boron isotopes and b ca in benthic foraminifera proxies for the deep ocean carbonate system abstract accurate records of the state of the ocean carbonate system are critical for understanding past changes in pco 2 ocean acidification and climate the chemical principles underlying the proxy of oceanic ph provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood but the proxy s reliability has been questioned we present 76 new multi collector inductively coupled plasma mass spectrometry mc icpms 11 b measurements on a range of benthic foraminifera from 23 late holocene samples from the atlantic that reaffirm the utility of the 11 b ph proxy our boron isotope measurements on 10 benthic foraminifera tests typically yield a precision of 0 25 at 2 s d equivalent to 0 03 ph units 11 b values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of b oh 4 from seawater and no vital effects using the independently determined fractionation factor of 1 0272 between 11 b 10 b of aqueous boron species infaunal foraminifera are consistent with this model but record the combined effects of lower pore water 11 b and ph no influence of partial dissolution or shell size on 11 b is observed we have also measured the b ca ratios of the same samples for individual cibicidoides species b ca shows a good correlation with co 3 2 but the b ca of different co occurring species morphotypes varies considerably these effects are not seen in 11 b which may therefore provide a more robust proxy of the ocean carbonate system whilst in theory 11 b and b ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate dic in practice this is precluded by propagated uncertainties 11 b data give significant constraints on foraminifera calcification mechanisms and seem most simply explained by incorporation of b oh 4 into a hco 3 pool which is then completely incorporated in foraminiferal caco 3 our demonstration of the predictable variation of 11 b with ph across a wide range of species and locations provides confidence in the application of mc icpms measurements of foraminiferal 11 b to reconstruct past changes in the ocean carbonate system

ross ice shelf oxygen isotopes and west antarctic climate history the ross ice shelf 18o profile at station j 9 covers at least the last 30 000 yr it identifies the depth in the core of ice from i the last glacial interglacial transition 266 to 286 m and ii the 1000 m surface elevation about 140 m various processes contribute to the 18o change observed in the core i climatic warming mainly caused by a decrease in winter sea ice extent around antarctica of about 6 latitude early in the glacial interglacial transition ii decreasing ice sheet thickness later in the glacial interglacial transition and during the holocene and iii decreases in elevation and effective distance from the open ocean as the source of the ice in the core shifts along the flow line toward j 9 average 18o values of the last 3000 yr imply a fairly stable climate yet shorter 102 to 103 yr 18o climatic oscillations up to 6 are seen in both the holocene and the glacial portion of the record

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

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

boron isotope composition of the cold water coral lophelia pertusa along the norwegian margin zooming into a potential ph proxy by combining bulk and high resolution approaches abstract high latitude cold water coral reefs are particularly vulnerable to climate change due to enhanced co2 uptake in these regions to evaluate their physiological functioning and potential application as ph archives we retrieved both recent and fossil samples of lophelia pertusa along the norwegian margin from oslofjord 59 n over to trondheimsfjord sula and lopphavet 70 6 n boron isotope analyses 11b were undertaken using solution based and laser ablation multi collector inductively coupled plasma mass spectrometry mc icp ms la icp ms and secondary ion mass spectrometry sims epi fluorescence microscopy was employed to provide a rapid pre screening routine for structure specific subsampling in the coral skeleton this integrated approach enabled us to assess heterogeneities within single specimens as well as to investigate the role of local environmental influences including recent and past variations all three mass spectrometry methods show substantial differences in the 11b of the theca wall tw and the centres of calcification coc s micro bulk subsamples milled from the theca wall of modern specimens originating from different habitats but with comparable seawater ph 8 8 16 gave consistent 11b values averaging 26 7 0 2 2 n 4 while coc subsamples systematically deviated towards lower b ca by 40 and depleted 11b values minimum 22 7 0 3 2 implying a difference of at least 4 between tw and coc sims and la icp ms measurements identified much larger internal heterogeneities with maximum variation of 10 between the distinct skeletal structures minimal sims 11b values of 17 3 1 2 2 were associated with the pure coc material our findings may be interpreted in terms of the occurrence of two main but likely different biomineralisation mechanisms in l pertusa with the coc s generally exhibiting minimal ph up regulation potentially supporting the use of bicarbonate in the early stages of biomineralisation furthermore we highlight the potential utility of l pertusa for palaeo proxy studies if targeting the compositionally homogenous tw zones devoid of coc admixtures which appear to provide highly reproducible measurements

modern and pleistocene boron isotope composition of the benthic foraminifer cibicidoides wuellerstorfi abstract here we present the first species specific study of boron isotopes in the epibenthic foraminifer species cibicidoides wuellerstorfi coretop samples from a water depth profile from 1000 to 4500 m on the northern flank of the walvis ridge are 4 4 lower than the values expected based on calculations of the 11bborate of ambient seawater similar values for this foraminifer species are presented from odp site 668b at the sierra leone rise in the equatorial atlantic the consistency between data of the same species suggests the offsets are primary rather than diagenetic glacial c wuellerstorfi from odp 668b and walvis ridge have boron isotope compositions only slightly different to interglacial samples that is no larger than 0 10 ph units or 23 mol kg 1 in co32 above the reconstructed glacial lysocline and 0 07 ph units or 14 mol kg 1 in co32 below we use these results to suggest that glacial deep water ph in the atlantic was similar to interglacial ph the new data resolve the inconsistency between the previously reported high bottom water ph and the lack of significant carbonate preservation of the glacial deep ocean

empirical relationship between ph and the boron isotopic composition of globigerinoides sacculifer implications for the boron isotope paleo ph proxy culture experiments were carried out with the planktonic foraminifera globigerinoides sacculifer at three different ph values 7 6 0 05 8 20 0 05 8 60 0 05 in order to establish the ph dependence of the boron isotopic fractionation between the calcitic tests of g sacculifer and seawater additional objectives were to compare the ph dependences of boron isotopic composition of g sacculifer with that of orbulina universa and inorganic calcite in order to evaluate the robustness of the boron isotope paleo ph proxy the relationship between the boron isotopic composition of g sacculifer and the culture water ph shows heavier boron isotopic values at higher ph this empirical relationship is similar but slightly offset by 3 per mil from that of o universa indicating the presence of biogenic influence vital effect on the boron isotopic composition of foraminifera however comparison of the boron isotopic composition of o universa and g sacculifer with that of inorganic calcite grown over a common ph range shows that inorganic processes are the dominant control on the boron isotopic composition of foraminifera and the vital effects play a small but not insignificant role the results imply that in spite of a small biogenic influence the variation in boron isotopic composition of foraminiferal shells with ph at least for o universa and g sacculifer is consistent with that for inorganic calcite demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

