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

biogenic silica fluxes and accumulation rates in the gulf of california the gulf of california though small in size plays an important role in the global silica cycle the seasonal pattern of biogenic silica flux in the gulf is closely related to that of phytoplankton biomass levels and is controlled by changes in weather and hydrographic conditions the highest opal fluxes approximately 0 35 g center dot m sup minus 2 center dot d sup minus 1 occur during winter and spring and they are comparable to those measured in some of the most productive ecosystems of the world approximately 15 25 of the biogenic silica produced in surface waters is preserved in gulf sediments a figure significantly higher than the average global ocean preservation rate however the flux of opal at 500 m water depth is less than 25 of that being produced at the surface suggesting that most of the recycling of biogenic silica in the gulf of california occurs in the upper water column 28 refs 3 figs

the bering and okhotsk seas modern and past paleoceanographic changes and gateway impact abstract the high biological productivity and an efficient biological pumping in the subarctic pacific and adjacent seas make this region important to the modern carbon cycle and both modern and the past climate of the earth knowledge of the northern marginal seas of the pacific however is unsubstantial the bering sea is located between the pacific ocean and the arctic sea and plays an important role in ocean circulation involving balances of heat salt and various chemical properties thus it is necessary to unravel the geologic history of the bering sea as a gateway to the pacific and the arctic atlantic during the last 5 million years and beyond the okhotsk sea is considered a locus of north pacific intermediate water formation today the intermediate water formation is linked with seasonal sea ice cover diatom records from the okhotsk sea demonstrate that sea ice cover was distributed on the western side of the sea and the eastern part was open water during the last glacial maximum this configuration permitted a better ventilation of the glacial okhotsk sea through increased quantity of intermediate water presumably formed there at that time

poleward reach of the california undercurrent extension 1 the california undercurrent is known to transport relatively warm high salinity nutrient rich water from the equatorial pacific to vancouver island along the western continental slope of north america this transport helps maintain the high productivity of the eastern boundary california current system in this study we use several decades of water property survey data for the coasts of oregon washington british columbia and alaska to show that equatorial pacific water carried poleward by the undercurrent can eventually reach the aleutian islands roughly 11 000 km from the source region long term current meter records confirm the undercurrent as far north as vancouver island where the current is found to be weakest in spring but then to strengthen through the summer and fall before merging with the wind forced poleward flowing davidson current in winter the core depth of the equatorial water increases from 150 m 25 m off northwest washington near the northern end of the western north america coastal upwelling domain to 225 m 25 m off southeast alaska near the southern end of the gulf of alaska coastal downwelling domain

response of diatom and silicoflagellate assemblages in the central gulf of california to regional climate change during the past 55 kyrs abstract high resolution studies of diatoms and silicoflagellates of the past 55 kyrs in cores md02 2517 2515 from the central gulf of california goc reveal profound changes in goc surface waters roperia tesselata a diatom proxy for late winter early spring upwelling and dictyocha stapedia a subtropical silicoflagellate indicative of goc sea surface temperatures ssts 24 c are common during the holocene but rare during marine isotope stage mis 2 and most of mis 3 a relationship that likely reflects a more northerly position of the north pacific high nph during the holocene in contrast during most of mis 2 27 15 ka the persistent presence of distephanus speculum a silicoflagellate associated with ssts during mis 3 55 27 ka increased dominance of azpeitia nodulifera diatom implies that stratified tropical waters were present year round whereas silicoflagellate assemblages suggest that stratified tropical conditions alternated with more productive upwelling conditions on millennial timescales reduced biosiliceous productivity during heinrich events likely reflected a reduction in both surface water nutrient levels and in the strength of northwest winds due to a weakened and more southerly nph conversely enhanced biosiliceous productivity during mis 3 interstadials was probably linked to heightened nutrient levels and a strengthened nph abrupt relative abundance increases of the silicoflagellate dictyocha aculeata approximate the termination of mis3 heinrich events and may signal times when nutrient rich deep waters associated with the resumption of enhanced atlantic meridional overturning circulation penetrated into the central gulf

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

consistent relationship between global climate and surface nitrate utilization in the western subarctic pacific throughout the last 500 ka 1 the open subarctic pacific is at present a high nitrate low chlorophyll hnlc region where nitrate is perennially abundant at the surface theoretically the hnlc status of this region is subject to modification by ocean circulation and or micronutrient supply with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior records of biogenic detritus in sediments from throughout the subarctic pacific indicate that export production was generally lower during glacial maxima while nitrogen isotope measurements from the bering sea have shown that nitrate consumption there was more complete during the last glacial period than it is today here nitrogen isotopic analyses of bulk sediments 15nbulk from three deep water sites in the open subarctic pacific are evaluated in terms of regional nitrate isotopic composition and local relative nitrate utilization the eastern subarctic pacific 15nbulk record bears great similarity to 15nbulk records from the western margin of north america over the last glacial cycle suggesting that variability in the isotopic composition of subeuphotic zone nitrate the growth substrate is reasonably coherent throughout the northeast pacific and dominates at these sites however the two western subarctic pacific records which lie at the heart of the hnlc region display a different pattern implying that significant changes in local relative nitrate utilization overlie the regional background variability after a novel correction intended to remove the background signal associated with denitrification in the eastern tropical north pacific these nitrate utilization records are correlated with a benthic oxygen isotope stack reflecting global deep ocean temperature and ice volume r2 0 65 the correlation implies a strong link between global climate and subarctic pacific nitrate utilization with nearly complete nitrate consumption during glacial periods when export production was low

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

late quaternary paleoproductivity history on the vancouver island margin western canada a multiproxy geochemical study multiproxy analysis of a 38 m long sediment core recovered from the vancouver island margin 48 97 n 127 04 w water depth 1243 m has yielded a millennial scale history of upwelling and export production over the last 50 ka higher concentrations of marine organic carbon opal and trace mo suggest that production was higher and sedimentary pore waters more anoxic during the warm holocene bolling allerod and interstadial events between 31 and 44 ka bp relatively lower production and higher inputs of terrigenous organic matter occurred during the last glacial 14 7 31 ka bp cordilleran ice sheet proximal to coring site at 19 5 ka bp and from 44 50 4 ka bp enrichments in sedimentary 15n during interstadial events are interpreted to reflect episodic delivery and upwelling of isotopically heavy nitrate to the surface waters and subsequent vectoring to the seafloor via settling planktonic detritus similar patterns are seen in southern california and other areas along the western margin of north a

geochemical cycles in sediments deposited on the slopes of the guaymas and carmen basins of the gulf of california over the last 180 years sediments deposited on the slopes of the guaymas and carmen basins in the central gulf of california were recovered in two box cores q mode factor analyses identified detrital clastic carbonate and redox associations in the elemental composition of these sediments the detrital clastic fraction appears to contain two source components a more mafic component presumably derived from the sierra madre occidental along the west coast of mexico and a more felsic component most likely derived from sedimentary rocks mostly sandstones of the colorado plateau and delivered by the colorado river the sediments also contain significant siliceous biogenic components and minor calcareous biogenic components but those components were not quantified in this study redox associations were identified in both cores based on relatively high concentrations of molybdenum which is indicative of deposition under conditions of sulfate reduction decreases in concentrations of molybdenum in younger sediments suggest that the bottom waters of the gulf have became more oxygenated over the last 100 years many geochemical components in both box cores exhibit distinct cyclicity with periodicities of 10 20 years the most striking are 20 year cycles in the more mafic components e g titanium particularly in sediments deposited during the 19th century in that century the titanium cycles are in very good agreement with warm phases of the pacific decadal oscillation implying that at times of greater influx of titanium rich

