calibration of the planktonic foraminiferal mg ca paleothermometer sediment trap results from the guaymas basin gulf of california 1 the mg ca ratio has been measured in two surface dwelling species of planktonic foraminifera globigerinoides ruber and globigerina bulloides from biweekly sediment trap samples collected in guaymas basin gulf of california between august 1992 and november 1997 the guaymas basin experiences significant seasonal changes in sea surface temperature sst 16 33 c and thus is an ideal location for testing the temperature dependence of mg incorporation into foraminiferal calcite the planktonic foraminiferal mg ca ratios are directly compared with concurrent temperature measurements from the study site the results from the sediment trap study reveal a strong positive correlation between sst and the mg ca ratio in both g ruber r2 0 86 and g bulloides r2 0 90 the mg ca ratio increases exponentially by 7 per 1 c change in temperature for g ruber and by 6 for g bulloides these results indicate that the mg ca ratio in g ruber and g bulloides accurately records the measured seasonal surface temperature cycle and interannual variability in the guaymas basin within 1 c the greatest deviation between mg ca estimated sst and observed sst occurs in the spring and fall for both species this variability is attributed to rapidly changing hydrographic conditions and possible offset between the time of calcification and the temperature measurements in addition g ruber and g bulloides exhibit very high mg ca ratios during the strong el nino southern oscillation years of 1992 and 1997 verifying their potential to record sst up to 33 c and 28 c respectively the trace metal data are compared with foraminiferal oxygen isotope and alkenone measurements made on the same suite of sediment trap samples to assess the internal consistency of these temperature proxies strong correlations exist between the 18o and mg ca for g ruber r2 0 86 and g bulloides r2 0 79 similarly sea surface temperature estimates from mg ca ratios are in good agreement with alkenone derived temperature estimates r2 0 89 for g ruber and r2 0 81 for g bulloides

a simple multicloud parameterization for convectively coupled tropical waves part i linear analysis abstract recent observational analysis reveals the central role of three multicloud types congestus stratiform and deep convective cumulus clouds in the dynamics of large scale convectively coupled kelvin waves westward propagating two day waves and the madden julian oscillation a systematic model convective parameterization highlighting the dynamic role of the three cloud types is developed here through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds a systematic moisture equation is developed where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation a nonlinear switch is developed that favors either deep or congestus convection depending on the relative dryness of the troposphere in particular a dry troposphere

a possible new mechanism for northward propagation of boreal summer intraseasonal oscillations based on trmm and merra reanalysis boreal summer intraseasonal oscillations bsisos manifest in the active and break spells and act as the primary building block of the indian summer monsoon although recent research has evolved a basic framework for understanding the scale selection and northward propagation of the bsiso the role of different hydrometeors in modulating these processes remains poorly explored in this study trmm 2a12 retrievals and modern era retrospective analysis for research and applications reanalysis data are examined to establish relationship between cloud hydrometeors and other atmospheric dynamical parameters with the northward propagation of the bsisos the study reveals that the cloud liquid water leads the deep convection during the northward propagation of bsisos in the lower troposphere while the cloud ice slightly lags the convection this distribution indicates the occurrence of a possible mechanism of the lower level moistening through the large scale moisture advection in lower atmosphere and boundary layer pbl convergence followed by triggering of the deep convection the analyses of moisture advection and the dynamical fields with respect to the convection center show that low level moistening is a manifestation of the barotropic vorticity and pbl convergence of moisture anomaly north of the convection center a new internal dynamical thermodynamical mechanism is unraveled to understand the reason behind the middle tropospheric heating maximum and its role on the northward propagation it is shown that the enhanced moisture perturbation in lower levels together with the heat transport by the sub grid scale eddies within the pbl induces lower level instability required to precondition the lower atmosphere for triggering the deep convection vigorous upward motion inside the deep convection uplifts the liquid hydrometeors to upper levels and the formation of precipitable ice leads to the heating maxima in the middle troposphere to check the robustness of the proposed hypothesis similar analysis is performed for the weak northward propagating bsiso cases

petrography relationships and petrogenesis of the gabbroic lithologies in northwest africa 773 clan members northwest africa 773 2727 3160 3170 7007 and 10656

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

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

reconstructing mid to high latitude marine climate and ocean variability using bivalves coralline algae and marine sediment cores from the northern hemisphere quantifying the role and contribution of the world s oceans in past present and future global change is an essential goal in climate paleoclimate and environmental studies although the global oceans interact and influence climate greatly the marine environment is substantially under represented in key climate assessment reports especially during the last millennium ipcc 2007 see palaeoclimate chapter 6 6 the last 2000 years the under representation of marine records in key climate documents likely results from the often imprecise chronologies associated with many marine based archives which greatly hinders singular climate comparisons lag lead phasing relationships with well dated and or annually resolved archives however several marine archive records have excellent chronological constraint in particular many marine bivalve taxa and coralline algae have annual increments that form within their carbonate framework that can be used to establish an absolutely dated chronology via cross dating techniques from the marine environment additionally in some cases where sedimentation rates are high and alternative chronological dating methods exist e g tephrochronology other than radiocarbon measurements often greater than 40 years uncertainty sediment archives can provide continuous sub decadal records of environmental change for centuries to millennia this brief introductory article and accompanying special issue will focus on the utilization of bivalves coralline algae and high resolution marine sediment cores in paleoclimate and environmental studies within the most recent millennium with a focus on the northern hemisphere

