Browsing by Author "Nothdurft, LD"
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- ItemEvolution of the Great Barrier Reef Halimeda carbonate factory in response to Holocene environmental changes, determined from radiocarbon and nitrogen isotope measurements(Australian Nuclear Science and Technology Organisation, 2021-11-17) McNeil, M; Hua, Q; Erler, DV; Nothdurft, LD; Webster, JM; Moss, PThe inter-reef Halimeda algal bioherms of the northern Great Barrier Reef (GBR) have accumulated up to 25 m of positive relief and up to four times greater volume of calcium carbonate than the nearby coral reefs during the Holocene. Covering > 6000 km² on the continental shelf, the Halimeda bioherms represent a significant contribution to the development of the northeast Australian neritic carbonate factory and sedimentary archive of post-glacial environmental changes. However, the geochronological record of initiation and development of the Halimeda bioherm carbonate factory throughout the Holocene was poorly constrained and based on very few radiocarbon dates, considering their vast area. Additionally, the main source of nitrogen (N) fuelling the productivity of these biogenic structures had not been traced geochemically, and there was no understanding of any temporal variation. A total of 63 samples of calcium carbonate Halimeda and foraminifera grains, mollusc shells, and bulk soil were dated by ¹⁴ C AMS using the VEGA facility at the ANSTO Centre for Accelerator Science. Changes in the terrestrial vegetation community were determined from palynological analysis at the University of Queensland. Nitrogen isotopes were measured on a subset of 27 Halimeda samples using isotope ratio mass spectrometry (IRMS) at the Centre for Coastal Biogeochemistry at Southern Cross University. Using the persulfate-denitrifier method previously developed for foraminifera and coral skeletal material, nitrogen bound within the Halimeda skeletal organic material (SOM) was targeted. This allowed for fossil samples down-core to be analysed, thus providing a 5000-year record of Halimeda δ¹⁵ N-SOM. A temporal sequence of facies transitions that record terrestrial and marine environmental changes over a full sea level cycle from the Last Interglacial, to Last Glacial Maximum (LGM) and deglacial, to transgressive estuarine sediments and shallow marine carbonates was reconstructed. Halimeda growth and carbonate deposition had established by 11,143 (+237/-277) cal. yr BP, just ~450 years after the marine transgression. The Halimeda carbonate factory was productive at least 2100 years earlier than Holocene coral reefs in the study area. Our results provide the first direct in-situ measurements of Halimeda bioherm ages from at or near the Holocene/Pleistocene boundary, recording the timing of bioherm initiation in response to post-glacial sea level rise. The average Halimeda skeletal δ¹⁵ N-SOM was 6.28 ± 0.26 ‰, consistent with δ¹⁵ N-NO₃ - from western tropical South Pacific (WTSP) thermocline waters, geochemically validating shelf-break upwelling of an oceanic N source. From 5000 to 2000 cal. yr BP, Halimeda δ¹⁵ N-SOM decreased by 1-2 ‰, reaching a minima of 5.5 ‰ that persisted for almost 1000 years. The Halimeda δ¹⁵ N-SOM variation reflects changes in regional climate and intensified El Niño activity and is consistent with other regional climate proxy records at this time. Thus, the inter-reef Halimeda algal bioherms of the GBR are an important carbonate ecosystem that record a >10,000-year near-continuous record of northeast Australian Holocene oceanographic and environmental changes in response to sea level and climatic drivers, potentially filling spatial and temporal gaps not covered by coral and other proxies. © The Authors
- ItemHas nitrogen supply to coral reefs in the south Pacific Ocean changed over the past 50 thousand years?(John Wiley & Sons, Inc, 2019-03-28) Erler, DV; Shepherd, BO; Linsley, BK; Nothdurft, LD; Hua, Q; Lough, JMTropical islands can facilitate surface ocean biological productivity by enhancing the supply of nitrogen to the euphotic zone. Yet in the world's most oligotrophic oceanic region, the South Pacific Subtropical Gyre (SPSG), this “island mass effect” appears diminished. If this is the case, where did island coral reefs in the SPSG get their nitrogen from, and has this changed over time? Here we use coral skeleton isotopes (δ15N and δ18O) and element/Ca ratios to identify the sources of nitrogen to a late Pleistocene coral reef in the SPSG (Cook Islands); we then compare these results to modern corals in the same region. The supply of nitrogen to the late Pleistocene reef appears dominated by upwelling of subsurface nitrogen during cool dry events, supplemented with nitrogen from island-induced N2 fixation (27 ± 3%) during warm wet periods. For the modern corals, N2 fixation supplies nitrogen to the island reefs during cool dry periods with groundwater providing nitrogen during wet periods. We propose that the subsurface supply of nitrogen to the modern reefs has declined as a result of reduced upwelling but this supply has been replaced with increasing nitrogen discharge from groundwater and an increase in island-induced N2 fixation. ©2019 American Geophysical Union
- ItemLarge variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes(Elsevier, 2015-04-21) Hua, Q; Webb, GE; Zhao, JX; Nothdurft, LD; Lybolt, M; Price, GJ; Opdyke, BNAccurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect. This effect for a particular site/region is generally assumed constant through time when calibrating marine 14C ages. However, recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late Quaternary and Holocene. Here we report marine radiocarbon reservoir correction Δ(R) for Heron Reef and Moreton Bay in southwestern (SW) Pacific for the last 8 ka derived from 14C analysis of 230Th-dated corals. Most of our ΔR for the last ∼5.4 ka agree well with their modern value, but large ΔR variability of ∼410 yr (from trough to peak) with possible decadal/centennial fluctuations is evident for the period ∼5.4–8 ka. The latter time interval also has significant variations with similar features in previously published Δ values for other sites in the Pacific, including southern Peru–northern Chile in southeastern (SE) Pacific, the South China Sea, Vanuatu and Papua New Guinea, with the largest magnitude of ∼920 yr from SE Pacific. The mechanisms for these large ΔR variations across the Pacific during the mid-Holocene are complex processes involving (1) changes in the quantity and 14C content of upwelled waters in tropical east Pacific (TEP) (frequency and intensity of ocean upwelling in the TEP, and contribution of Subantarctic Mode Water to the upwelled waters, which is influenced by the intensity and position of southern westerly winds), and (2) variations in ocean circulation associated with climate change (La Niña/El Niño conditions, intensity of easterly trade winds, positions of the Intertropical Convergence Zone and the South Pacific Convergence Zone), which control the spreading of the older upwelled surface waters in the TEP to the western sites. Our results imply the need for employing temporal changes in ΔR values, instead of constant (modern) values, for age calibration of Holocene marine samples not only for the SW Pacific sites but also for other tropical and subtropical sites in the Pacific. Crown Copyright ©2015
- ItemLife and death of Holocene reefs of Moreton Bay, Queensland, Australia(Australian Geosciences Council, 2012-08-05) Nothdurft, LD; Major, J; Leondard, ND; Zhao, JX; Price, GJ; Welsh, KJ; Webb, GE; Hua, QDead fringing coral reefs of Moreton Bay are the southernmost fringing reefs in eastern Australia and are significant examples of marginal environments for subtropical reef growth. Two sites were investigated in the western part of the bay at Wellington Point and Cleveland Point. Seven auger cores and 5 surface transects were made across the dead reef flats to record spatial data on coral distribution and elevation and to provide samples for dating to test the timing and potential causes of reef termination. A total of 78 coral samples were dated using 230Th/U and 14C techniques. 230Th dates were determined by TIMS U-series, and MC-ICP-MS and 14C dates by AMS. Dates of framework corals indicate that reef growth initiated at different elevations by ∼7000 ybp and was predominantly vertical with little or no lateral progradation. Reef growth was continuous until termination at ∼5800 ybp. Micro-atolls (6523, 6680 ybp) suggest a sea level of ∼+1.3m above current lowest astronomical tides and elevated sea level persisted through that interval. Small incipient coral colonies on the dead reef surface range in ages between ∼4850 and 4700 ybp suggesting conditions were again suitable at that time for a recolonisation of the reef flat, but reef growth was not reinitiated. No younger ages were recorded. Temporal changes in Moreton Bay conditions have resulted in periodic phase shifts between favourable and unfavourable conditions for reef growth, coincident with a small sea level fall ∼5800 ybp and including potentially cooler temperatures and decreased water quality within the bay.
- ItemMarine radiocarbon reservoir effect along the north-eastern coast of Australia during the Holocene(Accelerator Mass Spectrometry, 2013-10-15) Hua, Q; Webb, GE; Zhao, JX; Nothdurft, LD; Price, GJRadiocarbon dating of surface ocean samples involves estimates of marine radiocarbon reservoir effect (e.g., marine reservoir age (R) and correction (ΔR)). These values for a given location are generally assumed to be constant with time when calibrating marine 14C ages. However, recent studies have reported large variability in the marine radiocarbon reservoir effect of several hundred to a couple of thousand years for various regions in the Pacific, Atlantic and Mediterranean during the Late-glacial and Holocene (Siani et al., 2001; Bondevik et al., 2006; Burr et al., 2009; Hua et al., 2009; Yu et al., 2010; Ortlieb et al., 2011; Sarnthein et al., 2011). These variations result from changes in ocean circulation and the carbon cycle associated with climate change. In this paper we present an investigation of possible variability in the marine radiocarbon reservoir effect along the north-eastern coast of Australia in South-Western (SW) Pacific during the last 8000 years. This study aims to get a better understanding of ocean circulation changes associated with climate change for the study area during the Holocene and to improve radiocarbon dating of marine samples.
