Browsing by Author "Chivas, AR"
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- ItemA 50 ka hydrological record from northern Australia inferred from the chemistry of ostracod valves: implications for the Australian monsoon(18th INQUA Congress, 2011-07-21) Devriendt, D; Chivas, AR; Cendón, DIMost continuous records of environmental changes on continents over the last glacial cycle derive from the study of lake sediments. Such records are uncommon in Australia since lakes rarely remained permanent features over long periods of time. During most of the last glacial cycle, the largest lake on the Australian continent was located in the centre of the Carpentaria basin, an area covered by the sea today. The well preserved lacustrine sequence underlying the modern marine sediment of the Gulf of Carpentaria has been studied extensively in the past with the main phases of environmental changes with regard to marine versus non-marine conditions being well established. However, palaeoclimatic inferences during the lacustrine phase have remained challenging due to periodic marine influences, strong seasonality and the poor preservation of the lacustrine sequence at sites away from the depocentre of the basin. The elemental (Ca/Na/Mg/Sr/Ba/Mn/Fe/U) and isotopic (δ18O and δ13C) compositions of ostracod valves from the Gulf of Carpentaria lacustrine sequence provide a new palaeohydrological record for northern Australia covering the period 64-14 ka. In particular, inferences on the contributions of potential water sources to the palaeolake and their variations through time are drawn by comparing the ostracod Na/Sr/Ba relative concentrations to the chemical signatures of the rivers draining the modern Carpentaria basin. Wide climatic variations were recorded by the ostracod chemical and isotopic composition and reflect the changing state of the Australian monsoon through time. The monsoon appears weaker/absent during the LGM, although irregular precipitation patterns during this time provoked the oscillations of the palaeolake water-level. Immediately after the LGM, the monsoon progressively developed over northern Australia until 14 ka BP. This causes the rivers from the far south of the basin to reconnect with the palaeolake.
- ItemEvaporites with inherited marine and continental signatures: the Gulf of Carpentaria, Australia, at ~70 ka(Elsevier B. V., 2007-07-12) Cendón, DI; Playà, E; Chivas, AR; Trave, A; Wyndham, T; García, A; Hankin, SIChanges in sea-level and associated climatic fluctuations resulted in extreme and cyclic changes in depositional environments in the Gulf of Carpentaria region (N, Australia). Disconnection from the sea led to the establishment of “Lake Carpentaria”. In this environment, evaporitic conditions at ~70 ka produced an alternation of μm to mm-thick evaporitic and micritic laminae. These precipitates are primary features, deposited in a shallow lake. Elemental and isotope geochemistry of gypsum and micrite laminae show a complex evaporitic environment where initially marine waters evaporated with the input of continental waters compensating for evaporative losses. Reduced continental input could not support a lake of the initial dimensions and the lake retracted to the deepest part of the basin along the north-eastern side. In a lake with smaller water volume, continental solutes became dominant. The strontium contents of gypsum range from 691 to 1353 ppm, gypsum-δ34S values from +21.8 to +22.5%, gypsum-δ18O values from +14.1 to +16.5% and 87Sr/86Sr from 0.7093 to 0.7098. While Sr contents and sulfur isotopes indicate marine contributions, strontium isotopes and oxygen isotopes in sulfates reveal continental inputs and processes such as recycling of evaporites, sulfate reduction and potential reservoir effects. Carbonate-δ13C and δ18O values in micrite also reveal a continental influence and perhaps variations in organic matter signatures associated with climatic and vegetation changes. In order to assess the provenance of continental waters reaching Lake Carpentaria at this time, REE elements in evaporitic gypsum were analysed and compared to results from modern rivers in the area. The REE-normalized patterns in gypsum samples are like those found in northern Cape York rivers (and unlike seawater), restricting the potential continental inputs into the evaporatic basin to a limited geographical area. The thickness of the calcite-gypsum couplets is consistent with those precipitated annually in modern evaporitic environments. This and the marked fluctuation between dry (gypsum laminae) and wet (micritic layer) suggests a reduced monsoon-like rainfall pattern operating in northern Australia during evaporite precipitation. © 2007 Elsevier
- ItemThe Gulf of Carpentaria, Australia, at ~70 ka: Isotopic, trace and REE constraints(Centre for Groundwater Studies, 2006-12-13) Cendón, DI; Playà, E; Chivas, AR; Trave, A; Wyndham, T; García. A; Hankin, SINot available.
- ItemHydrogeochemistry of modern streams in the Riversleigh area (QLD-Australia): relationship with local carbonate lithologies-preliminary results(University of New South Wales, 2006) Cendón, DI; Graham, IT; Price, I; Hankin, SI; Chivas, ARNot available
- ItemLake Carpentaria(Geological Survey of Queensland, 2013-01-01) Chivas, AR; García, A; Cendón, DIThe modern drainage catchment of the Gulf of Carpentaria (Figure 9.2) comprises more than 25 monsoon-fed rivers that collectively provide 25% of the total fluvial run-off of the Australian continent (Figure 9.12). The Gulf is bounded to the east by Torress Strait(maximum water depth 12m) and by the Arafura Sill (water depth 53 m) to the west. The deepest, eastern central portion of the Gulf today is 71 m (Figure 9.13). Accordingly, during episodes of low Quaternary sea levels, the Gulf was separated from the open waters of the Indian and Pacific Oceans and formed the large freshwater-brackish Lake Carpentaria (Torgersen et al. 1983, 1985, 1988; Jones & Torgersen 1988). When most recently filled, the lake had a maximum depth of 15-18m and the lateral dimensions of about 600 x 300K, with overflow westwards into the Arafura Sea (Chivas et al. 2001). Among modern lakes, only the Caspian Sea has a larger surface area. Throughout the past glacial cycle of -125 000 years, there was at least one land bridge between Australia and New Guinea for more than 90% of this time. © 2013, Queensland Government.
- ItemMillennial to seasonal scale views of El Niño-Southern Oscillation from central Pacific corals(Australasian Quaternary Association, 2022-12-06) McGregor, HV; Wilcox, P; Fischer, MJ; Phipps, SJ; Gagan, MK; Wittenberg, A; Felis, T; Kölling, M; Wong, HKY; Devriendt, L; Woodroffe, CD; Zhao, JX; Fink, D; Gaudry, JJ; Chivas, AREl Niño-Southern Oscillation (ENSO) is naturally highly variable on interannual to decadal scales making it difficult to detect a possible response to climate forcing. Despite the high variability, several lines of evidence from tropical corals, mollusc, lake sediments, and foraminifera suggest that 5,000-3,000 years ago ENSO variance was on average reduced by 60-80% compared to the present day. We investigate the seasonal-to-centennial variation in ENSO amplitude and tropical climate during this ENSO ‘quiet period’ 5,000-3,000 years ago using a new Sr/Ca SST record from a 175-year-long 4,300-year-old coral, and new d18O and Sr/Ca results from a similar-aged ~180-year-long Porites sp. coral. Both corals were discovered on Kiritimati (Christmas) Island, an optimal ENSO ‘centre of action’ in the central tropical Pacific. Together, these corals confirm a reduction in ENSO amplitude and that ENSO amplitude is modulated on multi-decadal scales. Composites of month-by-month changes in Sr/Ca-SST show an unprecedented view of ENSO and detail which seasonal-scale features of ENSO are an inherent part of the system, and which are subject to change under altered climate states. We also investigate the millennial timescale changes in ENSO variance using combine coral oxygen isotope (18O) data from central Pacific corals and a suite of forced and unforced simulations conducted using the CSIRO Mk3L and GFDL CM2.1 climate system models. On millennial timescales, the coral data reveal a statistically significant increase in ENSO variance over the past 6,000 years. This trend is not reproduced by the unforced model simulations but can be reproduced once orbital forcing is accounted for. Together these views of past ENSO may contribute to advances in understanding the response of ENSO to future changes in climate forcings.
- ItemMillennial to seasonal scale views of El Niño-Southern Oscillation from central Pacific corals(2022-12-06) McGregor, HV; Wilcox, P; Fischer, MJ; Phipps, SJ; Gagan, MK; Wittenberg, A; Felis, T; Kölling, M; Wong, HKY; Devriendt, L; Woodroffe, CD; Zhao, JX; Fink, D; Gaudry, JJ; Chivas, AREl Niño-Southern Oscillation (ENSO) is naturally highly variable on interannual to decadal scales making it difficult to detect a possible response to climate forcing. Despite the high variability, several lines of evidence from tropical corals, mollusc, lake sediments, and foraminifera suggest that 5,000-3,000 years ago ENSO variance was on average reduced by 60-80% compared to the present day. We investigate the seasonal-to-centennial variation in ENSO amplitude and tropical climate during this ENSO ‘quiet period’ 5,000-3,000 years ago using a new Sr/Ca SST record from a 175-year-long 4,300-year-old coral, and new d18O and Sr/Ca results from a similar-aged ~180-year-long Porites sp. coral. Both corals were discovered on Kiritimati (Christmas) Island, an optimal ENSO ‘centre of action’ in the central tropical Pacific. Together, these corals confirm a reduction in ENSO amplitude and that ENSO amplitude is modulated on multi-decadal scales. Composites of month-by-month changes in Sr/Ca-SST show an unprecedented view of ENSO and detail which seasonal-scale features of ENSO are an inherent part of the system, and which are subject to change under altered climate states. We also investigate the millennial timescale changes in ENSO variance using combine coral oxygen isotope (18O) data from central Pacific corals and a suite of forced and unforced simulations conducted using the CSIRO Mk3L and GFDL CM2.1 climate system models. On millennial timescales, the coral data reveal a statistically significant increase in ENSO variance over the past 6,000 years. This trend is not reproduced by the unforced model simulations but can be reproduced once orbital forcing is accounted for. Together these views of past ENSO may contribute to advances in understanding the response of ENSO to future changes in climate forcings.
- ItemNon-marine evaporites with both inherited marine and continental signatures: the Gulf of Carpentaria, Australia, at similar ~ 70 ka(Elsevier, 2007-10-15) Playà, E; Cendón, DI; Trave, A; Chivas, AR; García, AChanges in sea-level and associated climatic fluctuations resulted in extreme and cyclic changes in depositional environments in the Gulf of Carpentaria region (N. Australia). Disconnection from the sea led to the establishment of a "Lake Carpentaria", perched above sea-level. In this environment, evaporitic conditions at about 70 ka produced a repetitive alternation of Pm to mm-thick evaporitic and micritic laminae with a varve-like appearance. These precipitates are interpreted as primary features, deposited in a shallow lake that retained limited water in its centre (core MD-32). Elemental and isotope geochemistry of gypsum and micrite laminae show a complex evaporitic environment where initially marine waters evaporated with the input of continental waters compensating for evaporative losses. Reduced continental input could not support a lake of the initial dimensions and the lake contracted to the deepest part of the basin along the north-eastern side of the basin. In a lake with smaller water volume, continental solutes became apparent. While Sr contents and sulfur isotopes indicate marine contributions, strontium isotopes and oxygen isotopes in sulfates reveal continental inputs and other processes such as recycling of previously precipitated evaporites, sulfate reduction and potential reservoir effects. Carbonate- delta C-13 and delta O-18 values in micritic levels also reveal a continental influence and perhaps variations in organic matter signatures associated with climatic variations and vegetation changes. The REE-normalized patterns in gypsum samples are like those found in northern Cape York rivers, restricting the potential continental inputs into the evaporatic basin to a limited geographical area. The small depletion in LREE-normalized patterns between gypsum and river samples is interpreted as a marine influence while depletions in HREE are considered to be the result of fractionation of HREE during gypsum crystallization. © 2007, Elsevier Ltd.
- ItemPrompt transgression and gradual salinisation of the Black Sea during the early Holocene constrained by amino acid racemization and radiocarbon dating(Elsevier, 2011-12) Nicholas, WA; Chivas, AR; Murray-Wallace, CV; Fink, DThe restricted environment of the Black Sea is particularly sensitive to climatic and oceanographic fluctuations, owing to its connection with the Mediterranean Sea via the narrow Bosphorus Strait. The exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post-glacial history of the Black Sea being dependent on radiocarbon dating for numerical ages. Here we present new 23 accelerator mass spectrometer (AMS) radiocarbon ages on peat and bivalve molluscs, supported by the first amino acid racemization (AAR) dating of bivalve molluscs (n = 66) in the Black Sea. These data indicate infilling of the Black Sea during the early Holocene from an initial depth 107 m below sea-level, and 72 m below that of the Bosphorus Sill. These data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post-glacial Black Sea. A sea-level curve based on conventional and AMS radiocarbon ages on peat and AMS-based ages on Dreissena sp. shells indicate the water-level in the earlier lake phase continued, until the early Holocene, to be lower than the Bosphorus Sill after the Younger Dryas ended. However, the absence of AMS-dated mollusc ages from the shelves of this basin older than the Younger Dryas is suggestive of sub-aerial exposure of the shelves, and comparatively lower water-levels when the Younger Dryas began. Thus post-glacial outflow from the Black Sea occurred through a lowered or open Bosphorus seaway. Basin-wide radiocarbon ages on peat indicate a prompt increase in water-level from that of the pre-existing and unconnected palaeo-lake during the earliest Holocene (9600–9200 cal a BP). Mass colonisation of the Black Sea by Mediterranean taxa did not occur until salinity had risen sufficiently, a process which took 1000 a or more from the initial transgressive event. This gradual change in salinity contrasts with the prompt transgression which would have taken ∼400 a to occur. © 2011 Published by Elsevier Ltd.
- ItemThe sedimentary record of palaeoenvironments and sea-level change in the Gulf of Carpentaria, Australia, through the last glacial cycle(Elsevier, 2008-05-15) Reeves, JM; Chivas, AR; García, A; Holt, S; Couapel, MJJ; Jones, BG; Cendón, DI; Fink, DEnvironmental evolution of the Gulf of Carpentaria region, the world's largest tropical epicontinental seaway, through the last glacial cycle has been determined from a series of six sediment cores. These cores form the focus of a multi-disciplinary study to elucidate sea level, climate and environmental change in the region. The sedimentary record reveals a series of facies including open shallow marine, marginal marine, estuarine, lacustrine and subaerial exposure, throughout the extent of the basin during this period. The partial or complete closure of the central basin from marine waters results from sea level falling below the height of one or both of the sills that border the Gulf—the Arafura Sill to the west (53 m below present sea level (bpsl)) and Torres Strait to the east (12 m bpsl). The extent and timing of these closures, and restriction of the shallow waterbody within, are intrinsic to local ocean circulation, available latent heat transport and the movement of people and animals between Australia and New Guinea. Whilst the occurrence of the palaeo-Lake Carpentaria has previously been identified, this study expands on the hydrological conditions of the lacustrine phases and extends the record through the Last Interglacial, detailing the previous sea-level highstand (MIS 5.5) and subsequent retreat. When sea levels were low during the MIS 6 glacial period, the Gulf was largely subaerially exposed and traversed by meandering rivers. The MIS 5 transgression (∼130 ka BP) led to marine then alternating marine/estuarine conditions through to MIS 4 (∼70 ka BP) when a protracted lacustrine phase, of varying salinity and depth/area, and including periods of near desiccation, persisted until about 12.2 cal ka BP. The lake expanded to near maximum size (∼190 000 km2) following the intensification/restoration of the Australian monsoon at 14 ka BP. This lake-full phase was short-lived, as by 12.2 cal ka BP, marine waters were entering the basin, coincident with the progressive sea-level rise. Fully marine conditions were restored by about 10.5 cal ka BP by westward connection to the Arafura Sea (Indian Ocean), whereas connections to the Pacific Ocean (Coral Sea) did not occur until about 8 cal ka BP. © 2007 Elsevier Ltd and INQUA.
- ItemUsing multiple geochemical proxies to trace origin of gypsum (Gulf of Carpentaria, Australia, -70ka)(Sociedad Geologica de Espana, 2007-05) Playà, E; Cendón, DI; Trave, A; Chivas, AR; García, AThis paper discusses the geochemical signature of the Carpentaria evaporitic levels using minor-trace and rare-earth elements (REE) and Sr, O, C and S isotopes. The chemistry of these evaporites reveals important criteria for distinguishing between ancient marine and non-marine evaporites. © 2007 Sociedad Geologica de Espana