constraints on hydraulic parameters and implications for groundwater flux across the upland estuary interface abstract analyses of independent laboratory and field scale measurements from two sites on sapelo island georgia reveal heterogeneity in hydraulic parameters across the upland estuary interface regardless of the method used short duration pumping tests amplitude attenuation of tidal pumping data sediment grain size distributions and falling head permeameter tests we obtain hydraulic conductivity of 10 4 m s 1 for the fine grained well sorted clean sands that make up the upland areas proximal to the upland estuary boundary the tidal pumping analyses and permeameter tests suggest that hydraulic conductivities decrease by more than two orders of magnitude a result consistent with the presence of a clogging layer such a clogging layer may arise due to a variety of physical chemical or biological processes the extent and orientation of the layers of reduced hydraulic conductivity near the upland estuary boundary influence the nature of the aquifer s response to tidal forcing where the lower conductivity layer forms a relatively flat creek bank tidal pumping produces a primarily mechanical response in the adjacent aquifer where the creek bank is nearly vertical there is a more direct hydraulic connection between the tidal creek and the adjacent aquifer the clogging layer likely contributes to the development of complicated flow pathways across the upland estuary boundary effective flow paths calculated from tidal pumping data terminate within the marsh beyond the boundary of the upland aquifer suggesting a diffuse regime of groundwater discharge in the marsh we postulate that in many settings submarsh flow may be as important as seepage faces for groundwater discharge into the marsh estuary complex

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

consistent relationship between global climate and surface nitrate utilization in the western subarctic pacific throughout the last 500 ka 1 the open subarctic pacific is at present a high nitrate low chlorophyll hnlc region where nitrate is perennially abundant at the surface theoretically the hnlc status of this region is subject to modification by ocean circulation and or micronutrient supply with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior records of biogenic detritus in sediments from throughout the subarctic pacific indicate that export production was generally lower during glacial maxima while nitrogen isotope measurements from the bering sea have shown that nitrate consumption there was more complete during the last glacial period than it is today here nitrogen isotopic analyses of bulk sediments 15nbulk from three deep water sites in the open subarctic pacific are evaluated in terms of regional nitrate isotopic composition and local relative nitrate utilization the eastern subarctic pacific 15nbulk record bears great similarity to 15nbulk records from the western margin of north america over the last glacial cycle suggesting that variability in the isotopic composition of subeuphotic zone nitrate the growth substrate is reasonably coherent throughout the northeast pacific and dominates at these sites however the two western subarctic pacific records which lie at the heart of the hnlc region display a different pattern implying that significant changes in local relative nitrate utilization overlie the regional background variability after a novel correction intended to remove the background signal associated with denitrification in the eastern tropical north pacific these nitrate utilization records are correlated with a benthic oxygen isotope stack reflecting global deep ocean temperature and ice volume r2 0 65 the correlation implies a strong link between global climate and subarctic pacific nitrate utilization with nearly complete nitrate consumption during glacial periods when export production was low

the cause of carbon isotope minimum events on glacial terminations the occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the indo pacific sub antarctic and south atlantic we use the 13 c record of a thermocline dwelling foraminifera neogloboquadrina dutertrei and surface temperature estimates from the eastern equatorial pacific to demonstrate that the onset of 13 c minimum events and the initiation of southern ocean warming occurred simultaneously timing agreement between the marine record and the 13 c minimum in an antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification renewed circumpolar deep water upwelling and advection of low 13 c waters to the convergence zone at the sub antarctic front on the basis of age agreement between the absolute 13 c minimum in surface records and the shift from low to high 13 c in the deep south atlantic we suggest that the 13 c rise that marks the end of the carbon isotope minima was due to the resumption of north atlantic deep water influence in the southern ocean

diatom bound 15n 14n new support for enhanced nutrient consumption in the ice age subantarctic 1 diatom bound 15n 14n was used to reconstruct the glacial nutrient status of the subantarctic zone in the southern ocean down core records from both the pacific and indian sectors show 15n of 5 to 6 during the last glacial maximum and a decrease coincident with the glacial termination to values as low as 2 the effect of either diatom assemblage or physiological change on the diatom bound 15n 14n is unknown and cannot yet be ruled out as a possible explanation for the observed change however the consistency between indian and pacific sector records and with other paleoceanographic data suggests that the glacial interglacial difference in diatom bound 15n 14n was driven by higher consumption of nitrate in the subantarctic surface during the last ice age such a change in nutrient consumption may have resulted from atmospheric iron fertilization and or decreased glacial mixed layer depths associated with sea ice melting enhanced nutrient consumption in the glacial subantarctic would have worked to lower the concentration of co2 in the ice age atmosphere it also would have reduced the preformed nutrient content of the low latitude thermocline leading to decreases in low latitude productivity suboxia and denitrification

variability in tropical thermocline nutrient chemistry on the glacial interglacial timescale abstract the organic carbon to calcite rain ratio in the tropical ocean may play a role in regulating global climate through its influence on co 2 draw down in the upper ocean the rain ratio may be altered by changes in the nutrient chemistry of the thermocline such changes in the tropical pacific are revealed by the carbon isotope values of thermocline dwelling planktonic foraminifera neogloboquadrina dutertrei the tropical pacific record over the last 30 kyr in the region south or along the equator which is fed by upwelling of deeper equatorial undercurrent water euc shows a carbon isotope signal distinct from any other in global mixed layer or benthic environments this unique record is consistent across the pacific unlike carbon isotope data from other basins and oceanic habitats the tropical pacific thermocline tracer shows last glacial values more positive than those of post glacial times the isotopic shift occurs in the early deglacial 20 17 kyr and leads to a deglacial carbon isotope minimum whose timing differs from that seen elsewhere the deglacial record of the pacific seems best interpreted as the progressive development of the modern nutrient rich thermocline under high nutrient low chlorophyll hnlc conditions the eastern tropical atlantic also has a unique glacial to modern carbon isotope record that is essentially opposite to that seen in the pacific strongly negative values in glacial times differ from those of the standard stratified ocean indicating higher nutrient concentrations a large shift to more positive values occurs rapidly at about 13 14 kyr this indicates a marked reduction in thermocline nutrients the implication is that nutrient flow to the tropics from the deep ocean via sub antarctic sources was stronger for the atlantic during the glacial but was weaker in the pacific transformation to modern conditions occurred in two steps at 17 18 and 13 14 kyr a timing that matches shifts in atmospheric co 2 concentrations and which would be compatible with driving those concentrations higher over deglacial time the mechanism could be an inherent difference in production regimes between the tropical pacific and atlantic

