changing atmospheric δ14c and the record of deep water paleoventilation ages we propose a new calculation method to better estimate the deep water ventilation age from benthic planktonic foraminifera 14 c ages our study is motivated by the fact that changes in atmospheric 14 c through time can cause contemporary benthic and planktonic foraminifera to have different initial 14 c values this effect can cause spurious ventilation age changes to be interpreted from the geologic data using a new calculation method 14 c projection ages we recalculate the data from the pacific ocean contrary to previous results we find that the pacific intermediate and deep waters were about 600 years older than today at the last glacial maximum in addition there are possible signals of ventilation age change prior to ice sheet melting and at the younger dryas however the data are still too sparse to constrain these ventilation transients

reefs of the deep the biology and geology of cold water coral ecosystems coral reefs are generally associated with shallow tropical seas however recent deep ocean exploration using advanced acoustics and submersibles has revealed unexpectedly widespread and diverse coral ecosystems in deep waters on continental shelves slopes seamounts and ridge systems around the world advances reviewed here include the use of corals as paleoclimatic archives and their biogeological functioning biodiversity and biogeography threats to these fragile long lived and rich ecosystems are mounting the impacts of deep water trawling are already widespread and effects of ocean acidification are potentially devastating

mediterranean sea surface radiocarbon reservoir age changes since the last glacial maximum sea surface reservoir ages must be known to establish a common chronological framework for marine continental and cryospheric paleoproxies and are crucial for understanding ocean continent climatic relationships and the paleoventilation of the ocean radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one 400 years during most of the past 18 000 carbon 14 years however reservoir ages increased by a factor of 2 at the beginning of the last deglaciation this is attributed to changes of the north atlantic thermohaline circulation during the massive ice discharge event heinrich 1

isotopic composition of carbonate bound organic nitrogen in deep sea scleractinian corals a new window into past biogeochemical change over the last two decades the skeletal remains of deep sea corals have arisen as a geochemical archive of pleistocene oceanographic change here we report the exploration of the isotopic composition of the carbonate bound organic nitrogen hereafter cb 15 n in the deep sea scleractinian coral desmophyllum dianthus as a possible tool for reconstructing past changes in the ocean nitrogen cycle the measurement protocol is adapted from a high sensitivity method for foraminifera shell bound 15 n we explored the variability of cb 15 n within specimens among corals collected at different depths in a given ocean region and among different ocean regions modern d dianthus cb 15 n is strongly correlated with the 15 n of n export as estimated from sediment traps shallow subsurface nitrate and surface sediments suggesting that cb 15 n is a reliable proxy for 15 n of n export d dianthus cb 15 n is consistently 8 9 8 9 higher than 15 n of n export indicating that d dianthus acquires its nutrition primarily from suspended particulate organic matter pom that derives from sinking pom not directly from sinking pom

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

glacial to deglacial changes in north atlantic meltwater advection and deep water formation centennial to millennial scale 14c records from the azores plateau abstract the last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric co2 and 14c we employed the 14c plateau tuning technique to a centennial scale planktic 14c record of core md08 3180 retrieved s w of the azores islands at 3060 m water depth to establish both a new standard of absolute age control and a record of past 14c reservoir ages of ocean surface waters both 18o minima of g bulloides and high planktic reservoir ages of 1600 to 2170 yr suggest two major melt water incursions that reached from the labrador sea up to the subtropics over heinrich stadial 1 hs 1 in parallel we established a record of apparent benthic ventilation ages that add the planktic 14c reservoir ages together with the benthic planktic 14c age difference at the site and time of deposition a sum finally adjusted to past changes in atmospheric 14c that occurred since the time of deep water formation near the azores apparent deep water ages of the last glacial maximum were as low as 340 740 yr which suggests a lateral advection of young north atlantic deep waters nadw from subpolar regions south of iceland in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep water formation during hs 1 local benthic ventilation ages increased up to 2200 2550 yr thus suggest an incursion of old southern source deep waters an unstable regime that was interrupted by brief pulses of nadw incursion near 16 15 6 cal ka and most salient near 14 9 14 7 ka

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

growth rates of the deep sea scleractinia desmophyllum cristagalli and enallopsammia rostrata with uranium rich skeletons and density bands similar to their surface coral counterparts deep sea scleractinia are a promising archive of past climate to improve the utility of fossil samples as monitors of deep ocean variability we have measured 210 pb and 226 ra activities in a variety of modern specimens to constrain the range of growth rates mechanical and chemical cleaning of each sample are required to isolate the radionuclides trapped in the coral skeleton from surface contaminants however in many cases mechanically cleaned samples show the same overall growth rate as parallel transects of samples subjected to the full chemical and mechanical cleaning but with much higher overall activities three samples of desmophyllum cristagalli show a range of vertical extension rates from 0 5 mm yr to 2 mm yr consistent with previous estimates a single enallopsammia rostrata from the north atlantic is over 100 years old its average radial growth rate is 0 07 mm yr and the clear banding in this direction is not consistent with annual periodicity a minimum vertical extension rate of 5 mm yr is estimated from the 210 pb data both of these species are found in the fossil record and with the growth rates determined here can record about 100 years of climate change the growth rates will allow the reconstruction of climate at subdecadal resolution in d cristagalli and even higher resolution in e rostrata d 2004 elsevier b v all rights reserved

