| 1. |
- Reimer, Paula J., et al.
(författare)
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The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)
- 2020
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Ingår i: Radiocarbon. - 0033-8222. ; 62:4, s. 725-757
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Tidskriftsartikel (refereegranskat)abstract
- Radiocarbon (C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.
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| 2. |
- Ashton, Susan, et al.
(författare)
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Aurora kinase inhibitor nanoparticles target tumors with favorable therapeutic index in vivo
- 2016
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Ingår i: Science Translational Medicine. - : American Association for the Advancement of Science (AAAS). - 1946-6234 .- 1946-6242. ; 8:325
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Tidskriftsartikel (refereegranskat)abstract
- Efforts to apply nanotechnology in cancer have focused almost exclusively on the delivery of cytotoxic drugs to improve therapeutic index. There has been little consideration of molecularly targeted agents, in particular kinase inhibitors, which can also present considerable therapeutic index limitations. We describe the development of Accurin polymeric nanoparticles that encapsulate the clinical candidate AZD2811, an Aurora B kinase inhibitor, using an ion pairing approach. Accurins increase biodistribution to tumor sites and provide extended release of encapsulated drug payloads. AZD2811 nanoparticles containing pharmaceutically acceptable organic acids as ion pairing agents displayed continuous drug release for more than 1 week in vitro and a corresponding extended pharmacodynamic reduction of tumor phosphorylated histone H3 levels in vivo for up to 96 hours after a single administration. A specific AZD2811 nanoparticle formulation profile showed accumulation and retention in tumors with minimal impact on bone marrow pathology, and resulted in lower toxicity and increased efficacy in multiple tumor models at half the dose intensity of AZD1152, a water-soluble prodrug of AZD2811. These studies demonstrate that AZD2811 can be formulated in nanoparticles using ion pairing agents to give improved efficacy and tolerability in preclinical models with less frequent dosing. Accurins specifically, and nanotechnology in general, can increase the therapeutic index of molecularly targeted agents, including kinase inhibitors targeting cell cycle and oncogenic signal transduction pathways, which have to date proved toxic in humans.
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| 3. |
- Chawchai, Sakonvan, et al.
(författare)
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Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho
- 2015
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 111, s. 62-71
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Forskningsöversikt (refereegranskat)abstract
- The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, delta C-13, biogenic silica, and XRF elemental data) study of a 1.5 m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS C-14 ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170-AD 370, AD 800-960, and after AD 1450; and a weakening of the summer monsoon between AD 370-800, and AD 1300-1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35 degrees N between BC 170-AD 370 and AD 800-960, whereas it likely did not reach above 17 degrees N during the drought intervals of AD 370-800 and AD 1300-1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.
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| 4. |
- Muscheler, Raimund, et al.
(författare)
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Testing and Improving the IntCal20 Calibration Curve with Independent Records
- 2020
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Ingår i: Radiocarbon. - 0033-8222. ; 62:4, s. 1079-1094
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Tidskriftsartikel (refereegranskat)abstract
- Connecting calendar ages to radiocarbon (C) ages, i.e. constructing a calibration curve, requires C samples that represent, or are closely connected to, atmospheric C values and that can also be independently dated. In addition to these data, there is information that can serve as independent tests of the calibration curve. For example, information from ice core radionuclide data cannot be directly incorporated into the calibration curve construction as it delivers less direct information on the C age-calendar age relationship but it can provide tests of the quality of the calibration curve. Furthermore, ice core ages on C-dated volcanic eruptions provide key information on the agreement of ice core and radiocarbon time scales. Due to their scarcity such data would have little impact if directly incorporated into the calibration curve. However, these serve as important anchor points in time for independently testing the calibration curve and/or ice-core time scales. Here we will show that such information largely supports the new IntCal20 calibration record. Furthermore, we discuss how floating tree-ring sequences on ice-core time scales agree with the new calibration curve. For the period around 40,000 years ago we discuss unresolved differences between ice core Be and C records that are possibly related to our limited understanding of carbon cycle influences on the atmospheric C concentration during the last glacial period. Finally, we review the results on the time scale comparison between the Greenland ice-core time scale (GICC05) and IntCal20 that effectively allow a direct comparison of C-dated records with the Greenland ice core data.
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| 5. |
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| 6. |
- Chawchai, Sakonvan, et al.
