Stable isotope data from tests of four planktonic foraminifer species in core tops on the Rio Grande Rise (RIO) fail a field test of reproducibility until corrections are made for various environmental effects. The regionally uniform and strongly stratified surface ocean hydrography across RIO allows the identification of causes of variability in δ18O and δ13C data in addition to the effects of surface ocean temperature and nutrient content. A previously calibrated calcite dissolution proxy indicates that the dissolution of foraminifer shells in sediments has no effect on δ18O and δ13C in tests of foraminifers from core tops on RIO. Furthermore, vital effects within and among foraminifer species are not sufficient to explain the large variability of δ18O and δ13C data observed on RIO. Instead, correctly estimating species‐specific habitat depth ranges and adjusting δ13C values for ocean/atmosphere carbon exchange are necessary to accurately reconstruct the hydrography of surface waters on RIO.
To examine N-isotope ratios (15N/14N) in tissues and shell organic matrix of bivalves as a proxy for natural and anthropogenic nutrient fluxes in coastal environments,
- PAR ID:
- 10018353
- Publisher / Repository:
- PeerJ
- Date Published:
- Journal Name:
- PeerJ
- Volume:
- 4
- ISSN:
- 2167-8359
- Page Range / eLocation ID:
- Article No. e2278
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Rationale The use of secondary ion mass spectrometry (SIMS) to perform micrometer‐scale
in situ carbon isotope (δ13C) analyses of shells of marine microfossils called planktic foraminifers holds promise to explore calcification and ecological processes. The potential of this technique, however, cannot be realized without comparison to traditional whole‐shell δ13C values measured by gas source mass spectrometry (GSMS).Methods Paired SIMS and GSMS δ13C values measured from final chamber fragments of the same shell of the planktic foraminifer
Orbulina universa Results Paired analyses of cleaned fragments of cultured specimens (
n = 7) yield no SIMS–GSMS δ13C difference. However, paired analyses of untreated (n = 18) and cleaned (n = 12) fragments of fossil shells yield average Δ13CSIMS‐GSMSvalues of 0.8‰ and 0.6‰ (±0.2‰, 2 SE), respectively, while vacuum roasting of fossil shell fragments (n = 11) removes the SIMS–GSMS δ13C difference.Conclusions The noted Δ13CSIMS‐GSMSvalues are most likely due to matrix effects causing sample–standard mismatch for SIMS analyses but may also be a combination of other factors such as SIMS measurement of chemically bound water. The volume of material analyzed via SIMS is ~105times smaller than that analyzed by GSMS; hence, the extent to which these Δ13CSIMS‐GSMSvalues represent differences in analyte or instrument factors remains unclear.
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