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1. Expedition 397 summary

   https://doi.org/10.14379/iodp.proc.397.101.2024  

   Hodell, DA; Abrantes, F; Alvarez_Zarikian, CA; Brooks, HL; Clark, WB; Dauchy-Tric, LFB; dos_Santos_Rocha, V; Flores, J-A; Herbert, TD; Hines, SKV; et al (June 2024, Proceedings of the International Ocean Discovery Program Expedition reports)

   During International Ocean Discovery Program Expedition 397, we recovered a total of 6176.7 m of core (104.2% recovery) at four sites (U1586, U1587, U1385, and U1588) from the Promontório dos Príncipes de Avis, a plateau located on the Portuguese continental slope that is elevated above the Tagus Abyssal Plain and isolated from the influence of turbidites. The drill sites are arranged along a bathymetric transect (4692, 3479, 2591, and 1339 meters below sea level [mbsl], respectively) to intersect each of the major subsurface water masses of the eastern North Atlantic. Multiple holes were drilled at each site to ensure complete spliced composite sections, which will be further refined postcruise by a campaign of X-ray fluorescence core scanning. At Site U1586 (4692 mbsl), the deepest and farthest from shore, a 350 m sequence was recovered in four holes that extend as far back as the middle Miocene (14 Ma), which is nearly twice as old as initially predicted from seismic stratigraphy. Sedimentation rates are lower (averaging 5 cm/ky in the Quaternary) at Site U1586 than other Expedition 397 sites, and a few slumped intervals were encountered in the stratigraphic sequence. Despite these limitations, Site U1586 anchors the deep end-member of the bathymetric transect and provides an important reference section to study deepwater circulation, ventilation and carbon storage in the deep eastern North Atlantic. At Site U1587 (3479 mbsl), the second deepest site along the depth transect, we recovered a 567 m sequence of late Miocene to Holocene sediments that accumulated at rates between 6.5 and 11 cm/ky. The high sedimentation rates and long continuous record at this site will permit climate reconstruction at high temporal resolution (e.g., millennial) for the past 7.8 My. The Messinian Stage (7.25–5.33 Ma) was recovered, which provides a valuable opportunity to study the Messinian Salinity Crisis in an open marine setting adjacent to the Mediterranean. Site U1385 (Shackleton site) was a reoccupation of a position previously drilled during Integrated Ocean Drilling Program Expedition 339. Expedition 339 Site U1385 has yielded a remarkable record of millennial-scale climate change for the past 1.45 My (Marine Isotope Stage 47). During Expedition 397, we deepened the site from 156 to 400 meters below seafloor, extending the record to near the base of the Pliocene (5.3 Ma). Sedimentation rates remained high, averaging between 9 and 11 cm/ky throughout the sequence. The newly recovered cores at Expedition 397 Site U1385 will permit the study of millennial climate variability through the entire Quaternary and Pliocene, prior to the intensification of Northern Hemisphere glaciation. Site U1588 is the shallowest, closest to shore, and youngest site drilled during Expedition 397 and is also the one with the highest sedimentation rate (20 cm/ky). The base of the 412.5 m sequence is 2.2 Ma, providing an expanded Pleistocene sequence of sediment deposited under the influence of the lower core of the Mediterranean Outflow Water (MOW). Together with other Expedition 339 sites, Site U1588 will be important for determining how the depth and intensity of the MOW has varied on orbital and millennial timescales. In addition, it also provides a marine reference section for studying Quaternary climate variability at very high temporal resolution (millennial to submillennial). A highlight of the expedition is that sediment at all sites shows very strong cyclicity in bulk sediment properties (color, magnetic susceptibility, and natural gamma radiation). Particularly remarkable are the precession cycles of the Pliocene that can be correlated peak-for-peak among sites. These cyclic variations will be used to derive an orbitally tuned timescale for Expedition 397 sites and correlate them into classic Mediterranean cyclostratigraphy. The cores recovered during Expedition 397 will form the basis of collaborative postcruise research to produce benchmark paleoclimate records for the late Miocene through Quaternary using the widest range of proxy measurements. It will take many years to complete these analyses, but the records will lead to major advances in our understanding of millennial and orbital climate changes and their underlying causes and evolving contextuality. Outreach during Expedition 397 was highly productive, reaching a record number of students and the general public across the world through several diverse platforms, including live ship-to-shore events, webinars, social media, videos, radio pieces, blog posts, and in-person activities. 

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2. Iberian Margin Paleoclimate

   https://doi.org/10.14379/iodp.proc.397.2024  

   Hodell, DA; Abrantes, F; Alvarez_Zarikian, CA (June 2024, Proceedings of the International Ocean Discovery Program Expedition reports)

   During International Ocean Discovery Program Expedition 397, we recovered a total of 6176.7 m of core (104.2% recovery) at four sites (U1586, U1587, U1385, and U1588) from the Promontório dos Príncipes de Avis, a plateau located on the Portuguese continental slope that is elevated above the Tagus Abyssal Plain and isolated from the influence of turbidites. The drill sites are arranged along a bathymetric transect (4692, 3479, 2591, and 1339 meters below sea level [mbsl], respectively) to intersect each of the major subsurface water masses of the eastern North Atlantic. Multiple holes were drilled at each site to ensure complete spliced composite sections, which will be further refined postcruise by a campaign of X-ray fluorescence core scanning. At Site U1586 (4692 mbsl), the deepest and farthest from shore, a 350 m sequence was recovered in four holes that extend as far back as the middle Miocene (14 Ma), which is nearly twice as old as initially predicted from seismic stratigraphy. Sedimentation rates are lower (averaging 5 cm/ky in the Quaternary) at Site U1586 than other Expedition 397 sites, and a few slumped intervals were encountered in the stratigraphic sequence. Despite these limitations, Site U1586 anchors the deep end-member of the bathymetric transect and provides an important reference section to study deepwater circulation, ventilation and carbon storage in the deep eastern North Atlantic. At Site U1587 (3479 mbsl), the second deepest site along the depth transect, we recovered a 567 m sequence of late Miocene to Holocene sediments that accumulated at rates between 6.5 and 11 cm/ky. The high sedimentation rates and long continuous record at this site will permit climate reconstruction at high temporal resolution (e.g., millennial) for the past 7.8 My. The Messinian Stage (7.25–5.33 Ma) was recovered, which provides a valuable opportunity to study the Messinian Salinity Crisis in an open marine setting adjacent to the Mediterranean. Site U1385 (Shackleton site) was a reoccupation of a position previously drilled during Integrated Ocean Drilling Program Expedition 339. Expedition 339 Site U1385 has yielded a remarkable record of millennial-scale climate change for the past 1.45 My (Marine Isotope Stage 47). During Expedition 397, we deepened the site from 156 to 400 meters below seafloor, extending the record to near the base of the Pliocene (5.3 Ma). Sedimentation rates remained high, averaging between 9 and 11 cm/ky throughout the sequence. The newly recovered cores at Expedition 397 Site U1385 will permit the study of millennial climate variability through the entire Quaternary and Pliocene, prior to the intensification of Northern Hemisphere glaciation. Site U1588 is the shallowest, closest to shore, and youngest site drilled during Expedition 397 and is also the one with the highest sedimentation rate (20 cm/ky). The base of the 412.5 m sequence is 2.2 Ma, providing an expanded Pleistocene sequence of sediment deposited under the influence of the lower core of the Mediterranean Outflow Water (MOW). Together with other Expedition 339 sites, Site U1588 will be important for determining how the depth and intensity of the MOW has varied on orbital and millennial timescales. In addition, it also provides a marine reference section for studying Quaternary climate variability at very high temporal resolution (millennial to submillennial). A highlight of the expedition is that sediment at all sites shows very strong cyclicity in bulk sediment properties (color, magnetic susceptibility, and natural gamma radiation). Particularly remarkable are the precession cycles of the Pliocene that can be correlated peak-for-peak among sites. These cyclic variations will be used to derive an orbitally tuned timescale for Expedition 397 sites and correlate them into classic Mediterranean cyclostratigraphy. The cores recovered during Expedition 397 will form the basis of collaborative postcruise research to produce benchmark paleoclimate records for the late Miocene through Quaternary using the widest range of proxy measurements. It will take many years to complete these analyses, but the records will lead to major advances in our understanding of millennial and orbital climate changes and their underlying causes and evolving contextuality. Outreach during Expedition 397 was highly productive, reaching a record number of students and the general public across the world through several diverse platforms, including live ship-to-shore events, webinars, social media, videos, radio pieces, blog posts, and in-person activities. 

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3. Site U1588

   https://doi.org/10.14379/iodp.proc.397.106.2024  

   Abrantes, F; Hodell, DA; Alvarez_Zarikian, CA; Brooks, HL; Clark, WB; Dauchy-Tric, LFB; dos_Santos_Rocha, V; Flores, J-A; Herbert, TD; Hines, SKV; et al (June 2024, Proceedings of the International Ocean Discovery Program Expedition reports)

   Site U1588 lies on the broad, gently inclined middle-slope region of the Promontório dos Príncipes de Avis (PPA) on the southwestern Iberian margin (Figures F1, F2, F3, F4). It is the shallowest (1339 meters below sea level [mbsl]) and the closest site to the coast drilled during Expedition 397. Seismic data indicate the location is part of an extensive plastered sediment drift deposit formed under the influence of Mediterranean Outflow Water (MOW) that extends from the Gulf of Cádiz along the Portuguese margin (Hernández-Molina et al., 2003, 2006; Llave et al., 2006). Site U1588 is positioned on Seismic Line TGS-NOPEC PD00-613 (Figures F5, F6) about 8 km northeast of the intersection with Seismic Line TGS-NOPEC PD00-510 (Figure F7), where the distal part of the contourite depositional system occurs as a highly expanded sedimentary record (Hernández-Molina et al., 2014). The combination of Site U1588 (1339 mbsl) and the intermediate, MOW-influenced sites drilled during Expedition 339 (560–1073 mbsl) span the full depth range of the MOW. The record of Site U1588 will be compared with the deeper sites of Expedition 397 (2591–4692 mbsl), which are removed from contourite input and are under the influence of Northeast Atlantic Deep Water (NEADW) and Lower Deep Water (LDW) (Figure F4). Expedition 339 and 397 sites will constitute a bathymetric transect from 560 to 4691 mbsl to be used for paleoconductivity-temperature-depth (paleo-CTD) studies. The record at Site U1588 is expected to be similar to that of Integrated Ocean Drilling Program Site U1391, which was drilled 70 km south–southeast of Site U1588 at a water depth of 1085 mbsl (Figure F2). Three holes were cored and drilled to a total depth of 672 mbsf, spanning the middle Pliocene to Holocene with sedimentation rates of 13–17 cm/ky (Expedition 339 Scientists, 2013). We expected similarly high sedimentation rates at Site U1588. The high accumulation rates associated with contourite deposition provide an expanded sedimentary record to reconstruct millennial climate variability (MCV) with a resolution of a hundred years. In addition, the shallow depth of Site U1588 compared to other Expedition 397 sites is expected to yield excellent preservation of carbonate microfossils. The primary objective of Site U1588 was to drill to 500 mbsf and recover an expanded Pliocene–Pleistocene sedimentary succession formed under the influence of lower MOW (Hernández-Molina et al., 2014). The sediments of Site U1588 and those collected during Expedition 339 provide valuable material for studying how the depth and intensity of the MOW has varied on orbital and millennial timescales. Site U1588 will also provide a marine reference section for studying Quaternary climate variability at high stratigraphic resolution. Surface temperature proxies of Site U1588 will document MCV well beyond the base of the polar ice core. Because Site U1588 is closest to the coast, we expect preservation of terrestrial pollen and biomarkers that will allow linkage of the continental and marine records. Site U1588 should also preserve an MCV record of coastal upwelling along the Portuguese margin. 

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4. Site U1385

   https://doi.org/10.14379/iodp.proc.397.105.2024  

   Hodell, DA; Abrantes, F; Alvarez_Zarikian, CA; Brooks, HL; Clark, WB; Dauchy-Tric, LFB; dos_Santos_Rocha, V; Flores, J-A; Herbert, TD; Hines, SKV; et al (June 2024, Proceedings of the International Ocean Discovery Program Expedition reports)

   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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5. 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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