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

environmental and biological controls on mg and li in deep sea scleractinian corals abstract deep sea scleractinian corals precipitate aragonite skeletons that provide valuable archives of past ocean conditions during calcification biological mediation causes variability in trace metal incorporation and isotopic ratios of the aragonite such that signals caused by environmental controls can be overwhelmed this complicates the interpretation of geochemical proxies used for paleo reconstructions in this study we examine the environmental controls on the mg li ratio of 34 individuals from seven genera of deep sea scleractinian corals desmophyllum balanophyllia caryophyllia enallopsammia flabellum trochocyanthus and lophelia in addition we examine the microscale distributions of mg and li in desmophyllum and balanophyllia using laser ablation inductively coupled plasma mass spectrometry la icp ms both mg ca and li ca ratios increased by more than a factor of two in the center of calcification regions compared to the outer fibrous regions of the coral skeleton as a result replicate 10 mg subsamples of coral show less variability in the mg li ratio than mg ca microscale mg and li results are consistent with rayleigh type incorporation of trace metals with additional processes dominating the composition within centers of calcification comparison of mg li to seawater properties near the site of collection shows that the ratio is not controlled by either carbonate ion or salinity it appears that temperature is the major control on the mg li ratio for all 34 samples the temperature correlation r2 0 62 is significantly better than for mg ca r2 0 06 for corals of the family caryophyllidae the r2 value increases to 0 82 with the exclusion of one sample that was observed to have an altered chalky texture despite this excellent correlation the scatter in the data suggests that the mg li ratio of deep sea corals cannot be used to reconstruct temperature to better than approximately 1 6 c without better temperature control and additional calibration points on modern coral samples

beyond the bipolar seesaw toward a process understanding of interhemispheric coupling abstract the thermal bipolar ocean seesaw hypothesis was advanced by stocker and johnsen 2003 as the simplest possible thermodynamic model to explain the time relationship between dansgaard oeschger do and antarctic isotope maxima aim events in this review we combine palaeoclimate observations theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of aim events we present four main results 1 changes in atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and pacific ocean this compensation is an integral part of interhemispheric coupling with a major influence on the global pattern of climate anomalies 2 we support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean to the north of the antarctic circumpolar current acc not the commonly assumed southern ocean 3 energy budget analysis indicates that the process driving antarctic warming during aim events is an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the southern ocean 4 the antarctic sea ice retreat is itself driven by eddy heat fluxes across the acc amplified by sea ice albedo feedbacks the lag of antarctic warming after amoc collapse reflects the time required for heat to accumulate in the ocean interior north of the acc predominantly the upper 1500 m before it can be mixed across this dynamic barrier by eddies

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

effects of seawater ph and biomineralization on the boron isotopic composition of deep sea bamboo corals abstract the ocean is currently absorbing excess carbon from anthropogenic emissions leading to reduced seawater ph termed ocean acidification instrumental records of ocean acidification are unavailable from well ventilated areas of the deep ocean necessitating proxy records to improve spatio temporal understanding on the rate and magnitude of deep ocean acidification here we investigate boron carbon and oxygen isotopes on live collected deep sea bamboo corals genus keratoisis from a phtot range of 7 5 8 1 these analyses are used to explore the potential for using bamboo coral skeletons as archives of past deep sea ph and to trace anthropogenic acidification in the subsurface north atlantic ocean 850 2000 m water depth boron isotope ratios of the most recently secreted calcite of bamboo coral skeletons are close to the calculated isotopic composition of borate anion in seawater 11bborate for north atlantic corals and 1 2 higher than 11bborate for pacific corals within individual coral skeletons carbon and oxygen isotopes correlate positively and linearly a feature associated with vital effects during coral calcification 11b variability of 0 5 2 is observed within single specimens which exceeds the expected anthropogenic trend in modern north atlantic corals 11b values are generally elevated in pacific corals relative to 11bborate which may reflect ph driven physiological processes aiding coral calcification in environments unfavorable for calcite precipitation elevated 11b values are also observed proximal to the central axis in multiple atlantic and pacific specimens relative to 11bborate which might reflect ontogenetic variability in calcification rates although the observed boron isotope variability is too large to resolve the present anthropogenic ocean acidification signal at the studied depths in the north atlantic 0 03 0 07 ph units ph changes 0 1 units might still be reconstructed using 11b measurements in bamboo corals

deep sea corals off brazil verify a poorly ventilated southern pacific ocean during h2 h1 and the younger dryas abstract simultaneous 14 c and th u dating of deep sea corals are useful for reconstructing the intensity of deep ocean circulation in the past as they deliver the time between the gas exchange of the water with the atmosphere and the incorporation of the 14 c in the carbonates adkins and boyle 1997 adkins et al 1998 mangini et al 1998 th u ages of deep sea corals sampled in sediment cores from locations off the coast of brazil bathed by antarctic intermediate water at depths between 600 and 800 m group close to heinrich events h2 h1 and the younger dryas the 14 c of the water bathing the corals starts to decrease approximately 2 kyr before the heinrich events and decreases to values 400 lower than the corresponding back tracked atmospheric values the timing and the magnitude of the decrease is similar to that observed in intermediate water in the n pacific off baja california marchitto et al 2007 and in the eastern pacific stott et al 2009 high ventilation ages partly exceeding 4000 years are an unambiguous indication for a reduction of north atlantic deep water formation during h2 h1 and the yd as deduced from higher 231 pa 230 th activity ratios and from end in n atlantic ocean sediments mcmanus et al 2004 pahnke et al 2008 yu et al 1996 they also could indicate a poorly oxygenated southern pacific ocean at the end of the heinrich events

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

glacial ventilation rates for the deep pacific ocean 1 a key constraint in attempts to reconstruct the patterns and rates of the ocean s thermohaline circulation during the last glacial period is the difference between the 14c to c ratio in surface and deep water while imperfect it is our best index of past deep sea ventilation rates in this paper we review published ventilation rate estimates based on the measured radiocarbon age difference between coexisting benthic and planktic foraminifera from glacial age pacific sediments we also present new results from a series of eastern equatorial pacific sediment cores the conclusion is that the scatter in these results is so large that the apparent 14c age of glacial deep pacific water could lie anywhere between double and half today s further it is not clear what is responsible for the wide scatter in the radiocarbon results

uranium series dating of marine and lacustrine carbonates of the possible uranium series dating schemes the most important and most widely applied to marine carbonates is 230th dating with 231pa dating playing an increasingly important role for this reason this review will focus on these two methods 230th dating also referred to as u th dating or 238u 234u 230th dating involves calculating ages from radioactive decay and ingrowth relationships among 238u 234u and 230th 232th is also typically measured as a long lived essentially stable index isotope over the time scales relevant to 230th dating at present 230th dating can in principle be used to date materials as young as 3 years and in excess of 600 000 years edwards et al 1987a 1993 edwards 1988 see stirling et al 2001 for an example of dating corals in excess of 600 000 years old 231pa dating also referred to as u pa dating involves calculating ages from the ingrowth of 231pa from its grandparent 235u at present 231pa dating can be used to date materials as young as 10 years and as old 250 000 years edwards et al 1997 230th dating covers all of the 231pa time range and more with somewhat higher precision and is therefore the method of choice if a single method is applied however the combination of 231pa and 230th dating is of great importance in assessing possible diagenetic mobilization of the pertinent nuclides and thereby the accuracy of the ages allegre 1964 ku 1968 even if the primary age exceeds the 250 000 year limit of 231pa dating the combined methods can be used to assess the degree to which the samples have remained closed over the past 250 000 years e g edwards et al 1997 thus

holocene shifts in sub surface water circulation of the north east atlantic inferred from nd isotopic composition in cold water corals abstract variations of the sub polar gyre spg and the sub tropical gyre stg circulation during the holocene are believed to be related to regional and global climate over this time period to improve our understanding of these phenomena we provide new constraints on variations in surface circulation patterns using neodymium isotopes end on precisely u th dated coral fragments of l pertusa the fragments were retrieved from two sediment cores taken from cold water coral cwc mounds at 127 134 m water depth in the mingulay reef complex located on the western british continental shelf the results have been combined with end analyzed on seawater samples from two stations located on the continental shelf and margin in order to establish whether end is a reliable proxy of the ocean circulation variations and notably of the relative contribution of water originating from the spg and stg end values in cwcs from the mingulay reef complex range from 14 5 0 4 to 11 8 0 3 highlighting two major variations unradiogenic end values 14 5 0 4 indicate a higher contribution of water from the spg around 2 8 ka conversely more radiogenic values at 3 4 ka 11 8 0 3 point to a declining spg strength accompanied by stronger northward penetration of stg water along the western european margin transported by the shelf edge current sec and or cooler and fresher waters from the interior seas the eastward extension of the spg at 2 8 ka is associated with lower 14c reservoir age 200 yrs compared to periods associated with a higher contribution of stg waters this indicates that 14c reservoir ages are mainly a function of vertical mixing of the sub surface of the ocean as stronger vertical ventilation is not associated with a higher proportion of local radiogenic surface water we hypothesize it could represent vertical ventilation in the north eastern atlantic active spg is associated with a better ventilation of the water masses within the spg and warmer climatic conditions in northern europe and in the eastern norwegian sea linked to an intensification of the surface limb of the amoc

