variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

late quaternary stratigraphic charcoal records from madagascar the classic view regarding the cause of the extinction of at least 17 species of large mammals birds and reptiles in madagascar during the late holocene implicates human use of fire to modify the environment however analysis of the charcoal stratigraphy of three sediment cores from madagascar shows that late pleistocene and early to mid holocene sediments deposited prior to human settlement often contain more charcoal than postsettlement and modern sediments this observation which is confirmed by independent measurements from direct assay and palynological counting techniques suggests that widely held but previously untested beliefs concerning the importance of anthropogenic fires in late holocene environmental changes and megafaunal extinctions of madagascar may be based on an overly simplified version of actual prehistoric conditions moderate to low charcoal values characterized only the late holocene millennia immediately prior to the presumed time of arrival of the first settlers human settlement is probably indicated in the stratigraphy by the sharp rise in charcoal content observed beginning ca 1500 yr b p fire appears to be a significant natural component of prehuman environments in madagascar but some factor probably climate has modulated the extent of natural burning

late quaternary pollen records from two ugandan mires evidence for environmental changes in the rukiga highlands of southwest uganda abstract high resolution pollen data from two mires in the rukiga highlands southwest uganda ahakagyezi swamp and muchoya swamp provide detailed evidence of the environmetal history of the region since ca 42 000 yr b p according to these data there a was period pre ca 42 000 yr b p when climatic conditions were similar to the present conditions considerably colder and drier than the present occurred during two periods in the past pre ca 42 000 yr b p to ca 32 000 yr b p and ca 21 000 yr b p to ca 12 000 yr b p the most recent period of climatic improvement began ca 14 000 yr b p moist lower montane forest colonised the muchoya catchment by ca 11 100 yr b p and the ahakagyezi catchment by ca 10 600 yr b p indicating the establishment there of climatic conditions broadly similar to the present pollen data from both mires reveal forest disturbances beginning ca 2200 yr b p this disturbances is likely to have been human induced

charcoal analysis for paleoenvironmental interpretation a chemical assay a nitric acid digestion and ignition technique developed to measure relative frequencies of charcoal in lake and bog sediments measures the weight of charcoal relative to the dry weight of the sample percentage charcoal and gives results comparable to counting of microscopic charcoal differences in the two techniques caused by changes in sediment type were found especially in postsettlement and late glacial parts of cores charcoal values from sediments less than 100 yr old cannot be compared to older charcoal values unless wood charcoal and charcoal from fossil fuel burning are separated microscopically tests of this chemical assay on mixtures of known weights of charcoal leaves and sand give correlations between observed and expected values of 0 99 to 1 00

late quaternary vegetation and fire dynamics on mount kenya abstract pollen and charcoal data generated from a 1469 cm core radiocarbon dated to 26 430 14 c yr bp recovered from rumuiku swamp on the southeast of mount kenya are used to document changes in the distribution and composition of montane vegetation and fire regimes over the late quaternary throughout the transition from the last glacial maximum lgm high resolution sub centennial scale analysis documents a highly dynamic ecosystem and fire regime the pollen record shows that under a cool but rather moist lgm climate ericaceae and stoebe species shifted down slope more than 1000 m relative to the present day rather than simple altitudinal lowering of current vegetation zonation these taxa formed a vegetation assemblage that mixed high altitude components with relatively lowland taxa in particular juniperus that is presently found at altitudes lower than the study site but on the drier side of mount kenya there is noticeable addition and co dominance of hagenia to the ecosystem from 20 500 14 c yr bp until around 14 000 14 c yr bp when a mix of ericaceous belt and upper montane forest taxa such as artemisia polycias schefflera and stoebe dominated the initial development of montane forest reduced levels of hagenia juniperus olea and podocarpus are recorded about the time of the younger dryas with highly variable presence of more mesic taxa such as polyscias and schefflera this development of montane forest over the late pleistocene to holocene transition reflects a significant reorganization of the ecosystem composition that was heavily influenced by a variable fire regime shifts in vegetation composition reflect the onset of a warmer moist climate from the beginning of holocene as mixed montane forest became more established the latter part of the holocene registers human impact and forest clearance with increased anthropogenic impact marked by a transition to open vegetation and increased fire frequency

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

comparing dust flux records from the subarctic north pacific and greenland implications for atmospheric transport to greenland and for the application of dust as a chronostratigraphic tool we present a new record of eolian dust flux to the western subarctic north pacific snp covering the past 27 000 years based on a core from the detroit seamount comparing the snp dust record to the north greenland ice core project ngrip ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation while the timing of abrupt changes is synchronous if dust deposition in the snp faithfully records its mobilization in east asian source regions then the difference in the relative amplitude must reflect climate related changes in atmospheric dust transport to greenland based on the synchronicity in the timing of dust changes in the snp and greenland we tie abrupt deglacial transitions in the 230th normalized 4he flux record to corresponding transitions in the well dated ngrip dust flux record to provide a new chronostratigraphic technique for marine sediments from the snp results from this technique are complemented by radiocarbon dating which allows us to independently constrain radiocarbon paleoreservoir ages we find paleoreservoir ages of 745 140 years at 11 653 year b p 680 228 years at 14 630 year b p and 790 498 years at 23 290 year b p our reconstructed paleoreservoir ages are consistent with modern surface water reservoir ages in the western snp good temporal synchronicity between eolian dust records from the subantarctic atlantic and equatorial pacific and the ice core record from antarctica supports the reliability of the proposed dust tuning method to be used more widely in other global ocean regions

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

freshwater impacts recorded in tetraunsaturated alkenones and alkenone sea surface temperatures from the okhotsk sea across millennial scale cycles 1 we present records of phytoplankton produced alkenones down a long piston core which reveal changes of sea surface temperature sst and sea surface salinity sss in the southwestern okhotsk sea over the past 120 ka between 20 and 60 ka b p alkenone derived temperatures typically increased by 6 c 8 c from periods corresponding within a few hundred years to stadials to those corresponding to interstadials recorded in greenland ice cores the abundance of c37 4 alkenone relative to total c37 alkenones percent c37 4 a possible proxy for salinity indicated that during most low sss was associated with high sst the warm freshwater events might be related to 1 a decline in the supply of saline water entering the okhotsk sea through the soya strait 2 strengthening of the freshwater supply from the amur river and precipitation over the okhotsk sea associated mainly with increased asian summer monsoon activity and 3 the effect of melting sea ice these findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the pacific and the atlantic sides of the northern hemisphere

pre bolling warming in santa barbara basin california surface and intermediate water records of early deglacial warmth abstract a new piston core from santa barbara basin california provides evidence of the timing magnitude and character of deglaciation including evidence of warming prior to termination ia images site md02 2503 570 m water depth consists of intermittently laminated hemipelagic sediments extending to interstadial d o event 6 34 ka that accumulated at 135 cm ka during the deglacial episode 16 75 10 ka 18 o values decreased by 3 2 in the planktonic species globigerina bulloides indicating a total warming of 8 9 c recorded by surface dwelling foraminifera inferred by removing the 1 influence of ice volume change similarly benthic species bolivina argentea and uvigerina peregrina record a 1 65 18 o decrease across the deglacial interpreted as a 2 3 c warming at upper intermediate depths 18 o values of both planktonic and benthics indicate that surface and intermediate waters began to warm 2 ka prior to termination ia beginning at 16 5 ka intermediate water warming exhibits similar structure and synchronous timing with surface waters these findings are consistent with a growing number of records from around the globe that exhibit pre bolling warming prior to termination ia and extends the record of such processes to the northern pacific

pleistocene megafloods in the northeast pacific massive discharges of freshwater from the glacial lake missoula to the northeast pacific ocean are thought to have sculpted the channeled scablands of eastern washington and debouched via the columbia river near 46 n the dynamics and timing of these events and their impact on northeast pacific circulation remain uncertain here we date marine records of anomalous freshwater inputs to the ocean based on freshwater diatoms oxygen isotopes in foraminifera and radiocarbon data low salinity plumes from the columbia river reduced sea surface salinities by as much as 6 psu practical salinity units more than 400 km away between 16 and 31 cal calendar ka b p anomalously high abundances of freshwater diatoms in marine sediments from the region precede generally accepted dates for the existence of glacial lake missoula implying that large flooding or freshwater routing events were common during the advance of the cordilleran ice sheet and that such events require multiple sources

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

late quaternary vegetation dynamics in a biodiversity hotspot the uluguru mountains of tanzania abstract late quaternary vegetation history and environmental changes in a biodiverse tropical ecosystem are inferred from pollen charcoal and carbon isotope evidence derived from a 48 000 yr sedimentary record from the uluguru mountains a component of the eastern arc mountains of kenya and tanzania results indicate that eastern arc forest composition has remained relatively stable during the past 48 000 yr long term environmental stability of the eastern arc forests has been proposed as a mechanism for the accumulation and persistence of species during glacial periods thus resulting in the diverse forests observed today the pollen and isotope data presented here indicate some marked changes in abundance but no significant loss in moist forest taxa through the last glacial maximum thereby providing support for the long term environmental stability of the eastern arc anthropogenic activities including burning and forest clearance were found to play a moderate role in shaping the mosaic of forest patches and high altitude grasslands that characterise the site today however this influence was tempered by the inaccessibility of the mountain

sea surface temperature and salinity changes in the northwest pacific since the last glacial maximum the oxygen isotope records of both benthic and planktonic foraminifera in five piston cores collected from the region between the oyashio and kuroshio currents near japan clearly show the marked latitudinal shifts of these two currents during the past 25 kyr under the present hydrographic condition a clear relationship between the sea surface temperature sst and oxygen isotope differences from benthic to planktonic foraminifera is observed in this region using this relationship we find decreased ssts of 12 13 c maximum 15 c in the southernmost core site at the last glacial maximum lgm indicating the oyashio current shifted southward the ssts at the southern two core sites abruptly increased more than 10 c at 10 11 ka suggesting the kuroshio current shifted northward over these sites at 10 11 ka in contrast the northern two core sites have remained under the influence of the cold oyashio current for the past 25 kyr with the reasonable estimate of bottom water temperature decrease of 2 5 c at the lgm the ssts estimated by this new method give exactly the same sst values calculated from mg ca ratio of planktonic foraminifera allowing palaeosea surface salinities to be reconstructed the result suggests that the ice volume effect was 1 0 0 1 at the lgm copyright 2004 john wiley sons ltd

deep water formation in the north pacific and deglacial co2 rise deep water formation in the north atlantic and southern ocean is widely thought to influence deglacial co 2 rise and climate change here we suggest that deep water formation in the north pacific may also play an important role we present paired radiocarbon and boron isotope data from foraminifera from sediment core md02 2489 at 3640 m in the north east pacific these show a pronounced excursion during heinrich stadial 1 with benthic planktic radiocarbon offsets dropping to 350 years accompanied by a decrease in benthic 11 b we suggest that this is driven by the onset of deep convection in the north pacific which mixes young shallow waters to depth old deep waters to the surface and low ph water from intermediate depths into the deep ocean this deep water formation event was likely driven by an increase in surface salinity due to subdued atmospheric monsoonal freshwater flux during heinrich stadial 1 the ability of north pacific deep water npdw formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity earth system model these experiments also show that breakdown of stratification in the north pacific leads to a rapid 30 ppm increase in atmospheric co 2 along with decreases in atmospheric 13 c and 14 c consistent with observations of the early deglaciation our inference of deep water formation is based mainly on results from a single sediment core and our boron isotope data are unavoidably sparse in the key hs1 interval so this hypothesis merits further testing however we note that there is independent support for breakdown of stratification in shallower waters during this period including a minimum in 15 n younging in intermediate water 14 c and regional warming we also re evaluate deglacial changes in north pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the bolling allerod is promoted by relatively stratified conditions with increased light availability and a shallow potent nutricline overall our work highlights the potential of npdw formation to play a significant and hitherto unrealized role in deglacial climate change and co 2 rise

palaeoenvironmental changes during the last ca 8590 calibrated yr 7800 radiocarbon yr in the dry forest ecosystem of the patia valley southern colombian andes a multiproxy approach two sediment cores were recovered from two swamps in the dry forest lowland ecosystem of the patia valley colombia the 500 cm long core el patia 1 was analysed using diatoms pollen lithostratigraphy geochemistry charcoal and radiocarbon dates the 270 cm long core patia 2 was analysed using pollen lithostratigraphy and radiocarbon dates the environmental reconstruction includes the local development and history of the patia 1 swamp and the regional vegetation history of the two swamps the environmental reconstruction shows a fluvial system in the area before 7830 14c yr bp ca 8590 cal yr bp after this date the river gradually moved away leading to the formation of the swamp patia 1 open vegetation with patches of dry forest surrounded the swamp between 7670 and 6860 14c yr bp 8350 7690 cal yr bp the swamp become partially isolated from the river and was a permanent water body which was alkaline and mesotrophic during this period the surroundings were covered by dry forest from 6860 to 5870 14c yr bp 7690 6690 cal yr bp the swamp was totally isolated from the river and suffered from frequent periods of desiccation and erosion from 5870 to 3570 14c yr bp 6690 3890 cal yr bp the swamp turned into a marsh terrestrial environment and in the surrounding area the dry forest alternated with open vegetation it is possible that there were human impacts on the environment during this period between 3570 and 1990 14c yr bp 3890 2000 cal yr bp unstable conditions prevailed after 1990 14c yr bp 2000 cal yr bp swamp conditions of permanent water were re established open vegetation surrounded the swamp agriculture and human activities were present and have continued since then the climatic reconstruction suggests an increase in humidity at ca 7670 14c yr bp 8350 cal yr bp and a dry climate between 6860 and 5870 14c yr bp 7690 6690 cal yr bp

northward and southward migrations of frontal zones during the past 40 kyr in the kuroshio oyashio transition area 1 the variation of sea surface temperature sst in the kuroshio oyashio transition area and the okhotsk sea during the last 40 kyr was estimated using long chain unsaturated alkyl ketones alkenones the temperature difference between the present and the last glacial period was about 5 6 c in the kuroshio oyashio transition area slightly larger than the 4 c previously reported moreover alkenones were not detected before 18 kyr b p in or near the okhotsk sea perhaps because of nearly year round sea ice expansion which would have prevented the growth of alkenone producers or because alkenones were less well preserved in surface sediments during the glacial period the northward and southward migrations of frontal zones were evaluated using differences in alkenone temperatures between stations located in the vicinity of the subarctic front saf subarctic boundary sab and kuroshio bifurcation front kbf all three frontal zones migrated southward during the glacial period compared with their present positions and their relative positions were different between the holocene and glacial periods in particular the distance between the saf and the sab was reduced during the glacial period compared with at present the northward and southward migration of the frontal zones may relate to both mid to low atmospheric circulation and polar atmospheric circulation

late pleistocene and holocene history at mubwindi swamp southwest uganda abstract deposits beneath mubwindi swamp provide a partial record of vegetation history since at least 43 000 yr ago we studied pollen from two cores and obtained nine radiocarbon ages from one of these cores and three radiocarbon ages from the other pollen deposited before and soon after the last glacial maximum represents vegetation very different from the modern vegetation of the mubwindi swamp catchment although species now associated with higher altitudes were dominant some elements of moist lower montane forest persisted possibly because of favorable soils or topography the pollen data provides evidence for a late glacial montane forest refuge near mubwindi swamp moist lower montane forest became much more widespread soon after the glacial maximum the only irrefutably holocene sediments from mubwindi swamp date to the past 2500 yr during this time a combination of climatic and human induced changes in vegetation can be seen in the pollen records

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

latest quaternary north pacific surface water responses imply atmosphere driven climate instability a full sequence of brief interstadials dansgaard oeschger d o cycles are recorded from 60 to 25 ka in santa barbara basin california ocean drilling program hole 893a by planktonic foraminiferal isotopic and assemblage changes at unparalleled high resolution for the oceans synchronous climatic response between north pacific surface waters and the greenland ice sheet during d o cycling is strongly indicated by remarkable similarities in speed magnitude and character of rapid oceanic and atmospheric reorganizations inferred sea surface temperature warmings of as much as 5 c within a few decades and brief warming overshoots of as much as 3 c suggest involvement of an atmospheric amplification top down in situ atmospheric warming of the ocean is implied by differential responses partial decoupling in the changes recorded in surface and thermoclinal waters

