pronounced zonal heterogeneity in eocene southern high latitude sea surface temperatures paleoclimate studies suggest that increased global warmth during the eocene epoch was greatly amplified at high latitudes a state that climate models cannot fully reproduce however proxy estimates of eocene near antarctic sea surface temperatures ssts have produced widely divergent results at similar latitudes with ssts above 20 c in the southwest pacific contrasting with ssts between 5 and 15 c in the south atlantic validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites here we present multiproxy data from seymour island near the antarctic peninsula that provides well constrained evidence for annual ssts of 10 17 c 1 sd during the middle and late eocene comparison of the same paleotemperature proxy at seymour island and at the east tasman plateau indicate the presence of a large and consistent middle to late eocene sst gradient of 7 c between these two sites located at similar paleolatitudes intermediate complexity climate model simulations suggest that enhanced oceanic heat transport in the south pacific driven by deep water formation in the ross sea was largely responsible for the observed sst gradient these results indicate that very warm ssts in excess of 18 c did not extend uniformly across the eocene southern high latitudes and suggest that thermohaline circulation may partially control the distribution of high latitude ocean temperatures in greenhouse climates the pronounced zonal sst heterogeneity evident in the eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands

controls on the 87sr 86sr composition of seawater from the middle eocene to oligocene hole 689b maud rise antarctica a 87sr 86sr isotope curve of the middle eocene to oligocene was produced from analysis of foraminifera in ocean drilling program hole 689b maud rise near the coast of antarctica sediments from the hole are well preserved with no evidence of diagenetic alteration the sequence is nearly complete from 46 3 to 24 8 ma with an average sampling interval of 166 kyr excellent magnetostratigraphy in hole 689b allows calibration to the geomagnetic polarity time scale of cande and kent 1992 marine strontium isotopic ratios were nearly stable from 46 3 to 35 5 ma averaging near 0 70773 after which they began to increase a slow increase began after 40 4 ma rising at a rate of only about 8 10 6 m y from base values of 0 707707 from 35 5 ma to 24 8 ma the average slope increased to 40 10 6 m y the slope remained constant at least until 24 8 ma when the record becomes discontinuous owing to unconformities we evaluate several possible controls on the marine strontium isotope curve that could have led to the observed growth in 87sr 86sr ratios near the eocene oligocene boundary three mechanisms are considered including the onset of antarctic glaciation increased mountain building in the himalayan tibetan region and decreased hydrothermal activity none of the mechanisms alone seems to adequately explain the increased 87sr 86sr ratios during the oligocene glaciation as a weathering agent was too episodic and probably began too late to explain the upturn in marine 87sr 86sr ratios there is evidence that uplift in the himalayan tibetan region began in the miocene much too late to control oligocene strontium isotope ratios lastly hydrothermal flux changes since the eocene were apparently not great enough alone to account for the rise in marine 87sr 86sr ratios we suggest that a combination of causes such as decreased hydrothermal activity perhaps followed by increased glaciation and mountain building might best explain the growth of the marine 87sr 86sr curve during the oligocene

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

eocene bipolar glaciation associated with global carbon cycle changes the transition from the extreme global warmth of the early eocene greenhouse climate 55 million years ago to the present glaciated state is one of the most prominent changes in earth s climatic evolution it is widely accepted that large ice sheets first appeared on antarctica 34 million years ago coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world s oceans and that glaciation in the northern hemisphere began much later between 10 and 6 million years ago here we present records of sediment and foraminiferal geochemistry covering the greenhouse icehouse climate transition we report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical pacific and south atlantic oceans from 42 million years ago with a permanent deepening 34 million years ago the most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1 5 per mil suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres variations in benthic carbon isotope ratios of up to 1 4 per mil occurred at the same time indicating large changes in carbon cycling we suggest that the greenhouse icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago between 55 and 34 million years ago earth switched from a warm greenhouse ocean climate system to the icehouse that we now enjoy frustratingly the few oceanographic datasets that exist for this key period are of low resolution tripati et al now present measurements of sediment and foraminiferal geochemistry that provide the first continuous high resolution records for this period the data suggest that northern hemisphere glaciation started 34 million years ago rather than between 10 and 8 million years ago as previously thought

along arc segmentation and interaction of subducting ridges with the lesser antilles subduction forearc crust revealed by mcs imaging highlights we image the deep structure of the lesser antilles subduction zone by mcs profiles the complex deformation of the outer forearc crust is induced by subducting ridges we discuss also the effect of the subducting compressive nam sam plate boundary along strike variations of the seaward edge of the outer forearc crust are discovered the updip limit proxy of the seismogenic part reaches 20 km trenchwards than believed abstract we present the results from a new grid of deep penetration multichannel seismic mcs profiles over the 280 km long north central segment of the lesser antilles subduction zone the 14 dip lines and 7 strike lines image the topographical variations of i the subduction interplate decollement ii the top of the arcward subducting atlantic oceanic crust toc under the huge accretionary wedge up to 7 km thick and iii the trenchward dipping basement of the deeply buried forearc backstop of the caribbean upper plate the four northernmost long dip lines of this new mcs grid reveal several kilometre high topographic variations of the toc beneath the accretionary wedge offshore guadeloupe and antigua islands they are located in the prolongation of those mapped on the atlantic seafloor entering subduction such as the barracuda ridge this mcs grid also provides evidences on unexpected huge along strike topographical variation of the backstop basement and of the deformation style affecting the outer forearc crust and sediments their mapping clearly indicates two principal areas of active deformation in the prolongation of the major barracuda and tiburon ridges and also other forearc basement highs that correspond to the prolongation of smaller oceanic basement highs recently mapped on the atlantic seafloor although different in detail the two main deforming forearc domains share similarities in style the imaged deformation of the sedimentary stratification reveals a time and space dependent faulting by successive warping and unwarping which deformation can be readily attributed to the forearc backstop sweeping over the two obliquely oriented elongated and localized topographical ridges the induced faulting producing vertical scarps in this transport does not require a regional arc parallel extensional regime as proposed for the inner forearc domain and may support a partitioned tectonic deformation such as in the case of an outer forearc sliver a contrasted reflectivity of the sedimentary layering at the transition between the outer forearc and accretionary domains was resolved and used to define the seaward edge of the outer forearc basement interpreted as being possibly a proxy to the updip limit of the interplate seismogenic zone its mapping documents along arc variations of some tens of kilometres of the subduction backstop with respect to the negative gravity anomaly commonly taken as marking the subduction trench with the exception of the southernmost part the newly mapped updip limit reaches 25 km closer to the trench thus indicating a possible wider seismogenic zone over almost the whole length of the study area

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

antarctic continental weathering changes during eocene oligocene cryosphere expansion clay mineral and oxygen isotope evidence we have analyzed clay minerals and oxygen isotopes over the eocene oligocene climate transition 33 8 32 5 ma in ocean drilling program site 689 maud rise antarctica distinct changes in clay mineral assemblages suggest major instability in the east antarctic climate for 0 7 m y during this time of general expansion of the antarctic cryosphere and cooling of the southern ocean increased illite abundance reflects enhanced physical weathering associated with cryospheric development nevertheless continued dominance of smectite indicates that chemical weathering continued to prevail during the early oligocene weathering was much more intense than in modern deglaciated areas the clay mineral data support evidence from marine sediments suggesting that continental and marine climatic conditions during the early oligocene were intermediate between relative eocene warmth and intense neogene cold the clay mineral variations during the transition reflect major changes in continental precipitation and related continental ice accumulation

magnitude frequency analysis of water redistribution along a climate gradient in spain abstract banded patterns in soils and vegetation form part of important discontinuities on semi arid slopes in spain at fine scales

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

contrasting effects of microbiotic crusts on runoff in desert surfaces abstract microbiotic crusts mcs play an important role in surface hydrology by altering runoff yield in order to study the crust s role on water redistribution rainfall and runoff were measured during 1998 2000 at three sites within the northern chihuahuan desert new mexico usa the sevilleta national wildlife refuge sev the white sands national monument ws and the jornada experimental range jer whereas quartz and gypsum sand characterize the sev and ws sites respectively both of which have high infiltration rates silty alluvial deposits characterize the jer site runoff was measured in four pairs of 1 8 6 4 m 2 plots having mcs one of which was scalped in each pair no runoff was generated at ws whether on the crusted or the scalped plots runoff was however generated at sev and jer being higher on the crusted plots at sev and lower on the jer plots the results were explained by the combined effect of a parent material and b the crust properties such as species composition microrelief surface roughness and exopolysaccharide eps content reflected in the ratio of carbohydrates to chlorophyll whereas the effective rainfall the fines and the eps content were found to explain runoff initiation the effective rainfall and the crust microrelief were found to explain the amount of runoff at sev and jer where runoff generation took place the findings attest to the fundamental role of the parent material and the crust s species composition and properties on runoff and hence to the complex interactions and the variable effects that mcs have on dryland hydrology

foraminiferal mg ca evidence for southern ocean cooling across the eocene oligocene transition constraining the magnitude of high latitude temperature change across the eocene oligocene transition eot is essential for quantifying the magnitude of antarctic ice sheet expansion and understanding regional climate response to this event to this end we constructed high resolution stable oxygen isotope 18o and magnesium calcium mg ca records from planktic and benthic foraminifera at four ocean drilling program odp sites in the southern ocean planktic foraminiferal mg ca records from the kerguelen plateau odp sites 738 744 and 748 show a consistent pattern of temperature change indicating 2 3 c cooling in direct conjunction with the first step of a two step increase in benthic and planktic foraminiferal 18o values across the eot in contrast benthic mg ca records from maud rise odp site 689 and the kerguelen plateau odp site 748 do not exhibit significant temperature change the contrasting temperature histories derived from the planktic and benthic mg ca records are not reconcilable since vertical 18o gradients remained nearly constant at all sites between 35 0 and 32 5 ma based on the coherency of the planktic mg ca records from the kerguelen plateau sites and complications with benthic mg ca paleothermometry at low temperatures the planktic mg ca records are deemed the most reliable measure of southern ocean temperature change we therefore interpret a uniform cooling of 2 3 c in both deep surface thermocline waters and intermediate deep waters of the southern ocean across the eot cooling of southern ocean surface waters across the eot was likely propagated to the deep ocean since deep waters were primarily sourced on the antarctic margin throughout this time interval removal of the temperature component from the observed foraminiferal 18o shift indicates that seawater 18o values increased by 0 6 0 15 across the eot interval corresponding to an increase in global ice volume to a level equivalent with 60 130 modern east antarctic ice sheet volume

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

temperature limits for preservation of primary calcite clumped isotope paleotemperatures abstract solid state reordering of c o bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations metrics commonly used to gauge preservation quality to correctly interpret the paleoenvironmental significance of clumped isotope derived paleotemperatures it is necessary to understand the temperature time domain in which solid state c o bond reordering is important we address this question using a combination of laboratory and natural geological experiments on paleozoic brachiopod shells the laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13 c 18 o bond reordering the resulting arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions we develop an alternative kinetic model for reordering that accounts for non first order reaction progress observed during the initial several hundred minutes of laboratory heating experiments and show that the simplified first order approximation model passey and henkes 2012 predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins we evaluate our laboratory based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories specifically we use the laboratory derived arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million year time steps reflecting the burial and exhumation temperature paths of each basin while this exercise is limited by the relatively large uncertainties in the temperature histories of these basins we find general correspondence within error between predicted and observed clumped isotope values we present simplified temperature time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved partially reordered and fully reordered in conclusion calcite samples dwelling at 100 c or lower for 10 6 10 8 year timescales should not be affected by solid state c o bond reordering

a field quantification of coastal dune perennial plants as indicators of surface stability erosion or deposition dune plants both modify the wind field around them and are impacted by various stress factors among them sand erosion and sand deposition as coastal dunes are being either stabilized or remobilized in response to the changes in the rates of sand and dune movement the vegetation cover and composition are expected to vary reflecting the differences in the sedimentary conditions in this field study 315 quadrats of 100 m2 in which the perennial plant species were sampled were analysed with respect to annual rates of sand erosion and deposition that were measured using erosion pins a visual exploratory data analysis was introduced based on selective filtering of samples according to their vegetation cover this method combined with established statistical tools enabled the authors to uncover the inclination and indicative power of nine perennial dune plants to either a stabilized or a mobile environment and to establish whether they are more prevalent in places undergoing sand erosion or sand burial two species were found to be clear indicators of a stabilized environment stipagrostis lanata and retama raetam of the species indicating a mobile environment only one may be stated as a clear indicator of sand erosion silene succulenta with cyperus macrorrhizus coming close to being an indicator of a less mobile erosive environment the best indicator species for sand burial was found to be as expected ammophila arenaria with artemisia monosperma also indicating high rates of sand mobility especially when its relative cover is higher than 80 such information can be used to monitor natural processes of dune stabilization or reactivation or to assess the success of a management plan that aims at stabilizing a dune or at remobilizing it by removing vegetation

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

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

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

millimeter scale microrelief affecting runoff yield over microbiotic crust in the negev desert abstract the negative effect of microrelief upon runoff yield explained by the increase in water storage and the slowdown in flow velocity is a known phenomenon however research concerning surface roughness hitherto focused on decimeter or centimeter scale microrelief owing to the heterogeneous character of many natural plots the effect of centimeter scale microrelief was mainly shown under controlled sprinkling experiments whereas no data was yet made available concerning the possible effect of a millimeter scale microrelief upon runoff yield under natural field conditions when runoff yield was measured over crusted i e surfaces covered by 1 3 mm of cyanobacterial crust and scalped 2 6 m 2 plots at the hallamish dune field negev desert israel during 5 winter seasons 1990 1995 no runoff was generated from the scalped plots during the first year following scalping while meagre quantities were received during the second year nevertheless during the third season and onward runoff yield at the scalped plots was consistently and significantly higher than that of the crusted control plots and this was so albeit the fact that the crust chlorophyll content of the scalped plots during the third season was as low as half the amount of the crusted plots these findings appeared to contradict previous findings that showed the existence of a positive linear relationship between the crust chlorophyll content and runoff yield the apparent contradiction was explained by the differences in the plot microrelief indicating that minute differences even of a millimeter scale may greatly affect runoff yield and thus may compensate for lower crust chlorophyll content surface smoothness which characterizes many of the arid zones may thus explain at least partially the high runoff yield obtained in deserts

no extreme bipolar glaciation during the main eocene calcite compensation shift major ice sheets were permanently established on antarctica approximately 34 million years ago1 2 3 close to the eocene oligocene boundary at the same time as a permanent deepening of the calcite compensation depth in the world s oceans4 until recently it was thought that northern hemisphere glaciation began much later between 11 and 5 million years ago1 2 3 5 this view has been challenged however by records of ice rafting at high northern latitudes during the eocene epoch6 7 and by estimates of global ice volume that exceed the storage capacity of antarctica8 at the same time as a temporary deepening of the calcite compensation depth 41 6 million years ago9 here we test the hypothesis that large ice sheets were present in both hemispheres 41 6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial atlantic ocean these records allow at most an ice budget that can easily be accommodated on antarctica indicating that large ice sheets were not present in the northern hemisphere the records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled ocean temperatures increased and carbon isotope values decreased in the equatorial atlantic the nature of these changes around 41 6 million years ago implies common links in terms of carbon cycling with events at the eocene oligocene boundary4 and with the hyperthermals of the early eocene climate optimum3 10 11 our findings help to resolve the apparent discrepancy between the geological records of northern hemisphere glaciation6 7 8 and model results12 13 that indicate that the threshold for continental glaciation was crossed earlier in the southern hemisphere than in the northern hemisphere

shifting ocean carbonate chemistry during the eocene oligocene climate transition implications for deep ocean mg ca paleothermometry to date no conclusive evidence has been identified for intermediate or deep water cooling associated with the 1 parts per thousand benthic delta o 18 increase at the eocene oligocene transition eot when large permanent ice sheets first appeared on antarctica interpretation of this isotopic shift as purely ice volume change necessitates bipolar glaciation in the early oligocene approaching that of the last glacial maximum to test this hypothesis it is necessary to have knowledge about deep water temperature which previous studies have attempted to reconstruct using benthic foraminiferal mg ca ratios however it appears likely that contemporaneous changes in ocean carbonate chemistry compromised the mg ca temperature sensitivity of benthic foraminifera at deep sites new geochemical proxy records from a relatively shallow core odp site 1263 estimated paleodepth of 2100 m on the walvis ridge reveal that carbonate chemistry change across the eot was not limited to deep sites but extended well above the lysocline critically limiting our ability to obtain reliable estimates of deep ocean cooling during that time benthic li ca measurements used as a proxy for co32 suggest that co32 increased by similar to 29 mu mol kg at site 1263 across the eot and likely impacted benthic foraminiferal mg ca a co32 benthic mg ca relationship is most apparent during the early eot when the overall increase in co32 is interrupted by an apparent dissolution event planktonic d18o and mg ca records suggest no change in thermocline temperature and a delta o 18 seawater increase of up to 0 6 parts per thousand at this site across the eot consistent with previous estimates and supporting the absence of extensive bipolar glaciation in the early oligocene

microbiotic crust control of runoff generation on sand dunes in the negev desert 1 the general belief that dune sands in arid regions are not likely to generate runoff and that runoff necessitates wet conditions is examined runoff generation was measured within an arid dune field in the western negev desert israel during 1990 1994 on 16 plots 1 2 6 6 m2 constructed along a continuum of crust covered crust the relationships between chlorophyll a and carbohydrates of the microbiotic crust and runoff yield were studied whereas chlorophyll a 15 45 mg m 2 and carbohydrates 4 9 17 6 g m 2 of the cyanobacterial crusts showed positive linear relationships with runoff coefficients a significant reduction in runoff yield was obtained once the moss dominated crust with 53 54 5 mg m 2 chlorophyll a and 28 5 28 9 g m 2 of carbohydrates which inhabited the wettest habitat within the dune field was also included in the analysis contrary to previous assumptions that an increase in runoff generation occurs on arid and semiarid sand dunes in wet climates wet climates may lead to the establishment of moss dominated crusts that in turn decrease runoff yield

oxygen isotope ranking of late eocene and oligocene planktonic foraminifers implications for oligocene sea surface temperatures and global ice volume abstract oxygen isotope analyses of late eocene and oligocene planktonic foraminifers from low and middle latitude sites in the atlantic basin show that different species from the same samples can yield significantly different isotopic values the range of isotopic values observed between species is greatest at low latitudes and declines poleward many planktonic foraminifers exhibit a systematic isotopic ranking with respect to each other and can therefore be grouped on the basis of their isotopic ranking the isotopic ranking of some taxa however appears to vary geographically and or through time isotopic and paleontologic data from dsdp site 522 indicate that commonly used isotopic temperature scales underestimate oligocene sea surface temperatures we suggest these temperature scales require revision to reflect the presence of oligocene glaciation comparison of isotopic and paleontologic data from sites 522 511 and 277 suggests cold low salinity surface waters were present in high southern latitudes during the early oligocene lowsalinity high latitude surface waters could be caused by eocene oligocene paleogeography or by the production of warm saline bottom water

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

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

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

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

runoff generation fostered by physical and biological crusts in semi arid sandy soils abstract biological soil crusts occur extensively in semi arid regions in the western part of niger they are associated with various types of physical soil crusts in fallows and in the tiger bush ecosystem a landscape with a typical banded pattern consisting of densely vegetated bands of small trees and shrubs alternating with bare soil bands despite their widespread occurrence not much research has been done regarding their role on runoff generation in the sahelian environment the present study aims at i highlighting the relative contribution of biological soil crusts in infiltration and runoff on crusted soil in respect with other soil factors ii assessing the impact of underlying physical crusts associated with a wide range of microbial cover and iii gathering the data required for an evaluation of the potential of microbial cover in water redistribution in an arid environment and for modelling purposes the study was based on runoff measurements performed in situ at the level of ten plots 1 m 2 each under two simulated rainfalls those experiments were coupled with the visual characterization and image analysis of soil surface conditions as well as micromorphological examinations using a light microscope both on the field and at the laboratory visual estimation of crust cover was found consistent with the estimation based on the image analysis biological soil crusts capped the summit of pre existing physical soil crusts i e structural crusts formed in situ by the impact of water drop and erosion crusts resulting from water or wind erosion of structural crusts the percentage of microbial cover in the 1 m 2 plots range from 39 to 80 55 in average on structural crusts compared to 4 to 29 17 in average on erosion crusts runoff coefficient varied with both the level of microbial cover and the type of physical soil crust higher runoff coefficients were found where biological soil crusts had developed on erosion crusts as compared to structural crusts runoff coefficients recorded from erosion crusts increased with the level of microbial cover while negative correlations were found on structural crusts they show that the clogging effect of microbial cover for the plasmic layer of erosion crusts is higher than that of the sand layer of structural crusts separating biological soil crusts according to the types of the underlying physical crusts explain therefore the contradictory findings related to their role on infiltration and runoff generation those data will help to evaluate the potential role of biological soil crusts in the modelling of water redistribution in the arid environment of the western part of niger

rainfall runoff relationship over encrusted dune surfaces nizzana western negev israel a thin microbial crust covers the lower part of longitudinal dunes in the western negev where average annual rainfall is 95 mm in order to study the effect of the microbial crust on rainfall runoff relationships under natural rainfall conditions runoff plots equipped with pressure gauges were established on opposite north and south facing slopes that differ in their vegetal cover and crust properties the study covered four years 1990 94 the first two years were wet and the following two years relatively dry one to five flow events were recorded per year no correlation was found between runoff yield rain amount and rain intensity unlike many microbial crusts reported in the literature the microbial crust in the western negev is not hydrophobic infiltration rate is high under dry surface conditions and of the order of 9 12 mm h 1 when the crust is saturated the high final infiltration rate is explained by the occurrence of large pores that do not seal when the crust is saturated typical hydrographs have very steep rising and falling limbs pointing at a limited contributing area most flows last less than 10 min and runoff volumes collected are on the whole very small owing to differences in crust properties runoff is higher on north than on south facing slopes 1997 john wiley sons ltd

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

surface properties of stabilizing coastal dunes combining spectral and field analyses the coastal dunes of israel have been undergoing a process of stabilization since 1948 one of the major features of this process is a change in the surface properties of the dunes the development of a biological soil crust bsc and a change in the properties of the sand grains themselves in ashdod at the southern coastal plain of israel sand properties that include the bsc their fines silt and clay content and free iron oxide indicating their degree of rubification have been analysed in detail using field and lab spectroscopy methods in addition sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above mentioned factors it was found that the bsc over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust especially in the blue band the crust was found to be particularly developed in the stable areas mainly the interdunes and on the north facing slopes rather than on the south facing slopes a positive correlation was found between the crust fines and chlorophyll content with stable areas showing more developed bsc the stable areas showed also a lower albedo and slightly more developed reddish colour indicating a slightly higher rate of rubification this study demonstrates that the intensity of sand erosion deposition rates affects soil properties with the bsc being the fastest to react to the stabilization process months to several years followed by the content of fine particles several years to a decade whereas the rubification process is a much weaker marker and may need much longer time periods to develop decades to centuries

