TY - JOUR
T1 - Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events
AU - Uveges, Benjamin T.
AU - Junium, Christopher K.
AU - Scholz, Christopher A.
AU - Fulton, James M.
N1 - Funding Information:
We are grateful to The National Science Foundation EAR-1455258 (CKJ) and EAR-1251946 (JMF). We would also like to thank Woo Kim, who helped with the initial sample processing and Jacqueline Corbett for core lab management. Field studies were supported by funds from the McArthur Foundation (Grant number: 11-97251-000-INP ) (CAS) and Vanoil Energy (CAS). Logistical support and guidance were provided by the Lake Kivu Monitoring Programme, and the University of Rwanda, College of Science and Technology, School of Science. We would also like to thank Prof. Jeremy Owens and an anonymous reviewer for their helpful comments and suggestions. Last, but certainly not least, we would like to thank the members of BTU's Dissertation committee Phoebe Cohen, Scott Samson, Zunli Lu, and Mark Teece, as well as Linda Ivany, Bruce Wilkinson and the rest of the Syracuse University PaleoX seminar group for all of their help and insight on this project.
Funding Information:
We are grateful to The National Science Foundation EAR-1455258 (CKJ) and EAR-1251946 (JMF). We would also like to thank Woo Kim, who helped with the initial sample processing and Jacqueline Corbett for core lab management. Field studies were supported by funds from the McArthur Foundation (Grant number: 11-97251-000-INP) (CAS) and Vanoil Energy (CAS). Logistical support and guidance were provided by the Lake Kivu Monitoring Programme, and the University of Rwanda, College of Science and Technology, School of Science. We would also like to thank Prof. Jeremy Owens and an anonymous reviewer for their helpful comments and suggestions. Last, but certainly not least, we would like to thank the members of BTU's Dissertation committee Phoebe Cohen, Scott Samson, Zunli Lu, and Mark Teece, as well as Linda Ivany, Bruce Wilkinson and the rest of the Syracuse University PaleoX seminar group for all of their help and insight on this project.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/10/15
Y1 - 2020/10/15
N2 - One of the outstanding issues in the study of nutrient dynamics during Oceanic Anoxic Events (OAEs) is the preservation of 15N-depleted nitrogen isotope signals, which are not observed in analogous modern environments. The favored mechanism for δ15N values below 0‰ is utilization of excess ammonium derived from underlying anoxic waters by primary producers. However, there are few modern examples available for testing this hypothesis, due to the overall well-oxygenated state of modern oceans. Here, we present sedimentary δ13Corg and δ15Nbulk data, as well as pigment biomarker ratios, from the sediments of Lake Kivu, a meromictic lake in East Africa. This system serves as a potential analogue for the development of strongly depleted δ15Nbulk in OAE black shales. We focus on intervals of organic carbon enrichment (sapropels) that are interpreted to have been the result of lake water column mixing events. Sediment δ13Corg and δ15Nbulk decrease by up to 6 and 4‰ respectively near the base of sapropel layers. These negative excursions provide evidence for the mixing of 13C-depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need, derived from the deeper anoxic basin of the lake. Support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status. Further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers.
AB - One of the outstanding issues in the study of nutrient dynamics during Oceanic Anoxic Events (OAEs) is the preservation of 15N-depleted nitrogen isotope signals, which are not observed in analogous modern environments. The favored mechanism for δ15N values below 0‰ is utilization of excess ammonium derived from underlying anoxic waters by primary producers. However, there are few modern examples available for testing this hypothesis, due to the overall well-oxygenated state of modern oceans. Here, we present sedimentary δ13Corg and δ15Nbulk data, as well as pigment biomarker ratios, from the sediments of Lake Kivu, a meromictic lake in East Africa. This system serves as a potential analogue for the development of strongly depleted δ15Nbulk in OAE black shales. We focus on intervals of organic carbon enrichment (sapropels) that are interpreted to have been the result of lake water column mixing events. Sediment δ13Corg and δ15Nbulk decrease by up to 6 and 4‰ respectively near the base of sapropel layers. These negative excursions provide evidence for the mixing of 13C-depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need, derived from the deeper anoxic basin of the lake. Support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status. Further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers.
KW - Oceanic Anoxic Events
KW - chemocline
KW - nitrogen cycle
KW - pigment biomarkers
KW - stable isotopes
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UR - http://www.scopus.com/inward/citedby.url?scp=85088747788&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2020.116459
DO - 10.1016/j.epsl.2020.116459
M3 - Article
AN - SCOPUS:85088747788
SN - 0012-821X
VL - 548
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
M1 - 116459
ER -