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Understanding Bulk Sediment Stable Isotope Records in the Eastern Equatorial Pacific, From Seven Million Years Ago to Present Day
Author(s) -
Reghellin Daniele,
Dickens Gerald R.,
Coxall Helen K.,
Backman Jan
Publication year - 2020
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2019pa003586
Subject(s) - foraminifera , geology , oceanography , benthic zone , calcite , sediment , carbonate , stable isotope ratio , δ18o , paleontology , chemistry , physics , organic chemistry , quantum mechanics
Abstract Stable isotope (δ 13 C and δ 18 O) records of bulk marine sediment carry information on past carbon cycling and oceanography, but origins and interpretations remain uncertain because such signals represent mixtures of different biogenic components, each with potential offsets from primary parameters. Studies of Neogene sediment from the eastern equatorial Pacific (EEP) exemplify this issue, because stable isotope records of bulk sediment and foraminifera at different sites exhibit similarities and differences in absolute value that somehow relate to depositional age. Here we measure δ 13 C and δ 18 O of bulk carbonate, two fine‐grained fractions (<63 and <20 μm), mixed‐species planktic and benthic foraminifera, and foraminifera fragments from sediments deposited over four time intervals within the last 7 Ma at ODP Site 851. These data are compared to published δ 13 C and δ 18 O records of multiple single‐species planktic foraminifera from the same site and benthic foraminifera from an adjacent site. Bulk sediment δ 13 C and δ 18 O records represent a mixed signal dominated by reticulofenestrid coccolith calcite but modified by variable amounts of different foraminifera. Similarities and differences between stable isotope records result from temporal changes in water chemistry and temperature, depths of calcite precipitation, and vital effects that impact fractionation of various biogenic components. The remarkable correlation of bulk stable isotope records within the EEP suggests that several factors change collectively over time across a broad oceanographic region. Ideally, multiple stable isotope records coupled with other proxy measurements might lead to an internally consistent paleoceanographic perspective of the EEP since the late Miocene.