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Applications of ocean transport modelling
Stockholm University, Faculty of Science, Department of Meteorology .
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The advective motion of seawater governs the transport of almost everything, animate or inanimate, present in the ocean and those lacking the ability to outswim the currents have to follow the flow. This makes modelling of advective ocean transports a powerful tool in various fields of science where a displacement of something over time is studied. The present thesis comprises four different applications of ocean-transport modelling, ranging from large-scale heat transports to the dispersion of juvenile marine organisms. The aim has been to adapt the method not only to the object of study, but also to the available model-data sets and in situ-observations.

  • The first application in the thesis is a study of the oceanic heat transport. It illustrates the importance of wind forcing for not only the heat transport from the Indian to the Atlantic Ocean, but also for the net northward transport of heat in the Atlantic.
  • In the next study focus is on the particle-transport differences between an open and a semi-enclosed coastal area on the Swedish coast of the Baltic Sea. The modelled patterns of sedimentation and residence times in the two basins are examined after particles having been released from a number of prescribed point sources.
  • In the two final studies the transport-modelling framework is applied within a marine-ecology context and the transported entities are larvae of some Scandinavian sessile and sedentary species and non-commercial fishes (e.g. the bay barnacle, the blue mussel, the shore crab and the gobies). The effects of depth distribution of dispersing larvae on the efficiency of the Marine Protected Areas in the Baltic Sea are examined. Further, the diversity in dispersal and connectivity depending on vertical behaviour is modelled for regions with different tidal regimes in the North Sea, the Skagerrak and the Kattegat.

The spatial scales dealt with in the studies varied from global to a highly resolved 182-metres grid. The model results, excepting those from the global study, are based on or compared with in situ-data.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University , 2012. , 40 p.
Keyword [en]
ocean transport modelling, connectivity, particle-tracking, sediment transport, Forsmark, marine protected areas, MPA, stream functions, heat flux, wind forcing, Carcinus maenas
National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-75344ISBN: 978-91-7447-496-1 (print)OAI: oai:DiVA.org:su-75344DiVA: diva2:516366
Public defence
2012-06-01, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. 4: Manuscript.

Available from: 2012-05-10 Created: 2012-04-16 Last updated: 2012-05-02Bibliographically approved
List of papers
1. Wind sensitivity of the inter-ocean heat exchange
Open this publication in new window or tab >>Wind sensitivity of the inter-ocean heat exchange
2009 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 61, no 5, 635-653 p.Article in journal (Refereed) Published
Abstract [en]

An idealised two-basin model is used to investigate the impact of the wind field on the heat exchange between the ocean basins. The scalar potential of the divergent component of the horizontal heat flux is computed, which gives a 'coarse-grained' image of the surface heat flux that captures the large-scale structure of the horizontal heat transport. Further the non-divergent component is examined, as well as the meridional heat transport and the temperature–latitude overturning stream function. A sensitivity analysis examines the heat transport response to changes in wind stress at different latitudes. The results are compared with results from an eddy-permitting global circulation model. The westerly wind stress over the Southern Ocean has two effects: a local reduction of the surface heat loss in response to the equatorward surface Ekman drift, and a global re-routing of the heat export from the Indo-Pacific. Without wind forcing, the Indo-Pacific heat export is released to the atmosphere in the Southern Ocean, and the net heat transport in the southern Atlantic is southward. With wind forcing, the Indo-Pacific export enters the Atlantic through the Aghulas and is released in the Northern Hemisphere. The easterlies enhance the poleward heat transport in both basins.

National Category
Oceanography, Hydrology, Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-34855 (URN)10.1111/j.1600-0870.2009.00414.x (DOI)000269810000008 ()
Available from: 2010-01-21 Created: 2010-01-13 Last updated: 2012-04-23Bibliographically approved
2. Difference in Particle Transport Between Two Coastal Areas in the Baltic Sea Investigated with High-Resolution Trajectory Modeling
Open this publication in new window or tab >>Difference in Particle Transport Between Two Coastal Areas in the Baltic Sea Investigated with High-Resolution Trajectory Modeling
2013 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 42, no 4, SI 455-463 p.Article in journal (Refereed) Published
Abstract [en]

A particle-tracking model based on high-resolution ocean flow data was used to investigate particle residence times and spatial distribution of settling sediment for two geo-morphologically different Swedish coastal areas. The study was a part of a safety assessment for the location of a future nuclear-waste repository, and information about the particle-transport patterns can contribute to predictions of the fate of a possible leakage. It is also, to our knowledge, the first time particle-transport differences between two coastal areas have been quantified in this manner. In Forsmark, a funnel-shaped bay shielded by a number of islands, the average residence time for clay particles was 5 times longer than in the modeled part of Simpevarp, which is open to the Baltic Sea. In Forsmark, < 10 % of the released particles left the domain compared to 60-80 % in Simpevarp. These site-specific differences will increase over time with the differences in land uplift between the areas.

