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  • Abstract: Changes to original version posted at NOAA (https://www.ncdc.noaa.gov/paleo-search/study/14173): Chronology has been updated to most recent NEEM-2011-S1 ice age and NEEM delta age. Age scale now constructed from annual-layer-counted ice age (Sigl et al., 2015, Nature). Two options for delta age provided a) constant delta age of 188 yr (Buizert et al. 2012, ACP & 2014 corrigendum), b) variable delta age transferred from main NEEM core (Rasmussen et al., 2013, COP) using offsets between GICC05 and NEEM-2011-S1 ice age provided by Sigl et al. 2015. Outliers at 387.2-387.4 m and 335.1-335.3 m depth removed. Publication abstract: Ancient air trapped inside bubbles in ice cores can now be analysed for methane concentration utilising a laser spectrometer coupled to a continuous melter system. We present a new ultra-high resolution record of atmospheric methane variability over the last 1800 yr obtained from continuous analysis of a shallow ice core from the North Greenland Eemian project (NEEM-2011-S1) during a 4-week laboratory-based measurement campaign. Our record faithfully replicates the form and amplitudes of multi-decadal oscillations previously observed in other ice cores and demonstrates the detailed depth resolution (5.3 cm), rapid acquisition time (30 m day-1) and good long-term reproducibility (2.6%, 2s) of the continuous measurement technique. In addition, we report the detection of high frequency ice core methane signals of non-atmospheric origin. Firstly, measurements of air from the firn-ice transition region and an interval of ice core dating from 1546-1560 AD (gas age) resolve apparently quasi-annual scale methane oscillations. Traditional gas chromatography measurements on discrete ice samples confirm these signals and indicate peak-topeak amplitudes of ca. 22 parts per billion (ppb). We hypothesise that these oscillations result from staggered bubble close-off between seasonal layers of contrasting density during time periods of sustained multi-year atmospheric methane change. Secondly, we report the detection of abrupt (20-100 cm depth interval), high amplitude (35-80 ppb excess) methane spikes in the NEEM ice that are reproduced by discrete measurements. We show for the first time that methane spikes present in thin and infrequent layers in polar, glacial ice are accompanied by elevated concentrations of carbon and nitrogen-based chemical impurities, and suggest that biological in-situ production may be responsible. Funding: * US National Science Foundation, Grant: 0944552, 0909541, 0968391 * ANR France, Grant: ANR-10-RPDOC-002-01, ANR-07-VULN-09-001 * European Research Council, Grant: FP7/2007-2013 Grant Agreement 291062 Category: geoscientificInformation Source: Supplement to: Rhodes, Rachael H; Faïn, Xavier; Stowasser, Christopher; Blunier, Thomas; Chappellaz, Jérôme A; McConnell, Joseph R; Romanini, Daniele; Mitchell, Logan E; Brook, Edward J (2013): Continuous methane measurements from a late Holocene Greenland ice core: Atmospheric and in-situ signals. Earth and Planetary Science Letters, 368, 9-19, https://doi.org/10.1016/j.epsl.2013.02.034 Supplemental Information: CHANGES TO ORIGINAL VERSION POSTED AT NOAA (https://www.ncdc.noaa.gov/paleo-search/study/14173) * Chronology has been updated to most recent NEEM-2011-S1 ice age and NEEM delta age. * Age scale now constructed from annual-layer-counted ice age (Sigl et al., 2015, Nature). * Two options for delta age provided a) constant delta age of 188 yr (Buizert et al. 2012, ACP & 2014 corrigendum). b) variable delta age transferred from main NEEM core (Rasmussen et al., 2013, COP) using offsets between GICC05 and NEEM-2011-S1 ice age provided by Sigl et al. 2015 * Outliers at 387.2-387.4 m and 335.1-335.3 m depth removed. Coverage: EVENT LABEL: * LATITUDE: 77.450000 * LONGITUDE: -51.060000 * ELEVATION: 2545.0 m * Penetration: 410 m * LOCATION: Greenland * METHOD|DEVICE: Ice drill
