Browsing by Author "Muscheler, R"

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    Changes in El Niño - Southern Oscillation (ENSO) conditions during the Greenland Stadial 1 (GS-1) chronozone revealed by New Zealand tree-rings
    (Elsevier, 2016-12-01) Palmer, JG; Turney, CSM; Cook, ER; Fenwick, P; Thomas, ZA; Helle, G; Jones, RT; Clement, A; Hogg, AG; Southon, J; Bronk Ramsey, C; Staff, R; Muscheler, R; Corrège, T; Hua, Q
    The warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning GS-1, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri (Agathis australis) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a ‘historic’ 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Niño – Southern Oscillation (ENSO). We then focus our study on a 1010-year sub-fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between ∼12,500 and 12,380 cal BP within GS-1. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency with ENSO and Southern Hemisphere atmospheric circulation change during this period. The driver(s) for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions. © 2016, Elsevier Ltd.
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    Constraints on long-term changes in solar activity from the range of variability of cosmogenic radionuclide records
    (Copernicus Publications, 2011-09-03) Muscheler, R; Heikkilä, UE
    There is a variety of different cosmogenic radionuclide-based reconstructions of solar activity variations for the past. Especially the longer-term changes and the absolute levels of past solar activity are uncertain as it is illustrated by the differences between these reconstructions. On the one hand there are differences between 10Be and 14C records that are commonly used as proxies for the varying solar modulation of galactic cosmic rays. On the other hand estimates of past changes in the geomagnetic shielding also include relatively large uncertainties. Here, we concentrate on variations in cosmogenic radionuclide records on time scales of 50 to 500 yr. We show that these are to a large extent independent of the geomagnetic field intensity. The range of variability of cosmogenic radionuclide records allows us to set constraints about long-term changes in solar activity. These records indicate that present solar activity levels were reached or exceeded regularly in the past. © Author(s) 2011.
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    Development of a multi-method chronology spanning the last glacial interval from Orakei maar lake, Auckland, New Zealand
    (European Geosciences Union, 2020-12-15) Peti, L; Fitzsimmons, KE; Hopkins, JL; Nilsson, A; Fujioka, T; Fink, D; Mifsud, C; Christl, M; Muscheler, R; Augustinus, PC
    Northern New Zealand is an important location for understanding Last Glacial Interval (LGI) palaeoclimate dynamics, since it is influenced by both tropical and polar climate systems which have varied in relative strength and timing. Sediments from the Auckland Volcanic Field maar lakes preserve records of such large-scale climatic influences on regional palaeo-environment changes, as well as past volcanic eruptions. The sediment sequence infilling Orakei maar lake is continuous, laminated, and rapidly deposited, and it provides a high-resolution (sedimentation rate above ∼ 1 m kyr−1) archive from which to investigate the dynamic nature of the northern New Zealand climate system over the LGI. Here we present the chronological framework for the Orakei maar sediment sequence. Our chronology was developed using Bayesian age modelling of combined radiocarbon ages, tephrochronology of known-age rhyolitic tephra marker layers, 40Ar∕39Ar-dated eruption age of a local basaltic volcano, luminescence dating (using post-infrared–infrared stimulated luminescence, or pIR-IRSL), and the timing of the Laschamp palaeomagnetic excursion. We have integrated our absolute chronology with tuning of the relative palaeo-intensity record of the Earth's magnetic field to a global reference curve (PISO-1500). The maar-forming phreatomagmatic eruption of the Orakei maar is now dated to > 132 305 years (95 % confidence range: 131 430 to 133 180 years). Our new chronology facilitates high-resolution palaeo-environmental reconstruction for northern New Zealand spanning the last ca. 130 000 years for the first time as most NZ records that span all or parts of the LGI are fragmentary, low-resolution, and poorly dated. Providing this chronological framework for LGI climate events inferred from the Orakei sequence is of paramount importance in the context of identification of leads and lags in different components of the Southern Hemisphere climate system as well as identification of Northern Hemisphere climate signals. © Author(s) 2020 This work is distributed under the Creative Commons Attribution 4.0 Licence.
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    Integrated age modelling of numerical, correlative and relative dating of a long lake sediment sequence from Orakei maar palaeolake, Auckland, New Zealand
    (Copernicus GmbH, 2019-04-11) Peti, L; Augustinus, PC; Fujioka, T; Mifsud, C; Nilsson, A; Muscheler, R; Fitzsimmons, KE; Hopkins, JL
    Accurate and precise chronologies are fundamental for successful Quaternary palaeo-climate/environment reconstruction and correlation with global climatic events. Aside from varved lake sequences, chronologies for sediment archives typically depend on age models developed from a limited number of dated horizons, often with large associated errors, age reversals, or minimum/maximum age constraints. Whilst the approach to generating chronologies for sediment cores has moved on from linear interpolation to considering age uncertainties and developing more nuanced accumulation models, these age models rarely reach the resolution and precision desired for millennial-scale palaeo-climatic correlations, particularly beyond the limits of the more precise radiocarbon method. Bayesian modelling offers the opportunity to optimise age models by combining all available information on the depositional history of the basin. Here we address this issue for the Orakei maar palaeolake sequence from Auckland, New Zealand. The Orakei maar sequence offers a high-resolution and continuous record of climatic variations spanning much of the last glacial cycle and is one of the few from the southern hemisphere mid-latitudes. The Orakei sequence spans ca. 120 to 10 ky; our chronology is derived from tephrochronology, radiocarbon dating, post-IR IRSL luminescence dating, relative palaeomagnetic intensity changes and meteoric Beryllium-10 flux. Prior to 40 ka, our age model relies on comparison with the global PISO-1500 palaeointensity stack and 10Be-flux. We generate our age model for the time interval ca. 50 to 10 ky using Bacon (rBacon in R), using non-normal error distribution of un-calibrated ages when necessary, facies-dependent variable mean accumulation rates and accounting for thick horizons of instantaneous deposition (i.e. tephra and mass movement deposits). This approach allows us to generate a high-resolution age model suitable for correlation of millennial-scale oscillations in our record, based on environmental magnetism and meteoric 10Be flux, with global records of past climate such as polar ice core, tropical lake and speleothem archives. © Author(s) 2018. CC Attribution 4.0 license.
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    Multi-method age model of a long lake sediment sequence from Orakei maar palaeolake, Auckland, New Zealand
    (International Union for Quaternary Research (INQUA), 2019-07-30) Peti, L; Fink, D; Fujioka, T; Mifsud, C; Nilsson, A; Muscheler, R; Fitzsimmons, KE; Hopkins, JL; Augustinus, PC
    Meaningful reconstructions of Quaternary palaeo-climate and -environmental reconstruction rely heavily on accurate and precise chronologies. Long and continuous lake sediment sequences are outstanding archives of past climatic change but, unless varved, depend on the development of detailed age models. Such models estimate the age-depth-relationship of the sequence from a limited number of dated horizons, which often carry large associated errors, age reversals, or minimum/maximum age constraints. Approaches to chronology development for sediment sequences have seen major improvements such as more nuanced Bayesian accumulation models but still rarely reach the resolution and precision desired for the study objectives in the context of high-resolution palaeo-climatic correlations of global events. This is particularly true beyond the limits of the well-established and more precise radiocarbon dating method. Sediment archives older than 50 ka have often not been used to its full potential for the lack of chronology estimates. In such cases, alternative methods including correlative and relative dating methods may need to be employed. Currently, a standardised method of integrating absolute dating with wiggle-matched curves of comparable proxies between the unknown and a dated sequence is lacking. Here we address this problem in the context of the Orakei maar palaeolake sequence from Auckland, New Zealand. This sediment record is a high-quality example of one of the rare high-resolution and continuous lacustrine archives of climatic variations in the southern hemisphere mid-latitudes over much of the last glacial cycle. Based on previous estimates, the Orakei sequence spans the interval ca. 126 cal ka BP to 9 cal ka BP. The presented Orakei chronology is based on absolute ages from tephrochronology, radiocarbon dating and post-IR IRSL luminescence dating. Prior to 40 ka, tuning of relative palaeomagnetic intensity changes and meteoric Beryllium-10 flux to the global PISO-1500 palaeointensity stack between absolute age markers allows to establish a novel accumulation model for the Orakei sequence. This approach allows us to generate a high-resolution age model suitable for correlation of millennial-scale oscillations from the SW Pacific to global records of past climate such as polar ice core, tropical lake and speleothem archives. © The Authors.
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    Phase of solar activity affects response of solar proxy 10Be
    (Esevier, 2013-10-15) Heikkilä, UE; Muscheler, R; Smith, AM
    The solar proxy 10Be, measured in natural archives, has previously been assumed to lag solar activity by 1–2 yr. This reflects its residence time in the stratosphere where its main source lies. This study, based on a 30-yr global model simulation of the atmospheric transport of 10Be, shows that the stratospheric fraction of production varies significantly with the phase of solar activity. This leads to a lag between production change and deposition response of ca. 1 yr during the decreasing phase of solar activity but nearly no lag when solar activity increases. No lag is found for 7Be. The fraction of 10Be production in the stratosphere varies from ca. 65% to 69% between solar minimum (ϕ=400 MV) and maximum (ϕ=1200 MV), being highest during low solar activity when production is highest. When solar activity starts to decrease and production rate increase, the change is largest in polar stratosphere where residence time is long. This leads to a delayed response in 10Be deposition. When production rate decreases, the relative production change is larger in the troposphere, leading to a quicker deposition response. The difference between phases is larger in southern hemisphere. The form of reconstructed 11-yr cycles based on high-resolution 10Be records could therefore be biased if no correction is applied. © 2013, Elsevier Ltd.