Combined effects of gametogenic calcification and dissolution on δ18O measurements of the planktic foraminifer Trilobatus sacculifer

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doi: 10.1029/2018GC007908
Author(s): Wycech, Jody B.; Kelly, Daniel Clay; Kitajima, Kouki; Kozdon, Reinhard; Orland, Ian J.; Valley, John W.
Author Affiliation(s): Primary:
University of Wisconsin-Madison, Department of Geoscience, Madison, WI, United States
Lamont-Doherty Earth Observatory, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 19(11), p.4487-4501. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 75 refs.; illus., incl. 2 tables
Summary: Oxygen isotope ratios (δ18O) measured from planktic foraminifer shells are commonly used to reconstruct past surface ocean conditions, yet the shells of many planktic foraminifers are an aggregate mixture of multiple carbonate phases with differing δ18O compositions. Here we demonstrate how secondary ion mass spectrometry can be used to measure intrashell δ18O heterogeneity by performing in situ analyses on micrometer-scale (3-10 µm) domains within individual shells of the extant, mixed layer species Trilobatus sacculifer. Secondary ion mass spectrometry measurements on shells taken from Holocene-aged sediments at three sites in different ocean basins confirm that the δ18O of gametogenic (GAM) calcite added to shells during the terminal (reproductive) stage of the life cycle is 1.0-1.4 ppm higher than that of pregametogenic calcite. Examination of shells in cross section reveals that many have suffered varying degrees of internal dissolution, which further skews whole-shell δ18O compositions toward higher values by preferentially removing low δ18O pregametogenic calcite. The results of this study echo the calls of earlier studies cautioning that spatiotemporal changes in the proportion of high δ18O GAM calcite should be considered when assessing T. sacculifer δ18O records generated via conventional isotope ratio mass spectrometry. Abstract Copyright (2018), American Geophysical Union. All Rights Reserved.
Year of Publication: 2018
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 24 Surficial Geology, Quaternary Geology; Atlantic Ocean; Calcification; Calcite; Carbonates; Carbonatites; Caribbean Sea; Cenozoic; Cores; Equatorial Pacific; Foraminifera; Holocene; Igneous rocks; Isotope ratios; Isotopes; Leg 130; Marine sediments; Microfossils; North Atlantic; North Pacific; Northwest Atlantic; Northwest Pacific; O-18/O-16; ODP Site 806; Ocean Drilling Program; Ontong Java Plateau; Oxygen; Pacific Ocean; Planktonic taxa; Quaternary; Sediments; Shells; Solution; Stable isotopes; Trilobatus sacculifer; West Pacific
Coordinates: N001906 N001907 E1592142 E1592140
Record ID: 2019048133
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom, Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union