Jones, Glenn A · Keigwin, Lloyd D

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Recent syntheses of the history of the last Northern Hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12,000 years BP is limited. After 12,000 yr BP, however, there is sufficient evidence from radiocarbon-dated morains, raised beaches, varved lake sediments and pollen records to provide a reasonable temporal and geographica picture of the decay of the ice sheets. Here we report on the first oxygen isotope record from the Norwegian-Greenland Sea that is radiocarbon-dated directly by accelerator mass spectrometry. A significant light-oxygen-isotope event is recorded at approximately 15,000 years BP which suggests that the marine.based Barents Shelf ice sheet disintegrated rapidly at this time. Recent studies have estimated that the decay of this ice sheet could have contributed as much as 15 metres to 9 eustatic sea-level rise. The decay of the Barents Shelf ice sheet is the earliest major deglacial event yet dated, and may have triggered subsequent deglacial events through eustatic sea-level effects.

Crawford, Kevin Richard · Kuhn, Gerhard · Hambrey, Mike J

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Investigations of the stratigraphy and facies within a 2.69m long gravity core (PS1423-2) from the southwestern Weddell Sea, Antarctica, indicate a significant change in the character of glaciomarine sedimentation since grounded ice withdrew from the continental shelf. Based On visual description, X-radiography, clast shape, particle-size analysis, physical properties and geochemical data, the core used in this analysis comprises five distinct units, from top to bottom: (i) massive diamicton, (ii) weakly to well-stratified diamicton, (iii) millimetre-scale laminated muds, with little or no coarse-clastic input, (iv) well- to weakly stratified diamicton, (V) massive diamicton. This succession is attributed to the variation in sedimentation associated with the recession of the grounding line of a previously advanced glacier. Grounded ice decoupled from the continental shelf to form an ice shelf, probably initiated by a rise in sea level in response to global climatic changes. Following disintegration of the ice shelf, sedimentation was influenced by marked variations in iceberg production. AMS derived 14C ages from the upper 46 cm of the core indicate that the succession has been deposited since the end of the most recent glacial maximum (late Plektocene), a conclusion supported by published data.

Kyle, Philip R

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One of the objectives of the Cape Roberts Project is to study the tectonic history of the western Ross Sea region. Timing of the uplift of the Transantarctic Mountains, which are adjacent to the drillsite, will be a component of the tectonic studies (International Steering Committee, 1994; Cale Roberts Science Team, 1998a). The study of the clast samples from the core will be an important means of providing insight into the timing of uplift of the Transantarctic Mountains. Tholeiitic igneous rocks of the Jurassic (180 Ma) Ferrar large igneous province (FLIP) are widespreaded along the Transantarctic Mountains and have the potential to provide distinct indicators of erosion during uplift of the mountains. In the Transantarctic Mountains adjacent to the Cape Roberts drill site the FLIP is represented by lavas and pyroclastic of the Kirkpatrick basalts and by thick Ferrar dolerite sills which intrude the Beacon Supergroup sediments and, occasionally, the granitic basement rocks. In the Prince Albert Mountains, the youngest Kirkpatrick basalt lava is over 150 m thick, and has a very distinct high TiO2 chemical composition which is unique in the FLIP. If such rocks can be identified in the core they may provide precise timing of the initiation of uplift and denudation of the Transantarctic Mountains. Here we report on an examination of 20 Ferrar dolerite clasts. This brief report is intended as a pilot study to the examination of FLIP clasts from older drillcore.

McIntosh, W C · McIntosh, Bill

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40Ar/39Ar dating of volcanic clasts and pumice provide constraints for depositional ages of the CRP-1 core. Laser-fusion analyses of anorthoclase phenocrysts from pumice clasts concentrated near 116 mbsf suggest a depositional age of 18.40 ± 1.12 Ma (± 2). Results from anorthoclase phenocrysts and groundmass concentrates from five clasts of reworked lava provide maximum depositional ages of 19.73 ± 0.86 Ma to 17.15 ± 0.80 Ma for the 61 to 114 mbsf interval of CRP-1. The most precise age determination is 19.32 ± 0.14 Ma for the trachytic clasts near 105 mbsf. Taken together, the 40Ar/39Ar results from the lower part of CRP-1 suggest that none of the sediment above 116 mbsf is older than 19.5 Ma, and the data are most compatible with rapid accumulation of the 61 to 116 mbsf segment of CRP-1 near 18 Ma. 40AR/39Ar results from a basaltic clast from the carbonate-rich layer at 33 mbsf provide a maximum depositional age of 1.2 ± 0.1 Ma for this horizon.

Raine, J Ian

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Sparse pollen and spores from the lower Miocene section of CRP-1 derive from at least three sources. A low-diversity but persitent angiosperm-moss-liverwort assemblage may reflect contemporaneous herb-moss tundra and a climate with summer temperatures similar to that of islands in the vicinity of the Antarctic Convergence today. More diverse Nothofagus-podocarp-Proteaceae assemblages at c. 70 mbsf and 100- 116 mbsf may rcflect woody vegetation growing nearby in warmer sites or periods, long distance transport, or redeposition from older strata. A contemporaneous local origin is preferred: although it is not possible to determine the precise form of this vegetation from palynological data, a conservative model with low-growing shrubs would imply July mean temperatures of at least 7°C. Reworked Permian-Triassic miospores are present in low numbers throughout the sequence. Pleistocene samples contain assemblages likely to have been reworked from older strata, mostly having similar taxa to the lower Miocene section, although one sample contains a Nothofagus-dominated pollen assemblage (also interpreted as reworked) similar to that of the Sirius Group of the Transantarctic Mountains

Müller, Peter J · Kirst, Georg · Ruhland, Götz · et al.

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We have analysed alkenones in 149 surface sediments from the eastern South Atlantic in order to establish a sediment-based calibration of the U37K' paleotemperature index. Our study covers the major tropical to subpolar production systems and sea-surface temperatures (SST's) between 0° and 27°C. In order to define the most suitable calibration for this region, the U37K' values were correlated to seasonal, annual, and production-weighted annual mean atlas temperatures and compared to previously published culture and core-top calibrations. The best linear correlation between U37K' and SST was obtained using annual mean SST from 0 to 10 m water depth (U37K' = 0.033 T + 0.069, r**2 = 0.981). Data scattering increased significantly using temperatures of waters deeper than 20 m, suggesting that U37K' reflects mixed-layer SST and that alkenone production at thermocline depths was not high enough to significantly bias the mixed-layer signal. Regressions based on both production-weighted and on actual annual mean atlas SST were virtually identical, indicating that regional variations in the seasonality of primary production have no discernible effect on the U37K' vs. SST relationship. Comparison with published core-top calibrations from other oceanic regions revealed a high degree of accordance. We, therefore, established a global core-top calibration using U37K' data from 370 sites between 60°S and 60°N in the Atlantic, Indian, and Pacific Oceans and annual mean atlas SST (0-29°C) from 0 m water depth. The resulting relationship (U37K' = 0.033 T + 0.044, r**2 = 958) is identical within error limits to the widely used E. huxleyi calibrations of and attesting their general applicability. The observation that core-top calibrations extending over various biogeographical coccolithophorid zones are strongly linear and in better accordance than culture calibrations suggests that U37K' is less species-dependent than is indicated by culture experiments. The results also suggest that variations in growth rate of algae and nutrient availability do not significantly affect the sedimentary record of U37K' in open ocean environments.

Kasten, Sabine · Glasby, Geoffrey P · Schulz, Horst D · et al.

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The mineralogy and geochemistry of a suite of nine manganese nodules from the South Atlantic have been determined. The Ce/La ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the Antarctic Bottom Water as has previously been successfully carried out in the Pacific Ocean. The Ce/La ratios of the nodules decrease in the sequence Lazarev Sea, Weddell Sea (10.4 and 9.7)>East Georgia Basin (6.5 and 7.1)>Argentine Basin (5.0), but then increase in the Brazil Basin (6.2) and Angola Basin (9.8 and 15.1). A further decrease was observed in the Cape Basin (7.6). An extremely high Ce/La ratio of 24.4 had already been determined for nodules sampled north of the Nares Abyssal Plain in the western North Atlantic. These data reflect the more complicated pattern of bottom water flow in the South Atlantic than in the South Pacific. The penetration of more oxygenated North Atlantic Deep Water into the South Atlantic accounts for the higher Ce/La ratios in the nodules from the Angola and Brazil basins. Based on this study, the flow path of the Antarctic Bottom Water could only be traced as far north as the Argentine Basin. The unique geochemistry of nodules from the central Angola Basin (high Mn/Fe and Ce/La ratios, high contents of Ni, Cu, Zn and Mo) appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules.

Matthies, Dietmar · Troll, Georg

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The influence of biogenic opal sediment input (mainly diatom skeletons) on the fluorine budget of marine sediments will be shown for 24 sampling stations of the antarctic regions of Bransfield Strait, Powell Basin, South Orkney Plateau and northwestern Weddell Sea. 4 bulk samples, one from each sedimentation area, contain 9 to 28 wt.-% of biogenic opal , the clay fraction of the 24 samples investigated have 2 to 82 wt.-%. The fluorine concentration in the amorphous biogenic component is 15 ppm. 300 to 800 ppm of fluorine were measured in the clay fractions, 330 to 920 ppm in their lithogenic components. Biogenic opal causes a decrease in fluorine concentration of the sediment by a considerable amount: 6 to 56 % relative to the clay fraction, due to the proportions involved. Biogenic opal is therefore taken into account as a 'diluting' factor for the fluorine budget in marine sediments.

Berger, Wolfgang H · Bickert, Torsten · Wefer, Gerold · et al.

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The age of the Brunhes-Matuyama boundary, until recently taken as 730 k.y. in standard time scales for the Quaternary (e.g., Imbrie et al., 1984; Prell et al., 1986, doi:10.1029/PA001i002p00137) and in Ocean Drilling Program results (Kroenke et al., 1991, doi:10.2973/odp.proc.ir.130.1991; Shackleton et al., 1992 doi:10.2973/odp.proc.ir.138.1992) has been revised to between 780 k.y. and 790 k.y., based on both orbital tuning of oxygen isotope data (e.g., Shackleton et al., 1990) and on new 40Ar-39Ar dates on volcanic rocks (e.g., Baksi et al., 1992, doi:10.1126/science.256.5055.356). We apply the revised chronology to an oxygen isotope record for Ontong Java Plateau (ODP Leg 130, western equatorial Pacific). Using this time scale, we find excellent agreement between the record and a template based on orbital forcing. The equation for the template is DeltaICE = IGR - INS a * ICE b * MEM L c [1] where the change in ice-mass is given as the difference between constant ice growth (IGR) and variable amounts of melting. Melting depends on summer insolation at 65°N (INS), the current ice?mass present (ICE), and the average ice?mass (MEM) over a given time interval (L). The memory base L and the exponents are adjusted for best fit. The fit to the relevant portion of the record yields an age of 790±6 k.y. for the Brunhes?Matuyama boundary. The age assignment is robust relative to substantial changes in parameter settings.

Lehman, Benoît · Laj, Carlo E · Kissel, Catherine · et al.

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3 numeric

Relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the Açores area. One core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation. Rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain-size distribution in the pseudo-single domain range for the three cores. Changes in the amount of magnetite do not exceed a factor of 10. Therefore, these cores appear to be suitable for relative palaeointensity determinations. Two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation (NRM), but the power at these frequencies is not significant at the 95% level for the normalised remanence records. For each core, normalisation of the NRM using different normalising parameters yields virtually identical results. Using saturation isothermal remanent magnetisation (SIRM) as the normalising parameter, the results of the three cores were then combined into a stacked curve. Squared coherence analysis between this stacked curve and bulk mineral-magnetic parameters reveals that the 18 kyear component is still present in the record, but that the power spectrum is barely above noise level at this frequency. Some of the features of this North Atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records. For instance, distinct periods of low intensity are observed around 40, 120, and 190 kyears, and periods of high intensity at 50 and 80 kyears. Because of the uniformity of the mineral-magnetic characteristics of the three cores, we suggest that this record may be a suitable palaeointensity reference curve for the Central North Atlantic Ocean region.

Friedrich, Jana

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In this thesis the distribution of 210Po and 210Pb in the upper 600 m of the Antarctic Circumpolar Current and the Weddell Sea was investigated along north-south transects in austral spring and autumn. 210Po and 210Pb can serve as sensitive tracers for the special hydrographic conditions of the Antarctic Circumpolar Current and the Weddell Sea as well as for biological processes during phytoplankton blooms. The 210Po/210Pb disequilibrium was used as a tracer for particle export. This tracer integrates export on a timescale of 276 days because of the 138 day half-life of 210Po and complements the 234Th/238U disequilibrium as another tracer for plankton production arid export on a shorter timescale of several weeks.The distribution of 210Pb and its granddaughter 210Po is determined by the hydrographic conditions, through decay of 226Ra in the water column and low atmospheric 210Pb input, especially in the study area, and is modified by biological processes in the surface water. Low 226Ra activity north of the Polar Front causes low activities of its daughter nuclides 210Pb and 210Po. South of the Polar Front, upwelling Circumpolar Deep Water transports higher activities of the three nuclides into the surface water.The phenomenon of a minimum in total 2l0Po at the base of the euphotic Zone reaching from the Polar Front to the central Weddell Sea was observed in austral spring and fall. It may be a characteristic feature of Antarctic Surface Waters and the following explanations are favoured:- Upwelling of Circumpolar Deep Water with high 210Po activity at the southern boundary of the Antarctic Circumpolar Current and northward advection with the Antarctic Surface Water can cause higher 210Po activity in the southern surface water. A water layer of low motion with more intense scavenging of 210Po by particles may exist at the interface between the southwardly rising Circumpolar Deep Water and northwardly moving Antarctic Surface Water, because of the prolonged water residence time. It is hypothesized that this effect, together with the preferential adsorption of 210Po (in excess of 210Pb) onto particles, creates the observed 210 minimum layer. - The 210Po minimum covers the layer of the temperature minimum of the Antarctic Surface Water. High 210Po, 210Pb and 234Th activities in sea ice samples support the hypothesis that particle-reactive radionuclides from the water column are adsorbed onto ice crystals during their formation.- The occurrence of large salp swarms in the spring conceivably produced part of the subsurface 210Po minimum. The salps graze on algae and accumulate the algal protein containing the Po.The deficiency of total 210Po relative to 210Pb was observed in the water column down to 600 m. This is due to the preferential adsorption of onto particles. During the development of a phytoplankton bloom in the Polar Frontal Region the increase in diatom abundance was reflected in the change of the particulate 210P0/210Pb ratio with time. The ratio dropped from 4 to 2 indicating that more 210Pb was adsorbed. 210Pb is better scavenged by siliceous plankton and 210Po adsorbs more effectively onto non siliceous particles. For this reason, 210Pb is a good tracer for biogenic silica export and 210Po for POC export.To quantify the particle export from the surface water in the study area, 210Po and export was calculated using the one-dimensional steady-state model of BACON et al. (1976). Because of the 138 day half-life of 210Po the calculated export integrates over a time scale of about nine months. To calculate recent export from changes in the 210Po and 210Pb activity with time during a phytoplankton bloom a non-steady-state solution for 210Po and 210Pb to the vertical scavenging model was developed after the 234Th model by BUESSELER et al. (1992). It transpired that with increasing half-life of the radionuclide the influence of water mass advection increases. Neglecting the advective and diffusive fluxes of 210Po and 210Pb under the hydrographic conditions of the ACC causes the calculated export to be to high or to small. The model gives realistic results only when calculating export from stations with identical temperature and salinity characteristics.The comparison of 210Po and 210Pb export, calculated with the steady-state model, out of the upper 100 m of the Polar Frontal Region, the southern ACC and the eastern Weddell Sea suggested highest export rates in the eastern Weddell Sea. This is in contradiction to the low sedimentation rates obtained from sediment traps and the low 210Pbxs sediment inventory. However, the high particle export signal could also be caused by adsorption of radionuclides onto sea ice, rather than by adsorption onto sinking particles.

Correns, Carl W

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Als Alfred Merz mich aufforderte, die sedimentpetrographische Bearbeitung der "Meteor"-Expedition zu übernehmen, schwebte mir von vornherein als Ziel vor, die Sedimente nicht nur in größerer Zahl als bisher und im Zusammenhang mit den übrigen Wissenschaften vom Meer nach den bisherigen Untersuchungsmethoden zu beschreiben. Es war mir klar, daß neue Ergebnisse nur zu erwarten waren, wenn die Untersuchung der Sedimente und damit ihre Beschreibung auf Grund vertiefter und neuer Methoden unternommen wurde. Ich erhoffte von einer solchen verfeinerten Beschreibung auch ein klareres Bild der Abhängigkeit der Sedimente von ihrer Umwelt. Wir werden diese Abhängigkeit nur verstehen, wenn wir die allgemeinen Gesetzmäßigkeiten herausarbeiten können. Diese werden dann auch eine Anwendung auf andere Sedimente ermöglichen. Für solche Untersuchungen sind Tiefseesedimente günstig, weil wir bei ihnen relativ einfache Bildungsumstände haben, einfacher jedenfalls, als es in der Flachsee im allgemeinen der Fall ist, ungünstig aber, weil diese Umwelteinflüsse weniger bekannt und schwerer zu erforschen sind und die Auswahl der Untersuchungspunkte nicht nach sedimentpetrographischen Gesichtspunkten erfolgen konnte.Die ersten Jahre nach der Rückkehr von der Expedition wurden deshalb auf methodische Untersuchungen verwandt. Insbesondere kam es mir darauf an herauszubekommen, wie die feinsten Bestandteile der Sedimente zusammengesetzt sind. Diese "tonigen" Bestandteile bilden nicht nur den wesentlichen Anteil der Roten Tone und der Blauschlicke, wir finden sie auch, durch Kalk verdünnt, in den Globigerinenschlämmen wieder. Sie sind von der Wissenschaft bisher recht stiefmütterlich behandelt worden. Die Ausarbeitung der Methoden, die gerade auf diesem Gebiet Neuland betreten mußte, ließ sich nicht rasch erzwingen. Es kam hinzu, daß ich mir in Rostock erst meine Arbeitsmöglichkeiten schaffen mußte. Ich habe hier der Notgemeinschaft der Deutschen Wissenschaft und der Mecklenburgischen Regierung für ihre Unterstützung mit Apparaten und Personal wärmstens zu danken. Ferner mußte als Vorbedingung für die Deutung der Sedimente zunächst festgestellt werden, zu welchen geologischen Zeiten sie gebildet worden sind und wie groß ihre Bildungsgeschwindigkeit überhaupt ist. Diese Untersuchungen hat W. Schott mit Hilfe der Foraminiferenfaunen als Notgemeinschaftsstipendiat durchgeführt.Diese Vorarbeiten, insbesondere der Ausbau der Methoden, hatten den Nachteil, daß die Veröffentlichung der Ergebnisse nicht so rasch erfolgen konnte, wie ich es selbst gewünscht hätte. Bald nachdem die Darstellung der Methoden und die Foraminiferenuntersuchungen als erste Lieferung erschienen waren, stellte es sich als notwendig heraus, eine beträchtliche Kürzung des restlichen Teiles vorzunehmen. Das hat zur Folge, daß die erste Lieferung breiter dargestellt ist als die Ergebnisse. Als die Nachricht von der Kürzung und dem notwendigen raschen Abschluß des Werkes mir bekannt wurde (Januar 1935), mußte eine Reihe von Untersuchungen eingestellt werden, insbesondere mikroskopische Untersuchungen, die besonders viel Zeit und in der Darstellung viel Raum beanspruchen. Deshalb ist systematisch nur das Guinea-Becken durch V. Leinz und das Kapverden-Becken durch O. E. Radczewski untersucht worden.

Shackleton, Nicholas J

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A careful comparison is made between the most detailed records of sea level over the last glacial cycle, and two high-quality oxygen isotope records. One is a high-resolution benthonic record that contains superb detail but proves to record temperature change as well as ice volume; the other is a planktonic record from the west equatorial Pacific where the temperature effect may be minimal but where high resolution is not available. A combined record is generated which may be a better approximation to ice volume than was previously available.This approach cannot yet be applied to the whole Pleistocene. However, comparison of glacial extremes suggests that glacial extremes of stages 12 and 16 significantly exceeded the last glacial maximum as regards ice volume and hence as regards sea level lowering. Interglacial stages 7, 13, 15, 17 and 19 did not attain Holocene oxygen isotope values; possibly the sea did not reach its present level. It is unlikely that sea level was glacio-eustatically higher than present by more than a few metres during any interglacial of the past 2.5 million years.

Sancetta, Constance A · Silvestri, Shaymaria

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Three piston cores in the subarctic region of the North Pacific show consistent changes in relative abundance of diatom species throughout the Brunhes magnetic epoch. These events can be used both as stratigraphic markers to subdivide the interval and as indicators of oceanographic conditions. The stratigraphic record shows an acme for A. ochotensis from about 625-350 Kyr (Isotope Stages 15-10); a marked increase in amplitude of abundance fluctuations for R. hebetata 300-0 Kyr (Stages 8-1), the extinction of R. curvirostris at 276 Kyr (Stage 8), and abundance fluctuations of D. seminae roughly in phase with the global oxygen isotope record from 450-0 Kyr (Stages 12-1). In the subarctic Pacific, an abrupt change in species abundance is not a reliable indicator of hiatus occurrence. Although details are not clear, there appears to have been a fundamental change of the subarctic gyre during the middle Brunhes (Stages 10-8 time), with more intense glacial intervals and stronger glacial-interglacial contrast occurring after that time. Coarse clastic detritus is not restricted to glacial intervals, suggesting that ice-rafting has occurred throughout the Brunhes interval; peak levels of ice-rafting may occur during ice-growth and decay, as well as during short intervals within a stage.

Mead, Gregory · Tauxe, Lisa · LaBrecque, John L

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Paleoceanographic changes during the Oligocene in the South Atlantic have been examined using paleomagnetic, rock magnetic, carbonate content, and sediment accumulation rate (SAR) data. We show that magnetic susceptibility (MS) is largely controlled by carbonate content at Deep-Sea Drilling Project site 522, which in turn is the primary control on SAR at the site. Over 5000 MS measurements were averaged over magnetostratigraphic polarity intervals for use as indicators of carbonate content and SAR proxies. The study produced three primary results: (1) a spectral analysis of the MS data from one upper Oligocene core reveals two dominant periodicities (44.7 +/- 10.4 kyr and 26.4 +/- 3.6 kyr) which approximate Milankovitch obliquity (41 kyr) and precession (23 kyr) periods: (2) four pulses of increased SAR lasting 1 to 2 m.y. punctuate the section, implying longer-term climatic changes (these events are also seen in the Contessa quarry section of the Italian (Tethyan) Oligocene); and (3) two of the SAR maxima correspond to times of global cooling and possible ice volume increases, at 31 and 36 Ma.

Morley, Joseph J · Pisias, Nicklas G · Leinen, Margaret W

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Time series analyses of atmospheric and oceanic variables in a late Pleistocene record from the northwest Pacific show the complex relationship of the response of various segments of the climate system to changes in the earth's orbit. Most variance spectra of time series from this subarctic record contain frequency peaks with periods corresponding to at least one of the major orbital components of eccentricity, obliquity, or precession. Although the radiolarian faunal (water mass) assemblages have prominent spectral peaks with 41,000-year periods which are coherent with obliquity at this frequency, only the Transitional faunal assemblage contains variance focused at a frequency corresponding to the 100,000-year period of eccentricity. Three of these faunal time series also show variance concentrated at a frequency with a 20,000-year period. These three time series are not coherent at a 20,000-year frequency with either of the dominant spectral peaks of precession. They are coherent, however, with variations in the second harmonic of the obliquity cycle. Changes in obliquity apparently affect siliceous faunal abundances in the northwest Pacific region of this high-latitude site more than variations in eccentricity or precession. Maxima in the time series of quartz abundance occur during low values of eccentricity and high glacial ice volume. Because atmospheric winds serve as the major source of supply of quartz to the sediments at this site, these high quartz values reflect increased aridity at the source region. Except for short periods during interglacials, the characteristics of the surface waters in this region of the subarctic Pacific during much of the last 460,000 years were similar to those which exist today in the Sea of Okhotsk. The spectrum of winter sea surface temperature estimates, derived from siliceous microfaunal abundances, contains dominant frequency peaks at periods of 100,000, 41,000, and 23,000 years which are coherent with eccentricity, obliquity, and precession, respectively. Based upon the relationship of the Subarctic Front with the dominance of specific faunal asemblages, the front was positioned south of its present-day location throughout much of the late Pleistocene.

Pisias, Nicklas G · Rea, David K

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Proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data, and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late Pleistocene: All indicators fluctuate at higher frequencies than the 100,000-year glacial-interglacial cycle, display reduced amplitude variations since 300,000 years ago, exhibit a change in the record character at about 300,000 years ago (the mid-Brunhes climatic event), and have higher amplitude variations in sediments 300,000-850,000 years old. Time series analyses were conducted to determine the spectral character of each record (delta18O of planktonic foraminifer, sea surface temperature values, equatorial divergence indicators, and wind intensity indicators) and to quantify interrecord coherence and phase relationships. The record was divided at the 300,000-year clear change in climatic variability (nonstationarity). The delta18O-based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402,000-774,000 years. The delta18O spectra show 100,000- and 41,000-year power in the younger portion, 0-300,000 years, and 100,000-, 41,000- and 23,000-year power in the older interval, all highly coherent and in phase with the SPECMAP average stacked isotope record. Unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31,000 years. This period is also important in the sea surface temperature signal where the dominant spectral peak is 100,000 years. The 31,000-year spectral component is coherent and in phase between the eolian and divergence records, confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record. Since the 31,000-year power appears in independent data sets within this core and also appears in other equatorial records [J. Imbrie personal communication, 1987], we assume it to be real and representative of both a nonlinear response to orbital forcing, possibly a combination of orbital tilt and eccentricity, and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component. The mid-Brunhes climatic event is an important aspect of these records, but its cause remains unknown.

Jasper, John P · Gagosian, Robert B

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The sedimentary record of a ratio (UK37) of long chain (C37) unsaturated alkenones is a useful indicator of glacial-interglacial climatic change in the Late Quaternary northern Gulf of Mexico where a planktonic foraminiferal delta18O-CaCO3 record is complicated by meltwater and/or fluvial events (Williams and Kohl, 1986, doi:10.2973/dsdp.proc.96.137.1986). Application of a laboratory temperature calibration of the UK37 ratio (Prahl and Wakeham, 1987, doi:10.1038/330367a0) to a Pigmy Basin hydraulic piston core record (Deep Sea Drilling Project core 619) suggested that the minimum glacial surface mixed layer (SML) temperature was 8°+/-1°C colder than the Holocene high SML temperature of 25.6°+/-0.5°C. This predicted glacial-interglacial temperature difference was significantly larger than the differences predicted by either the foraminiferal delta18O or foraminiferal assemblage temperature methods (0.8°-2.0°C). This large difference may be caused by local Prymnesiophyte assemblage changes in response to climatically induced hydrographic changes. Interglacial periods may be dominated by pelagic Prymnesiophyte assemblages, while glacial periods may be dominated by neritic assemblages. A combined mechanism of both climatically varying Prymnesiophyte species assemblage and depth of alkenone biosynthesis may account for the large difference between the temperature methods.

Broecker, Wallace S · Klas, Mieczyslawa · Clark, Elizabeth · et al.

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6 numeric · 1 text · 1 categorical

Radiocarbon ages on CaCO3 from deep-sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.