sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in early to middle ordovician greenhouse oceans article i nfo despite marine geochemical records indicating widespread oxygenation of the biosphere in the terminal neoproterozoic era late cambrian records point to the persistence of deep water anoxia and potential for development of euxinic conditions the late cambrian spice steptoean positive carbon isotope excursion event however is a globally recognized chemostratigraphic marker that likely represents significant organic carbon burial and subsequent liberation of oxygen to the biosphere here we present high resolution carbon and sulfur isotope profiles from early to middle ordovician carbonate rocks from the argentine precordillera and western newfoundland to constrain oceanic redox conditions in the post spice world marine c isotope profiles record relatively stable behavior excursions b3 that is characteristic of greenhouse climates ma rine s isotope profiles record short term b10 6 yr rhythmic variation superimposed over a longer term

changes in antarctic bottom water properties in the western south atlantic in the late 1980s data collected in 1988 1989 as part of the south atlantic ventilation experiment have been combined with the historical database to study the circulation and water mass variability of the abyssal water in the argentine basin a map of potential temperature at 4000 m used as an indication of geostrophic shear defines a south and western intensified crescent shaped abyssal recirculation within this recirculation and its northward extension to the brazil basin antarctic bottom water aabw properties have undergone two modifications during the 1980s 1 the water mass cooled 0 05 c and freshened 0 008 in salinity ratio on surfaces of constant density 2 the densest layer of aabw was altered to less dense water through mixing or advection out of the study area this water mass change does not appear to have affected the flow pattern data collected in 1983 and 1988 to the north in the brazil basin show penetration of the freshwater mass in the deep western boundary current to between 18 s and 10 s indicating very rapid propagation of the anomaly from the argentine basin into the brazil basin as a deep western boundary current it is suggested that open ocean convective events within the weddell sea contributed to the change in aabw documented here

modeling phosphorus cycling and carbon burial during cretaceous oceanic anoxic events article i nfo in the greenhouse world of the cretaceous there were episodes of oxygen depletion in the deep ocean associated with enhanced organic carbon burial in sediments black shale formation in this study we use a box model of the oceanic phosphorus p organic carbon orgc and oxygen cycles to explore the hypothesis that variations in marine p availability control deep ocean oxygen depletion anoxia and the formation of black shales under cretaceous ocean conditions we find that for the cretaceous ocean with large continental shelves slow oceanic overturning and high sea surface temperatures oceanic anoxic events oaes can be triggered by enhanced p supply from land and that the system is particularly sensitive to oceanic mixing in our baseline scenario the deep sea becomes completely anoxic while the shelves attain only partial anoxia sedimentary burial differs between the shelves and open ocean while organic carbon burial is enhanced in both regions deep sea reactive p burial decreases dramatically under anoxia but not on the shelves where oxygen depletion is not complete furthermore our model results imply that oaes can be sustained by p recycling from sediments under low oxygen conditions ultimately however the feedbacks which result in the accumulation of atmospheric oxygen terminate the anoxic event atmospheric oxygen is modulated by land processes such as forest fires and oxidative weathering which limit the rise of atmospheric o2 our model findings are corroborated by p burial data from the geological record for oae2 approximately 94 myr bp through a sensitivity analysis we identify two necessary criteria for oaes low mixing of surface and deep waters poor ocean ventilation and enhanced sedimentary p recycling under low oxygen conditions when these criteria are met ocean anoxia is a robust result to a mild increase of continental supply of phosphorus under a wide range of environmental conditions

faunal turnovers in central pacific benthic foraminifera during the paleocene eocene thermal maximum abstract although it is well known that the paleocene eocene thermal maximum petm coincided with a major benthic foraminiferal extinction event the detailed pattern of the faunal turnover has not yet been clarified our high resolution benthic foraminiferal and carbon isotope analyses at the low latitude pacific ocean shatsky rise have revealed the following record of major faunal transitions 1 an initial turnover which involved the benthic foraminiferal extinction event bfe the bfe marked by a sharp transition from pre extinction fauna to disaster fauna represented by small sized bolivina gracilis expresses the onset of the petm and the abrupt extinction of about 30 of taxa this faunal transition lasted about 45 74 kyr after the initiation of the petm and was followed by 2 the appearance of opportunistic fauna represented by quadrimorphina profunda which existed for about 74 91 kyr after the initiation of the petm these two faunas which appeared after the extinction event are characterized by low diversity and dwarfism possibly due to lowered oxygen condition and decreased surface productivity the second pronounced turnover involved the gradual recovery from opportunistic fauna to the establishment of recovery fauna which coincided with the recovery about 83 91 kyr after its initiation

evolution in the test size of deep sea benthic foraminifera during the past 120 m y evidence is presented for stratigraphic variations in test size of the largest deep water 1500 m water depth calcareous trochospiral benthic foraminifera for eight dominant lineages composed of ten genera over the past 120 m y variations in test size show 1 a general trend of increasing test size during the past 120 m y and 2 fluctuations highlighted by six minima and six maxima that are synchronized among genera the long term increase in size corresponds to an increase in the 18o of deep water benthic foraminifera the minimum and maximum sizes correspond to minima and maxima in the 18o respectively in addition three major minima in test size correspond to distinct low dissolved oxygen events these latter synchronisms indicate that oceanic climate and dissolved oxygen or related factors likely controlled evolution in test size of deep water calcareous trochospiral benthic foraminiferal genera

nearshore euxinia in the photic zone of an ancient sea part ii the bigger picture and implications for understanding ocean anoxia abstract biomarker palaeontological and isotopic evidence suggests that the late permian carbonate seas i e the northern npb and southern spb permian basins of northern pangea were characterized by significant spatial and temporal variations in the palaeowater column redox state this is particularly the case with regard to the deposition of the lopingian zechstein cycle 2 carbonate rocks a shelf to basin reconstruction of environmental conditions was achieved by analysing nearly 400 core samples from 49 wells this allowed an evaluation of the spatial variations in facies and broad oceanographic conditions at the basin scale specifically in the lower slope and shallow basin facies of the northern margin of the spb present day northern poland and eastern germany highly variable concentrations of the green sulphur bacterial biomarkers chlorobactane and isorenieratane and their likely degradation products c 15 to c 31 2 3 6 aryl isoprenoids indicative of photic zone euxinia and homohopane indices indicative of anoxia combined with the presence of a benthic fauna and bioturbation indicate a variable but occasionally anoxic euxinic water column locally in lagoonal facies in the northern and southern margin of the spb euxinic conditions also developed but these were likely associated with localised conditions or benthic production in association with microbialites the presence of gammacerane in the eastern spb south eastern germany and eastern poland suggests elevated salinities there compatible with the restricted configuration of the basin however a lack of these signatures in basinal settings of the eastern spb indicates that strongly reducing conditions were restricted to the lower slope and shallow basin locations and restricted lagoons and were not developed in the basin centre moreover this anoxia euxinia in marginal settings is restricted to the north eastern part of the spb the south eastern part of the spb se poland in contrast is devoid of evidence for pze the southern margin of the spb is also characterized by generally oxic suboxic conditions with local anoxia limited to more restricted embayments and elevated salinities limited to restricted oxic anoxic lagoons in the western spb ne england and adjacent offshore and the npb outer moray firth offshore scotland the water columns were oxic suboxic overall it appears that high but episodic primary bioproductivity of organic matter was concentrated on or even limited to the lower slopes of the spb s north eastern margin and the restricted lagoons and shallow basin of its southern margin leading to the formation of source rocks for petroleum in these areas in addition the temporal and geographical restriction of anoxia appears to have prevented the accumulation of large and more widespread quantities of organic matter in fact toc contents exhibit a poor correlation with ecological and anoxia indicators crucially this work confirms that the strong evidence for pze observed in shelf and lower slope shallow basin facies of the north eastern spb need not be associated with widespread basin scale anoxia this conclusion has implications for organic matter burial carbon cycling and biotic crises during other times in earth history