Place, publisher, year, edition, pages
Netherlands: Springer, 2013
Keyword
sediment, particle transport, particle-tracking model, resuspension, Lagrangian, trajectories
National Category
Oceanography, Hydrology, Water Resources Geosciences, Multidisciplinary Environmental Engineering
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-75604 (URN)10.1007/s13280-013-0397-3 (DOI)000318285100009 ()
Note

AuthorCount:2;

Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2017-12-07Bibliographically approved
3. Larval depth distribution critically affects dispersal and the efficiency of marine protected areas
Open this publication in new window or tab >>Larval depth distribution critically affects dispersal and the efficiency of marine protected areas
(English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599Article in journal (Refereed) Submitted
Abstract [en]

This study aims to improve estimates of dispersal by including information on larval traits, and in particular to explore how larval depth distribution affects connectivity and MPA functionality in the Baltic Sea. A field survey showed that both invertebrates and fish differed in their larval depth distribution ranging from surface waters to more than 100 m. A biophysical model of larval dispersal in the Baltic Sea showed that decreased depthdistribution increased average dispersal distance 2.5 times, decreased coastal retention and local recruitment, and increased connectivity substantially. Together with pelagic larval duration (PLD), depth distribution explained 80% of total variation in dispersal distance, whereas spawning season, geographic and annual variations in circulation had only marginal effects. Median dispersal distances varied between 8 and 46 km, with 10% of simulated trajectories dispersing beyond 30-160 km depending on drift depth and PLD. In the Baltic Sea, the majority of shallow Natura 2000 MPAs are smaller than 8 km. In the present study, only one of the 11 assessed larval taxa would have a local recruitment >10% within MPAs of this size. Connectivity between MPAs was expected to be low for most larval trait combinations. Our simulations and the empirical data suggest that the MPA size within the Natura2000 system is considerably below what is required for local recruitment of most sessile invertebrates and sedentary fish. Future designs of MPA networks would benefit from spatially explicit biophysical models that consider dispersal and connectivity for complex circulation patterns and informed larval traits.

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-75606 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2017-12-07Bibliographically approved
4. Larval behavior and dispersal mechanisms in shore crab larvae: Local adaptations to different tidal environments?
Open this publication in new window or tab >>Larval behavior and dispersal mechanisms in shore crab larvae: Local adaptations to different tidal environments?
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Recent studies indicate that local adaptations may occur in marine populations over relatively small geographic areas despite high dispersal potential if strong environmental gradients are present. Here we assess if local adaptations in larval behavior can develop in response to tidal gradients by studying the shore crab Carcinus maenas in the North Sea area using a combination of empirical and model studies. Specific aims of the study was to assess if shore crab larvae from different tidal environments have different swimming behaviors, and if these behaviors affect connectivity and recruitment success of the larvae.

Field and laboratory studies demonstrated that newly hatched shore crab larvae from mesotidal Danish Wadden Sea displayed an inherited vertical migration rhythm with a circatidal periodicity, and that postlarvae swam in surface water almost exclusively during flood tides, suggesting that larvae use selective tidal stream transport to control the dispersal process. In contrast, shore crab larvae from microtidal Skagerrak displayed a nocturnal vertical migration behavior that switched to a diurnal behavior at the end of the larval phase, indicating an adaptation to avoid visual predators and to use wind-driven transport to reach shallow settlement areas.

Results from a biophysical model showed that larval swimming behavior had a dominant role for the dispersal process and the recruitment success in the study area, and demonstrated that modeled tidal-migrating larvae in Wadden Sea had 2x higher recruitment success than larvae with a diel behavior. However, in microtidal Skagerrak no differences in recruitment success was found between the two larval behaviors. Lower fitness is suggested for tidal-migrating larvae in microtidal regions due to a predicted higher predation mortality. Consistent with recent population genetic studies, connectivity analyses indicated an oceanographic dispersal barrier in Eastern Wadden Sea that will restrict gene-flow between the two areas, and allow local adaptations in larval behavior. 

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-75611 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2012-04-23Bibliographically approved

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