Calibrating bulk and amino acid δ13C and δ15N isotope ratios between bivalve soft tissue and shell for paleoecological reconstructions

Organic Phases in Bivalve (Arctica Islandica) Shells: Their Bulk and Amino Acid Nitrogen Stable Isotope Compositions

“…The present study also revealed inter‐specimen variations in BSIA‐δ 15 N values of original shell organics (i.e., raw‐OM of the Control group), that is, Shell C showed lower δ 15 N values than the other two shells. As bivalves mainly filter phytoplankton from the water (Newell, 2004), δ 15 N values in primary producers (i.e., nitrogen isotope baseline) that register changes in environmental nitrogen sources influence the δ 15 N values in both soft and hard tissues of bivalves (e.g., Graniero et al., 2021; Vokhshoori et al., 2022). Given that we have measured the homogenized whole valve of each specimen, the inter‐specimen variation in shell nitrogen isotope compositions could be attributed to differences in the time intervals during which the shells formed.…”

“…Many bivalves are sessile residents that filter particulate organic matter (OM) from the ambient water and integrate such resources into their soft tissues and shell (Newell, 2004; O’Donnell et al., 2003). Unlike the soft tissues, shell OM is not continuously renewed and turned over by the metabolism but preserves temporally constrained information on changes in the food sources (Graniero et al., 2016; O’Donnell et al., 2003; Vokhshoori et al., 2022), that is, digested algae and bacteria as well as organic detritus deriving from decayed organisms belonging to higher trophic positions. Stable nitrogen isotope (δ 15 N) values of bulk tissues (bulk stable isotope analysis, BSIA) [BSIA‐δ 15 N] can provide important insights into the nitrogen sources (dissolved inorganic nitrogen, DIN) and the trophic position (TP) of organisms (Fry, 2006) with the underlying principals that (a) δ 15 N DIN values are reflected in primary producers (the so‐called nitrogen isotope baseline) (Post, 2002) and (b) an average increase of 3–4 ‰ occurs during each trophic transfer (Deniro & Epstein, 1981; Minagawa & Wada, 1984).…”

“…Stable nitrogen isotope (δ 15 N) values of bulk tissues (bulk stable isotope analysis, BSIA) [BSIA‐δ 15 N] can provide important insights into the nitrogen sources (dissolved inorganic nitrogen, DIN) and the trophic position (TP) of organisms (Fry, 2006) with the underlying principals that (a) δ 15 N DIN values are reflected in primary producers (the so‐called nitrogen isotope baseline) (Post, 2002) and (b) an average increase of 3–4 ‰ occurs during each trophic transfer (Deniro & Epstein, 1981; Minagawa & Wada, 1984). BSIA‐δ 15 N values of shell OM extracted from whole valves, shell fragments or individual annual growth increments can provide information on natural variations of the nitrogen isotope baseline in time and space (e.g., Graniero et al., 2021; Schöne & Huang, 2021; Vokhshoori et al., 2022) as well as nutrient and pollutant loadings affecting the aquatic biogeochemistry (e.g., Black et al., 2017; Kovacs et al., 2010; Oczkowski et al., 2016).…”

“…Many bivalves are sessile residents that filter particulate organic matter (OM) from the ambient water and integrate such resources into their soft tissues and shell (Newell, 2004;O'Donnell et al, 2003). Unlike the soft tissues, shell OM is not continuously renewed and turned over by the metabolism but preserves temporally constrained information on changes in the food sources (Graniero et al, 2016;O'Donnell et al, 2003;Vokhshoori et al, 2022), that is, digested algae and bacteria as well as organic detritus deriving from decayed organisms belonging to higher trophic positions. Stable nitrogen isotope (δ 15 N) values of bulk tissues (bulk stable isotope analysis, BSIA) [BSIA-δ 15 N] can provide…”

“…While BSIA-δ 15 N have limitations in the food web reconstruction, for instance, the large variability in isotope values of primary producers (e.g., Vizzini & Mazzola, 2003) and isotopic fractionations through the trophic transfer (e.g., Caut et al, 2009), CSIA-δ 15 N AA enables more precise estimates of the nitrogen isotope baseline and the TP (see review by Ohkouchi et al (2017)). Although CSIA-δ 15 N AA of shell organics is still in its infancy, vast potential has been revealed by using this technique to reconstruct organic sources and the nitrogen isotope baseline back in time (Ellis, 2012;Misarti et al, 2017;Vokhshoori et al, 2022) at an unprecedented temporal resolution (Huang, Wu, & Schöne, 2023).…”