Stable Isotopes of Nitrogen in Fossil Cladoceran Exoskeletons: Implications for Nitrogen Sources in the Central Baltic Sea During the Past Century |
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Authors: | Ulrich Struck Maren Voss Bodo von Bodungen Nicolai Mumm |
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Institution: | (1) Institut für Ostseeforschung Warnemünde, Seestrasse 15, D-18119 Rostock, Germany, DE;(2) Ocean Sciences Centre, Memorial University fo Newfoundand, st. John's, Newfoundland, A1C 5S7, Canada, CA |
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Abstract: | 15 N of bulk sediment, organic carbon concentrations, and abundances of exoskeletons of Bosmina
longispina
maritima in the sediment, the data are used to evaluate significant sources of nitrogen in the food web over the past century. Nitrogen
isotopic composition of bulk sediments ranges from 2.5 to 4.5?, that of exokeletons varies between 0.4 and 6.2?. The two are
positively correlated. A marked increase in the abundance of Bosmina since 1965 (from less than 500 specimen to more than 5000 specimen cm3 of sediment) is correlated with a significant increase in sedimentary organic carbon concentrations (from 4% to more than
10%). The isotopic data do not identify increased land-derived nitrate as the dominant nitrogen source fuelling the increase.
Instead, we postulate that nitrogen fixation by diazotrophic bacteria has been one of the larger sources of nitrogen in the
Baltic Sea, as it is today.
Received: 29 April 1998 / Accepted in revised form: 13 August 1998 |
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