009 pc suggests a strong atmospheric oceanic coupling throughout the holocene in this area

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

interpretation of fluid inclusions in quartz deformed by weak ductile shearing reconstruction of differential stress magnitudes and pre deformation fluid properties abstract a well developed theoretical framework is available in which paleofluid properties such as chemical composition and density can be reconstructed from fluid inclusions in minerals that have undergone no ductile deformation the present study extends this framework to encompass fluid inclusions hosted by quartz that has undergone weak ductile deformation following fluid entrapment recent experiments have shown that such deformation causes inclusions to become dismembered into clusters of irregularly shaped relict inclusions surrounded by planar arrays of tiny new formed neonate inclusions comparison of the experimental samples with a naturally sheared quartz vein from grimsel pass aar massif central alps switzerland reveals striking similarities this strong concordance justifies applying the experimentally derived rules of fluid inclusion behaviour to nature thus planar arrays of dismembered inclusions defining cleavage planes in quartz may be taken as diagnostic of small amounts of intracrystalline strain deformed inclusions preserve their pre deformation concentration ratios of gases to electrolytes but their h2o contents typically have changed morphologically intact inclusions in contrast preserve the pre deformation composition and density of their originally trapped fluid the orientation of the maximum principal compressive stress 1 at the time of shear deformation can be derived from the pole to the cleavage plane within which the dismembered inclusions are aligned finally the density of neonate inclusions is commensurate with the pressure value of 1 at the temperature and time of deformation this last rule offers a means to estimate magnitudes of shear stresses from fluid inclusion studies application of this new paleopiezometer approach to the grimsel vein yields a differential stress 1 3 of 300 mpa at 390 30 c during late miocene nnw sse orogenic shortening and regional uplift of the aar massif this differential stress resulted in strain hardening of the quartz at very low total strain 5 while nearby shear zones were accommodating significant displacements further implementation of these experimentally derived rules should provide new insight into processes of fluid rock interaction in the ductile regime within the earth s crust

a record of holocene summer climate from a canadian high arctic ice core melt layers in ice cores are formed by melting on the snow pack surface which produces water that percolates down and refreezes in the colder snow layers below melt layers are distinguished by their bubble texture because more ice forms in the snow pack in warm summers than in cool summers the changing concentration with depth of melt layers in snow pits1 2 and ice cores3 5 is an indicator of past summer climate here we report on studies of melt layers in two canadian high arctic surface to bedrock ice cores although changes in elevation of the drill site owing to isostatic depression and uplift may contribute up to 40 of the total climatic signal recorded in the melt layers we interpret their varying concentrations in terms of changing summer temperatures over the past 10 000 years the warmest summers occurred 8 10 kyr ago and the coldest only 150 years ago the summers over the past 100 years have been the warmest for more than 1 000 years but are still not as warm as those of the early holocene the melt layer record is in broad agreement with geological records of glacier retreat during the holocene6 8 indicating that these data also contain information of regional significance

reinterpretation of two diatom species from the west greenland margin thalassiosira kushirensis and thalassiosira antarctica var borealis hydrological consequences abstract two representatives of the planktonic diatom genus thalassiosira commonly associated together in the moderate to high latitude north atlantic ocean are demonstrated to be significantly different in both morphology and autecology thalassiosira antarctica comber var borealis fryxell doucette et hubbard mostly resting spores is a dominant species of the early spring phytoplankton bloom around greenland and in the arctic in most paleoclimatic paleoenvironmental studies of the last decades thalassiosira kushirensis takano resting spores r s have probably been included in t antarctica var borealis the present study of phytoplankton from ctd probes and a single surface sediment sample from a multi core and comparative analyses of piston cores from the west greenland margin show these taxa to be good indicators of environmental and hydrological changes related to the distribution of water masses in the studied area t antarctica var borealis is interpreted as an indicator of northern cold water influx especially increased meltwater input during spring bloom whereas t kushirensis r s appears to be related to temperate waters of atlantic origin and probably reflects reduced meltwater influx and increased ocean forcing an abundance of t kushirensis r s during the little ice age lia is interpreted to reflect an enhanced influence of the west greenland current wgc in this region

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

early preboreal cooling in the nordic seas region triggered by meltwater at the younger dryas preboreal transition a high resolution core from the northeastern norwegian sea reveals a two step warming of sea surface temperatures dated at respectively 10 200 10 000 and 9700 9500 14 c yr b p 11 450 11 350 and 11 150 11 000 cal yr b p warming was interrupted by a period having stable temperatures and a reduction in sea surface salinity and we suggest that this pause in warming was triggered by an increase in freshwater supply that may have hampered the north atlantic heat conveyor the freshwater influx correlates to an atmospheric cooling over both the greenland ice sheet and northwest europe and to cooling of surface temperatures in the nordic seas freshwater may have been supplied from the waning fennoscandian ice sheet

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

8000 year marine record of climate variability and fjord dynamics from southern greenland abstract holocene sediment records of glacio marine environmental and climatic changes from ikersuaq fjord and narsaq sound in southern greenland have been studied the ikersuaq fjord record representing the last c 500 years is dominated by turbidite sedimentation and very high sedimentations rates of up to 1 cm yr the adjacent narsaq sound site on the other hand represents a continuous and more slowly accumulating sedimentation record of the last c 8000 years the narsaq record reveals changes in position and melting rates of glacier termini of the nearby greenland ice sheet from the holocene thermal optimum period terminating at about 5 0 ka to the neoglaciation period during the late holocene from 8 0 ka to 4 8 ka ice rafted debris ird influx progressively became reduced supporting a landward retraction of glacier termini neoglaciation of the region appears to have been initiated at about 4 8 ka with a culmination of ird rain at about 4 6 ka 3 6 ka 2 2 ka 1 0 ka 0 7 ka and 0 5 ka and onward some of these ird events appear to be associated with enhanced melting and glacier instability during warming episodes however at the transition to the little ice age at about 1450 years ad a marked increase in ird influx took place the bottom water of narsaq sound appears to have been dominated by modified irminger water atlantic during most of the holocene bottom current flow was quite sluggish before 3 2 ka whereas the late holocene period appears to have been characterised by three pronounced episodes of increased bottom current velocity and increased calcareous benthic foraminifera productivity the long term climate pattern in the narsaq sound record follows climate changes consistent with patterns of east greenland current variability which is partly related to dominant north atlantic oscillation forcing of wind and ice drift patterns

mid to late holocene hydrological and climatic variability in disko bugt central west greenland diatom and lithological analyses were carried out on two sediment cores from disko bugt and the adjacent kangersuneq fjord west greenland in order to investigate mid to late holocene 6 9 0 7 kyr bp hydrographic and climatic variability while the disko bugt record is found to reflect mainly west greenland current wgc fluctuations that can be linked to north atlantic circulation variability the fjord record appears to be more representative of local climate conditions the records demonstrate that the period of investigation was marked by a late holocene thermal maximum beginning at c 4 8 kyr and ending between 3 5 and 3 1 kyr bp encompassing a colder period between c 4 0 and 3 8 kyr bp an episode of higher surface water temperature is also indicated in disko bugt between 2 2 and 1 5 kyr bp in contrast the record from kangersuneq fjord suggests persisting cooler summer surface waters for this interval interpreted to be attributable to increased meltwater outflow the warming episode recogni

