warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

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

direct measurement of the deep circulation within the brazil basin abstract in support of the deep basin experiment part of the world ocean circulation experiment a large number of neutrally buoyant floats were released within the brazil basin during the 1990s in an attempt to measure directly the circulation in the deep ocean interior three levels corresponding to the three major subthermocline water masses were selected and results from the deeper two north atlantic deep water nadw and antarctic bottom water aabw are described at this writing processing of acquired tracking data is incomplete hence this paper reports on the progress of the observational program and gives our initial conclusions it appears that the flow in the deep brazil basin is unlike previous conjectures in which the circulation patterns can be characterized as being primarily meridional both along the western boundary and in the interior the existence of a deep western boundary current dwbc is quite clear in the float data at the nadw level but less prominent in the aabw and the interior flow is dominantly zonal with unexpectedly small meridional space scales integral time scales are long of order 20 30 days and eddy kinetic energy levels are low of order 1 cm2 s2 in spite of the low energy levels a surprising number of our floats became caught up in vortices a line of seamounts extending offshore near 20 s known as the vitoria trindade seamounts interrupts the dwbcs and is the location for eddy formation and apparent flow away from the boundary into the interior although it has been speculated that this could feed a narrow zonal current of nadw the namib col current our float trajectories suggest a return to the western boundary rather than a continuation to the east

observations of the antarctic circumpolar current and deep boundary current in the southwest atlantic fourteen month velocity and temperature records from an array of 14 moorings north and west of the falkland plateau and supporting hydrographic and tracer data reveal a narrow boundary current that carries dense antarctic waters the current flows west along the northern flank of the falkland plateau with mean speeds of more than 10 cm s 1 at 5000 m and more than 30 cm s 1 at 2500 m the westward flow extends from the bottom to at least 1000 m but the upper portion of the current is a branch of the antarctic circumpolar current acc following the only deepwater route between the scotia sea and the argentine basin waters colder than 0 2 c are too cold to be associated with the acc at drake passage and must ultimately derive from the weddell sea as part of the deep thermohaline circulation the westward transport of water colder than 0 2 c is 8 2 106 m3 s 1 in the mean the bottom boundary current is similar to that predicted by the stommel arons model but considerable variability is introduced by the meandering of the overlying acc chlorofluorocarbon data suggest that new antarctic water from the georgia basin enters the argentine basin via the deep boundary current which passes beneath the acc some new water is also advected east after being entrained in the acc most of the water in the deep boundary current is recirculated water that has been in residence in the argentine basin for some time water colder than 0 2 c is relatively new to the basin and comprises about 2 5 106 m3 s 1 of the westward flow of the boundary current

decadal warming of the coldest antarctic bottom water flow through the vema channel a decadal warming trend of antarctic bottom water flowing through the vema channel is reanalyzed our data base consists of 94 high precision full depth stations from 19 visits to the vema sill plus twelve stopovers at two additional key locations originally a long term temperature increase in the near bottom jet was noted from 1992 onward after a period of rather constant abyssal temperatures since 1972 from today s perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2 8 mk yr 1 in the following 15 years however the clearly manifested temperature rise is superimposed with fluctuations for the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water an attempt is made to trace the observed variability back to its source region in the weddell sea

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

eddy length scales in the north atlantic ocean eddy length scales are calculated from satellite altimeter products and in an eddy resolving model of the north atlantic ocean four different measures for eddy length scales are derived from kinetic energy densities in wave number space and spatial decorrelation scales observational estimates and model simulation agree well in all these measures near the surface as found in previous studies all length scales are in general decreasing with latitude they are isotropic and proportional to the local first baroclinic rossby radius l r north of about 30 n while south of 30 n or for l r 30 km zonal length scales tend to be larger than meridional ones and scalar length scales show no clear relation to l r anymore instead they appear to be related to the local rhines scale in agreement with a recent theoretical prediction by theiss 2004 the observed and simulated pattern of eddy length scales appears to be indicative of two different dynamical regimes in the north atlantic anisotropic turbulence in the subtropics and isotropic turbulence in the subpolar north atlantic both regions can be roughly characterized by the ration between l r and the rhines scales l r with l r l r in the isotropic region and l r l r in the anisotropic region the critical latitude that separates both regions i e where l r l r is about 30 n

variability of antarctic bottom water at 24 5 n in the atlantic a recent hydrographic section at 24 5 n in the atlantic and 6 months of observations from a moored array show that antarctic bottom water aabw the densest and deepest water mass in the world oceans has been warming while johnson et al 2008 showed that northward aabw transport at 24 5 n has been declining from 1981 to 2004 suggesting that the lower cell of the overturning circulation could halt in the near future estimates from the latest hydrographic section in 2010 indicate a partial recovery of northward aabw transport from 6 months of temperature and salinity observations at a deep moored array at 24 26 n we find that short term variability between april and november 2009 is of the same magnitude as the changes observed from hydrographic sections between 1981 and 2004 these observations highlight the possibility that transport changes estimated from hydrographic sections may be aliased by short term variability the observed aabw transport variability affects present estimates of the upper meridional overturning circulation by 0 4 sv 1 sv 106 m3 s 1

scandinavia s north atlantic passive margin 1 the tectonics of the eastern passive margin of the north atlantic are reexamined the scandinavian north atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the scandinavian caledonides combined information from structural geology potential field data regional geology basin development and geomorphology made it possible to propose a new definition of the passive margin the rift shoulder is formed by linked faults defining the present rift flank these faults are the extensional structures located furthest to the east onshore norway sweden that can be linked to the rifting that led to the formation of the north atlantic this innermost boundary fault system ibf is formed by a set of normal west dipping crustal faults it extends over a distance exceeding 2000 km from the north sea across the caledonian mountain belt to the barents sea the passive margin width between the continent ocean boundary and the ibf ranges from 550 km in the south to over 700 km in mid norway to 165 km north of lofoten rifting and faulting on the ibf started in permo carboniferous and a succession of rift phases eventually culminated in continental breakup and the formation of the north atlantic basin development between permian and cretaceous was toward the future breakaway fault but faulting was also active on land from mesozoic to present onshore offshore crustal scale cross sections show the geometry of the passive margin the dip orientation of the major faults and the changes in crustal thickness

deformation and metamorphism of devonian rocks in the outer solund area western norway implications for models of devonian deformation many modern accounts of the devonian rocks of western norway which emphasise the extensional processes by which the basins were formed tend to ignore or gloss over the deformation and metamorphism which these rocks have suffered during contractional deformation the present account describes extensive ductile folding penetrative cleavage formation and low grade regional metamorphism developed in the devonian strata of the outer solund region although the deformation in this area is more intense than in other devonian basins it belongs to the same movement plan it will also be shown that the devonian rocks of the scandinavian caledonides apparently share a common tectonothermal development this regional contractional event conceptually may relate either to a mid late devonian arc continent collision or to a transpressional strain regime

recent western south atlantic bottom water warming 1 potential temperature differences are computed from hydrographic sections transiting the western basins of the south atlantic ocean from 60 s to the equator in 2005 2003 and 1989 1995 while warming is observed throughout much of the water column the most statistically significant warming is about 0 04 c in the bottom 1500 dbar of the brazil basin with similar but less statistically significant warming signals in the abyssal argentine basin and scotia sea these abyssal waters of antarctic origin spread northward in the south atlantic the observed abyssal argentine basin warming is of a similar magnitude to that previously reported between 1980 and 1989 the brazil basin abyssal warming is similar in size to and consistent in timing with previously reported changes in abyssal southern inflow and northern outflow the temperature changes reported here if they were to hold throughout the abyssal world ocean would contribute substantially to global ocean heat budgets

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

unabated bottom water warming and freshening in the south pacific ocean author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 124 3 2019 1778 1794 doi 10 1029 2018jc014775

helium accumulation in groundwater ii a model for the accumulation of the crustal 4he degassing flux abstract a model of 4 he accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of 4 he into the bottom of a confined aquifer the model is consistent with the measurements of 4 he concentration in the great artesian basin australia torgersen and clarke 1985 and also with the measurements of 4 he concentration in the auob sandstone of namibia heaton 1981 the measured value of the crustal degassing flux of 4 he from these two areas is comparable with the 4 he degassing flux calculated from the atmospheric budget of 4 he wasserburg et al 1963 ozima and podosek 1983 a literature review suggests that a crustal degassing 4 he source may account for the 4 he accumulation in many other groundwater systems it is concluded from the literature review the detailed modelling of 4 he accumulation in gab and the auob sandstone and the atmospheric budget that crustal degassing of 4 he may be a common and widespread phenomena

