1 research outputs found
Efficient recycling of nutrients in modern and past hypersaline environments
The biogeochemistry of hypersaline environments is strongly influenced by changes in biological
processes and physicochemical parameters. Although massive evaporation events have occurred
repeatedly throughout Earth history, their biogeochemical cycles and global impact remain poorly
understood. Here, we provide the first nitrogen isotopic data for nutrients and chloropigments from
modern shallow hypersaline environments (solar salterns, Trapani, Italy) and apply the obtained
insights to δ15N signatures of the Messinian salinity crisis (MSC) in the late Miocene. Concentrations
and δ15N of chlorophyll a, bacteriochlorophyll a, nitrate, and ammonium in benthic microbial mats
indicate that inhibition of nitrification suppresses denitrification and anammox, resulting in efficient
ammonium recycling within the mats and high primary productivity. We also suggest that the release
of 15N-depleted NH3(gas) with increasing salinity enriches ammonium 15N in surface brine (≈34.0‰).
Such elevated δ15N is also recorded in geoporphyrins isolated from sediments of the MSC peak (≈20‰),
reflecting ammonium supply sufficient for sustaining phototrophic primary production. We propose
that efficient nutrient supply combined with frequent bottom-water anoxia and capping of organic-rich
sediments by evaporites of the Mediterranean MSC could have contributed to atmospheric CO2
reduction during the late Miocene.This study was partly supported by a Japan Society for the Promotion of
Science (JSPS) Research Fellowship (16J07844) to YI, Grants-in-Aid (16H02236) and the JAMSTEC President
Fund to NO