Assessments of Marine Denitrification Using 15N Natural Abundance

1
Assessments of Marine DenitrificationUsing 15N
Natural Abundance

• Geography of open ocean denitrification
• d15N signal creation and preservation in
  sediments
• Sensitivity of denitrification to climate change
  over the last 60 ka and its implications
• New records for eutrophication effects over the
  last 300 yrs

Acknowledgements Matt Higginson, Tim Herbert ,
Matt McIlvin, Rehka Singh, Peng Feng, Tim
Elington, Steve DHondt, ODP, WHOI, OSU core
curators, NSF
2
N-Cycling
suboxia organic C, NO3-
Classic denitrification eq. (CH2O)106(NH3)16H3
PO4 94.4 HNO3 106 CO2 55.2 N2 177.2 H2O
H3PO4 Organic N 14.5 of N2 Produced
oligrotrophy warm T, stability Fe??
3
Locations of denitrification records
4
Global Nitrate Anomaly (N)
5
Water Column Denitrification Effects(N down,
d15N up)
1) N decreases 2) d15N increases, e 20 to 30

6
Denitrification Produced Isotopic Fractionation
in the Arabian Sea
7
Rayleigh Relationships
Dd15N -e x ln f
Dd15N e e x f
8
Steady State Marine d15N
d15N Input (-2) fwc x (Avg. d15N - ewc)
(fwc-1) x (Avg. d15N - esed)
d15N-N2 fix -2 esed den 0
9
Preservation of d15N Signal in Marine Sediments
10

Close coupling between Arabian Sea
denitrification and climate change
11
Co-occurrence with productivity and suboxiaa
detailed history at mm-scale (decadal) resolution
12
3 Denitrification Records
13
Composite Records
14
A Eutrophication Indicator
Surface Sediment d15N ()
15
LIS Eutrophication History
16
Chesapeake Bay Eutrophication(Bratton et al.
2003, GCA)
17
Quick Summary

• 15N natural abundance is a sensitive indicator
  for marine water column denitrification in the
  modern as well as in the past (101 to 106 yrs)
• In the modern, has the potential for quantitative
  verification of flux estimates through isotopic
  mass balance
• In the modern, can quantify partitioning of
  denitrification between sediments and water
  column (both locally and globally)
• In the past, quantitative reconstructions of
  regional water column denitrification requires
  development of adequate physical/biogeochemical
  models
• In the past, reconstructing changes in the global
  marine N balance and partitioning between
  sediment and water column denitrification
  requires reliable records from organic-poor
  sediments.