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

foraminiferal reconstruction of mid to late holocene ocean circulation and climate variability in disko bugt west greenland benthic foraminifera from two cores collected from disko bugt a large marine embayment in west greenland are used to investigate hydrographic changes during the mid to late holocene the records document fluctuations in the west greenland current wgc linked to large scale changes in north atlantic circulation and for one core impacts of local climate changes in particular changes in the cold east greenland current egc and the warm more saline irminger current ic influence the wgc and propagate into disko bugt the cores record subsurface warming associated with the holocene thermal maximum htm from c 6 to 5 ka cal bp gradual cooling of wgc from 5 ka cal bp was interrupted by an abrupt warm interval from 3 9 to 3 5 ka cal bp before cooling became more prominent from 3 5 to 2 ka cal bp this cold period corresponds to the well documented northern hemisphere cooling of the neoglacial and we interpret it as reflecting enhanced flux from the egc and reduced ic flux to the wgc in disko b

centennial scale benthic foraminiferal record of late holocene oceanographic variability in disko bugt west greenland a new centennial scale benthic foraminiferal record of late holocene climate variability and oceanographic changes off west greenland disko bugt highlights substantial subsurface water mass changes e g temperature and salinity of the west greenland current wgc over the past 3 6 ka bp benthic foraminifera reveal a long term late holocene cooling trend which may be attributed to increased advection of cold low salinity water masses derived from the east greenland current egc cooling becomes most pronounced from c 1 7 ka bp onwards at this point the calcareous atlantic benthic foraminiferal fauna decrease significantly and is replaced by an agglutinated arctic fauna superimposed on this cooling trend centennial scale variability in the wgc reveals a marked cold phase at c 2 5 ka bp which may correspond to the 2 7 ka bp cooling event recorded in marine and terrestrial archives elsewhere in the north atlantic region a warm phase recognized at c 1 8 ka bp is likely to correspond to the roman warm period and represents the warmest bottom water conditions during the time period of the medieval climate anomaly we observe only a slight warming of the wgc a progressively more dominant cold water contribution from the egc on the wgc is documented by the prominent rise in abundance of agglutinated arctic water species from 0 9 ka bp onwards this cooling event culminates at c 0 3 ka bp and represents the coldest episode of the little ice age gradually increased influence of cold low salinity water masses derived from the egc may be linked to enhanced advection of polar and arctic water by the egc these changes are possibly associated with a reported shift in the large scale north atlantic oscillation atmospheric circulation pattern towards a more frequent negative north atlantic oscillation mode during the late holocene

holocene climate changes in southern greenland evidence from lake sediments a holocene lake sediment record is presented from lake n14 situated on angissoq island 15 km off the main coast of southern greenland the palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica clastic material organic material and sulphur as well as sedimentation rate moss content and magnetic susceptibility a total of 43 radiocarbon dates has ensured a reliable chronology it is argued that varying sediment composition mainly reflects changing precipitation by analogy with the present meteorological conditions in southern greenland holocene climate development is inferred between 11550 and 9300 cal yr bp temperature and precipitation increase markedly but this period is climatically unstable from 9300 yr bp conditions become more stable and a holocene climatic optimum characterised by warm and humid conditions is observed from 8000 to 5000 cal yr bp from 4700 cal yr bp the first signs of a climatic deterioration are observed and from 3700 cal yr bp the climate has become more dry and cold superimposed on the climatic long term trend is climate variability on a centennial time scale that increases in amplitude after 3700 cal yr bp a climatic scenario related to the strength and position of the greenland high pressure cell and the iceland low pressure cell is proposed to explain the holocene centennial climate variability a comparison of the lake n14 record with a terrestrial as well as a marine record from the eastern north atlantic ocean suggests that the centennial climate variability was uniform over large areas at certain times less

late holocene atlantic bottom water variability in igaliku fjord south greenland reconstructed from foraminifera faunas a high resolution record of late holocene subsurface water mass characteristics in outer igaliku fjord south greenland is presented based on benthic foraminifera faunas from core po 243 451 collected from a water depth of 304 m strati cation with atlantic water masses present in the lower part of the water column is suggested to have prevailed during the last 3200 cal years except for a period referred to as the mediaeval warm period mwp during the mwp c ad 885 1235 the outer part of igaliku fjord experienced enhanced vertical mixing and a high hydrodynamic energy level which we ascribe to increasing wind stress through this period corresponding to the period of the norse settlement the transition from the mwp to the little ice age lia shows a two step pattern with a short climatic amelioration around ad 1520 before maximum cooling occurred the intensified wind stress and the overall environmental change are suggested to have contributed to the loss of the norse settlement in greenland periods with strong stratification and marked in uence of atlantic subsurface water masses around 2 6 1 3 ka bp and during the lia are correlated to north atlantic holocene ice rafting events reported by bond et al 1997

holocene climate variability at multidecadal time scales detected by sedimentological indicators in a shelf core nw off iceland a holocene sediment record is presented from the djupall trough situated on the inner shelf northwest of iceland the paleoclimatic development has been interpreted on the basis of mass accumulation rate carbonate content mean grain size sediment petrology and 29 radiocarbon dates the results demonstrate in the early holocene 10 000 8000 cal year bp high sediment accumulation rates attributable to the effect of enhanced sediment mobilisation under influence of a relatively low sea level and remobilisation of glacial sediments on the sparsely vegetated vestfirdir peninsula the data suggest that a general southward displacement of the polar front commenced around 5000 4000 cal year bp a new proxy for holocene climatic variability is presented by the basalt plagioclase ratio in the 63 100 mum fraction high basalt plagioclase values are primarily related to periods of increased storminess and bottom current energy which enhanced the transport of basaltic sediment from the coastal zone towards the outer shelf advection of polar waters containing basalt rich ird from the eastern greenland blosseville kyst basalt province may also have contributed to increased basalt plagioclase ratios the correlation between basalt plagioclase ratios and proxies of solar activity c 14 production and be 10 flux was explored and suggests that some of the centennial scale peaks in colder climate could be related to increased nuclide production in the upper atmosphere in addition it was found that the medieval warm period c 1100 700 cal year bp was characterised by strong cyclone activity over the iceland region intense atmospheric circulation during this period has been confirmed also by other studies in the northern north atlantic region less

late holocene diatom inferred reconstruction of temperature variations of the west greenland current from disko bugt central west greenland the diatom flora from a high resolution core collected from disko bugt central west greenland records variations in surface water temperature for the late holocene 1600 300 cal bp our data support the existence of a previously identified anti phase relationship between the surface water temperature from west greenland and climate events recorded in the ne atlantic and between surface and subsurface waters identified from benthic foraminifera of the west greenland current wgc the diatom flora record relatively cool surface water conditions during the end of the roman warm period and medieval warm period mwp and relatively warmer surface water conditions during the dark ages cold period and little ice age lia this is particularly pronounced during the mwp experiencing the coldest conditions and the lia experiencing the warmest conditions through the whole sequence studied the most likely explanation for this anti phase relationship is linked to the flux of meltwater delivered to the wgc from sea ice and the greenland ice sheet off the west greenland margin the generally warmer conditions of the mwp resulted in increased melting of sea ice and the greenland ice sheet producing an increased meltwater flux and cooling of the surface waters of the wgc in contrast reduced meltwater flux during the relatively cold lia resulted in reduced meltwater flux to the wgc producing a relative warming of the surface waters recorded by the diatom flora

millennial scale changes of surface and deep water flow in the western tropical atlantic linked to northern hemisphere high latitude climate during the holocene there is increasing evidence that the preceding holocene climate was as unstable as the last glacial period although variations occurred at much lower amplitudes however low latitude climate records that confirm this variability are sparse here we present a radiocarbon dated holocene marine record from the tropical western atlantic aragonite dissolution derived from the degree of preservation of the pteropod limacina inflata records changes in the corrosiveness of the bottom water at the core site due to the changing influence of northern versus southern water masses the 18 o difference between the shallow living planktonic foraminifera globigerinoides sacculifer and the deep living globorotalia tumida is used as proxy for changes in the vertical stratification of the surface water hence the trade wind strength at this latitude we compared our data to high latitude records of the north atlantic region a good agreement is found between the aragonite dissolution and the strength in the island scotland overflow water which contributes significantly to the north atlantic deep water this suggests that large scale variations in the atlantic thermohaline circulation occurred throughout the holocene concurrently the comparison of our 18 o with the gisp2 glaciochemical records points to global holocene atmospheric reorganizations seen in both the tropics and high northern latitudes

late holocene paleoceanographic evidence of the influence of the aleutian low and north pacific high on circulation in the seymour belize inlet complex british columbia canada foraminiferal and thecamoebian faunas from the seymour belize inlet complex sbic a fjord network situated on the mainland coast of british columbia were studied to assess climatic cycles and trends impacting the area through the ad 850 ad 2002 interval ocean circulation patterns prevalent in the sbic are strongly linked to precipitation which is closely linked to the relative strength and position center of action coa of the seasonally developed aleutian low al and north pacific high nph atmospheric circulation gyres through interpretation of cluster analysis and ordination methods a period of weak estuarine circulation was recognized to have impacted the sbic area between ad 850 and ad 1500 during this time waters in the sbic were dysoxic to anoxic and the sediment water interface was comprised of a depauperate foraminiferal fauna consisting of low diversity agglutinated forms these reduced oxygen conditions came about as a result of diminished precipitation in the sbic catchment as the coa of the al progressively migrated westward over time resulting in greatly reduced estuarine circulation and only infrequent and feeble incursions of well oxygenated open ocean water into the sbic basin by ad 1575 following a gradual transition period of 75 years when circulation patterns in the inlet were unstable very strong estuarine circulation developed in the sbic concomitant with the onset of the little ice age lia in western canada in the sbic this interval was characterized by higher levels of precipitation which greatly enhanced estuarine circulation resulting in frequent incursions of cold well oxygenated ocean currents into the bottom waters of the sbic and the development of a diverse calcareous foraminiferal fauna this circulation pattern began to break down in the late 19th century ad and by ad 1940 conditions similar to those that existed in the inlet prior to ad 1500 had redeveloped a process that continues at present

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

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

holocene marine diatoms from the faeroe islands and their paleoceanographic implications abstract temporal oceanographic changes based on mid and late holocene marine diatom floras from the faeroe islands region have been studied the four studied coring sites are located in the skalafjord and a more open ocean environment the mouth of the kaldbaksfjord at water depths ranging between 50 and 70 m comparison of the diatom records in the fjord sediments with those from the outer part of the fjord shows that the fjord provides a more optimum potential for paleoceanographic reconstructions the concentrations of marine taxa and relative abundance of freshwater diatom species in the marine environment were analyzed with the aim of relating them to environmental conditions estimated diatom concentrations were very low and ranged from a maximum of 14 4 10 6 valves per gram dry sediment in the inner part of the fjord to a minimum of 0 1 10 6 outside the fjord the freshwater diatom flora that occurred between 1200 and 700 cal yr bp in the inner part of the fjord suggests much higher precipitation during this time and increased freshwater discharge into the fjord presence of actinocyclus normanii which is an indicator of increasing trophy is related to the first human settlement on the faeroe islands maximum likelihood factor analysis mlfa was used to describe the most essential relationship among the diatom species and to employ these relationships for inferring holocene environmental changes in the faeroe islands the first two mlfa factors are related to oceanic influences in the region factor 1 is represented by a warmer water diatom assemblage and is suggested to correspond to inflow of the norwegian atlantic current to the skalafjord whereas factor 2 is an indicator of a colder water diatom assemblage that corresponds to inflow of arctic norwegian water mixing anwm during the 4900 3200 cal yr bp time interval

new faunal and isotopic evidence on the late weichselian holocene oceanographic changes in the norwegian sea downcore studies of planktonic and benthonic foraminifera and 18o and 13c in the planktonic foraminifer neogloboquadrina pachyderma sin in two piston cores from the southern part of the norwegian sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1 prior to oxygen isotope termination ia 16 000 13 000 yr b p an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice covered surface layer in the norwegian sea close to termination ia well oxygenated deep water probably with positive temperatures was introduced this deep water which must have had physical and or chemical parameters different from those of present deep water in the norwegian sea could have been introduced from the north atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the norwegian sea a seasonal ice cover in the southern part of the norwegian sea is proposed for the period between termination ia and the beginning of ib close to 10 000 yr b p the present situation with strong influx of warm atlantic surface water and deep water formation by surface cooling was established at termination ib

10be dating of the narsarsuaq moraine in southernmost greenland evidence for a late holocene ice advance exceeding the little ice age maximum in southernmost greenland near narsarsuaq the terminal narsarsuaq moraine was deposited well outside of a historical little ice age lia moraine adjacent to the modern ice margin using 10be surface exposure dating we determine narsarsuaq moraine abandonment at 1 51 0 11 ka a second set of 10be ages from a more ice proximal position shows that ice has been within or at its historical i e lia extent since 1 34 0 15 ka notably narsarsuaq moraine abandonment was coincident with climate amelioration in southern greenland southern greenland warming at 1 5 ka was also concurrent with the end of the roman warm period as climate along the northern north atlantic sector of europe cooled into the dark ages the warming of southern greenland and retreat of ice from the narsarsuaq moraine is consistent with studies suggesting possible anti phase centennial scale climate variability between northwestern europe and southern greenland other southernmost greenland ice margin records do not preclude a pre lia ice margin maximum potentially concurrent with a narsarsuaq advance prior to 1 51 ka but also lack sufficient ice margin control to confirm such a correlation we conclude that there is a clear need to further determine whether a late holocene pre lia maximum was a local phenomenon or a regional southern greenland ice maximum and if this advance and retreat reflects a regional fluctuation in climate

stable isotope and ar ar evidence of prolonged multiscale fluid flow during exhumation of orogenic crust example from the mont blanc and aar massifs nw alps the spatial and temporal scales and the geometry of fluid pathways in a collisional orogen are investigated using stable isotope analysis o c and h and 40ar 39ar dating of vein minerals formed at circa 11 16 ma in the mont blanc and the aar external crystalline massifs in both massifs 40ar 39ar dating of veins adularia provides evidence for progressive crystallization from 16 to 9 ma and mainly at 11 12 ma following veins opening during shear zone activity the fluid flow duration thus ranges from 4 to 5 ma in the two massifs the 18o values of vein quartz and calcite are similar to those of undeformed crystalline and sedimentary host rocks suggesting rock buffering while carbon isotope ratios of vein calcites fall into three compositional groups a type veins have 13c values that are buffered by the helvetic metasediments which suggests that these veins formed in a closed system from a locally derived co2 rich fluid the fluid in equilibrium with c type veins has depleted 13c values similar to mantle co2 while the intermediate 13c values of b type veins suggest mixing between the a type and c type fluids these results are in agreement with crustal to lithosphere scale upward vertical fluid flow along vertical shear zones related to the strike slip system bounding the adriatic block since 16 20 ma connecting a deep seated fluid to some downward flow in the sedimentary cover of external crystalline massifs

solar forcing as an important trigger for west greenland sea ice variability over the last millennium abstract arctic sea ice represents an important component of the climate system and the present reduction of sea ice in the arctic is of major concern despite its importance little is known about past changes in sea ice cover and the underlying forcing mechanisms here we use diatom assemblages from a marine sediment core collected from the west greenland shelf to reconstruct changes in sea ice cover over the last millennium the proxy based reconstruction demonstrates a generally strong link between changes in sea ice cover and solar variability during the last millennium weaker or stronger solar forcing may result in the increase or decrease in sea ice cover west of greenland in addition model simulations show that variations in solar activity not only affect local sea ice formation but also control the sea ice transport from the arctic ocean through a sea ice ocean atmosphere feedback mechanism the role of solar forcing however appears to have been more ambiguous during an interval around ad 1500 after the transition from the medieval climate anomaly to the little ice age likely to be driven by a range of factors

a mid holocene shift in arctic sea ice variability on the east greenland shelf records of iceberg rafting and palaeohydrography from two east greenland shelf cores jm96 1206 1 gc and jm96 1207 1 gc are reported benthic foraminifera stable isotopes and ird e uxes indicate a shift toward colder lower salinity polar conditions c 5 cal ka a new proxy of iceberg rafting on the east greenland shelf is the e ux of calcium carbonate tic thought to be derived from glacial erosion of cretaceous calcareous mudstones a change in the regularity and spacing of carbonate e ux peaks at c 4 7 cal ka in jm96 1207 coincides with the onset of neoglacial cooling in the renland ice core d 18 o record we propose that the carbonate e ux peaks between 4 7 and 0 4 cal ka are related to sea surface coolings associated with increased e ux of polar water and sea ice in the east greenland current these peaks are synchronous with sea surface coolings interpreted from north atlantic deep sea cores but additional peaks centred around 2 4 and 3 8 cal ka in jm96 1207 suggest that the shelf site captures higher frequency events the data indicate that severe arctic sea ice events began in the neoglacial interval and that earlier holocene cool events in deep sea records are associated with other processes such as release of meltwater from residual glacier ice and glacial lakes

late holocene climatic changes as detected by the growth and decay of ice wedges on the southern shore of hudson strait northern quebec canada the dating of cryoturbated palaeosols associated with past ice wedge activity on late holocene sandy fluvial terraces in a region of continuous permafrost leads to an interpretation of periods of ice wedge growth and active cracking that alternated with periods of decay dormancy and active layer deepening the reconstruc tion corresponds with palaeoclimatic information obtained from existing arctic wide and regional proxy rec ords the little ice age stands out as a period of intense ice wedge activity in the study area it was followed by a warm thawing interval during the first half of the twentieth century from ad 1946 to 1991 a well documented cooling of the climate took place which reactivated 94 of the studied ice wedges the pyramidal shape of ice wedge tops and the depths of the upgrowth features could be correlated between sites several kilometres apart clearly indicating a regional climatic response the mean annual air temperature dropped from about 7 8 c in 1946 to 8 9 c in 1991 the t

paleoceanographical development off sisimiut west greenland during the mid and late holocene a multiproxy study abstract a multiproxy study of paleoceanographic and climatic changes in holsteinsborg dyb on the west greenland shelf shows that the area is sensitive to variations in the mixing between the two components of the west greenland current i e the atlantic water of the irminger current and the polar water from the east greenland current a seismic profile illustrates the general development in the area since the deglaciation and analyses of benthic foraminifera stable isotopes 18 o and 13 c and x ray fluorescence elemental counts in two cores covering ca 6650 and 1100 years respectively provide details on the oceanographic changes during the mid and late holocene the chronology is based on 210 pb and ams 14 c age determinations during the time interval of 6650 1600 cal yr bp the bottom waters are characterized by the presence of modified atlantic water with some influence of meltwater either local or regional depleted 18 o values and relatively high si fe ratio suggest warmer conditions from 6650 to 3800 cal yr bp corresponding in time to part of the holocene thermal maximum followed by a general slight cooling with some fluctuation after 3800 cal yr bp at 1600 cal yr bp there is an abrupt change in almost all investigated proxies the foraminiferal assemblage and the 18 o values suggest cold low salinity bottom water conditions and there is indication of seasonal sea ice cover between 1400 and 1200 cal yr bp corresponding in time to the dark ages cold period and to a minimum in solar irradiance from ca 1150 to 580 cal yr bp a time interval equivalent to the historical medieval warm period mwp the foraminiferal fauna remains indicative of cold low salinity bottom waters but without any indication of sea ice cover the influence of polar water meltwater at the sea floor during the mwp is thought to be a result of enhanced mixing of the two components of the west greenland current caused by an increase in wind activity during generally positive north atlantic oscillation conditions maybe combined with a displacement of the irminger current pathway to the outer shelf during the little ice age lia there is a strong influence of modified atlantic water at the sea floor related to sea ice formation and stratification of the water column after ad 1900 the benthic foraminiferal assemblage suggests a slight increase in polar water influence and thereby mixing even though the environment is not much different from that during the lia

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

sedimentation and sediment accretion in michigan coastal wetlands u s a abstract sediment transport and accretion rates were studied for three different types of coastal wetlands of lake michigan u s a a forested intradunal wetland cranberry bog no 1 near stevensville michigan displayed sediments in the form of detritus and exported them very little sedimentary material entered by streamflow these features of bottom land wetlands were confirmed by radioisotope studies on cores which showed low accretion rates of 210 pb the mass fluxes were found to range from 0 01 to 0 2 g cm 2 yr 1 the equivalent linear growths are 0 5 9 0 mm yr 1 the suspended material from this wetland entered a filling shrub bog lake complex known as cranberry bog no 2 a considerable fraction of the incoming sediments were retained in this intradunal basin wetland this was confirmed via radioisotope studies with cores showing higher accretion rates than in the bottom land wetland the river delta wetland at pentwater michigan had little sediment trapping ability large amounts of water and suspended materials entered this riverine wetland but no annual average removal was found radioisotope studies of cores at selected locations within this system showed little or no accretion in stream channels and normal accumulation of organic material in non channel areas no net annual effect on water quality of the streams as they discharged to lake michigan was found storm events caused no notable import or export of suspended material presumably the sand substrate in the vicinity of all three wetlands caused runoff events to be mediated by subsurface flow through this porous soil these three sand based coastal wetlands appear to have little net effect on suspended solids the 210 pb method proved more valuable than 137 cs because of the small depth of occurrence of the latter isotope interpretation of isotope profiles required information on acid fraction soluble profiles results are expressed in terms of mass units since compaction of cores distorts the linear accretion rate delayed transfers of radionuclides appear to have occurred perhaps as a result of integration of atmospheric inputs by the watersheds the total activities of 210 pb and 137 cs are well correlated which indicates particle trapping efficiency as the primary factor for affecting accumulation of both isotopes

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

on the origin of co2 rich fluid inclusions in migmatites nearly pure co2 fluid inclusions are abundant in migmatites although h2o rich fluids are predicted from the phase equilibria processes which may play a role in this observation include 1 the effects of decompression on melt 2 generation of a co2 bearing volatile phase by the reaction graphite quartz biotite plagioclase melt orthopyroxene co2 rich vapour 3 selective leakage of h2o from co2 h2o inclusions when the pressure in the inclusion exceeds the confining pressure during decompression and 4 enrichment of grain boundary vapour in co2 by subsolidus retrograde hydration reactions

holocene palaeoceanographic evolution off west greenland benthic foraminiferal assemblages from a core southwest of disko bugt provide a holocene perspective last 7 ka bp on ice sheet ocean interactions between the west greenland current wgc and the west greenland ice sheet changes in the fauna reveal significant variations in the water mass properties temperature and salinity of the wgc through time from 7 3 to 6 2 ka bp a relatively warm strong wgc influences ice sheet melt in disko bugt and causes enhanced meltwater production resulting in low surface water productivity the most favourable oceanographic conditions occur from 5 5 to 3 5 ka bp associated with thermal optimum like conditions encompassing minimum ice sheet extent in the disko bugt area these conditions are attributed to 1 reduced meltwater influence as the ice sheet is land based and 2 enhanced contribution of warm saline water masses from the irminger current to the wgc the transition into the late holocene last 3 5 ka bp is characterized by a cooling of oceanographic conditions caused by increased advection of cold low salinity water masses from the east greenland current a longer term late holocene cooling trend within the wgc is attributed to the onset of neoglacial cooling within the north atlantic region superimposed on this cooling trend multicentennial scale variability within the wgc matches reconstructions from a nearby coring site in disko bugt as follows 1 cooling at 2 5 ka bp linked to the 2 7 ka bp cooling event 2 a warm phase centred at 1 8 ka bp associated with the roman warm period 3 slight warming between 1 4 and 0 9 ka bp linked to the medieval climate anomaly 4 severe cooling of the wgc after 0 9 ka bp culminating at 0 3 ka bp during the little ice age we show that multicentennial scale palaeoceanography variability along the west greenland margin is driven by ocean forcing i e variations in the relative contribution of atlantic irminger current and polar east greenland current water masses to the wgc during the last 7 ka bp influencing ice sheet dynamics

anthropogenic versus climatic control in a high resolution 1500 year chironomid stratigraphy from a southwestern greenland lake we performed a high resolution study of chironomid assemblages in a sediment core retrieved from lake igaliku in southern greenland the well dated core is located within the former norse eastern settlement and covered the last 1500 yr the comparison of chironomid stratigraphy pca axis scores with instrumental temperature data land use history and organic matter in the sediment over the last 140 yr suggested that the primary changes in chironomid fauna in 1988 2 yr were driven by the shift to modern agriculture in the catchment this unprecedented change in chironomid fauna was most likely triggered by a shift in in lake processes within the instrumental period subtle variations in the chironomid assemblages that occurred before 1988 2 yr were significantly correlated with summer temperatures even in times of traditional extensive sheep farming in the catchment the relevance of the chironomid derived climate signal over the last 1500 yr was supported by its good concordance with previous studies in west greenland and in the arctic the chironomid assemblage therefore appeared to be a valuable proxy for climate changes within the norse colony area synchronous changes in norse diet and chironomid reconstructed climate give new insights into the interplay of norse society with climate

quartz veins deformed by diffusion creep accommodated grain boundary sliding during a transient high strain rate event in the southern alps new zealand abstract the crystallographic preferred orientations cpos and microstructures of deformed quartz veins were measured for four samples in the hanging wall of the alpine fault in the southern alps new zealand their deformation and exhumation has occurred since 4 ma the quartz veins have been ductilely sheared to finite shear strains of 5 15 in late cenozoic shear zones at 450 50 c 310 90 mpa and strain rates between 2 10 11 and 2 10 9 s 1 the sheared veins have a polygonal microstructure with few subgrains and an average grain size of 100 m the cpo of the veins is random to very weak within the shear zones we suggest that dislocation creep accommodated initial shear deformation at high stresses and strain rates the deformation must have created a strong cpo and concomitant dynamic recrystallization reduced the grain size significantly dissipation of stresses during initial deformation lead to a stress and strain rate drop required for a switch to diffusion creep accommodated grain boundary sliding gbs continued shearing accommodated by gbs destroyed the cpo post deformational grain growth gave rise to a final polygonal microstructure with a similar grain size in veins and in the wall rocks analysis of existing experimental data suggest that this sequence of events is possible in the time available rates of all processes may have been enhanced by the presence of a water rich fluid within the shear zones these observations of naturally deformed rocks provide a model for the processes that may occur during short lived deformation at transiently high stresses at mid crustal depths or deeper

palynofacies analysis and organic walled dinoflagellate cysts in late holocene sediments from igaliku fjord south greenland this study characterizes late holocene past 3300 years variations in organic matter deposition in the outer part of igaliku fjord south greenland and uses this information to assess palaeohydrographic conditions except for two all residues were characterized by abundant organic matter with amorphous material dominating the late holocene sediments in the deeper parts of the outer igaliku fjord have generally been deposited under anoxic to suboxic conditions with relatively low terrestrial freshwater influx the organic walled dinoflagellate cyst assemblages suggest the continuous presence of water masses derived from the east greenland current while changes in sea surface temperature during the last 3300 years have also been interpreted terrestrial influx was reflected by the continuous occurrence of leaf tissue which increased in abundance in sediments younger than ad 960 pseudo amorphous phytoclasts occurred in sediments older than ad 770 and sporomorphs were rare throughout acritarchs and o

deformation by solution deposition and re equilibration of fluid inclusions in crystals depending on temperature internal pressure and stress abstract changes of shape and density of fluid inclusions in crystals were demonstrated when these crystals were subjected to temperatures and internal pressures greater than those of their growth experimental relations have been established between the rate of length change of the inclusions and the different parameters of the experiment nature of the crystal temperature and internal pressure state of stress on the crystal geometric characters of the inclusion length width orientation of the inclusion with respect to the optical axes of host mineral it is essentially the effect of the variation of surface energy with the curvature around the cavity which causes a mass transfer of the host crystal by diffusion through the fluid under pressure the rate of length change is limited by the rate of dissolution at the median part of elongate inclusions this change of shape and density is known to occur in naturally deformed crystals an example of such a behaviour is given which allowed us to use the inclusions as markers of the conditions of temperature and pressure subsequent to the growth of crystal

environmental change in eastern greenland during the last 1300 years evidence from foraminifera and lithofacies in nansen fjord 68 n lithofacies and benthic foraminiferal analyses of two sediment cores bs1191 k13b and k14 from nansen fjord eastern greenland show evidence of changing oceanographic and sea ice conditions from

holocene water mass changes in the labrador current the labrador current is part of the anticlockwise subpolar gyre and plays a major role in the formation of north atlantic deep water it is influenced by the west greenland and baffin currents supp

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

holocene palaeoclimatic reconstruction in northern iceland approaches and results abstract the period since the mid 19th century when instrumental meteorological recording first started in iceland has shown climate conditions close to or even at both holocene minimum and optimum levels the 19th century part of the little ice age represents a thermal minimum whilst the warmest decades of the 20th century are close to the estimated holocene thermal maximum a model describing sea ice climate ela relationships in northern iceland for this period has been developed providing a calibrated proxy climate record as a basis for palaeoclimatic reconstruction for the holocene as a whole glacier advances in the periods around 4700 bp around 4200 bp ca 3200 3000 bp around 2000 bp around 1500 bp and around 1000 bp based on radiocarbon dating and tephrochronology mark climatic minima of the post preboreal holocene when conditions were comparable to the extremes in the second half of the 19th century compared to optimal holocene thermal conditions with temperatures at least as high as in the 1930s the range of holocene temperature variation was ca 3 k this was accompanied by a doubling in precipitation from the thermal minima to the maxima

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 diatom based sea ice reconstruction for the vaigat strait disko bugt west greenland over the last 5000 yr abstract a diatom based sea ice concentration sic transfer function was developed by using 72 surface samples from west of greenland and around iceland and validated against associated modern sic canonical correspondence analysis on surface sediment diatoms and monthly average of sic indicated that april sic is the most important environmental factor controlling the distribution of diatoms in the area justifying the development of a diatom based sic transfer function the agreement between reconstructed sic based on diatoms from west greenland and the satellite and modelled sea ice data during the last 75 yr suggests that the diatom based sic reconstruction is reliable for studying the palaeoceanography off west greenland relatively warm conditions with a strong influence of the irminger current ic were indicated for the early part of the record 5000 3860 cal yr bp corresponding in time to the latest part of the holocene thermal maximum between 3860 and 1510 cal yr bp april sic oscillated around the mean value 55 and during the time interval 1510 1120 cal yr bp and after 650 cal yr bp was above the mean indicating more extensive sea ice cover in disko bugt agreement between reconstructed april sic and changes in the diatom species suggests that the sea ice condition in disko bugt was strongly influenced by variations in the relative strength of two components of the west greenland current i e the cold east greenland current and the relatively warm ic further analysis of the reconstructed sic record suggests that solar radiation may be an important forcing mechanism behind the historic sea ice changes

the role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates abstract experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction the lattice preferred orientation lpo of the recrystallized grains depends on the recrystallization mechanism at low temperatures and fast strain rates strain induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes resulting in an lpo of c axes parallel to the 1 direction at higher temperatures or slower strain rates progressive subgrain rotation produces recrystallized grains which inherit the small circle girdle lpo of their deformed host grains and which continue to re orient by slip at even higher temperatures and slower strain rates progressive subgrain rotation is accompanied by rapid grain boundary migration which does not favor grains of any particular orientation thus the lpo is again similar to that of non recrystallized grains in contrast when dynamic recrystallization involves grain growth driven by surface energy reduction a strong lpo of c axes parallel to 1 develops during grain growth but then evolves with increasing strain toward a small circle girdle the correlation of lpos with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of lpos and for interpreting natural lpos in recrystallized rocks

late holocene environment and climatic changes in ameralik fjord southwest greenland evidence from the sedimentary record sedimentological and geochemical xrf data together with information from diatom and benthic foraminiferal records of a 3 5 m long gravity core from ameralik fjord southern west greenland is used for reconstructing late holocene environmental changes in this area the changes are linked to large scale north atlantic ocean and climate variability ams 14c dating of benthic foraminifera indicates that the sediment core records the last 4400 years and covers the termination of the holocene thermal maximum htm the late htm 4 4 3 2 ka bp is characterized by high accumulation rates of fine silty sediments related to strong meltwater discharge from the inland ice the htm benthic foraminiferal fauna demonstrates the presence of well ventilated saline bottom water originating from inflow of subsurface west greenland current water of atlantic irminger sea origin the hydrographic conditions were further characterized by limited sea ice probably related to a mild and relatively windy winter climate af

relative sea level change in greenland during the last 700 yrs and ice sheet response to the little ice age this paper presents new evidence regarding relative sea level rsl changes and vertical land motions at three sites in greenland since 1300 a d a time interval that spans the later part of the medieval climate anomaly mca and the little ice age lia we observe rsl rise at two sites in central west greenland from c 0 80 0 20 m at c 1300 a d to c 0 20 m 0 25 m at c 1600 a d after which rsl slowed and then stabilised at a third site in south greenland we observe rsl rise from c 1 40 0 20 m at c 1400 a d until c 1750 a d after which rsl slowed and was stable during at least the latter part of the 20th century the c 1600 a d rsl slow down seen at the two former sites is surprising because it occurs during the lia when one might expect the ice sheet to be gaining mass and causing rsl to rise we interpret this rsl slowdown to indicate a period of enhanced regional mass loss from central west greenland since c 1600 a d and propose two hypotheses for this loss first a reduction in precipitation during cold and dry conditions and second higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards the latter hypothesis is compatible with a well established temperature seesaw between western greenland and northern europe and potentially a previously identified shift from a positive to generally more negative nao conditions around 1400 to 1600 a d our study shows how rsl data from greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern europe the ice sheet in west greenland gained mass

diatom evidence of climatic change in holsteinsborg dyb west of greenland during the last 1200 years diatom assemblages from holsteinsborg dyb on the west greenland shelf were analysed with high temporal resolution for the last 1200 years a high degree of consistency between changes in frequency

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

variable north atlantic climate seesaw patterns documented by a late holocene marine record from disko bugt west greenland abstract the reconstruction of past sea surface conditions in the labrador sea is essential for understanding climate fluctuations in the north atlantic region we here study late holocene sea surface conditions off west greenland in order to elucidate the possible relationship between a north atlantic seesaw and centennial to millennial scale climate fluctuations in the labrador sea region for that purpose we have studied the particulate organic matter especially dinoflagellate cysts and acritarchs from two marine sediment cores from disko bugt central west greenland our data show significant variations in sea surface temperature and sea ice cover during the last ca 3200 years after a cooling at ca 2 9 ka cal bp presumably related to the neoglacial cooling seen in large parts of the northern hemisphere the area was subjected to significant variability both in the entrainment of atlantic water west greenland current water and in atmospheric temperatures from 2 0 1 5 ka cal bp corresponding to the later part of the roman warm period the area experienced a return to a stronger influx of atlantic water and an increased fresh water influx from land probably related to increased precipitation or to melt water outflow from the nearby inland ice the dark ages 1 5 1 3 ka cal bp were characterised by an only minor cooling of the surface waters however as seen in other records from the labrador sea region the beginning of the medieval warm period 1 3 0 9 ka cal bp signified a severe cooling presumably due to a significant reduction in atlantic water entrainment the cold conditions continued through the little ice age after 0 9 ka cal bp although the area seems to have experienced a minor decrease in sea ice cover until 0 5 ka cal b p after which sea ice cover may again have increased the period of modern warming is not represented in our data our study shows that a north atlantic oscillation type pattern played a significant role in the late holocene centennial to millennial scale climate fluctuations in the labrador sea region however this cannot explain the full complexity of the climate signal the fact that a simple pattern of cold versus warm climate scenario does not exist demonstrates that it will hardly be feasible to select the correct baseline data set when modelling future climate development

diatom evidence of hydrographic changes and ice conditions in igaliku fjord south greenland during the past 1500 years biostratigraphic diatom analyses were carried out on two sediment cores from igaliku fjord south greenland in order to reconstruct hydrographic and climatic fluctuations during the late holocene ad 550 to present pronounced differences in hydrographic setting of the coring sites provide palaeoenvironmental information of both local and more regional character five diatom zones were identified from the subfossil diatom records each describing a hydrographic setting two major climate periods the mediaeval warm period ad 800 1250 and the little ice age ad 1580 1850 that were separated by a variable transitional period were recognized prior to these periods a cold and presumably moist climate regime prevailed between ad 500 and 700 cooling events were identified during the mediaeval warm period in the period ad 960 to 1140 the diatom data demonstrate that marked hydrographic changes occurred in the course of a relatively short timespan beginning at about ad 1300 and culminating around

a diatom based reconstruction of early holocene hydrographic and climatic change in a southwest greenland fjord abstract a diatom based reconstruction of surface water paleoclimatic and paleoceanographic changes in ameralik fjord southwest greenland is presented for the holocene interval 8800 to 3600 cal yrs b p a minor episode of cold surface water conditions is found at ca 8000 7800 cal yrs b p this may be due to the local conditions in the fjord and linked to the culmination of a strong melt water outflow rather than reflecting the widespread north atlantic 8 2 ka cooling event warming of surface water condition from 7800 to 7100 cal yrs b p probably corresponding to the early and warmest part of the holocene thermal maximum htm in this region is reflected in the diatom assemblages and supported by other proxies the west greenland current wgc influences the fjord strongly during this interval indicating enhanced advection of atlantic water masses derived from the irminger current ic a major sedimentary change with a hiatus between 6800 and 4400 cal yrs b p prevents a reconstruction of mid holocene paleoceanograpy the final and less prominent part of the htm is found after 4400 cal yrs b p previous studies from the same site have shown this final stage of the htm to end at 3200 cal yrs b p with the onset of the neoglaciation our study provides further evidence that the marine sedimentary record from west greenland fjords yields paleoenvironmental information reflecting a significant link between local and large scale north atlantic oceanographic and climatic changes

paleoceanographic changes in the disko bugt area west greenland during the holocene micropaleontological analyses of a sediment core raised in disko bugt west of greenland were undertaken in order to document paleoceanographical changes in the eastern baffin bay during the holoc

a 2500 year record of natural and anthropogenic soil erosion in south greenland the environmental impact of the norse landnam in greenland has been studied extensively but to date no study has quantified the soil erosion that norse agricultural practices are believed to have caused to resolve this problem a high resolution sedimentary record from lake igaliku in south greenland is used to quantitatively reconstruct 2500 years of soil erosion driven by climate and historical land use an accurate chronology allows for the estimation of detritic fluxes and their uncertainties land clearance and the introduction of grazing livestock by the norse around 1010 ad caused an acceleration of soil erosion up to 8 mm century in 1180 ad which is two fold higher than the natural pre landnam background from 1335 ad to the end of the norse eastern settlement in the mid fifteenth century the vegetation began to recover from initial disturbance and soil erosion decreased after an initial phase of modern sheep breeding similar to the medieval one the mechanization of agriculture in the 1980s caused an unprecedented soil erosion rate of up to 21 mm century five times the pre anthropogenic levels independently a suite of biological and geochemical proxies including ti and diatom concentrations c n ratio 13c and 15n of organic matter confirm that the medieval and modern anthropogenic erosion far exceeds any natural erosion over the last 2500 years our findings question the veracity of the catastrophic scenario of overgrazing and land degradation considered to have been the major factor responsible for norse settlement demise they also shed light on the sustainability of modern practices and their consequences for the future of agriculture in greenland

a 500 yr speleothem derived reconstruction of late autumn winter precipitation northeast turkey a verified instrumental calibration of annually resolved 18o for a stalagmite from gumushane in northeast turkey is presented and cross validated using a leave one out technique the amount of late autumn to winter precipitation is negatively correlated with stalagmite 18o between ad 1938 and 2004 the observed relationship is extrapolated back to ad 1500 leading to the first long winter precipitation reconstruction for this region modern day october to january precipitation is linked to pressure fields in western russia anomalously lower reconstructed rainfall is recorded in ad 1540 1560 at which time higher pressure over the caspian sea region is inferred

mid to late holocene oceanographic variability on the southeast greenland shelf a reconstruction of oceanographic variability of the past 5800 years on the southeast greenland shelf was obtained by analysing a combined marine sediment record based on two cores from the same site cores fox04g 05r were retrieved from a side basin to a cross shelf trough connecting the 900 m deep sermilik fjord with the irminger sea in the northwestern north atlantic the record was analysed in terms of grain size distribution xrf and benthic and planktonic foraminiferal content and the chronology was obtained on the basis of 210pb and 14c dating the late holocene paleoceanographic variations in the record were characterised by a marked influence from the irminger current ic at the onset of the record at 5800 cal yr bp and the regional holocene climatic optimum between 5200 and 4200 cal yr bp after 3600 cal yr bp neoglacial cooling with increased influence of polar waters from the east greenland current egc diminished the influence from the ic between 1500 and 700 cal yr bp the environment

an integrated geochemical and palynological study of human impacts soil erosion and storminess from southern greenland since c ad 1000 abstract an integrated pollen analytical and geochemical study is presented from qinngua kangilleq southwest greenland this site was formerly one of the largest farms in the eastern settlement of norse greenland the study is the first to determine what link if any exists between norse landnam early settlement vegetation change soil erosion climate change and peat geochemistry the data suggest that fluxes in lithogenic elements supplied to a peat column by terrestrial sources and atmospheric deposition were coupled to the pattern of local norse settlement beginning cal ad 1020 a severe phase of soil erosion is indicated which is coincident with the landnam horizon this may represent proxy evidence for the stripping of turf for the construction of turf and stone buildings at the farm radiocarbon dates suggest the presence of a hiatus in the sediment column spanning cal ad 1380 1950 following the recommencement of sediment accumulation the geochemical data indicate a critical change in site conditions which may be consistent with the well known change in northern hemisphere atmospheric circulation that started between c ad 1400 and 1420 bromine br and chlorine cl concentrations are demonstrably higher in the sediments dating to the 20th century relative to the pre 15th century deposits rising halogen concentrations at qinngua appear to be correlated with increased levels of na sea salt sodium precipitation in the gisp2 ice core which earlier studies have interpreted as indicative of increased north atlantic storminess

interaction between subsurface ocean waters and calving of the jakobshavn isbrae during the late holocene a marine sediment core from vaigat in disko bugt west greenland has been analysed in terms of lithology dinoflagellate cysts and foraminifera in order to evaluate the influence of oceanographic variability on west greenland glacier stability the data show that during the past 5200 years the atlantic foraminiferal abundance in the subsurface waters of the west greenland current wgc episodically increased indicating periods of increases in the inflow of subsurface warm atlantic water at 2000 1500 cal yr bp and 1300 cal yr bp as well as periods of less pronounced increased bottom water temperatures around 4700 4000 cal yr bp 3100 2800 2600 1000 800 500 400 and at 200 cal yr the sedimentological and dinoflagellate cyst data indicate that these episodes with enhanced advection of irminger sea derived waters are accompanied by increased iceberg rafting which we link to increased iceberg calving in relation to destabilization of the jakobshavn isbrae the long term trend in the data documents the end of a late holocene thermal maximum between 5200 and 4300 cal yr bp and a final onset of the neoglaciation at 3500 cal yr bp increased responses of the iceberg rafting after 3500 cal yr bp reflects a westward seaward advance of the glacier margin in relation to onset of neoglaciation and a development of the glacier into a floating tongue after 2000 cal yr bp a comparison of our record with a record from the eastern north atlantic indicates that a nao like anomaly pattern between subsurface waters in west greenland and atmospheric temperature in the eastern north atlantic may have been operating during most of the late holocene however during the past 1000 years the nao signal may have weakened as some other mode of climate variability overprints the anti phase climate signal in this region