- ItemA marine reservoir correction for the Houtman-Abrolhos Archipelago, East Indian Ocean, Western Australia(University of Arozina Department of Geosciences, 2013-01-01) Squire, P; Joannes-Boyau, R; Scheffers, AM; Nothdurft, LD; Hua, Q; Collins, LB; Scheffers, SR; Zhao, JXHigh-precision analysis using accelerator mass spectrometry (AMS) was performed upon known-age Holocene and modern, pre-bomb coral samples to generate a marine reservoir age correction value (Delta R) for the Houtman-Abrolhos Archipelago (28.7 degrees S, 113.8 degrees E) off the Western Australian coast. The mean Delta R value calculated for the Abrolhos Islands, 54 +/- 30 yr (1 sigma) agrees well with regional Delta R values for Leeuwin Current source waters (N-NW Australia-Java) of 60 +/- 38 yr. The Abrolhos Islands show little variation with Delta R values of the northwestern and north Australian coast, underlining the dominance of the more equilibrated western Pacific-derived waters of the Leeuwin Current over local upwelling. The Abrolhos Islands Delta R values have remained stable over the last 2884 cal yr BP, being also attributed to the Leeuwin Current and the El Nino Southern Oscillation (ENSO) signal during this period. Expected future trends will be a strengthening of the teleconnection of the Abrolhos Islands to the climatic patterns of the equatorial Pacific via enhanced ENSO and global warming activity strengthening the Leeuwin Current. The possible effect upon the trend of future Delta R values may be to maintain similar values and an increase in stability. However, warming trends of global climate change may cause increasing dissimilarity of Delta R values due to the effects of increasing heat stress upon lower-latitude coral communities. © 2013, University of Arizona.
- ItemTemporal variability in the Holocene marine radiocarbon reservoir effect for the Tropical and South Pacific(Elsevier, 2020-12-01) Hua, Q; Ulm, S; Yu, K; Clark, TR; Nothdurft, LD; Leonard, ND; Pandolfi, JM; Jacobsen, GE; Zhao, JXUnderstanding the marine radiocarbon reservoir effect (i.e., marine radiocarbon reservoir age (R) and/or correction (ΔR)) is important for the construction of robust radiocarbon chronologies for marine archives for various research areas including archaeology, palaeoecology, paleoceanography, Quaternary research and climate change studies. In this study, we examined temporal ΔR variability for the South China Sea (SCS) and the Great Barrier Reef (GBR) during the past ∼8.1 ka based on 14C analysis of 230Th-dated corals. Results show large ΔR variations of ∼410 yr and ∼490 yr for the SCS and the northern GBR for ∼5.5–8.1 ka and ∼5.5–7 ka, respectively, and a smaller ΔR variability of ∼200 yr for the SCS for ∼2–3.5 ka. Our data, together with those previously published for the Tropical and South Pacific, indicate that variability in ocean upwelling bringing old subsurface waters to the surface and/or changes in the sources (or 14C level) of the upwelled waters are responsible for seeing large ΔR variations in coastal areas along the eastern Pacific and the Tropical East Pacific (TEP) of several hundred to a thousand years mostly during the Early to Middle Holocene. ΔR variations in the central and western Pacific of several and a couple of hundred years during the Middle and Late Holocene, respectively, might be due to variability in Pacific-wide ocean circulation associated with climatic changes controlling the spread of upwelled waters from the TEP to the west. This mechanism together with local/regional effects, such as changes in ocean upwelling in the SCS resulting from East Asian monsoon variability and changes in upwelling and/or horizontal advection in the northern GBR associated with variability in the El Niño Southern Oscillation, might be responsible for the observed ΔR variations in these areas. The results of our study also indicate the need for regional marine radiocarbon calibration curves for improved radiocarbon dating of marine samples as the observed Holocene ΔR values for the Tropical and South Pacific are not fully reproduced by a recent modelling work using a 3D ocean model, which takes into account climate change effects. Ocean circulation changes were included in the model for the period of 11.5–50 cal kyr BP but possibly not considered or not well represented for the Holocene, which might explain the differences between the observed and modelled ΔR values. Crown Copyright©2020 Published by Elsevier Ltd
- ItemVariability in the Holocene marine radiocarbon reservoir effect for the Tropical West Pacific(Australian Nuclear Science and Technology Organisation, 2021-11-17) Hua, Q; Ulm, S; Yu, K; Clark, T; Nothdurft, LD; Leondard, ND; Pandolfi, JM; Jacobsen, GE; Zhao, JXReliable determination of the marine radiocarbon reservoir effect (e.g., marine radiocarbon reservoir correction (ΔR)) is important for the construction of robust radiocarbon chronologies for marine archives for various research areas including archaeology, palaeoecology, paleoceanography, Quaternary research and climate change studies. In this study, we examined temporal ΔR variability for the South China Sea (SCS) and the Great Barrier Reef (GBR) during the past ~8.1 ka based on ¹⁴ C analysis of ²³⁰ Th-dated corals. Coral samples, including Acropora sp., Cyphastrea sp., Favia sp. and Porites sp., were collected from Xisha (or Paracel) Islands and Yongshu Reef, Nansha (or Pratly) Islands in the SCS; Clerke Island, Gore Island, Haggerstone Island, Alexandra Reef and High Island in the northern GBR; and Great Keppel Island in the southern GBR. A total of 44 unaltered coral samples (based on SEM screening, δ²³⁴ U and initial ²³⁰ Th/²³²Th ratios) were analysed for ²³⁰ Th and ¹⁴ C. ²³⁰ Th dates were determined using a VG Sector-54 thermal ionization mass spectrometer (TIMS) or a Nu Plasma MC-ICP-MS in the Radiogenic Isotope Facility, The University of Queensland, with a precision better than 0.5% (2σ). Subsamples of these dated corals were then taken for radiocarbon analysis using the STAR AMS facility at ANSTO with a typical precision of ~0.3-0.4% (1σ). Results show large ΔR variations of ~410 yr and ~490 yr for the SCS and the northern GBR at ~5.5-8.1 ka and ~5.5-7 ka, respectively, and a smaller ΔR variability of ~200 yr for the SCS at ~2-3.5 ka. Changes in the sources (or ¹⁴ C level) of upwelled waters in the Tropical East Pacific, and variations in Pacific-wide and regional/local ocean circulation associated with climate change might be responsible for these observed ΔR variations [1]. The results of our study also indicate the need for regional marine radiocarbon calibration curves for improved radiocarbon dating of marine samples as the observed Holocene ΔR values for the Tropical Pacific are not fully reproduced by recent modelling work using a 3D ocean model [2], which takes into account climate change effects. Ocean circulation changes were included in the model for the period 11.5-50 ka but possibly not considered or not well represented for the Holocene, which might explain the differences between the observed and modelled ΔR values. © The Authors
- ItemVariations in marine reservoir corrections for the Great Barrier Reef during the last 7000 years(12th International Conference on Accelerator Mass Spectrometry (AMS-12), 2011-03-21) Hua, Q; Webb, GE; Zhao, JX; Nothdurft, LD; Price, GJFor calibration of marine 14C ages, marine reservoir correction value (ΔR) of a given location is generally assumed to be constant with time. However, variations in the marine reservoir effect of several hundred to a couple of thousand years have been observed for various regions in the Pacific, Atlantic and Mediterranean during the Late-glacial and Holocene. These variations result from changes in ocean circulation and the carbon cycle associated with climate change. Here we present a new data set of ΔR for the Great Barrier Reef (GBR) in south-western Pacific Ocean during the last 7000 years for the investigation of possible variability in the marine reservoir effect of this area and for improving radiocarbon dating of marine samples. Coral samples used in this study were from shallow cores and storm derived blocks collected on Heron Reef in southern GBR at 23º26'S, 151º55'E. Fifteen unaltered coral samples (based on SEM screening, δ234U and initial 230Th/232Th ratios) were analysed for 230Th/U and 14C. 230Th dates were determined by TIMS Useries in the Radiogenic Isotope Laboratory at the University of Queensland with a precision better than 0.5% (2σ). Aliquots of these dated corals were then taken for radiocarbon analysis. The samples were cut by diamond saw, cleaned in deionised water, oven dried, and homogenised in a mortar and pestle prior to 14C analysis using the STAR AMS facility at ANSTO. A typical precision for 14C analysis is <0.4% (1σ). The results of this investigation will be compared with those of previous studies for the Pacific, and variations in ΔR for the GBR for the mid- to late Holocene and their possible mechanisms will be then discussed. This work was supported by AINSE grant 09/056. Copyright (c) 2011 AMS12.