deep ocean early warning signals of an atlantic moc collapse a future collapse of the atlantic meridional overturning circulation moc has been identified as one of the most dangerous tipping points in the climate system it is therefore crucial to develop early warning indicators for such a potential collapse based on relatively short time series so far attempts to use indicators based on critical slowdown have been marginally successful based on complex climate network reconstruction we here present a promising new indicator for the moc collapse that efficiently monitors spatial changes in deep ocean circulation through our analysis of the performance of this indicator we formulate optimal locations of measurement of the moc to provide early warning signals of a collapse our results imply that an increase in spatial resolution of the atlantic moc observations i e at more sections can improve early detection because the spatial coherence in the deep ocean arising near the transition is better captured

changing climate states and stability from pliocene to present we present a recently developed method of potential analysis of time series data which comprises 1 derivation of the number of distinct global states of a system from time series data and 2 derivation of the potential coefficients describing the location and stability of these states using the unscented kalman filter ukf we test the method on artificial data and then apply it to climate records spanning progressively shorter time periods from 5 3 myr ago to the recent observational record we detect various changes in the number and stability of states in the climate system the onset of northern hemisphere glaciation roughly 3 myr bp is detected as the appearance of a second climate state during the last ice age in greenland there is a bifurcation representing the loss of stability of the warm interstadial state followed by the total loss of this state around 25 kyr bp the holocene is generally characterized by a single stable climate state especially at large scales however in the historical record at the regional scale the european monthly temperature anomaly temporarily exhibits a second highly degenerate unstable state during the latter half of the eighteenth century at the global scale temperature is currently undergoing a forced movement of a single stable state rather than a bifurcation the method can be applied to a wide range of geophysical systems with time series of sufficient length and temporal resolution to look for bifurcations and their precursors

interaction network based early warning indicators for the atlantic moc collapse 1 early warning indicators of the collapse of the atlantic meridional overturning circulation moc have up to now mostly been based on temporal correlations in single time series here we propose new indicators based on spatial correlations in the time series of the atlantic temperature field to demonstrate the performance of these indicators we use a meridional depth model of the moc for which the critical conditions for collapse can be explicitly computed an interaction network approach is used to monitor changes in spatial correlations in the model temperature time series as the critical transition is approached the new early warning indicators are based on changes in topological properties of the network in particular changes in the distribution functions of the degree and the clustering coefficient citation van der mheen m h a dijkstra a gozolchiani m den toom q feng j kurths and e hernandez garcia 2013 interaction network based early warning indicators for the atlantic moc collapse geophys res lett 40 2714 2719

thermohaline circulation hysteresis a model intercomparison we present results from an intercomparison of 11 different climate models of intermediate complexity in which the north atlantic ocean was subjected to slowly varying changes in freshwater input all models show a characteristic hysteresis response of the thermohaline circulation to the freshwater forcing which can be explained by stommel s salt advection feedback the width of the hysteresis curves varies between 0 2 and 0 5 sv in the models major differences are found in the location of present day climate on the hysteresis diagram in seven of the models present day climate for standard parameter choices is found in the bi stable regime in four models this climate is in the mono stable regime the proximity of the present day climate to the stommel bifurcation point beyond which north atlantic deep water formation cannot be sustained varies from less than 0 1 sv to over 0 5 sv

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

a modified method for detecting incipient bifurcations in a dynamical system 1 we assess the proximity of a system to a bifurcation point using a degenerate fingerprinting method that estimates the declining decay rate of fluctuations in a time series as an indicator of approaching a critical state the method is modified by employing detrended fluctuation analysis dfa which improves the estimation of short term decay especially in climate records which generally possess power law correlations when the modified method is applied to genie 1 model output that simulates collapse of the atlantic thermohaline circulation the bifurcation point is correctly anticipated in greenland ice core paleotemperature data for which the conventional degenerate fingerprinting is not applicable due to the short length of the series the modified method detects the transition from glacial to interglacial conditions the technique could in principle be used to anticipate future bifurcations in the climate system but this will require high resolution time series of the relevant data

numerical climate modeling a frontier in petroleum source rock prediction results based on cretaceous simulations organic productivity and preservation are primary controls of the distribution of petroleum source beds both organic productivity and preservation are in part a function of geographic setting and climate therefore the prediction of paleoclimates is a major frontier in petroleum source rock prediction a climate model based on the fundamental laws thought to govern atmospheric circulation is applied here to the prediction of upwelling regions associated with very high productivity and bottom conditions that may become anoxic despite a high oxygen supply the potential and limitations of climate modeling in the prediction of upwelling regions are examined by 1 demonstrating the ability of the model to predict present day winds and upwelling regions 2 demonstrating t at the model and the location of upwelling regions is sensitive to geography continental positions sea level and topography and 3 investigating whether the model sensitivity to past geographies is realistic i e if predicted upwelling regions for the cretaceous period correspond to source rock localities the model predictions of ocean and coastal upwelling compare very favorably with present day observations and with estimates of primary productivity the location of middle latitude and high latitude upwelling locations are sensitive to model specified geography the location of low latitude upwelling is less sensitive to changes in global geography if coastlines are oriented appropriately despite some limitations a comparison of source rock localities with model predictions is promising the results of these studies suggest that numerical climate modeling is a potential tool in petroleum source rock prediction

seismic stratigraphy of the frontal hawaiian moat implications for sedimentary processes at the leading edge of an oceanic hotspot trace multi channel seismic imaging reveals the seismic stratigraphy and associated sedimentary processes of the frontal hawaiian moat fhm to the southeast of the island of hawaii two sedimentary units are defined 1 a basal layer of pelagic sediment draping the oceanic basement and 2 a wedge of volcaniclastic material infilling the fhm and onlapping the frontal hawaiian arch three distinct seismic facies within the volcaniclastic unit are recognized a areas of chaotic or incoherent reflections interpreted as proximal debris avalanche or slump deposits b groups of hummocky and distorted reflections interpreted as distal debris avalanche or debris flow deposits and c regions of parallel and laterally continuous reflections interpreted as turbidite deposits the distribution of these facies delineates slope apron proximal basin and distal basin depositional environments respectively within the fhm the northwest drift of the pacific plate over the hawaiian hot spot results in the apparent southeasterly migration of the hawaiian chain advancement of the depositional environments within the fhm occurs as individual volcanoes evolve erode and are superseded by new volcanic centers the interplay between depositional processes and tectonic forces plate motion and lithospheric flexure predicts a coarsening upward stratigraphy within the fhm the combined accumulation of pelagic and volcaniclastic sediment defines a heterogeneous and potentially unstable layer of low strength material beneath the volcanic edifice that may influence the mobility of the island flanks

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

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

hydrocarbon shows and source rocks in scientific ocean drilling abstract scientific ocean drilling has been conducted for more than three decades the ocean drilling program odp and its predecessor the deep sea drilling project dsdp have conducted activities with riser less ships these two programs have examined more than 1200 localities and recovered more than 348 073 m of core nearly all of this material has been obtained from areas outside known hydrocarbon producing regions however limited coring has taken place within or near hydrocarbon bearing provinces such as the gulf of mexico offshore california santa barbara channel the northwest shelf of australia and along the west african margin extensive predrill site reviews are performed for safety reasons and to prevent pollution despite these reviews a number of minor hydrocarbon shows have been encountered suggesting the presence of viable deepwater petroleum systems in many parts of the globe scientific ocean drilling has also provided access to samples of possible hydrocarbon source rocks such rocks are well constrained stratigraphically and free of contamination by drilling fluids this paper is focused on how the results of these scientific drilling programs can be used as part of a hydrocarbon exploration program through an examination of black shales potential source rocks oil shows gas occurrences and gas hydrates such a study shows how a basic research program can be used as part of the global resource evaluation program by no means is it an attempt to synthesize all organic geochemical data that have been generated by the program

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

organic geochemical characteristics of atlantic ocean cretaceous and jurassic black shales abstract organic rich black shales have been observed in mesozoic strata penetrated by the deep sea drilling project dsdp these black shales represent a major carbon sink in the geologic record of paramount importance in establishing the origin of the black shales is the character and level of preservation of the organic matter within the north and south atlantic sample suite three types of organic matter were identified well preserved marine organic matter moderately well preserved terrestrial material and severely altered and or recycled organic matter the spatial and temporal distribution of the three types of organic matter suggest that the organic rich shales are not of a single origin these shales have developed as a result of high continental runoff from regions rich in sedimentary carbon and or elevated terrestrial productivity or high marine productivity and preservation in part due to rapid deposition by turbidity currents or mass slumping a detailed analysis of individual and closely spaced dsdp sites further documents that anoxia was probably not the result of synchronous major expansions of anoxic bottom water masses but represents isolated occurrences

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

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

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation

the 1968 andesitic lateral blast eruption at arenal volcano costa rica the magmatic andesitic eruption of arenal volcano on july 29 31 1968 after centuries of dormancy produced three new fissural craters a b and c on its western flank and a multilayered pyroclastic deposit emplaced by complex transport mechanisms the explosions were initially triggered by a volatile oversaturated 4 7 wt h2o magma several lines of evidences suggest a small blast surge where a wood rich pyroclastic deposit was emplaced as a ground layer followed by several units of coarse grained md between 0 65 and 5 40 tephra deposits lu lapilli units dau double ash units lu 1 2 3 dau 1 and 2 consist of unconsolidated and well to poorly sorted vesiculated bombs and lapilli of andesite some blocks ash and shredded wood the individual units are possibly correlated with the major explosions of july 29 the thickness of the deposits decreases with the distance from the volcano from 5 6 m to a few centimeters on average 90 of the components are juvenile 10 dense andesite and 90 vesicular these coarse grained beds were deposited in rapid succession by a complex transport process involving normal fallout strong ballistic trajectories with a lateral hot 400 c blast surge lu equivalent to a1 ballistic and coarse tephra sprayed in a narrow 85 area within about 5 5 km from the lowest crater and a high ca 10 km eruption column dispersed airfall fine lapilli ash 100 km from the volcano ashcloud forming explosions producing thin pyroclastic surge and muddy phreatomagmatic fallout deposits flau equivalent to a2 and a3 closed the blast surge sequence the successive explosions on july 30 31 mainly produced block and ash flows and widely dispersed ash fall the total volume of pyroclastic material is calculated as 25 8 5 5 10 6 m 3 9 4 2 0 10 6 m 3 dre a model is proposed to explain the peculiarities of the formation transportation and emplacement of the blast deposits the intrusion of the presumed andesitic cryptodome possibly happened through an active thrust fault favoring not only the formation of the lowest crater a but also the low angle explosive events prior to the eruption several minerals were settling to the bottom of the magma chamber as is suggested by the increase of incompatible elements towards the bottom of the stratigraphic section the major elements indicate that some crystal redistribution occurred and the maximum concentration of al2o3 and eu and sr support plagioclase enrichment in early phases of the eruption top of lu 1 and dau 1 from the about 20 recognized prehistoric and historic blast deposits in the world approximately half were produced by sector collapse of the volcano and the other half by sudden decompression of cryptodomes or lava dome collapses the recent blasts 1888 1990s elsewhere have an apparent recurrence of one event decade compared to just a