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Ridged sea ice modelling in climate applications
Stockholm University, Faculty of Science, Department of Meteorology .
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work aims to increase our understanding of the nature of large scale features of sea ice from a dynamics point of view.Sea ice plays an important part in the exchange of heat and humidity between sea and air and thus is an important component of the climate system. Its physical presence also directly impacts the various forms of life such as diatoms, polar bears and humans alike.The dynamics of sea ice affect both weather and climate, through the large scale drift in the Arctic from the Siberian coast towards Fram Strait, through creation of cracks in the ice called leads or polynyas, and through ridging and other mechanical deformations of ice floes.In this work, we have focused on modelling of ridged ice for a number of reasons. Direct observations of the internal ice state is very difficult to perform and in general, observations of sea ice are either sparse or of limited information density. Ridged ice can be seen as the memory of high ice stress events, giving us a view on these highly dynamic events. Ridging is of major importance for the ice thickness distribution, as the thickest ice can only be formed through mechanical processes. Further, ridged ice is of direct interest for anyone conducting shipping through seasonal or perennial ice covered seas as it can form impenetrable barriers or in extreme even cases crush a ship caught within the ice pack.

To this end, a multi-category sea ice model, the HELsinki Multi category Ice model (HELMI), was implemented into the Rossby Centre Ocean model (RCO). HELMI has explicit formulations for ridged and rafted ice, as well as sub-grid scale ice thickness distribution (a feature shared with other multi category models) and an ice strength based on energetics. These features give RCO better representation of sub-grid scale physics and gives us the possibility to study the deformed ice in detail.

In paper I we look at the change in behaviour in the Arctic as the ice becomes more mobile, leading to a slight increase in modelled ridged ice volume in the central Arctic, despite a general trend of a decreasing ice cover.Paper II takes us to the Baltic Sea and the possibilities of modelling ridge ice concentration with a statistical model.In Paper III we investigate how the diminishing ice cover in future scenarios affects the biological activity in the Baltic Sea.Finally Paper IV investigates how the ice stress and the internal ice force can be interpreted in terms of ice compression on the ship scale.

Place, publisher, year, edition, pages
Department of Meteorology, Stockholm University , 2013. , 37 p.
Keyword [en]
Arctic ocean, Baltic Sea, sea ice, ice dynamics, numerical modelling, climate, ice deformation, ice compression, physical and biogeochemical interactions
National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-93977ISBN: 978-91-7447-767-2 (print)OAI: oai:DiVA.org:su-93977DiVA: diva2:650546
Public defence
2013-10-22, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper 4: Manuscript

Available from: 2013-09-30 Created: 2013-09-22 Last updated: 2013-09-25Bibliographically approved
List of papers
1. Ridged sea ice characteristics in the arctic from a coupled multicategory sea ice model
Open this publication in new window or tab >>Ridged sea ice characteristics in the arctic from a coupled multicategory sea ice model
2012 (English)In: Journal of Geophysical Research: Oceans, ISSN 2169-9291, Vol. 117, no C8Article in journal (Refereed) Published
Abstract [en]

In this study, a multicategory sea ice model with explicit ice classes for ridged and rafted ice was used to examine the evolution of deformed ice during the period 1980-2002. The results show that (1) ridged ice comprises roughly 45-60% of Arctic sea ice volume and 25-45% of the sea ice area, (2) most of the perennial ice consists of ridged ice, and (3) ridged ice exhibits a small seasonal variability. Our results also show an increase in mean ridged ice thickness of 4-6 cm yr(-1) during the summer in an area north of the Canadian Archipelago and a corresponding decrease in the East Siberian Sea and Nansen Basin. At the same time, Arctic sea ice age has been observed to decline and ice drift speed to increase during the simulation period. We connect these findings with a modeled regional increase in the production rate of ridged ice. Comparison of the multicategory model and a two category reference model shows a substantially increased ice production rate due to a more frequent occurrence of leads, resulting in an ice thickness increase of up to 0.8 m. Differences in ice physics between the multicategory and reference models also affect the freshwater content. The sum of liquid and solid freshwater content in the entire Arctic Ocean is about 10% lower and net precipitation (P-E) is about 7% lower as compared to the reference model.