observed ocean bottom temperature variability at four sites in the northwestern argentine basin evidence of decadal deep abyssal warming amidst hourly to interannual variability during 2009 2019

reduced antarctic meridional overturning circulation reaches the north atlantic ocean 1 we analyze abyssal temperature data in the western north atlantic ocean from the 1980s 2000s showing that reductions in antarctic bottom water aabw signatures have reached even that basin trans basin oceanographic sections occupied along 52 w from 1983 2003 and 66 w from 1985 2003 quantify abyssal warming resulting from deepening of the strong thermal boundary between aabw and north atlantic deep water nadw hence a local aabw volume reduction repeat section data taken from 1981 2004 along 24 n also show a reduced zonal gradient in abyssal temperatures consistent with decreased northward transport of aabw the reduction in the antarctic limb of the moc within the north atlantic highlights the global reach of climate variability originating around antarctica

multi centennial variability controlled by southern ocean convection in the kiel climate model a quasi oscillatory multi centennial mode of open ocean deep convection in the atlantic sector of the southern ocean in the kiel climate model is described the quasi periodic occurrence of the deep convection causes variations in regional and global surface air temperature southern hemisphere sea ice coverage southern ocean and north atlantic sea surface height the antarctic circumpolar current and the atlantic meridional overturning circulation amoc the deep convection is stimulated by a strong built up of heat at mid depth when the heat reservoir is virtually depleted a coincidental strong freshening event at the sea surface shuts down the convection the heat originates from relatively warm deep water formed in the north atlantic the several decades lasting recharge process of the heat reservoir depends on the amoc and the weddell gyre and sets a minimum delay for the deep convection to recur while the strength of the amoc increases the weddell gyre weakens during the non convective regime convection onset and shutdown also depend on the stochastic occurrence of favorable sea surface conditions which contributes to the multi centennial period of the phenomenon the shutdown triggers a century long deviation in amoc strength caused by significant reductions in bottom water formation and surface salinity in the southern ocean s atlantic sector additional numerical experimentation reveals that sea ice has an important effect on the frequency of occurrence and intensity of the deep convection further we find intriguing similarities to the weddell polynya observed during the 1970s

svecofennian detrital zircon ages implications for the precambrian evolution of the baltic shield metasediments intruded by 1 90 1 87 ga old plutonic rocks form the oldest major proterozoic crustal component in the svecofennian domain of the baltic fennoscandian shield their ndtdm model ages and conventional multigrain zircon u pb ages between 2 4 and 2 1 ga have previously been interpreted either as mixing ages between 1 9 ga old juvenile materials and a minor archaean component or as actual rock and protolith ages to resolve the ensuing controversy 120 individual detrital zircons from svecofennian metasediments in sweden and finland were analysed using the shrimp ion microprobe the oldest materials in this array are a 3 44 ga old zircon from the tampere schist belt in finland and a 3 32 ga old crystal from southeastern sweden about 30 of the analysed crystals are 2 97 2 60 ga old while 65 have ages between 2 12 and 1 88 ga thus there is no evidence of 2 6 2 1 ga old protoliths but the age range of the proterozoic zircons indicates that a major area of 2 1 1 9 ga old crust was in erosional position 1 9 ga ago this implies that the formation of palaeoproterozoic crust in the baltic shield or its one time close neighbourhood must have commenced 100 200 ma earlier than hitherto assumed in conjunction with previously obtained isotopic data the youngest detritus ages of the present study constrain the age of svecofennian sedimentation it can also be concluded that the archaean zircons found in quartzites from southern sweden may have been derived from source areas to the southwest of the central svecofennian marine depositional basin the so called bothnian basin separating southern sweden from the archaean craton in the northeastern part of the shield

global contraction of antarctic bottom water between the 1980s and 2000s abstracta statistically significant reduction in antarctic bottom water aabw volume is quantified between the 1980s and 2000s within the southern ocean and along the bottom most southern branches of the meridional overturning circulation moc aabw has warmed globally during that time contributing roughly 10 of the recent total ocean heat uptake this warming implies a global scale contraction of aabw rates of change in aabw related circulation are estimated in most of the world s deep ocean basins by finding average rates of volume loss or gain below cold deep potential temperature surfaces using all available repeated hydrographic sections the southern ocean is losing water below 0 c at a rate of 8 2 2 6 106 m3 s 1 this bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near surface recovery apparently through a southward surge of circumpolar deep water from the north to the north smaller losses of bottom waters are see

helium degassing related to the kobe earthquake the sup 3 he sup 4 he ratios of groundwaters at nishinomiya city close to the epicenter decreased immediately after the 1995 kobe earthquake in japan while the sup 4 he sup 20 ne ratios increased the delta d and delta sup 18 o values of the groundwaters were identical before and after the earthquake apparent groundwater ages calculated by tritium sup 3 he concentrations also did not change if we correct the addition of radiogenic helium into the samples by the earthquake these observations may be attributed to following phenomenon 1 release of radiogenic he as a result of micro fracturing of rocks during the earthquake followed by degassing from the aquifer system in the amount of about 4 0 1 3 x 10 sup 9 cm sup 3 stp cm sup 3 rock 2 simple mixing of low tritium water with high radiogenic helium in the clay layer and high tritium water with atmospheric helium in the aquifer and 3 flow path mixing in the region of the sample screen if we take the 1 degassing hypothesis as a function of micro fracturing it is possible to calculate the total he degassing related to the kobe earthquake 4 x 10 sup 11 cm sup 3 stp which is about 3 of the steady state global he flux of 1 2 x 10 sup 13 cm supmore 3 stp year thus earthquake may play an important role in he degassing from the solid earth less

late mesozoic to early cenozoic components of vertical separation across the more trondelag fault complex norway abstract low temperature apatite fission track aft data from two horizontal transects across the more trondelag fault complex mtfc and along the coast of the fosen peninsula have defined a complicated series of structural blocks whose exhumation to temperatures cooler than the uppermost apatite partial annealing zone paz occurred during a broad mesozoic to cenozoic time span the 100 million year cooling difference between the innermost and outermost blocks indicates they were subjected to very different exhumation pathways track length histograms and inverse model results also suggest that significant differences in thermal histories are present over very short horizontal distances in conjunction with the offshore geological evidence the aft data and models strongly suggest that the innermost zones of the mtfc underwent between 2 and 4 km of structurally controlled net vertical rock column uplift subsidence following latest cretaceous time and potentially much of the tertiary as well the up to the east down to the west relative offset at the norwegian margin is interpreted in terms of a flexed nearly broken lithospheric plate architectural model for late mesozoic and tertiary scandes mountain building whose driving force was likely dominanted by erosionally induced loading unloading at the margin

structure and evolution of the abyssal jet in the vema channel of the south atlantic the vema channel represents the only major conduit through which the deepest and coldest 0 2 c potential temperature antarctic bottom water aabw flows from the argentine into the brazil basin from 2003 to 2007 two current meter moorings were present on each side of the vema sill close to the narrowest spot of the vema channel the data from the moorings are compared with earlier current and temperature observations on average the maximum current core lies 100 m above the bottom of the sill with a mean northward speed of 0 3 m s 1 farther up in the water column where lower circumpolar deep water and north atlantic deep water prevail one finds a level of sluggish currents with a southward tendency in the sub centimeter per second range the lower boundary of a layer of no motion was observed at 3700 m depth where the mean potential temperature amounts to 1 5 c the evolution of the abyssal warming phenomenon over the last decades with notable fluctuations at the choke point between the argentine and the brazil basin differs from the more stable attitude of deep horizontal currents starting with ctd observations in 1972 we find a steady increase of temperatures of the coldest aabw in the vema channel this general trend of rising abyssal potential temperatures of almost 2 mkelvin per year is based on mostly annual ctd observations the overall warming trend is fully compatible with our three year moored temperature series in agreement with earlier records with high temporal resolution distinct frequently fluctuating horizontal current shear between the western and eastern sides of the vema sill may be explained by two different catchment areas for aabw at the mouth of the vema channel one pathway originates at the american continental rise and advects bottom water in form of the deep western boundary current a second pathway is supplied by an eastern boundary current along the mid atlantic ridge in the argentine basin both source waters merge at the channel entrance mix and their respective strengths can alternate within the sill area

abyssal ocean warming and salinification after weddell polynyas in the gfdl cm2g coupled climate model abstractthe role of weddell sea polynyas in establishing deep ocean properties is explored in the noaa geophysical fluid dynamics laboratory s gfdl coupled climate model cm2g using statistical composite analysis of over 30 polynya events that occur in a 2000 yr long preindustrial control run the temperature salinity and water mass changes associated with the composite event are quantified for the time period following the composite polynya cessation termed the recovery warming between 0 002 and 0 019 c decade 1 occurs below 4200 m in the southern ocean basins temperature and salinity changes are strongest in the southern ocean and the south atlantic near the polynya formation region comparison of the model results with abyssal temperature observations reveals that the 1970s weddell polynya recovery could account for 10 8 of the recent warming in the abyssal southern ocean for individual southern ocean basins this percentage is as little as 6 11 or as much as 34 13

noble gas residence times of saline waters within crystalline bedrock outokumpu deep drill hole finland abstract noble gas residence times of saline groundwaters from the 2516 m deep outokumpu deep drill hole located within the precambrian crystalline bedrock of the fennoscandian shield in finland are presented the accumulation of radiogenic 4 he 40 ar and nucleogenic 21 ne noble gas isotopes in situ together with the effects of diffusion are considered fluid samples were collected from depths between 180 and 2480 m below surface allowing us to compare the modelled values with the measured concentrations along a vertical depth profile the results show that while the concentrations in the upper part are likely affected by diffusion there is no indication of diffusive loss at or below 500 m depth furthermore no mantle derived gases were found unequivocally previous studies have shown that distinct vertical variation occurs both in geochemistry and microbial community structuring along the drill hole indicating stagnant waters with no significant exchange of fluids between different fracture systems or with surface waters therefore in situ accumulation is the most plausible model for the determination of noble gas residence times the results show that the saline groundwaters in outokumpu are remarkably old with most of the samples indicating residence times between 20 and 50 ma although being first order approximations the ages of the fluids clearly indicate that their formation must predate more recent events such as quaternary glaciations isolation within the crust since the eocene miocene epochs has also direct implications to the deep biosphere found at outokumpu these ecosystems must have been isolated for a long time and thus very likely rely on energy and carbon sources such as h 2 and co 2 from groundwater and adjacent bedrock rather than from the ground surface

antarctic bottom water temperature changes in the western south atlantic from 1989 to 2014 warming of abyssal waters in recent decades contributes to global heat uptake and sea level rise repeat oceanographic section data in the western south atlantic taken mostly in 1989 1995 across the scotia sea 2005 and 2014 are used to quantify warming in abyssal waters that spread northward through the region from their antarctic origins in the weddell sea while much of the scotia sea warmed between 1995 and 2005 only the southernmost portion on the north side of the weddell gyre continued to warm between 2005 and 2014 the abyssal argentine basin also warmed between 1989 and 2005 but again only the southernmost portion continued to warm between 2005 and 2014 suggesting a slowdown in the inflow of the coldest densest antarctic bottom waters into the western south atlantic between 1989 and 2014 in contrast the abyssal waters of the brazil basin warmed both between 1989 and 2005 and between 2005 and 2014 at a rate of about 2 m c yr 1 this warming is also assessed in terms of the rates of change of heights above the bottom for deep isotherms in each deep basin studied these results together with findings from previous studies suggest the deep warming signal observed in the weddell sea after the mid 1970s weddell polynya was followed by abyssal warming in the argentine basin from the late 1970s through about 2005 then warming in the deep vema channel from about 1992 through at least 2010 and warming in the brazil basin from 1989 to 2014