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

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

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

soil and water components of banded vegetation patterns abstract banded landscapes are comprised of alternating bands of vegetation and bare ground aligned along the contours in arid and semi arid regions 50 750 mm rainfall on very gentle and uniform slopes 0 2 2 vegetated bands can be perpendicular to the direction of the dominant wind or more frequently of the slope under given climatic conditions slope gradient is the controlling factor of the type of pattern spotted broadly or typically banded for a given slope gradient mean annual rainfall determines the contrast between the vegetated and bare phase as well as the band length and the interband width band width ratio a typical transect through such two phase mosaic includes a dynamic succession of surface crusts which generates a run off run on system this favours the capture of limited water resources and thus a biomass production greater for banded patterns than spotted patterns or uniformly scattered vegetation moreover vegetated bands act as natural bench structures that greatly limit soil erosion as suggested by modelling banded vegetation patterns can equally be derived from nearly bare areas or from dense vegetation patterns because banded vegetation patterns have often been considered as a form of degradation of previous continuous vegetation cover many attempts have been made by foresters to restore this initial cover by reforestation of the bare interbands however the numerous failures of reforestation of the bare interbands illustrate the key role of these mosaic components in the maintenance of the tiger bush ecosystem banded vegetation patterns are more resilient to climate change than to human disturbances the loss of landscape patchiness due to the clearing of the bands either for fuelwood or for ephemeral cropping induces a rapid decline in soil fertility and water infiltration potential long term monitoring shows that the interband width band width ratio adapts to rainfall variations that are intrinsic of semi arid zones moreover climatic changes might also induce a change in the type of patterning suggesting that banded vegetation patterns are highly self sustainable the ecological differences between the pioneer and the decaying edges of the vegetated bands the temporal spatial succession of soil crusts as well as other indices such as the spatial distribution of soil organic matter and termite nests suggest the upslope migration of the bands nevertheless field evidence of such a shift remains scarce profound lessons can be learnt from the study of banded landscapes in terms of ecosystems functions when designing water harvesting systems or restoring degraded arid and semi arid land banded vegetation patterns should be imitated to optimize biomass production and limit land degradation

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

morphology and microstructure of microbiotic soil crusts on a tiger bush sequence niger sahel abstract microbiotic crusts resulting from the colonization of soil surfaces by communities of micro organisms dominated by cyanobacteria eucaryotic algae or lichens are widespread in arid and semi arid regions in the tiger bush of niger sahel microbiotic crusts occur in bare bands between densely vegetated bands the tiger bush soils are sandy loams with ph 4 7 6 5 three different microbiotic crusts are recognised forming strips parallel to the vegetation banding they are all formed mainly by filamentous cyanobacteria dominated by schizothrix other important genera are scytonema lyngbya microcoleus nostoc and phormidium the filamentous micro organisms trap sand particles and finer particles stick on the filament surfaces these effects enhance soil cohesion and resistance to erosion soil porosity is also increased by the microbial cover with additional pores delineated by filaments on the surfaces of crusts and porous organic bodies derived from microbial remains at depth the microbiotic crusts are essential components of the tiger bush ecosystem water leaving the lower sides of vegetated bands results in plant decay and on the upslope sides vegetation grows because of increased water supply microbial covers help resist erosion and increase water and nutrient retention thus providing substrates for the expansion of plants from adjacent vegetated bands

water repellency and pore clogging at early successional stages of microbiotic crusts on inland dunes brandenburg ne germany abstract biological soil crusts play a key role for hydrological processes in many open landscapes they seal the topsoil and generate surface run off utilization of the mineral substrate at early stages of microbiotic crusts was investigated using scanning electron microscopy sem water repellency indices were measured using the ethanol water microinfiltrometer method and steady state water flow was determined on the dry crusts and after 300 600 1200 and 1800 s of wetting thus allowing to follow pore clogging through swelling of extracellular polymeric substances eps it was found that water repellency increases with initial crust development where filamentous cyanobacteria and filamentous green algae were dominating but decreases as coccal algae bryophytes and fungi associated with bryophytes emerged swelling of eps took place immediately after wetting and its influence on steady state water flow was most pronounced when filamentous cyanobacteria and algae partially filled in the matrix pores and enmeshed sand grains still leaving micropore channels available for free water infiltration but prior to appearance of coccal algae bryophytes and associated fungi which formed a dense cover on the surface it was concluded that a new phase of crust succession was accompanied by easier wettability but slower infiltration transition from hydrophobicity to pore clogging as ruling mechanisms causing water run off may occur during wetting of individual biological crusts but also during crust succession over time

two stepping into the icehouse east antarctic weathering during progressive ice sheet expansion at the eocene oligocene transition in conjunction with increasing benthic foraminiferal 18 o values at the eocene oligocene transition eot ca 34 ma coarse grained ice rafted debris ird 425 m appears abruptly alongside fossil fish teeth with continentally derived neodymium nd isotope ratios e nd in kerguelen plateau southern ocean sediments increased antarctic weathering flux as inferred from two steps to less radiogenic e nd values coincides with two steps in benthic foraminiferal 18 o values these results indicate that two distinct surges of weathering were generated by east antarctic ice growth during the eot weathering by ice sheets during a precursor glaciation at 33 9 ma did not produce significant ird accumulation during the first e nd shift glacial weathering was sustained during a terrace interval between the two steps probably by small high elevation ice sheets a large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca 33 7 ma rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions parallel changes in antarctic weathering flux and deep sea carbonate accumulation suggest that ice sheet expansion during the eot had a direct impact on the global carbon cycle possible mechanisms include associated changes in silicate weathering on the east antarctic craton and enhanced fertilization of southern ocean waters both of which warrant further investigation

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

middle eocene through early oligocene climate history and paleoceanography in the southern ocean stable oxygen and carbon isotopes from odp sites on maud rise and kerguelen plateau mackensen a and ehrman w u 1992 middle eocene through early oligocene climate history and paleoceanography in the southern ocean stable oxygen and carbon isotopes from odp sites on maud rise and kerguelen plateau mar geol 108 l 27 paleogene stable oxygen and carbon isotopes were measured in foraminifera from odp sites 689 and 690 at maud rise in the atlantic ocean sector of the southern ocean and from sites 738 744 748 and 749 at the southern kerguelen plateau in the indian ocean sector these data were compared with sedimentological data from the same sample set both benthic and planktic 6180 values document a cooling trend beginning around 49 5 ma at all sites during the late middle eocene planktic lso values indicate a steepening latitudinal temperature gradient from 14 c at the northern sites towards 10 c at the southernmost sites terrigeneous sand grains of probably ice rafted origin and clay mineral assemblages point to the existence of a limited east antarctic ice cap with some glaciers reaching sea level as early as middle eocene time around 45 5 ma between 45 and 40 ma average paleotemperatures were between 5 and 7 c in deep and intermediate water masses while near surface water masses ranged between 6 and io c during the late eocene between 40 and 36 ma average temperatures further decreased to 4 5 c in the deep and intermediate water masses and to 5 8 c near the sea surface abruptly increasing 61so values at approximately 35 9 ma exactly correlate with a sharp pulse in the deposition of icerafted material on the kerguelen plateau a dramatic change in clay mineral composition and an altered southern ocean circulation indicated by a differentiation of benthic 61 c values between sites increasing opal concentrations and decreasing carbonate contents for planktic and benthic foraminifera this 80 increase ranges between 1 0 and 1 3 o and between 0 9 and 1 4 o respectively we favour a hypothesis that explains most of the 61so shift at 35 9 ma with a buildup of a continental east antarctic ice sheet consequently relatively warm oligocene antarctic surface water temperatures probably are explained by a temperate wet based nature of the ice sheet this would also aid in the fast build up of an ice sheet by enhancing the moisture transport on to the continent