stratigraphy and ductile structure of the presidential range new hampshire tectonic implications for the acadian orogeny the presidential range of new hampshire with its unique high relief contains exceptionally well exposed rocks of the acadian orogenic hinterland these rocks are within the central maine terrane a belt of complexly metamorphosed and deformed silurian and devonian metasedimentary rocks the presidential range lies between regions to the south dominated by refolded nappes and synkinematic high grade regional metamorphism and regions to the northeast dominated by overlapping multiple deformation and contact metamorphism produced by late and post acadian plutons to better understand these complex tectonic variations and in particular to clearly and accurately determine the effects of the devonian acadian orogeny in a well exposed region the bedrock geology in the alpine zone of the presidential range was mapped in great detail the results of the stratigraphic and ductile structural analyses are presented here five metasedimentary formations have been recognized and constitute a conformable stratigraphy which from oldest to youngest are the silurian rangeley perry mountain smalls falls and madrid formations and the devonian littleton formation the littleton formation has been subdivided into fifteen different members and three submembers based on variations in bedding style of the schists and quartzites and other lithologic peculiarities the madrid smalls falls and perry mountains formations are extremely thin consistent with their deposition near the silurian tectonic hinge the rangeley formation is interpreted as an olistostromal melange and has been subdivided into three different members and six submembers on the basis of lithologic variations in the gneiss and subordinate units the presidential range preserves three phases of ductile folding f1 f2 and f3 and a single phase of thrust faulting t1 well constrained southeast east or northeast facing directions and consistent asymmetry of f1 nappe limbs suggest that nappe vergence was easterly severe refolding of some nappes resulted during f2 collapse of the nappe pile the west vergent greenough spring thrust fault truncated f1 and f2 structures and juxtaposed nonmigmatized and migmatized rocks f3 east vergent folding dominates the alpine zone and represents the final tightening of acadian structures which occurred after early granitic plutonism and prior to the emplacement of postkinematic granitic sheets the structural and sedimentological evidence supports the existence of a subduction system that was active beginning in the early silurian on the east flank of the bronson hill anticlinorium with a west dipping subducting slab geometry this system persisted throughout the acadian

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

long period changes in the bottom water flowing through vema channel further details of the warming of bottom water flowing through the vema channel first reported by zenk and hogg 1996 are given because cross channel gradients of temperature are large and the channel is narrow careful analysis is required to determine whether or not the bottom water temperature minimum was adequately sampled by a particular station or cruise during a period from 1972 to 1996 at least 14 visits with quality hydrographic measurements have been made to the region of these 11 were judged successful and their data indicate an abrupt rise in potential temperature by 0 03 c from 0 18 c to 0 15 c in the early 1990s that has remained until the latest observation in the spring of 1996 although this observation is consistent with the report of warming of antarctic bottom water in the argentine basin by coles et al 1996 their associated conclusion that this water mass has also freshened by 0 008 psu on potential density surfaces is in contradiction with our finding of no measurable change

anomalous temperatures in central scotia sea sediments bottom water variation or pore water circulation in old ocean crust we report low temperature gradients from 60 to 12 of geothermal and extrapolated temperatures offset from modern bottom water temperatures in sediments from the central scotia sea we examine possible causes bearing in mind similar anomalous measurements 18 years previously attributed at the time to instrumental error small temperature offsets 0 1 c may reflect short term bottom temperature variation within eddies of the antarctic circumpolar current low sediment temperature gradients may be caused by horizontal advection of cold water within the upper oceanic basaltic layer documented in younger ocean floor elsewhere or by northward encroachment of colder bottom waters from the antarctic peninsula shelf or weddell sea for several years prior to measurement

variable marine productivity and high eolian input recorded by rhythmic black shales in mid cretaceous pelagic deposits from central italy rhythmic interbedding of dark gray to black laminated calcareous shale black shale with lighter colored limestone marlstone or mudstone is a prominent feature of the aptian albian scisti a fucoidi in the italian apennines organic carbon contents of most black shales in the scisti are less than 1 5 sedimentary structures and levels of bioturbation indicate that periods of poorly oxygenated benthic conditions alternated with more extended periods of well oxygenated benthic conditions during deposition of the scisti geoochemical isotopic and visual studies of organic matter indicate variable marine productivity generally low and relatively high input of eolian dust during deposition of the scisti black shales one organic rich black shale near the middle of the formation may represent a brief period of stimulated marine fertility and high productivity coincident with benthic stagnation production of warm saline brines in evaporitic coastal settings sinking of these brines into deepwater basinal settings and development of stable salinity stratification is suggested as a causal linkage between arid climate strong winds and poorly oxygenated bottom waters in the alpine mediterranean tethys during mid cretaceous time

causes of the marine productivity and oxygen changes associated with the permian triassic boundary a reevaluation with ocean general circulation models widespread anoxic and dysoxic deposition in marine sediments has been associated with a stagnant ocean at the permian triassic p tr boundary this p tr boundary is also associated with one of the largest mass extinctions of species of the paleozoic marking the transition to the mesozoic here we review recent three dimensional numerical model studies that have investigated possible circulation patterns at the p tr boundary in addition we conduct new sensitivity experiments with a coupled ocean atmosphere model of intermediate complexity including marine chemistry to study changes of the deep sea oxygen distribution associated with 1 a significant change in the hydrological cycle and 2 a massive release of methane gas hydrates from marine sediments freshening of sea surface water masses by a strong freshwater source along the west coast of south polar pangea produces a significant local minimum in oxygen in the eastern tropical panthalassa ocean at intermediate depth and at the sea floor the methane release experiment with an atmospheric co2 concentration of 18 times the preindustrial co2 level simulates a strong increase in sea surface temperature about 4 5 8c and a vigorous deep sea circulation in contrast to the conclusions drawn from previous studies this reanalysis of the ocean circulation at the p tr boundary favors a strong ventilation in most parts of the deep sea thus a significant change in the oceanic carbon inventories and a reorganization of the marine productivity associated with a stronger biological pump may be required to explain the anoxic sedimentary deposits d 2005 elsevier b v all rights reserved

anoxic events productivity rhythms and the orbital signature in a mid cretaceous deep sea sequence from central italy albian pelagic sediments from the umbrian apennines exhibit rhythmic bedding in outcrop high temporal resolution 4 kyr spacing sampling of carbonate si and al along a 1 6 m y interval of core demonstrates that changes in accumulation rate of calcareous and siliceous microorganisms were controlled by insolation cycles optical densitometry logging correlates variations of geochemical parameters to episodes of deep sea anoxia indicated by numerous black laminated zones black shales harmonic analysis of data shows oscillations at three frequencies which correspond closely in estimated duration and ratio to the modern eccentricity and precessional orbital cycles as in pleistocene marine sequences the eccentricity approximately 100 kyr term dominates the sedimentary variance in the umbrian cycles anoxic episodes occur in phase with a limestone marl repetition and reflect minima of the precessional 21 kyr cycle the covariance of carbonate and silica with estimates of foraminiferal abundances suggest that carbonate cycles are the result of changes in surface productivity of calcareous organisms rather than an effect of dissolution or diagenesis recognition of orbital cyclicity provides a tool for making quantitative estimates of these changes productivity during anoxic events was uniformly low 0 4 0 5 g cm2 kyr carbonate 0 05 g cm2 kyr silica but it rose to high levels during oxygenated periods 1 2 5 g cm2 kyr carbonate 0 1 0 3 g cm2 kyr silica vertical overturning and organic carbon flux decreased during anoxic episodes but decreased oxygenation of the deep water led to enhanced preservation of the organic matter delivered the degree of paleoceanographic variability indicated by this study requires that accepted notions of climate stability and oceanic quiescence during nonglacial times be reassessed

