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  • PANGAEA  (53)
  • American Meteorological Society  (6)
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  • 1
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    Antarctic and Southern Ocean Surface Temperatures in CMIP5 Models in the Context of the Surface Energy Budget* (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-02-24
    Description: This study examines the biases, intermodel spread, and intermodel range of surface air temperature (SAT) across the Antarctic ice sheet and Southern Ocean in 26 structurally different climate models. Over the ocean (40°–60°S), an ensemble-mean warm bias peaks in late austral summer concurrently with the peak in the intermodel range of SAT. This warm bias lags a spring–summer positive bias in net surface radiation due to weak shortwave cloud forcing and is gradually reduced during autumn and winter. For the ice sheet, inconsistencies among reanalyses and observational datasets give low confidence in the ensemble-mean bias of SAT, but a small summer warm bias is suggested in comparison with nonreanalysis SAT data. The ensemble mean hides a large intermodel range of SAT, which peaks during the summer insolation maximum. In summer on the ice sheet, the SAT intermodel spread is largely associated with the surface albedo. In winter, models universally exhibit a too-strong deficit in net surface radiation related to the downward longwave radiation, implying that the lower atmosphere is too stable. This radiation deficit is balanced by the transfer of sensible heat toward the surface (which largely explains the intermodel spread in SAT) and by a subsurface heat flux. The winter bias in downward longwave radiation is due to the longwave cloud radiative effect, which the ensemble mean underestimates by a factor of 2. The implications of these results for improving climate simulations over Antarctica and the Southern Ocean are discussed.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 2
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    Decadal–Interdecadal Climate Variability over Antarctica and Linkages to the Tropics: Analysis of Ice Core, Instrumental, and Tropical Proxy Data (2012)
    American Meteorological Society
    Details
    Publication Date: 2012-11-01
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 3
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    Observed Antarctic Interannual Climate Variability and Tropical Linkages (2012)
    American Meteorological Society
    Details
    Publication Date: 2012-06-15
    Description: This study reviews the mechanisms associated with Antarctic–tropical climate linkages and presents new analyses of the seasonality and spatial patterns of tropical climate signals in the Antarctic for the late 1950s to the present. Tropical climate signals are primarily communicated to the Antarctic via the Pacific–South America (PSA) pattern and the southern annular mode (SAM). The impacts of these circulation patterns and their tropical linkages are evident in regressions of seasonally stratified Antarctic station temperature data and annually resolved ice core records on global fields of sea surface temperature, sea level pressure, and precipitation. Temperature and ice core anomalies in the Antarctic Peninsula region and adjoining areas of West Antarctica are significantly impacted by the PSA, interpreted as a Rossby wave train driven by anomalous tropical deep convection during ENSO events. This pattern is most evident in the austral spring, consistent with recent studies, suggesting that atmospheric conditions for Rossby wave propagation are most favorable during this season. During austral summer at the peak of the ENSO cycle, temperature anomalies at East Antarctic coastal stations exhibit significant correlations with tropical Pacific anomalies. This linkage reflects the influence of anomalous tropical heating on the position and strength of the subtropical jets and is consistent with changes in eddy momentum fluxes that alter the mean meridional circulation associated with the SAM. Of the ice cores that exhibit tropical linkages, most tend to be associated with the PSA teleconnection. The implications of the study’s findings for understanding Antarctic climate variability and climate change from seasonal to decadal time scales are also discussed.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 4
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    Comparing the Impacts of Tropical SST Variability and Polar Stratospheric Ozone Loss on the Southern Ocean Westerly Winds* (2015)
    American Meteorological Society
    Details
    Publication Date: 2015-12-01
    Description: Westerly wind trends at 850 hPa over the Southern Ocean during 1979–2011 exhibit strong regional and seasonal asymmetries. On an annual basis, trends in the Pacific sector (40°–60°S, 70°–160°W) are 3 times larger than zonal-mean trends related to the increase in the southern annular mode (SAM). Seasonally, the SAM-related trend is largest in austral summer, and many studies have linked this trend with stratospheric ozone depletion. In contrast, the Pacific sector trends are largest in austral autumn. It is proposed that these asymmetries can be explained by a combination of tropical teleconnections and polar ozone depletion. Six ensembles of transient atmospheric model experiments, each forced with different combinations of time-dependent radiative forcings and SSTs, support this idea. In summer, the model simulates a positive SAM-like pattern, to which ozone depletion and tropical SSTs (which contain signatures of internal variability and warming from greenhouse gasses) contribute. In autumn, the ensemble-mean response consists of stronger westerlies over the Pacific sector, explained by a Rossby wave originating from the central equatorial Pacific. While these responses resemble observations, attribution is complicated by intrinsic atmospheric variability. In the experiments forced only with tropical SSTs, individual ensemble members exhibit wind trend patterns that mimic the forced response to ozone. When the analysis presented herein is applied to 1960–2000, the primary period of ozone loss, ozone depletion largely explains the model’s SAM-like zonal wind trend. The time-varying importance of these different drivers has implications for relating the historical experiments of free-running, coupled models to observations.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 5
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    Recent Climate Variability in Antarctica from Satellite-Derived Temperature Data (2004)
    American Meteorological Society
    Details
    Publication Date: 2004-04-01
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 6
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    Antarctic Sea Ice Climatology, Variability, and Late Twentieth-Century Change in CCSM4 (2012)
    American Meteorological Society
    Details
    Publication Date: 2012-07-15
    Description: A preindustrial control run and an ensemble of twentieth-century integrations of the Community Climate System Model, version 4 (CCSM4), are evaluated for Antarctic sea ice climatology, modes of variability, trends, and covariance with related physical variables such as surface temperature and sea level pressure. Compared to observations, the mean ice cover is too extensive in all months. This is in part related to excessively strong westerly winds over ~50°–60°S, which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the Southern Ocean. In spite of these biases in the climatology, the model’s sea ice variability compares well to observations. The leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the Atlantic and Pacific sectors. Both the El Niño–Southern Oscillation and the southern annular mode (SAM) project onto this mode. In twentieth-century integrations, Antarctic sea ice area exhibits significant decreasing annual trends in all six ensemble members from 1950 to 2005, in apparent contrast to observations that suggest a modest ice area increase since 1979. Two ensemble members show insignificant changes when restricted to 1979–2005. The ensemble mean shows a significant increase in the austral summer SAM index over 1960–2005 and 1979–2005 that compares well with the observed SAM trend. However, Antarctic warming and sea ice loss in the model are closely connected to each other and not to the trend in the SAM.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 7
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    Age determinations on sediment core PS2208-1 (2003)
    PANGAEA
    Details
    Publication Date: 2023-06-27
    Keywords: Age, 14C AMS; Age, 14C milieu/reservoir corrected; Age, comment; Age, dated; Age, dated standard deviation; ARK-VIII/3; AWI_Paleo; DEPTH, sediment/rock; MUC; MultiCorer; Nansen Basin; Paleoenvironmental Reconstructions from Marine Sediments @ AWI; Polarstern; PS19/234; PS19 ARCTIC91; PS2208-1; Quaternary Environment of the Eurasian North; QUEEN
    Type: Dataset
    Format: text/tab-separated-values, 16 data points
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  • 8
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    Distribution of Ivory Coast microtektite layer (1991)
    PANGAEA
    In:  Supplement to: Glass, B P; Kent, Dennis V; Schneider, David A; Tauxe, Lisa (1991): Ivory Coast microtektite strewn field: description and relation to the Jaramillo geomagnetic event. Earth and Planetary Science Letters, 107(1), 182-196, https://doi.org/10.1016/0012-821X(91)90054-L
    Details
    Publication Date: 2024-01-09
    Description: During the present study the Ivory Coast microtektite layer was found in cores from five equatorial Atlantic sites, bringing the total number of Ivory Coast microtektite-bearing cores to eleven. The strewn field appears to be restricted to between 9°N and 12°S latitude. There is a general increase in the concentration of microtektites towards the Bosumtwi crater, which is generally thought to be the source of the Ivory Coast tektites. The relationship between the onset of the Jaramillo subchron and the Ivory Coast microtektite layer has been investigated in six cores. A plot of the difference in depth between the base of the Jaramillo subchron and the microtektite layer versus sediment accumulation rate was used to determine the average post-depositional remanent magnetization (PDRM) acquisition depth and the age difference between the onset of the Jaramillo subchron and the deposition of the microtektites. Assuming that the PDRM acquisition depth does not vary with sediment accumulation rate, we find that the average PDRM acquisition depth is 7 cm and that the microtektites were deposited approximately 8 ky after the onset of the Jaramillo subchron. This indicates that the impact responsible for the Ivory Coast tektites and microtektites could not be causally related to the geomagnetic reversal at the base of the Jaramillo subchron.
    Keywords: 108-660A; 108-661A; 108-664C; 108-664D; 108-665A; 108-665B; DRILL; Drilling/drill rig; Equatorial Atlantic; GC; Gravity corer; Joides Resolution; K09-57; Leg108; Ocean Drilling Program; ODP; PC; Piston corer; RC13; RC13-210; RC13-213; RC16; RC16-75; Robert Conrad; South Atlantic Ocean; V26; V26-51; V27; V27-239; V30; V30-45; Vema
    Type: Dataset
    Format: application/zip, 7 datasets
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  • 9
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    Paleomagnetism of ODP Leg 115 sediments (1990)
    PANGAEA
    In:  Supplement to: Schneider, David A; Kent, Dennis V (1990): Paleomagnetism of Leg 115 sediments: implications for Neogene magnetostratigraphy and paleolatitude of the Réunion Hotspot. In: Duncan, RA; Backmann, J; Peterson, LC; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 115, 717-736, https://doi.org/10.2973/odp.proc.sr.115.197.1990
    Details
    Publication Date: 2024-01-09
    Description: Ocean Drilling Program Leg 115 was designed to study Neogene sedimentation history in the western Indian Ocean Basin as well as the Cenozoic evolution of the Reunion hotspot. We describe the paleomagnetic analysis of the sediments recovered on this leg, focusing on the sites that provided the most readily interpretable data: Sites 706, 709, 710, and 711. Sediments from Site 706 show no reversals but appear to give a reliable reversed polarity primary direction, judged on the basis of the demagnetization behavior of individual samples as well as from the results of a fold test formulated by comparing the two holes drilled at this site. Magnetic polarity stratigraphy in sediments from Site 709 can be deduced in two limited sections of Pliocene-Pleistocene and Oligocene-Miocene age. Sediments recovered at Site 710 (and, to a lesser extent, Site 711) render a relatively continuous magnetic polarity stratigraphy that spans most of the Neogene and adds significantly to the body of data available to address problems in Miocene geochronology. In addition to these magnetostratigraphic results, the paleomagnetism of these sediments can be used to determine paleolatitude. Using the most reliable inclination measurements from Sites 706, 710, and 711, we compared paleomagnetic estimates of paleolatitude with estimates derived from a hotspot-based absolute plate motion model. Our data, which covers the interval since 33 Ma, shows that paleolatitudes calculated with the geocentric axial dipole assumption are in general accord with the hotspot predictions. However, a correction for the long-term nondipole field brings the paleomagnetic results into even better agreement with plate motions that are based on the fixity of African hotspots.
    Keywords: 115-706A; 115-706B; 115-707A; 115-708A; 115-709A; 115-709B; 115-709C; 115-710A; 115-710B; 115-711A; 115-711B; DRILL; Drilling/drill rig; Joides Resolution; Leg115; Ocean Drilling Program; ODP; South Indian Ridge, South Indian Ocean
    Type: Dataset
    Format: application/zip, 8 datasets
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  • 10
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    Magnetostratigraphy of ODP Leg 138 sites (1995)
    PANGAEA
    In:  Supplement to: Schneider, David A (1995): Paleomagnetism of some Leg 138 sediments: detailing Miocene magnetostratigraphy. In: Pisias, NG; Mayer, LA; Janecek, TR; Palmer-Julson, A; van Andel, TH (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 138, 59-72, https://doi.org/10.2973/odp.proc.sr.138.105.1995
    Details
    Publication Date: 2024-01-09
    Description: The aims of this study are twofold. First, the study tries to provide the most reliable chronology possible for two critical sections by correlating the magnetic polarity stratigraphy measured in these sediments with a newly revised geomagnetic polarity time scale. Second, this study attempts to examine in detail the nature of seven short events not included in the shipboard standard time scale, but for which abundant magnetostratigraphic evidence was obtained during the Leg. Data presented here force some modifications of the shipboard interpretations of the magnetostratigraphy of Sites 845 and 844 on the basis of new data generated using discrete samples and from a greater appreciation of the magnetostratigraphic signature of Miocene-age short events. Those short events can be classified into two groups: those that probably reflect short, full-polarity intervals and those that more likely represent an interval of diminished geomagnetic intensity. Three of the seven events documented here correspond well with three subtle features, as seen in marine magnetic profiles, that have been newly included in the geomagnetic polarity time scale as short, full-polarity chrons. One of the seven events corresponds to a poorly defined feature of the marine magnetic record that has also been newly included in the geomagnetic polarity time scale, but which was considered of enigmatic origin. The three remaining events investigated here, although they have not been identified with features in the seafloor magnetic record, are suggested to be events of a similar nature, most likely times of anomalously low geomagnetic intensity. In addition to the Miocene magnetostratigraphic results given, several sets of averaged paleomagnetic inclinations are presented. Although these results clearly show the effects of a residual coring overprint, they demonstrate that paleomagnetic estimates of paleolatitudes can be made which are in good general agreement with ancient site positions calculated using hot spot-based plate reconstructions.
    Keywords: Ocean Drilling Program; ODP
    Type: Dataset
    Format: application/zip, 4 datasets
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