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1. Hawaiian Drowned Reefs

   https://doi.org/10.14379/iodp.proc.389.2025  

   Webster, JM; Ravelo, AC; Grant, HLJ (February 2025, Proceedings of the International Ocean Discovery Program Expedition reports)

   Our understanding of the mechanisms controlling eustatic sea level and global climate changes has been hampered by a lack of appropriate fossil coral records over the last 500 ky, particularly into and out of the glacial periods. This problem was addressed by International Ocean Discovery Program Expedition 389, which drilled a unique succession of Hawaiian drowned coral reefs now at 110–1300 meters below sea level (mbsl). The four objectives are to investigate (1) the timing, rate, and amplitude of sea level variability to examine cryosphere and geophysical processes, including the assessment of abrupt sea level change events; (2) the processes that determine changes in mean and high-frequency (seasonal–interannual) climate variability from times with different boundary conditions (e.g., ice sheet size, pCO2, and solar forcing); (3) the response of coral reef systems to abrupt sea level and climate changes; and (4) the variations through space and time of the subsidence and the volcanic evolution of the island. To achieve these objectives, 35 holes at 16 sites in water depths ranging 131.9–1241.8 mbsl were drilled during the expedition. A total of 425 m of core was recovered, comprising reef (83%) and volcanic (17%) material. Average core recoveries were 66%, with recoveries >90% in numerous intervals characterized by very well preserved coralgal and microbialite frameworks. Some science-critical shallow sites were not drilled due to a failure to secure permits to operate in Hawaiian state waters. Furthermore, apart from one site, the target penetration depths were not achieved. Preliminary radiometric dates indicate that the recovered reef deposits are from 488 to 13 ka in age. The Onshore Science Party took place in February 2024. Cores were computed tomography (CT) scanned and then opened and hyperspectral scanned and described. Standard measurements were made, and samples were taken for postcruise research. Preliminary assessment of the age and quality of the reef and volcanic cores suggest that many of the expedition objectives will be met. 

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2. Expedition 389 Preliminary Report: Hawaiian Drowned Reefs

   https://doi.org/10.14379/iodp.pr.389.2024  

   Webster, J.M.; Ravelo, A.C.; Grant, H.L.J. (May 2024, Preliminary report)

   Our understanding of the mechanisms controlling eustatic sea level and global climate changes has been hampered by a lack of appropriate fossil coral records over the last 500 ky, particularly into and out of the glacial periods. This problem was addressed by International Ocean Discovery Program Expedition 389 by drilling a unique succession of Hawaiian drowned coral reefs now at 110–1300 meters below sea level (mbsl). The four objectives are to investigate (1) the timing, rate, and amplitude of sea level variability to examine cryosphere and geophysical processes, including the assessment of abrupt sea level change events; (2) the processes that determine changes in mean and high-frequency (seasonal–interannual) climate variability from times with different boundary conditions (e.g., ice sheet size, pCO2, and solar forcing); (3) the response of coral reef systems to abrupt sea level and climate changes; and (4) the variation through space and time of the subsidence and the volcanic evolution of the island. To achieve these objectives, 35 holes at 16 sites ranging 131.9–1241.8 mbsl were drilled during the expedition. A total of 425 m of core was recovered, comprising reef (83%) and volcanic (17%) material. Average core recoveries were 66%, with numerous intervals characterized by very well preserved mixtures of coralgal and microbialite frameworks with recoveries >90%. Some science-critical shallow sites were not drilled due to a failure to secure permits to operate in Hawaiian state waters. Furthermore, apart from one site the target penetration depths were not achieved. Preliminary radiometric dates indicate that the recovered reef deposits are from 488 to 13 ka in age. The Onshore Science Party took place in February 2024. Cores were CT and hyperspectral scanned and described. Standard measurements were made, and samples were taken for postcruise research. Preliminary assessment of the age and quality of the reef and basalt cores suggest that many of the expedition objectives will be met. 

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3. Expedition 389 Scientific Prospectus: Hawaiian Drowned Reefs

   https://doi.org/10.14379/iodp.sp.389.2023  

   Webster, J.M.; Ravelo, A.C.; Grant, H.L.J. (August 2023, Scientific prospectus)

   Our understanding of the links and mechanisms that control eustatic sea level and global climate changes has been significantly hampered by a lack of appropriate fossil coral records over the last 500 ky, particularly into and out of the glacial periods. We propose to directly address this problem by drilling a unique succession of drowned coral reefs around Hawaii (USA) now at 134–1155 meters below sea level. Abundant observational and numerical modeling data indicate that the internal stratigraphy and tops of these reefs are highly sensitive to sea level and climate changes, thereby providing a firm template with which to conduct these operations. As a direct result of Hawaii’s rapid (2.5–2.6 m/ky) but nearly constant subsidence, a thick (100–200 m) expanded sequence of shallow coral reef dominated facies is preserved within the reefs. These reefs span important periods in the Earth’s climate history, and coral reef records are either not available or highly condensed on stable (Great Barrier Reef, Tahiti) and uplifted margins (Papua New Guinea, Barbados) because of a lack of accommodation space and/or unfavorable shelf morphology. Specifically, these data show that the reefs grew (for ~90–100 ky, albeit episodically) into, during, and out of the majority of the last five to six glacial cycles. Therefore, scientific drilling through these reefs will generate a new record of sea level and associated climate variability during several controversial and poorly understood periods over the last 500 ky. The project has four major objectives. The first objective will be to constrain the timing, rate, and amplitude of sea level variability over the last 500 ky allowing a definitive test of Milankovitch climate theory and an assessment of controversial abrupt sea level events (meltwater pulses) that occur on suborbital frequencies associated with events occurring in the extratropics (i.e., Dansgaard–Oeschger ice core temperature events and related Heinrich ice-rafted debris events in North Atlantic sediment cores). The second objective will be to investigate processes that determine changes in mean climate and high-frequency (seasonal–interannual) climate variability using high-resolution coral proxy data from times with different climate forcing boundary conditions (e.g., ice sheet size, pCO2, and solar forcing) over the last 500 ky. The third objective will be to determine the response of coral reef systems to abrupt sea level and climate changes, to test sedimentary models of reef evolution and ecological theories of coral reef resilience, and to establish the role of microbial communities in reef building. The fourth objective will be to refine the variation through space and time of the subsidence of Hawaii and contribute to understanding the volcanic evolution of the island. 

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4. Expedition 397 Scientific Prospectus: Iberian Margin Paleoclimate

   https://doi.org/10.14379/iodp.sp.397.2022  

    Hodell, D.A.; Abrantes, F.; Alvarez Zarikian, C.A. (February 2022, Scientific prospectus)

   The Iberian margin is a well-known source of rapidly accumulating sediment that contains a high-fidelity record of millennial climate variability (MCV) for the late Pleistocene. The late Sir Nicholas (Nick) Shackleton demonstrated that piston cores from the region can be correlated precisely to polar ice cores in both hemispheres. Moreover, the narrow continental shelf off Portugal results in the rapid delivery of terrestrial material to the deep-sea environment, thereby permitting correlation of marine and ice core records to European terrestrial sequences. Few places exist in the world where such detailed marine-ice-terrestrial linkages are possible. The continuity, high sedimentation rates, and fidelity of climate signals preserved in Iberian margin sediments make this region a prime target for ocean drilling. During Integrated Ocean Drilling Program Expedition 339 (Mediterranean Outflow), one of the sites proposed here was drilled to a total depth of 155.9 meters below seafloor in multiple holes. At Site U1385 (the “Shackleton site”) a complete record of hemipelagic sedimentation was recovered for the last 1.45 My corresponding to Marine Isotope Stage 47 with sedimentation rates of 10–20 cm/ky. Preliminary results from Site U1385 demonstrate the great promise of the Iberian margin to yield long records of millennial-scale climate change and land–sea comparisons. International Ocean Discovery Program (IODP) Expedition 397 will extend this remarkable sediment archive through the Pliocene and expand the depth range of available sites by drilling additional sequences in water depths from 1304 to 4686 meters below sea level (mbsl). This depth transect is designed to complement those sites drilled during Expedition 339 (560–1073 mbsl) where sediment was recovered at intermediate water depth under the influence of Mediterranean Outflow Water (MOW). Together, the sites recovered during Expeditions 339 and 397 will constitute a complete depth transect with which to study past variability of all the major subsurface water masses of the eastern North Atlantic. Because most of the mass, thermal inertia, and carbon in the ocean-atmosphere system is contained in the deep ocean, well-placed depth transects in each of the major ocean basins are needed to understand the underlying mechanisms of glacial–interglacial cycles and MCV. We have identified four primary sites (SHACK-4C, SHACK-10B, SHACK-11B, and SHACK-14A) at which multiple holes will be drilled to ensure complete recovery of the stratigraphic sections at each site, ranging in age from the latest Miocene to Holocene. Building on the success of Site U1385 and given the seminal importance of the Iberian margin for paleoclimatology and marine-ice-terrestrial correlations, the cores recovered during Expedition 397 will provide present and future generations of paleoceanographers with the raw material needed to reconstruct the North Atlantic climate at high temporal resolution for the entire Quaternary and Pliocene. 

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5. Site U1599

   Druitt, TH; Kutterolf, S; Ronge, TA; Beethe, S; Bernard, A; Berthod, C; Chen, H; Chiyonobu, S; Clark, A; DeBari, S; et al (July 2024, Proceedings of the International Ocean Discovery Program Expedition reports)

   Site U1599 is located ~6 km north of Anafi Island within the upper reaches of the Anafi Basin at a water depth of 592 meters below sea level (mbsl) (Figure F1). Permission to drill in this location was granted by the International Ocean Discovery Program (IODP) Environmental Protection and Safety Panel during the expedition (proposed Site CSK-22A). Three holes (U1599A–U1599C) were drilled to a maximum recovery depth of 698.1 meters below seafloor (mbsf) (all depths below seafloor are given using the core depth below seafloor, Method A [CSF-A] scale, except in Operations, where the drilling depth below seafloor [DSF] scale is used), with average hole core recoveries ranging 51%–83% (Figure F2). Whereas Site U1592 is situated on the axis of the Anafi Basin and penetrated a thick basin fill including mass-transported material, Site U1599 is located on the southeast margin of the basin. It was chosen to offer a condensed sequence of tephra without quantities of mass-wasting debris. As such, it provided a complete stratigraphy of volcanic tephra from Santorini and Kolumbo. The same six seismic units (U1–U6, from the bottom up; Preine et al., 2022a, 2022b) present at Site U1592 are present at Site U1599. Site U1599 is located within the area of the 2015 PROTEUS seismic tomography experiment, during which subbottom profiling, gravity, and magnetic data were also recorded (Hooft et al., 2017). Drilling at Site U1599 enabled us to reconstruct a near-complete volcanic stratigraphy consistent with both onshore and offshore constraints and pinned by chronological markers from biostratigraphy, magnetostratigraphy, and sapropel records. Benthic foraminifera from fine-grained sediments provided estimates of paleowater depths and, via integration with seismic profiles and chronologic data, of time-integrated basin subsidence rates. Drilling in the Anafi Basin addressed scientific Objectives 1–4 and 6 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022). It was complemented by Site U1589 in the Anhydros Basin because each basin tapped a different sediment distributary branch of the Christiana-Santorini-Kolumbo volcanic system. 

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