| 1. |
- Czymzik, Markus, et al.
(författare)
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Synchronizing 10Be in two varved lake sediment records to IntCal13 14C during three grand solar minima
- 2018
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 14:5, s. 687-696
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Tidskriftsartikel (refereegranskat)abstract
- Timescale uncertainties between paleoclimate reconstructions often inhibit studying the exact timing, spatial expression and driving mechanisms of climate variations. Detecting and aligning the globally common cosmogenic radionuclide production signal via a curve fitting method provides a tool for the quasi-continuous synchronization of paleoclimate archives. In this study, we apply this approach to synchronize Be-10 records from varved sediments of Tiefer See and Lake Czechowskie covering the Maunder, Homeric and 5500 a BP grand solar minima with C-14 production rates inferred from the IntCal13 calibration curve. Our analyses indicate best fits with C-14 production rates when the Be-10 records from Tiefer See were shifted for 8 (-12/+4) (Maunder Minimum), 31 (-16/+12) (Homeric Minimum) and 86 (-22/+18) years (5500 a BP grand solar minimum) towards the past. The best fit between the Lake Czechowskie Be-10 record for the 5500 a BP grand solar minimum and C-14 production was obtained when the Be-10 time series was shifted 29 (-8/+7) years towards present. No significant fits were detected between the Lake Czechowskie Be-10 records for the Maunder and Homeric minima and C-14 production, likely due to intensified in-lake sediment resuspension since about 2800 a BP, transporting "old" Be-10 to the coring location. Our results provide a proof of concept for facilitating Be-10 in varved lake sediments as a novel synchronization tool required for investigating leads and lags of proxy responses to climate variability. However, they also point to some limitations of Be-10 in these archives, mainly connected to in-lake sediment resuspension processes.
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| 2. |
- Brehm, Nicolas, et al.
(författare)
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Tree-rings reveal two strong solar proton events in 7176 and 5259 BCE
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- The Sun sporadically produces eruptive events leading to intense fluxes of solar energetic particles (SEPs) that dramatically disrupt the near-Earth radiation environment. Such events have been directly studied for the last decades but little is known about the occurrence and magnitude of rare, extreme SEP events. Presently, a few events that produced measurable signals in cosmogenic radionuclides such as 14C, 10Be and 36Cl have been found. Analyzing annual 14C concentrations in tree-rings from Switzerland, Germany, Ireland, Russia, and the USA we discovered two spikes in atmospheric 14C occurring in 7176 and 5259 BCE. The ~2% increases of atmospheric 14C recorded for both events exceed all previously known 14C peaks but after correction for the geomagnetic field, they are comparable to the largest event of this type discovered so far at 775 CE. These strong events serve as accurate time markers for the synchronization with floating tree-ring and ice core records and provide critical information on the previous occurrence of extreme solar events which may threaten modern infrastructure.
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| 3. |
- Czymzik, Markus, et al.
(författare)
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A varved lake sediment record of the Be-10 solar activity proxy for the Lateglacial-Holocene transition
- 2016
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 153, s. 31-39
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Tidskriftsartikel (refereegranskat)abstract
- Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on Be-10 records from ice cores and C-14 time-series from tree rings, all including archive-specific limitations. We present the first Be-10 record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, Be-10 deposition using a new approach based on regression analyses between our Be-10 record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our Be-10 record, but cannot be the main explanation for major Be-10 excursions. Corrected for these environmental influences, our Be-10 record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in Be-10 from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.
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| 4. |
- Czymzik, Markus, et al.
