Challenging the dipolar paradigm for Proterozoic Earth

ABSTRACT A robust, geology-based Proterozoic continental assembly places the northern and eastern margins of the Siberian craton against the southwestern margins of Laurentia in a tight, spoon-in-spoon conjugate fit. The proposed assembly began to break apart in late Neoproterozoic and early Paleozoic time. Siberia then drifted clockwise along the Laurussian margin on coast-parallel transforms until suturing with Europe in late Permian time. The proposed drift path is permitted by a geocentric axial dipole (GAD) magnetic field from Silurian to Permian time. However, the Proterozoic reconstruction itself is not permitted by GAD. Rather, site-mean paleomagnetic data plot ted on the reconstruction suggest a multipolar Proterozoic dynamo dominated by a quadrupole. The field may have resembled that of present-day Neptune, where, in the absence of a large solid inner core, a quadrupolar magnetic field may be generated within a thin spherical shell near the core-mantle boundary. The quadrupole may have dominated Earth’s geomagnetic field until early Paleozoic time, when the field became erratic and transitioned to a dipole, which overwhelmed the weaker quadrupole. The dipole then established a strong magnetosphere, effectively shielding Earth from ultraviolet-B (UV-B) radiation and making the planet habitable for Cambrian fauna.

Drift of an ocean bottom electromagnetometer from the Bonin to Ryukyu Islands: estimation of the path and travel time by numerical tracking experiments

Ocean bottom electromagnetometers (OBEMs) installed on the seafloor around Nishinoshima Island (Bonin Islands) were missing after a December volcanic eruption. In February 2021, one was found on a beach on Iriomote Island (Ryukyu Islands), implying that it drifted westward for 1700 km. The reason(s) for the disappearance of the OBEMs and the path followed by the recovered OBEM while drifting are important information for future ocean bottom observations and seafloor volcanology in general. We conducted particle drifting simulations with and without horizonal eddy diffusion to estimate the possible drift path and duration of the recovered OBEM. Our simulations show that particles arriving at Iriomote Island have a 7–10% probability of having been transported from Nishinoshima; thus, such transport is not a rare occurrence. Transport durations in our simulations varied widely between 140 and 602 days depending on the drift paths. More detailed insight into the path and duration of drift of the OBEM will require further comparison between drifting simulations and growth histories of barnacles attached on the OBEM. A similar drift duration and path was reported for pumices that erupted from Fukutoku-Oka-no-Ba submarine volcano (southern Bonin Islands) during 18–21 January 1986 and arrived in the Ryukyu Islands in late May 1986. Such drifting simulations may prove useful for identifying the sources of drift pumices, and thus otherwise undetectable eruptions. Finally, the Fukutoku-Oka-no-Ba submarine volcano erupted on 13 August 2021, producing abundant pumice rafts that, based on our results, would likely arrive in the Ryukyu Islands. In fact, the beginning of October 2021, they began to arrive in the Ryukyu Islands. Graphical Abstract

Ocean Bottom Electromagnetometer Carried From Bonin to Ryukyu Islands by Sea Currents

Ocean bottom electromagnetometers (OBEMs) installed on the seafloor around Nishinoshima Island (Bonin Islands) were missing after a December volcanic eruption. In February 2021, one was found on a beach on Iriomote Island (Ryukyu Islands), implying that it drifted westward for 1,700 km. The reason(s) for the disappearance of the OBEMs and the path followed by the recovered OBEM while drifting are important information for future ocean bottom observations and seafloor volcanology in general. We conducted particle drifting simulations with and without horizonal eddy diffusion to estimate the possible drift path and duration of the recovered OBEM. Our simulations show that particles transported from Nishinoshima have a 7-10 % probability of arriving at Iriomote Island, which is thus not a rare occurrence. Transport durations in our simulations varied widely between 140 and 602 days depending on the drift paths. The most likely drift duration in our simulation was 150 – 180 days, with or without eddy diffusion, corresponding to the release from the seafloor of the OBEM between 22 August and 21 September 2020. These dates follow shortly after intensifying eruptions at Nishinoshima, which may have affected the seafloor around the island. A similar drift duration and path was reported for pumices that erupted from Fukutoku-Oka-no-Ba submarine volcano (northern Bonin Islands) during 18-21 January 1986 and arrived in the Ryukyu Islands in late May 1986. Such drifting simulations may prove useful for identifying the sources of drift pumices, and thus otherwise undetectable eruptions. Finally, the Fukutoku-Oka-no-Ba submarine volcano erupted on 13 August 2021, producing abundant pumice rafts that, based on our results, will likely arrive in the Ryukyu Islands in the coming months.

Maritime Autonomous Surface Ship’s Path Approximation Using Bézier Curves

This work is devoted to the second order rational Bézier curve coefficients estimation. We present the methodology of unique coefficients for each type of ship computation. In the presented formulas of ship’s length, a draft and angular path combined with a drift path are used. This approach leads to the simplest and most accurate Maritime Autonomous Surface Ships (MASS) path modeling. Three rational curve control points are waypoints (WPT). Using WPTs as curve control points allows integrating a trajectory intuitive for the navigator with a path predicting model used as a reference in the control system. Research was done based on real-time data originating from the MASS autonomous trajectory tracking system. The presented mathematical modeling tool may be treated as the best way of future trajectory prediction due to low computation power required.

Variability of Lagrangian pathways and coherent structures in the Arctic and its effect on the predictability of MOSAiC drift and material transport

<p>Lagrangian particle tracking and associated diagnostics may be used to examine advective pathways of material and to identify coherent structures in the flow.  Lagrangian coherent structures are material transport barriers and act to separate different flow regimes.</p><p>The drift of the International Multidisciplinary Observatory for the Study of Arctic Climate (MOSAiC) expedition onboard R/V Polarstern began in October 2019 and will continue for the full year.   Our study has the goals to (i) characterise advective pathways and (ii) examine potential predictability of the MOSAiC drift.  Eddies, jets and boundary currents feature large spatiotemporally varying velocity gradients.  Since operational ocean forecasts have a limited time horizon (~weeks), we focused on hindcast to examine typical sea ice/ocean circulation scenarios for 2005-15.  We applied off-line ARIANE particle tracking in an eddying 1/12 deg. global NEMO sea ice-ocean model to estimate the most likely drift pathways. </p><p>Over 10,000 trajectories were initialised in October each year, started at the best estimated MOSAiC location, advected for one year and analysed for key coherent drift structures.  The advection and deformation of the initial particle cluster provided information about MOSAiC drift predictability, but also elucidated transport processes of the biogeochemical tracers, such as nutrients and carbon, and spread of pollution and microplastics. We analysed observations from a newly curated dataset of the Arctic to examine various watermass properties, their origin, fate and connectivity.</p><p>The MOSAiC surface drift trajectories depend on release time and location, but to leading-order, they are governed by the interannual variability of the wind and of the underlying ocean circulation.  Mesoscale flow deformation is linked to a spreading of the cluster of particles and is associated with reduced potential predictability of separation of particles within the cluster (~ 450 km after 12 months).  Gyre-scale flow affects the ensemble drift path over long times and influences whether particular coherent structures are encountered by the particles, their location and strength (in terms of velocity magnitude and gradient).  Saddle-type structures play a major role in bifurcation of particle trajectories.  In the examples studied, saddles north of Nares Strait, near Northern Greenland and Northern Iceland, topologically associated with streamline connectivity between gyres, coastal boundary currents and inflow/outflow at the Arctic gateways, were significant.  On seasonal-interannual scales, the position and strength of the Beaufort Gyre, as well as an anomalous cyclonic gyre in the eastern basin, affected both the ensemble drift path and the coherent flow structures.</p><p>The variability of ensemble drift path, cluster deformation and coherent flow structures across the full Arctic basin were often very different from the climatological advective behaviour of Trans-Polar Drift.  For estimation of advective pathways and sea ice drift it is important to consider the varying flow from gyre-scale to mesoscale, where velocity gradients are large, and to identify robust Lagrangian measures for steady features.</p><p>The study is supported from NE/R012865/1 (APEAR), part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF).</p><div> </div>

Origin of the coarse-grained (> 1 cm) clasts from the Mendeleev Ridge area (Central Arctic Ocean)

The morphometric and petrographic characteristics of the coarse-grained clasts (> 1 cm) sampled from the sediments of the Amerasian Basin, Central Arctic Ocean, were studied. Most of the clasts are represented by dolomites (46,4%), sandstones (22,8%) and limestones (19,8%); the amount of other rocks fragments (chert, shale, igneous) is about 10%. A variety of lithological types were identified among the studied rock fragments. Limestones and dolomitic limestones often contain fragments of fauna. The majority of clasts is poorly rounded and characterized by a wide variety of shapes. More than half of the studied clasts have a size of 1-2 cm, a quarter - 2-3 cm, and larger clasts only occur in insignificant amounts. Geophysical surveys across the sampling sites showed a lack of bedrock outcrops, so the studied coarse-grained clasts are not of local origin. It is concluded that they were predominantly delivered from the Canadian Arctic Archipelago (likely from the platform area, e.g., Victoria Island), mainly due to iceberg rafting during deglaciation periods. The maximum possible contribution of the clasts from the Siberian sources is less than 23%. Distribution of the coarse-grained clasts argues for the existence of a quite stable ice drift path in the past, which is similar to the modern Beaufort Gyre.