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

effect of precessional insolation changes on cretaceous climate and cyclic sedimentation the often striking presence of cyclical beddings has frequently been noted in cretaceous marine sediment deposits in many instances these beddings appear to have periodicities similar to those of the earth s orbit i e its precession obliquity and eccentricity variations in the primary deposition of ocean sediments are strongly linked to atmosphere land ocean interactions we report a set of numerical experiments using an atmospheric general circulation model that are designed to examine the sensitivity of mid cretaceous climate to insolation changes due to the precessional cycle we restrict attention to a single orbital parameter because most limestone black shale bedded sequences were deposited at low latitudes where precessional insolation variations predominate we varied systematically the precessional index between the maximum positive and negative values calculated over the last 2 m y and used mid cretaceous paleogeographic and paleotopographic reconstructions and zonally symmetric sea surface temperatures based on earlier work by barron and washington surface wetness and albedo values appropriate for grassland were prescribed uniformly over all land regions to capture the seasonality of precession we employed both perpetual january and perpetual july simulations changes in surface heating due to the imposed insolation anomalies resulted in a strong basically linear response of monsoonal circulations dominated by changes over the northern hemisphere the hydrologic cycle shows a significant response over many regions the low latitude proto south atlantic region varies from a strong net sink for water vapor excess precipitation to a strong source excess evaporation over the precession cycle this variation is consistent with an alternation between a stagnant stratified ocean basin with anoxic bottom water and an evaporative basin that produces bottom water that is warm saline and oxygenated the portion of the tethys ocean that overlays the limestone black shale sequences now found in present day italy does not exhibit comparable behavior but the reconstruction of orography and basin boundaries in this region is less known the simulations show however that as the monsoonal flow over south proto asia intensifies water vapor evaporated in this part of tethys is prevented from crossing the proto alps into the interior of the continent thereby remaining in the tethian drainage basin as a result central proto asia shifts between arid and moist conditions with precessional variations the water vapor budget over northeast africa varies systematically from zero seasonality to a marked wet dry seasonal cycle the deposition of eolian material can be inferred from a combination of continental aridity favorable mean wind directions and significant wind variances in our experiments the mean surface and upper winds often show a systematic response to precession but surface wind variances show a systematic response only in isolated regions our simulations do not provide a simple mechanism to explain the cyclicity in eolian deposition that has been reported for north central tethys

hunting for paleoclimatic periodicities in a geologic time series with an uncertain time scale an 8 m section of a mid cretaceous albian deep sea sediment core from piobbico italy contains 2 cycles m compositional oscillations as postdepositional chemical migration in the core is weak the relative amount of carbonate is a primary indicator of cretaceous paleoclimate variability we report results of spectral analysis of two series caco3 wt measurements taken at roughly 2 cm intervals and a more densely sampled photodensitometer record of light dark variation the uncertainty in the age depth relation i e unknown fluctuations in sedimentation rate hampers a detailed assessment of the suggested eccentricity correlation we fit for long term time scale greater than 75 kyr fluctuations in sedimentation rate by tracking the local frequency modulation of the dominant harmonic in the data series assuming the true input signal to be monochromatic we estimate uncertainty in the observed local frequency by means of a statistical jackknife we fit a smoothed cubic spline to the set of discrete frequency modulation estimates specifying a 2 n misfit criterion where n is the number of frequency estimates from this analysis we infer fluctuations of a factor of two in the sedimentation rate which occur predominately on a time scale of 400 kyr we generate tuned series using several candidate age depth relations from the carbonate and densitometer series the tuned carbonate series returns greater correlation with the modern milankovitch periodicities the 2 cycles m energy resolves principally into two harmonic components whose frequency ratio corresponds to an observational accuracy of 1 2 to that of the 97 0 and 127 6 kyr eccentricity oscillations at frequencies lower than 2 cycles m we find harmonic oscillations whose phase correlates with the beating envelope of the 2 cycles m energy in a manner consistent with the modern milankovitch insolation we also observe a sinusoidal oscillation of lower amplitude with period scaled by those of the presumed eccentricity oscillations of 39 2 1 1 kyr which agrees with the period of the modern obliquity cycle after correction for the effects of tidal friction oscillations corresponding to milankovitch precessional frequencies are not established owing possibly to low signal level and unknown short term deposition fluctuations the tuned densitometer series recovers few new periodic features although its inferred age depth relation correlates well with that of the carbonate series we calibrate the depth variable downcore to the orbital cycles to estimate r 5 0 0 15 m m y as the effective sedimentation rate

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

an intermediate complexity model for simulating marine biogeochemistry in deep time validation against the modern global ocean we present a new high resolution 1 d intermediate complexity box model icbm of ocean biogeochemical processes for paleoceanographic applications the model contains 79 reservoirs in three regions that should be generally applicable throughout much of earth history 1 a stratified gyre region 2 a high latitude convective region and 3 an upwelling region analogous to those found associated with eastern boundary currents transport processes are modeled as exchange fluxes between boxes and by eddy diffusion terms significant improvement in the representation of middepth oxygen budgets was achieved by implementing nonlocal mixing between the high latitude surface and gyre thermocline reservoirs the biogeochemical submodel simulates coupled c n p o and s systematics with explicit representation of microbial populations using a process based approach primary production follows redfield stoichiometry while water column remineralization is depth and redox couple dependent settling particulate organic matter is incorporated into a benthic submodel that accounts for burial and remineralization the c p ratio of burial depends on bottom water oxygen denitrification takes place both by classical and anammox pathways the icbm was tested against modern oceanographic observations from the global ocean data analysis project joint global ocean flux study and other databases comparisons of model output with circulation tracers including salinity cfc 12 and radiocarbon permit a test of the physical exchange scheme vertical profiles of biogeochemically reactive components in each of the three regions are in good agreement with observations under modern conditions the upwelling zone displays a pronounced oxygen minimum zone and water column denitrification while these are not present in the high latitude or gyre regions model generated global fluxes also compare well to independent estimates of primary production burial and phosphorous and nitrogen cycling the icbm appears to adequately simulate the long term kyr evolution of several biogeochemical cycles and improves on previous box models in several important ways in a companion paper the model s performance under euxinic conditions is tested against modern black sea data the simple and adaptable structure of the model should make it applicable to a wide range of paleoceanographic problems the model source code is available in matlabtm 7 m files provided as auxiliary material

biogeochemical effects of atmospheric oxygen concentration phosphorus weathering and sea level stand on oceanic redox chemistry implications for greenhouse climates abstract understanding the key factors influencing the global oceanic redox system is crucial to fully explaining the variations in oceanic chemical dynamics that have occurred throughout the earth s history in order to elucidate the mechanisms behind these variations on geological timescales numerical sensitivity experiments were conducted with respect to the partial pressure of atmospheric molecular oxygen p o 2 the continental shelf area a cs and the riverine input rate of reactive phosphorus to the oceans r p the sensitivity experiment for atmospheric p o 2 indicates that pervasive oceanic anoxia and euxinia appear when p o 2 p o 2 are higher than a previous estimate of 50 pal present atmospheric level due to redox dependent phosphorus cycling the sensitivity experiment regarding the shelf area demonstrates that changes in the shelf area during the phanerozoic significantly affected oceanic oxygenation states by changing marine biogeochemical cycling a large continental shelf acts as an efficient buffer against oceanic eutrophication and prevents the appearance of ocean anoxia euxinia we also found that an enhanced r p is an important mechanism for generation of widespread anoxia euxinia via expansion of both the oxygen minimum zone and coastal deoxygenation although the critical r p value depends significantly on p o 2 a cs and the redox dependent burial efficiency of phosphorus at the sediment water interface our systematic examination of the oceanic redox state under cretaceous greenhouse climatic conditions also supports the above results

paleophysiology and end permian mass extinction physiological research aimed at understanding current global change provides a basis for evaluating selective survivorship associated with permo triassic mass extinction comparative physiology links paleontological and paleoenvironmental observations supporting the hypothesis that an end permian trigger most likely siberian trap volcanism touched off a set of physically linked perturbations that acted synergistically to disrupt the metabolisms of latest permian organisms global warming anoxia and toxic sulfide probably all contributed to end permian mass mortality but hypercapnia physiological effects of elevated pco2 best accounts for the selective survival of marine invertebrates paleophysiological perspectives further suggest that persistent or recurring hypercapnia global warmth also played a principal role in delayed triassic recovery more generally physiology provides an important way of paleobiological knowing in the age of earth system science 2007 elsevier b v all rights reserved

heat flow from the southeast indian ridge flanks between 80 e and 140 e data review and analysis 1 we analyze available heat flow data from the flanks of the southeast indian ridge adjacent to or within the australian antarctic discordance aad an area with patchy sediment cover and highly fractured seafloor as dissected by ridge and fracture parallel faults the data set includes 23 new data points collected along a 14 ma old isochron and 19 existing measurements from the 20 to 24 ma old crust most sites of measurements exhibit low heat flux from 2 to 50 mw m 2 with near linear temperature depth profiles except at a few sites where recent bottom water temperature change may have caused nonlinearity toward the sediment surface because the igneous basement is expected to outcrop a short distance away from any measurement site we hypothesize that horizontally channelized water circulation within the uppermost crust is the primary process for the widespread low heat flow values the process may be further influenced by vertical fluid flow along numerous fault zones that crisscross the aad seafloor systematic measurements along and across the fault zones of interest as well as seismic profiling for sediment distribution are required to confirm this possible suspected effect

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

benthic foraminiferal shell weight deglacial species specific responses from the santa barbara basin abstract here we present a record of size normalized shell weight for four species of benthic foraminifera through a period of rapid environmental change during the most recent deglaciation santa barbara basin ca a strong oxygen minimum zone omz the product of high surface productivity and poor ventilation characterizes the eastern pacific this subsurface zone is mechanistically coupled with high concentrations of dissolved inorganic carbon the omz migrated vertically during warming of the last deglaciation leading to rapid shifts in the oxygenation and inorganic carbon system of the benthos the size normalized weight snw of benthic foraminifers uvigerina peregrina bolivina interjuncta and bolivina tumida reflects only the broad trends of the vertical migration of the omz and inorganic carbon system overshadowed by clear species specific trends the relative importance of omz migrations versus other environmental variables and optimal growth conditions differs across species of benthic foraminifera in u peregrina snw primarily peaks with foraminiferal density and increased abundance of that species while b interjuncta and b tumida increase in snw with a shrinking of the omz and carbon maximum in the late holocene bolivina argentea shows no long term trends in snw potentially due to its ability to migrate through the sediment our results suggest that while inorganic carbon and dissolved oxygen may play a role in determining shell weight across species of benthic foraminifera neither parameter alone is responsible for changes in benthic foraminiferal shell weight in the fossil record

presence of a long term lithospheric thermal anomaly evidence from apatite fission track analysis in northern new england abstract apatite fission track aft ages from 56 samples of paleozoic and mesozoic crystalline rocks in new hampshire northeastern vermont and western maine range from 70 to 140 ma and reflect widespread early to late cretaceous cooling the regional aft age distributions determined in this study suggest that reactivation of preexisting orogen parallel faults and the presence of a long lived thermal anomaly in the lithospheric mantle controlled the late unroofing history of this part of the northern appalachians a northeast trending zone of young dominantly late cretaceous aft ages 70 118 ma extends from southwestern new hampshire through the central white mountain region and continues into northern new hampshire northeastern vermont and western maine providing evidence for regional nw se extension and cooling at this time significantly older aft ages 125 140 ma in the region bounded by the bill little ammonoosuc and northey hill faults in northwestern new hampshire suggest a normal sense r

middle proterozoic ocean chemistry evidence from the mcarthur basin northern australia we report on the iron sulfur systematics and s isotopic compositions of upper paleoproterozoic carbonaceous shales from the wollogorang and lower reward formations mcarthur basin northern australia iron speciation in these rocks is similar to that of modern euxinic black sea sediments and distinct from sediments depositing from oxygenated water providing persuasive evidence of euxinic depositional environments in a mid proterozoic marine basin high values of degree of pyritization dop also indicate anoxic bottom water conditions at the time of shale deposition as does the relatively uniform isotopic composition of sedimentary sulfides the isotopic composition of the sulfides is however quite enriched in 3 4 s and for the lower reward formation similar to contemporaneous seawater sulfate these 3 4 s enriched sulfides are consistent with extensive or even complete sulfate depletion within the euxinic basins in which the sediments were deposited based on analogy with modern euxinic environments and further constrained by model results middle proterozoic seawater sulfate concentrations were probably within the range of 0 5 to 2 4 mm taken together our results indicate a relatively low sulfate late paleoproterozoic ocean and sulfidic deep waters in the mcarthur seaway a condition that could have encompassed much larger regions of the ocean

response of calcareous nannoplankton to the late cretaceous oceanic anoxic event 2 at oued bahloul central tunisia abstract oued bahloul is a reference section for the cenomanian turonian that was located on the north african palaeomargin where oceanic anoxic event 2 oae2 is represented by black limestones and grey marls biostratigraphic study allowed the identification of calcareous nannofossil uc3 to uc6 zones quantitative analyses of calcareous nannofossil assemblages indicate that high fertility surface water conditions predominated throughout most of the oae2 interval the most eutrophic conditions probably developed during deposition of the lowermost part of the whiteinella archaeocretacea zone uc3 to uc4 zones where nannofossil derived fertility indices reach high values and the small zeugrhabdotus gr predominates over biscutum spp the temperature index based on calcareous nannofossil assemblages indicates a warming at the beginning of the oae2 followed by progressive cooling the same trend indicated by 18 o bulk values the significant proportion of holococcoliths suggests high stress conditions in surface waters during most of the oae2 interval the enrichment in redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicates dysoxic conditions both in the deep water column and sea bottom at the beginning of the oae2 w archaeocretacea zone geochemical detrital proxies indicate an enhanced rate of terrigenous supply during the oae2 interval resulting from increased riverine influx related to a more humid climate enhanced fluvial run off increased nutrient input to marine surface waters contributing to eutrophication recorded by calcareous nannoplankton and planktic foraminifera plankton consumption of surface water nutrients increased organic matter production whose decay contributed to the decrease in dissolved oxygen generating increasingly dysoxic anoxic conditions and favoring preservation of organic matter although low latitude nannofossil assemblages such as those of oued bahloul reflect an increase in nutrient availability during the oae2 interval assemblages from mid latitude areas record a decreased nutrient content

ocean circulation and atmospheric co2 changes coupled use of models and paleoceanographic data we have perturbed a simple model of oceanic circulation in a series of sensitivity tests to determine how circulation changes associated with the last glacial maximum could affect observable or potentially observable paleoceanographic parameters ultimately we want to use such paleoceanographic data to construct models of glacial ocean circulation we have found that the different circulation patterns that we imposed in our sensitivity tests have dramatically different responses for the distribution of po4 o2 and 13c contents of the oceans they also produce different levels of low latitude productivity by comparing the coupled responses of several of these paleoceanographic parameters to the responses from the sensitivity tests it is possible to constrain the possible glacial circulation scenarios to a relatively small number we give as one example a case where intermediate turnover is significantly higher than the present and deep ocean turnover has dropped in addition exchange of waters between the intermediate and high latitude surface ocean is much lower the result of this scenario is an atmosphere with 60 ppm lower atmospheric co2 low latitudes with about 40 higher productivity and a change in the planktic benthic 13c contrast of about 0 3 when we compare our model to other independent paleoceanographic data we find that the major point of disagreement is in the distribution of surface water 13c in the antarctic region we believe that somewhat more complex box models which take open system effects into account will resolve this discrepancy

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

periodic mid cretaceous oceanic anoxic events linked by oscillations of the phosphorus and oxygen biogeochemical cycles 1 a series of oceanic anoxic events oaes occurred in the mid cretaceous warm period 120 80 ma that have been linked with high rates of organic carbon burial warm high and low latitude temperatures and sea level changes oaes have been studied individually but a causal mechanism that connects them has been lacking we show that peaks in phosphorus accumulation in marine sediments broadly coincide with oaes 1a 1b 1d 2 and 3 and exhibit a 5 6 myr periodicity which for reactive p is prominent over 100 80 ma oxic anoxic oscillations of this frequency are also found in a model of the coupled n p c and o2 biogeochemical cycles these oscillations are maintained by positive feedbacks between phosphate concentration biological productivity and anoxia in the global ocean and counteracting but slower negative feedbacks involving changes in atmospheric oxygen an increase in phosphorus weathering rate above a critical threshold can shift the system into self sustaining oscillation this could have been caused by tectonic and volcanic forcing increasing atmospheric co2 and global warmth 120 80 ma augmented by the rise of flowering plants around 100 ma with a plausible forcing scenario we are able to reproduce the approximate timing of oaes 1a 1b 1d 2 and 3 in the model

deep ocean temperature variations and implications for errors in seafloor heat flow determinations 1 the accuracy with which seafloor heat flow is determined depends on the temporal stability of bottom water temperature indirect tests for stability are provided most commonly by observing the uniformity of heat flow with depth this criterion is met to a high degree of certainty at two sites in the eastern north pacific ocean where colocated high quality probe and borehole heat flow data can be compared a more direct test for stability is provided by long term observations of bottom water temperature previously published records and new data show temperature variations of only a few hundredths of a degree at sites in the central and eastern north atlantic and the eastern north pacific resultant gradient perturbations are geothermally insignificant 5 mk m 1 at depths greater than 1 2 m below the seafloor consistent with the uniformity of heat flow with depth observed in these areas geothermally problematic bottom water temperature variations are observed or inferred in the western north and south atlantic and western south pacific variations range up to 0 15 k and are capable of producing gradient perturbations of up to 5 mk m 1 at depths as great as 5 m below the seafloor while these data are instructive their distribution is not adequate to provide general guidelines for estimating geothermal gradient perturbations data from shallower sites are needed in all oceans to define depth limits of acceptable bottom water temperature variability and from other deep ocean locations where near source bottom water transients or vigorous deep water circulation dynamics are likely to be present

heat flow in the western mediterranean thermal anomalies on the margins the seafloor and the transfer zones the western mediterranean basin has been formed by miocene back arc extension and is underlain by a thin and young lithosphere this young lithosphere is warm as testified by an overall elevated offshore heat flow heat flow within the western mediterranean is however highly variable and existing data are unevenly distributed and poorly studied in the central part of the liguro provencal and algero balearic basins this central part is floored by a young oceanic crust bordered by different continental margins cut by transform faults and filled by up to 8 km of sediments we present a total of 148 new heat flow data collected during the medsalt and westmedflux cruises in 2015 and 2016 and aligned along seven regional profiles that show an important heat flow variability on the basin scale but also locally on the margins a new heat flow map for the western mediterranean outlines the following regional features 1 a higher average heat flow in the algero balearic basin compared to the liguro provencal basin 94 13 mw m2 and 78 16 mw m2 respectively and 2 a regional thermal asymmetry in both basins but with opposed heat flow trends up to 20 of this heat flow difference can be explained by sediment blanketing but age and heterogeneity of ocean crust due to an asymmetric and polyphased opening of the basins are believed to have given the major thermal imprint estimates of the age of the oceanic crust based on the new heat flow suggest a considerably younger west algerian basin 16 23 ma compared to the east algerian basin and the west sardinia oceanic floor 31 37 ma on the margins and ocean continent transitions of the western mediterranean the new heat flow data point out the existence of two types of local anomalies length scale 5 30 km 1 locally increased heat flow up to 153 mw m2 on the gulf of lion margin results from thermal refraction of large salt diapirs and 2 the co existing of both low 110 mw m2 heat flow areas on the south balearic margin suggests a heat redistribution system we suspect the lateral heat advection is resulting from a regional fluid circulation in the sediments associated to the widespread plio pleistocene volcanism on the south balearic margin

simulated circulation of an idealized ocean for pangaean time an eight level dynamical ocean model driven by prescribed surface forcing wind stress temperature precipitation minus evaporation from a previously published pangaean time climate simulation is used to study possible features of ocean circulation temperature and salinity for the early mesozoic the simulations are sensitivity experiments rather than estimates of the actual circulation because many simplifying assumptions are made concerning the prescribed surface forcing and the ocean basin s shape and depth simulated features include relatively warm water in high latitudes warm deep water a westward flowing equatorial current across panthalassa and into the tethys sea poleward and eastward flowing currents along the tethys coasts and relatively vigorous meridional and longitudinal vertical overturning cells cool relatively fresh polar water combines with warm saline tethys water to produce the relatively warm deep water there are few geological estimates of early mesozoic pangaean time ocean circulation available for comparison with the simulated circulation

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

slow late paleozoic exhumation in the presidential range of new hampshire as determined by the 40ar 39ar relief method 40 ar 39 ar mineral ages from muscovite were used to determine exhumation rates in the multiply deformed and metamorphosed silurian and devonian metasedimentary rocks exposed on mount washington new hampshire the muscovite ages increase progressively from the bottom to the top of the mountain the oldest mount washington summit elevation 6200 ft 1900 m is 304 3 ma and the youngest route 16 elevation 1350 ft 410 ml is 274 3 ma the age and elevation data yield an exhumation rate of 0 04 mm yr the exhumation rate indicates that 1 the middle pennsylvanian through early permian was a period of very slow exhumation 2 rapid uplift associated with the acadian orogeny must have terminated by at least 305 ma 3 sometime after 274 ma renewed uplift created the present topography of the mount washington massif and 4 the relief method can be used successfully in older more deeply eroded orogenic belts if the topographic relief is adequate and cooling was slow

could the late permian deep ocean have been anoxic models of ocean circulation and biogeochemical cycles are used to speculate about possible mechanisms of deep sea anoxia across the permo triassic boundary two modes of likely late permian ocean thermohaline circulation are identified a vigorous thermal mode driven by cooling in southern polar latitudes and a weaker haline mode driven by evaporation from the subtropics we find that the thermal mode typical of climates such as our own is unlikely to surpport deep sea anoxia the haline mode which might exist in warm climates with enhanced hydrological cycles can lead to significant but periodic depletion of oxygen in the panthalassic deep ocean however owing to the inherent instability of the haline mode a deep sea anoxia persisting for millions of years is not clearly supported by this study though mechanisms emerge which might be consistent with the observed record the enhanced hydrological cycle or reduced oceanic diapycnal mixing required to obtain the haline mode remain unconstrained for the late permian

characterization of topographic steady state in taiwan abstract the arc continent collision in taiwan has resulted in surface uplift high relief and high rates of erosion because the collision is older in the north and has propagated southward taiwan offers the opportunity to study the evolution of topography as it evolves towards a large scale steady state in this paper we analyze a 40 m digital elevation model of taiwan to determine how topographic steady state is expressed in the landscape particular attention is paid to the eastern central range where major drainage basins are approximately aligned in the direction of the collision propagation analyses of orogen size regional topographic slope drainage basin hypsometry and local topographic slope reveal a geomorphological transition 100 125 km north of the southern tip of the island to the south of this transition topographic characteristics change with distance along the island to the north these characteristics are relatively constant which we interpret as representing large scale topographic steady state assuming that the collision has propagated southward at a rate of 55 mm yr the time to topographic steady state is 1 8 2 3 myr after emergence above sea level within the steady state region we evaluate regional variability in the topography and find that the most prominent deviations from a steady form are associated with large scale structures though our analyses of local topographic slope and river profile form suggest that spatial variations in rock strength and rock uplift rate also contribute to regional topographic variability

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

interannual variability of bottom temperatures in drake passage a continuous 4 year record of in situ bottom temperature measurements at 3690 m within drake passage 59 43 7s 55 29 5w from november 1992 to november 1996 is presented the record shows fluctuations of order 0 02 c over monthly periods throughout the 4 years but the annual mean temperature is the subject under discussion in this work between june 1994 and may 1995 the water sampled was of the order of 0 1 c cooler than the water sampled on either side of this time period this temporal temperature anomaly has only become apparent because of the availability of a continuous data set hydrographic data sampled from the same location as part of the world ocean circulation experiment sr1 repeat section provide potential temperature and salinity values that enable the bottom temperature record to be linked to variability in weddell sea deep water wsdw oxygen isotope measurements demonstrate that the year long period of cooler wsdw measured in drake passage is a signature of ice shelf water in the formation process of deep and bottom waters within the weddell sea