palaeoecology of late middle eocene planktic foraminifera and evolutionary implications the late middle eocene is marked by accelerated global cooling representing part of the long transitional interval separating the early eocene greenhouse and later oligocene icehouse climatic regimes this time interval is also regarded as having witnessed a decline in planktic foraminiferal diversity following the extinction of most of the muricate clade genera acarinina and morozovelloides at approximately 39 ma here we examine planktic foraminiferal assemblages recovered at odp site 1052 blake nose nw atlantic and by recording a high level of taxonomic diversity including several previously undocumented morphotypes we suggest that the diversity of late middle eocene planktic foraminifera may have been underestimated depth habitats of every species within these late middle eocene assemblages are reconstructed using oxygen and carbon stable isotope ratios furthermore because stable isotope analyses suggest that species of globoturborotalita appear to have generally calcified during winter months these taxa offer in combination with predominantly summer surface dwellers such as morozovelloides the potential to reconstruct patterns of seasonality during the late palaeogene using extremely well preserved glassy planktic foraminiferal calcite from a contemporaneous hemipelagic drill site detailed sem imaging of test microstructures and wall textures confirm that many modern features of foraminiferal ecology and test architecture had already evolved by the late middle eocene the common occurrence of the cancellate wall texture combined with the wide variety of reconstructed foraminiferal depth habitats indicates that there is no necessary relationship between foraminiferal wall textures and habitat and that wall textures are evolutionary conservative features of the foraminiferal test

properties and spatial distribution of microbiotic crusts in the negev desert israel abstract playing a cardinal role in surface stabilization and in carbon and nitrogen fixation microbiotic crusts play a crucial role in arid regions where they may serve as useful biomarkers for wind power and wetness duration this is especially the case on relatively unstable and infertile sand dunes in the negev desert where high correlations between the crust chlorophyll content and the daytime wetness duration were found yet only scarce data are available as to the possible link between the chlorophyll content and other physical color thickness strength crack density surface roughness and infiltrability and biological protein carbohydrate organic matter and species composition factors which determine in turn the crust type and its effect upon geomorphological and ecological processes no data are available on crust type distribution these were the aims of the current research when a cluster analysis was performed five types of microbiotic crusts were defined four of which were cyanobacterial a d and one moss dominated crust e the crusts differed in their physical and biological properties they showed an increase in chlorophyll content protein carbohydrates and organic matter from a to e with concomitant increase in species diversity thickness roughness and strength but with some variables crack density and infiltrability showing a reversed trend at the moss dominated crust the increase in the biomass components of the crust and the gradual change of the physical properties are explained by the improved physical conditions primarily wetness duration which facilitates longer hours of photosynthetic activity and consequently the introduction of additional more mesic species such as green algae lichens and mosses extended wetness duration was found to shift the crust type from cyanobacterial to moss dominated crust the spatial distribution of the crusts as verified by crust mapping coincided with the daylight surface duration which in turn was controlled by topography aspect angle and slope position it implies that whereas initial physical conditions dictates species composition and thus crust type the crust type in turn is responsible for characterizing the physical properties of the surface which may largely affect ecological and geomorphological processes

environmental magnetic record of antarctic palaeoclimate from eocene oligocene glaciomarine sediments victoria land basin summary the onset of continent wide glaciation in antarctica is still poorly understood despite being one of the most important palaeoclimatic events in the cenozoic the eocene oligocene boundary interval has recently been recognized as a critical time for antarctic climatic evolution and it may mark the preglacial glacial transition magnetic susceptibility intensity of natural and artificial remanences hysteresis parameters and magnetic anisotropy of the lower half late eocene early oligocene of the ciros 1 core from mcmurdo sound antarctica reveal alternating intervals of high and low magnetic mineral concentrations that do not correspond to lithostratigraphic units in the core pseudo single domain magnetite is the main magnetic mineral throughout the sequence and sharp changes in magnetite concentration match changes in clay mineralogy beneath and at the eocene oligocene boundary the detrital magnetite originated from weathering of the ferrar group which comprises basic extrusive and intrusive igneous rocks weathering processes and input of magnetite to the victoria land basin were intense during periods when the antarctic climate was warmer than today but during intervals when the climate was relatively cool chemical weathering of the ferrar group was suppressed and input of detrital magnetite to the victoria land basin decreased our results also indicate that a cold and dry climate was not established in antarctica until the eocene oligocene boundary with major ice sheet growth occurring at the early late oligocene boundary some earlier cold intervals are identified which indicate that climate had begun to deteriorate by the middle late eocene boundary

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

benthic foraminiferal li ca insights into cenozoic seawater carbonate saturation state benthic foraminiferal li ca decreases down a norwegian sea holothermal depth transect suggesting that the saturation state of seawater with respect to calcium carbonate influences foraminiferal li ca benthic foraminiferal li ca increases by 17 across the glaciation event in the early oligocene which likely reflects the increase in seawater saturation state evidenced by the concomitant deepening of the calcite compensation depth following the establishment of the antarctic ice sheet benthic foraminiferal li ca bears a remarkable resemblance to the estimated oxygen isotopic composition of seawater suggesting that during this time seawater saturation was largely controlled by glacioeustatically driven changes in shallow water carbonate accumulation rates

onset of long term cooling of greenland near the eocene oligocene boundary as revealed by branched tetraether lipids the eocene oligocene e o boundary interval is considered to be one of the major transitions in earth s climate witnessing the fi rst major expansion of the east antarctic ice sheet however the extent of the associated climatic cooling especially for high northern latitude continental landmasses is poorly constrained in this study we reconstruct the fi rst mean annual air temperature maat for the greenland landmass during the late eocene and early oligocene by applying a new proxy based on the distribution of branched tetraether lipids derived from soil bacteria preserved in a marine sediment core from the greenland basin the temperature estimates are compared with a composite continental temperature record based on bioclimatic analysis of pollen assemblages both proxies reveal comparable late eocene maats of 13 15 c and a gradual long term cooling of 3 5 c starting near the e o boundary these data are in agreement with other maat reconstructions from northern midlatitude continents and suggest a general cooling of the northern hemisphere during the e o transition

calibration and application of the clumped isotope thermometer to foraminifera for high resolution climate reconstructions the reconstruction of past ocean temperatures is fundamental to the study of past climate changes therefore considerable effort has been invested in developing proxies for seawater temperatures one of the most recent and promising new proxy is carbonate clumped isotope thermometry in particular because it is based on thermodynamic equilibrium and not on biogeochemical proxies here we present a new calibration of the clumped isotope thermometer to foraminifera based on seven species of planktic and benthic foraminifera spanning a growth temperature range of 2 28 c we used a newly developed technique for the measurements of small samples to improve the applicability of this method to paleoceanography our data have a comparable precision 0 005 0 013 and confirm previous calibration studies based on biogenic and inorganic calcite we discuss possible sources of uncertainty such as over underestimation of the calcification temperatures species specific vital effects ph variations between the seawater and the vacuole water of the species and possible kinetic effects on the clumped isotope calibration to validate our calibration study and test the applicability of our measuring technique to paleoclimate and paleoceanographic studies we measured the isotope composition of globigerinoides ruber white at high resolution in a sediment core covering the last 700 years in the gulf of taranto mediterranean sea the results show that it is necessary to average a relatively large number of analyses to achieve a consistent temperature signal for the detection of small sea surface temperature changes although with the current analytical system clumped isotope thermometry is only applicable to the analysis of relatively large sst changes in marine sediments further technical improvements may make this a very powerful technique for paleoceanographic studies

