sea surface and subsurface circulation dynamics off equatorial peru during the last 17 kyr the complex deglacial to holocene oceanographic development in the gulf of guayaquil eastern equatorial pacific is reconstructed for sea surface and subsurface ocean levels from isotope geochemical proxies based on marine sediment cores at sea surface southern sourced cold coastal water and tropical equatorial surface water tropical surface water are intimately related in particular since 10 ka independent sea surface temperature proxies capturing different seasons emphasize the growing seasonal contrast in the gulf of guayaquil which is in contrast to ocean areas further offshore cold coastal water became rapidly present in the gulf of guayaquil during the austral winter season in line with the strengthening of the southeast trades while coastal upwelling off peru gradually intensified and expanded northward in response to a seasonally changing atmospheric circulation pattern affecting the core locations intensively since 4 ka bp equatorial surface water instead was displaced and tropical surface water moved northward together with the equatorial front at subsurface the presence of equatorial under current sourced equatorial subsurface water was continuously growing prominently since 10 8 ka b p during heinrich stadial 1 and large parts of the bolling allerod and similarly during short holocene time intervals at 5 1 4 ka b p and 1 5 0 5 ka b p the admixture of equatorial subsurface water was reduced in response to both short term weakening of equatorial under current strength from the northwest and emplacement by tropical equatorial surface water considerably warming the uppermost ocean layers

glacial interglacial variability in denitrification in the world s oceans causes and consequences the late quaternary history of water column denitrifcation of the eastern pacific margins and the arabian sea is reconstructed using sedimentary 15n measurements the 15n values in six piston cores raised from these regions show remarkably similar cyclic variations being heavy 9 10 5 during the interglacials and 2 3 lighter during the glacials this implies that denitrification in these regions decreased substantially during the glacial periods the glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone since water column denitrification in these areas accounts for about half of the fixed nitrogen loss in the modern ocean the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods because nitrate is a limiting nutrient oceanic productivity and attendant changes in co2 may therefore have been modulated on glacial interglacial timescales by variations in the oceanic no3 content

altimeter observations of the peru chile countercurrent data from geosat and topex altimeters are used to infer the structure of the peru chile countercurrent a jet that flows from at least as far north as 10 s historical data suggests 7 s to 35 40 s maintaining its position between approximately 100 300 km offshore although the annual mean current cannot be determined from altimeter observations the nearly antisymmetric patterns in spring and fall combined with historical observations suggest that the countercurrent is poleward at most times and is maximum in spring and minimum in fall previous studies have linked the offshore countercurrent at 7 s to the equatorial undercurrent west of the galapagos islands suggesting that the countercurrent is part of a continuous flow that extends from the western equatorial pacific to the region off chile between 35 40 s

genesis of terrestrial oncoids cayman islands british west indies terrestrial oncoids up to 4 3 mm long are common in sinkholes that penetrate the dolostones of the oligocene miocene bluff formation on grand cayman and cayman brac the vaguely laminated terrestrial oncoids which generally lack a nucleus are formed of detrital material micrite clays dolomite calcified filaments and spores and insect fragments the abundant diverse assay of microorganisms includes six different types of filaments and five different types of spores which can be attributed to fungi algae and or cyanobacteria thin mats of mucus are commonly associated with the microorganisms the microorganisms contribute to the formation of the terrestrial oncoids by i calcification of the filaments and spores ii trapping and binding detrital material and iii binding with their mucus detrital material to the surface of the oncoids identification of terrestrial oncoids relies on i the recognition of a microbial assemblage ii the demonstration that the microorganisms played an ac

northern timing of deglaciation in the eastern equatorial pacific from alkenone paleothermometry 1 the equatorial cold tongue ect of the eastern pacific is the most dynamic ocean region in the world s tropics and sets the tempo for global climate anomalies arising from el nino southern oscillation enso events this region s deglaciation history and relationship with north and south polar climates remains poorly understood impeding integration of tropical pacific ocean atmosphere dynamics and enso variability in our understanding of glacial cycles here we present alkenone reconstructions of sea surface temperature sst across the last glacial termination from five ect cores east of the galapagos islands a composite index of sst based on these demonstrates strong temporal affinity with the two step deglaciation of the northern hemisphere composed of two distinct warming steps at the beginning of the bolling and the end of the younger dryas intervals within dating uncertainty warming in the ect began in phase with the bolling excursion was followed by a 2 3 ka plateau and resumed with a second pulse at the end of the younger dryas on the basis of our reconstructions about two thirds of the warming materialized at or after the end of the younger dryas implying a marked delay in the region s response to deglaciation the results challenge the prevailing paradigm that ect deglacial history conforms to an antarctic timing commonly attributed to advection from the southern ocean through an interior oceanic link or to synchronous response of both regions to co2 forcing our results emphasize instead the role of dynamical adjustments linked to northern hemisphere processes most likely transmitted through the atmosphere