evidence for platelet ice accretion in arctic sea ice development moderate quantities of platelet ice are reported in ice cores obtained from floes in the central and western beaufort sea arctic ocean the crystal structure characteristics include a fabric of long thin ragged edged crystals with randomly oriented c axes the cellular substructure that is characteristic of congelation ice is not evident in individual platelet ice crystals but they do occur together with congelation ice in layers ranging from 0 05 to 0 6 m thick platelet ice crystals are observed primarily in second year and multiyear floes the structural characteristics of arctic platelet ice are similar to those of antarctic platelet ice the platelet ice layers have a minimum 18o value of 5 3 and in some cases the platelet ice layers have more negative 18o values than the ice layers above and below them the salinity of platelet ice layers is not significantly different from other ice layers a number of platelet ice growth mechanisms and sources are discussed processes associated with the ellesmere ice shelves nearshore processes such as anchor ice growth in shallow waters off the north coast of alaska and ice growth in freshwater impounded behind grounded ice dams might be locally important but are unlikely to contribute significant quantities of platelet ice to pack ice floes two processes probably account for the presence of platelet ice the first is growth in underice melt ponds which form in inverted depressions at the base of floes when meltwater floes off the ice surface the second is the operation of ice pumps in which ice that is melted off the deeper parts of floes and ridges is deposited as platelet ice at a higher level in either case initially loose accumulations of platelet crystals are entrained in the floes by the growth of congelation ice the widespread occurrence of platelet ice in the central and western beaufort sea suggests that ice growth in both underice melt ponds and associated with the operation of ice pumps might be more common than was previously realized

evidence for ocean acidification in the great barrier reef of australia geochemical records preserved in the long lived carbonate skeleton of corals provide one of the few means to reconstruct changes in seawater ph since the commencement of the industrial era this information is important in not only determining the response of the surface oceans to ocean acidification from enhanced uptake of co2 but also to better understand the effects of ocean acidification on carbonate secreting organisms such as corals whose ability to calcify is highly ph dependent here we report an 200 year d 11 b isotopic record extracted from a long lived porites coral from the central great barrier reef of australia this record covering the period from 1800 to 2004 was sampled at yearly increments from 1940 to the present and 5 year increments prior to 1940 the d 11 b isotopic compositions reflect variations in seawater ph and the d 13 c changes in the carbon composition of surface water due to fossil fuel burning over this period in addition complementary ba ca d 18 o and mg ca data was obtained providing proxies for terrestrial runoff salinity and temperature changes over the past 200 years in this region positive thermal ionization mass spectrometry ptims method was utilized in order to enable the highest precision and most accurate measurements of d 11 b values the internal precision and reproducibility for d 11 b of our measurements are better than 0 2 2r which translates to a precision of better than 0 02 ph units our results indicate that the long term pre industrial variation of seawater ph in this region is partially related to the decadal interdecadal variability of atmospheric and oceanic anomalies in the pacific in the periods around 1940 and 1998 there are also rapid oscillations in d 11 b compositions equivalent changes in ph of almost 0 5 u the 1998 oscillation is co incident with a major coral bleaching event indicating the sensitivity of skeletal d 11 b compositions to loss of zooxanthellate symbionts importantly from the 1940s to the present day there is a general overall trend of ocean acidification with ph decreasing by about 0 2 0 3 u the range being dependent on the value assumed for the fractionation factor a b3 b4 of the boric acid and borate species in seawater correlations of d 11 b with d 13 c during this interval indicate that the increasing trend towards ocean acidification over the past 60 years in this region is the result of enhanced dissolution of co2 in surface waters from the rapidly increasing levels of atmospheric co2 mainly from fossil fuel burning this suggests that the increased levels of anthropogenic co2 in atmosphere has already caused a significant trend towards acidification in the oceans during the past decades observations of surprisingly large decreases in ph across important carbonate producing regions such as the great barrier reef of australia raise serious concerns about the impact of greenhouse gas emissions on coral calcification 2009 elsevier ltd all rights reserved

phosphate defects and apatite inclusions in coral skeletal aragonite revealed by solid state nmr spectroscopy abstract recent development of paleo nutrient proxies based on the phosphorus calcium p ca ratio in tropical and deep water corals also known as cold water corals require an understanding of the processes by which p is incorporated into the coral skeletal aragonite here we apply single and double resonance solid state nuclear magnetic resonance nmr spectroscopy to determine the speciation of p in coral aragonite the results show that the majority of p occurs as phosphate defects in the aragonite structure but in many samples a significant fraction of the p occurs also in crystalline hydroxylapatite inclusions quantification of the amount of hydroxylapatite indicates that its presence is not related simply to external environmental factors and that it can occur at varying abundances in different parts of the same corallite since there is currently no model available to describe the relationship between dissolved inorganic phosphate and its incorporation as apatite inclusions into carbonates careful screening of samples which contain only phosphate in the aragonite structure or selective microsampling could improve proxy development

boron occurrence in halite and boron isotope geochemistry of halite in the qarhan salt lake western china abstract previous studies have investigated boron b isotope composition of salt lake brines in the qaidam basin western china however the research on b isotope geochemistry of halite from a sediment core in a typical sedimentary basin has been very limited in this study a 102 m long drill core isl1a was recovered from qarhan salt lake in eastern qaidam basin forty three halite samples from upper 44 0 m in isl1a were collected and analyzed for chemical compositions k na ca 2 mg 2 cl so 4 2 sr 2 and b 3 and b isotopes in order to investigate their relationships and b isotope fractionation between halite and brines in the qarhan salt lake the results show that 1 more b 3 and mg 2 values in halite are low concentrations and more concentrated and low b 3 concentrations have a strong correlation with low mg 2 in halite which imply that they might be the same source 2 low mg 2 values in halite from isl1a have a similar trend with m mg 2 molarity of fluid inclusion brines from two sediment cores east to isl1a about 50 km in the study area suggesting that low b 3 and mg 2 concentrations should derive from fluid inclusions in halite based on x ray diffraction results in isl1a that no borate and small amount of magnesium salts were deposited 3 11 b values of halite in isl1a range from 0 35 to 5 84 which are in the range of those of river water and brines 1 0 to 9 6 and almost overlapped with those of brines 2 9 to 7 5 in the qarhan salt lake these results suggest that no or minor b isotope fractionation between halite and brine occurred

an improved boron isotope ph proxy calibration for the deep sea coral desmophyllum dianthus through sub sampling of fibrous aragonite abstract the isotopic composition of boron 11 b in marine carbonates is well established as a proxy for past ocean ph however its robust application to palaeo environments relies on the generation of species specific calibrations existing calibrations utilising the deep sea coral dsc desmophyllum dianthus highlight the potential application of this pervasive species to ph reconstructions of intermediate depth waters nevertheless considerable uncertainty remains regarding the estimation of seawater ph from these bulk skeletal 11 b measurements likely resulting from microstructural heterogeneities in 11 b of d dianthus to circumvent this problem thus improving the reliability of the d dianthus 11 b ph calibration we present a new 11 b calibration of micro sampled fibrous aragonite from this species modern coral specimens recovered from the atlantic pacific and southern oceans micro sampled using microdrilling micromilling and laser cutting extraction were analysed for trace element b ca mg ca sr ca and u ca and boron isotopic composition we find the best calibration against the 11 b of borate in local ambient seawater a function of ph and taken from hydrographic data sets ph range 7 57 to 8 05 utilises 11 b measurements of fibres with likely slow growth rates and minimal contamination from adjacent microstructures identified by low mg ca for each coral specimen this new calibration exhibits a stronger and better defined dependence on ambient seawater ph compared to bulk coral 11 b 11 b fibre 0 93 0 17 11 b borate 12 02 2 63 we suggest that the majority of the variability in measured 11 b between replicate bands of fibrous aragonite from a d dianthus specimen can be explained by small incorporation of non fibrous aragonite and surface impurities during microsampling and growth rate effects this study confirms the utility of d dianthus as an archive of precise palaeo ph 0 07 ph units provided that suitable sampling strategies are applied

