Browsing by Author "Ditchfield, A"

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    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.
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    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.
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    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
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    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
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    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
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    Verification of wavelet analysis interpretation of µ-XRF paleoclimate data from lake sediments using PCA, cluster analysis and empirical climate data
    (International Union for Quaternary Research (INQUA), 2019-07-30) Evans, G; Augustinus, PC; Gadd, PS; Zawadzki, A; Ditchfield, A
    Reliable interpretation of annual resolution climate proxies for wind, precipitation, and detrital influx are a necessity for understanding the onset and periodicities of climatic events. In particular, verification of individual climate proxies in a µ-XRF time series data set is essential for the evaluation of inter-annual, decadal, and centennial periodicities driven by shifting positions of the South Westerly Winds (SWW) and subsequent storm belts associated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO) using wavelet analysis. Chronology for the Late Holocene section of lake sediment cores from Lake Kanono, Northland, New Zealand indicate an annual to sub-annual accumulation rate at a 500 µm Itrax µ-XRF scanning resolution. This fast accumulation rate provides the opportunity to produce quasi-annual µ-XRF time series data. Here we present twelve ca. 2200 year long elemental and element ratio µ-XRF time series including P, S, Ti, Ca, K, Si, Fe, Mn/Fe, (Fe+Ti)/K, Sr/Ca, Br/Cl, and Inc/coh. These twelve variables were interpreted as environmental proxies 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 from Northland. 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 shows clear evidence of from both Polynesian and European settlement phases in this part of northern New Zealand as increased detrital influx. There is indication that Polynesian settlement impact was coeval with changes in ENSO intensity and a phase shift in SAM ca. 1350 CE, however European settlement is less associated with climatic shift. The Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) appear in the µ-XRF time series data as separate clusters. This data shows that the MCA is associated with windy/dry conditions with intermittent storms. During the LIA, the 2-16 year periodicity associated with ENSO decreased and centennial length periodicities increase, which may be an indication of an underlying SAM signal within the data. The combination of the methods of PCA, cluster analysis, and wavelet analysis indicates that sediment loading after ca. 1330 CE may be accentuating the climate signal in the Group I (detrital) proxies, and so interpretations after this time must be made with caution.