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    20100418_Herman_Ridderinkhof_Getijden 20100418_Herman_Ridderinkhof_Getijden Presentation Transcript

    • Tides and shallow water sea research at NIOZ Royal Netherlands Institute for Sea Research but first: crossing the Agulhas current NIOZ is part of the Netherlands Organisation for Scientific Research (NWO) Herman Ridderinkhof
    • Crossing the Agulhas current Sea surface temperature
    • Chlorophyll Crossing the Agulhas current
    • Temperature from CTD behind the clipper Crossing the Agulhas current 18 april 19 april till 09.00
    • Crossing the Agulhas current
    • Tides Herman Ridderinkhof NIOZ and Utrecht University
      • What are the causes of tides and what are their characteristics?
      • How do tides propagate in oceans (e.g. Atlantic), shelf seas (e.g. North Sea), shallow tidal basins (e.g. Wadden Sea)?
    • General pattern of the vertical tide at one station Daily inequality delay: moon phases - tidal phenomena Neap tide Spring tide Two highs and lows per day
    • Examples: “ Lunar” frequencies - lunar day - 2 x lunar day (dominant) - overtones - eccentricity lunar orbit - tilt lunar orbit - etc... “ Solar” frequencies - similar to moon freq. And all kinds of crossterms A tidal signal can be decomposed in a number of frequencies related to astronomical frequencies
    • Astronomical forces
      • Tides are caused by the gravitational force of the moon and sun and the motion of the earth-moon-sun system
      • The gravitational force causes a deformation of the ocean surface (equilibrium tide)
      • Frequencies of planetary motions result in different ‘astronomical frequencies’
    • Tidal frequencies: lunar day
      • A lunar day is the time that elapses between when the moon is directly overhead and the next time the moon is directly overhead.
      • During one complete rotation of Earth (the 24-hour solar day) the moon moves eastward 12.2 degrees, and Earth must rotate an additional 50 minutes to place the moon in the exact same position overhead.
      • Thus, a lunar day is 24 hours 50 minutes long (and a solar day 24 hours).
    • Tidal frequencies: spring-neap variability
    • There are lots of other “astronomical frequencies” : example: relative tilts of plane of the Moon’s orbit and equator plane. These variations are a.o. recognizable in geology.
    • Amplitudes of tidal component can differ enormously at different locations © 2002 Brooks/Cole, a division of Thomson Learning, Inc. Tide curves for three common types of tides.
    • Tide Patterns The worldwide distribution of the three tidal patterns.
      • Tide driven by astronomical forces is present only in the Southern Ocean.
      • Amplitude of tide due to astronomical force, the equilibrium tide, is 0.27 m due to the moon and 0.12 m due to the sun
      • Tides at any location outside the Southern Ocean are caused by propagation of the tidal wave from the Southern Ocean
      • How do tides propagate in oceans and shelf seas?
      William Thomson (Lord Kelvin) Sea level displacement for a Kelvin wave
    • Kelvin wave in a square tank: The Coriolis force lets the wave run along the wall on the right side (northern hemisphere)
    • Amplitudes and phase lines from a world ocean tidal model
    • The Kelvin waves in the Atlantic Ocean start in the south For the tidal wave it takes about 2-2.5 days to move from the Southern Ocean to the North Sea (spring tide is 2-2.5 after full moon)
    • Kelvin waves in the North Sea split up in three separate Kelvin waves The “Knots” are called Amphidromic points. Here is no vertical tide
    • Tides in Confined Basins: no Kelvin wave but possibility of amplification due to resonance Resonance occurs if reflected wave from landward end amplifies the incoming wave (length basin = .5 * tidal wave length)
    • The largest tidal range in the world occurs in Nova Scotia's Bay of Fundy. Even though the maximum spring tidal range at the mouth of the bay is only 2 meters, amplification of tidal energy causes a maximum tidal range at the northern end of Minas Basin of 17 meters.
    •  Bay of Fundy, High Tide Bay of Fundy, Low Tide 
    • Kelvin wave along Dutch coast
    • Near-resonance in Wadden Sea combined with strong bottom friction Tides in Wadden Sea have become stronger due to closure with Afsluitdijk!
      • Tide is excited by astronomical forces. ‘Ideal tide’ is present only in the Southern Ocean (no continents).
      • Frequencies of the tide are related to astronomical frequencies
      • Tides propagate through the world oceans as rotating (Kelvin) waves
      • Amplitude of the tide at a certain location strongly depends on the resonance characteristics of a sea basin
      Tides: important issues
    • Some NIOZ Wadden Sea studies based on our speciality: observations at sea
        • Ferry based observations and studies
        • Ecological studies based on (long term) field observations
      ‘ Navicula’ ‘ Stern’ (Tern) Flatboat ’t Horntje’
    • Continuous (sensor based) observations ferry jetty
    • Ferry observations since 1998
    • water Slib Netto fluxen water: naar Noordzee slib: naar Waddenzee (veel groter dan eerdere schattingen, nu als T0 meting ivm Maasvlakte-II aanleg)
    • Bottom depth of the Marsdiep inlet, and the changes over time showing migrating sandwaves
    • A Cross section of the bottom profile along section A Migrating sandwaves into the WaddenSea with a height of 2-3 m and a length of 100 m (dark is orinigal profile)
    • B Cross section of the bottom profile along section B Migrating sandwaves into the WaddenSea with a height of 7-8 m and a length of 300 m (dark is orinigal profile)
    • Temperature, Salinity since 1861 (van Aken) Now from NIOZ jetty
    • Into the field
    • Predicted intake rate of the knot (time-series since 1991)
    • Concurrent changes Wadden Sea communities Phosphate concentrations early spring Nutrient enrichment & reduction Phytoplankton NIOZ Macrozoobenthos NIOZ/RWS Estuarine birds SOVON Philippart et al. (under review) Ecosystems Observation : Correlation : Possible Cause : 1970 1977 1984 1991 1998 2005 -2 -1 0 1 2 3 Standardised units (-) Estuarine birds (PC2; following winter) Macrozoobenthos (PC1; following winter) Phytoplankton (PC2; summer)
    • Philippart & Peperzak (2006) Waddenbulletin < 1000 cells/ml > 1000 cells/ml Observation : Correlation : Possible Cause : Variations in seasonality Phaeocystis blooms Nutrients and/or climate change? Phaeocystis globosa December November October September August July June May April March February January 1975 1980 1985 1990 1995 2000 2005
    • Wadden Sea Observatory (2010 onward)
      • Sensorobservations from
      • Exisitng platforms
      • New poles
      • Field surveys (e.g. benthos)