amino acid epimerization implies rapid sedimentation rates in arctic ocean cores the palaeooceanography of the arctic ocean is less well known than any other ocean basin due to difficulties in obtaining cores and in providing a secure chronological framework for those cores that have been raised most recent investigators have suggested that low sedimentation rates 0 05 0 1 cm kyr 1 have characterized the deep basins over the past 5 myr refs 1 2 despite the glacial marine character of the sediment and proximity to major centres of shelf glaciation these calculations have been primarily based on the down core pattern in the inclination of magnetic minerals supported by uranium series 14c and micropalaeontological evidence here we analyse amino acid diagnesis in foraminifera from two gravity cores raised from the floor of the arctic ocean our results suggest that these cores span 200 kyr conflicting with the earlier estimate of 3 myr based on palaeomagnetic data the chronology of other arctic ocean cores and previous palaeoenvironmental interpretations need re evaluation

magnetostratigraphic data from late quaternary sediments from the yermak plateau arctic ocean evidence for four geomagnetic polarity events within the last 170 ka of the brunhes chron summary palaeomagnetic investigations of two sediment cores recovered from rv polarstern near the eastern slope of the yermak plateau sites ps 1533 and ps 2212 reveal convincing evidence for four polarity events of the earth s magnetic field during the last 170 ka a comprehensive rock magnetic study of the sediments proved that fine grained magnetite is the principal carrier of the remanent magnetization no changes in magneto mineralogy across the polarity transitions in the sediments investigated were found calcareous nannofossil biostratigraphy ams 14c accelerated mass spectrometry and oxygen isotope data and 10be and 230th stratigraphies yielded age ranges of 24 29 ka for the mono lake event 34 43 ka for the laschamp event 72 86 ka for the norwegian greenland sea event and 118 128 ka for the blake event two reverse polarity samples at the base of core ps 2212 3 kal are interpreted as the termination of the biwa i event 171 181 ka the events exhibit full inversion of inclination in both cores the data suggest that the transition process of the earth s magnetic field during such polarity events requires some 1 ka

character paleoenvironment rate of accumulation and evidence for seismic triggering of holocene turbidites canada abyssal plain arctic ocean abstract four box cores and one piston core show that holocene sedimentation on the southern canada abyssal plain for the last 8010 120 yr has consisted of a continuing rain of pelagic organic and ice rafted clastic sediment with a net accumulation rate during the late holocene of 10 mm 1000 yr and episodically emplaced turbidites 1 5 m thick deposited at intervals of 830 to 3450 yr average 2000 yr the average net accumulation rate of the mixed sequence of turbidites and thin pelagite interbeds in the cores is about 1 2 m 1000 yr physiography suggests that the turbidites originated on the mackenzie delta or its clinoform and 13c values of 27 to 25 in the turbidites are compatible with a provenance on a delta extant displaced neritic and lower slope to basin plain calcareous benthic foraminifers coexist in the turbidite units their joint occurence indicates that the turbidites originated on the modern continental shelf and entrained sediment from the slope and rise enroute to their final resting place on the canada abyssal plain the presence of middle pleistocene diatoms in the turbidites suggests in addition that the turbidites may have originated in shallow submarine slides beneath the upper slope or outer shelf small but consistent differences in organic carbon content and 13c values between the turbidite units suggest that they did not share an identical provenance which is at least compatible with an origin in slope failures the primary provenance of the ice rafted component of the pelagic beds was the glaciated terrane of northwestern canada and the provenance of the turbidite units was pleistocene and holocene sedimentary deposits on the outer continental shelf and upper slope of the mackenzie delta largely local derivation of the sediment of the canada abyssal plain indicates that sediment accumulation rates in the arctic ocean are valid only for regions with similar depositional sources and processes and that these rates cannot be extrapolated regionally the location of an elliptical zone of active seismicity over the inferred provenance of the turbidites suggests that they were triggered by large earthquakes distal turbidite sediment accumulation rates were more than two orders of magnitude greater than pelagic sediment accumulation rates on the canada abyssal plain during the last 8000 years this disparity reconciles the discrepancy between the high accumulation rates assumed by some for the arctic ocean because of the numerous major rivers and large ice sheets that discharge into this small mediterranean basin and the low pelagic sedimentation rates that have been reported from the arctic ocean

book review biogeochemistry of amino acids edited by p e hare t c hoering and k king jr wiley 1980 538 pp 30 50

biostratigraphy and late cenozoic paleoceanography of the arctic ocean foraminiferal lithostratigraphic and isotopic evidence detailed studies of benthonic foraminifera stable isotopes and lithofacies in cores from the southeastern alpha ridge central arctic ocean reveal some new aspects of arctic ocean paleoceanography high ratios of benthonic to planktonic foraminifera are found in most of the quaternary sediment units and ratios of 1 1 appear to characterize the arctic deep water sediments benthonic foraminifera in the carbonate mud unit m show a succession of calcareous species reflecting increased influx of norwegian sea bottom water to the arctic ocean during the past 0 4 m y foraminiferal and lithological data indicate less uniform sedimentation during a warmer interval from 0 4 to 0 6 ma when most of the silty lutite unit l was deposited at the cesar site lower pleistocene units j to i contain less limestone and more dolomite and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera upper pliocene units h to ab contain rare limestone and relatively large amounts of do lomite and quartz sand middle to upper pliocene units ab to a3 are marked by abundant sand sized ferromanganese coated particles which in many cases have a silt nucleus hence much of the coarse sand in these units does not indicate increased ice rafting the pliocene sediments mostly contain a low diversity assemblage of agglutinated foraminifera but a mixed calcareous arenaceous fauna occurs in a short interval above the matuyama gauss boundary 2 4 ma stable isotopic curves occur within sequences which broadly correspond to stages 1 9 of the global record below stage 9 the record is discontinuous strong vertical mixing apparently prevailed during most of the pliocene and early pleistocene then decreased during the past 0 4 m y owing to damping by a perennial ice cover isotopic and foraminiferal data however suggest that an interval of perennial sea ice also occurred during the late pliocene at the time of the earliest glacial event recorded in the north atlantic

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

an arctic perspective on dating mid late pleistocene environmental history to better understand pleistocene climatic changes in the arctic integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required not least for correlation to extra arctic records in this paper we discuss from an arctic perspective methods and correlation tools that are commonly used to date arctic pleistocene marine and terrestrial events we review the state of the art of arctic geochronology with focus on factors that affect the possibility and quality of dating and support this overview by examples of application of modern dating methods to arctic terrestrial and marine sequences event stratigraphy and numerical ages are important tools used in the arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes age control is commonly provided by radiocarbon luminescence or cosmogenic exposure ages arctic ocean deep sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition patterns in palaeomagnetic records and increasingly biostratigraphic data many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning recent advances in dating technology calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material i e foraminifera for c 14 and single grain luminescence however for much of the pleistocene there are still limits to the resolution of most dating methods consequently improving the accuracy and precision analytical and geological uncertainty of dating methods through technological advances and better understanding of processes are important tasks for the future another challenge is to better integrate marine and terrestrial records which could be aided by targeting continental shelf and lake records exploring proxies that occur in both settings and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

quaternary dinoflagellate cysts in the arctic ocean potential and limitations for stratigraphy and paleoenvironmental reconstructions abstract the arctic ocean is a siliciclastic depositional environment which lacks any rock forming biogenic calcareous and siliceous components during large parts of its quaternary history these hemipelagic sediments are nevertheless suitable for the study of organic walled microfossils of which the fossil remains of dinoflagellates dinoflagellate cysts are the most important group dinoflagellate cysts have become an important tool in paleoceanography of the high northern latitudes but their potential for quaternary biostratigraphy has remained largely unexplored dinoflagellate cysts are the dominant marine palynomorph group which is more continuously present in the marginal seas e g barents sea bering sea than in the arctic ocean itself throughout the quaternary most species have long stratigraphic ranges are temporary absent and show abundance variations on glacial interglacial timescales of the more than 30 taxa recorded only habibacysta tectata and filisphaera filifera became extinct in the pleistocene the highest persistent occurrence of h tectata at ca 2 0 ma and the top of f filifera acme at ca 1 8 ma can be used for supra regional stratigraphic correlation between the arctic ocean and adjacent basins these events corroborate a slow sedimentation rate model for the quaternary section on the central lomonosov ridge but a combination of different methods will have to be applied to provide a detailed chronostratigraphy the occurrence of cysts of phototrophic dinoflagellates in certain stratigraphic intervals on lomonosov ridge supports published evidence of episodic opening of the multiyear arctic sea ice cover during the quaternary probably related to a stronger inflow of atlantic water this contradicts the hypothesis of a permanently ice covered central arctic ocean in the quaternary

paleomagnetic constraints on sedimentation ratesin the eastern arctic ocean abstract deep sea sediments recovered from six sites visited during the international arctic ocean expedition of 1991 were examined to determine sedimentation rates in the eastern arctic ocean basin the dearth of age diagnostic biogenic material in these sediments precludes the application of biostratigraphic methods but ages can be deduced using paleomagnetism in conjunction with measurements of radiocarbon and carbonate concentration although no one of these techniques gives an unambiguous determination of age the interpretation most consistent with these diverse data implies that sedimentation rates in the eastern arctic are in general a few centimeters per thousand years such estimates of sedimentation rate are an order of magnitude greater than those previously determined from many sediment cores taken from the canada basin however one site examined on the morris jesup rise shows a relatively low rate of sediment accumulation less than 0 6 cm 103yr suggesting that although higher than in the canada basin sedimentation rates in the eastern arctic can be highly variable

optically stimulated luminescence dating supports central arctic ocean cm scale sedimentation rates 1 this paper presents new results from optically stimulated luminescence osl dating on a sediment core raised from the crest of the lomonosov ridge in the central arctic ocean there has been much debate about dating sediment cores from the central arctic ocean and by using an independent absolute dating technique we aim to test whether or not relatively fast cm scale ka sedimentation rates were typical of arctic s pleistocene depositional mode on the basis of mainly paleomagnetic reversal stratigraphy many previous studies suggest mm scale ka sedimentation rates a common feature in these studies is that the first down core paleomagnetic negative inclination is consistently interpreted as the brunhes matuyama boundary at about 780 ka our osl dating results indicate that this assumption is not generally valid and that the first encountered negative inclination represents younger age excursions within the brunhes chron implying reinterpretation of many published core studies where paleoenvironmental reconstructions have been made for the central arctic ocean our dating results furthermore corroborates a correlation of the uppermost 2 3 m of the lomonosov ridge cores to a well dated core located off the barents kara sea margin that in turn is correlated to cores in the fram strait valuable information on the paleoceanographical evolution in the arctic ocean from mis 6 to the holocene is given through this correlation of records from the central arctic ocean to records off the eurasian continental margin

pleistocene paleoceanographic correlations northern greenland sea to central arctic ocean abstract correlation of pleistocene paleoceanographic events across parts of the polar seas is accomplished with core mg 123 from the swedish ymer 80 cruise the 8 72 m sediment core one of the longest recovered from any part of the arctic ocean contains abundant microfossils and coarser grain sediment that are useful in interpretation and correlation of pleistocene events with shorter sediment cores in the central arctic ocean faunal and sediment correlations are constrained by 18 o correlations and a time series analysis that matches several possible sedimentation rates for mg 123 with central arctic ocean sedimentation rates and provides a best fit correlation of the cores the results of this study provide the first correlation of northern greenland sea southern arctic ocean sediment with that of the central arctic ocean more than 1000 km distant oceanic circulation patterns between the areas during the pleistocene involved increased circulation during interglacials with reduced circulation during glacials subpolar water was not present in the northern greenland sea during the past 600 000 years during this time alternating phases of the climate cycle show a strong relationship to the 100 000 year milankovitch cycle

testing models of past ocean chemistry using foraminifera 15n 14n previous models have attempted to explain glacial to interglacial changes in atmospheric pco2 by invoking changes in the ocean s nutrient concentration or regional changes in nutrient utilization nitrogen is limiting to primary production and has a residence time in the ocean compatible with glacial to interglacial variations but up to now there has been no geological indicator for glacial to interglacial changes in the ocean s nitrogen cycle we propose that 15n 14n ratios for the organic matrix of preserved foraminifera yield an interpretable 15n record we have developed models to study the relationship between plausible changes in the ocean s nitrogen cycle and resulting changes in the 15n 14n ratio of dissolved no3 our model results demonstrate that 15n 14n ratios exhibit excursions during periods in which the oceans are accumulating or losing nitrogen regardless of the means by which these changes occur foraminifera 15n 14n results for a pacific and an atlantic core provide evidence against wide spread glacial anoxia a consequence of many models of ocean chemistry we suggest that increasing shelf sediment denitrification upon deglaciation reduced nitrogen concentrations in the modern ocean ambiguities between the two foraminifera 15n 14n records indicate that local effects associated with changes in hydrography or ecology need to be studied further

a 2000 year tree ring record of annual temperatures in the sierra nevada mountains tree ring data have been used to reconstruct the mean late season june through january temperature at a timberline site in the sierra nevada california for each of the past 2000 years long term trends in the temperature reconstruction are indicative of a 125 year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records the results indicate that both the warm intervals during the medieval warm epoch a d 800 to 1200 and the cold intervals during the little ice age a d 1200 to 1900 are closely associated with the 125 year period significant changes in the phase of the 125 year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior

magnetostratigraphy and palynology demonstrate at least 4 million years of arctic ocean sedimentation it has long been recognized1 2 that the arctic ocean has a major role in regulating the timing of northern hemisphere glaciations global heat exchange and ocean circulation several recent studies3 7 have attempted to interpret the palaeoclimatic record in sediment cores from the arctic ocean but conflicting ages have been reported for palaeoclimatic events dated by different methods3 6 to establish a consistent chronology for cores from the central arctic ocean we performed detailed palaeomagnetic and palynological studies of three cores collected7 near the crest of the alpha ridge and obtained radiocarbon dates from planktonic foraminifers isolated from 1 cm thick intervals magnetic inclination values for these cores clearly record normal and reversed polarity intervals that apparently correspond to the brunnes and matuyama magnetochrons the longest core also includes polarity intervals typical of the gauss and gilbert magnetochrons this chronology is confirmed by the first and last occurrences of pollen and dinoflagellate species that can be correlated with european8 9 and dsdp10 12 chronostratigraphies dated by standard biochronological methods micromass radiocarbon dates for foraminifers indicate a sedimentation rate of 1 mm per 1 000 yr we believe that these data confirm a long 4 myr chronology for the alpha ridge cores the lithostratigraphy of which can be correlated over extensive areas of the western arctic ocean2 7 and more important provide dinoflagellate and palynomorph data that indicate the validity of early chronology

dating late quaternary planktonic foraminifer neogloboquadrina pachyderma from the arctic ocean using amino acid racemization the long term rate of racemization for amino acids preserved in planktonic foraminifera was determined by using independently dated sediment cores from the arctic ocean the racemization rates for aspartic acid asp and glutamic acid glu in the common taxon neogloboquadrina pachyderma were calibrated for the last 150 ka using 14c ages and the emerging quaternary chronostratigraphy of arctic ocean sediments an analysis of errors indicates realistic age uncertainties of about 12 for asp and 17 for glu fifty individual tests are sufficient to analyze multiple subsamples identify outliers and derive robust sample mean values the new age equation can be applied to verify and refine age models for sediment cores elsewhere in the arctic ocean a critical region for understanding the dynamics of global climate change

late pleistocene stratigraphy and micropaleontology of a part of the eurasian basin fram basin central arctic ocean during the 1979 lomonosov ridge experiment lorex 12 short gravity cores were collected from the fram basin part of the eurasian basin on the eastern flank of the lomonosov ridge sediments of these cores are organized into 11 lithologic units that constitute the first stratigraphy for any part of the deeper eurasian basin foraminifera are the same species that have been described elsewhere in the central arctic ocean but are abundant only in the uppermost part of the cores neogloboquadrina pachyderma is the most abundant species but the presence ofeponides tumidulus horvathi andstetsonia arctica in core ssk 2 provide a general chronologic framework for interpreting the fram basin sediment the stratigraphy a k is unique and is only partially correlated with other sediments of the north polar region including that of the adjacent lomonosov ridge and makarov basin amerasian basin differences in stratigraphies of the lomonosov area are interpreted to be at least in part the result of winnowing by turbidity currents and by currents crossing the ridge from the fram basin toward the makarov basin the sediment consists of silty lutites and sandy lutites as well as laminated lutites interpreted to have been deposited as a result of glacial marine and turbidite sedimentation these short cores document the same sedimentary processes in part of the arctic ocean east of the lomonosov ridge as have been previously reported for the western amerasian basin

organic carbon burial rates across the arctic ocean from the 1994 arctic ocean section expedition abstract estimates of organic carbon burial rates were obtained from the canada us 1994 arctic ocean section expedition using a relationship between dissolved ammonium gradients in sediment pore water and organic carbon burial rates data from 9 locations more than 200 km west of the lomonosov ridge indicate that organic carbon burial rates average 0 01 g c m 2 year 1 at 4 stations within 100 km of the lomonosov ridge carbon burial rate increases 9 fold to an average of 0 09 g c m 2 year 1 enhanced carbon burial rates and organic carbon concentrations at the lomonosov ridge and in the eurasian basin appear to be related to higher terrestrial carbon supply to the eurasian basin and to the role that the lomonosov ridge plays in the circulation and mixing of the different water masses from the two major basins on either side of the lomonosov ridge

amino acid epimerization in planktonic foraminifera suggests slow sedimentation rates for alpha ridge arctic ocean interpretations of the palaeoclimatic and palaeooceanographic histories of the arctic ocean1 2 have been hampered by conflicting chronologies obtained using different dating methods magnetostratigraphic and micropalaeontological data1 4 have suggested a sedimentation rate of 1 mm kyr 1 whereas the rate indicated by amino acid epimerization analyses on foraminifera5 is an order of magnitude higher to establish a firm chronology for cores from the alpha ridge arctic ocean and to help resolve the controversy between the ages assigned by different dating methods we have carried out detailed amino acid epimerization analyses on planktonic foraminifera neogloboquadrina pachyderma sinistral from a long gravity core assuming that the temperature in the arctic ocean did not exceed 3 c during the past 1 myr the alloisoleucine isoleucine alle ile ratios obtained from this core suggest a sedimentation rate of 1 mm kyr 1 supporting previous magnetostratigraphic and micropalaeontological studies

andean uplift and climate change sedimentological data indicate that a semi arid arid climate prevailed across the central andes from 15 ma to 4 ma between 4 and 3 ma a switch to hyperaridity occurred along the western margin of south america palaeoaltitude data suggest that a substantial proto central andean mountain range was in place between 15 and 9 ma these data support the idea that the andean rain shadow existed by 15 ma and that it reinforced the pre existing climatic regime rather than changing it the change to hyperaridity in western south america is attributed to a combination of global climate cooling and enhanced upwelling of the humboldt current generated by closure of the central american seaway between 3 5 and 3 ma and not to the andean rain shadow

stable isotope stratigraphy sedimentation rates and salinity changes in the latest pleistocene to holocene eastern central arctic ocean a high resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents has been performed on undisturbed near surface 0 40 cm sediment sequences taken in the eastern arctic ocean during the international arctic 91 expedition based on the oxygen stable isotope records measured on neogloboquadrina pachyderma sin and ams 14c dating the upper 10 to 20 cm of the sediment sequences represent isotope stage 1 and the base of termination i 15 7 ka can be identified very well stage 1 sedimentation rates vary between 0 4 and 2 0 cm kyr in general glacial stage 2 sedimentation rates are probably lower and vary between 0 4 and 0 7 cm kyr the glacial interglacial shifts in 18o values of n pachyderma sin may reach values of 1 3 to 2 5 indicating 1 that in addition to the glacial interglacial global ice volume signal changes in surface water salinity have effected the isotope records and 2 that these salinity changes have varied laterally glacial interglacial differences in salinity were small in the lomonosov ridge area 0 0 4 and relatively high in the morris jesup rise area up to 1 4 this implies that the supply of low saline waters onto the eurasian shelves and its further transport into the central arctic ocean via the transpolar drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central arctic on the morris jesup rise on the other hand the glacial low saline water signal at that time was strongly reduced in comparison to the modern situation at the glacial interglacial stage 12 boundary a strong meltwater signal is recorded in a sharp depletion in 18o as well as 13c this central arctic ocean meltwater event can be correlated from the makarov basin through the lomonosov ridge and amundsen basin to the eastern gakkel ridge the beginning of this event is ams 14c dated at 15 7 ka i e significantly older than the major decrease in the global ice volume signal which occurs between 9 and 13 5 ka large amounts of freshwater meltwater were probably supplied from the eurasian continent due to the decay of the barents sea ice sheet causing this distinct early meltwater anomaly in the central arctic ocean the extension of a well oxygenated surface near water mass in the arctic ocean and at least seasonal open ice conditions and some increased bioproductivity were probably established at the end of termination i as indicated by the increase in 13c to modern values as well as increased carbonate i e foraminifers coccoliths ostracodes and total organic carbon contents

upper cenozoic history of the labrador sea baffin bay and the arctic ocean a paleoclimatic and paleoceanographic summary foraminifera palynomorphs and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern labrador sea southern baffin bay and the alpha ridge region of the central arctic ocean foraminifera in cores from the labrador sea and southern baffin bay show glacial interglacial 18o values similar to those reported from the norwegian and greenland seas in contrast to the eastern north atlantic ocean however peaks of subarctic foraminifera and dinoflagellates in the western north atlantic cores show that relatively warm atlantic surface water continued to flow into the northern labrador sea during the early glaciation growth phases of isotopic stages 2 4 6 and 8 boreal and subarctic pollen suggest that warm atlantic air flowed into the northern labrador sea and baffin bay during the ice sheet growth phases the advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the laurentide innuitian and greenland ice sheets isotopic and microfossil records in arctic cores can also be tentatively correlated with major high latitude north atlantic glacial interglacial events magnetostratigraphic palynological and amino acid dating however shows that sedimentation on the alpha ridge has been very slow during the past 0 73 m y therefore events of less than 20 000 years duration cannot be clearly discerned interpretation of pre pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils