a constraint to the wisconsinan glacial history canadian arctic archipelago thick ice bearing permafrost is not observed today beneath the deeper channels of the central queen elizabeth islands canadian arctic archipelago analysis of a precision temperature log recently obtained at an offshore well near ellef ringnes island indicates that the thermal regime beneath the seabed is in equilibrium with today s marine environment if thick permafrost similar to that observed on land today had existed in the pleistocene in areas that are presently offshore then such permafrost must have started melting no later than 25000 years ago in order to allow the present thermal regime to evolve this suggests that the inter island channels must have been water filled at least by that date

canadian arctic permafrost observatories detecting contemporary climate change through inversion of subsurface temperature time series 1 we describe long term permafrost temperature and climate change observatories established in the northeastern canadian high arctic 77 82 5 n two sites have deep temperature logs 165 and 800 m and thermistor cables and automatic loggers have been installed in the upper 65 m the third site has multiple temperature logs at three 61 m boreholes with thermistor cables frozen into the permafrost a fourth deep site 750 m is included for regional completeness geothermal spectrum inversion is used to determine ground surface temperature histories the little ice age is resolved from the mid 1700s to mid 1800s with surface temperatures 1 k below the long term mean a subsequent recovery yields late 20th century surface temperatures 3 k higher these results correlate with similar reconstructions reported for greenland ice cap holes grip and dye 3 to the southeast the canadian and greenland surface temperatures show a weak inverse correlation with the north atlantic oscillation suggesting recent climate change as a common causal source simultaneous inversions of multiple logs over 22 years at the 61 m holes resolve two to three major cycles in ground surface temperature variation over the latter half of the 20th century here permafrost ground temperatures increase 0 3 0 5 c decade compared to 0 6 c decade for air temperatures annual total snow increases 22 cm decade and may insulate permafrost from the larger transient trends in air temperatures finally atmospheric temperature inversions prevalent in arctic winters may contribute to anomalously high ground surface temperatures observed at two locations

low pco2 in the pore water not in the archean air arising from m t rosing d k bird n h sleep c j bjerrum 744 747 2010 10 1038 nature08955 the solar luminosity during the archean 3 8 to 2 5 billion years ago was 20 25 lower than at present and was probably compensated at least in part by a stronger greenhouse effect1 2 3 rosing et al 4 estimate the archean partial pressure of carbon dioxide to have been about 10 3 bar on the basis of the simultaneous occurrence of magnetite fe3o4 and siderite feco3 in banded iron formations bifs a type of chemical sediment here we question a central assumption by rosing et al 4 that the mineralogy of bifs reflects near thermodynamic equilibrium with the atmosphere ocean system just as the presence of authigenic pyrite in modern sediments does not imply that the modern atmosphere is anoxic the mineralogy of bifs cannot be used to argue for a low archean atmosphere carbon dioxide is therefore still a viable greenhouse gas candidate with which to explain the warm archean climate

geothermal inversion of canadian arctic ground temperatures and effect of permafrost aggradation at emergent shorelines we apply traditional geothermal spectrum inversion to precision temperature logs and thermal conductivity from 10 wells in the canadian arctic archipelago 75 to 81 n sites lie beyond the holocene marine limit and no effect of deep permafrost dynamics is expected ground surface temperature gst changes correlate with the little ice age and little climatic optimum with average amplitudes relative to 1980 of 2 7 k and 1 6 k respectively results correlate broadly with similar reconstructions for this area and greenland ice cap holes grip and dye 3 to the southeast an offshore site in 244 m water yields a little ice age seabed temperature amplitude of 0 7 k suggesting a moderated climate impact on regional ocean temperatures nearshore boreholes where permafrost is aggrading owing to glacioisostatic emergence are excluded we demonstrate that traditional inversion codes without latent heat of phase change predict the magnitude of the emergence signal but a timing far too recent

large scale magnetic field perturbation arising from the 18 may 1980 eruption from mount st helens washington abstract a traveling magnetic field disturbance generated by the 18 may 1980 eruption of mount st helens at 1532 ut was detected on an 800 km linear array of recording magnetometers installed along the san andreas fault system in california from san francisco to the salton sea arrival times of the disturbance field from the most northern of these 24 magnetometers 996 km south of the volcano to the most southern 1493 km s23 e are consistent with the generation of a traveling ionospheric disturbance stimulated by the blast pressure wave in the atmosphere the first arrivals at the north and the south ends of the array occurred at 26 and 48 min respectively after the initial eruption apparent average wave velocity through the array is 309 14 m s 1 but may have approached 600 m s 1 close to the volcano the horizontal phase and the group velocity of 300 m s 1 at periods of 70 80 min and the attenuation with distance strongly suggest that the magnetic field perturbations at distances of 1000 1500 km are caused by gravity mode acoustic gravity waves propagating at f region heights in the ionosphere

precambrian paleosols and atmospheric co2 levels abstract precambrian atmospheric pco2 levels were previously estimated using a simple thermodynamic model based on the mineral assemblage in paleosols in addition to theoretical flaws with that model recalculation of pco2 levels using more recent thermodynamic data gives significantly lower values a new model based on the mass balance of weathering in paleosols gives consistent results from three separate 2 2 ga old paleosols the calculated pco2 value of 23 3 3 times present atmospheric levels is insufficient to overcome the faint young sun paradox suggesting that another greenhouse gas such as ch4 was present at elevated levels relative to the present atmosphere to account for the discrepancy applying this new approach to other precambrian paleosols a proterozoic pco2 curve is generated which indicates consistently high pco2 from 2 5 to 1 8 ga ago and a substantial drop in atmospheric pco2 at some time between 1 8 and 1 1 ga ago

mineralogical constraints on precambrian pco2 arising from m t rosing d k bird n h sleep c j bjerrum 744 747 2010 10 1038 nature08955 rosing and others1 recently proposed a new model for the early earth s atmospheric composition they suggest on the basis of mineral assemblages in sedimentary rocks that atmospheric co2 and ch4 concentrations have been consistently overestimated this proposal is intriguing given that high concentrations of these gases are traditionally considered to be the solution to the faint young sun paradox of why the earth did not freeze over in our sun s youth when solar luminosity was greatly decreased rosing and others1 instead invoke a decreased planetary albedo during the earth s early history new insights into this problem which has long captivated those interested in the earth s early climate and biological history are welcome however we believe that the arguments presented by rosing and others1 for roughly modern values of the partial pressure of co2 are not robust

constraints on ocean carbonate chemistry and pco2 in the archaean and palaeoproterozoic one of the great problems in the history of earth s climate is how to reconcile evidence for liquid water and habitable climates on early earth with the faint young sun predicted from stellar evolution models possible solutions include a wide range of atmospheric and oceanic chemistries with large uncertainties in boundary conditions for the evolution and diversification of life and the role of the global carbon cycle in maintaining habitable climates increased atmospheric co 2 is a common component of many solutions but its connection to the carbon chemistry of the ocean remains unknown here we present calcium isotope data spanning the period from 2 7 to 1 9 billion years ago from evaporitic sedimentary carbonates that can test this relationship these data from the tumbiana formation the campbellrand platform and the pethei group exhibit limited variability such limited variability occurs in marine environments with a high ratio of calcium to carbonate alkalinity we are therefore able to rule out soda ocean conditions during this period of earth history we further interpret this and existing data to provide empirical constraints for carbonate chemistry of the ancient oceans and for the role of co 2 in compensating for the faint young sun

a constant daylength during the precambrian era the semidiurnal atmospheric thermal tide would have been resonant with free oscillations of the atmosphere when the day was approximately 21 h long c 600 ma ago very large atmospheric tides would have resulted with associated surface pressure oscillations in excess of 10 mbar in the tropics near resonance the sun s gravitational torque on the atmospheric tide accelerating earth s rotation would have been comparable in magnitude to the decelerating lunar torque upon the oceanic tides the balance of the opposing torques may have long maintained a resonant approximately 21 h day perhaps for much of the precambrian because the timescale of lunar orbital evolution is not directly affected a constant daylength would result in fewer days month the hypothesis is shown not to conflict with the available stromatolitic evidence escape from the resonance could have followed a relatively abrupt global warming such as that occurring at the end of the precambrian alternatively escape may simply have followed a major increase in the rate of oceanic tidal dissipation brought about by the changing topography of the world s oceans we integrate the history of the lunar orbit with and without a sustained resonance finding that the impact of a sustained resonance on the other orbital parameters of the earth moon system would have not been large

blast dynamics at mount st helens on 18 may 1980 at 8 32 a m on 18 may 1980 failure of the upper part of the north slope of mount st helens triggered a lateral eruption the blast that devastated the conifer forests in a sector covering 500 km2 north of the volcano i present here a steady flow model for the blast dynamics and propose that through much of the devastated area the blast was a supersonic flow of a complex multiphase solid liquid vapour mixture the shape of the blast zone pressure temperature velocity mach number and density distributions within the flow positions of weak and strong internal shocks and mass flux energy flux and total energy are calculated the shape of blast zone was determined by the initial areal expansion from the reservoir by internal expansion and compression waves including shocks and by the density of the expanding mixture the pressure within the flow dropped rapidly away from the source of the blast until at a distance of 11 km the flow became underpressured relative to the surrounding atmosphere weak shocks within the flow subparallel to the east and west margins coalesced at about this distance into a strong mach disk shock across which the flow velocities would have dropped from supersonic to subsonic as the pressure rose back towards ambient the positions of the shocks may be reflected in differences in the patterns of felled trees at the limits of the devastated area the temperature had dropped only 20 from the reservoir temperature because the entrained solids thermally buffered the flow the dynamic and thermodynamic effects of the admixture of the surrounding atmosphere and the uprooted forest and soils into the flow are not considered the density of the flow decreased with distance until at the limits of the blast zone 20 25 km from the volcano the density became comparable with that of the surrounding dirty atmosphere and the flow became buoyant and ramped up into the atmosphere according to the model the mass flux per unit area at the source was 0 6 104 g s 1 cm 2 and the energy flux per unit area was 2 5 mw cm 2 from the measured total ejected mass 0 25 1015 g the total energy released during the eruption was 1024 erg or 24 megatons the model triggering of the eruption and the transition from unsteady to steady flow and applications to eyewitness observations and atmospheric effects are discussed in ref 1

climatic factors on the archean earth abstract there is no strong evidence for extreme climates during the archean galciogenics rokcs are rare while evaporites are about as widespread as in later geological periods sedimentary rocks suggest processes of erosion and weathering not particularly anomalous this findings is surprising in the light of simple physical reasons to believe that the sun was less bright although the area of exposed land was probably low the albedo change associated with more extensive oceans could hardly have been large enough to prevent glaciation a stronger atmospheric greenhouse is indicated carbon dioxide was the most likely candidate gas a variety of arguments suggest that it was much more abundant methane is another possible contributor to the greenhouse while abiotic sources of this gas were probably negligible then as now biogenic sources could have sustained methane mixing ratios in the range 10 4 to 10 6 other climatic factors of uncertain impact include more rapid rotation of the earth the lenght of the day was probably about fifteen hours throughout most of archean time and little or no continental land areas which would have reduced the importance of landsea circulations while permitting less restricted zonal flow of ocean currents

