Historical climate variation in the Maldives, Indian Ocean, based on proxy data from Scleractinian coral skeletons
Final Report Abstract
Coral archives serve as a tool for subtropical and tropical climate reconstructions, when instrumental climate data are sparse, and for pre-instrumental times. This study investigated geochemical signatures in stony corals from the central Maldives (Rasdhoo Atoll) for 1917-2007. The Maldives are among the largest carbonate platforms in the world and are situated in the Indian monsoon-influenced NW Indian Ocean. Powdered samples from the coral skeletons were milled and analyzed for the stable oxygen isotopic composition (d18O) along the growth axis. This geochemical value depends on sea surface temperature (SST) and seawater d18O. Seasonal, interannual and decadal fluctuations in coral d18O can be linked to oceanographic and atmospheric variability in the Indian Ocean. The measured strontium-to-calcium ratio (Sr/Ca) in corals depends on the ambient SST during the formation of the coral skeleton. The Sr/Ca-ratio does not reflect the SST warming in this area, since it is likely that the Sr/Ca ratio in seawater was variable through the recorded time. The invariance of seawater Sr/Ca is, however, the precondition for the application of Sr/Ca as a paleothermometer. The annual mean extension in corals is influenced by several environmental factors, such as light, SST, and water motion in the habitat. This study shows that interannual variation of annual extension rates in the investigated atoll lagoon coral are driven by SST and summer monsoon current velocities during the summer monsoon. This is the first study, which found a link between current variations and coral growth. Therefore, annual extension rates can serve as a climate archive for the Indian monsoon strength. The study also indicates that the location of the coral within the reef system can possibly determine the potential of corals to track regional climate variations. For a better understanding of the Indian monsoon variability, long climate records of the Indian Ocean and Indian subcontinent are crucial. The instrumental rainfall record over Indian only reaches back to the mid 19th century. Until now, tree ring records from the Indian subcontinent, speleothems from Peninsular Arabia, and sediments from the Arabian Sea were used as archives to decipher monsoon activity over the last centuries and millennia. Coral archives from the NW Indian contribute to a better coverage of monsoon records in pre-instrumental periods. The good correlation between skeletal extension rates and instrumental climate data was not expected, since it Is widely suggested that this parameter is influenced by a number of different environmental forcers. While a few studies already found a link between extension rates and SST anomalies, which are driven by climate variation such as ENSO or Atlantic Multidecadal Oscillation (AMO), this project detected a connection between temporal coral growth and monsoon current variations. As a consequence, a new monsoon proxy for the marine realm was developed in this study. Both the specific geomorphology of Rasdhoo Atoll and the location of the core within the lagoon presumably favoured the climate signature in the extension rate record. Additionally, this study shows the limits in the application of Sr/Ca as SST proxy in areas influenced by upwelling, implying that this proxy cannot be used to reconstruct pre-instrumental SST in this region.
Publications
- (2007) Historical climate variation in the Maldives, Indian Ocean, based on proxy from Scleractinian coral skeletons. "The ocean in the earth System". International Conference 2007 and 97th Annual Meeting of the Geologische Vereinigung e.V. (GV), Bremen, 1-5 October 2007, Abstract Volume 2007/1-2
Storz, D. & Gischler, E.
- (2008) Coral proxy data record historical climate in the Maldives, Indian Ocean. European Geoscience Union (EGU) General Assembly, Vienna, 13-18 April 2008, Geophysical Research Abstracts Volume 10. p. 4
Storz, D. & Gischler, E.
- (2008) Historical climate variability recorded by massive corals in the Maldives, Indian Ocean. International Conference 2008, 160th Annual Meeting. Deutsche Gesellschaft für Geowissenschaften, 98th Annual Meeting Geologische Vereinigung e.V. (GV), Aachen, 29 September - 2 October 2008, Abstract Volume, p. 77
Storz, D. & Gischler., E
- (2009) Pacific climate forcing detected in a coral record from the NW Indian Ocean. "Earth control on planetary life and environment". International Conference 2009 and 98th Annual Meeting of the Geologische Vereinignung e.V. (GV), Göttingen. 5-9 October 2009, Abstract Volume, p. 134
Storz, D. & Gischler, E.
- (2009) Pacific climate forcing recorded in a coral proxy record from the Maldives (Indian Ocean). American Geophysical Union (AGU), Fall Meeting, San Francisco, 14-18 December 2009. Abstract #PP11A-1299
Storz, D. & Gischler, E.
- (2010) Skeletal extension-rate record of a coral from the Maldives tracks ENSO and Indian monsoon variability. 2nd International Sclerochronology Conference, Mainz, 24-28 July 2010, Program and Abstracts p. 79
Storz, D. & Gischler, E.