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

biomarker temperature estimates for modern and last glacial surface waters of the california current system between 33 and 42 n sea surface temperature sst estimates were made using data for c37 39 alkenones analyzed in modern and glacial age intervals of sediment cores collected along an east west 42 n from 125 to 132 w and a north south 41 33 n transect of the california current system ccs the prymnesiophyte biomarker results suggest that surface waters warmed significantly throughout this region since the last glacial maximum lgm but the magnitude of warming varied spatially stratigraphic profiles from four sediment cores along the north south transect indicate the warming period was confined to the glacial interglacial transition 15 10 ka with sst reaching a maximum value at 10 ka and maintaining a uniformly high value throughout the holocene comparison of estimates derived from analysis of modern and lgm sediment intervals indicates the magnitude of the sst change was minimal for locations south of about 36 n 1 2 c and increased significantly 3 5 c north of this latitude using a simple heat balance model we calculate from the latitudinal gradient in sst that southward flow in the california current system during the lgm was about 60 of that measured today at 36 n our findings support the conclusion of others based on pollen data that coastal upwelling in the region of the northeast pacific off northern california was significantly reduced or even completely shutdown during the lgm

middle holocene dry period in the northern midwestern united states lake levels and pollen stratigraphy abstract four cores from lake mendota in the yahara river valley of south central wisconsin provide pollen charcoal and sediment stratigraphic evidence of a middle holocene dry period in the northern midwest the lake level was lower between about 6500 and 3500 yr b p indicating that runoff from the upper yahara river basin may have ceased during the drier seasons of the year derived estimates of precipitation between 6500 and 3500 yr b p indicate a decrease of about 10 down to about 700 mm from the present precipitation value of 800 mm a warming between 6500 and 3500 yr b p is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr b p to quercus savanna with increased charcoal abundances after that time after 3500 yr b p a closed quercus forest and decreased charcoal suggest a cooler and wetter climate the qualitative paleoecological interpretations quantitative precipitation reconstructions based on pollen from the region including the lake mendota data and estimates of hydrologic budget based on lake level changes all show indications of a dry and warm middle holocene evidence from a large regional array of sites also supports these interpretations

millennial climate oscillations in ne pacific surface waters over the last 82 kyr new evidence from alkenones 1 a climate instability in the last glacial corresponding to dansgaard oeschger d o events has been already recognized in the california margin in northeast pacific detailed sea surface temperature sst changes in this region however have not been so far well elucidated here we report estimates of alkenone derived ssts with the do time scale from odp hole 1017e off point conception over the last 80 kyr our results show that alkenone ssts clearly record d o and heinrich events we also found that alkenone ssts during 82 58 ka and 18 15 ka were considerably higher and those in 15 12 ka were lower than those derived from 18o of planktonic foraminifera these results appear to reflect fluctuations of water masses

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

glacial holocene environment of the southeastern okhotsk sea evidence from geochemical and palaeontological data abstract environmental conditions and productivity changes in the southeastern okhotsk sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate organic carbon and opal content data from two sediment cores species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence ams radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 14 c kyr and for correlation between environmental variations in the okhotsk sea and regional and global climate changes benthic foraminiferal assemblages in the two cores depth 1590 and 1175 m varied with time so that we could recognise seven zones with different species composition changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations during the last glaciation fluxes of organic matter to the sea floor showed strong seasonal variations indicated by the presence of abundant a weddellensis and infaunal uvigerina spp benthic foraminiferal assemblages changed with warming at 12 5 11 and 10 8 14 c kyr bp when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1a and 1b younger dryas cooling caused a decline in productivity 11 10 kyr bp affecting the benthic faunal community subsequent warming triggered intensive diatom production opal accumulation and a strong oxygen deficiency causing significant changes in benthic fauna assemblages from 5 26 4 4 kyr bp to present time

charcoal recognition taphonomy and uses in palaeoenvironmental analysis abstract charcoal predominantly the product of wildfires is abundant in many sedimentary rocks deposited in a wide range of environments from terrestrial to marine it also occurs in some volcanic rocks this paper outlines aspects of charcoal formation both natural and experimental and briefly considers the taphonomic processes leading to a final assemblage this is done using examples from recent fires and through experimentation the ways in which charcoal assemblages are recognized in the field and extraction in the laboratory are also considered methods of charcoal identification are presented the range of charcoalified plant organs that can be found is discussed and a wide range of study methods outlined including light microscopy dark field light microscopy reflectance microscopy scanning electron microscopy and synchrotron radiation x ray tomographic microscopy emphasis in this paper is on the study of macro and meso charcoal above180 m finally there is a consideration of the broad use of charcoal from plant evolution studies fire history studies vegetation studies anatomical studies climate and atmospheric studies and the wider importance of charcoal for the earth and biological sciences charcoal is information rich but yet is an under utilized resource

tracing long term tropical montane ecosystem change in the eastern arc mountains of tanzania pollen charcoal stable carbon and nitrogen isotope and radiocarbon analyses are used to reconstruct a palaeoenvironmental record from the eastern arc mountains eam tanzania dating back 45 000 years a sedimentary hiatus covering the last glacial interglacial transition lgit and early to mid holocene follows the lead up to the last glacial maximum lgm period a late holocene portion of the record is included as a modern analogue before 45 000 cal a bp very low regional pollen counts imply open vegetation surrounding the site subsequently the development of extensive montane forest characterizes a relatively mesic pre lgm the transition into the lgm witnessed a marked shift from c3 t o c4 dominated biomass representing an expansion of open forest dominated by grasses these changes may be attributed to a combination of enhanced moisture stress and co2 limitation factors that may have been exacerbated by an intensive fire regime as evident from the charcoal record this is supported by a decrease in montane forest taxa coupled with an associated expansion of c4 graminoids and ericaceous heathland to form a montane grassland mosaic similar to that previously recorded on other east african mountains around the time of the lgm but not to date having been shown in the eastern arc mountains copyright 2014 john wiley sons ltd

intensification of the oxygen minimum zone in the northeast pacific off vancouver island during the last deglaciation ventilation and or export production 1 the oxygen minimum zone omz off vancouver island was more oxygen depleted relative to modern conditions during the allerod 13 5 to 12 6 calendar kyr and again from 11 to 10 kyr the timing of omz intensification is similar to that seen throughout the north pacific although the onset appears to have been delayed by 1500 years off vancouver island radiocarbon dating of coeval benthic and planktonic foraminifera shows that between 16 0 and 12 6 kyr the age contrast between surface and intermediate waters 920 m depth off vancouver island was similar to or slightly less than that today there is no evidence of an increased age difference i e decreased ventilation during the deglaciation particularly during the allerod however sedimentary marine organic carbon concentration and mass accumulation rate increased substantially in the allerod suggesting that increased organic matter export was the principal cause of late pleistocene omz intensification off vancouver island

observations of the aleutian north slope current bering sea 1996 2001 1 cyclonic circulation dominates flow in the bering sea basin the eastward flowing aleutian north slope current ansc flows along the north slope of the aleutian islands turning northwestward in the southeast corner of the basin to form the bering slope current bsc during the period 1997 to 2007 a pair of hydrographic lines was occupied 14 times in the southeastern portion of the basin one transect was across the ansc and the second was across the bsc in addition a series of five yearlong moorings was deployed in a water depth of 1000 m in the ansc and a single yearlong mooring was deployed to the northeast in a water depth of 2200 m at the primary mooring site strong variability in temperature and salinity occurred at fortnightly and annual periods while strong variability in the currents occurred at fortnightly and semiannual periods the mean geostrophic flow relative to 1500 m calculated from the 14 occupations of the hydrographic lines was 3 1 106 m3 s 1 in the ansc and 3 3 106 m3 s 1 in the bsc a significant barotropic component measured by the current meters adds 3 106 m3 s 1 to the transport

high resolution palaeofire signals from christina lake alberta a comparison of the charcoal signals extracted by two different methods abstract two high resolution palaeofire signals were extracted from the annually laminated sediment of christina lake in the boreal forest of alberta canada a charcoal curve focusing on large charcoal fragments 125 m was extracted by the sieving method described by whitlock and millspaugh a carbon curve which includes all size fractions of charcoal was extracted by a method modified from winkler s chemical assay method modifications included increasing the duration of nitric acid treatment to 2 h and using a total carbon analyser tca rather than standard loss on ignition these adjustments resulted in a carbon curve which is unaffected by clay water losses and subtle changes in sedimentology which were problematic in the original gravimetric technique the sensitivity of the tca allowed subtle shifts in carbon i e charcoal abundance to be detected in lake sediments with low levels of charcoal when compared with the known fire history near the lake since 1900 the sieved charcoal curve was most responsive to fires known to burn near the shore of the lake and less responsive to fires burning elsewhere in the watershed the tca carbon curve was somewhat more sensitive than the sieved charcoal curve for detecting fires in the drainage basin which did not burn to the lake edge the tca carbon curve was strongly correlated with sediment influx suggesting stream inputs of charcoal are the dominant influence on this signal the peak in response of the tca curve to known fire events was sometimes lagged by several years suggesting that it can take several seasons for the bulk of stream transported charcoal to make its way from the watershed to its final deposition site in the lake very large fires burning just outside the drainage basin of the lake were not detected by either method suggesting that both of the methods used are sensitive only to fires burning in the watershed and that long distance aerially dispersed charcoal is insignificant at this site