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

the accumulation of silver in marine sediments a link to biogenic ba and marine productivity 1 the concentrations of ag and a suite of redox sensitive trace metals re cd and mo were measured in surface sediments from the western canadian mexican peruvian and chilean continental margins in all regions ag content increases from 80 ng g 1 i e lithogenic values on the shelf up to as high as 1483 ng g 1 on the lower slope however the trend of increasing ag with increasing water depth breaks down at deepwater sites 2500 m where only lithogenic concentrations are documented silver content does not correlate with the distributions of redox sensitive trace metals suggesting that sedimentary redox conditions are not the primary control on ag accumulation instead a positive correlation between ag and ba in surface and near surface sediments suggests that ag is scavenged by and delivered to the sediment with the organic particle flux scavenging probably results from the precipitation of ag2s within the organic particles due to the development of anoxia and sulfate reduction if this hypothesis is correct then ag has the potential to be a paleoproductivity proxy

silica burial enhanced by iron limitation in oceanic upwelling margins marine sediments deposited beneath the eastern pacific upwelling margin are a substantial sink for silica the geochemistry of these sediments suggests that periods of intense upwelling result in iron limitation which enhances the export of silica from the surface to the deep ocean and sediments

deglacial climatic oscillations in the gulf of california a high resolution accelerator radiocarbon dated climate record of the interval 8 000 18 000 years b p from deep sea drilling project site 480 guaymas basin gulf of california shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation nonlaminated sediments are associated with cooler climatic conditions during the late glacial up to 13 000 years b p and from 10 300 to 10 800 years b p equivalent to the younger dryas event of the north atlantic region we propose that the changes from laminated varved to nonlaminated sediments resulted from increased oxygen content in pacific intermediate waters during the glacial and the younger dryas episodes and that the forcing for the latter event was global in scope prominent events of low 18o are recorded in benthic foraminifera from 8 000 to 10 000 and at 12 000 years b p evidence for an earlier event between 13 500 and 15 000 years b p is weaker maximum 18o is found to have occurred 10 500 13 500 and 15 000 years ago and beyond oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of pacific waters of intermediate depth during deglaciation or environmental changes within the gulf of california region several lines of evidence suggest that during deglaciation the climate of the american southwest was marked by increased precipitation that could have lowered salinity in the gulf of california recent modelling studies show that cooling of the gulf of mexico due to glacial meltwater injection which is believed to have occurred at least twice during deglaciation would have resulted in increased precipitation with respect to evaporation in the american southwest during summertime the timing of deglacial events in the gulf of mexico and the gulf of california supports such an atmospheric teleconnection

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

rhenium geochemical cycling insights from continental margins abstract we measured rhenium re in sediments both pore waters and solid phase from three locations on the mid atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments greater reduction intensity is reflected by shallower oxygen penetration greater ammonium concentrations at depth and shallower first appearances of mn and fe in pore waters this comparison suggests that for the three sites along the mab the reduction intensity from greatest to least is en433 1 oc426 en433 2 all of the pore water profiles show removal of re from pore waters modeled pore water re fluxes follow the trend in reducing conditions en433 1 2 0 0 2 pmol cm 2 y oc426 0 9 0 1 pmol cm 2 y and en433 2 0 60 0 03 pmol cm 2 y respectively solid phase profiles show authigenic re enrichment in sediments from all three locations and the calculated re accumulation rates also mirror the trend in reducing conditions with the values decreasing from en433 1 oc426 en433 2 1 5 0 2 pmol cm 2 y 0 29 0 09 pmol cm 2 y 0 19 0 09 pmol cm 2 y respectively controls on re accumulation are determined from the mab data and from the literature and include 1 the extent of reducing conditions with greater removal of re from pore waters with greater anoxic organic carbon oxidation as determined by the net dissolved ammonium production consistent with the expected removal of pore water re coincident with fe iii and sulfate reduction 2 irrigation which results in net removal of re to sediments augments the diffusive flux of re across the sediment water interface and is more important in shallow coastal sediments rather than locations from deeper water depths mab sites and 3 seasonal remobilization of re from surface sediments due to deepening oxygen penetration depth from 0 2 cm to 1 cm although smaller seasonal changes in oxygen penetration depth e g 0 2 cm to 0 6 cm are less conducive for remobilizing re from sediments there is an empirical relationship with larger re accumulation rates present when the oxygen penetration depth is shallow however there is a stronger correlation between organic carbon oxidation and re accumulation rates this latter relationship is more appropriate since the oxidation of labile organic matter in sediments dictates the sedimentary reducing conditions that are then conducive for re accumulation in the solid phase

sea surface temperature records of termination 1 in the gulf of california challenges for seasonal and interannual analogues of tropical pacific climate change 1 centennial scale records of sea surface temperature and opal composition spanning the last glacial maximum and termination 1 circa 25 6 ka are presented here from guaymas basin in the gulf of california through the application of two organic geochemistry proxies the u37k index and the tex86h index we present evidence for rapid stepped changes in temperatures during deglaciation these occur in both temperature proxies at 13 ka 3 c increase in 270 years 10 0 ka 2 c decrease over 250 years and at 8 2 ka 3 c increase in 200 years an additional rapid warming step is also observed in tex86h at 11 5 ka in comparing the two temperature proxies and opal content we consider the potential for upwelling intensity to be recorded and link this millennial scale variability to shifting intertropical convergence zone position and variations in the strength of the subtropical high the onset of the deglacial warming from 17 to 18 ka is comparable to a southern hemisphere signal although the opal record mimics the ice rafting events of the north atlantic heinrich events neither the modern seasonal cycle nor el nino southern oscillation patterns provide valid analogues for the trends we observe in comparison with other regional records fully coupled climate model simulations confirm this result and in combination we question whether the seasonal or interannual climate variations of the modern climate are valid analogues for the glacial and deglacial tropical pacific

seam dip angle based mining subsidence model and its application the novel mining subsidence prediction model is developed with the dip angle of a bedded ore deposit as a variable it is applicable for coal seams with a dip angle ranging from 0 to 90 application of the model for seams with varying dip angles well demonstrates it s good adaptability

