- Coastal hydrodynamics
- Transport of suspended sediment
- Regional sea level variability
- Internal waves
Dr. Theo Gerkema
Wind makes the Wadden Sea dynamic
Physical oceanographer Theo Gerkema investigates the sea level in the Wadden Sea and the Zeeland delta. ‘Global mean sea level is measured to an accuracy of a few millimetres with the help of satellites. Climate change and sea level rise are clearly measurable in those data. Nevertheless, that does not say a lot about regional values; considerable differences exist across the world. Furthermore, the annual mean sea level along the Dutch coast can vary by ten or even twenty centimetres from year to year. That is mainly due to the mean direction and strength of the wind in that year. Was the prevailing wind more easterly than normal? Then the mean sea level on the Dutch coast can easily be ten centimetres lower!’
Long-term measurements
‘Those variations become relatively less important when we take a very long time series. The sea level along our coast has been accurately measured for more than a century. Over that period, trends can therefore be recognized. However, in relation to climate change and sea level rise, we also want to know what has happened to the sea level over the past ten years, for example. We need to be able to account for the effects of the wind to determine that. So that is an important part of our research too.'
Sand, silt and nutrients
‘Just how large an influence the wind has on water movements in the Wadden Sea is something we have only recently become aware of. These water movements are important for almost everything that happens in the Wadden Sea. What comes through the inlets between the islands twice per day is not just a lot of water but also sand, sediment and nutrients. These nutrients, in turn, ensure that the algae can grow, as a result of which shellfish, fish and birds can find food.’
‘Freshwater also regularly comes in from the sluices in the Afsluitdijk, the dyke that separates the IJsselmeer lake from the Wadden Sea. How that freshwater subsequently spreads through the channels and over the mudflats strongly depends on the wind. This way, the variable wind leaves a strong mark on the Wadden Sea and makes its dynamics very much event-driven.’
Read more +Introductory textbook on tides
Theo Gerkema, An introduction to tides. Cambridge University Press, 2019.
Contains the following chapters: 1. Introductory Concepts; 2. Tidal Forcing; 3. Celestial Motions; 4. Tidal Constituents and the Harmonic Method; 5. Tidal Wave Propagation; 6. Tides in Coastal Seas and Basins; 7. Internal Tides.
ENW LOCO-EX project (The Wadden Sea as an event-driven system: long-term consequences for exchange), jointly with TU/e and IOW Warnemünde.
The Wadden Sea is the largest backbarrier tidal system in the world and a UNESCO world heritage site because of its ecological significance. It is under increased pressure due to human activities and climate change. A key governing component of the overall system is the exchange of water, salt, nutrients, sediment, larvae, etc. between basins and with the North Sea. Recently, we have shown that the nature of this exchange is very different than previously thought due to the dominant role of the wind, which imposes an enormous variability, with storms having a disproportionately high impact. This view of the Wadden Sea as an event-driven system means that understanding and quantifying the exchanges and transports requires the inclusion of a wide range of forcing conditions over a long time span.
In this project, we investigate the exchange between the tidal basins and the North Sea for a 35-year period in the Dutch Wadden Sea. For this, we will develop and apply new tools to quantify the exchange, the flushing characteristics of the basins, and the connectivity in the system. We will analyse results of new long-term numerical simulations of the hydrodynamics to link the variability in the forcing to the exchange and transport in the region. Finally, the results will allow us to estimate how the exchange would be altered under climate change. The results of this project will help to inform protection plans and policy decisions for the region.
Regional sea level variability
Annual mean sea level varies in the order of a decimeter from year to year. This inter-annual variability is also in large part due to the prevailing wind climate in different years. Regional sea level variability forms a core topic at the department of Estuarine & Delta Systems. Therefore I am also part of the NIOZ Sea Level Centre of expertise.
Education & positions
I am a member of the department of Estuarine & Delta Systems (NIOZ-Yerseke) since 2016. Before I worked as senior researcher on coastal dynamics at NIOZ-Texel, after having been postdoctoral researcher at NIOZ, LEGI Grenoble (France) and Utrecht University. Until 2010, I worked for many years on internal tides, solitons, and the effects of Earth rotation.
