Distribution and nature of incorporation of trace elements in modern aragonitic corals*

Abstract

The objective of this study is to locate as closely as possible the sites of strontium, magnesium, sodium, and potassium in modern aragonitic corals, specifically whether these cations are adsorbed, or are substituted in the carbonate lattice or are incorporated in organic components. In addition to locating the sites of each of these four elements we wanted to find out quantitatively how much of each element occurs at each site. The experiments in this study are based on the dissolution rate of aragonite in distilled water and on the substitution of strontium and magnesium by calcium and sodium. Special attention has been given to the occurrence of strontium, magnesium, sodium, and potassium in the organic components of the corals. The main site for strontium in the corals is in the aragonite lattice. Twenty‐five per cent of the total magnesium occurs in adsorbed sites and in organic compounds. The rest of the magnesium may be located in the aragonite lattice, but it is easily removed by repeated leaching or by replacement with calcium ions. Another possibility is that magnesium may occur in a dispersed mineral phase more soluble than aragonite because magnesium was released at a higher Mg to Ca ratio than is found in the solid coral; also because no local concentration of magnesium could be detected with an electron microprobe. About 12% of the total sodium is in adsorbed sites and is included in the organic compounds. The rest of the sodium might be in the lattice replacing calcium, but the low total exchange capacity is not enough to provide the needed charge balance. Another possibility is that sodium is located in a proposed mineral phase. Potassium is in adsorbed sites and incorporated in the organic compounds to an extent greater than all the other elements studied (30% of the total potassium), but again the evidence suggests that the remaining potassium is in a proposed mineral phase. Calcite is detected on the surfaces of aragonite corals after 5 months in the substitution experiment. The change of argonite to calcite took place after the inhibitor magnesium was exchanged from the surface sites and replaced by calcium. The organic compounds in corals contain small amounts of strontium, magnesium, sodium and potassium. Strontium is preferentially enriched in the organic compounds over magnesium.

Na/Ca variability in coral skeletons

“…It is known that significant amounts of Na and Mg are adsorbed, as ionic forms, on the surface of coral skeletons and that the ions adsorbed on the skeletal surface can be removed by treating the skeletons with distilled/ deionized water (DDW) or a very weak acid solution (e.g., Amiel et al, 1973;Yoshioka et al, 1985Yoshioka et al, , 1986Mitsuguchi et al, 2001;Watanabe et al, 2001b). Our element/Ca ratio data are probably completely free from the influence of such adsorption, because we treated coral samples with DDW, very dilute HNO 3 and H 2 O 2 , under ultrasonic agitation (see Section "Materials and Methods").…”

“…The slab was ultrasonically cleaned in distilled/ deionized water (DDW) and dried, then X-rayed. The Xradiography revealed coral skeletal growth patterns and Element/Ca ratio General range (mmol/mol) References Na/Ca 15−24 Amiel et al (1973), Land and Hoops (1973), Polyakov and Krasnov (1976), Swart (1981), Oomori et al (1982), Busenberg and Plummer (1985), Kitano (1990), Bar-Matthews et al (1993), Tsukamoto and Tsukamoto (1995), Mitsuguchi et al (2001), Ramos et al (2004) Sr/Ca 8.0−10.0 Weber (1973), Polyakov and Krasnov (1976), Goreau (1977), Smith et al (1979), Oomori et al (1982), Schneider and Smith (1982), Beck et al (1992), de Villiers et al (1994, Fallon et al (1999Fallon et al ( , 2003, Gagan et al S/Ca 4.0−10.0 Tokuyama et al (1972), Oomori et al (1982), Busenberg and Plummer (1985), Kitano (1990), Bar-Matthews et al (1993), Tsukamoto and Tsukamoto (1995) F/Ca 3.0−7.0 Carpenter (1969), Ohde et al (1978), Ohde and Ramos (2004), Ramos et al (2005) Mg/Ca 2.5−6.5 Chave (1954), Weber (1974), Goreau (1977), Oomori et al (1982), Mitsuguchi et al (1996Mitsuguchi et al ( , 2001Mitsuguchi et al ( , 2003Mitsuguchi et al ( , 2008, Sinclair et al (1998), Fallon et ...…”

Impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in Porites corals

“…The sequence of preference with respect to dissolution in seawater was Mg > Ca > Sr [Schroeder, 1969]. Amiel et al [1973] also found incongruent dissolution for Mg/Ca but reported congruent dissolution for Sr/Ca. Recently, incongruent dissolution of Mg, Sr, and Na relative to Ca from powered coral aragonite has been observed in laboratorybased, freshwater-leaching experiments [Fairchild and Killawee, 1995;I.…”

Trace metals in contemporary and seventeenth-century Galapagos coral: Records of seasonal and annual variations

“…TRACE METAL CONCENTRATIONS in coral skeletal aragonite have been suggested to reflect concentmtions in surface seawater (AMIEL et al, 1973;SCHNEIDER and SMITH, 1982;HOWARD and BROWN, 1984;SHEN, 1986;SHEN and BOYLE, 1988). Banded aragonitic corals have been useful recorders of surface water composition changes over time because annual and sub-annual sections can be assigned ages based on growth patterns.…”