Miller PhD thesis 2014

March 26, 2014
lottiemiller

Miller, C.S. (2014) 520,000 years of environmental change in West Africa. PhD Thesis, Department of Environment, Earth & Ecosystems, The Open University.

Lottie 2014

CSM (2014)

Abstract:

Global temperatures are predicted to rise by 2–2.5°C by 2065, profoundly affecting the Earth’s environment. The response of ecosystems to past climate fluctuations can inform on how systems will respond in the future. This thesis focuses on Quaternary environmental changes in West Africa, a region important because of its high ecological value and role in the global carbon cycle.

In 2004, the International Continental Drilling Program recovered c. 291m of sediments spanning the last c. 1 Myr from Lake Bosumtwi (Ghana). Pollen, charcoal and nitrogen isotopes (d15N) were analysed from the most recent c. 150m (c. 520 kyr). The latitudinal position and long duration of this core makes it unique for understanding West African monsoon dynamics and vegetation change.

To aid characterisation of the Bosumtwi pollen succession, an atlas of present-day pollen was constructed for 364 pollen and spore taxa.

The pollen record from Bosumtwi reveals dynamic vegetation change over the last c. 520 kyr, characterized by eleven biome shifts between savannah and forest. Savannah vegetation is dominated by Poaceae (>55%) associated with Cyperaceae, Chenopodiaceae-Amaranthaceae and Caryophyllaceae. Forest vegetation is palynologically diverse, but broadly characterised by Moraceae, Celtis, Uapaca, Macaranga and Trema. Low d15N values correspond to forest expansion and these are driven by high lake levels. The timescale indicates that the six periods of forest expansion correspond to global interglacial periods. The record indicates that the wettest climate occurred during the Holocene, and the driest during Marine Isotope Stage 7.

The vegetation and d15N records show a strong response to glacial-interglacial variability between c. 520–320 kyr and 130–0 kyr. Between c. 320–130 kyr there is a weaker response to glacial-interglacial cycles probably related to high eccentricity during the peak of the 400-kyr component of eccentricity, with high eccentricity resulting in greater seasonality and ultimately drier conditions.

Supervisors: Dr. William Gosling, Dr. Angela Coe (both The Open University) and Dr. Tim Shanahan (University of Texas at Austin)

Examined by: Prof. Henry Lamb (University of Aberystwyth) and Dr. Pallavi Anand (The Open University).

To borrow a copy from The Open University Library click here.

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PCRG PhD studentship opportunity

December 16, 2013
WDG

Funded PhD studentship opportunity, October 2014 start
Department of Environment, Earth & Ecosystems, The Open Univeristy
Central England NERC Training Alliance (CENTA)
Closing date for applications : 31/01/2014

Past tropical vegetation stability: forest-savannah dynamics in tropical West Africa

William D. Gosling & Phil Jardine

  • Maintain a modern pollen monitoring network in lowland tropical West Africa
  • Reconstruct past vegetation change from fossil pollen records
  • Identify signature of approaching tipping points
  • Field work in tropical Africa (Ghana)

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Forests of the tropical eastern Andean flank during the middle Pleistocene: An insight of how highly biodiverse forests lived without us

October 31, 2013
WDG

Photo taken close by the study site. The road that pass through Eastern Andes, and the magnificent Montane forest of western Amazonia behind. (Photo by M. L. Cárdenas)

Photo taken close by the study site. The road that pass through Eastern Andes, and the magnificent Montane forest of western Amazonia behind. (Photo by M. L. Cárdenas)

Who would have thought that building a road in Andes would have allowed us to gain new and unique insight of pristine western- Amazonian forests? (I would have thought completely the opposite). Initially Patricia Mothes, chief of the volcanologist section of the Intituto de Geofisica in Ecuador, was called to look at sediments exposed by road works on the eastern flank of the Ecuadorian Andes. Arriving at the site she found thick (>20 vertical meters) deposits of grayish and dark brown interbedded layers of sediments which looked like they have been recently deposited. At closer inspection Patricia discovered that there were even wood pieces and leaves within the dark sediments (now known to be highly organic) that had the appearance of have been deposited within modern time. She wanted to know more. So a PhD student was recruited (a.k.a. Macarena Cárdenas) to work with the sediments at the Palaeoenvironmental Change Research Group at the Open University under the supervision of Dr William Gosling… And so the study began.

After several years spent dating the sediments, analyzing their composition (physical and elemental) and the fossils (pollen and wood) contained within them preliminary insights into vegetation change on the eastern Andean flank during the middle Pleistocene (c. 200,000-300,000 years ago) were revealed and published (Cárdenas et al., 2011a; Cárdenas et al., 2011b). Further work covering stratigraphically lower sediments (older than those previously published; c. 500,000 year) and more detailed sedimentary and fossil analysis of the entire sequence completed a PhD thesis (Cárdenas, 2011).

I am now pleased to announce that the extended work included in my PhD thesis has now been published in a new article in Palaeogeography, Palaeoclimatology, Palaeoecology (Cárdenas et al., online). The new paper is an extended version from previous publications from the same research and provides further evidence of the unique insights that can be gained from palaeoenvironmental studies in this region. These are some of the oldest Quaternary sediments ever discovered and studied from the mid-elevation eastern Andean flank / western Amazon and upon their analyses we were able to get for the first time an insight of how human-untouched Amazonian forests were back in time (up to 500,000 years ago!), how was their diversity and how they responded to intense volcanic activity and climatic change.

By Dr Macarena L. Cárdenas

REFERENCES

Cárdenas, M.L. (2011) The response of western Amazonian vegetation to fire and climate change: A palaeoecological study. In: Department of Earth & Environmental Sciences, p. 242. The Open University, Milton Keynes

Cárdenas, M.L., Gosling, W.D., Pennington, R.T., Poole, I., Sherlock, S.C. & Mothes, P. (online) Forests of the tropical eastern andean flank during the middle pleistocene. Palaeogeography, Palaeoclimatology, Palaeoecology. DOI: 10.1016/j.palaeo.2013.10.009

Cárdenas, M.L., Gosling, W.D., Sherlock, S.C., Poole, I., Pennington, R.T. & Mothes, P. (2011a) The response of vegetation on the Andean flank in western Amazonia to Pleistocene climate change. Science, 331, 1055-1058. DOI: 10.1126/science.1197947

Cárdenas, M.L., Gosling, W.D., Sherlock, S.C., Poole, I., Pennington, R.T. & Mothes, P. (2011b) Response to comment on “the response of vegetation on the Andean flank in western Amazonia to Pleistocene climate change”. Science, 333, 1825. DOI: 10.1126/science.1207888

 

PCRG publications 2009

February 15, 2013
WDG

Gosling, W.D., Hanselman, J.A., Knox, C., Valencia, B.G. & Bush, M.B. (2009) Long term drivers of change in Polylepis woodland distribution in the central Andes. Journal of Vegetation Science, 20, 1041-1052

Gosling, W.D., Mayle, F.E., Tate, N.J. & Killeen, T.J. (2009) Differentiation between Neotropical rainforest, dry forest, and savannah ecosystems by their modern pollen spectra and implications for the fossil pollen record. Review of Palaeobotany and Palynology, 153, 70-85

Marchant, R., Cleef, A., Harrison, S.P., Hooghiemstra, H., Markgraf, V., Van Boxel, J., Ager, T., Almeida, L., Anderson, R., Baied, C., Behling, H., Berrio, J.C., Burbridge, R., Björck, S., Byrne, R., Bush, M., Duivenvoorden, J., Flenley, J., De Oliveira, P., Van Gee, B., Graf, K., Gosling, W.D., Harbele, S., Van Der Hammen, T., Hansen, B., Horn, S., Kuhry, P., Ledru, M.P., Mayle, F., Leyden, B., Lozano-García, S., Melief, A.M., Moreno, P., Moar, N.T., Prieto, A., Van Reenen, G., Salgado-Labouriau, M., Schäbitz, F., Schreve-Brinkman, E.J. & Wille, M. (2009) Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago. Climate of the Past, 5, 725-767

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