PhD Oral Defense of Jędrzej Majewski: Coral microatoll based sea level records from the Sunda Shelf

PhD Oral Defense of Jędrzej Majewski: Coral microatoll based sea level records from the Sunda Shelf

Event Type: 

  • Oral Defense

Venue: 

EOS Seminar Room (N2-01b-28)

Date: 

14 Nov 2017

Start Time: 

2:00PM

End Time: 

4:00PM

About the Event: 

Coral microatolls are an important sea-level proxy. They have been used to reconstruct Holocene relative sea-level (RSL) change, land-level changes related to the earthquake deformation cycle and oceanographic processes such as the El Niño/Southern Oscillation. Yet not all aspects of the coral microatoll methodology have been fully resolved. In particular, there are few studies that define the relationship between coral microatolls and sea level. One aspect, ponding, a process whereby a microatoll is separated from the low tides behind a rampart of stone, shingle or sand, remains a source of uncertainties within microatoll reconstructions that is rarely considered.

I have studied RSL records from 25 coral microatolls from 8 sites on the Sunda Shelf in Indonesia and Malaysia, to address four research questions. Firstly, I investigated the accuracy of coral microatoll RSL reconstructions and reliability. I demonstrate that open-ocean microatolls track sea level and may be used to reconstruct sea-level trends. Ponded microatolls, in contrast, are only partially influenced by the tidal cycle and cannot be used to recover sea-level trends.  

Secondly, I applied the coral microatoll methodology to reconstruct RSL from Mapur and Belitung Islands, Indonesia, using living, open-ocean coral microatolls. A comparison of the Mapur RSL reconstruction with tide gauge data from Singapore and Malaysia shows a correspondence between coral diedowns and both the nodal tidal cycle (1986 to 2005) and mean sea level (1972 to 2016). The full living microatoll records show a RSL change of 0.01 ±0.89 mm/yr from 1915 to 2005 in Mapur, and a range from 1.6 ±2.1 to 4.7 ±2.2 mm/yr from 1967 to 2005 in Belitung.

Thirdly, I reconstructed Holocene RSL from western Sarawak, Malaysia using surveyed and U-Th dated fossil microatolls. These data show that RSL rose to 1.45 ±0.8 above present by 7439 BP and remained stable (<0.3 m change) from then until 7006 BP. Following this, RSL rose to 2.3 +1.15/-0.8 m above present between 6128 and 6042 BP. These reconstructions were compared to a regional glacio-isostatic adjustment (GIA) model that was itself calibrated to data from Thailand and the Malay Peninsula. My comparison shows a disagreement between the RSL reconstructions and the GIA model which shows rising sea level over this period. I also infer local tectonic effects on at least one of the Sarawak sites, with up to ~1.1 m of vertical motion on the Serabang fault since 7000 yr BP; this structure was previously considered to be inactive.

Finally, I reconstruct 115 years of a mid-Holocene RSL from Mapur, Indonesia by combining seven coral microatoll sequences from two sites on the Island. They demonstrate RSL reached ~0.4 m above present by 7282 cal yr BP and rose at least a further ~0.5 m over the following 115 years. Here I also define Sea Level Index sequences, a data format more suitable to continuous RSL records such as those reconstructed from coral microatolls.

This thesis contributes to our understanding of coral microatoll methodology, and demonstrates the utility of coral microatolls for long composite sequences of RSL. The thesis also contributes RSL records from the Sunda Shelf, in the recent pre-instrument past and in the mid-Holocene.

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Members of the Examination Committee:

  • Associate Professor Michael David Gumert (Chair), School of Humanities and Social Sciences, Singapore
  • Dr Graham Oliver (Internal Examiner), Asian School of the Environment, Singapore
  • Associate Professor Scott Smithers (External Examiner), James Cook University, Australia
  • Associate Professor Sarah Woodroffe (External Examiner), Durham University, United Kingdom

Oral Examination Committee:

  • Dr Graham Oliver (Internal Examiner), Asian School of the Environment, Singapore
  • Associate Professor Adam Switzer, Earth Observatory of Singapore and Asian School of the Environment, Singapore
  • Associate Professor Charles Rubin, Asian School of the Environment, Singapore
  • Associate Professor Nathalie Goodkin, Earth Observatory of Singapore and Asian School of the Environment, Singapore

Advisors:

  • Associate Professor Adam Switzer, Earth Observatory of Singapore and Asian School of the Environment, Singapore
  • Associate Professor Charles Rubin, Asian School of the Environment, Singapore

About the Speaker: 

Jędrzej Majewski
PhD candidate

Interdisciplinary Graduate School, Nanyang Technological University

Jędrzej Majewski (Yen) received a BA/MA degree in Environmental Archaeology from the Nicolaus Copernicus University in Toruń, Poland. At ASE he conducted his research under the supervision of Associate Professor Adam Switzer. His research focuses on changes in relative sea level in Southeast Asia through the Holocene and the past 100 years. His work focused on coral microatolls as a proxy for sea-level change. More specifically, his work examines the reliabilty of the coral microatoll methodology and bring new data on mid-Holocene relative sea level from sites in Malaysian Borneo and Indonesia.

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