the low level atmospheric circulation near tongoy bay point lengua de vaca chilean coast 30 s abstractstrong southerly terrain parallel winds often occur along the coast of north central chile 25 35 s embedded in the marine atmospheric boundary layer and the lower part of the capping temperature inversion their offshore structure and variability have received considerable attention because of the effect on open ocean processes and connection with the southeast pacific cloud layer mesoscale low level circulations linked to the coastal topography e g coastal jets and sea breeze are less studied in chile but are particularly relevant as they alter the upper ocean circulation and the cloud pattern in the nearshore strip surface radiosonde and airborne meteorological observations near point lengua de vaca ldv tongoy bay tb at 30 s are used alongside numerical modeling to understand the local circulation near a prominent upwelling center most observations were gathered during the variability of the american monsoon systems vamos ocean cloud atmosphere land study chilean upwelling exp

the role of lithospheric flexure in the landscape evolution of the wilkes subglacial basin and transantarctic mountains east antarctica reconstructions of the bedrock topography of antarctica since the eocene oligocene boundary ca 34 ma provide important constraints for modelling antarctic ice sheet evolution this is particularly important in regions where the bedrock lies below sea level since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change here we use 3d flexural modelling to reconstruct the evolution of the topography of the wilkes subglacial basin wsb and transantarctic mountains tam in east antarctica we estimate the spatial distribution of glacial erosion beneath the east antarctic ice sheet and restore this material to the topography which is also adjusted for associated flexural isostatic responses we independently constrain our post 34 ma erosion estimates using offshore sediment stratigraphy interpretations our reconstructions provide a better defined topographic boundary condition for modelling early east antarctic ice sheet history we show that the majority of glacial erosion and landscape evolution occurred prior to 14 ma which we interpret to reflect more dynamic and erosive early ice sheet behaviour in addition we use closely spaced 2d flexural models to test previously proposed hypotheses for a flexural origin of the tam and wsb the pre 34 ma topography shows lateral variations along the length of the tam and wsb that cannot be explained by uniform flexure along the front of the tam we show that some of these variations may be explained by additional flexural uplift along the south western flank of the wsb and the rennick graben in northern victoria land

influence of the subtropical andes on baroclinic disturbances a cold front case study abstract the andes cordillera produces a significant disruption to the structure and evolution of the weather systems that cross south america in particular cold fronts tend to be channeled to the north immediately to the east of the andes fostering the advance of cold air incursions cold surges well into subtropical and sometimes tropical latitudes in contrast active cold fronts hardly reach subtropical latitudes along the western side of the andes pacific sea border instead as a cold front moves equatorward along the east side of the andes a marked low level warming tends to appear along the west side of the subtropical andes leading to the formation of a mesoscale coastal low or trough in this region to further understand the processes that lead to a contrasting evolution of the cold front at each side of the andes a typical frontal passage is studied in this work using synoptic observations and a regional model eta centro de previsao de tempo e estudos climaticos cptec simula

structure and dynamics of the benguela low level coastal jet generations of coupled atmosphere ocean general circulation models have been plagued by persistent warm sea surface temperature sst biases in the southeastern tropical atlantic the sst biases are most severe in the eastern boundary coastal upwelling region and are sensitive to surface wind stress and wind stress curl associated with the benguela low level coastal jet bllcj a southerly jet parallel to the angola namibia coast however little has been documented about this atmospheric source of oceanic bias here we investigate the characteristics and dynamics of the bllcj using observations reanalyses and atmospheric model simulations satellite wind products and high resolution reanalyses and models represent the bllcj with two near shore maxima one near the angola benguela front abf at 17 5 s and the other near 25 27 5 s whereas coarse resolution reanalyses and models represent the bllcj poorly with a single broad more offshore maximum model experiments indicate that convex coastal geometry near the abf supports the preferred location of the bllcj northern maximum by supporting conditions for a hydraulic expansion fan intraseasonal variability of the bllcj is associated with large scale variability in intensity and location of the south atlantic subtropical high through modulation of the low level zonal pressure gradient

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

the structure of the marine inversion layer off the central california coast mesoscale conditions abstract data collected on board an instrumented aircraft during the marine atmospheric boundary layer experiments west coast mables wc field study are examined the data were collected at several levels in the marine and inversion layers approximately 200 km west of the central california coast during august 1978 composite sounding and cross sections of wind and temperature variables are presented to provide an overview of the mesoscale structure of the offshore marine and inversion layers at the time of mables wc under typical summertime synoptic conditions which prevailed early in the study period three flights examined a strong inversion is found base heights and temperature increases across the inversion base are comparable to values observed in the san francisco bay area the topography of the inversion base shows a slope downward toward the east during all three of these flights and also suggests the presence of convective activity gravity wave activity or both during two of the three

evidence for an earliest oligocene ice sheet on the antarctic peninsula there is growing consensus that development of a semipermanent ice sheet on antarctica began at or near the eocene oligocene e o boundary beyond ice rafted debris in oceanic settings however direct evidence for a substantial ice sheet at this time has been limited and thus far restricted to east antarctica it is unclear where glacier ice first accumulated and how extensive it was on the antarctic continent in the earliest oligocene sediments at the top of the eocene marine shelf section on seymour island antarctic peninsula include glacial marine deposits and a lodgment till with clasts derived from a variety of rock units on the peninsula dinoflagellate biostratigraphy and strontium isotope stratigraphy indicate an age at or very close to the e o boundary glacier ice extending to sea level in the northern peninsula at this time suggests the presence of a regionally extensive west antarctica ice sheet and thus an even more dramatic response to the forcing factors that facilitated high latitude ice expansion in the earliest oligocene