a case for late archaean continental emergence from thermal evolution models and hypsometry abstract the secular cooling of the earth s mantle and the growth of the continental crust together imply changes in the isostatic balance between continents and oceans in the oceanic bathymetry and in the area of emerged continental crust the evolution of these variables is of fundamental importance to the geochemical coupling of mantle continental crust atmosphere and ocean to explore this further we developed a model that evaluates the area of emerged continental crust as a function of mantle temperature continental area and hypsometry in this paper we investigate the continental freeboard predicted using different models for the cooling of the earth we show that constancy of the continental freeboard 200 m is possible throughout the history of the planet as long as the potential temperature of the upper mantle was never more than 110 210 c hotter than present such numbers imply either a very limited cooling of the planet or most likely a change in continental freeboard since the archaean during the archaean a greater radiogenic crustal heat production and a greater mantle heat flow would have reduced the strength of the continental lithosphere thus limiting crustal thickening due to mountain building processes and the maximum elevation in the earth s topography rey p f coltice n neoarchean strengthening of the lithosphere and the coupling of the earth s geochemical reservoirs geology 36 635 638 2008 taking this into account we show that the continents were mostly flooded until the end of the archaean and that only 2 3 of the earth s area consisted of emerged continental crust by around 2 5 ga these results are consistent with widespread archaean submarine continental flood basalts and with the appearance and strengthening of the geochemical fingerprint of felsic sources in the sedimentary record from 2 5 ga the progressive emergence of the continents as shown by our models from the late archaean onward had major implications for the earth s environment particularly by contributing to the rise of atmospheric oxygen and to the geochemical coupling between the earth s deep and surface reservoirs

a heat flow profile across the sverdrup basin canadian arctic islands an average geothermal gradient of 25 5 mk m and an average heat flow of 46 5mw m2 have been determined for 16 out of 20 analyzed wells along a profile across the sverdrup basin in the canadian arctic these estimates based on deep bottom hole temperature bht data from exploration wells and the permafrost base boundary temperature together with assumed heat conductivities from net rock analysis are surprisingly low and disagree with previously published results based on shallow data the differences may be due to the dramatic changes in boundary temperature conditions from moderate subsea conditions to ground surface low temperatures as a result of marine regression because of these effects it appears that deep bht temperature data are valuable in providing information about the deep heat flow the heat flows thus determined indicate that the basin has approached thermal equilibrium

relating modis derived surface albedo to soils and rock types over northern africa and the arabian peninsula 1 we use the moderate resolution imaging spectroradiometer modis aboard the terra spacecraft to derive surface albedo for the arid areas of northern africa and the arabian peninsula albedo in seven modis spectral bands for land and three broad bands for shortwave near infrared and visible portions of the spectrum is produced surface albedo is derived from modis observations during a sixteen day period and is analyzed at 1 km spatial resolution modis data show considerable spatial variability of surface albedo in the study region that is related to soil and geological characteristics of the surface for example solar shortwave white sky albedo varies by a factor of about 2 5 from the darkest volcanic terrains to the brightest sand sheets vegetation contribution to surface reflectance is essentially negligible since we only considered pixels with under 10 percent fractional canopy cover few if any coupled land atmosphere global or regional models capture this observed spatial variability in surface reflectance or albedo here we suggest a scheme that relates soil groups based on the united nations food and agriculture organization fao soil classification and rock types based on the united states geological survey usgs geological maps to modis derived surface albedo statistics this approach is a first step towards the incorporation of the observed spatial variability in surface reflective properties into climate models

faint young sun problem more severe due to ice albedo feedback and higher rotation rate of the early earth 1 during the archean 3 8 2 5 billion years ago the sun was up to 25 less luminous than today yet there is strong evidence that the earth s ocean surface was not completely frozen the most obvious solutions to this faint young sun problem demand high concentrations of greenhouse gases such as carbon dioxide here we present the first comprehensive 3 dimensional simulations of the archean climate that include processes as the sea ice albedo feedback and the higher rotation rate of the earth these effects lead to co2 partial pressures required to prevent the earth from freezing that are significantly higher than previously thought for the early archean we find a critical co2partial pressure of 0 4 bar in contrast to 0 06 bar estimated in previous studies with 1 dimensional radiative convective models our results suggest that currently favored greenhouse solutions could be in conflict with constraints emerging for the middle and late archean

geothermal gradients and terrestrial heat flow along a south north profile in the sverdrup basin canadian arctic archipelago data from eleven petroleum exploration wells along a south north profile in the sverdrup basin of the canadian arctic islands indicate large variations in temperature gradients 18 2 to 39 2 mk m and heat flow values 38 8to73 11mw m2 high values occur near the axis of the basin and values decrease systematically toward the southern and northern flanks of the basin the basin axis in this area is the zone of maximum crustal attenuation and lower cretaceous dike and sill intrusion but any thermal anomaly associated with these events will have dissipated by now the present heat flow pattern is likely the result of thermal refraction or fluid flow in the basin

