a 160 k y old record of el nino southern oscillation in marine production and coastal runoff from santa barbara basin california usa a 160 k y old laminated sediment record from the santa barbara basin california analyzed using scanning electron microscope techniques provides a history of interannual variability of marine production and coastal runoff we used backscatter electron imagery to measure the components of the varve these include a terrigenous lamina formed by seasonal runoff from winter rains together with a diatomaceous lamina that records marine production during the spring and early summer spectral analysis of terrigenous and diatomaceous laminae thickness reveals significant periodicities of 3 1 and 8 4 yr in the terrigenous series these are indistinguishable within the frequency resolution of the spectra from significant periodicities of 3 5 and 7 6 yr in the diatomaceous series the 3 1 and 3 5 yr periodicities record el nino modulation of coastal runoff and marine production the 8 4 and 7 6 yr periodicities are consistent with modulation by strong to very strong el nino events this is supported by the results of cross spectral analysis of the terrigenous and diatomaceous records which reveal inverse or antiphase relationships at 3 5 and 7 6 yr our work adds to a body of evidence that suggests that el nino has been a persistent feature of late quaternary climate variability

millennial scale climate variability of the northeast pacific ocean and northwest north america based on radiolaria and pollen abstract radiolaria and pollen abundances in marine sediment cores from the northeast pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle 0 150 kyr these data allow direct comparison of the climate response of continental and oceanic systems detailed 18 o and ams 14 c measurements provide a link into global stratigraphic frameworks canonical correlation analysis extracts two modes of variation common to both the radiolaria and pollen records the first mode of variation correlates an assemblage of radiolaria associated with coastal upwelling with increased redwood western hemlock and alder pollen this association is consistent with the modern relationship between coastal upwelling coastal fog and redwood forests a second canonical mode relates an oceanic fauna now found in highest abundance in the far north pacific with reduced pine and western hemlock pollen abundance comparison of these records to an ice core 18 o record suggests that at wavelengths 3000 years warm events in greenland are correlated to intervals of increased coastal upwelling off oregon decreases in importance of very cold north pacific fauna suggesting warming and increases in pollen associated with wetter coastal environments radiolarian based sea surface temperature estimates suggest that the variability of the northeast pacific on this time scale is about 2 c warming in the coastal regions reflects reduced advection of the california current but is moderated by increases in cool coastal upwelling we infer that the response of the northeast pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid to high latitudes preliminary analysis suggests that oceanic variability off oregon at wavelengths 18 o records this variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements this finding suggests that unlike longer period millennial scale events the propagation of the shorter wavelength events to the northeast pacific is through subtropical or tropical teleconnections

amphibole composition as an indicator of subtle grade variation in epidote glaucophane schists the paragenetic relations of epidote glaucophane schists are described in terms of the system al2o3 fe2o3 fe2o3 mgo cao with excess of quartz albite and epidote if alkali amphibole is free from ca and aliv its composition when associated with epidote is invariant univariant or divariant at a given pressure and temperature on miyashiro s 1957 diagram of alkali amphibole solid solution if it is also associated respectively with three two or one additional minerals in the system using a group of epidote glaucophane schists from the kotu area of the sanbagawa metamor phic belt in shlkoku japan isophysical compositional univariant boundary lines were determined for the assemblages that in addition to the ubiquitous quartz albite phengitic mica contain hematite chlorite garnet chlorite and actinolite chlorite respectively the slopes of the univariant boundary lines obtained from petrographical data are in good agreement with those calculated in a model system the positions of isophysical univariant boundary lines on the amphibole compositional diagram serve to distinguish the grade of metamorphism among the rocks of the same mineral facies the hematite chlorite univariant boundary line can be used to divide the zone of epidote glaucophane schists of the sanbagawa metamorphic belt into three and the garnet chlorite paragonite invariant equilibrium can be used to divide the epidote zone of new caledonia into three

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

carbon isotope records in a mesoproterozoic epicratonic sea carbon cycling in a low oxygen world abstract carbon isotope profiles of sedimentary strata are widely used as both a tool for stratigraphic correlation and as a mechanism for inferring important changes in earth s biogeochemical cycles chemostratigraphic interpretations however often rely on the assumption that the isotopic composition of dissolved inorganic carbon dic in the surface oceans is broadly homogeneous at times of globally high sea level when epicratonic epeiric environments dominate our sedimentary record carbon isotope records reveal substantial lateral variability here we investigate lateral variability in the marine carbon isotope record from pericratonic to epicratonic environments of the mesoproterozoic 1 1 ga atar el mreiti groups of the taoudeni basin west africa restricted marine epicratonic environments are consistently 2 4 lighter than open marine pericratonic environments suggesting input of an isotopically light carbon source that preferentially affected epicratonic environments in contrast to epicratonic environments in the paleozoic where input of isotopically light carbon is generally attributed to input of terrestrial organic matter we suggest that in situ remineralization of organic carbon via anaerobic microbial cycling drove observed isotopic variability within epicratonic el mreiti group strata the extent of organic matter remineralization and thus degree of 13 c depletion is correlated with water depth and associated with distinct differences in both total organic carbon toc and pyrite concentration suggesting a potential linkage to both the persistence of anoxia and the availability of sulfate within epicratonic environments in such settings the isotopic effects of organic carbon remineralization are potentially enhanced by either methane oxidation following methanogenic decomposition or the intermittent oxidation of an enhanced dissolved organic carbon doc pool

stable isotope stratigraphy and paleoceanography during the last deglaciation on the continental shelf off troms northern norway a stable oxygen and carbon isotope stratigraphy is established for a late weichselian holocene glaciomarine marine sequence in andfjorden and malangsdjupet on the continental shelf off troms northern norway the stratigraphy demonstrates that the global signals termination i b and possibly also i a upper parts are present and radiocarbon date to 10 3 9 7 kyr b p and 14 13 5 kyr b p respectively a temperature increase of 5 6 c and possibly a small salinity increase occurred during term i a near glacial environment between 13 and 14 kyr b p was characterized by poorly ventilated bottom waters followed by a meltwater pulse at circa 13 kyr b p during the beginning intrusion of atlantic water between 13 and 10 kyr b p the bottom water was characterized by somewhat fluctuating temperatures and salinities temperatures close to those of the present were established around 9 7 kyr b p and seem to have been rather stable since

a 900 year stable isotope record of interdecadal and centennial change from the california current this paper describes the development of a high resolution record of interdecadal and centennial variability of ocean climate of the california current from continuous 5 year sampling intervals based on varve counts from santa barbara basin sediments we show the importance of the choice of species and size fraction as well as the practice of making multiple measurements per interval to obtain a clear environmental signal capable of resolving interdecadal change changes in temperature and salinity from oceanographic surveys of the past 50 years indicate that thermal variability dominates the 18o signal a 18o record from neogloboquadrina dutertrei spanning 1030 1905 a d contains interdecadal thermal fluctuations within the upper thermocline that are centered around periods of roughly 55 70 and 90 years the interdecadal changes comprise the major share of total variability compared to a low amplitude mode of underlying multicentennial variability corresponding to the medieval warm period and the little ice age

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

deglacial changes in ocean circulation from an extended radiocarbon calibration temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon based age estimates of biogenic material that do not agree with true calendar age this problem is particularly severe beyond the limit of the high resolution radiocarbon calibration based on tree ring data which stretches back only to1 2 about 11 8 kyr before present bp near the termination of the younger dryas cold period if a wide range of palaeoclimate records are to be exploited for better understanding the rates and patterns of environmental change during the last deglaciation extending the well calibrated radiocarbon timescale back further in time is crucial several studies attempting such an extension using uranium thorium dated corals3 4 5 and laminae counts in varved sediments6 7 8 9 show conflicting results here we use radiocarbon data from varved sediments in the cariaco basin in the southern caribbean sea to construct an accurate and continuous radiocarbon calibration for the period 9 to 14 5 kyr bp nearly 3 000 years beyond the tree ring based calibration a simple model compared to the calculated atmospheric radiocarbon concentration and palaeoclimate data from the same sediment core suggests that north atlantic deep water formation shut down during the younger dryas period but was gradually replaced by an alternative mode of convection possibly via the formation of north atlantic intermediate water

late holocene sedimentation in saanich inlet british columbia and its paleoseismic implications eight piston cores of sediment spanning the last 1500 years were collected from saanich inlet an anoxic fiord on southern vancouver island to obtain information on sedimentation and prehistoric earthquake activity the cores consist mainly of fine grained varved sediments but include massive layers deposited by subaqueous debris flows the debris flows may have been triggered by earthquakes or by the buildup of fine sediment on the walls of the inlet cesium 137 and 2bopb data i4c ages and varve counts were used to date and correlate massive layers in the eight cores the uppermost massive layer in two cores may record a magnitude 7 2 earthquake that occurred in 5946 near comox british columbia 200 km north northwest of saanich inlet seven older layers are found in two or more cores and are about 200 440 550 800 850 1050 1100 1100 1150 and 1450 1500 years old two of these older layers may correlate with previously documented earthquakes in the region there is an average of one massive layer per 116 varves in the core with the greatest number of such layers which is broadly consistent with the expected periodicity of moderate to large earthquakes in the region on average one earthquake producing local modified mercalli intensity vii or viii per century saanich inlet may contain a proxy record of all moderate and large earthquakes that have affected southwestern british columbia during holocene time but some of the massive layers do not appear to correlate from core to core and undoubtedly are nonseismically generated deposits

glaciation and sea level change for ireland and the irish sea since late devensian midlandian time the sea level change around the coast of ireland and the irish sea for the past 20 000 years is primarily the combined result of the glacio isostatic adjustment of the crust to the removal of ice over the british isles and the total eustatic change from the global ice sheets however the isostatic effects due to the removal of ice from northern europe and north america and the addition of meltwater into the oceans also make a significant contribution predictions of sea level change based on glacio hydro isostatic models are compared with observations to constrain the ice volume over ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m the models predict well the spatial variability in sea level change observed across the region for holocene and lateglacial time with levels above present being predicted only for northeastern ireland and north of about morecambe bay the models do not support suggestions that lateglacial levels along the east coast of ireland or the coast of wales were 50 150 m above their present levels consistent models that would produce such large lateglacial highstands are incompatible with all other sea level and glacial evidence for the british isles palaeobathymetry and palaeoshoreline reconstructions for the irish sea indicates that a tenuous landbridge between britain and ireland developed only across the celtic sea between about 18000 and 14000 years bp

palaeotidal modelling of continental shelves marine implications of a land bridge in the strait of dover during the holocene and middle pleistocene

palaeo flux records from electron microscope studies of holocene laminated sediments saanich inlet british columbia holocene varved sediments recovered from saanich inlet odp leg 169s have been analysed using high resolution scanning electron microscope techniques the individual centimetre scale varves form couplets comprising diatom ooze diatomaceous mud deposited during spring to autumn and silty clay deposited during winter each individual varve may contain up to 19 laminae recording sub seasonal to seasonal scale processes these intra annual laminae contain a range of components including pelagic faecal pellets and aggregates of diatomaceous material the combination of these individual components in varying proportions with a heterogeneous sediment leads to a range of laminae fabrics these include intact monospecific skeletonema costatum and thalassiosira pacifica diatom oozes and highly fragmented aggregate and faecal pellet dominated diatom oozes which are typically chaetoceros spp dominated additional laminae fabrics include diatomaceous mud stringer type diatomaceous mud which contains discrete diatom aggregates homogeneous and pelleted silty clay the varved diatom succession typically commences in early spring with thalassiosira spp chaetoceros spp followed by chaetoceros spp in late spring during late spring early summer blooms of s costatum may be recorded and summer to autumn production is characterised by one to several chaetoceros spp dominated blooms inter annual variability in diatom flux typically comprises the presence absence of thalassiosira spp and s costatum in addition resting spores of chaetoceros spp thalassiosira nordenskioeldii and leptocylindricus danicus are intermittently recorded there is a major change in varve thickness from thinner varves prior to approximately 2100 yr bp to thicker varves after this date which is attributed to increased terrigenous input throughout the varve the identification of laminae fabrics diatom successions and a unique massive interval has enabled an inter site correlation between sites 1033b and 1034b

a wet heterogeneous lunar interior lower mantle and core dynamo evolution while recent analyses of lunar samples indicate the moon had a core dynamo from at least 4 2 3 56 ga mantle convection models of the moon yield inadequate heat flux at the core mantle boundary to sustain thermal core convection for such a long time past investigations of lunar dynamos have focused on a generally homogeneous relatively dry moon while an initial compositionally stratified mantle is the expected consequence of a postaccretionary lunar magma ocean furthermore recent re examination of apollo samples and geophysical data suggests that the moon contains at least some regions with high water content using a finite element model we investigate the possible consequences of a heterogeneously wet compositionally stratified interior for the evolution of the moon we find that a postoverturn model of mantle cumulates could result in a core heat flux sufficiently high to sustain a dynamo through 2 5 ga and a maximum surface dipolar magnetic field strength of less than 1 t for a 350 km core and near 2 t for a 450 km core we find that if water was transported or retained preferentially in the deep interior it would have played a significant role in transporting heat out of the deep interior and reducing the lower mantle temperature thus water if enriched in the lower mantle could have influenced core dynamo timing by over 1 0 gyr and enhanced the vigor of a lunar core dynamo our results demonstrate the plausibility of a convective lunar core dynamo even beyond the period currently indicated by the apollo samples

dansgaard oeschger cycles and the california current system planktonic foraminiferal response to rapid climate change in santa barbara basin ocean drilling program hole 893a high resolution planktonic foraminiferal census data from santa barbara basin ocean drilling program hole 893a demonstrate major assemblage switches between 25 and 60 ka that were associated with dansgaard oeschger cycles stadials dominated by neogloboquadrina pachyderma sinistral and globigerinoides glutinata suggest a strong subpolar california current influence while interstadials marked by abundant n pachyderma dextral and g bulloides indicate a relative increase in subtropical countercurrent influence modern analog technique and transfer function f 20rsc temperature reconstructions support 18o evidence of large rapid 70 years or less sea surface temperature shifts 3 to 5 c between stadials and interstadials changes in the vertical temperature gradient and water column structure thermocline depth are recorded by planktonic faunal oscillations suggest bimodal stability in the organization of north pacific surface ocean circulation santa barbara basin surface water demonstrates the rapid response of the california current system to reorganization of north pacific atmospheric circulation during rapid climate change supporting assemblage data are available on diskette or via anonymous ftp from kosmos agu org directory apend username anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 5 00 payment must accompany order

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

biotic response to late quaternary rapid climate switches in santa barbara basin ecological and evolutionary implications benthic foraminiferal assemblages from santa barbara basin exhibit major faunal and ecological switches associated with late quaternary millennial to decadal scale global climate oscillations repeated turnovers of entire faunas occurred rapidly 40 400 yr without extinction or speciation in conjunction with dansgaard oeschger shifts in thermohaline circulation ventilation and climate confirming evolutionary model predictions of roy et al consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late quaternary and possibly other transitional intervals in the history of the earth s ocean atmosphere cryosphere system these data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change

evolution of seasonal stratification in the celtic sea during the holocene seasonal thermocline development in the shelf seas of nw europe results in the formation of pronounced frontal regions which separate stratified from well mixed water numerical m 2 palaeotidal modelling of the nw european continental shelf during successive stages of the holocene transgression indicates that seasonal stratification started to develop in the central celtic sea once a critical threshold water depth had been exceeded at around 9000 years bp this hypothesis has been tested through faunal isotopic and geochemical analysis of an ams 14 c dated british geological survey vibrocore from the celtic deep bathymetric basin a record which spans the last 12 000 years marked positive trends in the stable oxygen isotopic data from the benthic foraminifera ammonia batavus and quinqueloculina seminulum between 9000 and about 5000 years bp represent a 4 5 c cooling in summer bottom water temperature caused by the progressive replacement of tidally well mixed by stratified water stable carbon isotopic data from the same species measured through the same core intervals show a negative trend consistent with net oxygen utilization and decomposition of organic matter beneath the productive frontal zone these geological data indicate the progressive evolution of seasonally stratified water in the celtic sea during the earlier part of the holocene modern shelf sea frontal and thermocline development are known to influence biological productivity sedimentation rates the organic content of shelf sediments and the climate of surrounding landmasses hence these palaeodata have significance in defining the role of shelf sea environments in the climate system

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

thermocline control on coccolith diversity and abundance in recent sediments from the celtic sea and english channel abstract the first systematic record of the abundance and species diversity of coccolith assemblages in the recent shelf sediments of the celtic sea and english channel is presented eighteen coccolith species occur in the sediments although the assemblages are dominated by emiliania huxleyi which frequently forms over 90 of the total flora highest coccolith numbers occur in sediments from the celtic sea 10 9 coccoliths g 10 of the fine fractions coccoliths are either scarce 10 6 g kn assemblages deposited beneath a pronounced thermocline contain high numbers of coccoliths a sparse nannoflora limited to six or fewer species occurs in assemblages deposited from a tidally mixed water column similar controls on coccolith distribution are likely to have occurred in the past the abundance and mode of preservation of coccoliths may therefore provide information on the degree of turbulence in ancient shelf environments

late pleistocene sea level variations derived from the argentine shelf 1 neritic littoral marine sedimentary deposits from the argentine shelf provide a record of late pleistocene sea level variation sediments interpreted to reflect the last glacial maximum low stand are 150 m below present using a simple airy isostatic model for hydroisostatic compensation and correcting for a minor tectonic component yields a local eustatic sea level lowering of 105 m at the last glacial maximum the deglacial sea level curve records two rapid sea level rises consistent with mwp1 a and 1 b as documented by the barbados coral based sea level curve comparison with relative sea level variations predicted by the ice4g vm2 viscoelastic model have highlighted a deficiency in the model s predicted sea level history for this region detailed data model comparisons of late pleistocene sea level variations are necessary in the face of climate change induced sea level perturbations to determine regional and or systematic biases in the treatment of lithosphere viscosity and accurate predictions of future sea level

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

a 6000 yr varve record of holocene climate in saanich inlet british columbia from digital sediment colour analysis of odp leg 169s cores abstract high resolution grey value time series were extracted from digital images of varved sediments in saanich inlet british columbia odp sites 1033 and 1034 results allowed reconstruction of a 6000 yr long record with annual resolution composite records were compiled for sites 1033 and 1034 by correlation of massive beds which represent gravity flows and of characteristic features in the varve patterns the varve count age scale was calibrated with published radiocarbon ages results demonstrate that the odp leg 169s record is virtually complete saanich inlet varve record has the potential to provide a high resolution climate record temporal variation in varve thickness is interpreted to reflect regional precipitation history with thick varves representing wet conditions long term changes in varve thickness during the past 6000 yr coincide with known changes in global climate but without an obvious one to one correlation between wet dry in saanich inlet and warm cold periods elsewhere varve thickness indicates that the climate around saanich inlet was wet from the start of the varved sequence at 6000 to 3250 yr bp between 2100 and 1750 yr bp roman warm period and from 500 yr bp onward including during little ice age

overview of late quaternary stratigraphy in saanich inlet british columbia results of ocean drilling program leg 169s abstract continuous coring in saanich inlet ocean drilling program odp leg 169s british columbia canada yielded a detailed record of late quaternary climate oceanography marine productivity and terrestrial vegetation two sites 1033 and 1034 were drilled to maximum depths of 105 and 118 m recovering sediments ranging in age from 13 300 to less than 300 14 c yr earliest sediments consist of dense largely massive gray glaciomarine muds with dropstones and sand and silt laminae deposited during the waning stages of glaciation deposition of organic rich olive gray sediments began in the fjord about 12 000 14 c yr ago under well oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community at about 10 500 14 c yr a massive gray unit 40 50 cm thick was emplaced in a very short span of time the unit is marked by a sharp lower contact a gradational upper contact and an abundance of reworked tertiary microfossils it has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the fraser valley of mainland british columbia progressively greater anoxia in bottom waters of saanich inlet began about 7000 14 c yr ago this is reflected in the preservation of varved sediments consisting of diatomaceous spring summer laminae and terrigenous winter laminae correlation of the sediments was based on marked lithologic changes the presence of massive intervals reflecting localized sediment gravity flow events the mazama ash occasional thin gray laminae indicative of abnormal flood events in nearby watersheds varve counts between marker horizons and 71 accelerator mass spectrometry ams radiocarbon dates

climatically related millennial scale fluctuations in strength of california margin oxygen minimum zone during the past 60 k y a strong oxygen minimum zone omz currently exists along the california margin because of a combination of high surface water productivity and poor intermediate water ventilation however the strength of this omz may have been sensitive to late quaternary ocean circulation and productivity changes along the margin although sediment lamination strength has been used to trace ocean oxygenation changes in the past oxygen levels on the open margin are not sufficiently low for laminations to form in these regions benthic foraminifera are highly sensitive monitors of omz strength and their fossil assemblages can be used to reconstruct past fluctuations benthic foraminiferal assemblages from ocean drilling program site 1017 off point conception exhibit major and rapid faunal oscillations in response to late quaternary millennial scale climate change dansgaard oeschger cycles on the open central california margin these faunal oscillations can be correlated to and are apparently synchronous with those reported from santa barbara basin together they represent major fluctuations in the strength of the omz which were intimately associated with global climate change weakening perhaps disappearing during cool periods and strengthening during warm periods these rapid major omz strength fluctuations were apparently widespread on the northeast pacific margin and must have influenced the evolution of margin biota and altered biogeochemicalmore cycles with potential feedbacks to global climate change less

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

quaternary shelf sea palaeoceanography recent developments in europe abstract high quality palaeoceanographic reconstructions based on sequences preserved in shallow marine environments demonstrate that these constitute significant archives of climatic and oceanographic change such sequences are important first because their often very high resolution sometimes laminated nature enables high frequency cycles to be resolved and provides the basis for establishing spatial and temporal variability in the marine radiocarbon reservoir effect second sea level index points from shelves are important for the validation of glacio hydro isostatic geophysical models and for understanding sea level change during early deglaciation third shallow marine sequences contain excellent records of land ocean interaction often preserving paired terrestrial marine proxies in the same stratigraphic sequence a new development in shelf sea palaeoceanography is documenting the long term dynamics of shelf sea stratification this is the dominant hydrodynamic phenomenon of tide dominated shelf seas in the middle and high latitudes and has a profound influence on productivity and therefore global change through the carbon cycle detailing the evolution of seasonal stratification during eustatic highstands is therefore of relevance to the climate system

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation