holocene foraminiferal radiocarbon record of paleocirculation in the santa barbara basin differences in radiocarbon apparent ages between coexisting planktonic and benthic b p foraminifers in the santa barbara basin contain information about changes in the age and thus the source of water entering the basin the holocene sequence indicates a greater variability in circulation than previously detected during the early holocene ca 9 ka b p 1 4 c apparent age differences fluctuated between 220 and 560 1 4 c yr similar to rapid variations seen during the younger dryas and the last glacial episode during the relatively stable middle holocene 8 5 2 ka b p 1 4 c apparent age differences averaged 440 1 4 c yr after 2 ka the average b p 1 4 c apparent age difference increased to 620 1 4 c yr which has persisted until the present the shift in b p 1 4 c apparent age differences likely represents a change in the strength or source of north pacific intermediate water production and is concurrent with changes in regional climate patterns as well as with changes in temperature and accumulation rates measured in the greenland ice sheet project 2 ice core suggesting large scale changes in atmospheric circulation patterns

late quaternary relative sea level changes and the role of glaciation upon continental shelves sea levels of the past 20 kyr are largely determined by the response of the earth to the last ice age consequently sea level indicators are an important source of information about the interaction between cryosphere and hydrosphere and the solid earth based on the material presented at a recent european science foundation conference the present paper pin points some of the topics currently under discussion with respect to sea level evidence found on continental shelves these topics include possible effects of erosion and changes in palaeotidal ranges on indicators of former relative sea levels as well as the problems involved in the determination of palaeo water depth in addition to former sea levels more evidence is being gathered for substantial small scale patterns in the sea level changes at or nearby to the former ice margins these patterns are not reproduced by the available geophysical models which reconcile on first order level only the large scale pattern

human responses to middle holocene climate change on california s channel islands abstract high resolution archaeological and paleoenvironmental records from california s channel islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses available climate records in western north america 7 3 8 ka indicate a severe dry interval between 6 3 and 4 8 ka embedded within a generally warm and dry middle holocene very dry conditions in western north america between 6 3 and 4 8 ka correlate with cold to moderate sea surface temperatures sst along the southern california coast evident in ocean drilling program odp core 893a b santa barbara basin an episode of inferred high marine productivity between 6 3 and 5 8 ka corresponds with the coldest estimated ssts of the middle holocene otherwise marked by warm low productivity marine conditions 7 5 3 8 ka the impact of this severe aridity on humans was different between the northern and southern channel islands apparently related to degree of island isolation size and productivity of islands relative to population fresh water availability and on going social relationships between island and continental populations northern channel islanders seem to have been largely unaffected by this severe arid phase in contrast cultural changes on the southern channel islands were likely influenced by the climatically induced environmental changes we suggest that productive marine conditions coupled with a dry terrestrial climate between 6 3 and 5 8 ka stimulated early village development and intensified fishing on the more remote southern islands contact with people on the adjacent southern california coast increased during this time with increased participation in a down the line trade network extending into the western great basin and central oregon genetic similarities between middle holocene burial populations on the southern channel islands and modern california uto aztecan populations suggest middle holocene movement of people at this time from southern california desert environs westward to the southern islands a migration perhaps stimulated by increased continental aridity

radiocarbon age differences between coexisting foraminiferal species radiocarbon age measurements on single species of foraminifera from a core on the ceara rise demonstrate the importance of the joint effect of bioturbation and variable rain abundance of foraminifera the relatively high mixed layer ages for pulleniatina obliquiloculata reflect at least in part an early holocene peak in its abundance while the relatively young ages for globorotalia menardii reflect the delay until mid holocene of its reappearance in the atlantic ocean these results clearly demonstrate that core top sediment samples need not be representative foraminifera falling from today s surface ocean rather at least on the ceara rise such samples consist of a composite of changing species groupings these results also reconfirm the pitfalls associated with attempts to reconstruct the radiocarbon age of deep ocean water on the basis of benthic planktonic foraminiferal age differences

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

genes diversity and geologic process on the pacific coast abstract we examine the genetics of marine diversification along the west coast of north america in relation to the late neogene geology and climate of the region trophically important components of the diverse west coast fauna including kelp alcid birds e g auks puffins salmon rockfish abalone and cancer crabs appear to have radiated during peaks of upwelling primarily in the late miocene and in some cases secondarily in the pleistocene phylogeographic barriers associated with mio pliocene estuaries of the mid california coast the pliocene opening of the gulf of california tectonic and eustatic evolution of the california bight as well as the influence of pleistocene and holocene climate change on genetic structure are assessed in a geologic context comparisons to east coast and western freshwater systems as well as upwelling systems around the globe provide perspective for the survey

evidence for temporal fluctuations in marine radiocarbon reservoir ages in the santa barbara channel southern california abstract differences in the 14 c ages of closely associated marine shell and carbonized plant material from stratified archaeological deposits on san miguel island california suggest holocene 10 000 present fluctuations in marine 14 c reservoir ages these fluctuations coincide with 18 o and 13 c shifts measured in mytilus californianus shells from the same stratigraphic contexts and general atmospheric oceanic circulation models for the region based on these data we make three primary observations 1 significant changes appear to have occurred in the radiocarbon reservoir during the holocene 2 these fluctuations appear to correlate with regional oceanographic changes and 3 high resolution 14 c dating of marine shells may require different r values for different periods of time

carbon isotope diatom and pollen evidence for late holocene salinity change in a brackish marsh in the san francisco estuary analysis of diatoms pollen and the carbon isotopic composition of a sediment core from a brackish marsh in the northern part of the san francisco estuary has provided a paleosalinity record that covers the past 3000 yr changes in marsh composition and diatom frequencies are assumed to represent variations in freshwater inflow to the estuary three periods of relatively high salinity low freshwater inflow are indicated 3000 to 2500 cal yr b p 1700 to 730 cal yr b p and ca a d 1930 to the present the most recent period of high salinity is primarily due to upstream storage and water diversion within the sacramento san joaquin watershed although drought may also have been a factor the two earlier high salinity periods are likely the result of reduced precipitation low salinity high freshwater flow is indicated for the period 750 cal yr b p to a d 1930 c 2001 university of washington

limits on the ventilation rate for the deep ocean over the last 12000 years in this paper we present accelerator radiocarbon measurements on hand picked benthic and planktonic foraminifera separated from two deep sea cores raised from the south china sea from the benthic planktonic age differences we are able to place limits on the extent to which the ventilation rate of the deep pacific ocean has changed over the last 12000 years while much work remains to be done before any definitive answers for the global oceans can be given these results on cores with sedimentation rates suitably high to avoid major corrections for bioturbation effects suggest that the ventilation rate of the deep pacific ocean has remained nearly the same throughout holocene time further there is no suggestion that the rate was slower during the period of major glacial retreat these results confirm that the changes in atmospheric14c c ratio over the last 10000 years owe their origin to radiocarbon production rate changes

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

rapid climatic change in coastal southern california inferred from pollen analysis of san joaquin marsh pollen analysis and five radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of newport bay orange county california sediment deposition kept pace with sea level rise during the early history of the marsh from ca 7000 to 4500 yr b p the site was a freshwater marsh trees were more abundant than today and grassland was the regional vegetation as sea level rose salt marsh gradually invaded the site brief periods of freshwater marsh 3800 2800 2300 and after 560 yr b p correlate with episodes of global cooling during the neoglacial the historic period is marked by the appearance of exotic species particularly erodium cf cicutarium and eucalyptus and the spores of fungi sporormiella and thecaphora peak influx of pollen spores and charcoal probably reflect greater frequency of flooding and erosion ca 5000 yr b p and during the last 1000 yr

silica depletion of the thermocline in the eastern north pacific during glacial conditions clues from ocean drilling program site 893 santa barbara basin california sedimentation of opaline skeletons diatoms radiolarians is greatly reduced during the last glacial period in the santa barbara basin compared with the holocene the overall pattern is similar to that of the accumulation of organic matter but differs in detail apparently both silicate and phosphate supply are reduced during glacial time within the basin which derives its surface waters and thermocline waters from the california current the pattern of reduced glacial diatom productivity suggests a decrease in the estuarine aspects of the subarctic north pacific as a result of decrease in excess precipitation which dominates the present situation variability is greater in silicate accumulation than in organic matter accumulation we hypothesize that this difference is due to greater sensitivity of silicate to changes in nutrient enrichment and depletion in subsurface waters as compared with phosphate

ventilation changes in the northeast pacific during the last deglaciation under present climate conditions convection at high latitudes of the north pacific is restricted to shallower depths than in the north atlantic to what extent this asymmetry between the two ocean basins was maintained over the past 20 kyr is poorly known because there are few unambiguous proxy records of ventilation from the north pacific we present new data for two sediment cores from the california margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repeatedly in the northeast pacific over the course of deglaciation the evidence includes benthic foraminiferal cd ca 18o 16o and 13c 12c data as well as radiocarbon age differences between benthic and planktonic foraminifera a number of features in the shallower of the two cores including an interval of laminated sediments are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the santa barbara basin and the gulf of california keigwin and jones 1990 kennett and ingram 1995 behl and kennett 1996 data from the deeper of the two california margin cores suggest that during times of reduced ventilation at 800 m ventilation was enhanced at 1600 m depth and vice versa this pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the north pacific and the north atlantic

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

cohesion influences on erosion and bed load transport 1 studies on erosion and transport rates of cohesive sediment mixtures containing gravel are not reported so far in the literature to the best of our knowledge results from laboratory experiments on the process of erosion of cohesive sediment mixtures by open channel flow are presented the sediment used for experimentation consisted of fine gravel mixed with clay in proportions varying from 10 to 50 and fine gravel fine sand in equal proportion by weight mixed with clay proportions again varying from 10 to 50 by weight experimental observations have revealed that the process of detachment of cohesive sediment mixtures containing gravel is significantly different from that of cohesionless sediments also it is different from the detachment process of cohesive sediment mixtures not containing coarser size material experimental data on transport rates of the bed load of the cohesive sediment mixtures are presented on the basis of dimensional considerations a computational procedure is proposed to determine the bed load transport rates generated from erosion of the different size fractions of sediment mixtures clay percentage and unconfined compressive strength of the sediment bed were the main parameters controlling bed load transport rate of such sediments in the absence of cohesion the proposed method reduces to the patel and ranga raju 1996 method for bed load transport rate computation of nonuniform cohesionless sediments

differences in radiocarbon age between shell and charcoal from a holocene shellmound in northern california abstract the west berkeley shellmound the oldest well dated archaeological site in the san francisco bay region contains shell and charcoal ranging in age from ca 1200 to 5700 cal yr b p radiocarbon ages of marine shell and charcoal collected from fifteen stratigraphic levels in the west berkeley shellmound suggest changes in the 14 c content of san francisco bay surface waters relative to the atmosphere the oceanic reservoir age over the past 5000 yr the reservoir age of san francisco bay waters fluctuated between 870 and 170 14 c yr over the past 5000 yr with the lowest values occurring 2900 to 3800 cal yr b p and the highest values between 1200 and 2000 cal yr b p changes in the radiocarbon reservoir age may be due to changes in the strength of seasonal wind driven upwelling off coastal california where upwelling brings 14 c depleted waters to the surface the period of lowest r values at 3500 to 3900 cal yr b p is coincident with relatively low salinity in san francisco bay indicating high freshwater inflow and wet climate in california based on lake level records the period of high r values 1200 2000 cal yr b p is coincident with one of the driest periods in california during the late holocene these data suggest a link between coastal upwelling and precipitation over central california the age of the top of west berkeley mound and several other mounds in the san francisco bay region 1100 to 1300 cal yr b p coincides with a prolonged dry period in california and low river inflow to san francisco bay perhaps the sites were abandoned because of the drought

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

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

a 9000 year flood history for southern california a revised stratigraphy of varved sediments in santa barbara basin abstract the center of santa barbara basin sbb preserves annual laminations through most of the holocene providing an important locality for high resolution late quaternary paleoclimate and paleoceanography reconstructions an accurate chronology is necessary for these sediment based records and enables comparisons with more distal data time series of similar quality here we present an improved high resolution radiocarbon chronology for the last 9000 yrs based on 89 accelerator mass spectrometric ams 14c dates of mixed planktonic foraminiferal carbonate from three sediment cores collected in sbb mv0811 14jc spr0901 06kc and odp hole 893a accurate core to core correlation is demonstrated using prominent gray flood and olive turbidite layers identified in sbb and dated in multiple cores gray layer deposits were found more frequently in wetter intervals as determined by multi proxy hydroclimate records in southern california e g lake deposits and tree rings mass accumulation rates mars calculated for the sbb depocenter using the improved radiocarbon age model indicate high mars are associated with these gray layers that have been associated with floods thus sediment accumulation in sbb is largely controlled by sediment delivery via river runoff following precipitation events although mars may also be influenced by other factors that enhance erosion in river catchments folded sediment is observed within the basal core section of mv0811 14jc which stratigraphically correlates with 14c age reversals in odp hole 893a we associate this sediment slump feature with the large goleta submarine slide complex in santa barbara channel and estimate the submarine slide event occurred at 9000 200 yrs bp furthermore small olive turbidite layers identified and dated in sbb can be temporally linked with large earthquakes along san andreas fault and can therefore potentially reconstruct earthquake history in southern california

resolving varve and radiocarbon chronology differences during the last 2000 years in the santa barbara basin sedimentary record california abstract santa barbara basin sbb is well known for producing high quality paleoclimate reconstructions but the validity of correlations between the basin and other regions rests upon age model accuracy yet the two independent and well established chronologies based on varve counting and radiocarbon dating do not consistently agree during the last two millennia here the validity of age model assumptions is tested including whether 1 the regional reservoir age of surface waters was invariably 641 119 years through time and or 2 sbb laminae couplets are consistently annual varves and counted with sufficient precision this high resolution 14 c study of sbb sediments compares 49 mixed planktonic foraminiferal carbonate and 20 terrestrial organic carbon 14 c dates to the varve chronology to extend the high resolution paleoclimate chronology of the basin back 2000 years evidence indicates that regional reservoir ages do not remain constant through time with r i e regional reservoir age minus variations in the global mixed layer ocean reservoir age fluctuating between 80 and 350 years second there is a consistent r 2 0 96 undercounting of the varves between 150 and 1700 ad based on a new varying r 14 c chronology indicating that some laminae couplets may not be annual loss of varves may occur when low riverine input and infrequent winter storm activity during drought intervals fail to supply a siliciclastic layer

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation