Past daily light cycle recorded in the strontium/calcium ratios of giant clam shells

Abstract

The historical record of daily light cycle in tropical and subtropical regions is short. moreover, it remains difficult to extract this cycle in the past from natural archives such as biogenic marine carbonates. Here we describe the precise analysis of sr/Ca, mg/Ca, and Ba/Ca ratios in a cultivated giant clam shell, using a laterally high-resolution secondary ion mass spectrometer with 2 µm resolution. The sr/Ca ratio exhibits striking diurnal variations, reflecting the daily light cycle. A clear seasonal variation in sr/Ca is also observed in another longer set of measurements with 50 µm resolution. Light-enhanced calcification and elemental transportation processes, in giant clam and symbiotic algae, may explain these diurnal and annual variations. This opens the possibility to develop the sr/Ca ratio from a giant clam shell as an effective proxy for parameters of the daily light cycle.

Sr/Ca differences within and among three Tridacnidae species from the South China Sea: Implication for paleoclimate reconstruction

“…The high-resolution Sr/Ca profiles of Tridacna determined by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) did not yield any clear link between Sr/Ca ratio and environmental variables (Elliot et al, 2009;Batenburg et al, 2011). In contrast, high resolution Tridacna Sr/Ca profiles from Ishigaki Island, determined by high-resolution secondary ion mass spectrometry (NanoSIMS) and ICP-MS, and from South China Sea, determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), display clear annual cycles and are negatively correlated to climatic parameters such as SST and insolation (Sano et al, 2012;Yan et al, 2013), indicating that the Sr/Ca ratio of Tridacnidae retains its potential to be a climate proxy.…”

“…The large size and long life span of from several decades to a few centuries makes Tridacnidae particularly suitable for sampling and geochemical analysis (Watanabe and Oba, 1999;Sano et al, 2012). Its shell growth rate is very high (Bonham, 1965), and large individuals can grow to over 1 m in length.…”

“…Biological and geochemical parameters such as growth rate, δ 18 O and Sr/Ca ratios of Tridacnidae samples have been considered as reliable proxies for palaeo-environmental change in recent papers (Aharon et al, 1980;Aharon, 1983;Aharon and Chappell, 1986;Aharon, 1991;Watanabe and Oba, 1999;Watanabe et al, 2004;Aubert et al, 2009;Elliot et al, 2009;Batenburg et al, 2011;Sano et al, 2012;Yan et al, 2013). For example, several studies reported that the growth increments of Tridacnidae shells are seasonally governed by the SST, with larger growth increments occurring during the summer (Watanabe and Oba, 1999;Aubert et al, 2009).…”

“…The Sr/Ca ratio of skeletal material has been extensively utilized as a paleo-thermometer in fossil corals (Beck et al, 1992;McCulloch et al, 1994McCulloch et al, , 1996Alibert and McCulloch, 1997), and has also been investigated recently in Tridacnidae specimens (Elliot et al, 2009;Batenburg et al, 2011;Sano et al, 2012;Yan et al, 2013). The high-resolution Sr/Ca profiles of Tridacna determined by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) did not yield any clear link between Sr/Ca ratio and environmental variables (Elliot et al, 2009;Batenburg et al, 2011).…”

Fluctuations of sulfate, S-bearing amino acids and magnesium in a giant clam shell

“…Long-lived bivalves such as reef-dwelling giant clams are geologically important producers of biominerals that provide long-term records (up to ∼ 100 years) of environmental conditions in tropical and subtropical oceans (e.g., Watanabe et al, 2004;Aubert et al, 2009). Previous studies have analyzed the element profiles of divalent cations and Sr / Ca ratios, the primary objective being to evaluate them as environmental proxies (e.g., Elliot et al, 2009;Sano et al, 2012;Yan et al, 2013).…”