(författare)
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Solar cycles and depositional processes in annual Be-10 from two varved lake sediment records
- 2015
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 428, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- Beryllium 10 concentrations (Be-10(con)) were measured at annual resolution from varved sediment cores of Lakes Tiefer See (TSK) and Czechowskie (JC) for the period 1983-2009 (similar to solar cycles 22 and 23). Calibrating the Be-10(con) time-series against complementing proxy records from the same archive as well as local precipitation and neutron monitor data, reflecting solar forced changes in atmospheric radionuclide production, allowed (i) identifying the main depositional processes and (ii) evaluating the potential for solar activity reconstruction. Be-10(con) in TSK and JC sediments are significantly correlated to varying neutron monitor counts (TSK: r = 0.5, p = 0.05, n = 16; JC: r = 0.46, p = 0.03, n = 22). However, the further correlations with changes in organic carbon contents in TSK as well as varying organic carbon and detrital matter contents in JC point to catchment specific biases in the 10Be(con) time-series. In an attempt to correct for these biases multiple regression analysis was applied to extract an atmospheric Be-10 production signal (Be-10(atmosphere)). To increase the signal to noise ratio a Be-10 composite record (Be-10(composite)) was calculated from the TSK time-series. Be-10(composite) and JC Be-10(atmosphere) is significantly correlated to variations in the neutron monitor record (r = 0.49, p = 0.01, n = 25) and matches the expected amplitude changes in 10Be production between solar cycle minima and maxima. This calibration study on 10Be from two sites indicates the large potential but also, partly site-specific, limitations of Be-10 in varved lake sediments for solar activity reconstruction. (C) 2015 Elsevier B.V. All rights reserved.
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| 5. |
- Erhardt, Tobias, et al.
(författare)
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High-resolution aerosol data from the top 3.8kyr of the East Greenland Ice coring Project (EGRIP) ice core
- 2023
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Ingår i: Earth System Science Data. - 1866-3508. ; 15:11, s. 5079-5091
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Tidskriftsartikel (refereegranskat)abstract
- Here we present the high-resolution continuous flow analysis (CFA) data from the top 479m of the East Greenland Ice coring Project (EGRIP) ice core covering the past 3.8kyr. The data consist of 1mm depth-resolution profiles of calcium, sodium, ammonium, nitrate, and electrolytic conductivity as well as decadal averages of these profiles. The nominally 1mm data represent an oversampling of the record as the true resolution is limited by the analytical setup to approximately 1cm. Alongside the data we provide a description of the measurement setup, procedures, the relevant references for the specific methods as well as an assessment of the precision of the measurements, the sample-to-depth assignment, and the depth and temporal resolution of the data set. The error in absolute depth assignment of the data may be on the order of 2cm; however, relative depth offsets between the records of the individual species are only on the order of 1mm. The presented data have sub-annual resolution over the entire depth range and have already formed part of the data for an annually layer-counted timescale for the EGRIP ice core used to improve and revise the multi-core Greenland ice-core chronology (GICC05) to a new version, GICC21 . The data are available in full 1mm resolution and decadal averages on PANGAEA (10.1594/PANGAEA.945293, ).
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| 6. |
- Mekhaldi, Florian, et al.
(författare)
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Multiradionuclide evidence for the solar origin of the cosmic-ray events of ᴀᴅ 774/5 and 993/4.
- 2015
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The origin of two large peaks in the atmospheric radiocarbon ((14)C) concentration at AD 774/5 and 993/4 is still debated. There is consensus, however, that these features can only be explained by an increase in the atmospheric (14)C production rate due to an extraterrestrial event. Here we provide evidence that these peaks were most likely produced by extreme solar events, based on several new annually resolved (10)Be measurements from both Arctic and Antarctic ice cores. Using ice core (36)Cl data in pair with (10)Be, we further show that these solar events were characterized by a very hard energy spectrum with high fluxes of solar protons with energy above 100 MeV. These results imply that the larger of the two events (AD 774/5) was at least five times stronger than any instrumentally recorded solar event. Our findings highlight the importance of studying the possibility of severe solar energetic particle events.
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| 7. |
- Mekhaldi, Florian, et al.
(författare)
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Radionuclide wiggle matching reveals a nonsynchronous early Holocene climate oscillation in Greenland and western Europe around a grand solar minimum
- 2020
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Ingår i: Climate of the Past. - : COPERNICUS GESELLSCHAFT MBH. - 1814-9324 .- 1814-9332. ; 16:4, s. 1145-1157
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Tidskriftsartikel (refereegranskat)abstract
- Several climate oscillations have been reported from the early Holocene superepoch, the best known of which is the Preboreal oscillation (PBO). It is still unclear how the PBO and the number of climate oscillations observed in Greenland ice cores and European terrestrial records are related to one another. This is mainly due to uncertainties in the chronologies of the records. Here, we present new, high-resolution Be-10 concentration data from the varved Meerfelder Maar sediment record in Germany, spanning the period 11 310-11 000 years BP. These new data allow us to synchronize this well-studied record, as well as Greenland ice core records, with the IntCal13 timescale via radionuclide wiggle matching. In doing so, we show that the climate oscillations identified in Greenland and Europe between 11 450 and 11 000 years BP were not synchronous but terminated and began, respectively, with the onset of a grand solar minimum. A similar spatial anomaly pattern is found in a number of modeling studies on solar forcing of climate in the North Atlantic region. We further postulate that freshwater delivery to the North Atlantic would have had the potential to amplify solar forcing through a slowdown of the Atlantic meridional overturning circulation (AMOC) reinforcing surface air temperature anomalies in the region.
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| 8. |
- O'Hare, Paschal, et al.
(författare)
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Multiradionuclide evidence for an extreme solar proton event around 2,610 BP (similar to 660 BC)
- 2019
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 116:13, s. 5961-5966
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Tidskriftsartikel (refereegranskat)abstract
- Recently, it has been confirmed that extreme solar proton events can lead to significantly increased atmospheric production rates of cosmogenic radionuclides. Evidence of such events is recorded in annually resolved natural archives, such as tree rings [carbon-14 (C-14)] and ice cores [beryllium-10 (Be-10), chlorine-36 (Cl-36)]. Here, we show evidence for an extreme solar event around 2,610 years B.P. (similar to 660 BC) based on high-resolution Be-10 data from two Greenland ice cores. Our conclusions are supported by modeled C-14 production rates for the same period. Using existing Cl-36 ice core data in conjunction with Be-10, we further show that this solar event was characterized by a very hard energy spectrum. These results indicate that the 2,610-years B.P. event was an order of magnitude stronger than any solar event recorded during the instrumental period and comparable with the solar proton event of AD 774/775, the largest solar event known to date. The results illustrate the importance of multiple ice core radionuclide measurements for the reliable identification of short-term production rate increases and the assessment of their origins.
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| 9. |
- Paleari, Chiara I., et al.
(författare)
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Cosmogenic radionuclides reveal an extreme solar particle storm near a solar minimum 9125 years BP
- 2022
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- During solar storms, the Sun expels large amounts of energetic particles (SEP) that can react with the Earth’s atmospheric constituents and produce cosmogenic radionuclides such as 14C, 10Be and 36Cl. Here we present 10Be and 36Cl data measured in ice cores from Greenland and Antarctica. The data consistently show one of the largest 10Be and 36Cl production peaks detected so far, most likely produced by an extreme SEP event that hit Earth 9125 years BP (before present, i.e., before 1950 CE), i.e., 7176 BCE. Using the 36Cl/10Be ratio, we demonstrate that this event was characterized by a very hard energy spectrum and was possibly up to two orders of magnitude larger than any SEP event during the instrumental period. Furthermore, we provide 10Be-based evidence that, contrary to expectations, the SEP event occurred near a solar minimum.
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| 10. |
- Paleari, Chiara I., et al.
(författare)
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Evaluating the 11-year solar cycle and short-Term 10Be deposition events with novel excess water samples from the East Greenland Ice-core Project (EGRIP)
- 2023
-
Ingår i: Climate of the Past. - 1814-9324. ; 19:11, s. 2409-2422
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Tidskriftsartikel (refereegranskat)abstract
- 10Be is produced by the interaction between galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with the Earth's atmospheric constituents. The flux of GCRs is modulated by the varying strength of the magnetic fields of the Earth and the Sun. Measurement of 10Be concentrations from polar ice cores is thus a valuable tool to reconstruct the variations in the geomagnetic field and solar activity levels. The interpretation of 10Be records is, however, complicated by non-production-related effects on the 10Be deposition rate caused by climate-or weather-induced variability. Furthermore, volcanic eruptions have been proposed to lead to short-Term 10Be deposition enhancements. In this study, we test the use of excess meltwater from continuous flow analysis (CFA) to measure 10Be, allowing less time-consuming and more cost-effective sample preparation. We compare two records obtained from CFA and discrete samples from the East Greenland Ice core Project (EGRIP) S6 firn core, reaching back to 1900gCE. We find that the two records agree well and that the 10Be record from CFA samples agrees as well as the discrete samples with other records from Greenland. Furthermore, by subtracting the theoretically expected GCR-induced signal, we investigate the high-frequency variability in the 10Be records from Greenland and Antarctica after 1951gCE, focusing on SEP events and volcanic eruptions. Finally, we use the 10Be records from Greenland and Antarctica to study the 11-year solar cycles, allowing us to assess the suitability of the CFA samples for the reconstruction of solar activity. This result opens new opportunities for the collection of continuous 10Be records with less time-consuming sample preparation, while saving an important portion of the ice cores for other measurements.
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| 11. |
- Zheng, Minjie, et al.
(författare)
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Modeling Atmospheric Transport of Cosmogenic Radionuclide 10Be Using GEOS-Chem 14.1.1 and ECHAM6.3-HAM2.3 : Implications for Solar and Geomagnetic Reconstructions
- 2024
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 51:2
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Tidskriftsartikel (refereegranskat)abstract
- A prerequisite to applying 10Be in natural archives for solar and geomagnetic reconstructions is to know how 10Be deposition reflects atmospheric production changes. However, this relationship remains debated. To address this, we use two state-of-the-art global models GEOS-Chem and ECHAM6.3-HAM2.3 with the latest beryllium production model. During solar modulation, both models suggest that 10Be deposition reacts proportionally to global production changes, with minor latitudinal deposition biases (<5%). During geomagnetic modulation, however, 10Be deposition changes are enhanced by ∼15% in the tropics and attenuated by 20%–35% in subtropical and polar regions compared to global production changes. Such changes are also hemispherically asymmetric, attributed to asymmetric production between hemispheres. For the solar proton event in 774/5 CE, 10Be shows a 15% higher deposition increase in polar regions than in tropics. This study highlights the importance of atmospheric mixing when comparing 10Be from different locations or to independent geomagnetic field records.
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| 12. |
- Adolphi, Florian, et al.
(författare)
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Connecting the Greenland ice-core and U/Th timescales via cosmogenic radionuclides : Testing the synchroneity of Dansgaard-Oeschger events
- 2018
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 14:11, s. 1755-1781
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Tidskriftsartikel (refereegranskat)abstract
- During the last glacial period Northern Hemisphere climate was characterized by extreme and abrupt climate changes, so-called Dansgaard-Oeschger (DO) events. Most clearly observed as temperature changes in Greenland ice-core records, their climatic imprint was geographically widespread. However, the temporal relation between DO events in Greenland and other regions is uncertain due to the chronological uncertainties of each archive, limiting our ability to test hypotheses of synchronous change. In contrast, the assumption of direct synchrony of climate changes forms the basis of many timescales. Here, we use cosmogenic radionuclides (10Be, 36Cl, 14C) to link Greenland ice-core records to U=Th-dated speleothems, quantify offsets between the two timescales, and improve their absolute dating back to 45 000 years ago. This approach allows us to test the assumption that DO events occurred synchronously between Greenland ice-core and tropical speleothem records with unprecedented precision. We find that the onset of DO events occurs within synchronization uncertainties in all investigated records. Importantly, we demonstrate that local discrepancies remain in the temporal development of rapid climate change for specific events and speleothems. These may either be related to the location of proxy records relative to the shifting atmospheric fronts or to underestimated U=Th dating uncertainties. Our study thus highlights the potential for misleading interpretations of the Earth system when applying the common practice of climate wiggle matching.
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| 13. |
- Adolphi, Florian, et al.
(författare)
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Intercomparison of C-14 Dating of Wood Samples at Lund University and Eth-Zurich Ams Facilities: Extraction, Graphitization, and Measurement
- 2013
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Ingår i: Radiocarbon. - 0033-8222. ; 55:2-3, s. 391-400
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Tidskriftsartikel (refereegranskat)abstract
- We conducted an interlaboratory comparison between our radiocarbon-related research group at Lund University and the established ETH-Zurich facility to test the quality of the results obtained in Lund and to identify sources of potential background differences and scatter. We did find differences between the 2 laboratories in the contributions of chemical preparation, graphitization, and measurements to the overall background. The resulting overall background is, however, almost similar. Multiple measurements on 2 wood samples of known calendar age yield consistent and accurate C-14 ages in both laboratories. However, one of our known samples indicates that IntCal09 is similar to 38 +/- 16 C-14 BP too young at 7020 calendar yr BP, which is consistent with one of the raw data sets contributing to IntCal09. Overall, our results show that a systematic approach to compare the different steps involved in C-14 age determination is a useful exercise to pinpoint targets for improvement of lab routines and assess interlaboratory differences. These effects do not necessarily become apparent when comparing C-14 measurements that integrate over the whole process of preparation and measurement of different laboratories.
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| 14. |
- Adolphi, Florian, et al.
(författare)
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Persistent link between solar activity and Greenland climate during the Last Glacial Maximum
- 2014
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Ingår i: Nature Geoscience. - 1752-0908 .- 1752-0894. ; 7:9, s. 662-666
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Tidskriftsartikel (refereegranskat)abstract
- Changes in solar activity have previously been proposed to cause decadal- to millennial-scale fluctuations in both the modern and Holocene climates(1). Direct observational records of solar activity, such as sunspot numbers, exist for only the past few hundred years, so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as Be-10 and C-14 from ice cores and tree rings(2,3). Here we present a high-resolution Be-10 record from the ice core collected from central Greenland by the Greenland Ice Core Project (GRIP). The record spans from 22,500 to 10,000 years ago, and is based on new and compiled data(4-6). Using C-14 records(7,8) to control for climate-related influences on Be-10 deposition, we reconstruct centennial changes in solar activity. We find that during the Last Glacial Maximum, solar minima correlate with more negative delta O-18 values of ice and are accompanied by increased snow accumulation and sea-salt input over central Greenland. We suggest that solar minima could have induced changes in the stratosphere that favour the development of high-pressure blocking systems located to the south of Greenland, as has been found in observations and model simulations for recent climate(9,10). We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions.
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| 15. |
- Adolphi, Florian, et al.
(författare)
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Radiocarbon calibration uncertainties during the last deglaciation : Insights from new floating tree-ring chronologies
- 2017
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 170, s. 98-108
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Tidskriftsartikel (refereegranskat)abstract
- Radiocarbon dating is the most commonly used chronological tool in archaeological and environmental sciences dealing with the past 50,000 years, making the radiocarbon calibration curve one of the most important records in paleosciences. For the past 12,560 years, the radiocarbon calibration curve is constrained by high quality tree-ring data. Prior to this, however, its uncertainties increase rapidly due to the absence of suitable tree-ring 14C data. Here, we present new high-resolution 14C measurements from 3 floating tree-ring chronologies from the last deglaciation. By using combined information from the current radiocarbon calibration curve and ice core 10Be records, we are able to absolutely date these chronologies at high confidence. We show that our data imply large 14C-age variations during the Bølling chronozone (Greenland Interstadial 1e) – a period that is currently characterized by a long 14C-age plateau in the most recent IntCal13 calibration record. We demonstrate that this lack of structure in IntCal13 may currently lead to erroneous calibrated ages by up to 500 years.
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| 16. |
- Adolphi, Florian
(författare)
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Solar Activity Changes at the End of the Last Ice Age - Influences on Climate and Applications for Dating
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Throughout its history Earth experienced a variety of natural climate changes. By investigating their spatial and temporal evolution we can increase the understanding of the mechanisms and dynamics underlying natural climate change and improve our general comprehension of the climate system. Prerequisites of these investigations are reliable reconstructions of past forcing variations as well as sound and consistent chronologies of paleoclimate records. The Sun is by far Earth’s most important source of energy and variations in its irradiance have been shown to influence climate on different temporal and spatial scales. The exact mechanisms of these solar influences on climate are, however, not fully understood. Variations in solar activity also cause changes in the atmospheric production rates of cosmogenic radionuclides, such as 10Be and 14C. These radionuclides get subsequently deposited in various environments which can, hence, provide information about past solar activity levels. Furthermore, these records can be synchronized to each other by identifying coherent production rate related patterns in their radionuclide records. This project aims to extend solar activity reconstructions back into the late glacial and investigate potential sun-climate relationships. Furthermore, the consistency of the time scales underlying different records is tested by comparing their cosmogenic radionuclide records. In addition, it aims to improve radiocarbon dating calibration by extending its tree-ring based section further back in time. We present the first solar activity reconstruction for the late glacial based new and published 10Be data from the GRIP and GISP2 ice cores, supported by published 14C data. We infer that late glacial and Holocene solar activity variations have been comparable in both patterns and amplitudes. We find a persistent influence of solar activity changes on Greenland climate during the Last Glacial Maximum which appears coherent with modern day observations and climate model results. This suggests that a similar solar forcing mechanism may have been operating under otherwise very different climate regimes. We propose a time scale transfer function between Greenland ice core and radiocarbon dated records by synchronizing the temporal variations of ice core 10Be and tree-ring 14C records. We outline a statistical framework that allows time scale differences and uncertainties to be inferred. We find that there is a continuously growing difference between Greenland ice core and radiocarbon based chronologies throughout the Holocene. Furthermore, we identify a rapid shift in this time scale difference around 12,500 years ago, that cannot be explained with ice core layer counting uncertainties alone. Instead, we propose that this effect may arise from uncertainties in the absolute dating of tree-ring records. We present new 14C data on floating tree-ring chronologies that can improve radiocarbon dating calibration between 14,000 to 14,700 years ago. We introduce a method of how combined information from 14C and 10Be records can aid us to infer absolute ages for these chronologies. These new records add substantial structure to the calibration curve and we note that missing this structure can lead to erroneous calibration of 14C dates by up to 500 years.
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| 17. |
- Adolphi, Florian, et al.
(författare)
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Synchronizing the Greenland ice core and radiocarbon timescales over the Holocene-Bayesian wiggle-matching of cosmogenic radionuclide records
- 2016
-
Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 12:1, s. 15-30
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Tidskriftsartikel (refereegranskat)abstract
- Investigations of past climate dynamics rely on accurate and precise chronologies of the employed climate reconstructions. The radiocarbon dating calibration curve (IntCal13) and the Greenland ice core chronology (GICC05) represent two of the most widely used chronological frameworks in paleoclimatology of the past 1/4 g50g000 years. However, comparisons of climate records anchored on these chronologies are hampered by the precision and accuracy of both timescales. Here we use common variations in the production rates of 14C and 10Be recorded in tree-rings and ice cores, respectively, to assess the differences between both timescales during the Holocene. Compared to earlier work, we employ a novel statistical approach which leads to strongly reduced and yet, more robust, uncertainty estimates. Furthermore, we demonstrate that the inferred timescale differences are robust independent of (i) the applied ice core 10Be records, (ii) assumptions of the mode of 10Be deposition, as well as (iii) carbon cycle effects on 14C, and (iv) in agreement with independent estimates of the timescale differences. Our results imply that the GICC05 counting error is likely underestimated during the most recent 2000 years leading to a dating bias that propagates throughout large parts of the Holocene. Nevertheless, our analysis indicates that the GICC05 counting error is generally a robust uncertainty measurement but care has to be taken when treating it as a nearly Gaussian error distribution. The proposed IntCal13-GICC05 transfer function facilitates the comparison of ice core and radiocarbon dated paleoclimate records at high chronological precision.
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| 18. |
- Bernhardson, Martin, et al.
(författare)
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Sand drift events and surface winds in south-central Sweden : From the deglaciation to the present
- 2019
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 209, s. 13-22
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Tidskriftsartikel (refereegranskat)abstract
- During the transition from the last glacial into the Holocene interglacial, the atmospheric circulation in the North Atlantic area changed from a glacial mode, influenced by the presence of large ice sheets, into a system more similar to that of the present day. This change had implications for wind, temperature and precipitation patterns that can be traced in geological archives. Here, we focus on reconstructing past wind directions over southern Scandinavia, as inferred from the net sediment transport direction of inland dunes in south-central Sweden. We analysed single dunes and dune fields along a 540-km-long S-N transect with LiDAR (Light detection and ranging) derived DEMs (digital elevation models) to determine their geomorphological type and the directional mode of the wind that led to their formation. Luminescence ages of sand drift and dune formation were compiled from previous studies, allowing us to build a chronology of sand drift after the deglaciation of south-central Sweden. The majority of the dunes appear to have been formed by westerly or northwesterly winds and stabilised ∼10.5–9.0 ka. Although this is rather close in time to the local deglaciation for the northern sites, it is long after the disappearance of ice from the more southern sites. The coeval dune stabilisation over such a large geographical area suggests that regional environmental conditions played an important role. It is likely that an unstable climate in conjunction with low groundwater tables during the early Holocene locally delayed vegetation from stabilising the dunes.
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| 19. |
- Björck, Svante, et al.
(författare)
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A South Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial
- 2019
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:6, s. 1939-1958
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..
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| 20. |
- Brehm, Nicolas, et al.
(författare)
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Eleven-year solar cycles over the last millennium revealed by radiocarbon in tree rings
- 2021
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 14:1, s. 10-15
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Tidskriftsartikel (refereegranskat)abstract
- The Sun provides the principal energy input into the Earth system and solar variability represents a significant external climate forcing. Although observations of solar activity (sunspots) cover only the last about 400 years, radionuclides produced by cosmic rays and stored in tree rings or ice cores serve as proxies for solar activity extending back thousands of years. However, the presence of weather-induced noise or low temporal resolution of long, precisely dated records hampers cosmogenic nuclide-based studies of short-term solar variability such as the 11-yr Schwabe cycle. Here we present a continuous, annually resolved atmospheric 14C concentration (fractionation-corrected ratio of 14CO2 to CO2) record reconstructed from absolutely dated tree rings covering nearly all of the last millennium (ad 969–1933). The high-resolution and precision 14C record reveals the presence of the Schwabe cycle over the entire time range. The record confirms the ad 993 solar energetic particle event and reveals two new candidates (ad 1052 and ad 1279), indicating that strong solar events that might be harmful to modern electronic systems probably occur more frequently than previously thought. In addition to showing decadal-scale solar variability over the last millennium, the high-temporal-resolution record of atmospheric radiocarbon also provides a useful benchmark for making radiocarbon dating more accurate over this interval.
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| 21. |
- Bronk Ramsey, Christopher, et al.
(författare)
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Development of the Intcal Database
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Ingår i: Radiocarbon. - 0033-8222.
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Tidskriftsartikel (refereegranskat)abstract
- The IntCal family of radiocarbon (14C) calibration curves is based on research spanning more than three decades. The IntCal group have collated the 14C and calendar age data (mostly derived from primary publications with other types of data and meta-data) and, since 2010, made them available for other sorts of analysis through an open-access database. This has ensured transparency in terms of the data used in the construction of the ratified calibration curves. As the IntCal database expands, work is underway to facilitate best practice for new data submissions, make more of the associated metadata available in a structured form, and help those wishing to process the data with programming languages such as R, Python, and MATLAB. The data and metadata are complex because of the range of different types of archives. A restructured interface, based on the "IntChron"open-access data model, includes tools which allow the data to be plotted and compared without the need for export. The intention is to include complementary information which can be used alongside the main 14C series to provide new insights into the global carbon cycle, as well as facilitating access to the data for other research applications. Overall, this work aims to streamline the generation of new calibration curves.
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| 22. |
- Cooper, Alan, et al.
(författare)
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A global environmental crisis 42,000 years ago
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 371:6531, s. 811-818
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Tidskriftsartikel (refereegranskat)abstract
- Geological archives record multiple reversals of Earth’s magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.
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| 23. |
- Cooper, Alan, et al.
(författare)
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Response to comment on “A global environmental crisis 42,000 years ago”
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 374:6570
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Tidskriftsartikel (refereegranskat)abstract
- Our paper about the impacts of the Laschamps Geomagnetic Excursion 42,000 years ago has provoked considerable scientific and public interest, particularly in the so-called Adams Event associated with the initial transition of the magnetic poles. Although we welcome the opportunity to discuss our new ideas, Hawks’ assertions of misrepresentation are especially disappointing given his limited examination of the material.
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| 24. |
- Czymzik, Markus, et al.
(författare)
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Mid-Holocene humid periods reconstructed from calcite varves of the Lake Woserin sediment record (north-eastern Germany)
- 2016
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Ingår i: Holocene. - : SAGE Publications. - 0959-6836. ; 26:6, s. 935-946
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Tidskriftsartikel (refereegranskat)abstract
- Time-series of varve properties and geochemistry were established from varved sediments of Lake Woserin (north-eastern Germany) covering the recent period AD 2010–1923 and the mid-Holocene time-window 6400–4950 varve years before present (vyr BP) using microfacies analyses, x-ray fluorescence (µ-XRF) scanning, microscopic varve chronology, and 14C dating. The microscopic varve chronology was compared with a macroscopic varve chronology for the same sediment interval. Calcite layer thickness during the recent period is significantly correlated to increases in local annual precipitation (r = 0.46, p = 0.03) and reduced air-pressure (r = −0.72, p < 0.0001). Meteorologically consistent with enhanced precipitation at Lake Woserin, a composite 500 hPa anomaly map for years with >1 standard deviation calcite layer thickness depicts a negative wave train air-pressure anomaly centered over southern Europe, with north-eastern Germany at its northern frontal zone. Three centennial-scale intervals of thicker calcite layers around the mid-Holocene periods 6200–5900, 5750–5400, and 5300–4950 vyr BP might reflect humid conditions favoring calcite precipitation through the transport of Ca2+ ions into Lake Woserin, synchronous to wetter conditions in Europe. Calcite layer thickness oscillations of about 88 and 208 years resemble the solar Gleissberg and Suess cycles suggesting that the recorded hydroclimate changes in north-eastern Germany are modified by solar influences on synoptic-scale atmospheric circulation. However, parts of the periods of thicker calcite layers around 5750–5400 and 5200 vyr BP also coincide with enhanced human catchment activity at Lake Woserin. Therefore, calcite precipitation during these time-windows might have further been favored by anthropogenic deforestation mobilizing Ca2+ ions and/or lake eutrophication.
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| 25. |
- Dinauer, Ashley, et al.
(författare)
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Mysteriously high I14C of the glacial atmosphere : Influence of 14C production and carbon cycle changes
- 2020
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 16:4, s. 1159-1185
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Tidskriftsartikel (refereegranskat)abstract
- Despite intense focus on the span classCombining double low lineinline-formulag1/4190/span drop in atmospheric span classCombining double low lineinline-formulaI14C/span during Heinrich Stadial 1 at span classCombining double low lineinline-formulag1/417.4/span-14.6 span classCombining double low lineinline-formulaka/span, the specific mechanisms responsible for the apparent span classCombining double low lineinline-formulaI14C/span excess in the glacial atmosphere have received considerably less attention. The computationally efficient Bern3D Earth system model of intermediate complexity, designed for long-term climate simulations, allows us to address a very fundamental but still elusive question concerning the atmospheric span classCombining double low lineinline-formulaI14C/span record: how can we explain the persistence of relatively high span classCombining double low lineinline-formulaI14C/span values during the millennia after the Laschamp event? Large uncertainties in the pre-Holocene span classCombining double low lineinline-formula14C/span production rate, as well as in the older portion of the span classCombining double low lineinline-formulaI14C/span record, complicate our qualitative and quantitative interpretation of the glacial span classCombining double low lineinline-formulaI14C/span elevation. Here we begin with sensitivity experiments that investigate the controls on atmospheric span classCombining double low lineinline-formulaI14C/span in idealized settings. We show that the interaction with the ocean sediments may be much more important to the simulation of span classCombining double low lineinline-formulaI14C/span than had been previously thought. In order to provide a bounded estimate of glacial span classCombining double low lineinline-formulaI14C/span change, the Bern3D model was integrated with five available estimates of the span classCombining double low lineinline-formula14C/span production rate as well as reconstructed and hypothetical paleoclimate forcing. Model results demonstrate that none of the available reconstructions of past changes in span classCombining double low lineinline-formula14C/span production can reproduce the elevated span classCombining double low lineinline-formulaI14C/span levels during the last glacial. In order to increase atmospheric span classCombining double low lineinline-formulaI14C/span to glacial levels, a drastic reduction of air-sea exchange efficiency in the polar regions must be assumed, though discrepancies remain for the portion of the record younger than span classCombining double low lineinline-formulag1/433/span span classCombining double low lineinline-formulaka/span. We end with an illustration of how the span classCombining double low lineinline-formula14C/span production rate would have had to evolve to be consistent with the span classCombining double low lineinline-formulaI14C/span record by combining an atmospheric radiocarbon budget with the Bern3D model. The overall conclusion is that the remaining discrepancies with respect to glacial span classCombining double low lineinline-formulaI14C/span may be linked to an underestimation of span classCombining double low lineinline-formula14C/span production and/or a biased-high reconstruction of span classCombining double low lineinline-formulaI14C/span over the time period of interest. Alternatively, we appear to still be missing an important carbon cycle process for atmospheric span classCombining double low lineinline-formulaI14C/span.
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