First evidence for fin whale migration into the Pacific from Antarctic feeding grounds at Elephant Island

Funding: This work was funded by IWC-SORP and by the DFG within the priority programme SPP 1158 ‘Antarctic Research with comparative investigations in Arctic ice areas’ by grant HE5696/3-1. Additional funding from National Geographic / Disney+ supported field efforts by Hickmott.This study presents the first long-distance tracks of fin whales (Balaenoptera physalus) equipped with satellite transmitters off the Antarctic Peninsula. Southern Hemisphere fin whales were severely depleted by twentieth century industrial whaling, yet recently, they have returned to historical feeding grounds off the northern Antarctic Peninsula, forming large aggregations in austral summers. To date, our knowledge only extended to summer behaviour, while information regarding migration routes and the location of breeding and wintering grounds are lacking. During the austral autumn of 2021, we deployed nsatellite transmitters on four fin whales at Elephant Island. Two transmitters stopped working while the animals were still at the feeding grounds, while two continued to transmit during the transition from feeding activity to migration. Both migrating animals left the feeding ground on 15 April 2021, travelling northward into the Pacific and up along the Chilean coast. The most northerly position received before all tags stopped transmitting on 1 May 2021 was at 48°S. These tracks provide initial evidence of seasonal migratory routes and a first indication toward possible locations of winter destinations. This information, even if preliminary, is critical for investigations of population connectivity, population structure and the identification of breeding grounds of Southern Hemisphere fin whales.Publisher PDFPeer reviewe

Discontinuous Galerkin Time-Domain method for nanophotonics

International audienceThe numerical study of electromagnetic wave propagation in nanophotonic devices requires among others the integration of various types of dispersion models , such as the Drude one, in numerical methodologies. Appropriate approaches have been extensively developed in the context of the Finite Differences Time-Domain (FDTD) method, such as in [1] for example. For the discontinuous Galerkin time-domain (DGTD), stability and convergence studies have been recently realized for some dispersion models, such as the Debye model [2]. The present study focuses on a DGTD formulation for the solution of Maxwell's equations coupled to (i) a Drude model and (ii) a generalized dispersive model. Stability and convergence have been proved in case (i), and are under study in case (ii). Numerical experiments have been made on classical situations, such as (i) plane wave diffraction by a gold sphere and (ii) plane wave reflection by a silver slab

ANALYSIS OF A GENERALIZED DISPERSIVE MODEL COUPLED TO A DGTD METHOD WITH APPLICATION TO NANOPHOTONICS

In this paper, we are concerned with the numerical modelling of the propagation of electromagnetic waves in dispersive materials for nanophotonics applications. We focus on a generalized model that allows for the description of a wide range of dispersive media. The underlying differential equations are recast into a generic form and we establish an existence and uniqueness result. We then turn to the numerical treatment and propose an appropriate Discontinuous Galerkin Time Domain framework. We obtain the semi-discrete convergence and prove the stability (and in a larger extent, convergence) of a Runge Kutta 4 fully discrete scheme via a technique relying on energy principles. Finally, we validate our approach through two significant nanophotonics test cases. 1. Introduction. Among the numerous phenomena encountered in electromag-netics, many rely on the dispersive properties of materials, e.g. the fact that their phase velocity varies with frequency. Indeed, in specific ranges of wavelengths, biological tissues [GGC96], noble [JC72] and transition metals [JC74], but also glass [Fle78] and certain polymers [CC41] exhibit non-negligible dispersive behaviors. From the mathematical modeling point of view, this phenomenon is modeled by a frequency-dependent permittivity function ε(ω), often derived from physical considerations. Regarding nanophotonics applications, an accurate modeling of the permittivity function for metals in the visible spectrum is crucial. Indeed, the free electrons of metals are the key ingredient in the propagation of surface modes of particular interest, called surface plasmons [NH07]. The implementation of dispersion models in time-domain electromagnetics solvers can be achieved by different methods. The most common is certainly the Additional Differential Equation (ADE) technique, which consists in the addition of one or more ODEs to the Maxwell system, the coupling being made via source terms. A consequent literature on this topic exists in the context of Finite-Difference Time-Domain (FDTD) (see e.g. [VLDC11] and references therein). More recently, more papers are concerned with Finite Element or even Discontinuous Galerkin Time-Domain approaches (DGTD) (see e.g. [GYKR12] and [BKN11] and references therein), aiming at overcoming the limitations of FDTD. In this context, some works are more precisely focused on the numerical analysis. Several proofs exist for the standard dispersive media models and the most classical time and space discretization schemes (see e.g. all the papers of J. Li and co-authors such as [JL06, Li07, LCE08, Li09]). Let us also mention the approach of [WXZ10] for the integro-differential version of the classical dispersive models. The latter reference propose to analyze a semi-discrete divergence free discontinuous Galerkin framework. Finally, in a previous work [LS13], the authors analyzed, for the Debye model, a fully discrete scheme based on a centered fluxes nodal Discontinuous Galerkin formulation and Leap frog discretization in time. In this paper, we present a complete study of a generalized dispersive model that encapsulates a wide range of dispersive media, its higher efficiency being demonstrate