radiocarbon reservoir age of high latitude north atlantic surface water during the last deglacial the radiocarbon reservoir age of high latitude north atlantic ocean surface water is essential for linking the continental and marine climate records and is expected to vary according to changes in north atlantic deep water nadw production measurements from this region also provide important input and or tests of oceanic radiocarbon using 3 d global ocean circulation models here we present a surface water radiocarbon reservoir age record of the high latitude western north atlantic for the deglacial period via the use of fossil cold water corals growing in waters that are rapidly exchanged with nearby surface waters the reservoir age of high latitude north atlantic surface waters was computed from the radiocarbon age difference between our radiocarbon calibration record http radiocarbon ldeo columbia edu and our marine radiocarbon data 230th 234u 238u dates provide the absolute coral ages our high latitude north atlantic ocean reservoir age data combined with recalculated reservoir ages based on published coexisting terrestrial and marine material and vedde ash radiocarbon dates from central and eastern north atlantic show modern values 380 140 year n 14 during the bolling and allerod warm period and a 200 year increase in reservoir age 590 130 year n 10 during the entire younger dryas yd cold episode the reservoir age then decreased to 270 20 year n 2 at the preboreal yd transition although the dates are too sparse for us to be confident in this estimate we are not able to resolve the timing of the transition to increased reservoir ages from the mid allerod to the yd due to the relatively small change and correspondingly large uncertainty in the estimates the atmospheric 14c record derived from our atmospheric radiocarbon record displays a 40 per mil increase from 12 900 to 12 650 cal years bp coincident with the shift to high reservoir ages in the early yd cold event intrusion of 14c depleted antarctic intermediate water aaiw to the high latitude north atlantic and reduction of nadw formation are possible causes for the coincident shift to high reservoir ages in the north atlantic surface ocean and increased atmospheric 14c during the beginning of the yd event

precise th u dating of small and heavily coated samples of deep sea corals marine carbonate skeletons like deep sea corals are frequently coated with iron and manganese oxides hydroxides which adsorb additional thorium and uranium out of the sea water a new cleaning procedure has been developed to reduce this contamination in this further cleaning step a solution of na2edta na2h2tb and ascorbic acid is used which composition is optimised especially for samples of 20 mg of weight it was first tested on aliquots of a reef building coral which had been artificially contaminated with powdered ferromanganese nodule applied on heavily contaminated deep sea corals scleractinia it reduced excess 230th by another order of magnitude in addition to usual cleaning procedures the measurement of at least three fractions of different contamination together with an additional standard correction for contaminated carbonates results in th u ages corrected for the authigenic component a good agreement between th u and 14c ages can be achieved even for extremely coated corals

dynamic intermediate ocean circulation in the north atlantic during heinrich stadial 1 a radiocarbon and neodymium isotope perspective the last deglaciation was characterised by a series of millennial scale climate events that have been linked to deep ocean variability while often implied in interpretations few direct constraints exist on circulation changes at mid depths here we provide new constraints on the variability of deglacial mid depth circulation using combined radiocarbon and neodymium isotopes in 24 north atlantic deep sea corals their aragonite skeletons have been dated by uranium series providing absolute ages and the resolution to record centennial scale changes while transects spanning the lifetime of a single coral allow sub centennial tracer reconstruction our results reveal that rapid fluctuations of water mass sourcing and radiocarbon affected the mid depth water column 1 7 2 5 km on timescales of less than 100 years during the latter half of heinrich stadial 1 the neodymium isotopic variability 14 5 to 11 0 ranges from the composition of the modern northern sourced waters towards more radiogenic compositions that suggest the presence of a greater southern sourced component at some times however in detail simple two component mixing between well ventilated northern sourced and radiocarbon depleted southern sourced water masses cannot explain all our data instead corals from 15 0 ka and 15 8 ka may record variability between southern sourced intermediate waters and radiocarbon depleted northern sourced waters unless there was a major shift in the neodymium isotopic composition of the northern endmember in order to explain the rapid shift towards the most depleted radiocarbon values at 15 4 ka we suggest a different mixing scenario involving either radiocarbon depleted deep water from the greenland iceland norwegian seas or a southern sourced deep water mass since these mid depth changes preceded the bolling allerod warming and were apparently unaccompanied by changes in the deep atlantic they may indicate an important role for the intermediate ocean in the early deglacial climate evolution

constraints on deep water formation from the oceanic distributions of 10be 1 an analysis of the oceanic distribution of cosmogenic 10be shows that deep waters are formed by descending of cold dense surface waters at a rate of 18 sv 106 m3 s 1 in the northern north atlantic and 21 sv of which 17 sv enters the pacific in the antarctic over the last mixing cycle of 800 years lending support to the estimates based on radiocarbon and nutrient distributions it also indicates that deep water production in the northern north atlantic is 50 higher averaging over the recent 100 years than over the last mixing cycle suggesting a possible increase in the thermohaline ventilation of the north atlantic during the past century

deep sea coral evidence for rapid change in ventilation of the deep north atlantic 15 400 years ago coupled radiocarbon and thorium 230 dates from benthic coral species reveal that the ventilation rate of the north atlantic upper deep water varied greatly during the last deglaciation radiocarbon ages in several corals of the same age 15 41 0 17 thousand years and nearly the same depth 1800 meters in the western north atlantic ocean increased by as much as 670 years during the 30 to 160 year life spans of the samples cadmium calcium ratios in one coral imply that the nutrient content of these deep waters also increased our data show that the deep ocean changed on decadal centennial time scales during rapid changes in the surface ocean and the atmosphere

the pacemaker always rings twice we generated new long high resolution climate proxy records from deep sea drilling project dsdp sites 607 and 609 in the subpolar north atlantic over the interval 225 970 ka which have pronounced variability at periods f 1 7 kyr variance in our north atlantic climate proxy records is shown using bispectral and cross bispectral methods to be explainable as harmonics and or combination tones of orbital scale climatic variability of the north atlantic region itself thus the timing and amplitude of high frequency climate change in the north atlantic region appears to be a nonlinear function of variations in high latitude climate at milankovitch frequencies

south atlantic intermediate water advances into the north east atlantic with reduced atlantic meridional overturning circulation during the last glacial period the nd isotopic composition end of seawater and cold water coral cwc samples from the gulf of cadiz and the alboran sea at a depth of 280 827 m were investigated in order to constrain middepth water mass dynamics within the gulf of cadiz over the past 40 ka end of glacial and holocene cwc from the alboran sea and the northern gulf of cadiz reveals relatively constant values 8 6 to 9 0 and 9 5 to 10 4 respectively such values are similar to those of the surrounding present day middepth waters from the mediterranean outflow water mow end 9 4 and mediterranean sea water msw end 9 9 in contrast glacial end values for cwc collected at thermocline depth 550 827 m in the southern gulf of cadiz display a higher average value 8 9 0 4 compared to the present day value 11 7 0 3 this implies a higher relative contribution of water masses of mediterranean msw or south atlantic origin east antarctic intermediate water eaaiw our study has produced the first evidence of significant radiogenic end values 8 at 19 23 24 and 27 ka which are coeval with increasing iceberg discharges and a weakening of atlantic meridional overturning circulation amoc since mow end values remained stable during the last glacial period it is suggested that these radiogenic end values most likely reflect an enhanced northward propagation of glacial eaaiw into the eastern atlantic basin

a scheme for improving scatterometer surface wind fields a method is presented for improving quikscat surface wind fields the university of washington planetary boundary layer model is used to retrieve a surface pressure field from any swath of quikscat surface wind vectors an alternate set of surface wind vectors is computed from the newly calculated pressure field the latter can be smoothed and the process can be iterated new surface wind vectors can be calculated where ambiguity removal fails and where measurements are missing the present methodology preserves boundary layer dynamics and is an improvement over a statistical filter

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

a deep sea coral record of north atlantic radiocarbon through the younger dryas evidence for intermediate water deepwater reorganization requires the existence of large mobile gradients of d 14 c in the ocean during the younger dryas the d 14 c water column profile from keigwin 2004 provides direct evidence for the presence of one such gradient at the beginning of the younger dryas 12 9 ka with a 100 offset between shallow 2400 m and deep water our early younger dryas data are consistent with this profile and also show a d 14 c inversion with 35 more enriched water at 2400 m than at 1700 m this feature is probably the result of mixing between relatively well 14 c ventilated northern source water and more poorly 14 c ventilated southern source intermediate water which is slightly shallower over the rest of the younger dryas our intermediate water deepwater coral d 14 c data gradually increase while the atmosphere d 14 c drops for a very brief interval at 12 0 ka and at the end of the younger dryas 11 5 ka intermediate water d 14 c 1200 m approached atmospheric d 14 c these enriched d 14 c results suggest an enhanced initial d 14 c content of the water and demonstrate the presence of large lateral d 14 c gradients in the intermediate deep ocean in addition to the sharp vertical shift at 2500 m the transient d 14 c enrichment at 12 0 ka occurred in the middle of the younger dryas and demonstrates that there is at least one time when the intermediate deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records

rapid climate change in the north atlantic during the younger dryas recorded by deep sea corals research on global climate change has increasingly focused on rapid century scale and decadal changes one such climate shift the younger dryas cooling event1 took place during the last deglaciation from 13 000 to 11 700 years bp climate records from greenland ice cores and north atlantic sediment cores show high frequency fluctuations implying significant 5 c shifts in temperature at this time taking place within 50 100 years ref 2 the origin of the younger dryas has recently been attributed to a reduction or cessation of deep water production in the north atlantic and a concurrent lessening of the heat flux from low latitudes3 4 the role of intermediate waters 1 000 2 000 m depth is less certain however because climate proxies for this ocean reservoir are rare and ambiguous here we report on the use of a new climate archive deep sea corals from orphan knoll 1 600m depth in the northwestern atlantic ocean the oxygen isotope ratios in the coral skeletons accurately dated by the 230th 234u chronometric method change markedly coincident with the initiation of the younger dryas suggesting that there were profound changes in intermediate water circulation at this time

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

in situ measurements of oxygen isotopic composition in deep sea coral lophelia pertusa re examination of the current geochemical models of biomineralization abstract we present ion microprobe measurements of oxygen isotopic compositions in the deep sea coral lophelia pertusa compared to bulk skeletal aragonite fibres the emz early mineralization zone near the inside of the calyx was systematically depleted in 18 o rayleigh fractionation from a semi closed fluid reservoir does not explain this and other geochemical differences furthermore ph values estimated from skeletal 11 b data are inconsistent with the idea that emz or centres of calcification 18 o depletion reflects a more alkaline calcification environment our data combined with microstructural and geochemical observations indicate that the aragonitic fibres and emz are formed by a compartmentalized mineralization calicoblastic ectoderm which exerts strong biological control on the composition of the skeleton hence we propose a new model whereby amorphous calcium carbonates acc are precursors to the emz whereas the fibre precipitation is probably governed by kinetic processes

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

biogeochemical controls on palaeoceanographic environmental proxies a review scientific observations of our oceans and climate go back no more than a couple of hundred years most of our information about the evolution of earth s ocean climate system relies instead on proxies primarily measurements of sediment components that respond to changes in environmental parameters this paper provides an overview of some of the most important biological and geochemical proxies and outlines their contribution to our understanding of the ocean climate system we also discuss some of the challenges that need to be overcome to obtain accurate records these include better understanding of the controls on the mechanisms of biomineralization the impacts of post depositional dissolution and diagenesis on primary proxy relationships proxy validation and analytical considerations

uranium series and radiocarbon geochronology of deep sea corals implications for southern ocean ventilation rates and the oceanic carbon cycle we present new uranium series and radiocarbon measurements for deep sea corals from the southern ocean these data are used to reconstruct ventilation ages both at present and at the end of the last glacial period approximately 16 500 years ago we apply an improved two component mixing approach to correct uranium series dates for contaminant thorium and protactinium present in oxide coatings calculated seawater radiocarbon values for contemporary samples decrease with depth in the water column and agree with direct seawater radiocarbon measurements for this area this indicates that deep sea corals can accurately record seawater radiocarbon distributions two of three glacial samples experienced open system uranium series systematics however a third sample from the drake passage yields concordant thorium and protactinium dates as well as seawater values for initial 234u 238u this coral yields a ventilation age that is approximately 20 40 greater than modern values for its location this increase is consistent with published deep sea coral and calibrated planktonic benthic foraminifera radiocarbon data suggesting that the glacial oceans as a whole may have been substantially less ventilated presumably due to decreased formation of north atlantic deep water an overall decrease in oceanic mixing rates could have contributed to lower dissolved carbon in surface ocean water and lower atmospheric pco2 during the past glacial period

primary u distribution in scleractinian corals and its implications for u series dating in this study we use microsampling techniques to explore diagenetic processes in carbonates these processes are important as they can affect the accuracy of u series chronometry fission track maps of deep sea scleractinian corals show a threefold difference between the minimum and maximum u in modern corals which is reduced to a factor of 2 in fossil corals we use micromilling and mc icp ms to make detailed analyses of the u and 234uinitial distributions in corals from 218 ka to modern within each fossil coral we observe a large range of 234uinitial values with high 234uinitial values typically associated with low u a simple model shows that this observation is best explained by preferential movement of alpha decay produced 234u atoms alpha recoil diffusion open system addition of 234u may occur when alpha recoil diffusion is coupled with a high u surface layer such as organic material this process can result in large whole coral 234uinitial elevations with little effect on the final age the diagenetic pathways that we model are relevant to both shallow water and deep sea scleractinian corals since both exhibit primary u heterogeneity and may be subject to u addition

shell midden sclerochronology abstract sclerochronological analysis of shell midden faunal remains offers a unique opportunity to study climate and environmental change in relation to human activity middens exist near most aquatic habitats almost worldwide for much of the late pleistocene and holocene they afford good preservation of accretionary calcium carbonate remains such as mollusk shells and fish otoliths in comparatively well dated contexts as such midden samples are a source of sequential proxy records of past climate and environmental conditions and may provide detailed pictures of human environment interaction however midden samples present several challenges to the development and application of sclerochronological proxies including unique taphonomic concerns here these challenges are outlined within descriptions of the major applications of midden sclerochronology archeological concerns including season of capture reconstructing the history of anthropogenic environmental impacts and paleoclimate environment proxy reconstructions

in situ u series dating by laser ablation multi collector icpms new prospects for quaternary geochronology the capabilities and potential applications of in situ dating of quaternary materials using laser ablation mc icpms are explored 234 u 238 u and 230 th 234 u can be measured with precision sufficient for dating at a spatial resolution of 100mm or better in samples that contain as a little as 1 ppm uranium moreover u and th concentrations and u series isotope ratios can be continuously profiled to determine changes in age that occur with sample growth e g in speleothems these capabilities additionally permit the dating of bones teeth and possibly molluscs which are subject to post mortem open system behaviour of useries isotopes and can be employed to elucidate processes of u series migration during weathering and diagenesis a drawback of laser ablation mc icpms is that it cannot in general provide u series age estimates with the high precision and accuracy of conventional tims or solution mc icpms methods however sample preparation is straightforward the amount of sample consumed negligible and it can be used to rapidly characterise or screen and select samples from which more precise and accurate dates can be obtained using conventional methods given further instrumental developments and the establishment of suitable matrix matched standards for carbonates and other materials we foresee that laser ablation mc icpms will play an increasingly important role in quaternary dating research r 2005 published by elsevier ltd

elastic parabolic equation solutions for underwater acoustic problems using seismic sources several problems of current interest involve elastic bottom range dependent ocean environments with buried or earthquake type sources specifically oceanic t wave propagation studies and interface wave related analyses additionally observed deep shadow zone arrivals are not predicted by ray theoretic methods and attempts to model them with fluid bottom parabolic equation solutions suggest that it may be necessary to account for elastic bottom interactions in order to study energy conversion between elastic and acoustic waves current elastic parabolic equation solutions must be modified to allow for seismic starting fields for underwater acoustic propagation environments two types of elastic self starter are presented an explosive type source is implemented using a compressional self starter and the resulting acoustic field is consistent with benchmark solutions a shear wave self starter is implemented and shown to generate transmission loss levels consistent with the explosive source source fields can be combined to generate starting fields for source types such as explosions earthquakes or pile driving examples demonstrate the use of source fields for shallow sources or deep ocean bottom earthquake sources where down slope conversion a known t wave generation mechanism is modeled self starters are interpreted in the context of the seismic moment tensor

proteinaceous corals as proxy archives of paleo environmental change abstract high resolution marine data are critical to evaluating anthropogenic impacts on our environment considering the spatial and temporal limitations of direct instrumental measurements proxy data extracted from marine environmental archives are necessary to separate anthropogenic changes from those that would occur naturally the majority of late holocene high resolution environmental reconstructions are derived from marine carbonates including tropical scleractinian corals bivalves crustose coralline algae and sclerosponges however these archives are restricted to the top hundreds of meters of the water column and only preserve environmental variability that is captured by calcium carbonate skeletons at a very few select locations marine sediments archive annual environmental variability in organic and inorganic materials recently additional types of corals are proving to yield information complimentary to these traditional marine archives including cold water scleractinian corals and proteinaceous corals a taxonomically diverse group the proteinaceous corals are broadly defined as those having a branching gross morphology with skeleton comprised at least partly of protein rich organic material they encode characteristics of their food and ambient environment into the chemical and physical composition of their skeleton this environmental encoding combined with their banded skeleton and significant longevity means that proteinaceous corals hold information in their skeleton that helps fill the spatial and temporal gaps in our knowledge of past and present ocean conditions here i review the environmental reconstructions derived from geochemical measurements of the proteinaceous coral skeletons this information is grouped into the mesopelagic environmental variability captured in the skeleton of bamboo corals surface processes captured in the organic skeletons of corals across all ocean depths and environmental variability documented by skeletal radiometric isotopes we include animals from two separate subclasses within the class anthozoa including the parasitic zoanthids that secrete a sclero proteic skeleton since the proteinaceous corals are taxonomically diverse we consider the unique features that define this group of corals including their distribution morphology nutrition and longevity we find that uncertainty surrounding biological parameters limits the precision of reconstructions derived from the calcitic skeleton in contrast analytical effort and cost constrain the number of reconstructions from the organic skeleton through this discussion we provide insights into the uses challenges and directions for future research for this important environmental archive

cold water coral carbonate mounds as unique palaeo archives the plio pleistocene challenger mound record ne atlantic through the interplay of a stabilising cold water coral framework and a dynamic sedimentary environment cold water coral carbonate mounds create distinctive centres of bio geological accumulation in often complex continental margin settings the iodp expedition 307 drilling of the challenger mound eastern porcupine seabight ne atlantic not only retrieved the first complete developmental history of a coral carbonate mound it also exposed a unique early pleistocene sedimentary sequence of exceptional resolution along the mid latitudinal ne atlantic margin in this study a comprehensive assessment of the challenger mound as an archive of quaternary palaeo environmental change and long term coral carbonate mound development is presented new and existing environmental proxy records including clay mineralogy planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts planktonic foraminifer oxygen isotopes and siliciclastic particle size are thereby discussed within a refined chronostratigraphic and climatic context overall the development of the challenger mound shows a strong affinity to the plio pleistocene evolution of the northern hemisphere climate system albeit not being completely in phase with it the two major oceanographic and climatic transitions of the plio pleistocene the late pliocene early pleistocene intensification of continental ice sheet development and the mid pleistocene transition to the more extremely variable and more extensively glaciated late quaternary mark two major thresholds in challenger mound development its late pliocene 2 74 ma origin and its middle late pleistocene to recent decline distinct surface water perturbations i e water mass polar front migrations productivity changes melt water pulses are identified throughout the sequence which can be linked to the intensity and extent of ice development on the nearby british irish isles since the earliest pleistocene glaciation induced shifts in surface water primary productivity are thereby proposed to fundamentally control cold water coral growth which in turn influences on mound sediment accumulation and hence coral carbonate mound development throughout the pleistocene as local factors such as proximal ice sheet dynamics and on mound changes in cold water coral density significantly affected the development of the challenger mound they can potentially explain the nature of its palaeo record and its offsets with the periodicities of global climate variability on the other hand owing to this unique setting a regionally exceptional high resolution palaeo record of early pleistocene ca 2 6 to 2 1 ma environmental change including early british irish ice sheet development broadly in phase with the 41 ka paced global climate system is preserved in the lower challenger mound all in all the challenger mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic continental margin environments

