Deep advection of young waters through the Maldives carbonate edifice

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Author(s): Blättler, Clara L.; Higgins, John A.; Moore, Evan; Swart, Peter K.
Author Affiliation(s): Primary:
University of Chicago, Chicago, IL, United States
Princeton University, United States
University of Miami, United States
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The chemistry of pore fluids extracted from sediment cores from the Maldives Inner Sea reveal the presence of large interstitial water masses that have been advected laterally through the Maldives carbonate edifice. These drillcores were recovered in 2015 during IODP (International Ocean Discovery Program) Expedition 359 and penetrate late Oligocene to modern sediments including carbonate platform, slope, pelagic, and drift facies. Combined shipboard and shore-based analyses of pore fluid composition show linearly co-varying changes in the concentration of chloride and δ18O and δD values of ca. 25 mM, 1.2 ppm, and 10 ppm, respectively. Additionally, down-hole strontium concentrations and calcium isotope ratios of pore fluids are strongly correlated with each other and occasionally piecewise correlated with chloride and water isotope ratios. Multiple reversals in these geochemical properties with depth indicate the existence of several distinct interstitial water masses. These variations in pore fluid chemistry are interpreted to reflect the origin and reactive history of relatively recent water masses advecting through much older sedimentary formations. The elevated chloride and water isotope ratios suggest that seawater from the Last Glacial Maximum (LGM) is preserved in the subsurface, where it occupies over 400 m of the sediment column within Mid- to Late Miocene sediments. At greater depths (> 600 mbsf), a reversal in pore fluid chloride and strontium concentrations as well as δ18O, δD, and δ44/40Ca values point to the advection of younger Holocene seawater into the Maldives carbonate edifice, possibly driven by thermal (Kohout) convection. These observations demonstrate the potential for water-rock interaction in carbonate platform systems with fluids that are millions of years younger than the sediments. Some of the identifiable interstitial water masses vary laterally across short (1s to 10s of km) spatial scales, suggesting that post-depositional alteration may be able to explain variation in sedimentary geochemistry on similar outcrop scales based on different histories of advection and reactivity of pore fluids.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Advection; Carbonates; Cores; Expedition 359; Geochemistry; Indian Ocean; Indian Ocean Islands; International Ocean Discovery Program; Isotope ratios; Isotopes; Maldive Islands; Marine sediments; O-18/O-16; Ocean circulation; Oxygen; Sediments; Stable isotopes
Coordinates: N044600 N045600 E0730500 E0725700
Record ID: 2019061737
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