exposure ages for pleistocene periglacial deposits in australia abstract pleistocene periglacial landforms are widespread in australia and provide valuable information on past temperatures but dating the time of their formation has proven difficult to remedy this we have explored the use of cosmogenic 36 cl for direct dating of periglacial deposits we sampled six deposits in four locations in southeastern australia ranging from blockstreams and block slopes to former rock glaciers eighteen exposure ages reveal a concentration of periglacial activity during the last glacial maximum lgm between 16 and 23 ka with a population having a weighted mean age of 21 9 0 5 ka this age is shortly before the time of maximum ice advance during the lgm in southeastern australia exposure dating of block deposits provides a way of extending the chronology of cold climate activity beyond glaciated regions

oldest isotopically characterized fish otoliths provide insight to jurassic continental climate of europe large shallow epeiric seas and adjacent lagoons such as those described herein likely played a significant role in moderating jurassic coastal and continental climate jurassic bathonian ocean surface temperatures in scotland have been calculated from 18o caco3 values of a suite of the oldest well preserved fish otoliths analyzed to date otolith 18o values range from 4 7 to 1 9 vienna peedee belemnite vpdb while 13c caco3 values vary from 5 4 to 1 5 vpdb representing the oldest stable isotopic record of paleodiet paleoecology and fish migration to date using a global ocean 18o h2o value of 1 0 vienna standard mean ocean water vsmow for an ice free jurassic fish species that migrated from estuarine to open marine water record time averaged temperatures of 23 c estuarine fish assuming a similar temperature record variation in 18o h2o values from 3 7 to 2 0 vsmow that significant mixing of fresh water and seawater occurred in the jurassic in scotland is in general agreement with data presented by others molluscan fauna lithostratigraphy paleogeography and paleocirculation models the 18o values and temperatures derived in this study correspond to the meteorologic and hydrologic parameters of a mid latitude maritime climate with low seasonality a mean temperature of 23 c and abundant precipitation and humidity the 18o h2o values calculated from estuarine fish indicate that rainfall must have a 18o h2o value lower than 3 7 vsmow values of 18o and 13c suggest an environment hydrologically similar to that observed in the everglades of south florida or the estuaries of south texas both notable fish nurseries today however sea surface temperatures were lower than those of modern florida or texas as evidenced by reduced evaporative enrichment of 18o h2o values

palaeoenvironmental change recorded in the palaeodunefields of the western murray basin south australia new data from single grain osl dating this study is concerned with the reconstruction of the palaeoenvironmental history of southeastern australia for the last 300 ka by establishing a luminescence chronology of dune sand deposition in the western murray basin south australia in the study area vast fields of palaeodunes stabilised by vegetation provide evidence of past environmental change in total 98 samples were collected from dune sand layers at 13 different dune sections the time of their deposition was determined using optically stimulated luminescence dating of single quartz grains accounting for the impact of post depositional mixing by the use of a finite mixture model the oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western murray basin ranging up to at least 380 ka phases of substantial dune sand deposition were identified for the periods 18 38 ka and 63 72 ka older depositional phases also exist but are poorly resolved due to relatively large errors of the luminescence ages aeolian deposition during the last termination and the holocene is relatively limited with a slight clustering of ages at the time of the antarctic cold reversal and from 5 8 ka two modern ages give evidence of very recent dune sand deposition comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases thus although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward the palaeodunes of the western murray basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction

238u234u230th disequilibrium in hydrogenous oceanic femn crusts palaeoceanographic record or diagenetic alteration abstract a detailed tims study of 234uexc 238u 230th 232th and th u ratios have been performed on the outermost margin of ten hydrogenous fe mn crusts from the equatorial pacific ocean and west central indian ocean th u concentration ratios generally decrease from the crust s surface down to 0 5 1 mm depth and growth rates estimated by uranium and thorium isotope ratios are significantly different in fe mn crusts from the peru basin and the west central indian ocean fe mn crusts from the same geographical area define a single trend in plots of ln 234uexc 238u vs ln 230th 232th and th u ratios vs age of the analysed fractions results suggest that l hydrogenous fe mn crusts remain closed systems after formation and consequently 2 the discrepancy observed between the 230th and 234u chronometers in fe mn crusts and the variations of the th u ratios through the margin of femn crusts are not due to redistribution of uranium and thorium isotopes after oxyhydroxide precipitation but rather to temporal variations of both th u and initial thorium activity ratios recorded by the fe mn layers implications of these observations for determination of fe mn crust growth rates are discussed variations of both th u and initial th activity ratios in fe mn crusts might be related to changes in particle input to seawater and or changes in ocean circulation during the last 150 ka

sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

ferromanganese nodules and micro hardgrounds associated with the cadiz contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents abstract ferromanganese nodule fields and hardgrounds have recently been discovered in the cadiz contourite channel in the gulf of cadiz 850 1000 m this channel is part of a large contourite depositional system generated by the mediterranean outflow water ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals we present a complete characterisation of these deposits based on submarine photographs and geophysical petrographic mineralogical and geochemical data the genesis and growth of ferromanganese deposits strongly enriched in fe vs mn av 39 vs 6 in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes the interaction of the mediterranean outflow water with the continental margin has led to the formation of late pleistocene holocene ferromanganese mineral deposits in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events the diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons 13 c pdb 20 to 37 and organic matter within the channel floor sediments promoting the formation of fe mn carbonate nodules high 87 sr 86 sr isotopic values up to 0 70993 0 00025 observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep seated fluid venting across the fault systems in the diapirs below the cadiz contourite channel erosive action of the mediterranean outflow water undercurrent could have exhumed the fe mn carbonate nodules especially in the glacial periods when the lower core of the undercurrent was more active in the study area the growth rate determined by 230 th excess 232 th was 113 11 mm ma supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka ca rich layers in the nodules could point to the interaction between the mediterranean outflow water and the north atlantic deep water during the heinrich events siderite rhodochrosite nodules exposed to the oxidising sea bottom waters were replaced by fe mn oxyhydroxides slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds which show imprints of the mediterranean outflow water with low 87 sr 86 sr isotopic values down to 0 70693 0 00081 we propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents we also compare and discuss the generation of ferromanganese deposits in the cadiz contourite channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

surface and subsurface seawater temperature reconstruction using mg ca microanalysis of planktonic foraminifera globigerinoides ruber globigerinoides sacculifer and pulleniatina obliquiloculata laser ablation inductively coupled plasma mass spectrometry microanalyses of mg ca across individual final chambers of three planktonic foraminifera species globigerinoides ruber g sacculifer and pulleniatina obliquiloculata reveal significant interspecies differences in test mg concentrations whereas these three species have similar mg ca values at low sea surface temperatures similar to 22 degrees c they diverge markedly at high sea surface temperatures similar to 29 degrees c explanations for these differences in species mg ca values based on detailed comparison of species intratest mg ca distributions suggest that compositional variability within tests cannot account for the observed deviation of species mg ca values in warm water equatorial regions multiple regression modeling and delta o 18 analysis of globigerinoides sacculifer tests indicate that interspecies differences in mg ca values result from different depth habitats the average mg ca values of g ruber final chambers reflect the temperature of the surface mixed layer 0 25 m whereas those of g sacculifer and pulleniatina obliquiloculata correlate best with subsurface temperatures at 50 75 m and 100 125 m water depths respectively mg ca calibration to the temperatures at these depths reveals a similar temperature control on mg test composition in all species combining our results with mg ca values from published culturing experiments we derive a generalized equation for the effect of temperature and seawater salinity on foraminiferal mg ca we also show that the mg ca composition of specific calcite layers within foraminiferal tests including the low mg ca layers of globigerinoides ruber and g sacculifer and the cortex layer of pulleniatina obliquiloculata correlates with seawater temperature and can be used as an additional proxy for seawater temperature

radiochemical observations on manganese nodules from three sedimentary environments in the north pacific abstract decay series isotopes were measured on manganese nodules from three sedimentary environments characterized by substrates of red clay r siliceous ooze s and hemipelagic clay h growth rates of nodules are shown to be site dependent 1 2 mm myr at site r 3 8 mm myr at sites s and 20 50 mm myr at site h correlation between growth rate and the parameter mn fe2 suggests that regional diagenetic variations control the compositions and growth rates of the nodules the frequency of nodule turnover and the period of their growth are assessed from the top vs bottom distributions of several nuclides based on the 230th 231pa and 226ra data turnover times of 103 to 105 years are estimated and they vary with relative size and shape of the specimens at a given site the presence of unsupported 210pb and 228th in the top surfaces but not in the bottom surfaces of the surface nodules suggests active growth during the last decades or years despite their old ages the data also indicate that turnover rates are not more frequent than once every several years or decades the 230th 226ra 226ra 210pb and 232th 228th disequilibrium relationships in the nodules allow the migratory behavior of 226ra 222rn and 228ra and their fluxes to be deduced thus radium leaves the top sides but enters the bottom sides of the surface nodules at sites r and s at site r there is a net loss of radium to the sea the opposite is true at site s surface nodules at site h trap radium from both sides probably due to more intense diagenetic input of radium from sediment pore water the effective diffusivities of 226ra in nodules vary from 3 10 12 to 8 10 14 cm2 s dependent on the textural variation of the nodule material which crudely reflects the growth rate and hence sedimentary environment 222rn diffuses out of nodules from all sides with an effective diffusivity of ca 2 6 10 8 cm 2 s at all sites nodules serve as a more effective source of 222rn to sea water than their adjacent sediments the outward flux of 222rn from nodules relative to that from adjacent sediments tends to be higher in more reduced environments an effect caused by the fact that mn rich nodules from more reduced environment act as a more efficient trap for 226ra

an interdependent relationship between microbial ecosystems and ferromanganese nodules from the western pacific ocean abstract ferromanganese fe mn nodules are being widely explored for their significant economic potential microbial activity is often emphasized with respect to nodule formation however the relationship between microbial activity and fe mn nodule growth is still obscure here we investigate the microbial community elemental distributions mineral compositions and pore structural characteristics within fe mn nodules from the western pacific ocean abundant bacterial and archaeal communities were found in the studied nodules and some species may be related to iron reduction and manganese oxidation and anammox abundant mineralized manganese oxidizing bacteria were also observed in the nodules in addition more reduced manganese more organic carbon micron sized pores and higher bacterial diversity were detected on the younger surface layers of the nodules these results reveal that more biogeochemical reactions occur in younger areas of nodules than in inner areas we suggest that micro and nano structures within nodules provide a beneficial micro environment and nutrition channels for biogeochemical activity that contribute fe mn nodule growth and an interdependent relationship occurs between microbial ecosystems and nodules our work provides valuable insights into abyssal biogeochemical cycling at the deep ocean sediment water reaction interface

climatic influences on the growth rates of mn crusts during the late quaternary abstract the concentration of 230 th in mn crust va13 2 146 w 9 25 s 4830 m from the pacific ocean was measured with high depth resolution 0 02 mm to a depth of 1 4 mm corresponding to an age of 226 ka b p the mean growth rate estimated from these results is 6 2 0 4 mm ma however the exponential curve obtained shows two drastic events in the 230 th concentration record with durations of 41 4 ka and 37 6 ka which are interpreted as growth standstills the decay corrected 230 th concentration is inversely correlated with those of mn fe and co indicating that the 230 th flux into the crust has been constant throughout time and that the observed fluctuations in 230 th are due to dilution by the main components by applying a constant 230 th flux model high resolution growth rates were derived from every sample investigated a detailed comparison of the growth pattern with the specmap time table reveals that the va13 2 growth rates tend to be higher during interglacial than during glacial periods in particular the observed growth standstills are associated with glacial stages 6 and 8 further investigation of mn crust 72 dk 9 taken from shallower water 170 35 w 20 13 n 1550 m tend to confirm that there is a link between the growth rates of hydrogenetic crusts and the climate of the late quaternary

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

reconstructing palaeoenvironments on desert margins new perspectives from eurasian loess and australian dry lake shorelines abstract desert margins preserve evidence of more extensive arid conditions in the past and represent global hot spots with respect to climate change the balance of scientific evidence now suggests that dryland landscape reactivation did not correspond simply to ice age aridity peaks as previously assumed this paper provides a new perspective on and more nuanced understanding of desert marginal landscapes as palaeoenvironmental archives the two case studies represent ends of a sediment availability spectrum both environments experience substantial spatial and temporal variability in deposition with implications for reconstructing past environments at individual sites recently generated chronostratigraphic data from the dry subhumid dobrogea loess romania are synthesised to provide quantitative insights into the spatial and temporal organisation of loess plateaux loess accumulation peaks during the lgm and mis4 but not at all sites accumulation rates vary substantially between sites comparison of geographical context yields no clear driving mechanism for this variability secondly two transverse lunette dunes in semi arid willandra lakes australia yield comparable chronostratigraphies and distribution of stratigraphic units a first attempt is made to identify changes in wind regime through time on the australian desert margins and suggests that high latitude climate forcing may have acted upon semi arid australia over millennial scales the novel perspectives generated from the new datasets provide unprecedented insights into past climate circulation and land surface processes along desert margins these new perspectives coupled with the new geochronological and quantitative palaeoclimate proxy tools now available represent the next frontier for palaeoenvironmental research on desert margins

characterization and quantification of magnetofossils within abyssal manganese nodules from the western pacific ocean and implications for nodule formation this work was supported financially by southern university of science and technology sustech grant y01316111 to y m c the national key r d program of china 2016yfa0601903 to q s l the national natural science foundation of china 41430962 to q s l the australian research council dp160100805 and dp200100765 to a p r and the 13th five year plan project of international maritime resources investigation and development dy135 c1 1 06 and dy135 r2 1 01 to x m s and the guangdong provincial key laboratory of marine resources and coastal engineering we thank the guangzhou marine geological survey for supplying the samples

in situ oxygen isotope micro analysis of faunal material and human teeth using a shrimp ii a new tool for palaeo ecology and archaeology a sensitive high resolution ion microprobe shrimp ii has been used to make high spatial resolution in situ micro analyses of oxygen isotopes in fish otoliths and teeth from fossil herbivores and a neanderthal large intra tooth variations in the oxygen isotopic composition up to 9 were observed in the enamel of herbivores from the neanderthal fossil site of payre consistent with preservation of seasonal cyclicity the range of isotopic compositions observed in neanderthal tooth enamel was much smaller w3 possibly the result of a longer enamel maturation time averaging out variability an archaeological otolith from a preceramic site in northern peru exhibited marked changes in d 18 o over life due either to the fish occasionally migrating from the sea to a lower salinity habitat or to short lived rises in sea water temperature a fish otolith from australia s willandra lakes world heritage area showed clear seasonal variations but also a general trend towards isotopically heavier and more saline water as indicated by higher d 18 o and sr ca values resulting from increased evaporation the results of these case studies are compared to results of oxygen isotope analysis using more conventional methods and demonstrate the ability of the shrimp ii to provide precise high spatial resolution in situ oxygen isotope analyses of a variety of biogenic materials this approach has major advantages over conventional methods it can provide rapid micro scale isotopic analyses of sub permil precision without the need for chemical preparation of the sample

238u234u230th chronometry of femn crusts growth processes and recovery of thorium isotopic ratios of seawater abstract comparison of 234 u excess 238 u and 230 th 232 th activity ratios in oceanic fe mn deposits provides a method for assessing the closed system behaviour of 238u 234u 230th as well as variations in the initial uranium and thorium isotopic ratios of the precipitated metal oxides this approach is illustrated using a fe mn crust from lotab seamount marshall islands west equatorial pacific here we report uranium and thorium isotopic compositions in five subsamples from the surface of one large 5 cm diameter botryoid of this crust and from two depth profiles of the outermost rim of the same botryoid the decrease of 234 u excess 238 u and 230 th 232 th activity ratio with depth in the two profiles gives mean growth rates for the last 238u 212th 150 ka of 7 8 2 mm ma and 6 6 1 mm ma respectively all data points surface and core samples but one define a linear correlation in the ln 230 th 232 th ln 234 u excess 238 u diagram this correlation indicates that for all points the u th system remained closed after the fe mn layer precipitated and that the different samples possessed the same initial uranium and thorium isotope ratios furthermore these results show that the preserved surface of this fe mn crust may not be the present day growth surface and that the thorium and uranium isotopic ratios of seawater in west equatorial pacific have not changed during the past 150 ka the initial thorium activity ratio is estimated from the correlation obtained between ln 230 th 232 th ln 234 u excess 238 u

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

geologic nitrogen and climate change in the geochemical budget of karkevagge swedish lapland abstract while nitrogen is an essential nutrient for plant growth in the terrestrial environment and generally fixed by biological processes in soils in arctic and alpine environments n is a severely limited nutrient because of both climatic and soil constraints it is widely believed that geologic nitrogen is such a small component of the nitrogen cycle that this source is generally not viewed as being a significant component however it has been estimated that in fact as much as 20 of the total nitrogen budget may be stored in geological materials and where n is severely limited such as in arctic and alpine environments geologic n may in fact be a dominant source of n for biological processes nitrogen saturation may therefore have substantial impacts on geochemical cycles involving both soil and water chemistry in order to determine the potential for the rocks and soils of karkevagge to be significant sources of n samples of the principal rock units of the valley along with soil developed on a variety of rock types were sampled ammonia ammonium contents were determined using ion chromatography ammonia ammonium contents of the sampled rock materials display a wide range of abundances with marble containing a mean nh4 abundance of 4300 mg n kg quartz schist 1600 mg n kg biotite schist 4300 mg n kg and garnet mica schist 4500 mg n kg soil ammonia ammonium abundances were found to be 1600 mg n kg n pool abundances range from 2 5 kg m3 for marble to 8 7 for garnet mica schist soil n pools were found to be 3 0 kg m3 the inorganic n present as ammonia ammonium measured in bedrock represents substantial n input into the geochemical budget the n in bedrock originates from organically bound nitrogen associated with sediment or geothermal waters representing a mixture of sedimentary mantle and meteoric sources nitrogen in the soil originates from the weathering of n rich rocks the presence of unweathered nitrate minerals or fluid inclusions released to the soil and ultimately to plants by assimilation by biota or nitrification geologic nitrogen in karkevagge rocks and soils may represent a large and reactive pool with the potential for considerable impact on the geochemical system to investigate the potential responses of nitrogen release as well as other nutrients to increasing co2 concentration scenarios flow through leaching experiments were conducted on crushed rock samples and soils from the study area leaching experiments revealed two to three fold increases in both n and k release with a tripling of carbon dioxide concentrations ammonium shows more rapid release than potassium which suggests substantial changes in nitrogen cycling with increasing co2 enrichment of the atmosphere

regional variability in ferromanganese nodule composition northeastern tropical pacific ocean abstract ferromanganese nodules are products of both direct and indirect precipitation in the marine environment therefore they potentially posses an important record of the oceanographic conditions under which they have grown previous attempts to extract useful paleoceanographic interpretations from ferromanganese nodules have been hampered by the scarcity of data and analytical inconsistencies which make the separation of locally controlled versus regionally controlled variations in nodule composition difficult between 1978 and 1981 the ocean minerals company omco conducted extensive surveys in the northeastern tropical pacific ocean during this time the average bulk geochemistry of nodules from 4657 grab samples collected from an area of approximately 1 5 million km2 was determined using highly uniform and closely controlled analytical protocols because of its broad areal coverage large sample size and the consistency of the analytical techniques employed this data set is ideally suited to quantitatively examine longstanding hypotheses concerning the factors that control the regional scale variability of nodule compositions a combination of geostatistical techniques have been employed to achieve this objective the results of a q mode factor analysis of the geochemical data indicate that the nodules are composed of a two component mixture of material acquired from both sediment and seawater sources via diagenetic and hydrogenetic accretionary processes respectively linear modeling of these results determined that diagenetic accretion is the predominant accretionary processes in this region of the pacific finally a kriging analysis was employed to examine the spatial variability of nodule composition contour maps of the kriging results suggest that variations in primary productivity levels and sedimentation rates are the primary influences on the regional scale variability of nodule composition and that the influence of diagenetic accretion is maximally approaching the equatorial zone of high productivity the nodules examined in this study are likely oligocene to miocene in age the probable paleolocations of these nodules at that time as determined by backtracking from the inferred northwesterly movement of the pacific plate would still place the nodules well within the zone of equatorial high productivity consequently while these nodules may have been subject to variations in the magnitudes of primary productivity and sedimentation rate during their active growth phase the observed compositional trends suggest that the overall spatial pattern of productivity has remained essentially the same

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

the non tropical coral cladocora caespitosa as the new climate archive for the mediterranean high resolution weekly trace element systematics abstract high resolution weekly laser ablation icp ms trace element analyses b sr u mg ba are reported for the scleractinian coral cladocora caespitosa collected from the northern adriatic sea geochemical ratios sr ca b ca mg ca u ca ba ca were measured in a 38 mm long 10 years growth external coralline portion wall region and generally exhibit a close relationship with the in situ measured weekly fortnightly data on sea surface temperature sst available for the last 6 years in particular b ca ratios tuned to fine scale variations in sst show a high degree of correlation r 0 856 n 136 with sst and indicate that coral calcification only occurs above a minimum temperature threshold of 14 16 c in addition the ranges of trace element variability are larger than those typically recorded in tropical corals consistent with the large seasonal variations in sst of the adriatic this study thus demonstrates the feasibility of extracting and exploiting high resolution geochemical records from non tropical corals such as c caespitosa as a proxy for sst

late holocene climate change for the eastern interior united states evidence from high resolution δ 18 o values of sagittal otoliths abstract stable oxygen isotope values were determined for freshwater drum aplodinotus grunniens sagittal otoliths recovered from the eastman rockshelter archaeological site in northeast tennessee to evaluate climate change for the eastern interior united states from 5500 calendar years ago to the present micromilled samples representing less than six days of otolith growth were extracted to acquire high resolution intra otolith variation in 18 o values freshwater drum sagittal otoliths form annual bands due to thermally induced growth cessation below 10 c 18 o h 2 o values can be calculated once a high resolution carbonate sample representing the beginning of the growing season is isolated maximum summer temperature can be calculated using the seasonal minimum 18 o caco 3 value and the 18 o h 2 o value maximum summer temperatures calculated from the freshwater drum sagittae suggest that summer temperatures generally decrease from 29 c at 5 5 ka to 22 c at 0 3 ka however warmer climates at 2 9 1 7 1 6 and 1 2 1 0 ka punctuate this trend a more complete picture of the climate is reconstructed because 18 o h 2 o values which are a function of the ratio of summer to winter precipitation are also calculated a relatively low average 18 o h 2 o value of 8 1 vsmow was calculated at 1 0 ka suggesting cold winters dry summers and or wet winters may have prevailed during part of the medieval warm period in tennessee contrary to studies suggesting that the holocene was extremely stable and the hypsithermal was invariably warm and dry additional evidence suggesting both significant climate variability and evidence for a wetter mid holocene is presented

rhythmic growth of pacific ferromanganese nodules and their milankovitch climatic origin the internal microstructure of a ferromanganese nodule 2392 from 154 37 52 w 9 37 56 n at water depth 5194 m was examined in detail on polished sections and radiometrically dated 230thex 232th along a high resolution 0 1 mm depth profile 0 1 3 mm spanning approximately 271 ka the fabric shows typical stromatolithic structure and exhibits four orders of basic cyclic growth pattern namely laminae bands laminae zones laminae groups and laminae pairs having average thicknesses of 402 454 185 206 58 67 and 15 18 m respectively a profile from the depth of 200 2661 m was selected to obtain the geochemical series using line scanning electron microprobe analyses which provide a record of paleoceanographic oscillations during the growth period power spectral analysis of the geochemical series for al mn fe and fe mn from the depth of 200 1220 m where no obvious discontinuity could be observed display conspicuous cyclicities the cycles of laminae zones laminae groups and laminae pairs are reflected in the spectral patterns as well the significant spectral peaks are located at 186 108 66 m together with the cycle of laminae bands the ratios of these cyclicities are close to those of milankovitch orbital cycles through tuning to orbital cycles a net growth rate of 4 5 mm ma is derived for the profile which is in perfect agreement with the growth rate of 4 6 mm ma determined by 230thex 232th dating therefore the rhythmic growth of ferromanganese nodules appears definitely associated with milankovitch cycles and the growth cyclicities may offer a new tool for estimating growth rates of ferromanganese nodules and paleoenvironmental reconstruction at substage resolution when supported by radiometric dating

the formation of manganese nodules between the clarion and clipperton fracture zones southeast of hawaii abstract three areas in the equatorial north pacific between the clarion and clipperton fracture zones were investigated regarding depositional and diagenetic processes during manganese nodule formation the areas lie on a nw se trending trace of the pacific plate southeast of hawaii the manganese nodule facies shows low nodule abundance and low grade cu ni co nodules in the northwest but high abundance and high grade nodules in the southeast the abundance size structure and composition of the nodules are determined by the nature of the underlying sediment breaks in sedimentation during the oligocene and miocene play a highly significant role in the formation of manganese nodules this was the time when the growth of most nodules began favoured by an abundance of potential nuclei ample supply of organic matter and of skeletal material was important for the diagenetic growth of nodules rich in cu ni and co a large amount of organic matter stimulated bioturbation and hence lifting by benthic organisms which in turn kept the nodules on top of the sediment even during the post hiatus periods the two areas in the southeast were always located in a zone of high biological productivity and hence much organic matter was supplied to the seafloor as a consequence most of the fields containing a great abundance of nodules rich in cu ni and co are found there due to the northwestward motion of the pacific plate the northwestern area has been located at least since the early miocene outside the region with such favourable conditions nodules of low abundance and poor in cu ni and co are dominant in spite of this distinct differentiation into two major or regional nodule facies areas each area within itself is very complex the development of the minor or local nodule facies is determined mainly by the position of the nodules in relation to the calcite compensation depth the post hiatus sediment thickness the degree of reworking the potential for formation of nuclei during hiatus periods and the rate of supply or decomposition of organic matter these factors are in turn strongly controlled by the morphology of the seafloor and the activity of bottom currents

an assessment of bottom current controlled sedimentation in pacific ocean abyssal environments the effect of the circulation of polar sourced dense waters on the deep seafloor is still largely unknown this paper presents multibeam bathymetric evidence for the existence of present day contourite drifts on the central pacific ocean at depths ranging between 4000 and 5000 m based on the identification of their diagnostic erosive moats linear moats furrows and abyssal sinuous channels and depositional plastered elongated separated and abyssal contourite fan drifts contourite morphological features these contourite drifts display a patchy distribution sculpted by the secondary flows of the lower circumpolar water lcpw and the north pacific deep waters npdw as well as local dynamics of the flow in the form of internal waves and bottom currents modulated by tides which are capable of accelerating the typically sluggish bottom currents and contribute to the erosion transport and deposition of sediments the formation of contourites is also predominantly controlled by the presence of large scale tectonic and volcanic features ridges seamounts and deep elongated valleys which affect the morphology and distribution of the basins and induce the acceleration of bottom currents overall this study allows to re assess the effects distribution and significance of bottom current controlled sedimentation in abyssal environments where examples of contourite features are still rather scarce in part because of the technical challenges and their remote location but also because the effect of bottom currents is not well known in the central oceanic basins and only capable of marginally affecting their sedimentological record

otolith microchemistry of modern versus well dated ancient naked carp gymnocypris przewalskii implication for water evolution of lake qinghai there is ongoing debate over how the water level and composition of the water in lake qinghai changed in the past and might change in future this study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from lake qinghai during the little ice age lia a close correlation between the ages measured on fish bone and otoliths by ams 14c and by optically stimulated luminescence on overlying sediments confirms a high water level in lake qinghai before 680 300 years ago the contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18o mg li b and to a lesser extent ba but depleted in 13c owing to strong evaporation authigenic carbonates precipitation micro organism activity and less fresh water input after it was isolated if there were long term fresh water input however a reverse trend might occur the most important observation is that because the waters have been supersaturated with respect to carbonates authigenic carbonate precipitation would result in low but consistent sr ca ratios in the lakes as recorded by both the ancient and modern otoliths the geochemical records of ancient versus modern biogenic carbonates provide insights into the long term hydroclimatic evolution processes of an inland water body

origin and order of cyclic growth patterns in mat ministromatolite bioherms from the proterozoic wumishan formation north china abstract the mat ministromatolite bioherms from the proterozoic wumishan formation exhibit three orders of cyclic growth patterns the growth cycle can be interpreted in terms of daily monthly and seasonal periodicities mat ministromatolite bioherms used as palaeontological clocks are limited to a short daily and monthly growth cycle based on the study of these stromatolites it is estimated that there may have been about 40 to 49 palaeo days per palaeo month of 1200 ma age

growth response of a deep water ferromanganese crust to evolution of the neogene indian ocean abstract a deep water ferromanganese crust from a central indian ocean seamount dated previously by 10 be and 230 th excess was studied for compositional and textural variations that occurred throughout its growth history the 10 be 9 be dated interval upper 32 mm yields an uniform growth rate of 2 8 0 1 mm ma frank m o nions r k 1998 sources of pb for indian ocean ferromanganese crusts a record of himalayan erosion earth planet sci lett 158 pp 121 130 which gives an extrapolated age of 26 ma for the base of the crust at 72 mm and is comparable to the maximum age derived from the co model based growth rate estimates this study shows that fe mn oxyhydroxide precipitation did not occur from the time of emplacement of the seamount during the eocene 53 ma until the late oligocene 26 ma this paucity probably was the result of a nearly overlapping palaeo ccd and palaeo depth of crust formation increased early eocene productivity instability and reworking of the surface rocks on the flanks of the seamount and lack of oxic deep water in the nascent indian ocean crust accretion began older zone with the formation of isolated cusps of fe mn oxide during a time of high detritus influx probably due to the early miocene intense erosion associated with maximum exhumation of the himalayas op cit this cuspate textured zone extends from 72 mm to 42 mm representing the early miocene period intense polar cooling and increased mixing of deep and intermediate waters at the close of the oligocene might have led to the increased oxygenation of the bottom water in the basin a considerable expansion in the vertical distance between the seafloor depth and the ccd during the early miocene in addition to the influx of oxygenated bottom water likely initiated fe mn crust formation pillar structure characterises the younger zone which extends from 40 mm to the surface of the crust i e 15 ma to present this zone is characterised by 25 higher content of oxide bound elements than in the older zone possibly corresponding to further increased oxygenation of bottom waters increased stability of the seamount slope and gradually reduced input of continental detritus from the erosion of the himalayas middle miocene antarctic glaciation which peaked 12 13 ma ago increased the oxic bottom water influx to the basin resulting in accretion of the crust with low detritus therefore the younger crust started to accrete in response to a shift in bottom water circulation towards the contemporary pattern which produced a uniform growth rate and pillar structure up to the present

fish otolith geochemistry environmental conditions and human occupation at lake mungo australia abstract fish otoliths from the willandra lakes region world heritage area south western new south wales australia have been analysed for oxygen isotopes and trace elements using in situ techniques and dated by radiocarbon the study focused on the lunettes of lake mungo an overflow lake that only filled during flooding events and emptied by evaporation and lake mulurulu which was part of the running willandra creek system samples were collected from two different contexts from hearths directly associated with human activity and isolated surface finds ams radiocarbon dating constrains the human activity documented by five different hearths to a time span of less than 240 years around 19 350 cal bp these hearths were constructed in aeolian sediments with alternating clay and sand layers indicative of fluctuating lake levels and occasional drying out the geochemistry of the otoliths confirms this scenario with shifts in sr ca and ba ca marking the entry of the fish into lake mungo several years before their death and a subsequent increase in the 18 o by 4 indicating increasing evaporation of the lake during sustained lake full conditions there are considerably fewer traces of human presence it seems that the evaporating lake mungo attracted people to harvest fish that might have become sluggish through oxygen starvation in an increasingly saline water body easy prey hypothesis in contrast surface finds have a much wider range in radiocarbon age as a result of reworking and do not necessarily indicate evaporative conditions as shown by comparison with otoliths from upstream lake mulurulu

lacustrine fluvial interactions in australia s riverine plains climatic forcing of fluvial systems has been a pre occupation of geomorphological studies in australia since the 1940s in the riverine plain southeastern australia the stable tectonic setting and absence of glaciation have combined to produce sediment loads that are amongst the lowest in the world surficial sediments and landforms exceed 140 000 yr in age and geomorphological change recorded in the fluvial fluvio lacustrine and aeolian features have provided a well studied record of quaternary environmental change over the last glacial cycle the region includes the willandra lakes whose distinctive lunette lakes preserve a history of water level variations and ecological change that is the cornerstone of australian quaternary chronostratigraphy the lunette sediments also contain an ancient record of human occupation that includes the earliest human fossils yet found on the australian continent to date the lake level and palaeochannel records in the lachlan willandra system have not been fully integrated making it difficult to establish the regional significance of hydrological change here we compare the willandra lakes environmental record with the morphology and location of fluvial systems in the lower lachlan an ancient channel belt of the lachlan willandra creek acted as the main feeder channel to willandra lakes before channel avulsion caused the lakes to dry out in the late pleistocene electromagnetic surveys geomorphological and sedimentary evidence are used to reconstruct the evolution of the first new channel belt following the avulsion single grain optical dating of floodplain sediments indicates that sedimentation in the new middle billabong palaeochannel had commenced before 18 4 1 1 ka a second avulsion shifted its upper reaches to the location of the present lachlan river by 16 2 0 9 ka the timing of these events is consistent with palaeohydrological records reconstructed from willandra lakes and with the record of palaeochannels on the lachlan river upstream willandra lakes shows high inflows during the last glacial maximum 22 ka but their subsequent drying between 20 5 ka and 19 ka was caused by river avulsion rather than regional aridity this case study highlights the benefits of combining fluvial with lacustrine archives to build complementary records of hydrological change in lowland riverine plains

stromatolites and earth sun moon dynamics inclination of stromatolite columns caused by nonvertical direction of averaged incident solar radiation provides a signal for deducing astronomical and geophysical data at time of stromatolite formation a sample of anabaria juvensis bitter springs formation central australia shows a sinusoidal growth pattern which interpreted as an annual signal obliquity of the ecliptic with daily production of laminae indicates 435 days per year a result consistent with other available estimates a sample of inzeria from the same formation also shows a sinusoidal pattern and a similar estimate for days per year both samples indicate growth rates of centimeters per year several laboratory measurement techniques offer systematic procedures for extracting data

alteration of otolith aragonite effects of prehistoric cooking methods on otolith chemistry geochemical analyses of fish otoliths from archaeological sites are a valuable source of paleoclimate data a common assumption in such research is that the otolith chemistry is unaltered from the time of capture until excavation although post depositional diagenesis will vary between sites according to local burial conditions the effects of common pre depositional treatment such as cooking or trash disposal can be evaluated experimentally six atlantic croaker micropogonius undulatus and six gafftopsail catfish bagre marinus were treated using five different methods to simulate cooking and trash disposal the left sagittal otolith was removed as an experimental control prior to cooking or burning each fish after cooking or burning the remaining otolith was removed and each otolith pair was tested to measure changes in crystallography carbon and oxygen isotope content and elemental chemistry recrystallization and changes in isotope chemistry only occurred in burned otoliths in contrast elemental composition was altered during each treatment method these experiments validate the use of carbon and oxygen isotope analyses of unburned otoliths in paleoclimate research but suggest caution in the interpretation of elemental data

episodic fluvial activity of inland rivers in southeastern australia palaeochannel systems and terraces of the lachlan river inland rivers in southeastern australia preserve a long record of surface palaeochannels accompanied by alluvial terraces that reflect changes in water and sediment discharges from the southeastern highlands through much of the last glacial cycle a compilation of ages on rivers of the southern murray darling basin together with new dates from the lachlan river suggest that the fluvial response to climate change has been regionally consistent and responsive to climate change on timescales 10 ka for much of the last glacial cycle inland rivers were mixed load sinuous single and anabranching channels that carried bankfull discharges of between 3 and 11 times present day rivers incision of the upper alluvial plains and valleys occurred in the lead up to the coldest part of the last glacial cycle this was followed at 34 ka by the synchronous development of large meandering channels that may have been associated with lower evapotranspiration from alpine highland catchments accompanied by higher precipitation smaller channels and declining lateral channel sedimentation suggests arid climates during the last glacial maximum and late glacial period with seasonally large actively migrating channels being maintained in rivers dominated by snowmelt runoff from the australian alps during the holocene sensitivity to recorded changes in precipitation amounts and variability differed between catchments with some rivers constructing larger or more actively migrating channels in the early to mid holocene

using 234u 238u to assess diffusion rates of isotope tracers in ferromanganese crusts abstract ferromanganese crusts record seawater isotope history for several elements useful for paleoceanography interpreting crust isotope profiles however requires an assessment of the rate of diffusion of each element within the crust we address this issue using u and th isotope profiles coupled with concentration measurements of some trace elements whose isotopes are often measured in crusts a depth profile of 230thxs 234u for a north atlantic crust alv539 yields a growth rate of 3 05 mm myr consistent with an existing 10be 9be record but the growth rate implied by a 234u 238u profile in the same crust is 6 times faster due to diffusion of u in the crust the difference between the observed 234u 238u profile and that expected from 230thxs 234u enables the effective diffusivity of u to be calculated as 1 2 10 6 cm2 year recalculated literature data indicate that other crusts have diffusivities which range down to 4 7 10 8 cm2 yr this variation is to be expected given the range of porosity observed for ferromanganese crusts concentration measurements of various elements in the surface layer of the crust provide relative distribution coefficients for each element between seawater and crust these distribution coefficients enable the effective diffusivity of each element to be calculated by comparison with the diffusivity of u such diffusivities are assessed for crust alv539 and give a first indication of the expected preservation of isotope signals in ferromanganese crusts li os and sr have diffusivities of 2 10 4 3 10 5 and 2 10 5 cm2 year respectively and diffusion is expected to be sufficiently fast that crusts will not accurately preserve past seawater compositions th nd pb and be have diffusivities less than 10 9 cm2 year and are highly immobile in crusts a reassuring result for th and be crust chronologies and for nd and pb isotope tracing of past water masses using crusts hf has a diffusivity of 3 10 8 in alv539 fast enough to perturb but not destroy its isotope history for studies of hf in this and other crusts diffusion should therefore be considered measuring u isotope profiles provides a potential way of assessing such diffusion for hf or for other elements with relatively low distribution coefficients into ferromanganese crusts

depositional history and archaeology of the central lake mungo lunette willandra lakes southeast australia abstract lake mungo presently a dry lake in the semi arid zone of southeastern australia preserves a unique record of human settlement and past environmental change within the transverse lunette that built up on its downwind margin the lunette is 30 km long and the variable morphology along its length suggests spatial variability in deposition over time consequently this presents differential potential for the preservation of past activity traces of different ages along the lunette earlier work at lake mungo focused primarily on the southern section of the lunette where two ritual burials of considerable antiquity were found here we describe the depositional history of the central section of the lake mungo lunette together with the first single grain optically stimulated luminescence osl chronology of the full stratigraphic sequence and of three hearths we thereby lay the foundation for systematic investigation of the distribution of archaeological traces through the sedimentary record the older depositional units lower and upper mungo were deposited ca 50 40 ka and 34 ka respectively and are substantially thinner in the central section of the lunette compared with the south by contrast the overlying unit of interbedded sands and clayey sands arumpo zanci units deposited ca 25 14 ka is markedly thicker and dominates the stratigraphic sequence in the central portion of the lunette although the sequence broadly reflects previous models of the lunette s depositional history and changing hydrological conditions our results indicate spatially variable deposition of sediments possibly as a result of changes in prevailing wind regimes archaeological traces are exposed in all stratigraphic units deposited after ca 50 ka including sediments deposited after the final lake drying ca 15 ka indicating human occupation of the area under a range of palaeoenvironmental conditions dating and stratigraphical examination of individual hearth features demonstrates that even within individual stratigraphic units human occupation persisted under variable conditions mid holocene occupation of the area following the final lake retreat took place during a period of relatively humid climate

characterization of mg ca distributions in planktonic foraminifera species by electron microprobe mapping 1 the distribution of mg ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping species include several that are commonly used for estimation of past seawater temperatures globigerinoides ruber g sacculifer neogloboquadrina incompta synonym of n pachyderma dex n dutertrei and g truncatulinoides each of the investigated species displays large variations in mg ca composition within individual tests however the pattern of mg ca variation is notably different between symbiont bearing and symbiont free species in symbiotic species cyclic mg ca compositional banding occurs that is characterized by narrow 1 3 m high mg ca typically 8 11 mmol mol bands intercalated between broader low mg ca typically 1 5 mmol mol bands this factor of 2 3 difference equates to an apparent calcification temperature change of 10 c or more such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of mg ca into the tests of symbiont bearing species these vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures symbiont free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr