orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

high resolution carbon isotope records of the aptian to lower albian from se france and the mazagan plateau dsdp site 545 a stratigraphic tool for paleoceanographic and paleobiologic reconstruction high resolution carbon isotope stratigraphy is established for the aptian to lower albian of the vocontian basin se france and correlated to the carbon isotope record of the mazagan plateau dsdp site 545 the carbon isotope stratigraphy of the vocontian basin is proposed as a standard reference curve for the aptian to lower albian due to the completeness and high temporal resolution of the stratigraphic succession the good biostratigraphical time control and the frequent occurrence of regional to global black shale horizons including oceanic anoxic events 1a oae 1a of the lower aptian and oae 1b of the lower albian the carbon isotope record appears better suited for long distance short term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types however the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography and to correlate regional to global black shale horizons in different marine environments this combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species based on the demonstrated diachroneity of important biostratigraphic markers of the aptian albian boundary the globally observed break point between the end of the uppermost aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13c values is an alternative criterion the distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the aptian to lower albian

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

morphological variation of emiliania huxleyi and sea surface salinity morphometric analysis of coccoliths of various coccolithophore species from core top and culture samples has revealed that the morphology of single placoliths can be affected by environmental parameters such as temperature salinity and productivity in this study we have tested the morphological variations of placoliths of emiliania huxleyi the most common coccolithophore species in the modern ocean with respect to environmental gradients we have investigated especially the potential effect of salinity on the morphology as it is known from culture studies that the growth of e huxleyi placoliths is strongly influenced by varying salinities morphometric analysis of about 2150 placoliths from 37 globally distributed core top and plankton samples revealed that the morphology of e huxleyi varies significantly along a sea surface salinity gradient from 33 to 38 morphological parameters such as the mean size of placoliths are used as explaining variables in multiple regression analysis to reconstruct sea surface salinities sss the best model for mean sss yields an r 2 of 0 88 with a standard error of 0 49 whereas statistical models describing surface water temperature or productivity are less reliable and accurate application of the best model to plankton samples allows the prediction of in situsalinitieswithingivenerrorestimates theapplicationofthebestmodeltofossilassemblagesfromthelgm however ismore puzzling paleosalinity reconstructions in the south atlantic the caribbean sea and the subtropical atlantic are in good agreement with the published values 2007 elsevier b v all rights reserved

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

widespread loess like deposit in the martian northern lowlands identifies middle amazonian climate change consistently mappable units critical to distinguishing the style and interplay of geologic processes through time are sparse in the martian lowlands this study identifies a previously unmapped middle amazonian ca 1 ga unit middle amazonian lowland unit mal that postdates the late hesperian and early amazonian lowland plains by 2 b y the unit is regionally defined by subtle marginal scarps and slopes has a mean thickness of 32 m and extends 3 1 10 6 km 2 between lat 35 n and 80 n pedestal type craterforms and nested arcuate ridges thumbprint terrain tend to occur adjacent to unit mal outcrops suggesting that current outcrops are vestiges of a more extensive deposit that previously covered 16 10 6 km 2 exposed layers surface pits and the draping of subjacent landforms allude to a sedimentary origin perhaps as a loess like deposit emplaced rhythmically through atmospheric fallout we propose that unit mal accumulated coevally with and at the expense of the erosion of the north polar basal units identifying a major episode of middle amazonian climate driven sedimentation in the lowlands this work links ancient sedimentary processes to climate change that occurred well before those implied by current orbital and spin axis models

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

wide distribution and glacial origin of polar gypsum on mars the north polar cap of mars is associated with different kinds of superficial sediments including the circumpolar dune field interior dune fields and sedimentary veneers scattered over the ice cap in order to resolve the mineralogical composition and the regional distribution of these sediments we processed omega and crism hyperspectral data with an original method based on spectral derivation we find that gypsum is present in all areas where undefined hydrated minerals had been previously detected including superficial sedimentary veneers covering the north polar cap interior dune fields and the whole circumpolar dune field morphological and structural analyses reveal that these gypsum crystals derive directly from the interior of the ice cap the source of superficial sedimentary veneers is the dust that was previously contained in the upper part of the ice cap the ice rich north polar layered deposits npld this gypsum bearing dust was released on south facing slopes of spiral troughs and arcuate scarps by ice ablation controlled by katabatic winds by the analysis of all associations of erosional scarps and dune fields over the north polar cap we also demonstrate that the polar dunes are composed of sand sized particles that were previously contained in the sediment rich basal unit bu corresponding to the lower part of the ice cap these particles contain gypsum and were released from the bu by regressive ablation of ice at marginal scarps that border the north polar cap and by vertical ablation of ice on olympia planum from a reconstruction of wind streamlines over and around the ice cap we infer that katabatic winds descending from the polar high and rotating around the north polar cap control the release of these gypsum bearing particles by ice ablation and the redistribution of these particles in the circumpolar dune field 2011 elsevier b v

three dimensional structure and origin of a 1 8 km thick ice dome within korolev crater mars korolev is an 80 km diameter impact crater located at 72 7 n 164 5 e containing a large domed deposit perennial water ice is thought to be currently unstable there however using a 3 d analysis of the dome s internal radar stratigraphy we estimate that korolev s central mound contains between 1400 and 3500 km3 of water ice that is up to 1 8 km thick furthermore the stratigraphic structure of this ice dome is strikingly similar to the north polar layered deposits npld on planum boreum approximately 600 km to the north additionally our stratigraphic analysis suggests that korolev ice was not previously part of a once larger polar ice sheet but rather it was deposited locally we conclude that korolev crater s ice likely deposited during the same climate regime as planum boreum s npld but independently this implies that the incorporation of circumpolar ice deposits such as korolev may prove useful in reconstructing a unique mars polar climate history

meter scale morphology of the north polar region of mars mars north pole is covered by a dome of layered ice deposits detailed 30 centimeters per pixel images of this region were obtained with the high resolution imaging science experiment on board the mars reconnaissance orbiter mro planum boreum basal unit scarps reveal cross bedding and show evidence for recent mass wasting flow and debris accumulation the north polar layers themselves are as thin as 10 centimeters but appear to be covered by a dusty veneer in places which may obscure thinner layers repetition of particular layer types implies that quasi periodic climate changes influenced the stratigraphic sequence in the polar layered deposits informing models for recent climate variations on mars

density of mars south polar layered deposits both poles of mars are hidden beneath caps of layered ice we calculated the density of the south polar layered deposits by combining the gravity field obtained from initial results of radio tracking of the mars reconnaissance orbiter with existing surface topography from the mars orbiter laser altimeter on the mars global surveyor spacecraft and basal topography from the mars advanced radar for subsurface and ionospheric sounding on the mars express spacecraft the results indicate a best fit density of 1220 kilograms per cubic meter which is consistent with water ice that has 15 admixed dust the results demonstrate that the deposits are probably composed of relatively clean water ice and also refine the martian surface water inventory

observations of the north polar region of mars from the mars orbiter laser altimeter elevations from the mars orbiter laser altimeter mola have been used to construct a precise topographic map of the martian north polar region the northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5 kilometer deep hemispheric depression that is contiguous with the area into which most outflow channels emptied polar cap topography displays evidence of modification by ablation flow and wind and is consistent with a primarily h2o composition correlation of topography with images suggests that the cap was more spatially extensive in the past the cap volume of 1 2 3 10 6 to 1 7 3 10 6 cubic kilometers is about half that of the greenland ice cap clouds observed over the polar cap are likely composed of co 2 that condensed out of the atmosphere during northern hemisphere winter many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

dielectric constant estimation of the uppermost basal unit layer in the martian boreales scopuli region abstract an electromagnetic inversion model has been applied to echoes from the subsurface sounding shallow radar sharad to retrieve the dielectric properties of the uppermost basal unit bu beneath the north polar layered deposits of mars sharad data have been carefully selected to satisfy the assumption of the inversion model which requires a stratigraphy consisting of mostly plane parallel layers the resulting values of the dielectric constant have been interpreted in terms of a variable percentage of dust in an ice dust mixture through the use of a mixing model for dielectric properties the resulting dust content exceeds 65 reaching perhaps 95 depending on the permittivity values assumed for the dust such a concentration is higher than that obtained by selvans et al selvans m m plaut j j aharonson o 2010 j geophys res 115 e09003 this discrepancy could be justified considering that our observations refer to the uppermost bu layer whereas selvans et al selvans m m plaut j j aharonson o 2010 j geophys res 115 e09003 probed the bu full thickness moreover if the bu is considered spatially inhomogeneous with very different dust content and thickness tanaka k l skinner j a fortezzo c m herkenhoff k e rodriguez j a p bourke m c kolb e j okubo c h 2008 icarus 196 318 358 the discrepancy could be furtherly reconciled

geology and insolation driven climatic history of amazonian north polar materials on mars a wealth of image and topographic data from the mars global surveyor and mars odyssey missions has been combined in a detailed geological map of the north polar region of mars one intriguing finding is a cycle of ice deposition similar in duration to a 1 470 year climate cycle of unknown origin on earth if both are externally driven a mechanism that affects both planets such as variation in solar luminosity must be involved mariner 9 and viking spacecraft images revealed that the polar regions of mars like those of earth record the planet s climate history however fundamental uncertainties regarding the materials features ages and processes constituting the geologic record remained1 2 3 4 5 6 recently acquired mars orbiter laser altimeter data7 and mars orbiter camera high resolution images8 from the mars global surveyor spacecraft and moderately high resolution thermal emission imaging system visible images9 from the mars odyssey spacecraft permit more comprehensive geologic and climatic analyses10 11 12 13 14 15 16 17 here i map and show the history of geologic materials and features in the north polar region that span the amazonian period 3 0 gyr ago to present 18 19 erosion and redeposition of putative circumpolar mud volcano deposits15 formed by eruption of liquefied fine grained material led to the formation of an early amazonian polar plateau consisting of dark layered materials crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the amazonian suggesting generally higher obliquity and insolation conditions at the poles than at present brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4 5 myr ref 20 finally the uppermost layers post date the latest downtrend in obliquity 20 000 years ago20

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

structural identification of steryl alkyl ethers in marine sediments steryl alkyl ethers have been reported to occur in immature marine sediments up to cretaceous age here we report their unambiguous structural identification in holocene sediments from the arabian sea pleistocene sediments from the southeast atlantic and a miocene sediment from the monterey formation through chemical degradation experiments and synthesis we show that the main steryl alkyl ethers in sediments from the southeast atlantic are cholest5 enyl 3b 2 dodecanyl ether and cholest 5 enyl 3b 3 dodecanyl ether together with their 24 methyl and 24 ethyl pseudo homologues steryl alkyl ethers in sediments from the arabian sea are dominated by cholest 5 enyl 3b 5 decanyl ether and cholest 5 enyl 3b 4 decanyl ether together with their 24 methyl and 24 ethyl pseudo homologues the structures suggest that these compounds are formed by direct biosynthesis by as yet unknown marine organisms 2005 elsevier ltd all rights reserved

crater population and resurfacing of the martian north polar layered deposits present day accumulation in the north polar layered deposits npld is thought to occur via deposition on the north polar residual cap understanding current mass balance in relation to current climate would provide insight into the climatic record of the npld to constrain processes and rates of npld resurfacing a search for craters was conducted using images from the mars reconnaissance orbiter context camera one hundred thirty craters have been identified on the npld 95 of which are located within a region defined to represent recent accumulation high resolution imaging science experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal a classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth diameter ratios were determined the temporal and spatial distribution of crater degradation is interpreted to be close to uniform through comparison of the size frequency distribution of these craters with the expected production function the craters are interpreted to be an equilibrium population with a crater of diameter d meters having a lifetime of 30 75d 1 14 years accumulation rates within these craters are estimated at 7 2d 0 14 mm yr which corresponds to values of 3 4 mm yr and are much higher than rates thought to apply to the surrounding flat terrain the current crater population is estimated to have accumulated in the last 20 kyr or less

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

three dimensional radar imaging of structures and craters in the martian polar caps abstract over the last decade observations acquired by the shallow radar sharad sounder on individual passes of the mars reconnaissance orbiter have revealed the internal structure of the martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate however a complete picture of the cap interiors has been hampered by interfering reflections from off nadir surface features and signal losses associated with sloping structures and scattering foss et al the leading edge 36 43 57 2017 https doi org 10 1190 tle36010043 1 addressed these limitations by assembling three dimensional data volumes of sharad observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously the radar volumes provide unprecedented views of subsurface features readily imaging structures previously inferred from time intensive manual analysis of single orbit data e g trough bounding surfaces a buried chasma and a basal unit in the north massive carbon dioxide ice deposits and discontinuous layered sequences in the south our new mapping of the carbon dioxide deposits yields a volume of 16 500 km 3 11 larger than the prior estimate in addition the radar volumes newly reveal other structures including what appear to be buried impact craters with no surface expression our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a hesperian age for the substrate consistent with that of the surrounding plains as determined from statistics of surface cratering rates planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits the radar volumes also provide new topographic data between the highest latitudes observed by the mars orbiter laser altimeter and those observed by sharad in general mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes

geochemistry and organic petrography of cretaceous sediments of the calabar flank southeastern nigeria abstract detailed bulk geochemistry and organo petrography of outcrop cretaceous sediments with no significant effects of weathering from the calabar flank southeast nigeria were performed to understand the organic carbon source accumulation and degradation and paleo climatic paleoceanographic and paleoenvironmental conditions in west africa during early cretaceous aptian to maastrichtian times this study was based on microscopic elemental analyses organic carbon nitrogen iron and sulphur rock eval pyrolysis and carbon isotope analyses in general the calabar flank shales are characterised by highly variable total organic carbon toc contents which range between 0 1 in aptian albian mfamosing limestone and 9 9 in the awi formation sediments the organic matter om is a mixture of immature to early mature marine and terrigenous om of types iii and iv this is indicated by low hydrogen indices hi value 10 190 mg hc g toc tmax 417 460 c vitrinite reflectance ro 0 39 0 62 ro low to high c n ratios 3 4 1158 0 and high amounts of terrigenous macerals vitrinite inertinite based on carbon isotope c n ratios and sulphate reduction index sri om degradation up to 70 sri 2 5 is most pronounced for shales deposited in a marine environment the geochemical and petrographic data indicate that local factors such as low bioproductivity down slope transport and redeposition of sediments from a fluvial deltaic basin to nearshore facies shallower oxic and mildly oxygen deficient environments humid arid paleogeographic conditions specifically controlled the amount and quality of the om during aptian mastrichtian stages where marine sediments have been assumed to be deposited during the global anoxic events therefore the order of the main factors controlling om content in sediments are input of terrigenous material transported from the land low om productivity by marine photoautotrophs low preservation

warming the fuel for the fire evidence for the thermal dissociation of methane hydrate during the paleocene eocene thermal maximum dramatic warming and upheaval of the carbon system at the end of the paleocene epoch have been linked to massive dissociation of sedimentary methane hydrate however testing the paleocene eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events the cause of the paleocene eocene thermal maximum carbon isotope excursion remains speculative primarily due to uncertainties in the timing and duration of the paleocene eocene thermal maximum we present new high resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from ocean drilling program site 690 weddell sea southern ocean demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming both of these findings support the thermal dissociation of methane hydrate as the cause of the paleocene eocene thermal maximum carbon isotope excursion furthermore the data reveal that the methane derived carbon was mixed from the surface ocean downward suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation

flexure of the lithosphere beneath the north polar cap of mars implications for ice composition and heat flow the geodynamical response of the lithosphere under stresses imposed by the geologically young north polar cap is one of the few clues we have to constrain both its composition and the present day t

organic carbon deposition in the cretaceous of the ionian basin nw greece the paquier event oae 1b revisited we present new stable c o isotopic biostratigraphic and organic geochemical data for the vigla shale member of the ionian zone in nw greece in order to characterize organic carbon rich strata that potentially record the impact of cretaceous oceanic anoxic events oaes in a section exposed near gotzikas nw epirus we sampled a number of decimetre thick organic carbon rich units enclosed within marly locally silicified vigla limestone berriasian turonian all these units are characterized by largely comparable bulk geochemical characteristics indicating a common marine origin and low thermal maturity however the stratigraphically highest of these black shales is further distinguished by its much higher total organic carbon toc content 28 9 wt and hydrogen index hi 529 and much enriched delta 13corg value minus sign 22 1 planktonic foraminiferal and calcareous nannofossil biostratigraphy indicate a lower to middle albian age for the strata immediately above and a lower aptian age for the strata below the uppermost black shale in terms of molecular organic geochemistry the latter black shale is also relatively enriched in specific isoprenoidal compounds especially monocyclic isoprenoids whose isotopic values are as high as minus sign 15 indicating a substantial archaeal contribution to the organic matter the striking similarities between the molecular signatures of the uppermost vigla black shale and coeval organic rich strata from se france and the north atlantic odp site 1049c indicate that this level constitutes a record of the paquier event oae 1b

origin and characteristics of the mars north polar basal unit and implications for polar geologic history building upon previous studies we have used mars orbiter camera and mars orbiter laser altimeter data to characterize in detail the newly discovered north polar basal unit lying stratigraphically between the polar layered deposits from which it is likely separated by an unconformity and the vastitas borealis formation this unit has introduced new complexity into north polar stratigraphy and has important implications for polar history exposures of the basal unit in olympia planitia and chasma boreale reveal relatively dark layers which exhibit differential erosion eroded primarily by wind the basal unit may be the major if not sole source for the north polar dunes and ergs and has contributed material to the lower polar cap layers we investigate four possible origins for the basal unit outflow channel oceanic deposits basal ice paleopolar deposits and eolian deposits the patchy layering within the unit its likely sandy grain size and presence only in the north polar basin suggest that it is primarily an eolian deposit supporting byrne and murray s 2002 earlier conclusion this implies that at some time during the early to late amazonian migrating sand was mixed with water ice forming a relatively dark sandy deposit during this time either no classic polar layered deposits were forming or smaller caps were growing and shrinking possibly adding material to the basal unit

buried ice and sand caps at the north pole of mars revealing a record of climate change in the cavi unit with sharad nasa mars data analysis program nnx15am52g landmark software and services a halliburton company

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

surface ages and resurfacing rates of the polar layered deposits on mars interpretation of the polar stratigraphy of mars in terms of global climate changes is complicated by the significant difference in surface ages between the north and south polar layered terrains inferred from crater statistics we have reassessed the cratering record in both polar regions using viking orbiter and mariner 9 images no craters have been found in the north polar layered terrain but the surface of most of the south polar layered deposits appears to have been stable for many of the orbital axial cycles that are thought to have induced global climate changes on mars the inferred surface age of the south polar layered deposits about 10 ma is two orders of magnitude greater than the surface age of the north polar layered deposits and residual cap at most 100 ka similarly modeled resurfacing rates are at least 20 times greater in the north than in the south these results are consistent with the hypotheses that polar layered deposit resurfacing rates are highest in areas covered by perennial ice and that the differences in polar resurfacing rates result from the 6 4 km difference in elevation between the polar regions deposition on the portion of the south polar layered deposits that is not covered by the perennial ice cap may have ceased about 5 million years ago when the obliquity of mars no longer exceeded 40

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

internal structure of planum boreum from mars advanced radar for subsurface and ionospheric sounding data 1 an investigation of the internal structure of the ice rich planum boreum pb deposit at the north pole of mars is presented using 178 orbits of mars advanced radar for subsurface and ionospheric sounding data for each radargram bright laterally extensive surface and subsurface reflectors are identified and the time delay between them is converted to unit thicknesses using a real dielectric constant of 3 results include maps of unit thickness for pb and its two constituent units the stratigraphically older basal unit bu and the stratigraphically younger north polar layered deposits npld maps of the individual units surface elevation are also provided estimates of water ice volume in each unit are 1 3 0 2 106 km3 in pb 7 8 1 2 105 km3 in the npld and 4 5 1 0 105 km3 in the bu no lithospheric deflection is apparent under pb in agreement with previous findings for only the gemina lingula lobe which suggests that a thick elastic lithosphere has existed at the north pole of mars since before the emplacement of the bu the extent of bu material in the olympia planum lobe of pb is directly detected providing a more accurate map of bu extent than previously available from imagery and topography a problematic area for mapping the bu extent and thickness is in the distal portion of the 290 e 300 e region where marsis data show no subsurface reflectors even though the bu is inferred to be present from other lines of evidence

climate driven deposition of water ice and the formation of mounds in craters in mars north polar region this paper explores the origins and evolution of ice rich interior mounds found within craters of the north polar region of mars we present a systematic study of impact craters above 65 n and identify 18 craters that have interior mounds at least 11 of these mounds are composed of water ice and geometric similarities suggest that dune covered mounds may also have a water ice core the mounds are found in the deeper craters in the north polar area and we suggest that these form a specific microclimate favorable for mound initiation and growth it is likely that at least seven of the mounds have evolved as individual outliers rather than conterminous with the main polar cap our observations suggest that the mounds are built up by atmospheric deposition similar to that of the north polar layered deposits using a combination of remote sensing techniques enabling topographic spectral radar and image data analyses we have documented the morphology composition and stratigraphy of selected mounds we advance and test four hypotheses for formation of these mounds artesian outpouring from a deep aquifer hydrothermal activation of ground ice remnants of a more extensive polar cap and atmospheric deposition on ice caps in meteorologically isolated locations we propose that during periods when the perihelion was located in northern summer most recently 10 25 ka before present the microclimate in these craters retarded the sublimation of co2 and water ice in northern spring thus creating a cold trap for volatiles released as the seasonal cap retreated this created a thick enough deposit of water ice to withstand sublimation over the summer and initiate a positive feedback leading to mound building mounds without complete dune cover may be in dynamic equilibrium with the ambient climate and show evidence of both present day and past periods of erosion and aggradation we conclude that the water ice mounds formed in deep impact craters in mars north polar region may contain sensitive records of past polar climate that may enhance our understanding of the co2 h2o system in the polar regions

the paleocene eocene carbon isotope excursion in higher plant organic matter differential fractionation of angiosperms and conifers in the arctic abstract a study of upper paleocene lower eocene p e sediments deposited on the lomonosov ridge in the central arctic ocean reveals relatively high abundances of terrestrial biomarkers these include dehydroabietane and simonellite derived from conifers gymnosperms and a tetra aromatic triterpenoid derived from angiosperms the relative percentage of the angiosperm biomarker of the summed angiosperm conifer biomarkers was increased at the end of the paleocene eocene thermal maximum petm different when observed with pollen counts which showed a relative decrease in angiosperm pollen stable carbon isotopic analysis of these biomarkers shows that the negative carbon isotope excursion cie during the petm amounts to 3 for both conifer biomarkers dehydroabietane and simonellite comparable to the magnitude of the cie inferred from marine carbonates but significantly lower than the 4 5 of the terrestrial c29 n alkane m pagani n pedentchouk m huber a sluijs s schouten h brinkhuis j s sinninghe damste g r dickens and the iodp expedition 302 expedition scientists 2006 arctic s hydrology during global warming at the paleocene eocene thermal maximum nature 442 671 675 which is a compound sourced by both conifers and angiosperms conspicuously the angiosperm sourced aromatic triterpane shows a much larger cie of 6 and suggests that angiosperms increased in their carbon isotopic fractionation during the petm our results thus indicate that the 4 5 c29 n alkane cie reported previously represents the average cie of conifers and angiosperms at this site and suggest that the large and variable cie observed in terrestrial records may be partly explained by the variable contributions of conifers and angiosperms the differential response in isotopic fractionation of angiosperms and conifers points to different physiological responses of these vegetation types to the rise in temperature humidity and greenhouse gases during the petm

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

a geophysical study of the hatton bank volcanic margin a summary of the results from a combined seismic gravity and magnetic experiment abstract this paper summarizes the results of a geophysical study of the hatton bank volcanic margin in the north atlantic normal incidence and synthetic aperture profiles saps show seaward dipping reflectors interpreted as subaerial basalt flows on the continental slope and in the adjacent ocean basin velocity depth profiles derived from expanding spread profiles esps shot along strike show elevated velocities in the lower crust on the continental slope the high velocities are interpreted as evidence for igneous underplating or intrusion gravity modelling shows high densities in the lower crust supporting a model of igneous accretion an ocean bottom seismometer obs and multichannel refraction line shot perpendicularly to strike through the midpoints of the esps further constrained the velocity structure across the margin the velocity model was refined as each dataset was processed clearly showing that multiple datasets were required in order to constrain the velocity structure tightly in particular esps were found to produce misleading results in places where the assumption that the sub surface structure is one dimensional inherent in the esp technique was not valid the final velocity model is used to infer the thickness of igneous material accreted across the hatton margin which is estimated to increase westwards from zero at the top of the bank to 18 km at the bottom of the continental slope and then thin rapidly to 11 km in the adjacent iceland basin as the oceanic crust thins its seismic velocity decreases suggesting a decrease in percentage partial melting these observations strongly support a model in which volcanic margins are produced by elevated asthenospheric temperatures

density variations within the south polar layered deposits of mars 1 the south polar layered deposits spld constitute the largest known reservoir of water on mars previous studies solved for the best fit uniform density of the deposits using a forward approach here we invert for the lateral density variations in the layered deposit using gravity data from radio tracking of mars reconnaissance orbiter topography from mola on board mars global surveyor and radar sounding data from marsis on board mars express we use the gravity anomalies outside the spld to construct a wiener filter which is applied to the gravitational signature of the spld to remove the short wavelength anomalies over the spld that are spectrally consistent with an origin in the crust or mantle we then use a constrained inversion for the vertically averaged density within the spld as a function of position the results suggest significant density variations within the spld an inverse relationship between the density and thickness of the spld suggests that thicker portions of the cap contain less dust alternatively the dorsa argentea formation may extend beneath the spld and result in the observed high gravity anomaly in the marginal area of the spld we find these conclusions to be robust against the choice of inversion constraint and perturbations to the applied filter a synthetic test is also performed to verify the recoverability of the density variation in our approach

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

south polar layered deposits of mars the cratering record data from the mars orbiter laser altimeter mola and mars orbiter camera moc instruments aboard the mars global surveyor mgs were used in a detailed search of a selected part of the south polar layered deposits spld for impact craters impact craters with diameters from 0 8 to 5 km were identified from a mola derived shaded relief map and were primarily validated using individual mola tracks and in select cases moc narrow angle images the resultant crater population determined in this study is at least four times the density of the crater population previously recognized from these new statistics we estimate the mean apparent surface age of the spld to be 30 100 ma depending on the established production model isochrons used all of these craters are considerably shallower than other martian craters in the same diameter range we attribute this shallowness to be the cause of the lower detection rates of previous studies there is a correlation between crater depth and rim height which suggests that both erosion and infilling have affected the crater forms a similar study of the north polar layered deposits uncovered no craters in this diameter range a limited population of craters smaller than 800 m was uncovered in higher resolution moc narrow angle images these do not appear to have been degraded to the same degree this separate population implies a surface exposure age of only 100 000 years and perhaps indicates an event that erased all small craters and degraded and infilled the larger ones

evolution of tropical watersheds and continental hydrology during the late cretaceous greenhouse impact on marine carbon burial and possible implications for the future abstract regional climate modelling for the late cretaceous greenhouse and high resolution marine stratigraphic records from both sides of the low latitude atlantic show that tropical south american and african hydrology and watersheds had a strong effect on freshwater transfer into the equatorial atlantic and subsequently the marine carbon record this conclusion is derived from new detailed geochemical records from demerara rise off suriname drilled at ocean drilling program odp site 1261 combined with frequency analyses and climate simulations providing evidence for mainly eccentricity driven changes in carbon burial in the western tropical atlantic shorter orbital frequencies in particular precession clearly dominating black shale cycles off tropical africa odp site 959 are far less dominant at demerara rise despite comparable time resolution of the geochemical records we suggest that these different frequency patterns in carbon burial were related to the regional evolution of cretaceous watersheds and hydrology in tropical south america and africa river discharge deduced from simulations indicates higher and less variable discharge from south america compared to western africa at that time this runoff pattern would have supported more permanent anoxic conditions off south america compared to africa at least indirectly and caused the lack of strong higher frequency geochemical cycles in the western sector of the equatorial atlantic furthermore climate simulations show a general switch of primary runoff from either side of the cretaceous equatorial atlantic every half precession cycle i e every 10 kyr similarities between the developments of cretaceous and holocene hydrology in the tropical atlantic area imply that orbital scale evolution of watersheds is a robust feature through time that is independent from the mean global climate state based upon the comparison of cretaceous and holocene trends in hydrology we infer that future hydrology in the study region may develop in a comparable direction to the one observed in the cretaceous if true this suggests that the modern amazon rain forest could shrink over the next millennium due to a 30 loss of moisture while the congo rain forest in africa is likely to expand in response to a 14 gain in moisture

