weathering and evolution of soils formed on granitic glacial deposits results from chronosequences of swiss alpine environments abstract two soil chronosequences of mountainous ecosystems in switzerland served as the basis to calculate the accumulation of soil organic matter transformation of pedogenic fe and al and net losses of the main elements ca mg k na fe al mn and si by means of mass balance calculations elemental losses due to deglaciation and exposure to the weathering environment were calculated these mass balance calculations indicate that extensive mineral weathering resulted in significant leaching losses of si major base cations and al particularly from the upper horizons the losses are especially pronounced in the early stages of soil formation in most cases the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering the greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000 4000 years of soil development later the weathering rates decreased rapidly and the overall depletion of elements nearly reached an asymptote we also found that the mean ratio of al t fe d al d fe t of the fine earth of the a e and b horizons is closely linked to the duration of soil development a very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years consequently this ratio could be a good indicator of the age of alpine soils furthermore there is a close relationship between the mass of organic c or n in the whole profile and the soil age the older the soil the higher the corresponding mass per unit area the chronofunctions presented give a first attempt of the chemical soil evolution in the alps however only little data has been available up until now regarding alpine soils and this fact inhibits a more detailed observation of the changes that have occurred over a period of 2000 8000 years of soil formation under similar climatic conditions

late pleistocene and early holocene climate and limnological changes in the sierra nevada california usa inferred from midges insecta diptera chironomidae chironomid and stratigraphic analyses of a lake sediment core recovered from a high elevation lake in the central sierra nevada california usa was undertaken to assess chironomid community development during the pleistocene holocene transition and to quantitatively reconstruct the thermal regime that existed during this interval between 14 800 cal yr bp and 13 700 cal yr bp the chironomid community consisted almost exclusively of heterotrissocladius suggesting this period was characterized by extremely cold climatic conditions evidence of post glacial climatic amelioration as manifested by increases in thermophilous chironomid taxa head capsule concentrations and taxon richness and diversity commenced at approximately 13 300 cal yr bp in order to quantify the magnitude of the water temperature changes associated with post glacial climatic amelioration a recently developed chironomid based inference model for surface water temperature was applied to the subfossil chironomid assemblages the one component weighted averaging partial least squares wa pls model has an r2jack 0 72 rmsepjack 1 1 c and a maximum bias of 1 24 c the reconstructed surface water temperatures suggest a minimum warming of approximately 4 7 c occurred during the pleistocene holocene transition however warming during this interval may not have been monotonic evidence of the younger dryas has been previously discovered in the study area and adjacent regions our research indicates that changes in chironomid community composition and an inferred short term cooling event occurred between 12 000 cal yr bp and 11 500 cal yr bp which may represent a local manifestation of the younger dryas chironomid community development during the pleistocene holocene transition appears to primarily reflect the influence of changing climate conditions

natural responses to quaternary climatic change in the greater nevada test site region u s a abstract many natural processes particularly those that occur at or near the earth s surface e g erosion infiltration soil formation and plant growth are influenced or altered by climatic change migration of hazardous and radioactive contaminants into and through the environment depends on these natural processes climatic fluctuations can affect the nature magnitude and rate of these processes in any long term environmental evaluation of natural processes responses to climatic change must be considered four generalized categories of natural responses to quaternary climatic change are recognized for the greater nevada test site nts region of southern nevada and adjacent california 1 biologic 2 geomorphic 3 hydrologic including surface and subsurface and 4 pedologic diagenetic specific examples that correspond to the four categories illustrate the broad range of complex natural processes that are affected by climatic change these responses dictate the potential effect of climatic change on waste isolation and contaminant transport this effect is being examined by existing and planned environmental restoration and waste management programs within the region regulatory requirements for many of these programs include long term 10 000 year waste isolation because of radiologic components an overview is presented of the slowly growing data base of the complex relationships between climate and natural processes that must be considered in performance and risk assessments for environmental programs in this region limitations in and inconsistencies between various data sets are noted as appropriate in particular better quantified estimates or ranges of estimates of magnitudes and rates are commonly needed for these processes and responses these estimates allow climatic change and related responses to be incorporated explicitly into conceptual and numerical models and into performance and risk assessments of the various environmental restoration and waste management programs within the greater nts region

effect of ocean gateways on the global ocean circulation in the late oligocene and early miocene 1 we investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns using a fully coupled climate model in an idealized setup we compare situations corresponding to the late oligocene the early miocene and present day the model results show the existence of a flow reversal through the panama seaway between the oligocene and miocene this flow reversal is induced by global tectonic changes related to the widening of the southern ocean passages and the closing of the tethys seaway it mainly involves the wind driven ocean circulation in agreement with previous model studies the global thermohaline circulation in the oligocene and miocene simulations is significantly different from the present day conveyor circulation as there is deepwater formation in both the north atlantic and the north pacific oceans in particular in the oligocene simulation the salinity contrast between the atlantic and pacific oceans is reduced because of water mass exchange through the low latitude connections between the two oceans

biogeochemical weathering in sedimentary chronosequences of the rhone and oberaar glaciers swiss alps rates and mechanisms of biotite weathering abstract we analysed the composition of phyllosilicate minerals in sediments deposited by the rhone and oberaar glaciers swiss alps in order to identify processes and rates of biogeochemical weathering in relation to glacial erosion the investigated sediments are part of chronosequences consisting of a suspended fresh sediment in melt water b terminal moraines from the little ice age lia approximately 1560 1850 and c tills of the younger dryas interval yd approximately 11 500y bp secondary weathering products associated with the suspended sediment have not been observed we therefore exclude intermittent subglacial storage and weathering of this material and assume that the suspended sediment is directly derived from mechanically abraded bedrock this implies that biogeochemical weathering processes started once the glacially derived sediment was deposited in the proglacial area the combination of a developing vegetation cover the generally high permeability allowing the percolation of precipitation and the chemical reactivity related to the dominance of fine grained material biotite weathering rates are calculated using the difference in the biotite content between unweathered and weathered glacial sediments within the investigated profiles the reactive mineral surface area is estimated geometrically both with regards to the total relative surface wr t as well as to the relative edge surface wr e wr t biotite weathering rates are estimated as 10 13 10 15 mol biotite m 2 biotite s 1 wr e biotite weathering rates are on the order of 10 13 10 14 mol biotite m 2 biotite s 1 biotite weathering rates obtained by this study are in the order of one magnitude higher in comparison to other published field based weathering rates using biotite as an indicator we therefore suggest that glacially derived material in the area of the oberaar and rhone glaciers is generally subjected to enhanced biogeochemical weathering starting immediately after deposition in the proglacial zone and subsequently continuing for thousands of years after glacier retreat

palynological evidence for early holocene aridity in the southern sierra nevada california sediments of balsam meadow have produced a 11 000 yr pollen record from the southern sierra nevada of california the balsam meadow diagram is divided into three zones 1 the artemisia zone 11 000 7000 yr b p is characterized by percentages of sagebrush artemisia and other nonarboreal pollen higher than can be found in the modern local vegetation vegetation during this interval was probably similar to the modern vegetation on the east slope of the sierra nevada and the climate was drier than that of today 2 pinus pollen exceeded 80 from 7000 to 3000 yr b p in the pinus zone the climate was moister than during the artemisia zone 3 fir abies cupressaceae and oak quercus percentages increased after 3000 yr b p in the abies zone as the modern vegetation at the site developed and the present cool moist climatic regime was established decreased fire frequency after 1200 yr b p is reflected in decreased abundance of macroscopic charcoal and increased concentration of abies magnifica and pinus murrayana needles

n alkane evidence for the onset of wetter conditions in the sierra nevada california usa at the mid late holocene transition 3 0 ka abstract n alkane biomarker distributions in sediments from swamp lake sl in the central sierra nevada of california usa provide evidence for an increase in mean lake level 3000 yr ago in conjunction with widespread climatic change inferred from marine and continental records in the eastern north pacific region length distributions of n alkane chains in modern plants growing at sl were determined and compared to sedimentary distributions in a core spanning the last 13 ka as a group submerged and floating aquatic plants contained high proportions of short chain lengths nc27 were dominant changes in the sedimentary n alkane distribution over time were driven by variable inputs from plant sources in response to changing lake level sedimentation and plant community composition a shift toward shorter chain lengths nc21 nc23 occurred between 3 1 and 2 9 ka and is best explained by an increase in the abundance of aquatic plants and the availability of shallow water habitat in response to rising lake level the late holocene expansion of sl following a dry mid holocene is consistent with previous evidence for increased effective moisture and the onset of wetter conditions in the sierra nevada between 4 0 and 3 0 ka

