heart mountain wyoming detachment lineations are they in microbreccia or in volcanic tuff the concept of tectonic denudation followed by deposition of lower middle eocene wapiti formation volcanic rocks on the exposed heart mountain detachment has been challenged by hauge his extending allochthon interpretation requires that the wapiti formation be fault emplaced and that lineations in a volcanic tuff overlying the fault north of jim smith peak be fault striae in microbreccia our re examination of the field evidence in minute detail indicates that these lineations were produced by flowage of volcanic rocks on a thin layer of air fall tuff the following lines of evidence indicate that this tuff was deposited on the detachment surface during the brief interval that the denuded surface was exposed 1 field relations indicate that the wapiti volcanic rocks are younger than the detachment and so they could not have been fault emplaced 2 lineations occur only on the upper surface of wapiti formation tuff none were found at the contact of the tuff with the detachment surface 3 the reported direction of translation indicated by the lineations is not consistent many lineations in the tuff indicate north and northeast movement a direction that is consistent with lineations produced by lava flowing from a known vent but inconsistent with a southeast direction of detachment movement 4 the lineations are restricted to the northwestern part of the area covered by the wapiti formation which is also consistent with their derivation as volcanic flow lineations from a known vent if the wapiti had been tectonically emplaced fault striae should occur elsewhere on the detachment surface but none have been observed 5 the lower contact of the tuff with the detachment surface as seen in thin sections is irregular suggesting that it is a depositional rather than a fault contact 6 the contact between the tuff and overlying wapiti as seen in thin sections is also irregular as would be expected if the wapiti volcanic breccia had been deposited on the tuff thin sections of the microbreccia suggest that it is a sedimentary rock not a fault rock 7 a remnant of the tectonic carpet of all carbonate fault breccia lying on the detachment surface unmixed with the overlying wapiti volcanic rock is compatible with the depositional emplacement of the wapiti but is not compatible with wapiti formation being moved many kilometers across the carpet of all carbonate fault breccia and not removing or becoming mixed with it

greatly expanded tropical warm pool and weakened hadley circulation in the early pliocene the pliocene warm interval has been difficult to explain we reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago during the early pliocene our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced implying a vast poleward expansion of the ocean tropical warm pool corroborating evidence indicates that the pacific temperature contrast between the equator and 32 n has evolved from 2 c 4 million years ago to 8 c today the meridional warm pool expansion evidently had enormous impacts on the pliocene climate including a slowdown of the atmospheric hadley circulation and el nino like conditions in the equatorial region ultimately sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake such as enhanced ocean vertical mixing

cool la nina during the warmth of the pliocene the role of el nino southern oscillation enso in greenhouse warming and climate change remains controversial during the warmth of the early mid pliocene we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial pacific consistent with the prevalence of a la nina like state rather than the proposed persistent warm el nino like conditions our pliocene paleothermometer supports the idea of a dynamic ocean thermostat in which heating of the tropical pacific leads to a cooling of the east equatorial pacific and a la nina like state analogous to observations of a transient increasing east west sea surface temperature gradient in the 20th century tropical pacific

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

the termination of the equatorial undercurrent in the eastern pacific abstract the termination of the equatorial undercurrent euc in the eastern tropical pacific has been studied through analysis of the historical hydrographic station data in the region bounded by 5 n 10 s 80 w and 100 w three distinctive hydrographic features associated with the euc are used along with dynamic topography to trace the mean path of the euc and to investigate aspects of its seasonal variation these features are 1 the 13 c thermostad 2 the high salinity core and 3 the high dissolved oxygen concentration tongue the thermostad is thickest just south of the equator to the west of the galapagos islands with a decreasing maximum extending southeast to the coast of south america near 7 s the thermostad is poorly developed in the mean near the equator east of the galapagos islands this pattern appears to be produced by convergence of eastward flow in the euc and in the southern subsurface countercurrent as the euc flows southeastward from the galapagos this interpretation is supported by the geostrophic flow calculated from the mean dynamic topography the isolated high salinity core is found to the south of the equator and is traced all the way to the coast of south america the high oxygen tongue associated with the euc splits at the galapagos with the southward projecting branch disappearing rapidly as an identifiable feature the other branch of the tongue continues around the islands to the north and along the equator to the coast of ecuador some evidence of recirculation of euc water in the south equatorial current is seen to the northwest of the galapagos a strong seasonal pulsation of the euc affects these features in a consistent way with the pulse occurring first west of the galapagos and later along the coast the thermostad first reaches maximum development and then a pronounced downwelling of the thermocline occurs rapidly leading to minimum thermostad extent associated wtih this downwelling is an eastward protruding high salinity tongue near the equator which is later seen as an isolated core along the coast at 4 s and 6 s pressure gradients along the equator and the coast inferred from dynamic topography suggest that this pulse is associated with an increase in the flow of the euc and ultimately the peru chile undercurrent the pressure gradient reversal along the equator occurs prior to the annual wind reversal suggesting that remote forcing plays a role in the seasonal pulse of the euc in the eastern pacific

