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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Mead, Gregory; Tauxe, Lisa; LaBrecque, John L (1986): Oligocene paleoceanography of the South Atlantic: paleoclimatic implications of sediment accumulation rates and magnetic susceptibility measurements. Paleoceanography, 1(3), 273-284, https://doi.org/10.1029/PA001i003p00273
    Publication Date: 2017-08-04
    Description: 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.
    Type: Dataset
    Format: text/tab-separated-values, 66 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Sancetta, Constance A; Silvestri, Shaymaria (1984): Diatom stratigraphy of the late Pleistocene (Brunhes) subarctic Pacific. Marine Micropaleontology, 9(3), 263-274, https://doi.org/10.1016/0377-8398(84)90016-1
    Publication Date: 2017-08-04
    Description: 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.
    Type: Dataset
    Format: text/tab-separated-values, 3 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Pisias, Nicklas G; Rea, David K (1988): Late Pleistocene paleoclimatology of the central equatorial Pacific: sea surface response to the southeast trade winds. Paleoceanography, 3(1), 21-37, https://doi.org/10.1029/PA003i001p00021
    Publication Date: 2017-11-17
    Description: 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.
    Type: Dataset
    Format: text/tab-separated-values, 525 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Shackleton, Nicholas J (1987): Oxygen isotopes, ice volume and sea level. Quaternary Science Reviews, 6(3-4), 183-190, https://doi.org/10.1016/0277-3791(87)90003-5
    Publication Date: 2017-08-04
    Description: 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.
    Type: Dataset
    Format: text/tab-separated-values, 82 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Lehman, Benoît; Laj, Carlo E; Kissel, Catherine; Mazaud, Alain; Paterne, Martine; Labeyrie, Laurent D (1996): Relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the Acores area. Physics of The Earth and Planetary Interiors, 93(3-4), 269-284, https://doi.org/10.1016/0031-9201(95)03070-0
    Publication Date: 2017-08-04
    Description: 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.
    Type: Dataset
    Format: text/tab-separated-values, 30 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Jasper, John P; Gagosian, Robert B (1989): Alkenone molecular stratigraphy in an oceanic environment affected by glacial freshwater events. Paleoceanography, 4(6), 603-614, https://doi.org/10.1029/PA004i006p00603
    Publication Date: 2017-08-08
    Description: 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.
    Type: Dataset
    Format: text/tab-separated-values, 99 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Singer, Alex; Shemesh, Aldo (1995): Climatically linked carbon isotope variation during the past 430,000 years in Southern Ocean sediments. Paleoceanography, 10(2), 171-178, https://doi.org/10.1029/94PA03319
    Publication Date: 2017-08-04
    Description: We use the isotopic composition of carbon from organic matter enclosed within diatom frustules as a proxy for paleoproductivity and paleo-dissolved carbon dioxide concentrations in ocean surface waters. A Southern Ocean record from south of the Antarctic Polar Front and spanning 430,000 years of carbon isotopic variation in diatomaceous organic matter is presented for the first time. The most refractory diatomaceous organic matter fraction was extracted and analyzed to avoid problems associated with diagenesis. The results clearly indicate cyclic changes in organic carbon isotopic ratios, with 13C depleted values associated with all of the last five glacial periods, reflecting changes in surface water properties and primary productivity. Changes in dissolved carbon dioxide concentrations are the most probable cause of these cycles, but the possible effect of seawater pH changes cannot be excluded.
    Type: Dataset
    Format: text/tab-separated-values, 170 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Chapman, Mark R; Shackleton, Nicholas J; Zhao, Meixun; Eglinton, Geoffrey (1996): Faunal and alkenone reconstructions of subtropical North Atlantic surface hydrography and paleotemperature over the last 28 kyr. Paleoceanography, 11(3), 343-358, https://doi.org/10.1029/96PA00041
    Publication Date: 2017-12-18
    Description: Two techniques for estimating past variations in sea surface temperature (SST) have been used to investigate climatic change in Biogeochemical Oceanic Flux Study (BOFS) core 31K (19°N, 20°W) from the eastern subtropical Atlantic. High-resolution SST records for the last 28 kyr have been produced using planktonic foraminiferal assemblages, based on the Imbrie-Kipp transfer function technique, and the UK' 37 index derived from abundances of C37 alkenones biosynthesized by prymnesiophyte algae. Modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean: the UK? 37 index corresponds to the temperature at the time of maximum coccolith productivity, typically late spring-early summer in the study area today, whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures. In general, the faunal and biomarker paleotemperature records display comparable SST variations during the last glacial and deglacial, but although the overall trends are similar, differences exist in the magnitude and timing of these temperature changes. Most notably, the faunal T warm and UK' 37 SST estimates diverge by 3°C between 8 ka and 6 ka, and this offset persists through the late Holocene. This difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels. We therefore propose that the deviation in SST estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring-early summer in the modern ocean. Our results suggest that a dual approach to SST estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late Quaternary.
    Type: Dataset
    Format: text/tab-separated-values, 210 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Hemleben, Christoph; Meischner, Dieter; Zahn, Rainer; Almogi-Labin, Ahuva; Erlenkeuser, Helmut; Hiller, Birgit (1996): Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea: Influence of global sea level change on hydrography. Paleoceanography, 11(2), 147-156, https://doi.org/10.1029/95PA03838
    Publication Date: 2017-08-04
    Description: Stable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive delta18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53 per mil and 55 per mil are inferred from pteropod and benthic foraminifera delta18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic delta18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates.
    Type: Dataset
    Format: text/tab-separated-values, 110 data points
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  • facet.materialart.
    PANGAEA
    In:  Supplement to: Kettler, Richard M (1998): Preliminary results of bitumen and kerogen analyses of the CRP-1. Terra Antartica, 5(3), 669-672, hdl:10013/epic.28326.d001
    Publication Date: 2017-08-04
    Description: Sediments and rocks recovered in CRP-1 coring operations contain relatively little organic matter (average 0.4% TOC) and very small amounts of solvent-soluble organic matter ( average 60 µg bitumen/g rock). The kerogen recovered from these rocks has atomic H:C ratios that range from 0.7 to 1.0 and atomic O:C ratios that range from 0.14-0.22. This range of values could be produced by mixing coal detritus with aquatic organic matter. Coal with the O:C ratios necessary to produce the kerogen present in the CRP-1 samples occurs in outcrops of the Permian Beacon Supergroup proximal to the drillsite.
    Type: Dataset
    Format: text/tab-separated-values, 250 data points
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