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  • Abstract: Available overwash records from coastal barrier systems document significant variability in North Atlantic hurricane activity during the late Holocene. The same climate forcings that may have controlled cyclone activity over this interval (e.g., the West African Monsoon, El Niño-Southern Oscillation (ENSO)) show abrupt changes around 6000 yrs B.P., but most coastal sedimentary records do not span this time period. Establishing longer records is essential for understanding mid-Holocene patterns of storminess and their climatic drivers, which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity. Storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep-sea, and bank-edge sediments may offer an unexplored archive of long-term hurricane activity. Here, we develop this new approach, reconstructing more than 7000 years of North Atlantic hurricane variability using coarse-grained deposits in sediment cores from the leeward margin of the Great Bahama Bank. High energy event layers within the resulting archive are (1) broadly correlated throughout an offbank transect of multi-cores, (2) closely matched with historic hurricane events, and (3) synchronous with previous intervals of heightened North Atlantic hurricane activity in overwash reconstructions from Puerto Rico and elsewhere in the Bahamas. Lower storm frequency prior to 4400 yrs B.P. in our records suggests that precession and increased NH summer insolation may have greatly limited hurricane potential intensity, outweighing weakened ENSO and a stronger West African Monsoon-factors thought to be favorable for hurricane development. Category: geoscientificInformation Source: Supplement to: Toomey, Michael R; Curry, William B; Donnelly, Jeffrey P; vam Hengstum, Peter J (2013): Reconstructing 7000 years of North Atlantic hurricane variability using deep-sea sediment cores from the western Great Bahama Bank. Paleoceanography, 28(1), 31-41, https://doi.org/10.1002/palo.20012 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 24.590700 * LONGITUDE: -79.268700 * DATE/TIME: 2002-01-21T00:00:00 * ELEVATION: -528.0 m * Recovery: 3.64 m * LOCATION: Florida Strait * CAMPAIGN: KNR166-2 * BASIS: Knorr * METHOD|DEVICE: Gravity corer EVENT LABEL: * LATITUDE: 24.590600 * LONGITUDE: -79.268700 * DATE/TIME: 2002-01-21T00:00:00 * ELEVATION: -531.0 m * Recovery: 0.41 m * LOCATION: Florida Strait * CAMPAIGN: KNR166-2 * BASIS: Knorr * METHOD|DEVICE: MultiCorer EVENT LABEL: * LATITUDE: 24.590500 * LONGITUDE: -79.268700 * DATE/TIME: 2002-01-21T00:00:00 * ELEVATION: -529.0 m * Recovery: 17.05 m * LOCATION: Florida Strait * CAMPAIGN: KNR166-2 * BASIS: Knorr * METHOD|DEVICE: Piston corer EVENT LABEL: * LATITUDE: 24.836000 * LONGITUDE: -79.218500 * DATE/TIME: 2002-01-23T00:00:00 * ELEVATION: -445.0 m * Recovery: 2.8 m * LOCATION: Florida Strait * CAMPAIGN: KNR166-2 * BASIS: Knorr * METHOD|DEVICE: Gravity corer EVENT LABEL: * LATITUDE: 24.835800 * LONGITUDE: -79.218700 * DATE/TIME: 2002-01-23T00:00:00 * ELEVATION: -446.0 m * Recovery: 17.28 m * LOCATION: Florida Strait * CAMPAIGN: KNR166-2 * BASIS: Knorr * METHOD|DEVICE: Piston corer
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  • frequencies,... oscillation
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  • Abstract: We present a 3000-yr rainfall reconstruction from the Galápagos Islands that is based on paired biomarker records from the sediment of El Junco Lake. Located in the eastern equatorial Pacific, the climate of the Galápagos Islands is governed by movements of the Intertropical Convergence Zone (ITCZ) and the El Niño-Southern Oscillation (ENSO). We use a novel method for reconstructing past ENSO- and ITCZ-related rainfall changes through analysis of molecular and isotopic biomarker records representing several types of plants and algae that grow under differing climatic conditions. We propose that dD values of dinosterol, a sterol produced by dinoflagellates, record changes in mean rainfall in El Junco Lake, while dD values of C34 botryococcene, a hydrocarbon unique to the green alga Botryococcus braunii, record changes in rainfall associated with moderate-to-strong El Niño events. We use these proxies to infer changes in mean rainfall and El Niño-related rainfall over the past 3000 yr. During periods in which the inferred change in El Niño-related rainfall opposed the change in mean rainfall, we infer changes in the amount of ITCZ-related rainfall. Simulations with an idealized isotope hydrology model of El Junco Lake help illustrate the interpretation of these proxy reconstructions. Opposing changes in El Niño- and ITCZ-related rainfall appear to account for several of the largest inferred hydrologic changes in El Junco Lake. We propose that these reconstructions can be used to infer changes in frequency and/or intensity of El Niño events and changes in the position of the ITCZ in the eastern equatorial Pacific over the past 3000 yr. Comparison with El Junco Lake sediment grain size records indicates general agreement of inferred rainfall changes over the late Holocene. Category: geoscientificInformation Source: Supplement to: Atwood, Alyssa R; Sachs, Julian P (2014): Separating ITCZ- and ENSO-related rainfall changes in the Galápagos over the last 3 kyr using D/H ratios of multiple lipid biomarkers. Earth and Planetary Science Letters, 404, 408-419, https://doi.org/10.1016/j.epsl.2014.07.038 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -0.895000 * LONGITUDE: -89.480000 * ELEVATION: 670.0 m * LOCATION: Pacific Ocean * METHOD|DEVICE: Composite Core
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  • Abstract: The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0-200 m) and primary productivity over the last 9000 yr BP (before present) in the western Antarctic Peninsula (WAP) margin from a sedimentary core collected in the Palmer Deep Basin. Employing a multi-proxy approach, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEXL86 for temperature) and micropaleontological data (diatom assemblages), we derived new Holocene records of sea ice conditions and upper water column temperatures. The early Holocene (9000-7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~7000-3800 yr BP), local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~2100 yr) was characterized by warmer temperatures and increased sea ice presence, accompanied by reduced local primary productivity, likely in response to a shorter growing season compared to the early or mid-Holocene. The gradual increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation, despite increasing summer insolation. We postulate that, in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of the El Nino-Southern Oscillation (ENSO). However, between 3800 and 2100 yr BP, the lack of correlation between ENSO and climate variability in the WAP suggests that other climatic factors might have been more important in controlling WAP climate at this time. Category: geoscientificInformation Source: Supplement to: Etourneau, Johan; Collins, L G; Willmott, Verónica; Kim, Jung-Hyun; Barbara, Loïc; Leventer, Amy; Schouten, Stefan; Sinninghe Damsté, Jaap S; Bianchini, A; Klein, Vincent; Crosta, Xavier; Massé, Guillaume (2013): Holocene climate variations in the western Antarctic Peninsula: evidence for sea ice extent predominantly controlled by changes in insolation and ENSO variability. Climate of the Past, 9(4), 1431-1446, https://doi.org/10.5194/cp-9-1431-2013 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: -64.883330 * LONGITUDE: -64.200000 * ELEVATION: -905.0 m * Recovery: 13.33 m * LOCATION: Palmer Deep Basin * CAMPAIGN: NBP99-03 * BASIS: Nathaniel B. Palmer * METHOD/DEVICE: Piston corer
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  • Abstract: Rapid climate changes at the onset of the last deglaciation and during Heinrich Event H4 were studied in detail at IMAGES cores MD95-2039 and MD95-2040 from the Western Iberian margin. A major reorganisation of surface water hydrography, benthic foraminiferal community structure, and deepwater isotopic composition commenced already 540 years before the Last Isotopic Maximum (LIM) at 17.43 cal. ka and within 670 years affected all environments. Changes were initiated by meltwater spill in the Nordic Seas and northern North Atlantic that commenced 100 years before concomitant changes were felt off western Iberia. Benthic foraminiferal associations record the drawdown of deepwater oxygenation during meltwater and subsequent Heinrich Events H1 and H4 with a bloom of dysoxic species. At a water depth of 3380 m, benthic oxygen isotopes depict the influence of brines from sea ice formation during ice-rafting pulses and meltwater spill. The brines conceivably were a source of ventilation and provided oxygen to the deeper water masses. Some if not most of the lower deep water came from the South Atlantic. Benthic foraminiferal assemblages display a multi-centennial, approximately 300-year periodicity of oxygen supply at 2470-m water depth. This pattern suggests a probable influence of atmospheric oscillations on the thermohaline convection with frequencies similar to Holocene climate variations. For Heinrich Events H1 and H4, response times of surface water properties off western Iberia to meltwater injection to the Nordic Seas were extremely short, in the range of a few decades only. The ensuing reduction of deepwater ventilation commenced within 500-600 years after the first onset of meltwater spill. These fast temporal responses lend credence to numerical simulations that indicate ocean-climate responses on similar and even faster time scales. Category: geoscientificInformation Source: Supplement to: Schönfeld, Joachim; Zahn, Rainer; de Abreu, Lucia (2003): Surface to deep water response to rapid climate changes at the western Iberian Margin. Global and Planetary Change, 36(4), 237-264, https://doi.org/10.1016/S0921-8181(02)00197-2 Supplemental Information: Not Availble Coverage: EVENT LABEL: (MD952039) * LATITUDE: 40.578500 * LONGITUDE: -10.348500 * DATE/TIME: 1995-07-07T00:00:00 * ELEVATION: -3381.0 m * Recovery: 36 m * LOCATION: Porto Seamount * CAMPAIGN: MD101 * BASIS: Marion Dufresne (1995) * METHOD/DEVICE: Calypso Corer EVENT LABEL: (MD952040) * LATITUDE: 40.581833 * LONGITUDE: -9.861167 * DATE/TIME: 1995-07-07T00:00:00 * ELEVATION: -2465.0 m * Recovery: 35 m * LOCATION: Porto Seamount * CAMPAIGN: MD101 * BASIS: Marion Dufresne (1995) * METHOD/DEVICE: Calypso Corer
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  • frequency... oscillating
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  • Abstract: We combine environmental magnetism, geochemical measurements and colour reflectance to study two late Quaternary sediment cores: GeoB 4905-4 at 2° 30 N off Cameroon and GeoB 4906-3 at 0° 44 N off Gabon. This area is suitable for investigating precipitation changes over Central and West Africa because of its potential to record input of aeolian and fluvial sediments. Three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified. The magnetic signature is dominated by fine-grained magnetite, while residual haematite prevails in the reduced intervals, showing increase in concentration and fine grain size at wet intervals. Our records also show millennial-scale changes in climate during the last glacial and interglacial cycles. At the northern location, the past 5.5 ka are marked by high-frequency oscillations of Ti and colour reflectance, which suggests aeolian input and hence aridity. The southern location remains under the influence of the Intertropical Convergence Zone and thus did not register aeolian signals. The millennial-scale climatic signals indicate that drier and/or colder conditions persisted during the late Holocene and are synchronous with the 900 a climatic cycles observed in Northern Hemisphere ice core records. Category: geoscientificInformation Source: Supplement to: Itambi, Achakie C; von Dobeneck, Tilo; Adegbie, Adesina T (2010): Millennial-scale precipitation changes over Central Africa during the late Quaternary and Holocene: evidence in sediments from the Gulf of Guinea. Journal of Quaternary Science, 25(3), 267-279, https://doi.org/10.1002/jqs.1306 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 2.500000 * LONGITUDE: 9.390000 * DATE/TIME: 1998-03-01T06:48:00 * ELEVATION: -1328.0 m * Recovery: 12.18 m * LOCATION: off Cameroon * CAMPAIGN: M41/1 * BASIS: Meteor (1986) * METHOD/DEVICE: Gravity corer (Kiel type) EVENT LABEL: * LATITUDE: -0.690000 * LONGITUDE: 8.376667 * DATE/TIME: 1998-03-02T03:48:00 * ELEVATION: -1274.0 m * Recovery: 12.36 m * LOCATION: off Gabun * CAMPAIGN: M41/1 * BASIS: Meteor (1986) * METHOD/DEVICE: Gravity corer (Kiel type)
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  • Abstract: A multi-proxy chronological framework along with sequence-stratigraphic interpretations unveils composite Milankovitch cyclicity in the sedimentary records of the Last GlacialeInterglacial cycle at NE Gela Basin on the Sicilian continental margin. Chronostratigraphic data (including foraminifera-based eco-biostratigraphy and d18O records, tephrochronological markers and 14C AMS radiometric datings) was derived from the shallow-shelf drill sites GeoB14403 (54.6 m recovery) and GeoB14414 (27.5 m), collected with both gravity and drilled MeBo cores in 193 m and 146 m water depth, respectively. The recovered intervals record Marine Isotope Stages and Substages (MIS) from MIS 5 to MIS 1, thus comprising major stratigraphic parts of the progradational deposits that form the last 100-ka depositional sequence. Calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher-frequency (20-ka) sea level cycles punctuating this 100-ka cycle. This becomes most evident in the alternation of thick interstadial highstand (HST) wedges and thinner glacial forced-regression (FSST) units mirroring seaward shifts in coastal progradation. Albeit their relatively short-lived depositional phase, these subordinate HST units form the bulk of the 100-ka depositional sequence. Two mechanisms are proposed that likely account for enhanced sediment accumulation ratios (SAR) of up to 200 cm/ka during these intervals: (1) intensified activity of deep and intermediate Levantine Intermediate Water (LIW) associated to the drowning of Mediterranean shelves, and (2) amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions. Equally, the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of MIS 5 Interstadials, which bear a striking resemblance to modern equivalents forming on late-Holocene prodeltas of other Mediterranean shallow-shelf settings. Category: geoscientificInformation Source: Supplement to: Kuhlmann, Jannis; Asioli, Alessandra; Trincardi, Fabio; Klügel, Andreas; Huhn, Katrin (2015): Sedimentary response to Milankovitch-type climatic oscillations and formation of sediment undulations: evidence from a shallow-shelf setting at Gela Basin on the Sicilian continental margin. Quaternary Science Reviews, 108, 76-94, https://doi.org/10.1016/j.quascirev.2014.10.030 Supplemental Information: Not Availble Coverage: Not Available
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  • Abstract: Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at AD 750-1330, although with some oceanographic variability after AD 1000. A pronounced oceanographic shift occurred at AD 1330, corresponding in time to the transition from the so-called 'Medieval Warm Period' (MWP) to the 'Little Ice Age' (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at AD 1330-1350, AD 1400-1575 and AD 1660-1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations. Category: geoscientificInformation Source: Supplement to: Sha, Longbin; Jiang, Hui; Knudsen, Karen Luise (2012): Diatom evidence of climatic change in Holsteinsborg Dyb, west of Greenland, during the last 1200 years. The Holocene, 22(3), 347-358, https://doi.org/10.1177/0959683611423684 Supplemental Information: Not Availble Coverage: EVENT LABEL: * LATITUDE: 66.744700 * LONGITUDE: -53.940300 * DATE/TIME START: 2006-08-01T00:00:00 * DATE/TIME END: 2007-04-01T00:00:00 * ELEVATION: -445.0 m * Recovery: 0.35 m * LOCATION: Greenland Sea * CAMPAIGN: Galathea 3 * BASIS: HDMS Vaedderen * METHOD|DEVICE: Box corer EVENT LABEL: * LATITUDE: 66.744700 * LONGITUDE: -53.940300 * DATE/TIME START: 2006-08-01T00:00:00 * DATE/TIME END: 2007-04-01T00:00:00 * ELEVATION: -445.0 m * Recovery: 5.01 m * LOCATION: Greenland Sea * CAMPAIGN: Galathea 3 * BASIS: HDMS Vaedderen * METHOD|DEVICE: Gravity corer
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