The Pennsylvania State University The Graduate School Department of Geosciences INTERPRETING NITROGEN ISOTOPE EXCURSIONS IN THE SEDIMENTARY RECORD A Dissertation in Geosciences and Biogeochemistry by James M. Fulton 2010 James M. Fulton Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2010 The dissertation of James Mark Fulton was reviewed and approved* by the following: Michael A. Arthur Professor of Geosciences Dissertation Co-Advisor Co-Chair of Committee Katherine H. Freeman Professor of Geosciences Associate Head for Graduate Programs and Research in Geosciences Dissertation Co-Advisor Co-Chair of Committee Lee R. Kump Professor of Geosciences John M. Regan Associate Professor of Environmental Engineering *Signatures are on file in the Graduate School iii ABSTRACT This dissertation presents an examination of the biological and chemical processes that determine the nitrogen stable-isotope compositions of organic matter (OM)-rich sediments. Using the Black Sea and Fayetteville Green Lake (FGL), NY as natural laboratories, I evaluate processes that lead to low 15N values of phytoplankton and sediments in anoxic basins. I synthesize sedimentary profiles of bulk N and C stable isotope values with down-core pigment distributions and pigment-specific 15N and 13C values to infer ecological changes responsible for variability in sedimentary 15N values. The primary goal of this research is to test the hypothesis that cyanobacterial N2 fixation is responsible for black shale 15N values that are near and below 0‰. Oceanic anoxia has been prevalent during specific times in geological history. These intervals often are associated with broadly distributed deposits of OM-rich black shales. Widespread anaerobic ammonium oxidation (anammox) and denitrification in anoxic waters near the chemocline (interfaces between oxygenated and anoxic waters) are expected to have led to fixed-N deficiencies that favor cyanobacterial N2 fixation. Such conditions have also been identified in modern meromictic water bodies, most notably the Black Sea. I present sedimentary scytonemin data from the Black Sea that indicate that cyanobacterial growth in the Holocene Black Sea was variable and responded to climate-induced changes in salinity stratification. The sediment intervals 15 with scytonemin also have low Ntot values, indicative of cyanobacteria using N2 as a substrate. Green sulfur bacterial (GSB) pigments in Black Sea sediments correlate inversely with scytonemin, leading to a phytoplankton productivity model whereby iv strong density stratification inhibits mixing of high phosphate, low N:P waters to the sea surface. This model may be applied to ancient marine settings, such as the Paleotethys Ocean during the Permian-Triassic oceanic anoxic event. FGL has a shallow (~20 m) chemocline that allows purple sulfur bacteria (PSB) to thrive. This compares with a Black Sea chemocline at 80-100 m, which allows GSB growth but inhibits PSB. A similar shallow chemocline may have been present in the Mesoproterozoic ocean, as PSB biomarkers have been identified in the ancient sediments. Pigments from PSB and GSB are abundant in the chemocline and sediments of FGL. Sedimentary intervals with high PSB pigment concentrations correlate with low bulk 15 13 N and Corg values, supporting my assertion that an increased proportion of PSB biomass causes the low stable-isotope values. Low water-column particulate 15N and 13C values at the chemocline support this model. I also analyzed 13C and 15N values of specific pigments to examine responses of chemocline productivity to elevated mixolimnion productivity. These data demonstrate that sedimentary PSB and GSB pigments were derived from the chemocline, and they provide a ~500-year record of 13 15 CDIC surface-deep gradients and deep water ammonium N values. v TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................... viii LIST OF TABLES ....................................................................................................... x ACKNOWLEDGEMENTS ......................................................................................... xi Chapter 1 Introduction: Modern Analogues for Nitrogen Cycling in Ancient Anoxic Oceans ...................................................................................................... 1 1.1 Introduction .................................................................................................... 1 1.2 Nitrogen Isotope Excursions in Black Shales ................................................ 3 1.3 Ecosystem Responses to Redox-Stratification .............................................. 5 1.4 Dissertation Outline and Publication Information ......................................... 7 1.5 Cited References ............................................................................................ 10 Chapter 2 Scytonemin Production and Nitrogen Fixation in the Holocene Black Sea ......................................................................................................................... 17 Abstract ................................................................................................................. 17 2.1 Introduction .................................................................................................... 18 2.2 Methods ......................................................................................................... 20 2.2.1 Sediments ............................................................................................ 20 2.2.2 Pigments .............................................................................................. 20 2.2.3 Nitrogen Isotopes ................................................................................. 21 2.3 Results............................................................................................................ 22 2.4 Discussion ...................................................................................................... 25 2.4.1 Scytonemin Sources ............................................................................ 25 2.4.2 Ecology of Scytonemin Production in the Black Sea .......................... 26 2.4.3 Modern Analogue to Ancient ―Anoxic Events‖ .................................. 29 2.5 Cited References ............................................................................................ 31 Chapter 3 Black Sea Nitrogen Cycling and Phytoplankton 15N Signal Preservation during the Holocene ......................................................................... 38 Abstract ................................................................................................................. 38 3.1 Introduction .................................................................................................... 39 3.2 Methods ......................................................................................................... 43 3.2.1 Samples ................................................................................................ 43 3.2.2 N and C Stable Isotopes ..................................................................... 44 3.2.3 N and C Compositions ......................................................................... 45 vi 3.2.4 Pigments .............................................................................................. 46 3.2.5 Pigment Isotope Measurements ........................................................... 47 3.3 Results............................................................................................................ 48 3.3.1 Organic Carbon ................................................................................... 48 3.3.2 Sedimentary Nitrogen .......................................................................... 49 3.3.3 Pigments .............................................................................................. 51 3.4 Discussion ...................................................................................................... 52 3.4.1 Sedimentary Nitrogen .......................................................................... 52 3.4.2 Compound-Specific N Isotopes ........................................................... 55 3.4.3 Nitrogen Fixation ................................................................................. 60 3.4.4 Conceptual Model for N Isotope Distributions ................................... 62 3.5 Summary ........................................................................................................ 66 3.6 Cited References ............................................................................................ 67 Chapter 4 Chemocline-Induced C and N Isotope Excursions Preserved in the Sediments of a Meromictic Lake .......................................................................... 89 Abstract ................................................................................................................. 89 4.1 Introduction .................................................................................................... 90 4.1.1 Study Site .............................................................................................. 93 4.2 Methods ......................................................................................................... 94 4.2.1 Sampling .............................................................................................. 94 4.2.2 Instrumentation