a 2100 year trace element and stable isotope record at decadal resolution from rice lake in the northern great plains usa a 2100 year multiple proxy record at decadal resolution from a topographically closed but hydrolog ically open lake basin was used to reconstruct changes in lake salinity and evaporative intensity and to evaluate the reliability of different proxies for inferring climatic change in the glaciated northern great plains ngp at rice lake north dakota the ostracode mg ca ratios show good correlation with other ostracode diatom and aeolian proxy records from other sites in the ngp all of these records show significant century scale periodicities which have been related to solar variability as inferred from atmospheric radiocarbon records this coherent and consistent pattern suggests that these sites record climatic variability at regional scales the interval of the mediaeval climatic anomaly from 900 to 550 cal yr bp contains two pronounced dry periods during the following little ice age a single period of frequent drought that peaked at 300 cal yr bp was bracketed by wet periods before and af

droughts in the east asian summer monsoon margin during the last 6 kyrs link to the north atlantic cooling events abstract teleconnections to the high latitudes forcing by the tropical oceans and solar variability have all been suggested as dominant factors in the sub millennial global climate changes yet there is little consensus as to the relative importance of these factors for the east asian summer monsoon easm variability this study presents the results of high resolution analyses of ca and mg concentrations mg ca ratio 18 o and 13 c values of endogenic calcites from a sediment core from dali lake in the easm margin in order to investigate the sub millennial easm variability and its possible driving forces during the last 6 kyrs increases in these chemical proxy data were interpreted as drought events in the region due to the intensive evaporation losses overwhelming the water input to the lake the chemical proxy data in this study combined with multi proxy indicators including grain size component and total organic carbon concentrations from the same sediment core imply that declines in the easm intensity may have played a dominant role in triggering the drought events during the last 6 kyrs the results indicate that the easm intensity significantly declined at the intervals of 5 8 4 75 3 2 2 8 1 65 1 15 and 0 65 0 2 kyrs bp large declines in the easm intensity during the last 6 kyrs correspond in time to occurrences of ice rafted debris in the north atlantic indicating that millennial to centennial scale changes in the easm intensity were mainly controlled by climatic processes occurring in the northern high latitudes these data imply that persistent global warming may be favorable for the strengthening of the easm circulation and for the transportation of more rainfall to the semi arid regions of northern china on sub millennial scales

enso and solar driven sub milankovitch cyclicity in the palaeogene greenhouse world high resolution pollen records from eocene lake messel germany the annually laminated oil shale from the eocene maar lake at messel germany provides unique palaeoenvironmental and palaeoclimatological information for the palaeogene greenhouse phase two palynological analyses of 6 3 and 70 kyr long records with a temporal resolution of 70 and 700 years respectively confirm vegetation and climate variability in the sub milankovitch range this variability clearly corresponds to cyclic climate fluctuations indicating the influence of solar activity and a millennial scale variability of the el nino southern oscillation also seen during the quaternary icehouse system this provides strong evidence of cyclic fluctuations in the sub milankovitch frequency band that represent a pervasive and persistent system not only of the quaternary icehouse but also throughout the entire neogene and the palaeogene greenhouse this is proof for the long term stability of the driving forces of natural climate change on earth fluctuations in the frequency of palynomorphs indicate cyclic short term quantitative changes in the composition of the vegetation these changes were related to precipitation and corresponding fluctuations of the lake level as well as to changes in pollen production transport and deposition supplementary material a complete list of variables and palynomorphs used for pollen diagrams and statistical analyses as well as additional time series analyses are available at https doi org 10 6084 m9 figshare c 3458778

preliminary assessment of resources and economic potential of individual gas hydrate accumulations in the gulf of mexico continental slope abstract some global estimates suggest that gas hydrates represent the largest reservoir of fossil fuel however only a few studies of the resource and economic potential of individual gas hydrate accumulations exist here we estimate the volume of hydrate bound gas at gc green canyon blocks 184 185 gc 234 235 gb garden banks 388 mc mississippi canyon 798 842 gc 204 mc 852 853 and at atwater valley 425 426 sites in the gulf of mexico at water depths 500 2000 m the structural accumulations may contain from 4 7 10 8 to 1 3 10 11 m 3 of gas at standard temperature and pressure the resources in individual gas hydrate accumulations are comparable by volume with the reserves in very small to major conventional gas fields various geologic technologic and economic factors affect the economic potential of studied accumulations the mc 852 853 appears to be characterized by the most favorable combination of these factors and thus is suggested to have the highest economic potential the economic potential of gas hydrate accumulations at gc 204 gb 388 and at 425 426 sites is ranked as average gas hydrate accumulations at gc 234 235 gc 184 185 and mc 798 842 sites contain only small volumes of hydrate bound gas and likely have no economic potential future gas hydrate research should focus on the detailed study of large structural gas hydrate accumulations from which gas may be profitably recovered e g the mc 852 853 site

response to comment on are there connections between earth s magnetic field and climate earth planet sci lett 253 328 339 2007 by bard e and delaygue m earth planet sci lett in press 2007

rates timing and cyclicity of holocene eolian activity in north central united states evidence from varved lake sediments most of the sediment components that accumulated in elk lake northwestern minnesota during the holocene are autochthonous or biogenic delivered to the sediment water interface on a seasonal schedule preserved in distinct annual laminae varves the main allochthonous component is detrital clastic material as measured by bulk sediment concentrations of aluminum sodium potassium titanium and quartz that enters the lake mostly as eolian dust the eolian clastic influx to elk lake was considerably greater during the mid holocene 8 4 ka than it has been for the past 4000 yr when periods of increased eolian activity correspond to the time of the little ice age and the dust bowl geochemical records of eolian activity exhibit distinct cyclicities with dominant periodicities of 400 and 84 yr

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

late pleistocene holocene radiolarian paleotemperatures in the norwegian sea based on artificial neural networks artificial neural networks ann were trained by using an extensive radiolarian census dataset from the nordic greenland norwegian and iceland seas the regressions between observed and predicted summer sea temperature sst indicate that lower error margins and better correlation coefficients are obtained for 100 m sst100 compared to 10 m sst10 water depth and by using a subset of species instead of all species the trained anns were subsequently applied to radiolarian data from two norwegian sea cores hm 79 4 and md95 2011 for reconstructions of ssts through the last 15 000 years the reconstructed sst is quite high during the bolling allerod when it reaches values only found later during the warmest phase of the holocene the climatic transitions in and out of the younger dryas are very rapid and involve a change in sst100 of 6 2 and 6 8 8c taking place over 440 and 140 years respectively sst100 remains at a maximum during the early holocene and this radiolarian holocene optimum temperature interval rhoti predates the commonly recognized middle holocene climatic optimum hco during the 8 2 ka event sst100 decreases by ca 3 8c and this episode marks the establishment of a cooling trend roughly spanning the middle holocene until ca 4 2 ka successively since then and through the late holocene sst100 follows instead a statistically significant warming trend the general patterns of the reconstructed ssts agree quite well with previously obtained results based on application of imbrie and kipp transfer functions iktf to the same two cores for sst0 a statistically significant cyclic component of our sst record period of 278 years has been recognized this is close to the de vries or suess cycle linked to solar variability and documented in a variety of other high resolution holocene records d 2005 elsevier b v all rights reserved

a high resolution record of climate variability and landscape response from kettle lake northern great plains north america abstract a decadal scale multiproxy record of minerals pollen and charcoal from kettle lake north dakota provides a high resolution record of climate and vegetation change spanning the entire holocene from the northern great plains ngp in north america the chronology is established by over 50 ams radiocarbon dates this record exhibits millennial scale trends evident in other lower resolution studies but with much more detail on short term climate variability and on the rapidity and timing of major climatic shifts as a proxy for precipitation we utilize the rate of endogenic carbonate sedimentation which depends on groundwater inflow which in turn depends on precipitation independent cluster analyses of mineral and pollen data reveal major holocene mode shifts at 10 73 ka ka cal yr bp 9 25 ka and 4 44 ka the early holocene 11 7 9 25 ka was generally wet with perhaps a trend to higher evaporation associated with warming temperatures a switch from calcite to aragonite deposition associated with a severe but brief drought occurred at 10 73 ka from 10 73 ka to 9 25 ka climate was generally humid but punctuated at 100 300 yr intervals by brief droughts including the most severe drought of the entire holocene at 9 25 ka this event was coeval with the 9 3 9 2 ka event in the greenland ice cores and observed at a number of sites worldwide in contrast the prominent 8 2 ka event in greenland is not remarkable at kettle lake the prominence of the 9 25 event locally in the ngp may be due to a major drawdown and northward retreat of lake agassiz at this time reducing its mesoclimatic effect on the ngp and thrusting the region into an insolation controlled regime the mid holocene 9 25 4 44 ka was characterized by great variability in moisture on a multi decadal scale with severe droughts alternating with more humid periods the high abundance of the weedy but drought intolerant ambrosia generally during the mid holocene and specifically during the multi decadal drought periods is seemingly paradoxical but can be explained by high interannual variability of moisture overlaid on the multi decadal variability the late holocene 4 44 ka present was also characterized by multi decadal variability in moisture but was generally wetter than the mid holocene and the magnitude of variability was less the trends in wet dry mineral pollen and charcoal proxies were similar to the mid holocene but late holocene mineral pollen assemblages are distinct from mid holocene the shift to wetter climate in the late holocene was more gradual than the abrupt shift to arid conditions 9 25 ka which may explain the asymmetric retreat and readvance of forest along the eastern margin of the ngp precipitation variations in the ngp have been linked with pacific and atlantic sea surface temperatures and mid holocene drought in the ngp has been linked with sustained la nina like conditions in the pacific these linkages may explain the decadal and millennial scale variations seen in the ngp but cause of the prominent century scale variations remains elusive