assessing the ability of the 14c projection age method to constrain the circulation of the past in a 3 d ocean model radiocarbon differences between benthic and planktonic foraminifera b p ages and radiocarbon projection ages are both used to determine changes of the past ocean circulation rate a global 3 d ocean circulation model with a constant modern ocean circulation is used to study which method is less influenced by atmospheric 14c variations three factors cause uncertainties first the long equilibration time of the ocean after atmospheric 14c changes second different mixing processes in the ocean which cause an ocean response of smaller amplitude than the atmospheric forcing and third the unknown source region and corresponding initial surface 14c reservoir age of subsurface waters the model suggests that b p ages and projection ages have lower uncertainties the closer they are to deepwater formation zones in the north atlantic the b p age method is less influenced by atmospheric 14c variations than the projection age method projections ages vary less in the pacific as long as atmospheric 14c decreases linearly a more irregular atmospheric 14c evolution leads to age variations of similar magnitude with both methods on the basis of the model experiment we suggest a potential improvement of the projection age method

correlation of boron isotopic composition with ultrastructure in the deep sea coral lophelia pertusa implications for biomineralization and paleo ph using the crpg cnrs cameca 1270 ion microprobe facility we have measured boron isotopic compositions b 11 b 10 in different ultrastructural components of the deep sea aragonitic scleractinian coral lophelia pertusa we observe a systematic difference in b isotopic composition between the early mineralization zone emz and adjacent fibrous skeleton in emz the measured delta 11 b values are consistently low fibrous aragonite is characterized by systematically higher delta 11 b values but also displays b isotopic heterogeneity associated with specific growth bands in the calyx wall the magnitude of the observed b isotopic variations cannot be explained by changes in environmental conditions and is likely caused by biological processes involved in the biomineralization of new skeleton i e vital effects the observed b isotopic variations are opposite to the predictions of geochemical models for vital effects these models are based on the idea that stable isotopic fractionations including c and o in coral skeleton are driven by changes in ph of the fluid from which the skeleton is presumed to precipitate our data indicate that ph variations are not responsible for the observed stable isotopic fractionations geochemical models therefore do not provide an adequate framework within which to understand coral skeletal formation without a better understanding of these processes the use of b isotopic composition to reconstruct paleo ph variations in the oceans must be considered problematic at least as far as lophelia pertusa is concerned

bamboo coral ba ca calibration of a new deep ocean refractory nutrient proxy abstract it is poorly understood how intermediate water masses are affected by decadal scale climate via biogeochemical cycling export production and changes in circulation ventilation to this end a geochemical nutrient proxy from deep sea bamboo corals would provide decadal to centennial scale records of deep and intermediate water nutrient dynamics seawater barium basw has a nutrient like distribution in the water column similar to silicate so ba ca records in foraminifera shallow water surface corals and other deep sea corals have been used to trace refractory nutrients here we present the first calibration of a nutrient proxy from skeletal barium preserved in the calcitic internodes of deep sea bamboo corals collected from intermediate water depths a calibration was calculated from a broadly distributed suite of isidella and keratoisis corals spanning a silicate and basw gradient n 33 corals 300 2800 m ba ca b a m b o o c o r a l mol mol 0 079 0 008 ba sw nmol kg 4 205 0 870 r 2 0 77 n 33 the strong linear correlation between ba cabamboo coral and basw suggests that coral ba ca is a reliable recorder of seawater barium and therefore silicate we find a distribution coefficient dba for ba cabamboo coral of 1 3 0 2 similar to that of other corals surface and deep sea dwelling and inorganic calcium carbonate precipitation experiments dba 1 2 1 5 this suggests that ba incorporation is primarily driven by cationic substitution in bamboo corals and holds promise as a globally applicable refractory nutrient proxy we find interannual decadal scale variability in a ba cabamboo coral timeseries from a california margin coral san juan seamount 1295 m these data suggest that additional high resolution ba cabamboo coral records may reveal a connection between regional scale intermediate water biogeochemistry and low latitude surface ocean atmospheric climate

226ra in barite absolute dating of holocene southern ocean sediments and reconstruction of sea surface reservoir ages absolute dating of marine sediments is necessary to achieve reliable correlations of paleoclimate records the 2 2 6 ra decay in barite separated from a deep sea core of the southern ocean was used to determine absolute ages for the holocene epoch comparison with 1 4 c ages measured on planktic foraminifers provides the first past sea surface reservoir ages in the antarctic zone of the southern ocean throughout the middle to late holocene our results indicate a reservoir age of ca 1100 yr comparable to modern estimates a significantly higher reservoir age ca 1900 yr is obtained for the early holocene which suggests a major change in the southern ocean circulation at that time