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During Expedition 339, Site U1385 (37°34.2849′N, 10°7.5616′W) was drilled to a maximum penetration of 151.5 meters below seafloor (mbsf) (Expedition 339 Scientists, 2013) (Figure F1). Site U1385 was a proof of concept to test the continuity and fidelity of the sedimentary record and to support further drilling on the Iberian margin. Results from Site U1385 demonstrated the great promise of the Iberian margin to yield long, continuous records of millennial climate variability (MCV) and detailed land-sea comparisons. Almost exactly 11 y later, we reoccupied Site U1385 (37°34.0128′N, 10°7.6580′W) during Expedition 397 to deepen the sequence. We elected to retain the same site designation, beginning with Hole U1385F, and distinguish the two sites as Site 339-U1385 and Site 397-U1385. Site 397-U1385 is located <1 km southwest of Site 339-U1385 (Figure F2), and seismic data indicate the stratigraphy is continuous between the two locations. On 25–29 November 2011, Site 339-U1385 was drilled in the lower slope of the Portuguese margin to provide a marine reference section of Pleistocene MCV. Five holes were cored (Holes U1385A–U1385E) using the advanced piston corer (APC) system (Figure F3) (Expedition 339 Scientists, 2013). Hole U1385C consisted of a single core in an attempt to retrieve the mudline. With only 4 days of drilling for Site 339-U1385, we were only able to drill to a maximum depth of 156 mbsf. A composite section was constructed using all holes to 166.5 corrected revised meters composite depth (crmcd) by correlating elemental ratios (Ca/Ti) measured by core scanning X-ray fluorescence (XRF) at 1 cm resolution (Hodell et al., 2015). For Site 397-U1385, we eventually intend to correlate the top part of the section to the holes drilled during Expedition 339 and provide an integrated composite reference splice (Hodell et al., 2015). This will permit isotope and other proxy measurements from existing Expedition 339 Holes U1385A–U1385E to be integrated with new data from Expedition 397 Holes U1385F–U1385J. The Site 339-U1385 record extends to 1.45 Ma (Marine Isotope Stage [MIS] 47) with an average sedimentation rate of 11 cm/ky (Figures F3, F4). Sedimentation rates are expected to be similar throughout the Quaternary. The record is mostly complete except for a short hiatus at Termination V that has removed part of late MIS 12 and early MIS 11. It is hoped that drilling at the new location of Site 397-U1385 would avoid this hiatus and provide a continuous sequence, filling the gap at Site 339-U1385. Because the existing working halves of Expedition 339 Holes U1385A–U1385E have been largely depleted to meet intense sampling demand, the uppermost 150 m were duplicated at Site 397-U1385 to provide additional sediment for future studies. Site 339-U1385 has been studied extensively since it was recovered over a decade ago (see the Expedition 339 Expedition-related bibliography [Stow, Hernández-Molina, Alvarez Zarikian, and the Expedition 339 Scientists, 2013]) and has provided a high-resolution benchmark record of MCV for the past 1.45 My (Hodell et al., 2023). Extending this remarkable sediment archive further back in time was the primary goal of reoccupying Site U1385 during Expedition 397. Site 397-U1385 is located ~1 km southwest of Expedition 339 Site U1385 at a water depth of 2591 meters below sea level (mbsl), placing it in the core of Lower Northeast Atlantic Deep Water (LNEADW) today (Figure F5). It is the second shallowest site along the Expedition 397 bathymetric transect (paleo-conductivity-temperature-depth [paleo-CTD]) (Figure F6) and is located along an elevated ridge (Figure F7), thereby decreasing the chances of disturbance by downslope transport. It is located on Seismic Line JC089-9 close to the intersection of Seismic Line JC089-13 (Figure F2) and near the position of Piston Core MD01-2444 (Figure F1). The objective is to recover the deeper part of the section below Site 339-U1385 to the base of the Pliocene (orange reflector) at 400 mbsf (Figures F8, F9), which will more than double the section recovered at Site 339-U1385. The specific objectives of Site 397-U1385 are as follows: Document the nature of MCV for older glacial cycles of the Quaternary beyond the penetration limit of Site 339-U1385 (1.45 Ma). Derive a marine sediment proxy record for Greenland and Antarctic ice cores to examine the amplitude and pacing of MCV during the Quaternary. Determine interhemispheric phase relationships (leads/lags) by comparing the timing of proxy variables that monitor surface (linked to Greenland) and deepwater (linked to Antarctica) components of the climate system. Study how changes in orbital forcing and glacial boundary conditions affect the character of MCV and, in turn, how MCV interacts with orbital geometry to produce the observed glacial-to-interglacial patterns of climate change. Determine how MCV evolved during the Pliocene–Pleistocene as glacial boundary conditions changed with the progressive intensification of Northern Hemisphere glaciation (NHG). Reconstruct the history of changing local dominance of northern-sourced versus southern-sourced deep water by comparing Site U1385 with the other sites along the bathymetric transect (Figure F6). Investigate climate during past interglacial periods, including the warm Pliocene period prior to the intensification of NHG. Link terrestrial, marine, and ice core records by analyzing pollen and terrestrial biomarkers that are delivered to the deep-sea environment of the Iberian margin. Develop an orbitally tuned age model by correlating sediment physical properties at Site U1385 to eccentricity-modulated precession and integrating this record into Mediterranean cyclostratigraphy.
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This content will become publicly available on December 14, 2026
PP41D-1176 A 0.5-Million-Year Benthic Stable Isotope Record of Climate and Deep North Atlantic Circulation at the Iberian Margin
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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- Award ID(s):
- 2442513
- PAR ID:
- 10651129
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Format(s):
- Medium: X
- Location:
- New Orleans
- Sponsoring Org:
- National Science Foundation
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