This project will provide a high-resolution record of climatic and environmental change for the southern hemisphere region of Patagonia in the vicinity of the Cordillera Darwin Icefield (~54°S). The palaeoclimatic history of southern South America is dominated by the strength and latitudinal position of the Southern Westerly storm tracks and the sub-Antarctic front (Figure 1). Patagonia lies along this zone of high precipitation and past migrations of these storm fronts can be tracked through fluctuations of the Patagonian ice fields and the response of the surrounding vegetation cover. Our current understanding of late Quaternary southern hemisphere ocean-atmosphere change is largely derived from reconstruction of glacier fluctuations during the Last Glacial / Interglacial transition (LGIT) (Hulton et al 2002; McCulloch et al 2005) but this provides an episodic view of the changing environment that may simply reflect the changing precipitation signal. In the northern hemisphere the Greenland oxygen-isotope record suggests the LGIT was characterised by rapid high-magnitude climatic changes (Rasmussen et al 2014). However, the duration and magnitude of southern hemisphere climatic events, such as the Antarctic Cold Reversal (ACR), and their significance in driving Fuego-Patagonian glacial and vegetation change is unclear.
This project will provide high-resolution palaeo-ecological records to provide a regional synthesis from which we will be able to infer the timing and nature of southern hemisphere climatic fluctuations and their impacts on the landscape and vegetation resources of southern Patagonia (Figure 2). This research will provide valuable empirical data with which the science and policy communities can assess the extent to which future climate changes in the context of a CO2 enriched atmosphere will impact on present vegetation and resource patterns of Patagonia.
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Figure 1 Sub Antarctic frontal and current system
Figure 2 Montane woodland landscape, Tierra del Fuego, South America.
This project will produce high-resolution (sub-centennial) records of chironomid inferred temperature change (Brooks et al 2012; 2016) from lake sediments in Fuego-Patagonia. These climate records will be further supported by pollen analysis (input from Dr McCulloch) which is excellent for the reconstruction of past landscape change. However, there is a lag between climate change and the evidence recorded in the vegetation record (Mansilla et al 2018) and it is anticipated that the inferred chironomid temperature record will be more sensitive to climate. Differences in the timing and characteristics of the response between the chironomids and vegetation will help disentangle the major climate forcings in the region. Deep basin sediments, spanning the past ~20 ka, have been identified along an east-west transect between 53°S and 55°S (Figure 1). It is anticipated that the chironomid records will circumscribe the timing and extent of temperature changes during the LGIT and enable us to separate the shifts in the focus of precipitation during the LGIT at a sub-centennial scale. These records will be reinforced through lithostratigraphic analyses (organic content and XRF-geochemistry and constrained in time using radiocarbon dating and tephrochronology (dating using volcanic ash layers). Furthermore, these records of temperature and environmental change will complement the innovation of GDGT Biomarker temperature reconstructions, British Antarctic Survey (Dr Roberts) and Newcastle University (Prof. Juggins). The development of GDGT biomarkers has resulted in a better understanding of the taphonomy of these biomarkers for example within lacustrine systems they can enter via soils or accumulate as part of lacustrine eutrophication. Here we propose to generate palaeotemperature records from two independent climate proxies, GDGT biomarkers and chironomids this novel approach to the generation of such data sets will increase the accuracy and precision of the palaeotemperature record. A multiproxy approach, robust records of palaeotemperature interpreted alongside evidence for environmental change will be used to infer the timing and nature of southern hemisphere climatic fluctuations.
In the first year the student will receive training in chironomid analysis (NHM – Steve Brooks and NERC-ATSC) and review the extant palaeoclimate literature for the region.
The 1st field coring campaign (Tierra del Fuego, Figure 1, point 1) will take place in the austral summer 2021 (Jan-Feb) and cores will be returned to Stirling. XRF-ITRAX geochemical analysis will be followed by chironomid analysis, lithostratigraphic analyses and GDGT biomarkers (BAS Cambridge). 1st 14C dating submission to NERC-RCF in the autumn 2021.
The 2nd field coring campaign (Cordillera Darwin, Figure 1, point 2) will take place in the austral summer 2022 (Jan-Feb) followed by XRF-ITRAX and chironomid analysis, lithostratigraphic analyses and GDGT biomarkers. 2nd 14C submission to NERC-RCF in the autumn 2022.
Synthesis of chironomid inferred temperature using modern surface data (input from Newcastle & NHM) and GDGT Biomarker data sets, Bayesian analysis of 14C data, NERC (Oxford) training course Radiocarbon dating and Bayesian chronological analysis. Second half of year 3 collate and review written work and begin writing up PhD thesis.
Final data analysis, complete writing up, publication production and project dissemination
The PhD student will receive training in field techniques and lake sediment coring (Dr Tisdall and Dr McCulloch) and develop expertise in palaeoclimate reconstruction techniques (Prof Juggins and Dr Roberts), specifically chironomidae analysis (with input from Dr Eileen Tisdall and Steve Brooks, NHM) and application of GDGT Biomarkers in temperature reconstructions (Dr Roberts). He/she will also receive training in a range of lithostratigraphic and geochemical techniques, including XRF-ITRAX geochemical analysis (Dr Davies, University of Aberystwyth) and grain discrete electron microprobe analysis for tephra characterisation (University of Edinburgh). The PhD student will also receive training in chronology building and AMS age interpretation and Bayesian age-depth modelling (NERC Oxford).
The student will also receive complementary training in transferable skills; these involve seminars/workshops in project management, data analysis, oral and poster presentations, paper writing, thesis writing, compiling bibliographies, employability, dealing with the Media, the Viva and troubleshooting (University of Stirling Graduate School). All students are expected to present their work annually at internal seminars and conferences and externally. Students are also required to produce annual reports and undergo annual review meetings to ensure that they are progressing and receiving appropriate support for submission to a high standard. The student will also attend training and networking events within the IAPETUS2 DTP and offered via NERC.
References & further reading
Brooks et al 2012 Chironomid inferred summer temperatures for the Last Glacial-Interglacial Transition from a lake sediment sequence in Muir Park Reservoir, west central Scotland. Journal of Quaternary Science, 31 (3); 214-224
Brooks et al 2012 High Resolution Late-glacial and early Holocene summer air temperature records from Scotland inferred from chironomid assemblages. Quaternary Science Reviews, 41: 67-82.
Hulton et al 2002 The last glacial maximum and deglaciation in southern South America. Quaternary Science Reviews, 21;233-241.
Mansilla et al 2018 The vulnerability of the Northofagus forest steppe ecotone to climate change: Palaeoecological evidence from Tierra del Fuego (~53ËšS). Palaeogeography, Palaeoclimatology, Palaeoecology, 508; 59-70.
McCulloch et al 2005 Chronology of the last glaciation in central Strait of Magellan and BahÃa InÃºtil, southernmost South America. Geografiska Annaler Series A, 87(2);289-312.
Rasmussen et al 2014 A stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized Greenland ice-core records; refining and extending the INTIMATE event stratigraphy. Quaternary Science Reviews, 106;14-28.
Please contact: Dr Eileen Tisdall, Biological & Environmental Sciences, University of Stirling. Email: firstname.lastname@example.org