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

possible linkages of late holocene drought in the north american midcontinent to pacific decadal oscillation and solar activity oxygen isotopic composition d 18 o the d 18 o record of the past 3100 years reveals that droughts of greater severity and duration than during the 20th century occurred repeatedly especially prior to 300 ad drought variability was anomalously low during the 20th century 90 of the variability values during the last 3100 years were greater than the 20th century average d 18 o is strongly correlated with the index of the pacific decadal oscillation pdo during the past 100 years and periodicities of the lateholocene d 18 o record are similar to those of the pdo furthermore time series of d 18 o and atmospheric d 14 ca re generally coherent after 700 ad both the pacific climate and solar irradiance probably played a role in drought occurrence but their effects were non stationary through the late holocene citation tian j d m nelson and f s hu 2006 possible linkages of late holocene drought in the north american midcontinent to pacific decadal oscillation and solar activity geophys res lett 33 l23702 doi 10 1029 2006gl028169

subdecadally resolved paleoceanography of the peru margin during the last two millennia 1 using multiproxy sediment core data from the el nino southern oscillation enso sensitive peru margin subdecadally resolved down to 0 6 year surface productivity and subsurface denitrification are reconstructed for the last 2300 years scanning xrf generated major elemental data ti fe si correlate well with discrete inductively coupled plasma atomic emission spectometry icp aes analyses and together with x radiography core density are used as productivity indices as surface productivity in this marine region is strongly impacted by enso higher lower periods of surface productivity are inferred to represent a persistent normal la nina el nino like state surface productivity and subsurface denitrification appear to have remained intimately coupled during this period due to direct stimulation of requisite subsurface suboxia and or hydrographic restructuring the late holocene peru margin is characterized by persistent moderate productivity and subsurface denitrification punctuated at centennial scale by shorter duration periods of high production and intense denitrification these centennial scale events are likely analogous to modern observations of decadal scale regime shifts but of higher amplitude and provide a background history for future natural changes to this system solar irradiance variability is suggested to have influenced peru productivity as evidenced in numerous high resolution paleorecords from the northern hemisphere

a holocene paleoclimate reconstruction for eastern canada based on δ18o cellulose of sphagnum mosses from mer bleue bog we present a 9200 yr high resolution oxygen isotope record of plant cellulose 18ocel from the peat deposits of mer bleue bog ontario and apply it as a proxy for paleotemperature reconstruction in eastern canada the results show that 18ocel of sphagnum follows the general pattern of the northern hemisphere reconstructed paleotemperature record for the last 2000 years at a ratio of 2 18ocel c the 18ocel record of ombrotrophic phase of mer bleue bog is also in accordance with major features of the holocene sunspot number reconstruction three distinct time intervals have low 18ocel values 200 800 cal bp little ice age 2800 3400 cal bp synchronous to a cooling period reported elsewhere in north america and 4200 4600 cal bp corresponding to a cooling interval in the north atlantic region these cooling periods also correlate well with negative excursions in the holocene sunspot and cosmogenic 10be records a fourth period of low 18ocel values between ad 1810 and 1820 may be related to t

hydroclimatic change in southern manitoba since a d 1409 inferred from tree rings abstract a record of estimated annual prior august to current july precipitation derived from a regional bur oak quercus macrocarpa michx tree ring chronology indicates that southern manitoba s hydroclimate has been relatively stable over the last 200 yr although this stability was interrupted briefly by pronounced wet intervals in the late a d 1820s and 1850s hydroclimatic conditions since permanent euro canadian settlement were much less variable and persistent than those prior to a d 1790 the reconstruction indicates that the red river basin experienced extremely dry conditions between a d 1670 and 1775 with below normal precipitation occurring approximately 2 years out of 3 annual precipitation was estimated at more than two standard deviations below the mean during a d 1477 1485 1556 1595 1612 1644 1661 1743 1900 and 1980 comparisons with limnological records from north dakota and minnesota suggest that multidecadal fluctuations in regional hydroclimate have been remarkably coherent across the northeastern great plains during the last 600 yr however individual dry years in the red river basin were usually associated with larger scale drought across much of the north american interior

geochemistry of ostracode calcite part 2 the effects of water chemistry and seasonal temperature variation on candona rawsoni abstract reconstruction of lake paleochemistry from the isotope and trace element composition of fossil ostracodes requires an understanding of geochemical variations induced by the seasonality of shell formation monthly field collections of live candona rawsoni from two hyposaline lakes in the eastern dakotas reveal large variations in 18 o values 2 5 o and mg ca and sr ca ratios up to 35 among individual adults within the same assemblage because the measured variations in water chemistry were small the amplitude of ostracode 18 o and mg ca variations must result from seasonal temperature variation ostracode sr ca ratios which should be temperature independent shows strong positive covariance with shell mg ca these results imply that sr uptake in ostracode calcite increases with the mg content of the shell the partitioning coefficient for mg on the other hand appears to decreases at high values of mg ca in the host water the geochemical variability in the field collections indicates that c rawsoni populations are composed of multiple overlapping generations that attain maturity at different times many juveniles apparently undergo several molts in mid summer and persist as penultimate instars a 1 into the following spring geochemical analysis of late instar juvenile c rawsoni from lacustrine sedimentary records is likely to provide information on mid summer conditions large numbers of fossil ostracodes should be analyzed from each stratigraphic interval to eliminate seasonal noise from the paleochemistry records of temperate region lakes

asymmetric vegetation responses to mid holocene aridity at the prairie forest ecotone in south central minnesota abstract the mid holocene ca 8000 4000 cal yr bp was a time of marked aridity throughout much of minnesota and the changes due to mid holocene aridity are seen as an analog for future responses to global warming in this study we compare the transition into ca 9000 7000 yr ago and out of ca 5000 2500 yr ago the mid holocene mh period at kimble pond and sharkey lake located along the prairie forest ecotone in south central minnesota using high resolution 5 36 yr sampling of pollen charcoal sediment magnetic and loss on ignition properties changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland forest dominated landscape to a more open mix of grassland and woodland savanna in contrast at the end of the mh grassland remained an important component of the landscape despite increasing effective moisture and high charcoal influxes median 2 7 4 0 vs 0 6 1 7 mm 2 cm 2 yr 1 at start of mh suggest the role of fire in limiting woodland expansion asymmetric vegetation responses variation among and within proxies and the near absence of fire today suggest caution in using changes associated with mid holocene aridity at the prairie forest boundary as an analog for future responses to global warming

temperature responses to quasi 100 yr solar variability during the past 6000 years based on δ18o of peat cellulose in hongyuan eastern qinghai tibet plateau china abstract during the past 6000 years the temperature variation trend inferred from 18o of peat cellulose in a peat core from hongyuan eastern qinghai tibet plateau southwestern china is similar to the atmospheric 14c concentration trend and the modeled solar output trend the general trend of hongyuan 18o during the past millennium also coincides well with the atmospheric 14c concentration trend the 10be concentration trend in an ice core from the south pole the reconstructed total solar irradiance trend as well as the modeled solar output trend in addition temperature events also correspond well to solar perturbations during the past 6000 years therefore the driving force of holocene temperature variations should be properly ascribed to solar activity the spectrum analysis further illustrates that quasi 100 yr fluctuation of solar activity was probably responsible for temperature variations in northeast qinghai tibet plateau during the past 6000 years

a 1000 year record of centennial scale cyclical vegetation change from maar lake sanjiaolongwan in northeastern china abstract to examine possible relationships between regional changes in vegetation and climate and fluctuations in solar activity we obtained a high resolution 1000 year pollen record from the sanjiaolongwan maar lake sjml in northeastern china an age model was established using analyses of 210pb 137cs and ams 14c the pollen assemblages indicate that during the last millennium the vegetation of the study area was temperate coniferous and deciduous broadleaved mixed forest although pinus is the most abundant pollen type in the record various lines of evidence suggest that it is not especially temperature sensitive however the analysis of the changes in pollen assemblages over the past 1000 years and a comparison with pollen records from other lakes in the region indicate that the quercus frequencies can be used as a relatively sensitive temperature index for the study area several notable cold periods with lower quercus frequencies occurred at approximately 1200 ad 1410 ad 1580 ad 1770 ad and 1870 ad these centennial scale cold periods basically correspond to major minima in solar activity suggesting that variations in solar activity may have been an important driver of climate and vegetation change in the study area during the last millennium

the magnitude of error in conventional bulk sediment radiocarbon dates from central north america abstract although the carbon reservoir problem with bulk sediment radiocarbon dates from lakes has long been recognized many synoptic studies continue to use chronologies derived from such dates for four sites in central north america we evaluate chronologies based on conventional radiocarbon dates from bulk sediment versus chronologies based on accelerator mass spectrometry ams radiocarbon dates from terrestrial plant macrofossils the carbon reservoir error varies among sites and temporally at individual sites from 0 to 8000 yr an error of 500 2000 yr is common this error has important implications for the resolution of precise event chronologies

a 1600 year multiproxy record of paleoclimatic change from varved sediments in lake xiaolongwan northeastern china 1 a multiproxy record from lake xiaolongwan northeastern china reveals distinct stratigraphical patterns in organic carbon total nitrogen organic carbon isotope nitrogen isotope clastic content and dinocyst concentration over the past 1600 years high atomic c n ratios in the sediment suggest that a large amount of organic matter in the sediments is derived from vascular plants and soil in the catchment based on the good agreement between cyclical variations of 13corg in the sediments and the spring drought index from historical documents we interpret that the variation of 13corg in the sediments is an indicator of humidity or precipitation in the study area several notable drought periods with heavier 13corg occurred during ad 490 570 ad 780 990 ad 1360 1450 ad 1590 1670 and the last 150 years these century scale drought episodes correspond to solar activity it suggests that solar forcing plays an important role for the 13corg variation in the sediments through driving the changes in humidity vapor pressure deficit dinocyst concentration is high during most of the medieval warm period and low during the european dark age and the little ice age the increase in dinocyst concentration is generally synchronous with decrease of 15n value the 15n values in the studied lake are most likely influenced by the duration and intensification of lake overturn which regulates the amount of depleted 15n nutrients dissolved organic nitrogen and ammonium and dinoflagellate blooms

geomorphic and climatic change over the past 12 900 yr at swiftcurrent lake glacier national park montana usa abstract glaciated alpine landscapes are sensitive to changes in climate shifts in temperature and precipitation can cause significant changes to glacier size and terminus position the production and delivery of organic mass and in the hydrologic energy related to the transport of water and sediment through proglacial environments a sediment core representing a 12 900 yr record collected from swiftcurrent lake located on the eastern side of glacier national park montana was analyzed to assess variability in holocene and latest pleistocene environment the spectral signature of total organic carbon content toc since 7 6 ka matches that of solar forcing over 70 500 yr timescales periodic inputs of dolomite to the lake reflect an increased footprint of grinnell glacier and occur during periods when sediment sinks are reduced glacial erosion is increased and hydrologic energy is increased grain size carbon nitrogen c n ratios and toc broadly define the termination of the younger dryas chronozone at swiftcurrent lake as well as major holocene climate transitions variability in core parameters is linked to other records of temperature and aridity in the northern rocky mountains over the late pleistocene and holocene

cat scan analysis of sedimentary sequences an ultrahigh resolution paleoclimatic tool paleoclimate research is essential to determine the natural variability of climate and to place the current climate change into its natural context the current need is to generate the highest temporal resolution paleoclimatic reconstructions possible in order to assess the natural variability of the climate system but also to test the ability of numerical models to simulate conditions different from the ones observed with the relatively short instrumental records in this paper we show that cat scan analysis of sedimentary sequences with its 1 mm downcore resolution can be used to identify millennial to seasonal cycles in sedimentary sequences in examples from the st lawrence estuary eastern canada spectral analysis of the cat scan data from holocene postglacial sediments revealed millennial to centennial scale oscillations possibly associated with either solar variability changes in relative sea level or tidal amplitude similarly spectral analysis of holocene and sangamonian glaciomarine sequences revealed decadal to annual scale oscillations with periods close to the one previously associated with the north atlantic oscillation nao whereas spectral analysis of the cat scan data from the sangamonian rhythmites possibly revealed seasonal cycles

climate change and decadal to centennial scale periodicities recorded in a late holocene ne pacific marine record examining the role of solar forcing abstract we present a decadal scale late holocene climate record based on diatoms biogenic silica and grain size from a 12 m sediment core vec02a04 obtained from frederick sound in the seymour belize inlet complex of british columbia canada sediments are characterized by graded massive and laminated intervals laminated intervals are most common between c 2948 2708 cal yr bp and c 1992 1727 cal yr bp increased preservation of laminated sediments and diatom assemblage changes at this time suggest that climate became moderately drier and cooler relative to the preceding and succeeding intervals spectral and wavelet analyses are used to test for statistically significant periodicities in time series of proxies of primary production total diatom abundance biogenic silica and hydrology grain size preserved in the frederick sound record periodicities of c 42 53 60 70 82 89 241 243 and 380 yrs are present results are compared to reconstructed sunspot number data of solanki et al 2004 using cross wavelet transform to evaluate the role of solar forcing on ne pacific climate significant common power of periodicities between c 42 60 70 89 241 243 and of 380 yrs occur suggesting that celestial forcing impacted late holocene climate at frederick sound replication of the c 241 243 yr periodicity in sunspot time series is most pronounced between c 2900 cal yr bp and c 2000 cal yr bp broadly correlative to the timing of maximum preservation of laminated sedimentary successions and diatom assemblage changes high solar activity at the suess de vries band may have been manifested as a prolonged westward shift and or weakening of the aleutian low in the mid late holocene which would have diverted fewer north pacific storms and resulted in the relatively dry conditions reconstructed for the seymour belize inlet complex

a holocene pollen record of persistent droughts from pyramid lake nevada usa pollen and algae microfossils preserved in sediments from pyramid lake nevada provide evidence for periods of persistent drought during the holocene age we analyzed one hundred nineteen 1 cm thick samples for pollen and algae from a set of cores that span the past 7630 years the early middle holocene 7600 to 6300 cal yr b p was found to be the driest period although it included one short but intense wet phase we suggest that lake tahoe was below its rim for most of this period greatly reducing the volume and depth of pyramid lake middle holocene aridity eased between 5000 and 3500 cal yr b p and climate became variable with distinct wet and dry phases lake tahoe probably spilled intermittently during this time no core was recovered that represented the period between 3500 and 2600 cal yr b p the past 2500 years appear to have had recurrent persistent droughts the timing and magnitude of droughts identified in the pollen record compares favorably with previously published y 18 o data from pyramid lake the timing of these droughts also agrees with the ages of submerged rooted stumps in the eastern sierra nevada and woodrat midden data from central nevada prolonged drought episodes appear to correspond with the timing of ice drift minima solar maxima identified from north atlantic marine sediments suggesting that changes in solar irradiance may be a possible mechanism influencing century scale drought in the western great basin d 2004 university of washington all rights reserved

late holocene flood probabilities in the black hills south dakota with emphasis on the medieval climate anomaly abstract a stratigraphic record of 35 large paleofloods and four large historical floods during the last 2000 years for four basins in the black hills of south dakota reveals three long term flooding episodes identified using probability distributions at a d 120 395 900 1290 and 1410 to present during the medieval climate anomaly a d 900 1300 the four basins collectively experienced 13 large floods compared to nine large floods in the previous 800 years including the largest floods of the last 2000 years for two of the four basins this high concentration of extreme floods is likely caused by one or more of the following 1 instability of air masses caused by stronger than normal westerlies 2 larger or more frequent hurricanes in the gulf of mexico and atlantic ocean and or 3 reduced land covering vegetation or increased forest fires caused by persistent regional drought

holocene highstand deposits in the gulf of cadiz sw iberian peninsula a high resolution record of hierarchical environmental changes a comparison of the internal structure of holocene highstand shallow marine deposits with emerged spit bar systems in the gulf of cadiz margin sw iberian peninsula is presented in order to increase the knowledge about the patterns of environmental fluctuations of sub milankovitch periodicity during the recent highstand period a high resolution seismic database of boomer profiles was interpreted focusing on shallow marine deposits of the gulf of cadiz shelf such as the guadalquivir river prodelta the guadiana river depositional system and the faro tavira infralittoral prograding wedge the results indicate that the internal architecture of recent highstand shelf deposits is complex as the recognition of three main types of seismic unit motifs suggests the existence of a hierarchical pattern of environmental fluctuations a major scale motifs the most significant feature observed in the seismic records is the pervasive occurrence of two major scale motifs lower and upper within the holocene highstand systems tract b intermediate scale motifs each major scale motif is composed of two intermediate scale motifs defining four intermediate scale motifs h1 to h4 c minor scale motifs the internal structure of major and intermediate scale motifs reveals a high degree of environmental variability during the recent highstand probably led by climatic cyclicities of submillenial scale the lower major scale motif is characterised by alternating progradational aggradational minor scale motifs whereas the upper major scale motif presents a more uniform internal structure dominated by progradational units the influence of two distinct trends or asymmetric cycles of sea level change seems to have been significant in the generation of the major scale architecture the transition between both major phases was probably related with a major sea level rise other factors such as changes in the magnitude and or direction of storm events and climatically induced changes of sediment supply are proposed to have controlled the generation of intermediate and minor scale architectures

stratigraphy and geochronology of upper quaternary eolian sand on the southern high plains of texas and new mexico united states eolian sand in dune fields and sand sheets cover 10 000 km 2 10 of the southern high plains of northwestern texas and eastern new mexico these deposits are concentrated in three west east trending belts of dunes the muleshoe lea yoakum and andrews dune fields from north to south that appear to be eastern extensions of the mescalero monahans dune system in the pecos river valley and in the seminole sand sheet a discontinuous accumulation of sheet sands between the lea yoakum and monahans andrews dunes the most common landforms are parabolic dunes associated with blowouts coppice dunes and sand sheets all typical of sandy vegetated semiarid landscapes barchan dunes in keeping with a relatively limited sand supply and an underlying surface that is relatively hard blackwater draw formation pleistocene and fence row dunes historic dunes formed along field boundaries these eolian deposits accumulated episodically in the late pleistocene and holocene and provide clues to the history of regional drought and aridity the earliest phase of sedimentation occurred when sheet sands were deposited between 11 000 and 8000 14 c yr b p probably in several phases based on archaeological data as a result of episodic drought beginning between 11 000 and 10 000 yr b p eolian deposits dating between 8000 and 3000 yr b p are rare although eolian sediment 8000 4500 14 c yr b p is ubiquitous in the draws that cross the region and paleoenvironmental indicators show that the region was subjected to aridity throughout middle holocene time the middle holocene deposits most likely were remobilized in late holocene time most of the deposits and landforms of the dune fields and sand sheets are late holocene dating before 4000 14 c yr b p and mostly before 1500 14 c yr b p the muleshoe and lea yoakum dunes and the seminole sand sheet underwent substantial eastward expansion in late holocene time buried soils and radiocarbon ages show that the eolian sand accumulated in several stages probably in response to cyclic drought the muleshoe dunes accumulated after ca 1300 cal yr b p ca 1400 14 c yr b p after ca 750 670 cal yr b p ca 850 750 14 c yr b p just after ca 500 cal yr b p ca 450 14 c yr b p and during the nineteenth and twentieth centuries the lea yoakum dunes were active after ca 3400 cal yr b p ca 3200 14 c yr b p and historically the seminole sand sheet was active ca 430 330 cal yr b p ca 360 14 c yr b p and in the twentieth century the andrews dunes were subjected to at least two phases of eolian sedimentation after ca 2320 cal yr b p ca 2320 14 c yr b p comparisons with eolian chronologies from other regions on the great plains suggest that dune mobilization was a regional phenomenon after ca 2300 cal yr b p ca 2300 14 c yr b p after ca 1500 1400 cal yr b p ca 1650 1550 14 c yr b p after ca 700 cal yr b p ca 800 14 c yr b p between 500 and 300 cal yr b p ca 450 300 14 c yr b p and in the nineteenth century the climatic fluctuations responsible for mobilizing the dunes probably were relatively minor yet the landscape impacts were substantial resulting in widespread wind erosion and dune construction

evidence for multiple episodic mid holocene hypsithermal recorded in two soil profiles along an alluvial floodplain catena southeastern tennessee usa abstract floodplain soil paleosol successions are valuable archives for reconstructing pleistocene holocene climate changes but have been relatively unstudied in the southern appalachian region two soil profiles on a small floodplain in southeastern tennessee usa were described and sampled in detail using both pedological and geological approaches including stable carbon isotope analysis of soil organic matter som correlation between the 2 profiles was constrained by uncalibrated ams 14c ages of bulk humates and using som 13c values both mobile and immobile elements four distinct 2 5 4 shifts towards less negative 13c values for som suggest 300 yr cyclicity and transient warmer and drier climate events with either water stressed c3 vegetation or as much as 35 c4 plants present during the mid holocene these postulated multi episodic drier climate conditions have never before been documented in the southern appalachian region and are tentatively correlated with mid holocene warming and drying in the eastern us the nearly time equivalent mid holocene events documented in texas the us high plains and in the gulf of mexico high rates of floodplain sediment accumulation 0 5 3 mm yr high clay content and maintenance of poorly drained soil conditions favor preservation of high resolution climate archives in floodplain deposits by inhibiting oxidation and translocation of organic c

centennial eolian cyclicity in the great plains usa a dominant climate pattern of wind transport over the past 4000 years proxy evidence at decadal resolution from late holocene sediments from pickerel lake northeastern south dakota shows distinct centennial cycles 400e700 years in magnetic susceptibility contents of carbonate organic carbon and major elements abundance in ostracodes and d 18 o and d 13 c values in calcite proxies indicate cyclic changes in eolian input productivity and temperature maxima in magnetic susceptibility are accompanied by maxima in aluminum and iron mass accumulation rates mars and in abundances of the ostracode fabaeformiscandona rawsoni this indicates variable windy and dry conditions with westerly wind dominance including during the medieval climate anomaly maxima in carbonates organic carbon phosphorous and high d 13 c values of endogenic calcite indicate moister and less windy periods with increased lake productivity including during the little ice age and alternate with maxima of eolian transport times of the maunder sporer and wolf sunspot minima are characterized by maxima in d 18 o values and aluminum mars and minima in d 13 c values and organic carbon content we interpret these lake conditions during sunspot minima to indicate decreases in lake surface water temperatures of up to 4e5 c associated with decreases in epilimnetic productivity during

lake sediments record large scale shifts in moisture regimes across the northern prairies of north america during the past two millennia six high resolution climatic reconstructions based on diatom analyses from lake sediment cores from the northern prairies of north america show that shifts in drought conditions on decadal through multicentennial scales have prevailed in this region for at least the last two millennia the predominant broad scale pattern seen at all sites is a major shift in moisture regimes from wet to dry or vice versa depending on location that occurred after a period of relative stability these large scale shifts at the different sites exhibit spatial coherence at regional scales the three canadian sites record this abrupt shift between anno domini 500 and 800 and subsequently conditions become increasingly variable all three u s sites underwent a pronounced change but the timing of this change is between anno domini 1000 and 1300 thus later than in all of the canadian sites the mechanisms behind these patterns are poorly understood but they are likely related to changes in the shape and location of the jet stream and associated storm tracks if the patterns seen at these sites are representative of the region this observed pattern can have huge implications for future water availability in this region

hydrologic response of the crow wing watershed minnesota to mid holocene climate change in this study we have integrated a suite of holocene paleoclimatic proxies with mathematical modeling in an attempt to obtain a comprehensive picture of how watersheds respond to past climate change a three dimensional surface water groundwater model was developed to assess the effects of mid holocene climate change on water resources within the crow wing watershed upper mississippi basin in north central minnesota the model was first calibrated to a 50 yr historical record of average annual surface water discharge monthly ground water levels and lake level fluctuations the model was able to reproduce reasonably well long term historical records 1949 1999 of water table and lake level fluctuations across the watershed as well as stream discharge near the watershed outlet the calibrated model was then used to reproduce paleo groundwater and lake levels using climate reconstructions based on pollen transfer functions from williams lake just outside the watershed computed declines in mid holocene lake levels for two lakes at opposite ends of the watershed were between 6 and 18 m simulated streamflow near the outlet of the watershed decreased to 70 of modern average annual discharge after 200 yr the area covered by wetlands for the entire watershed was reduced by 16 the mid holocene hydrologic changes indicated by these model results and corroborated by several lake core records across the crow wing watershed may serve as a useful proxy of the hydrologic response to future warm dry climatic forecasts ca 2050 made by some atmospheric general circulation models for the glaciated midwestern united states