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

circulation in the archipielago de colon galapagos islands november 1993 abstract dcp and ctd data are used to investigate the circulation pattern in the region of the archipielago de colon during the period 8 21 november 1993 surface flow was dominated by the westward flowing south equatorial current except in a small region to the west of isla fernandina where eastward flow associated with the shoaling of the equatorial undercurrent was observed the equatorial undercurrent was observed to the west of the archipelago centered along 0 5 s at 70 m with peak velocities 0 6 m s 1 and at 92 w a transport of 6 6 sv between 92 w and the archipielago a distance of only 40 km the undercurrent surfaced the eastward flow decelerated and meridional flow diverged on either side of 0 5 s the southward flow appearing to be stronger and better developed than the northward flow at 89 w the undercurrent and its associated salinity maximum were observed at 50 m depth at 1 s with greatly reduced speed 0 2 m s 1 subsurface eastward flow also appeared in the northern hemisphere but this flow was at greater depth 140 m the interaction of the undercurrent and the archipielago appeared to enhance the thickness of the 16 c thermostad

the influence of the galapagos islands on tropical temperatures currents and the generation of tropical instability waves 1 the galapagos islands provide a topographic barrier for the southern equatorial current sec and the equatorial undercurrent euc an island wake effect can be diagnosed from the difference of an ocean general circulation model simulation which includes the galapagos islands and one which ignores their presence cold thermocline water upwells on the western side of the islands and only during boreal winter season these cold waters can linger around the islands at a depth of about 80 m and affect the far eastern equatorial pacific surface waters this effect is partly offset by the westward transport of cold surface waters by the sec which creates a wake on the western side of the islands it is furthermore shown that changes in horizontal current shear induced by the presence of the galapagos islands modify the generation of tropical instability waves and lead to a basin scale sst anomaly pattern

physical volcanology and structural development of cerro azul volcano isabela island galapagos implications for the development of galapagos type shield volcanoes erupted from circumferential vents near the summit these flows are nearly an order of magnitude smaller in volume than the predominantly aa flows erupted from radial eruptive fissures near the break in slope 0 06 0 1 km3 the differences in volume and flow morphology with altitude are due to slower eruption rates from summit vents than from flank vents which in turn are attributable to the different heights the magmas must ascend from shallow reservoirs these observations support the contention that the steep upper flanks were constructed by the buildup of short lava flows rather than by the structural deformation of originally gently dipping flanks in addition to the higher eruption rates a subdued lower flank geometry is promoted by the deposition of lava deltas onto the shallow galapagos platform on the western northern and eastern flanks of the volcano 40ar 39ar geochronology and volume estimates show that despite their morphologic differences the growth of the western galapagos shields has been nearly synchronous precluding an evolutionary model for their development the wide variations in elevation volume area and the distribution of slope angles among the western volcanoes can be linked instead to different long term eruption rates and to a lesser degree the position of each volcano relative to the edge of the galapagos platform

high sea surface temperatures in tropical warm pools during the pliocene sea surface temperatures in the tropical oceans were thought to have remained stable during a period of warmth about five million years ago reconstructions of the sea surface temperature from the caribbean and pacific suggest that tropical temperatures have in fact changed in concert with global mean temperatures over the past five million years

the effect of the galapagos islands on the equatorial pacific cold tongue abstract a reduced gravity ocean general circulation model of the tropical pacific ocean is used to determine potential improvements to the simulated equatorial pacific cold tongue region through choices in horizontal resolution and coastline geometry in particular for the galapagos islands four simulations are performed with identical climatological forcing results are compared between model grids with and without the galapagos islands with coarse and fine resolutions it is found that properly including the galapagos islands results in the obstruction of the equatorial undercurrent euc which leads to improvements in the simulated spatial structure of the cold tongue including a basinwide warming of up to 2 c in the east central pacific the obstruction of the euc is directly related to the improvements east of the galapagos islands and for the basinwide reduction of the tropical cold bias through an equatorial dynamical adjustment the pattern of sst warming resulting from the inclusion of the

paleoceanography of the eastern equatorial pacific over the past 4 million years and the geologic origins of modern galapagos upwelling abstract an isolated volcanic archipelago at the confluence of several major ocean currents the galapagos archipelago ga is among the most biologically diverse places on earth there remain many open questions concerning evolution and speciation in the ga with the details of the geologic formation of the islands over the past millions of years representing a key source of uncertainty paleoceanographic sea surface temperature sst proxy records from the far eastern equatorial pacific eep indicate that the modern gradient of sst across the ga the cross island sst gradient or ci t emerged relatively abruptly 1 6 ma as the modern ci t is the result of a blockage and subsequent upwelling of the equatorial undercurrent euc by the ga we infer from these paleoceanographic data that the modern period during which the ga is arranged such that the islands constitute a significant topographic barrier to the euc began 1 6 ma an extensive suite of ocean circulation model experiments new and previously published confirms that the sign and magnitude of the change in ci t captured in paleoceanographic records can be explained by the islands impinging upon the euc implications for the geologic history of the galapagos and related biogeographical questions are discussed additionally these results suggest that investigations of the pan pacific sst gradient pp t should use one of the available proxy sites in the eep that is not influenced by regional geologically forced oceanographic changes such an analysis supports recent suggestions of a more gradual development of the modern pp t over the plio pleistocene

reply to pliocene warmth and gradients brierley et al 1 question our findings of elevated temperatures in the tropical warm pools during the pliocene2 focusing specifically on the mid pliocene warm period about 3 3 to 3 million years ago as framed by brierley et al we continue to find evidence for warmer than holocene temperatures in the western pacific warm pool in good agreement with pliomip simulations especially in light of new pco2 reconstructions3

strong sea surface cooling in the eastern equatorial pacific and implications for galapagos penguin conservation the galapagos is a flourishing yet fragile ecosystem whose health is particularly sensitive to regional and global climate variations the distribution of several species including the galapagos penguin is intimately tied to upwelling of cold nutrient rich water along the western shores of the archipelago here we show using reliable high resolution sea surface temperature observations that the galapagos cold pool has been intensifying and expanding northward since 1982 the linear cooling trend of 0 8 c per 33 years is likely the result of long term changes in equatorial ocean circulation previously identified moreover the northward expansion of the cold pool is dynamically consistent with a slackening of the cross equatorial component of the regional trade winds leading to an equatorward shift of the mean position of the equatorial undercurrent the implied change in strength and distribution of upwelling has important implications for ongoing and future conservation measures in the galapagos

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

the effect of the galapagos islands on enso in forced ocean and hybrid coupled models abstract an ocean general circulation model ogcm of the tropical pacific ocean is used to examine the effects of the galapagos islands on the el nino southern oscillation enso first a series of experiments is conducted using the ogcm in a forced context whereby an idealized el nino event may be examined in cases with and without the galapagos islands in this setup the sensitivity of the sea surface temperature sst anomaly response to the presence of the galapagos islands is examined second with the ogcm coupled to the atmosphere via zonal wind stress experiments are conducted with and without the galapagos islands to determine how the galapagos islands influence the time scale of enso in the forced setup the galapagos islands lead to a damped sst anomaly given an identical zonal wind stress perturbation mixed layer heat budget calculations implicate the entrainment mixing term which confirms that the difference is due to the galapagos islands changing the background mean state that is

new volcanological and volatile data provide strong support for the continuous existence of galapagos islands over the past 17 million years the first systematic rock sampling of volcanoes along the galapagos hotspot tracks the aseismic cocos carnegie malpelo and coiba ridges and adjacent seamounts in the area between the galapagos islands and central and south america was carried out on r v sonne cruise 144 3 guyot shaped seamounts paleo beach or intertidal wave cut platform deposits the structure and texture of volcanic rocks and low sulfur contents of fresh glasses dredged at these volcanoes imply that ocean islands existed continuously above the galapagos hotspot for at least the past 17 million years these new data significantly extend the time period over which the unique endemic galapagos fauna could have evolved providing a complete solution to the long standing enigma of the evolution of galapagos land and marine iguanas

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

intensification of the walker and hadley atmospheric circulations during the pliocene pleistocene climate transition when comparing new sea surface temperature sst records between the western and eastern equatorial pacific spanning the last 3 2 ma we found that the zonal temperature gradient over the entire tropical pacific irreversibly increased by 3 to 4 degrees c from 2 2 to 2 0 ma here we suggest a pronounced increase in atmospheric circulation from a weak to a strong zonal walker circulation wc during the early pleistocene evidence from other oceanic areas also suggests a strengthening in the meridional hadley circulation hc during the same time period therefore we also suggest that the invigoration of both atmospheric circulation patterns was intimately coupled during the plio pleistocene transition and likely linked to a shrinkage in the zonal extension of the tropical to subtropical warm sphere associated with a prominent increase in the pole to equator temperature gradient our conclusion refutes assumptions that the intensification of atmospheric circulation in the tropics and subtropics significantly contributed to the initiation of continental ice sheet formation at high latitudes since the onset of extensive northern hemisphere glaciation nhg occurred similar to 2 75 ma ago in the late pliocene instead the development of a stronger atmospheric circulation similar to 2 2 2 0 ma ago could have significantly contributed to the plio pleistocene climate cooling c 2010 elsevier b v all rights reserved

multiple expressions of plume ridge interaction in the galapagos volcanic lineaments and ridge jumps 1 anomalous volcanism and tectonics between near ridge mantle plumes and mid ocean ridges provide important insights into the mechanics of plume lithosphere interaction we present new observations and analysis of multibeam side scan sonar sub bottom chirp and total magnetic field data collected during the r v melville flamingo cruise mv1007 may june 2010 to the northern galapagos volcanic province ngvp the region between the galapagos archipelago and the galapagos spreading center gsc on the nazca plate and to the region east of the galapagos transform fault gtf on the cocos plate the ngvp exhibits pervasive off axis volcanism related to the nearby galapagos hot spot which has dominated the tectonic evolution of the region observations indicate that 94 of the excess volcanism in our survey area occurs on the nazca plate in three volcanic lineaments identified faults in the ngvp are consistent with normal ridge spreading except for those within a 60 km wide swath of transform oblique faults centered on the gtf these transform oblique faults are sub parallel to the elongation direction of larger lineament volcanoes suggesting that lineament formation is influenced by the lithospheric stress field we evaluate current models for lineament formation using existing and new observations as well as numerical models of mantle upwelling and melting the data support a model where the lithospheric stress field controls the location of volcanism along the lineaments while several processes likely supply melt to these eruptions synthetic magnetic models and an inversion for crustal magnetization are used to determine the tectonic history of the study area results are consistent with creation of the gtf by two southward ridge jumps part of a series of jumps that have maintained a plume ridge separation distance of 145 km to 215 km since 5 ma

plio pleistocene climate sensitivity evaluated using high resolution co2 records theory and climate modelling suggest that the sensitivity of earth s climate to changes in radiative forcing could depend on the background climate however palaeoclimate data have thus far been insufficient to provide a conclusive test of this prediction here we present atmospheric carbon dioxide co2 reconstructions based on multi site boron isotope records from the late pliocene epoch 3 3 to 2 3 million years ago we find that earth s climate sensitivity to co2 based radiative forcing earth system sensitivity was half as strong during the warm pliocene as during the cold late pleistocene epoch 0 8 to 0 01 million years ago we attribute this difference to the radiative impacts of continental ice volume changes the ice albedo feedback during the late pleistocene because equilibrium climate sensitivity is identical for the two intervals when we account for such impacts using sea level reconstructions we conclude that on a global scale no unexpected climate feedbacks operated during the warm pliocene and that predictions of equilibrium climate sensitivity excluding long term ice albedo feedbacks for our pliocene like future with co2 levels up to maximum pliocene levels of 450 parts per million are well described by the currently accepted range of an increase of 1 5 k to 4 5 k per doubling of co2