Description: The eastern Weddell Sea region is an alley for drifting icebergs, which calve further east along the coastline of East Antarctica. Our analysis is focussed is on the region north of the Ekström Ice Shelf. Since at the Ekström Ice Shelf a landing place is used for the supply of the German overwintering station Neumayer III and the South-African station Sanae IV, it is important to monitor the drifting routes taken by the icebergs in this region. We use a series of ENVISAT WSM data to follow the iceberg D18 and two smaller ones (IB1 and IB2) through the eastern Weddell Sea region in 2006. Model simulations of the iceberg drift are carried out to get more detailed information about the relative influence of different forces on the iceberg drift in this region. In this poster, we provide an overview about the first results.

Description: 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.

Description: The continental shelf of the eastern Weddell Sea is known as “iceberg alley”. Icebergs that calve at the coast of East Antarctica drift with the coastal current along the Fimbul Ice Shelf towards the Weddell Sea (Gladstone et al., 2001). In the beginning of 2006, three large icebergs passed the Ekström Ice Shelf close to the sea ice edge. Using a series of ENVISAT Wide Swath images, they were monitored for nearly one year to investigate the influence of wind, ocean currents, sea ice and the iceberg draft on their drift patterns and to validate corresponding model simulations. The iceberg drift model is driven by the Finite-Elements Sea-ice Ocean Model (FESOM, Timmermann et al., 2009). It was run with a temporal resolution of 6 hours and a spatial resolution of 10 km close to the coast and 30 km further offshore. Besides comparison between iceberg drift observations and computer simulations for improving the model, the observation of icebergs in this region is of great importance for the logistic department at Alfred Wegener Institute because of the supply of the German overwintering station Neumayer III. The drift of the three icebergs is modeled with different input configurations and parameters. Events with large differences between the modeled and the observed positions are investigated in detail. The goal of this study is to improve the accuracy of the iceberg drift model in the region of the Weddell Sea “drift alley” and thus to be able to forecast iceberg positions as support for marine traffic in this region. References: Gladstone, R. M.; Bigg, G. R. & Nicholls, K. W. (2001), Iceberg trajectory modeling and melt water injection in the Southern Ocean, Journal of Geophysical Research, 106(C9), 19903-19915 Timmermann, R.; Danilov, S.; Schröter, J.; Böning, C.; Sidorenko, D. & Rollenhagen, K. (2009), Ocean circulation and sea ice distribution in a finite element global sea ice-ocean model, Ocean Modelling, 27(3-4), 114-129

Description: The eastern Weddell Sea region is an alley for drifting icebergs, which calve further east along the coastline of East Antarctica. Our analysis is focused on the region north of the Ekstr¨om Ice Shelf. Since at the Ekstr¨om Ice Shelf a landing place is used for the supply of the Ger- man overwintering station Neumayer III and the South- African station Sanae IV, it is important to monitor the drifting routes taken by the icebergs in this region. We use a series of ENVISAT ASAR WSM data to follow a larger (D18) and a smaller (IB1) iceberg through the east- ern Weddell Sea region in 2006. Model simulations are carried out to get more detailed information about the rel- ative influence of different forces on the iceberg drift in this region.

Description: We describe the global configuration of a coupled atmosphere/ocean model. The atmosphere is simulated by the ECHAM5 and the ocean by the Finite-Element Sea-Ice Ocean Model (FESOM), which supports unstructured meshes and allows for variable resolution. Coupling between structured and unstructured meshes is a technically challenging task due to different geometry, resolution and representation of coastlines in both components. This has been achieved via the parallel OASIS4 coupler and additional use of a regular exchange mesh. The latter has been introduced in the ocean model. The conservation of flux moments requires additional care since model grids are different in both components. The heat and moisture fluxes are computed in the atmospheric model so that the flux variance is defined by the resolution in the atmosphere. Since it is problematic to downscale the variance onto the fine resolved parts of the ocean, a few interpolation techniques are suggested. We validate the coupled setup on the basis of an integration run for 300 years.

Description: We present a global climate model setup where the Finite-Element Sea-Ice Ocean Model (FESOM) has been coupled to the atmospheric model ECHAM5. The major difference of this setup to other climate models is the ocean component which supports variable resolution. The latter allows to refine the areas of particular interest in the global context and to resolve narrow straits where it is needed. Current model setup has a resolution varying from 30 to 200 km in the ocean and T63L31 (~1.8°) configuration in the atmosphere. We present 300 year integration results, discuss model variability and trends. It is shown that the climate state simulated by FESOM/ECHAM is in most cases within the spread of other models. On another hand we address the technical complexity of this setup, linked to an exchange between unstructured and structured meshes. These have different geometry, representation of coastlines and different rules for the flux definition. This implies that additional strategies have to be developed in order to preserve the flux conservation. We summarize the problems and suggest our compromised solutions.

Description: In der vorliegenden Arbeit wird ein dynamisch-thermodynamisches Eisbergmodell als Erweiterung des Finite-Elemente-Meereis-Ozean-Modells FESOM des Alfred-Wegener- Instituts für Polar- und Meeresforschung (AWI) in Bremerhaven entwickelt. Dieser Entwicklungsprozess wird umfassend dargestellt und kann ausgehend von den zugrundeliegenden physikalischen Gleichungen und deren numerischer Diskretisierung bis hin zur Implementierung in Fortran nachvollzogen werden. Diese Arbeit kann daher als ausführliche Dokumentation des entwickelten Eisbergmodells dienen. Abschließend werden eine Validierung des Modells anhand von Beobachtungsdaten im Bereich des Weddellmeeres sowie einige Sensitivitätsstudien durchgeführt, um die Bedeutung der verschiedenen physikalischen Prozesse für die Eisbergdrift zu untersuchen. Das Eisbergmodell wird zur Beschreibung der charakteristischen Drift von Eisbergen im Weddellmeer eingesetzt und erlaubt in der bestehenden Form bereits einige physikalische Einblicke, von denen hier folgendes Ergebnis erwähnt sei: Im Gegensatz zu kleinen Eisbergen, die in eisfreien Regionen einem starken Einfluss von Wind und Ozeanströmungen unterworfen sind, werden große Eisberge bis hin zu riesigen Tafeleisbergen (giant tabular icebergs) in diesen Regionen stark von der Balance zwischen Corioliskraft und der Hangabtriebskraft aufgrund einer geneigten Meeresoberfläche beeinflusst. Möglicherweise stellt die Kraft aufgrund der Neigung der Meeresoberfläche den fehlenden Antrieb in eisfreien Regionen dar, der in einer früheren AWI-Modellstudie von Lichey und Hellmer [2001] bei der Simulation eines Tafeleisbergs beobachtet wurde. Durch die Entwicklung des Eisbergmodells steht in Verbindung mit dem Finite-Elemente- Meereis-Ozean-Modell FESOM ein nützliches Werkzeug zur Verfügung, das in zahlreichen Gebieten Anwendung finden könnte. Ein Beispiel ist die Berechnung von Schmelzraten vieler modellierter Eisberge, die nach einer statistischen Verteilung im Meereis-Ozean-Modell FESOM gestartet werden könnten, um den Süßwasserfluss aufgrund von Eisbergen in physikalisch sinnvoller Weise über den Ozean zu verteilen. Dies wäre ein weiterer Schritt, um den Kreislauf des Wassers im Erdsystem zu schließen. Martin und Adcroft [2010] nutzen bereits eine solche Verteilung des Süßwasserflusses durch Eisberge, die in Modellrechnungen für den nächsten Assessment Report des Intergovernmental Panel on Climate Change (IPCC) Verwendung finden wird.