neoarchean paleoweathering of tonalite and metabasalt implications for reconstructions of 2 69ga early terrestrial ecosystems and paleoatmospheric chemistry abstract field and laboratory investigations of a 2690 83 ma 207pb 206pb age of saganaga tonalite unconformity exposed in outcrop in northeastern minnesota usa reveal evidence for development of a deep paleoweathering profile with geochemical biosignatures consistent with the presence of microbial communities and weakly oxygenated conditions weathering profiles are characterized by a 5 50 m thick regolith that consists of saprolitized saganaga tonalite and paulson lake succession basaltic metavolcanic rocks retaining rock structure which is cross cut by a major unconformity surface marking development of a successor basin infilled with alluvial deposits the regolith and unconformity are overlain by thick conglomerate deposits that contain both intrabasinal saprock as well as extrabasinal detritus thin section microscopy and electron microprobe analyses reveal extensive hydrolysis and sericitization of feldspars exfoliation and chloritization of biotite and weathering of fe mg silicates and cu fe sulfides weathering of fe ti oxides was relatively less intense than for other minerals and evidence was found for precipitation of fe oxides geochemical analyses of the tonalite assuming immobile tio2 during weathering ti j show depletion of sio2 al2o3 na2o cao mgo and mno and to a lesser degree of k2o relative to least weathered parent materials significant fe was lost from the tonalite a paleoatmospheric pco2 of 10 50 times pal is estimated based on geochemical mass balance of the tonalite profile and assuming a formation time of 50 500 kyr interpretations of metabasalt paleoweathering are complicated by additions of sediment to the profile and extensive diagenetic carbonate dolomite overprinting patterns of release of p and fe and retention of y and cu in tonalite are consistent with recent laboratory experiments of granite weathering and with the presence of acidic conditions in the presence of organic ligands produced for example by a primitive microbial community during weathering cu metal in the profile may document lower po2 than present day at the surface comparison with previous studies of weathered tonalite and basalt denison 2 45 2 22 ga in ontario canada reveal general similarities in paleoweathering with our study as well as important differences related to lower paleoatmospheric po2 and terrestrial biosignature for the older minnesota profile a falling water table in the alpine lake locality is presumed to have promoted formation of this gossan like deep weathering system that extends to 50 m depth

climate simulations of neoproterozoic snowball earth events similar critical carbon dioxide levels for the sturtian and marinoan glaciations abstract the sturtian and marinoan snowball earth episodes initiated 720 and 650 million years ago respectively are among the most dramatic events in earth s history the ultimate causes of these events remain obscure however and there is still uncertainty about the critical levels of greenhouse gas concentrations at which the snowball transition occurs furthermore earlier modelling results with incomplete representations of important boundary conditions provided conflicting indications for differences between the critical carbon dioxide concentrations for the marinoan and the sturtian reporting either the earlier or the later epoch to be more susceptible to global glaciation both the absolute values of and possible differences between these glaciation thresholds have profound implications for scenarios of snowball initiations during the neoproterozoic here we present coupled climate simulations using an ocean general circulation model with dynamic thermodynamic sea ice coupled to a fast atmosphere focusing on the differences between the neoproterozoic glaciations for the first time our simulations use realistic boundary conditions in terms of changes in solar luminosity between the two epochs and the most recent continental reconstructions in agreement with previous studies with models including ocean and sea ice dynamics we report low values for the critical carbon dioxide concentration during the neoproterozoic but in contrast to hints from earlier studies we find very similar values of 100 130 ppm for the snowball bifurcation point during the sturtian and marinoan this highlights the importance of realistic boundary conditions for climate simulations of the neoproterozoic glaciations