High order curvilinear DGTD methods for local and nonlocal plasmonics

International audienceThe DGTD (Discontinuous Galerkin Time-Domain) method has emerged in nanophotonics in the recent years [1] as a complementary or alternative modeling approach for time-domain nanoscale light-matter interactions beside the widely used FDTD (Finite Difference Time-Domain) method. A DG method [2] can be seen as a classical Finite Element (FE) method for which the global continuity of the approximation is lifted. Similarly to a FE method, the physical unknowns are approximated on a finite set of basis functions. However, for DG, the support of basis functions are restrained to a single discretization cell. Hence, the solution produced by a DG method is discontinuous (similarly to finite volumes), and different field values are stored for each element interface degree of freedom. The three main consequences are that (i) a DG method naturally handles material and field discontinuities, (ii) the weak formulation is local to an element, implying no large mass matrix inversion in the solving process if an explicit time scheme is used, and (iii) the order of the polynomial approximation in space can be made arbitrarily high by adding more degrees of freedom inside the elements. The connection between cells is restored by the use of a numerical flux. The discontinuity of the approximation makes room for numerous methodological improvements, such as efficient parallelization or the use of non-conforming and hybrid meshes A DG method os also very flexible with regards to time integration, motivating the design of local time stepping as well as locally implicit strategies. In the quest of higher accuracy and lower time to solution, a tailored treatment of the approximation of curvilinear geometrical features [3] is worth considering, especially in the presence of nanogaps or when assessing imperfect design of nanostructures. The use of very coarse discretization meshes leveraging tetrahedral curvilinear elements for the simulation of three-dimensional nanoscale light-matter interactions is assessed in this study, which is conducted in the framework of high order DGTD methods for solving the system of Maxwell equations coupled to a generalized model of local dispersion effects [3], as well as to a (linearized) hydrodynamic Drude model [4] for dealing with nonlocal dispersion effects [5]. REFERENCES 1. K. Busch, M. König, and J. Niegemann. Discontinuous Galerkin methods in nanophotonics. DGTD method for the numerical modeling of the interaction of light with nanometer scale metallic structures taking into account non-local dispersion effects. J. Comput. Phys., 316:396-415, 2016. 5. A. Moreau, C. Cirac`Cirac`ı, and D.R. Smith. The impact of nonlocal response on metallo-dielectric multilayers and optical patch antennas. Phys. Rev. B, pages 1-12, 2012

Blue whale sightings in Antarctica west of the Greenwich meridian, Januart 2015

During the RV Polarstern PS 89 (ANT-XXX/2) expedition from Cape Town to Atka Bay and back, 20 sightings of 26 individual blue whales (Balaenoptera musculus) were recorded in Antarctic waters west of the Greenwich Meridian between 16-20 January 2015. These observations suggest a more westerly extension of a reported hot spot between the Greenwich Meridian and 20°E

Identifying seasonal distribution patterns of fin whales across the Scotia Sea and the Antarctic Peninsula region using a novel approach combining habitat suitability models and ensemble learning methods

Following their near extirpation by industrial whaling of the 20th century, the population status of Southern Hemisphere fin whales (SHFW) remains unknown. Systematic surveys estimating fin whale abundance in the Southern Ocean are not yet available. Records of fin whale sightings have been collected by a variety of organisations over the past few decades, incorporating both opportunistic data and dedicated survey data. Together, these isolated data sets represent a potentially valuable source of information on the seasonality, distribution and abundance of SHFW. We compiled records across 40 years from the Antarctic Peninsula and Scotia Sea from multiple sources and used a novel approach combining ensemble learning and a maximum entropy model to estimate abundance and distribution of SHFW in this region. Our results show a seasonal distribution pattern with pronounced centres of distribution from January-March along the West Antarctic Peninsula. Our new approach allowed us to estimate abundance of SHFW for discrete areas from a mixed data set of mainly opportunistic presence only data.publishedVersio

Identifying seasonal distribution patterns of fin whales across the Scotia Sea and the Antarctic Peninsula region using a novel approach combining habitat suitability models and ensemble learning methods

Following their near extirpation by industrial whaling of the 20th century, the population status of Southern Hemisphere fin whales (SHFW) remains unknown. Systematic surveys estimating fin whale abundance in the Southern Ocean are not yet available. Records of fin whale sightings have been collected by a variety of organisations over the past few decades, incorporating both opportunistic data and dedicated survey data. Together, these isolated data sets represent a potentially valuable source of information on the seasonality, distribution and abundance of SHFW. We compiled records across 40 years from the Antarctic Peninsula and Scotia Sea from multiple sources and used a novel approach combining ensemble learning and a maximum entropy model to estimate abundance and distribution of SHFW in this region. Our results show a seasonal distribution pattern with pronounced centres of distribution from January-March along the West Antarctic Peninsula. Our new approach allowed us to estimate abundance of SHFW for discrete areas from a mixed data set of mainly opportunistic presence only data

Identifying seasonal distribution patterns of fin whales across the Scotia Sea and the Antarctic Peninsula region using a novel approach combining habitat suitability models and ensemble learning methods

Following their near extirpation by industrial whaling of the 20th century, the population status of Southern Hemisphere fin whales (SHFW) remains unknown. Systematic surveys estimating fin whale abundance in the Southern Ocean are not yet available. Records of fin whale sightings have been collected by a variety of organisations over the past few decades, incorporating both opportunistic data and dedicated survey data. Together, these isolated data sets represent a potentially valuable source of information on the seasonality, distribution and abundance of SHFW. We compiled records across 40 years from the Antarctic Peninsula and Scotia Sea from multiple sources and used a novel approach combining ensemble learning and a maximum entropy model to estimate abundance and distribution of SHFW in this region. Our results show a seasonal distribution pattern with pronounced centres of distribution from January-March along the West Antarctic Peninsula. Our new approach allowed us to estimate abundance of SHFW for discrete areas from a mixed data set of mainly opportunistic presence only data