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

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

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

effects of productivity glaciation and ventilation on late quaternary sedimentary redox and trace element accumulation on the vancouver island margin western canada variations in chalcophile and redox sensitive trace elements are examined at high resolution intervals from a 50 kyr long sediment core md02 2496 from the vancouver island margin enrichments of ag cd re u and mo above lithogenous levels signifying sedimentary suboxia and anoxia occurred during the early holocene and bolling allerod and during warm interstadial events of marine isotope stage mis 3 down core trace element profiles co vary with productivity proxy records opal caco3 and marine organic carbon and with sedimentary nitrogen isotope ratios which reflect variably enriched nitrate upwelled from intermediate waters that were transported northward from the eastern tropical north pacific the similarity of the md02 2496 record with records from the southern portion of the california current system ccs and to the greenland ice core oxygen isotope record during warm climate intervals suggests that sedimentary redox conditions along the california current responded to local productivity to north atlantic climate change and to tropical pacific surface water processes via long distance teleconnections concentrations of trace elements and productivity proxies were relatively depleted during the younger dryas cool stadial events of mis 3 and in two episodes of glaciomarine sedimentation from 14 7 to 30 5 kyr bp last glacial maximum lgm and from 44 to 50 4 kyr bp cordilleran ice sheet advancement onto the vancouver island continental shelf during the lgm led to intervals of increased terrigenous sedimentation and greatly reduced productivity not seen in the southern portion of the ccs and along with ventilation of north pacific intermediate waters resulted in brief sedimentary oxic conditions

thermohaline circulation in the gulf of california the gulf of california a narrow semienclosed sea is the only evaporative basin of the pacific ocean as a result of evaporative forcing salinities in the gulf are 1 to 2 higher than in the adjacent pacific at the same latitude this paper examines the thermohaline structure of the gulf and the means by which thermohaline exchange between the pacific and the gulf occurs over time scales of months to years in addition to evaporative forcing air sea heat fluxes and momentum fluxes are important to thermohaline circulation in the gulf from observations presented here it appears that the gulf gains heat from the atmosphere on an annual average unlike the mediterranean and red seas which have comparable evaporative forcing as a result outflow from the gulf tends to be less dense than inflow from the pacific winds over the gulf change direction with season blowing northward in summer and southward in winter this same seasonal pattern appears in near surface transports averaged across the gulf the thermohaline circulation then consists of outflow mostly between about 50 m and 250 m inflow mostly between 250 m and 500 m and a surface layer in which the direction of transport changes with seasonal changes in the large scale winds using hydrographic observations from a section across the central gulf total transport in or out of the northern gulf is estimated to be 0 9 sv heat gain from the atmosphere is estimated to be 20 to 50 w m 2 and evaporation is estimated to be 0 95 m yr 1 these estimates are annual averages based on cruises from several years seasonal variations in thermohaline structure in the gulf are also examined and found to dominate the variance in temperature and density in the top 500 m of the water column salinity has little seasonal variability but does exhibit more horizontal variablility than temperature or density major year to year variations in thermohaline structure may be attributable to el nino southern oscillation events

climate forcing primary production and the distribution of holocene biogenic sediments in the gulf of california abstract the gulf of california is a marginal seaway under the influence of a monsoon climate that produces cool dry winters and warm humid summers winds tidal mixing and coastal trapped waves forced by climate and the pacific ocean control nutrient advection and primary productivity pp strong northwest winds from the subtropical east pacific high pressure system begin in november and last until april and drive coastal upwelling along the mainland margin especially in the central and southern gulf in the northern gulf particularly around the midrift island tidal mixing and turbulence occurs year round advecting nutrients into the mixed layer and high productivity during summer and early fall months winds are variable of less intensity and mainly blow cross basin except in the most northern gulf summer pp is generally low in the central and southern gulf except along the mainland where coastal trapped waves associated with tropical surges and hurricanes generate mixing over the continental shelf mesoscale eddies or gyres often associated with jets and filaments extend to depths of 1000 m and transport nutrient enriched upwelled waters and plankton detritus across the gulf the largest and most persistent gyres rotate in an anti cyclonic direction east to west and are a principal source of the plankton export to the peninsula margin two major biogenic sediment patterns are present in core top sediments hemipelagic biosiliceous rich muds are accumulating beneath upwelling areas of high productivity in the central gulf and along the mainland margin calcium carbonate and organic carbon rich oc sediments are concentrated along the peninsula margin generally beneath lower productivity waters with the highest oc content in areas with the lowest productivity the high uniform biosiliceous content in guaymas basin extending southward into carmen basin reflects the redistribution by mesoscale gyres of phytoplankon debris produced in mainland coastal upwelling and tidally forced areas around the midrift islands holocene biogenic patterns are similar to the present day with the major difference in rates of accumulation phytoplankton production prior to about 8200 yr bp was significantly higher in the central and southern gulf decreased though the mid holocene and has been reasonably steady for the past 2500 yr the strong north south and east west gradients in present day phytoplankton productivity patterns are also reflected in the holocene sediment record a series of depositional cycles occur in the biogenic record with the strongest peaks of variability at about 150 144 18 200 198 5 and 350 350 40 yrs longer periodicities are present prior to 3200 yr bp but the 350 yr cycle dominates in the late holocene where it is best expressed as productivity dissolution cycles in the carbonate record

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

ventilation of north pacific intermediate waters the role of the alaskan gyre hydrographic data tritium data and potential vorticity calculations suggest that although north pacific intermediate water is formed in the northwest the alaskan gyre might be an additional ventilation site the proposed ventilation is quantified by a vertical column tritium inventory which indicates an excess of 0 08 kg of tritium in the alaskan gyre an evaluation of the energy stored in the water column and of wind and buoyancy forcing shows that during winter conditions enough energy can be pumped into the system to force 26 80 to outcrop in the alaskan gyre model results suggest that relatively limited outcrops in time and space tens of days and several hundred kilometers in diameter can account for the excess tritium

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

influence of biological productivity on silver and redox sensitive trace metal accumulation in southern ocean surface sediments pacific sector abstract accurate interpretation of paleoproductivity proxies in the southern ocean requires ground truthing these proxies here the concentrations of total ba organic carbon c org and biogenic silica si bio along with other redox sensitive trace metals cd re and mo are compared with the distribution of silver ag in core top sediments from the pacific sector of the southern ocean conventional thinking holds that enrichment of trace metals should be muted or absent in southern ocean sediments despite high export of c org from surface waters because deposition under well oxygenated bottom waters inhibits accumulation of reduced metal phases while our data support this prediction detectable preserved vertical fluxes of ag cd and re exist beneath the opal belt and faithfully record surface productivity patterns therefore we suggest ag fluxes into southern ocean sediments occur via biodetritus associated with high export production rather than accumulation by redox driven diagenetic processes sedimentary ag concentrations are likely altered at the seafloor by biogenic particle remineralization due to high bottom water o 2 nevertheless zonal ag fluxes are similar to surface productivity patterns highlighting the potential of ag to serve as a proxy for diatom export production

mid holocene serpulid build ups in an estuarine environment buenos aires province argentina abstract a bed with several serpulid build ups is described from a holocene outcrop at quequen grande river argentina the tubes were dated at 6360 80 years bp the morphology and size parameters of the serpulids were compared to different species of serpulids from the literature and tubes of ficopomatus enigmaticus hydroides dianthus and hydroides plateni from argentinean waters in spite of the fact that today only f enigmaticus constructs build ups in argentine brackish environments the fossil tubes could not be assigned to this species but instead they show close similarities to those of the two species of hydroides the sequence is interpreted as having originated from a brackish environment at present neither the endemic h plateni nor any other species of hydroides construct build ups in brackish waters of southern south america this suggests that suitable environments to construct aggregates were more widespread than today or that the invasion of f enigmaticus replaced hydroides alternatively various causes may have acted jointly

intermittent existence of a southern californian upwelling cell during submillennial climate change of the last 60 kyr 1 application of a high resolution multiproxy approach to a sedimentary section drilled at ocean drilling program site 1017 located under a highly active upwelling cell off point conception california provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr the proxies include bulk sediment major and minor elements organic carbon and carbonate concentrations 15n and planktonic foraminiferal species assemblage and carbon isotope determinations the collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial scale climate oscillations of marine isotope stage mis 3 during that interval the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events however the last glacial maximum was also relatively productive productivity increased dramatically during the bolling warm interval while the allerod and younger dryas were much less productive high coccolithophorid abundance commenced during the earliest holocene after 10 ka the complexity of the productivity response was probably related to interplay between local winds as well as california undercurrent strength

molybdenum in the northeast pacific ocean1 the concentration of dissolved molybdenum has been determined in several profiles from the northeast pacific ocean the salinity normalized concentration is essentially constant in all open ocean samples 107 nm 1 2 5 nm the dissolved distribution is not significantly affected by biological cycling

variability in north pacific intermediate and deep water ventilation during heinrich events in two coupled climate models the responses of north pacific intermediate and deep water ventilation and ocean biogeochemical properties to northern north atlantic glacial freshwater perturbations are evaluated with a coupled atmosphere ocean general circulation model miroc and an earth system model of intermediate complexity loveclim when the atlantic meridional overturning circulation amoc is weakened as a result of the north atlantic freshwater discharge both models simulate subthermocline and intermediate water warming in the pacific ocean the sensitivities of the pacific meridional overturning circulation pmoc to amoc weakening differ significantly between the two models miroc simulates a small enhancement of the deep sinking branch of the pmoc in the north pacific on the contrary the loveclim freshwater experiment exhibits intensified deep water formation in the north pacific associated with a maximum transport change of 19 sv despite the significant differences in ocean circulation response both models successfully reproduce high oxygen and low nutrient conditions of intermediate and deep waters in accordance with sediment core based paleoproxy reconstructions from the north pacific and bering sea during heinrich event 1 emergence of younger intermediate and deep water in the north pacific can be partly attributed to an overall enhanced mixing as well as intensified overturning circulation of the subpolar north pacific our models simulate broad features observed in several paleoproxy data of the pacific ocean biological production decrease in northern japan cooling in the western north pacific ocean and the southward shift of the pacific intertropical convergence zone

atmospheric transmission of north atlantic heinrich events this research was supported by the u s geological survey global change program and nsf under grants atm 9523584 atm 9632029 and ear 9725554

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

the relative role of oceanic heat transport and orography on glacial climate abstract during the last glacial maximum the earth s orography and oceanic heat transport contribute to a cooling in the north atlantic by using an atmospheric general circulation model of intermediate complexity we investigate the sensitivity of the atmospheric temperature and circulation during glacial climate focussing on the impact of the orography and different oceanic heat transports the results show a strong dependence of the glacial northern hemisphere circulation pattern to the changed orography the blocking effect of the elevated orography due to the laurentide ice sheet over the north american continent forced a deflection of westerlies their enhancement and a southward displacement over the atlantic independently the glacial climate is influenced by the oceanic heat transport the reduced oceanic heat transport on the glacial climate shows a 20 40 contribution for the total cooling relative to the present day climate in the north atlantic and polar regions finally we find that the altered orography in the northern hemisphere and different oceanic heat transports result in a changed hydrological cycle a reduction of the hadley circulation and a southward shift of the intertropical convergence zone in the boreal winter during glacial times

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

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

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

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

records of seasonal flux in holocene laminated sediments gulf of california holocene laminated sediments from guaymas basin gulf of california mexico have in the past been described as annual couplets of sedimentation couplets comprise an alternation of diatom and terrigenous rich sediment reflecting winter and summer flux to the sediment respectively new data from backscattered electron imagery bsei show that a three component pattern of sedimentation is preserved comprising 1 a lithogenic lamina consisting of clays silt and minor diatomaceous material deposited during the summer and autumn wet season 2 a mixed flora diatomaceous lamina deposited during the early winter collapse of the thermocline and onset of water column mixing and 3 a near monospecific flora lamina of chaetoceros resting spores or more rarely skeletonema costatum representing deposition from or at the end of the spring coastal upwelling bloom recent sediment trap biogenic and terrigenous flux data also show three to four major flux events per year direct comparisons are possible between bsei records and recent sediment trap flux data to facilitate high resolution palaeoceanaographic and palaeoclimatic reconstructions throughout the holocene

on the preservation of laminated sediments along the western margin of north america 1 piston gravity and multicores as well as hydrographic data were collected along the pacific margin of baja california to reconstruct past variations in the intensity of the oxygen minimum zone omz gravity cores collected from within the omz north of 24 n did not contain laminated surface sediments even though bottom water oxygen bwo concentrations were close to 5 mol kg however many of the cores collected south of 24 n did contain millimeter to centimeter scale brown to black laminations in holocene and older sediments but not in sediments deposited during the last glacial maximum in addition to the dark laminations holocene sediments in soledad basin silled at 290 m also contain white coccolith laminae that probably represent individual blooms two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated holocene sediment occurring at 12 9 and 11 5 ka respectively the transition is delayed and more gradual 11 3 10 0 ka in another dated core from soledad basin the observations indicate that bottom water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors with the caveat that laminated sections should therefore not be correlated without independent age control the pattern of older sequences of laminations along the north american western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr

geochemical signatures of redepositional environments the namibian continental margin abstract trace metal abundances in marine sediments have been used extensively to interpret periods of elevated primary productivity and ancient ocean redox conditions however sediment reworking that results in post depositional oxidation such as bio irrigation or lateral sediment transport through oxic water can modify the primary geochemical signal of the sediment which in turn may impact paleo redox and or productivity interpretations in the case of sediments on the namibian continental margin ncm lateral transport and redeposition contribute to the accumulation of organic matter on the margin slope to better constrain the geochemical effects of lateral transport on the ncm we examined the trace metal signature including solid phase fe mo v ni cu and ag and pore water fe mo and v in surface sediments up to 25 cmbsf along a transect from shelf to slope through the primary shelf and secondary upper slope depositional zones of the margin despite varying bottom water redox conditions ranging from seasonally anoxic upper shelf suboxic shelf break and oxic upper slope each site has elevated total organic carbon contents average toc content of 9 1 3 2 and 6 8 wt respectively due to high surface water primary productivity and lateral transport of organic rich material from the shelf to the upper slope our results show that the solid phase contents of the productivity proxies ni cu and ag parallel the organic carbon accumulations largely irrespective of the local redox conditions in contrast the solid phase contents of v mo and fe respond to the local bottom water redox conditions at each site being enriched under strongly reducing conditions and less enriched under oxic bottom waters despite enhanced toc at all three investigated sites thus the enrichment of trace metal and toc at each site on the ncm can not only be used to reconstruct primary depositional bottom water redox conditions but also to identify zones of sediment redeposition using an offshore transect allows for the identification of intense lateral transport and redeposition of organic rich sediments that are occurring along the margin the relative concentrations of both redox sensitive and productivity related trace metals suggest that the decoupling of trace metals and organic carbon enrichments occasionally observed in the geological record could be explained by the process of lateral transport and redeposition

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

what regulates rhenium deposition in euxinic basins abstract rhenium is greatly enriched in black shales and euxinic basin sediments relative to its crustal abundance the enrichment process is generally assumed to involve reduction of reo 4 the principal re species in seawater to an insoluble re iv oxide or sulfide in suboxic and anoxic environments the specific biotic or abiotic mechanism of reduction has so far defeated efforts to discover it here an alternative mechanism of fixing re in sediments is examined experimentally thiolation of reo 4 leading to particle reactive thioperrhenates re vii o n s 4 n or to re vii sulfide precipitates or coprecipitates using optical absorption methodology we obtain the first measurements of equilibrium constants for formation of reo 3 s and res 4 as well as a solubility constant for a colloidal re 2 s 7 polymer from these constants we conclude that most euxinic environments contain insufficient sulfide to stabilize thioperrhenates as major species similarly re 2 s 7 polymers are too soluble to form in near neutral ph waters although they might form in acidic mine waters or during supergene hypogene enrichment processes to explain remarkable similarities between mo and re vertical profiles in the black sea we propose that both elements become thiolated at surfaces of a fe mo s colloidal phase and consequently coprecipitate coprecipitation implies that the triggering mechanism for re removal from euxinic basins is neither reduction nor thiolation of reo 4 but instead saturation of sulfidic waters with the fe mo s phase coprecipitation favors removal of mo more than re from the aqueous phase explaining increasing aqueous phase re mo ratios as these elements are depleted from sulfidic waters the raleigh fractionation law describes the process well similar partition coefficients describe the evolution of re mo ratios quantitatively both in sulfidic black sea waters and in sulfidic hingham bay pore waters

numerical analysis and prediction of ground surface movement induced by coal mining and subsequent groundwater flooding abstract ground surface movement shows different features during mining and post mining period if the mine goaf is dry surface subsidence is observed in both periods if the mine goaf is flooded by groundwater however ground surface uplift can be observed although much smaller in amplitude compared to the preceding subsidence a numerical modeling strategy is proposed to predict uplift during the flooding process of an excavated coal mining area under complex geological conditions the modeling approach considers three phases virgin state before mining stage immediately after mine closure flooding phase the model considers elasto plastic material behavior including faults represented by interfaces in situ measurements are used for calibration of the model the oelsnitz abandoned coal mine is used for model validation and prediction the measured subsidences up to 17 m were reproduced as well as the uplift within the last 10 years with values between 0 5 2 0 mm year spatial distribution of uplift areas is well reproduced predictions up to the year 2051 show an increase in uplift velocity between 0 5 3 0 mm year and additional total uplift of up to 300 mm

the deglaciation of the northern hemisphere a global perspective orbitally induced increase in northern summer insolation after growth of a large ice sheet triggered deglaciation and associated global warming ice albedo sealevel and greenhouse gas feedbacks together with tropical warming from weakening winds in response to polar amplification of warming caused regionalto global near synchronization of deglaciation effects were larger at orbital rather than millennial frequencies because ice sheets and carbon dioxide vary slowly ice sheet linked changes in freshwater delivery to the north atlantic and possibly free oscillations in the climate system forced millennial climate oscillations associated with changes in north atlantic deep water nadw flow the north atlantic typically operates in one of three modes modern glacial and heinrich deglaciation occurred from a glacial mode ocean that in comparison to modern had shallower depth of penetration of nadw formed further south causing strong northern cooling and the widespread cold dry and windy conditions associated with the glacial maximum and the cold phases of the millennial dansgaard oeschger oscillations the glacial mode was punctuated by meltwater forced heinrich conditions that caused only small additional cooling at high northern latitudes but greatly reduced the formation of nadw and triggered an oceanic seesaw that warmed some high latitude southern regions centered in the south atlantic

identifying global vs basinal controls on paleoproterozoic organic carbon and sulfur isotope records abstract paleoproterozoic sedimentary successions are important archives of the redox evolution of earth s atmosphere and oceans efforts to unravel the dynamics of our planet s early oxygenation from this archive rely on various geochemical proxies including stable carbon and sulfur isotopes however ancient metasedimentary rocks often experienced early and late stage bio geochemical processes making it difficult to discern primary environmental signals from bulk rock 13corg and 34s values such complexity in carbon and sulfur isotope systematics contributes to uncertainty about the redox structure of paleoproterozoic oceans a currently popular idea is that following the great oxidation event global changes led to low oxygen environments and temporally fluctuating ocean redox conditions that lasted until the neoproterozoic the volcano sedimentary rocks of the onega basin have figured prominently in this concept particularly the exceptionally organic rich rocks of the 1 98 ga zaonega formation however a growing body of evidence shows that local depositional processes acted to form the 13corg and pyrite 34s records of the zaonega formation thus calling for careful assessment of the global significance of these isotope records placing new and existing organic carbon and sulfur isotope data from the zaonega formation into the context of basin history and by comparing those results with key paleoproterozoic successions of the francevillian basin gabon the pechenga greenstone belt nw russia and the animikie basin canada we show that the stratigraphic 13corg and pyrite 34s trends can be explained by local perturbations in biogeochemical carbon and sulfur cycling without requiring global drivers despite their temporal disparity we also demonstrate that individual successions share certain geological traits e g magmatic and or tectonic activity hydrocarbon generation basin restriction suggesting that their pyrite 34s and 13corg trends were governed by common underlying mechanisms e g similar basinal evolution and biogeochemical feedbacks and are not necessarily unique to certain time intervals we further show that pyrites in these successions that are most likely to capture ambient seawater sulfate isotopic composition have consistent 34s values of 15 18 which hints at remarkable stability in the marine sulfur cycle over most of the paleoproterozoic era

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

influence of overburden mass behavioural properties on subsidence limit characteristics abstract an analytical calculation model for the angle of draw is introduced in this paper on the supposition that the roof is considered as an elastic beam this model indicates the importance of the main factors which control the extent of subsidence produced on the surface and also provides some appreciation of the influence of overburden strength on the angle of draw a finite element model has been developed for application to subsidence related rock mechanics problems by the use of this model the authors have investigated the effects rock mass behavioural properties on the limit angle and also the effects of a distinct bed strong or weak in the overburden on the subsidence affected area at the surface relevant u k data from monitored sites for determining the three limit angles variation with the dip of seam are discussed the trend of the limit angle from the north of england to the midland coalfields is also discussed in the paper it has been found that the results from the data are in good agreement with numerical model results