thirty thousand years of vegetation changes in the alabama hills owens valley california abstract twenty packrat neotoma middens recovered from three sites 1265 1535 m in the alabama hills inyo county california provide a ca 31 450 yr record of vegetation change located ca 7 km east of the sierra nevada the middens document that utah juniper juniperus osteosperma joshua tree yucca brevifolia and bitterbush purshia tridentata occupied the site between 31 450 and 19 070 yr b p joshua tree and bitterbush departed by ca 17 760 yr b p with cliffrose purshia mexicana and joint fir ephedra viridis appearing by 13 350 yr b p blackbush coleogyne ramosissima and cholla opuntia echinocarpa entered the record between 9540 and 7990 yr b p utah juniper and other species now extralocal to the sites departed and modern components such as wolfberry lycium andersonii and rubber rabbitbrush chrysothamnus teretifolius appeared the middle holocene records little variation in plant macrofossil composition however pollen analysis reflects an increase in aquatic pollen types which might suggest more open conditions the transition to the modern vegetation associations at the sites occurred after ca 2800 yr b p the record from the alabama hills correlates well with that of other regional vegetation data but documents conditions of increasing aridity earlier than many other packrat midden sites a shift in understory vegetation between 19 070 and 17 760 yr b p may reflect a transition from glacial maximum to post maximum conditions in the eastern sierra nevada

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

an organic geochemical record of sierra nevada climate since the lgm from swamp lake yosemite abstract sediment records from swamp lake sl in the central sierra nevada california provide evidence of climatic change on millennial and centennial timescales over the last 20 000 years total organic carbon toc abundance varied in concert with elemental and isotopic tracers of organic matter c n 13 c org 15 n biogenic silica content total magnetic susceptibility and sediment lithology we interpret the down core proxy records as representing the response of the lake environment in terms of temperature seasonal ice cover mixing regimes runoff and in situ om and nutrient cycling to shifting climate states these environmental factors in turn drove changes in algal productivity om sources microbial om regeneration and secondary production and detrital input the late pleistocene 19 7 10 8 cal kyr bp was dominated by fluctuations between relatively warm dry intervals with high toc 17 4 16 5 15 8 15 0 13 9 13 2 11 4 11 0 cal kyr bp and cold wet intervals 16 5 15 8 14 8 13 9 13 1 11 6 11 0 10 7 cal kyr bp characterized by low toc and high detrital input the holocene 10 7 cal kyr bp present was characterized by three abrupt increases in toc after 10 8 8 0 and 3 0 cal kyr bp and numerous century scale fluctuations toc increases reflected enhanced lake productivity and om recycling and reduced detrital input in response to changing winter temperature and hydrologic regimes inferred environmental changes at sl correlate with other sierra nevada paleorecords and with reconstructed sea surface temperatures along the california margin parallel changes in the sl and sst records over the past 20 000 years provide new evidence that continental climate in the sierra nevada and the california current system have responded on multiple timescales to common drivers in north pacific ocean atmospheric circulation

mapping modeling and visualization of the influences of geomorphic processes on the alpine treeline ecotone glacier national park mt usa spatially explicit digital technologies are integrated within a geographic information science gisc context to map model and visualize selected direct and indirect geomorphic processes that influence the spatial organization of the alpine treeline ecotone ate in glacier national park gnp mt gisc is used to examine alpine treeline and its biotic and abiotic controls through the application of multi resolution remote sensing systems geospatial information and product derivatives and simulations of treeline spatial organization three geomorphic features are examined relict solifluction terraces evidence of nonlinearity in the development of a catena and the locations of isolated boulders the significance of these features is in constraining subsequent geomorphic and biogeographic processes thus leading to disequilibrium exploration of these features though gisc indicates that visualizations for characterizing the relations of geomorphic patterns and processes within a three dimensional context show promise for improved alpine slope models in the future by defining landscape attributes within a spatially and temporally explicit context

