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  1. Semiquantitative elemental results from X-ray fluorescence (XRF) scanning of sediment cores from International Ocean Discovery Program (IODP) Site U1574 in the Vøring Plateau, Norwegian Margin, are presented in this report. XRF elemental data were collected every 1 cm from a stratigraphically complete and continuous cored section with 102% recovery from the sea bottom to ~170 meters below seafloor in Hole U1574C. We report raw element intensities (counts) for Al, Si, K, Ca, Ti, Fe, Br, Sr, and Zr and identify covariation patterns consistent with lithofacies variations. Our high-resolution XRF scanning was conducted to better characterize the sediment depositional history at Site U1574 and to aid interpretation of past environmental and oceanographic conditions in the Norwegian Margin, targeting the earliest incursion of deep water into the young North Atlantic Ocean during the Early to Middle Eocene. The high-resolution XRF data also may help improve the age-depth model for the sediment succession at Site U1574. 
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    Free, publicly-accessible full text available October 11, 2025
  2. The North Atlantic and Arctic Oceans are unquestionably major players in the climatic evolution of the Northern Hemisphere and in the history of the meridional overturning circulation of the Atlantic Ocean. The establishment of the modern North Atlantic Water (NAW) transporting heat, salt, and moisture to the Northern Hemisphere has been indicated as one of the main forcing mechanisms for the onset of Northern Hemisphere glaciation. NAW controls the extent and dynamics of circum-Arctic and circum-North Atlantic ice sheets and sea ice in addition to deep water and brine production. How the ocean system and cryosphere worked during past warmer intervals of high insulation and/or high atmospheric CO2 content is still largely unknown and debated. The required information can only be attained by offshore scientific drilling in high-resolution continuous expanded sedimentary sequences identified on the western continental margin of Svalbard (and eastern side of the Fram Strait) along the main pathway and northern penetration of the NAW flowing into the Arctic Ocean. The area around Svalbard is very sensitive to climatic variability and can be considered a sentinel of climate change. Furthermore, the reconstruction of the dynamic history of the marine-based paleo-Svalbard–Barents Sea Ice Sheet is important because it is considered the best available analog to the modern, marine-based West Antarctic Ice Sheet, for which the loss of stability is presently the major uncertainty in projecting future global sea level rise in response to the present global climate warming. 
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    Free, publicly-accessible full text available September 24, 2025
  3. Site U1595 (proposed Site CSK-08B) is located in the southern basin of the Santorini caldera at 291 meters below sea level (mbsl) (Figure F1). It was drilled in three holes (U1595A–U1595C) to a maximum recovery depth of 127.0 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). Average hole core recoveries range 46%–77%. Site U1594 addresses the same drilling objectives and lies northeast of Site U1595. Two additional sites (U1596 and U1597) lie in the northern caldera basin. Four seismic units (S1–S4) were previously recognized in the Santorini caldera (Johnston et al., 2015; Nomikou et al., 2016) (Figure F2). Seismic Units S1–S3 were thought to consist of muds and sands from cliff mass wasting (Unit S1); compacted (possibly lithified) sandy volcaniclastics from Kameni Volcano (Unit S2); and consolidated coarse blocky intracaldera tuffs, landslide debris, and/or flood gravels (Unit S3). Unit S4 was thought to be intracaldera tuff from the Late Bronze Age eruption. The four caldera sites were planned to sample Units S1–S3; test the published correlations between the two caldera basins; penetrate below Unit S3 into Unit S4; and address scientific Objectives 1, 4, 5, and 7 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022). By drilling both caldera basins and exploiting our dense seismic reflection coverage, we gained access to the 3D architecture of the entire caldera fill. We also targeted the question of why the northern basin is 100 m deeper than the southern one. Finally, we tested whether Unit S3 consisted of flood debris from the caldera flooding event (Nomikou et al., 2016) or whether it was Late Bronze Age intracaldera tuff (Johnston et al., 2015). The intracaldera sites were used for microbiological work of Objective 7. 
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    Free, publicly-accessible full text available July 30, 2025
  4. The principal aim at Site U1589 (proposed Site CSK-01A) was to reconstruct the evolution of the Anhydros Basin, including its history of subsidence, as well as to document the presence of volcanic event layers in the basin sediments and draw conclusions regarding the links between volcanism and crustal tectonics. The site is located about 10 km southwest of Amorgos Island at 484 meters below sea level (mbsl) (Figure F1). The drill site targeted the volcano-sedimentary fill of the Anhydros Basin. We received permission from the International Ocean Discovery Program (IODP) Environmental Protection and Safety Panel to touch the Alpine basement using an advanced piston corer/extended core barrel/rotary core barrel (APC/XCB/RCB) drilling strategy. The site involved three holes (U1589A–U1589C) and terminated in basement limestone at 612.4 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). Core recovery was good in Holes U1589A (78%) and U1589B (87%) and poor in Hole U1589C (24%). Site U1589 was chosen to sample the eruptive histories of both Santorini and the Kolumbo chain and was expected to yield volcaniclastics from many Kolumbo eruptions and the major Santorini eruptions. Many deposits from smaller Santorini eruptions were not expected at this distance from the volcano, in part due to flow blocking by the Kolumbo volcanic chain. Santorini has been active since 0.65 Ma, with many large explosive eruptions since about 0.36 Ma (Druitt et al., 2016). Kolumbo Volcano was known from seismic profiles to have had at least five eruptions (Hübscher et al., 2015), the last of which was in 1650 Common Era (CE) and killed 70 people on Santorini (Fuller et al., 2018). Seismic profiles provided constraints on the relative ages of the Kolumbo cones (Preine et al., 2022c) but not on the absolute ages. The site offered a near-continuous time series of volcanism in the area since rift inception. The site was also chosen to develop a core-log-seismic integration stratigraphy and compare it with the recently published seismic stratigraphy for the basin (Preine et al., 2022a) and the paleotectonic reconstruction of the region (Nomikou et al., 2016, 2018) to promote a holistic view of the Anhydros Basin evolution (Figure F2). The site transects all six seismic packages of the Anhydros rift basin, as well as the onlap surfaces between them (Nomikou et al., 2016, 2018; Preine et al., 2022a). The anticipated lithologies were undisturbed hemipelagic muds, volcaniclastics, turbidites, and finally continental basement rocks. A gravity core recovered 7 km to the east indicated that the uppermost sediments on site would consist of hemipelagic muds and volcaniclastic layers, as well as sapropels (Kutterolf et al., 2021). The Anhydros Basin is crossed by many seismic profiles obtained in campaigns between 2006 and 2019, many of them multichannel (Hübscher et al., 2015; Nomikou et al., 2016, 2018), and its southwestern part is included 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). The basin bathymetry had been studied in several marine campaigns, and fault distributions and throws had been mapped (Nomikou et al., 2016; Hooft et al., 2017). Previously published analyses of the seismic data suggested the following possible interpretations (from the bottom up; Preine et al., 2022b, 2022c): Units U1 and U2: sediment packages predating Santorini and Kolumbo volcanism; Unit U3: sediments and the products of the early Kolumbo volcanism and some of the Kolumbo cones; Unit U4: sediments associated with a major rift pulse; and Units U5 and U6: sediments and the products of Santorini activity, some of the Kolumbo cones, and the later eruptions of Kolumbo including the 1650 CE eruption. Units U3–U6 were believed to be of Pleistocene age, and Units U1 and U2 were believed to be of possible Pliocene age. The site enabled us to test these interpretations by using the cores 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. Coring at Site U1589 in the Anhydros Basin addressed scientific Objectives 1–4 and 6 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022). It was complemented by Site U1592 in the Anafi Basin because each basin taps a different sediment distributary branch of the Christiana-Santorini-Kolumbo volcanic system. 
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    Free, publicly-accessible full text available July 30, 2025
  5. Site U1593 (proposed Site CSK-04C) is located 8 km northwest of the submarine Kolumbo caldera on its flank in the Anhydros Basin at a water depth of 402 meters below sea level (mbsl) (Figure F1). It lies on Seismic Line HH06-44, offset 600 m northeast from Seismic Line HH06-22 (Figure F2). We drilled to a maximum recovery depth of 250.9 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) in three holes (U1593A–U1593C) with average core recoveries of 60%, 67%, and <1%, respectively. The seismic profiles across the Kolumbo edifice reveal five units interpreted as Kolumbo-derived volcaniclastics (K1 to K5 from the base up), with Seismic Unit K5 representing the 1650 Common Era (CE) eruption (Hübscher et al., 2015; Preine et al., 2022). The submarine cones northeast of Kolumbo postdate Unit K2 on seismic profiles, but their products were not expected to be prominent in our drill cores. The aim of drilling on the flanks of Kolumbo was to penetrate the different seismically recognized volcanic eruption units from that volcano (K1–K3 and K5 or their thin, lateral equivalents) as well as many eruption units from Santorini and traces from the submarine cones northeast of Kolumbo. This enabled characterization of the products of the Kolumbo eruptions and construction of a coherent stratigraphy for Santorini and the submarine Kolumbo volcano chain together. The anticipated lithologies were volcaniclastics, muds, and turbidites. Site U1593 lies at the foot of the Kolumbo edifice, 3 km northwest of Site U1590. Owing to poor recovery at the latter site, we decided to also drill at Site U1593, which lies on the other side (northwest) of the Kolumbo Fault from Site U1590. This had two advantages. First, we could measure the offset across the Kolumbo Fault by correlating key marker layers from one site to the other. Second, the sequence at Site U1593 was more condensed than at Site U1590, offering us older recovery and better hole stability. Like Site U1590, Site U1593 allowed us to drill Seismic Units K1–K3 and K5, and therefore nearly the entire history of Kolumbo Volcano, within the proposed drilling target depth of 581 mbsf. Intercalated seismic units were believed to contain the products of Santorini eruptions, including potentially those of smaller magnitude than recorded at the more distal basin sites. 
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    Free, publicly-accessible full text available July 30, 2025
  6. Site U1594 (proposed Site CSK-07B) is located in the southern basin of Santorini caldera at a water depth of 291 meters below sea level (mbsl) (Figure F1). It was drilled to a maximum recovery depth of 50.1 meters below seafloor (mbsf) in a single hole (U1594A) with 93% recovery before hole instability set in and the hole was terminated (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). Site U1595 addresses the same drilling objectives and lies southwest of Site U1594. Two additional sites (U1596 and U1597) lie in the northern caldera basin. Four seismic units have been recognized in the caldera (Johnston et al., 2015; Nomikou et al., 2016) (Figure F2). They were thought to consist of muds and sands from cliff mass wasting (Seismic Unit S1); compacted (possibly lithified) sandy volcaniclastics from Kameni Volcano (Unit S2); and consolidated coarse blocky intracaldera tuffs, landslide debris, and/or flood gravels (Unit S3). Unit S4 was thought to be intracaldera tuff from the Late Bronze Age eruption. The four caldera sites were planned to sample Units S1–S3; test the published correlations between the two caldera basins; penetrate below Unit S3 into Unit S4; and address scientific Objectives 1, 4, 5, and 7 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022). By drilling both caldera basins and exploiting our dense seismic reflection coverage, we gained access to the 3D architecture of the entire caldera fill. We also targeted the question of why the northern basin is 100 m deeper than the southern one. Finally, we tested whether Unit S3 consisted of flood debris from the caldera flooding event (Nomikou et al., 2016) or was Late Bronze Age intracaldera tuff (Johnston et al., 2015). The intracaldera sites were used for microbiological work of scientific Objective 7. 
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    Free, publicly-accessible full text available July 30, 2025
  7. Site U1592 (proposed Site CSK-09A) is located ~10 km southeast of Anhydros Island in the Anafi Basin at 693 meters below sea level (mbsl) (Figure F1). The aim at the site was to penetrate the entire volcano-sedimentary fill as far as the Alpine basement to reconstruct the evolution of the Anafi Basin: history of subsidence, presence of volcanic event layers in the basin sediments, and links between volcanism and crustal tectonics. We drilled to a maximum recovery depth of 519.8 meters below seafloor (mbsf) in two holes (U1592A and U1592B), terminating in limestone basement (all depths below seafloor [mbsf] 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). Average core recoveries were 71% (Hole U1592A) and 50% (Hole U1592B). The Anafi Basin potentially recorded the full volcanic history of Santorini (and any older centers) since rift inception, but it was envisaged to probably also contain few eruptive products from Kolumbo. Drilling enabled reconstruction of the volcanic, sedimentary, and tectonic histories of the Anafi Basin, allowing us to compare its evolution with that of the Anhydros Basin. The site was also chosen to develop a core-log-seismic integration stratigraphy and compare it with the recently published seismic stratigraphy for the basin (Preine et al., 2022a, 2022b) and the paleotectonic reconstruction of the region (Nomikou et al., 2016, 2018). The site transects six seismic packages of the Anafi rift basin, as well as the onlap surfaces between them (Nomikou et al., 2016, 2018; Preine et al., 2022a) (Figure F2). The Anafi Basin is crossed by many seismic profiles obtained in campaigns between 2006 and 2019, many of them multichannel (Hübscher et al., 2015; Nomikou et al., 2016, 2018). It is included 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). The basin bathymetry had been studied in several marine campaigns, and fault distributions and throws had been mapped (Nomikou et al., 2016; Hooft et al., 2017). Previously published analyses of the seismic data suggested the following possible interpretations (from the bottom up; Preine et al., 2022a, 2022b): Units U1 and U2: sediment packages predating Santorini and Kolumbo volcanism; Unit U3: sediments and the products of the early Kolumbo volcanism and some of the Kolumbo cones; Unit U4: sediments associated with a major rift pulse; and Units U5 and U6: sediments and the products of Santorini activity, some of the Kolumbo cones, and the later eruptions of Kolumbo including the 1650 Common Era (CE) eruption. Units U3–U6 were believed to be of Pleistocene age, and Units U1 and U2 were believed to be possibly Pliocene. The site enabled us to test these interpretations by using the cores 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, through integration with seismic profiles and chronologic data, of time-integrated basin subsidence rates. Coring at Site U1592 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 taps a different sediment distributary branch of the Christiana-Santorini-Kolumbo volcanic system. 
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    Free, publicly-accessible full text available July 30, 2025
  8. Site U1590 (proposed Site CSK-03A) is located 5 km northwest of the submarine Kolumbo crater on its flank in the Anhydros Basin at 397 meters below sea level (mbsl) (Figure F1). It lies on the intersection of Seismic Lines HH06-22 and HH06-34 (Figure F2). Drilling took place in two holes (U1590A and U1590B) to a maximum recovery depth of 627.8 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). Average core recovery in Hole U1590A was moderate (61%), but recovery in Hole U1590B was poor (14%). The seismic profiles across the Kolumbo edifice reveal five units interpreted as Kolumbo-derived volcaniclastics (K1–K5, from the base up; Figure F2) with Unit K5 representing the 1650 Common Era (CE) eruption (Hübscher et al., 2015; Preine et al., 2022). The submarine cones northeast of Kolumbo postdate Unit K2 on seismic profiles, but their products are not expected to be prominent in our drill cores. The aim of drilling on the flanks of Kolumbo was to penetrate the different seismically recognized volcanic eruption units from that volcano (K1, K2, K3, and K5 or their thin, lateral equivalents) as well as many eruption units from Santorini and traces from the submarine cones northeast of Kolumbo. This enabled characterization of the products of the Kolumbo eruptions and construction of a coherent stratigraphy for Santorini and the submarine Kolumbo volcano chain together. The anticipated lithologies were volcaniclastics, muds, and turbidites. Site U1590 lies at the foot of the Kolumbo edifice; it allowed us to drill Seismic Units K1, K2, K3, and K5 and therefore nearly the entire history of Kolumbo Volcano. Intercalated seismic units are believed to contain the products of Santorini eruptions, including potentially those of smaller magnitude than recorded at the more distal basin sites. 
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    Free, publicly-accessible full text available July 30, 2025
  9. The objectives of International Ocean Discovery Program Expedition 398, Hellenic Arc Volcanic Field (11 December 2022 to 10 February 2023), were to study the volcanic record of the central Hellenic island arc; document the links and feedbacks between volcanism/magmatism, crustal tectonics, and sea level; investigate the processes and products of shallow submarine eruptions of silicic magma; and groundtruth the seismic stratigraphy of Santorini caldera. Reconstructing the subsidence history of the southern Aegean Sea and searching for deep life inside and outside of Santorini caldera were additional objectives. During the expedition, 10 primary and alternate sites that were originally proposed were drilled, in addition to 2 extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from on land and others hitherto unknown, pushing back the onset of volcanism in the area into the Early Pleistocene or even Pliocene. Significant events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and open the way to unraveling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy, as diagenetic effects complicated the magnetic reversal record significantly. Drilling penetrated the Alpine basement at three basin sites northeast of Santorini, whereas in the Christiana Basin to the southwest it penetrated a thick sequence of Messinian evaporites. Drilling inside Santorini caldera penetrated to ~120 meters below seafloor, less than planned due to hole instability issues but deep enough to groundtruth the seismic stratigraphy and sample the different layers. One intracaldera hole yielded a detailed tephra record of the history of the Kameni Islands, as well as possible evidence for deep bacterial colonies within the caldera. Despite variable recovery in the unstable pumice and ash deposits, the expedition was a significant success that may address almost all the scientific objectives once the laboratory work has been done. 
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    Free, publicly-accessible full text available July 30, 2025
  10. Site U1598 (proposed Site 14A) is located ~8 km northwest of Christiana Island and ~20 km southwest of Santorini (Figure F1) at 521.5 meters below sea level (mbsl). The drill site targeted the volcano-sedimentary fill of the Christiana Basin in two holes (U1598A and U1598B), with a maximum recovery depth of 95.7 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) and core recoveries of 69% and 34%, respectively. The drill site targeted the volcano-sedimentary fill of the Christiana Basin. This basin was believed to have formed by subsidence along an ENE–WSW fault system before the changing tectonic regime activated the current northeast–southwest rift system in which the Christiana-Santorini-Kolumbo (CSK) volcanic field lies (Tsampouraki-Kraounaki and Sakellariou, 2018; Preine et al., 2022a, 2022b). The Christiana Basin is deeper than the Anhydros and Anafi Basins; its volcano-sedimentary fill potentially recorded the earlier volcanic history of the CSK volcanic field (including the products of Christiana and early Santorini), as well as the younger Santorini and possibly the Milos Volcano to the west along the Hellenic volcanic arc. The now-extinct Christiana Volcano produced lavas and tuffs of unknown ages (Aarburg and Frechen, 1999). An ignimbrite found on Christiani Island (one of the two small islands of the Christiana Volcano), Santorini, and the nonvolcanic island of Anaphi, called the Christiani Ignimbrite, was identified (Keller et al., 2010). Site U1598 was chosen to complement the previously drilled Site U1591. The aim was to retarget a thick pumice layer found at Site U1591 (uppermost ~65 mbsf; Figure F2), for which we had insufficient samples for our scientific aims, to increase our recovery of the interval. The site addresses scientific Objectives 1–4 and 6 of the Expedition 398 Scientific Prospectus (Druitt et al., 2022). 
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    Free, publicly-accessible full text available July 30, 2025