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Hans Renssen - One of the best experts on this subject based on the ideXlab platform.

  • Representing Icebergs in the iLOVECLIM model (version 1.0) – a sensitivity study
    Geoscientific Model Development, 2015
    Co-Authors: M Bugelmayer, D. Roche, Hans Renssen
    Abstract:

    Recent modelling studies have indicated that Icebergs play an active role in the climate system as they interact with the ocean and the atmosphere. The Icebergs' impact is due to their slowly released meltwater, which freshens and cools the ocean and consequently alters the ocean stratification and the sea-ice conditions. The spatial distribution of the Icebergs and their meltwater depends on the atmospheric and oceanic forces acting on them as well as on the initial Icebergs' size. The studies conducted so far have in common that the Icebergs were moved by reconstructed or modelled forcing fields and that the initial size distribution of the Icebergs was prescribed according to present-day observations. To study the sensitivity of the modelled Iceberg distribution to initial and boundary conditions, we performed 15 sensitivity experiments using the iLOVECLIM climate model that includes actively coupled ice sheet and Iceberg modules, to analyse (1) the impact of the atmospheric and oceanic forces on the Iceberg transport, mass and melt flux distribution, and (2) the effect of the initial Iceberg size on the resulting Northern Hemisphere climate including the Green-land ice sheet, due to feedback mechanisms such as altered atmospheric temperatures, under different climate conditions (pre-industrial, high/low radiative forcing). Our results show that, under equilibrated pre-industrial conditions, the oceanic currents cause the Icebergs to stay close to the Greenland and North American coast, whereas the atmospheric forcing quickly distributes them further away from their calving site. Icebergs remaining close to Greenland last up to 2 years longer as they reside in generally cooler waters. Moreover , we find that local variations in the spatial distribution due to different Iceberg sizes do not result in different climate states and Greenland ice sheet volume, independent of the prevailing climate conditions (pre-industrial, warming or cooling climate). Therefore, we conclude that local differences in the distribution of their melt flux do not alter the prevailing Northern Hemisphere climate and ice sheet under equilibrated conditions and continuous supply of Icebergs. Furthermore, our results suggest that the applied radiative forcing scenarios have a stronger impact on climate than the initial size distribution of the Icebergs.

  • representing Icebergs in the iloveclim model version 1 0 a sensitivity study
    Geoscientific Model Development, 2014
    Co-Authors: M Bugelmayer, Didier M Roche, Hans Renssen
    Abstract:

    Abstract. Recent modelling studies have indicated that Icebergs play an active role in the climate system as they interact with the ocean and the atmosphere. The Icebergs' impact is due to their slowly released meltwater, which freshens and cools the ocean and consequently alters the ocean stratification and the sea-ice conditions. The spatial distribution of the Icebergs and their meltwater depends on the atmospheric and oceanic forces acting on them as well as on the initial Icebergs' size. The studies conducted so far have in common that the Icebergs were moved by reconstructed or modelled forcing fields and that the initial size distribution of the Icebergs was prescribed according to present-day observations. To study the sensitivity of the modelled Iceberg distribution to initial and boundary conditions, we performed 15 sensitivity experiments using the iLOVECLIM climate model that includes actively coupled ice sheet and Iceberg modules, to analyse (1) the impact of the atmospheric and oceanic forces on the Iceberg transport, mass and melt flux distribution, and (2) the effect of the initial Iceberg size on the resulting Northern Hemisphere climate including the Greenland ice sheet, due to feedback mechanisms such as altered atmospheric temperatures, under different climate conditions (pre-industrial, high/low radiative forcing). Our results show that, under equilibrated pre-industrial conditions, the oceanic currents cause the Icebergs to stay close to the Greenland and North American coast, whereas the atmospheric forcing quickly distributes them further away from their calving site. Icebergs remaining close to Greenland last up to 2 years longer as they reside in generally cooler waters. Moreover, we find that local variations in the spatial distribution due to different Iceberg sizes do not result in different climate states and Greenland ice sheet volume, independent of the prevailing climate conditions (pre-industrial, warming or cooling climate). Therefore, we conclude that local differences in the distribution of their melt flux do not alter the prevailing Northern Hemisphere climate and ice sheet under equilibrated conditions and continuous supply of Icebergs. Furthermore, our results suggest that the applied radiative forcing scenarios have a stronger impact on climate than the initial size distribution of the Icebergs.

  • the effect of dynamic thermodynamic Icebergs on the southern ocean climate in a three dimensional model
    Ocean Modelling, 2009
    Co-Authors: J I Jongma, Hans Renssen, E Driesschaert, Thierry Fichefet, Hugues Goosse
    Abstract:

    Melting Icebergs are a mobile source of fresh water as well as a sink of latent heat. In most global climate models, the spatio-temporal redistribution of fresh water and latent heat fluxes related to Icebergs is parameterized by an instantaneous more or less arbitrary flux distribution over some parts of the oceans. It is uncertain if such a parameterization provides a realistic representation of the role of Icebergs in the coupled climate system. However, Icebergs could have a significant climate role, in particular during past abrupt climate change events which have been associated with armada’s of Icebergs. We therefore present the interactive coupling of a global climate model to a dynamic thermodynamic Iceberg model, leading to a more plausible spatio-temporal redistribution of fresh water and heat fluxes. We show first that our model is able to reproduce a reasonable Iceberg distribution in both hemispheres when compared to recent data. Second, in a series of sensitivity experiments we explore cooling and freshening effects of dynamical Icebergs on the upper Southern Ocean and we compare these dynamic Iceberg results to the effects of an equivalent parameterized Iceberg flux. In our model without interactive Icebergs, the parameterized fluxes are distributed homogeneously South of 55°S, whereas dynamic Icebergs are found to be concentrated closer to shore except for a plume of Icebergs floating North–East from the tip of the Antarctic Peninsula. Compared to homogeneous fluxes, the dynamic Icebergs lead to a 10% greater net production of Antarctic bottom water (AABW). This increased bottom water production involves open ocean convection, which is enhanced by a less efficient stratification of the ocean when comparing to a homogeneous flux distribution. Icebergs facilitate the formation of sea-ice. In the sensitivity experiments, both the fresh water and the cooling flux lead to a significant increase in sea-ice area of 12% and 6%, respectively, directly affecting the highly coupled and interactive air/sea/ice system. The consequences are most pronounced along the sea-ice edge, where this sea-ice facilitation has the greatest potential to affect ocean stratification, for example by heat insulation and wind shielding, which further amplifies the cooling and freshening of the surface waters.

Christine Wesche - One of the best experts on this subject based on the ideXlab platform.

  • c band radar polarimetry useful for detection of Icebergs in sea ice
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Christine Wesche, Wolfgang Dierking
    Abstract:

    This paper is focused on investigations of polarimetric C-band radar signatures of Icebergs in sea-ice-covered ocean regions. The main objective is to assess the potential improvement of Iceberg detection when using radar polarimetry. The dominant backscattering mechanisms of Icebergs are deduced by evaluating different polarimetric parameters. Magnitudes of the cross-polarization ratios, the correlation coefficients between HH- and VV-polarized signals, and the entropy/alpha parameters indicate a strong contribution of volume scattering in many cases. Over most Icebergs, the phase differences between HH- and VV-polarization are larger than zero. Spatial patterns of the polarimetric parameters differ from Iceberg to Iceberg and between different parameters. On some bergs, they only exhibit slight variations, whereas on others, they show noiselike textures, but also, more systematic changes are observed. Occasionally, radar intensities of Icebergs are of similar magnitude as those of sea ice. Only for a number of these cases, the combined use of the investigated polarimetric parameters together with intensity improves the discrimination performance between Icebergs and sea ice.

