Geochemical and Microstructural Signals in Giant ClamTridacna maximaRecorded Typhoon Events at Okinotori Island, Japan

Abstract

To validate the usability of the giant clam shell as a recorder of short‐term environmental changes such as typhoons, we collected a live Tridacna maxima from Okinotori Island, Japan, on 15 June 2006. Growth increment thickness, stable isotope ratio (δ18Oshell, δ13Cshell), and the barium/calcium ratio (Ba/Ca) in the T. maxima shell sample were measured and compared to Okinotori Island instrumental environmental data. In the outer layer of the shell sample, there were 365 ± 6 growth increments per year, as estimated by the δ18Oshell profile compared with sea surface temperature. The growth increments in the specimen were formed daily, and thus, we can determine the date of the sampling points of δ18Oshell, δ13Cshell and the Ba/Ca ratio by counting growth increments. After typhoon approach, there is a decrease in increment thickness and some disturbed growth increments. The positive peaks in the shell Ba/Ca ratio and δ18Oshell corresponded to lower sea surface temperature caused by typhoons. These results indicated that the microstructural and geochemical record in Tridacna maxima shells could be useful for detecting past typhoon events.

Extreme weather events recorded by daily to hourly resolution biogeochemical proxies of marine giant clam shells

“…S12 for dating results of collected subfossil shells from SCS). Meanwhile, using the oxygen isotope and elements/ Ca, the fossil shells can provide monthly to decadal mean climatic conditions of shell growth stage and distinguish different seasons (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). The previous monthly resolution climate records, together with the daily to hourly proxy records developed in the present study (see SI Appendix, Figs.…”

“…The strong wind, high sea wave action, ocean surface cooling, and rainy and cloudy conditions caused by TCs (SI Appendix, Figs. S2 and S8) would hinder the growth of Tridacna, resulting in a decrease in the daily growth increment (24). Thus, the rapid decreases of DGR of the Tridacna shell during the summer−autumn periods have the potential to be used as a proxy of TC activity.…”

“…The vertical distributions of oceanic trace nutrient elements have an increased concentration from the surface to the subsurface (24,26). The enhancement of vertical mixing during the TC activities around the North Reef could bring Fe-enriched subsurface seawater to the surface, leading these elements to rise abruptly in the surface seawater and then be recorded in the daily layer of the Tridacna shell (24,(26)(27)(28)(29). Thus the pulsed Fe/Ca peaks of the Tridacna shell during the summer−autumn periods could be used as a further potential proxy of TC activity (Fig.…”

“…(14)(15)(16)(17)(18)(19)(20). Using microscope and scanning electron microscopy (21)(22)(23)(24), some studies have shown that Tridacna shells even have daily growth bands, implying that the Tridacna shells have the potential for reconstruction of the past WEEs.…”

Interspecific and Intrashell Stable Isotope Variation Among the Red Sea Giant Clams

“…δ 18 O values were converted to equivalent temperatures of formation using a paleotemperature equation of Grossman and Ku (1986), previously used in other studies of T. maxima (Batenburg et al, 2011; Komagoe et al, 2018; Romanek et al, 1987): We used a seawater δ 18 O value of 1.8‰ relative to Vienna Standard Mean Ocean Water (VSMOW) based on direct measurements from the northern Red Sea (Al‐Rousan et al, 2003) and from near the mouth of the Gulf of Aqaba (Andrié & Merlivat, 1989), applying the 0.27‰ correction as discussed in Gonfiantini et al, 1995.…”