ALBERT

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Estapa, M., Buesseler, K., Durkin, C. A., Omand, M., Benitez-Nelson, C. R., Roca-Marti, M., Breves, E., Kelly, R. P., & Pike, S. Biogenic sinking particle fluxes and sediment trap collection efficiency at Ocean Station Papa. Elementa: Science of the Anthropocene, 9(1), (2021): 00122, https://doi.org/10.1525/elementa.2020.00122.

Description: Comprehensive field observations characterizing the biological carbon pump (BCP) provide the foundation needed to constrain mechanistic models of downward particulate organic carbon (POC) flux in the ocean. Sediment traps were deployed three times during the EXport Processes in the Ocean from RemoTe Sensing campaign at Ocean Station Papa in August–September 2018. We propose a new method to correct sediment trap sample contamination by zooplankton “swimmers.” We consider the advantages of polyacrylamide gel collectors to constrain swimmer influence and estimate the magnitude of possible trap biases. Measured sediment trap fluxes of thorium-234 are compared to water column measurements to assess trap performance and estimate the possible magnitude of fluxes by vertically migrating zooplankton that bypassed traps. We found generally low fluxes of sinking POC (1.38 ± 0.77 mmol C m–2 d–1 at 100 m, n = 9) that included high and variable contributions by rare, large particles. Sinking particle sizes generally decreased between 100 and 335 m. Measured 234Th fluxes were smaller than water column 234Th fluxes by a factor of approximately 3. Much of this difference was consistent with trap undersampling of both small (〈32 μm) and rare, large particles (〉1 mm) and with zooplankton active migrant fluxes. The fraction of net primary production exported below the euphotic zone (0.1% light level; Ez-ratio = 0.10 ± 0.06; ratio uncertainties are propagated from measurements with n = 7–9) was consistent with prior, late summer studies at Station P, as was the fraction of material exported to 100 m below the base of the euphotic zone (T100, 0.55 ± 0.35). While both the Ez-ratio and T100 parameters varied weekly, their product, which we interpret as overall BCP efficiency, was remarkably stable (0.055 ± 0.010), suggesting a tight coupling between production and recycling at Station P.

Description: The authors would like to acknowledge funding support from the NASA EXPORTS program (Award 80NSSC17K0662) for all sediment trap data presented here. Net primary production data collection was supported by EXPORTS (Award 80NSSC17K568) to Oregon State University. Thorium data collection was supported by EXPORTS (Award 80NSSC17K0555) to KB, CRBN, and L. Resplandy.

Description: The geological evolution of the western Mediterranean exhibits complicated interactions between orogenic processes and widespread extensional tectonics. The region is located in a convergent plate margin separating Africa and Europe, and consists of marine basins – the Alboran Sea, the Algerian- Provençal Basin, the Valencia trough, the Ligurian Sea and the Tyrrhenian Sea- which formed as back-arc basins since the Oligocene. In most reconstructions, it has been stressed that back-arc extension led to drifting of continental blocks and to large-scale block rotations. The opening of the Ligurian Sea. is in fact the result of counterclockwise rotation of Corsica and Sardinia. From the point of view of seismicity, the south western Alps and northern part of the Ligurian basin are subject to frequent earthquakes of low to moderate magnitudes. However significantly destructive events are known to have occurred in the past (e.g. 1564 and 1887). Apart from these rare large events, regional studies agree in concluding that the important local microseismicity appears to be poorly focused (e.g., COURBOULEX et alii, 2007) and that, if some tectonic lines are documented onland (COURBOULEX et alii, 2001), the active structures at sea remain unknown. It is therefore an essential prerequisite to gain better insight into the deep seismogenic structures along the North Ligurian margin and even farther offshore, in the identified oceanic domain. The fact that some of these structures can undergo ruptures of Mw~6.5, such as the 1887 event (BAKUN & SCOTTI, 2006), suggests that, at least to some extent, instrumental insufficiencies in the detection and location of microseismicity is a limit to identify active faults that have not experienced large instrumented ruptures to date. The irregular coverage provided by regional seismic networks produces a bias in the recording of local seismicity. Permanent stations are naturally limited to land areas and fail to properly constrain seismicity offshore. Taking into consideration the peculiarities of regional dynamics (low strain rates, rare large events and a regular seismic activity limited to small events with M 〈 3-4), even onshore seismicity is insufficiently covered by permanent networks and requires dense temporary instrumenting by mobile stations. Considering the potential threat of strong offshore earthquakes, it is of first importance to characterize faults that are prone to rupture in order to quantify associated seismic and tsunami hazards. Assuming some weak seismicity exists along these faults and remains undetected by onland networks, some marine stations are necessary to address instrumental remoteness and help delineate active structures. Moreover, since the velocity models used for locations are obtained by inverting seismic data and the reliability of their locations depend, in turn, from the quality of the velocity model used for their hypocentral parameters, the constraints on the seismic path provided by a more dense seismic network may contribute to a more accurate reference model. In this study, we profited from the recent developments in sea bottom seismic instrumentation to deploy OBSs above the zones of the North Ligurian to perform seismic shots and obtain the distribution of seismic velocities with 3D active tomography. We also took the opportunity of the long term (6 months) OBSs reduced array to decrease both the detection threshold and recording distances so as to obtain more complete catalogs and better localisations.