Linked news
Linked blogs
NIOZ publications
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2023
Chen, S.; Jiang, L.; Cheng, X.; Liao, G.; Gerkema, T. (2023). A physical perspective of recurrent water quality degradation: a case study in the Jiangsu coastal waters, China. JGR: Oceans 128(8): e2022JC019607. https://dx.doi.org/10.1029/2022jc019607Fajardo-Urbina, J. M.; Arts, G.; Gräwe, U.; Clercx, H. J. H.; Gerkema, T.; Duran-Matute, M. (2023). Atmospherically Driven Seasonal and Interannual Variability in the Lagrangian Transport Time Scales of a Multiple‐Inlet Coastal System. JGR: Oceans 128(6): e2022JC019522. https://dx.doi.org/10.1029/2022jc019522van der Sande, W.M.; Roos, P.C.; Gerkema, T.; Hulscher, S.J.M.H. (2023). Shorter estuarine dunes and upstream migration due to intratidal variations in stratification. Est., Coast. and Shelf Sci. 281: 108216. https://dx.doi.org/10.1016/j.ecss.2023.108216van Maren, D.S.; Maushake, C.; Mol, J.-W.; van Keulen, D.; Jürges, J.; Vroom, J.; Schuttelaars, H.; Gerkema, T.; Schulz, K.; Badewien, T.H.; Gerriets, M.; Engels, A.; Wurpts, A.; Oberrecht, D.; Manning, A.J.; Bailey, T.; Ross, L.; Mohrholz, V.; Horemans, D. M.L.; Becker, M.; Post, D.; Schmidt, C.; Dankers, P.J.T. (2023). Synoptic observations of sediment transport and exchange mechanisms in the turbid Ems Estuary: the EDoM campaign. ESSD 15(1): 53-73. https://dx.doi.org/10.5194/essd-15-53-2023
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2022
Donatelli, C.; Duran-Matute, M.; Gräwe, U.; Gerkema, T. (2022). Statistical detection of spatio-temporal patterns in the salinity field within an inter-tidal basin. Est. Coast. 45: 2345-2361. https://dx.doi.org/10.1007/s12237-022-01089-3Donatelli, C.; Duran-Matute, M.; Gräwe, U.; Gerkema, T. (2022). Residual circulation and freshwater retention within an event-driven system of intertidal basins. J. Sea Res. 186: 102242. https://dx.doi.org/10.1016/j.seares.2022.102242Zhu, Z.; Slangen, A.; Zhu, Q.; Gerkema, T.; Bouma, T.J.; Yang, Z. (2022). The role of tides and winds in shaping seed dispersal in coastal wetlands. Limnol. Oceanogr. 67(3): 646-659. https://dx.doi.org/10.1002/lno.12024
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2021
de Smit, J.C.; Kleinhans, M.G.; Gerkema, T.; Bouma, T.J. (2021). Quantifying natural sediment erodibility using a mobile oscillatory flow channel. Est., Coast. and Shelf Sci. 262: 107574. https://dx.doi.org/10.1016/j.ecss.2021.107574Schulz, K.; Klingbeil, K.; Morys, C.; Gerkema, T. (2021). The fate of mud nourishment in response to short-term wind forcing. Est. Coast. 44: 88-102. https://doi.org/10.1007/s12237-020-00767-4van der Kaaden, A.-S.; Mohn, C.; Gerkema, T.; Maier, S.R.; de Froe, E.; van de Koppel, J.; Rietkerk, M.; Soetaert, K.; van Oevelen, D. (2021). Feedbacks between hydrodynamics and cold-water coral mound development. Deep-Sea Res., Part 1, Oceanogr. Res. Pap. 178: 103641. https://dx.doi.org/10.1016/j.dsr.2021.103641van der Sande, W.M.; Roos, P.C.; Gerkema, T.; Hulscher, S.J.M.H. (2021). Gravitational circulation as driver of upstream migration of estuarine sand dunes. Geophys. Res. Lett. 48(14): e2021GL093337. https://dx.doi.org/10.1029/2021gl093337Zhu, Q.; Zhu, Z.; Nauta, R.; Timmermans, K.R.; Jiang, L.; Cai, Y.; Yang, Z.; Gerkema, T. (2021). Impact of off-bottom seaweed cultivation on turbulent variation in the hydrodynamic environment: A flume experiment study with mimic and natural Saccharina latissima thalli. Sci. Total Environ. 797: 149048. https://dx.doi.org/10.1016/j.scitotenv.2021.149048
