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Climate cycles following the mid-Pleistocene transition include the coldest and longest glaciations of the Quaternary, punctuated by repeated rapid climate oscillations and sharp transitions into exceptionally warm, atmospheric CO₂-rich interglacial intervals. Such dramatic climate shifts reflect major reorganizations of the Earth system, with complex feedbacks between North Atlantic ice sheets and ocean–atmosphere carbon cycling believed to have played a central role in the pacing and amplitude of past climate variability. Yet, the response of the deep-ocean, the Earth’s largest reservoir of exchangeable carbon, to abrupt climate change remains elusive, posing a significant challenge to our understanding of the relationship between deep-ocean circulation and past, present, and future climate changes. The recently recovered sedimentary sequence from International Ocean Discovery Program Site U1587 (37°35′N, 10°22′W, 3479n meters below sea level [mbsl]), positioned in a mixing zone of northernand southern-sourced deep waters, offers a valuable archive for reconstructing orbital- to millennial-scale variations in climate and deepocean structure. This study presents new, high-resolution (~1 kyr) benthic foraminifera δ¹⁸O and δ¹³C records from Site U1587, spanning ~ 800 - 300 ka, with a focus on intense glaciations (Marine Isotope Stage [MIS] 16, 12, 10) and subsequent deglaciations (MIS 15, 11, 9). The U1587 δ¹⁸O record was aligned to the established chronology of the nearby Site U1385 (37°34′N, 10°08′W, 2578 mbsl), providing a refined age model for Site U1587 and enabling calculation of vertical δ¹³C gradients across the water column. Site U1587 consistently recorded more negative δ¹³C than the shallower Site U1385, with an average offset of –0.455‰ overall. The vertical δ¹³C gradient between sites is most pronounced during glacial intervals, reaching –1.64‰ at ~465 ka during MIS 12, and is notably reduced during interglacials, with an average of –0.264‰ in MIS 11. These results suggest enhanced deep-ocean stratification and carbon storage during intense glaciations, while the subsequent gradient collapse during deglaciations underscores the link between abrupt changes in deep-ocean circulation and rapid climate transitions into interglacial states.
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Decomposition of Deglacial Pacific Radiocarbon Age Controls Using an Isotope‐Enabled Ocean Model
Abstract During the last deglaciation Earth’s climate experienced strong and abrupt variations, resulting in major changes in global temperature, sea level, and ocean circulation. Although proxy records have significantly improved our understanding of climate during this period, questions remain regarding the connection between ocean circulation evolution and resulting geotracer distributions, including those of deep waters in the Pacific. Here we use the C‐iTRACE simulation, a transient ocean‐only, isotope‐enabled version of the Community Earth System Model, to better understand deglacial deep Pacific radiocarbon evolution in the context of circulation and reservoir age changes. Throughout the deglaciation, the Pacific Ocean circulation in C‐iTRACE responds strongly to glacial meltwater forcing, leading to large changes in deep Pacific Δ14C age. A multi‐millennial weakening of the overturning circulation from 20 to 15 ka BP leads to increases in deep Pacific Δ14C ages, but from 20 to 18 ka BP, nearly half (40%–60%) of this aging is controlled by changing surface reservoir age, corroborating previous studies showing that Δ14C is not solely a circulation age tracer. As the deglaciation proceeds, circulation change controls progressively more of the Δ14C age, accounting for more than 75% of it across the deep Pacific from 15 to 8 ka BP.
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- Award ID(s):
- 1566432
- PAR ID:
- 10370454
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 37
- Issue:
- 8
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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