the role of crust thickness in runoff generation from microbiotic crusts contrary to humid areas where runoff takes place following the saturation of the soil column runoff in arid and semiarid zones takes place when rain intensities exceed the infiltration capability of the upper soil crust whether physical crust or microbiotic crust mc this type of overland flow known as hortonian overland flow hof is not fully understood especially in the case of mc in particular little is known regarding the effect of crust thickness and its fine silt and clay content on runoff generation with some scholars claiming that runoff generation is positively correlated with crust thickness and fine content in an attempt to determine the effect of crust thickness and to assess the role played by the silt and clay on runoff generation a set of field and lab experiments were undertaken on mcs inhabiting sand dunes in the negev desert israel these included sprinkling experiments coupled with measurements of the physical thickness silt and clay and biological chlorophyll protein total carbohydrates properties of 0 5 10 mm thick crusts the data showed that runoff generation took place on surfaces as thin as 0 5 0 7 mm only and was not correlated with the fine silt and clay content the implications for hof and for arid ecosystems are discussed copyright 2014 john wiley sons ltd

increased seasonality through the eocene to oligocene transition in northern high latitudes a profound global climate shift took place at the eocene oligocene transition approximately 33 5 million years ago when cretaceous early palaeogene greenhouse conditions gave way to icehouse conditions during this interval changes in the earth s orbit and a long term drop in atmospheric carbon dioxide concentrations resulted in both the growth of antarctic ice sheets to approximately their modern size and the appearance of northern hemisphere glacial ice however palaeoclimatic studies of this interval are contradictory although some analyses indicate no major climatic changes others imply cooler temperatures increased seasonality and or aridity climatic conditions in high northern latitudes over this interval are particularly poorly known here we present northern high latitude terrestrial climate estimates for the eocene to oligocene interval based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the norwegian greenland sea our data indicate a cooling of approximately 5 degrees c in cold month winter mean temperatures to 0 2 degrees c and a concomitant increased seasonality before the oi 1 glaciation event these data indicate that a cooling component is indeed incorporated in the delta 18 o isotope shift across the eocene oligocene transition however the relatively warm summer temperatures at that time mean that continental ice on east greenland was probably restricted to alpine outlet glaciers

global budget of water isotopes inferred from polar ice sheets 1 water isotope ratios in ice cores and marine sediments are a key indicator of past temperature and global ice volume quantitative interpretation of these ratios requires understanding of the storage capacity and exchanges among the ocean atmosphere and cryosphere we combine numerical models of ice dynamics and tracer transport to predict bulk ice properties by simulating the fine layering of ice sheets locally validated at ice core sites the 18o 16o content of ice sheets is found to vary between the present and 20 kyr ago from 34 to 37 for greenland from 41 to 42 5 for west antarctica and always remained near 56 5 for east antarctica their combined effect on sea water 18o 16o is a 0 08 0 12 increase 20 kyr ago a 1 11 decrease if ice sheets were to vanish we confirm that ice volume changes in antarctica and greenland linearly affect ocean composition though at different rates

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

paleoclimate reconstruction using carbonate clumped isotope thermometry carbonate clumped isotope thermometry is a relatively new paleotemperature proxy based on measurements of the degree of ordering of 13 c and 18 o into bonds with each other making the 13 c 18 o 16 o 2 2 ion group in lattices of carbonate minerals this technique has several unusual properties that complement existing methods of paleoclimate reconstruction most importantly it is based on a homogeneous isotope exchange equilibrium and thus constrains temperature independent of the isotopic composition of waters from which carbonates grew this method also appears to be generally insensitive to vital effects that compromise many other paleothermometers based on the chemical properties of biominerals or organic matter at least for those organisms that have been subjected to systematic study to date corals and foraminifera however discrepancies among some calibrations particularly at low temperatures may point toward the existence of vital effects in mollusks and other organisms this review discusses the principles and calibrations of the technique its uses in combination with conventional stable isotope measurements to constrain the 18 o of past waters preservation of paleotemperatures in ancient materials as well as current problems in our understanding of calibrations and interlaboratory data comparisons

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

runoff induced sediment yield over dune slopes in the negev desert 1 quantity and variability although extensive data exist on runoff erosion and rates for non sandy hillslopes data for arid dune slopes are scarce owing to the widespread perception that the high infiltrability of sand will reduce runoff however runoff is generated on sandy dunes in the hallamish dune field western negev desert israel p 95 mm due to the presence of a thin usually 1 3 mm microbiotic crust the runoff in turn produces erosion sediment yield was measured on ten plots 140 1640 m2 on the north and south facing slopes of longitudinal dunes two plots facing north and two facing south were subdivided into three subplots the subplots represented the crest of the active dune devoid of crust the extensively crusted footslope of the dune and the midslope section characterized by a patchy crust the remaining plots extended the full length of the dune slope no runoff and consequently no water eroded sediments were obtained from the crest subplots devoid of crust however runoff and sediment were obtained from the mid and footslope crusted subplots sediment yield from the footslope subplots was much higher than from the midslopes despite the higher sediment concentration that characterized the midslope subplots the mean annual sediment yield at the hallamish dune field was 432 g per metre width and was associated with high average annual concentrations of 32 g l 1 the data indicate that owing to the presence of a thin microbiotic crust runoff and water erosion may occur even within arid sandy dune fields copyright 2001 john wiley sons ltd

runoff generation in a sandy area the nizzana sands western negev israel this paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors data obtained show that these two surface units respond quickly to rainstorms runoff generation can be expected for any storm exceeding 2 3 mm and runoff coefficients are high when the topsoil algal crust 1 to 2 mm thick is removed from the surface of the dune infiltration increases drastically and eliminates any possibility of runoff generation under present day rainfall conditions this data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes

differential water distribution over dune slopes as affected by slope position and microbiotic crust negev desert israel runoff is one of the main water sources responsible for water redistribution within a given ecosystem water redistribution is especially important in arid regions and may be of great importance on sandy dunes where the likelihood of runoff is low owing to the high infiltration rates of sand redistribution of water may significantly affect plant and animal distribution and may explain vegetation patterns within an ecosystem runoff yield over sandy dune slopes in the western negev desert was measured under natural conditions during 1990 1994 the magnitude of runoff yield on different slope sections and on north and south exposures was established the results demonstrate that while slope position controlled the microbiotic crust cover crust cover and crust biomass controlled the amounts of runoff obtained whereas no runoff was measured on the upper dune sections devoid of crust only meagre quantities were measured on the midslope sections characterized by discontinuous crust cover substantially larger amounts were however obtained at the bottoms of the slopes characterized by continuous crust cover north facing slopes usually characterized by a chlorophyll a content of 29 41 mg m 2 yielded on average 3 2 times more runoff than south facing footslopes characterized by a 17 mg m 2 chlorophyll a content whereas microbiotic crust was found to be responsible for runoff generation additional water supply owing to runoff may also explain the occurrence of a high biomass crust and the dense vegetation belt at the dune interdune interface of the northern exposure where runoff tends to collect thus whereas crust may reduce infiltration in certain habitats runoff generated by crust may also be responsible for the promotion of crust growth in other habitats runoff may also be used to promote vegetation growth at the dune footslopes the possibility of using runoff to facilitate agroforestry is discussed copyright 1999 john wiley sons ltd

cenozoic benthic foraminiferal mg ca and li ca records toward unlocking temperatures and saturation states the sensitivities of benthic foraminiferal mg ca and li ca to bottom water temperature and carbonate saturation state have recently been assessed here we present a new approach that uses paired mg ca and li ca records to calculate simultaneous changes in temperature and saturation state using previously published records we first use this approach to document a cooling of deep ocean waters associated with the establishment of the antarctic ice sheet at the eocene oligocene climate transition we then apply this approach to new records of the middle miocene climate transition from odp site 761 to estimate variations in bottom water temperature and the oxygen isotopic composition of seawater we estimate that the oxygen isotopic composition of seawater varied by 1 between the deglacial extreme of the miocene climatic optimum and the glacial maximum following the middle miocene climate transition indicating large amplitude variations in ice volume however the longer term change between 15 3 and 12 5 ma is marked by a 1 c cooling of deep waters and an increase in the oxygen isotopic composition of seawater of 0 6 we find that bottom water saturation state increased in the lead up to the middle miocene climate transition and decreased shortly after this supports decreasing pco2 as a driver for global cooling and ice sheet expansion in agreement with existing boron isotope and leaf stomatal index co2 records but in contrast to the published alkenone co2 records

antarctic ice growth before and after the eocene oligocene transition new estimates from clumped isotope paleothermometry across the eocene oligocene transition the oxygen isotopic composition 18o of benthic and planktonic foraminifera increased by over 1 this shift is thought to represent a combination of global cooling and the growth of a large ice sheet on the antarctic continent to determine the contribution of each of these factors to the total change in 18o we measured the clumped isotopic composition of planktonic foraminifera tests from ocean drilling program site 689 in the southern ocean near surface temperatures were 12 c in the intervals 0 1 5 myr before and 1 2 myr after the major oi 1 transition in agreement with estimates made using other proxies at nearby sites temperatures cooled by 0 4 1 1 c between these intervals indicating that the long term change in 18o seen in planktonic foraminifera at this site is predominantly due to changes in ice volume a larger instantaneous cooling may have occurred during oi 1 but is not captured in this study due to sampling resolution the corresponding change in the isotopic composition of seawater 18osw is 0 75 0 23 which is within the range of previous estimates and represents global ice growth equivalent to roughly 110 120 of the volume of the modern antarctic ice sheet or 80 90 m of eustatic sea level change

late cretaceous neogene trends in deep ocean temperature and continental ice volume reconciling records of benthic foraminiferal geochemistry δ18o and mg ca with sea level history 1 we reconstruct trends in ice volume and deep ocean temperature for the past 108 myr resolving variations on timescales of 2 myr and longer we use a sea level record as a proxy for ice volume a benthic foraminiferal mg cabf record as a proxy for temperature and a benthic foraminiferal 18obf record as a proxy for both this allows us to construct dual estimates of temperature and ice volume variations for the interval 10 60 ma extracting temperature from 18obf by using sea level as a proxy for ice volume to constrain the 18osw component and extracting seawater 18osw which reflects ice volume from 18obf by using mg cabf to constrain the temperature component each of these approaches requires numerous assumptions but the range of plausible solutions are concordant on timescales 2 myr and within an uncertainty of 2 c temperature and 0 4 18osw the agreement between the two approaches for the last 50 myr provides empirical justification for the use of 18obf mg cabf and sea level records as robust climate proxies our reconstructions indicate differences between deep ocean cooling and continental ice growth in the late cenozoic cooling occurred gradually in the middle late eocene and late miocene pliocene while ice growth occurred rapidly in the earliest oligocene middle miocene and plio pleistocene these differences are consistent with climate models that imply that temperatures set by the long term co2 equilibrium should change only gradually on timescales 2 myr but growth of continental ice sheets may be rapid in response to climate thresholds due to feedbacks that are not yet fully understood

productivity and sea surface temperature changes recorded during the late eocene early oligocene at dsdp site 511 south atlantic this study investigates paleoenvironmental changes during the eocene oligocene transition eot at deep sea drilling project dsdp site 511 south atlantic as inferred from lipid biomarker long chain diols alkenones and calcareous nannofossil accumulation rates as well as changes in sedimentation regime i e relative contributions of total organic carbon toc calcium carbonate and biogenic silica sea surface temperatures ssts reconstructed from the alkenone unsaturation index uk 37 indicate a progressive but significant cooling 8 c from 34 5 ma to 33 6 ma consistent with estimates derived from other temperature proxies tex86 18o at the same site and for the same time interval this cooling is associated with a marked increase in primary productivity as indicated by high accumulation rates of biogenic silica toc alkenones long chain diols and calcareous nannofossils together these results are consistent with an enhancement of upwelling conditions favorable to the development of siliceous organisms at dsdp site 511 possibly induced by the oi 1 glaciation in antarctica that occurred during this period

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

global implications of lower to middle eocene sequence boundaries on the new jersey coastal plain the icehouse cometh wedocumentninelower middleeocenesequencesonthenewjerseycoastalplainand comparethemwithglobal d 18 oandhaqetal records earlyeocenehiatusesdonotmatch d 18 ochanges anditisunlikelythattheyaretheresultofglacioeustasy consistentwithan ice free early eocene early middle eocene 49 43 ma evidence for a link between sequencesand d 18 oisequivocal andthepresenceoflargeicesheetsisuncertain beginning in the late middle eocene 43 42 ma concomitant increases in planktonic and benthic d 18 o records coincide with the timing of hiatuses on the new jersey coastal plain and a change from carbonate dominated to siliciclastic dominated sedimentation these represent the development of the antarctic ice cap and the beginning of the icehouse world of the 14 sequences predicted by haq et al for this interval 9 are resolvable on the new jersey margin and the other 5 appear to be combined with others we conclude that although ice volume changes controlled sequences since at least 42 ma mechanisms for sea level change prior to then are still not fully understood

the eocene oligocene transition changes in sea level temperature or both abstract the eocene oligocene transition eot 34 ma reflects the onset of major antarctic glaciation the primary geochemical signature of the eot is two 300 kyr spaced shifts in increasing deep sea oxygen isotope values possibly reflecting both global cooling and or increasing ice volume a way to assess the respective contribution of continental ice is to quantify concomitant glacio eustatic sea level change this is usually expressed in relatively shallow marine depositional settings one potentially suitable region is in the vicentinian alps ne italy where marginal marine deposits document sea level changes during the eot by correlating stable isotope bio and magnetostratigraphic information between three distant regions we are able to relate the shallow marine sections to the pacific oxygen isotope record from ocean drilling program odp site 1218 of coxall et al 2005 microfacies sedimentological and biotic analysis suggests that associated with the first isotope shift eot 1 sea level fell 20 m and with the ultimate shift the oligocene isotope event 1 oi 1 sea level fell some 50 60 m distribution patterns of temperature sensitive dinoflagellates from a coeval central italian section reveal that the early stages of the eot were accompanied by sea surface cooling whereas no sustained cooling is noted in association with the oi 1 this suggests that the initial eot shift s reflect a mixed signal of ice volume and temperature whereas the oi 1 primarily reflects expansion of the antarctic cryosphere

multiproxy record of abrupt sea surface cooling across the eocene oligocene transition in the gulf of mexico the eocene oligocene transition eot ca 33 34 ma was a time of pronounced climatic change marked by the establishment of continental scale antarctic ice sheets the timing and extent of temperature change associated with the eot is controversial here we present multiproxy eot climate records 15 34 k y resolution from st stephens quarry alabama usa derived from foraminiferal mg ca d18o and tex86 we constrain sea surface temperatures ssts in the latest eocene and early oligocene and address the issue of climatic cooling during the eot paleotemperatures derived from planktic foraminifera mg ca and tex86 are remarkably consistent and indicate late eocene subtropical ssts of 28 c there was substantial and accelerated cooling of ssts 3 4 c through the latest eocene precursor d18o shift eot 1 prior to oligocene isotope 1 oi 1 our multispecies planktic foraminiferal d18o records diverge at the e o boundary 33 7 ma signifying enhanced seasonality in the earliest oligocene in the gulf of mexico