marine transgression shoreline emergence evidence in seabed and terrestrial ground temperatures of changing relative sea levels arctic canada precise temperatures to depths of several hundred meters have been measured in abandoned petroleum exploration wells in coastal and offshore areas of the canadian arctic in these regions changes in relative sea level during the quaternary have left a strong thermal signature on deep ground temperatures surface temperature changes of the order of 10 20 k accompanied shoreline emergence due to uplift in some regions and marine transgression due to eustatic changes in sea levels in others classical analytic techniques are used to demonstrate that these anomalous features are a direct consequence of recent changes in sea level in coastal areas of the queen elizabeth islands modelling of the large near surface temperature depth gradients and the distinct curvature in the measured profiles yield emergence times in general agreement with dates taken from emergence curves the analysis suggests that surface temperatures of these coastal areas were 16 19 k higher than at present from the late wisconsinan until emergence in the holocene suggesting either marine conditions for this period or glacial ice cover with basal temperatures near the pressure melting point in contrast at two offshore wells on the beaufort shelf analyses of the negative temperature depth gradients below the seabed and profile curvature yield times of marine transgression generally consistent with the published sea level curve for the area the analyses suggest that surface temperatures of some present offshore areas were 10 16 k lower than today s sea bottom temperatures from the late wisconsinan until marine transgression in the holocene the characteristic ground temperature profiles measured in such arctic areas provide independent evidence for the relative changes in sea level indicated by proxy data it is especially valuable for these areas where there is little historical record and from which datable material such as shells driftwood and pumice fragments may be scarce or ambiguous these effects may not be observable in temperate areas because of the smaller contrast in sea bottom and terrestrial temperatures

mobility of nutrients and trace metals during weathering in the late archean abstract the evolution of the geosphere and biosphere depends on the availability of bio essential nutrients and trace metals consequently the chemical and isotopic variability of trace elements in the sedimentary record have been widely used to infer the existence of early life and fluctuations in the near surface environment on the early earth particularly fluctuations in the redox state of the atmosphere in this study we applied late archean weathering models hao et al 2017 developed to estimate the behavior of major elements and the composition of late archean world average river water to explore the behavior of nutrient and trace metals and their potential for riverine transport we focused on p mn cr and cu during the weathering of olivine basalt in our standard late archean weathering model pco2 g 10 1 5 bars ph2 g 10 5 0 bars crustal apatite was totally dissolved by the acidic rainwater during weathering our model quantitatively links the pco2 g of the atmosphere to phosphate levels transported by rivers the development of late archean river water ph 6 4 resulted in riverine phosphate of at least 1 7 molar much higher than at the present day at the end of the early proterozoic snowball earth event when pco2 g could be 0 01 0 10 bars river water may have transported up to 70 molar phosphate depending on the availability of apatite thereby stimulating high levels of oxygenic photosynthesis in the marine environment crustal levels of mn in olivine dissolved completely during weathering except at large extents of weathering where mn was stored as a component of a secondary carbonate mineral the corresponding mn content of river water about 1 2 molar is higher than in modern river water whiffs of 10 5 mole o2 gas or hno3 kg 1 h2o resulted in the formation of pyrolusite mno2 and abundant hematite and simultaneous dramatic decreases in the concentration of mn ii in the river water chromite dissolution resulted in negligible dissolved cr in archean river water however amorphous cr oh 3 representing easily weatherable cr bearing minerals dissolved totally during the weathering simulations resulting in concentrations of cr iii in the river water of up to 0 14 molar higher than at the present day late archean weathering of accessory chalcopyrite produced chalcocite and bornite and extremely low concentrations of cu 10 15 molar because of the low solubilities of the copper sulfides however pulses of either o2 g or hno3 produced native copper chalcocite and bornite much more hematite and river water containing levels of dissolved cu comparable to the present day copper mineralogy predicted by weathering models might provide a new correlation with evidence from studies of copper mineral evolution overall our results implied that the redox state of the atmosphere the ph of surface waters and the availability of easily weatherable minerals are all important factors controlling the dissolution of trace elements in river water interpretation of the sedimentary signatures of trace elements should consider not only the redox state but also the ph and availability of accessory minerals