a mid holocene transition in the nitrogen dynamics of the western equatorial pacific evidence of a deepening thermocline sedimentary delta 15 n records from the oligotrophic western equatorial pacific wep off mindanao show that late holocene sedimentary delta 15 n is substantially lower than that of the early holocene following a gradual 3 parts per thousand decrease that occurred between 7 and 3 kyrs ago analyses of modem day nitrate isotope profiles from the same region indicate the sensitivity of the wep n pools towards 1 the advection of 15 n enriched nitrate from the eastern equatorial pacific eep by the north equatorial current nec and the mindanao current in subsurface waters and 2 at shallow depths the input of new and 15 n depleted nitrate through n fixation we suggest that the holocene decrease in sedimentary delta 15 n reflects a diminished relative input of 15 n enriched nitrate to the surface biota either through an increase of regional nitrogen fixation a change in nitrate consumption along the advective path of nitrate supply or a decrease in the vertical supply of 15 n enriched nitrate from the nec the latter mechanism is consistent with a holocene deepening of the wep nitracline thermocline citation kienast m m f lehmann a timmermann e galbraith t bolliet a holboum c normandeau and c laj 2008 a mid holocene transition in the nitrogen dynamics of the western equatorial pacific evidence of a deepening thermocline geophys res lett 35 l23610 doi 10 1029 2008gl035464

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

the δ15n of nitrate in the southern ocean nitrogen cycling and circulation in the ocean interior we report analyses of the nitrogen isotopic composition of nitrate in the eastern indian and pacific sectors of the southern ocean in this paper we focus on the subsurface data as well as data from the deep waters of other ocean basins nitrate 15n is relatively invariant in much of the abyssal ocean i e below 2 5 km with a value of 4 8 0 2 observed in lower circumpolar deep water north atlantic deep water and central pacific deep water the isotopic invariance of deep ocean nitrate stems fundamentally from the completeness of nitrate utilization in most of the global surface ocean the southern ocean surface being an important exception in the subantarctic zone north of the polar frontal zone the nitrate 15n of upper circumpolar deep water is 0 7 greater than that of lower circumpolar deep water this isotopic enrichment appears to result from denitrification in the low latitude water masses with which upper circumpolar deep water communicates the isotopic enrichment of upper circumpolar deep water is diminished in the antarctic probably because of the remineralization of sinking organic n which has a low 15n in the antarctic relative to the other water masses of the southern ocean the subantarctic thermocline has a very low nitrate 15n for its nitrate concentration because of exchange with the low latitude thermocline where this isotopic signature appears to originate this signature of the low latitude thermocline has two probable causes 1 mixing with low nitrate surface water and 2 the oxidation of newly fixed n

deglacial changes in dust flux in the eastern equatorial pacific abstract atmospheric dust levels may play important roles in feedbacks linking continental source areas tropical convection marine productivity and global climate these feedbacks appear to be particularly significant in the tropical pacific where variations in local convection and productivity have been demonstrated to have impacts on climate at higher latitudes modeling of past dust levels and related feedbacks has been limited however by a paucity of observational data in this study we present a temporal and spatial survey of dust fluxes to the eastern equatorial pacific over the past 30 kyr glacial and holocene fluxes of 232th a proxy for continental material were calculated by normalization to 230th from a north south transect of cores along 110 w between 3 s and 7 n odp sites 848 853 fluxes were 30 100 higher during the last glacial suggesting increased dustiness in both hemispheres during the glacial period in both time periods dust fluxes decrease towards the south reflecting scavenging of northern hemisphere dust by precipitation at the itcz the holocene meridional dust flux gradient between 7 n and 3 s is characterized by a steep drop in dust levels at the southern edge of the modern range of the itcz while the gradient is shallower and more nearly linear during the last glacial this change may indicate that the glacial itcz in this region was a less effective barrier to inter hemispheric dust transport most likely due to a decrease in convective intensity and precipitation during the last glacial alternatively the change in gradient may be explained by increased variability in the location of the glacial itcz our data do not appear to require a mean southerly displacement of the glacial itcz as suggested by the results of other studies

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

oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation concentrations lamination preservation and d 15 n values from cores located between 540 750 m water depth in the gulf of tehuantepec southern mexico these results differ from similar proxies found even 5 n of the site where there is evidence for omz changes related to rapid climate change in the northern hemisphere instead omz expansion in the gulf was contemporaneous with changes in sea ice extent and zonal wind shifts around antarctica pointing to subantarctic mode water and antarctic intermediate water as likely sources of oxygen depleted water these observations reinforce the importance of the southern ocean as a primary modulator of northern hemisphere ocean climate as far as 15 n in the etnp citation hendy i l and t f pedersen 2006 oxygen minimum zone expansion in the eastern tropical north pacific during deglaciation geophys res lett 33 l20602 doi 10 1029 2006gl025975

evidence for enhanced convection of north pacific intermediate water to the low latitude pacific under glacial conditions we provide high resolution foraminiferal stable carbon isotope 13c records from the subarctic pacific and eastern equatorial pacific eep to investigate circulation dynamics between the extratropical and tropical north pacific during the past 60 kyr we measured the 13c composition of the epibenthic foraminiferal species cibicides lobatulus from a shallow sediment core recovered from the western bering sea so201 2 101kl 58 52 52 n 170 41 45 e 630 m water depth to reconstruct past ventilation changes close to the source region of glacial north pacific intermediate water gnpiw information regarding glacial changes in the 13c of subthermocline water masses in the eep is derived from the deep dwelling planktonic foraminifera globorotaloides hexagonus at odp site 1240 00 01 31 n 82 27 76 w 2921 m water depth apparent similarities in the long term evolution of 13c between gnpiw intermediate waters in the eastern tropical north pacific and subthermocline water masses in the eep suggest the expansion of relatively 13c depleted nutrient enriched and northern sourced intermediate waters to the equatorial pacific under glacial conditions further it appears that additional influence of gnpiw to the tropical pacific is consistent with changes in nutrient distribution and biological productivity in surface waters of the glacial eep our findings highlight potential links between north pacific mid depth circulation changes nutrient cycling and biological productivity in the equatorial pacific under glacial boundary conditions

millennial scale variations in hydrography and biogeochemistry in the eastern equatorial pacific over the last 100 kyr abstract in this study we use records of nitrogen isotope ratios 15n uk 37 temperature estimates organic carbon and opal percentages from high resolution sediment cores located in the eastern equatorial pacific eep to explore the mechanisms linking millennial scale changes in low latitude sea surface temperature water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100 000 yr our results support a hypothesis that the southern hemisphere and its connection to the low latitudes via shallow subsurface ocean circulation has a primary influence on the biogeochemistry of the eep in addition our results suggest that during the last glacial stage denitrification rates fluctuated on millennial timescales in response to water column ventilation rather than upstream oxidant demand in intermediate depth waters however due to the poor age constraints available for marine isotopic stage mis 3 the eep sedimentary data presented here could support two conflicting mechanisms one driven by enhanced intermediate overturning circulation in the southern ocean during heinrich events antarctic warm events implying that subsurface flow rates control thermocline ventilation and a second one consistent with more sluggish intermediate circulation during antarctic warm events and giving a central role to the temperature control on oxygen solubility in southern ocean surface waters

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

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

expansion of pelagic denitrification during early pleistocene cooling bioavailable nitrogen is removed from the oceans in oxygen deficient benthic and pelagic environments by denitrification future warming is predicted to reduce ocean oxygenation and to cause hypoxic regions to expand potentially accelerating denitrification a compilation of high resolution sedimentary nitrogen isotope delta n 15 records from the eastern tropical pacific north pacific and the arabian sea and a global multi site survey are presented as evidence for weak pelagic denitrification at the end of the pliocene warm period mean delta n 15 values increased in the major oxygen minimum zones omzs between 2 1 and 1 5 ma pelagic denitrification strengthened during a period of long term global cooling despite solubility driven increases in initial oxygen contents of antarctic intermediate and subantarctic mode waters ventilating the omzs this trend is opposite to the predicted mean trend for a cooling ocean as well as to the observed glacial interglacial variation several alternatives to explain the shift are proposed including a rise in net respiration a progressive increase in the ventilation age of the deep ocean associated with million year scale secular cooling and a shoaling of the remotely ventilated thermocline to shallow depths corresponding to the zone of peak subsurface respiration given no evidence for a net increase in production we assert that large scale climate driven changes in ocean circulation regulate long timescale variations in the extent of pelagic denitrification additional data and modeling are required to fully explain the observations c 2013 elsevier b v all rights reserved

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

denitrification under glacial and interglacial conditions a physical approach 1 recent analysis of sedimentary 15n records over the last 200 000 years has shown an expansion of water column denitrification zones during warmer periods and a shrinkage of these oxygen poor regions during glacial periods two different mechanisms could be responsible for driving the changes in the denitrification records variations in local productivity leading to a change in remineralization rates and or changes in the ocean circulation and ocean temperature resulting in variations of the physical supply of dissolved oxygen here we focus on the supply mechanism by using a fully coupled atmosphere ocean sea ice land surface scheme model the university of victoria earth system climate model to examine oxygen supply under varying physical conditions while maintaining an invariant biological oxygen utilization scheme we show that circulation changes can be the cause for the observed changes in dissolved oxygen in the glacial ocean lower temperatures and enhanced formation of antarctic intermediate water and north pacific intermediate water during glacial periods increase the physical supply of oxygen and therefore decrease water column denitrification in our last glacial maximum simulations the change in water characteristics in the eastern tropical pacific is important enough to reduce denitrification by 46 to 65 compared to present day conditions depending on the wind fields used as boundary conditions the consequences of our findings could be substantial for the near future with a warming climate denitrification zones could expand leading to changes in the biological pump and the flux of n2o into the atmosphere

atypical δ 15 n variations at the southern boundary of the east pacific oxygen minimum zone over the last 50 ka abstract we report a nitrogen isotope record odp site 1233 from the southern chile margin at 41 s the site is located slightly south of the southern boundary of the peru chile upwelling system and the associated oxygen minimum zone off peru and northern chile we show that our nitrogen isotope record from the time interval 0 50 calendar kiloyears before present ka b p bears an atypical pattern both in shape and timing when compared with records obtained from either the continental margin of the eastern pacific or the subantarctic zone saz of the southern ocean the 15 n values at site 1233 are relatively high throughout the record varying between 9 and 13 the major features are a pronounced 15 n increase at the beginning of the deglaciation a maximum from 19 to 10 ka b p thereafter a large decrease during the early holocene and millenial scale oscillations showing an antarctic timing we propose that the record results from an amalgam of low latitude and high latitude processes low latitude processes including a stronger advection signal of heavy nitrates from the denitrifying zones off peru and northern chile would explain the timing of the deglaciation rise and the heaviest values found over this interval excluding the antarctic cold reversal period the overall differences between site 1233 and records from peru and northwest american margins suggest however that the origin of the 15 n signal off chile is largely controlled by hydrologic and climatic changes in the southern ocean we propose that the interplay between nutrient demand in the saz and latitudinal shifts of hydrologic fronts controlled both the concentrations and the isotopic signature of the remaining nitrate delivered to the chile margin then the glacial surface waters of the southern chile margin were likely lower in nitrate concentration and bear a higher 15 n than during interglacial periods

intermittent existence of a southern californian upwelling cell during submillennial climate change of the last 60 kyr 1 application of a high resolution multiproxy approach to a sedimentary section drilled at ocean drilling program site 1017 located under a highly active upwelling cell off point conception california provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr the proxies include bulk sediment major and minor elements organic carbon and carbonate concentrations 15n and planktonic foraminiferal species assemblage and carbon isotope determinations the collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial scale climate oscillations of marine isotope stage mis 3 during that interval the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events however the last glacial maximum was also relatively productive productivity increased dramatically during the bolling warm interval while the allerod and younger dryas were much less productive high coccolithophorid abundance commenced during the earliest holocene after 10 ka the complexity of the productivity response was probably related to interplay between local winds as well as california undercurrent strength

nitrogen isotopic evidence for micronutrient control of fractional no3 utilization in the equatorial pacific during the u s jgofs eqpac program variations in nitrogen isotopic ratio d15n and their control by relative no3 drawdown were examined in detail near surface d15n data clearly conform to rayleigh isotopic fractionation during phytoplankton utilization of no with a fractionation factor of about 5 this isotopic signal both propagates into particulate nitrogen pools and is a persistent large scale characteristic of the system decreasing near surface no3 with distance from the equator strongly correlates with increasing d15n in euphotic zone particulate organic matter pom as well as sinking particles during both surveys 1 el nino and 2 non el nino cruises despite a doubling of no3 accompanying relaxation of el nino conditions d15n values in near surface pom and deeply sinking particles as a function of latitude were similar for the two periods since d15n varies with relative nutrient drawdown and not its concentration this parameter appears to not have varied significantly in both cases about 50 of upwelled no3 was consumed in the immediate vicinity of the equator as estimated from the d15n data the moored sediment trap time series provided a more highly resolved temporal view of the 15n dynamics of this system at the equator and to the south there is little temporal variation in d15n and hence in relative no3 utilization over the 1 yr duration of the program at 28 and 58 n there is a large 5 decrease in d15n during the transition to non el nino conditions in response to the northward movement of no3 rich waters which probably reflects the intensification of the north equatorial current overall no3 utilization at the equator remained between 40 and 60 over the observation period despite large hydrographic and dynamical changes this observation implies a tight control of relative no3 utilization consistent with iron fe limitation since fe is supplied in this region by upwelling relative no3 utilization is likely determined by the product of the ratio of fe to no3 in upwelled waters and the no3 fe utilization ratio given no change in the chemistry of source waters increases in upwelling as observed during the transition away from el nino will affect surface no3 new and export production but it will not affect relative no3 utilization in this light downcore d15n records in the equatorial pacific should reflect past changes in the limitation of no3 drawdown by fe perhaps through changes in equatorial undercurrent chemistry

a cool nutrient enriched eastern equatorial pacific during the mid pleistocene transition this work was supported in part by nsf mgg 1060779 and usssac postcruisesupportforleg202tor s r we thank p rumford and the iodp core repository for providing samples and assistance with xrf core scanning k kelley for analytical assistance and z kerrigan j freedman and a stahl for the help with sample preparation new data will be archived at the ncei paleoceanography data repository

a review of discrete element simulation of ice structure interaction sea ice loads on marine structures are caused by the failure process of ice against the structure the failure process is affected by both the structure and the ice thus is called icestructure int

testing the silica leakage hypothesis with sedimentary opal records from the eastern equatorial pacific over the last 150 kyrs 1 we have measured 230th normalized opal fluxes in several cores from the eastern equatorial pacific eep to test the validity of the silica leakage hypothesis which purports that redistribution of silicic acid from the southern ocean to the low latitudes was responsible for a significant portion of the reduction in atmospheric carbon dioxide co2 during the last glacial period the silica leakage hypothesis predicts higher opal fluxes in the eep and lower opal fluxes in the southern ocean during periods of low atmospheric co2 these predictions are not borne by the sedimentary record during glacial oxygen isotope stage 2 ois 2 13 27 kyrs b p however we find a prominent opal flux maximum in the eep in the middle of ois 3 ca 40 60 kyrs bp coinciding with low opal fluxes in several cores from the subantarctic zone this observation is consistent with silica leakage from the southern ocean to the equatorial upwelling region during ois 3 when both low dust flux and extended sea ice could have contributed to limiting diatom productivity in the southern ocean since this event is not associated with a clear minimum in the vostok ice record of co2 its impact on atmospheric co2 appears to be small

melting of the patagonian ice sheet and deglacial perturbations of the nitrogen cycle in the eastern south pacific local 230 th normalized biogenic vertical fluxes from the chilean continental margin they document in detail the sharp transition from relatively low wcd rates during the last glacial maximum lgm to high ones during the deglaciation and holocene but give no evidence that the glacial interglacial difference of wcd could have been caused by changes in local primary productivity furthermore we found no evidence that changes in ventilation due to samw formation could explain the nitrogen isotope record we present evidence for an alternative mechanism related to the melting of the patagonian ice sheet pis which is consistent with recent published proxy data and the regional physical oceanography

the release of 14 c depleted carbon from the deep ocean during the last deglaciation evidence from the arabian sea article i nfo during the last deglaciation the concentration of co2 in the atmosphere increased and the radiocarbon activity 14 c of the atmosphere declined in two steps corresponding in timing to heinrich stadial 1 and the younger dryas these changes have been attributed to the redistribution of 14 c depleted carbon from the deep ocean into the upper ocean and atmosphere recently reconstructions of 14 c in intermediate waters of the eastern tropical pacific have revealed pulses of very old water during the deglaciation consistent with the release of 14 c depleted carbon from the deep ocean at this time here we present reconstructions of intermediate water 14 c from the northern arabian sea near the coast of oman these reconstructions record significant aging of intermediate waters in the arabian sea during heinrich stadial 1 and to a lesser extent during the younger dryas the timing and magnitude of 14 c depletion in the arabian sea during heinrich stadial 1 is very similar to that previously observed in the eastern north pacific near baja california indicating that similar mechanisms were involved in controlling 14 c at these two sites the most parsimonious explanation of the 14 c records from the arabian sea and baja california remains the release of 14 c depleted carbon from the deep ocean by renewal of upwelling and mixing in the southern ocean these

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

tectonic processes in papua new guinea and past productivity in the eastern equatorial pacific ocean phytoplankton growth in the eastern equatorial pacific ocean today accounts for about half of the new production the fraction of primary production fuelled by externally supplied nutrients in the global ocean the recent demonstration that an inadequate supply of iron limits primary production in this region1 supports earlier speculation that in the past fluctuations in the atmospheric deposition of iron bearing dust may have driven large changes in productivity2 but we argue here that only small 2 nm increases in the iron concentration in source waters of the upwelling equatorial undercurrent are needed to fuel intense diatom production across the entire eastern equatorial pacific ocean episodic increases in iron concentrations of this magnitude or larger were probably frequent in the past because a large component of the undercurrent originates in the convergent island arc region of papua new guinea which has experienced intensive volcanic erosional and seismic activity over the past 16 million years cycles of plankton productivity recorded in eastern equatorial pacific sediments may therefore reflect the influence of tectonic processes in the papua new guinea region superimposed on the effects of global climate forcing

export fluxes of calcite in the eastern equatorial pacific from the last glacial maximum to present 1 the eastern equatorial pacific eep is an important center of biological productivity generating significant organic carbon and calcite fluxes to the deep ocean we reconstructed paleocalcite flux for the past 30 000 years in four cores collected beneath the equatorial upwelling and the south equatorial current sec by measuring ex230th normalized calcite accumulation rates corrected for dissolution with a newly developed proxy for fraction of calcite preserved this method produced very similar results at the four sites and revealed that the export flux of calcite was 30 50 lower during the lgm compared to the holocene the internal consistency of these results supports our interpretation which is also in agreement with emerging data indicating lower glacial productivity in the eep possibly as a result of lower nutrient supply from the southern ocean via the equatorial undercurrent however these findings contradict previous interpretations based on mass accumulation rates mar of biogenic material in the sediment of the eep which have been taken as reflecting higher glacial productivity due to stronger wind driven upwelling

alternating influence of northern versus southern sourced water masses on the equatorial pacific subthermocline during the past 240 ka the eastern equatorial pacific eep is a key area to understand past oceanic processes that control atmospheric co2 concentrations many studies argue for higher nutrient concentrations by enhanced nutrient transfer via southern ocean intermediate water soiw to the low latitude pacific during glacials recent studies however argue against soiw as the primary nutrient source at least during early marine isotope stage 2 mis 2 as proxy data indicate that nutrients are better utilized in the southern ocean under glacial conditions new results from the subarctic pacific suggest that enhanced convection of nutrient rich glacial north pacific intermediate water gnpiw contributes to changes in nutrient concentrations in equatorial subthermocline water masses during mis 2 however the interplay between soiw versus gnpiw and its influence on the nutrient distribution in the eep spanning more than one glacial cycle are still not understood we present a carbon isotope 13c record of subthermocline waters derived from deep dwelling planktonic foraminifera globorotaloides hexagonus in the eep which is compared with published 13c records around the pacific results indicate enhanced influence of gnpiw during mis 6 and mis 2 compared to today with largest contributions of northern sourced intermediate waters during glacial maxima these observations suggest a mechanistic link between relative contributions of northern and southern intermediate waters and past eep nutrient concentrations a switch from increased gnpiw decreased soiw to diminished gnpiw enhanced soiw influence on equatorial subthermocline waters is recognized during glacial terminations and marks changes to modern like conditions in nutrient concentrations and biological productivity in the eep

nitrogen isotope variations in santa barbara basin sediments implications for denitrification in the eastern tropical north pacific during the last 50 000 years nitrogen isotope variations preserved in santa barbara basin sediments are used to evaluate changes in denitrification in the eastern tropical north pacific etnp during the last 50 000 years a significant component of the subsurface waters 100 400 m that presently fill the santa barbara basin is derived from the low oxygen denitrifying zone in the etnp and the nitrate in these waters has a 15n value of 8 9 during the last glacial the 15n values of santa barbara basin sediments were typically 6 7 indicating decreased denitrification in the etnp and a better oxygenated intermediate water mass in the santa barbara basin at this time this reduced denitrification during the last glacial would have increased the pool of fixed nitrogen and may have contributed to the higher productivity previously reported for various regions of the global ocean during this period at the onset of deglaciation sediment 15n values increase by more than 2 indicating increased denitrification in the etnp during younger dryas time 15n values decreased by 3 and record a brief return to better ventilated conditions in the subsurface waters of the etnp this is followed by an increase in 15n to over 9 at 10 000 years ago indicating intense denitrification at the beginning of the holocene

lower export production during glacial periods in the equatorial pacific derived from 231pa 230th xs 0 measurements in deep sea sediments 1 the 231pa 230th xs 0 records obtained from two cores from the western md97 2138 1 25 s 146 24 e 1900 m and eastern ocean drilling program leg 138 site 849 0 11 59 n 110 31 18 w 3851 m equatorial pacific display similar variability over the last 85 000 years i e from isotopic stages 1 to 5a with systematically higher values during the holocene isotopic stage 3 and isotopic stage 5a and lower values approaching the production rate ratio of the two isotopes 0 093 during the colder periods corresponding to isotopic stages 2 and 4 we have also measured the 230th normalized biogenic preserved and terrigenous fluxes as well as major and trace elements concentrations in both cores the 231pa 230th xs 0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial pacific during glacial periods the 231pa 230th xs 0 variations in the western equatorial pacific also seem to be controlled by productivity carbonate and or opal the generally high 231pa 230th xs 0 ratios 0 093 of the profile could be due to opal and or mno2 in the sinking particles the profiles of 231pa 230th xs 0 and 230th normalized fluxes indicate a decrease in exported carbonate and possibly opal during isotopic stages 2 and 4 in md97 2138 using 230th normalized flux we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability

comparison of eastern tropical pacific tex 86 and globigerinoides ruber mg ca derived sea surface temperatures insights from the holocene and last glacial maximum abstract the use of the tex 86 temperature proxy has thus far come to differing results as to whether tex 86 temperatures are representative of surface or subsurface conditions in addition although tex 86 temperatures might reflect sea surface temperatures based on core top holocene values this relationship might not hold further back in time here we investigate the tex 86 temperature proxy by comparing tex 86 temperatures to mg ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical pacific on the cocos and carnegie ridges across the holocene and last glacial maximum core top and holocene tex 86 h temperatures at both study regions agree well within error with the mg ca temperatures of globigerinoides ruber a surface dwelling planktonic foraminifera however during the last glacial maximum tex 86 h temperatures are more representative of upper thermocline temperatures and are offset from g ruber mg ca temperatures by 5 8 c and 2 9 c on the cocos ridge and carnegie ridge respectively this offset between proxies cannot be reconciled by using different tex 86 temperature calibrations and instead we suggest that the offset is due to a deeper export depth of gdgts at the lgm we also compare the degree of glacial cooling at both sites based on both temperature proxies and find that tex 86 h temperatures greatly overestimate glacial cooling especially on the cocos ridge this study has important implications for applying the tex 86 paleothermometer in the eastern tropical pacific

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

pleistocene equatorial pacific dynamics inferred from the zonal asymmetry in sedimentary nitrogen isotopes 1 there is little agreement among models in predicting the average state of the tropical pacific when subjected to enhanced greenhouse gas forcing this uncertainty emphasizes the importance of reconstructing past variability in tropical pacific climate through episodes of significant and estimable radiative forcing thus far efforts along these lines have concentrated primarily on inferences of sea surface temperature variability from deep sea sediments here we offer a different view of the equatorial pacific over the past 1 2 million years myr before and after the mid pleistocene shift in the structure of ice ages the zonal gradient in the nitrogen isotopic composition of sediment across the equatorial pacific reflects nutrient delivery to the surface and by extension ocean dynamical properties over the last 1 2 myr the variability of eastern equatorial pacific nutrient upwelling inferred from relative nitrate utilization was highly correlated with local seasonal insolation by contrast nitrate utilization was insensitive to the 100 000 year cycle that dominated many other aspects of the pleistocene ice ages including greenhouse gas concentrations a strong linear relationship between relative nitrate utilization and seasonal insolation over the past 1 million years suggests a predictable response of one primary determinant of tropical pacific climate change

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

eastern pacific warm pool paleosalinity and climate variability 0 30 kyr multiproxy geologic records of 18o and mg ca in fossil foraminifera from sediments under the eastern pacific warm pool epwp region west of central america document variations in upper ocean temperature pycnocline strength and salinity i e net precipitation over the past 30 kyr although evident in the paleotemperature record there is no glacial interglacial difference in paleosalinity suggesting that tropical hydrologic changes do not respond passively to high latitude ice sheets and oceans millennial variations in paleosalinity with amplitudes as high as 4 practical salinity units occur with a dominant period of 3 5 ky during the glacial deglacial interval and 1 0 1 5 ky during the holocene the amplitude of the epwp paleosalinity changes greatly exceeds that of published caribbean and western tropical pacific paleosalinity records epwp paleosalinity changes correspond to millennial scale climate changes in the surface and deep atlantic and the high northern latitudes with generally higher lower paleosalinity during cold warm events in addition to intertropical convergence zone itcz dynamics which play an important role in tropical hydrologic variability changes in atlantic pacific moisture transport which is closely linked to itcz dynamics may also contribute to hydrologic variations in the epwp calculations of interbasin salinity average and interbasin salinity contrast between the epwp and the caribbean help differentiate long term changes in mean itcz position and atlantic pacific moisture transport respectively

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

elevated foraminifera bound nitrogen isotopic composition during the last ice age in the south china sea and its global and regional implications 1 we report a new foraminifera bound d 15 n fb d 15 n record from the south china sea scs extending back to 42 ka this record shows a 1 2 glacial to interglacial d 15 n decrease with a deglacial d 15 n maximum similar to that observed in many bulk sedimentary d 15 n records and in a caribbean fb d 15 n record the glacial to interglacial d 15 n decrease is smaller than in the caribbean record indicating that at least half of the caribbean d 15 n decrease into the holocene was regional not global supporting the interpretation of a holocene increase in atlantic nitrogen fixation at the same time the glacial to interglacial d 15 n decrease observed in the scs may also be explained as a regional signal of increasing nitrogen fixation into the holocene other aspects of the scs record suggest an effect of physical circulation on fb d 15 n fb d 15 n starts to increase toward its deglacial maximum before the last ice age ends and it continues to decrease through the later holocene in contrast to the more pure glacial deglacial interglacial steps in the caribbean record these changes have parallels in other pacific d 15 n records precessionally driven east asian monsoon records and the slow holocene warming of scs surface waters in addition the scs record exhibits two one point high d 15 n spikes in multiple foraminiferal species that coincide with apparent hydrographic events thinning or weakening of the thermocline in the late glacial and early holocene as well as during the noted events may have yielded a higher d 15 n for thermocline nitrate and thus a higher fb d 15 n

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

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

late quaternary variability of sedimentary nitrogen isotopes in the eastern south pacific ocean 1 we present high resolution bulk sedimentary 15n data from the southern edge of the present day oxygen minimum zone of the eastern south pacific the record is interpreted as representing changes in water column nitrogen removal during the last 70 000 years we found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales these fluctuations were not related to other millennial scale changes like the northern hemisphere s dansgaard oeschger climate swings or local changes in primary productivity so appear to be dictated by the southern hemisphere s climate rhythm this is preliminarily corroborated by an overall agreement between our 15n data and the sedimentary proxy of ice sheet dynamics in patagonia which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern south pacific intermediate waters finally potential implications on late quaternary changes in atmospheric co2 concentrations are discussed

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

centennial to millennial scale changes in oxygenation and productivity in the eastern tropical south pacific during the last 25 000 years oxygen minimum zones omz have expanded in all tropical oceans during the last 50 years resulting in habitat contraction and considerable changes in marine biogeochemistry however for a better understanding of the omz dynamics under the current climate change two questions are relevant 1 how do the magnitude and temporal changes in oceanic dissolved oxygen of the last few decades compare to the natural variability on longer timescales and 2 what were the local and remote factors driving omz changes in the past in the present study we use a stacked record covering the last 25 kyr from the eastern tropical south pacific etsp omz to reconstruct changes in oxygenation and productivity we use a suite of proxies including the presence of laminations redox sensitive metals u mo re ni and cu total organic carbon and 15 n measurements water column denitrification and sediment redox conditions show pronounced centennial to millennial scale variability during the last 25 kyr with oxygenation levels as low as at present global cold periods at different timescales such as the last glacial maximum 23 19 kyr bp and the little ice age 1500 1850 ad were associated with a weak omz and low export production while warm intervals such as the deglaciation part of the medieval climate anomaly and the last 100 years are associated with a stronger omz and high export production water column denitrification and sediment redox conditions were strongly coupled during the last 25 kyr bp apart from one remarkable exception during the antarctic cold reversal sediments were less reducing but the water column denitrification was high resulting in a strong but shallow omz this may have been produced by an enhanced antarctic intermediate water flow contrary to our expectations and modeling predictions for the next few decades we observe a weak etsp omz during the warm mid holocene which may have been the result of a stronger walker circulation that brought oxygen rich waters to intermediate depths off peru via equatorial undercurrents in combination with other paleoceanographic reconstructions our results show that oxygenation variability in the etsp omz was influenced by ocean circulation changes in the tropical pacific high latitude oceanographic and climatic changes and local productivity

productivity patterns in the equatorial pacific over the last 30 000 years the equatorial pacific traverses a number of productivity regimes from the highly productive coastal upwelling along peru to the near gyre like productivity lows along the international dateline making it an ideal target for investigating how biogeochemical systems respond to changing oceanographic conditions over time however conflicting reconstructions of productivity during periods of rapid climate change like the last deglaciation render the spatiotemporal response of equatorial pacific productivity ambiguous in this study surface productivity since the last glacial period 30 000 years ago is reconstructed from seven cores near the line islands central equatorial pacific and integrated with productivity records from across the equatorial pacific three coherent deglacial patterns in productivity are identified 1 a monotonic glacial holocene increase in productivity primarily along the equator associated with increasing nutrient concentrations over time 2 a deglacial peak in productivity 15 000 years ago due to transient entrainment of nutrient rich southern sourced deep waters and 3 possible precessional cycles in productivity in the eastern equatorial pacific that may be related to intertropical convergence zone migration and potential interactions with el nino southern oscillation dynamics these findings suggest that productivity was generally lower during the glacial period a trend observed zonally across the equatorial pacific while deglacial peaks in productivity may be prominent only in the east

evidence for changes in subsurface circulation in the late eocene equatorial pacific from radiolarian bound nitrogen isotope values microfossil bound organic matter represents an important archive of surface ocean environmental information sedimentary nitrogen n isotope reconstructions of surface nitrate consumption and nitrogen source changes are made using fossil diatom autotrophs and planktic foraminiferal heterotrophs bound organic matter with success however because diatoms and planktic foraminifera are poorly preserved and sedimentary organic matter content is near zero during the late eocene our ability to examine nutrient dynamics across this important climate transition is limited here we present new data exploring the use of n isotope records from radiolarian tests a comparison of surface ocean nitrate and core top bulk and radiolarian n isotope values as 15n from the equatorial pacific indicates that radiolarian n records 15n variability with fidelity but that a significant offset exists between bulk sedimentary and diatom 15n values and those measured from radiolarians 7 1 1 1 a downcore profile of radiolarian 15n values is compared to siliceous microfossil assemblage changes across the eocene oligocene boundary average of radiolarian bound 15n values is 0 5 2 0 which when corrected using the offset derived from the modern surface samples suggests that the mean nitrogen isotopic composition of the early cenozoic eastern pacific was not significantly different from today the overall trend of decreasing 15n values with decreasing export productivity is consistent with either a regional decline in pelagic denitrification or a large scale change in nutrient sources to the eastern equatorial pacific eep both linked to the cooling climate and changing intermediate water circulation decreasing low 15n values cooccur with high radiolarian species turnover at 35 5 and 34 ma suggestive of a significant ecological change in the eep consistent with cooling and water mass distribution changes the preliminary results suggest that radiolarian bound organic nitrogen represents another promising archive and underscores the fact that the different microfossil fractions must be separated to ensure robust results

