1 / 32

Intertidal Zones, Tides and the Coastline

Intertidal Zones, Tides and the Coastline. Overview:. Coastline Tidal Cycle Intertidal Zones Sand Flow Coastal Strand Community. California Coastline. 1100 miles long. With varying inland climates from warm by San Diego to Cool in Humboldt.

zorion
Download Presentation

Intertidal Zones, Tides and the Coastline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Intertidal Zones, Tides and the Coastline

  2. Overview: • Coastline • Tidal Cycle • Intertidal Zones • Sand Flow • Coastal Strand Community

  3. California Coastline • 1100 miles long. • With varying inland climates from warm by San Diego to Cool in Humboldt. • Coast rarely freezes, or exceeds 100 °F. Temperature moderate year-round. • San Francisco January 51 °F average, and in September 62 °F. • Water is cold around 50 °F. Down South warms to about 60 °F. • Summer fog, fog drip. • Nutrient rich Upwelling off shore

  4. Coastline Geology • Coastal rocks are uplifted from sea floor. (Emergent Coastline) • North Coast Franciscan sedimentary Rocks about 100-150 MYA. • South 60 MYA sedimentary rocks. • Easily eroded, soft rocks. Cuts deep surf-cut shelves or benches. • With uplifting these shelves become terraces, but also erode away. • River mouths cut through valleys, form wide lagoons with a sand bars. • Form shoreline lakes dammed by sand

  5. Tidal Cycle • Approximately Every “day” (24 hrs. 48 mins.) has two high tides and two low tides. • One high tide is higher than the other: Hi-Hi • One low tide is lower: Lo-Lo • Daily Tidal cycle: • Hi-Hi; Lo-Lo; Hi-Lo; Lo-Hi repeat……. • tides change every 6 hrs. 12 mins. • full cycle in 24 hrs. 48 mins. (one Lunar orbit) • offset by about an hour per day

  6. Sea level • Means slightly different things depending on how precise you need to know. • Mean Sea level- the average between hi’s and lo’s of tides over 19 years, measured in the water compared to land based points of reference • Surface of open ocean (used to calculate altitude for aviation) satellite • Also used is Mean Lower Low Water (MLLW) average lo-lo tide

  7. Tidal Sequence Higher-High tide Lower-High Sea level Higher- Low tide Lower-Low tide

  8. Tides • Influence of gravitational pull from Sun and Moon. Moon’s pull is stronger because it is closer. • Centrifugal force also important. • Spring tides (Upwelling) every two weeks or so • Sun’s pull adds to moon’s pull • Neap tides (Scarce) every two weeks or so. • Moon’s pull partially counteracts sun’s pull. • Sun’s influence changes with season, • closer in June and December stronger tides. • Moon’s distance varies by 15,000 miles over a month • Perigee (2x month) is when moon is closest makes stronger tides • perigee with a spring tide increases by 40% • At Apogee (2x month) moon is farthest and weakens tides • Most extreme spring tides are at perigee in June and December !!

  9. Spring tide • Spring and Neap Tides Neap tide

  10. Pull of moon and Centrifugal force

  11. Phases of the moon

  12. From Spring to Neap Tide:

  13. A typical Month in the spring

  14. This April 2007

  15. April – May 2008

  16. Why we have to be there early

  17. Friday April 20th • Low tide is at 8:13 a.m. • Meet at Schoolhouse beach, 7:45 a.m., need to leave DVC at 6:00 a.m. • At Beach till 8:45 • Dunes from 9:00- 10:00 • Home by noon !!!

  18. Intertidal Zones(from highest above to lowest in water) • Splash / Spray Zone wetted by surf • crustose lichens, sea lice • High Tide Zone - covered at high tide exposed most of the day • Limpets, sea lettuce, acorn barnacles, rockweed • Middle Tide Zone -exposed only for short periods • barnacles, mussels, sea stars, chitons, urchins • Low Tide Zone -exposed only at lowest tides • Top of lower intertidal is sea level for that area. • sea palm, surf grass • Sub-tidal Zone - never exposed • Highly productive

  19. Fig 12.7

  20. Vertical Zonation • Total number of hours exposed to air increase towards top of rock • Predation changes • Heat • Desiccation • Wave action

  21. Intertidal Succession • Sever competition for space • Rocks over-turned over in storms, leave bare areas. • Filamentous and foliose green algae colonize bare rock • Crustose and Coralline algae take over • Acorn barnacles colonize by prying off algae as they take over • Gooseneck barnacles and mussels take over, growing over an preying off acorn barnacles. • Gooseneck barnacles and mussels remain as climax, unless predator invades or rock is over turned. • One-year sequence.

  22. Keystone species • Pisaster (Sea Star) defends tide pool from being taken over by mussels, barnacles.

  23. Sea Otters maintain Kelp forest • Otters are a Keystone species • Kelp are the base of the kelp forest community • Urchins eat kelp at their base • Otters eat urchins, keeping their numbers low. • Otter numbers along California are dropping. • Alaska- Orcas starting to eat otters, because seal numbers are dropping • No fish for seals

  24. Competition for space on the rocks Weak competitors stuck higher up in the intertidal

  25. Sand flow • Sand from weathered rocks up in mountains. • banks of Merced River in Yosemite • Moves out to sea - westward • Waves come form the NW moving sand southward and back towards shore. • Zig- Zag flow with seasonal cycles - beach erosion with storms. • In winter • beach (more narrow) smaller, • more sand moved farther off shore • In summer • Wide beaches • Sand pushed back on to shore, now farther south.

  26. Erosion & Beach decline • River of sand slows: damming up stream, beaches disappear • Bodega head pushes out into sea, traps southward sand flow forming dunes • Sea walls impede southward flow of sand from north. • Headlands erode in surf, waves wrap around and hit sides • Resistant rocks remain longer forming stacks and arches.

  27. Coastal Strand Communities • Dunes • Three zones: • Fore dune – the beach area • Crest – highest point on dunes • Back dune- protected areas behind front dunes

  28. Dune Plant adaptations • prostrate growth- rhizomes • gray hairs on leaves deflect light, air • nitrogen-fixing bacteria • thick waxy cuticle • deep roots • mycorrhizae

  29. Fore dune • shifting sands • heavy winds and sand-blasting • Lots of sun-light, uv radiation • drains quickly, dry substrate • Not salty! Rain, fog wash out salt spray residue (doesn’t bind to sand)

  30. Crest and Back dune • Crest • Strongest wind • European beach grass • Back dune- • sheltered by crest • warmer • calm, less breeze • beginnings of soil (organic debris) • mature trees, shrubs

More Related