factors controlling the silicon isotope distribution in waters and surface sediments of the peruvian coastal upwelling we present the first systematic study of the silicon isotope composition in the water column 30sisi oh 4 and in diatoms 30sidiatom from the underlying surface sediments in a coastal upwelling region the surface waters upwelling on the shelf off peru are mainly fed by southward flowing subsurface waters along the coast which show a mean 30sisi oh 4 of 1 5 the concentration of dissolved silicic acid si oh 4 increases towards the south in these waters and with increasing water depth suggesting lateral mixing with water masses from the south and intense remineralisation of particulate biogenic silica bsio2 in the water column and in the surface sediments surface waters in the realm of the most intense upwelling between 5 s and 15 s have only marginally elevated 30sisi oh 4 values 30sisi oh 4 1 7 with respect to the source si isotope composition whereas further north and south where upwelling is less pronounced surface waters are more strongly fractionated 30sisi oh 4 up to 2 8 due to the stronger utilisation of the smaller amounts of available si oh 4 the degree of si oh 4 utilisation in the surface waters along the shelf estimated from the si oh 4 concentration data ranges from 51 to 93 the 30sidiatom values of hand picked diatoms in the underlying surface sediments vary from 0 6 to 2 0 which is within the range of the expected fractionation between surface waters and diatoms the fractionation signal in the surface waters produced during formation of the diatoms is reflected by the 30sidiatom values in the underlying sediments with the lowest 30sidiatom values in the main upwelling region the silicon isotope compositions of bsio2 30sibsio2 from the same surface sediment samples are generally much lower than the 30sidiatom signatures indicating a significant contamination of the bsio2 with biogenic siliceous material other than diatoms such as sponge spicules this shift towards lighter 30sibsio2 values by up to 1 3 compared to 30sidiatom signatures for the same surface sediment samples potentially biases the interpretation of 30si paleorecords from sediments with low bsio2 concentrations and thus the reconstruction of past si oh 4 utilisation in surface waters

eastern equatorial pacific ocean t s variations with el nino 1 temperature salinity t s relationship variability in the pycnocline of the eastern equatorial pacific ocean nino3 region 5 s 5 n 150 w 90 w over the last two decades is investigated using observational data and model simulation a numerical model simulation using the mitgcm massachusetts institute of technology general circulation model suggests that during el nino years the water in the eastern equatorial pacific ocean becomes saltier by 0 1 to 0 2 and warmer by 0 5 to 1 c on density surfaces within the pycnocline this simulation is consistent with conductivity temperature depth ctd data collected mostly during tropical atmosphere ocean tao mooring maintenance cruises

subsurface connections in the eastern tropical pacific during la nina 1999 2001 and el nino 2002 2003 1 the subsurface connections between the equatorial current system ecs and the peru current system pcs between 1999 and 2005 are investigated with a primitive equation eddy resolving regional model that is forced with realistic atmospheric and lateral oceanic conditions specific attention is given to the 1999 2000 la nina and the 2002 2003 el nino the model s skill is assessed through a comparison with satellite derived sea level anomalies and in situ sea surface temperature time series the model reproduces fairly well the known dynamics of the region for climatological conditions and the numerical solution obtained for the particular 1999 2000 and 2002 2003 events presents patterns rather typical of cold and warm phases of el nino southern oscillation enso eulerian and lagrangian diagnoses are used to derive relevant information about the density and velocity vertical structures of the ecs and the pcs the transports of the major currents in the region are shown to differ a lot between the 1999 2000 la nina and the 2002 2003 el nino the equatorial subsurface currents transfer significantly more water into the eastern tropical pacific during la nina than during el nino whereas the peru chile undercurrent pcuc carries more water during el nino the equatorial subsurface currents and especially the primary southern subsurface countercurrent contribute to 80 of the pcuc transport during the 1999 2000 cold phase this ratio falls down to only 20 during the 2002 2003 warm phase

