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Abstract Down‐core changes in the coiling direction ofGloborotalia truncatulinoidesin the northwestern subtropical Atlantic (KNR140‐37PC and Ocean Drilling Program Sites 1063, 1059, 1056, 1058) provide a tracer for the hydrographic conditions in the western boundary current over the past 700 kyr (Marine Isotope Stage, MIS, 1–17). A consistent association between percentG. truncatulinoides(sinistral) abundances, total test counts, and bulk sediment CaCO3content is established by MIS 11 suggesting a response to ocean‐atmosphere interactions during the mid Brunhes event. Commencing with MIS 11, interglacial maxima are associated with high total test counts and either distinct sinistral test minima (MIS 9e, 11c) or maxima (MIS 1, 5e, 7a). High sinistral test abundances with relatively high test counts is similar to the late Holocene relationship at the study sites. Low sinistral test abundances despite high test counts means that coiling ratios are dominated by dextral forms. We interpret this pattern to indicate more intense flow in the subtropical gyre either via the western boundary current drawing toward the gyre center, or a more northern influence of the North Equatorial and Antilles Currents. This suggests that the western boundary current may have been more intense during MIS 11c and MIS 9e then during MIS 7a, MIS 5e, and MIS 1 consistent with climate warm anomalies in northern Europe at these times. Regardless of the mechanism, the observation that minima and maxima in sinistral test abundances are prolonged at these times indicates that the western gyre boundary remained stable during relative warm intervals.
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A High‐Resolution Speleothem Record of Marine Isotope Stage 11 as a Natural Analog to Holocene Asian Summer Monsoon Variations
Abstract A full‐spectrum characterization of past interglacial climate is a necessary prerequisite for the detection and attribution of climate changes during the current interglacial. Here we present a speleothem record of Asian summer monsoon (ASM) during Marine Isotope Stage (MIS) 11 interglacial (MIS 11c), from Yongxing cave, China. The record's unprecedented chronologic constraints and decadal‐scale temporal resolution allow a precise and direct comparison of ASM between the MIS 11c and the Holocene. Our data suggest that orbital‐centennial patterns of ASM were remarkably similar during both interglacial, including their pacing and structure. Notably, a multi‐millennial stronger monsoon late in MIS 11c, the “Late‐MIS 11c shift,” is similar to the Late Holocene strengthening of the ASM, the “2‐Kyr shift.” Thus, the multicentennial ASM weakening at the end of the Late‐MIS 11c shift could imply that the current century‐long ASM waning trend may persist into the future, if only natural forcings are considered.
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- Award ID(s):
- 1702816
- PAR ID:
- 10453931
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 46
- Issue:
- 16
- ISSN:
- 0094-8276
- Format(s):
- Medium: X Size: p. 9949-9957
- Size(s):
- p. 9949-9957
- Sponsoring Org:
- National Science Foundation
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