the lower atmosphere over the gulf of california automated meteorological observations at coastal and island stations instrumented aircraft flights and coastal soundings were made between july 1983 and june 1985 to define the variations of the lower atmosphere over the northern half of the gulf of california during the two important climatic seasons the mid latitude winter and the subtropical summer a marine layer is well defined over water during both seasons but dissipates within a few kilometers inland the winter large scale pressure field is dominated by the great basin high over the southwestern united states modulated by upper level synoptic activity it causes 3 to 6 days events of northwesterly winds 8 12 m s 1 directed along the gulf s axis which are coherent over basin scales and bring cool dry desert air over the gulf the vertical scale of these winds is 700 1000 m over land on the western side of the gulf close to the height of the baja california mountains but only 100 400 m over water defined by the wintertime inversion cross gulf winds related to topographic effects during upper level trough passages over baja california are particularly intense in the northwestern portion of the gulf the winter marine layer is defined by a 1 to 4 5 c temperature inversion and a dew point temperature of 6 11 c a moisture content of 6 8 g kg 1 weak subsidence reduces dew point values to 4 c above the inversion winter winds above the marine layer are coherent 0 8 across the width of the gulf the summer large scale pressure field is dominated by a thermal low over the southwestern united states and drives weak 2 5 m s 1 southeasterly winds also directed primarily along the gulf which are less spatially uniform than winter winds air temperature and moisture content are rather constant and topographic effects are absent the summer marine layer is on the order of 200 300 m thick with dew point temperatures of 26 28 c 21 24 g kg 1 and capped by a weak temperature inversion 1 2 c over water aloft the dew point temperature is 17 21 c and winds are weak and uncorrelated across the width of the gulf during june and early july 1984 four week long pulses of southeasterly winds 10 m s 1 support the existence reported previously of moisture surges from the gulf into the sonoran desert a dynamical analysis of subdiurnal motions shows that the cross gulf momentum balance is geostrophic the along gulf balance is ageostrophic with the along gulf pressure gradient opposed by friction at the surface these results are consistent with a scale analysis of the equations of motion in the marine layer over the gulf of california

large fluctuations of dissolved oxygen in the indian and pacific oceans during dansgaard oeschger oscillations caused by variations of north atlantic deep water subduction a s and s h were supported by the paleoclimate program of the national science foundation as part of the paleovar project atm 0602395

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

the geochemical record of the last 17 000 years in the guaymas basin gulf of california abstract sediments deposited on the western slope of the guaymas basin in the central gulf of california are composed predominantly of detrital clastic material and biogenic silica biopal with minor organic material average of 2 8 organic carbon and calcium carbonate the caco 3 is derived from calcareous plankton and is highly variable ranging from 0 to 16 in general the caco 3 content of the sediments varies inversely with the biopal content reflecting the relative abundance of calcareous and siliceous plankton in the photic zone siliceous plankton dominate when winds are predominantly out of the northwest producing strong upwelling calcareous plankton indicates weak southeasterly winds that bring warm tropical pacific surface water into the gulf based mainly on relative abundances of biopal and caco 3 the sediments deposited over the last 17 000 years in the western guaymas basin can be divided into five intervals in general the sediments in the intervals with high biopal and low caco 3 are laminated but this is not always true unlike most other continental margins of the world with well developed oxygen minimum zones where highest concentrations of organic carbon and redox sensitive trace metals occur in laminated sediments the laminated sediments on the anoxic slope of the western guaymas basin do not always have the highest concentrations of organic carbon and trace metals such as mo and cd

late quaternary climate change record from two long sediment cores from guaymas basin gulf of california modern guaymas basin gulf of california mexico is a region of high diatom productivity where exceptional preservation factors maintain biannually alternating sediment deposition as annual varves new sediment cores from guaymas basin md02 2512 and md02 2515 present the opportunity to construct climate records from below the last glacial period a low resolution age model has been constructed from oxygen isotope analysis correlation with other dated short piston cores from guaymas basin and an estimate of sedimentation rate md02 2512 from eastern guaymas basin has an age range from the holocene to late marine isotope stage 6 mis 6 md02 2515 from western guaymas basin has an age range from 8000 to 40 000 yr shipboard analyses of colour reflectance magnetic susceptibility and sediment density are combined with continuous x ray fluorescence scans to reconstruct a picture of glacial climate in the gulf of california eastern guaymas basin is affected by glacial sea level fall which results in a drastic change in productivity rates and sediment type the laminated record of mis 5 allows comparison with the holocene showing a similarity of sedimentation patterns during deglaciation and a series of very rapid variations just prior to the last glaciation in western guaymas basin there are a series of younger dryas like events during the glacial typified by low productivity and high terrigenous input long term climate and productivity changes appear to be caused by the southward displacement of the subtropical high pressure zone copyright 2005 john wiley sons ltd

glacial interglacial variability in the eastern tropical north pacific oxygen minimum zone recorded by redox sensitive trace metals 1 changes in the intensity of the oxygen minimum zone omz in the eastern tropical north pacific over the past 140 kyr are recorded as enrichments and depletions of redox sensitive metals in sediments of two piston cores one within and one below the modern omz from the continental margin off mazatlan mexico 22 41 n 106 28 w concentrations of al 7 7 0 6 ti 0 37 0 03 fe 3 1 0 25 mn 320 31 ppm and ba 560 82 ppm in core nh15p within the omz at 420 m water depth were relatively constant over the last 110 kyr in contrast concentrations of cd 4 8 2 ppm cu 29 8 9 1 ppm u 9 1 3 7 ppm mo 12 1 5 0 ppm v 138 2 51 9 ppm and re 45 8 25 5 ppb were all at least 30 higher in interglacial stages compared to glacial stages concentrations of al 7 4 0 3 ti 0 35 0 03 fe 3 5 0 4 and mn 385 77 ppm in core nh22p below the omz at 2025 m water depth were comparable to those in core nh15p while concentrations of ba 1662 292 ppm were about a factor of three higher in contrast concentrations of cd 0 9 0 3 ppm u 6 6 0 9 ppm mo 3 2 1 2 ppm v 81 8 10 1 ppm and re 25 4 12 ppb were lower in sediments of comparable age than the concentrations of these same metals in the omz core and the differences in their concentrations over glacial interglacial cycles were less pronounced than those in shallower core comparison of the nonlithogenic fraction of metals in the sediments with their estimated contribution from plankton suggests that organic matter is probably the major source of cu ba and perhaps cd to the sediment whereas the indirect effects of organic carbon and low bottom water oxygen concentrations on sediment redox state appear to be more important controls on the distributions u re mo and v changes in the depth at which re and mo precipitated in the sediments and in the re mo ratio suggest that the redox state of the surface sediment and overlying water at both core depths varied over time re and mo removal depths were shallower and re mo ratios were lower at the omz site than in deeper water suggesting that a more reducing environment prevailed over time at the shallower site although the redox state of the waters and sediment at both sites varied over glacial interglacial cycles the omz likely was never anoxic in the last 140 kyr this variability in redox state could be attributed to changes in regional export productivity changes in ocean circulation or a combination of both processes a paleoproductivity reconstruction from biogenic ba data suggests that glacial productivity was considerable lower than it was during interglacial stages model results suggest that the oxygen penetration depth an indicator of sediment redox state changed less than 1 cm as a result of the change in productivity changes in oxygen penetration depth estimated from re and u removal depths are significantly larger suggesting that changes in ventilation are a more important control on sediment redox state overall trace metal results confirm the tight coupling between ocean circulation marine productivity and global change

intermediate and deep water mass distribution in the pacific during the last glacial maximum inferred from oxygen and carbon stable isotopes intermediate ocean circulation changes during the last glacial maximum lgm in the north pacifi ch ave been linked with northern hemisphere climate through airesea interactions although the extent and the source of the variability of the processes forcing these changes are still not well resolved the ventilated volumes and ages in the upper wind driven layer are related to the wind stress curl and surface buoyancy fluxes at mid to high latitudes in the north pacific in contrast the deeper thermohaline layers are more effectively ventilated by direct atmosphere sea exchange during convective formation of subantarctic mode waters samw and antarctic intermediate waters aaiw in the southern ocean the precursors of pacific intermediate waters piw in the north pacific results reported here show a fundamental change in the carbon isotopic gradient between intermediate and deep waters during the lgm in the eastern north pacific indicating a deepening of nutrient and carbon rich waters these observations suggest changes in the source and nature of intermediate waters of southern ocean origin that feed piw and enhanced ventilation processes in the north pacific further affecting paleoproductivity and export patters in this basin furthermore oxygen isotopic results indicate these changes may have been accomplished in part by changes in circulation affecting the intermediate depths during the lgm 2010 elsevier ltd all rights reserved

role of a strong oxygen deficient zone in the preservation and degradation of organic matter a carbon budget for the continental margins of northwest mexico and washington state rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest mexico and washington state with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen deficient zone and on a typical western continental margin total carbon oxidation rates including rates for individual electron acceptors o2 no3 and so4 were determined at depths ranging from 100 to 3000 m on both margins carbon oxidation rates were generally higher on the washington margin than on the mexican margin the relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of o2 and no3 from the overlying water the relative contribution of o2 consumption increased in deeper sediments 2000 m as aerobic processes began to dominate the total carbon oxidation rate denitrification rates were highest in washington sediments however denitrification represented a larger fraction of the total carbon oxidation rate in the mexican sediments 40 for mexico vs 30 for washington sulfate reduction accounted for as much as 79 of the total carbon oxidation rate in shallow sediments and less than 20 in deep sediments on both margins the offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate pore water o2 and no3 penetration depths were shallowest in nearshore stations and increased offshore regeneration ratios of c n p reveal non redfield behavior on both margins carbon budgets for the two margins demonstrate that off mexico a much greater percentage of the organic matter produced in the surface ocean reached the sediments 15 vs 8 for mexico and washington respectively on the mexican margin 8 of the primary production escaped oxidation in the surface sediments to be permanently buried as compared with only 1 2 of the primary production on the washington margin this suggests that oxygen deficient conditions on mexican margin are linked to enhanced carbon preservation

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

varve formation in the gulf of california insights from time series sediment trap sampling and remote sensing the varved sediments that accumulate in the central gulf of california guaymas and carmen basins provide a record that allows for the resolution of annual to decadal scale climate variability in this region time series sediment trapping combined with remotely sensed observations of sea surface temperature avhrr and color czcs have been used to examine the mechanism of varve formation in the central gulf sst and surface pigment concentration records for both the mainland and baja sides of the gulf display similar seasonal trends high temperatures and low pigment concentrations occur synchronously on both sides of the central gulf from june through to october in association with the 1991 92 el nino warm temperatures persist in the central gulf until december low ssts typically occur from december through may with high pigment concentrations marking the period from november through april the summer early fall june october is a time of high terrigenous and biogenic sediment fluxes during this time of year the total flux is dominated by eolian transported lithogenic material and dark laminae are deposited during this period during el nino years high terrigenous fluxes may extend into winter light laminae represent deposition from november through may during which time biogenic material dominates the total sediment flux high opal fluxes beginning in november are attributed to seasonal cooling of surface water and upward mixing of nutrients true upwelling conditions do not develop in the gulf until late winter spring during this time the total flux is still dominated by opal but the magnitude of the flux is reduced this may be an artifact of phytoplankton grazing and not lower production rates

late quaternary climatic and oceanographic changes in the northeast pacific as recorded by dinoflagellate cysts from guaymas basin gulf of california mexico a high resolution record of organic walled dinoflagellate cyst production in guaymas basin gulf of california mexico reveals a complex paleoceanographic history over the last 40 ka guaymas basin is an excellent location to perform high resolution studies of changes in late quaternary climate and paleo productivity because it is characterized by high primary productivity high sedimentation rates and low oxygen bottom waters these factors contribute to the deposition and preservation of laminated sediments throughout large portions of the core md02 2515 in this study we document dinoflagellate cyst production at a centennial to millennial scale throughout the late quaternary based on the cyst assemblages three dinoflagellate cyst zones were established and roughly correspond to marine isotope stages miss 1 to 3 miss 1 and 3 are dominated by cysts of heterotrophic dinoflagellates whereas mis 2 is characterized by enhanced variability and a greater proportion of cysts produced by autotrophic taxa the most dominant dinoflagellate cyst taxa found throughout the core were brigantedinium spp and operculodinium centrocarpum dansgaard oeschger event 8 is observed in the dinoflagellate cyst record where it is characterized by an increase in warm taxa such as spiniferites pachydermus other intervals of interest are the younger dryas where warmer conditions are recorded and the holocene which is characterized by the consistent presence of tropical species stelladinium reidii tuberculodinidum vancampoae bitectatodinium spongium and an increase in quinquecuspis concreta changes in cyst assemblages concentrations and species diversity along with geochemical data reflect major orbital to millennial scale climatic and oceanographic changes reference price a m k n mertens v pospelova t f pedersen and r s ganeshram 2013 late quaternary climatic and oceanographic changes in the northeast pacific as recorded by dinoflagellate cysts from guaymas basin gulf of california mexico paleoceanography 28 doi 10 1002 palo 20019

water mass formation in the gulf of california the gulf of california is a long narrow marginal sea lying between the baja california peninsula and the mainland of mexico air sea fluxes of heat and moisture in the gulf are enhanced because of geographical isolation from the pacific provided by the mountainous baja california peninsula in the northern gulf annual evaporation rates are about 1 m y 1 unlike most evaporative basins however the gulf gains heat from the atmosphere at an annual average rate of 20 to 80 w m 2 bray 1988 given the unusual air sea forcing of the gulf what form or forms should water mass formation take the annual moisture loss and heat gain require that high salinity surface water be transported downward to an intermediate depth and that cold fresh inflow be transported upward to an intermediate depth this is accomplished through several mechanisms 1 winter convection this occurs only in a limited geographical region the wagner basin of the far northern gulf except in el nino southern oscillation years when convection appears to be more widespread 2 dispersion of convected water in small eddylike features this occurs within a large scale southward transport possibly driven by the large scale density gradient associated with atmospheric fluxes 3 an anticyclonic circulation in the northern gulf this is found south of the convection region and transports high salinity water off the shallow shelves and to substantial depths where it may mix with water of central gulf origin 4 tidal mixing most of the energy available for mixing in the northern gulf derives from the tides in particular tidal mixing over the sill in the island region is responsible for the substantial reduction in salinity of northern gulf waters as they enter the central gulf

