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Marine Geology
Elsevier Science B.V.
Marine Geology

Elsevier Science B.V.

0025-3227

Marine Geology/Journal Marine GeologySCIISTPAHCIEI
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    Dynamic evolution of a secondary turbidity maximum under various forcing conditions in a microtidal estuary

    Seo, Jun YoungChoi, Byoung-JuRyu, JongseongHa, Ho Kyung...
    12页
    查看更多>>摘要：Axial survey and in situ mooring in microtidal Masan Bay were conducted to reveal the mechanism for movement of secondary turbidity maximum (STM) and sediment resuspension. The Bay is characterized by sluggish water circulation with a vertically well-mixed water column. The strength of the residual estuarine current (& UDelta;u) was enhanced by the combined effects of decreased tidal currents, increased precipitation, and down-estuary (northerly) winds, whereas & UDelta;u was weakened by increased tidal currents and up-estuary (southerly) winds. The variability of current asymmetry originated from & UDelta;u contributed to the entrapment of suspended sediments, creating a mobile sediment pool in central regions of the Bay. The sediments resuspended from the mobile sediment pool were more influenced by residual currents than the tidal currents, and they remained in suspension near bed. When the down-estuary winds were applied to the mobile sediment pool, the near-bed sediments were readily resuspended to form an STM > 40 mg l(-1). The STM moved up-estuary by persistent high & UDelta;u and down-estuary by an intermittent low & UDelta;u. Over the entire measurement periods, the STM moved by at least 450 m toward the up-estuary. As the consolidated sediment layer was exposed by the movement of the STM, near-bed currents were ineffective in resuspending sediments from the consolidated layer even though the winds provided sufficient current strength. Due to the depletion of available sediments for resuspension, the STM was not fully generated. This study highlights that the STM in a microtidal estuary can be determined by the combined function of various forcings such as tide, wind, and precipitation.
      原文链接:
    • NSTL
    • Elsevier

    Deep-water sedimentation processes on a glaciated margin: The Foula Wedge trough mouth fan, West of Shetland

    Caruso, SimonaMaselli, VittorioRea, BriceSpagnolo, Matteo...
    25页
    查看更多>>摘要：Trough Mouth Fans (TMF) are sedimentary depocenters located at glaciated continental margins and consist predominantly of glacigenic debris flow deposits. The Foula wedge is a Pleistocene TMF accumulated offshore West of Shetland over the Northeast Atlantic margin. This study presents an analysis of a 3D seismic reflection dataset imaging the distal Foula wedge basin fan deposits between 1010 and 1100 m water depth, directly downslope from a gully system which was active untill the end of the last deglaciation. Results reveal, in un-precedented detail, the basal surface of this fan system and its internal complex architecture. Features typical of both debris flow deposits and turbidites are identified, including a basin channel network with linear and diverging erosional features forming distinctive terminal lobes, stacked and backstepping. The study links the seafloor morphology of the basin fan with its subsurface geomorphology, showing connection with the down-slope gully system to the east. It presents evidence for a complex distal depositional system on glaciated margins, characterised by heterogeneous sediment delivery processes and deposits. A conceptual evolution model is proposed, with a glacigenic debris flow-dominated TMF at the LGM, subsequently influenced by meltwater discharges, with deposition occurring as a function of the shelf margin and slope paleo-morphology, slope substrate composition, interaction of downslope and along slope processes and ice-margin dynamics.
      原文链接:
    • NSTL
    • Elsevier

    Complex drivers of reef-fronted beach change

    Mikkelsen, Anna B.Anderson, Tiffany R.Coats, SloanFletcher, Charles H....
    15页
    查看更多>>摘要：Royal Hawaiian Beach in Waiki over bar ki over bar plays an essential role in Hawai'i's tourism-based economy. To inform development of management policies, we conduct two years of weekly ground and aerial surveys (April 2018 to February 2020) to track change on this chronically eroding beach. We use multiple linear regressions, Self-Organizing Maps (a form of cluster analysis), remotely sensed nearshore sand fields, hydrodynamic modelling, and monitoring of key physical processes to identify the principal drivers of beach change. Our results show 12 months of subaerial accretion (+2400 +/- 59 m(3)) followed by 10 months of erosion (-3090 +/- 51 m(3)) for a net loss of 690 +/- 51 m(3), and document that interannual variations in beach width and volume overprint seasonal pat-terns. Notably, a seasonal signal is recorded in the topographic structure of the beach. We test the relationship of beach volume and width to variations in wind, water level, wave energy flux generated from southern hemi-sphere swell, and wave energy flux from locally generated trade-wind waves. We identify three beach segments and three nearshore sand fields that form a sand-sharing, source-sink network, yet operate quasi-independently. Our analysis reveals that individual beach segments and their adjacent sand fields experience coherent (simul-taneous) gains and losses of sand, suggesting that alongshore sediment exchange is dominant over cross-shore exchange. The main drivers of beach change are variations in water level and wave energy flux. Beach volume and width both vary with nearshore sand cover, indicating that free exchange with nearshore sources is intrinsic to beach variability. Our results suggest that rising sea level and extreme El Nino-Southern Oscillation events will contribute to Royal Hawaiian Beach destabilization, which may amplify erosional events and increase the cost of future beach maintenance.
      原文链接:
    • NSTL
    • Elsevier

    Hydrodynamics and sedimentary processes in the modern Rion strait (Greece): Interplay between tidal currents and internal tides

    Rubi, RomainHubert-Ferrari, AureliaFakiris, EliasChristodoulou, Dimitris...
    22页
    查看更多>>摘要：Straits are crossed by marine currents that are amplified due to constrictions. These nearshore high-velocity flows are problematic for offshore infrastructures (bridge pillars, cables, pipelines, etc), but constitute an interesting carbon-free energy source. Many modern straits are dominated by tidal currents which flow axially, with reversal directions and phase difference between the two interlinked basins. These tidal currents interplay with: sediment sources (including in situ carbonate production and deltas), tectonic activity, and inherited lowstand features, all shaping the seafloor into complex geomorphologies. Previous studies have highlighted a common tidal strait depositional model with a strait-center zone in erosion and on each side a dune-bedded strait zone with 3D and 2D tidal dunes and tidal ripples. Even if the internal waves associated with and generated by the straits are widely documented, the effects of the internal waves on the seafloor need to be further investigated. The aim of this study is to unravel the combined effects of the tidal currents and the internal tides on current pattern and on the morphosedimentary features. We present a strait example based on an interdisciplinary approach using high-resolution geophysical and oceanographical data to better constrain the hydrodynamics and the processes acting on the seafloor. We focus on the Rion Strait in Greece which controls the connection between the Corinth Gulf and the Mediterranean Sea. Based on high-resolution multibeam bathymetry (MBES) over an area of 211 km2, we identify and quantify different morphologies by extracting bathymetric swath profiles. These results are integrated with currents data (ADCP) and CTD profiles. In addition, we use high-resolution chirp sub-bottom profiles and sparker seismic reflection profiles to document the morphology and internal architectures of the sedimentary deposits and the erosional features in the strait bottom. To complete this dataset, we analyzed Sea Surface Temperatures (SST) from satellite sensors. The Rion Strait displays complex bathymetric features without tidal dunes. At the excepted depositional location of tidal dunes, we identify an erosive area with a pool and crest morphology. This new example completes the tidal strait depositional model by a re-localization of erosion, bypass and deposition in an asymmetric strait swept by baroclinic currents. This example illustrates the key role of internal tides in straits located between a confined deep basin and an open sea.
      原文链接:
    • NSTL
    • Elsevier

    Glacial-aged development of the Tunisian Coral Mound Province controlled by glacio-eustatic oscillations and changes in surface productivity

    Corbera, GuillemLo Iacono, ClaudioStandish, Christopher D.Gracia, Eulalia...
    17页
    查看更多>>摘要：Cold-water corals are key species of benthic ecosystems, sensitive to changes in climate and capable of recording them in the chemical composition of their skeletons. The study of cold-water coral mound development in relation to palaeoceanographic variations during the Pleistocene and Holocene stages in the Mediterranean Sea has mainly been focussed in the Alboran Sea (Western Mediterranean). The present study describes the coral deposits and corresponding ages of 3 gravity cores, acquired from the newly discovered Tunisian Coral Mound Province (Central Mediterranean), which comprises several ridge-like mounds. All the cores acquired displayed dense coral deposits, dominated by Desmophyllum pertusum fragments embedded within a muddy sediment matrix. Overall, 64 coral samples have been dated with the U-Th laser ablation MC-ICP-MS method, revealing corals of mostly Pleistocene age ranging from ~MIS 11 to 8.4 ka BP. Although coral mound formation was reduced for most of the last 400 kyr, a main stage of pronounced mound formation occurred during the last glacial period, which contrasts to the findings previously published for coral mounds in other regions of the Mediterranean Sea. Coral mound formation during the last glacial was most likely associated with a colder seawater temperature than the one observed in the present-day, an increased surface productivity and an appropriate depth of the interface between Atlantic Waters and Levantine Intermediate Waters. The combination of the data acquired here with that of previous mound formation studies from the Alboran Sea also suggests that cold-water coral mounds located at greater depths develop at slower rates than those found in shallower settings.
      原文链接:
    • NSTL
    • Elsevier

    Geological footprints of the 1945 Makran tsunami from the west coast of India

    Prizomwala, S. P.Vedpathak, ChintanTandon, AashnaDas, Archana...
    7页
    查看更多>>摘要：27th Nov 1945, witnessed a Mw -7.8 earthquake which triggered a tsunami in the coastlines of the northern Arabian sea. The 1945 Makran tsunami caused tremendous loss to the coastal communities of Iran, Pakistan, Oman and India. Despite the recent thrust in tsunami research along the western coast of India, the geological signatures of the 1945 Makran tsunami remained elusive. Here we present the first geological evidence of this event inform of a sand-sheet archived in the palaeomudflats of northwestern Saurashtra coast, western India. Based on the optical simulated luminiscence ages and available storm record of the Arabian Sea, the sand horizon seems to be linked with the 1945 Makran tsunami. The documented sand-sheet shows physical, geochemical and biological characteristics such as basal erosional/sharp contact with the underlying unit and lack of sorting along with the presence of mud-clasts. The sedimentary layer also shows an abnormal inland extent of >570 m from the present high-water line. The sedimentary character of the deposit would serve as a templet at other similar activities in the region as well as will contribute to the overall coastal hazard assessment in the rapidly developing region.
      原文链接:
    • NSTL
    • Elsevier

    Trace fossil characterization during Termination V and MIS 11 at the western Mediterranean: Connection between surface conditions and deep environment

    Gonzalez-Lanchas, AlbaDorador, JavierRodriguez-Tovar, Francisco J.Sierro, Francisco J....
    10页
    查看更多>>摘要：Trace fossil assemblages are studied at Ocean Discovery Program (ODP) Site 977 to characterize the response of the macrobenthic trace maker community to deep paleoenvironmental conditions during the Termination V (TV) and interglacial Marine Isotope Stage (MIS) 11 at the western Mediterranean Alboran Sea. An assemblage composed of Chondrites, Planolites, Scolicia, Thalassinoides and Zoophycos is identified, showing notable variations in ichnodiversity, abundance and Bioturbation Index, that were analyzed in detail. The integration of ichno-logical information with sediment color and high-resolution coccolithophore records from Site 977, evidenced that variations in macrobenthic trace maker community are primarily controlled by oxygen availability and surface organic productivity patterns. During TV, high surface organic productivity by intense Alboran Upwelling System enhanced the deep organic accumulation that, together with reduced deep-water removal, resulted in a decrease of bioturbation and the formation of an Organic Rich Layer. Moderate and stable surface production through MIS 11c reduced deep food availability, resulting in an oligotrophic and stable deep environment. This is reflected by relatively abundant trace fossils in lighter sediments. Intra-interglacial increase in surface organic production at ~405 ka is evidenced by increased organic matter preservation. Minor impact of western Medi-terranean circulation on deep-water removal, but a plausible stronger control by Bernoulli aspiration intensities in the region, is, in overall, observed during these intervals. During the Heinrich -type (Ht) events 3 and 2, increased trace fossil diversity and ameliorated oxygenation is driven by limited surface organic production, but intense western Mediterranean deep-water circulation and enhanced regional deep-water removal.
      原文链接:
    • NSTL
    • Elsevier

    Genesis of the distal axis East Longjing-2 hydrothermal field on the ultraslow-spreading Southwest Indian Ridge: Evidences from fluid inclusions

    Yu, JunyuChen, MingWang, NannanChen, Kaiying...
    10页
    查看更多>>摘要：Tectonic-related hydrothermal fields constitute about half of the hydrothermal activities on slow-ultraslow spreading ridges, and may form sulfides large in size and rich in precious metals. Ore-forming fluids are critical for element migration progressions, thus are key parameter to reveal their genesis and sulfide mineralization processes. However, previous studies of this kind of hydrothermal activities primarily focused on vent fluids which have transient effects or based on surface samples, while the ore-forming fluid evolution and related subseafloor mineralization process are still poorly constrained. In this study, we analyzed the characteristics of fluid inclusions in the stockwork mineralization of the East Longjing-2 hydrothermal field (ELHF-2) on the Southwest Indian Ridge. The results showed that the fluids evolved gradually from medium-high temperatures (260-315 degrees C, mean of 284 degrees C) and low salinities (0.70-3.70 wt.% NaCl eq.) in the disseminated pyrite mineralization stage (Stage I) to medium temperatures (239-261 degrees C, mean of 249 degrees C) and low salinities (1.05-3.85 wt.% NaCl eq.) in the chalcopyrite-pyrite-quartz veinlet mineralization stage (Stage II). Laser Raman specular analysis indicated the fluid inclusions were mainly composed of H2O. The low salinity (lowest 0.7 wt.% NaCl eq.) and various vapor volume (0.05-0.5) observed in these fluid inclusions suggested the ore-forming fluids were probably mixtures of the low-salinity vapor phase formed by phase separation with large amounts of seawater. The precipitation of the ore-forming elements was likely induced by temperature decreasing. We propose that hydrothermal circulation in ELHF-2 was a result of coupled high-permeability detachment fault and shallow gabbro intrusion. Our results suggest that high temperature hydrothermal activities could be developed on distal axis area on ultraslow spreading ridges.
      原文链接:
    • NSTL
    • Elsevier

    Reliability assessment and paleo-oceanographic signals of geochemical and isotopic indicators in the North Pacific Subtropical Gyre

    Qiu, YushengChen, QiannaChen, MinYang, Zifei...
    13页
    查看更多>>摘要：As the largest marine ecosystem on our planet, the North Pacific Subtropical Gyre (NPSG) plays an important role in global environmental and climate change. However, little is known about its environmental changes in an orbital scale. In this study, a constant flux model with excess 230Th was used to establish a time frame for our sediment core. Several geochemical and isotopic indicators were evaluated for their reliability in reconstructing paleoenvironment, including grain size distribution (GSD), Ti, Cu, Zn, Ba, total organic carbon (TOC), total nitrogen (TN), TOC/TN ratio, organic carbon and nitrogen isotopic composition (delta C-13, delta N-15). In addition, appropriate indicators were used to reveal changes in atmospheric dust deposition and biological productivity during the glacial and interglacial periods in the NPSG. Our results show that in such a low sedimentary environment, TOC, TN, TOC/TN ratio, delta C-13, delta 15N, Cu and Zn has been altered with the degradation of organic matter in the early diagenesis process. In contrast, GSD and Ti-derived eolian dust flux (Feolian) are suitable indicators for atmospheric dust deposition, and the mass accumulation rate of biogenic silica (MARBSi) and the deposition flux of excess Ba after correction for diffusion (Fexess Ba) are suitable for the reconstruction of biological productivity. The productivity during the glacial periods of Marine Isotope Stage (MIS) 2-4 and 6 is higher than the interglacial periods of MIS 1, 5, which corresponds well to the coarser dust particles and higher eolian dust supply. Therefore, we propose that different with former works in the subtropical Pacific, the fluctuations in productivity in the NPSG is mainly controlled by atmospheric dust deposition on a millennial scale.
      原文链接:
    • NSTL
    • Elsevier