a study on the regulation of the concentrations of some trace metals rb sr zn pb cu v cr ni mn and mo in saanich inlet sediments british columbia canada abstract bulk metal concentrations were measured in the sediments of saanich inlet in an attempt to establish the occurrence of trace metal enrichment in the anoxic central basin ba ni v cr zn pb cu and mo were found to be enriched in the anoxic ooze over the possible contributions from lithogenic sources spatial and seasonal variations in the chemical composition of the settling particulates collected with interceptor traps gave further indications of the mode of incorporation of these metals biogenic ba and cr appeared to be associated with opaline silica although alternative explanations are also possible particularly for ba zinc seemed to be added to the sediment essentially in association with planktonic materials while cu required an additional source directly linked to the anoxic environment similarly ni v and mo were added to the anoxic sediments by reactions occurring at the sediment water interface in the nearshore environment studied here these metals particularly ni and mo were not associated to any significant extent with planktonic materials of all the elements analyzed mo showed the largest enrichment in the anoxic sediments of saanich inlet

crustal growth associated with anorogenic mid proterozoic anorthosite massifs in northeastern north america abstract mid proterozoic anorthosite massifs north of the grenville front tectonic zone in labrador are believed to have been emplaced in an anorogenic setting chemistry of the adirondack anorthosite mangerite charnockite suite suggests that it is bimodal and was also emplaced anorogenically by inference it is assumed that the intervening massifs of the grenville province are of anorogenic derivation as well geochronologic data indicates that these complexes formed during an interval of 500 m y from 1600 1100 ma with most magma emplaced during the last 300 m y the currently exposed area of the anorthosite fraction of the massifs represents 13 of the area into which they were emplaced if this proportion is continued downward throughout a 35 40 km thick crust its volume yields a computed maximum crustal growth rate of 5 10 km 3 ma per kilometer of magmatic belt if the anorthosites are continued only to 5 km the growth rate becomes 1 2 km 3 ma per kilometer of magmatic belt although considerably less than rates of crustal addition in volcanic arcs the computed rates are substantial and indicate that mid proterozoic anorthositic magmatism made significant local contributions to continental crust during the complicated evolution of northeastern north america

distinguishing between water column and sedimentary denitrification in the santa barbara basin using the stable isotopes of nitrate 1 below its sill depth the santa barbara basin sbb is commonly suboxic o2 3 m with only brief periods of ventilation associated with development of suboxia the concentration of nitrate decreases with depth into the basin without an associated decrease in phosphate indicating that a substantial fraction of the nitrate supplied to the basin is removed by denitrification coincident with the decrease in nitrate concentration across the redoxcline the interface between oxic and suboxic waters within the sbb there is an increase in the 15n 14n of that nitrate as would be anticipated from the isotopic fractionation associated with denitrification however the increase in 15n 14n of nitrate is much smaller than occurs in the open eastern tropical north pacific etnp for a comparable amount of nitrate loss both the concentrations of n species within the basin and measurements of nitrate 18o 16o suggest that the lower than expected 15n enrichment in the suboxic sbb involves denitrification rather than being due to some unknown source of low 15n 14n n to the deep sbb calculations with a range of models of nitrate supply and consumption indicate that the degree of nitrate consumption in the basin is too small for differences in water circulation to explain the isotopic differences between the santa barbara basin and the open etnp previous studies indicate that the isotope effect of sedimentary denitrification is negligible due to nitrate diffusion in sediment pore waters thus we infer that the small magnitude of the isotopic enrichment of sbb water column nitrate is due to the importance of sedimentary denitrification within the basin assuming that water column and sedimentary denitrification have isotope effects of 25 and 1 5 per mil respectively our results suggest that sedimentary denitrification accounts for more than 75 of the nitrate loss within the suboxic sbb

glacial interglacial variability in denitrification in the world s oceans causes and consequences the late quaternary history of water column denitrifcation of the eastern pacific margins and the arabian sea is reconstructed using sedimentary 15n measurements the 15n values in six piston cores raised from these regions show remarkably similar cyclic variations being heavy 9 10 5 during the interglacials and 2 3 lighter during the glacials this implies that denitrification in these regions decreased substantially during the glacial periods the glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone since water column denitrification in these areas accounts for about half of the fixed nitrogen loss in the modern ocean the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods because nitrate is a limiting nutrient oceanic productivity and attendant changes in co2 may therefore have been modulated on glacial interglacial timescales by variations in the oceanic no3 content

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

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

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation concentrations lamination preservation and d 15 n values from cores located between 540 750 m water depth in the gulf of tehuantepec southern mexico these results differ from similar proxies found even 5 n of the site where there is evidence for omz changes related to rapid climate change in the northern hemisphere instead omz expansion in the gulf was contemporaneous with changes in sea ice extent and zonal wind shifts around antarctica pointing to subantarctic mode water and antarctic intermediate water as likely sources of oxygen depleted water these observations reinforce the importance of the southern ocean as a primary modulator of northern hemisphere ocean climate as far as 15 n in the etnp citation hendy i l and t f pedersen 2006 oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation geophys res lett 33 l20602 doi 10 1029 2006gl025975