dependence of simulation of boreal summer tropical intraseasonal oscillations on the simulation of seasonal mean the link between realism in simulation of the seasonal mean precipitation and summer tropical intraseasonal oscillations and their dependence on cumulus parameterization schemes is investigated using the florida state university global spectral model fsugsm forty member model ensemble simulations of the northern summer season are generated for three different cumulus parameterization schemes namely arakawa schubert naval research laboratory nrl zhang and mcfarlane national center for atmospheric research ncar and emanuel massachusetts institute of technology mit the mit scheme simulates the regional pattern of seasonal mean precipitation over the indian monsoon region well but has large systematic bias in simulating the precipitation over the western pacific and the maritime continent although the simulation of details of regional distribution of precipitation over the indian monsoon region by the nrl and ncar schemes is not accurate they simulate the spatial pattern of precipitation over the tropical indo pacific domain closer to observation the nrl scheme seems to captures the observed northward and eastward propagation of intraseasonal precipitation anomalies realistically however the simulations of the ncar and mit schemes are dominated by a westward propagating component the westward propagating mode seen in the model as well as observations is indicated to be an equatorial rossby wave modified by the northern summer mean flow an examination of the relationship between simulation of the model climatology and eastward propagating character of monsoon intraseasonal oscillations isos in a limited sample shows that the scheme that simulates better seasonal mean pattern of rainfall over the tropical indo pacific domain also simulates better intraseasonal variance and more realistic eastward propagation of monsoon isos among the parameters known to be important for meridional propagation of the summer monsoon isos the meridional gradient of mean humidity in the lower atmosphere seems to be crucial in determining the northward propagation in the equatorial indian ocean between 10 s and 10 n for better prediction of the seasonal mean indian monsoon therefore the model climatology should have minimum bias not only over the indian monsoon region but also over the entire indo pacific basin

laminated sediments in the bay of la paz gulf of california a depositional cycle regulated by pluvial flux core bap96 cp sampled from the deepest part of the bay of la paz gulf of california has been analysed sedimentologically taking into account regional climate and oceanography laminated sediments at the bottom of the bay are essentially not bioturbated by benthic fauna a subanoxic condition o 2 0 2 ml l 1 inhibits the proliferation of benthic fauna within the bay the relative abundances of terrigenous and biogenic inputs change periodically the terrigenous input is greater than the biogenic input and apparently experiences larger fluctuations the terrigenous input dominates in dark laminae whereas the biogenic input mostly occurs in light laminae thus it is assumed that down the core the alternation of dark and light laminae represents cycles in the extent of dilution of the biogenic input by terrigenous input the terrigenous input into the bay of la paz is mostly regulated by pluvial runoff thus its temporal fluctuation follows the periods shown by the regional pluvial regime particularly the 11 2 year period this is equal to the frequency of sunspot cycles

silica polymorphs in lunar granite implications for granite petrogenesis on the moon granitic lunar samples largely consist of granophyric intergrowths of silica and k feldspar the identification of the silica polymorph present in the granophyre can clarify the petrogenesis of the lunar granites the presence of tridymite or cristobalite would indicate rapid crystallization at high temperature quartz would indicate crystallization at low temperature or perhaps intrusive slow crystallization allowing for the orderly transformation from high temperature silica polymorphs tridymite or cristobalite we identify the silica polymorphs present in four granitic lunar samples from the apollo 12 regolith using laser raman spectroscopy typically lunar silica occurs with a hackle fracture pattern we did an initial density calculation on the hackle fracture pattern of quartz and determined that the volume of quartz and fracture space is consistent with a molar volume contraction from tridymite or cristobalite both of which are less dense than quartz moreover we analyzed the silica in the granitic fragments from apollo 12 by electron probe microanalysis and found it contains up to 0 7 wt tio2 consistent with initial formation as the high temperature silica polymorphs which have more open crystal structures that can more readily accommodate cations other than si the silica in apollo 12 granitic samples crystallized rapidly as tridymite or cristobalite consistent with extrusive volcanism the silica then inverted to quartz at a later time causing it to contract and fracture a hackle fracture pattern is common in silica occurring in extrusive lunar lithologies e g mare basalt the extrusive nature of these granitic samples makes them excellent candidates to be similar to the rocks that compose positive relief silicic features such as the gruithuisen domes

realistic initiation and dynamics of the madden julian oscillation in a coarse resolution aquaplanet gcm 1 the main mechanisms for the initiation and propagation of the madden julian oscillation mjo are still widely debated the capacity of operational global climate models gcms to correctly simulate the mjo is hindered by the inadequacy of the underlying cumulus parameterizations here we show that a coarse resolution gcm coupled to a simple multicloud model parameterization mimicking the observed dynamics and physical structure of organized tropical convection simulates the mjo in an idealized setting of an aquaplanet without ocean dynamics we impose a fixed nonhomogeneous sea surface temperature replicating the indian ocean western pacific warm pool this results in a succession of mjos with realistic phase speed amplitude and physical structure each mjo event is initiated at a somewhat random location over the warm pool and dies sometimes near the eastern boundary of the warm pool and sometimes at a random location way beyond the warm pool also occasionally the mjo events stall at the center of maximum heating this is reminiscent of the fact that in nature some mjos stall over the maritime continent while others reach the central pacific ocean and beyond the initiation mechanism in the model is believed to be a combination of persistent intermittent convective events interacting with observed large scale flow patterns and internal tropical dynamics the large scale flow patterns are associated with planetary scale dry kelvin waves that are triggered by preceding mjo events and circle the globe while congestus cloud decks on the flanks of the warm pool are believed to force rossby gyres which then funnel moisture toward the equatorial region

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

the asian summer monsoon an intercomparison of cmip5 vs cmip3 simulations of the late 20th century the boreal summer asian monsoon has been evaluated in 25 coupled model intercomparison project 5 cmip5 and 22 cmip3 gcm simulations of the late twentieth century diagnostics and skill metrics have been calculated to assess the time mean climatological annual cycle interannual variability and intraseasonal variability progress has been made in modeling these aspects of the monsoon though there is no single model that best represents all of these aspects of the monsoon the cmip5 multi model mean mmm is more skillful than the cmip3 mmm for all diagnostics in terms of the skill of simulating pattern correlations with respect to observations additionally for rainfall convection the mmm outperforms the individual models for the time mean the interannual variability of the east asian monsoon and intraseasonal variability the pattern correlation of the time pentad of monsoon peak and withdrawal is better simulated than that of monsoon onset the onset of the monsoon over india is typically too late in the models the extension of the monsoon over eastern china korea and japan is underestimated while it is overestimated over the subtropical western central pacific ocean the anti correlation between anomalies of all india rainfall and nino3 4 sea surface temperature is overly strong in cmip3 and typically too weak in cmip5 for both the enso monsoon teleconnection and the east asian zonal wind rainfall teleconnection the mmm interannual rainfall anomalies are weak compared to observations though simulation of intraseasonal variability remains problematic several models show improved skill at representing the northward propagation of convection and the development of the tilted band of convection that extends from india to the equatorial west pacific the mmm also well represents the space time evolution of intraseasonal outgoing longwave radiation anomalies caution is necessary when using gpcp and cmap rainfall to validate 1 the time mean rainfall as there are systematic differences over ocean and land between these two data sets and 2 the timing of monsoon withdrawal over india where the smooth southward progression seen in india meteorological department data is better realized in cmap data compared to gpcp data

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

climate and ocean variability during the middle and late holocene recorded in laminated sediments from alfonso basin gulf of california mexico a laminated sequence core bap96 cp 24 38 12 n 110 33 24 w 390 m depth from the alfonso basin in bay of la paz southern gulf of california contains a record of paleoceanographic and paleoclimatic changes of the past 7900 yr radiolarian assemblages and magnetic susceptibility are used as proxies of oceanographic and climatic variability the records provide a regional scenario of the middle and late holocene suggesting two major climatic regimes and several millennial scale events conditions relatively warmer and drier than today occurred from 7700 to 2500 cal yr bp promoting the intensification of evaporation processes and the prevalence of the gulf of california water in the basin these conditions correlate with strong droughts in the middle holocene of north america and with minimal incursion of tropical waters into the gulf of california proxies indicate a warm scenario and the dominance of the equatorial surface water in the alfonso basin from 2400 to 700 cal yr bp suggesting the intensification of enso cycles a climatic signal between 1038 and 963 cal yr bp may be correlated with global signal of the medieval warm period several cooling events are recognized at 5730 3360 2700 1280 and 820 cal yr bp and are associated with intensification of northwest winds leading to upwellings and enhanced productivity in the basin

temperature variability in the gulf of california during the last century a record of the recent strong el nino the oxygen isotopic ratio of diatom silica from a box core collected on the eastern slope of the guaymas basin gulf of california has been analyzed this core covers the last 90 years the isotopic record indicates a progressive and continuous temperature increase of about 8 c from the end of the last century until 1980 with superimposed rapid temperature fluctuations of 2 to 4 c although the gulf of california is not directly under the influence of el nino short temperature increases may be associated with the el nino events described by quinn et al 1987 the longer term changes are attributed to a decrease of upwelling intensity linked to weakening of the trade winds in the northern hemisphere

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

antecedents and self induction of active break south asian monsoon unraveled by satellites 1 understanding the origin and perpetuation of the monsoon cycle has eluded scientists for decades using a suite of unprecedented satellite measurements we show that the antecedents of the active break monsoon emerge in the western equatorial indian ocean eio the initiation of a new rainy phase in the western eio is preceded by in situ surface wind convergence and central eio warming both are induced by the subdued condition over the eastern eio set up in the previous cycle thus a self induction mechanism appears to be operating in maintenance of the indian monsoon intraseasonal oscillation the finding here offers a focus for prediction of the active break indian monsoon with potential predictability about four weeks in advance

a 20 year varve record of siliceous phytoplankton variability in the central gulf of california abstract year to year variability in the structure of the preserved siliceous phytoplankton assemblage is reconstructed from a box core retrieved from the varved sediments along the guaymas slope of the gulf of california a 20 year record from 1953 through 1972 is obtained from interpretation of the varve stratigraphy supported by 210 pb and 228 th dating ecological time series derived from microfossil analysis show a strong coherence with interannual sea level anomalies indicating a response to large scale climatic variability associated with the el nino southern oscillation phenomenon el nino periods are generally marked by increases in preserved abundances of the total siliceous assemblage and in particular by greater numbers of individuals within species whose distribution is limited to tropical and subtropical waters

the annual particle cycle in lake van turkey abstract the varved sediments of lake van provide a high quality continental archive of seasonal to decadal scale climate variability in order to read the natural record modern varve formation was studied on the basis of 1 remotely sensed total suspended matter tsm rs concentrations 2 time series of particle flux and water temperatures and 3 turbidity temperature and oxygen profiles tsm rs validated by contemporaneous water column sampling shows great temporal and lateral variations whitings and turbidity plumes from 2006 to 2009 sequential sediment traps recorded high particle fluxes during spring and fall medium fluxes during summer and almost zero flux during winter the mean total mass flux of 403 mg m 2 day 1 comprised 33 seasonally up to 67 calcium carbonate 7 aquatic organic matter 6 biogenic opal and 54 detrital minerals the caco 3 fluxes are controlled by river discharge precipitation and snowmelt during spring by high productivity during summer and by river discharge precipitation before snowfall starts and mixing during fall in november 2007 an anomalously high caco 3 flux occurred as a result of a warm water surface supersaturated with calcite coinciding with an anomalous runoff event the results demonstrate that the couplets of light and dark laminae in the short sediment cores are true varves representing spring summer fall and winter conditions respectively consequently varve formation can be linked to the seasonal climate pattern providing a calibration that can be used to interpret the partially varved paleo record of lake van and related environmental processes

oceanographic considerations for the application of the alkenone based paleotemperature u37k index in the gulf of california abstract alkenone concentrations were determined in sediment trap samples and surficial sediments collected from guaymas basin gulf of california to investigate the factors that control the relationship between the u37k index and sst the results from the sediment trap study reveal a positive correlation r2 0 5 between alkenone fluxes and satellite avhrr sea surface temperature sst and a strong correlation r2 0 9 between u37k and sst over an annual temperature range of 20 c although sst and u37k are tightly coupled throughout two upwelling seasons the relationship deviates from the expression developed by prahl et al 1988 at temperatures higher than 26 c the possible reasons for this deviation are varied but include the observed changes in the coccolithophore species assemblage and the evolution of the thermocline during periods of high sst the seasonal pattern of alkenone fluxes higher fluxes during warm periods observed throughout the 1996 to 1997 study period causes a bias in the annually averaged u37k record resulting in temperature estimates that are 1 c higher than the annual avhrr sst average furthermore the u37k ratios obtained from core top sediments indicate an additional 2 c warm bias in the sedimentary record that may be related to the lateral inputs of alkenones from other regions of the gulf these results highlight the importance of oceanographic processes in determining the alkenone temperature signal that is preserved in sediments after accounting for such effects u37k ratios from a box core were used to reconstruct a sst record extending back to the 18th century for the guaymas basin these results indicate a steady 2 c warming of the surface waters of the gulf from early 1700s to the 1950s followed by a rapid apparent 1 c cooling between the 1950s and the 1980s