runoff induced sediment yield over dune slopes in the negev desert 2 texture carbonate and organic matter runoff induced sediments were collected in the hallamish dune field for four years 1990 1994 runoff and consequently water transported sediments were generated on the dunes owing to the presence of a thin microbiotic crust these sediments were analysed for their particle size distribution and carbonate content in addition the organic matter content was calculated by measuring the chlorophyll content within the runoff the results were compared to the slope parent material i e the crust and the underlying sand as well as to playa sediments which are scattered within the hallamish interdunal areas and which were previously hypothesized to originate from runoff induced sediments higher amounts of fines silt and clay and carbonate characterize the footslopes in comparison to the midslopes intermediate contents of fines 17 per cent and carbonate 8 per cent characterized the sediments in comparison to the fines 27 per cent and carbonate 15 per cent of the crust and to the fines 4 per cent and carbonate 4 per cent of the underlying sand the runoff induced fines and carbonate contents were significantly different from those of the playas suggesting that the playa flats do not originate from runoff induced sediments the sediments were enriched with organic matter organic matter which originates from the crust amounted to 0 3 0 4 per cent as compared to 0 1 per cent in the bare sand nevertheless the crust was found to be relatively resilient to water flow only 0 1 0 5 per cent of the crust was annually eroded off the slope by water with south facing crusts showing higher resilience than north facing crusts the data may thus assist in the evaluation of the crust s residence time copyright 2001 john wiley sons ltd

contrasting hydrological response of coastal and desert biocrusts biocrusts abound in southern israel covering the hallamish dune field near nizzana niz in the negev mean annual precipitation of 95 mm and the coast of nizzanim nim near ashdod mean annual precipitation of 500 mm while the hydrological response of the niz crust to natural rain events was thoroughly investigated no data is available on the hydrological response of the nim crust runoff was monitored in runoff plots during the years 2005 2008 and in addition sprinkling experiments were carried out on nim and niz crusts for the evaluation of the possible factors that may control runoff initiation fine content of the parent material crust thickness compressional strength hydrophobicity surface microrelief organic matter biomass chlorophyll a and total carbohydrates and the crust s species composition of nim were studied and compared to that of niz the data showed that in comparison to the niz crust that readily generated runoff no runoff was produced by the nim crust this was so despite the fact that 1 microculeus vaginatus predominated in both crusts 2 the substantially higher rain intensities in nim 3 the greater thickness and higher chlorophyll content and 4 the lower microrelief at nim in comparison to niz the lack of runoff in nim was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation the absence of runoff and its consequences on the nim ecosystem are discussed copyright 2012 john wiley sons ltd

planktonic foraminiferal turnover diversity fluctuations and geochemical signals across the eocene oligocene boundary in tanzania a major turnover in planktonic foraminifera occurred across the eocene oligocene e o boundary new drill holes through the e o boundary in southern tanzania contain extremely well preserved and diverse assemblages of planktonic foraminifera here we document a 1 2 million year record of assemblages diversity and stable isotope fluctuations through this critical interval which is often dissolved and or recrystallised in carbonate rich facies the e o boundary is marked by the abrupt extinction of all five remaining species of the family hantkeninidae and a distinct size reduction in the genus pseudohastigerina the boundary is preceded over a short stratigraphic interval by the extinction of turborotalia cerroazulensis turborotalia cocoaensis and turborotalia cunialensis quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages we compare diversity fluctuations to the stable isotope record of pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species a major shift in the evenness occurs at 33 8 ma associated with the extinction of the t cerroazulensis group suggesting acute ecological disturbance we propose that the extinction of the t cerroazulensis group at 33 8 ma was directly related to cooling of sea surface temperatures while the extinction of hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes after the extinctions renewed origination and diversification occurred leading to a characteristic oligocene planktonic foraminifer assemblage

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

the potential roles of biological soil crusts in dryland hydrologic cycles biological soil crusts bscs are the dominant living cover in many drylands of the world they possess many features that can influence different aspects of local hydrologic cycles including soil porosity absorptivity roughness aggregate stability texture pore formation and water retention the influence of biological soil crusts on these factors depends on their internal and external structure which varies with climate soil and disturbance history this paper presents the different types of biological soil crusts discusses how crust type likely influences various aspects of the hydrologic cycle and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers unfortunately this greatly complicates interpretation of the results applied disturbances alter many soil features such as soil texture roughness aggregate stability physical crusting porosity and bulk density in ways that would not necessarily be the same if crusts were not naturally present combined these studies show little agreement on how biological crusts affect water infiltration or runoff however when studies are separated by biological crust type and utilize naturally occurring differences among these types results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff have mixed effects in arid regions and increase infiltration and reduce runoff in semiarid cool and cold drylands however more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff we especially need studies that control for sub surface soil features such as bulk density micro and macropores and biological crust structure unlike the mixed effects of biological crusts on infiltration and runoff among regions almost all studies show that biological crusts reduce sediment production regardless of crust or dryland type copyright 2006 john wiley sons ltd

eocene oligocene magnetobiochronology of odp sites 689 and 690 maud rise weddell sea antarctica magnetostratigraphic studies of paleogene sediments piston cored on maud rise weddell sea odp sites 689 and 690 are a cornerstone of southern ocean paleogene and neogene chronostratigraphy however parts of previous magnetostratigraphic interpretations have been called into question and recent reinvestigation of the upper paleocene middle eocene portion of site 690 suggested that the records might be contaminated by spurious magnetizations which raises doubts about the reliability of these important records we undertook a high resolution magnetostratigraphic study of eocene oligocene u channel samples from odp holes 689b 689d 690b and 690c in order to address these concerns a pervasive overprint appears to be present below the middle eocene which compromises magnetobiostratigraphic interpretations for the upper cretaceous and lower paleogene nevertheless our new results provide a robust record of geomagnetic field behavior from 38 5 to 25 ma and confirm the reliability of these sediments for calibration of biostratigraphic datum events during a crucial phase of earth history when major antarctic ice sheets developed also comparison of magnetozone thicknesses in multiple holes at the same site indicates that 1 2 1 8 m of the stratigraphic record is missing at each core break which corresponds to time breaks of 120 360 k y lack of a continuous record within a single hole renders useless spectral analyses for investigating long geomagnetic and paleoclimatic time series this observation reinforces the need for coring of multiple offset holes to obtain continuous paleoceanographic records sedimentary hiatuses have been identified only at the deeper of the two investigated sites site 690 which could mark a local response to the onset of the antarctic circumpolar current

clumped isotope signatures in modern brachiopod carbonate abstract we present a temperature to 47 relationship for naturally occurring modern brachiopods which was established using a suite of thirteen brachiopod specimens from twelve sampling localities that span a mean annual seawater temperature range of 0 8 to 29 0 c sample locations and depths were selected to maximize the range of temperatures covered by the calibration while minimizing the seasonal temperature variability impacting the samples linear least squares regression analysis yields the following relationship expressed using the ghosh et al 2006 reference frame 47 0 0478 0 0099 10 6 t 2 0 1164 0 1203 n 13 r 2 0 91 95 ci this equation lies within the 95 confidence interval of the original relationship determined using synthetic calcite ghosh et al 2006 but is in better agreement with the newly revised calibration of zaarur et al 2013 however despite this broad agreement our equation has a shallower slope than the equations for synthetic calcites and yields temperatures at the warm end of the calibration temperature range 47 0 640 that are as much as 3 1 c offset from those predicted using the equation of zaarur et al 2013 on the other hand our new equation has a steeper slope than the henkes et al 2013 equation for modern brachiopods and mollusks this finding is consistent with the hypothesis that differences in the protocols employed by laboratories that use different temperatures of phosphoric acid digestion cause the observed discrepancies between the 47 values reported by various laboratories