eastern pacific ocean circulation near the onset of the 1982 1983 el nino over a 1 month period october 5 to november 6 1982 during the initial stages of the 1982 1983 el nino hydrographic and velocity profiling measurements were made in the eastern equatorial pacific by two research vessels track lines approximated a square centered near the galapagos islands with approximately meridional sections at 95 w and 85 w and nearly zonal sections at about 5 n and 5 s water mass characteristics and estimated currents of these sections are discussed sea surface temperature nearly everywhere was warmer than 25 c an anomaly of 2 c 3 c the equatorial thermocline represented by the 20 c isotherm was depressed by nearly 50 m at 85 w and more than 100 m at 95 w relative to a historical mean profile across 95 w estimated geostrophic relative to 500 dbar and directly measured near equatorial velocity profiles indicated significant eastward surface flow the south equatorial current south of the equator had disappeared estimated warm water transport t 24 5 kg m 3 indicated an influx into the region which was approximately that required to balance the observed low frequency sea level change at the galapagos islands temperature and salinity properties as well as the transport estimates indicated that this warm water came predominantly from the west

the origin of the pacific equatorial 13 c water abstract examination of the vertical distributions of temperature salinity oxygen and nutrient salts in the thermostad of the equatorial 13 c water in the eastern pacific ocean indicates that local vertical mixing is unimportant in creating the thermostad and the characteristics of the 13 c water maps are presented that show the oceanwide distributions of depth geostrophic flow salinity oxygen phosphate silica and nitrate on the 160 cl t 1 isanosteric surface which nearly coincides with the core of the 13 c water the maps suggest that the original characteristics of the 13 c water are acquired in the surface and thermocline layers to the northeast of new zealand and in the tasman sea by winter convection and vertical mixing the acquired characteristics are advected to the thermostad in the eastern pacific via a long route starting from the source region the flow is first eastward in high latitudes and then returns westward in low latitudes around the anticyclonic subtropical gyre of the sout

nitrogen isotopic evidence for deglacial changes in nutrient supply in the eastern equatorial pacific 1 the eastern equatorial pacific eep is a high nutrient low chlorophyll region of the ocean downcore nitrogen isotope records from the eep have been previously interpreted as a direct reflection of changes in nutrient consumption however the observed changes in sedimentary 15n since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron to nitrate ratio of the surface waters rather downcore n isotope records in the eep strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary 15n records along the western margin of the americas this similarity is attributed to the overprinting of the n isotopic composition of nitrate in the eep through the advection of nitrate westward from the margins in the subsurface a local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary 15n records of denitrification changes from two new eep 15n records tr163 22 and odp site 1240 the denitrification records used are from 1 the central american margin odp site 1242 and 2 the south american margin geob7139 2 the degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11 13 ka and finally it increases into the holocene the derived eep nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand the influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the southern ocean and the release of sequestered co2 and nutrient rich o2 poor waters from the deep ocean this has important implications for understanding the glacial interglacial scale variation in intermediate water suboxia and water column denitrification

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

spatio temporal variability of the equatorial front in the eastern tropical pacific from remote sensing salinity data 2010 2015 abstract in the eastern pacific the equatorial front ef separates the relatively cold and salty equatorial surface water to the south from the relatively warm and fresh surface tropical water to the north although previous studies have succinctly described the main ef characteristics little is known about its spatial pattern and temporal variability beyond seasonal scale in this study we used 5 years of remote sensing sea surface salinity sss data acquired by smos in a synoptic and continuous manner to describe the spatio temporal variability of the haline ef hef after validating the sss satellite dataset with concomitant in situ data we developed an algorithm based on maximum sss gradients to automatically identify the hef position on every smos sss map this algorithm applied to the 4 day resolution smos sss product allows us to investigate the spatio temporal variability of the hef between 2010 and 2015 seasonally west of the galapagos islands the hef is centered at 2 n and shows relatively weak meridional displacements in contrast east of the galapagos archipelago the hef varies on average between 4 s in spring and 2 n in autumn at intraseasonal scales the hef shows meridional fluctuations of 1 25 around its average position these intraseasonal fluctuations are partly related to kelvin waves which was more noticeable since 2014 over the 5 year studied period the hef position showed a northward trend of 0 3 0 4 latitudinal degrees per year between 2010 and 2015 however the relatively short time series does not permit to investigate whether this low frequency trend is due to long term variability or interdecadal fluctuations

