NUTRIENT CYCLING AND THE BIOGEOCHEMISTRY OF MANGANESE, IRON, AND ZINC IN JELLYFISH LAKE, PALAU

The oxic waters in Jellyfish Lake, a stagnant marine lake in Palau, are depleted in NO3-, PO43-, dissolved Si, Mn, Fe, and Zn, while the underlying anoxic waters are significantly enriched in these species and NH3. NH3 and PO4(3-) regeneration and dissolved sulfide production in the anoxic zone yield a stoichiometry of C138N13P for organic matter undergoing recycling in the anoxic waters. In the anoxic zone, dissolved Mn, Fe, and Zn reach maximum concentrations of 30, 22, and 2.5 nM. The Fe concentrations are consistent with mackinawite or greigite solubility control. Mn approaches saturation with respect to haurite. Zn may be controlled by the solubility of ZnS coprecipitate. The sediments are enriched in Fe and depleted in Zn relative to Asian dust at Enewetak. A two-box model is used to calculate an eddy diffusion coefficient of 0.0015 cm2 s-1 across the chemocline. The upward diffusive loss of NH3 added to the sedimentation rate of N and multiplied by the stoichiometric C:N ratio yields an organic carbon flux into the anoxic waters of 1,200-mu-mol C cm-2 yr-1, which is approximately 13% of the total primary productivity.