deep temperature variability in drake passage observations made on 21 occupations between 1993 and 2016 of go ship line sr1b in eastern drake passage show an average temperature of 0 53 c deeper than 2000 dbar with no significant trend but substantial year to year variability standard deviation 0 08 c using a neutral density framework to decompose the temperature variability into isopycnal displacement heave and isopycnal property change components shows that approximately 95 of the year to year variance in deep temperature is due to heave changes on isopycnals make a small contribution to year to year variability but contribute a significant trend of 1 4 0 6 m c per year largest for density n 28 1 south of the polar front pf the heave component is depth coherent and results from either vertical or horizontal motions of neutral density surfaces which trend upward and northward around the pf downward for the densest levels in the southern section and downward and southward in the subantarctic front and southern antarctic circumpolar current front saccf a proxy for the locations of the antarctic circumpolar current acc fronts is constructed from the repeat hydrographic data and has a strong relationship with deep ocean heat content explaining 76 of deep temperature variance the same frontal position proxy based on satellite altimeter derived surface velocities explains 73 of deep temperature variance the position of the pf plays the strongest role in this relationship between acc fronts and deep temperature variability in drake passage although much of the temperature variability in the southern half of the section can be explained by the position of the saccf this article is protected by copyright all rights reserved

volcanic rocks in the devonian solund basin western norway large landslides of silurian 439 ma rhyolites abstract the devonian solund basin in sw norway is the only old red sandstone basin in the scandinavian caledonides from which volcanic rocks have been described these rhyolitic lavas yield a concordant id tims u pb zircon age of 439 1 ma early silurian interpreted as dating the crystallization of the rhyolite and are thus too old to be syndepositional with the devonian sedimentary rocks this new age constraint combined with field observations suggests that the volcanic rocks form part of a 30 km 2 landslide of rhyolite granite gabbro and metasedimentary rocks rather than extension related volcanism as previously suggested the landslides show an inverted stratigraphy with respect to the nearby solund stavfjord ophiolite complex and its overlying volcanic arc which was formed immediately prior to obduction of caledonian exotic terranes onto baltica the dated rocks thus appear to record the youngest pre collisional volcanism in the scandinavian caledonides tectonic models involving devonian old red volcanic rocks in the scandinavian caledonides must thus be revised

quantifying antarctic bottom water and north atlantic deep water volumes 1 a near global census of antarctic bottom water aabw and north atlantic deep water nadw is essayed through a nonnegative least squares analysis of conservative and quasi conservative seawater properties aabw thickness generally decreases from south to north modulated by ocean bathymetry likewise nadw thickness generally decreases from north to south in the atlantic ocean nadw dominates below the thermocline of the atlantic ocean at least as far south as the subtropical gyre of the south atlantic with a lesser but still significant influence around the entire antarctic circumpolar current in the indian ocean and in the pacific ocean however in the pacific and indian oceans aabw dominates below the thermocline in addition measurable quantities of aabw reach into the abyssal north atlantic on both sides of the mid atlantic ridge the census results suggest that aabw occupies roughly twice the volume of nadw in the three main oceans and that aabw is in contact with roughly twice the area of the deep main ocean floor compared with nadw however these results are somewhat sensitive to choices of water masses their values of seawater properties and the weightings of the seawater properties used in the analysis

sensitivity of antarctic bottom water to changes in surface buoyancy fluxes abstractthe influence of freshwater and heat flux changes on antarctic bottom water aabw properties are investigated within a realistic bathymetry coupled ocean ice sector model of the atlantic ocean the model simulations are conducted at eddy permitting resolution where dense shelf water production dominates over open ocean convection in forming aabw freshwater and heat flux perturbations are applied independently and have contradictory surface responses with increased upper ocean temperature and reduced ice formation under heating and the opposite under increased freshwater fluxes aabw transport into the abyssal ocean reduces under both flux changes with the reduction in transport being proportional to the net buoyancy flux anomaly south of 60 s through inclusion of shelf sourced aabw a process absent from most current generation climate models cooling and freshening of dense source water is facilitated via reduced on shelf off shelf exchange flow such cooling is propagated to the abyssal ocea

isotope fractionation of neon during stepheating extraction a comment on re interpretation of the existence of a primitive plume under australia based on neon isotope fractionation during step heating by gautheron and moreira 2003 using a rayleigh distillation fractionation model we calculate that the maximum isotope fractionation potentially achievable is less than 5 during the early stages of gas release from a sample our calculation corrects the erroneous conclusions of gautheron and moreira 2003 who re interpreted the plume like neon isotopic compositions found in metasomatic apatite from a south eastern australian xenolith matsumoto et al 1997 to be the result of rayleigh type isotope fractionation of originally morb type neon during stepheating gas extraction we stress that the modelling of neon isotopic fractionation by gautheron and moreira 2003 is incorrect and that the finding of a plume like neon isotopic composition in the apatite by matsumoto et al 1997 remains a quite valid and robust conclusion