trace metals in contemporary and seventeenth century galapagos coral records of seasonal and annual variations we report trace element calcium ratios for modern cuca mnca cdca and pbca and seventeenth century cuca mnca and pbca specimens of pavona clavus collected in the galapagos islands these data include the first reliable measurements of cuca ratios in coralline aragonite we estimate that the ratio of cuca in the lattice to that in seawater i e the effective distribution coefficient is 0 3 lower than the value of 1 observed for several other divalent elements we estimate the effective distribution coefficient for mn is 1 distribution coefficients in coral aragonite for 8 divalent metals are near unity despite different ionic radii and chemical speciation in seawater investigation of where these substituents are incorporated in the aragonite lattice is clearly warranted in a modern hood island coral quarter annually sampled from 1964 73 cuca ratios decrease twofold from the late 1960s to early 1970s mnca and cdca ratios vary seasonally with upwelling and the generic el nino the el nino southern oscillation enso events of 1965 1969 and 1972 are marked by suppression of cdca ratios by about 2 5 nmol mol while the mnca ratio is highest during the strong 1972 enso pbca ratios were relatively constant throughout this period from the cuca record of a seventeenth century urvina bay coral annually sampled from 1600 1725 and the estimated cu distribution coefficient surface seawater cu concentrations at galapagos during the seventeenth century were similar to present day at 0 7 1 4 nmol kg estimated pb concentrations were lower at 5 20 pmol kg and mn concentrations were slightly higher at 1 6 2 8 nmol kg

el nino southern oscillation like variability during glacial terminations and interlatitudinal teleconnections interannual decadal variability in the equatorial pacific el nino southern oscillation enso induces climate changes at global scale but its potential influence during past global climate change is not yet well constrained new high resolution eastern equatorial pacific proxy records of thermocline conditions present new evidence of strong orbital control in enso like variability over the last 275 000 years recurrent intervals of saltier thermocline waters are associated with the dominance of la nina like conditions during glacial terminations coinciding with periods of low precession and high obliquity the parallel dominance of 13c depleted waters supports the advection of antarctic origin waters toward the tropical thermocline this oceanic tunneling is proposed to have reinforced orbitally induced changes in enso like variability composing a complex high and low latitude feedback during glacial terminations

the obduction of equatorial 13 c water in the pacific identified by a simulated passive tracer the obduction of equatorial 13 degrees c water in the pacific is investigated using a simulated passive tracer of the consortium for estimating the circulation and climate of the ocean ecco the result shows that the 13 degrees c water initialized in the region 8 degrees n 8 degrees s 130 degrees 90 degrees w enters the surface mixed layer in the eastern tropical pacific mainly through upwelling near the equator in the costa rica dome and along the coast of peru approximately two thirds of this obduction occurs within 10 years after the 13 degrees c water being initialized with the upper portion of the water mass reaching the surface mixed layer in only about a month the obduction of the 13 degrees c water helps to maintain a cool sea surface temperature year round equivalent to a surface heat flux of about 6 0 w m 2 averaged over the eastern tropical pacific 15 degrees s 15 degrees n 130 degrees w eastern boundary for the period of integration 1993 2006 during el nino years when the thermocline deepens as a consequence of the easterly wind weakening the obduction of the 13 degrees c water is suppressed and the reduced vertical entrainment generates a warming anomaly of up to 10 w m 2 in the eastern tropical pacific and in particular along the coast of peru providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone the situation is reversed during la nina years

correlation of current and sea level in the eastern equatorial pacific abstract upper ocean current and temperature records from neat 0 110 w are compared with galapagos island sea level measurements 0 3 s 91 28 w for the period march 1980 to july 1981 low frequency periods greater than 30 days near surface zonal currents 20 and 50 m were well correlated with local wind but deeper currents 100 and 150 m and sea level were not response to the local wind was studied in terms of linear dynamics periods where zonal acceleration was in phase with zonal wind stress were found however overall these two series were uncorrelated the direct relation of low frequency wind stress and surface current rather than acceleration suggests a quasi equilibrium response on these time scales the response at deeper levels was investigated by comparing the zonal transport per unit width vertically averaged zonal velocity in the upper 200 m with sea level these series were significantly correlated with 95 confidence at a lag of 10 5 d indicating eastward phase propagation

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

sensitivity of the northern humboldt current system nearshore modeled circulation to initial and boundary conditions 1 the influence of the eastern pacific equatorial circulation on the dynamics of the northern humboldt current system is studied using an eddy resolving regional circulation model forced by boundary conditions from three distinct ocean general circulation models the seasonal variability of the modeled nearshore circulation and the mesoscale activity are contrasted in order to evaluate the role of the density forcing the seasonal variability of the surface and subsurface alongshore currents strongly depends on the amplitude and timing of the seasonal eastward propagating equatorial waves the equatorward flow and upwelling intensity are also impacted by nonlinear processes such as the seasonal generation of nearshore mesoscale eddies which create alongshore pressure gradients modulating the surface current boundary conditions affect differently the intensity and phase of the eddy kinetic energy as baroclinic instability is triggered by coastal waves during austral summer and fall whereas it is sustained by the wind driven upwelling during austral winter

on the dynamics of equatorial subsurface countercurrents abstract the equatorial subsurface countercurrents sscc are strong steady geostrophically balanced eastward flows situated below the high speed core of the equatorial undercurrent euc at 3 5 n and s the dynamics of these currents are explored using a continuously stratified vertically diffusive linear steady state ocean model forced by zonal winds with effectively no wind stress curl model results agree favorably with observations in that both euc and sscc like structures are generated a diagnosis of the model momentum vorticity and continuity balances at various depths and latitudes reveals that the sscc lie outside a vertically diffusive equatorial momentum boundary layer so that both components of velocity are geostrophically balanced they are however located at the poleward of a broader diffusive equatorial vorticity boundary layer within this boundary layer cyclonic vorticity associated with the euc diffuses to the level of the sscc where it is balanced by poleward advection of pla

upwelling signals in radiocarbon from early 20th century peruvian bay scallop argopecten purpuratus shells abstract we quantified 14c 18o and 13c cycles along ontogeny within four bay scallop argopecten purpuratus shells collected from callao bay salaverry and sechura bay peru following the 1907 1908 non el nino years and the 1925 1926 el nino 14c and 13c generally covary 14c and 18o vary inversely simultaneous decreases in 14c and increases in 18o in non el nino shells are followed by constant 14c and gradually decreasing 18o which we interpret as evidence for discrete marine upwelling events followed by warming of the initially cold upwelled water upwelling changes from el nino events are detectable with difficulty in mollusk shell 14c

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

plio pleistocene denitrification in the eastern tropical north pacific intensification at 2 1 ma 1 global climate has changed substantially over the past 4 million years ma toward on average colder conditions and higher amplitude oscillation between glacial and interglacial periods corresponding changes in marine biogeochemistry could have linked oceanic circulation changes to the global carbon cycle but remain poorly understood we report a high resolution 4 ma long 15n record from ocean drilling program site 1012 on the california margin which monitors denitrification intensity in one of the principal oxygen minimum zones omzs of the open ocean the 15n record demonstrates that eastern tropical north pacific etnp denitrification was weak for much of the late pliocene though there was no apparent change associated with northern hemisphere glaciation nhg at 2 7 ma denitrification strengthened substantially by 2 in 15n at 2 1 ma since 2 1 ma intense denitrification in the etnp occurred during interglacial periods and was generally very climate sensitive we infer that two oceanic changes the shoaling of the thermocline in the eastern pacific and thus the strengthened walker circulation and the development of a modern like frontal system in high latitude southern ocean around 2 1 ma provided favorable conditions for intensification of etnp denitrification that was also likely mirrored south of the equator intermediate water circulation changes likely created the poorly ventilated zones susceptible to the suboxic condition required by denitrification 2 1 ma thus marks a critical point for the reorganization of the ocean s nitrogen cycle in which open ocean denitrification became a significant loss term during interglacial phases of climate given linkage between the ocean s n and c cycle etnp denitrification changes probably contributed to plio pleistocene climatic changes

a discussion of flow pathways in the central and eastern equatorial pacific abstract an eddy permitting global ocean model is used to interpret kinematics within the central and eastern equatorial pacific ocean from 160 e to the coast of america because of high levels of variability in this region observational studies of meridional flow are contradictory in particular as to whether the net flow is northward or southward unlike most oceanographic datasets model output can be analyzed at high temporal and spatial resolution providing clues as to real ocean behavior in the model a net southward flow occurs across the equator east of 160 w at most density layers throughout the year in the central pacific from 160 e to 160 w the net flow is northward but varies with season and occurs primarily in the mixed layer this is a key region for the flow of equatorial undercurrent water into the northern hemisphere the three dimensional flow is very complex and seasonally dependent it is vital that these flows are analyzed in an isopycnal framework or else the pathways are ve

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

a model of the equatorial sea surface temperature field and associated circulation dynamics abstract a linear continuously stratified analytical model of the equatorial ocean is developed and used to simulate the major features of the equatorial sea surface temperature sst field and current system the model is bounded by meridional barriers to flow in the east and west and is forced by an idealized southeast trade wind field the steady state response is studied here although the model is time periodic and capable of simulating the annual cycle or a more general time dependence the surface heat flux forcing is set to zero so that the contribution of the equatorial upwelling field in maintaining the cool equatorial surface water can be isolated many of the observed features of the equatorial sst field and current system are simulated the model generates cool sst anomalies an the equator in the eastern half of the basin the cool water core is located to the south of the equator in the easternmost regions of the basin with the coldest water along the eastern boundary the latitudinal and

northern galapagos corals reveal twentieth century warming in the eastern tropical pacific models and observations disagree regarding sea surface temperature sst trends in the eastern tropical pacific we present a new sr ca sst record that spans 1940 2010 from two wolf island corals northern galapagos trend analysis of the wolf record shows significant warming on multiple timescales which is also present in several other records and gridded instrumental products together these data sets suggest that most of the eastern tropical pacific has warmed over the twentieth century in contrast recent decades have been characterized by warming during boreal spring and summer especially north of the equator and subtropical cooling during boreal fall and winter especially south of the equator these sst trends are consistent with the effects of radiative forcing mitigated by cooling due to wind forcing during boreal winter as well as intensified upwelling and a strengthened equatorial undercurrent

southern ocean control on the extent of denitrification in the southeast pacific over the last 70 ka abstract temporal changes in oceanic denitrification the bacterial reduction of nitrate under suboxic conditions highlight the potential importance of n inventory changes and the production of n 2 o on the climate system at the same time the cause of the globally observed variation in denitrification remains unclear high resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from odp site 1234 on the chile margin record integrated denitrification changes within the peru chile upwelling system over the last 70 ka denitrification changes in the southeast pacific are coherent with antarctic climate changes recorded by the byrd ice core 18 o record and lead northern hemisphere climate events the southern hemisphere character of the chile margin 15 n record suggests that episodes of reduced denitrification in the se pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of subantarctic mode water samw which forms in the subantarctic zone of the southern ocean and feeds into the low latitude thermocline

differences between mono generic and mixed diatom silicon isotope compositions trace present and past nutrient utilisation off peru in this study we combine for the first time silicon si isotope compositions of small mixed diatom species 30sibsio2 and of large handpicked mono generic i e genus coscinodiscus diatom samples 30sicoscino with diatom assemblages extracted from marine sediments in the peruvian upwelling region in order to constrain present and past silicate utilisation the extension of a previous core top data set from the peruvian shelf demonstrates that 30sicoscino values record near complete si utilisation as these are similar to the isotopic composition of the subsurface source waters feeding the upwelling in contrast the 30sibsio2 of small mixed diatom species increase southward along the shelf as well as towards the shore we attribute highest 30sibsio2 values partly to transient iron limitation but primarily to the gradual increase of si isotope fractionation within the seasonal diatom succession which are mainly recorded by small diatom species during intense bloom events in contrast lower 30sibsio2 values are related to initial si isotope utilisation during periods of weak upwelling when low si oh 4 concentrations do not permit intense blooms and small diatom species record substantially lower 30si signatures as such we propose that the intensity of the upwelling can be deduced from the offset between 30sibsio2 and 30sicoscino 30sicoscino bsio2 which is low for strong upwelling conditions and high for prevailing weak upwelling we apply the information extracted from surface sediments to generate a record of the present day main upwelling region covering the past 17 700 years and find that this location has also been characterized by a persistent offset 30sicoscino bsio2 by comparison with the diatom assemblages we show that the coastal upwelling system changed markedly between weak and strong upwelling conditions in addition our model calculations to quantify species specific si isotope fractionation effects based on the diatom assemblages indicate an overall minor influence that cannot explain the high amplitude in the measured 30sibsio2 record