correlation of late pleistocene glaciation in the western united states with north atlantic heinrich events a survey of the chronology of late pleistocene glaciers in the western united states indicates a record of glacier advances during the last glaciation which is more variable than that predicted by orbital forcing numerical dating of late pleistocene deposits from the puget lobe of the cordilleran ice sheet and alpine glaciers and ice caps in the rocky mountains and cascade range suggests that advances and retreats of these glaciers were in phase with episodes of growth and collapse of the laurentide ice sheet associated with the north atlantic heinrich events specifically the existing chronologies indicate that these glaciers were advancing to their terminal areas up to several thousand years before a heinrich event and retreated shortly thereafter because midlatitude glaciers respond relatively rapidly to climate change this complex record of glacial fluctuations suggests mechanisms of climate forcing in western north america that are in some way tied to heinrich events one possible mechanism involves southerly and northerly displacement of the jet stream across the western united states in response to growth and collapse of the laurentide ice sheet

closing of the central american seaway and the ice age a critical review 1 what role did the closing of the central american seaway play in enabling continental ice sheets to wax and wane over north america and fennoscandia a summary of relevant evidence presented here permits a causal relationship between them but can be interpreted to show none the common denominator of such evidence is the approximate simultaneity of that closing with global cooling and the first major ice advance at the resolution of paleoclimate however geologic evidence from central america places only weak constraints on when interchange between pacific and caribbean water ceased the strongest evidence for when north and south america became connected by a continuous land bridge the great american exchange of vertebrates assigns climate change the causal role for an arid central american climate typical of glacial times seems necessary for animals that inhabited savannas to pass through panama paleoceanographic and geochemical studies of environments and water masses in the eastern pacific western caribbean and atlantic in general call for continual change since 6 ma or earlier if evidence concurrent with global change near 3 5 3 ma seems more widespread than for other times hypothesized connections between a closed seaway and glaciation commonly call for profoundly different north atlantic ocean circulation but simulations using general circulation models provide a spectrum of differences in circulation for open and closed seaways might much not all of the evidence implicating the closing of the seaway in global climate change in fact be a consequence of that change and blind to central america s tectonic development

packrat midden evidence of late quaternary vegetation change in the white mountains california nevada packrat neotoma spp middens from the white mountains indicate climatic and plant community conditions for the last 19 000 yr during full glacial times ca 19 000 yr b p and at the pleistocene holocene boundary juniper woodlands were 600 m lower in elevation than at present midden assemblages and stable isotope data suggest lower temperatures and increased precipitation relative to the present into the early holocene two early holocene middens ca 8000 yr b p from lower elevations of the white mountains contain fragments of pinyon pine and indicate that both pinyon and juniper grew at a site that today supports only a pinyon woodland two middle holocene middens ca 5000 yr b p indicate that there was an upward migration of pinyon juniper woodlands along a high elevation ecotone but little change in the middle of the pinyon juniper woodland middens from the late holocene indicate that present day plant communities were in place by ca 2000 yr b p or before

assessing ams 14c ages of detrital organics from holocene and late pleistocene moraines east central sierra nevada california usa obtaining age estimates of moraines which have insufficient carbon for conventional 14 c dating may be possible by ams 14 c dating of detrital organic material in the till matrix sufficient detrital carbon was available in the till matrix of holocene and late pleistocene moraines of upper laurel creek canyon east central sierra nevada california for ams 14 c measurements radiocarbon analysis of till matrix organics from the moraine closest to the headwall ml reveals an age of 2875 60 bp eth 13550 the next oldest moraine m2 yields 4450 60 bp eth 12810 m3 the oldest moraine in the bloody mountain cirque yielded organics with a radiocarbon age of 13 600 120 bp eth 12812 while results are preliminary these ages are among the first on till matrix in the sierra nevada and are consistent with geomorphic context other palaeoecologic records in the sierra nevada and palaeolake records in the western united states