eocene oligocene global climate and sea level changes st stephens quarry alabama we integrate upper eocene lower oligocene lithostratigraphic magnetostratigraphic biostratigraphic stable isotopic benthic foraminiferal faunal downhole log and sequence stratigraphic studies from the alabama st stephens quarry ssq core hole linking global ice volume sea level and temperature changes through the greenhouse to icehouse transition of the cenozoic we show that the ssq succession is dissected by hiatuses associated with sequence boundaries three previously reported sequence boundaries are well dated here north twistwood creek cocoa 35 4 35 9 ma mint spring red bluff 33 0 ma and bucatunna chickasawhay the mid oligocene fall ca 30 2 ma in addition we document three previously undetected or controversial sequences midpachuta 33 9 35 0 ma shubuta bumpnose lowermost oligocene ca 33 6 ma and byram glendon 30 5 31 7 ma an 0 9 18 o increase in the ssq core hole is correlated to the global earliest oligocene oi1 event using magnetobiostratigraphy this increase is associated with the shubutabumpnose contact an erosional surface and a biofacies shift in the core hole providing a fi rst order correlation between ice growth and a sequence boundary that indicates a sea level fall the 18 o increase is associated with a eustatic fall of 55 m indicating that 0 4 of the increase at oi1 time was due to temperature maximum 18 o values of oi1 occur above the sequence boundary requiring that deposition resumed during the lowest eustatic lowstand a precursor 18 o increase of 0 5 33 8 ma mid chron c13r at ssq correlates with a 0 5 increase in the deep pacifi c ocean the lack of evidence for a sea level change with the precursor suggests that this was primarily a cooling event not an ice volume event eocene oligocene shelf water temperatures of 17 19 c at ssq are similar to modern values for 100 m water depth in this region our study establishes the relationships among ice volume 18 o and sequences a latest eocene cooling event was followed by an earliest oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

late quaternary coastal evolution and aeolian sedimentation in the tectonically active southern atacama desert chile abstract analyses of aeolianites and associated dune surficial carbonate and marine terrace sediments from north central chile 27 54 s yield a record of environmental change for the coastal southern atacama desert spanning at least the last glacial interglacial cycle optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130 111 98 77 69 and 41 28 ka thin section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases aeolianites appear to have accumulated mainly from tectonically uplifted interglacial marine sediments that were deflated during windier and or stormier intervals bedding orientations indicate that sand transporting winds varied in direction from s ese during mis 5e and wnw ese during mis 5c 5a winds from the southeast quadrant are unusual today in this region of the atacama suggesting either major shifts in atmospheric circulation or topographic airflow modification thin section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate tentatively linked to wetter periods around 70 and 45 ka tectonic uplift in the area has proceeded at an average rate of 305 542 mm kyr 1 the study illustrates the complexity of understanding onshore offshore sediment fluxes in the context of late quaternary sea level fluctuations for an area undergoing rapid tectonic uplift

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

relative sea level rise around east antarctica during oligocene glaciation during the middle and late eocene 48 34 myr ago the earth s climate cooled and an ice sheet built up on antarctica the stepwise expansion of ice on antarctica induced crustal deformation and gravitational perturbations around the continent close to the ice sheet sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet here we identify the crustal response to ice sheet growth by forcing a glacial hydro isostatic adjustment model with an antarctic ice sheet model we find that the shelf areas around east antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed the inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice sheet margins consequently the coasts experienced a progressive relative sea level rise our analysis of sediment cores from the vicinity of the antarctic ice sheet are in agreement with the spatial patterns of relative sea level change indicated by our simulations our results are consistent with the suggestion that near field processes such as local sea level change influence the equilibrium state obtained by an ice sheet grounding line

some insights into the characteristics and dynamics of the chilean low level coastal jet abstract the characteristics and dynamics of the chilean low level coastal jet cllcj are examined here through diagnosing real time mesoscale model forecasts in support of the variability of the american monsoon system vamos ocean cloud atmosphere land study vocals and additional sensitivity simulations the forecasted surface winds over the southeast pacific compare favorably with available observations according to the forecasts and sensitivity simulations the southeast pacific high pressure system seph plays a primary role in driving the cllcj the andes significantly intensify the cllcj mainly through interacting with the seph and anchoring a baroclinic zone along the chilean coast the land sea differential heating also enhances the cllcj by strengthening the coastal baroclinic zone based on the location of the seph center the cllcj can be separated into two types a strong forcing jet with the seph close to the central chilean coastline and a weak forcing jet with the seph centered fa

calibration between eustatic estimates from backstripping and oxygen isotopic records for the oligocene eustatic estimates from the backstripping of oligocene sections are compared quantitatively with d 18 o data each of the nine oligocene d 18 o events maxima identified in previous studies correlates with a stratigraphically determined sea level lowstand oxygen isotopic records from planktonic foraminifers from western equatorial atlantic ocean drilling program odp site 929 indicate an isotopic increase of 0 16 per 10 m decrease in the depth of the ocean apparent sea level asl amplitudes of asl change also correlate with moderate and high resolution benthic foraminiferal d 18 o records from odp sites 803 western tropical pacific and 929 and from deep sea drilling project dsdp site 522 south atlantic ocean with an isotopic change of 0 22 per 10 m of asl change r 2 5 0 807 and 0 960 respectively and with records from odp site 689 southern ocean 0 13 per 10 m of asl change r 2 5 0 704 this correlation suggests that southern ocean deep water temperature changes were smaller than tropical sea surface temperature changes between million year scale glacials and interglacials it also suggests that the deep sea southern ocean records may provide the best means to calibrate sea level to oxygen isotopes

stratocumulus cloud top height estimates and their climatic implications a depth dependent boundary layer lapse rate was empirically deduced from 156 radiosondes released duringsixmonth longresearchcruisestothe southeastpacificsamplingavarietyofstratocumulusconditions thelapse ratedependenceonboundarylayerheightisweak decreasingfromabestfitof7 6to7 2k km 21 as theboundarylayerdeepensfrom800mto2km ship basedcloud baseheightsupto800mcorrespondwellto liftingcondensationlevels indicatingwell mixedconditions withcloud bases 800moften 200 600m higher than the lifting condensation levels the lapse rates were combined with moderate resolution imaging spectrometer 11 mm derived cloud top temperatures and satellite microwave derived sea surface temperatures to estimate stratocumulus cloud top heights the october mean cloud top height structure of the southeast pacific was then spatially and diurnally characterized coastal shoaling is apparent but so is a significant along coast cloud top height gradient with a pronounced elevation of the cloud top heights above thearicabightat 208s diurnalcloud topheightvariations inferredfromirregular4 times dailysampling can locally reach 250 m in amplitude and they can help to visualize offshore propagation of free tropospheric vertical motions a shallow boundary layer associated with the chilean coastal jet expands to its north and west in the afternoon cloud top heights above the arica bight region are depressed in the afternoon which may mean that increased subsidence from sensible heating of the andes dominates an afternoon increase in convergence upward motion at the exit of the chilean coastal jet in the southeast atlantic during october thestratocumuluscloud topheightsaretypicallylowerthanthoseinthesoutheastpacific acoastaljetregion can also be identified through its low cloud top heights coastal shoaling of the south atlantic stratocumulus region is mostly uniform with latitude in keeping with the more linear namibian angolan coastline the southeast atlantic shallow cloudy boundary layer extends farther offshore than in the southeast pacific particularly at 158s

the mmco eot conundrum same benthic δ18o different co2 knowledge on climate change during the cenozoic largely stems from benthic 18o records which document combined effects of deep sea temperature and ice volume information on co2 is expanding but remains uncertain and intermittent attempts to reconcile 18o sea level and co2 by studying proxy data suffer from paucity of data and apparent inconsistencies among different records one outstanding issue is the difference suggested by proxy co2 data between the eocene oligocene boundary eot and the middle miocene climatic optimum mmco while similar levels of 18o are shown during these times this conundrum implies changing relations between 18o co2 and temperature over time here we use a coupled climate ice sheet model forced by two different benthic 18o records to obtain continuous and mutually consistent records of 18o co2 temperature and sea level over the period 38 to 10 myr ago we show that the different co2 levels between the eot and mmco can be explained neither by the standard configuration of our model nor by altering the uncertain ablation parametrization on the east antarctic ice sheet however we offer an explanation for the mmco eot conundrum by considering erosion and or tectonic movement of antarctica letting the topography evolve over time a decreasing height of the antarctic continent leads to higher surface temperatures reducing the co2 needed to maintain the same ice volume this also leads to an increasing contribution of ice volume to the 18o signal this result is however dependent on how the topographic changes are implemented in our ice sheet model

ocean circulation along the southern chile transition region 38 46 s mean seasonal and interannual variability with a focus on 2014 2016 satellite and atmospheric model fields are used to describe the wind forcing surface ocean circulation temperature and chlorophyll a pigment concentrations along the coast of southern chile in the transition region between 38 and 46 s located inshore of the bifurcation of the eastward south pacific current into the equatorward humboldt and the poleward cape horn currents the region also includes the chiloe inner sea and the northern extent of the complex system of fjords islands and canals that stretch south from near 42 s the high resolution satellite data reveal that equatorward currents next to the coast extend as far south as 48 51 s in spring summer they also display detailed distributions of forcing from wind stress and wind stress curl near the coast and within the inner sea between 38 46 s both winds and surface currents during 1993 2016 change directions seasonally from equatorward during summer upwelling to poleward during winter downwelling with cooler sst and greater surface chlorophyll a concentrations next to the coast during upwelling opposite conditions during downwelling over interannual time scales during 1993 2016 there is a strong correlation between equatorial el nino events and sea level and a moderate correlation with alongshore currents looking more closely at the 2014 2016 period we find a marginal el nino during 2014 and a strong el nino during 2015 that connect the region to the tropics through the oceanic pathway with some atmospheric connections through the phenomenon of atmospheric blocking as noted by others the period also includes a harmful algal bloom of the dinoflagellate alexandrium catenella during early 2016 that occurred during a sequence of physical conditions winds currents and temperatures that would favor such a bloom the most anomalous physical condition during this specific bloom is an extreme case of atmospheric blocking that creates a long period of calm in austral autumn after strong upwelling in austral summer the blocking is related to the 2015 2016 el nino and an unusual coincident positive phase of the southern annular mode

upwelling response to atmospheric coastal jets off central chile a modeling study of the october 2000 event the spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes in this study regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central chile the event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern pacific region during october 2000 a robust feature of the simulation is a sharp coastal wind dropoff which is insensitive to model resolution as expected the simulated oceanic response is a significant sea surface cooling a surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation this is because total upwelling i e the sum of coastal upwelling and ekman pumping depends on the scale of wind dropoff because the latter is much larger than the upwelling scale coastal wind dropoff has only a weak positive effect on vertical velocities driven by ekman pumping but has a strong negative effect on coastal upwelling interestingly though the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection with both effects contributing to a reduction of cooling

coastal lows along the subtropical west coast of south america mean structure and evolution the typical conditions of the eastern boundary of the subtropical anticyclone e g well defined marine boundary layer mbl equatorward low level flow that prevail along the mountainous west coast of subtropical south america are frequently disrupted by shallow warm core low pressure cells with alongshore and crossshore scales of 1000 and 500 km respectively these so called coastal lows cls occur up to five times per month in all seasons although they are better defined from fall to spring marked weather changes along the coast and farther inland are associated with the transition from pressure drop to pressure rise the mean structure and evolution of cls is documented in this work using a compositing analysis of 57 episodes selected from hourly pressure observations at a coastal station at 30 8s during the austral winters of 1991 1993 and 1994 and concurrent measurements from a regional research network of nine automatic weather stations ncep ncar reanalysis fields and high resolution visible satellite imagery coastal lows tend to develop as a migratory surface anticyclone approaches southern chile at about 408s producing a poleward oriented pressure gradient and geostrophically balanced offshore component in the low level wind at subtropical latitudes the transition from negative to positive geopotential anomalies occurs around 850 hpa enhanced mid and lowlevel subsidence near the coast and downslope flow over the coastal range and andes mountains leads to the replacement of the cool marine air by adiabatically warmed air lowering the surface pressure at the coast and offshore as the midlatitude ridge moves to the east of the andes the alongshore pressure gradient reverts back and the easterly wind ceases to act the recovery of the surface pressure toward mean values occurs as the cool cloud topped mbl returns to the subtropical coast although the pressure rise can be attenuated by midlatitude troughing the return of the mbl resembles a kelvin wave propagating along the coast from northern chile where the mbl eventually thickened into subtropical latitudes in about a day

the low level jet off the west coast of subtropical south america structure and variability abstract the subtropical anticyclone over the southeast pacific drives low level southerly flow along the west coast of south america in turn the alongshore flow induces coastal upwelling that supports a wealth of fishery resources within this region satellite data marine reports and coastal observations indicate the existence of a southerly coastal jet i e a maximum of wind speed off central chile 26 36 s the mean features and variability of this southerly jet is documented in this work using 4 yr of satellite derived sea surface winds complemented by satellite derived cloud amount fields and atmospheric reanalysis furthermore analysis of in situ data and model results of a well defined jet event during october 2000 allows a preliminary description of the jet s three dimensional structure and a comparison with the northerly jet off the coast of california southerly jet events off central chile occur year round but they are more frequent during spring summer over 60 of the time the

evidence for a heavily glaciated antarctica during the late oligocene warming 27 8 24 5 ma stable isotope records from odp site 690 high 18o values 3 0 from a 9 kyr resolution benthic foraminiferal stable isotope record from the ocean drilling program odp site 690b located on the maud rise antarctica indicate a heavily glaciated antarctic continent during late oligocene 27 8 24 5 ma values ranging 2 5 3 0 during interglacial periods and 3 0 3 6 during glacial intervals are consistent with an ice sheet near or larger than modern size in addition this record does not exhibit the long term late oligocene warming trend seen in records from low latitude drill sites oxygen isotope values from 26 0 24 5 ma are comparable ranging between 2 5 and 3 3 to values that preceded the 18o event oi2b at 26 7 ma indicating no significant glacial collapse occurred during the late oligocene a gradient between ocean basins during the oligocene has already been linked to the development of a modern multi layered ocean and worked to bathe the low to mid latitude deep sea records with a warmer water mass we suggest this masked the significant antarctic glaciation in low latitude paleoceanographic records additionally we propose a resolution for conflicting lines of evidence from some antarctic proximal records suggesting significant glaciation and others suggesting reduced glaciation during the late oligocene by allowing a modern sized ice sheet to grow on an antarctic continent as more land surface area existed above sea level during this time this could allow at least some portions of the antarctic coastline to remain ice free during glacial minima while still maintaining modern or near modern ice volume

coastal jets in the lower atmosphere abstract low level winds over land ocean boundaries are generally alongshore two types of forcing that generate alongshore jets in the lower atmosphere are considered here using as simple a model as possible the first type of forcing is the blocking of the low level zonal winds by topographies winter alongshore wind off the west coast of north america is topography forced our simple model produces wind fields that have horizontal structure similar to the observed based on the distribution of zonal wind stress with latitudes the model suggests that the alongshore wind over the west coast of the united states reveres its direction near 40 n in fair agreement with observations however the linear model underestimates the alongshore wind off the california coast by a factor of about 1 7 2 consequently linear prediction of nearshore wind stress is about 3 4 times smaller than the observed the discrepancy is attributed to nonlinear effects a nonlinear analysis is presented to show how nonlinearity

influence of large scale oscillations on upwelling favorable coastal wind off central chile 1 along the central coast of chile is typically equatorward upwelling favorable wind associated with the southeast pacific anticyclone a coastal low level jet often develops and its wind speed is mostly controlled by the meridional pressure gradient while the low level jet is a mesoscale feature forced by an interaction between synoptic conditions and coastal topography regional sea level pressure anomalies are associated with changes of the antarctic madden julian and el nino southern oscillation the connection between the alongshore wind and changes to the large scale circulation is examined and quantified using 31 years of the climate forecast system reanalysis which resolves coastal features better than previous coarser analyses composites based on each index reveal the modulation of the sea level pressure and significant alongshore wind anomalies of 0 5 1 5 m s 1 that correlate well to meridional surface pressure gradient changes and are centered near 35s constructive and destructive interference exists between the three indices that either enhance or cancel the alongshore wind anomaly during favorable upwelling conditions the distribution of meridional wind is generally clustered around positive anomalies with a tail toward negative values representing a stronger and persistent anticyclone during unfavorable upwelling conditions the anomalies are generally more normally distributed representing a weaker anticyclone and the passage of more cyclones

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

seasonal dynamics of the near surface alongshore flow off central chile 1 the seasonal cycle of the near surface circulation off central chile was analyzed using satellite altimetry and an oceanic model to evaluate the role of the wind stress curl on the circulation we performed two identical simulations except for the wind forcing the control run used long term monthly mean wind stress and the no curl run used a similar wind stress field but without curl the observed and modeled control run surface currents showed a strong seasonal cycle and a well defined equatorward flow with a jet like structure this jet develops during spring and summer consistent with the presence of a low level wind jet south of punta lavapie cape 37 s the equatorward surface current remains close to the coast after the flow passes this cape however it separates to become an offshore jet in contrast in the no curl simulation the separation at punta lavapie is not observed and the offshore jet farther north is not present demonstrating the importance of the wind stress curl on the dynamics of this flow although the offshore integrated sverdrup transport was similar to the model transport the offshore jet was not located where the wind stress curl was maximum instead the position of the jet followed approximately the zero wind stress curl which corresponds to the climatological location of the low level wind jet axis these results illustrate the importance of the offshore upwelling downwelling associated with curl driven ekman pumping which tilts isopycnals upward downward toward the east west of the wind jet forcing a northward flow through thermal wind balance

early east antarctic ice sheet growth recorded in the landscape of the gamburtsev subglacial mountains the gamburtsev subglacial mountains are regarded as a key nucleation site for the antarctic ice sheet and they retain a unique long term record of pre glacial and early glacial landscape evolution here we use a range of morphometric analyses to constrain the nature of early glaciation and subsequent ice sheet evolution in the interior of east antarctica using a new digital elevation model of the gamburtsev subglacial mountains derived from an extensive airborne radar survey we find that an inherited fluvial landscape confirms the existence of the gamburtsev subglacial mountains prior to the onset of glaciation at the eocene oligocene climate boundary ca 34 ma features characteristic of glaciation at a range of scales are evident across the mountains high elevation alpine valley heads akin to cirques identified throughout the mountains are interpreted as evidence for early phases of glaciation in east antarctica the equilibrium line altitudes associated with these features combined with information from fossil plant assemblages suggest that they formed at or prior to 34 ma it cannot be ruled out that they may have been eroded by ephemeral ice between the late cretaceous and the eocene 100 34 ma hanging valleys overdeepenings truncated spurs and steep sided linear valley networks are indicative of a more widespread alpine glaciation in this region these features represent ice growth at or before 33 7 ma and provide a minimum estimate for the scale of the east antarctic ice sheet between ca 34 and 14 ma when dynamic fluctuations in ice extent are recorded at the coast of antarctica the implications are that the early east antarctic ice sheet grew rapidly and developed a cold based core that preserved the alpine landscape the patterns of landscape evolution identified provide the earliest evidence for the development of the east antarctic ice sheet and can be used to test coupled ice climate evolution models

