Maldives Monsoon and Sea Level1
Published March 2016
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International Ocean Discovery Program Expedition 359 was designed to address changes in sea level and currents, along with monsoon evolution in the Indian Ocean. Eight drill sites are located in the carbonate edifice of the Republic of Maldives, which bears a unique and mostly unread Indian Ocean archive of the evolving Cenozoic icehouse world. This tropical marine record is key for better understanding the effects of this global evolution in the Indo-Pacific realm. The bank geometries of the growing carbonate archipelago provide a physical record of changing sea level and ocean currents. The bank growth occurs in pulses of aggradation and progradation that are controlled by sea level fluctuations during the early and middle Miocene, including the mid-Miocene Climate Optimum. A dramatic shift in development of the carbonate edifice from a sea level–controlled to a predominantly current-controlled system appears to be directly linked to the evolving Indian monsoon. This phase led to a twofold configuration of bank development: bank growth continued in some parts of the edifice, whereas in other places, banks drowned. Drowning steps seem to coincide with onset and intensification of the monsoon-related current system and deposition of contourite fans and giant sediment drifts. Expedition 359 cores are intended for reconstructing the changing current system through time that is directly related to the evolution of the Indian monsoon. As such, the drift deposits will provide a continuous record of Indian monsoon development in the region of the Maldives.
Expedition 359 had two main focus points. The first was to date precisely the onset of the current system that is potentially in concert with the onset or the intensification of the Indian monsoon and coincides with the onset of the modern current system in the world’s ocean. The second important outcome of Expedition 359 is groundtruthing the hypothesis that the dramatic, pronounced change in style of the sedimentary carbonate sequence stacking was caused by a combination of relative sea level fluctuations and ocean current system changes. These questions were directly addressed by the shipboard scientific data.
In addition, Expedition 359 cores will provide a complete Neogene δ13C record of the platform and platform margin sediments and a comparison with pelagic records over the same time period. This comparison will allow assessment of the extent to which platform carbonates record changes in the global carbon cycle and whether changes in the carbon isotopic composition of organic and inorganic components covary and the implications this has on the deep-time record. This determination is important, as such records are the only type that exist in deep time.
1Betzler, C.G., Eberli, G.P., Alvarez Zarikian, C.A., and the Expedition 359 Scientists, 2016. Expedition 359 Preliminary Report: Maldives Monsoon and Sea Level. International Ocean Discovery Program. http://dx.doi.org/10.14379/iodp.pr.359.2016