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2020
de Smit, J.; Kleinhans, M.G.; Gerkema, T.; Timmermans, K.R.; Bouma, T.J. (2020). Introducing the TiDyWAVE field flume: A method to quantify natural ecosystem resilience against future storm waves. Limnol. Oceanogr., Methods 18(10): 585-598. https://dx.doi.org/10.1002/lom3.10386Hermans, T.H.J.; Le Bars; Katsman, C.A.; Camargo; Gerkema, T.; Calafat, F.M.; Tinker, J.; Slangen, A.B.A. (2020). Drivers of interannual sea‐level variability on the Northwestern European Shelf. JGR: Oceans 125(10): e2020JC016325. https://dx.doi.org/10.1029/2020jc016325Jiang, L,; Gerkema, T.; Kromkamp, J.; van der Wal, D.; Carrasco de la Cruz, P.M.; Soetaert, K. (2020). Drivers of the spatial phytoplankton gradient in estuarine–coastal systems: generic implications of a case study in a Dutch tidal bay. Biogeosciences 17(16): 4135-4152. https://dx.doi.org/10.5194/bg-17-4135-2020Jiang, L.; Gerkema, T.; Idier, D.; Slangen, A.; Soetaert, K. (2020). Effects of sea-level rise on tides and sediment dynamics in a Dutch tidal bay. Ocean Sci. 16: 307-321. https://doi.org/10.5194/os-16-307-2020Philippart, K.; Blauw, A.; Bolhuis, H.; Brandenburg, K.; Brussaard, C.; Gerkema, T.; Herman, P.; Hommersom, A.; Jacobs, P.; Laanen, M.; van Leeuwe, M.A.; van den Oever, A.; Peters, S.; Philippart, M.; Pitarch, J.; Prins, T.; Ruddick, K.; Spaias, L.; van de Waal, D.; Van der Zande, D.; Zuur, A. (2020). Quick scan zeeschuim. NIOZ/Bureau Waardenburg/Deltares/Highland Statistics/CNR/KBIN/NIOO-KNAW/Rijkswaterstaat (RWS-WVL)/Technische Universiteit Delft/Universiteit van Amsterdam/Universiteit Utrecht/Rijksuniversiteit Groningen/Water Insight BV: Texel. 51 pp.Rovira-Navarro, M.; Gerkema, T.; Maas, L.R.M.; van der Wal, W.; van Ostayen, R.; Vermeersen, B. (2020). Tides in subsurface oceans with meridional varying thickness. Icarus 343: 113711. https://dx.doi.org/10.1016/j.icarus.2020.113711Schulz, K.; Burchard, H.; Mohrholz, V.; Holtermann, P.; Schuttelaars, H.M.; Becker, M.; Maushake, C.; Gerkema, T. (2020). Intratidal and spatial variability over a slope in the Ems estuary: Robust along-channel SPM transport versus episodic events. Est., Coast. and Shelf Sci. 243: 106902. https://dx.doi.org/10.1016/j.ecss.2020.106902
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2019
Baptist, M.J.; Gerkema, T.; Van Prooijen, B.C.; Van Maren, D.S.; van Regteren, M.; Schulz, K.; Colosimo, I.; Vroom, J.; van Kessel, T.; Grasmeijer, B.; Willemsen, P.; Elschot, K.; De Groot, A.V.; Cleveringa, J.; van Eekelen, E.M.M.; Schuurman, F.; De Lange, H.J.; van Puijenbroek, M.E.B. (2019). Beneficial use of dredged sediment to enhance salt marsh development by applying a ‘Mud Motor’. Ecol. Eng. 127: 312-323. https://doi.org/10.1016/j.ecoleng.2018.11.019Gerkema, T. (2019). An introduction to tides. Cambridge University Press.: Cambridge. ISBN 9781316998793. 