Chemical Oceanography

Homogeneous magnesium isotopic composition of seawater: an excellent geostandard for Mg isotope analysis

by Josiah Strauss

Photochemical production of ammonium in the oligotrophic Cyprus Gyre (Eastern Mediterranean)

by Georgina Spyres

Kitidis V. et al., 2006. Biogeosciences, 3, 439–449

Overview of the CYCLOPS P addition Lagrangian experiment in the Eastern Mediterranean

by Georgina Spyres

Krom M.D., et al., (2005) Deep Sea Research, 52, pp.3090-3108

Nutrient Cycling in the south east Levantine basin of the eastern Mediterranean: Results from a phosphorus starved system

by Georgina Spyres

Krom et al., 2005. Deep Sea Research II 52: 2879-2896

A preliminary methods comparison for measurement of dissolved organic nitrogen in seawater

by Georgina Spyres

2002

Dissolved organic matter fluxes at the Iberian Margin

by Georgina Spyres

http://www.bodc.ac.uk/omex/omexii-ii/report/04ab_sr.pdf

Effect of P and N addition to oligotrophic Eastern Mediterranean waters influenced by near-shore waters: A microcosm experiment

by Georgina Spyres

Kress et al., 2005. Deep-Sea Research II 52: 3054–3073

Molybdenum isotope records as a potential new proxy for paleoceanography

by Chris Siebert

British Columbian continental shelf as a source of dissolved iron to the subarctic northeast Pacific Ocean

by Jay Cullen

Evidence for bias in C/N, δ13C and δ15N values of bulk organic matter, and on environmental interpretation, from a lake sedimentary sequence by pre-analysis acid treatment methods.

by Chris Brodie

In Press - Quaternary Science Reviews

Lead Author: Dr. Chris Brodie (Hong Kong University, Hong Kong)

Co-Authors: Dr. James Casford (Durham University); Dr. Jeremy Lloyd (Durham University, UK); Prof. Melanie Leng (NIGL, UK); Dr. Timothy Heaton (NIGL, UK); Christopher Kendrick (NIGL, UK); Dr. Zong Yongqiang (Hong Kong University, Hong Kong).

ABSTRACT:
There is a known bias in C/N, d13C and d15N values of organic matter (OM) due to pre-analysis acid... more ABSTRACT:
There is a known bias in C/N, d13C and d15N values of organic matter (OM) due to pre-analysis acid treatment methods. We report here, for the first time, the results of a pre-analysis acid treatment method comparison of measured C/N, d13C and d15N values in bulk OM from a sedimentary sequence of samples to illustrate this bias. Here we show that acid treatment significantly reduces the accuracy (between method biases) and precision (within method bias) of C/N, d13C and d15N values of OM, suggesting a differential response of sample OM between methods and sample horizons, and in some cases inefficient removal of inorganic carbon. We show that different methods can significantly influence environmental interpretation in some of our sample horizons (i.e. interpretation of aquatic vs. terrestrial OM source; C3 vs. C4 vegetation). Specifically, there are unpredictable and non-linear differences between methods for C/N values in the range of ~ 1 – 100; d13C values in the range of 0.2 – 6.8 ‰ and; d15Nvalues in the range of 0.3 – 0.7 ‰. Importantly, these ranges are mostly much greater than the instrument precision (defined as the standard deviation of replicate analysis of standard reference materials; for this study, ± 0.5 for C/N values, ± 0.1 ‰ for d13C values and; ± 0.1 ‰ for d15N). The accuracy and precision of measured C/N, d13C and d15N values of bulk OM is not just dependent upon environmental variability, but on acid pre-treatment, residual inorganic carbon and organic matter state and composition. Collectively, this makes the correlation between samples prepared in different ways, including those from down core reconstructions, highly questionable.

Keywords: C/N ratios, δ13C, δ15N, organic matter; pre-analysis acid treatment methods, environmental interpretation, palaeoclimate.

Evidence for bias in measured δ15N values of terrestrial and aquatic organic materials due to pre-analysis acid treatment methods.

by Chris Brodie

Rapid Communications in Mass Spectrometry. 25, 1089 - 1099.

Lead Author: Dr. Chris Brodie (Durham University, UK; Hong Kong University, Hong Kong)

Co-Authored with Dr. Tim Heaton (NIGL, UK); Prof. Melanie Leng (NIGL, UK) Christopher Kendrick (NIGL, UK); Dr. James Casford (Durham University, UK) and; Dr. Jeremy Lloyd (Durham University, UK)

ABSTRACT:
We investigate the effect of acid treatment methods on δ15N from a range of environmental organic... more ABSTRACT:
We investigate the effect of acid treatment methods on δ15N from a range of environmental organic materials in the context of the increased application of “dual-mode” isotope analysis (the simultaneous measurement of δ13C and δ15N from the same acid treated sample). Three common methods are compared; (i) untreated samples; (ii) acidification followed by sequential water rinse (rinse method); (iii) acidification in silver capsules (capsule method). The influence of capsule type (silver and tin) on δ15N is also independently assessed (as the capsule and rinse methods combust samples in different capsule; silver and tin respectively). We find significant differences in δ15N values between methods and the precision of any one method varies significantly between sample materials and above instrument precision (> 0.3 ‰). δ15N of untreated samples did not produce the most consistent data on all sample materials. In addition, the capsule type appears to influence the measured δ15N value of some materials, particularly those combusted only in silver capsules. We also compare the new δ15N data with previously published δ13C on the same materials. The response of δ13C and δ15N within and between methods and sample materials to acidification appears to be relatively disproportionate, which can influence environmental interpretation of the measured data. In addition, statistical methods used to estimate inorganic nitrogen are shown to be seriously flawed.

Keywords: acid treatment, capsule method, rinse method, acid method comparison, δ15N, inorganic nitrogen.

Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation techniques

by Chris Brodie

Chemical Geology. 282, 67 - 83.

Lead Author: Dr. Chris Brodie (Durham University, UK; Hong Kong University, Hong Kong)

Co-Authors: Prof. Melanie Leng (NIGL, UK), Dr. James Casford (Durham University, UK), Christopher Kendrick (NIGL, UK), Dr. Jeremy Lloyd (Durham University, UK), Dr. Zong Yongqiang (Hong Kong University, Hong Kong), Prof. Michael Bird (James Cook University, Australia).

ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the... more ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the reliability of organic carbon [C] and nitrogen [N], and carbon isotope (δ13C) values on a range of terrestrial and aquatic, modern and geological environmental materials. We investigated the 3 most common methods; (i) acidification followed by sequential deionised water rinses (“rinse method”); (ii) acidification in silver capsules (“capsule method”); and (iii) acidification by exposure to an acid vapour (“fumigation method”). We also investigated the effect of sample size and capsule type (silver and tin) on C/N ratio and δ13C values. We find (i) %C, %N, C/N and δ13C showed significant within and between method variability; (ii) disproportionate and non-linear offsets of %C, %N and C/N values after acidification within and between methods and within and between sample materials; (iii) that alterations in %C did not necessarily manifest themselves in shifts in δ13C, and vice-versa; (iv) small (~ 90 μg C) sample sizes showed consistent overestimations and inaccuracies after acidification; (v) The effect of capsule type was not significant on most samples, but did show a notable effect on our aquatic materials, generally increasing %C and %N, and producing depleted δ13C values. These findings raise cause for concern on the interpretative nature of C/N ratios and their support for carbon isotope values. The comparability between laboratories (different preparation methods) and environmental settings (amount, type and nature of OM) are also likely to be problematic. We conclude that the response of C and N concentrations in organic matter to acid treatment in environmental materials is neither negligible nor systematic.

Keywords: δ13C; C/N ratio; Method comparison; Rinse method; Capsule method; Fumigation method; environmental reconstruction