Latitudinal variations in δ30Si and δ15N signatures along the Peruvian shelf : Quantifying the effects of nutrient utilization versus denitrification over the past 600 years
Doering, Kristin LU
; Ehlert, Claudia
; Martinez, Philippe
; Frank, Martin
and Schneider, Ralph
(2019)
In Biogeosciences
16(10).
p.2163-2180
- Abstract
The stable sedimentary nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and the silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification, causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO-3) upwelled to the surface. Such conditions are found in the oxygen minimum zone off the coast of Peru, where, at present, an increase in subsurface δ15NO-3 from north... (More)
The stable sedimentary nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and the silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification, causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO-3) upwelled to the surface. Such conditions are found in the oxygen minimum zone off the coast of Peru, where, at present, an increase in subsurface δ15NO-3 from north to south along the shelf is observed due to ongoing denitrification within the poleward-flowing subsurface waters, while the δ30Si signature of silicic acid (δ30Si.OH/4) at the same time remains unchanged. Here, we present three new δ30SiBSi records between 11 and 15 S and compare these to previously published δ30SiBSi and δ15Nbulk records from Peru covering the past 600 years. We present a new approach to calculate past subsurface δ15NO-3 signatures based on the direct comparison of δ30SiBSi and δ15Nbulk signatures at a latitudinal resolution for different time periods. Our results show that, during the Current Warm Period (CWP, since 1800 CE) and prior shortterm arid events, source water δ15NO-3 compositions have been close to modern values, increasing southward from 7 to 10 ‰ (between 11 and 15 S). In contrast, during the Little Ice Age (LIA) we calculate low δ15NO-3 values between 6 ‰ and 7.5 ‰. Furthermore, the direct δ30SiBSi versus δ15Nbulk comparison also enables us to relate the short-term variability in both isotope compositions to changes in the ratio of nutrients (NO-3 V Si.OH/4) taken up by different dominating phytoplankton groups (diatoms and non-siliceous phytoplankton) under the variable climatic conditions of the past 600 years. Accordingly, we estimate a shift from a 1 V 1 (or 1 V 2) ratio during the CWP and a 2 V 1 (up to 15 V 1) ratio during the LIA, associated with a shift from overall high nutrient utilization to NO-3-dominated (and thus non-siliceous phytoplankton) utilization.
(Less)
- author
- Doering, Kristin
LU
; Ehlert, Claudia
; Martinez, Philippe
; Frank, Martin
and Schneider, Ralph
- publishing date
- 2019-05-23
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- silicon isotopes, Nitrogen Isotopes, Peru upwelling system
- in
- Biogeosciences
- volume
- 16
- issue
- 10
- pages
- 18 pages
- publisher
- Copernicus GmbH
- external identifiers
-
- scopus:85066108853
- ISSN
- 1726-4170
- DOI
- 10.5194/bg-16-2163-2019
- language
- English
- LU publication?
- no
- additional info
- Funding Information: Acknowledgements. This work is a contribution of the Collaborative Research Centre 754 “Climate-Biogeochemistry interactions in the Tropical Ocean” (https://www.sfb754.de/, last access: 21 May 2019), which is supported by the Deutsche Forschungsgemeinschaft (DFG). Publisher Copyright: © 2019 Author(s).
- id
- a3160759-7d35-4cbc-a676-2b7a64dfd5d7
- date added to LUP
- 2022-09-05 12:20:39
- date last changed
- 2022-09-15 21:42:46
@article{a3160759-7d35-4cbc-a676-2b7a64dfd5d7,
abstract = {{<p>The stable sedimentary nitrogen isotope compositions of bulk organic matter (δ<sup>15</sup>Nbulk) and the silicon isotope composition of diatoms (δ<sup>30</sup>SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ<sup>15</sup>Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification, causing an increase in the subsurface δ<sup>15</sup>N signature of dissolved nitrate (δ<sup>15</sup>NO<sup>-</sup><sub>3</sub>) upwelled to the surface. Such conditions are found in the oxygen minimum zone off the coast of Peru, where, at present, an increase in subsurface δ<sup>15</sup>NO-3 from north to south along the shelf is observed due to ongoing denitrification within the poleward-flowing subsurface waters, while the δ<sup>30</sup>Si signature of silicic acid (δ<sup>30</sup>Si.OH/4) at the same time remains unchanged. Here, we present three new δ<sup>30</sup>SiBSi records between 11 and 15 S and compare these to previously published δ<sup>30</sup>SiBSi and δ<sup>15</sup>Nbulk records from Peru covering the past 600 years. We present a new approach to calculate past subsurface δ<sup>15</sup>NO-3 signatures based on the direct comparison of δ<sup>30</sup>SiBSi and δ<sup>15</sup>Nbulk signatures at a latitudinal resolution for different time periods. Our results show that, during the Current Warm Period (CWP, since 1800 CE) and prior shortterm arid events, source water δ<sup>15</sup>NO-3 compositions have been close to modern values, increasing southward from 7 to 10 ‰ (between 11 and 15 S). In contrast, during the Little Ice Age (LIA) we calculate low δ<sup>15</sup>NO-3 values between 6 ‰ and 7.5 ‰. Furthermore, the direct δ<sup>30</sup>SiBSi versus δ<sup>15</sup>Nbulk comparison also enables us to relate the short-term variability in both isotope compositions to changes in the ratio of nutrients (NO-3 V Si.OH/4) taken up by different dominating phytoplankton groups (diatoms and non-siliceous phytoplankton) under the variable climatic conditions of the past 600 years. Accordingly, we estimate a shift from a 1 V 1 (or 1 V 2) ratio during the CWP and a 2 V 1 (up to 15 V 1) ratio during the LIA, associated with a shift from overall high nutrient utilization to NO<sup>-</sup><sub>3</sub>-dominated (and thus non-siliceous phytoplankton) utilization.</p>}},
author = {{Doering, Kristin and Ehlert, Claudia and Martinez, Philippe and Frank, Martin and Schneider, Ralph}},
issn = {{1726-4170}},
keywords = {{silicon isotopes; Nitrogen Isotopes; Peru upwelling system}},
language = {{eng}},
month = {{05}},
number = {{10}},
pages = {{2163--2180}},
publisher = {{Copernicus GmbH}},
series = {{Biogeosciences}},
title = {{Latitudinal variations in δ30Si and δ15N signatures along the Peruvian shelf : Quantifying the effects of nutrient utilization versus denitrification over the past 600 years}},
url = {{http://dx.doi.org/10.5194/bg-16-2163-2019}},
doi = {{10.5194/bg-16-2163-2019}},
volume = {{16}},
year = {{2019}},
}