Browsing by Author "Augustinus, PC"

Now showing 1 - 20 of 23
  • Thumbnail Image
    Item
    21Ne, 10Be and 26Al cosmogenic burial ages of near-surface eolian sand from the Packard Dune field, McMurdo Dry Valleys, Antarctica
    (XIX INQUA Congress "Quaternary Perspectives on Climate Change, Natural Hazards and Civilization", 2015-07-26) Fink, D; Augustinus, PC; Rhodes, E; Bristow, C; Balco, G
    The McMurdo Dry Valleys, Antarctica, have been ice-free for at least 10 Ma. In Victoria Valley, the largest of the Dry Valleys, permafrosted yet still actively migrating dune-fields, occupy an area of 8 km2 with dune thicknesses varying from 5 to 70 meters. High-resolution ground penetrating radar (GPR) imaging of selected dunes reveal numerous unconformities and complex stratigraphy inferring cycles of sand accretion and deflation from westerly katabatic winter winds sourced from the East Antarctic Ice Sheet and anabatic summer winds sourced from the Ross Sea. Samples above permafrost depth were taken for OSL and cosmogenic 26Al/10Be burial ages. OSL ages from shallow (<1m) pits range from modern to 1.3ka suggesting that deposition/reworking of the dunes is ongoing and their present configuration is a late Holocene feature. The same 7 samples gave a mean 26Al/10Be = 4.53 +/- 5% with an average apparent continuous 10Be surface exposure age of 525 +/- 25 ka surprisingly indicating a common pre-history independent of depth. Correcting for minor post-burial production based on OSL ages, the minimum (integrated) burial period for these sand grains is 0.51+/- 0.12 Ma which represents the burial age at the time of arrival at the dune. A possible explanation is that this common burial signal reflects recycling episodes of exposure, deposition, burial and deflation, sufficiently frequent to move all grains towards a common pre-dune deposition history. However, it is unclear over what length of time this processes has been active and fraction of time the sand has been buried. Consequently we also analysed purified quartz aliquots of the same samples for a third and stable nuclide, 21Ne, to determine the total surface and burial exposure periods. Using the 21Ne/10Be system we obtain burial ages of 1.10 +/- 0.10 Ma. Further coring below permafrost is planned for austral summer 2015. © Copyright, 2015 XIX INQUA Congress LOC.
  • No Thumbnail Available
    Item
    A cosmogenic nuclide chronology of the last glacial transition in North-West Nelson, New Zealand—new insights in Southern Hemisphere climate forcing during the last deglaciation
    (Elsevier, 2005-05-15) Shulmeister, J; Fink, D; Augustinus, PC
    We present a new glacial chronology for the last glacial interglacial transition, c. 20 to 10 ka, from the Cobb Valley, NW Nelson, New Zealand, based on a suite of 10Be and 26Al cosmogenic exposure ages. This chronology describes one of the most comprehensive deglaciation sequences from a late Quaternary valley system in the Southern Hemisphere. We chronicle the decay from the last (local) glacial maximum as follows: onset of the last deglaciation that commenced no earlier than 18–19 ka, followed by numerous short-term still-stands and/or minor re-advances over the ensuing 3–4 kyr, and complete evacuation of ice by 14 ka. We find no evidence to indicate a late glacial re-advance commensurate with the Northern Hemisphere Younger Dryas chronozone. The absence of a major glacial re-advance in this valley during the latter stages of the last glacial interglacial transition (LGIT) precludes a thermal decline in excess of about 3 °C and suggests no decline. The absence of late LGIT re-advances in the mountains of North-West Nelson, while deglacial readvances occurred in the main ranges of the Southern Alps can be best explained if westerly wind forcing rather than large-scale thermal decline is the primary control on glacier fluctuations, at least during the deglaciation. These findings challenge models of global climate change predicated on synchrony of millennial-scale glacial transitions due to thermal changes between Northern and Southern Hemispheres. © 2005 Elsevier B.V.
  • Thumbnail Image
    Item
    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.
  • No Thumbnail Available
    Item
    Estimated chronology in a continuous lake sediment sequence from Kai Iwi Lake, New Zealand using MIS boundaries as age markers
    (International Union for Quaternary Research (INQUA), 2019-07-30) Evans, G; Augustinus, PC; Gadd, PS; Zawadzki, A; Ditchfield, A
    It is a common problem in paleoclimate research to have long sediment sequences that are difficult to date due to the ~50 ka age limitation of 14C dating. A possible solution where other laboratory methods are not available is to approximate the chronology using Marine Isotope Stages (MIS) as age markers via robust interpretation of environmental proxy data. A 9.3 m lake sediment core obtained from dune impounded Kai Iwi Lake in Northland, New Zealand provides a nearly continuous record of environmental changes in multi-proxy and µ-XRF data estimated to MIS 5d. Chronology for the upper 3 m of the core is well established until ca. 45 ka via 210Pb, 14C and tephrochronology. To identify patterns in the µ-XRF proxy data associated with environmental change, principal component analysis (PCA) and cluster analysis were performed on a data set including nine common elements in lake sediments (P, S, Fe, Ti, K, Ca, Si, Al, and Zr) and six element ratios (Sr/Ca, Br/Cl, Mn/Fe, (Fe+Ti)/K, Ti/K, and Inc/coh). PCA indicates that Component 1 represents the detrital fraction, and Component 2 is associated with nutrient influx and biological productivity. The elements and ratios in the Component 2 µ-XRF variables also indicate a wind component to the data as P, Mn/Fe, Fe, Ca and S are also indicators of anoxic/oxic conditions as a result of wind driven mixing in the water column. The cool periods of MIS 2 and 4 are well-defined in the µ-XRF data as having increased detrital influx (Ti, K, Si, Al), less thermal stratification in the water column (P), and more sea spray (Br/Cl, S). Warm periods are identified by high P variability, less detrital influx and increased organic productivity (Inc/coh). MIS 5b is estimated from similar changes in the data as MIS 2 and 4, however the difference between MIS 5c and 5d is not as evident and so the alignment of the cluster analysis of the µ-XRF proxy data was used as the definition of this boundary. These environmental interpretations define a framework of age markers from the MIS boundary ages and allow an age/depth profile estimated from a sediment accumulation rate to be calculated in addition to the age profile established via 210Pb, 14C and tephrochronology. Since MIS 2 has a slower accumulation rate in the Kai Iwi Lake chronology and the proxy data profile for MIS 2 is similar to MIS 4, it may also be possible to further refine the estimated chronology for MIS 4 by adjusting the accumulation rate for that section of the core.
  • No Thumbnail Available
    Item
    Glacial chronologies across Southern Hemisphere latitudes during the past 30 ka and correlations to Antarctic ice cores
    (Australasian Quaternary Association, 2006-02-10) Fink, D; Williams, P; Augustinus, PC; Schulmeister, J
    On orbital time scales of glacial cycles (≈120 ka), Southern Hemisphere ice caps and alpine glacial systems appear to be in phase with major Northern Hemisphere ice sheet changes. However, recent advances in exposure dating of cirque and moraine sequences in Tasmania, New Zealand and Patagonia on sub-orbital timescales reveal a glacial variability that may respond to different forcing mechanisms.
  • Thumbnail Image
    Item
    The glacial history of Tasmania from mid-pleistocene to the last glacial maximum – new challenges and new ideas for hemispheric glacial climate correlations.
    (Centro De Estudios Cientificos, 2010-02-01) Fink, D; Augustinus, PC
    The study of the Quaternary glacial history of Tasmania using various relative dating methods (weathering, geomagnetic stratigraphy, U-Th series and radiocarbon) has resulted in the identification of a complex system of multiple glaciations and isolated ice caps active over the past one million years. The application of cosmogenic nuclides 10Be and 26Al for the exposure age dating of glacial landforms, such as terminal and lateral moraines, recessional moraine sequences, erratics and exposed polished bedrock throughout the Western and Central regions of Tasmania during the midlate Pleistocene up to the LGM has forced a re-examination of the existing glacial chronology. This new chronology indicates a very different mode of glacial climate change in the high Southern Hemisphere latitudes – in both timing and extent- compared to that in the Northern Hemisphere. Moraines in the Pieman River valley and Tyndall Ranges of the west coast region, previously attributed to marine isotope-18O Stage (MIS) 6 and 8 are now considered more likely to have been deposited during MIS 10-12. Glacial advances from MIS 2 to 6 appear to have been restricted and are much less extensive than suggested previously. 10Be and 26Al exposure age dating of LGM moraines from a range of sites in western Tasmania indicates that the sequence is more complex than hitherto considered. Significantly, there is no evidence for a Younger Dryas glacier re-advance in western Tasmania which supports palynological evidence for no significant regional cooling at this time. Our general conclusions based on over 150 exposure ages from multiple valley sites containing cirque and retreat phase moraines are: (1) MIS-8 (~240 ka) to MIS-16 (~660) glacial cycles are extensive in the lowlying plains of the west coast ranges and northern outlet valleys for the Central Plateau. 2) Stadials within the Last Glacial Cycle, i.e. <120 ka (MIS-2 to 6), are weakly represented throughout all regions studied. 3) The onset of the local LGM period is variable and appears to range from 24-28 ka and deglaciation appears to commence at ~19-22 ka. 4) Valley glacial systems were ice-free by at most 14-16 ka and no YD-chron readvance is apparent.
  • Thumbnail Image
    Item
    Holocene environmental change in northern New Zealand: the view through the lens of Lake Spectacle
    (Australasian Quaternary Association Inc, 2014-06-29) Augustinus, PC; Horrocks, M; Munro, H; Gadd, PS; Linnell, T
    During 30th anniversary Australasian Quaternary Association (AQUA) Biennial Conference Professor Jim Bowler and Professor Roger Jones delivered public lectures to a full house at the Grand Ball Room, Mildura. This event was introduced by Glenn Milne, Mayor, Mildura rural city council, and conducted by Dr. Jessica Reeves, former president of AQUA. In the first lecture Jim engaged us with his passionate talk on “Journey to Discover, Who are we”, where he focussed on his lifelong research at Lake Mungo. Jim reminded us about the six decades of scientific research at Mungo, including a vivid description of the day he discovered Mungo Man’s skeleton in the dunes at Joulni, which was to go on to change our understanding of Aboriginal occupation of Australia. However, his emphasis then moved onto the challenges for future research. This included the key role that the current traditional owners have in managing and facilitating science, their potential role in researching their history, and the need to establish a keeping place onsite at Mungo to repatriate the archaeological finds, both past and future. Jim finished by encouraging young researchers to engage with the site, particularly given the continued erosion of the dunes and destruction of cultural and natural heritage, especially given the world heritage listing. In the second lecture Roger focused on our future world in the face of climate change, and how we will experience it. Roger began by highlighting the dominance of uniformitarianism over catastrophism in scientific thinking during the past few centuries. He described how this trend in thought has shaped our perspective, and narratives on trends in present and future climates, highlighting the overall gradual increases in temperature with time. Roger contended that this is only part of the story, and that we miss the importance of non-linearity in the climate system – or alternatively stochastic variation along with a gradual change. He described the importance of this variability in influencing the lived experience and response of people to climate change, with particular focus on how we feel an abrupt shift given the step changes in the nature of extreme events. I think this fact should be communicated properly to make people concerned about possible future abrupt change for proper adaptation and better management. Along with all the conference attendees, many non-scientists, indigenous people and local electronic and print media reporters attended the public lecture. People were engaged by the lectures and posed some interesting questions. Both lecturers were happy to answer questions and share their practical and research experience. The public lecture got media attention and huge public interest. I think it was a great idea to arrange a public lecture during the AQUA conference as it is the best way to engage some of the community and let them know our scientific findings. I hope it will continue at all AQUA events in future. © 2014, AQUA Biennial Meeting Mildura.
  • No Thumbnail Available
    Item
    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.
  • Thumbnail Image
    Item
    Integrated age modelling of numerical, correlative and relative dating of a long lake sediment sequence from Orakei maar paleolake, Auckland, New Zealand
    (Australiaian Quaternary Association Inc., 2018-12-10) Peti, L; Augustinus, PC; Woodward, C; Nilson, A
    Accurate and precise chronologies are fundamental for any successful Quaternary paleo-climate/-environment reconstruction. Aside from varved lake sequences, all records depend on sediment core age models developed from a limited number of dated horizons, often with large errors. Hence, it is crucial to combine every piece of available information on the depositional history of the basin with modelling tools used for chronology development such as Bacon, a Bayesian age modelling package. Whilst sediment core chronology development has progressed from linear interpolation between dated horizons to considering uncertainties and Bayesian accumulation models, these age models rarely reach the resolution and precision desired for reliable paleo-climatic interpretations, especially in pre-Holocene sequences as errors increase and radiocarbon dating is not suitable anymore. We address this issue here in the context of Orakei maar paleolake sequence, Auckland, New Zealand. This record spans ca. 120 to 10 cal ka BP and is underpinned by tephrochronology, radiocarbon dating and relative changes in paleointensity of the earth magnetic field. Pre-40 cal ka BP, the age model relies on comparison with and correlation to the global PISO-1500 paleointensity stack through dynamic time warping (DTW in R). The chronology for the time interval ca. 50 to 10 cal ka BP has been estimated in Bacon (rBacon in R) with non-normal error distribution of un-calibrated ages, variable mean accumulation rates and accounting for many “slumps” (horizons of instantaneous deposition).The Orakei maar paleo-lake age model is a work in progress but serves as an example for extended age modelling from lake sediment sequences, particularly beyond the radiocarbon age limit. Furthermore, the Orakei maar sequence offers a high-resolution and continuous record of climatic variations that span much of the last glacial cycle and is one of the few from the mid-latitudes of the Southern Hemisphere. The rarity of records of this type makes Orakei maar a crucial record for development of an improved understanding of the global climate system because of its potential to be tied directly to the polar ice core and tropical lake and speleothem records.
  • No Thumbnail Available
    Item
    Itrax μ-XRF core scanning for rapid tephrostratigraphic analysis: a case study from the Auckland Volcanic Field maar lakes
    (John Wiley & Sons, Inc, 2019-07-23) Peti, L; Gadd, PS; Hopkins, J; Augustinus, PC
    Itrax micro X-ray fluorescence (μ-XRF) core scanning is a non-destructive, rapid approach to measuring elemental concentrations and their variability in sediment cores. As such, it records elemental signatures of tephra layers, which serve as correlation tie points and chronological markers for these sedimentary archives of past climatic changes. The traditional tephra identification approach using electron microprobe-based geochemical fingerprinting of glass shards is a slow and invasive process, whilst μ-XRF scanning of rhyolite tephra in sediment cores from Auckland (New Zealand) could provide a faster, non-invasive approach to aid the recognition of tephra layers. This study highlights the potential and pitfalls in this novel approach: changes in most scanning parameters, and the use of two different Itrax core scanners, still led to similar chemical characterizations of the tephra layers. Changes in other scanning parameters have a biasing influence on the chemical characterization of the tephra, which would lead to misidentification of unknown layers. We demonstrate that μ-XRF core scanning provides a faster and non-invasive approach to correlation of sediment sequences using chemically distinct, visually pure tephra layers if a strict scanning protocol is followed. Nevertheless, an extensive database of μ-XRF-scanned rhyolite tephra is required for recognition of unknown tephra units using this approach. Copyright © 2019 John Wiley & Sons, Ltd.
  • No Thumbnail Available
    Item
    Lithological and geochemical record of mining-induced changes in sediments from Macquarie Harbour, southwest Tasmania, Australia.
    (Springer, 2010-08) Augustinus, PC; Barton, CE; Zawadzki, A; Harle, KJ
    Macquarie Harbour in southwest Tasmania, Australia, has been affected severely by the establishment of mines in nearby Queenstown in the 1890s. As well as heavy metal-laden acid rock drainage from the Mount Lyell mine area, over 100 Mt of mine tailings and slag were discharged into the Queen and Ring Rivers, with an estimated 10 Mt of mine tailings building a delta of ca. 2.5 km2 and ca. 10 Mt of fine tailings in the harbour beyond the delta. Coring of sediments throughout Macquarie Harbour indicated that mine tailings accreted most rapidly close to the King River delta source with a significant reduction in thickness of tailings and heavy metal contamination with increasing distance from the King River source. Close to the King River delta the mine tailings are readily discriminated from the background estuarine sediments on the basis of visual logging of the core (laminations, colour), sediment grain size, sediment magnetic susceptibility and elemental geochemistry, especially concentrations of the heavy metals Cu, Zn and Pb. The high heavy metal concentrations are demonstrated by the very high contamination factors (CF > 6) for Cu and Zn, with CF values mostly >50 for Cu for the mine-impacted sediments. Although the addition of mine waste into the King River catchment has ceased, the catchment continues to be a source of these heavy metals due to acid rock drainage and remobilisation of mine waste in storage in the river banks, river bed and delta. The addition of heavy metals to the harbour sourced from the Mount Lyell mines preceded the advent of direct tailings disposal into the Queen River in 1915 with the metals probably provided by acid rock drainage from the Mount Lyell mining area. © 2010, Springer.
  • Thumbnail Image
    Item
    Lochnagar landslide-dam - Central Otago, New Zealand: geomechanics and timing of the event
    (New Zealand Geotechnical Society, 2013-11) Sweeney, CG; Brideau, MA; Augustinus, PC; Fink, D
    The stability of natural rockslide dams with respect to sudden breaching is a major safety issue in mountain areas, although unbreached rockslide-dammed lakes such as Lochnagar in Central Otago, New Zealand, may persist in the landscape for millennia. Consequently it is important to attempt to understand the mode and drivers of these failures as they may impact on our expanding populations. The Lochnagar landslide-dam is located within the steep schistose mountains of the Southern Alps of New Zealand. During an extensive study of the site, structural and Schmidt hammer measurements were taken from the immediate area of the failure, as well as samples collected for laboratory analysis. Point load estimates of the uniaxial compressive strength were of 85 MPa perpendicular and 18 MPa parallel to the schistosity. The rock mass quality was estimated using the Geological Strength Index (GSI) with values of 35-45 observed. These results were used in a series of numerical modelling techniques: kinematic analysis (DIPS), limit equilibrium (Swedge) and distinct element modelling (3DEC). The results of the numerical modelling suggest that a wedge failure with toe buckling or ploughing through its rockmass is the likely failure mechanism. An observed fault zone at the base of the landslide may have preconditioned the slope to failure by weakening the toe. Preliminary ages from a program of Terrestrial Cosmogenic Nuclide (TCN) 10Be exposure age dating, indicate that the slide mass that formed the dam is of at least early Holocene age and therefore glacial retreat after the LGM could also be a contributing factor.
  • No Thumbnail Available
    Item
    Managing land-use effects on Northland dune lakes: lessons from the past
    (Taylor & Francis, 2018-02-02) Stephens, T; Augustinus, PC; Rip, B; Gadd, PS; Zawadzki, A
    The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation. © 2018 Informa UK Limited
  • No Thumbnail Available
    Item
    Millennial-scale periodicities associated with changes in wind ansd precipitation over the last glacial cycle (ca. 117 ± 8.5 ka BP) recorded in sediments from Lake Kai Iwi, Northland, New Zealand
    (Elsevier B. V., 2022-01) Evans, G; Augustinus, PC; Gadd, PS; Zawadzki, A; Ditchfield, A; Hopkins, JL
    Mid-latitude Southern Hemisphere proxy records of changing environment, especially those that demonstrate past variability of the South Westerly Winds (SWW), are poorly-constrained prior to the Last Glacial Interglacial Transition (LGIT; ca. 14–11.7 ka BP) and are typically located far enough south or north that they often do not reflect both tropical and SWW signals. With this deficiency in mind, we present a ca. 117 ± 8.5 ka BP lake sediment record from Lake Kai Iwi, Northland, New Zealand (~36°S), located at a latitude that demonstrates changes in precipitation associated with both the northward expansion of the SWW belt and from tropical El Niño Southern Oscillation (ENSO) variability. We converted Lake Kai Iwi μ-XRF proxy data to even time-steps in order to apply Morelet wavelet analysis for identification of millennial-scale periodicities in the data that were likely driven by orbital forcing. The results indicate that Lake Kai Iwi records a ~1 ka periodicity possibly associated with Northern Hemisphere ice sheet dynamics; a ~2–4 ka periodicity associated with ~2.4 ka Hallstatt solar cycles, and a ~9 ka periodicity linked to CO2 outgassing from upwelling in the Southern Ocean driven by changes in intensity and position of the SWW. © 2021 Elsevier B.V.
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    A multi-proxy paleoenvironmental interpretation spanning the last glacial cycle (ca. 117 ± 8.5 ka BP) from a lake sediment stratigraphy from Lake Kai Iwi, Northland, New Zealand
    (Springer Nature, 2020-09-09) Evans, G; Augustinus, PC; Gadd, PS; Zawadzki, A; Ditchfield, A; Hopkins, J
    A 9.3-m-long lake sediment core from dune-impounded Lake Kai Iwi in Northland, New Zealand provides a nearly continuous record of environmental changes from multi-proxy organic, physical index, and µ-XRF elemental data sets. The chronology for the upper 3 m of the core was established by 210Pb, 14C and tephrochronology and includes Marine Isotope Stage (MIS) 1 (Holocene), MIS 2 and late MIS 3. From this well-dated section of the core stratigraphy we were able to infer the environmental proxies that respond to wind and/or precipitation during cool periods (MIS 2 and 4) and with the warm periods (MIS 1 and 5). Principal component analysis (PCA) and cluster analysis were performed on the µ-XRF elemental data set including elements common in lake sediments (P, S, Fe, Ti, K, Ca, and Si) and five ratios (Sr/Ca, Br/Cl, Mn/Fe, Ti/K, and Inc/coh) to identify patterns in the µ-XRF proxy data associated with environmental change manifesting as changes in precipitation and wind deposition. The PCA indicates that Component (PC)-1 represents detrital versus organic deposition, and PC-2 is associated with nutrient influx versus anoxic conditions in the lake. The cool periods of MIS 2 and 4 are apparent in the µ-XRF data as having increased detrital influx in the form of Sr/Ca from marine derived sediments from the exposed continental shelf during low sea level indicating cool and dry conditions. Warmer and wetter periods (MIS 1 and 5) are identified by increased Ti/K influx from precipitation runoff and increased organic productivity as shown by Inc/coh and total organic carbon. The Holocene warm equivalent conditions of MIS 5e are not represented in the lower part of the Lake Kai Iwi core stratigraphy consistent with an extrapolated basal age of 117 ± 8.5 ka BP. © Springer Nature B.V. 2020
  • No Thumbnail Available
    Item
    A multi-proxy record of environmental change through the last 53,000 years recorded in the sediments of Lake Kanono, Northland, New Zealand
    (Society for Sedimentary Geology, 2021-11-01) Evans, G; Augustinus, PC; Gadd, PS; Zawadzki, A; Ditchfield, A; Shane, P
    Lake sediment archives from Southern Hemisphere mid-latitude regions provide invaluable records of late Quaternary environmental change. Here, changes in depositional environment over the past ca. 53,000 years were reconstructed using a range of physical, sedimentological, geochemical, and μ-XRF elemental proxy datasets analyzed from lake sediment cores obtained from Lake Kanono, Northland, New Zealand. The Lake Kanono stratigraphy displays a terrestrial peat environment (ca. 53,700–6,670 cal yr BP), followed by a trend of increased influx of detrital sediment during the Late Glacial–Interglacial Transition (LGIT) at ca. 14,000 cal yr BP with a peak from ca. 12,000 to 9,000 cal yr BP driven by increasingly dry conditions. The increase in sediment influx continued during the early to mid-Holocene, leading to dune reactivation which altered the catchment dynamics of the region, leading to the inception of a shallow lake basin at ca. 6,670 cal yr BP. The timing of the formation of this lake basin can be associated with changes in intensity of the Southern Westerly Winds (SWW) and the appearance and increase in intensity of the El Niño Southern Oscillation (ENSO) after ca. 7,500–7,000 cal yr BP (Moy et al. 2002; Moreno et al. 2018). Drier conditions peaked from ca. 4,000 to 2,400 cal yr BP, possibly culminating in decreased lake levels that persisted from ca. 2,400 to 2,210 cal yr BP, renewed dune accumulation, and blocked stream outlets, resulting in a deep lake basin with thermal stratification that persisted to the present. Cluster analysis of the μ-XRF data demonstrates that the most prominent change in chemistry is near the onset of the Last Glacial Maximum (LGM) at ca. 26,700 cal yr BP associated with a transition to a drier, windier climate. The second most prominent change in the μ-XRF data is during the Polynesian phase of human settlement at ca. 612–575 cal yr BP (1338– 1375 CE). Hence, we can demonstrate the utility and power of a multi-proxy approach coupled with μ-XRF element data to interpret changing sediment sources to a lake basin. Such an approach allows rapid and reliable evaluation of catchment processes influenced by climate events and land-use changes at a resolution not available using other approaches. © 2021 Society for Sedimentary Geology
  • No Thumbnail Available
    Item
    A multi-proxy μ-XRF inferred lake sediment record of environmental change spanning the last ca. 2230 years from Lake Kanono, Northland, New Zealand
    (Elsevier, 2019-12-01) Evans, G; Augustinus, PC; Gadd, PS; Zawadzki, A; Ditchfield, A
    Reliable interpretation of annual-resolution climate proxies for wind, precipitation, and detrital influx are required for identifying the onset and periodicities of climatic events. In particular, this is essential for the evaluation of inter-annual, decadal, and centennial trends driven by shifting positions of the Southern Westerly Winds (SWW) and subsequent storm belts associated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Here we present a quasi-annual data set of μ-XRF time series spanning ca. 2230 years from lake sediment cores from Lake Kanono, Northland, New Zealand. The μ-XRF time series were interpreted using a combination of principal component analysis (PCA) and cluster analysis, then verified with comparison to regionally averaged empirical rainfall and wind climate station data. Our results show that the wavelet patterns align with the PCA results allowing the μ-XRF time series to be classified into: Group I (detrital) and Group II (biological productivity and normalized climate proxies). The normalized Group II μ-XRF time series wavelet analyses displayed periodicities in the 2–16 year frequency, likely associated with ENSO, from ca. 237 BCE – 1330 CE. The data show clear evidence of both Polynesian and European settlement phases in this part of northern New Zealand, and that Polynesian settlement impact was coeval with changes in ENSO intensity and a phase shift in SAM ca. 1350 CE. The Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) appear in the μ-XRF time series data as separate clusters. This data suggests that the MCA is associated with windy/dry conditions with intermittent storminess. During the LIA, the 2–16 year periodicity associated with ENSO decreased and centennial to multi-decadal length periodicities increase, which may be an indication of an underlying SAM signal within the data. European settlement also had a direct impact on the lake basin via increased detrital influx, likely from farming activities and intensification of local forestry operations. ©2019 Elsevier Ltd
  • Thumbnail Image
    Item
    Orakei maar paleolake (Auckland, NZ):A multi-method approach to the composite stratigraphy of a long sediment core
    (Australiasian Quaternary Association Inc., 2018-12-10) Peti, L; Augustinus, PC; Woodward, C
    The development of records of Quaternary environmental and –climatic changes relies largely on long, complete sediment sequences. However, coring techniques do not allow extraction of one continuous record of sedimentation to be recovered from a single drill hole. In order to reconstruct a complete record, it is common practice to drill two or more overlapping cores with a depth offset to overcome coring-induced loss and disturbance and then stitch these records together using stratigraphic markers to produce a master stratigraphy. However, details of the process used and critical uncertainties are rarely reported despite the fact that spurious correlations may alter subsequent paleoenvironmental interpretations. Here we detail the procedure employed to build a composite stratigraphy from three overlapping long lake sediment cores from Orakei maar paleolake (Auckland). Orakei maar was created by a phreato-magmatic eruption to forming a lake basin of a low surface-to-depth ratio and virtually no catchment. The accumulated sediment can be considered a direct recorder of climatic and environmental changes over the Last Glacial Cycle in the Southern Hemisphere mid-latitudes, a crucial but under-studied part of the global climatic system. Finely laminated sediment in the Orakei record can be aligned and correlated along visually distinct marker horizons, as well as tephra layers (Fig. 1), with sub-cm to mm resolution, supplemented by μ-XRF core scanning elemental and X-ray density variability. Complications arise from lateral inhomogeneities in sedimentation along the lake bottom and hence, larger differences between the three cores. These sections, usually of coarser grain size, likely caused by local landslides from the crater rim, are correlated based on: visual logging, common pattern in μ-XRF elemental and Xray density variation, and typical depth offset between the observed debris flows in the cores. Figure 1: Composite stratigraphy and lithology of Orakei maar paleo-lake record built from three overlapping sediment cores. © The Authors
  • No Thumbnail Available
    Item
    Re-assessment of the mid to late Quaternary glacial and environmental history of the Boco Plain, western Tasmania
    (Elsevier, 2017-03-15) Augustinus, PC; Fink, D; Fletcher, MS; Thomas, I
    The glacial geomorphology and drill core-based stratigraphy of the Boco Plain, western Tasmania, reveal a complex sequence of Quaternary glacial and non-glacial episodes. The upper part of the southern Boco Plain stratigraphy was previously dated by 14C and U-series on interbedded organics of MIS 1 to MIS 5 affinity. U-series dating of ferricretes associated with glacial diamictons from Boco Plain cores suggested that there were glacial advances broadly correlative with MIS 6, 8 and ≥10. However, terrestrial cosmogenic nuclide (10Be and 26Al) exposure ages for the moraine sequence preserved on the wider Boco Plain area indicate that moraines previously attributed to MIS 6 and 8 advances were deposited during MIS 10 or earlier cold stages. There is no evidence for MIS 2, 4 or 6 affinity glacial advances onto the Boco Plain with ice of this age restricted to the West Coast Range. New palynological records from the Boco Plain core 6690 confirmed the late Quaternary ages of the upper part of the sequence, whilst extinct palynomorphs indicate a pre-Quaternary age for the glacial diamictons at the base of core Boco 4 and 10. Consequently, the mid-Pleistocene glacial sequence preserved in the Boco Plain is significantly older than previously envisaged, with the post MIS 10 to 12 geomorphology of the plain dominated by fluvial deltaic, swamp peat and lacustrine environments. © 2017 Elsevier Ltd.