Haig, Jordahna Ellan-Ann (2015) Investigating long-term, high-resolution records of climate and extreme events in the southeast Indian and southwest Pacific oceans using the δ¹⁸O of stalagmites. PhD thesis, James Cook University.

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Abstract

There has been much debate in recent years over the impact of rising global temperatures on the climatology of tropical storms. Various disciplines employ a range of differing techniques to assess the likely impact of enhanced greenhouse conditions on the frequency and severity of natural hazards such as severe tropical storms and tropical cyclones. Often, highly sophisticated statistical and climate models and geological proxy records are used to obtain a picture of historical and prehistorical climatology. Geological proxy records are often of low temporal resolution (decades to centuries) while statistical and climate models are based on instrumental records of tropical cyclones (covering only the last 50 years) which are not of sufficient length to decipher natural variability from human induced change. This complicates the issue of identifying long-term trends in tropical cyclone activity and the associated causes and may explain to a certain extent the disparity between current trend estimates. This thesis investigates long-term tropical cyclone activity over the last 1500 years using the stable isotope composition of seasonal growth layers in stalagmites from Eastern and Western Australia (Chillagoe, Queensland and Cape Range Western Australia respectively). Specifically does tropical cyclone activity within the instrumental record reflect natural variability, are there any discernible trends in activity and do these have climatic control/s, and lastly, what impact have these changes had (if any) on the natural environment. The approach that this thesis takes to addressing this issue is three fold. The first step, and thus first aim of the thesis was to develop a new palaeo-tropical cyclone activity index thus extending the current tropical cyclone record 1500 years back in time (Chapter 4) in order to compare the present to the past, comparing the new record with long-term climatic indices (Chapter 5) and lastly, investigating the potential environmental impacts of a changing tropical cyclone regime on both regions (Chapter 6).

This thesis effectively bridges the gap between the high-temporal resolution instrumental tropical cyclone record and geological proxy record by generating one seamless, quantifiable record spanning the last 1.5 millennia at two locations in Eastern and Western Australia (Chapter 4). This involved the development of a new tropical cyclone index (CAI) by linking isotope dynamics within tropical cyclones with their meteorological characteristics, and applying these principles to long-standing, annually resolved records of rainfall δ¹⁸O from terrestrial carbonate deposits (stalagmites). The components of CAI were tested against measured records of tropical cyclone rainfall δ¹⁸O. The high-resolution, long-term isotope record was then calibrated against the instrumental tropical cyclone record after de-trending the influence of the monsoon from the carbonate δ¹⁸O. The second aim of this thesis was to examine the tropical cyclone climatology in these two regions at annual, decadal and centennial scales in an attempt to decipher natural variability from anthropogenically induced change. The third aim was to take steps towards applying this new index, by comparing the long-term CAI against other climate indices in an attempt to identify potential drivers of change within the geological record and thus shortlist potential inputs for long-range tropical cyclone forecast models (Chapter 5). In Chapter 6 we assess the potential impacts (if any) on the surrounding environment by applying a duel isotope approach thus, investigating changes in δ¹³C within the stalagmite carbonate in conjunction with the observed enrichment in δ¹⁸O over the most recent 100 years (the period corresponding to the reduction in tropical cyclone activity noted in Chapter 4.)

The results of this thesis indicate that tropical cyclone activity has been highly variable over the past 1,500 yr and wavelet analysis indicates the presence of decadal, interdecadal, centennial and inter-centennial scale oscillations at both sites. Trend analysis indicates that tropical cyclone activity in the Australian region has been significantly less in recent years when compared to the last 550-1,500 yr. In fact, tropical cyclone activity on the West coast of Australia is at an all time low. Analysis of the CAI using classical statistical techniques indicate that high-frequency oscillations in CAI may be driven by other climate phenomena such as the Northern Oscillation Index, highlighting the influence of meridional atmospheric patterns in addition to zonal atmospheric patterns (e.g. Southern Oscillation Index), and cross basin teleconnections between CAI in Western Australia and the ENSO Precipitation Index, Northern Oscillation Index, Trade-wind Index and between CAI in Eastern Australia and Atlantic Meridional Mode which have not been previously identified (with the exception of Trade-wind Index). In addition, cross wavelet analysis reveals a link between tropical cyclone activity in Western and Eastern Australia and solar cycles at decadal, and centennial scales, within both the instrumental record (Sun Spot Number) and over geological time scales through the comparison with cosmogenic isotope data i.e. southern hemisphere tree ring δ¹⁴C data and NGRIP Greenland. Be concentration data. The application of a dual isotope approach (δ : δ defined later in Chapter 6) indicates that the reduction in tropical cyclone activity noted in both regions has an alternate effect, resulting in a reduction in vegetation cover in Western Australia (the C4 community) which we believe is owing largely to the dominance of grasses at the site and the large contribution of seasonal tropical cyclone activity to annual rainfall totals at the site and conversely, an increase in vegetation cover in the C3 community (the Eastern Australian site) due to a reduction in large scale disturbances within the dry tropical woodland.

Item ID:	44643
Item Type:	Thesis (PhD)
Keywords:	climate records; cyclone activity; extreme events; global climate model; hurricanes; Indian Ocean; Pacific Ocean; stalagmites; tropical cyclones; tropical storms; typhoons
Related URLs:	http://researchonline.jcu.edu.au/31790/ http://researchonline.jcu.edu.au/45023/
Additional Information:	Publications arising from this thesis are available from the Related URLs field. The publications are: Chapter 4: Haig, Jordahna, Nott, Jonathan, and Reichart, Gert-Jan (2014) Australian tropical cyclone activity lower than at any time over the past 550-1,500 years. Nature, 505 (7485). pp. 667-672. Chapter 5: Haig, Jordahna Ellan-Ann, and Nott, Jonathan (2016) Solar forcing over the last 1500 years and Australian tropical cyclone activity. Geophysical Research Letters, 43 (6). pp. 2843-2850.
Date Deposited:	30 Aug 2016 23:14
FoR Codes:	05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 34% 04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040604 Natural Hazards @ 33% 04 EARTH SCIENCES > 0401 Atmospheric Sciences > 040199 Atmospheric Sciences not elsewhere classified @ 33%
SEO Codes:	96 ENVIRONMENT > 9602 Atmosphere and Weather > 960299 Atmosphere and Weather not elsewhere classified @ 33% 96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 33% 96 ENVIRONMENT > 9610 Natural Hazards > 961099 Natural Hazards not elsewhere classified @ 34%
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