  • Southern ocean Iceberg drift
    2013
    Co-Authors: Christine Wesche, Thomas Rackow, Wolfgang Dierking
    Abstract:

    Icebergs are fragments of glacier ice, which break-off from the ice shelves and glacier tongues all around Antarctica. After calving, Icebergs drift through the ocean, driven by a number of forces. The main forces are the ocean currents and the wind, but also the Coriolis force, sea surface tilt, sea ice concentration and strength, as well as the wave radiation do influence the drift of Icebergs. The relative contributions of the individual forces depend on the environmental conditions (e. g. sea ice or open water) and the Iceberg size and thickness. A drift algorithm is used to simulate the drift of Icebergs through the Southern ocean. The Iceberg drift algorithm is implemented in the Finite Elemente Sea-ice Ocean Model (FESOM), which has a spatial resolution of 10 km close to the ice shelf edge and 30 km offshore. A test was carried out to study the effect of Iceberg size and thickness as well as model set ups on the drift pattern. “Test Icebergs” of a simplified shape were released into the model domain from 77 locations around Antarctica to simulate and analyse their path. The model results were compared with available observations. Additionally to the drift, the model also calculates the melting of Icebergs and therefore the freshwater input into the ocean.

  • Combining SAR images with an Iceberg drift model for improving mass loss estimations caused by Iceberg calving - a case study
    2012
    Co-Authors: Christine Wesche, Thomas Rackow, Wolfgang Dierking
    Abstract:

    Recent estimations of mass loss caused by Iceberg calving are limited to huge Icebergs (>18.5km edge length) or are spatially limited. Since the 1970s, the course of huge Icebergs is permanently tracked using satellite images by the National Ice Center (NIC). A large brake off event is undetected very likely and huge Icebergs are easily to track on their way through the ocean. In many cases, calving of smaller Icebergs takes place unobserved, which hampers the estimation of calving rates and mass loss caused by Iceberg calving. The surface structures of the floating ice masses around Antarctica give information about the size and shape of potential calved Icebergs, so that the origin of Icebergs drifting in the ocean can be restricted to a few calving fronts. SAR images at different resolutions and an edge detection were used to map the surface structures of the floating ice masses around Antarctica and regarding to this, a calving front classification was done. Using the results of the classification, Icebergs within SAR images could be assigned to their potential calving front. An Iceberg drift model is then used to certify the origin. The Iceberg drift model is implemented in a Finite Element Sea ice Ocean Model (FESOM), and the course and the velocity of Icebergs are calculated. With this information it is possible to track Iceberg ensembles back to their calving front to estimate local calving rates.

  • Separation of Icebergs and sea ice in SAR images
    2010
    Co-Authors: Christine Wesche, Wolfgang Dierking
    Abstract:

    The largest loss term in Antarctic mass balance is Iceberg calving from the ice shelves and to estimate the amount of the loss, it is necessary to observe Icebergs in every size. Because current mass loss calculations only include Icebergs with an edge length of > 10 km, we focus on smaller Icebergs (0.1 to 10 km edge length) in a test region north of Berkner Island in the Weddell Sea. Images of the ENVISAT ASAR at different imaging modes are used to analyse the backscattering coefficients of Icebergs depending on the season. To detect Icebergs in SAR images we need to find differences to the surrounding sea ice. Therefore, the backscattering coefficients of the sea ice are analysed for seasonal variations as well.Statistical analyses of the backscattering of Icebergs and sea ice in ASAR image mode data show varying backscatter coefficients over the period of one year. The radar intensity contrast between Icebergs and sea ice is smallest in the summer months and highest in winter and spring. The Iceberg and sea-ice backscattering is investigated for seasonality in medium and low resolution ASAR images as well and compared to the results derived from image mode data. We will also include other frequency bands from other sensors to achieve a complete view of Iceberg signature in radar images and their contrast to the surrounding. These statistics will improve the automatic extraction of Icebergs from SAR images. As a next step, the extracted Iceberg positions will be used to calculate the drift.

  • Detection of Icebergs using ERS SAR images
    2009
    Co-Authors: Christine Wesche, Wolfgang Dierking
    Abstract:

    Within the framework of the DFG project BergCAT we develop a method for detecting small Icebergs in SAR images from the Weddell Sea, Antarctica. Dependent on the season, Icebergs appear as bright or dark targets in SAR images. Statistical analyses of 624 Iceberg regions of interest (ROIs) show that the threshold between bright and dark appearing Icebergs is -7.5 dB. For a first classification, SAR data were divided into images with mainly bright and mainly dark appearing Icebergs, independent from the background signature. The Iceberg and background pixels were investigated separately for the two image groups to reveal possible correlations between thesignatures. We calculated the mean and the standard deviation and use the 1-sigma interval. The 1-sigma intervals show overlapping ranges of the backscattering coefficients of Icebergs and background in the image groups and with the aid of these information we formulated detection conditions. Then we used a combination of thresholds in the non-overlapping ranges and a constant false alarm rate (CFAR) in the overlapping ranges. This detection algorithm detected 72 % of former extracted Iceberg pixels as Icebergs and 84 % of the background pixels as background.