(författare)
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Lake Kumphawapi revisited – a synthesis of Holocene environmental and climatic changes for NE Thailand
- 2016
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 26:4, s. 614-626
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Tidskriftsartikel (refereegranskat)abstract
- Kumphawapi, which is Thailand’s largest natural freshwater lake, contains a >10,000-year-long climatic and environmental archive. New data sets (stratigraphy, chronology, hydrogen isotopes, plant macrofossil and charcoal records) for two sedimentary sequences are here combined with earlier multi-proxy studies to provide a comprehensive reconstruction of past climatic and environmental changes for Northeast Thailand. Gradually higher moisture availability due to a strengthening of the summer monsoon led to the formation of a large shallow lake in the Kumphawapi basin between >10,700 and c. 7000 cal. BP. The marked increase in moisture availability and lower evaporation between c. 7000 and 6400 cal. BP favoured the growth and expansion of vegetation in and around the shallow lake. The increase in biomass led to gradual overgrowing and infilling, to an apparent lake level lowering and to the development of a wetland. Multiple hiatuses are apparent in all investigated sequences between c. 6500 and 1400 cal. BP and are explained by periodic desiccation events of the wetland and erosion due to the subsequent lake level rise. The rise in lake level, which started c. 2000 cal. BP and reached shallower parts c. 1400 cal. BP, is attributed to an increase in effective moisture availability. The timing of hydroclimatic conditions during the past 2000 years cannot be resolved because of chronological limitations.
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| 7. |
- Steinthorsdottir, Margret, et al.
(författare)
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Stomatal proxy record of CO2 concentrations from the last termination suggests an important role for CO2 at climate change transitions
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 68, s. 43-58
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Tidskriftsartikel (refereegranskat)abstract
- A new stomatal proxy-based record of CO2 concentrations ([CO2]), based on Betula nana (dwarf birch) leaves from the Hasseldala Port sedimentary sequence in south-eastern Sweden, is presented. The record is of high chronological resolution and spans most of Greenland Interstadial 1 (GI-1a to 1c, Allerod pollen zone), Greenland Stadial 1 (GS-1, Younger Dryas pollen zone) and the very beginning of the Holocene (Preboreal pollen zone). The record clearly demonstrates that i) [CO2] were significantly higher than usually reported for the Last Termination and ii) the overall pattern of CO2 evolution through the studied time period is fairly dynamic, with significant abrupt fluctuations in [CO2] when the climate moved from interstadial to stadial state and vice versa. A new loss-on-ignition chemical record (used here as a proxy for temperature) lends independent support to the Hasseldala Port [CO2] record. The large-amplitude fluctuations around the climate change transitions may indicate unstable climates and that tipping-point situations were involved in Last Termination climate evolution. The scenario presented here is in contrast to [CO2] records reconstructed from air bubbles trapped in ice, which indicate lower concentrations and a gradual, linear increase of [CO2] through time. The prevalent explanation for the main climate forcer during the Last Termination being ocean circulation patterns needs to re-examined, and a larger role for atmospheric [CO2] considered.
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| 8. |
- Steinthorsdottir, Margret, et al.
(författare)
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Synchronous records of pCO(2) and Delta C-14 suggest rapid, ocean-derived pCO(2) fluctuations at the onset of Younger Dryas
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 99, s. 84-96
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Tidskriftsartikel (refereegranskat)abstract
- Just before the onset of the Younger Dryas (YD) cold event, several stomatal proxy-based pCO(2) records have shown a sharp increase in atmospheric CO2 concentration (pCO(2)) of between ca 50 and 100 ppm, followed by a rapid decrease of similar or even larger magnitude. Here we compare one of these records, a high-resolution pCO(2) record from southern Sweden, with the IntCal13 record of radiocarbon (Delta C-14). The two records show broadly synchronous fluctuations at the YD onset. Specifically, the IntCal13 record documents decreasing Delta C-14 just before the YD onset when pCO(2) peaks, consistent with a source of old CO2 from the deep ocean. We propose that this fluctuation occurred due to a major ocean flushing event. The cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor. We confirm that the earth system can produce such large multi-decadal timescale fluctuations in pCO(2) through simulating an artificial ocean flushing event with the GENIE Earth System Model. We suggest that sharp transitions of pCO(2) may have remained undetected so far in ice cores due to inter-firn gas exchange and time-averaging. The stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change.
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| 9. |
- Wohlfarth, Barbara, et al.
(författare)
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Climate and environment in southwest Sweden 15.5-11.3 cal. ka BP
- 2018
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 47:3, s. 687-710
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Tidskriftsartikel (refereegranskat)abstract
- Lake sedimentary records that allow documentation of the distinct climatic and environmental shifts during the early part of the Last Termination are scarce for northern Europe. This multi-proxy study of the sediments of Attekopsmosse, southwest Sweden, therefore fills an important gap and provides detailed information regarding past hydroclimatic conditions and local environmental responses to climatic shifts. Lake infilling started c. 15.5 cal. ka BP, but low aquatic productivity, cold summer lake water temperatures, unstable catchments, and scarce herb and shrub vegetation prevailed until c. 14.7-14.5 cal. ka BP. Inflow of warmer air masses and higher July air temperatures favoured a rise in aquatic productivity and lake water summer temperatures, and the establishment of a diverse herb, shrub and dwarf shrub vegetation, which also included tree birch c. 14.5 cal. ka BP. Freshening of the moisture source region c. 13.7-13.6 cal. ka BP does not seem to have had a large impact on the ancient lake and its catchment, as lake aquatic productivity increased further and lake water summer temperatures and minimum mean July air temperatures remained around 12-14 degrees C. In contrast, further freshening of the moisture source region c. 13 cal. ka BP triggered a decrease in lake productivity, drier conditions and lower lake water summer temperatures. Macroscopic finds of tree Betula and Pinus sylvestris at 13-12.8 cal. ka BP demonstrate the presence of these trees in the lake's catchment. The transition into the Holocene (11.6-11.5 cal. ka BP) is marked by a change in chironomid assemblages and by a rise in lake water summer temperatures and aquatic productivity. These changes were followed by the re-establishment of a diverse aquatic and terrestrial vegetation, including tree birch and Pinus sylvestris at 11.4 cal. ka BP.
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| 10. |
- Wohlfarth, Barbara, et al.
(författare)
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Holocene environmental changes in Northeast Thailand as reconstructed from a tropical wetland
- 2012
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 92-93, s. 148-161
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Tidskriftsartikel (refereegranskat)abstract
- Geochemical variables (TOC, C/N, TS, delta C-13) and diatom assemblages were analyzed in a lake sediment sequence from Nong (Lake) Han Kumphawapi in northeast Thailand to reconstruct regional climatic and environmental history during the Holocene. By around c. 10,000-9400 cal yr BP, a large shallow freshwater lake had formed in the Kumphawapi basin. Oxygenated bottom waters and a well-mixed water column were characteristic of this early lake stage, which was probably initiated by higher effective moisture and a stronger summer monsoon. Decreased run-off after c. 6700 cal yr BP favored increased aquatic productivity in the shallow lake. Multiple proxies indicate a marked lowering of the lake level around 5900 cal yr BP, the development of an extensive wetland around 5400 cal yr BP, and the subsequent transition to a peatland. The shift from shallow lake to wetland and later to a peatland is interpreted as a response to lower effective moisture. A hiatus at the transition from wetland to peatland suggests very low accumulation rates, which may result from very dry climatic conditions. A rise in groundwater and lake level around 3200 cal yr BP allowed the re-establishment of a wetland in the Kumphawapi basin. However, the sediments deposited between c. 3200 and 1600 cal yr BP provide evidence for at least two hiatuses at c. 2700-2500 cal yr BP, and at c. 1900-1600 cal yr BP, which would suggest surface dryness and consequently periods of low effective moisture. Around 1600 cal yr BP a new shallow lake became re-established in the basin. Although the underlying causes for this new lake phase remain unclear, we hypothesize that higher effective moisture was the main driving force. This shallow lake phase continued up to the present but was interrupted by higher nutrient fluxes to the lake around 1000-600 cal yr BP. Whether this was caused by intensified human impact in the catchment or, whether this signals a lowering of the lake level due to reduced effective moisture, needs to be corroborated by further studies in the region. The multi-proxy study of Kumphawapi's sediment core CP3A clearly shows that Kumphawapi is a sensitive archive for recording past shifts in effective moisture, and as such in the intensity of the Asian summer monsoon. Many more continental paleorecords, however, will be needed to fully understand the spatial and temporal patterns of past changes in Asian monsoon intensity and its ecosystem impacts.
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