Cenozoic evolution of the Campbell Plateau, Subantarctic New Zealand: Insights from sub-bottom profile data

<p>The Campbell Plateau represents ~30% of the submerged continent of Zealandia and represents part of the Gondwana super-continent that began to break-up ~98Ma. The focus of this MSc thesis is to use sub-bottom, profile data collected in 2017 and 2018 from Campbell Plateau to improve our understanding of the Cenozoic evolution of the region. The sub-bottom profiles show a rugged basement overlain by a variety of sedimentary sequences and subsurface features such as volcanoes, onlap, and downlap surfaces as well as multiple unconformities that can be traced throughout the Cenozoic (65Ma). The sub-bottom profiles are compared to 2 drill cores; Ocean Drilling Program (ODP) site 1120 on the eastern side of the plateau and Deep Sea Drilling Program (DSDP) site 277 in the south. These drill cores indicate that the lithology from the Cretaceous onwards is predominantly biogenic calcareous sandstone and mudstone, which changes to nannofossil-rich oozes in the Miocene and foraminiferal oozes and nannofossil oozes dated early to late Pleistocene. The northern plateau appears to be relatively quiescent with thin, relatively uniform strata, only influenced by small reverse faults. Sedimentary deposits such as wedges and contourites are also evident in the central and north-western part of the study area. The southern plateau appears to be have been highly dynamic with onlap/downlap surfaces, interpreted as current scours, and erosional surfaces. There is a plateau-wide unconformity during the Pliocene, as derived from the nannofossils of the ODP1120 drill core, which appears to have been a large-scale erosional event. The Southern Ocean circulation, dominated by Antarctic Circumpolar Current, the Subtropical Front, and local wind-driven currents, are the main drivers of these lithological changes and plateau-wide sedimentological structures. Previous interpretations of the sub-surface structure of the plateau are seen to be invalid in relation to this study, with the sub-surface seen to be relatively undeformed with only minor reverse faulting present. Areas of possible uplifted basement seen near Campbell Island also indicate that the Campbell Plateau has been through substantial erosion and deformation since its’ separation from Gondwana ~98Ma and movement to its modern-day position.</p>

Cenozoic evolution of the Campbell Plateau, Subantarctic New Zealand: Insights from sub-bottom profile data

<p>The Campbell Plateau represents ~30% of the submerged continent of Zealandia and represents part of the Gondwana super-continent that began to break-up ~98Ma. The focus of this MSc thesis is to use sub-bottom, profile data collected in 2017 and 2018 from Campbell Plateau to improve our understanding of the Cenozoic evolution of the region. The sub-bottom profiles show a rugged basement overlain by a variety of sedimentary sequences and subsurface features such as volcanoes, onlap, and downlap surfaces as well as multiple unconformities that can be traced throughout the Cenozoic (65Ma). The sub-bottom profiles are compared to 2 drill cores; Ocean Drilling Program (ODP) site 1120 on the eastern side of the plateau and Deep Sea Drilling Program (DSDP) site 277 in the south. These drill cores indicate that the lithology from the Cretaceous onwards is predominantly biogenic calcareous sandstone and mudstone, which changes to nannofossil-rich oozes in the Miocene and foraminiferal oozes and nannofossil oozes dated early to late Pleistocene. The northern plateau appears to be relatively quiescent with thin, relatively uniform strata, only influenced by small reverse faults. Sedimentary deposits such as wedges and contourites are also evident in the central and north-western part of the study area. The southern plateau appears to be have been highly dynamic with onlap/downlap surfaces, interpreted as current scours, and erosional surfaces. There is a plateau-wide unconformity during the Pliocene, as derived from the nannofossils of the ODP1120 drill core, which appears to have been a large-scale erosional event. The Southern Ocean circulation, dominated by Antarctic Circumpolar Current, the Subtropical Front, and local wind-driven currents, are the main drivers of these lithological changes and plateau-wide sedimentological structures. Previous interpretations of the sub-surface structure of the plateau are seen to be invalid in relation to this study, with the sub-surface seen to be relatively undeformed with only minor reverse faulting present. Areas of possible uplifted basement seen near Campbell Island also indicate that the Campbell Plateau has been through substantial erosion and deformation since its’ separation from Gondwana ~98Ma and movement to its modern-day position.</p>

Reconsideration of winds, wind waves, and turbulence in simulating wind-driven currents of shallow lakes in the Wave-current Coupled Model (WCCM) version 1.0

Winds, wind waves, and turbulence are essential variables and playing critical role in regulating a series of physical and biogeochemical processes in large shallow lakes. However, parameterizing winds, waves, currents and turbulence and simulating the interaction between them in large shallow lakes haven’t been evaluated strictly because of a lack of field observations of lake hydrodynamics process. To address this problem, two process-based field observations were conducted to record the development of summer and winter wind-driven currents in Lake Taihu, a large shallow lake in China. Based on these observations and numerical experiments, a wave-current coupled model (WCCM) is developed by rebuilding expression of wind drag coefficient, introducing wave-induced radiation stress, and adopting a simple turbulence scheme, and then used to simulate wind-driven currents in Lake Taihu. The results show that, the WCCM can accurately simulate the upwelling process resulting from the wind-driven currents during the field observations. Comparing with other model, there is a 42.9 % increase of WCCM-simulated current speed which is mainly attributed to the new expression of wind drag coefficient. Meanwhile WCCM-simulated current direction and field are also improved due to the introduction of wave-induced radiation stress. Furthermore, the use of the simple turbulent scheme in the WCCM makes the simulation of the upwelling processes more efficient. The WCCM provides a sound basis for simulating shallow lake ecosystems.

Inner-core sea surface cooling induced by a moving tropical cyclone

As a key to modulate the negative feedback to tropical cyclone (TC) intensity, the TC-induced inner-core sea surface cooling (SSCIC) is poorly understood. Using a linear two-layer theory and OGCM experiments, this study illustrates that the pattern of the inner-core mixing can be well interpreted by the wind-driven currents in the mixed layer (ML). This interpretation is based on: 1) the mixing is triggered by the ML bulk shear instability; 2) the lag of upwelling makes the inner-core bulk shear equivalent to the inner-core wind-driven currents. Overall, the patterns of the inner-core bulk shear and mixing resemble the crescent body of a sickle. As an accumulative result of mixing, the SSCIC is clearly weaker than the maximum cold wake because of the weaker mixing ahead of the inner core and nearly zero mixing in a part of the inner core. The SSCIC induced by a rectilinear-track TC is mainly dominated by the inner-core mixing. Only for a slow-moving case, upwelling and horizontal advection can make minor contributions to the SSCIC by incorporating them with mixing. The SSCIC strength is inversely proportional to the moving speed, suggesting the mixing time rather than the mixing strength dominates the SSCIC. Despite inability in treating the mixing strength, this study elucidates the fundamental dynamical mechanisms of SSCIC, especially emphasizes the different roles of mixing, upwelling and horizontal advection for fast- and slow-moving TCs, and thus provides a good start point to understand SSCIC.

Hydrodynamic Climate of Port Phillip Bay

This study is dedicated to the hydrodynamic climate of Port Phillip Bay (PPB)—a largest coastal lagoon system in Victoria, Australia. Novelty of the present study includes long-term hydrodynamic hindcast simulations integrated with a spectral wave model. Specifically, a coupled unstructured grid wave–current modelling system (SCHISM + WWM) was built upon a high resolution and advanced wave physics (ST6). This coupling system was thoroughly calibrated and validated against field observations prior to applying for 27-year hindcast and case scenarios. Data from these simulations were then used to investigate the hydrodynamic climate of PPB focusing on three main aspects: water levels, waves and currents. For sea levels, this study shows that tidal and extreme sea levels (storm tides) across a large part of PPB have a similar magnitude. The highest storm tide level is found along eastern coasts of the bay in line with the wind pattern. In the vicinity of the entrance, the extreme sea level slightly reduced, in line with wave decay due to coupling effects. This extreme level is lower than results reported by previous studies, which were not built on a wave–current coupled system. For the wave field, the mean wave direction inside PPB is strongly affected by seasonality, in line with wind patterns. The 100-year return significant wave height is above 2 m along the eastern coasts. At PPH, waves get refracted after passing the narrow entrance. For currents, this study shows that both mean variations and high percentile currents are not affected by seasonality. This highlights the fact that tidal currents dominate flow movements in PPB. However, in extreme conditions, the circulation in PPB is also driven by wind patterns, forming two gyre systems. Based on case scenarios simulations, the strongest magnitude of wind-driven currents is above 0.5 m/s and found in the confined shallow region in the southern portion of PPB.

Estimating Met-Ocean Parameters during a Tropical Cyclone for Marine Science and Engineering

During a tropical cyclone (TC) worldwide, the Regional and Mesoscale Meteorological Branch (RAMMB) of NOAA/NESDIS (http://rammb.cira.colostate.edu/) issues real-time TC surface wind analyses. The purpose of this article is to provide value-added estimations of several meteorological and oceanographic (met-ocean) parameters including overwater friction velocity and turbulence intensity, variation of the wind speed with height, significant wave height, peak or dominant wave period, wind-driven currents and wind-stress tides. Since these proposed value-added parameters are also validated by other independent methods available from the literature, these met-ocean parameters may be used for marine science and engineering including offshore energy (such as oil, gas and wind power) research, development, operation and maintenance.

Assessing Controls on Isolated Carbonate Platform Development in Central Luconia, NW Borneo, from a Regional 3D Seismic Facies and Geomorphology Investigation

The Central Luconia province in the South China Sea, offshore Sarawak, features extensive development of Middle to Late Miocene isolated carbonate platforms. This study presents a regional seismic architecture - seismic facies review of platform flank geometries and off-platform depositional styles, with the goals of understanding their patterns and exploring the controlling processes. The information on flank steepness and predominant shedding direction is contextualized with respect to extrinsic and intrinsic factors of carbonate platform growth, including tectonics, eustatic sea level fluctuations, hydrodynamics and regional paleogeography. Results reveal that flank geometries are consistent throughout the Middle to Late Miocene. In the north of the province eastern flanks are dominantly aggradational, steep, and sediment-starved escarpments, whereas western flanks show more progradation and are accretionary in nature. Discrepancies from this pattern are observed among closely spaced platforms. The eastern aggrading flanks are interpreted to have been highly influenced by monsoonal wind driven currents. Further south in the province tidal currents, antecedent topography and syn-depositional tectonics were more important controls on platform architectural development. This study of regional processes and geomorphic products provides a basis for enhanced conceptual facies models and reservoir quality predictions.

THE EVOLUTIONARY DEVELOPMENT AND CURRENT STATE OF LAKE NERO ACCORDING TO SAPROPEL ANALYSIS

The paper presents the characteristics of sapropel based on the results of analysis of samples collected at 21 stations in Lake Nero. Its current state is assessed based on hydrophysical and hydrochemical parameters. A layer-by-layer (0–10, 30–40 and 60–70 cm) granulometric composition of stratigraphic cores made it possible to compare the evolutionary development of the lake corresponding to the periods 100, 300–400 and 600–800 years ago. It is found that natural hydrodynamic processes (wind-driven waves and wind-driven currents) cause erosion and mixing of the surface (0–10 cm) polluted sapropel layer with clean underlying horizons and carry pollutants absorbed on suspended particles outside the lake. The approach used made it possible to identify the ways of a shallow lake ecosystem formation and outline promising directions

In-Stream Energy by Tidal and Wind-Driven Currents: An Analysis for the Gulf of California

We analyzed the peak spring tidal current speeds, annual mean tidal power densities ( T P D ) and annual energy production ( A E P ) obtained from experiment 06.1, referred as the “HYCOM model” throughout, of the three dimensional (3D), global model HYCOM in an area covering the Baja California Pacific and the Gulf of California. The HYCOM model is forced with astronomical tides and surface winds alone, and therefore is particularly suitable to assess the tidal current and wind-driven current contribution to in-stream energy resources. We find two areas within the Gulf of California, one in the Great Island Region and one in the Upper Gulf of California, where peak spring tidal flows reach speeds of 1.1 m per second. Second to fifth-generation tidal stream devices would be suitable for deployment in these two areas, which are very similar in terms of tidal in-stream energy resources. However, they are also very different in terms of sediment type and range in water depth, posing different challenges for in-stream technologies. The highest mean T P D value when excluding TPDs equal or less than 50 W m−2 (corresponding to the minimum velocity threshold for energy production) is of 172.8 W m−2, and is found near the town of San Felipe, at (lat lon) = (31.006–114.64); here energy would be produced during 39.00% of the time. Finally, wind-driven currents contribute very little to the mean T P D and the total A E P . Therefore, the device, the grid, and any energy storage plans need to take into account the periodic tidal current fluctuations, for optimal exploitation of the resources.