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

northeastern pacific oxygen minimum zone variability over the past 70 kyr impact of biological production and oceanic ventilation 1 during the last glacial period the oxygen minimum zone omz within the northeastern pacific ocean strengthened and weakened on a millennial time scale demonstrating a tight linkage with northern high latitude climate although the precise mechanisms responsible remain unknown core md02 2508 retrieved off baja california was analyzed for major and trace elements br ca ti fe mn and sr using a xrf scanner and redox sensitive trace elements cu ni cd as v cr mo and u using the icp ms the trace element content the fe ti ratio and br based organic carbon exhibit higher values during the holocene and during warm dansgaard oeschger events than during the last glacial maximum lgm stadials and heinrich h events a principal component analysis of the element al ratio indicated that the following two main factors controlled the chemical composition of the sediments 1 export production as represented by organic carbon that was lower during cold periods and 2 regional intermediate water oxygenation as represented by u and mo variability that was not supported by a change in export production the latter suggests that intermediate water oxygenation improved during h events but slightly deteriorated during late marine isotope stage mis 3 and mis 2 a local biogeochemical effect forced by atmospheric processes impacted the lgm and h events in the same manner whereas regional intermediate oceanic circulation varied in an opposite manner during the lgm and h events possibly as a result of the global reorganization of intermediate water circulation during the lgm

trace metal evidence for changes in the redox environment associated with the transition from terrigenous clay to diatomaceous sediment saanich inlet bc abstract we measured the concentrations of redox sensitive trace metals mn v mo u cd and re in sediments from odp leg 169s hole 1033b in saanich inlet british columbia to determine changes in redox conditions associated with the onset of laminated sediments at 12 5 kyr the most striking result is a large peak in authigenic re along with detrital levels of mo at the glacial terrigenous clay diatomaceous sediment transition in contrast the underlying glacial terrigenous clay which extends throughout the bottom section of the core is chemically similar to detrital concentrations either cowichan river particulates or average shale values these data suggest a period of oxic bottom waters but reducing pore waters this could be due to the dramatic transformation of saanich inlet during the late deglaciation from an open bay to an inlet which restricted circulation and slowed bottom water oxygen renewal a peak and gradual increase in authigenic mn in younger sediments subsequent to the re peak suggests that increasingly oxic conditions followed the authigenic enrichment in re these conditions could be connected to the younger dryas cooling period which was coincident with an increase in well oxygenated upwelled waters on the west coast of north america that form the bottom waters of saanich inlet metal concentrations in a gray clay bed 11 kyr are similar to their concentrations in the glacial terrigenous clay implying that they have a common source authigenic enrichments of re with little authigenic mo and cd suggest that before the deposition of this bed bottom waters were oxic and pore water oxygen was consumed in the top centimeter or less laminations above the clay layer suggest anoxic conditions which are also indicated by higher authigenic mo and cd and slightly lower re mo ratios in these sediments the basin remained mostly anoxic after the gray clay was emplaced as seen by continuous authigenic enrichment of the redox sensitive trace metals these results are consistent with increased stratification of the water column brought about by an influx of fresh water to the basin by a large flood

intensification of the northeast pacific oxygen minimum zone during the bolling allerod warm period although climate records from several locations around the world show nearly synchronous and abrupt changes the nature of the inferred teleconnection is still poorly understood on the basis of preserved laminations and molybdenum enrichments in open margin sediments we demonstrate that the oxygen content of northeast pacific waters at 800 m depth during the bolling allerod warm period 15 13 kyr was greatly reduced existing oxygen isotopic records of benthic and planktonic foraminifera suggest that this was probably due to suppressed ventilation at higher latitudes of the north pacific comparison with ventilation records for the north atlantic indicates an antiphased pattern of convection relative to the north pacific over the past 22 kyr perhaps due to variations in water vapor transport across central america

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

geochemical response to pulsed sedimentation implications for the use of mo as a paleo proxy abstract deglacial sediments in piston core jt96 02 from the continental slope off western canada contain numerous centimeter thick iron sulfide rich layers major and minor element chemistry as well as c and n isotopic data suggest that these layers represent background hemipelagic sedimentation intervening gray silty clay layers each of which exhibits a fining upward trend are distal turbidites the iron sulfides precipitated in response to the emplacement of each turbidite which slowed oxygen diffusion into the sediment allowing anoxic conditions to develop in the underlying relatively organic rich deposits resulting sulfate reduction and precipitation of fe sulfide fostered mo enrichment 2 g g it may also explain ni cr v and co enrichments although differences in detrital mineralogy cannot be ruled out particularly for ni and cr rhenium is also enriched albeit slightly within the sulfide layers but low re mo ratios 0 78 ng g g g suggest that anoxic conditions developed very rapidly metals with high lithogenic concentrations cd and u are not obviously enriched in the sulfide layers because there was insufficient time for noticeable authigenic accumulation before deposition of the next turbidite which severed diffusive communication with overlying seawater the primary source of metals silver is also slightly higher in the sulfide layers possibly linked to higher marine organic matter content in summary the pulsed character of sedimentation during the deglaciation led to episodic enrichment of mo and occurred independently of changes in bottom water oxygen or organic carbon content this observation potentially complicates the use of mo as a paleo proxy in some continental margin environments