more humid interglacials in ecuador during the past 500 kyr linked to latitudinal shifts of the equatorial front and the intertropical convergence zone in the eastern tropical pacific 1 studying past changes in the eastern equatorial pacific ocean dynamics and their impact on precipitation on land gives us insight into how the intertropical convergence zone itcz movements and the el nino southern oscillation modulate regional and global climate in this study we present a multiproxy record of terrigenous input from marine sediments collected off the ecuadorian coast spanning the last 500 kyr in parallel we estimate sea surface temperatures sst derived from alkenone paleothermometry for the sediments off the ecuadorian coast and complement them with alkenone based sst data from the panama basin to the north in order to investigate sst gradients across the equatorial front near the equator today s river runoff is tightly linked to sst reaching its maximum either during the austral summer when the itcz migrates southward or during el nino events our multiproxy reconstruction of riverine runoff indicates that interglacial periods experienced more humid conditions than the glacial periods the north south sst gradient is systematically steeper during glacial times suggesting a mean background climatic state with a vigorous oceanic cold tongue resembling modern la nina conditions this enhanced north south sst gradient would also imply a glacial northward shift of the intertropical convergence zone at least in vicinity of the cold tongue a pattern that has not yet been reproduced in climate models

on the pathways of the equatorial subsurface currents in the eastern equatorial pacific and their contributions to the peru chile undercurrent 1 theconnections between theequatorial currentsystem andtheperu currentsystem in the eastern tropical pacific etp are examined with a primitive equations eddy resolving regional model the quasi equilibrium solutions reproduce three eastward equatorial subsurface currents of interest the equatorial undercurrent euc located between 1 n and 1 s the primary southern subsurface countercurrent psscc between 3 and 4 s and farther south the secondary southern subsurface countercurrent ssscc between 7 and 8 s using a lagrangian tracking procedure the fate of these currents in the etp and their contribution to the peru chile undercurrent pcuc are studied lagrangian diagnostics show that for the most part the euc water contributes to westward flows including the south equatorial current and deeper flows below it and strikingly only a very little fraction feeds the pcuc while a significant part of both ssccs contribute substantially mesoscale eddies are shown to exert an effect on these connections in addition about 30 of the pcuc is fed by the three subsurface equatorial flows euc psscc ssscc the remaining part of the pcuc comes from an alongshore recirculation associated with flows below it and from the southern part of the domain south of 9 s

cadomian lower crustal contributions to variscan granite petrogenesis south bohemian pluton austria constraints from zircon typology and geochronology whole rock and feldspar pb sr isotope systematics zircons show a mean pb pb evaporation age of 355 a hybrid pyroxene bearing weinsberg type granitoid of the south 9 ma interpreted as the age of zircon growth during a carboniferous bohemian batholith austria consists of two independent mineral partial melting event in the lower crust granite emplacement at assemblages that were formed during two different magmatic events 345 5 ma is inferred from u pb analysis of the anhedral the older inherited assemblage forms unevenly distributed millimetrezircon population the comparably low radiogenic common pb sized multi grain patches of quartz mesoperthitic alkali feldspar isotope composition of megacrystic alkali feldspars suggests that at andesine bytownite clinopyroxene xmg 0 50 0 54 least some domains of these crystals are inherited from the older orthopyroxene xmg 0 35 0 42 ilmenite accessories pyroxene bearing mineral assemblage rb sr whole rock dating is it is interpreted to represent remnants of a mangeritic igneous thus severely jeopardized by the presence of the inherited alkali rock with a superimposed granulite facies re equilibration texture feldspar crystals leading to widely scattering data points and characterized by unzoned pyroxenes and plagioclase the enclosing errorchron ages of no geological significance younger assemblage with alkali feldspar oligoclase andesine quartz biotite accessories crystallized from a biotite bearing granitic melt with feldspars exhibiting typical magmatic zoning