Vera Fofonova

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

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Karen Helen Wiltshire

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Alexey Androsov

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Sergey Danilov

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Ivan Kuznetsov

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Sven Harig

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Natalja Rakowsky

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Lasse Sander

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Markus Janout

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

H Christian Hass

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Elena Golubeva

Institute of Computational Mathematics and Mathematical Geophysics

Cooperative Institutions

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

University of Bremen

Universität Hamburg

Carl von Ossietzky Universität Oldenburg

Institute of Oceanology. PP Shirshov Russian Academy of Sciences

National Research Council

Australian Wool Innovation (Australia)

Constructor University

Helmholtz-Zentrum Hereon

Russian Academy of Sciences

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Dynamical reconstruction of the upper-ocean state in the central Arctic during the winter period of the MOSAiC expedition

Ocean science (2024)

Ivan Kuznetsov Benjamin Rabe Alexey Androsov Ying‐Chih Fang Mario Hoppmann

Abstract. This paper presents a methodological tool for dynamic reconstruction of the state of the ocean, based, as an example, on observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) experiment. The data used in this study were collected in the Amundsen Basin between October 2019 and January 2020. Analysing observational data to assess tracer field and upper-ocean dynamics is highly challenging when measurement platforms drift with the ice pack due to continuous drift speed and direction changes. We have equipped the new version of the coastal branch of the global Finite-volumE sea ice–Ocean Model (FESOM-C) with a nudging method. Model nudging was carried out assuming a quasi-steady state. Overall, the model can reproduce the lateral and vertical structure of the temperature, salinity, and density fields, which allows for projecting dynamically consistent features of these fields onto a regular grid. We identify two separate depth ranges of enhanced eddy kinetic energy located around two maxima in buoyancy frequency: the depth of the upper halocline and the depth of the warm (modified) Atlantic Water. Simulations reveal a notable decrease in surface layer salinity and density in the Amundsen Basin towards the north but no significant gradient from east to west. However, we find a mixed-layer deepening from east to west, with a 0.084 m km−1 gradient at 0.6 m km−1 standard deviation, compared to a weak deepening from south to north. The model resolves several stationary eddies in the warm Atlantic Water and provides insights into the associated dynamics. The model output can be used to further analyse the thermohaline structure and related dynamics associated with mesoscale and submesoscale processes in the central Arctic, such as estimates of heat fluxes or mass transport. The developed nudging method can be utilized to incorporate observational data from a diverse set of instruments and for further analysis of data from the MOSAiC expedition.

Halocline

Temperature salinity diagrams

Argo

Eddy

Isopycnal

10.5194/os-20-759-2024

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Citations (0)

Reply on CEC1

Vera Fofonova

Abstract. We present a test case of river plume spreading to evaluate numerical methods used in coastal ocean modeling. It includes an estuaryâshelf system whose dynamics combine nonlinear flow regimes with sharp frontal boundaries and linear regimes with cross-shore geostrophic balance. This system is highly sensitive to physical or numerical dissipation and mixing. The main characteristics of the plume dynamics are predicted analytically but are difficult to reproduce numerically because of numerical mixing present in the models. Our test case reveals the level of numerical mixing as well as the ability of models to reproduce nonlinear processes and frontal zone dynamics. We document numerical solutions for the Thetis and FESOM-C models on an unstructured triangular mesh, as well as ones for the GETM and FESOM-C models on a quadrilateral mesh. We propose an analysis of simulated plume spreading which may be useful in more general studies of plume dynamics. The major result of our comparative study is that accuracy in reproducing the analytical solution depends less on the type of model discretization or computational grid than it does on the type of advection scheme.

10.5194/gmd-2020-438-ac1

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Reply on AC4

Vera Fofonova

10.5194/gmd-2020-438-ac5

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Modeling of Nonhydrostatic Dynamics and Hydrology of the Lombok Strait

Water (2020)

Alexey Androsov N. Voltzinger Ivan Kuznetsov Vera Fofonova

The long-wave dynamics of the Lombok Strait, which is the most important link of the West Indonesian throughflow connecting the Pacific and Indian Ocean waters, was simulated and analyzed. A feature of the strait is its extremely complex relief, on which water transport creates a field of pronounced vertical velocities, which requires consideration of the nonhydrostatic component of pressure. The work presents a 3-D nonhydrostatic model in curvilinear coordinates, which is verified on a test problem. Particular attention is paid to the method of solving the 3-D elliptical solver for a nonhydrostatic problem in boundary-matched coordinates and a vertical σ level. The difference in transport through the Lombok Strait is determined by the difference in atmospheric pressure over the Pacific and Indian Oceans. Based on the results of the global simulation, the role of these factors in terms of their variability is analyzed, and the value of nonhydrostatic pressure in the dynamics of the Lombok Strait is revealed and evaluated. The vertical dynamics of the Lombok Strait are considered in detail based on hydrostatic and nonhydrostatic approaches.

Throughflow

Hydrostatic equilibrium

10.3390/w12113092

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Citations (2)

Ensemble Mapping and Change Analysis of the Seafloor Sediment Distribution in the Sylt Outer Reef, German North Sea from 2016 to 2018

Water (2021)

Daphnie Galvez Svenja Papenmeier Lasse Sander H Christian Hass Vera Fofonova

Recent studies on seafloor mapping have presented different modelling methods for the automatic classification of seafloor sediments. However, most of these studies have applied these models to seafloor data with appropriate numbers of ground-truth samples and without consideration of the imbalances in the ground-truth datasets. In this study, we aim to address these issues by conducting class-specific predictions using ensemble modelling to map seafloor sediment distributions with minimal ground-truth data combined with hydroacoustic datasets. The resulting class-specific maps were then assembled into a sediment classification map, in which the most probable class was assigned to the appropriate location. Our approach was able to predict sediment classes without bias to the class with more ground-truth data and produced reliable seafloor sediment distributions maps that can be used for seafloor monitoring. The methods presented can also be used for other underwater exploration studies with minimal ground-truth data. Sediment shifts of a heterogenous seafloor in the Sylt Outer Reef, German North Sea were also assessed to understand the sediment dynamics in the marine conservation area during two different short timescales: 2016–2018 (17 months) and 2018–2019 (4 months). The analyses of the sediment shifts showed that the western area of the Sylt Outer Reef experienced sediment fluctuations but the morphology of the bedform features was relatively stable. The results provided information on the seafloor dynamics, which can assist in the management of the marine conservation area.

Seafloor Spreading

Ground truth

Bedform

10.3390/w13162254

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Citations (4)

Numerical Analysis and Reconstruction of the Temperature Regime of the Lena River Segment

Segmentigor Zhilyaev Vera Fofonova

The data series from several gauging stations on the Lena River are considered. The difference of the water temperature between Kusur station and 200 kilometers downstream to the north Habarova station often becomes anomaly large during open water season (June-September). The analysis of the observational data is presented. The non-representativeness of measurements on Kusur station is supposed, reconstruction of the real temperature regime on the base of the statistical and deterministic modeling as well as the optimization tools is carried out.

Anomaly (physics)

Statistical Analysis

Open water

10.1109/mcsi.2016.049

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Citations (1)

Benthic microbial biogeographic trends in the North Sea are shaped by an interplay of environmental drivers and bottom trawling effort

ISME Communications (2023)

Guido Bonthond Jan Beermann Lars Gutow Andreas Neumann Francisco R. Barboza

Microbial composition and diversity in marine sediments are shaped by environmental, biological, and anthropogenic processes operating at different scales. However, our understanding of benthic microbial biogeography remains limited. Here, we used 16S rDNA amplicon sequencing to characterize benthic microbiota in the North Sea from the top centimeter of 339 sediment samples. We utilized spatially explicit statistical models, to disentangle the effects of the different predictors, including bottom trawling intensity, a prevalent industrial fishing practice which heavily impacts benthic ecosystems. Fitted models demonstrate how the geographic interplay of different environmental and anthropogenic drivers shapes the diversity, structure and potential metabolism of benthic microbial communities. Sediment properties were the primary determinants, with diversity increasing with sediment permeability but also with mud content, highlighting different underlying processes. Additionally, diversity and structure varied with total organic matter content, temperature, bottom shear stress and bottom trawling. Changes in diversity associated with bottom trawling intensity were accompanied by shifts in predicted energy metabolism. Specifically, with increasing trawling intensity, we observed a transition toward more aerobic heterotrophic and less denitrifying predicted metabolism. Our findings provide first insights into benthic microbial biogeographic patterns on a large spatial scale and illustrate how anthropogenic activity such as bottom trawling may influence the distribution and abundances of microbes and potential metabolism at macroecological scales.

Bottom trawling

Benthos

10.1038/s43705-023-00336-3

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Citations (6)

On discretizing sea-ice dynamics on triangular meshes using vertex, cell or edge velocities

Ocean Modelling (2021)

Sergey Danilov Carolin Mehlmann Vera Fofonova

Spurious relationship

10.1016/j.ocemod.2021.101937

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Citations (12)

Dynamical reconstruction of the upper-ocean state in the Central Arctic during the winter period of the MOSAiC Expedition

Ivan Kuznetsov Benjamin Rabe Alexey Androsov Ying‐Chih Fang Mario Hoppmann

Abstract. The Arctic Ocean is a region important for global and regional climate. Although generally quiescent compared to mid-latitudes, the upper Arctic ocean hosts mesoscale and smaller scale processes. These processes can have a profound impact on vertical ocean fluxes, stratification, and feedback with the sea ice and atmosphere. Sparse and non-synoptic in-situ observations of the polar oceans are limited by the distribution of manual observing platforms and autonomous instrumentation. Analyzing observational data to assess tracer field gradients and upper ocean dynamics becomes highly challenging when measurement platforms drift with the ice pack due to continuous changes in drift speed direction. This work presents a dynamical reconstruction of the ocean state, based on observations of the Multidisciplinary Observatory for the Study of Arctic Climate (MOSAiC) experiment. Overall, the model can reproduce the lateral and vertical structure of the temperature, salinity, and density fields, which allows for projecting dynamically consistent features of these fields onto a regular grid. We identify two separate depth ranges of enhanced eddy kinetic energy, which are located around two maxima in buoyancy frequency: the depth of the upper halocline and the depth of the warm (modified) Atlantic Water. Simulations reveal a notable decrease in surface layer salinity and density towards the north, accompanied by high variability in the mixed layer depth in the south-north direction. And no significant horizontal gradients in salinity and density fields but an increase in mixed layer depth from west to east 0.084 m/km gradient with 0.6 m/km standard deviation, indicating opposite characteristics compared to the south-north direction. The model resolves several stationary eddies in the warm Atlantic Water and provides insights into the associated dynamics. The obtained three-dimensional fields of temperature and salinity can be used for further analysis of the thermohaline structure and related dynamics associated with submesoscale processes in the Central Arctic. Dynamic characteristics and eddy fields can be used for further analysis and comparison with state-of-the-art climate and Earth System Models. The developed nudging method can be used to utilize future observational data obtained from a diverse set of instruments.

Halocline

Stratification (seeds)

Argo

Neutral buoyancy

Temperature salinity diagrams

10.5194/egusphere-2023-1353

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Citations (3)

The water temperature characteristics of the Lena River at basin outlet in the summer period

Vera Fofonova Igor Zhilyaev Marina Krayneva Dina Yakshina Nikita Tananaev

Abstract. The water temperature characteristics of the Lena River at basin outlet during the summer season (June–September) are considered. The analysis is based on a long-term data series covering the period from the beginning of observation (1936) to the present time (2012) at Kusur (Kyusyur) gauging station and complementary data at several stations downstream and one station upstream. These additional data are rarely used, but their analysis is important for understanding processes in the basin outlet area. The differences between the stream surface temperatures at Kusur station and 200 km downstream to the north at Habarova (Khabarova) station have almost always been an anomalously large and negative for the considered period since the beginning of observation during open water season from July to September. The description of this difference and its analysis are presented. To sort the problem out, we consider the observational data in terms of the hydrology and morphology of the Lena River delta and main channel area and apply statistical and deterministic modelling approaches. The inability of water temperature observational data at Kusur station to represent the mean cross-sectional temperature is addressed. The analysis of the water temperature trends at the Kusur and Habarova stations is also presented.

Statistical Analysis

10.5194/hess-2016-254

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Citations (4)