paleoproduction and environmental change at mono lake eastern sierra nevada during the pleistocene holocene transition abstract the late quaternary limnological history of mono lake 16 6 4 3 cal kyr bp a hydrologically closed basin in the eastern sierra nevada california is inferred based on a multi indicator analysis of a long 10 8 m composite sediment core constructed from overlapping deepwater piston cores the composite core dated by 14c and tephra correlation shows variations in sedimentology magnetic susceptibility elemental geochemistry and stable isotopes through time consistent with changes in aquatic productivity hydroclimate and volcanism in the late pleistocene deepwater stratigraphy was influenced by high amplitude water level changes and runoff from a glaciated watershed in contrast mono lake s elevation was lower in the early to middle holocene low amplitude water level changes wave reworking of the shoreline and water column stratification were important controls on facies during that time the data suggest that the chief controls on organic facies development in mono lake productivity preservation and dilution dynamics are sensitive to climate changes that influence lake level elevation water chemistry and the position of deltas the study shows that deepwater sediments from certain locales in mono lake are well preserved continuous and can be reliably dated with 14c applied to terrestrial materials when paired with precisely dated paleoshoreline data these sediments provide a high resolution archive of deglacial and holocene environmental information for the eastern sierra nevada

mid miocene paleoproductivity in the atlantic ocean and implications for the global carbon cycle 1 a prominent middle miocene 17 5 13 5 ma carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13c depleted organic carbon in marine sediments or enhanced carbon burial in peat lignite deposits on land here we test the hypothesis that the marine 13c record reflects a change in productivity with proxy records from three atlantic ocean sites deep sea drilling program site 608 and ocean drilling program sites 925 and 1265 our multiproxy approach is based on benthic foraminiferal accumulation rates elemental ratios ba al and p al the 13c of bulk sedimentary organic matter and dissolution indices we compare these proxies to benthic foraminiferal 13c values measured on the same samples our results indicate that marine paleoproductivity in the atlantic ocean is not related to the benthic foraminiferal 13c excursion a numerical box model confirms that marine productivity cannot account for the 13c maximum the model shows that sequestration of 1 5 1018 mol c in the terrestrial realm over a period of 3 ma leads to a 0 9 13c increase in the deep ocean which is near the observed records therefore an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean s carbon pool with 13c which is consistent with coeval lignite deposits worldwide the 13c values of bulk sedimentary organic matter parallel the 13c of dissolved inorganic carbon as reflected by benthic foraminiferal 13c values suggesting no significant change in atmospheric pco2 levels over the investigated period

sedimentary charcoal as an indicator of late holocene drought in the sierra nevada california and its relevance to the future a holocene record of climate fire and vegetation regimes was reconstructed for siesta lake yosemite national park california using fossil pollen and charcoal from lake sediments these reconstructions were generated to provide a long term perspective on drought in the sierra nevada the sedimentary record is in agreement with other long term records of climate and vegetation from the sierra nevada and the records of climate and fire for the last c 1000 years are in agreement with tree ring and hydrological studies this correspondence suggests that sedimentary charcoal and pollen are reliable indicators of change in climate vegetation and fire frequency through time the fire frequencies associated with the droughts of the mediaeval warm period are only half as great as those recorded during the early holocene insolation maximum model results suggest that the temperature increases associated with the insolation maximum are a good analogue for those expected with global warming if this is the ca

late pleistocene vegetation of kings canyon sierra nevada california seven packrat midden samples make possible a comparison between the modern and late pleistocene vegetation in kings canyon on the western side of the southern sierra nevada one modern sample contains macrofossils and pollen derived from the present day oak chaparral vegetation macrofossils from the six late pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers juniperus occidentalis pinus cf ponderosa and p monophylla the pollen spectra of these pleistocene middens are dominated by pinus sp taxodiaceae cupressaceae taxaceae tct and artemisia sp mesophytic conifers are represented by low macrofossil concentrations sequoiadendron giganteum is represented by a few pollen grains in the full glacial edaphic control and snow dispersal are the most likely causes of these mixed assemblages the dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the sierra nevada these assemblages suggest that late wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values this conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late wisconsin the records in these middens also suggest that s giganteum grew at lower elevations along the western side of the range and that p monophylla was more widely distributed in cismontane california during the pleistocene

the paleoecology and stratigraphy of nichols meadow sierra national forest california usa sediment stratigraphy and pollen plant macrofossil and charcoal analyses along with nine radiocarbon dates from nichols meadow provides the most intensive investigation of sierra nevada montane meadow development and paleoecology during pollen zone nm i ca 18 500 12 500 yr b p the nichols meadow area contained a stream during the tioga glacial stage the presence of high artemisia and gramineae pollen percentages along with a very low pollen influx rate reflects a cold dry steppe woodland environment pollen zone nm ii ca 12 500 8800 yr b p documents the development of a lower montane forest and giant sequoia sequoiadendron giganteum community which existed around a small meadow the higher sediment accumulation rates suggest that fallen trees contributed to the aggregation of meadow sediments arly holocene aridity is recorded in pollen zone nm iii ca 8800 6000 yr b p by poorly preserved pollen we infer that the forest trees closed in on the meadow and occupied the meadow floor the reduction in available moisture caused giant sequoia to become locally extinct in the nichols meadow area probably moving into their current distribution within the nelder grove pollen zone nm iv 6000 yr b p present reflects the development of the modern nichols meadow less sand in the meadow sediments due to stable vegetation surrounding nichols meadow allowed the increased retention of ground water this along with the neoglacial cooling trend at ca 3000 yr b p caused ground water to rise and saturate the meadow these events excluded the conifers from the meadow surface and allowed herbaceous vegetation associated with wet meadows to dominate overgrazing and channeling of the meadow s outflowing stream caused the water table to drop resulting in the incision of the meadow

late neogene benthic stable isotope record of ocean drilling program site 999 implications for caribbean paleoceanography organic carbon burial and the messinian salinity crisis we report on epibenthic foraminiferal 18o and 13c and percentage coarse fraction records from caribbean ocean drilling program odp site 999 12 44 n 78 44 w water depth 2828 m spanning the interval from 8 5 to 5 3 ma low epibenthic 13c values and low amounts of sand sized particles mostly foraminifer shells indicate a poorly ventilated deep caribbean throughout the late miocene at this time the deep caribbean was dominated by a nutrient rich and corrosive water mass a generally constant 13c gradient between the caribbean and deep atlantic records during the late miocene suggests that the fluctuations in 13c reflect global changes in 13c of the dissolved inorganic carbon due to varying erosion of organic carbon from terrigenous soils and shelf sediments the observed 100 kyr cyclicity of epibenthic 13c is in good accordance with the variability of terrigenous input to the equatorial atlantic as recorded by magnetic susceptibility records of the ceara rise however some short term gradient changes between 7 0 and 4 5 ma indicate a poorer ventilation of the deep atlantic related to a reduced production of deep water in the atlantic the messinian salinity crisis between 6 0 and 5 3 ma did not affect the intermediate to deep water gradient between the caribbean and the atlantic comparison to the bahama platform record of odp site 1006 however indicates a poorer ventilation of the shallower northern caribbean basins coincident with the isolation of the mediterranean sea

lithic humicryods and haplocryods disjunct alpine subalpine soils of the northern hemisphere abstract lithic humicryods and haplocryods occur in alpine subalpine regions across the northern hemisphere these soils form on acidic crystalline parent materials in cold 3 to 5 c and wet 900 2800 mm year environments with abundant 2 10 m snowfall and support circumpolar biota the profiles contain abundant c with a mean value of 26 kg m2 to a depth of 50 cm because the soils are enriched in short range order minerals the spodic horizon has a high cation exchange capacity mean 62 cmol kg the soils are ultra to very strongly acidic ph 3 4 4 6 are highly saturated with al average 90 and are depleted in base cations average 1 5 lithic humicryods and haplocryods develop strong acidity particularly that related to al3 form al humus complexes and imogolite and often have an isotic mineral class as with the organisms they support these soils are an example of disjunct soil taxa that develop on isolated cold mountains following the retreat of continental ice sheets four soil series classified as lithic humicryods in northeastern us couchsachraga saddleback skylight and stratton that comprise 46 000 ha can be considered unique and endangered soils

paleofire reconstruction for high elevation forests in the sierra nevada california with implications for wildfire synchrony and climate variability in the late holocene abstract here we present two high resolution records of macroscopic charcoal from high elevation lake sites in the sierra nevada california and evaluate the synchroneity of fire response for east and west side subalpine forests during the past 9200 yr charcoal influx was low between 11 200 and 8000 cal yr bp when vegetation consisted of sparse pinus dominated forest and montane chaparral shrubs high charcoal influx after 8000 cal yr bp marks the arrival of tsuga mertensiana and abies magnifica and a higher than present treeline that persisted into the mid holocene coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the sierra nevada after 3800 cal yr bp independent fire response occurs between 9200 and 5000 cal yr bp and significant synchrony at 100 to 1000 yr timescales emerges between 5000 cal yr bp and the present especially during the last 2500 yr indistinguishable fire return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late holocene fires after 1200 cal yr bp are often synchronous and corroborate with inferred droughts holocene fire activity in the high sierra nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the el nino southern oscillation

late glacial and early holocene vegetation and climate change near owens lake eastern california abstract pollen and algae from owens lake in eastern california provide evidence for a series of climatic oscillations late in the last glaciation juniper woodland which dominated the owens valley from 16 200 to 15 500 cal yr b p suggests much wetter conditions than today although still wetter and cooler than today the area then became fairly warm and dry with woodland being replaced by shrubs mainly sagebrush from 15 500 to 13 100 cal yr b p next chenopodiaceae shadscale increased woody species declined and lake levels fell all evidence for a brief ca 100 200 yr drought about 13 000 cal yr b p the climate continued to oscillate between wet and dry from 13 000 to 11 000 cal yr b p after 11 000 cal yr b p low lake levels and the increased dominance of desert shrubs indicate the beginning of warm dry holocene conditions the region s climate was unstable during the younger dryas but uncertainities in dating prevent identification of the younger dryas interval in the owens lake record comparison of the owens lake record with studies in the sierra nevada and great basin suggest that the climate was generally wetter between 13 000 and 11 000 cal yr b p with warmer summers although no consistent pattern of climate change emerges

late wisconsin paleoecologic record from swamp lake yosemite national park california a 7 86 m sediment core from swamp lake in yosemite national park california provides a continuous record of environmental change over the last ca 16 000 yr as inferred from pollen macrofossil and microscopic charcoal analyses the core stratigraphy documents late wisconsin tioga stage deglaciation between 16 000 and 13 700 yr b p approximately 6000 3500 yr earlier than higher elevation sierra nevada records the core includes five volcanic ash layers chemically identified as four mono craters ashes and the tsoyawata ash mt mazama oregon the fossil record shows that herbs and sagebrush dominated the glacial environment at swamp lake by 12 000 yr b p a mixed conifer forest composed of high and mid elevation conifers grew around the lake suggesting a cool wet late glacial environment the modern sierra montane forest did not become established until ca 10 400 yr b p when maximum charcoal concentrations and minimum fir pollen percentages indicate an early holocene xeric period the record suggests that a cooling trend began ca 6500 yr b p and persisted until ca 3700 yr b p when the modern climatic regime was established

teaching about relict no analog landscapes abstract only a few very young landforms are the result of currently operating geomorphic processes because the time scale for landscape evolution is much longer than the time scale for late cenozoic climate changes almost all landscapes are palimpsests written over repeatedly by various combinations of climate determined processes relict glacial and periglacial landforms are widely identified in mid latitude regions that have been traditionally described as having been shaped by the normal processes of fluvial erosion less confidently deeply weathered regolith and associated relict landforms in the middle and high latitudes are attributed to early tertiary warmth however assemblages of geomorphic processes specific to certain climatic regions like faunal and floral assemblages cannot be translated across latitude so in spite of the many books about the geomorphology of specific modern climate regions there are few sources that discuss former warm high latitude or cold low latitude low altitude geomorphic processes that have no modern analogs students and teachers alike who attempt to interpret landforms by extrapolating modern climatic conditions to other latitudinal zones will find their outlook broadened and they become better prepared to consider the geomorphic impacts of global climate change

middle miocene ice sheet dynamics deep sea temperatures and carbon cycling a southern ocean perspective 1 relative contributions of ice volume and temperature change to the global 1 18o increase at 14 ma are required for understanding feedbacks involved in this major cenozoic climate transition a 3 ma benthic foraminifer mg ca record of southern ocean temperatures across the middle miocene climate transition reveals 2 2 c cooling 14 2 13 8 ma indicating that 70 of the increase relates to ice growth seawater 18o calculated from mg ca and 18o suggests that at 15 ma antarctica s cryosphere entered an interval of apparent eccentricity paced expansion glaciations increased in intensity revealing a central role for internal climate feedbacks comparison of ice volume and ocean temperature records with inferred pco2 levels indicates that middle miocene cryosphere expansion commenced during an interval of southern ocean warmth and low atmospheric pco2 the antarctic system appears sensitive to changes in heat moisture supply when atmospheric pco2 was low suggesting the importance of internal feedbacks in this climate transition

a late quaternary chironomid inferred temperature record from the sierra nevada california with connections to northeast pacific sea surface temperatures chironomid remains from a mid elevation lake in the sierra nevada california were used to estimate quantitative summer surface water temperatures during the past 15 000 yr reconstructed temperatures increased by 3 c between lake initiation and the onset of the holocene at 10 600 cal yr bp calibrated years before present temperatures peaked at 6500 cal yr bp displayed high variability from 6500 to 3500 cal yr bp and stabilized after 3500 cal yr bp this record generally tracks reconstructed santa barbara basin sea surface temperatures ssts through much of the holocene highlighting the correspondence between sst variability and california land temperatures during this interval

miocene ocean circulation inferred from marine carbon cycle modeling combined with benthic isotope records 1 in a modeling sensitivity study we investigate the evolution of the ocean circulation and of marine carbon isotope 13c records during the miocene about 23 5 million years ago for this purpose we ran an ocean circulation carbon cycle model of intermediate complexity large scale geostrophic hamburg ocean carbon cycle model version 2s exploring various seaway configurations our investigations confirm that the central american seaway played a decisive role in the history of the miocene ocean circulation in simulations with a deep central american seaway depth range 1 3 km typical for the early to middle miocene deep water production in the north atlantic is absent or weak while the meridional overturning circulation is dominated by water mass formation in the southern ocean deep water formation in the north atlantic begins when the central american seaway shoals to a few hundreds of meters which is typical for the late miocene our results do not support ideas that the mid miocene closing of the eastern tethys contributed to antarctic glaciation on the other hand we find some water exchange between the indian ocean and the atlantic via the eastern tethys during the early miocene our model results for the atlantic meridional overturning circulation and for atlantic 13c during the late miocene are largely independent from depth variations of the greenland scotland ridge to a large extent the evolution of miocene deep sea 13c records can be explained with large scale ocean circulation changes our model data comparison for the middle and early miocene suggests that during the early neogene the seaway effect on benthic 13c may have been superimposed by further factors such as climate regime shifts and or terrestrial carbon cycle changes

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

130 000 yr continuous pollen record from clear lake lake county california pollen analysis of a 115 m sediment core from clear lake lake county california provides a climatic record that is continuous for the past 130 000 yr the pollen record reflects migrations of the tree species of the california coast ranges in response to the climatic changes of the last glacial cycle during interglacials the clear lake pollen rain was dominated by quercus oak pollen during cooler periods oak pollen was replaced by pollen of coniferous species the curve for quercus pollen strongly resembles and is used to correlate with both deep sea oxygen isotope curves and the climatic record from certain european pollen studies

neogene evolution of atlantic thermohaline circulation perspective from walvis ridge southeastern atlantic ocean 1 we present new nd isotope records from walvis ridge ocean drilling program odp sites 1262 1264 southeastern atlantic spanning the past 24 ma to investigate the neogene evolution of atlantic thermohaline circulation the new data indicate that deepwater nd t values from odp site 1262 decrease from 11 0 at 10 6 ma to 12 5 by 7 3 ma this decrease parallels the nd isotope trends contained in fe mn crust records from the northwestern atlantic however the shift at odp site 1262 4755 m water depth occurred up to 6 ma earlier than the corresponding changes in crust records from the atlantic and earlier than any atlantic site shallower than 2700 m paleowater depth recent interpretations of the rapid decrease in fe mn crust nd nd t ssvalues invoke changes in weathering inputs to the labrador sea region rather than a fundamental change in deepwater convection in the labrador sea however the new evidence for significant depth stratification of the nd isotope signal in the southeastern atlantic between 10 6 and 7 3 ma suggests that the onset of deepwater convection in the labrador sea may have played a role in the deepwater decrease in nd isotopic composition climatic conditions during the middle to late miocene likely favored an increase in the importance of glacially induced mechanical weathering while at the same time promoting deep convection in the labrador sea