See more from this Division: Topical Sessions
See more from this Session: From Mud to Mudrock: Use of Modern Depositional Settings as Analogs for the Interpretation of Ancient Mudrocks
Abstract:
We have previously determined that the nitrogen isotopic value of bulk sediment could possibly serve as a proxy for the redox state of the water column at the time of deposition, and proposed a correlation between δ15N and O2 concentrations. The relatively fast and extreme changes in water column redox chemistry in the Black Sea on glacial-interglacial time scales provide an opportunity to test our model. The Black Sea is unique in that the water column switches from an anoxic, stratified marine water body in the interglacial periods to an oxic freshwater lake in glacial phases in a cyclical pattern.
Our data indicate that higher δ15N values occur during the transition from one redox end-member to another, implying a relative increase in denitrification, while the periods of fully oxic and completely anoxic conditions are characterized by low sedimentary δ15N, due to predominant nitrification and complete nitrate utilization, respectively. This study strongly suggests that the pre-anthropogenic nitrogen cycle in the Black Sea was strongly dependent on the oxygen content of the water column on glacial-interglacial time scales, and that the changes in nitrogen cycling as a result of changes in redox can be identified in the sedimentary record.
See more from this Division: Topical Sessions
See more from this Session: From Mud to Mudrock: Use of Modern Depositional Settings as Analogs for the Interpretation of Ancient Mudrocks