sources of fe to the equatorial pacific ocean from the holocene to miocene abstract biological productivity in the modern equatorial pacific ocean a region with high nutrients and low chlorophyll is currently limited by the micronutrient fe in order to test whether fe was limiting in the past and to identify potential pathways of fe delivery that could drive fe fertilization i e dust delivery from eolian inputs vs fe supplied by the equatorial undercurrent we chemically isolated the terrigenous material from sediment along a cross equatorial transect in the central equatorial pacific at 140 w and at ocean drilling program site 850 in the eastern equatorial pacific we quantified the contribution from each potential fe bearing terrigenous source using a suite of chemical and isotopic discrimination strategies as well as multivariate statistical techniques we find that the distribution of the terrigenous sources i e asian loess south american ash papua new guinea and ocean island basalt varies through time latitude and climate regardless of which method is used to determine accumulation rate there also is no relationship between flux of any particular fe source and climate moreover there is no connection between a particular fe source or pathway eolian vs undercurrent to total productivity during the last glacial maximum pleistocene glacial episodes and the miocene biogenic bloom this would suggest an alternative process such as an interoceanic reorganization of nutrient inventories may be responsible for past changes in total export in the open ocean rather than simply fe supply from dust and or equatorial undercurrent processes additionally perhaps a change in fe source or flux is related to a change in a particular component of the total productivity e g the production of organic matter calcium carbonate or biogenic opal

export production fluctuations in the eastern equatorial pacific during the pliocene pleistocene reconstruction using barite accumulation rates export production is an important component of the carbon cycle modulating the climate system by transferring co2 from the atmosphere to the deep ocean via the biological pump here we use barite accumulation rates to reconstruct export production in the eastern equatorial pacific over the past 4 3 ma we find that export production fluctuated considerably on multiple time scales export production was on average higher 51 g c m 2 yr 1 during the pliocene than the pleistocene 40 g c m 2 yr 1 decreasing between 3 and 1 ma from more than 60 to 20 g c m 2 yr 1 followed by an increase over the last million years these trends likely reflect basin scale changes in nutrient inventory and ocean circulation our record reveals decoupling between export production and temperatures on these long million years time scale on orbital time scales export production was generally higher during cold periods glacial maxima between 4 3 and 1 1 ma this could be due to stronger wind stress and higher upwelling rates during glacial periods a shift in the timing of maximum export production to deglaciations is seen in the last 1 1 million years results from this study suggest that in the eastern equatorial pacific mechanisms that affect nutrient supply and or ecosystem structure and in turn carbon export on orbital time scales differ from those operating on longer time scales and that processes linking export production and climate modulated oceanic conditions changed about 1 1 million years ago these observations should be accounted for in climate models to ensure better predictions of future climate change

controls on sedimentary nitrogen isotopes along the chile margin chilean margin sedimentary n isotope records have been the focus of paleoceanographic studies examining the extent of water column denitrification in the eastern south pacific in the past here we use 15n 14n of nitrate and surface sedimentary n along the chilean coast to investigate the relative contributions of water column denitrification and surface nitrate assimilation by phytoplankton to the sedimentary n isotope record off northern and central chile subsurface enrichment of 15no3 is associated with the lowest oxygen concentrations and maximum nitrate deficits the product of water column denitrification locally at 21 s and through the transport of denitrified waters to the south while elevated the 15n of pycnocline nitrate shows no distinct trend with distance from the omz and is nearly homogenous within the shallow subsurface layer presumably due to lateral circulation along the margin moreover an isotopically depleted and relatively uniform layer exists within the shallow subsurface possibly as a result of the remineralization of newly fixed nitrogen that may work to further homogenize the 15n of the upwelling nitrate whereas the high 15n of sedimentary n in the region is clearly a product of denitrification and its isotopic imprint on nitrate along the margin the northward increase in sedimentary 15n from higher southern latitudes also reflects the degree of surface layer nitrate consumption by phytoplankton the northward increase in sedimentary 15n corresponds to a regional decrease in the surface nitrate concentration and isotopic fractionation during nitrate assimilation is apparent in shallow nitrate 15n a comparison of the 15n in shallow subsurface nitrate and sedimentary n suggests that north of 30 s nearly complete nitrate consumption causes the 15n of sediments to converge on that of the nitrate supply such that denitrification should be the dominant signal in downcore 15n records from these latitudes moreover the lateral homogeneity of the denitrification signal in the subsurface within this region suggests that such records will provide robust reconstructions of denitrification intensity

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone

spatial reorganization in the equatorial divergence in the eastern tropical pacific during the last 150 kyr 1 high resolution downcore records of bulk sediment nitrogen isotopes 15n and organic carbon corg contents from multiple eastern tropical pacific sites show remarkable uniformity during the last glacial stage whereas during the holocene and the last interglacial period they diverge significantly the close covariation of 15n records during glacial stages points toward regional changes in the background isotopic signal of the inorganic nitrate pool likely caused by variations in the denitrification rates in the nearby suboxic zones on the other hand we attribute the divergence of the 15n and corg records during interglacial periods to a spatial reorganization in the equatorial divergence we posit a southward displacement of the zone of strongest upwelling in the south equatorial current to explain the reduced productivity and higher nitrate consumption recorded at the equator during warmer intervals