Description: Highlights • Core-log-seismic correlation allows to assign ages to the Scotia Sea seismic record. • Major implications are derived on the relation between regional and global events. • The main stratigraphic events are much younger than previously proposed. • Three major phases for the regional oceanography are observed from late Miocene. • These phases appear to be closely linked to the Antarctic Ice Sheet dynamics. Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11.

Description: International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world.

Description: We present the results of P-to-S receiver function analysis to improve the 3D image of the sedimentary layer, the upper crust, and lower crust in the Pannonian Basin area. The Pannonian Basin hosts deep sedimentary depocentres superimposed on a complex basement structure and it is surrounded by mountain belts. We processed waveforms from 221 three-component broadband seismological stations. As a result of the dense station coverage, we were able to achieve so far unprecedented spatial resolution in determining the velocity structure of the crust. We applied a three-fold quality control process; the first two being applied to the observed waveforms and the third to the calculated radial receiver functions. This work is the first comprehensive receiver function study of the entire region. To prepare the inversions, we performed station-wise H-Vp/Vs grid search, as well as Common Conversion Point migration. Our main focus was then the S-wave velocity structure of the area, which we determined by the Neighborhood Algorithm inversion method at each station, where data were sub-divided into back-azimuthal bundles based on similar Ps delay times. The 1D, nonlinear inversions provided the depth of the discontinuities, shear-wave velocities and Vp/Vs ratios of each layer per bundle, and we calculated uncertainty values for each of these parameters. We then developed a 3D interpolation method based on natural neighbor interpolation to obtain the 3D crustal structure from the local inversion results. We present the sedimentary thickness map, the first Conrad depth map and an improved, detailed Moho map, as well as the first upper and lower crustal thickness maps obtained from receiver function analysis. The velocity jump across the Conrad discontinuity is estimated at less than 0.2 km/s over most of the investigated area. We also compare the new Moho map from our approach to simple grid search results and prior knowledge from other techniques. Our Moho depth map presents local variations in the investigated area: the crust-mantle boundary is at 20–26 km beneath the sedimentary basins, while it is situated deeper below the Apuseni Mountains, Transdanubian and North Hungarian Ranges (28–33 km), and it is the deepest beneath the Eastern Alps and the Southern Carpathians (40–45 km). These values reflect well the Neogene evolution of the region, such as crustal thinning of the Pannonian Basin and orogenic thickening in the neighboring mountain belts.

Description: Highlights • Rayleigh-wave phase velocity in the wider Dinarides region using the two-station method. • Uppermost mantle shear-wave velocity model of the Dinarides-Adriatic Sea region. • Velocity model reveals a robust high-velocity anomaly present under the whole Dinarides. • High-velocity anomaly reaches depth of 160 km in the northern Dinarides to more than 200 km under southern Dinarides. • New structural model incorporating delamination as one of the processes controlling the continental collision in the Dinarides. The interaction between the Adriatic microplate (Adria) and Eurasia is the main driving factor in the central Mediterranean tectonics. Their interplay has shaped the geodynamics of the whole region and formed several mountain belts including Alps, Dinarides and Apennines. Among these, Dinarides are the least investigated and little is known about the underlying geodynamic processes. There are numerous open questions about the current state of interaction between Adria and Eurasia under the Dinaric domain. One of the most interesting is the nature of lithospheric underthrusting of Adriatic plate, e.g. length of the slab or varying slab disposition along the orogen. Previous investigations have found a low-velocity zone in the uppermost mantle under the northern-central Dinarides which was interpreted as a slab gap. Conversely, several newer studies have indicated the presence of the continuous slab under the Dinarides with no trace of the low velocity zone. Thus, to investigate the Dinaric mantle structure further, we use regional-to-teleseismic surface-wave records from 98 seismic stations in the wider Dinarides region to create a 3D shear-wave velocity model. More precisely, a two-station method is used to extract Rayleigh-wave phase velocity while tomography and 1D inversion of the phase velocity are employed to map the depth dependent shear-wave velocity. Resulting velocity model reveals a robust high-velocity anomaly present under the whole Dinarides, reaching the depths of 160 km in the north to more than 200 km under southern Dinarides. These results do not agree with most of the previous investigations and show continuous underthrusting of the Adriatic lithosphere under Europe along the whole Dinaric region. The geometry of the down-going slab varies from the deeper slab in the north and south to the shallower underthrusting in the center. On-top of both north and south slabs there is a low-velocity wedge indicating lithospheric delamination which could explain the 200 km deep high-velocity body existing under the southern Dinarides.

Description: Early Pleistocene Marine Isotope Stage (MIS)-31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000-year resolution, spanning 1.110–1.030 Ma, diatom-based reconstruction of primary productivity, relative sea surface temperature changes, sea-ice proximity/open ocean conditions and diatom species absolute abundances during MIS-31, from the Scotia Sea (59°S) using deep-sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time-stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS-31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere-phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea-ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub-ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS-31, a warmer than Holocene interglacia

Description: The Tierra Blanca (TB) eruptive suite comprises the last four major eruptions of Ilopango caldera in El Salvador (≤45 ka), including the youngest Tierra Blanca Joven eruption (TBJ; ∼106 km3): the most voluminous event during the Holocene in Central America. Despite the protracted and productive history of explosive silicic eruptions at Ilopango caldera, many aspects regarding the longevity and the prevailing physicochemical conditions of the underlying magmatic system remain unknown. Zircon 238U-230Th geochronology of the TB suite (TBJ, TB2, TB3, and TB4) reveals a continuous and overlapping crystallization history among individual eruptions, suggesting persistent melt presence in thermally and compositionally distinct magma reservoirs over the last ca. 80 kyr. The longevity of zircon is in contrast to previously determined crystallization timescales of 〈10 kyr for major mineral phases in TBJ. This dichotomy is explained by a process of rhyolitic melt segregation from a crystal-rich refractory residue that incorporates zircon, whereas a new generation of major mineral phases crystallized shortly before eruption. Ti-in-zircon temperatures and amphibole geothermobarometry suggest that rhyolitic melt was extracted from different storage zones of the magma reservoir as indicated by distinct but synchronous thermochemical zircon histories among the TB suite eruptions. Zircon from TBJ and TB2 suggests magma differentiation within deeper and hotter parts of the reservoir, whereas zircon from TB3 and TB4 instead hints at crystallization in comparatively shallower and cooler domains. The assembly of the voluminous TBJ magma reservoir was also likely enhanced by cannibalization of hydrothermally altered components as suggested by low-δ18O values in zircon (+4.5 ± 0.3‰).

Description: Ice loss in the Southern Hemisphere has been greatest over the past 30 years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg-rafted debris (IBRD) sourced from the Pacific- and Atlantic-facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm-scale coarse-grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal-rich sediments deposited ∼1.2 Ma during a relatively warm regional climate. Our microCT-based analysis of the layer's in-situ fabric confirms its ice-rafted origin. We further infer that it is the product of an intense but short-lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic 40Ar/39Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to “dirty” icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366-m thick Pliocene and early Pleistocene sequence that is much more dropstone-rich than its overlying sediments. We speculate this fact may reflect that WAIS mass-balance was highly dynamic during the ∼41-kyr (inter)glacial world. Key Points - We present the first provenance data generated for Pleistocene-aged iceberg-rafted debris deposited in Iceberg Alley - We conclude that prominent iceberg-rafted debris layers deposited at Pirie Basin Site U1538 ∼1.2 Ma were sourced from West Antarctica - They represent intense suborbitally-paced episodes of iceberg discharge from tidewater glaciers, most likely in the Weddell Embayment

Description: Export of sinking particles from the surface ocean is critical for carbon sequestration and to provide energy to the deep biosphere. The magnitude and spatial patterns of this export have been estimated in the past by in situ particle flux observations, satellite-based algorithms, and ocean biogeochemical models; however, these estimates remain uncertain. Here, we use a recent machine learning reconstruction of global ocean particle size distributions (PSDs) from Underwater Vision Profiler 5 measurements to estimate carbon fluxes by sinking particles (35 μm–5 mm equivalent spherical diameter) from the surface ocean. We combine global maps of PSD properties with empirical relationships constrained against in situ flux observations to calculate particulate carbon export from the euphotic zone (5.8 ± 0.1 Pg C y−1) and annual maximum mixed layer depths (6.1 ± 0.1 Pg C y−1). The new flux reconstructions suggest a less variable seasonal cycle in the tropical ocean and a more persistent export in the Southern Ocean than previously recognized. Smaller particles (less than 418 μm) contribute most of the flux globally, while larger particles become more important at high latitudes and in tropical upwelling regions. Export from the annual maximum mixed layer exceeds that from the euphotic zone over most of the low-latitude ocean, suggesting shallow particle recycling and net heterotrophy in the deep euphotic zone. These estimates open the way to fully three-dimensional global reconstructions of particle fluxes in the ocean, supported by the growing database of in situ optical observations.

Description: The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is similar to 60% larger in models (-0.72 vs. -0.44 PgC year-1, 1998-2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year-1 in observational product and +0.54 PgCO2-e year-1 in model median) and CH4 (+0.21 PgCO2-e year-1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%-60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate. The coastal ocean regulates greenhouse gases. It acts as a sink of carbon dioxide (CO2) but also releases nitrous oxide (N2O) and methane (CH4) into the atmosphere. This synthesis contributes to the second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2) and provides a comprehensive view of the coastal air-sea fluxes of these three greenhouse gases at the global scale. We use a multi-faceted approach combining gap-filled observation-based products and ocean biogeochemical models. We show that the global coastal ocean is a net sink of CO2 in both observational products and models, but the coastal uptake of CO2 is similar to 60% larger in models than in observation-based products due to model-product differences in seasonality. The coastal CO2 sink is strengthening but the magnitude of this strengthening is poorly constrained. We also find that the coastal emissions of N2O and CH4 counteract a substantial part of the effect of coastal CO2 uptake in the atmospheric radiative balance (by 30%-60% in CO2-equivalents), highlighting the need to consider these three gases together to understand the influence of the coastal ocean on climate. We synthesize air-sea fluxes of CO2, nitrous oxide and methane in the global coastal ocean using observation-based products and ocean models The coastal ocean CO2 sink is 60% larger in ocean models than in observation-based products due to systematic differences in seasonality Coastal nitrous oxide and methane emissions offset 30%-60% of the CO2 coastal uptake in the net radiative balance

Description: Submarine groundwater discharge (SGD) is a globally important process supplying nutrients and trace elements to the coastal environment, thus playing a pivotal role in sustaining marine primary productivity. Along with nutrients, groundwater also contains allochthonous microbes that are discharged from the terrestrial subsurface into the sea. Currently, little is known about the interactions between groundwater‐borne and coastal seawater microbial populations, and groundwater microbes' role upon introduction to coastal seawater populations. Here, we investigated seawater microbial abundance, activity and diversity in a site strongly influenced by SGD. In addition, through laboratory‐controlled bottle incubations, we mimicked different mixing scenarios between groundwater and seawater. Our results demonstrate that the addition of 0.1 μm filtered groundwater stimulated heterotrophic activity and increased microbial abundance compared to control coastal seawater, whereas 0.22 μm filtration treatments induced primary productivity and Synechococcus growth. 16S rRNA gene sequencing showed a strong shift from a SAR11‐rich community in the control samples to Rhodobacteraceae dominance in the 〈0.1 μm treatment, in agreement with Rhodobacteraceae enrichment in the SGD field site. These results suggest that microbes delivered by SGD may affect the abundance, activity and diversity of intrinsic microbes in coastal seawater, highlighting the cryptic interplay between groundwater and seawater microbes in coastal environments, which has important implications for carbon cycling. Plain Language Summary Submarine groundwater discharge (SGD) is an important process where groundwater flows into the ocean along the coast. When the groundwater mixes with seawater, the microbes from both sources interact with each other, which can impact the diversity, activity, and amount of microbes in the coastal environment. Currently, little is known about how groundwater‐borne microbes affect marine microbial populations. Our research shows that when groundwater microbes are removed before mixing groundwater with seawater, the abundance and activity of certain microbes that consume organic matter significantly increase. Additionally, we noticed a significant difference in the types of microbes present between the sites where SGD occurs versus background (uninfluenced) coastal water, especially in terms of the microbes that consume organic matter. Overall, this study suggests that there is a connection between groundwater and seawater microbes, which can influence the delicate balance between organisms that produce carbon and those that consume it. This has important implications for how carbon cycles globally. Key Points Groundwater discharge into the coastal zone delivers both nutrients and allochthonous microbes Groundwater microbes interact with seawater populations, by which affecting the delicate autotroph‐heterotroph balance Subterranean microbial processes are key drivers of food webs, potentially affecting biogenic carbon fluxes in the ocean