Publication Date:
2023-06-27
Description:
High-resolution stable isotopic records are presented for the epi-benthic foraminifer Cibicidoides, the inferred shallow-dwelling planktonic Globigerinoides quadrilobatus, and the inferred deep-dwelling planktonic Globoquadrina dehiscens from the middle Miocene (~16-12 Ma) of Deep Sea Drilling Project site 588A, Lord Howe Rise, southwest Pacific. High-resolution, multiple species oxygen and carbon isotopic data define the timing and character of the well-known middle Miocene climatic-oceanographic transition with a resolution comparable to Quaternary records. The benthic foraminiferal delta18O record is marked by several large fluctuations from ~16 to 14.8 Ma, followed by a series of rapid (〈50 kyr) delta18O increases that suggest a new state of the ocean-climate system after 14.8 Ma. The total middle Miocene benthic oxygen isotopic increase of 1.2 per mil is largely incorporated in two steps, an increase of 0.8 per mil from 14.5 to 14.0 Ma and a second increase of 0.7 per mil from 13.45 to 12.45 Ma. Each step is comprised of a series of marked delta18O increases, indicative of rapid East Antarctic ice sheet growth and contemporaneous deepwater cooling. A strong covariance of 0.7 per mil between the benthic and deep-dwelling planktonic species from 14.5 to 14.0 Ma (including a rapid increase from 14.1 to 14.05 Ma) suggests a 0.7 per mil increase in the delta18O composition of seawater (delta18Osw) because of East Antarctic ice sheet growth. Comparison of the delta18O record of Gs. quadrilobatus suggests that surface waters warmed at this site by ~3°C from 14.1 to 13.6 Ma. Carbon isotopic time series for each species generally covary throughout the early to middle Miocene interval (~16-12 Ma), confirming that delta13C variations in this interval largely represent reservoir changes. High-resolution delta13C data allow improved resolution of the latter five of six delta13C maxima within the well-known early to middle Miocene carbon isotopic excursion (the Monterey Carbon Isotopic Excursion from 17.0 to 13.5 Ma). This is useful for global correlation. The last of these maxima ends with a 1 per mil decrease centered from 13.9 to 13.7 Ma, ~300 kyr after the delta18O increase considered to reflect East Antarctic ice growth. Covariance between benthic delta18O and delta13C from ~16 to 13.8 Ma suggests a sensitive relation between global carbon cycling and the ocean-climate system prior to 13.8 Ma. Episodic increases in organic carbon burial may have contributed to deep-sea benthic delta13C maxima and synchronous global cooling. The positive relationship ended at ~13.8 Ma, indicative of changing relations between global carbon cycling and the ocean-climate system brought on by the increased stability of the East Antarctic ice sheet after a major growth phase from 14.5 to 14.0 Ma.
Keywords:
90-588A; AGE; Cibicidoides coryelli, δ13C; Cibicidoides coryelli, δ18O; Cibicidoides mundulus, δ13C; Cibicidoides mundulus, δ18O; Cibicidoides wuellerstorfi, δ13C; Cibicidoides wuellerstorfi, δ18O; Deep Sea Drilling Project; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Globigerinoides quadrilobatus, δ13C; Globigerinoides quadrilobatus, δ18O; Globoquadrina dehiscens, δ13C; Globoquadrina dehiscens, δ18O; Glomar Challenger; Leg90; Mass spectrometer Finnigan MAT 251; Sample code/label; South Pacific/Tasman Sea/CONT RISE
Type:
Dataset
Format:
text/tab-separated-values, 3494 data points
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