Lofi Johanna

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  • Article
    Offshore freshened groundwater in continental margins
    (American Geophysical Union, 2020-11-20) Micallef, Aaron ; Person, Mark ; Berndt, Christian ; Bertoni, Claudia ; Cohen, Denis ; Dugan, Brandon ; Evans, Rob L. ; Haroon, Amir ; Hensen, Christian ; Jegen, Marion ; Key, Kerry ; Kooi, Henk ; Liebetrau, Volker ; Lofi, Johanna ; Mailloux, Brian J. ; Martin-Nagle, Renée ; Michael, Holly A. ; Müller, Thomas ; Schmidt, Mark ; Schwalenberg, Katrin ; Trembath-Reichert, Elizabeth ; Weymer, Bradley ; Zhang, Yipeng ; Thomas, Ariel T.
    First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyze it to establish the general characteristics and controlling factors. We also assess methods used to map and characterize OFG, identify major knowledge gaps, and propose strategies to address them. OFG has a global volume of 1 × 106 km3; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea level lowstands. Key factors influencing OFG distribution are topography-driven flow, salinization via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection profiling, electromagnetic surveying, and numerical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three-dimensional hydrological models. We show that such advances, combined with site-specific modeling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub-seafloor geomicrobiology.
  • Article
    High-resolution and high-precision correlation of dark and light layers in the Quaternary hemipelagic sediments of the Japan Sea recovered during IODP Expedition 346
    (Springer, 2018-03-26) Tada, Ryuji ; Irino, Tomohisa ; Ikehara, Ken ; Karasuda, Akinori ; Sugisaki, Saiko ; Xuan, Chuang ; Sagawa, Takuya ; Itaki, Takuya ; Kubota, Yoshimi ; Lu, Song ; Seki, Arisa ; Murray, Richard W. ; Alvarez-Zarikian, Carlos A. ; Anderson, William T. ; Bassetti, Maria-Angela ; Brace, Bobbi J. ; Clemens, Steven C. ; da Costa Gurgel, Marcio H. ; Dickens, Gerald R. ; Dunlea, Ann G. ; Gallagher, Stephen J. ; Giosan, Liviu ; Henderson, Andrew C. G. ; Holbourn, Ann E. ; Kinsley, Christopher W. ; Lee, Gwang Soo ; Lee, Kyung Eun ; Lofi, Johanna ; Lopes, Christina I. C. D. ; Saavedra-Pellitero, Mariem ; Peterson, Larry C. ; Singh, Raj K. ; Toucanne, Samuel ; Wan, Shiming ; Zheng, Hongbo ; Ziegler, Martin
    The Quaternary hemipelagic sediments of the Japan Sea are characterized by centimeter- to decimeter-scale alternation of dark and light clay to silty clay, which are bio-siliceous and/or bio-calcareous to a various degree. Each of the dark and light layers are considered as deposited synchronously throughout the deeper (> 500 m) part of the sea. However, attempts for correlation and age estimation of individual layers are limited to the upper few tens of meters. In addition, the exact timing of the depositional onset of these dark and light layers and its synchronicity throughout the deeper part of the sea have not been explored previously, although the onset timing was roughly estimated as ~ 1.5 Ma based on the result of Ocean Drilling Program legs 127/128. Consequently, it is not certain exactly when their deposition started, whether deposition of dark and light layers was synchronous and whether they are correlatable also in the earlier part of their depositional history. The Quaternary hemipelagic sediments of the Japan Sea were drilled at seven sites during Integrated Ocean Drilling Program Expedition 346 in 2013. Alternation of dark and light layers was recovered at six sites whose water depths are > ~ 900 m, and continuous composite columns were constructed at each site. Here, we report our effort to correlate individual dark layers and estimate their ages based on a newly constructed age model at Site U1424 using the best available paleomagnetic datum and marker tephras. The age model is further tuned to LR04 δ18O curve using gamma ray attenuation density (GRA) since it reflects diatom contents that are higher during interglacial high-stands. The constructed age model for Site U1424 is projected to other sites using correlation of dark layers to form a high-resolution and high-precision paleo-observatory network that allows to reconstruct changes in material fluxes with high spatio-temporal resolutions.