dissolved helium isotopes and tritium in lakes further results for uranium prospecting in central labrador dissolved helium and neon the 3 he 4 he isotope ratio and tritium concentrations were measured in samples collected from 107 lakes and ponds in central labrador during 1975 and 1976 excess 4 he values relative to solubility equilibrium and tritium 3 he residence times were used to calculate relative values of radiogenic 4 he flux into each lake as indicators of possible nearby uranium mineralization the ratio of percent excess 4 he to tritium 3 he residence time is called the helium prospecting index i diagrams of i values are given for three areas the area surrounding walker lake which includes the michelin deposit and the kitts post hill area were sampled to test and extend the results of our previous survey in 1974 the agreement between these results and the 1974 results is reasonably good the distribution of i values in the moran lake area approximately 60 km west southwest of the michelin deposit indicates four favorable zones comparison of the locations of these zones with known uranium mineralization is inconclusive at present because exploration in this area is much less extensive than in the other two areas dissolved uranium and radon were also measured in many of the lakes sampled for helium uranium concentrations are weakly correlated with i values however no correlation was observed between radon concentrations and i values

deep zonal subequatorial currents large scale westward extending tongues of warm pacific and cold atlantic water are found between 2000 and 3000 meters both north and south of the equator in the pacific and atlantic oceans they are centered at 5 to 8 north and 10 to 15 south pacific and 5 to 8 north and 15 to 20 south atlantic they are separated in both oceans by a contrasting eastward extending tongue centered at about 1 to 2 south in agreement with previous helium isotope observations pacific thus the indicated deep tropical westward flows north and south of the equator and eastward flow near the equator may result from more general forcing than the hydrothermal forcing previously hypothesized

weddell polynya transport mechanisms in the abyssal ocean abstractweddell polynya transport mechanisms in the deep and abyssal oceans are examined in the noaa geophysical fluid dynamics laboratory s gfdl coupled climate model cm2g during an 1820 yr long integration of the model polynyas are forced every 29 years in the weddell sea via an increase in the diapycnal diffusivity composites of the events are used to examine the mechanisms responsible for transporting polynya signals away from the weddell sea polynya signal transport is governed by two dynamical mechanisms that act on different time scales and spread at different rates large scale waves such as kelvin and planetary and topographic rossby waves propagate the polynya signal rapidly on interannual to decadal time scales while advection transports the signal more slowly on decadal to centennial time scales despite their different spreading rates these mechanisms can act contemporaneously and it is often their combined effect that governs the property changes in the global deep and abyssal o

structural analysis of the smeaheia fault block a potential co2 storage site northern horda platform north sea abstract smeaheia a prominent fault block located on the horda platform northern north sea is identified as a potential subsurface co2 storage site we utilise the gn1101 3d seismic survey to generate a high resolution subsurface geomodel to inform the structural style and evolution of the fault block to investigate geological controls on proposed co2 storage and provide a geometric framework as a basis for future analyses two basement involved first order north south trending fault systems the vette fault zone vfz and the oygarden fault complex ofc bound the 15 km wide fault block the vfz bifurcates down section where it is hard linked with two separate basement structures a phenomenon we term as dual rooted apart from activity during the permo triassic rift phase 1 and the late jurassic early cretaceous rift phase 2 we present evidence that rifting in this part of the north sea continued into the late cretaceous with minor reactivation in the palaeocene eocene two segments of the vfz interacted and linked at a relay ramp during rift phase 2 second order thin skinned faults show basement affinity and developed during rift phase 2 in two distinct pulses a population of polygonal faults intersects the overburden and developed during the eocene to middle miocene we have revised the areal extent of two structural closures that define the smeaheia fault block alpha vfz footwall and beta ofc hanging wall which consist of upper jurassic viking group target formations simplified cross fault juxtaposition analysis of the vfz and second order intra block faults are presented and inform pressure communication pathways between the smeaheia and tusse fault block as well as reservoir integrity and compartmentalisation the geomodel further identifies important geological controls on co2 storage in the fault block including a thinning caprock above the alpha structure and identification of hard linkage between deep tectonic faults and shallow polygonal faults