Impact of sample pretreatment on the measured element concentrations in the bivalveArctica islandica

Abstract

[1] Correlating metal to calcium (Me/Ca) ratios of marine biogenic carbonates, such as bivalve shells, to environmental parameters has led to contradictory results. Biogenic carbonates represent complex composites of organic and inorganic phases. Some elements are incorporated preferentially into organic phases, and others are incorporated into inorganic phases. Chemical sample pretreatment to remove the organic matrix prior to trace element analysis may increase the applicability of the investigated proxy relationship, though its efficiency and side effects remain questionable. We treated inorganic calcium carbonate and bivalve shell powder (Arctica islandica) with eight different chemical treatments including H 2 O 2 , NaOH, NaOCl, and acetone and analyzed the effects on (1) Me/Ca ratios (Sr/Ca, Mg/Ca, Ba/Ca, and Mn/Ca), (2) organic matter (≈N) content, and (3) mineralogical composition of the calcium carbonate. The different treatments (1) cause element and treatment specific changes of Me/Ca ratios, (2) vary in their efficiency to remove organic matter, and (3) can even alter the phase composition of the calcium carbonate (e.g., formation of Ca(OH) 2 during NaOH treatment). Among all examined treatments there were none without any side effects. In addition, certain Me/Ca changes we observed upon chemical treatment contradict our expectations that lattice-bound elements (Sr and Ba) should not be affected, whereas non-lattice-bound elements (Mg and Mn) should decrease upon removal of the organic matrix. For instance, we observe that NaOCl treatment did not alter Sr/Ca ratios but caused unexpected changes of the Mg/Ca ratios. The latter demonstrates that the buildup of complex biogenic composites like the shell of Arctica islandica are still poorly understood.

Microchemistry of juvenile Mercenaria mercenaria shell: implications for modeling larval dispersal

“…Importantly, recent work by Krause-Nehring et al (2011) demonstrates that treatment of biogenic carbonate with (31%) H 2 O 2 influences the elemental concentrations present. This is problematic for the interpretation of investigations concerning the chemical composition of biominerals that have been cleaned with H 2 O 2 .…”

Geochemical and microstructural characterisation of two species of cool-water bivalves (<i>Fulvia tenuicostata</i> and <i>Soletellina biradiata</i>) from Western Australia

“…tion in coral cores (Nategaal et al, 2012). Krause-Nehring et al (2011) performed their study on powdered, pre-cleaned shells (manual removal of the periostracum) and found very little effect. In our study, where intact shells were pretreated with NaOCl, we suggest that the geochemical and crystallographic composition of the bivalves studied here was not significantly altered despite having some hypochlorite solution percolate through.…”

“…According to Krause-Nehring et al (2011), the treatment of biogenic calcium carbonate to remove organic matter may have an impact on the elemental and crystallographic composition in the bivalve Arctica islandica. The effects of sodium hypochlorite (NaOCl) pretreatment (also used in our study) on A. islandica shell powder were insignificant compared to other treatments tested in that study.…”

Earth System Science: Bridging the Gaps between Disciplines

“…The efficiency of this approach, however, remains questionable and chemical treatment itself may alter the outcome of subsequent Me/Ca analysis (Love and Woronow, 1991). Thus, we first examine the efficiency of eight chemical treatments and their impact on the carbonate composition (for further details see Krause-Nehring et al (2011)) (Effect of sample preparation).…”