stable isotope 18o 16o tracing of fresh brackish and sea ice in multi year land fast sea ice ellesmere island canada la salinite de la glace et les rapports 18 o 16 o ont ete mesures sur 12 carottes de glace prelevees sur la glace marine au large de la cote nord de ellesmere island canada les 3 types de glace douce saum tre et marine ont ete identifies dans les carottes en utilisant les rapports isotopiques 18 o 16 o l utilisation des mesures 18 o pour identifier la glace marine et saum tre est discutee la proportion de chaque type de glace presente est etablie et les implications pour les proprietes et la structure de l eau sous glaciaire sont presentees

the geochemistry of deep sea coral skeletons a review of vital effects and applications for palaeoceanography deep sea corals were discovered over a century ago but it is only over recent years that focused efforts have been made to explore the history of the oceans using the geochemistry of their skeletal remains they offer a promising archive of past oceanic environments given their global distribution layered growth patterns longevity and preservation as well as our ability to date them using radiometric techniques this paper provides an overview of the current state of the art in terms of geochemical approaches to using deep sea coral skeletons to explore the history of the ocean deep sea coral skeletons have a wide array of morphologies e g solitary cup corals branching colonial corals and materials calcite aragonite and proteins as such their biomineralization strategies are diverse leading to complex geochemistry within coral skeletons notwithstanding these complications progress has been made on developing methods for reconstructing the oceanographic environment in the past using trace elements and isotopic methods promising approaches within certain coral groups include clumped isotopes and mg li for temperature reconstructions boron isotopes and radiocarbon for carbon cycling end and radiocarbon for circulation studies and 15 n p ca and ba ca for nutrient tracer studies likewise there is now a range of techniques for dating deep sea corals skeletons e g u series radiocarbon and determining their growth rates e g radiocarbon and 210 pb dating studies on historic coral populations in the atlantic southern ocean and pacific point to climate and environmental changes being dominant controls on coral populations over millennial and orbital timescales this paper provides a review of a range of successes and promising approaches it also highlights areas in which further research would likely provide new insights into biomineralization palaeoceanography and distribution of past coral populations

arctic ice shelves and ice islands origin growth and disintegration physical characteristics structural stratigraphic variability and dynamics ice shelves are thick floating ice masses most often associated with antarctica where they are seaward extensions of the grounded antarctic ice sheet and sources of many icebergs however there are also ice shelves in the arctic primarily located along the north coast of ellesmere island in the canadian high arctic the only ice shelves in north america and the most extensive in the north polar region the ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands the tabular icebergs of the arctic ocean the present state of knowledge and understanding of these ice features is summarized in this paper it includes historical background to the discovery and early study of ice shelves and ice islands including the use of ice islands as floating laboratories for polar geophysical research growth mechanisms and age the former extent and the twentieth century disintegration of the ellesmere ice shelves and the processes and mechanisms of ice island calving are summarized surface features thickness thermal regime and the size shape and numbers of ice islands are discussed the structural stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described large scale and small scale dynamics of ice islands are described and the results of modeling their drift and recurrence intervals are presented the conclusion identifies some unanswered questions and future research opportunities and needs

oceanic ph control on the boron isotopic composition of foraminifera evidence from culture experiments culture experiments were carried out with the species orbulina universa at four different ph values 7 70 0 05 8 15 0 05 8 60 0 05 and 9 00 0 10 in order to establish the ph dependence of boron isotope fractionation between seawater and foraminifera a clear relationship between the boron isotopic composition of the foraminifera and the ph of the seawater culture solutions was found showing heavier boron isotopic composition at higher ph this finding supports the viability of boron isotopes as a paleo ph tool it is important to note that orbulina universa cultured in natural seawater as well as those obtained from coretop samples have a significantly lighter boron isotopic ratio than globigerinoides sacculifer from coretop samples suggesting that at least for this species a vital effect is active

boron and magnesium isotopic composition of seawater the isotopic systems of boron and magnesium are increasingly being used as proxies for a number of environmental variables and processes the isotopic composition of seawater for both systems plays a central role in these studies and is an important interlaboratory standard given the long residence times of both elements 10 7 years it is commonly assumed that seawater is isotopically homogenous for these systems yet no systematic studies currently exist here we present the b and mg isotopic composition of 26 28 seawater samples from a number of ocean basins that encompass a significant range in salinity 32 to 38 psu temperature 0 3 to 25 9c and water depth 0 to 1240 m we find no significant or systematic variation for either system in accordance with their long residence times we recommend that the mean values we report 11 b 39 61 0 04 2 s e n 28 25 mg 0 43 0 01 2 s e n 26 26 mg 0 82 0 01 2 s e n 26 be used in future studies involving mg and b isotopes copyright 2010 by the american geophysical union

evaluation of boron isotope ratio as a ph proxy in the deep sea coral desmophyllum dianthus evidence of physiological ph adjustment the boron isotope ratio 11b of foraminifers and tropical corals has been proposed to record seawater ph to test the veracity and practicality of this potential paleo ph proxy in deep sea corals samples of skeletal material from twelve archived modern desmophyllum dianthus d dianthus corals from a depth range of 274 1470 m in the atlantic pacific and southern oceans ambient ph range 7 57 8 05 were analyzed for 11b the 11b values for these corals spanning a range from 23 56 to 27 88 are found to be related to seawater borate 11b by the linear regression 11bcoral 0 76 0 28 11bborate 14 67 4 19 1 standard error se the d dianthus 11b values are greater than those measured in tropical corals and suggest substantial physiological modification of ph in the calcifying space by a value that is an inverse function of seawater ph this mechanism partially compensates for the range of ocean ph and aragonite saturation at which this species grows enhancing aragonite precipitation and suggesting an adaptation mechanism to low ph environments in intermediate and deep waters consistent with the findings of trotter et al 2011 for tropical surface corals the data suggest an inverse correlation between the magnitude of a biologically driven ph offset recorded in the coral skeleton and the seawater ph described by the equation ph ph recorded by coral seawater ph 0 75 0 12 phw 6 88 0 93 1 se error analysis based on 95 confidence interval ci and the standard deviation of the regression residuals suggests that the uncertainty of seawater ph reconstructed from 11bcoral is 0 07 to 0 12 ph units this study demonstrates the applicability of 11b in d dianthus to record ambient seawater ph and holds promise for reconstructing oceanic ph distribution and history using fossil corals

the freshwater budget and under ice spreading of mackenzie river water in the canadian beaufort sea based on salinity and 18o 16o measurements in water and ice observations of salinity and oxygen isotope composition 18o were made for the beaufort shelf mackenzie estuary waters in september 1990 just prior to ice formation and for both the water column and ice in april may 1991 at the end of winter these measurements are used to determine the apportioning of fresh water in the estuary between its two main sources runoff and sea ice melt changes in disposition of water between seasons and amounts frozen into the growing ice sheet are also derived two domains are considered in order to construct a freshwater budget for the mackenzie shelf the nearshore within which landfast ice grows in winter and the outer shelf most of the winter inflow from the mackenzie river appears to remain impounded as liquid under the ice within the landfast zone at the end of winter and about 15 of it is incorporated into the landfast ice oxygen isotopes 18o in ice cores collected from across the shelf record the progress beneath the ice of new mackenzie inflow as it invades the nearshore throughout winter rates of spreading are about 0 2 cm s 1 away from the coast and 1 3 cm s 1 along the coast as this inflow spreads across the shelf it progressively shuts off convection driven by brine production at locations within the landfast ice salinity and 18o in the offshore water column suggest that about 3 m of sea ice was formed in the outer shelf domain since both brine and newly formed sea ice can be advected off the shelf a complete budget for brine or sea ice production cannot be established without first measuring the advection of one of these two components

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

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

paleointensity in hawaiian scientific drilling project hole hsdp2 results from submarine basaltic glass 1 paleointensity estimates based on the high quality thellier thellier data from the early brunhes 420 780 ka are rare only 30 in the published literature the second hawaiian scientific drilling project hsdp2 drill hole recovered submarine volcanics spanning the approximate time period of 420 550 ka these are of particular interest for absolute paleointensity studies owing to the abundance of fresh submarine basaltic glass which can preserve an excellent record of ancient geomagnetic field intensity we present here new results of thellier thellier paleointensity experiments that nearly double the number of reliable paleointensity data available for the early brunhes we also show that the magnetizations of the associated submarine basalts are dominated by viscous magnetizations and therefore do not reflect the true ancient geomagnetic field intensity at the time of extrusion the viscous contamination is particularly severe because of a combination of low blocking temperatures in the basalts and relatively high temperatures in the deeper parts of the drill core our new data when placed on the approximate timescale available for hsdp and hsdp2 are at odds with other contemporaneous paleointensity data the discrepancy can be reconciled by adjusting the hsdp timescales to be younger by about 35 kyr

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

holocene geomagnetic field intensity variations contribution from the low latitude canary islands site abstract new absolute paleomagnetic intensity pi are investigated from 37 lava flows located at tenerife and gran canaria canary islands they complete previously published directional results from the same flows and therefore allow to examine the time variations of the full geomagnetic vector twenty eight flows are radiocarbon dated between 1706 ad and about 13 200 bc and one is historical eight other flows are not dated but they have stratigraphic links with the dated flows and archeomagnetic ages had been attributed to them based on their paleomagnetic directions various mineralogical analyses were conducted giving access to the nature of the magnetic minerals and to their grain size we performed the original thellier and thellier paleointensity pi experiments with a success rate of about 65 coupling this experiment with the strict set of selection criteria picrit 03 the mean pis at the flow level are based on 3 to 12 independent pi determinations except for one site in which only one reliable determination could be obtained the data indicate some variability in the local field intensity with a prominent pi peak centered around 600 bc and reaching 80 t vadm 16 10 22 a m 2 documented for the first time in this region combined with the published data obtained from western africa spain portugal morocco and the azores within a 2000 km radius around the canary islands our data allow to construct a curve illustrating the earth magnetic field intensity fluctuations for southwestern europe western africa this curve compared to the one produced for the middle east and one calculated for central asia shows that maximum intensity patches have a very large geographical extent they do not yet appear clearly in the models of variations of the dipolar field intensity

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

linear correlations in bamboo coral δ 13 c and δ 18 o sampled by sims and micromill evaluating paleoceanographic potential and biomineralization mechanisms using δ 11 b and 47 composition abstract bamboo corals represent an intriguing paleoceanographic archive with the potential to reconstruct variations throughout the water column over multiple centuries realizing this potential partially depends on if and at what resolution timeseries of variability can be generated recent work demonstrates that bamboo coral growth temperature averaged over its entire lifespan can be derived from linear correlations in its carbon and oxygen isotope composition 13 c 18 o when the apparent equilibrium fractionations for a coral s growth rate and calcifying ph are used building on this method this study applies it to coeval coral skeleton to assess the possibility of extracting paleoceanographic timeseries from bamboo coral skeletons using boron isotope 11 b based ph estimates micromilled samples yield accurate paleotemperatures with uncertainties of 2 c this is attributed to the inability to measure 13 c and 18 o in exactly the same skeleton as is the case for micromilled samples a micromilled sampling strategy is therefore likely the most practical means of applying the method carbonate clumped isotopes 47 estimate temperatures slightly warmer than observed suggesting they may not accurately record the subtle variations of the latest holocene when interpreted in conjunction 18 o 11 b and 47 data suggest that ph up regulation plays a role in generating linear 13 c 18 o trends however oxygen isotope fractionation and 47 are lower than would be predicted by ph alone potential explanations for this discrepancy include biological processes that favor the incorporation of carbonate ion into coral skeleton uncertainties in the 11 b ph proxy the influence of magnesium on calcite fluid isotope fractionation or uncertainties in the fractionation factors used to calculate apparent equilibrium despite some remaining uncertainties the method can resolve many observed decadal scale thermocline temperature anomalies suggesting that appropriately located bamboo corals could help constrain the behavior of similar temporal variability prior to instrumental monitoring

calcification generates protons for nutrient and bicarbonate uptake abstract the biosphere s great carbonate deposits from caliche soils to deep sea carbonate oozes precipitate largely as by products of autotrophic nutrient acquisition physiologies protons constitute the critical link calcification generates protons which plants and photosynthetic symbioses use to assimilate bicarbonate and nutrients a calcium atpase based trans mechanism underlies most biological calcification this permits high calcium carbonate supersaturations and rapid carbonate precipitation the competitive advantages of calcification become especially apparent in light and nutrient deficient alkaline environments calcareous plants often dominate the lower euphotic zone in both the benthos and the plankton geographically and seasonally massive calcification concentrates in nutrient deficient environments including alkaline soils coral reefs cyanobacterial mats and coccolithophorid blooms structural and defensive uses for calcareous skeletons are sometimes overrated

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

stable oxygen and carbon isotopes in planktic foraminifers from arctic ocean surface sediments reflection of the low salinity surface water layer planktic foraminifers neogloboquadrina pachyderma sin from 87 eastern and central arctic ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition additional results from 52 stations were taken from the literature the lateral distribution of 18o full size image 33 atlantic waters entering the arctic ocean through the fram strait 18o values decrease both to the barents shelf and to the north pole in accordance with the decreasing salinities of the halocline waters in the nansen basin a strong n s 18o gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources i e salinity reduction from sea ice meltwater in the south and from light isotope waters meteoric precipitation and river runoff in the northern part of the basin north of the gakkel ridge 18o and salinity gradients are in good accordance and suggest less influence of sea ice melting processes the 13c full size image 1 k values of n pachyderma sin from arctic ocean surface sediment samples are generally high 0 75 0 95 lower values in the southern eurasian basin appear to be related to the intrusion of atlantic waters the high 13c values are evidence for well ventilated surface waters because the perennial arctic sea ice cover largely prevents atmosphere ocean gas exchange ventilation on the seasonally open shelves must be of major importance lack of 13c gradients along the main routes of the ice drift from the siberian shelves to the fram strait suggests that primary production i e co2 consumption does probably not change the co2 budget of the arctic ocean significantly

ice island detection and characterization with airborne synthetic aperture radar a 1 300 000 scale airborne synthetic aperture radar sar image of an area of the arctic ocean adjacent to the queen elizabeth islands canadian high arctic is examined to determine the number and characteristics of ice islands in the image and to assess the capability of airborne and satellite sar to detect ice islands twelve ice islands have been identified and their dimensions range from as large as 5 7 km by 8 7 km to as small as 0 15 km by 0 25 km a significant sar characteristic of the shelf ice portions of ice islands is a return with a ribbed texture of alternating lighter and darker grey tones resulting from the undulating shelf ice surfaces of the ice islands the appearance of the ribbed texture varies according to the ice islands orientation relative to the illumination direction and consequently the incidence angle some ice islands also include extensive areas of textureless dark tone attached to the shelf ice the weak returns correspond to 1 multiyear landfast sea ice that was attached to the front of the ward hunt ice shelf at the time of calving and which has remained attached since then and 2 multiyear pack ice that has become attached and consolidated since the calving indicating that ice islands can increase their area and mass significantly as they drift other sar characteristics include straight bright returns along the edges arising from sea ice pressure ridges or shelf ice cliffs other physical characteristics of ice islands that make them identifiable in sar images include their greater size and shapes longer thinner and more angular than those of surrounding pack ice floes it is evident that ice islands are easily discernible in sar images and for the future sar represents a promising technique to obtain a census of ice islands in the arctic ocean however any sar based census probably will be conservative because ice islands smaller than 300 400 m across are likely to remain undetected particularly in areas of heavy ice ridging which produces strong sar clutter

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

a comparative study of the northwest africa and eastern equatorial pacific upwelling zones as sources of co2 during glacial periods based on boron isotope paleo ph estimation paleo ph reconstructions based on boron isotopic composition of foraminifera have been used to estimate glacial interglacial changes in surface ocean pco2 of the northwest african upwelling zone on comparison with a similar study for the eastern equatorial pacific upwelling zone it can be concluded that the two major upwelling zones acted quite differently during the glacial periods as compared to today while the ph of the surface ocean off northwest africa was 0 2 0 07 units higher during the glacial period compared to that during holocene there was no significant glacial interglacial change in the surface ocean ph in the eastern equatorial pacific carbonate chemistry reconstructions based on the estimated ph changes suggest that the ocean atmosphere pco2 gradient off northwest africa was lower by at least 70 40 atm during glacial periods compared to during the holocene in contrast the ocean atmosphere pco2 gradient in the eastern equatorial pacific was higher by at least 80 40 atm during glacial periods as compared to during the holocene hence the eastern equatorial pacific upwelling system was a significantly larger source of co2 to the atmosphere while the one off northwest africa was a significantly smaller source of co2 during the last glacial period the pco2 reconstructions further indicate that in spite of higher glacial productivity compared to during the holocene neither of the two areas became a sink of co2

quantifying the ph vital effect in the temperate zooxanthellate coral cladocora caespitosa validation of the boron seawater ph proxy boron isotopic and elemental systematics are used to define the vital effects for the temperate shallow water mediterranean coral cladocora caespitosa the corals are from a range of seawater ph conditions pht 7 6 to 8 1 and environmental settings 1 naturally living colonies harvested from normal ph waters offshore levanto 2 colonies transplanted nearby a subsea volcanic vent system and 3 corals cultured in aquaria exposed to high 700 atm and near present day 400 atm pco2 levels b ca compositions measured using laser ablation inductively coupled mass spectrometry la icpms show that boron uptake by c caespitosa cultured at different pco2 levels is independent of ambient seawater ph being mainly controlled by temperature dependent calcification in contrast the boron isotope compositions 11bcarb of the full suite of corals determined by positive thermal ionisation mass spectrometry ptims shows a clear trend of decreasing 11bcarb from 26 7 to 22 2 with decreasing seawater ph reflecting the strong ph dependence of the boron isotope system the 11bcarb compositions together with measurements of ambient seawater parameters enable calibration of the boron ph proxy for c caespitosa by using a new approach that defines the relationship between ambient seawater ph phsw and the internally controlled ph at the site of calcification phbiol c caespitosa exhibits a linear relationship between phsw and the shift in ph due to physiological processes ph phbiol phsw giving the regression phclad 4 80 0 52 phsw for this species we further apply this method ph phsw to calibrate tropical species of porites acropora and stylophora reported in the literature the temperate and tropical species calibrations are all linearly correlated r2 0 9 and the biological fractionation component ph between species varies within 0 2 ph units our ph phsw approach provides a robust and accurate tool to reconstruct palaeoseawater phsw for both temperate and tropical corals further validating the boron fractionation factor b3 b4 1 0272 determined experimentally by klochko et al 2006 and the boron isotope ph proxy both of which have been the foci of considerable debate

environmental constraints on holocene cold water coral reef growth off norway insights from a multiproxy approach high latitude cold water coral cwc reefs are particularly susceptible due to enhanced co2 uptake in these regions using precisely dated u th cwcs lophelia pertusa retrieved during research cruise pos 391 lopphavet 70 6 n oslofjord 59 n we applied boron isotopes 11b ba ca li mg and u ca ratios to reconstruct the environmental boundary conditions of cwc reef growth the sedimentary record from these cwc reefs reveals a lack of corals between 6 4 and 4 8 ka the question remains if this phenomenon is related to changes in the carbonate system or other causes the initial postglacial setting had elevated ba ca ratios indicative of meltwater fluxes showing a decreasing trend towards cessation at 6 4 ka with a oscillation pattern similar to continental glacier fluctuations downcore u ca ratios reveal an increasing trend which is outside the range of modern u ca variability in l pertusa suggesting changes of seawater ph near 6 4 ka the reconstructed bwt at lopphavet reveals a striking similarity to barent sea surface and sub sea surface temperature records we infer that meltwater pulses weakened the north atlantic current system resulting in southward advances of cold and co2 rich arctic waters a corresponding shift in the 11b record from 25 0 to 27 0 probably implies enhanced ph up regulation of the cwcs due to the higher pco2 concentrations of ambient seawater which hastened mid holocene cwc reef decline on the norwegian margin

an evaluation of benthic foraminiferal b ca and δ11b for deep ocean carbonate ion and ph reconstructions reliable reconstructions of deep ocean carbonate ion concentration co32 and ph are crucial to understand mechanisms responsible for the past atmospheric co2 variations observed in ice cores however it is challenging to reconstruct past deep water co32 and ph and literature results from different proxies conflict warranting careful investigations on possible reasons for the existing inconsistencies here we present the first down core b ca and 11b records measured in an epifaunal benthic foraminifer cibicidoides wuellerstorfi from the caribbean sea during the last 160 kyr the two proxies yield quantitatively comparable deep water co3 2 and ph results showing high values during glacials relative to inter glacials differences in co32 and ph are 35 mol kg and 0 15 respectively consistent with past ocean circulation changes in the caribbean sea our data provide convincing evidence that both proxies serve as faithful proxies to estimate deep ocean co32 and ph despite our incomplete understanding of boron incorporation into foraminiferal carbonates

testing the izzi protocol of geomagnetic field intensity determination 1 a new paleointensity determination protocol the izzi method was recently proposed the izzi technique combines the aitken in field zero field iz and coe zero field in field zi methods the izzi protocol of paleointensity method was experimentally tested showing a strong angular dependence resulting from the undemagnetized portions of partial thermoremanent magnetization ptrm tails the izzi method is better than the conventional techniques aitken coe and thellier in three respects 1 it can easily detect the angular dependence 2 it provides a quantitative estimate for the consistency of the outcome between iz and zi step and 3 it is quicker because the extra ptrm tail check step is unnecessary

geochemical perspectives on coral mineralization corals open an exceptional window into many phenomena of geological geochemical climatic and paleontological interest from the paleozoic to the present corals provide some of the finest high resolution archives of marine conditions corals are likewise exceptional for chronometric purposes and even the terrestrial 14c timescale has now been calibrated against coral 230th 234u corals also represent a testing ground for basic ideas about mineralogy and geochemistry the shapes sizes and organization of skeletal crystals have been attributed to factors as diverse as mineral supersaturation levels and organic mediation of crystal growth the coupling between calcification and photosynthesis in symbiotic corals is likewise attributed to everything from photosynthetic alkalinization of the water to efforts by the coral to prevent photosynthetic alkalinization corals also leave a significant geochemical imprint on the oceans their aragonite skeletons accept about 10 times more strontium than does calcite hence the proportion of marine aragonite precipitation affects the oceanic chemical balance biological carbonates represent the biosphere s largest carbon reservoir hence calcareous organisms affect the ocean s ph co2 content and ultimately global temperatures through the greenhouse gas connection finally corals present some geochemical puzzles for ecology and conservation how do symbiotic corals obtain nutrients in some of the most nutrient deficient parts of the planet are global geochemical changes partially responsible for the widespread declines in coral reefs during recent decades we will address many of these issues but will concentrate on coral skeletal structure and calcification mechanism these topics bear most directly on the biomineralization process and generally affect the choice of skeletal materials and analytical techniques used in geochemical investigations the coral reef is probably the planet s most spectacular biomineralization product these grand and complex ecosystems build on the accumulated skeletal debris of countless generations of organisms especially calcareous algae and symbiotic

calibration of the boron isotope proxy in the planktonic foraminifera globigerinoides ruber for use in palaeo co2 reconstruction abstract the boron isotope ph proxy applied to mixed layer planktic foraminifera has great potential for estimating past co2 levels which in turn is crucial to advance our understanding of how this greenhouse gas influences earth s climate previous culture experiments have shown that although the boron isotopic compositions of various planktic foraminifera are ph dependent they do not agree with the aqueous geochemical basis of the proxy here we outline the results of culture experiments on globigerinoides ruber white across a range of ph 7 5 8 2 and analysed via multicollector inductively coupled plasma mass spectrometry mc icpms and compare these data to core top and sediment trap samples to derive a robust new species specific boron isotope ph calibration consistent with earlier culture studies we show a reduced ph dependency of the boron isotopic composition of symbiont bearing planktonic foraminifera compared to borate ion in seawater we also present evidence for a size fraction effect in the 11b of g ruber finally we reconstruct atmospheric co2 concentrations over the last deglacial using our new calibration at two equatorial sites odp site 999a and site geob1523 1 these data provide further grounding for the application of the boron isotope ph proxy in reconstructions of past atmospheric co2 levels

stable isotope clues to the formation and evolution of refrozen melt ponds on arctic sea ice author posting american geophysical union 2018 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 123 12 2018 8887 8901 doi 10 1029 2018jc013797

deep sea corals evidence periodic reduced ventilation in the north atlantic during the lgm holocene transition abstract nine new intermediate water ages estimated with coupled uranium series and radiocarbon measurements on deep sea corals from the northeastern atlantic are presented together with six intermediate and deep water ages from the western north atlantic adkins et al science 280 1998 725 728 and one from the equatorial atlantic mangini et al nature 392 1998 347 348 they span the time period from 15 400 to 560 yr ago and show abrupt variations of intermediate and deep water ages from 270 up to 2320 yr both major pulses of meltwater discharge mwp 1a following heinrich event 1 and mwp 1b after the younger dryas cold event are followed by enhanced supply of southern source water at intermediate depths in the north atlantic together with reduced formation of well ventilated glacial north atlantic intermediate water 1000 2000 m this result gives strong support to numerical models predicting fast and sharp increase of bottom water age in the atlantic triggered by pulses of freshwater discharge into the north atlantic rahmstorf nature 372 1994 82 85 stocker and wright radiocarbon 40 1998 359 366

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

experimental measurement of boron isotope fractionation in seawater abstract the boron isotopic composition of marine carbonates is considered to be a tracer of seawater ph use of this proxy benefits from an intimate understanding of chemical kinetics and thermodynamic isotope exchange reactions between the two dominant boron bearing species in seawater boric acid b oh 3 and borate ion b oh 4 however because of our inability to quantitatively separate these species in solution the degree of boron isotope exchange has only been known through theoretical estimates in this study we present results of a spectrophotometric procedure wherein the boron isotope equilibrium constant 11 10 k b is determined empirically from the difference in the dissociation constants of 11 b oh 3 and 10 b oh 3 in pure water 0 6 mol kg 1 h 2 o kcl and artificial seawater within experimental uncertainty our results show no dependence of 11 10 k b on temperature but 11 10 k b at 25 c in pure water was statistically different than results obtained in solutions at high ionic strength 11 10 k b of the seawater s 35 b t 0 01 mol kg 1 h 2 o at 25 c is 1 0272 0 0006 this result is significantly larger than the theoretical value used in numerous paleo ph studies 11 10 k b 1 0194

crystallographic control on the boron isotope paleo ph proxy when using the boron isotopic composition 11b of marine carbonates as a seawater ph proxy it is assumed that only the tetrahedral borate ion is incorporated into the growing carbonate crystals and that no boron isotope fractionation occurs during uptake however the 11b of the calcium carbonate from most modern foraminifera shells or corals skeletons is not the same as the 11b of seawater borate which depends on ph an observation commonly attributed to vital effects in this study we combined previously published high field 11b mas nmr and new 11b measurements on the same synthetic calcite and aragonite samples precipitated inorganically under controlled environments to avoid vital effects our results indicate that the main controlling factors of 11b are the solution ph and the mineralogy of the precipitated carbonate mineral whereas the aqueous boron concentration of the solution caco3 precipitation rate and the presence or absence of growth seeds all appear to have negligible influence in aragonite the nmr data show that boron coordination is tetrahedral bo4 in addition its 11b is equal to that of aqueous borate thus confirming the paleo ph hypothesis in contrast both trigonal bo3 and tetrahedral bo4 are present in calcite and its 11b values are higher than that of aqueous borate and are less sensitive to solution ph variations compared to 11b in aragonite these observations are interpreted in calcite as a reflection of the incorporation of decreasing amounts of boric acid with increasing ph moreover the fraction of bo3 measured by nmr in calcite is higher than that inferred from 11b which indicates a coordination change from bo4 to bo3 upon boron incorporation in the solid overall this study shows that although the observed differences in 11b between inorganic and biological aragonite are compatible with a ph increase at calcification sites the b speciation and isotope composition of biological calcites call for a more complex mechanism of boron incorporation

snowfall and oxygen isotope variations off the north coast of ellesmere island n w t canada snow pack along the lan d fast ice fringe off the north coast of ellesmere island was generally characterized by depth hoar overl ain by dense snow and wind slab mean snow depth in the study area was 0 54 m 1982 85 and the mean 6180 value of the sno w pack was 31 3 0 00 isotope data were not obtained previously for this geographic region and therefore complement a previous study of 6180 variations in high arctic snow koer ner 1979 the data are consistent with an arctic ocean moisture source the 6180 profiles show seasonal variat ions with winter snow being more depleted in 180 than fall and spring snow however the 6180 profiles are dominated by a trend to higher 6180 values with increasing depth this is attributed to a decrease in 6180 values as conden sation temperatures fall during the autumn winter acc umulation period during this time there is also a chan ge from relatively open to almost complete ice cover in the arctic ocean the change in evaporation conditions and consequent effect on 6 values gives rise to a sharp dis continuity in the 6180 prof iles and a bi m odal 6180 freq uency dist ribution the bi modal distribution is reinforced by a secon dary isotope fracti onation that occurs during dept h hoar formation this isotope effect leads to a wider 6180 range but does not signific antly alter the mean 6180 value

a 23 000 year record of surface water ph and pco2 in the western equatorial pacific ocean the oceans play a major role in defining atmospheric carbon dioxide co2 levels and although the geographical distribution of co2 uptake and release in the modern ocean is understood little is known about past distributions boron isotope studies of planktonic foraminifera from the western equatorial pacific show that this area was a strong source of co2 to the atmosphere between approximately 13 800 and 15 600 years ago this observation is most compatible with increased frequency of la nina conditions during this interval hence increased upwelling in the eastern equatorial pacific may have played an important role in the rise in atmospheric co2 during the last deglaciation

stratigraphy stable isotopes and salinity in multi year sea ice from the rift area south george vi ice shelf antarctic peninsula results from a detailed profile in a 5 54m multi year sea ice core from the rift area in the southern part of george vi ice shelf are presented stratigraphy stable isotopes and na content are used to investigate the growth processes of the ice cover and to relate them to melting processes at the bottom of the ice shelf the thickest multi year sea ice in the sampling area appears to be second year sea ice that has survived one melt season combined salinity stable isotope analyses show large scale sympathetic fluctuations that can be related to the origin of the parent water brackish ice occurs between 450 and 530cm in the core it is demonstrated that this results from the feezing of brackish water formed by mixing of normal sea water with melted basal shelf ice with dilution percentages of maximum 80 fresh water from authors

arctic ocean water mass balance from isotope data the distributions of the oxygen 18 and tritium isotopes and of salinity yield a residence time of 10 years for the surface and halocline waters of the arctic basin we find a yearly net production of 0 59 m of sea ice and an input of 1 16 m of freshwater from continental river runoff local precipitation and bering strait salinity deficiency using the basin area value with these numbers gives long term average total net production and transport rates of 0 15 sv of ice and 0 18 sv of meteoric component bering strait water not included if in addition a reasonable depth profile of relative current velocity is assumed for the outflow a yearly input of 2 8 sv of atlantic and bering strait water is needed to replenish the upper and halocline waters these numbers should be good to 20 and are multiyear averages the isotope data clearly indicate that the barents sea is an inflow area for atlantic water to the basin but that net export of ice occurs there

morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater insights into the biomineralization response to ocean acidification 1 we reared primary polyps new recruits of the common atlantic golf ball coral favia fragum for 8 days at 25 c in seawater with aragonite saturation states ranging from ambient 3 71 to strongly undersaturated 0 22 aragonite was accreted by all corals even those reared in strongly undersaturated seawater however significant delays in both the initiation of calcification and subsequent growth of the primary corallite occurred in corals reared in treatment tanks relative to those grown at ambient conditions in addition we observed progressive changes in the size shape orientation and composition of the aragonite crystals used to build the skeleton with increasing acidification densely packed bundles of fine aragonite needles gave way to a disordered aggregate of highly faceted rhombs the sr ca ratios of the crystals measured by sims ion microprobe increased by 13 and mg ca ratios decreased by 45 by comparing these variations in elemental ratios with results from rayleigh fractionation calculations we show that the observed changes in crystal morphology and composition are consistent with a 80 decrease in the amount of aragonite precipitated by the corals from each batch of calcifying fluid this suggests that the saturation state of fluid within the isolated calcifying compartment while maintained by the coral at levels well above that of the external seawater decreased systematically and significantly as the saturation state of the external seawater decreased the inability of the corals in acidified treatments to achieve the levels of calcifying fluid supersaturation that drive rapid crystal growth could reflect a limit in the amount of energy available for the proton pumping required for calcification if so then the future impact of ocean acidification on tropical coral ecosystems may depend on the ability of individuals or species to overcome this limitation and achieve the levels of calcifying fluid supersaturation required to ensure rapid growth

reconstructing hydrographic change in petersen bay ellesmere island canada inferred from sar imagery abstract synthetic aperture radar sar satellite imagery was used to reconstruct the change in limnological conditions adjacent to an arctic ice shelf by examining the backscatter values of coastal ice in mid winter scenes high sar backscatter values 6 db suggest that an ice dammed lake was present adjacent to the south coast of petersen bay from 1992 until 2005 following a large calving event of the adjacent petersen ice shelf 8 07 km2 in august 2005 the lake drained through a region where the ice shelf had separated from the coastline this loss of freshwater and replacement of lake ice with sea ice along the southern coast of petersen bay were confirmed from analyses of ice core samples and conductivity temperature depth ctd profiles the exception to this pattern was one distinct area where terrestrial streams entered the edge of petersen bay and freshwater continued to collect from 2006 to 2008 however this ephemeral area of freshwater has not reformed since 2009 due to the persistence of open water events in petersen bay observed in optical satellite imagery which likely facilitated mixing of freshwater with sea water based on the continued break ups of petersen ice shelf and the frequency of open water events it is unlikely that this ice dammed lake will reform the results of this study underscore the utility of sar for reconstructing past hydrographic conditions in the water column below

a late quaternary full vector geomagnetic record from el golfo section el hierro canary islands regional full vector palaeosecular variation psv curves are essential to further our understanding of geodynamo operation such curves typically lack palaeointensity information with palaeodirectional being much more common particularly for periods before the holocene notably low palaeointensity values have been reported for significant portions of the late quaternary here we present full vector palaeomagnetic from the el golfo section on el hierro canary islands spain spanning the age range between 120 and 450 ka to substantiate these reported low palaeointensity values for the canary islands we sampled 28 flows mostly alkaline oceanic basalts of the shield building stage along the camino de jinama a few kilometres to the south of a section studied by szeremeta et al for psv in line with their results we observe an easterly declination deviation of 14 for the middle and lower part of our section we relate this to undersampling of the complete psv spectrum rotation of el hierro since 500 ka is deemed unlikely attempts to date the flows with the 40ar 39ar method on a multicollector instrument were unsuccessful due to the presence of copious amounts of methane in the extracted gases stratigraphic correlation to szeremeta et al s section lends support to ages technically of very low quality obtained for the sites reported on here importantly we add palaeointensity information in the present study for the first time on el hierro three different palaeointensity protocols were utilized izzi thellier multispecimen and pseudo thellier to provide an additional consistency check and to increase the success rate after applying strict selection criteria reliable palaeointensities could be obtained for 18 flows a success rate of 64 per cent if more than one protocol yielded results for the same flow the obtained intensities were often within error of each other testifying to their robustness flows with a common true mean direction tend to produce similar intensity values as well this testifies to the presumed under sampling of psv within the section obtained palaeointensity values typically range between 20 and 35 t distinctly lower than the present day field value of 39 t and lower than the average intensity during the brunhes chron the determinations are in line with other rather low values obtained elsewhere for this particular time span

instability of seawater ph in the south china sea during the mid late holocene evidence from boron isotopic composition of corals abstract we used positive thermal ionization mass spectrometry ptims to generate high precision 11b records in porites corals of the mid late holocene from the south china sea scs the 11b values of the holocene corals vary significantly ranging from 22 2 to 25 5 the paleo ph records of the scs reconstructed from the 11b data were not stable as previously thought but show a gradual increase from the holocene thermal optimal and a sharp decrease to modern values the latter is likely caused by the large amount of anthropogenic co2 emissions since the industrial revolution but variations of atmospheric pco2 cannot explain the ph change of the scs before the industrial revolution we suggest that variations of monsoon intensity during the mid late holocene may have driven the sea surface ph increase from the mid to late holocene results of this study indicate that the impact of anthropogenic atmospheric co2 emissions may have reversed the natural ph trend in the scs since the mid holocene such ocean ph records in the current interglacial period can help us better understand the physical and biological controls on ocean ph and possibly predict the long term impact of climate change on future ocean acidification