Description: Published

Description: 789-791

Description: 1T. Struttura della Terra

Description: N/A or not JCR

Description: The comparison between crustal stress and surface strain azimuthal patterns has provided new insights into several complex tectonic settings worldwide. Here, we performed such a comparison for Egypt taking into account updated datasets of seismological and geodetic observations. In north-eastern Egypt, the stress field shows a fan-shaped azimuthal pattern with a WNW–ESE orientation on the Cairo region, which progressively rotated to NW–SE along the Gulf of Aqaba. The stress field shows a prevailing normal faulting regime, however, along the Sinai/Arabia plate boundary it coexists with a strike–slip faulting one (σ1 ≅ σ2 〉 σ3), while on the Gulf of Suez, it is characterized by crustal extension occurring on near-orthogonal directions (σ1 〉 σ2 ≅ σ3). On the Nile Delta, the maximum horizontal stress (SHmax) pattern shows scattered orientations, while on the Aswan region, it has a WNW–ESE strike with pure strike–slip features. The strain-rate field shows the largest values along the Red Sea and the Sinai/Arabia plate boundary. Crustal stretching (up to 40 nanostrain/yr) occurs on these areas with WSW–ENE and NE–SW orientations, while crustal contraction occurs on northern Nile Delta (10 nanostrain/yr) and offshore (~35 nanostrain/yr) with E–W and N–S orientations, respectively. The comparison between stress and strain orientations over the investigated area reveals that both patterns are near-parallel and driven by the same large-scale tectonic processes.

Description: This research was partially funded by the Programa Operativo FEDER Andalucía 2014-2020—A call made by the University of Jaén 2018.

Description: Published

Description: 1398

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: A comparative analysis of geodetic versus seismic moment-rate estimations makes it possible to distinguish between seismic and aseismic deformation, define the style of deformation, and also to reveal potential seismic gaps. This analysis has been performed for Egypt where the present-day tectonics and seismicity result from the long-lasting interaction between the Nubian, Eurasian, and Arabian plates. The data used comprises all available geological and tectonic information, an updated Poissonian earthquake catalog (2200 B.C.–2020 A.D.) including historical and instrumental datasets, a focal-mechanism solutions catalog (1951–2019), and crustal geodetic strains from Global Navigation Satellite System (GNSS) data. The studied region was divided into ten (EG-01 to EG-10) crustal seismic sources based mainly on seismicity, focal mechanisms, and geodetic strain characteristics. The delimited seismic sources cover the Gulf of Aqaba–Dead Sea Transform Fault system, the Gulf of Suez–Red Sea Rift, besides some potential seismic active regions along the Nile River and its delta. For each seismic source, the estimation of seismic and geodetic moment-rates has been performed. Although the obtained results cannot be considered to be definitive, among the delimited sources, four of them (EG-05, EG-06, EG-08, and EG-10) are characterized by low seismic-geodetic moment-rate ratios (〈20%), reflecting a prevailing aseismic behavior. Intermediate moment-rate ratios (from 20% to 60%) have been obtained in four additional zones (EG-01, EG-04, EG-07, and EG-09), evidencing how the seismicity accounts for a minor to a moderate fraction of the total deformational budget. In the other two sources (EG-02 and EG-03), high seismic-geodetic moment-rates ratios (〉60%) have been observed, reflecting a fully seismic deformation

Description: This research has been partially funded in the frame of the Programa Operativo FEDER Andalucía 2014–2020-call made by the University of Jaén, 2018.

Description: Published

Description: 7836

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: Dataset: Sediment trap sinking particle data

Description: This dataset includes general measurements for sediment trap casts at 5 stations along a transect between Hawaii and Alaska. Data was collected in August 2017 onboard R/V Kilo Moana cruise KM1712. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/860424

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1220600, NSF Division of Ocean Sciences (NSF OCE) OCE-1220302

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(1), (2021): e2020JC016802, https://doi.org/10.1029/2020JC016802.

Description: The neodymium isotopic composition of the detrital (lithogenic) fraction (εNd‐detrital) of surface sediments and sinking particles was examined to constrain transport trajectories associated with hemipelagic sedimentation on the northwest Atlantic margin. The provenance of resuspended sediments and modes of lateral transport in the water column were of particular interest given the energetic hydrodynamic regime that sustains bottom and intermediate nepheloid layers over the margin. A large across‐margin gradient of ∼5 εNd units was observed for surface sediments, implying strong contrasts in sediment provenance, with εNd‐detrital values on the lower slope similar to those of “upstream regions” (Scotian margin) under the influence of the Deep Western Boundary Current (DWBC). Sinking particles collected at three depths at a site (total water depth, ∼3,000 m) on the New England margin within the core of the DWBC exhibited a similarly large range in εNd‐detrital values. The εNd‐detrital values of particles intercepted at intermediate water depths (1,000 and 2,000 m) were similar to each other but significantly higher than those at 3,000 m (∼50 m above the seafloor). These observations suggest that lithogenic material accumulating in the upper two traps was primarily advected in intermediate nepheloid layers emanating from the adjacent shelf, while that at 3,000 m is strongly influenced by sediment resuspension and along‐margin, southward lateral transport within the bottom nepheloid layer via entrainment in the DWBC. Our results highlight the importance of both along‐ and across‐margin sediment transport as vectors for lithogenic material and associated organic carbon transport.

Description: This research was funded by the NSF Ocean Sciences Chemical Oceanography program (OCE‐0425677; OCE‐0851350). JH was partly supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (2020R1A2C1008378).

Description: 2021-06-04