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

redox stratification and anoxia of the early precambrian oceans implications for carbon isotope excursions and oxidation events abstract an updated compendium of 13c data offer compelling evidence that 13c positive excursions of unsurpassed magnitude in the recorded earth history 8 and up to 18 pdb occurred in the early proterozoic the lomagundi event questions whether or not these unprecedented positive 13c shifts were contemporaneous in various basins and represent local or global events remain unresolved the framework of major geologic events that occurred in the paleoproterozoic argues against a snowball earth scenario as a backdrop to these exceptional 13c enrichments substantial increases of carbon flux ratio fo fc eight times the phanerozoic average and organic carbon burial rate fo three times the phanerozoic average are required to account for the observed 13c enrichments under steady state and dynamic equilibrium modes respectively these enhanced ratios and rates are conditional on the availability of a flux of nutrients to the contemporaneous biota producers in excess of the riverine flux and a decoupling of the p and c cycles it is argued that these two conditions were met between 2 25 and 2 11 ga in a redox stratified ocean with weak upwelling and sluggish meridional surface circulation the alternative that the major disturbance in the terrestrial carbon cycle occurred in a rapidly ventilated ocean is assessed as being unlikely a large pulse of o2 equivalent to six to seven times the present terrestrial oxygen budget was rapidly scavenged and spent in the oxidation of reduced fe and s transported to the shelves by rivers this contention is consistent with data inferring low oxygen levels 10 5 to 10 2 pal in the paleoproterozoic atmosphere and the occurrence of ocean anoxia until the late precambrian

paleoceanography and paleoclimatology an earth system perspective abstract the purpose of this paper is to provide an overview of paleoceanography and paleoclimatology as a framework for other papers dealing with the earth system geochemical perspectives an introduction to both paleoceanography and paleoclimatology is followed by examples of the temporal changes through the phanerozoic the important and interactive role of the biosphere is emphasized many important changes in the earth system have affected the coupled ocean atmosphere system and many in turn have been reflected in biotic events many such changes can be tracked through time using geochemical signatures as proxy indicators whereas the scale of past paleoceanographic and paleoclimatic changes have been generally appreciated for some time the recognition of periodic rapid change in the ocean climate state and the ability to study and measure these precisely is only a recent accomplishment the potential for such rapid change in the ocean climate biosphere of the earth system raises concerns for events in the near future that may be forced by anthropogenic activities that enhance natural variability

dynamics of anoxia abstract a simple steady state one dimensional advective diffusive model of the ocean s coupled carbon oxygen and phosphorous system is developed the model is an extension of wyrtki s 1962 model of the oxygen distribution the occurrence of anoxia requires two conditions 1 sufficiently high productivity and 2 sufficiently low oxygen concentration in the bottom water it is shown that anoxic layers are most likely to occur fairly high in the water column anoxic events may be associated with timesof vigorous thermohaline circulation in contrast to stagnation arguments often invoked the model results are used to interpret both modern and ancient oceanic anoxic events

on the effects of thermal properties structure and water bottom temperature variation on temperature gradients in lake sediments in heat flow determinations it is customary to treat the surface temperature variation as a finite sum of fourier components the medium is assumed to be homogeneous or horizontally stratified wit

acceleration and overturning of the antarctic slope current by winds eddies and tides all exchanges between the open ocean and the antarctic continental shelf must cross the antarctic slope current asc previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability yet the mechanisms responsible for setting the asc s transport and structure have received relatively little attention in this study the roles of winds eddies and tides in accelerating the asc are investigated using a global ocean sea ice simulation with very high resolution 1 48 grid spacing it is found that the circulation along the continental slope is accelerated both by surface stresses ultimately sourced from the easterly winds and by mesoscale eddy vorticity fluxes at the continental shelf break the asc exhibits a narrow 30 50 km swift 0 2 m s 1 jet consistent with in situ observations in this jet the surface stress is substantially reduced and may even vanish or be directed eastward because the ocean surface speed matches or exceeds that of the sea ice the shelfbreak jet is shown to be accelerated by tidal momentum advection consistent with the phenomenon of tidal rectification consequently the shoreward ekman transport vanishes and thus the mean overturning circulation that steepens the antarctic slope front asf is primarily due to tidal acceleration these findings imply that the circulation and mean overturning of the asc are not only determined by near antarctic winds but also depend crucially on sea ice cover regionally dependent mesoscale eddy activity over the continental slope and the amplitude of tidal flows across the continental shelf break

application of an eutrophic lake model to the origin of ancient organic carbon rich sediments in this paper we approach the problem of the origin of organic carbon rich sediments by using an integrated isotopic and organic geochemical study of the annual productivity eutrophication cycle in the water column of lake greifen switzerland and the historical expression of such cycles as found in the sediments the lake greifen water column and sediment studies reveal that 13c carbonate organic matter is correlated with the hydrogen indices hi of kerogens explicable in terms of changing productivity and preservation of the organic matter and the co2 budget of the water body the lake model implies that if high productivity in co2 limited surface waters high nutrient co2 ratio was controlling the preservation of organic matter a correlation between decreasing 13c carbonate organic matter and increasing hi values may be observed in contrast if low to moderate productivity in co2 unlimited surface waters low nutrient co2 ratio where bottom water anoxia promotes the preservation of organic matter a correlation between increasing 13c carbonate organic matter and increasing hi values may be observed application of this model to two well known jurassic sequences gave a correlation of increasing hi values with decreasing 13c carbonate organic matter for the kimmeridge clay formation united kingdom and increasing hi values with increasing 13c carbonate organic matter for the early toarcian shales france this suggests that the controlling factor of the former deposit was high primary bioproductivity and of the latter deposit anoxic bottom water conditions

re os age and depositional environment for black shales from the cambrian ordovician boundary green point western newfoundland chemical and isotopic signatures for black shales serve as potential proxies for reconstruction of paleoenvironmental conditions here we bring rock eval major and trace element and re os isotopic data together to examine the environmental record at the cambrian ordovician global stratotype section and point gssp at green point in western newfoundland canada the green point shales are oil mature and contain type ii organic material of marine origin a re os isochron for the shales provides the first radiometric age for shale deposition at the gssp at 484 16 ma with an initial 187os 188os ratio of 0 74 0 05 model 3 age mswd 21 n 13 2 uncertainties factor analysis of the geochemical data set shows association of most trace elements with total organic carbon toc and s contents ensuring an authigenic origin for most elements and hence their validity for evaluating the paleo redox state relatively high enrichment factors for redox sensitive elements e g re u and mo compared to average shale but comparatively low enrichment compared to modern black sea sediments suggest deposition in anoxic but not euxinic waters comparison of lower ordovician shale geochemistry data sets at a global scale leads us to suggest that anoxic conditions and warm oceanic regimes were restricted to the margins of laurentia and baltica whereas depositional basins with colder waters e g avalonia and gondwana were less reducing these outcomes underscore the important role of paleogeography in regulating oceanic conditions and marine life

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

paleoceanographic evolution of the gulf of tehuantepec mexican pacific during the last 6 millennia oceanographic dynamics in the gulf of tehuantepec gt are the direct consequence of climate variability mainly influenced by the strong wind regime locally called tehuanos and the interactions

constraints on 87sr 86sr of late ediacaran seawater insight from siberian high sr limestones abstract in se siberia carbonate formations with 13 c carb values ranging between 12 and 7 v pdb and sr concentrations of up to 2 5 occupy an area of 40 000 km 2 several successions exceed 1000 m in thickness and represent the world9s largest known exposures of sedimentary carbonates exhibiting extreme depletion in 13 c the carbonates were deposited on a carbonate platform evolving from a mixed carbonate siliciclastic ramp to a carbonate ramp and then from a peritidal rimmed shelf to a deep water open shelf all sequences reveal a facies independent upward rise in marine 13 c carb from 12 to 7 the trend and magnitude of the values mimic those that are characteristic of the 600 550 ma shuram wonoka isotope event a coincident stratigraphic rise in 87 sr 86 sr from 0 70802 to 0 70862 in several sections of limestones containing 4400 g g 1 sr on average is considered to be by far the best available constraint on a temporal variation of seawater isotopic composition through the late ediacaran if the greatest temporal rate of change in seawater 87 sr 86 sr observed in the cenozoic is applied to the siberian sections the calculated minimum duration for the suram wonoka event is 10 ma supplementary material xrf and icp aes analysis c o and sr isotopic data are available at http www geolsoc org uk sup18324

bottom temperature fluctuations on the continental slope of the northwest atlantic ocean abstract temperature fluctuations on the western continental slopes of the atlantic ocean have been measured at three stations on the ocean bottom at depths from 1400 to 2100 m and from 17 to 35 n all three stations were in or near the deep western boundary current daily readings were taken for four to six years maximum to minimum fluctuations of the isotherms were 800 m off cape hatteras with average temperature of 3 80 c temperature appeared episode driven with minima consistently near 3 60 c and maxima near 4 10 c large swings in temperature had a duration of 10 30 days data from antigua also appeared episode driven but showed fewer large shifts in temperature but the maximum to minimum fluctuations of the isotherms were 400 m hence interesting motions may exist in the seldom studied region near the bend in the antilles islands chain these two stations are vastly different from previously reported data from the blake plateau in which temperature increases are consistently more rapid than de

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

organic facies of middle cretaceous black shales in deep north atlantic the middle cretaceous black shales of the deep north atlantic consist of alternating layers of sediment rich in total organic carbon toc that contains abundant amorphous types of organic matter and sediment poor in toc that contains mostly woody and coaly types of organic matter the amorphous materials are derived mostly from marine organisms in the eastern north atlantic off africa in the caribbean and on the demerara rise off surinam and from higher land plants in the western north atlantic and off europe marine amorphous material is important off africa because this was an area of upwelling and highly productive surface water amorphous marine organic matter was deposited across the entire north atlantic basin in the cenomanian in response to an ocean wide upwell ng event connected with the opening of the equatorial atlantic the difference between the toc rich and background toc layers reflects deposition of the former under reducing conditions which allowed the preservation of labile amorphous materials of marine and terrestrial orgin and of the latter under oxidizing conditions when nearly all that was preserved was refractory organic material

high resolution heat flow density in the lower congo basin 1 heat flow density hfd has been derived in the lower congo basin from 293 conventional probe measurements 424 oil exploration data and about 1 000 000 bottom simulating reflector bsr values each set of data provides independent estimates of temperature gradients associated with specific uncertainties and geographic distributions but a statistical comparison in overlapping domains shows a relatively good consistency in situ conductivity has been measured in conventional surveys and estimated from rock composition and porosity in oil exploration boreholes in the deep offshore measurements and estimates are consistently low and increase significantly toward the shelf domain thermal conductivity does not change significantly in the interval between the water bottom and the bsr and can be estimated from the surface measurements to provide an inference of hfd the combined sets of hfd in the lower congo basin cover the overall domain of the continental margin and a part of the oceanic domain high resolution imaging of the bsr by three dimensional 3 d seismic studies provides in addition good quality nominal resolution of 500 m in the deep offshore at short length scales on the order of kilometers large variations of hfd from 30 to 140 mwm 2 exist above salt diapirs and canyons related to heat refraction on the other hand no small scale effect related to fluid flow has been detected although active venting is known at larger length scale hfd in the deep offshore is different on both sides of the congo submarine channel 54 8 mwm 2 to the north and 48 12 mwm 2 to the south which are also characterized by different basin tectonic styles at the margin scale hfd is significantly different in the oceanic domain 42 3 mwm 2 the deep continental offshore 52 10 mwm 2 and the continental shelf 65 15 mwm 2 a progressive reduction of the radiogenic heat contribution in the extended continental crust is the more likely the cause of these differences mantle heat flow below the continental margin is consequently high compared to that expected 15 mwm 2 for old shields such as congo

rethinking the use of seabed sediment temperature profiles to trace submarine groundwater flow submarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment yet few studies have investigated spatially distributed groundwater fluxes in deep ocean environments such as continental slopes heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity these assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow ocean temperature changes and seabed thermal conductivity variations on deep ocean sediment temperature profiles temperature observations from the sediment and bottom ocean water on the scotian slope off eastern canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid the spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper middle slope and discharge on the lower slope we speculate that the downward groundwater flow inferred on the scotian slope is due to density driven processes arising from underlying salt domes in contrast with upward slope systems driven by geothermal convection improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length

climate simulations of the permian triassic boundary ocean acidification and the extinction event 1 the causes for the permian triassic boundary ptb extinction the largest mass extinction on record remain enigmatic the period is marked by large scale volcanic eruptions and evidence for widespread ocean anoxia which have led to suggestions that these events generated or played a part in the extinction furthermore hypercapnia and ocean acidification caused by volcanic emissions of co2 and ch4 have been put forward as potential kill mechanisms we present the first ptb climate simulations in which ocean acidity is evaluated directly with a coupled climate carbon cycle model the experiments also address the sensitivity of ocean circulation and oxygen levels to uncertainties in paleogeography and to different bottom topographies modeled temperature and precipitation evaporation are in good agreement with reconstructions and climate sensitive sediments there is also good agreement between modeled vegetation and reconstructed biomes the reduction in ocean ph brought about by the increase in atmospheric co2 is biologically significant aragonite saturation levels are low enough to make the whole ocean unsuitable to aragonitic species and large areas of the ocean become unsaturated in relationship to calcite no general bottom anoxia is reproduced modeled deep ocean o2 concentrations are not significantly impacted by changes in paleogeography and bathymetry an indication that in our model a change in ocean dynamics resulting from climate warming is not sufficient by itself to generate widespread anoxic conditions during the period

towards determining the thermal state of old ocean lithosphere heat flow measurements from the blake bahama outer ridge north westem atlantic summary detailed suites of heat flow measurements have been completed at four sites on and to the east of the southern end of the blake bahama outer ridge in the north west atlantic on ocean crust which ranges in age from roughly 115 to 155 ma the principal purpose of these measurements was to compare instrumental techniques and to examine the decay of heat flow with age on old ocean floor multi penetration gradient measurements were made at the youngest site with a 2 5 m outrigger probe and multipenetration heat flow measurements at the other three sites with a new 3 5 m violin bow type instrument in addition at all four sites the gradient was measured using outriggers on a 9 m piston or gravity corer and conductivities were measured on the sediment recovered the average of thermal conductivities measured on cored sediments agreed to better than 2 per cent with the average of conductivities measured in situ at the oldest three sites such good agreement is surprising given the problems associated with making measurements on sediments recovered in cores the greatest measurement errors in determining heat flow were found to be caused by temperature disturbances generated by the piston coring process gravity coring reduced these disturbances but provided a less representative section for measuring thermal conductivity the violin bow probe which measures average interval conductivities in situ provided the most reliable heat flow determinations the accuracy of these determinations was limited primarily by the presence of thermal disturbances due to bottom water temperature variations the heat flow averages at all four sites are virtually identical they range from 47mw m 2 1 12 cal cm 2s 1 to 49mw m 2 1 17 cal cm 2s 1 with standard errors of less than 2 mw m 2 0 05 cal cm 2s 1 the constancy and the value of heat flow over lithosphere of this age and the local shallowing of depth with increasing age in the region containing the heat flow sites cannot be explained by either a simple plate or a boundary layer lithosphere cooling model the unexpectedly high heat flow and shallow depths may result from lithospheric thinning and perhaps dynamic forces associated with a thermal perturbation beneath the plate

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

co evolution of eukaryotes and ocean oxygenation in the neoproterozoic era the oxygenation of the earth s deep oceans is often thought to have triggered the evolution of simple animals a review article proposes that instead the evolution of animal life set off a series of biogeochemical feedbacks that promoted the oxygenation of the deep sea

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

a constraint on the shear stress at the pacific australian plate boundary from heat flow and seismicity at the kermadec forearc new heat flow measurements and relocated hypocenters that constrain the subduction geometry of the pacific plate at the kermadec trench yield an estimate of shear stress on the thrust fault with the exception of a few relatively high values 60 mw m 2 on the upper forearc region near the active volcanic ridge most of the 64 heat flow values along two profiles across the forearc range from 20 to 40 mw m 2 corrections for bottom water temperature variations that caused nonuniform temperature gradients were required for most measurements the means of the most reliable values for the northern and southern profiles are 28 9 5 8 mw m 2 n 33 and 28 9 7 2 mw m 2 n 19 respectively and the measurements show no apparent systematic variation along the profiles over the range 50 to 150 km distance from the trench the means of the 10 values at each of two sites on the pacific plate seaward of the profiles are 57 2 6 3 and 60 2 6 6 mw m 2 redeterminations of focal depths and fault plane solutions of earthquakes in the vicinity of the heat flow profiles indicate thrust faulting on a plane dipping 17 2 calculated values of heat flow for a two dimensional analytical approximation to conduction through the upper plate diffusion into the downgoing slab and advection by that slab are consistent with either a uniform stress of 40 17 mpa along the thrust fault or stress increasing linearly at 0 5 0 2 mpa km 1 with distance from the trench axis the comparable scatter in the heat flow measurements about those calculated from these simple stress distributions does not show one to be a better approximation than the other

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

enhanced preservation of marine derived organic matter in cenomanian black shales from the southern angola basin black shales possessing high concentrations of organic carbon1 were deposited in many parts of the proto south atlantic ocean during the cretaceous period2 the way such sediments accumulated is not fully understood but is likely to have occurred through a combination of low oxygen availability and abundant supply of organic matter thin centimetre thick layers of black shales are commonly interbedded with thicker layers of organic carbon deficient green claystones as found in strata of aptian to coniacian age at deep sea drilling project dsdp site 530 in the southern angola basin3 and elsewhere these differences in carbon content and colour reflect the conditions of deposition and possibly variations in the supply of organic matter4 5 we have compared using organic geochemical methods the compositions of organic matter in three pairs of closely bedded black and green cenomanian claystones obtained from site 530 kerogen analyses and distributions of biological markers show that the organic matter of the black shales is more marine and better preserved than that of the green claystones

models for the deposition of mesozoic cenozoic fine grained organic carbon rich sediment in the deep sea the widespread occurrence of organic carbon rich strata black shales in certain portions of jurassic cretaceous and cenozoic sequences has been well documented from deep sea drilling project sites in the atlantic and pacific oceans and from sequences now exposed on land originally deposited in the tethyan ocean these ancient black shales usually have been explained by analogy with examples of modern deep sea sediments in which organic matter locally is preserved by 1 increasing the supply of organic matter 2 increasing the rate of sedimentation and or 3 decreasing the oxygen content of the bottom water however detailed examination of many black shales reveals characteristics that cannot be explained by simple local models including their approximate coincidence in time globally their occurrence in a variety of different environments including open oxygenated oceans restricted basins deep and shallow water their interbedding with organic carbonpoor strata which often dominate a so called black shale sequence their deposition by pelagic hemipelagic turbiditic and other processes and the variations in type and amount of organic matter that occur even within the same sequence a more complex model for the origin of black shales therefore appears most appropriate in which the cyclic preservation of organic matter depends on the interplay of the three main variables namely supply of organic matter sedimentation rate and deep water oxygenation each of which varies independently to some extent the variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea level climate and related changes in oceanic circulation an important and often overlooked factor for the supply of organic matter to deep basin sediments is the frequency and magnitude of redepositional processes the interplay of these variables is discussed in relation to the middle cretaceous and cenozoic organic carbon rich strata in particular which show marked differences in the relative importance of the different variables

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

causes of anoxia in the world ocean we examine the hypothesis that global scale episodes of anoxia such as occurred in the cretaceous are due to

sedimentation and accumulation of organic carbon in the angola basin and on walvis ridge preliminary results of deep sea drilling project leg 75 leg 75 investigated two periods of accumulation of sediments rich in organic matter in the upper cretaceous section more than 200 beds of gray or black shale and mudstone rich in organic carbon as much as 18 are intercalated within a sequence of red and green mudstones that contain less than 1 organic carbon the black shale beds are 1 to 62 cm thick and constitute less than 10 of the section in the 20 cores in which they were recovered both turbiditic and pelagic processes were involved in the deposition of these black shale beds a combination of factors including increased productivity and warm saline bottom waters probably resulted in a delicate balance between oxic and anoxic conditions that periodically favored the accumulation and preservation of organic matter in the basinal sediments the pliocene pleistocene sediments are thoroughly bioturbated and there is no evidence of persisting anoxia in the overlying water in spite of the high organic carbon content of the sediments these two different periods of accumulation of organic matter both resulted in significant concentration of organic carbon 2 maximum 18 but the pliocene pleistocene sediments contain the greater mass of organic carbon per unit volume of the solid sediment

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

apatite fission track evidence for the cretaceous development of kilometer scale relief and steady state tertiary topography in new england abstract apatite fission track aft ages in samples collected along the 5000 foot relief 1500 m exposed at mt washington in the presidential range of new hampshire are used to constrain the cretaceous cooling history of this area in the northern appalachians nine aft ages for samples of the littleton and rangeley formations collected along this profile range in age from 150 ma at the highest elevations of 1900 m to 100 ma at the base 500 m thermal histories based on these results and on model time temperature histories based on the distribution of fission track lengths in the higher elevations samples show three stages of cooling from 1 5 2 0 c m y 170 130 ma to 0 2 c 130 65 ma to 0 6 c m y 65 ma to the present in contrast the thermal history calculated for the lower elevations sample shows cooling delayed until 120 ma at 2 c m y 120 100 ma followed by monotonic cooling of 0 6 c m y from 100 ma to the present the convergence of these histories from high intermediate and low elevations suggests a common cooling history independent of elevation differences of 1 km structural tectonic explanations for this thermal convergence are implausible and we conclude that the most likely explanation for the common cooling history across 1 km of relief is that the relief was established by the end of the cretaceous and has persisted with steady state topography through the tertiary to the present the aft results are consistent with an earlier relief method study employing 40 ar 39 ar muscovite cooling ages geothermal gradients calculated from the results of both studies yield 40 c km suggesting that this gradient persisted throughout permian and mesozoic times

conditions required for oceanic anoxia euxinia constraints from a one dimensional ocean biogeochemical cycle model article i nfo widespread black shale depositional intervals termed oceanic anoxic events oaes occurred repeatedly during the phanerozoic eon here we developed a new vertical one dimensional ocean biogeochemical cycle model that involves several chemical reactions in an oxic anoxic sulfidic water column to explore the theoretical constraints for global oceanic anoxia euxinia quantitatively and systematically we conducted sensitivity analyses of the proposed causal mechanisms including elevated rates of riverine phosphorus p input ocean stagnation and lowered oxygen solubility due to climate warming we gave special attention to the vertical chemical structure of the ocean and also to the characteristic behaviors of the marine p cycle under anoxic conditions because the relationship between the depth of anoxia and the benthic phosphorus flux could be important for the occurrence of oceanic anoxia euxinia steady state simulations indicated that 1 a decrease in ocean stagnation or oxygen solubility is not enough by itself to achieve widespread anoxia with the present reactive p river input rate and 2 shallow water anoxia followed by massive p liberation from surface sediments can lead to widespread eutrophication and anoxia euxinia we conclude that elevated riverine flux of reactive p is the most important factor for triggering global anoxic events via a positive feedback loop among ocean anoxia phosphorus regeneration and surface biological productivity

geochemical evidence for enhanced preservation of organic matter in the oxygen minimum zone of the continental margin of northern california during the late pleistocene the present upper water mass of the northeastern pacific ocean off california has a well developed oxygen minimum zone between 600 and 1200 m wherein concentrations of dissolved oxygen are less than 0 5 ml l even at such low concentrations of dissolved oxygen benthic burrowing organisms are abundant enough to thoroughly bioturbate the surface and near surface sediments these macro organisms together with micro organisms also consume large quantities of organic carbon produced by large seasonal stocks of plankton in the overlying surface waters which are supported by high concentrations of nutrients within the california current upwelling system in contrast to modern conditions of bioturbation laminated sediments are preserved in upper pleistocene sections of cores collected on the continental slope at water depths within the present oxygen minimum zone from at least as far north as the california oregon border and as far south as point conception comparison of sediment components in the laminae with those delivered to sediment traps as pelagic marine snow demonstrates that the dark light lamination couplets are indeed annual varves these upper pleistocene varved sediments contain more abundant lipid rich sapropelic type ii organic matter than the overlying bioturbated oxidized holocene sediments the baseline of stable carbon isotopic composition of the organic matter in these slope cores does not change with time indicating that the higher concentrations of type ii organic matter in the varved sediments represent better preservation of organic matter rather than any change in the source of organic matter