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

paleomagnetic field properties at high southern latitude 1 statistical analyses of paleomagnetic data from lava flows are used to study geomagnetic field behavior on million year timescales previous paleomagnetic studies have lacked high latitude measurements necessary to investigate the persistence of geomagnetic anomalies observed in the recent and historical field and replicated in some numerical geodynamo simulations these simulations suggest that reduced convective flow inside the tangent cylinder may affect the magnetic field at high latitude whereas lower latitude observations are expressions of columnar helical flow outside the tangent cylinder this paper presents new paleointensity and paleodirectional data from 100 volcanic sites in the erebus volcanic province evp antarctica and 21 new age determinations by the 40ar 39ar incremental heating method the new evp data are combined with previously published paleomagnetic and geochronological results providing 133 sites 91 having radioisotopic dates modified thellier thellier paleointensity estimates are reported for 47 sites 37 have dates ages for the combined data set span 0 03 to 13 42 ma the 125 high quality evp directional data selected from the merged data set have a non fisherian distribution and a mean direction with an inclination anomaly of 3 but 95 confidence limits include the prediction from a geocentric axial dipole virtual geomagnetic pole vgp dispersions for brunhes matuyama and the combined 0 5 ma data set are consistently high compared with values from middle to low latitude regions regardless of the criterion used to determine transitional fields with vgp latitude cut off at 45 the dispersion 23 9 2 1 for the combined 0 5 ma evp data set is consistent with earlier high latitude data and paleosecular variation psv in model g but not with some more recent statistical psv models mean evp paleointensity of 31 5 2 4 t derived from 41 high quality sites is about half the current value at mcmurdo 63 t the result is essentially independent of data selection criteria high vgp dispersion and low intensity values support the global observation of anticorrelation between directional variability and field strength simulations of time varying dipole strength show that uneven temporal sampling may bias the mean evp intensity estimate but the possibility of persistently anomalous field behavior at high latitude cannot be excluded

geological evolution of seawater boron isotopic composition recorded in evaporites the abundance of boron isotopes in ancient marine carbonates can be used to estimate oceanic ph that reflects atmospheric co 2 levels this proxy requires that the boron isotopic composition of seawater at the time the carbonate has formed is known and thus the past changes in seawater chemistry here we report the boron isotopic composition of selected ancient marine halites and modern sea salts the signal interpreted as marine reveals a clear evolution of the boron isotopic composition of seawater to 8 variations over the cenozoic comparison between this reconstructed curve and the mg ca ratio reveals a high level of consistency that will help to better define oceanic geochemical cycles

seawater nutrient and carbonate ion concentrations recorded as p ca ba ca and u ca in the deep sea coral desmophyllum dianthus as paleoceanographic archives deep sea coral skeletons offer the potential for high temporal resolution and precise absolute dating but have not been fully investigated for geochemical reconstructions of past ocean conditions here we assess the utility of skeletal p ca ba ca and u ca in the deep sea coral d dianthus as proxies of dissolved phosphate remineralized at shallow depths dissolved barium trace element with silicate type distribution and carbonate ion concentrations respectively measurements of these proxies in globally distributed d dianthus specimens show clear dependence on corresponding seawater properties linear regression fits of mean coral element ca ratios against seawater properties yield the equations p cacoral lmol mol 0 6 0 1 p casw lmol mol 23 18 r 2 0 6 n 16 and ba cacoral lmol mol 1 4 0 3 ba casw lmol mol 0 2 r 2 0 6 n 17 no significant relationship is observed between the residuals of each regression and seawater temperature salinity pressure ph or carbonate ion concentrations suggesting that these variables were not significant secondary dependencies of these proxies four d dianthus specimens growing at locations withoarag 6 0 6 displayed markedly depleted p ca compared to the regression based on the remaining samples a behavior attributed to an undersaturation effect these corals were excluded from the calibration coral u ca correlates with seawater carbonate ion u cacoral lmol mol 0 016 0 003 co 2 3 lmol kg 3 2 0 3 r 2 0 6 n 17 the residuals of the u ca calibration are not significantly related to temperature salinity or pressure scatter about the linear calibration lines is attributed to imperfect spatialtemporal matches between the selected globally distributed specimens and available water column chemical data and potentially to unresolved additional effects the uncertainties of these initial proxy calibration regressions predict that dissolved phosphate could be reconstructed to 0 4 lmol kg for 1 3 1 9 lmol kg phosphate and dissolved ba to 19 nmol kg for 41 82 nmol kg basw carbonate ion concentration derived from u ca has an uncertainty of 31lmol kg for 60 120 lmol kg co 2 3

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

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

atmospheric carbon dioxide concentration across the mid pleistocene transition the dominant period of pleistocene glacial cycles changed during the mid pleistocene from 40 000 years to 100 000 years for as yet unknown reasons here we present a 2 1 million year record of sea surface partial pressure of co2 pco2 based on boron isotopes in planktic foraminifer shells which suggests that the atmospheric partial pressure of co2 pco2 was relatively stable before the mid pleistocene climate transition glacial pco2 was approximately 31 microatmospheres higher before the transition more than 1 million years ago but interglacial pco2 was similar to that of late pleistocene interglacial cycles 450 000 years ago these estimates are consistent with a close linkage between atmospheric co2 concentration and global climate but the lack of a gradual decrease in interglacial pco2 does not support the suggestion that a long term drawdown of atmospheric co2 was the main cause of the climate transition

surface ocean ph response to variations in pco2 through two full glacial cycles abstract knowledge of past atmospheric pco 2 is important for evaluating the role of greenhouse gases in climate forcing ice core records show the tight correlation between climate change and pco 2 but records are limited to the past 900 kyr we present surface ocean ph and pco 2 data reconstructed from boron isotopes in planktonic foraminifera over two full glacial cycles 0 140 and 300 420 kyr the data co vary strongly with the vostok pco 2 record and demonstrate that the coupling between surface ocean chemistry and the atmosphere is recorded in marine archives allowing for quantitative estimation of atmospheric pco 2 beyond the reach of ice cores

drifting arctic sea ice archives changes in ocean surface conditions 18o profiles in drifting arctic sea ice are coupled with back trajectories of ice drift and an ice growth model to reconstruct the surface hydrography of the arctic ocean interior the results compare well with 18o values obtained by traditional oceanographic methods and known water mass distributions analysis of the stable isotopic composition of sea ice floes sampled at strategic and relatively accessible locations e g fram strait could aid in mapping spatial and temporal variations in arctic ocean surface waters