planum boreum basal unit topography mars irregularities and insights from sharad shallow radar investigations of planum boreum mars basal unit bu deposit have revealed multiple reentrants morphologic irregularities and thickness trends that differ from those of the overlying north polar layered deposits we present detailed subsurface maps for these features and offer explanation for genesis of the deposit s morphologic asymmetry expressed in different erosional characteristics between 0 e 180 e and 180 e 360 e additionally this work revealed a depression in the basal unit that may have provided a site for spiral trough initiation interpretations of the findings suggest that antecedent bu topography has a marked impact on modern morphology and that aeolian forces have been the dominant driver of polar deposit accumulation since at least the end of rupes unit emplacement we find no results requiring explanation beyond common martian surface processes including aeolian erosion and impact armoring to add to the detailed morphologic study of the bu we mapped the variability of the bu radar reflection character combining generalized katabatic wind flow with the radar mapping results suggests that rupes unit material sourced the younger cavi we present clear evidence that while compositionally distinct from the overlying layered deposits the bu and its morphology are intimately linked to the morphology of the north polar layered deposits combining geologic evidence with paleoclimate modeling the deposits contain evidence for a long history of aeolian emplacement and modification

rapid warming and salinity changes of cretaceous surface waters in the subtropical north atlantic paleomarine carbon isotopic records reveal occasional and rapid release of greenhouse gases into the atmosphere the regional consequences on surface ocean properties and time relationships between the atmosphere and the ocean however are still far from understood we observe a sudden 1 5 shift in leaf wax n alkane 13c values at the onset of oceanic anoxic event oae 1b from early albian sediments off northwest africa deep sea drilling project site 545 that is best explained by the rapid release of isotopically light carbon into the cretaceous atmosphere this 1 5 shift in the n alkanes precedes a negative isotope excursion of similar magnitude observed in marine carbonate organic matter and algal steranes a tex86 based record of sea surface temperature sst confirms almost instantaneous warming by 3 5 c along with the marine isotope shifts at site 545 paralleled by an 2 c tex86 sst increase and a freshening of surface water salinity from 43 to 41 at blake nose ocean drilling program site 1049 multiproxy evidence indicates that once established these warm ssts prevailed and were stable during oae 1b suggesting that the emission of 13c depleted carbon started abruptly but then continued over tens of thousands of years the sst cooled by 1 2 c at the end of the event not reaching pre excursion levels the new records provide evidence for a time lag best estimate 1 3 k y between atmospheric and oceanic processes that we interpret as a direct response to changes in the atmospheric greenhouse gas concentrations followed by propagation into the ocean and subsequent heating of surface waters

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

viscous relaxation of craters within the martian south polar layered deposits abstract the south polar layered deposits pld are of fundamental importance to martian climatology as they may comprise the largest reservoir of near surface water on mars the south pld exhibit relatively young crater retention surface ages which are widely attributed to recent resurfacing however we show that both constructional and destructional resurfacing mechanisms such as dust deposition and water ice sublimation respectively are inconsistent with the size depth and spatial distributions of south pld craters we demonstrate that another process viscous creep relaxation of dusty water ice is more compatible with the observed cratering of south pld surfaces the results of our finite element relaxation simulations suggest that despite their apparent youthfulness the pld have been stable for at least several hundred million and perhaps even over a billion years consequently our modeling implies that the time scales for the formation and preservation of the layers characteristic of the south and possibly north pld are much longer than generally assumed

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

recent formation and evolution of northern martian polar layered deposits as inferred from a global climate model 1 we present a time marching model which simulates the exchange of water ice between the martian northern cap the tropics and a high latitude surface reservoir net annual exchange rates of water and their sensitivity to variations in orbital rotational parameters are examined using the martian water cycle modeled by the lmd three dimensional global climate model these rates are propagated over the last 10 myr to follow the thickness of the reservoirs the effect of a sublimation dust lag is taken account to test simple models of layer formation periods of high mean polar summer insolation 5 10 ma ago lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers the formation of a northern cap and of a high latitude icy mantle may have started 4 ma ago with the average decrease of polar insolation tropical ice may have disappeared around 2 7 ma ago but small glaciers could have formed during the last peaks of polar summer insolation over the last 4 myr most of the present cap may have formed at the expense of tropical and high latitude reservoirs forming distinct layers at almost each 51 kyr 120 kyr insolation cycle layers thickness ranges from 10 to 80 m variations being produced by the modulation of the obliquity with 2 4 and 1 3 myr periods because only 30 insolation cycles have occurred since 4 ma ago we found an inconsistency between the recent astronomical forcing the observed number of layers and simple astronomically based scenarios of layers formation

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity

consequences of moderate 25 000 yr lasting emission of light co 2 into the mid cretaceous ocean future warming is predicted to shift the earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming this study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not vert similar 112 myr ago our study focuses on the cretaceous oceanic anoxic event oae 1b and explores how the earth system responded to a moderate not vert similar 25 000 yr lasting climate perturbation that is modelled to be less than 1 c in global average temperature using a new chronological model for oae 1b we present high resolution elemental and bulk carbon isotope records from dsdp site 545 from mazagan plateau off nw africa and combine this information with a coupled atmosphere land ocean model the simulations suggest that a perturbation at the onset of oae 1b caused almost instantaneous warming of the atmosphere on the order of 0 3 c followed by a longer not vert similar 45 000 yr period of not vert similar 0 8 c cooling the marine records from dsdp site 545 support that these moderate swings in global climate had immediate consequences for african continental supply of mineral matter and nutrients phosphorous subsequent oxygen availability and organic carbon burial in the eastern subtropical atlantic however without turning the ocean anoxic the match between modelling results and stratigraphic isotopic data support previous studies summarized in jenkyns h c 2003 evidence for rapid climate change in the mesozoic palaeogene greenhouse world the royal society 361 1885 1916 in that methane emission from marine hydrates albeit moderate in dimension may have been the trigger for oae 1b though we can not finally rule out alternative mechanisms following the hydrate mechanism a total of 1 15 1018 g methane carbon 13c 60 equivalent to about 10 to the total modern gas hydrate inventory generated the 13ccarb profile recorded in the section modelling suggests a combination of moderate scale methane pulses supplemented by continuous methane emission at elevated levels over not vert similar 25 000 yr the proposed mechanism though difficult to finally confirm in the geological past is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously this study shows that once set off this mechanism can maintain earth s climate in a perturbed mode over geological time leading to pronounced changes in regional climate

correlation of aptian albian carbon isotope excursions in continental strata of the cretaceous foreland basin eastern utah u s a abstract nodular carbonates calcretes in continental foreland basin strata of the early cretaceous cedar mountain formation cmf in eastern utah yield 13c and 18o records of changes in the exogenic carbon cycle related to oceanic anoxic events oaes and terrestrial paleoclimate chemostratigraphic profiles of both forebulge and foredeep sections show two prominent positive 13c excursions each with a peak value of 3 0 vpdb and having background 13c values of about 6 0 vpdb these excursions correlate with the global early aptian ap7 and late aptian early albian ap12 al1 carbon isotope excursions aptian albian positive 13c excursions in the cmf also correspond to 3 4 per mil increases in carbonate 18o these phenomena record local aridification events the chemostratigraphic profile on the thinner forebulge section of the cmf is calibrated for the first time by a radiogenic u pb date of 119 4 2 6 ma on a carbonate bed and by detrital zircon u pb dates on two bounding sandstone units maximum depositional ages of 146 ma and 112 ma petrographic observations and diagenetic analyses of micritic to microsparitic carbonates from nodules indicate palustrine origins and demonstrate that they crystallized in shallow early meteoric phreatic environments meteoric calcite lines derived from cmf carbonates have 18o values ranging between 8 1 to 7 5 0 vpdb supporting an estimate of zonal mean groundwater 18o of 6 0 vsmow for an aptian albian paleolatitude of 34 n furthermore our two chemostratigraphic profiles exhibit a generally proportionate thinning of correlative strata from the foredeep on to the forebulge suggesting that there were consistently lower rates of accumulation on the forebulge during the aptian albian identification of the global aptian albian 13c excursions in purely continental strata as demonstrated in this paper opens a new avenue of research by identifying specific stratigraphic intervals that record the terrestrial paleoclimatic impacts of perturbations of the global carbon cycle

stratigraphy of promethei lingula south polar layered deposits mars in radar and imaging data sets 1 the south polar layered deposits spld of mars have been studied through imagery for decades now two subsurface sounding radar instruments have collected data the mars advanced radar for subsurface and ionospheric sounding marsis instrument on mars express and the shallow radar sharad instrument on mars reconnaissance orbiter are observing the spld at multiple frequencies 1 8 5 and 20 mhz respectively both instruments detect subsurface reflections in the promethei lingula region of the spld marsis detects up to three reflections within promethei lingula in addition to detecting the basal contact between the spld and the underlying plains sharad detects 10s of reflections without penetrating to the base of the spld marsis reflections likely correlate to the boundaries of packets of reflections in the sharad data whatever change in composition of the spld that causes the sharad reflections to occur in packets may also be the source of the marsis reflections in several locations sharad reflections can be compared directly with images of layers an individual reflection corresponds to 3 7 layers in images at resolutions of 6 m pixel reflection surfaces are calculated using the radar observations and extrapolated to the spld margins where they are compared to the stratigraphy observed in images we find that the marsis reflections and thus the packet structure within the sharad observations are likely related to distinctive groups of layers rather than individual layers the radar data sets allow us to confirm several predictions concerning the interior of the spld from stratigraphic studies of images including that most of the layers extend throughout the region and that they decrease in elevation toward the margin of the spld

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick