PhD student, The University of Adelaide
How the south-eastern Australian climate changed coming into and out of the Last Glacial Maximum
The drivers of long-term variability in climate in the Southern Hemisphere mid-latitudes are not well understood. The instrumental record does not extend far enough to encompass the full range of possible climatic variability in the Southern Hemisphere, including changes of a magnitude similar to what we might see in the future. The Last Glacial Period (LGP; ~30,000-10,000 yr. BP) was punctuated by abrupt and extreme millennial-scale climate fluctuations, beyond what is preserved in the instrumental record. The LGP is therefore an ideal period in which to investigate the response of SH mid-latitude climates to external forcing factors.
During my Ph.D. research, I therefore aim to address the following key objective: to increase our understanding of Southern Hemisphere mid-latitude climate variability during the LGP, with a specific focus on temperature and hydrological change in south-eastern Australia. I am researching this using various geochemical methods, including using the chemistry of lake sediments to reconstruct past changes in the plants around the lake, and also using the chemistry of fossil snail shells to reconstruct the temperature and rainfall over their lifespan. For a three-minute introduction to using snail chemistry to infer past climate, see this video! https://www.dropbox.com/s/ipraddbloebwzqh/Georgy%20Falster.mp4?dl=0
Abstract: It has been difficult to access projections of global-scale climate change with high temporal resolution spaning the late Pleistocene and Holocene. This has limited our ability to discern how climate fluctuations have affected species’ range dynamics and extinction processes, turn-over in ecological communities and changes in genetic diversity. PaleoView is a new freeware tool, which provides a comprehensive but easy-to-use way to generate and view paleoclimate data at temporal and spatial resolutions suitable for detecting biotic responses to major climate shifts since the last glacial maximum. Regional to global scale simulations of temperature, precipitation, humidity and mean sea level pressure can be generated from PaleoView as gridded or time series data at time intervals as short as a decade for any period during the last 21 000 yr. They can be viewed using a built-in geographical user interface or saved as data files. Modelled climate reconstructions are based on daily simulation output from the Community Climate System Model ver. 3 (CCSM3). This global coupled atmosphere–ocean–sea ice–land general circulation model accurately reproduces major climatic features associated with the most recent deglaciation event, and predicts present-day patterns of climate conditions with verified hindcast skill. By providing a portal for readily accessing climate reconstructions at high temporal resolutions, PaleoView can help to better establish the consequences of past climate fluctuations on macro-ecological patterns of biological and genetic diversity.
Pub.: 12 May '17, Pinned: 27 Jul '17
Abstract: Spatial and temporal variations of the isotopic composition of precipitation were investigated to better understand their controlling factors. Precipitation was collected from six locations in Hokkaido, Japan, and event-based analyses were conducted for a period from March 2010 to February 2013. Relatively low δ values and a high d-excess for annual averages were observed at three sites located along the Japan Sea compared to the three sites at Pacific Ocean side. Lower δ values in spring and fall and higher d-excess in winter were observed for the region along the Japan Sea. In total, 264 precipitation events were identified. Precipitation originated predominantly from low-pressure system (LPS) events, which were classified as northwest (LPS-NW) and southeast (LPS-SE) events according to the routes of the low-pressure center, that passed northwest and southeast of Hokkaido, respectively. LPS-SE events showed lower δ18O than LPS-NW events, which is attributable to the lower δ18O of water vapor resulting from heavy rainfalls in the upstream region of the LPS air mass trajectories over the Pacific Ocean. This phenomenon observed in Hokkaido can be found in other midlatitude coastal regions and applied for hydrological, atmospheric, and paleoclimate studies. A characteristic spatial pattern was found in LPS-NW events, in which lower δ18O was observed on the Japan Sea side than on the Pacific Ocean side in each season. This is likely due to the location of the sampling sites and their distance from the LPS: Precipitation with lower δ18O in the region along the Japan Sea occurs in a well-developed cloud system near the low-pressure center in cold and warm sectors of LPS, whereas precipitation with higher δ18O on the Pacific side mainly occurs in a warm sector away from the low-pressure center. Air mass from the north does not always cause low δ in precipitation, and the precipitation process in the upstream region is another important factor controlling the isotopic composition of precipitation, other than the local temperature and precipitation amount.
Pub.: 06 Jul '17, Pinned: 27 Jul '17
Abstract: Paleoclimate studies play a crucial role in understanding past and future climates and their environmental impacts. Current methodologies for performing highly sensitive elemental analysis at micrometre spatial resolutions are restricted to the use of complex and/or not easily applied techniques, such as synchrotron radiation X-ray fluorescence micro-analysis (μ-SRXRF), nano secondary ion mass spectrometry (nano-SIMS) or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Moreover, the analysis of large samples (>few cm²) with any of these methods remains very challenging due to their relatively low acquisition speed (~1-10 Hz), and because they must be operated in vacuum or controlled atmosphere. In this work, we proposed an imaging methodology based on laser-induced breakdown spectroscopy, to perform fast multi-elemental scanning of large geological samples with high performance in terms of sensitivity (ppm-level), lateral resolution (up to 10 μm) and operating speed (100 Hz). This method was successfully applied to obtain the first megapixel images of large geological samples and yielded new information, not accessible using other techniques. These results open a new perspective into the use of laser spectroscopy in a variety of geochemical applications.
Pub.: 13 Jul '17, Pinned: 27 Jul '17
Abstract: Understanding discontinuities in the Australian archaeological record currently represents a major challenge for researchers especially where different interpretive frameworks are used to explain the same phenomena. The widespread Last Glacial Maximum (LGM) absence of dated archaeological evidence in desert lowlands is often interpreted as a lack of human occupation. While this scenario may be true in many cases, we believe this inference requires critical re-appraisal. Using case studies from the coastal Carnarvon bioregion, located in a maritime desert of NW Australia, we argue that discontinuities and occupational lacunae may be the result of a variety of different geomorphic and human behavioural processes where the absence of people may be only part of the equation. We argue that, by reconceptualising discontinuities with an explicit multi-scalar focus on depositional regimes and landscape patterns, richer explanations about human occupational patterning at both the local and regional levels can be generated.
Pub.: 02 Sep '16, Pinned: 27 Jul '17
Abstract: Publication date: 1 November 2016 Source:Earth and Planetary Science Letters, Volume 453 Author(s): Maria A. Reimi, Franco Marcantonio Accurate paleo-latitudinal reconstructions of the Intertropical Convergence Zone (ITCZ) are necessary for understanding tropical hydroclimate and atmospheric circulation. Paleoclimate models and records suggest that as global temperatures increase, the ITCZ should migrate towards the warmer hemisphere. Many uncertainties remain regarding the magnitude of this migration, and few studies have focused on the Central Equatorial Pacific (CEP). Here, we use eolian dust records recovered from three locations in the CEP to address changes in dust provenance across the paleo ITCZ since the last glacial maximum (LGM). Radiogenic isotope compositions of Nd and Pb show that dust delivered to the CEP was sourced mainly from two regions: East Asia and South America. From these data we deduced that since Marine Oxygen Isotope Stage 2 (MIS2) the ITCZ has migrated north to its modern position, being displaced by as much as 7°, to as little as 2.5°. We find that the ITCZ migrated further north during the early Holocene (∼9 kyr), reaching its position furthest north during the mid-Holocene warm interval (∼7 kyr), based on an increase in South American dust at the northernmost sites.
Pub.: 22 Aug '16, Pinned: 27 Jul '17
Abstract: The mid-Late Pleistocene and Holocene aeolianites of the Tamala Limestone on the northern Swan Coastal Plain in southwestern Western Australia consist of six members that show cyclic deposition of coastal aeolianite, overlain by calcrete/microbialite, karstified surface and palaeosol. Field work, combined with mineralogical, chemical, stable isotope analysis and uranium-thorium (U/Th) and optically stimulated luminescence (OSL) dating, provides an insight into the repetitive glacial and interglacial climatic periods over the past 500 kyr. Deposition of the carbonate aeolianites occurred during interglacial episodes (marine isotope stage (MIS) 1, 5, 7, 9, 11, and possibly 13), due to migration of coastal dunes under the influence of strong southerly to southwesterly winds. Rainfall was insufficient to support vegetation cover on the dunes, and so was probably limited or seasonal. The transition from interglacial to glacial climates was characterised by higher effective rainfall, accompanied by aeolianite dissolution and karstification. During the colder climates and less effective rainfall of the glacial periods, there was no carbonate sand deposition; instead laminated microbialite and/or laminar calcrete formed, followed by palaeosol formation. The oxygen isotope composition of the microbialites indicates average temperatures during glacial periods ~ 4 °C − 8 °C lower than today, and δ13C values demonstrate a higher proportion of C4 plants and therefore a drier or more seasonal climate. Data from individual members of the Tamala Limestone show that the wettest interglacial period was MIS 5, when extensive karstification and pinnacle development occurred, and rainfall was probably higher than at any other time in the past 500 kyr. Of the glacial periods, MIS 10 was relatively wet or less seasonal, whereas MIS 8 and the Last Glacial Maximum (LGM) were relatively dry and windy. The low rainfall during the peak of the glacial periods was probably intensified by colder water offshore, due to weakening of the Leeuwin Current and its replacement by the cold, north-flowing West Australian Current.
Pub.: 10 Jan '17, Pinned: 27 Jul '17
Abstract: This paper presents the results of a palynological investigation into the late Last Glacial Maximum (LGM) and last deglaciation (ca. 20 000–9000 cal a BP) from Little Llangothlin Lagoon, in the sub-tropics of eastern Australia. The Lagoon held permanent water during the late LGM and early deglaciation but was intermittently dry during the late deglaciation. During the late LGM, local vegetation was dominated by a sub-alpine herbfield but the significant presence of rainforest taxa in the pollen record indicates the survival of rainforest, rainforest margin or wet sclerophyll communities close to the site. By ca. 17 000 cal a BP, open Eucalyptus forest replaced the alpine herbfield vegetation indicating that warming had commenced. Rainforest taxa disappeared at this time but re-appeared at the end of the deglaciation. The LGM conditions are consistent with a dominant circulation system whereby persistent high pressure over eastern Australia brings onshore easterlies to this region and maintains humid conditions along the east coast and highlands of the Great Dividing Range. This is similar to modern winter circulation but the persistence of rainforest and wet sclerophyll taxa suggests an increase in easterly flow over modern conditions during the LGM.
Pub.: 03 Jul '17, Pinned: 27 Jul '17
Abstract: Few phylogeographic studies have been undertaken of species confined to narrow, linear coastal systems where past sea level and geomorphological changes may have had a profound effect on species population sizes and distributions. In this study, a phylogeographic analysis was conducted of Eucalyptus gomphocephala (tuart), a tree species restricted to a 400 × 10 km band of coastal sand-plain in south west Australia. Here, there is little known about the response of coastal vegetation to glacial/interglacial climate change, and a test was made as to whether this species was likely to have persisted widely through the Last Glacial Maximum (LGM), or conforms to a post-LGM dispersal model of recovery from few refugia.The genetic structure over the entire range of tuart was assessed using seven nuclear (21 populations; n = 595) and four chloroplast (24 populations; n = 238) microsatellite markers designed for eucalypt species. Correlative palaeodistribution modelling was also conducted based on five climatic variables, within two LGM models.The chloroplast markers generated six haplotypes, which were strongly geographically structured (GST = 0·86 and RST = 0·75). Nuclear microsatellite diversity was high (overall mean HE 0·75) and uniformly distributed (FST = 0·05), with a strong pattern of isolation by distance (r(2) = 0·362, P = 0·001). Distribution models of E. gomphocephala during the LGM showed a wide distribution that extended at least 30 km westward from the current distribution to the palaeo-coastline.The chloroplast and nuclear data suggest wide persistence of E. gomphocephala during the LGM. Palaeodistribution modelling supports the conclusions drawn from genetic data and indicates a widespread westward shift of E. gomphocephala onto the exposed continental shelf during the LGM. This study highlights the importance of the inclusion of complementary, non-genetic data (information on geomorphology and palaeoclimate) to interpret phylogeographic patterns.
Pub.: 29 Nov '13, Pinned: 27 Jul '17
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