post depositional mobility of platinum iridium and rhenium in marine sediments the discovery of high concentrations of iridium in cretaceous tertiary boundary sediments engendered the hypothesis1 that a meteorite collided with the earth 65 million years ago coincident with the mass extinction that occurred at that time iridium spikes of various magnitudes have subsequently been reported at more than 10 other extinction horizons2 11 it has been suggested on the other hand that geochemical processes might create or modify many of these spikes5 11 4 but a critical evaluation of these suggestions has been hindered by incomplete understanding of low temperature iridium geochemistry other platinum group elements ru rh pd re os pt au are often found to be associated with ir spikes and inter element ratios have been used to assess the cosmic or terrestrial nature of the enrichments5 7 9 28 29 but the geochemical influences on these relative abundances are also poorly constrained here we describe analyses of recent abyssal marine sediments which allow us to characterize the behaviour of pt re and ir during early diagenesis these elements are redistributed by changes in sedimentary redox conditions such changes can probably account for many of the small platinum group element spikes found in the geological record and may render ambiguous attempts to interpret inter element ratios

sediment geochemical records of productivity and oxygen depletion along the margin of western north america during the past 60 000 years teleconnections with greenland ice and the cariaco basin abstract many sediment records from the margins of the californias alta and baja collected in water depths between 60 and 1200 m contain anoxic intervals laminated sediments that can be correlated with interstadial intervals as defined by the oxygen isotope composition of greenland ice dansgaard oeschger d o cycles these intervals include all or parts of oxygen isotope stage 3 ois3 60 24 cal ka the bolling allerod warm interval b a 15 13 cal ka and the holocene this study uses organic carbon corg and trace element proxies for anoxia and productivity namely elevated concentrations and accumulation rates of molybdenum and cadmium in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom water oxygen bwo conditions on open highly productive continental margins the main conclusion from these proxies is that during the last glacial interval lgi 24 15 cal ka and the younger dryas cold interval yd 13 11 6 cal ka productivity was lower and bwo levels were higher than during ois3 the b a and the holocene on all margins of the californias the corg and trace element profiles in the lgi b a holocene transition in the cariaco basin on the margin of northern venezuela are remarkably similar to those in the transition on the northern california margin correlation between d o cycles in greenland ice with gray scale measurements in varved sediments in the cariaco basin also is well established synchronous climate driven changes as recorded in the sediments on the margins of the californias sediments from the cariaco basin and in the gisp 2 greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka millennial scale cycles in productivity and oxygen depletion on the margins of the californias demonstrate that the california current system was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern north pacific ocean it is likely that the pacific and atlantic oceans were linked through the atmosphere warmer air temperatures during interstadials would have strengthened hadley and walker circulations which in turn would have strengthened the subtropical high pressure systems in both the north pacific and the north atlantic producing increased rainfall over the cariaco basin and increased upwelling along the margins of the californias

intense reducing conditions during the last deglaciation and heinrich events h1 h2 h3 in sediments from the oxygen minimum zone off goa eastern arabian sea abstract two sediment cores abp 32 gc 01r and abp 32 gc 03 were collected at a water depth of 642 m and 1086 m off goa from the present day oxygen minimum zone omz of eastern arabian sea eas cover time span of last 18 ka and 32 ka respectively were analysed for multi proxy redox sensitive elements to understand the variation in the redox conditions and factors responsible for its development redox sensitive elements concentration and their normalized ratios mn al u th mo al and ce ce suggest that sediment core abp 32 gc 01r is under more reducing conditions due to its location within the centre of omz compared to core abp 32 gc 03 which is at the base of omz sediments from the eas are of non euxinic environments where dissolved sulfide is present but restricted to the sediment pore waters lack of significant correlation r n yb n ratio is 1 during the last 10 ka holocene 14 10 ka includes younger dryas and b lling aller d 18 14 ka last deglaciation and heinrich events suggesting less reducing terrigenous dominated and intense reducing condition respectively

community benthic paleoecology from high resolution climate records mollusca and foraminifera in post glacial environments of the california margin abstract paleoecological reconstructions of past climate are often based on a single taxonomic group with a consistent presence less is known about the relationship between multi taxon community wide change and climate variability here we reconstruct paleoecological change in a late quaternary 16 1 3 4 ka sediment core from the california margin 418 m below sea level of santa barbara basin sbb usa using mollusca animalia and foraminifera rhizaria microfossils building upon previous investigations we use multivariate ordination and cluster analyses to interpret community scale changes in these distinctly different taxonomic groups across discrete climate episodes the strongest differences between seafloor biological communities occurred between glacial prior to termination ia 14 7 ka and interglacial climate episodes holocene communities were well partitioned indicating that sub millennial oceanographic variability was recorded by these microfossils we document strong evidence of chemosynthetic trophic webs and sulfidic environments from gastropod alia permodesta and bivalve lucinoma aequizonata which characterized restricted intervals previously interpreted as well oxygenated such as the pre bolling warming mollusc records indicate first order trophic energetic shifts between detrital and chemosynthetically fixed carbon molluscs associated with widely different physiological preferences occur here within single decadal intervals of sediment and as such mollusc assemblages may reflect significant inter decadal oceanographic variability foraminifera assemblages provide exceptional records of the sequential chronological progression of the deglacial climatic and oceanographic events whereas mollusc assemblages reflect non chronological similarities in reoccurring communities foraminifera taxa that drive community similarity here are also independently recognized as marker species for seafloor hypoxia regimes which provides support for the idea that oxygenation change is a principal driver of seafloor environmental variability

atypical δ 15 n variations at the southern boundary of the east pacific oxygen minimum zone over the last 50 ka abstract we report a nitrogen isotope record odp site 1233 from the southern chile margin at 41 s the site is located slightly south of the southern boundary of the peru chile upwelling system and the associated oxygen minimum zone off peru and northern chile we show that our nitrogen isotope record from the time interval 0 50 calendar kiloyears before present ka b p bears an atypical pattern both in shape and timing when compared with records obtained from either the continental margin of the eastern pacific or the subantarctic zone saz of the southern ocean the 15 n values at site 1233 are relatively high throughout the record varying between 9 and 13 the major features are a pronounced 15 n increase at the beginning of the deglaciation a maximum from 19 to 10 ka b p thereafter a large decrease during the early holocene and millenial scale oscillations showing an antarctic timing we propose that the record results from an amalgam of low latitude and high latitude processes low latitude processes including a stronger advection signal of heavy nitrates from the denitrifying zones off peru and northern chile would explain the timing of the deglaciation rise and the heaviest values found over this interval excluding the antarctic cold reversal period the overall differences between site 1233 and records from peru and northwest american margins suggest however that the origin of the 15 n signal off chile is largely controlled by hydrologic and climatic changes in the southern ocean we propose that the interplay between nutrient demand in the saz and latitudinal shifts of hydrologic fronts controlled both the concentrations and the isotopic signature of the remaining nitrate delivered to the chile margin then the glacial surface waters of the southern chile margin were likely lower in nitrate concentration and bear a higher 15 n than during interglacial periods

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

comparative behavior of authigenic re u and mo during reoxidation and subsequent long term burial in marine sediments the trace element re is enriched in mildly reducing suboxic sediments close to or slightly later in the redox sequence than u and before reduction of mo in more reducing sulfidic sediments this work investigates the behavior of authigenic re during oxidation and long term burial in the sediments of several turbidites from the madeira abyssal plain exposure to bottom water o2 clearly remobilizes authigenic re as found in previous work but reimmobilization occurs in reducing sediments below the oxidation front over a depth range of 0 5 3 m the large spread of the re burndown peak must be kinetically controlled perhaps influenced by the corg content once reimmobilized however the authigenic re signal remains immobile for at least 3 4 myr authigenic u in contrast consistently forms peaks 0 5 m broad whereas authigenic mo is lost on oxidation and does not appear to be refixed unless authigenic pyrite is formed these results imply that any paleoenvironmental significance of authigenic re will be compromised in low sedimentation rate environments 10 cm kyr where there is significant exposure of authigenic re to bottom water o2 however authigenic re records from rapidly accumulating continental margin sediments with much less exposure to bottom water o2 still offer considerable potential as high fidelity recorders of past reducing conditions

nitrogen isotopic evidence for micronutrient control of fractional no3 utilization in the equatorial pacific during the u s jgofs eqpac program variations in nitrogen isotopic ratio d15n and their control by relative no3 drawdown were examined in detail near surface d15n data clearly conform to rayleigh isotopic fractionation during phytoplankton utilization of no with a fractionation factor of about 5 this isotopic signal both propagates into particulate nitrogen pools and is a persistent large scale characteristic of the system decreasing near surface no3 with distance from the equator strongly correlates with increasing d15n in euphotic zone particulate organic matter pom as well as sinking particles during both surveys 1 el nino and 2 non el nino cruises despite a doubling of no3 accompanying relaxation of el nino conditions d15n values in near surface pom and deeply sinking particles as a function of latitude were similar for the two periods since d15n varies with relative nutrient drawdown and not its concentration this parameter appears to not have varied significantly in both cases about 50 of upwelled no3 was consumed in the immediate vicinity of the equator as estimated from the d15n data the moored sediment trap time series provided a more highly resolved temporal view of the 15n dynamics of this system at the equator and to the south there is little temporal variation in d15n and hence in relative no3 utilization over the 1 yr duration of the program at 28 and 58 n there is a large 5 decrease in d15n during the transition to non el nino conditions in response to the northward movement of no3 rich waters which probably reflects the intensification of the north equatorial current overall no3 utilization at the equator remained between 40 and 60 over the observation period despite large hydrographic and dynamical changes this observation implies a tight control of relative no3 utilization consistent with iron fe limitation since fe is supplied in this region by upwelling relative no3 utilization is likely determined by the product of the ratio of fe to no3 in upwelled waters and the no3 fe utilization ratio given no change in the chemistry of source waters increases in upwelling as observed during the transition away from el nino will affect surface no3 new and export production but it will not affect relative no3 utilization in this light downcore d15n records in the equatorial pacific should reflect past changes in the limitation of no3 drawdown by fe perhaps through changes in equatorial undercurrent chemistry

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

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

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

deconstructing the last glacial termination the role of millennial and orbital scale forcings using an earth system model of intermediate complexity forced by continuously varying boundary conditions and a hypothetical profile of freshwater forcing the model simulates heinrich event 1 h1 the bolling warm period the older dryas the antarctic cold reversal acr and the younger dryas in close agreement with paleo proxy data from different regions worldwide the acr can be simulated as the bipolar seesaw response to the amoc recovery during the termination of h1 however this study also demonstrates that the amplitude of the acr can be further amplified by a rapid deglacial retreat of the antarctic ice sheets we suggest that melting from both the laurentide and the antarctic ice sheets contributed to the sea level rise associated with meltwater pulse 1 a mwp 1a it is hypothesized that the northern hemispheric source of mwp 1a caused the older dryas cooling in the northern hemisphere whereas the southern hemispheric source contributed to the acr the study also documents that for the majority of paleo climate proxies considered here the relative timing can be qualitatively reproduced by the transient modeling experiments the climate model solution presented here may provide a means to further constrain dating uncertainties of some of paleo climate proxies during the last glacial termination

paleoceanographic changes on the farallon escarpment off central california during the last 16 000 years abstract new benthic and planktic foraminiferal assemblage census data and benthic foraminiferal oxygen index bfoi values previously published marine climate proxy data stable isotopes and ca cd and unpublished results of total carbon organic carbon and calcium carbonate analyses of sediments recovered off central california on the farallon escarpment 1605 m water depth 37 13 4 n 123 14 6 w core f 8 90 g21 document paleoceanographic changes during the latest quaternary which reflect the intensity and source of north pacific intermediate water npiw and surface productivity accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age depth model for the last 16 000 years covering the latest glacial bolling allerod younger dryas and early middle and late holocene intervals a q mode cluster analysis separated the benthic fauna into three clusters one pleistocene and two holocene whereas the planktic fauna was divided only into pleistocene and holocene clusters stable oxygen isotope values show an increase in water temperature of 1 c from the late glacial to late holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well a general trend of decreasing dissolved oxygen concentration from the pleistocene high oxic 3 0 6 0 ml l o2 to the holocene low oxic 1 5 3 0 ml l o2 suggested by the bfoi and cd ca data reflect decreased ventilation as the source of the npiw shifted from the sea of okhotsk to the tropical east pacific at 11 000 cal bp the middle holocene cooling reported in other central and northern california margin studies is not apparent in f 8 90 g21 which compares more favorably with studies from southern california and british columbia total carbon and organic carbon values are highest in the bolling allerod early holocene and late holocene similarly calcium carbonate values are high in the bolling allerod and peak in the early holocene but decrease significantly in the latest middle and late holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60 cm 70000 0 cal bp of the core and poor preservation of the benthic foraminiferal fauna at 40 cm 3000 cal bp decoupling is evident between the planktic and benthic faunal response to changing climatic conditions with the surface dwelling assemblage often leading the bottom dwelling assemblage by several millennia

oxygen minimum zone biotic baseline transects for paleoceanographic reconstructions in santa barbara basin ca abstract we describe modern ocean floor biological trends employing exploratory remotely operated vehicle rov hercules dives in the santa barbara basin california usa through the nautilus exploration program using rov videos in situ measurements and sediment cores we described oxygenation temperature biological zonation and bulk sediment 15n across three 120 meter vertical transects from 380 to 500 m m that cross the depth of the ventilating sill 475 m and upper omz boundary these observations revealed major changes in the distribution of biota tied largely to changes in dissolved oxygen concentration upward increases in oxygen and temperature were coincident with successive disappearance and appearance of megafauna and foraminifera species and overall increases in community diversity the most significant and abrupt change in seawater measurements biological communities sediment textures and nitrogen isotopes were observed near the depth of the ventilating sill from 480 to 450 m microbial mats were observed up to the depth of 475 m dense populations of alia permodesta were identified at depths where dissolved oxygen o2 was

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

determining the post glacial evolution of a northeast pacific coastal fjord using a multiproxy geochemical approachthis article is one of a series of papers published in this special issue on the theme polar climate stability network a 40 32 m piston core recovered from effingham inlet on the west coast of vancouver island provides the basis for a high resolution geochemical study of the last deglaciation and the holocene glacial retreat basin isolation sea level rise and productivity variations are determined using proxies for sediment composition k al fe al mg al grain size ti al zr al sedimentary redox conditions mo al u al and productivity wt organic carbon wt opal as local ice retreated and marine waters inundated the basin coarse grained glacimarine sediments were replaced by finer grained laminated opal rich sediments during meltwater pulse 1a the dominance of local crustal rise over eustatic sea level rise resulted in the progressive restriction of ocean circulation in effingham inlet and the formation of a temporary freshwater lake the transition into stable holocene conditions was initiated at 12 700 bp which corresponds to the onset of the younger dryas as identified by the greenland ice

paleoceanography of the gulf of alaska during the past 15 000 years results from diatoms silicoflagellates and geochemistry article i nfo abruptly during the bolling allerod bo al warm interval 14 7 12 9 cal ka declined during the younger dryas yd cold interval 12 9 to 11 7 cal kyr bp and rose again during the earliest holocene at this site the record after 11 cal kyr bp is dominated by oceanic diatoms and silicoflagellates with geochemical proxies displaying more subtle variation cores ew0408 66jc in the yakobi sea valley near cross sound and ew0408 11jc in the gulf of esquibel contain an expanded composite record along the southeast alaskan margin core 66jc contains a detailed record of the bo al and yd diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the bo al but declined during the yd sea ice related diatoms increased in abundance during the yd indicating cooler but less productive waters

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

pleistocene to holocene contrasts in organic matter production and preservation on the california continental margin organic matter in sediments from cores collected from the upper continental slope 200 2700 m off california and southern oregon shows marked differences in concentration and marine character between the last glacial interval ca 24 10 ka and either holocene time or last interstadial oxygen isotope stage 3 ca 60 24 ka in general sediments deposited during holocene time and stage 3 contain higher amounts of marine organic matter than those deposited during the last glacial interval and this contrast is greatest in cores collected off southern california the most profound differences in stage 3 sediments are between predominantly bioturbated sediments and occasional interbeds of laminated sediments the sediments are from cores collected within the present oxygen minimum zone on the upper continental slope from as far north as the oregon california border to as far south as point conception these upper pleistocene laminated sediments contain more abundant hydrogen rich type ii marine algal organic matter than even surface sediments that have large amounts of nonrefractory organic matter the stable carbon isotopic composition of the organic matter does not change with time between bioturbated and laminated sediments indicating that the greater abundance of type ii organic matter in the laminated sediments is not due to a change in source but rather represents a greater degree of production and preservation of marine organic matter the presence of abundant well preserved organic matter supports the theory that the oxygen minimum zone in the northeastern pacific ocean was more intense and possibly anoxic during late pleistocene time as a result of increased coastal upwelling that enhanced algal productivity

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

abrupt termination of marine isotope stage 16 termination vii at 631 5 ka in santa barbara basin california the marine isotope stage 16 15 boundary termination vii is the first deglacial warming step of the late quaternary following the mid pleistocene transition mpt when 41 kyr climatic cycles shifted to strong 100 kyr cycles the detailed structure of this important climatic event has remained unknown until now core mv0508 19jpc from santa barbara basin california contains a decadal scale climatic and geochemical sediment record of 4000 years duration that includes the early part of this deglacial episode this record reveals that the climatic shift during the early deglacial occurred rapidly 700 years in a progression of three abrupt warming steps the onset of marine isotope stage mis 15 was remarkably abrupt with 4 5 c sea surface warming in 50 years the deglacial sequence contains the well dated lava creek tephra 631 3 4 ka from yellowstone caldera used to date the onset of termination vii at 631 5 ka the late mis 16 and early mis 15 interval exhibits multiple decadal scale negative excursions in 13c of planktic foraminifera likely the result of repeated discharges of methane from methane hydrates associated with both ocean warming and low sea level a warm interstadial that interrupts late mis 16 is marked by elevated concentrations of redox sensitive elements indicating sulfidic oxygen deficient bottom and pore waters and elevated concentrations of total organic carbon and cd reflecting increased surface productivity unlike younger sediments on the california margin these indicators of increased productivity and low dissolved oxygen do not consistently correspond with each other or with preserved laminations possibly reflecting instability of a still evolving ocean atmosphere system following the mpt

expansion of the southern california oxygen minimum zone during the early to mid holocene due to reduced ventilation of the northeast pacific abstract oceanic deoxygenation observed since the 1950s has drawn increasing concern as dissolved oxygen do regulates marine biodiversity and biogeochemical cycles yet the do time series from direct instrumental measurements is insufficiently long several decades to constrain the centennial to millennial variability here we present redox sensitive metal re u and mo records from santa barbara basin sbb california to reconstruct subsurface do through the holocene significantly higher authigenic metal fluxes and coherent benthic foraminifera faunal responses along a published depth transect reveal vertical expansion and intensification of the southern california oxygen minimum zone omz prior to 6 ka comparison with post industrial trace metal records suggests low oxygen conditions were more extreme during early to mid holocene mh highlighting the magnitude of omz variability in the absence of anthropogenic influences inconsistencies between authigenic metal fluxes and local oxygen control indicate a remote weakening of the north pacific intermediate water npiw formation prior to the mh reduced ventilation of the mid depth north pacific is supported by state of the art earth system model simulations with realistic mh 6 ka forcing highlighting the importance of brine rejection during sea ice formation in changing the buoyancy of npiw and its basin wide influences on north pacific omz evidence from holocene marine lake records and model simulations further suggests a southward intertropical convergence zone itcz migration and a consequent deepening of the aleutian low al towards late holocene which favors more sea ice brine rejection thus mid depth ventilation in the north pacific was closely associated with atmospheric circulation during the holocene

interhemispheric leakage of isotopically heavy nitrate in the eastern tropical pacific during the last glacial period denitrification zone while the nicaragua site is at the southern boundary the d 15 n record from nicaragua shows an antarctic timing similar to denitrification changes observed off peru chile but is radically different from the northern records we attribute this to the leakage of isotopically heavy nitrate from the south pacific oxygen minimum zone omz into the nicaragua basin the nicaragua record leads the other eastern tropical north pacific etnp records by about 1000 years because denitrification peaks in the eastern tropical south pacific etsp before denitrification starts to increase in the northern hemisphere omz i e during warming episodes in antarctica we find that the influence of the heavy nitrate leakage from the etsp is still noticeable although attenuated in the gulf of tehuantepec record particularly at the end of the heinrich events and tends to alter the recording of millennial timescale denitrification changes in the etnp this implies 1 that sedimentary d 15 n records from the southern parts of the etnp cannot be used straightforwardly as a proxy for local denitrification and 2 that denitrification history in the etnp like in the arabian sea is synchronous with greenland temperature changes these observations reinforce the conclusion that on millennial timescales during the last ice age denitrification in the etnp is strongly influenced by climatic variations that originated in the highlatitude north atlantic region while commensurate changes in southern ocean hydrography more directly and slightly earlier affected oxygen concentrations in the etsp furthermore the d 15 n records imply ongoing physical communication across the equator in the shallow subsurface continuously over the last 50 70 ka citation pichevin l e r s ganeshram s francavilla e arellano torres t f pedersen and l beaufort 2010 interhemispheric leakage of isotopically heavy nitrate in the eastern tropical pacific during the last glacial period paleoceanography 25 pa1204 doi 10 1029 2009pa001754

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

glacial interglacial variability in upwelling and bioproductivity off nw mexico implications for quaternary paleoclimate sedimentary accumulation of biogenic components organic carbon opal and biogenic barium on the northwestern mexican margin declined during every glacial interval of the past 140 kyr indicating decreases in upwelling induced productivity during cold periods the glacial interglacial contrasts in upwelling on this margin are attributed to reversals in land ocean thermal contrast the waxing and waning of the laurentide ice sheet and consequent responses of the western hemisphere wind fields this scenario is consistent with three independent lines of evidence terrestrial paleoclimatic data general circulation model results and our marine records this pattern of glacial interglacial variability in upwelling off nw mexico is opposite to that observed in other low latitude and midlatitude upwelling areas such as the eastern equatorial pacific these results add to a growing pool of observations that the response of oceanic upwelling to glacial climatic forcing has been regionally variable

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

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

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

the dansgaard oeschger cycles discovered in the up stream source region of the north pacific intermediate water formation 1 millennial scale oceanographic oscillations were identified in the southern okhotsk sea based on high resolution measurements of total organic carbon toc c n ratios and biogenic opal employing core md01 2412 53 m with the bottom age of 115 ka the oscillations are linked with the dansgaard oeschger d o climatic cycles inadequate data existed in the source regions of the north pacific intermediate water npiw formation thus far we report the first decisive documentation of the d o cycles in the up stream source region of the npiw illustrating that the d o cycles observed in the down stream regions e g santa barbara basin due to expansion of the npiw were in part governed by the climatic variations occurred in the okhotsk sea increases in toc and c n ratios reflect abrupt sea level rises associated with 14 interstadial events over the past 115 kyrs attributing to the downward transport of eroded continental shelf sediments

influence of northwest pacific productivity on north pacific intermediate water oxygen concentrations during the bolling allerod interval 14 7 12 9 ka elevated productivity in the northwest pacific is suggested as a new possible control driving past intervals of low o2 intermediate water along the western continental margin of north america according to this mechanism o2 consumption would occur near the site of formation of north pacific intermediate water npiw due to increased respiration of organic carbon in response to a high productivity event evidence is provided for such a productivity increase during the bolling allerod interval 14 7 12 9 ka a time when laminated sediments were deposited along the northern california margin by this mechanism low o2 events in intermediate waters off the western north american margin could occur without significant changes in the rate of npiw ventilation

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

irregular plate boundary controls on foreland basin sedimentation miocene kahramanmaras foreland basin se turkey abstract the northern movement of the arabian plate led to the development of a compressional regime in the south eastern part of turkey after the late cretaceous the collision of the arabian plate with the anatolide taurides platform and subsequent development of the kahramanmaras foreland basin at the beginning of the miocene evolved as a result of this movement an irregular plate geometry or promontory of the arabian plate caused partitioning of the plate margin precollision collision postcollision this irregular plate boundary was delimited by western and northern boundary faults and an interior basin fault the nw oriented small wedge top basins on the overlying anatolide taurides platform obliquely cut through the foredeep basin the region across the wedge top basin on the irregular promontory of the underlying arabian plate contains different sedimentation depocentres small fining upward submarine fan deposits including pebbly channel deposits and coarsening upward lobe sequences are located at the centre of the irregular part of the plate in the tanir region and overlie planktic foraminifera bearing claystones these submarine fan sediments pass outboard into distal interbedded turbidite claystones and siltstones in a downdip direction s se the boundary fault intersection of the promontory led to the development of a submarine slope environment with irregular sea floor topography in the firniz area 4 5 km south east of the tanir region the slump deposits sandy debrites and fine grained thin bedded turbidites filled this region structural alignments and seismicity associated with the plate margin were the main controlling factors on the geometry of the depocentre sediment quantity sediment input sedimentary facies local sea level changes and post sedimentary deformation in the kahramanmaras foreland basin

sediment fluxes and varve formation in santa barbara basin offshore california results from a year long sediment trap study provide the first direct observations of seasonal variability in sediment fluxes to the sea floor in santa barbara basin offshore california and are used to evaluate varve formation in this basin sediment fluxes throughout the year are dominated by lithogenic material biogenic sediments primarily silica are of secondary importance we conclude that the combination of high lithogenic fluxes and low biogenic fluxes during the fall winter period results in the deposition of dark laminae the onset of upwelling and high surface productivity in the spring results in high biogenic silica fluxes that last into the summer the relative contribution of silica to the total sediment flux is highest during this spring summer period and we suggest that light laminae are formed at that time this is consistent with previous suggestions that sediment input is the primary factor controlling varve formation in this basin

sensitivity of the phosphate cadmium carbon isotope relation in the ocean to cadmium removal by suboxic sediments reconstructions of past deep ocean nutrient concentrations rely largely on the carbon isotopic composition and cadmium content of shells of benthic foraminifera when comparing records of these two paleonutrient tracers a relation similar to the phosphate cadmium carbon isotope relation in the water column today is generally assumed we present new water column sediment and pore water data from the california continental margin which demonstrate that cd accumulation is enhanced in suboxic sediments these results suggest that the oceanic cd inventory is sensitive to changes in the areal extent and redox intensity of suboxic sediments and thus that the phosphate cadmium relation in the ocean could have been different in the past the magnitude of this effect and its evolution through time is presently hard to quantify because the oceanic cd budget is poorly constrained

variations in the isotopic composition of molybdenum in freshwater lake systems variations in molybdenum isotopic composition spanning the range of similar to 2 3 parts per thousand in the terms of mo 97 mo 95 ratio have been measured in sediment cores from three lakes in northern sweden and north western russia these variations have been produced by both isotopically variable input of mo into the lakes due to mo isotopic heterogeneity of bedrock in the drainage basins and fractionation in the lake systems due to temporal variations in limnological conditions mo isotope abundances of bedrock in the lake drainage basins have been documented by analysis of mo isotope ratios of a suite of molybdenite occurrences collected in the studied area and of detrital fractions of the lake sediment cores the median delta mo 97 value of the investigated molybdenites is 0 26 parts per thousand with standard deviation of 0 43 parts per thousand n 19 whereas the median delta mo 97 value of detrital sediment fractions from two lakes is 0 40 parts per thousand with standard deviation of 0 36 parts per thousand n 15 the isotopic compositiori of mo in the sediment cores has been found to be dependent on redox conditions of the water columns and the dominant type of scavenging phases hydrous fe oxides have been shown to be an efficient scavenger of mo from porewater under oxic conditions oxidative precipitation of fe ii in the sediments resulted in co precipitation of mo and significant authigenic enrichment at the redox boundary in spite of a pronounced increase in mo concentration associated with fe oxides at the redox boundary the isotopic composition of mo in this zone varies insignificantly suggesting little or no isotope fractionation during scavenging of mo by hydrous fe oxides in a lake with anoxic bottom water a chironomid inferred reconstruction of o 2 conditions in the bottom water through the holocene indicates that increased o 2 concentrations are generally associated with low delta mo 97 mo 95 values of the sediments whereas lowered o 2 contents of the bottom water are accompanied by relatively high delta mo 97 mo 95 values thus confirming the potential of mo isotope data to be a proxy for redox conditions of overlying waters however it is pointed out that other processes including input of isotopically heterogeneous mo and mn cycling in the redox stratified water column can be a primary cause of variations in mo isotopic compositions of lake sediments less

determining the influences of late quaternary ventilation and productivity variations on santa barbara basin sedimentary oxygenation a multi proxy approach abstract a correlation between warm interstadials implied by 18oice in the gisp greenland ice core and anoxic events recorded by the sediments drilled at odp site 893 in santa barbara basin sbb has been used previously to relate variations in bottom water oxygenation to high frequency changes in the ventilation of the sbb nature 379 1996 243 however an additional control on the oxygen content at depth is the local settling flux of metabolizable organic matter to assess the impact of oxygen consumption related to this source mo cd re and u concentration data are used here in conjunction with corg and 15n to deduce past redox conditions variations in the sedimentary redox boundary depth and the impact of local organic flux on the oxygenation of sbb deep waters comparisons between odp sites 893 1017 and 1019 allow the differentiation of regional signals dominated by ventilation changes from local signals dominated by vertical organic flux it is concluded that prior to the holocene local productivity changes in the santa barbara basin are not solely the cause of sedimentary anoxia episodic injections of low oxygen intermediate water identified on the regional scale strongly influenced the oxygen content of the sbb during this time however over the last 10 000 years the influence of local productivity has increased and the regional similarity among the three sites is complicated by local signals

measuring quaternary time a 50 year perspective over the last 50 years there have been significant developments in the range and sophistication of the chronological tools now available to quaternary scientists notable milestones include the introduction of new methods e g optically stimulated luminescence cosmogenic radionuclide dating ice layer counting molecular clocks and the refinement of established techniques e g accelerator mass spectrometry 14c dating 14c calibration high precision uranium series dating argon argon dating cryptotephra analysis developing new techniques and methodologies for measuring quaternary time is not an end in itself however it is stimulated by a parallel need which is a deeper understanding of the mode pattern and rates of environmental processes and how different processes inter connect here we review some of the important limitations that continue to constrain our ability to provide coherent chronologies for quaternary environmental reconstructions at both millennial and sub millennial timescales we focus our discussion on two unique stratigraphic templates first the marine oxygen isotope sequence that spans the full quaternary period and second the greenland ice core record which provides a basis for dating environmental changes through the last glacial cycle

palynological evidence for late quaternary climate and marine primary productivity changes along the california margin a high resolution sedimentary record of dinoflagellate cysts from ocean drilling program hole 1017e off point conception california margin reflects how marine primary productivity has changed in response to major shifts in climate and ocean circulation along the california margin over the past 42 kyr throughout the studied sequence dinoflagellate cyst assemblages are dominated by upwelling related taxa signifying the continued presence of coastal upwelling on the margin during the late quaternary the cyst record suggests that marine primary productivity was enhanced during the holocene and bolling and to a lesser extent during the late glacial and most dansgaard oeschger events while an apparent reduction in primary productivity can be seen during the younger dryas the best analogue technique based on a modern dinoflagellate cyst assemblage database from the northeast pacific was used for quantitative reconstruction of past sea surface conditions it points to dynamic changes in annual marine primary productivity 235 331 g c m 2 yr 1 and sea surface temperature 10 1 12 6 c in winter 13 1 14 3 c in summer while sea surface salinity appears to be confined to a narrower range 32 9 33 4 in summer our results also indicate noticeable climate variability during the holocene in this region

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability