| 1. |
- Turney, Chris S M, et al.
(författare)
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Rapid global ocean-atmosphere response to Southern Ocean freshening during the last glacial
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Contrasting Greenland and Antarctic temperatures during the last glacial period (115,000 to 11,650 years ago) are thought to have been driven by imbalances in the rates of formation of North Atlantic and Antarctic Deep Water (the 'bipolar seesaw'). Here we exploit a bidecadally resolved 14C data set obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate data sets spanning iceberg-rafted debris event Heinrich 3 and Greenland Interstadial (GI) 5.1 in the North Atlantic (~30,400 to 28,400 years ago). We observe no divergence between the kauri and Atlantic marine sediment 14C data sets, implying limited changes in deep water formation. However, a Southern Ocean (Atlantic-sector) iceberg rafted debris event appears to have occurred synchronously with GI-5.1 warming and decreased precipitation over the western equatorial Pacific and Atlantic. An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can generate climate changes that are propagated globally via an atmospheric Rossby wave train.
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| 2. |
- Turney, Chris S M, et al.
(författare)
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High-precision dating and correlation of ice, marine and terrestrial sequences spanning Heinrich Event 3 : Testing mechanisms of interhemispheric change using New Zealand ancient kauri (Agathis australis)
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 137, s. 126-134
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Tidskriftsartikel (refereegranskat)abstract
- Robustly testing hypotheses of geographic synchroneity of abrupt and extreme change during the late Pleistocene (60,000 to 11,650 years ago) requires a level of chronological precision often lacking in ice, marine and terrestrial sequences. Here we report a bidecadally-resolved New Zealand kauri (Agathis australis) tree-ring sequence spanning two millennia that preserves a record of atmospheric radiocarbon (14C) during ice-rafted debris event Heinrich Event 3 (HE3) in the North Atlantic and Antarctic Isotope Maximum 4 (AIM4) in the Southern Hemisphere. Using 14C in the marine Cariaco Basin and 10Be preserved in Greenland ice, the kauri 14C sequence allows us to precisely align sequences across this period. We observe no significant difference between atmospheric and marine 14C records during HE3, suggesting no stratification of surface waters and collapse in Atlantic Meridional Overturning Circulation (AMOC). Instead our results support recent evidence for a weakened AMOC across at least two millennia of the glacial period. Our work adds to a growing body of literature confirming that Heinrich events are not the cause of stadial cooling and suggests changes in the AMOC were not the primary driver of antiphase temperature trends between the hemispheres. Decadally-resolved 14C in ancient kauri offers a powerful new (and complementary) approach to polar ice core CH4 alignment for testing hypotheses of abrupt and extreme climate change.
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| 3. |
- Staff, Richard A., et al.
(författare)
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Reconciling the Greenland ice-core and radiocarbon timescales through the Laschamp geomagnetic excursion
- 2019
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X. ; 520, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Cosmogenic radionuclides, such as 10Be and 14C, share a common production signal, with their formation in the Earth's upper atmosphere modulated by changes to the geomagnetic field, as well as variations in the intensity of the solar wind. Here, we use this common production signal to compare between the radiocarbon (IntCal)and Greenland ice-core (GICC05)timescales, utilising the most pronounced cosmogenic production peak of the last 100,000 years – that associated with the Laschamp geomagnetic excursion circa 41,000 years ago. We present 54 new 14C measurements from a peat core (‘TP-2005’)from Tenaghi Philippon, NE Greece, contiguously spanning between circa 47,300 and 39,600 cal. BP, demonstrating a distinctive tripartite structure in the build up to the principal Laschamp production maximum that is not present in the consensus IntCal13 calibration curve. This is the first time that a continuous, non-reservoir corrected 14C dataset has been generated over such a long time span for this, the oldest portion of the radiocarbon timescale. This period is critical for both palaeoenvironmental and archaeological applications, with the replacement of Neanderthals by anatomically modern humans in Europe around this time. By placing our Tenaghi Philippon 14C dataset on to the Hulu Cave U-series timescale of Cheng et al. (2018)via Bayesian statistical modelling, the comparison of TP-2005 14C with Greenland 10Be fluxes also implicitly relates the underlying U-series and GICC05 timescales themselves. This comparison suggests that whilst these two timescales are broadly coherent, the IntCal13 timescale contains erroneous structure circa 40,000 cal. BP.
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