Intratest Variations in Trace Element Composition of Amphistegina lessonii Using Femtosecond‐Laser Ablation‐ICP‐Mass Spectrometry: A Field Study From Akajima, Okinawa Prefecture, Japan.

Amphistegina are common larger benthic foraminifer in coral reefs, with a nearly circumtropical distribution, and are major contributors to the CaCO3 budget of shallow marine environments. The family Amphisteginidae is dominant in Cenozoic carbonates. However, its potential as a proxy for paleoclimate reconstruction has not been completely explored. The intratest variability in trace elements of Amphistegina lessonii has been investigated using femtosecond‐laser ablation‐inductively coupled plasma‐mass spectrometry (fs‐LA‐ICP‐MS). We collected and analyzed adult specimens of A. lessonii in September 2003, November 2003, January 2004, and March 2004, from ∼2 m water depth in the coral reefs of Akajima, Okinawa, Japan. Tests of A. lessonii from these four collections were analyzed for Mg/Ca of the septa to observe Test Size‐Lifespan relationships. The lifespan of a specimen of A. lessonii of 1,200 µm in diameter is estimated at ∼3 and ∼2 months for specimens 900 µm in size. Over the estimated lifespans, Mg/Ca of individual specimens of A. lessonii is highly variable and displays co‐variation with temperature and tidal heights. Future projects may apply and further test this approach for the reconstruction of the tropical shallow marine paleoenvironments. Plain Language Summary: Larger Benthic Foraminifera (LBF) have slow growth rates and can be used as a proxy to reconstruct seasonal variations in temperature. Amphistegina, a common genus of LBF found within the Cenozoic era including the past 55 million years, was sampled across four seasons from a modern coral reef of Okinawa, Japan. The trace element concentrations in nine specimens of A. lessonii were measured using femtosecond LA‐ICP‐MS. The intratest variation in Mg/Ca covaried with tidal heights and seawater temperature, assuming the ages of the specimens to be 2–3 months. We provide a temperature calibration equation for A. lessonii for reconstructing paleotemperatures of shallow marine environments of the Cenozoic. Key Points: Specimens of Amphistegina lessonii sampled across 4 months from Akajima are used for calibration for Mg/Ca temperature using femtosecond‐laser ablation‐inductively coupled plasma‐mass spectrometry.The Mg/Ca along the septa of A. lessonii covaries with seawater temperature and tidal heights while Na/Ca and Sr/Ca show no correlationIntratest variations in Mg/Ca of A. lessonii are affected by light intensity attenuation by sediment re‐suspension caused by tidal currents [ABSTRACT FROM AUTHOR]