tracer transport in the greenland ice sheet three dimensional isotopic stratigraphy abstract polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models the stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent we describe a coupled model of ice and tracer dynamics that is realized by adding a semi lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model model skill is demonstrated by using ice core data from the grip site near summit greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites the success of this effort indicates that when compensated for the effects of ice flow and elevation all the deep cores relate a coherent glacial history over the past 120 000 years according to the simulation results the oldest greenland ice lies beneath the grip gisp2 and northgrip sites although comparably old ice may also be found in north greenland and east central greenland

thurston island west antarctica between gondwana subduction and continental separation a multistage evolution revealed by apatite thermochronology

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of peru from satellite observations 2000 2008 1 the tropical rainfall measuring mission microwave imager sea surface temperature sst and quikscat wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of peru over the period 2000 2008 two regions of peak variance correspond to the central peru region pisco region 15 s and the northern peru region piura region 5 s a covariance analysis reveals a significant coherency between winds and sst anomalies off pisco consistent with ekman pumping and transport dynamics the upwelling cell consists in a meridionally extended fringe of colder warmer water extending as far as 250 km from the coast at 15 s in the piura region the intraseasonal covariability pattern is represented by two modes one relevant to the direct ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic kelvin wave two regimes of variability are evidenced a low period regime 10 25 days is the signature of ekman transport pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern pacific anticyclone a high period regime 35 60 day band is associated with the combined forcing of oceanic equatorial kelvin waves and migratory atmospheric disturbances in the midlatitudes in particular the modes of covariability exhibit a prominent 50 day period energy peak it is shown that this period arises from the impact of the first two baroclinic modes kelvin wave with the second baroclinic mode kelvin wave being more influential on the piura region

stepwise transition from the eocene greenhouse to the oligocene icehouse the eocene oligocene transition is the largest global cooling in the cenozoic period a comparison of three independent proxies from the continental shelf and deep ocean reveals a three step transition to cold glacial conditions with ice sheets 25 larger than their present size

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

fast sst error growth in the southeast pacific ocean comparison between high and low resolution ccsm4 retrospective forecasts sea surface temperature errors that develop after 1 week are investigated as a function of resolution using retrospective forecasts from the community climate system model one version resolves the ocean and atmosphere to approximately 1 while the second version resolves the ocean to 0 1 and the atmosphere to 0 5 the forecasts are initialized on january 1 from 1982 to 2003 the spatial pattern of the pacific basin sea surface temperatures errors after 1 week is mostly similar at both resolutions with the exception of the coast of south america the coastal ocean surface cools within the higher resolution simulations but warms within the lower resolution simulations the difference in the ocean surface temperature is instead attributed to differing changes in the upwelling coastal upwelling increases within the higher resolution simulation increasing the lower tropospheric stability and encouraging the cloud cover in contrast the upwelling decreases within the lower resolution simulations at 27 s allowing the ocean surface to warm in spite of cooling from the atmosphere in both simulations the northward winds and surface currents weaken because the south pacific sea level pressure high moves westward the increased oceanic upwelling in the high resolution simulation is instead attributed to an increase in the westward zonal currents the high resolution model resolves the narrow humboldt current while the low resolution model does not this study demonstrates that the processes responsible for sst errors in eastern upwelling boundary current regions change when the oceanic grid spacing becomes fine enough to allow resolution of the oceanic boundary currents

preglacial to glacial sediment thickness grids for the southern pacific margin of west antarctica circum antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions which are important for paleo ice sheet formation histories by compiling old and new seismic data we identify sequences representing pre glacial transitional and full glacial deposition processes along the pacific margin of west antarctica the pre glacial sediment grid depicts 1 3 to 4 0 km thick depocenters relatively evenly distributed along the margin the depocenters change markedly in the transitional phase at or after the eocene oligocene boundary when the first major ice sheets reached the shelf full glacial sequences starting in the middle miocene indicate new depocenter formation north of the amundsen sea embayment and localized eastward shifts in the bellingshausen sea and antarctic peninsula basins using present day drainage paths and source areas on the continent our calculations indicate an estimated observed total sedimentary volume of 10 x 106 km3 was eroded from west antarctica since the separation of new zealand in the late cretaceous of this 4 9 x 106 km3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 ma whereas 5 1 x 106 km3 postdate the onset of glaciation of which 2 5 x 106 km3 were deposited in post mid miocene full glacial conditions this article is protected by copyright all rights reserved

organic rich sedimentation in the south pacific ocean associated with late paleocene climatic cooling abstract a distinctive organic rich marine mudstone of late paleocene age occurs in most of new zealand s sedimentary basins and has been identified as a potential source rock for oil and gas identified as the waipawa formation in the east coast basin and the tartan formation in the great south and canterbury basins the unit is a relatively uniform massive mudstone that varies greatly in thickness 2 70 m and grades laterally into distinctive facies equivalents notably greensand and a thin bedded siliceous mudstone all these facies are characterised by relatively high toc 0 5 10 wt and 13 c enrichment 13 c toc 24 and we refer to them collectively as waipawa organofacies our detailed stratigraphic and geochemical studies refine the age 58 7 to 59 4 ma distribution and nature of the waipawa organofacies we have determined that deposition occurred in continental margin settings throughout much of the southwest pacific under cool dysoxic conditions associated with a significant influx of terrestrial organic matter high marine productivity a global fall in sea level and a regional unconformity across shallow and deep marine settings the combination of cool temperatures lowered sea level and bathyal erosion suggests that deposition was linked to short lived growth of an antarctic ice sheet in the earliest late paleocene 59 ma

west antarctic paleotopography estimated at the eocene oligocene climate transition 1 one generally recognized limitation of models for rapid growth of antarctic ice near the eocene oligocene transition is that they are based on present topography corrected only for removal of modern ice for west antarctica this results in large areas below sea level that would not readily host ice in the recently active west antarctic rift system other factors may have contributed to significant vertical motions since the eocene additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 ma restore most of west antarctica to above sea level increasing total antarctic land area by 10 20 because ice sheets have convex slopes the potential increase in ice volume is larger than the increase in land area accounting for large changes in west antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early large west antarctic ice sheet

mineral sources of aqua regia extractable base cations in scottish soils interpreted from cubist models trained with quantitative mineralogy data abstract the long term potential capacity for soils to deliver essential elements to plants and the soil solution is often assessed using aqua regia ar extractions and understanding specific mineral contributions to extracted element concentrations is central to the accurate interpretation of such data the objective of this study was to assess whether the supplying quantitative soil mineralogy data to the cubist machine learning algorithm could result in accurate prediction of ar extractable base cation concentrations naaqr mgaqr kaqr and caaqr and consequently facilitate the interpretation of meaningful mineral sources of these elements mineral concentrations were quantified in 191 soil samples collected by horizon from 96 sites across scotland these mineral concentrations together with ph and soil organic matter data were used to train cubist models for the prediction of log naaqr log mgaqr log kaqr and log caaqr yielding concordance correlation coefficients of 0 77 0 87 0 78 and 0 71 respectively when assessed by cross validation the dominant variables selected by cubist for the conditions of the models contrasted substantially between the four elements aligning with the independent nature of each base cation interpreted from compositional biplot analysis namely plagioclase concentrations were predominantly selected by cubist for log naaqr prediction chlorite concentrations for log mgaqr prediction dioctahedral mica concentrations for log kaqr prediction and ph for log caaqr prediction the selection of these variables is found to be geochemically appropriate for each element demonstrating how data driven methods can yield meaningful conclusions with respect to mineral sources of ar extractable elements in validating the utility of combining quantitative soil mineralogy data with the cubist machine learning algorithm on the relatively well characterised base cations future work can progress towards using similar approaches to define mineral sources of more challenging trace elements in new detail

unraveling complex 2 μm clay mineralogy from soils using x ray diffraction profile modeling on particle size sub fractions implications for soil pedogenesis and reactivity a specific methodology was developed to refine the complex clay mineralogy commonly encountered in soil environments the soil examined was a cambisol developed into a ferralitic paleosol the sample was split into four sub fractions of different particle sizes 0 05 0 05 0 1 0 1 0 2 and 0 2 2 mu m and their respective mass contributions to the overall 2 mu m clay fraction were determined for each sub fraction x ray diffraction xrd patterns were modeled using a trial and error approach based on the direct comparison of experimental and calculated profiles quantitative information derived from the fitting procedure for the different sub fractions allowed for the determination of the complex mineralogy of the 2 mu m clay fraction through the identification and quantification of eight clay phases the results show that the finest and most reactive clay fraction 0 05 pm was totally hidden in the xrd pattern of the 2 mu m fraction the fraction commonly considered in soil mineralogical analyses similarly this procedure revealed the presence of illite smectite chlorite and kaolinite illite mixed layer minerals seldom described in soil literature using classical methods the use of this methodology improved our understanding of the pedogenesis of this soil through the identification and quantification of clay phases structural properties the analysis of the evolution of structural parameters with particle size allowed for the detection of local modifications in the interlayer composition of expandable and hydroxy interlayered vermiculite layers following this approach key information can be derived to determine subtle changes in clay mineralogical composition that are related to microorganism and or plant activity

a case study of the interaction of the summertime coastal jet with the california topography coast parallel low level jets are commonplace in the marine boundary layer off the west coast of the united states during summer a field study was conducted in early summer of 1997 to document the forcing of boundary layer winds in the near coastal environment off california on 8 june 1997 the wyoming king air collected data along a 350 km stretch of coastal margin from cape mendocino to san francisco in order to examine the interaction between the coastal topography and the low level jet during the course of the flight 32 soundings were conducted the maximum speed of the coastal jet was found near the top of the marine boundary layer at altitudes from 200 to 600 m analysis of the data revealed a westward increase in the height of the marine boundary layer and maximum jet wind speeds strongest jet winds were observed southwest of cape mendocino with a maximum speed of 28 m s21 the coastal jet was characterized by a broad horizontal extent wind maxima were found at distances approximately 30 km to more than 100 km offshore hydraulic features such as jumps and expansion fans have previously been observed downwind of coastal capes and points along the california coast the flow upwind of cape mendocino and point arena was found to be supercritical but the king air data showed that accelerations associated with possible expansion fan phenomena were minimal it is proposed that the sloping inversion at the top of the marine boundary layer and attendant coastal jet are fundamentally the result of a geostrophic adjustment process arising because of the horizontal temperature contrast between the cool ocean and warm continent this view emphasizes that the coastal jet is a ubiquitous large scale feature of the summertime coastal environment terrain induced wind speed variations associated with expansion fans and hydraulic jumps only modulate the primary jet structure

dynamics of the low level jet off the west coast of subtropical south america the subtropical west coast of south america is under the influence of the southeast pacific anticyclone year round which induces persistent southerly winds along the coast of north central chile these winds often take the form of a low level coastal jet in many aspects similar to the coastal jet existing off the california coast extensive diagnostics of mesoscale model results for a case in october 2000 are used here to describe the mean momentum budget supporting the coastal jet the jet appears to occur when midlatitude synoptic conditions induce a northerly directed pressure gradient force along the coast of northcentral chile the very steep coastal terrain precludes the development of a significant easterly low level wind that would geostrophically balance the pressure gradient instead the meridional flow accelerates until turbulent friction in the marine boundary layer balances the meridional pressure gradient the resulting force balance is semigeostrophic with geostrophy valid only in the zonal cross shore direction at higher levels the topographic inhibition of the easterlies relaxes and a small easterly flow ensues which turns out to be very important in the temperature and stability budgets of the layer capping the marine boundary layer

the summertime low level jet and marine boundary layer structure along the california coast abstract this paper examines the strong summertime northerly low level jet llj that frequently exists along the california coast the persistent synoptic scale pressure distribution north pacific high to the west thermal low to the east and baroclinity created by the juxtaposition of the heated continent and the cool marine layer produce the mean structure of this llj strong diurnal thermal forcing coupled with topographic influences on the flow modulate the jet structure position and intensity a mesoscale model is used to examine many of the complex facets of the llj flow dynamics several sensitivity studies in addition to a control experiment aid in this investigation principal findings of this study include the following the pronounced east west slope of the marine planetary boundary layer mpbl is not due primarily to colder sst values along the coast dynamically forced low level coastal divergence coupled with synoptic scale divergence appears to be dominant in determining mpbl i

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

deep water temperature carbonate ion and ice volume changes across the eocene oligocene climate transition 1 paired benthic foraminiferal stable isotope and mg ca data are used to estimate bottom water temperature bwt and ice volume changes associated with the eocene oligocene transition eot the largest global climate event of the past 50 myr we utilized odp sites 1090 and 1265 in the south atlantic to assess seawater 18o w antarctic ice volume and sea level changes across the eot 33 8 33 54 ma we also use benthic 13c data to reconstruct the sources of the deep water masses in this region during the eot our data together with previously published records indicate that a pulse of northern component water influenced the south atlantic immediately prior to and following the eot benthic 18o records show a 0 5 increase at 33 8 ma eot 1 that represents a 2 c cooling and a small 10 m eustatic fall that is followed by a 1 0 increase associated with oi 1 the expected cooling of deep waters at oi 1 33 54 ma is not apparent in our mg ca records we suggest the cooling is masked by coeval changes in the carbonate saturation state co32 which affect the mg ca data to account for this the bwt ice volume and w estimates are corrected for a change in the co32 of deep waters on the basis of recently published work corrected bwt at sites 1090 and 1265 show a 1 5 c cooling coincident with oi 1 and an average w increase of 0 75 the increase in ice volume during oi 1 resulted in a 70 m drop in global sea level and the development of an antarctic ice sheet that was near modern size or slightly larger

influence of the opening of the drake passage on the cenozoic antarctic ice sheet a modeling approach we evaluate the opening of the drake passage dp between antarctica and south america and associated changes in ocean circulation as forcing factor for the onset of antarctic glaciation near the eocene oligocene transition 34 million years ago in this paper this hypothesis is tested through sensitivity experiments using numerical models for the global ocean and atmosphere and for the antarctic ice sheet the response of the antarctic continent to the opening of the dp and to the establishment of the antarctic circumpolar current is examined two different climate states are reproduced with ocean gateway configurations similar to the late eocene and to the late oligocene before and after the opening of the dp a reduced southward heat flux and a decrease of surface temperature are found in the antarctic realm when the dp is open a more massive ice sheet develops on the continent in case of dp open compared to the configuration with closed dp

assessing potassium reserves in northern temperate grassland soils a perspective based on quantitative mineralogical analysis and aqua regia extractable potassium abstract increasing demand for locally produced farm products with a lower input of mineral fertilisers leads to a greater reliance on the inherent capacity of soils to supply plant nutrients typically 98 of all soil potassium k is found in k feldspars and phyllosilicates however the potential bioavailability of k from different mineral forms varies significantly as a basis for improving sustainable nutrient management options for grassland systems we set out to determine 1 how soil parent material influences the amount of k in soils 2 how the k is quantitatively distributed between mineral groups 3 relationships between quantitative mineralogy x ray powder diffraction xrpd total k x ray fluorescence and the more widely available measurement of aqua regia extractable k and 4 how the studied soils could be ranked in terms of their long term potential capacity to deliver k to plants soils representing eight of the most extensive soil associations defined by different parent materials under improved grassland in scotland were analysed soil samples represented a wide range of total k concentrations from 1 3 to 39 g kg 1 quantitative mineralogical data from xrpd were combined with mineral compositions to obtain the mineralogical apportionment of k apportionment of k varied significantly from those soils with almost all k present in various phyllosilicates to others where almost all k is held in k feldspars aqua regia extractable k is related to k in phyllosilicates excluding muscovite mica and unrelated to k in k feldspars the studied soils are ranked in terms of their potential capacity to release k based on their mineralogical and geochemical characteristics

impact of phyllosilicate mineralogy on organic carbon stabilization in soils incomplete knowledge and exciting prospects abstract soil mineral phases strongly influence soil organic carbon soc dynamics clay size particles have been recognized as protecting soc from microbial decomposition among clay size minerals phyllosilicates clay minerals have been shown to efficiently protect soc there is an important variety of phyllosilicate types present in soils which have contrasting surface properties specific surface area charge density although these differing surface properties should influence their ability in protecting soc this has not been clearly established yet publications comparing the ability of the different phyllosilicates to protect soc are reviewed in this study relatively few studies dealing with the link between phyllosilicate mineralogy and soc protection exist the few existing studies have followed different methodologies and are based on various analytical techniques such that direct comparisons among them are difficult more problematic they provide different conclusions indeed if experiments conducted in suspension using pure clay phases and recent meta analyses suggest that phyllosilicate mineralogy has a significant importance for soc stabilization and soc stock response to land use change these results are not clearly corroborated by studies conducted on a reduced number of soils the recent technical developments which allow improving both quantitative and qualitative descriptions of the soil clay mineral assemblages together with nanoscale investigations of phyllosilicate om interactions offer exciting perspectives for determining more accurately the efficiency of the different phyllosilicate types in soc protection such information may provide a much clearer understanding of the impact of phyllosilicate mineralogy on soc dynamics in the coming years

numerical study of the diurnal cycle along the central oregon coast during summertime northerly flow abstract a triply nested mesoscale atmospheric numerical model is used to study the dynamics of the diurnal cycle of the summertime lower atmosphere along the central oregon coast simulations of four consecutive days in september 1998 during which the winds were strong and northerly are analyzed comparisons with profiler observations suggest that the model performed well enough to provide a useful estimate of the diurnal circulation during the four days of interest the low level wind pattern has a broad maximum between cape blanco and cape mendocino with a large north south gradient along the oregon coast the low level jet undergoes diurnal horizontal and vertical displacements which partially resemble previous observational and modeling results along the california coast in both the model and the profiler data there is a minimum in northerly wind between 1500 and 1800 utc 0700 and 1000 local time and a double maximum in offshore flow above the marine boundary layer with peaks near 0700 and

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

extreme temperature and precipitation events in march 2015 in central and northern chile from 18 to 27 march 2015 northern central and southern chile experienced a series of extreme hydrometeorological events first the highest surface air temperature ever recorded in santiago with reliable records dating to 1877 36 8 c at quinta normal was measured at 15 47 local time on 20 march 2015 immediately following this high heat event an extreme precipitation event with damaging streamflows from precipitation totals greater than 45 mm occurred in the semiarid and hyperarid atacama regions finally concurrent with the heavy precipitation event extremely warm temperatures were recorded throughout southern chile these events were examined from a synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each analysis which provides operational context by which to identify and predict similar events in the future primary findings were as follows 1 record warm temperatures in central chile resulted from anomalous lower troposphere ridging and easterly downslope flow both of which developed in response to an anomalous midtroposphere ridge trough pattern 2 a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25 s by circulation around a very strong ridge anomalies more than 3 standard deviations above normal centered near 60 s 3 anomalously high precipitable water content 20 mm above climatological norms over the peruvian bight region was advected southward and eastward ahead of the cutoff low by low level northwesterly flow greatly enhancing observed precipitation over northern chile

initiation of the west antarctic ice sheet and estimates of total antarctic ice volume in the earliest oligocene 1 reconstructions of antarctic paleotopography for the late eocene suggest that glacial erosion and thermal subsidence have lowered west antarctic elevations considerably since then with antarctic land area having decreased 20 a new climate ice sheet model based on these reconstructions shows that the west antarctic ice sheet first formed at the eocene oligocene transition 33 8 33 5ma e o in concert with the continental scale expansion of the east antarctica ice sheet and that the total volume of east and west antarctic ice 33 4 35 9 10 6 km 3 w as 1 4 times greater than previously assumed this larger modeled ice volume is consistent with a modest cooling of 1 2 c in the deep ocean during the e o transition lower than other estimates of 3 c cooling and suggests the possibility of substantial ice in the antarctic interior before the eocene oligocene boundary citation wilson d s d pollard r m deconto s s r jamieson and b p luyendyk 2013 initiation of the west antarctic ice sheet and estimates of total antarctic ice volume in the earliest oligocene geophys res lett 40 doi 10 1002 grl 50797

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

which 2 1 clay minerals are involved in the soil potassium reservoir insights from potassium addition or removal experiments on three temperate grassland soil clay assemblages field and laboratory observations based on x ray diffraction techniques suggest that 2 1 clay minerals behave as a k reservoir however 2 1 soil clay assemblages are most often composed of a mixture of different 2 1 clay mineral populations and the role of these different clay mineral populations in k absorption or k release are not fully understood this present work addressed this question through laboratory experiments by using an x ray pattern decomposition program to quantify peak area modifications of different clay mineral populations induced by k addition and k removal through plant action this study was performed on three typical temperate grassland soil clay assemblages containing illite interstratified illite smectite and soil vermiculite our results revealed that the quantities of well crystallized illite increased at the expense of soil vermiculite as a result of k absorption whereas the opposite trend was observed following k depletion this particular relationship between well crystallized illite and soil vermiculite suggests that they constitute a subgroup among 2 1 clay minerals poorly crystallized illite and interstratified clay minerals were also significantly affected by k absorption or removal indicating that they are also involved in soil k dynamics moreover we observed that these short term clay mineral modifications occurring at the day scale induced by root k extraction are reversible we also observed that the linear relationship between clay k content and the centre of gravity position of x ray diffraction patterns in the 2 1 clay mineral range seem to be a general property for soil clay assemblages dominated by illite and interstratified illite smectite materials our results support the view of 2 1 clay minerals as a k reservoir and specify the role of each of the 2 1 clay mineral populations in k absorption and release all the 2 1 clay minerals commonly found in temperate grassland soil clay assemblages take part in the soil k reservoir

antarctic topography at the eocene oligocene boundary we present a reconstruction of the antarctic topography at the eocene oligocene ca 34 ma climate transition this provides a realistic key boundary condition for modeling the first big antarctic ice sheets at this time instead of using the present day bedrock topography which has changed significantly from millions of years of tectonism and erosion we reconstruct topography using a set of tools including ice sheet erosion models models of thermal subsidence and plate movement erosion estimates are constrained with offshore sediment volumes estimated from seismic stratigraphy maximum and minimum topographic reconstructions are presented as indicators of the range of uncertainty our results point to a significant upland area in the ross sea marie byrd land and weddell sea sectors in addition east antarctic coastal troughs are much shallower than today due to the restoration of material that has been selectively eroded by the evolving ice sheets parts of east antarctica have not changed since the e o boundary because they were protected under non erosive cold based ice the reconstructions provide a better defined boundary condition for modeling that seeks to understand interaction between the antarctic ice sheet and climate along with more robust estimates of past ice volumes under a range of orbital settings and greenhouse gas concentrations

diurnal cycle of surface winds over the subtropical southeast pacific 1 the diurnal variability of surface winds over the se pacific is characterized with quikscat data for years 2000 2006 the twice daily satellite passes occur around 0600 and 1800 lt referred to as am and pm respectively the pm am wind difference maximizes in a region between 20 s and 30 s extending from the chilean coast up to 75 w this difference is mostly meridional along the coast with seasonal variation characterized by summertime weakening of the morning winds the observational analysis is supplemented with mesoscale model results for december 2003 they show that the coastal zonal flow increases between 0600 and 1200 local time lt but then decreases in the next 6 hours which explains the absence of an onshore component in the quikscat pm am difference additional model diagnostics show that in this region the diurnal cycle hodographs are more simple and larger above the marine boundary layer mbl than at the surface evaluation of the momentum and temperature budgets reveals the importance of the diurnal cycle of vertical velocity coupled with the thermal structure in controlling the diurnal cycle of the low level winds around 1300 lt coastal subsidence maximizes in a layer sloping from 1000 m at 36 s to 3000 m at 22 s inducing the development of a coastal trough at the surface during the night the passage of a high pressure perturbation reverses the surface meridional pressure gradient force inducing the decrease of the coastal meridional winds these results stress the important role played by the dynamics of the low troposphere above the mbl e g the heating of the andes cordillera to the east in controlling the wind diurnal cycles near the surface