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

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

a 36 kyr geochemical record from the sea of japan of organic matter flux variations and changes in intermediate water oxygen concentrations intervals of organic c and carbonate rich laminated sediments occur in the sea of japan with roughly the same frequency as temperature changes observed in greenland ice cores providing clear evidence of rapid oceanographic change during the past 36 kyr planktonic foraminiferal 18o data suggest that only the laminated sediments deposited during the last glacial maximum lgm and perhaps one other interval formed during a period of increased water column stratification sedimentary re and mo data are consistent with bottom waters that were sulfidic during the lgm and suboxic during other laminated intervals results of a numerical model of corg and re burial are consistent with a mechanism whereby an increased corg flux to the seafloor drove oxygen concentrations toward depletion during times of deposition of the suboxic laminated intervals such a process could have resulted from increased upwelling driven either by increased deep water formation due to colder and or more saline surface waters or by stronger northeasterly monsoonal winds

is pore water oxygen content decoupled from productivity on the california margin trace element results from ocean drilling program hole 1017e san lucia slope california 1 trace element evidence from the california margin ocean drilling program hole 1017e shows significant changes in sediment redox chemistry at intermediate water depths over the last 60 kyr the influence of export production on intermediate water oxygen content can be distinguished from lateral ventilation through comparisons among proxies representing export production flux percent corg and sediment surface i br and pore water mo ag cd re and u oxygenation proxies sulfate reduction within the uppermost sediment column occurred during late quaternary interstadials and the holocene indicating reduced intermediate water ventilation however sulfate reduction was most intense during major interstadials when productivity was enhanced decoupling between export production and pore water oxygen content is demonstrated during deglaciation when the sediment pore water oxygen content increases without a corresponding reduction in export productivity thus both export production and intermediate water ventilation play a role in oxygen minimum zone processes on the california margin

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

a model for uranium rhenium and molybdenum diagenesis in marine sediments based on results from coastal locations abstract the purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium u rhenium re and molybdenum mo in marine sediments we analyzed these redox sensitive metals rsm in benthic chamber pore water and solid phase samples at a site in buzzards bay massachusetts usa that has high bottom water oxygen concentrations 230 300 mol l and high organic matter oxidation rates 390 mol c cm2 y the oxygen penetration depth varies from 2 to 9 mm below the sediment water interface but pore water sulfide is below detection release of rsm to pore waters during the remineralization of solid phases occurs near the sediment water interface at depths above the zone of authigenic rsm formation this release occurs consistently for mo at both sites but only in the winter for re in buzzards bay and intermittently for u at the buzzards bay site re removal to the solid phase extends to the bottom of the profile while the zone of removal is restricted to 2 9 cm for u and mo authigenic re formation is independent of the anoxic remineralization rate which is consistent with an abiotic removal mechanism the rate of authigenic u formation and its modeled removal rate constant increase with increasing anoxic remineralization rates and is consistent with u reduction being microbially mediated authigenic mo formation is related to the formation of sulfidic microenvironments the depth and extent of mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation pore water rsm reach constant asymptotic concentrations in sulfidic sediments but only pore water re is constant at depth in buzzards bay the increases in pore water u at the buzzards bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone deep pore water mo concentrations exceed its bottom water concentration due to irrigation induced oxidation and remobilization from the solid phase in sulfidic sediments there is no evidence for higher pore water u or mo concentrations at depth due to the absence of irrigation and or the presence of more stable authigenic rsm phases there are good correlations between benthic fluxes and authigenic accumulation rates for u and mo in sulfidic sediments however results from buzzards bay suggest irrigation ultimately results in the partial loss of u and mo from the solid phase with accumulation rates that are 20 30 of the modeled flux irrigation can augment re possibly u or compromise u mo authigenic accumulation in sediments and is important when determining burial rates in continental margin sediments

new insights into productivity and redox controlled trace element ag cd re and mo accumulation in a 55 kyr long sediment record from guaymas basin gulf of california a high resolution 55 kyr long record of chalcophile and redox sensitive trace element accumulation ag cd re and mo from md02 2515 western guaymas basin is investigated in conjunction with patterns in stratigraphy and productivity high opal concentrations 59 wt representing increased diatom production coincide with laminated sediments and dilute the concentrations of organic carbon corg and metals a similarity between opal and normalized corg ag and cd concentrations suggests delivery to the sediments by diatom export production while patterns in normalized re and mo accumulation suggest a different emplacement mechanism although mo enrichment in organic rich laminated sediments typically represents anoxic conditions at other locations mo and re in guaymas basin is enriched in nonlaminated and bioturbated sediments that are representative of oxygenated conditions adsorption onto fe and or mn oxyhydroxide surfaces during oxygenation inadequately explains both the re and mo enrichments thus recently published mechanisms invoking direct re and mo removal from the water column and bioturbation assisted irrigation of re into the sediments are used to explain the counterintuitive observations in guaymas basin the md02 2515 stratigraphic and proxy records are also different from other records in the northeast pacific in that there is little correspondence with greenland dansgaard oeschger interstadials there is some correlation with heinrich events suggesting that ventilation of intermediate waters and or reduced productivity may be important in controlling stratigraphy and trace element accumulation the results question whether md02 2515 records can be compared to northeast pacific open margin records especially before 17 kyr b p

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

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

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

paleoceanographic history of the guaymas basin gulf of california during the past 15 000 years based on diatoms silicoflagellates and biogenic sediments high resolution records of calcium carbonate biogenic opal diatoms and silicoflagellates from western guaymas basin gravity core ggc55 and piston core jpc56 and eastern guaymas basin dsdp site 480 reveal a complex paleoceanographic history of the central gulf of california during the past 15 000 years prior to 6 2 ka the eastern and western guaymas basin proxy records were remarkably similar after conditions similar to those of today during the bolling allerod the younger dryas yd saw a major drop in diatom production coincident with increased calcium carbonate and tropical microfossils suggestive of el nino like conditions biosiliceous productivity began increasing during the latter part of the yd but it was only during the earliest holocene 11 6 to 11 0 ka that conditions similar to those of the bolling allerod returned to the central gulf between around 11 0 and 6 2 ka tropical diatoms and silicoflagellates were virtually absent from the central gulf as relatively cooler and fresher surface waters resembling those of the modern northern gulf were present in the central gulf beginning at about 6 2 ka tropical diatoms and silicoflagellates began increasing in the central gulf and coccoliths returned to western gulf sediments the onset of modern day monsoon conditions in the american southwest required the presence of warm ssts in the northern gulf which probably did not occur until after about 5 4 ka when tropical diatoms and silicoflagellates became relatively common in the central gulf modern east west contrasts which arise from late winter early spring coastal upwelling on the mainland side and lower diatom productivity on the western side of the gulf commenced between 6 2 and 5 4 ka possibly due to a shift in the direction of late winter early spring winds more towards the southeast or down the axis of the gulf this proposed wind shift might have ultimately been due to a late holocene strengthening of enso like conditions in the eastern equatorial pacific published by elsevier b v

silicic acid biogeochemistry in the gulf of california insights from sedimentary si isotopes reflects transient iron limitation our new d 30 si record from the guaymas basin shows dramatic variations at millennial timescales low d 30 si values synchronous with heinrich events are interpreted as resulting from the decline in si oh 4 utilization at times of decreased upwelling strength while nearly complete si oh 4 utilization was observed at times of invigorated upwelling and increased opal burial during the holocene the bolling allerod and the last glacial period we attribute the complete utilization of si oh 4 to the occurrence of transient fe limitation at these times our study highlights the importance of fe limitation on si and c cycling in coastal upwelling regions and suggests that upwelling dynamics in combination with fe availability have the potential to modulate marine si distribution and opal burial even at short timescales citation pichevin l r s ganeshram b c reynolds f prahl t f pedersen r thunell and e l mcclymont 2012 silicic acid biogeochemistry in the gulf of california insights from sedimentary si isotopes paleoceanography 27 pa2201