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

glacial age hydrography of the far northwest pacific ocean stable isotope data on benthic foraminifera from more than 30 cores on the northern emperor seamounts and in the okhotsk sea are synthesized in paleohydrographic profiles spanning the depth range 1000 4000 m holocene core top benthic foraminiferal 18o and 13c data are calibrated to modern hydrographic properties through measurements of 13c of co2 and 18o of seawater cibicidoides stable isotope ratios are close to the 13c and equilibrium 18o of seawater whereas uvigerina 18o and 13c are variably offset from cibicidoides glacial maximum 13c of cibicidoides displays a different vertical profile than that of the holocene when results are adjusted by 0 32 to account for the secular change in 13c during the last glacial maximum the data coincide with the modern seawater and foraminiferal curves deeper than 2 km however at shallower depths 13c gradually increases by as much as 1 above the modern value furthermore above 2 km the benthic 18o decreases by 0 5 these results are consistent with a benthic front at 2 km in the north pacific see herguera et al 1992 but they differ from interpretations based on trace metal data which indicate a source of nutrient depleted deep water during glaciation the isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern pacific it was relatively fresher than deep waters there and deep waters were as nutrient rich as today

deglacial development of sub sea surface temperature and salinity in the subarctic northwest pacific implications for upper ocean stratification based on models and proxy data it has been proposed that salinity driven stratification weakened in the subarctic north pacific during the last deglaciation which potentially contributed to the deglacial rise in atmospheric carbon dioxide we present high resolution subsurface temperature tmg ca and subsurface salinity approximating 18oivc sw records across the last 20 000 years from the subarctic north pacific and its marginal seas derived from combined stable oxygen isotopes and mg ca ratios of the planktonic foraminiferal species neogloboquadrina pachyderma sin our results indicate regionally differing changes of subsurface conditions during the heinrich stadial 1 and the younger dryas cold phases our sites were subject to reduced thermal stratification brine rejection due to sea ice formation and increased advection of low salinity water from the alaskan stream in contrast the bolling allerod warm phase was characterized by strengthened thermal stratification stronger sea ice melting and influence of surface waters that were less diluted by the alaskan stream from direct comparison with alkenone based sea surface temperature estimates sstuk 37 we suggest deglacial thermocline changes that were closely related to changes in seasonal contrasts and stratification of the mixed layer the modern upper ocean conditions seem to have developed only since the early holocene

stable isotope and lithologic evidence of late glacial and holocene oceanography of the northwestern pacific and its marginal seas abstract stable isotopes geochemical lithological and micropaleontological results from cores from the far northwest fnw pacific and the okhotsk and bering seas are used to reconstruct the regional environment for the last glaciation the deglacial transition and the holocene 18 o records of planktonic foraminifera of the region show two light shifts during deglacial time provoked by the freshening of the surface water and climate warming these north pacific terminal events t1anp and t1bnp with ages of 12 500 and 9300 yr b p respectively occur almost simultaneously with two episodes of accelerated glacier melting around the north atlantic along with the isotopic shifts the caco 3 content in regional sediments increased abruptly 1a and 1b carbonate peaks probably due to changes of productivity and pore water chemistry of surface sediments organic matter and opal concentration increased during the transition between t1anp and t1bnp events in the sediments of the fnw pacific and the southern part of the bering sea and opal content increased in the holocene in the bering and okhotsk seas 13 c records of cores from the okhotsk and bering seas and the fnw pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation during deglaciation accumulation of the coarse terrigenous component decreased in sediments of the bering sea and the fnw pacific before the t1anp event probably as a result of rising sea level and opening of the bering strait

galileo multispectral imaging of earth nearly 6000 multispectral images of earth were acquired by the galileo spacecraft during its two flybys the galileo images offer a unique perspective on our home planet through the spectral capability made possible by four narrowband near infrared filters intended for observations of methane in jupiter s atmosphere which are not incorporated in any of the currently operating earth orbital remote sensing systems spectral variations due to mineralogy vegetative cover and condensed water are effectively mapped by the visible and near infrared multispectral imagery showing a wide variety of biological meteorological and geological phenomena global tectonic and volcanic processes are clearly illustrated by these images providing a useful basis for comparative planetary geology differences between plant species are detected through the narrowband ir filters on galileo allowing regional measurements of variation in the red edge of chlorophyll and the depth of the 1 m water band which is diagnostic of leaf moisture content although evidence of life is widespread in the galileo data set only a single image at 2 km pixel shows geometrization plausibly attributable to our technical civilization water vapor can be uniquely imaged in the galileo 0 73 m band permitting spectral discrimination of moist and dry clouds with otherwise similar albedo surface snow and ice can be readily distinguished from cloud cover by narrowband imaging within the sensitivity range of galileo s silicon ccd camera ice grain size variations can be mapped using the weak h2o absorption at 1 m a technique which may find important applications in the exploration of the moons of jupiter the galileo images have the potential to make unique contributions to earth science in the areas of geological meteorological and biological remote sensing due to the inclusion of previously untried narrowband ir filters the vast scale and near global coverage of the galileo data set complements the higher resolution data from earth orbiting systems and may provide a valuable reference point for future studies of global change

10 000 yr record of extreme hydrologic events well dated lacustrine sediments provide a hydrologic record indicating that the frequency and magnitude of runoff events and by inference storms have varied over the past 10 k y in northern new england we used five sediment cores and radiocarbon dating to develop a chronology of holocene hydrologic events for the ritterbush pond basin northern vermont chemical and physical analyses allow us to identify 52 distinct layers of predominately inorganic sediment that represent terrestrially derived material delivered to the pond by runoff events the thickness of some layers suggests hydrologic events at least equal in size to and probably much larger than any storm or flood recorded during nearly 300 yr of written regional history layer thickness and frequency and by analogy storm size and recurrence change through the holocene the largest events occurred 2620 6840 and 9440 calibrated 14c years before present cal 14c yr b p the most frequent hydrologic events occurred in three periods 1750 to 2620 6330 to 6840 and 8600 cal yr b p the recurrence interval of layer deposition during stormy periods averages 130 100 cal yr whereas the recurrence interval during less stormy periods is longer 270 170 cal yr the ritterbush pond event record illustrates the potential of inorganic lacustrine sediment to serve as a proxy record for estimating paleoflood frequency and deciphering climate change

biomass burning and oceanic primary production estimates in the sulu sea area over the last 380 kyr and the east asian monsoon dynamics abstract coccolithophorid assemblages and micro charcoal content were analysed in giant piston core md97 2141 recovered in the sulu sea philippines these proxies help to reconstruct respectively the dynamics of the oceanic primary production pp and biomass burning in that area pp in the sulu sea intensifies during the east asian winter monsoon eawm and therefore pp constitutes a proxy for eawm dynamics most of the precipitation in the sulu sea region occurs during the east asian summer monsoon easm because the intensity of biomass burning is related to dryness of the surrounding area the sedimentary micro charcoal content can be used as an inverse proxy for easm intensity our results show that the eawm intensifies during glacial times in agreement with previous studies precessional forcing appears to act directly on eawn because of the early response of pp in that frequency band the micro charcoal record exhibits complex dynamics which we attribute to the competing influence of the long term el nino southern oscillation enso like forcing and the glacial interglacial cycle on easm these influences create an unusual frequency spectrum with power around 30 kyr and 19 kyr attributed to the non linear response to the 100 kyr cycle glacial and the 23 kyr enso cycle a factor of two increase in the amplitude of the micro charcoal variability between 51 and 10 ka bp could correspond to homo sapiens biomass burning in the style of the fire stick farming of the australian aborigines we also find on precession cycles an opposite phase between easm and eawm records and an advance of 18 o and 18 o respectively by 2000 yr

large changes in seasonal sea ice distribution and productivity in the sea of okhotsk during the deglaciations changes in the surface environment of the central sea of okhotsk were reconstructed using tex86 paleothermometry facilitated by the bit index in order to investigate paleoenvironmental changes during the glacial interglacial cycles the core top tex86 derived temperature is the same as the present day summer sea surface temperature sst suggesting that tex86 records seasonal rather than annually averaged ssts in this region the tex86 record reveals 3 c lower summer sst during glacial maxima than during interglacial periods and significant warming during the deglaciations 15 10 ka and 136 130 ka this is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present day and its substantial retreat during the deglaciation timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations the relationship could reflect an increase in the supply of fresh and warm water from the amur river during deglaciation which significantly impacted hydrology by facilitating sea surface stratification which in turn promoted production of coccolithophids

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

burial of different types of organic carbon in core 17962 from south china sea since the last glacial period abstract total organic carbon toc black carbon bc and land derived organic carbon loc extracted from marine sediment core 17962 from the southern south china sea and analyzed by pyrolysis gas chromatography elemental analyzers and mass spectroscopy can be interpreted in terms of regional land biomass burning climatic conditions vegetation cover and ocean paleoproductivity carbon from terrestrial sources including bc and loc appears to be a significant component of toc 3 1 39 3 range 16 5 average for bc 4 4 56 6 range 14 6 average for loc the production of bc and loc was only slightly higher during the last maximum glaciation lgm than during the holocene therefore dramatic changes in climate and vegetation cover do not seem to have occurred at the pleistocene holocene boundary paleoproductivity data calculated from marine organic carbon proved to be more accurate than those calculated from toc and exhibit the same pattern of temporal variation however the glacial interglacial contrast in the refined palaeoproductivity is less evident than that calculated from toc

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

synchronization of north pacific and greenland climates preceded abrupt deglacial warming some proposed mechanisms for transmission of major climate change events between the north pacific and north atlantic predict opposing patterns of variations others suggest synchronization resolving this conflict has implications for regulation of poleward heat transport and global climate change new multidecadal resolution foraminiferal oxygen isotope records from the gulf of alaska goa reveal sudden shifts between intervals of synchroneity and asynchroneity with the north greenland ice core project ngrip 18 o record over the past 18 000 years synchronization of these regions occurred 15 500 to 11 000 years ago just prior to and throughout the most abrupt climate transitions of the last 20 000 years suggesting that dynamic coupling of north pacific and north atlantic climates may lead to critical transitions in earth s climate system

orbital suppression of wind driven upwelling in the california current at 6 ka 1 marine records clearly show activity in the california current cc system to have been altered during the mid holocene however the specific nature of cc activity during this period remains ambiguous as proxies that suggest cooler than present sea surface temperatures co occur in mid holocene marine sediments with multiple proxies that suggest decreased coastal upwelling to test the sensitivity of wind driven upwelling in the cc to mid holocene orbital forcing we have employed a high resolution regional climate model rcm the seasonality of modern cc wind driven coastal upwelling simulated by the rcm is in strong agreement with observational data further we show that changes in the seasonality of solar insolation induced by mid holocene milankovitch forcing decrease early and peak season coastal upwelling in the cc along with increasing late season coastal upwelling these results are in agreement with several marine and terrestrial proxies suggesting that relative to present cc activity during the mid holocene was characterized by a longer and less vigorous upwelling season with decreased seasonal contrast

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 pleistocene holocene oceanographic variability in the okhotsk sea geochemical lithological and paleontological evidence sedimentary geochemical and paleontological data extracted from a sediment core taken from the central okhotsk sea record climatic and sedimentary changes over the past 100 ky benthic foraminiferal oxygen isotope record and accelerator mass spectrometry ams 14c data provide the basis for the core age chronology planktonic and benthic foraminiferal 18o and 13c measurements magnetic susceptibility ice rafted debris and coarse fraction content carbonate and organic carbon content and diatom and pollen spectra show major changes in regional climate sea surface conditions ice extent and sedimentary regime which are correlated with the global glacial interglacial changes of marine isotope stages mis 1 through 5 3 regional cooling and intensification of winter sea ice formation during the last glaciation increased the northern shelf surface water density and sea of okhotsk intermediate water soiw formation in addition to major milankovitch scale changes lithological geochemical and paleontological indices also show suborbital oscillations in okhotsk sea hydrology sedimentation and regional climate these shorter term oscillations are characterized by coupled maxima in ice rafted debris and sediment coarse fraction lithodynamic indices ldi values and most are associated with cold events involving enhanced winter ice formation and intensification of soiw and north pacific intermediate water npiw formation the terminations of ldi maxima were induced by climate warming and reductions in ice formation and were accompanied by sharp decreases in planktonic foraminiferal 18o during the glacial terminations of mis 2 and 4 however the onset of suborbital scale ldi maxima occurs close to sharp negative 18o shifts in planktonic foraminifera 18opf associated with climate warming in these special cases the ldi maxima occurred under warm climate and rising sea levels and did not lead to increases in soiw or npiw ventilation

sea surface temperature changes in the okhotsk sea and adjacent north pacific during the last glacial maximum and deglaciation abstract we estimated sea surface temperatures ssts in the western okhotsk sea during the last glacial maximum lgm and the last glacial termination from measurements of the alkenone unsaturation index u k 37 the t etra e ther inde x of tetraethers consisting of 86 carbon atoms tex 86 and tex 86 l in piston core sediments which reveal the climate response of this region to different types of forcings tex 86 l is a modification of tex 86 proposed for high latitude ocean regions the tex 86 l derived temperatures were not different from the alkenone derived temperatures from the same and nearby sediment samples during the lgm alkenone derived temperatures in the okhotsk sea were relatively warm these and similarly warm alkenone derived temperatures found at many other sites in the western north pacific may reflect a shift in the season of biomarker production from early summer and autumn to mid summer during the lgm as a result of the expansion of the season of sea ice cover empirical orthogonal function eof analysis of alkenone derived temperatures at 14 sites from the north pacific suggested substantial cooling between 20 and 14 cal kyr bp during the deglaciation at 11 of the sites including 4 sites in the okhotsk sea this dominant eof mode suggests either an overall seasonal bias in alkenone derived temperatures or potential shifts in the haptophyseae production season the second eof mode of variability indicated a deglacial warming trend punctuated by millennial scale cold events associated with reorganizations of the atlantic meridional overturning circulation the sst pattern corresponding to this eof mode is indicative of millennial scale meridional shifts of the axis of the westerly jet which may have affected heat transport across the kuroshio reconstructed temperature changes in particular in the okhotsk sea provide insight into the conditions that modulated the ventilation history of intermediate waters in the north pacific

black carbon records in chinese loess plateau over the last two glacial cycles and implications for paleofires abstract to study the temporal and spatial changes in paleofires over the chinese loess plateau black carbon concentrations were analyzed on the loess paleosol samples from three sections along a north south transect using the orbitally tuned time scales of the sections the black carbon mass sedimentation rates bcmsr were calculated results show that in the last two glacial cycles the bcmsr values in glacial periods are 2 3 times higher than in interglacial periods and the bcmsr variability has a relatively strong precession associated 23 ky period suggesting that the glacial cold dry climate conditions were apt to induce natural fires over the loess plateau comparison of the bcmsr records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern loess plateau than in the southern part coinciding with the previous conclusion that the northern plateau has experienced a drier climate regime in both glacial and interglacial periods the substantial increase in bcmsr of the upper s0 relative to the lower s0 at lingtai and weinan indicates that human activities have exerted a significant influence on fire regimes in the middle and southern loess plateau during late holocene due to the relatively intensive agricultural usage of land

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

pollen inferred climatic fluctuations in ethiopia during the last 3000 years abstract although lake levels fluctuations are known from ethiopia during the late holocene few continuous paleoclimatic records are available from the high plateau a 3000 yr high resolution pollen record from the arsi mountain in arussi province of southeastern ethiopia provides information on recent changes in the vegetation above the upper tree line at 3600 m elevation the organic sediment was deposited into the dega sala swamp ca 3000 yr b p on top of a coarse gravel reepresenting a solifuxion deposit linked to neoglacial the surrounding vegetation was established as that of the ericaceous belt with ericaceae shrub dominant the pollen diagram registers significant changes in the relative frequencies of the local herbaceous pollen component versus the arboreal taxa from the upper forest limit allowing the high altitude of the site such changes indicate downward movements of the vegetation belts that are due mainly to temperature variations an estimated cooling of 2 c is registered at 560 120 yr b p ams date contemporaneous with the little ice age the successive upward regrowth of the forest is rather indicative of a recent warming than linked to recolonization of the forest following anthropogenic deforestation unlikely at altitude above potential cultivation

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

the reconstruction of boreal forest fire history from lake sediments a comparison of charcoal pollen sedimentological and geochemical indices abstract fossil charcoal fossil pollen sedimentological and geochemical analyses of lake sediments have been used previously to reconstruct a history of local fires and resulting vegetation change the rationale behind these approaches is described and the usefulness of each technique for reconstructing fire history in the boreal forest is assessed empirically historical and dendrochronological records provide regional and local fire histories for a site in wood buffalo national park alberta canada the local and regional history of fires is compared with the microscopic charcoal content macroscopic charcoal content elemental carbon content fossil pollen content sedimentology and geochemistry of annually laminated sediments from a small lake there is no significant correlation between the abundance of microscopic charcoal macroscopic charcoal and total elemental carbon content of the sediments automated measures of microscopic charcoal abundance made with an image analysis system are correlated significantly with optical counts of microscopic charcoal none of the charcoal measures provide unequivocal records of local fire activity and the abundance of microscopic charcoal appears to be influenced by variations in regional fire activity however the highest depositional rate of macrofossil charcoal occurred during the time of a fire that burned within the drainage basin variations in sedimentological measures and geochemistry do not correlate with local fire activity fossil pollen percentages and accumulation rates display a pattern of variation that is consistent with observed vegetation responses to fire in the boreal forest what is likely apparent in the pollen record are the results of a series of burns of sufficient extent and intensity to kill most of the above ground biomass of the vegetation in an area at least as great as the drainage basin the inability of evidence from lake sediments to provide detailed histories of past fire activity is not surprising given the wide range of variation in the spatial extent proximity intensity and impact of individual fires

glacialanterglacial record from intertropical africa high resolution pollen and carbon data at rusaka burundi abstract in northern intertropical africa many geological data have documented several abrupt climatic fluctuations taking place during the time of the last deglaciation one of them is an aridity event generally placed in the interval 11 000 10 000 bp and synchronous with the younger dryas cold episode of the temperate regions that has been explained by the influence of the atlantic ocean circulation on global climate in this paper we present high resolution 50 to 150 years studies of organic matter and pollen undertaken on a new core from the rusaka peat bog 3 26 south 29 37 east 2070 m altitude dated by the conventional l2 dates and the ams methods 18 dates obtained on bulk sediment and macroremains although the sediment at the bottom of the core was deposited during the last glacial period prior to 21 000 bp the dating provides a reliable chronology for the last 12 000 bp only several vegetational changes are documented in the interval 12 000 9000 bp but their chronological placement can only be achieved with a few years of uncertainties a great dispersion of ams dates is attributed to contamination by charcoal dated between 11 700 and 11 500 bp and to a possible age plateau at ca 10 000 bp therefore the results are preferably presented versus depth to keep synchronism in the stratigraphic placement of the successive events at rusaka increase in carbon storage c n ratio for terrestrial plants and tree cover began at ca 12 000 bp soon after the swamp had been established this date is in good agreement with a major increased hydrological balance well documented throughout the intertropical region the forest installation is progressive rather complex and seen as a two step process the first forest phase 11 700 bp to 10 600 bp is dominated by hagenia a montane taxon in good correspondance with previous records from other authors in east african mountains the second forest regeneration took place post 10 000 bp after a clearly reversed trend of tree cover from 10 600 to 10 000 bp ending with a short episode of minimum trees lasting no more than about 200 years but there is no indication of cooling whatsoever and the opening of the forest is better explained by increased aridity rather than normal pattern of forest succession this will remain a controversal interpretation among palynologists until high resolution pollen data can be obtained for the 13 000 bp and earlier period nevertheless the timing of the arid episode at rusaka is in good agreement with other evidence mentioned from highland and lowland pollen data a detailed comparison with 25 available pollen diagrams is limited by poor or inconsistent dating or low resolution of the pollen data nevertheless pollen from four of them document an arid event in good agreement with its timing at rusaka and high resolution isotopic results from two sites in equatorial lowlands and from the sahel this work shows that the arid younger dryas occurred at the same time both in lowlands and highlands and therefore was most likely a precipitation signal rather than a response to temperature decrease

millennial scale climate change and intermediate water circulation in the bering sea from 90 ka a high resolution record from iodp site u1340 1 millennial scale climate events in the north pacific are thought to be related to changes in the circulation of north pacific intermediate water which may have formed in the bering sea in the past to advance our understanding of the mechanisms that underlie millennial scale events bering sea sediment cores from the integrated ocean drilling program site u1340 were used to construct high resolution multiproxy climate records of the last 90 000 years sediment density records show millennial scale events resembling dansgaard oeschger events several of which are laminated interstadials were characterized by 3 5 c warming increased productivity driven by upwelling and reduced benthic oxygenation bering sea intermediate water also changed over longer timescales our records show the presence of intermediate water with lower salinity and higher oxygen content than modern beginning around 60 ka and persisting until the beginning of the deglaciation the bolling allerod was characterized by high productivity laminated sediments and strong denitrification signature our data support the idea that productivity derived changes in oxygenation at intermediate water source regions may have contributed to the intensification of the north pacific wide oxygen minima during the bolling allerod

alkenones and alkenes in surface waters and sediments of the southern ocean implications for paleotemperature estimation in polar regions abstract the concentration of c37 c39 long chain alkenones and alkenes were determined in surface water and surface sediment samples from the subpolar waters of the southern ocean distributions of these compounds were similar in both sample sets indicating little differential degradation between or within compound classes the relative amounts of the tri to tetra unsaturated c37 alkenones increased with increasing temperature for temperatures below 6 c similar to the di and tri unsaturated c37 alkenones the c37 di tri and tetra unsaturated methyl alkenones are used in paleotemperature calculations via the u37k and the u37k ratios in these datasets the relative abundances of the c37 2 and the c37 3 alkenones as a proportion of the total c37 alkenones were opposite and strongly related to temperature the latter with more scatter but the abundance of the c37 4 alkenone showed no relationship with temperature the original definition of u37k includes the abundance of 37 4 in both the numerator and denominator and thus it is perhaps not surprising that there is considerable scatter in the values obtained for u37k at low temperatures of the two we suggest that u37k is the better parameter for use in paleotemperature estimations even in cold locations u37k values in the sediments fall on virtually the same regression line obtained for the water column samples of sikes and volkman 1993 indicating that their calibration is suitable for use in southern ocean sediments the comparison of water column data with sedimentary temperature estimates suggests that the alkenone distributions are dominated by contributions from the summer when the biomass of emiliania huxleyi and presumably flux to the sediment is expected to be high

environmental change in montane southwest uganda a pollen record for the holocene from ahakagyezi swamp the environmental history of montane southwest uganda over the last c 12 300 years is described using data from a 22 84 m long core of sediment from ahakagyezi swamp rukiga highlands these data include plant microfossils and macrofossils charcoal and nine radiocarbon dates according to evidence from plant fossils and radiocarbon dates vegetation in the ahakagyezi catchment was very different to the expected climax today until c 10500 bp the surface of the swamp was dominated by sedges whilst the adjacent hillsides were largely devoid of trees changes in pollen suggest that a form of dry montane scrub was replaced by moist lower montane forest from c 11000bp subsequent fluctuations in pollen indicate that once established the composition of moist lower montane forest varied during the holocene and that unreversed forest reduction commenced in the ahakagyezi catchment at c 800 bp on the surface of the swamp itself syzygium dominated swamp forest increased in extent from c 5800 bp and mor

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

development of the california current during the past 12 000 yr based on diatoms and silicoflagellates detailed diatom and silicoflagellates records in three cores from the offshore region of southern oregon to central california reveal the evolution of the northern part of the california current during the past 12 000 yr the early holocene prior to 9 ka was characterizedbyrelativelywarmseasurfacetemperatures sst owingtoenhancednortherlyflowofthesubtropicalwaterscomparable tothemoderndavidsoncurrent progressivestrengtheningof thenorthpacifichighleadtointensificationofthesouthwardflowofthe california current at 8 ka resulting in increased coastal upwelling and relatively cooler sst which persisted until 5 ka reduced southward flow of the california current between 4 8 ka and 3 6 ka may have been responsible for a period of decreased upwelling modern seasonal oceanographic cycles as evidenced by increased spring early summer coastal upwelling and warming of early fall sst evolved between 3 5 and 3 2 ka widespread occurrence of paleoceanographic and paleoclimatic change between 3 5 3 0 ka along the eastern margins of the north pacific was likely a response to increasing enso variability in the tropical pacific published by elsevier b v

particle size evidence for source areas of charcoal accumulation in late holocene sediments of eastern north american lakes abstract two methods of analyzing charcoal in sediment reveal changes in charcoal accumulation across temperate eastern north america during the last several hundred years in one method the analyst counts mostly small particles that reflect regional emissions in the other the analyst counts only larger particles derived mostly from such local sources as catchment fires we used these methods to compare charcoal accumulation at 14 lakes from the prairie forest border in minnesota to eastern maine the two methods gave concordant accumulation rates for sediments of pre 1850 age at each of 4 lakes analyzed by both methods this concordance is consistent with the interpretation that pre 1850 emissions were controlled by broad scale factors such as climatically controlled regional differences in fuels and moisture since 1900 large particles decreased greatly and small particles decreased slightly in minnesota and wisconsin by contrast in the northeast the large particle accumulation has remained at the low values measured in pre 1900 sediments at most sites while small particles increased everywhere east of central new york and pennsylvania the observed patterns suggest that 1 large particles primarily reflect local fires that were common in the midwest before fire suppression became effective 2 large particles were rare in the northeast especially before extensive land clearance 3 small particles reflect regional combustion that increased in the northeast after extensive use of fire for land clearance and wood burning for industrial purposes of the 19th century and 4 small particles remain abundant in the midwest long after effective fire suppression probably because these well dispersed small particles have a large source area that extends beyond the local wildfires that account for large particles before european settlement

late glacial and holocene environmental and climatic changes from a limnological transect through colombia northern south america abstract we present a synthesis of the palaeolimnological and palaeoclimatic reconstructions of four sites in colombia the record from lake el caimito the westernmost site on the pacific coast dates from the late holocene and shows lacustrine sedimentation frequently interrupted by fluvial pulses these pulses probably reflect periods of increased precipitation related to la nina phases east of el caimito site is the patia swamp situated between the western and central andean cordilleras the patia records the dynamics of forest expansion reduction and changes in water levels although the climatic signal of the patia core is difficult to reconstruct there is a clear increase in humidity in the mid holocene the fuquene lake record on the eastern andean cordillera records dry and cold conditions during the late pleistocene very humid conditions for the early mid holocene and dry conditions during the mid late holocene las margaritas site on the eastern savannas records dry conditions during the early holocene and overall humid conditions for the mid and late holocene climate conditions from the fuquene and las margaritas sites seem to reflect the holocene movements of the intertropical convergence zone itcz the latter site being more affected by humidity coming from the amazon region

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

late quaternary peat formation and vegetation dynamics in a lowland tropical swamp nee soon singapore abstract cores of sediment from nee soon a peat forming freshwater swamp located in the perimarine zone of singapore have yielded a record of vegetation history that comprises parts of the last glacial and holocene periods the evidence includes two conventional and four ams radiocarbon dates the oldest of which is 23 050 330 b p uncalibrated radiocarbon years and variations in the abundances of sub fossil pollen and spores and charcoal the results of a study of the relationship between contemporary vegetation and modern pollen accumulation facilitated interpretation of sub fossil tree pollen data peat formation occurred at nee soon during the last glacial when sea levels on the sunda continental shelf were well below those at present the occurrence of montane pollen types notably podocarpaceae in sediment samples dated to the late glacial and early holocene suggests either temperatures substantially lower than those of the present and possibly humid conditions or cold seasonally dry climates and reduced levels of atmospheric co 2 the abundance of charcoal indicates the widespread occurrence of fires throughout the entire period represented by the cores for the mid holocene the evidence indicates an increased saline influence presumably as a result of relatively high sea levels falling sea levels during the late holocene appear to have preceded the onset of the most recent period of peat formation at nee soon the evidence confirms that long last glacial interglacial records of lowland vegetation history are available from terrestrial locations in the humid core of southeast asia and suggests that the complexity of perimarine swamp dynamics is not captured fully by anderson s model which assumes a close relationship between peat formation and sea level

a 12 000 year history of vegetation and climate for cape cod massachusetts abstract pollen and charcoal analysis of radiocarbon dated sediment cores from duck pond in the cape cod national seashore provide a continuous 12 000 yr vegetation and climate history of outer cape cod a picea hudsonia parkland and then a picea pinus banksiana alnus crispa boreal forest association grew near the site between 12 000 and 10 000 yr b p this vegetation was replaced by a northern conifer forest of pinus strobus p banksiana and subsequently by a more mesophytic forest pinus strobus tsuga quercus fagus acer ulmus fraxinus ostrya as the climate became warmer and wetter by 9500 yr b p by 9000 yr b p a pinus rigida quercus association dominated the landscape high charcoal frequencies from this and subsequent levels suggest that the pine barrens association developed during a warmer and drier climate that lasted from 9000 to about 5000 yr b p increased percentages of pinus strobus pollen indicate a return to moister and cooler conditions by about 3500 yr b p a doubled sedimentation rate increased charcoal and increased herb pollen suggest land disturbance near the pond before european settlement these results suggest a rapid warming in the northeast in the early holocene and support a hypothesis of a rapid sea level rise at that time comparison of the pollen results from duck pond with those from rogers lake connecticut illustrates the importance of edaphic factors in determining the disturbance frequency and vegetation history of an area

postglacial evolution of a fine grained alluvial fan in the northern great plains canada abstract this paper reports on the first subsurface core taken from an alluvial fan in the interior plains of western canada sedimentary structures grain size grain roundness loss on ignition charcoal abundance bulk authigenic geochemistry colour mineralogy and microscopic charcoal identifications show that a fine grained fan developed through a succession of depositional environments within each environment sediment erosion transportation and deposition processes were conditioned by changing dominant partial area contributions and complex geomorphic responses neither the rate nor the processes of aggradation have been constant through time succession from one depositional environment to another involved the crossing of geomorphic thresholds while climate may have affected sediment yield and therefore the timing of threshold crossings the basic sequence was controlled by aggradation alone the sensitivity of this site to climate change is thus overwhelmed by internal processes

sea surface temperature across the subarctic north pacific and marginal seas through the past 20 000 years a paleoceanographic synthesis abstract deglacial sea surface conditions in the subarctic north pacific and marginal seas are the subject of increasing interest in paleoceanography however a cohesive picture of near surface oceanography from which to compare inter and intra regional variability through the last deglaciation is lacking we present a synthesis of sea surface temperature covering the open north pacific and its marginal seas spanning the past 20 ka using proxy records from foraminiferal calcite 18o and mg ca and coccolithophore alkenones uk 37 sea surface temperature proxies tend to be in agreement through the holocene though uk 37 records are often interpreted as warmer than adjacent 18o or mg ca records during the last glacial maximum and early deglaciation in the sea of okhotsk holocene discrepancies between 18o and uk 37 may be the result of changes in near surface stratification we find that sea surface warming occurred prior to the onset of the bolling allerod 14 7 ka and coincident with the onset of the holocene 11 7 ka in much of the north pacific and bering sea proxy records also show a cold reversal roughly synchronous with the younger dryas 12 9 11 7 ka after the onset of the holocene the influence of an intensified warm kuroshio current is evident at higher latitudes in the western pacific and an east west seesaw in sea surface temperature likely driven by changes in the strength of the north pacific gyre characterizes the open interglacial north pacific

glacial to deglacial ventilation and productivity changes in the southern okhotsk sea abstract as a source region of north pacific intermediate water the okhotsk sea plays an important role in the ventilation of the north pacific to understand the detailed oceanographic changes in this marginal sea since the last glaciation we studied decadal to centennial scale proxy records from new sediment cores from the southwestern okhotsk sea glacial to holocene 14 c records of benthic foraminiferal shells suggested enhanced ventilation in the okhotsk sea during the early deglacial period between 18 and 15 ka corresponding to heinrich event 1 although the 14 c reconstruction has considerable uncertainties the okhotsk sea may have acted as a source for vigorous ventilation of the subarctic pacific during this period caco 3 preservation events appear to be better explained by the ventilation history of the okhotsk sea than by coccolithophores and foraminifera production caco 3 preservation started to improve during 18 to 15 ka and pronounced peaks in the caco 3 content corresponded to the bolling allerod 15 to 13 ka and preboreal 11 5 to 10 ka warm periods diatom and coccolithophore productivity remained low in the okhotsk sea throughout the glacial to deglacial periods different from the situation in the open subarctic pacific where high productivity was observed during the bolling allerod period after the preboreal period biogenic opal gradually increased and 15 n decreased in the southern okhotsk sea suggesting that productivity was enhanced by a relaxation of the nitrate limitation

charcoal fragments in surface samples following a fire and the implications for interpretation of subfossil charcoal data abstract following an uncontrolled fire in an area of heathland in sw england surface samples were taken from selected positions charcoal concentrations charcoal pollen ratio and size class frequencies were measured and the data from burned unburned and forest areas are compared charcoal concentrations show distinct variability between closely spaced samples but despite this differences are shown between the burned and unburned areas selected size classes are suggested as being appropriate for distinguishing between burned and unburned areas in palaeoecological studies while in need of replication these data should provide a basis for further studies of this type

determination of black carbon by chemical oxidation and thermal treatment in recent marine and lake sediments and cretaceous tertiary clays abstract several sample treatments and analytical methods for the measurement of black carbon in a wide variety of sediments were considered in which the removal of organic carbon is a critical step in the procedure a comparison between chemical oxidation and thermal treatment was conducted and the latter was shown to be inappropriate due to the polymerisation of organic matter using acid dichromate oxidation reactive kerogen was separated from black carbon in a variety of lake and marine and recent and ancient sediments with relatively small and quantifiable losses 1 6 of black carbon under carefully controlled reaction conditions

late holocene vegetation and fire history at the southern boreal forest margin in alberta canada abstract a transect of three shallow ponds across the aspen parkland boreal forest transition in elk island national park alberta canada shows changes in late holocene vegetation and disturbance dynamics and consequent carbon storage in response to climate change and to recent anthropogenesis pollen and charcoal analyses reveal unexpected changes in fire regime although there is the expected decline in fire activity during the historic period presumed due to agricultural clearance around the park there is also a prehistoric fluctuation in fire regime at one of the sites pollen evidence suggests that the fluctuations in fire regime may be due to changes in hydrology declining groundwater levels during the medieval warm period allowed the replacement of substantial areas of shrub birch betula glandulosa with the less fire prone aspen populus tremuloides causing a decline in fire frequency and or severity while increasing carbon storage on the landscape this is counter to the intuitive increase in fire activity with warmer and drier climate canadian national parks are currently managed under a natural processes and conditions paradigm the changes in conditions and consequent changes in processes evident due to the relatively minor climatic fluctuations of the little ice age and medieval warm period shown here suggest a need to revisit this paradigm in consideration of future anthropogenic climate change

glacial interglacial changes in subantarctic sea surface temperature and δ18o water using foraminiferal mg laboratory culturing experiments with living globigerina bulloides indicate that mg ca is primarily a function of seawater temperature and suggest that mg ca of fossil specimens is an effective paleotemperature proxy using culturing results and a core top neogloboquadrina pachyderma calibration we have estimated glacial interglacial changes in sea surface temperature sst using planktonic mg ca records from core rc11 120 in the subantarctic indian ocean 43 s 80 e and core e11 2 in the subantarctic pacific ocean 56 s 115 w our results suggest that glacial sst was about 4 c cooler in the subantarctic indian ocean and 2 5 c cooler in the subantarctic pacific comparison of sst and planktonic 18o records indicates that changes in sst lead changes in 18o by on average 1 3 kyr the glacial interglacial temperature change indicated by the subantarctic mg ca records suggests that temperature accounts for 40 60 of the foraminiferal 18o change we have used the mg ca based sst estimates and 18o determinations to generate site specific seawater 18o records which suggest that seawater 18o was on average 1 more positive during glacial episodes compared with interglacial episodes

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

spatial and temporal variability of surface water in the kuroshio source region pacific ocean over the past 21 000 years evidence from planktonic foraminifera abstract the kuroshio current is the major western boundary current of the north pacific ocean and has had a large impact on surface water character and climate change in the northwestern pacific region the kuroshio current becomes a distinctive surface flow in the ryukyu arc region after diverging from the north equatorial current and passing through the okinawa trough therefore the ryukyu arc area can be called the kuroshio source region we reconstructed post 21 ka time space changes in surface water masses in the ryukyu arc region using 15 piston cores which were dated by planktonic 18 o stratigraphy and ams 14 c ages our analysis utilized spatial and temporal changes in planktonic foraminiferal assemblages which were classified into the kuroshio subtropical coastal and cold water groups on the basis of modern faunal distributions in the study region these results indicate that the kuroshio current and adjacent surface water masses experienced major changes during 1 the last glacial maximum lgm and 2 the so called pulleniatina minimum event pme from 4 500 to 3 000 yr bp the kuroshio lgm event corresponds to severe global cooling and is marked by decreases in planktonic 18 o values and estimated sea surface temperature sst with the dominance of the cold water group of planktonic foraminifera cooling within the kuroshio source region was enhanced during the lgm event because the kuroshio current was forced eastward due to the formation of a land bridge between taiwan and the southern ryukyu arc which prohibited its flow into the okinawa trough except for the severe reduction and disappearance of the pulleniatina group no clear cooling signal was identified during the pme based on 18 o values estimated sst values and variations in the composition of planktonic foraminiferal faunas the pme assemblages are marked by high abundances of neogloboquadrina dutertrei a distinctive kuroshio type species along with other species assigned to the coastal and central water groups subtle ecological differences exist between pulleniatina obliquiloculata and n dutertrei i e p obliquiloculata exhibits lower rates of reproduction under conditions of lower primary productivity in the central equatorial pacific ocean el nino like conditions in the equatorial pacific ocean result in lower rates of surface transport in the kuroshio current in turn this response triggers lower rates of primary productivity in central equatorial surface waters as well as in the upstream kuroshio source region ultimately resulting in a lower abundance of p obliquiloculata thus we interpret the pme as a possible proxy signal of el nino like conditions and enhancement of the el nino southern oscillation climate system after the pme in the tropical and sub tropical pacific ocean

sea surface temperature variability and sea ice extent in the subarctic northwest pacific during the past 15 000 years past changes in north pacific sea surface temperatures and sea ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the north atlantic here we present new alkenone based sea surface temperature records from the subarctic northwest pacific and its marginal seas bering sea and sea of okhotsk for the time interval of the last 15 kyr indicating millennial scale sea surface temperature fluctuations similar to short term deglacial climate oscillations known from greenland ice core records past changes in sea ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the ip25 biomarker related to sea ice diatoms the deglacial variability in sea ice extent matches the sea surface temperature fluctuations these fluctuations suggest a linkage to deglacial variations in atlantic meridional overturning circulation and a close atmospheric coupling between the north pacific and north atlantic during the holocene the subarctic north pacific is marked by complex sea surface temperature trends which do not support the hypothesis of a holocene seesaw in temperature development between the north atlantic and the north pacific key points millennial scale changes in sst in the north pacific during the last 15 kyr changes in sea ice extent suggest a close coupling to sst fluctuations middle to late holocene ssts show no clear sst trend in the north pacific

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters