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Abstract Orbital‐scale Indian Summer Monsoon variability is often interpreted as a direct response to northern hemisphere summer insolation. Here we present a continuous (0–640 kyr) orbital scale precipitation isotope (δDprecip) record using leaf wax δD from the core monsoon zone of India. The δDpreciprecord is quantitatively coherent with, and δDprecipminima in phase with, greenhouses gas maxima, and ice volume minima across all orbital bands. The δDpreciprecord is also coherent and in phase with the two existing orbital‐scale Indian speleothem δ18O records, demonstrating a consistent regional response among independent proxies. These findings preclude interpretation of Indian precipitation isotope records as a direct response to northern hemisphere summer insolation. Rather, they dominantly reflect changes in moisture source and transport paths associated with changes in greenhouse gases and ice volume. The orbital‐scale precipitation isotope responses of the Indian and East Asian monsoon systems are uncoupled and are driven by different forcings.
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Distinguishing Between Insolation‐Driven and Phase‐Locked 100‐Kyr Ice Age Scenarios Using Example Models
Abstract Glacial‐interglacial oscillations exhibit a periodicity of approximately 100 Kyr during the late Pleistocene. Insolation variations are understood to play a vital role in these ice ages, yet their exact effect is still unknown; the 100 Kyr ice ages may be explained in two different ways. They could be purely insolation‐driven, such that ice ages are a consequence of insolation variations and would not have existed without these variations. Or, ice ages may be self‐sustained oscillations, where they would have existed even without insolation variations. We develop several observable measures that are used to differentiate between the two scenarios and can help to determine which one is more likely based on the observed proxy record. We demonstrate these analyses using two representative models. First, we find that the self‐sustained model best fits the ice volume proxy record for the full 800‐Kyr time period. Next, the same model also shows a 100 Kyr peak consistent with observations, yet the insolation‐driven model exhibits a dominant 400 Kyr spectral peak inconsistent with observations. Our third measure indicates that midpoints in ice volume during terminations do not always occur during the same phase of insolation in both observations and the self‐sustained scenario, whereas they do in the insolation‐driven scenario. While some of these results suggest that the self‐sustained ice ages are more consistent with the observed record, they rely on simple representations of the two scenarios. To draw robust conclusions, a broader class of models should be tested using this method of producing observable differences.
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- Award ID(s):
- 2303486
- PAR ID:
- 10498978
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 39
- Issue:
- 3
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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