sediment accumulation in the central western black sea over the past 5100 years the postdepositional particle flux accumulation rate over the last 5100 years was studied in the anoxic sediment units i and ii from the central western black sea deposition of unit ii sapropel in the deep black sea basin was divided further into two subunits the beginning of the deposition of the sapropel in the black sea 5100 3100 years b p subunit iib was characterized by higher organic carbon accumulation rates due largely to higher primary production accumulation rates of lithogenic matter were at a minimum compared to younger units during the subsequent 2100 years 3100 1000 years b p subunit iia organic carbon accumulation rates decreased considerably while accumulation rates of lithogenic matter increased to the present level at 1000 years b p unit i total mass accumulation rates increased by a factor of 3 this increase was largely a result of an increase in carbonate accumulation rates by a factor of 11 which was caused by the rapid appearance of emiliania huxleyi in the black sea higher carbonate accumulation rates in unit i are mainly the cause for the considerably lower organic carbon content compared to unit ii since the organic carbon accumulation rate in unit i did not decrease general correspondence of accumulation rates of lithogenic matter in different cores through time suggests overregional long term 100 year scale climatic effects on the terrigenous particle supply to the black sea

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

evidence for abrupt climate changes in annually laminated marine sediments annually laminated sediments from marine or lacustrine settings represent valuable high resolution archives of climate change that record variation due to changing precipitation and run off from land or variation in biological productivity and flux in the water column because of their annual resolution such sediments may capture abrupt changes of interannual to decadal scales rivaling corals and ice cores in resolution laminated sediments often occur intermittently in the sediment column and the onset and cessation of laminae commonly record the abrupt crossing of thresholds related to climate change for example in the degree of oxygenation of bottom waters such records from marginal basins and continental margins have been pivotal in demonstrating that abrupt changes hitherto documented only in high latitude ice cores are synchronous with climatic change at low latitudes these insights into global teleconnections have improved our understanding of the mechanisms of rapid climate change in deep sea settings the discovery of the episodic occurrence of laminated diatom rich sediments in the equatorial pacific and southern ocean provides evidence for massive climate related biogeochemical excursions tied to abrupt changes in the input distribution and availability of nutrients in the oceans

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

iunconsistencies in accumulation rates of black sea sediments inferred from records of laminae and 210pb recently published estimates for the age of the unit 1 unit 2 contact in black sea sediments based on accelerator mass spectrometry ams 14c measurements jones 1990 calvert et al 1991 appear to be older than those based on the previously published chronology based on lamina couplets degens et al 1980 hay 1988 by a factor of 2 to 3 to help reconcile the differences we compare sediment accumulation rates based on the 210pb method with estimates based on lamina counts for two cores from the black sea abyssal plain accumulation rates estimated using the 210pb technique have varied little over the last 150 years from the averages of 55 and 50 g m 2 yr 1 at stations in the western and eastern basins respectively these values are about a factor of 2 lower than accumulation rates derived by counting lamina couplets over the dated intervals close examination of the laminae suggests that the discrepancy exists both because it is difficult to count the very fine laminae and because a complete couplet is not deposited every year in order to provide a useful stratigraphic horizon for future investigators studying sedimentary records of the black sea we estimate the age of a distinct black marker horizon which can be easily identified across the entire abyssal plain to be 150 8 years deposited in 1838 8 a d

variations of upwelling intensity recorded in varved sediment from the gulf of california during the past 3 000 years circulation in the pacific ocean is periodically affected by el nino events which are a direct response to intensity changes in trade winds1 2 the appearance of anomalously warm surface water in the eastern equatorial pacific ocean is one of the most spectacular manifestations of this event warm surface water anomalies are also observed in the northern hemisphere along the californian coast and in the gulf of california in the gulf strengthened trade winds induce upwelling during the winter whereas in the summer prevailing southerly winds provoke an input of warm water from the south3 we have sampled laminated sediments from the slopes of guaymas basin to reconstruct with high resolution variations of the hydrology of surface waters in the central part of the gulf of california sedimentation rate is of the order of 4 mm yr 1 at the top and 1 2 mm yr 1 down core by analysing the oxygen isotope ratio of biogenic silica of diatoms4 we have recorded the surface water temperature variations in the guaymas basin the comparison of these fluctuations and variations of silicoflagellate abundance has allowed us to reconstruct changes in upwelling intensity during the past three thousand years the present conditions of low upwelling activity are seen to be abnormal in comparison with those prevailing in the past

opal and organic carbon in laminated diatomaceous sediments saanich inlet santa barbara basin and the miocene monterey formation abstract laminated biosiliceous sediments from saanich inlet british columbia si the monterey formation california mf and santa barbara basin california sbb are organic rich and were studied to assess the suitability of si and sbb as modern analogs of the miocene mf and to explore the controls on distributions of opal and organic carbon to this end individual laminae and groups of laminae extracted from odp cores and outcrop samples were analyzed using a multi tracer geochemical approach total organic carbon opal c n ratios 13 c of organic matter om kerogen type and major and minor element abundances were measured si sediments are 52 84 detrital 15 45 opal and 1 2 organic carbon 13 c and c n ratios indicate a marine source of the om present in the sediments samples from the upper siliceous member of the mf are 6 41 detritus 28 87 opal and 1 5 organic carbon kerogen types c n ratios and 13 c data are suggest mixed but predominantly marine om sbb samples are 59 90 detritus 6 34 opal 3 22 calcite and 1 5 percent organic carbon si and sbb have similar bulk compositions with the exception of the presence of calcite in sbb samples mf sediments have significantly lower detrital and higher opal contents than si and sbb samples these large differences suggest that si and sbb are not appropriate modern analogs for the mf in si sediments organic carbon is concentrated in opal rich detritus lean laminae and intervals this distribution suggests that the coupling of opal and om created in the surface ocean by diatom productivity is preserved in the sediment record in the mf opal and toc are negatively correlated implying that the coupling of opal and organic carbon did not survive the processes of settling sedimentation diagenesis and or weathering this decoupling of organic carbon and opal in the mf is attributed to dilution of om by high opal flux rates and or the respiration and or redistribution of om during diagenesis and or weathering

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

reconstructing benthic carbon oxidation rates using δ13c of benthic foraminifers abstract in non bioturbated organic rich marine sediments the concentration and carbon isotope gradient of total dissolved carbon dioxide co2 primarily reflects the rate of carbon oxidation and co2 diffusion within the sediment pore waters here we investigate whether the calcium carbonate secreted by benthic foraminifers that inhabit discrete depths within the sediments record the pore water 13c co2 gradient and hence can be used as proxies to reconstruct a history of carbon oxidation change the distribution and live abundance of bolivina argentea s l bolivina subadvena s l and buliminella tenuata inhabiting the dysoxic marine sediments along the california margin is similar among sites that differ in co2 gradient by up to a factor of three bolivina argentea inhabits the sediments at the sediment water interface whereas b subadvena s l is most abundant at depths of between 2 and 4 mm buliminella tenuata is most abundant at deeper depths of between 4 and 6 mm the 13c of calcite precipitated by these species matches the 13c of the pore water co2 at the depth of their maximum live abundance indicating that each species has a preferred depth for calcification the 13c difference between the species increases as the rate of carbon oxidation increases these results indicate the carbon isotopic difference between these species in fossil assemblages can be used to estimate changes in the rate of carbon oxidation

highly silicic compositions on the moon using data from the diviner lunar radiometer experiment we show that four regions of the moon previously described as red spots exhibit mid infrared spectra best explained by quartz silica rich glass or alkali feldspar these lithologies are consistent with evolved rocks similar to lunar granites in the apollo samples the spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar the variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the moon basaltic underplating is the preferred mechanism for silicic magma generation leading to the formation of extrusive landforms this mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

sea surface temperature anomalies associated with the 1997 1998 el nino recorded in the oxygen isotope composition of planktonic foraminifera anomalously warm sea surface temperatures and associated high rainfall propagated northward from the eastern equatorial pacific along the western margin of north america during the 1997 1998 el nino we present data from the guaymas basin gulf of california and the santa barbara basin southern california borderlands that clearly demonstrate that the oxygen isotope composition of planktonic foraminifera accurately records the local sea surface temperature changes related to the el nino phenomenon on the basis of this observation the varved sediments accumulating in these basins should contain a detailed history of both the occurrence and intensity of past el nino events

response of the north american monsoon to regional changes in ocean surface temperature 1 the north american monsoon nam an onshore wind shift occurring between july and september has evolved in character during the holocene largely due to changes in northern hemisphere insolation published paleoproxy and modeling studies suggest that prior to 8000 cal years bp the nam affected a broader region than today extending westward into the mojave desert of california holocene proxy sst records from the gulf of california goc and the adjacent pacific provide constraints for this changing nam climatology prior to 8000 cal years bp lower goc ssts would not have fueled northward surges of tropical moisture up the goc which presently contribute most of the monsoon precipitation to the western nam region during the early holocene the north pacific high was further north and ssts in the california current off baja california were warmer allowing monsoonal moisture flow from the subtropical pacific to take a more direct northwesterly trajectory into an expanded area of the southwestern u s west of 114 w a new upwelling record off southwest baja california reveals that enhanced upwelling in the california current beginning at 7500 cal year bp may have triggered a change in nam climatology focusing the geographic expression of nam in the southwest usa into its modern core region east of 114 w in arizona and new mexico holocene proxy precipitation records from the southwestern u s and northwestern mexico including lakes vegetation pollen and caves are reviewed and found to be largely supportive of this hypothesis of changing holocene nam climatology

simulation of monsoon intraseasonal oscillations in a coarse resolution aquaplanet gcm the skill of the global climate models gcms to realistically simulate the monsoon intraseasonal oscillations misos is related to the sensitivity of their convective parameterization schemes here we show that by coupling a simple multicloud parameterization to a coarse resolution aquaplanet gcm realistic misos can be simulated we conduct three different simulations with a fixed nonhomogeneous sea surface temperature mimicking the indian ocean western pacific warm pool wp centered at the three latitudes 5 n 10 n and 15 n respectively to replicate the seasonal migration of the tropical convergence zone tcz this results in the generation of mean circulation resembling the monsoonal flow pattern in boreal summer succession of eastward propagating madden julian oscillation mjo disturbances with phase speed amplitude and structure similar to summer mjos are simulated when the wp is at 5 n when the wp is located over 10 n northward and eastward propagating misos are simulated this case captures the meridional seesaw of convection between continental and oceanic tcz observed during boreal summer over south asia westward propagating rossby wave like disturbances are simulated when the wp is over 15 n congruous with the synoptic disturbances seen over the monsoon trough the initiation of intraseasonal oscillations in the model can occur internally through organization of convective events above the wp associated with internal dynamics

dinoflagellate cysts and enso pdo climate forcing in the southern gulf of california abstract this paper presents a high resolution analysis of dinoflagellate cyst groups 1959 to 2009 in the southern gulf of california goc we analyzed 100 samples of laminated sediments with an effective sampling resolution of 7 months our primary goal is to clarify the relation between changes in these groups and the climate forcing defined by the el nino southern oscillation enso and pacific decadal oscillation pdo indices principal component analysis indicates three groups a1 a2 and a3 a1 and a3 are mostly constituted by dinoflagellate cysts of heterotrophic taxa while a2 is composed mainly of autotrophic taxa strong el nino events decrease the contribution of all dinoflagellate cyst groups while extreme la nina events increase the contribution of the a2 and a3 groups also the pdo modulates the marine productivity in the southern goc with cold phases increasing productivity while the warm stages decrease productivity as with climatic events in the southern goc autotrophic and heterotrophic taxa of dinoflagellate cysts respond clearly when pdo and enso are in phase finally dinoflagellate cyst concentrations in laminated sediments can be used regionally as a chronostratigraphic tool in the last 50 years

northward propagation initiation and termination of boreal summer intraseasonal oscillations in a zonally symmetric model abstracta simple multilayer zonally symmetric model using a multicloud convective parameterization and coupled to a dynamical bulk atmospheric boundary layer is used here to simulate boreal summe

early holocene decadal scale ocean variability recorded in gulf of california laminated sediments scanning electron microscope examination of holocene laminated sediment from guaymas basin gulf of california resolves up to five depositional events per year each lamina sublamina of an early holocene section of continuously laminated sediment was recorded from backscattered electron imagery photomosaic analysis diatom mat laminae composed predominantly of thalassiothrix longissima are associated with early winter mixed diatom flora laminae mats are probably brought into the gulf with pacific water during the summer concentrated at the surface or at the pycnocline and then rapidly deposited in the early winter as water column stratification breaks down time series analysis of one 300 year section from piston core jpc56 revealed significant periodicities in the deposition of mat laminae at 50 years 11 years and 22 24 years an 50 year cycle in fish populations has been related to changing north pacific ocean atmosphere circulation these pacific wide changes in circulation affect the currents dominant at the mouth of the gulf when the california current is dominant fewer diatom mats are imported into the gulf and when the north equatorial pacific gyre is dominant more are imported the 11 year 22 to 24 year and 50 year cycles are all suggested to be influenced by solar cycles

the origin of eucrites diogenites and olivine diogenites magma ocean crystallization and shallow magma chamber processes on vesta the asteroid 4 vesta is one of the very few heavenly bodies to have been linked to samples on earth the howardite eucrite diogenite hed meteorite suite this large and diverse suite of meteorites provides a detailed picture of vesta s igneous and postigneous history we have used the range of igneous rock types and compositions in the hed suite to test a series of chemical models for solidification processes following peak melting magma ocean conditions on vesta fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive fe enrichment in the melt models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates diogenites our best models invoke 60 70 equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush magmatic recharge can produce all of the igneous hed lithologies noncumulate and cumulate eucrites diogenites dunites harzburgites and olivine diogenites magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites we predict an internal structure for vesta that permits excavation of the heds during the formation of the rheasilvia basin while remaining consistent with observations from the dawn mission and most impact models

biogenic and abiogenic components of laminated hemipelagic sediments in the central gulf of california abstract alternating light and dark submillimeter to millimeter thick layered sediments rhythmites are found along the slopes of the central and southern gulf of california where a strong oxygen minimum zone intersects the sediment water interface two short intervals of distinct alternations were sampled lamina by lamina from two cores in the central gulf both cores are from the slope of the guaymas basin one core is from the mainland side the other core is from the baja side each lamina sample was analyzed for its opal micro floral assemblage textural character trace metal and bulk chemical cu mn fe ni zn ca k al sio2 and c org content and mineralogy on both sides of the gulf the light laminae contain more diatom frustules up to 90 and less terrigenous and organic material than the dark laminae the sediment is predominantly silt sized the dark laminae contain more terrigenous material which is primarily clay size on both sides of the gulf the light laminae apparently represent sedimentation during the dry winter season of northwesterly winds whereas the dark laminae represent the wet summer season of southeasterly winds

the great lunar hot spot and the composition and origin of the apollo mafic lkfm impact melt breccias thorium rich mafic impact melt breccias from the apollo 14 17 missions that is those breccias identified with the composition known as lkfm are regarded largely as products of basin forming impacts that penetrated the feldspathic crust and sampled underlying mafic material and magma ocean residuum carrying the compositional signature of kreep potassium rare earth elements phosphorous despite considerable compositional variation among such breccias compositions of all of them correspond to mixtures of only four components 1 a norite with composition generally similar to that of apollo 15 basalt mean abundance 58 range 30 95 2 fo 90 dunite mean 13 range 1 27 3 feldspathic upper crust mean 29 range 4 50 and feni metal 0 1 1 7 petrographic evidence has shown that much of the feldspathic component but none of the kreep component is clastic this observation and the high proportion of kreep norite component in the breccias suggest that the melt zone of the impact or impacts forming the breccias contained little feldspathic material but consisted predominantly of material with the average composition of kreep norite the dunite component probably derives ultimately from the upper mantle these conclusions support the hypothesis that the breccias were not formed in typical feldspathic crust but instead by one or more impacts into what is designated here the great lunar hot spot that is the anomalous th rich terrane in the imbrium procellarum area identified by the apollo and lunar prospector gamma ray spectrometers the lkfm composition is a special product of the great lunar hot spot and is not the average composition of the lower crust in typical feldspathic highlands similarly mg suite and alkali suite plutonic rocks of the apollo collection are likely all differentiation products of the hot spot not of plutons that might occur in typical feldspathic crust

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

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

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

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

the madden julian oscillation in echam6 and the introduction of an objective mjo metric this study presents a quantitative evaluation of the simulated madden julian oscillation mjo in an ensemble of 42 experiments performed with echam6 and previous echam versions the echam6 experiments differ in their parameter settings resolution and whether the atmosphere is coupled to an ocean or not the analysis concentrates on a few basic features of the mjo namely the signatures of convection precipitation coupled with the circulation system and the eastward propagation strength of outgoing longwave radiation olr and 850 and 200 hpa zonal winds within the mjo related frequency wavenumber range it also examines whether precipitation and olr show similar signatures in the mjo as simulated by echam the experiments reveal an mjo however to different degrees and in different aspects so that a sound assessment requires a multivariate approach in particular the convective rainfall signatures are decoupled from the dynamic signature of the mjo in the simulations herein which eventually leads to the introduction of a new mjo diagram and metric that incorporate olr and the zonal winds in 850 and 200 hpa the analysis here confirms the importance of the convection scheme only with the nordeng modifications to the tiedtke scheme can realistic mjo features be simulated high resolution coupled experiments better represent the mjo as compared to low resolution amip experiments this is shown to follow from two more general findings namely that 1 air sea interaction mainly increases the convective signature and 2 increased resolution enhances eastward propagation

shelf to basin iron shuttle in the guaymas basin gulf of california abstract enrichments of highly reactive iron fe sum of fe oxyhydr oxide carbonate and sulfide minerals in marine sediments and sedimentary rocks are commonly interpreted as an indication of anoxic conditions in the bottom water at the time of deposition the model system for this proxy rationale is the semi restricted black sea where sediments underneath the anoxic and sulfidic i e euxinic deep water are enriched in reactive fe which was mobilized from the surrounding shelf areas to test whether such a shelf to basin fe shuttle can operate in semi restricted basins without euxinic deep water we investigated sedimentary fe speciation and fe isotope compositions in sediments of the guaymas basin gulf of california sediments on the slope underneath the eastern equatorial pacific oxygen minimum zone and sediments within the oxic deep basin are both enriched in reactive fe with reactive fe making up 45 11 of the total fe pool the following mechanisms may contribute to these fe enrichments 1 release of dissolved fe from anoxic shelf and slope sediments followed by lateral transport of dissolved and or particulate fe in the water column 2 preferential transport of fine grained terrigenous particles with a high reactive fe content into the basin 3 microbially mediated conversion of non reactive silicate minerals to reactive fe minerals during transport 4 hydrothermal venting and lateral fe transport within the deep water the first process can explain reactive fe enrichments in slope sediments whereas all processes may contribute to sedimentary fe enrichments in the deeper basin the 56 fe value of sediments increases from shelf to slope and decreases from the slope into the basin this lateral pattern of 56 fe as well as the pattern of fe enrichment is similar to that observed in other marine systems with a fe shuttle however the size of the fe enrichment and the range in 56 fe 0 06 to 0 16 is smaller this difference is due to higher terrigenous sedimentation rates in the guaymas basin and therefore more intense dilution of shuttle derived reactive fe we argue that depending on the extent of bathymetric restriction and terrigenous background sedimentation reactive fe enrichments can form under a broad range of redox conditions and in diverse sedimentary environments the concepts applied in this study can be used to identify those circumstances in the paleo record

organized convection parameterization for the itcz abstractmesoscale convective systems mcss are of fundamental importance in the dynamics of the atmospheric circulation and the climate system they are often observed to develop over significant terrain in ambient shear flows in midlatitudes and embedded within the madden julian oscillation mjo and convectively coupled equatorial wave ccew envelopes as well as in the intertropical convergence zone itcz yet general circulation models gcms fail to resolve these systems and their underlying convective parameterizations are not directed to represent organized circulations shear parallel mcss which are common in the itcz have a three dimensional structure and as such present a serious modeling challenge here a previously developed multicloud model mcm is modified to parameterize mcss one of the main modifications is the parameterization of stratiform condensation to capture extended stratiform outflows which characterize mcss resulting from strong upper level jets linear analysis show

solar forcing of gulf of california climate during the past 2000 yr suggested by diatoms and silicoflagellates abstract high resolution records of the past 2000 yr are compared in a north south transect 28 n to 24 n of three cores from the eastern slopes of the guaymas carmen and pescadero basins of the gulf of california hereafter referred to as the gulf evenly spaced samples from the varved sediments in each core allow sample resolution ranging from 16 to 37 yr diatoms and silicoflagellates capture the seasonal variation between a late fall to early spring period of high biosiliceous productivity that is driven by northwest winds and a summer period of warmer more stratified waters during which these winds slacken and or reverse direction monsoonal flow as these winds decrease tropical waters enter the gulf and spread northward individual samples represent a composite of 7 to 23 yr of deposition and are assumed to record the relative dominance of the winter vs summer floral components intervals of enhanced summer incursion of tropical waters alternating with periods of increased late fall to early spring biosiliceous productivity are recorded in all three cores regularly spaced cycles 100 yr duration of octactis pulchra a silicoflagellate proxy for lower sst and high productivity and azpeitia nodulifera a tropical diatom occur between a d 400 and 1700 in the more nearshore carmen basin core nh01 21 26 3 n suggesting a possible solar influence on coastal upwelling cores bam80 e 17 27 9 n and nh01 26 24 3 n contain longer duration cycles of diatoms and silicoflagellates the early part of medieval climate anomaly a d 900 to 1200 is characterized by two periods of reduced productivity warmer sst with an intervening high productivity cool interval centered at a d 1050 reduced productivity and higher sst also characterize the record of the last 100 to 200 yr in these cores solar variability appears to be driving productivity cycles as intervals of increased radiocarbon production sunspot minima correlate with intervals of enhanced productivity it is proposed that increased winter cooling of the atmosphere above southwest u s during sunspot minima causes intensification of the northwest winds that blow down the gulf during the late fall to early spring leading to intensified overturn of surface waters and enhanced productivity a new silicoflagellate species dictyocha franshepardii bukry is described and illustrated

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

multicloud models for organized tropical convection enhanced congestus heating abstract despite the recent advances in supercomputing the current general circulation models gcms poorly represent the large scale variability associated with tropical convection multicloud model convective parameterizations based on three cloud types congestus deep and stratiform introduced recently by the authors have been revealed to be very useful in representing key features of organized convection and convectively coupled waves here a new systematic version of the multicloud models is developed with separate upper and lower troposphere basis functions for the congestus and stratiform clouds it naturally leads to a new convective closure for the multicloud models enhancing the congestus heating in order to better pinpoint the congestus preconditioning and moistening mechanisms the models are studied here for flows above the equator without rotation effects first the new model results consist of the usual synoptic scale convectively coupled moist gravity wave packets moving at 15 20 m

the mjo and convectively coupled waves in a coarse resolution gcm with a simple multicloud parameterization abstract the adequate representation of the dominant intraseasonal and synoptic scale variability in the tropics characterized by the madden julian oscillation mjo and convectively coupled waves is still problematic in current operational general circulation models gcms here results are presented using the next generation ncar gcm the high order methods modeling environment homme as a dry dynamical core at a coarse resolution of about 167 km coupled to a simple multicloud parameterization the coupling is performed through a judicious choice of heating vertical profiles for the three cloud types congestus deep and stratiform that characterize organized tropical convection important control parameters that affect the types of waves that emerge are the background vertical gradient of the moisture and the stratiform fraction in the multicloud parameterization which set the strength of large scale moisture convergence and unsaturated downdrafts in the wake of deep convection respectively three

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

proteinaceous corals as proxy archives of paleo environmental change abstract high resolution marine data are critical to evaluating anthropogenic impacts on our environment considering the spatial and temporal limitations of direct instrumental measurements proxy data extracted from marine environmental archives are necessary to separate anthropogenic changes from those that would occur naturally the majority of late holocene high resolution environmental reconstructions are derived from marine carbonates including tropical scleractinian corals bivalves crustose coralline algae and sclerosponges however these archives are restricted to the top hundreds of meters of the water column and only preserve environmental variability that is captured by calcium carbonate skeletons at a very few select locations marine sediments archive annual environmental variability in organic and inorganic materials recently additional types of corals are proving to yield information complimentary to these traditional marine archives including cold water scleractinian corals and proteinaceous corals a taxonomically diverse group the proteinaceous corals are broadly defined as those having a branching gross morphology with skeleton comprised at least partly of protein rich organic material they encode characteristics of their food and ambient environment into the chemical and physical composition of their skeleton this environmental encoding combined with their banded skeleton and significant longevity means that proteinaceous corals hold information in their skeleton that helps fill the spatial and temporal gaps in our knowledge of past and present ocean conditions here i review the environmental reconstructions derived from geochemical measurements of the proteinaceous coral skeletons this information is grouped into the mesopelagic environmental variability captured in the skeleton of bamboo corals surface processes captured in the organic skeletons of corals across all ocean depths and environmental variability documented by skeletal radiometric isotopes we include animals from two separate subclasses within the class anthozoa including the parasitic zoanthids that secrete a sclero proteic skeleton since the proteinaceous corals are taxonomically diverse we consider the unique features that define this group of corals including their distribution morphology nutrition and longevity we find that uncertainty surrounding biological parameters limits the precision of reconstructions derived from the calcitic skeleton in contrast analytical effort and cost constrain the number of reconstructions from the organic skeleton through this discussion we provide insights into the uses challenges and directions for future research for this important environmental archive

coccolithophore export production in guaymas basin gulf of california response to climate forcing abstract the flux and taxonomic composition of coccolithophores has been determined for sediment trap samples collected over a two year period from guaymas basin central gulf of california the gulf of california is a subtropical marginal sea with exceptionally high rates of primary productivity the annual biogenic sediment fluxes are largely dominated by silica with diatoms as the major contributor to the opal flux for the july 1990 through november 1992 study period the total coccolithophore export production in guaymas varied in response to the strength of el nino southern oscillation enso coccolithophore production follows the general surface primary productivity pattern with relatively high fluxes from late fall to late winter and low production in the summer when the water column is highly stratified and nutrient depleted high fluxes of up to 10 9 coccoliths m 2 day 1 and 3 10 6 coccospheres m 2 day 1 indicate that coccolithophores are an important component of the phytoplankton population in guaymas basin the intensification of enso conditions during 1992 altered the typical hydrography of the gulf of california by increasing sst and reducing the strength of spring upwelling this is reflected in reduced opal and diatom fluxes during this period conversely these more oligotrophic conditions resulted in higher total coccolithophore fluxes during spring and summer 1992 gephyrocapsa oceanica is present in the gulf throughout the study period but is dominant during weak or non enso times emiliania huxleyi and to a lesser degree florisphaera profunda are abundant during strong enso periods two major coccolithophore signals are indicative of strong enso conditions and could be used as paleo enso indicators in the gulf of california a the switch in dominance between g oceanica and e huxleyi and b high abundances of the deep dwelling species f profunda the abundance of this latter species shows a strong inverse relationship with opal fluxes a comparison of the annual coccolith flux with coccolith accumulation rates in the surface sediments indicates that only about 10 20 of the coccolith export production is preserved in the anoxic sediments of guaymas basin this very low level of preservation is probably due to bacterial processes on the sea floor which cause acidification of the bottom waters at the sediment water interface coccolith accumulation rates are higher in surface sediments from the western coast of the central gulf suggesting both higher coccolithophore production and better preservation in this region probably associated with lower diatom production tintinnids which agglutinate coccoliths are strongly selective for both coccolith size and species

role of stratiform heating on the organization of convection over the monsoon trough it has been recently demonstrated that stratiform heating plays a critical role in the scale selection of organized tropical convection in an aquaplanet version of a coarse resolution atmospheric general circulation model coupled to a stochastic multicloud cumulus parameterization scheme it is shown that madden julian oscillation like organization dominates when the model is tuned to produce strong and long lived stratiform heating while it gives rise to mostly convectively coupled waves in the case of weak and short lived stratiform clouds the study is extended here to the case of an asymmetric forcing mimicking the migration of the intertropical convergence zone itcz during summer to understand the impact of changes in stratiform heating on the monsoon dynamics consistent with the equatorial itcz case strong and long lived stratiform heating promotes northward and eastward moving intraseasonal disturbances while weak and short lived stratiform heating yields mostly westward propgating synoptic scale low pressure systems moreover the underlying intraseasonal versus low pressure system activity seems to impact the strength and extend of the monsoon trough mt in the regime with intraseasonal activity the mt is much stronger and extends northward while in the low pressure system case mt is some what weaker in strength but extends further westward in the low pressure dominated regime the background vorticity and zonal wind profiles over the monsoon trough are consistent with the observations

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

effect of stratiform heating on the planetary scale organization of tropical convection abstractit is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front to rear tilt in the heating profile precipitating stratiform anvils that form from deep convection play a central role in the dynamics of tropical mesoscale convective systems the wide spreading of downdrafts that are induced by the evaporation of stratiform rain and originate from in the lower troposphere strengthens the recirculation of subsiding air in the neighborhood of the convection center and triggers cold pools and gravity currents in the boundary layer leading to further lifting here aquaplanet simulations with a warm pool like surface forcing based on a coarse resolution gcm of approximately 170 km grid mesh coupled with a stochastic multicloud parameterization are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales when the model paramet

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