biotic and abiotic response to palaeoenvironmental changes at lake pannons western margin central europe late miocene a multidisciplinary study was performed on a c 30 m thick limnic deltaic sequence in the styrian basin austria geophysical gamma ray activity rock magnetism geochemical organic carbon sulphur and sedimentological observations were combined with palaeontological information mainly ostracods on this base several ecological factors were deduced terrigenous influx salinity water depth and oxygenation based on integrated stratigraphy as well as on palaeomagnetic results the whole section is set to chron c5r 2r 1n 11 308 11 263 ma and covers a period of less than 45 kyr in addition to the long term record we analysed short term changes by high resolution sampling 5 mm sample interval ostracods magnetic susceptibility this 2 3 m thick interval spans in total 3500 yr with an individual sample resolution of a few years only the combination of these data permit the description of the palaeoenvironmental evolution of the section in detail at the base of the section the development of a conifer swamp on the lakeside of lake pannon is documented this almost freshwater swamp existed for some centuries before it became extinct within a few decades due to a rise of the water table the drowning is related to a transgression of lake pannon which triggered the establishment of a brackish water fauna as well as greigite formation in the lake sediments in general the ongoing transgression favoured benthic life due to increased salinity up to mesohaline conditions the high resolution ostracod and magnetic susceptibility record reflect short term fluctuations in bottom water ventilation these oscillations probably range in the order of centuries and decades and are possibly related to climatic shifts later the successive deepening of the lake resulted in a significant faunal turnover a meromictic system with a well established oxygen depleted hypolimnion developed finally the limnic phase was replaced by a prograding deltaic system where the amplified input of coarse grained material and freshwater also affected benthic life periodic changes in clay illite content were detected by the gamma ray log throughout the entire section the observed cycles 5 12 kyr of the gamma ray log may reflect a super ordinate modulation of the sedimentary record by climatically forced changes in precipitation or run off

solar influence and hydrological variability during the holocene from a speleothem annual record molinos cave ne spain this study is a contribution to the ctm2013 48639 c2 1 r opera cgl2009 10455 and hidropast cgl2010 16376 projects spanish government european regional development fund the uz2014 cie 04 project university of zaragoza the ga lc 030 2011 project aragon government la caixa and the e 28 and s 97 research groups aragon government

possible solar forcing of century scale drought frequency in the northern great plains a 2100 yr decadal resolution salinity and aridity proxy record of lacustrine ostracode shell mg ca ratios from a closed basin lake in the northern great plains shows statistically significant periodicities of 400 200 130 and 100 yr these periodicities are similar to the three principal solar oscillation periods 420 218 143 yr as inferred from the atmospheric radiocarbon record suggesting strong solar forcing of century scale drought frequency with a fundamental 400 yr period and its 2nd 3rd and 4th harmonics our proxy record correlates visually and statistically cross spectral analysis with the atmospheric 14 c record solar proxy and the gisp2 greenland ice sheet project two 18 o record climate proxy showing that solar minima are in phase with drought periods in the northern great plains and cold periods in greenland this spectral similarity together with phase correlation indicates a possible teleconnection of century scale global climate fluctuations through common solar forcing

foraminiferal evidence of major environmental changes driven by the sun climate coupling in the western portuguese coast 14th century to present abstract new paleoclimatic data from the casa branca salt marsh in the southwest coast of portugal are compared with records previously published on the northwest coast caminha salt marsh to offer a more comprehensive overview of the environmental evolution of the west iberian margin over the last six centuries these reconstructions are based on the foraminiferal records of two dated sediment cores retrieved from the high marsh settings and supported by geochemical sedimentological data both marshes were originally formed in the ad 1300s between the medieval climatic anomaly mca and the little ice age lia highlighting a major episode of increased sediment supply in lower estuaries linked to climate driven changes in continental runoff afterwards the two marshes evolved under different climatic regimes as reflected by their foraminiferal assemblages the environmental conditions are characterized by higher salinity in casa branca southwest with jadammina macrescens and trochammina inflata as dominant species than in caminha northwest where haplophragmoides spp dominates we suggest that a long term trend of a net gain in evapotranspiration at casa branca inducing a higher marsh salinity baseline may explain this microfaunal contrast trochammina inflata seems to be a good indicator of drier periods in the studied area connected to key events of aeolian large dust input to the southwest coast of portugal the influence of the most important climate drivers was assessed namely external solar and internal north atlantic oscillation nao forcings spectral and wavelet transform coherence analyses were used to detect solar footprints on foraminiferal and climate related time series a main significant quasi periodicity was identified within the range of the secular gleissberg cycle of solar activity modulating the annual nao and regional spring summer simulated temperatures after ad 1700 this stronger solar climate coupling may be related to the known upward secular trend in the total solar irradiance after the maunder minimum

abstract molecular and isotopic properties of high flux gas seeps northwestern gulf of mexico study of the molecular distributions and carbon isotopic properties of methane from 160 high flux seep sites across the gulf of mexico from the outer shelf to the lower slope reveals new insight to the complex origin of gas at the sea floor each site represents the intersection of a major migration conduit from the deep subsurface to the sea floor related to salt or faults sites were selected to minimize bias from known gas and oil fields mean concentration of methane is 99 407 ppm means of ethane 1 837 ppm iso butane 825 ppm and normal butane 607 ppm are anomalous to provide perspective typical gulf sediment has methane 10 ppm and higher hydrocarbons may be in low abundance or below detection limits the mean carbon isotopic composition per mil pdb standard of methane is 74 0 whereas the range is from 30 1 to 116 6 the occurrence of isotopically heavy methane probably represents bacterially oxidized thermogenic methane but the occurrence of extremely light methane implies that carbon is recycled through bacterial hydrocarbon oxidation and reduction of carbon dioxide in natural bioreactors molecular and isotopic properties of gas suggest that nearly all high flux gas seeps across the gulf are a mixture of bacterial and thermogenic hydrocarbons contrary to previous generalizations much bacterial methane may originate from several kilometers depth the carbon isotopic threshold between bacterial and thermogenic methane often cannot be defined because considerable overlap exists and bacterial alteration is common

climate cyclicity in late holocene anoxic marine sediments from the seymour belize inlet complex british columbia abstract an 8 72 m late holocene sediment core vec02a07 obtained from alison sound in the belize seymour inlet complex of central british columbia canada was deposited between 3500 1000 yr bp under primarily anoxic marine conditions this core contains a detailed cyclic record of land sea interactions as evidenced by significant fluctuations in marine primary productivity and changes in the supply of terrigenous material that can be related to long term variation in the relative influence of the aleutian low al and north pacific high nph sedimentologically the core is characterized by alternating intervals of fine grained massive intervals 70 laminated intervals 23 turbidites 5 and graded silt clay layers 2 the laminated intervals are comprised of couplets that vary between light coloured diatom rich layers deposited primarily during the summer months and dark coloured mineral rich layers deposited during winter laminated couplets are most common in portions of the core deposited between 3150 and 2700 yr bp which corresponds to an episode of regional neoglaciation time series analysis was carried out on high resolution particle size measurements obtained from core sub samples and on sediment grey scale colour variability derived from x ray scans of the core non linear time series analyses revealed that the succession of massive and laminated sedimentation displayed characteristics of self organization following a power law relationship for core length segments of 13 cm 50 years of deposition contained evidence of sedimentary depositional cycles of 70 96 135 155 and 250 330 years that reflect changes in al and nph mediated regional precipitation patterns that can in turn be related to larger scale climate drivers such as the pacific decadal oscillation pdo or solar irradiance cyclicity

gravity waves propagating into an ice covered ocean a viscoelastic model 1 a viscoelastic model is proposed to describe the propagation of gravity waves into various types of ice cover the ice ocean system is modeled as a homogeneous viscoelastic fluid overlying an inviscid layer both layers have finite thickness the viscosity is imagined to originate from the frazil ice or ice floes much smaller than the wavelength and the elasticity from ice floes which are relatively large compared to the wavelength a compact form of the dispersion relation is obtained under proper limiting conditions this dispersion relation can be reduced to several previously established models including the mass loading model the viscous layer model and the thin elastic plate model the full dispersion relation contains several propagating wave modes under the ice cover the following two criteria are used to select the dominant wave mode 1 wave number is the closest to the open water value and 2 attenuation rate is the least among all modes the modes selected from those criteria coincide with the ones discussed in previous studies which are shown to be limiting cases in small or large elasticity regimes of the present model in the intermediate elasticity regime however it appears that there are three wave modes with similar wavelengths and attenuation rates implications of this intermediate elasticity range remain to be seen the general viscoelastic model bridges the gap among existing models it also provides a unified tool for wave ice modelers to parameterize the polar regions populated with various types of ice cover

increased precipitation and weathering across the paleocene eocene thermal maximum in central china global warming during the paleocene eocene thermal maximum petm 55 5 million years ago ma was associated with a massive release of carbon to the ocean atmosphere system as evidenced by a prominent negative carbon isotope excursion cie and widespread dissolution of marine carbonates the paleohydrologic response to the petm warming has been studied worldwide however relevant records of environmental perturbation in asia are lacking so far here we extend the record of this event in central china a subtropical paleosetting through geochemical and mineralogical analyses of lacustrine sediments geochemical indicators of authigenic carbonates including molar mg ca and sr ca ratios suggest an overall increased precipitation across the petm compatible with the disappearance of authigenic dolomite and the appearance of kaolinite in the strata the relatively humid conditions persisted long after the carbon cycle perturbation had stopped implying that the transient hyper greenhouse warming might have forced the regional climate system into a new climate state that was not easily reversed additionally a gradual increase in chemical index of alteration cia and the appearance of kaolinite are associated with the petm indicating an intensified silicate weathering and pedogenesis in the watershed in response to warmer and more humid climate our results corroborate the theory that an accelerated continental chemical weathering served as a negative feedback to sequester carbon and lower the atmospheric greenhouse gas levels during the petm

characteristics of the east asian summer monsoon in the south sea of korea during the little ice age abstract the sediment record of a drilled core ssdp 103 and four ams 14 c datings were used to generate oxygen and carbon isotope data over the last 2000 years of the benthic foraminifer cibicides lobatulus in the south sea of korea high sedimentation rates facilitated a decadal resolution throughout the study period significant periodicities of 316 249 144 and 88 years were observed in the 18 o record of the benthic foraminifera similar periodicities of 310 220 143 and 120 years were identified in the 13 c record these periodicities were close to those of solar origin which are related to changes in the oceanic and atmosphere circulation in east asia the three point smoothed 18 o curve of benthic foraminifera in the study area was closely correlated with the stalagmite 18 o record from chinese caves for the last 2000 years except during the dramatic cooling interval of the little ice age lia during the cooling period the benthic foraminifera 18 o values significantly increased while stalagmite 18 o values decreased such an inverse relationship during the lia reflects synchronous strengthening of the east asian summer monsoon easm and weakening of the indian summer monsoon ism under the present climatic system an inverse relationship between these two asian monsoons has frequently occurred when an el nino event developed the results suggest that late holocene cold events are associated with el nino like climatic patterns

determining the sun s influence on lateglacial and holocene climates a focus on climate response to centennial scale solar forcing at 2800 cal bp abstract the influence of solar variability on the climate of the lateglacial and holocene periods has been the subject of increasing discussion during the last decade in the mid holocene several studies have identified cold wet events that occur at ca 2800 cal bp and a link with a reduction in solar activity inferred from the 14c record has been postulated we present results from a multi proxy study of peat humification plant macrofossils and testate amoebae from a raised bog at glen west northwest ireland that indicate that dry bog surface conditions were experienced in the north of ireland at the time of the solar anomaly starting at 2800 cal bp with the aid of 14c wiggle matching and tephrochronology an abrupt shift to wetter conditions is dated to ca 2700 cal bp coinciding with a 14c maximum but clearly post dating the 2800 cal bp event identified elsewhere in europe we explore the significance of this apparent lag in the irish record considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the north atlantic region we conclude that these complexities are likely to give rise to time transgressive climate responses around the north atlantic that will only be recognised by more critical chronological approaches

ostracod shell chemistry as proxy for paleoenvironmental change abstract the application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades most studies have investigated mg and sr in ostracod shells as proxies for temperature and salinity and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems only a few preliminary studies have used trace metals in paleolimnological studies such as cd ba and zn as paleonutrient indicators or mn fe and u as redox and oxygenation indicators this paper reviews the state of the art of geochemical analyses in microfossils such as ostracods foraminifera and corals and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies in paleoceanography foraminifera and corals are most prominently used to reconstruct past climate conditions well established proxies such as 18o mg ca and sr ca provide information about changes in sea surface temperatures in addition a great number of new proxies have been developed recently such as radiogenic isotopes and redox sensitive trace elements in paleolimnology ostracod shell chemistry is widely used to assess paleohydrological changes reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as mg ca and sr ca ratios but depending on the hydrological and geological settings of the lake system local calibrations are needed to assess which proxy is suited to reflect which processes new proxies need to be tested by novel techniques that recently have become available compared to conventional instrumentation used in ostracod shell chemistry methods such as laser ablation icp ms and nanosims allow single shell analysis and provide high resolution data the potential of ostracods in paleolimnology is not yet fully assessed but can be developed by learning from paleoceanographic studies

multispectral analysis of northern hemisphere temperature records over the last five millennia aiming to describe spatio temporal climate variability on decadal to centennial time scales and longer we analyzed a data set of 26 proxy records extending back 1 000 5 000 years all records chosen were calibrated to yield temperatures the seven irregularly sampled series in the data set were interpolated to a regular grid by optimized methods and then two advanced spectral methods namely singular spectrum analysis ssa and the continuous wavelet transform were applied to individual series to separate significant oscillations from the high noise background this univariate analysis identified several common periods across many of the 26 proxy records a millennial trend as well as oscillations of about 100 and 200 years and a broad peak in the 40 70 year band to study common nh oscillations we then applied multichannel ssa temperature variations on time scales longer than 600 years appear in our analysis as a dominant trend component which shows climate features consistent with the medieval warm period and the little ice age statistically significant nh wide peaks appear at 330 250 and 110 years as well as in a broad 50 80 year band strong variability centers in several bands are located around the north atlantic basin and are in phase opposition between greenland and western europe

century scale solar variability and alaskan temperature change over the past millennium 1 correlation of geologic histories from 130 alaskan glaciers with a record of solar variation suggests that multi decadal to century scale temperature variations in the north pacific and arctic sectors have been influenced by solar forcing over the past thousand years mountain glacier fluctuations are primarily a record of summer cooling and the composite glacial history from three climatic regions across alaska shows ice expansions approximately every 200 years compatible with a solar mode of variability the modulating effects of the cold phases of the pacific decadal oscillation and the arctic oscillation may when in phase with decreased solar activity serve to amplify cooling forcing glacier advance

a 900 year pollen inferred temperature and effective moisture record from varved lake mina west central minnesota usa abstract drought is endemic to the north american great plains causing severe economic consequences however instrumental climate data only exist from ca ad 1890 and limited tree ring paleolimnological archeological and eolian records document the last two millennia to address this lack of monitoring and paleoclimatic data the pollen preserved in the varved sediments of lake mina minnesota on the northeastern border of the great plains were analyzed may and february mean monthly temperatures and annual precipitation minus potential evapotranspiration were reconstructed at a 4 year resolution using a pre settlement pollen climate calibration set the period of the so called little ice age lia ad 1500 1870 was colder than the medieval climate anomaly mca ad 1100 1500 in west central minnesota winter temperatures in the lia declined more than summer ones the pollen record suggests that the lia occurred in three phases an initial cold phase from ad 1505 to ad 1575 a warmer phase and then a very cold phase from ad 1625 to ad 1775 there were severe droughts detected in the lake mina record from ad 1660 to ad 1710 and ad 1300 to ad 1400 suggesting that high resolution pollen records can detect events previously defined from the tree ring records this latter century scale drought is concurrent with the widely reported ad 1250 1400 mega drought which exceeds the severity of 20th century droughts

wave attenuation by sea ice turbulence the dissipation of wave energy in the marginal ice zone is often attributed to wave scattering and the dissipative mechanisms associated with the ice layer in this study we present observations indicating that turbulence generated by the differential velocity between the sea ice cover and the orbital wave motion may be an important dissipative mechanism of wave energy through field measurements of under ice turbulence dissipation rates in pancake and frazil ice it is shown that turbulence induced wave attenuation coefficients are in agreement with observed wave attenuation in the marginal ice zone the results suggest that the turbulence induced attenuation rates can be parameterized by the characteristic wave properties and a coefficient the coefficient is determined by the ice layer properties

hydrologic variation in the northern great plains during the last two millennia abstract reconstructions of lake water salinity at decadal resolution for the last 2000 yr are compared among three lakes in north dakota to infer regional patterns of drought the intersite comparisons are used to distinguish local variation in climate or hydrology from regional patterns of change at one lake diatom inferred salinity and lake water mg ca inferred from ostracode shell chemistry are coherent both in terms of direction and magnitude of change indicating that each is a robust technique for reconstructing lake water chemistry the data show that the last 2000 yr have been characterized by frequent shifts between high and low salinity suggesting shifts between dry and moist periods long intervals of high salinity suggest periods of multiple decades when droughts were intense and frequent thus indicating times when drought was more persistent than in the 20th century both the medieval period and little ice age were hydrologically complex and there is no clear evidence to suggest that either interval was coherent or unusual in effective moisture relative to long term patterns differences among the three sites may be attributed to variation in local hydrology and these differences emphasize the need for multiple sites in deriving regional climate interpretations from paleoecological data

holocene environmental and climatic change in the northern great plains as recorded in the geochemistry of sediments in pickerel lake south dakota the sediments in pickerel lake northeastern south dakota provide a continuous record of climatic and environmental change for the last 12000 yr sediments deposited between 12 and 6 ka radiocarbon show extreme variations in composition oxygen and carbon isotopic composition of bulk carbonate carbon isotopic composition of organic matter and magnetic susceptibility these variations re ect changes in sources of moisture regional vegetation types precipitation evaporation balance ground and surface water in ux water residence time erosion lake productivity water level and water temperature the total carbonate content of late pleistocene sediments steadily increased from 20 at the base of the core to as much as 80 in sediments deposited between 11 and 9 ka by about 8 ka the total carbonate content of the sediments had declined to about 40 where it remained with little variation for the past 8 kyr suggesting relatively stable conditions there are marked increases in values of d13c and d18 oi n bulk carbonate and d13c of organic matter in sediments deposited between 10 and 6 ka as evaporation increased and the vegetation in the watershed changed from forest to prairie this shift toward more 18o enriched carbonate may also re ect a change in source or seasonality of precipitation during this early holocene interval the organic carbon oc content of the sediments remained relatively low 2 3 but then increased rapidly to 4 5 between 7 and 6 ka re ecting the rapid transition to a prairie lake the oc content uctuates slightly between 4 and 6 in sediments deposited over the past 6 kyr like oc and total carbonate most variables measured show little variation in the 13 m of sediment deposited over the past 6 kyr particularly when compared with early holocene variations although the magnetic susceptibility of this upper 13 m of sediment is generally low 10 si units the upper six meters of the section is marked by striking 1 m cycles ca 400 500 yr periodicity in susceptibility these cycles are interpreted as being due to variations in the in ux of eolian detrital clastic material century scale cyclic variations in di erent proxy variables for aridity and eolian activity from sediments deposited over the past 2000 yr in other lakes in the northern great plains as well as in sand dune activity suggest that aridity cycles were the dominant feature of late holocene climate of the northern great plains 2000 elsevier

high resolution proxy record of holocene climate from a loess section in southwestern nebraska usa abstract multi proxy analysis was used to produce a high resolution paleoclimatic record from an exceptionally thick section of the holocene bignell loess near wauneta southwestern nebraska in the central great plains the wauneta section has excellent age control based on optically stimulated luminescence osl and radiocarbon dating and records multiple episodes of rapid loess deposition alternating with slower deposition and soil formation the lowermost and uppermost osl ages obtained from the bignell loess are 10 250 610 years 5 9 m depth and 100 10 years 0 1 m depth respectively as a result the holocene has been temporally confined stratigraphically the bignell loess overlies the late pleistocene peoria loess deposited 21 14 ka and the two units are separated by the brady soil which is distinguished by its color and other pedogenic features l a b color parameters and organic carbon content of bignell loess are sensitive proxies to differentiate drought induced aeolian sediment layers from the intercalated soil horizons soil organic carbon derived 13 c data suggest that the c 3 dominated floral environment during peoria loess deposition shifted dramatically to a c 4 dominated environment during brady soil formation in response to a warming trend even greater c 4 abundance characterized the late holocene high resolution 13 c data support the contention that c 3 vs c 4 vegetation change in the holocene reflects ecosystem response to frequent vegetation disturbance under arid conditions time series analysis reveals that 13 c and color parameters display high frequency variation with periodicities of 103 118 years and 103 years respectively similar periodicities were also reported in studies of north dakota lakes though the physical mechanism responsible is uncertain comparison of bignell loess color and tropical pacific sea surface temperatures ssts allows evaluation of a proposed teleconnection between drought in the great plains and la nina like conditions in the tropical pacific the loess color index and eastern tropical pacific sst display broad similarities through the late pleistocene and holocene that are consistent with this teleconnection on the other hand drought centered at 3800 years ago is not consistent with the teleconnection and the end of early holocene aridity at the wauneta section around 6500 years ago is much earlier than the corresponding rise in sst and increase in el nino frequency in the eastern tropical pacific

gas venting and subsurface charge in the green canyon area gulf of mexico continental slope evidence of a deep bacterial methane source abstract questions as to the role of modern carbon in methanogenesis and the maximum depth of methane sources in the gulf of mexico continental slope remain unanswered a research submersible was used to sample mixed bacterial and thermal gas 13 c of methane 62 8 d 176 venting to the water column from the gulf slope in green canyon gc 286 the 14 c value of the methane 998 is consistent with fossil carbon another gas vent on gc 185 is 100 methane 13 c 62 9 d 155 and may be from a bacterial source the 14 c 997 of this bacterial methane is also consistent with fossil carbon fossil bacterial methane and thermal hydrocarbons are present in pliocene to pleistocene reservoirs 3509 4184 m of genesis field gc 205 161 160 oil in these reservoirs is biodegraded but gas is not suggesting that gas charge to reservoirs continues presently at 3 4 km depth mixed thermal and bacterial methane may charge the deep reservoirs and fossil methane from depth may ultimately vent on the sea floor at gc 286 and gc 185 results of this study of green canyon suggest that bacterial methane in gas vents and in reservoirs is from deep fossil sources

differential hydrogen isotopic ratios of sphagnum and vascular plant biomarkers in ombrotrophic peatlands as a quantitative proxy for precipitation evaporation balance abstract we have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound specific hydrogen isotope ratios of vascular plant and sphagnum biomarkers in ombrotrophic peatland sediments we show that the contrast in h isotopic ratios of water available to living sphagnum top 20 cm and in the rooting zone of peatland vascular plants can be used to estimate the fraction of water remaining after evaporation vascular plant leaf waxes record h isotopic ratios of acrotelm water which carries the d h ratio signature of precipitation and is little affected by evaporation whereas the sphagnum biomarker c 23 n alkane records h isotopic ratios of the water inside its cells and between its leaves which is strongly affected by evaporation at the bog surface evaporation changes can then be deduced by comparing h isotopic ratios of the two types of biomarkers we calibrated d h ratios of c 23 n alkane to source water with lab grown sphagnum we also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the midwestern united states finally we generated a 3000 year downcore reconstruction from minden bog michigan usa our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss

a possible solar pacemaker for holocene fluctuations of a salt marsh in southern italy abstract this study is aimed at verifying the possible influence of solar activity on the coastal vegetation development in the tavoliere plain south adriatic region italy between 6350 and 4000 cal bp when regular fluctuations of halophilic vegetation are recorded by pollen a wavelet analysis applied to the percentage values of glasswort vegetation is consistent with periodicities of solar activity and other palaeoenvironmental and palaeoclimate proxies in the literature a comparison of salt marsh pollen indicators salicornia type and ruppia maritima with the 10be dataset from the greenland ice core gisp2 on the basis of their independent chronologies reveals a strong visual correlation indicating that the minima of salt marsh percentages match minima in the 10be curve corresponding to solar activity maxima associated with warm and arid phases at the middle latitudes the tavoliere salt marsh appears to have contracted during the arid warm phases associated to maxima of solar activity and to have expanded during the wet cold phases of solar minima this coastal area characterized by a very flat topography and arid climate appears to have been very sensitive to even minor hydrological and climate changes changes of solar activity determining extensive environmental transformations were also possibly responsible for the abandonment of the human coastal settlements of one of the most important neolithic archaeological districts of italy

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

holocene changes in sea ice cover and polynya formation along the eastern north greenland shelf new insights from biomarker records abstract understanding the processes controlling the natural variability of sea ice in the arctic one of the most dynamic components of the climate system can help to constrain the effects of future climate change in this highly sensitive area for the first time a high resolution biomarker study was carried out to reconstruct past sea ice variability off eastern north greenland this area is strongly influenced by cold surface waters and drift ice transported via the east greenland current meltwater pulses from the outlet glaciers of the northeast greenland ice stream and the build up of landfast ice the well dated holocene sedimentary section of core ps93 025 provides insights into variations of the sea ice conditions regional and local sea ice signal oceanic and atmospheric circulation and the biotic response to these changes these biomarker records show a reduced to variable sea ice cover during the early holocene between 10 2 and 9 3 ka followed by a steady increase in sea ice conditions during the mid holocene during the last 5 6 ka sea ice conditions remained more stable representing a seasonal to marginal sea ice situation based on our biomarker records stable sea ice edge conditions with a fully developed polynya situation occurred since the last 1 ka

interactions of climate and fire at two sites in the northern great plains usa abstract the relationship of fire and climate in explaining the origin and maintenance of the grasslands of the northern great plains has long been of interest i examined the hypothesis that burning was more frequent during wet years using charcoal to reconstruct fire histories near coldwater lake in southcentral nd and rice lake in northcentral nd and published records of ostracod mg ca ratios as a proxy for climate at these same two sites over the past 10 000 years charcoal influx rates for coldwater 0 04 5 68 mm 2 cm 2 year 1 greatly exceeded influx rates for rice 2 cm 2 year 1 both sites showed strong significant periodicities of 1500 1800 800 900 and 130 140 years but charcoal maxima and minima were only similar at 4200 cal years bp charcoal influx during the past 2000 years also revealed strong periodicities of between 310 400 and 140 years at both sites comparison of smoothed charcoal influxes and ostracod mg ca ratios suggests that both proxies are responding to changes in climate when smoothed with a 320 400 year window increases in charcoal influx typically preceded rises in ostracod mg ca ratio by 50 100 years and further smoothing 140 year window of the residuals suggested a variable relationship between mg ca ratios and charcoal influx these results do not clearly support or reject the fuel limitation hypothesis and this lack of clear support may result from a climate driven shifts in the mix of c 3 and c 4 grasses resulting in maximum productivity at intermediate moisture levels b possibly different responses of charcoal and mg ca ratios to summer vs winter precipitation or c ground water driven lags in the response of mg ca ratios to shifts in climate comparison of the results from this study with other studies suggests that links between fire and fuels at finer time scales 0 100 years may be broadly constrained by longer term 500 2000 years patterns of climate in the northern great plains

a 1000 year record of forest fire drought and lake level change in southeastern british columbia canada high resolution charcoal analysis of lake sediments and stand age information were used to reconstruct a 1000 year fire history around dog lake which is located in the montane spruce zone of southeastern british columbia macroscopic charcoal 125 um accumulation rates char from lake sediment were compared with a modern stand origin map and fire scar dates in the kootenay valley to determine the relative area and proximity of fires recorded as char peaks small fires close to the lake and larger more distant fires appear as similar sized peaks in the record this information reinforces previous findings where char peaks represent a complex spatial aggregation of local to extra local fires around a lake site char peaks indicate frequent stand destroying fires during the mediaeval warm period ad 1000 1300 and other significant fires at c 1360 1500 1610 and 1800 we also present a proxy measure of lake level changes based on a comparison of accumulation rates of chara globulanis type oospores

persistent millennial scale shifts in moisture regimes in western canada during the past six millennia inferences of past climatic conditions from a sedimentary record from big lake british columbia canada over the past 5 500 years show strong millennial scale patterns which oscillate between periods of wet and drier climatic conditions higher frequency decadal to centennial scale fluctuations also occur within the dominant millennial scale patterns these changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core after periods of relative stability abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1 220 years the correspondence of these shifts to millennial scale variations in records of glacial expansion recession and ice rafting events in the atlantic suggest that abrupt millennial scale shifts are important to understanding climatic variability in north america during the mid to late holocene unfortunately the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions

alluvial stratigraphic evidence for channel incision during the mediaeval warm period on the central great plains usa alluvial valley fills from tributaries to the upper republican river southwest nebraska usa provide soil and morpho stratigraphic evidence for an episode of channel incision that occurred between c 1100 and 800 1 4 cyr bp based on 11 new radiocarbon ages this local episode of channel incision correlates with other alluvial stratigraphic studies from the central great plains and demonstrates regionally synchronous fluvial behaviour proxy records of palaeohydrologic conditions in and around the great plains including lacustrine aeolian and geomorphological sources indicate that channel incision correlates with a multicentennial episode of common widespread drought temporally this drought episode corresponds to the period recognized in many regions as the mediaeval warm period mwp therefore this research demonstrates 1 a relationship in the semi arid central great plains between drought and increased fluvial incision and 2 a local regional geomorphic response to a particular episode of global climate change

what do 14c changes across the gerzensee oscillation gi 1b event imply for deglacial oscillations high resolution studies were performed on late glacial sediments from a small lake in western denmark with respect to lithology geochemistry stable isotopes pollen stratigraphy and radiocarbon dating on terrestrial macrofossils one purpose was to detect the so called gerzensee oscillation or the gi 1b event in the later part of the allerod warm period and to describe the environmental impact of this short cooling the other aim was to test the hypothesis that considerable 14c changes occur over this time which can be related to ocean ventilation thermohaline circulation changes we find that the gi 1b event had a major impact on both terrestrial and limnic ecosystems large vegetation changes increased soil erosion and lowered aquatic production by correlations to events in the grip ice core and 14c patterns in the cariaco basin we also transformed our 14c dated record into calendar years to calculate 14c values the 14c dates show that the gi 1b event both preceded and was part of the 11 400 11 300 14c yr bp radiocarbon plateau and was followed by the 11 000 10 900 14c yr bp plateau thus the later part of the event coincides with a distinct age decline this delayed age drop 14c rise in relation to the hypothetical triggering mechanism behind the event decreased ocean ventilation could be explained by redeposited macrofossils at the onset of gi 1b this phenomenon also seen at the onset of younger dryas may also reflect increased soil erosion and redeposition at the start of cold periods the independent cariaco basin record however implies that the very end of the cool gi 1b event is related to a distinct rise in 14c likewise the 10be record from gisp2 shows a distinct rise in the middle of the event precluding decreased solar forcing as the trigger of the climate event but making it likely that high cosmic ray flux low solar activity may be the cause of the rising atmospheric 14c content we thus conclude that the 14c changes over the gerzensee oscillation gi 1b being one of several coolings during the last termination does not seem to be related to ocean ventilation changes the reason behind this lack of coincidence between rising 14c and a fairly distinct northern hemisphere cooling may be due to the fact that the oceanic changes during some of these coolings are too subtle to give an atmospheric 14c imprint or that an anti phase relationship between the two hemispheres blurs the 14c signal or finally that a partly unknown mechanism may lie behind such coolings copyright 2000 john wiley sons ltd

late holocene dune activity linked to hydrological drought nebraska sand hills usa dunee elds of the great plains contain stratigraphic records of episodic holocene aeolian activity potentially providing a valuable record of climatic change it has been dife cult to establish unambiguous links between activity at specie c sites and regional palaeoclimate however here we demonstrate that widespread late holocene aeolian activity in the nebraska sand hills the largest dunee eld on the great plains of north america occurred during a period of hydrological drought aeolian sand sheets are interbedded with peat that accumulated in interdunes throughout much of the holocene the youngest of these sand sheets was deposited between 950 and 650 cal bp about the same time as the most recent major episode of aeolian activity at upland sites up to 120 km apart sand sheets could only have advanced across the interdunes if the local groundwater e ow systems that maintain interdune wetlands were temporarily reduced or eliminated by a reduction in recharge both reduced recharge and upland aeolian activity are best explained by regional megadrought

palaeoclimatic and archaeological evidence for a 200 yr recurrence of floods and droughts linking california mesoamerica and south america over the past 2000 years conspicuous grey clay rich flood deposits in the predominantly olive varved sediment in the central santa barbara basin california were dated via varve counting to c ad 212 440 603 1029 1418 and 1605 the 200 yr quasi periodicity and the timing of individual floods match time periods of known supraregional climatic changes and the documented 200 yr periodicity in palaeoclimate records elsewhere the floods of c ad 440 and ad 1418 occurred during global reorganizations of atmospheric circulation cold spells seem to have accompanied the floods of c ad 1029 and ad 1605 california floods and other palaeoclimate records suggest that expressions of regional climates are modulated by solar variability with a 200 yr periodicity our compilation of palaeoclimatic and mesoamerican and south american archaeological records provides evidence that palaeoenvironmental and cultural changes were often coincident within their respective dating uncertainties and occurred in 200 yr steps the matching patte