Jellyfish Lake, Palau: Regeneration of C, N, Si, and P in anoxic marine lake sediments

Abstract

Sediment cores from Jellyfish Lake were processed under an inert atmosphere and the pore waters extracted and analyzed for the following parameters: pH, titration alkalinity (TA), Cl−, H4SiO4, PO43−, NH4+, Ca2+, Mg2+, SO42−, and H2S. Additionally, in one set of pore‐water samples (core 10), the δ13C of the ∑CO2 was also determined. The TA, H4SiO4, PO43−, NH4+, and H2S increased with depth in the pore waters above anoxic bottom‐water values. H2S values increased to 3.8 M. In one case, both H4SiO4 and PO43− concentrations increased to a maximum value and then decreased with depth, suggesting removal into solid phases. The H4SiO4 concentrations are equal to or greater than pore‐water value observed in sediments underlying upwelling areas. PO43− concentrations are, in general, lower than pore‐water values from terrigenous nearshore areas but higher than nearshore carbonate pore‐water values from Florida Bay or Bermuda. The Ca2+, Cl−, and Mg2+ : Cl− ratios show slight decreases in the top 15–20 cm, suggesting that authigenic carbonate may be forming. This suggestion is supported by the fact that the pore waters are saturated with respect to CaCO3 due to the very high TAs. The δ13C measurements of the pore‐water ∑CO2 are from a shorter core. These measurements reach their most negative concentration at 72 cm and then become slightly heavier. This change is accompanied by a decrease in TA, suggesting the onset of methanogenesis at this location in this core.