213 pp.Jiang, L.; Gerkema, T.; Wijsman, J.W.M.; Soetaert, K. (2019). Comparing physical and biological impacts on seston renewal in a tidal bay with extensive shellfish culture. J. Mar. Syst. 194: 102-110. https://doi.org/10.1016/j.jmarsys.2019.03.003Jiang, L.; Soetaert, K.; Gerkema, T. (2019). Decomposing the intra-annual variability of flushing characteristics in a tidal bay along the North Sea. J. Sea Res. 115: 101821. https://dx.doi.org/10.1016/j.seares.2019.101821Rovira-Navarro, M.; Rieutord, M.; Gerkema, T.; Maas, L.R.M.; van der Wal, W.; Vermeersen, B. (2019). Do tidally-generated inertial waves heat the subsurface oceans of Europa and Enceladus? Icarus 321: 126-140. https://dx.doi.org/10.1016/j.icarus.2018.11.010
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2018
Frederikse, T.; Gerkema, T. (2018). Multi-decadal variability in seasonal mean sea level along the North Sea coast. Ocean Sci. 14(6): 1491-1501. https://dx.doi.org/10.5194/os-14-1491-2018Schulz, K.; Gerkema, T. (2018). An inversion of the estuarine circulation by sluice water discharge and its impact on suspended sediment transport. Est., Coast. and Shelf Sci. 200: 31-40. https://doi.org/10.1016/j.ecss.2017.09.031Vermeersen, B.L.A.; Slangen, A.B.A.; Gerkema, T.; Baart, F.; Cohen, K.M.; Dangendorf, S.; Duran-Matute, M.; Frederikse, T.; Grinsted, A.; Hijma, M.P.; Jevrejeva, S.; Kiden, P.; Kleinherenbrink, M.; Meijles, E.W.; Palmer, M.D.; Rietbroek, R.; Riva, R.E.M.; Schulz, E.; Slobbe, D.C.; Simpson, M.J.R.; Sterlini, P.; Stocchi, P.; van de Wal, R.S.W.; Van der Wegen, M. (2018). Sea-level change in the Dutch Wadden Sea. Geol. Mijnb. 97(3): 79-127. https://doi.org/10.1017/njg.2018.7
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2017
Gerkema, T.; Duran-Matute, M. (2017). Interannual variability of mean sea level and its sensitivity to wind climate in an inter-tidal basin. Earth System Dynamics 8(4): 1223-1235. https://dx.doi.org/10.5194/esd-8-1223-2017Gerkema, T.; Philippart, C.J.M.; van der Veer, H.W. (2017). North Sea coastal ecology: Preface. J. Sea Res. 127: 1. https://doi.org/10.1016/j.seares.2017.06.016Hufnagl, M.; Payne, M.; Lacroix, G.; Bolle, L.J.; Daewel, U.; Dickey-Collas, M.; Gerkema, T.; Huret, M.; Janssen, F.; Kreus, M.; Pätsch, J.; Pohlmann, T.; Ruardij, P.; Schrum, C.; Skogen, M.D.; Tiessen, M.C.H.; Petitgas, P.; van Beek, J.K.L.; van der Veer, H.W.; Callies, U. (2017). Variation that can be expected when using particle tracking models in connectivity studies. J. Sea Res. 127: 133-149. https://dx.doi.org/10.1016/j.seares.2017.04.009Nauw, J.; Philippart, C.J.M.; Duran-Matute, M.; Gerkema, T. (2017). Estimates of exposure times in the Wadden Sea : A comparison of methods. J. Sea Res. 127: 12-25. https://dx.doi.org/10.1016/j.seares.2017.03.015Philippart, C.J.M.; Gerkema, T.; van der Veer, H.W. (2017). North Sea coastal ecology : Future challenges. J. Sea Res. 127: 227-230. https://dx.doi.org/10.1016/j.seares.2017.07.004Tiessen, M.C.H.; Eleveld, M.A.; Nauw, J.J.; Nechad, B.; Gerkema, T. (2017). Depth dependence and intra-tidal variability of Suspended Particulate Matter transport in the East Anglian plume. J. Sea Res. 127: 2-11. https://dx.doi.org/10.1016/j.seares.2017.03.008van der Hout, C.M.; Witbaard, R.; Bergman, M.J.N.; Duineveld, G.C.A.; Rozemeijer, M.J.C.; Gerkema, T. (2017). The dynamics of suspended particulate matter (SPM) and chlorophyll- a from intratidal to annual time scales in a coastal turbidity maximum. J. Sea Res. 127: 105-118. https://dx.doi.org/10.1016/j.seares.2017.04.011
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2016
Aguiar-González, B.; Gerkema, T. (2016). Limiting amplitudes of fully nonlinear interfacial tides and solitons. Nonlinear Process Geophys. 23: 285–305. dx.doi.org/10.5194/npg-23-285-2016Bordois, L.; Auclair, F.; Paci, A.; Dossmann, Y.; Gerkema, T.; Nguyen, C. (2016). Tidal energy redistribution among vertical modes in a fluid with a mid-depth pycnocline. Phys. Fluids 28(10): 101701. dx.doi.org/10.1063/1.4964759Duran-Matute, M.; Gerkema, T.; Sassi, M. (2016). Quantifying the residual volume transport through a multiple-inlet system in response to wind forcing: The case of the western Dutch Wadden Sea. JGR: Oceans 121(12): 8888-8903. https://dx.doi.org/10.1002/2016JC011807Gerkema, T. (2016). An Introduction to Tides. NIOZ: Yerseke. 88 pp.Gerkema, T.; Duran-Matute, M. (2016). Grilligheid én regelmaat in de getijperiode. Ned. Tijdschr. Natuurkd. 82(7): 265-267Gräwe, U.; Flöser, G.; Gerkema, T.; Duran-Matute, M.; Badewien, T.H.; Schulz, E.; Burchard, H. (2016). A numerical model for the entire Wadden Sea: Skill assessment and analysis of hydrodynamics. JGR: Oceans 121: 5231-5251. https://dx.doi.org/10.1002/2016JC011655Sassi, M.G.; Gerkema, T.; Duran-Matute, M.; Nauw, J.J. (2016). Residual water transport in the Marsdiep tidal inlet inferred from observations and a numerical model. J. Mar. Res. 74(1): 21–42. dx.doi.org/10.1357/002224016818377586
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2015
Duran Matute, M.; Gerkema, T. (2015). Calculating residual flows through a multiple-inlet system: the conundrum of the tidal period. Ocean Dynamics 65: :1461–1475. dx.doi.org/10.1007/s10236-015-0875-1Sassi, M.G.; Duran-Matute, M.; van Kessel, T.; Gerkema, T. (2015). Variability of residual fluxes of suspended sediment in a multiple tidal-inlet system: the Dutch Wadden Sea. Ocean Dynamics 65: 1321–1333. dx.doi.org/10.1007/s10236-015-0866-2van der Hout, C.M.; Gerkema, T.; Nauw, J.J.; Ridderinkhof, H. (2015). Observations of a narrow zone of high suspended particulate matter (SPM) concentrations along the Dutch coast. Cont. Shelf Res. 95: 27-38. dx.doi.org/10.1016/j.csr.2015.01.002
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2014
Duran-Matute, M.; Gerkema, T.; de Boer, G.J.; Nauw, J.; Grawe, U. (2014). Residual circulation and freshwater transport in the Dutch Wadden Sea: a numerical modelling study. Ocean Sci. 10: 611– 632. dx.doi.org/10.5194/os-10-611-2014Gerkema, T.; Nauw, J.J.; van der Hout, C.M. (2014). Measurements on the transport of suspended particulate matter in the Vlie Inlet. Geol. Mijnb. 93(3): 95-105. dx.doi.org/10.1017/njg.2014.7Tiessen, M.C.H.; Fernand, L.; Gerkema, T.; van der Molen, J.; Ruardij, P.; van der Veer, H.W. (2014). Numerical modelling of physical processes governing larval transport in the southern North Sea. Ocean Sci. 10: 357-376. dx.doi.org/10.5194/os-10-357-2014
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2013
Gerkema, T. (2013). The distribution of bathymetric slopes in the ocean in relation to critical reflection of internal waves. Fundamentalnaja i Prikladnaja Gidrofizika = Fundamental and Applied Hydrophysics 6(3): 14-18Gerkema, T.; Maas, L. (2013). Wiskundige aspecten van interne golven. Nieuw Arch. Wisk. 5/14(3): 172-176Gerkema, T.; Maas, L.R.M.; van Haren, H. (2013). A Note on the Role of Mean Flows in Doppler-Shifted Frequencies. J. Phys. Oceanogr. 43(2): 432-441. dx.doi.org/10.1175/JPO-D-12-090.1Magalhaes, J.M.; da Silva, J.C.B.; Batista, M.; Gostiaux, L.; Gerkema, T.; New, A.L.; Jeans, D.R.G. (2013). On the detectability of internal waves by an imaging lidar. Geophys. Res. Lett. 40(13): 3429–3434. hdl.handle.net/10.1002/grl.50669
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2012
da Silva, J.C.B.; Magalhães, J.M.; Gerkema, T.; Maas, L.R.M. (2012). Internal solitary waves in the Red Sea: An unfolding mystery. Oceanography 25(2): 96-107. dx.doi.org/10.5670/oceanog.2012.45Gerkema, T.; Gostiaux, L. (2012). A brief history of the Coriolis force. Europhys. News 43(2): 14-17. hdl.handle.net/10.1051/epn/2012202Gerkema, T.; van Haren, H. (2012). Absence of internal tidal beams due to non-uniform stratification. J. Sea Res. 74: 2-7. hdl.handle.net/10.1016/j.seares.2012.03.008King, B.; Stone, M.; Zhang, H.P.; Gerkema, T.; Marder, M.; Scott, R.B.; Swinney, H.L. (2012). Buoyancy frequency profiles and internal semidiurnal tide turning depths in the oceans. J. Geophys. Res. 117. dx.doi.org/10.1029/2011JC007681Mercier, M.J.; Mathur, M.; Gostiaux, L.; Gerkema, T.; Magalhães, J.M.; da Silva, J.C.B.; Dauxois, T. (2012). Soliton generation by internal tidal beams impinging on a pycnocline: laboratory experiments. J. Fluid Mech. 704: 37-60. dx.doi.org/10.1017/jfm.2012.191Tiessen, M.; Nauw, J.J.; Ruardij, P.; Gerkema, T. (2012). Numerical modeling of physical processes in the North Sea and Wadden Sea with GETM/GOTM, in: Kranenburg, W.M. et al. Jubilee Conference Proceedings NCK-days 2012 : crossing borders in coastal research. pp. 197-200. http://dx.doi.org/10.3990/2.197van der Hout, C.M.; Gerkema, T.; Nauw, J.J.; Ridderinkhof, H. (2012). Observations of suspended matter along the Dutch coast, in: Kranenburg, W.M. et al. Jubilee Conference Proceedings NCK-days 2012 : crossing borders in coastal research. pp. 213-217. dx.doi.org/10.3990/2.200
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2011
Gerkema, T. (2011). Comment on “Internal-tide energy over topography” by S. M. Kelly et al. J. Geophys. Res. 116(C07029): 1-3. hdl.handle.net/10.1029/2010JC006611Grisouard, N.; Staquet, C.; Gerkema, T. (2011). Generation of internal solitary waves in a pycnocline by an internal wave beam: a numerical study. J. Fluid Mech. 676: 491-513. dx.doi.org/10.1017/jfm.2011.61Winters, K.B.; Bouruet-Aubertot, P.; Gerkema, T. (2011). Critical reflection and abyssal trapping of near-inertial waves on a ß-plane. J. Fluid Mech. 684: 111-136. dx.doi.org/10.1017/jfm.2011.280
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