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-80754 (URN)10.1029/2010JC006936 (DOI)000302857600001 ()
Note

AuthorCount:4;

Available from: 2012-10-01 Created: 2012-09-27 Last updated: 2014-10-06Bibliographically approved
2. Long-term characteristics of simulated ice deformation in the Baltic Sea (1962–2007)
Open this publication in new window or tab >>Long-term characteristics of simulated ice deformation in the Baltic Sea (1962–2007)
2013 (English)In: Journal of Geophysical Research - Oceans, ISSN 2169-9291, Vol. 118, no 2, 801-815 p.Article in journal (Refereed) Published
Abstract [en]

The North Atlantic Oscillation (NAO) index is a frequently used measure for the mean winter conditions in Northern Europe. A positive, high index is associated with strong westerlies and anomalous warm temperatures. The effects on sea ice conditions in the Baltic Sea are twofold. Warm temperatures prevent sea ice formation. If ice is present nevertheless, the strong winds can promote the formation of ice ridges which hinders ship traffic. We use an ocean-sea ice model to investigate the NAO impact on the ridged ice area fraction in the Baltic during 1962–2007. Our simulations indicate that in the northern Bothnian Bay, a high NAO index is related to an anomalous accumulation of ridges, while in the rest of the Baltic Sea, the relationship is contrary. The NAO explains locally at most only 20–25% of the ridged ice fraction interannual variability which indicates the systems complexity. However, we find high skill with local correlations around 0.8 for annually averaged ridged ice fraction reconstructed from multilinear regression using winter averaged wind extremes, surface air temperature, and sea surface temperature (SST). This suggests that the amount of ridged ice in late winter can be derived from these routinely measured quantities. In large parts of the basin, it is sufficient to use the atmospheric parameters as a predictor, while in the eastern Bothnian Bay and southern Gulf of Finland, the SST is required to reconstruct the bulk of the ridged ice fraction.

National Category
Oceanography, Hydrology, Water Resources
Research subject
Oceanography
Identifiers
urn:nbn:se:su:diva-93964 (URN)10.1002/jgrc.20089 (DOI)000317840700017 ()
Note

Authorcount: 4;

Available from: 2013-09-20 Created: 2013-09-20 Last updated: 2014-12-03Bibliographically approved
3. Modeling the impact of reduced sea ice cover in future climate on the Baltic Sea biogeochemistry
Open this publication in new window or tab >>Modeling the impact of reduced sea ice cover in future climate on the Baltic Sea biogeochemistry
2013 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 1, 149-154 p.Article in journal (Refereed) Published
Abstract [en]

In a warming future climate, the sea ice cover is expected to decrease, with very likely large consequences for the marine ecosystem. We investigated the impact of future sea ice retreat on the Baltic Sea biogeochemistry at the end of the century, using an ensemble of regionalized global climate simulations. We found that the spring bloom will start by up to one month earlier and winds and wave-induced resuspension will increase, causing an increased transport of nutrients from the productive coastal zone into the deeper areas. The internal nutrient fluxes do not necessarily increase because they also depend on oxygen and temperature conditions of the bottom water. Winter mixing increases in areas having reduced ice cover and in areas having reduced stratification due to increased freshwater supply. The reduced sea ice cover therefore partly counteracts eutrophication because increased vertical mixing improves oxygen conditions in lower layers.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-90205 (URN)10.1029/2012GL054375 (DOI)000317826300028 ()
Funder
EU, European Research Council, 217246FormasKnut and Alice Wallenberg FoundationSwedish Research CouncilThe Middle East in the Contemporary World
Note

AuthorCount:3;

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2017-12-06Bibliographically approved
4. Note on methods for assessing ice compression in continuum scale geophysical models
Open this publication in new window or tab >>Note on methods for assessing ice compression in continuum scale geophysical models
(English)Manuscript (preprint) (Other academic)
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:su:diva-93976 (URN)
Available from: 2013-09-22 Created: 2013-09-22 Last updated: 2013-09-24

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