Wolfgang Dierking - One of the best experts on this subject based on the ideXlab platform.

  • c band radar polarimetry useful for detection of Icebergs in sea ice
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Christine Wesche, Wolfgang Dierking
    Abstract:

    This paper is focused on investigations of polarimetric C-band radar signatures of Icebergs in sea-ice-covered ocean regions. The main objective is to assess the potential improvement of Iceberg detection when using radar polarimetry. The dominant backscattering mechanisms of Icebergs are deduced by evaluating different polarimetric parameters. Magnitudes of the cross-polarization ratios, the correlation coefficients between HH- and VV-polarized signals, and the entropy/alpha parameters indicate a strong contribution of volume scattering in many cases. Over most Icebergs, the phase differences between HH- and VV-polarization are larger than zero. Spatial patterns of the polarimetric parameters differ from Iceberg to Iceberg and between different parameters. On some bergs, they only exhibit slight variations, whereas on others, they show noiselike textures, but also, more systematic changes are observed. Occasionally, radar intensities of Icebergs are of similar magnitude as those of sea ice. Only for a number of these cases, the combined use of the investigated polarimetric parameters together with intensity improves the discrimination performance between Icebergs and sea ice.

  • Southern ocean Iceberg drift
    2013
    Co-Authors: Christine Wesche, Thomas Rackow, Wolfgang Dierking
    Abstract:

    Icebergs are fragments of glacier ice, which break-off from the ice shelves and glacier tongues all around Antarctica. After calving, Icebergs drift through the ocean, driven by a number of forces. The main forces are the ocean currents and the wind, but also the Coriolis force, sea surface tilt, sea ice concentration and strength, as well as the wave radiation do influence the drift of Icebergs. The relative contributions of the individual forces depend on the environmental conditions (e. g. sea ice or open water) and the Iceberg size and thickness. A drift algorithm is used to simulate the drift of Icebergs through the Southern ocean. The Iceberg drift algorithm is implemented in the Finite Elemente Sea-ice Ocean Model (FESOM), which has a spatial resolution of 10 km close to the ice shelf edge and 30 km offshore. A test was carried out to study the effect of Iceberg size and thickness as well as model set ups on the drift pattern. “Test Icebergs” of a simplified shape were released into the model domain from 77 locations around Antarctica to simulate and analyse their path. The model results were compared with available observations. Additionally to the drift, the model also calculates the melting of Icebergs and therefore the freshwater input into the ocean.

  • Combining SAR images with an Iceberg drift model for improving mass loss estimations caused by Iceberg calving - a case study
    2012
    Co-Authors: Christine Wesche, Thomas Rackow, Wolfgang Dierking
    Abstract:

    Recent estimations of mass loss caused by Iceberg calving are limited to huge Icebergs (>18.5km edge length) or are spatially limited. Since the 1970s, the course of huge Icebergs is permanently tracked using satellite images by the National Ice Center (NIC). A large brake off event is undetected very likely and huge Icebergs are easily to track on their way through the ocean. In many cases, calving of smaller Icebergs takes place unobserved, which hampers the estimation of calving rates and mass loss caused by Iceberg calving. The surface structures of the floating ice masses around Antarctica give information about the size and shape of potential calved Icebergs, so that the origin of Icebergs drifting in the ocean can be restricted to a few calving fronts. SAR images at different resolutions and an edge detection were used to map the surface structures of the floating ice masses around Antarctica and regarding to this, a calving front classification was done. Using the results of the classification, Icebergs within SAR images could be assigned to their potential calving front. An Iceberg drift model is then used to certify the origin. The Iceberg drift model is implemented in a Finite Element Sea ice Ocean Model (FESOM), and the course and the velocity of Icebergs are calculated. With this information it is possible to track Iceberg ensembles back to their calving front to estimate local calving rates.

  • Separation of Icebergs and sea ice in SAR images
    2010
    Co-Authors: Christine Wesche, Wolfgang Dierking
    Abstract:

    The largest loss term in Antarctic mass balance is Iceberg calving from the ice shelves and to estimate the amount of the loss, it is necessary to observe Icebergs in every size. Because current mass loss calculations only include Icebergs with an edge length of > 10 km, we focus on smaller Icebergs (0.1 to 10 km edge length) in a test region north of Berkner Island in the Weddell Sea. Images of the ENVISAT ASAR at different imaging modes are used to analyse the backscattering coefficients of Icebergs depending on the season. To detect Icebergs in SAR images we need to find differences to the surrounding sea ice. Therefore, the backscattering coefficients of the sea ice are analysed for seasonal variations as well.Statistical analyses of the backscattering of Icebergs and sea ice in ASAR image mode data show varying backscatter coefficients over the period of one year. The radar intensity contrast between Icebergs and sea ice is smallest in the summer months and highest in winter and spring. The Iceberg and sea-ice backscattering is investigated for seasonality in medium and low resolution ASAR images as well and compared to the results derived from image mode data. We will also include other frequency bands from other sensors to achieve a complete view of Iceberg signature in radar images and their contrast to the surrounding. These statistics will improve the automatic extraction of Icebergs from SAR images. As a next step, the extracted Iceberg positions will be used to calculate the drift.

  • Detection of Icebergs using ERS SAR images
    2009
    Co-Authors: Christine Wesche, Wolfgang Dierking
    Abstract:

    Within the framework of the DFG project BergCAT we develop a method for detecting small Icebergs in SAR images from the Weddell Sea, Antarctica. Dependent on the season, Icebergs appear as bright or dark targets in SAR images. Statistical analyses of 624 Iceberg regions of interest (ROIs) show that the threshold between bright and dark appearing Icebergs is -7.5 dB. For a first classification, SAR data were divided into images with mainly bright and mainly dark appearing Icebergs, independent from the background signature. The Iceberg and background pixels were investigated separately for the two image groups to reveal possible correlations between thesignatures. We calculated the mean and the standard deviation and use the 1-sigma interval. The 1-sigma intervals show overlapping ranges of the backscattering coefficients of Icebergs and background in the image groups and with the aid of these information we formulated detection conditions. Then we used a combination of thresholds in the non-overlapping ranges and a constant false alarm rate (CFAR) in the overlapping ranges. This detection algorithm detected 72 % of former extracted Iceberg pixels as Icebergs and 84 % of the background pixels as background.

Till J. W. Wagner - One of the best experts on this subject based on the ideXlab platform.

  • Modeling the breakup of tabular Icebergs.
    Science advances, 2020
    Co-Authors: Mark R. England, Till J. W. Wagner, Ian Eisenman
    Abstract:

    Nearly half of the freshwater flux from the Antarctic Ice Sheet into the Southern Ocean occurs in the form of large tabular Icebergs that calve off the continent’s ice shelves. However, because of difficulties in adequately simulating their breakup, large Antarctic Icebergs to date have either not been represented in models or represented but with no breakup scheme such that they consistently survive too long and travel too far compared with observations. Here, we introduce a representation of Iceberg fracturing using a breakup scheme based on the “footloose mechanism.” We optimize the parameters of this breakup scheme by forcing the Iceberg model with an ocean state estimate and comparing the modeled Iceberg trajectories and areas with the Antarctic Iceberg Tracking Database. We show that including large Icebergs and a representation of their breakup substantially affects the Iceberg meltwater distribution, with implications for the circulation and stratification of the Southern Ocean.

  • Wave inhibition by sea ice enables trans-Atlantic ice rafting of debris during Heinrich events
    Earth and Planetary Science Letters, 2018
    Co-Authors: Till J. W. Wagner, Rebecca W. Dell, Ian Eisenman, Ralph F. Keeling, Laurie Padman, Jeffrey P. Severinghaus
    Abstract:

    Abstract The last glacial period was punctuated by episodes of massive Iceberg calving from the Laurentide Ice Sheet, called Heinrich events, which are identified by layers of ice-rafted debris (IRD) in ocean sediment cores from the North Atlantic. The thickness of these IRD layers declines more gradually with distance from the Iceberg sources than would be expected based on present-day Iceberg drift and decay. Here we model Icebergs as passive Lagrangian particles driven by ocean currents, winds, and sea surface temperatures. The Icebergs are released in a comprehensive climate model simulation of the last glacial maximum (LGM), as well as a simulation of the modern climate. The two simulated climates result in qualitatively similar distributions of Iceberg meltwater and hence debris, with the colder temperatures of the LGM having only a relatively small effect on meltwater spread. In both scenarios, meltwater flux falls off rapidly with zonal distance from the source, in contrast with the more uniform spread of IRD in sediment cores. To address this discrepancy, we propose a physical mechanism that could have prolonged the lifetime of Icebergs during Heinrich events. The mechanism involves a surface layer of cold and fresh meltwater formed from, and retained around, large densely packed armadas of Icebergs. This leads to wintertime sea ice formation even in relatively low latitudes. The sea ice in turn shields the Icebergs from wave erosion, which is the main source of Iceberg ablation. We find that sea ice could plausibly have formed around the Icebergs during four months each winter. Allowing for four months of sea ice in the model results in a simulated IRD distribution which approximately agrees with the distribution of IRD in sediment cores.

  • On the representation of capsizing in Iceberg models
    Ocean Modelling, 2017
    Co-Authors: Till J. W. Wagner, A. A. Stern, Rebecca W. Dell, Ian Eisenman
    Abstract:

    Abstract Although Iceberg models have been used for decades, they have received far more widespread attention in recent years, due in part to efforts to explicitly represent Icebergs in climate models. This calls for increased scrutiny of all aspects of typical Iceberg models. An important component of Iceberg models is the representation of Iceberg capsizing, or rolling. Rolling occurs spontaneously when the ratio of Iceberg width to height falls below a critical threshold. Here we examine previously proposed representations of this threshold, and we find that there have been crucial flaws in the representation of rolling in many modeling studies to date. We correct these errors and identify an accurate model representation of Iceberg rolling. Next, we assess how Iceberg rolling influences simulation results in a hierarchy of models. Rolling is found to substantially prolong the lifespan of individual Icebergs and allow them to drift farther offshore. However, rolling occurs only after large Icebergs have lost most of their initial volume, and it thus has a relatively small impact on the large-scale freshwater distribution in comprehensive model simulations. The results suggest that accurate representations of Iceberg rolling may be of particular importance for operational forecast models of Iceberg drift, as well as for regional changes in high-resolution climate model simulations.

  • An Analytical Model of Iceberg Drift
    Journal of Physical Oceanography, 2017
    Co-Authors: Till J. W. Wagner, Rebecca W. Dell, Ian Eisenman
    Abstract:

    AbstractThe fate of Icebergs in the polar oceans plays an important role in Earth’s climate system, yet a detailed understanding of Iceberg dynamics has remained elusive. Here, the central physical processes that determine Iceberg motion are investigated. This is done through the development and analysis of an idealized model of Iceberg drift. The model is forced with high-resolution surface velocity and temperature data from an observational state estimate. It retains much of the most salient physics, while remaining sufficiently simple to allow insight into the details of how Icebergs drift. An analytical solution of the model is derived, which highlights how Iceberg drift patterns depend on Iceberg size, ocean current velocity, and wind velocity. A long-standing rule of thumb for Arctic Icebergs estimates their drift velocity to be 2% of the wind velocity relative to the ocean current. Here, this relationship is derived from first principles, and it is shown that the relationship holds in the limit of ...

  • wind driven upwelling around grounded tabular Icebergs
    Journal of Geophysical Research, 2015
    Co-Authors: A. A. Stern, Till J. W. Wagner, Keith W Nicholls, Eric S Johnson, David M Holland, Peter Wadhams, Richard Bates, Povl E Abrahamsen, Anna J Crawford, Jonathan Gagnon
    Abstract:

    Temperature and salinity data collected around grounded tabular Icebergs in Baffin Bay in 2011, 2012, and 2013 indicate wind-induced upwelling at certain locations around the Icebergs. These data suggest that along one side of the Iceberg, wind forcing leads to Ekman transport away from the Iceberg, which causes upwelling of the cool saline water from below. The upwelling water mixes with the water above the thermocline, causing the mixed layer to become cooler and more saline. Along the opposite side of the Iceberg, the surface Ekman transport moves towards the Iceberg, which causes a sharpening of the thermocline as warm fresh water is trapped near the surface. This results in higher mixed layer temperatures and lower mixed layer salinities on this side of the Iceberg. Based on these in situ measurements, we hypothesize that the asymmetries in water properties around the Iceberg, caused by the opposing effects of upwelling and sharpening of the thermocline, lead to differential deterioration around the Iceberg. Analysis of satellite imagery around Iceberg PII-B-1 reveals differential decay around the Iceberg, in agreement with this mechanism.

Grant R. Bigg - One of the best experts on this subject based on the ideXlab platform.

  • A model for assessing Iceberg hazard
    Natural Hazards, 2018
    Co-Authors: Grant R. Bigg, Thomas E. Cropper, Clare K. O’neill, Alex Arnold, Andrew Fleming, Robert Marsh, V. Ivchenko, Nicolas Fournier, Mike Osborne, Robin Stephens
    Abstract:

    With the polar regions opening up to more marine activities but Iceberg numbers more likely to increase than decline as a result of global warming, the risk from Icebergs to shipping and offshore facilities is increasing. The NW Atlantic Iceberg hazard has been well monitored by the International Ice Patrol for a century, but many other polar regions have little detailed climatological knowledge of the Iceberg risk. Here, we develop a modelling approach to assessing Iceberg hazard. This uses the region of the Falklands Plateau and its shipping routes for a case study, but the approach has general geographical applicability and can be used for assessing Iceberg hazard for routes or fixed locations. The Iceberg risk for a number of locations selected from the main shipping routes in the SW Atlantic is assessed by using an Iceberg model, forced by the output from a high-resolution ocean model. The Iceberg model was seeded with Icebergs around the edge of the modelled region using a number of scenarios for the seeding distribution, based on a combination of idealised, modelled and observed Iceberg fluxes from the Southern Ocean. This enabled us to determine measures of Iceberg risk linked to a mix of starting location and the likelihood of Icebergs being encountered in such a position. For our study area, the main area of Iceberg risk is linked to the East Falklands Current, but small, yet nonzero, risk covers much of the east and north of the region.

  • Prospects for seasonal forecasting of Iceberg distributions in the North Atlantic
    Natural Hazards, 2018
    Co-Authors: Grant R. Bigg, Robert Marsh, V. Ivchenko, Yifan Zhao, Matthew J. Martin, Jeffrey R. Blundell, Simon A. Josey, Edward Hanna
    Abstract:

    An efficient approach to ocean–Iceberg modelling provides a means for assessing prospects for seasonal forecasting of Iceberg distributions in the northwest Atlantic, where Icebergs present a hazard to mariners each spring. The stand-alone surface (SAS) module that is part of the Nucleus for European Modelling of the Ocean (NEMO) is coupled with the NEMO Iceberg module (ICB) in a “SAS-ICB” configuration with horizontal resolution of 0.25°. Iceberg conditions are investigated for three recent years, 2013–2015, characterized by widely varying Iceberg distributions. The relative simplicity of SAS-ICB facilitates efficient investigation of sensitivity to Iceberg fluxes and prevailing environmental conditions. SAS-ICB is provided with daily surface ocean analysis fields from the global Forecasting Ocean Assimilation Model (FOAM) of the Met Office. Surface currents, temperatures and height together determine Iceberg advection and melting rates. Iceberg drift is further governed by surface winds, which are updated every 3 h. The flux of Icebergs from the Greenland ice sheet is determined from engineering control theory and specified as an upstream flux in the vicinity of Davis Strait for January or February. Simulated Iceberg distributions are evaluated alongside observations reported and archived by the International Ice Patrol. The best agreement with observations is obtained when variability in both upstream Iceberg flux and oceanographic/atmospheric conditions is taken into account. Including interactive Icebergs in an ocean–atmosphere model with sufficient seasonal forecast skill, and provided with accurate winter Iceberg fluxes, it is concluded that seasonal forecasts of spring/summer Iceberg conditions for the northwest Atlantic are now a realistic prospect.

  • Icebergs: Their Science and Links to Global Change
    2016
    Co-Authors: Grant R. Bigg
    Abstract:

    Preface Acknowledgements 1. Appointment with the Titanic Part I. The Science of Icebergs: 2. The origin of Icebergs 3. The physics of Icebergs 4. Inputs from Icebergs to the ocean 5. Icebergs and the sea floor Part II. Icebergs and their Impacts: 6. Icebergs and past climates 7. Abrupt climate change due to Icebergs 8. Iceberg risk 9. Icebergs: a freshwater source? 10. Icebergs and the future Index.

  • Sensitivity of the glacial ocean to Heinrich events from different Iceberg sources, as modeled by a coupled atmosphere‐Iceberg‐ocean model
    Paleoceanography, 2008
    Co-Authors: Richard C. Levine, Grant R. Bigg
    Abstract:

    [1] We introduce explicit Icebergs from a dynamic and thermodynamic Iceberg model into an intermediate complexity climate model, which includes the coupled atmosphere-ocean system. This modeling approach allows Iceberg meltwater to be injected into the ocean on the basis of thermodynamical considerations along the Iceberg trajectories. Icebergs are seeded from known ice sheets in both hemispheres. Adding Icebergs to the present-day climate model has a minimal impact, but during the Last Glacial Maximum (LGM), Atlantic overturning strength is reduced by a third, while producing a model state that is consistent with a steady state climate. We test the sensitivity of the model at the LGM to additional Heinrich event-scale fluxes of Icebergs from three possible sources: Hudson Strait, the Gulf of Saint Lawrence, and the Norwegian Channel Ice Stream (NCIS). The sensitivity of the ocean is similar for all locations, with differences dominated by the length of the Iceberg meltwater pathways to the main ocean convection region. The NCIS events result in more variability and a distinctly different, more northerly, salinity anomaly. We compare these results to a more typical modeling approach, whereby meltwater is injected directly into the ocean at the Iceberg source locations, and find that these floods overestimate the oceanic response compared to the Iceberg events. Our results suggest that 0.3–0.4 Sv of additional freshwater flux, either as Icebergs or freshwater, is required to shut down the North Atlantic meridional overturning, a larger freshwater flux than sometimes suggested because of the localized nature of the release of the freshwater.

  • contribution of giant Icebergs to the southern ocean freshwater flux
    Journal of Geophysical Research, 2006
    Co-Authors: Tiago H Silva, Grant R. Bigg, Keith W Nicholls
    Abstract:

    [1] In the period 1979–2003 the mass of “giant” Icebergs (Icebergs larger than 18.5 km in length) calving from Antarctica averaged 1089 ± 300 Gt yr−1 of ice, under half the snow accumulation over the continent given by the Intergovernmental Panel on Climate Change (2246 ± 86 Gt yr−1). Here we combine a database of Iceberg tracks from the National Ice Center and a model of Iceberg thermodynamics in order to estimate the amount and distribution of meltwater attributable to giant Icebergs. By comparing with published modeled meltwater distribution for smaller bergs we show that giant Icebergs have a different melting pattern: An estimated 35% of giant Icebergs' mass is exported north of 63°S versus 3% for smaller bergs, although giant bergs spend more of the earlier part of their history nearer to the coast. We combine both estimates to produce the first Iceberg meltwater map that takes into account giant Icebergs. The average meltwater input is shown to exceed precipitation minus evaporation (P − E) in certain areas and is a nonnegligible term in the balance of freshwater fluxes in the Southern Ocean. The calving of giant Icebergs is, however, episodic; this might have implications for their impact on the freshwater budget of the ocean. It is estimated that over the period 1987–2003 the meltwater flux in the Weddell and Ross seas has varied by at least 15,000 m3 s−1 over a month. Because of the potential sensitivity of the production of deep waters to abrupt changes in the freshwater budget, variations in Iceberg melt rates of this magnitude might be climatologically significant.