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

Sonal Khanolkar,Pratul Kumar Saraswati,Gerald H Haug,Ulrike Weis,Klaus Peter Jochum,Asmita Singh,Ralf Schiebel,Brigitte Stoll

doi:10.1029/2020gc009443

Abstract

AbstractAmphistegina 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.

Highlights

Foraminiferal calcite is the most widely used biogenic carbonate to generate proxy geochemical data for paleoclimate reconstruction (Fischer & Wefer, 1999; Kucera, 2007)
Test sizes for nine A. lessonii specimens that were analyzed for trace elements vary between ∼900 and 1,200 μm (Table 1)
The lifespan of A. lessonii is assumed at ∼3–4 months according to the growth curve

Summary

Introduction

Foraminiferal calcite is the most widely used biogenic carbonate to generate proxy geochemical data for paleoclimate reconstruction (Fischer & Wefer, 1999; Kucera, 2007). The Larger Benthic Foraminifera (LBF) are K-strategists Their size is proportional to their lifespan (Wefer & Berger, 1980). To understand the growth rates of the various LBF species, different techniques have been explored like stable isotope analyses, micro-CT Scan, and culture studies (Hallock, 1981; Hohenegger et al, 2019; Wefer & Berger, 1980). The oxygen and carbon isotope ratios of the LBF Marginopora vertebralis (test diameter: 6.8 mm) and Cyclorbuculina compressa (test diameter: 5.2 mm) suggest lifespans of ∼2 and ∼1 year, respectively (Wefer & Berger, 1980). Hohenegger et al (2019) used the micro-CT Scan technique to estimate the growth rates of Nummulites venosus and estimated the life

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