Late Miocene Seasonal to Subdecadal Climate Variability in the Indo-West Pacific (East Kalimantan, Indonesia) Preserved in Giant Clams

Abstract

Two late Miocene Tridacna (giant clam) shells from East Kalimantan (Indonesia) were investigated in order to evaluate their potential as subannually resolved paleoenvironmental archives. Via a combination of X-ray diffraction (XRD), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) trace element analysis, scanning electron microscopy (SEM) and cathodoluminescence (CL) imaging, pristine versus diagenetically altered domains within the shells were identified. LA-ICPMS transects targeting altered aragonite and calcite zones reveal distinct compositional differences in elemental ratios (B/Ca, Mg/Ca, Sr/Ca/ Ba/Ca, Mn/Ca, Al/Ca, La/Ca, Ce/Ca) relative to primary shell aragonite. Pristine shell domains are characterized by an intact banding pattern of alternating dark and light growth bands, with which spatially resolved LA-ICPMS element/Ca and micromilled d 18 O records were aligned. Light d 18 O values correspond to dark growth bands, indicating growth during warm seasons. The Mg/Ca and/or Sr/Ca ratios covary with oscillating stable oxygen isotope profiles. Progressive increase in Mg/Ca with age demonstrates that besides temperature, growth kinetics exert control over Mg incorporation. If interpreted as temperature controlled only, d 18 O from both shells represents average seasonal sea-surface temperature (SST) variability of 2.7 ± 2.1 and 4.6 ± 1.7 uC, respectively. Using published temperature equations and assuming d 18 O sw = 20.88%, corresponding mean annual paleo-sea-surface temperatures of 27.8 ± 0.2 and 28.5 ± 0.2 uC are estimated. Although the fossil Tridacna shells were noticeably affected by alteration on their external surfaces, their internal aragonitic structure is, to a large extent, well preserved. These corresponding paleoproxy records provide detailed insight into tropical SST variability of the Indo-Pacific region during the late Miocene.

Phylogeographical patterns and a cryptic species provide new insights into Western Indian Ocean giant clams phylogenetic relationships and colonization history

“…From the fossil records ascribed to the genus Tridacna (Harzhauser, Mandic, Piller, Reuter, & Kroh, and references therein; Warter, Müller, Wesselingh, Todd, & Renema, ), for molecular‐clock calibration we used Warter et al () late Miocene record of the subfamily Tridacninae. Warter et al () referred to a series of seven specimens from the Tortonian (≤9.92 Ma) reef‐associated fossil fauna embedded in clay‐rich carbonate sediments from eastern Borneo. We chose this record as the single calibration point for the time‐tree, because (a) it represents the oldest unambiguous identified Tridacna .…”

“…The generic assignment of another giant clam fossil, the early Miocene Tridacna evae Harzhauser & Mandic, 2008 is not fully elucidated because of poor preservation. (b) The age of these seven shells, along with several associated scleractinian corals, was determined using strontium isotope stratigraphy and gave concordant estimates (Warter et al, ). We applied a lognormal prior distribution, with an offset of 9.8 Ma, a mean in real space of 1.0, and a standard deviation (Log(StDev)) of 1.0 (95% HPD: 9.81–12.25 Ma).…”

Marine Bivalve Feeding Strategies and Radiocarbon Ages in Northeast Atlantic Coastal Waters

“…Simstich et al 2005aSimstich et al , 2005bMcConnaughey and Gillikin 2008;Mettam et al 2014;Reich et al 2015) and trace metal composition (Mg/Ca, Sr/Ca) (e.g. Batenburg et al 2011;Warter et al 2015). The shell composition of many mollusk species is likely to represent ambient seawater conditions and can be used to trace the physical and chemical properties of the surrounding waters.…”

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

“…Symbiont algae (zooxanthellae) in their hypertrophied mantle enable rapid growth, for example, approximately 15 mm/yr in a Tridacna gigas inner shell layer (Watanabe et al, 2004). Annual and daily growth increments were recognizable in the shells of T. gigas, Tridacna maxima, Tridacna squamosa, and Hippopus hippopus (Aharon & Chappell, 1986;Aubert et al, 2009;Bonham, 1965;Duprey et al, 2014;Pannella & MacClintock, 1968;Pätzold et al, 1991;Sano et al, 2012;Warter et al, 2015;Watanabe et al, 2004;Watanabe & Oba, 1999). Counting daily growth increments provides us exact deposition dates for daily increments.…”

“…In addition, Tridacnidae precipitates a dense aragonite shell resistant to diagenetic alternation. Growth increments are well preserved in a fossil shell specimen and give accurate paleoenvironmental records (Aharon & Chappell, 1986;Ayling et al, 2015;Komagoe et al, 2016;Warter et al, 2015;Watanabe et al, 2004;Warter & Müller, 2017).…”