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| White, Lee F.; Bailey, Ian; Foster, Gavin L.; Allen, Georgina; Kelley, Simon P.; Andrews, John T.; Hogan, Kelly; Dowdeswell, Julian A.; Storey, Craig D.. |
| The provenance of sand-sized ice-rafted debris (IRD) sourced from Greenland is currently difficult to determine. Such knowledge, if it could be ascertained with a high degree of certainty, could be applied to the Greenland-proximal marine records to improve both our understanding of modern-day spatial patterns of iceberg rafting and the past history of the Greenland Ice Sheet (GIS). Recent studies have highlighted the utility of the Pb-isotope composition of individual sand-sized feldspars and the Ar-40/Ar-39 ages of individual sand-sized hornblendes in this regard. However, before any such provenance toolkit can be applied to the palaeo-record, it is necessary first to determine whether this approach can be used to track the sources of known recent... |
| Tipo: Text |
Palavras-chave: Greenland; Ice rafted debris; Ar-Ar; Pb isotopes; Icebergs; Provenance. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00421/53292/54130.pdf |
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| Bugelmayer-blaschek, Marianne; Roche, Didier M.; Renssen, Hans; Andrews, John T.. |
| The climate of the Holocene, the current interglacial covering the past 11,700 years, has been relatively stable compared to previous periods. Nevertheless, repeating occurrence of rapid natural climate changes that challenged human society are seen in proxy reconstructions. Ocean sediment cores for example display prominent peaks of enhanced ice rafted debris (IRD) during the Holocene with a multidecadal to millennial scale periodicity. Different mechanisms were proposed that caused these enhanced IRD events, for example variations in the incoming total solar irradiance (TSI), volcanic eruptions and the combination of internal climate variability and external forcings. We investigate the probable mechanisms causing the occurrence of IRD-events over the... |
| Tipo: Text |
Palavras-chave: Greenland ice sheet; Holocene; Bond events; Icebergs; Climate modeling. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00421/53253/54711.pdf |
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| Patterson, William P.; Dietrich, Kristin A.; Holmden, Chris; Andrews, John T.. |
| delta(18)O values of mollusks recovered from near-shore marine cores in northwest Iceland quantify significant variation in seasonal temperature over the period from similar to 360 B:C: to similar to A:D: 1660. Twenty-six aragonitic bivalve specimens were selected to represent intervals of climatic interest by using core sedimentological characteristics. Carbonate powder was sequentially micromilled from shell surfaces concordant with growth banding and analyzed for stable oxygen (delta(18)O) and carbon (delta(13)C) isotope values. Because delta(18)O values record subseasonal temperature variation over the lifetime of the bivalves, these data provide the first 2,000-year secular record of North Atlantic seasonality from ca. 360 cal yr B.C. to cal yr A.D.... |
| Tipo: Text |
Palavras-chave: Climate change; Stable isotopes; Vikings; Micromilling. |
| Ano: 2010 |
URL: https://archimer.ifremer.fr/doc/00231/34231/32834.pdf |
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| Andrews, John T.; Kristjansdottir, Greta B.; Eberl, Dennis D.; Jennings, Anne E.. |
| This paper re-evaluates how well quantitative x-ray diffraction (qXRD) can be used as an exploratory method of the weight percentage (wt%) of volcaniclastic sediment, and to identify tephra events in marine cores. In the widely used RockJock v6 software programme, qXRD tephra and glass standards include the rhyodacite White River tephra (Alaska), a rhyolitic tephra (Hekla-4) and the basaltic Saksunarvatn tephra. Experiments of adding known wt% of tephra to felsic bedrock samples indicated that additions >= 10 wt% are accurately detected, but reliable estimates of lesser amounts are masked by amorphous material produced by milling. Volcaniclastic inputs range between 20 and 50 wt%. Primary tephra events are identified as peaks in residual qXRD glass wt%... |
| Tipo: Text |
Palavras-chave: X-ray diffraction; Tephras; Iceland Holocene. |
| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00265/37578/36528.pdf |
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| Andrews, John T.; Bigg, Grant R.; Wilton, David J.. |
| We examine variations in the ice-rafted sources for sediments in the Iceland/East Greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg-ocean model. Surface samples from around Iceland and along the E/NE Greenland shelf are used to define potential sediment sources, and these are examined within the context of the down-core variations in mineralogy in the <2 mm sediment fraction from a transect of cores across Denmark Strait. A sediment unmixing model is used to estimate the fraction of sediment <2 mm off NW and N Iceland exported across Denmark Strait; this averaged between 10 and 20%. Both the sediment unmixing model and the coupled iceberg-ocean model are consistent in finding that the... |
| Tipo: Text |
Palavras-chave: Holocene; Ice-rafting; Ice bergs; East Greenland; Iceland. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40150/39091.pdf |
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| Hoffman, Jeremy S.; Carlson, Anders E.; Winsor, Kelsey; Klinkhammer, Gary P.; Legrande, Allegra N.; Andrews, John T.; Strasser, Jeffrey C.. |
| The 8.2 ka event was the last deglacial abrupt climate event. A reduction in the Atlantic meridional overturning circulation (AMOC) attributed to the drainage of glacial Lake Agassiz may have caused the event, but the freshwater signature of Lake Agassiz discharge has yet to be identified in delta O-18 of foraminiferal calcite records from the Labrador Sea, calling into question the connection between freshwater discharge to the North Atlantic and AMOC strength. Using Mg/Ca-paleothermometry, we demonstrate that similar to 3 degrees C of near-surface ocean cooling masked an similar to 1.0 parts per thousand decrease in western Labrador Sea delta O-18 of seawater concurrent with Lake Agassiz drainage. Comparison with North Atlantic delta O-18 of seawater... |
| Tipo: Text |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00496/60740/65179.pdf |
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| Stoner, Joseph S.; Jennings, Anne; Kristjansdottir, Greta B.; Dunhill, Gita; Andrews, John T.; Hardardottir, Jorunn. |
| We report the intercalibration of paleomagnetic secular variation (PSV) and radiocarbon dates of two expanded postglacial sediment cores from geographically proximal, but oceanographically and sedimentologically contrasting settings. The objective is to improve relative correlation and chronology over what can be achieved with either method alone. Core MD99-2269 was taken from the Hunafloaall Trough on the north Iceland shelf. Core MD99-2322 was collected from the Kangerlussuaq Trough on the east Greenland margin. Both cores are well dated, with 27 and 20 accelerator mass spectrometry (14)C dates for cores 2269 and 2322, respectively. Paleomagnetic measurements made on u channel samples document a strong, stable, single-component magnetization. The... |
| Tipo: Text |
Palavras-chave: Holocene; Paleomagnetic secular variation; Radiocarbon dating. |
| Ano: 2007 |
URL: https://archimer.ifremer.fr/doc/00233/34436/32934.pdf |
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