| dc.description.abstract | According to the IPCC report of 2013, anthropogenic warming has increased the Earth’s global energy inventory since the industrial revolution. 93% of this warming is taken up and locked in the oceans. However, heat uptake is not equally distributed over the oceans. Sea Surface Temperatures (SST) in the South-Central Indian Ocean are shown to have a larger increase than the global average SST increase. Interannual SST variability in the Indian Ocean is known to be the result of the interplay between the East Asian monsoon, El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Correlation between the Pacific Decadal Oscillation (PDO) and ENSO suggests that intercorrelation between climatological drivers complicates regional SST patterns. How the climatological drivers developed over time and what the trend will be in the future is not known. The precession-driven shift of the Intertropical Convergence Zone (ITCZ) in combination with an obliquity maximum led to the Holocene Climatic Optimum (HCO) around 9000-5000 years ago. This period was characterized with warmer summers in the Northern Hemisphere and colder on the Southern Hemisphere. The African climate is driven by climate variability on the Northern Hemisphere; Asian monsoon strengthening led to the African Humid Period (AHP). After the HCO, the Southeast African region was characterized by general cooling and drying. Speleothems are known to be an excellent archive of the past, able of reconstructing precipitation and temperature variability. Rodrigues Island is located in the Southwestern Indian Ocean. The location of the island is optimal for deciphering the interplay between modulating climate phenomena and interconnection between the shifting positions of the ITCZ and the Mascarene High in the Indian Ocean. In this thesis, a 1550-year isotope record derived from a stalagmite from Rodrigues Island is presented from the Late Holocene (2700-1200 BP). An oxygen and carbon isotope record in combination with XRF data and clumped isotopes led to a paleo-climatological reconstruction. Temperature was reconstructed with both clumped isotopes and fluid inclusion data from Spliethoff [2015]. The record showed increasing aridity over the whole record with stable temperatures, agreeing with the global trend and the subtropical climate. Zonally shifting high-pressure areas in the Indian Ocean possibly caused rainfall variability in the region. A significant increase in humidity occurred between 1375-1275 BP and was linked to an increase in El Niño intensity, forcing the system in a positive Indian Ocean Dipole (IOD) state. Wavelet analysis showed a 300-year cyclicity of these decadal-scale transitions to a positive IOD, agreeing with other research on Mauritius by De Boer et al. [2014]. Due to global warming, increased heat uptake by the Indian Ocean is expected in the future, causing further desiccation of the Rodrigues Island area. | |
