1. Measuring Sea Level Change

2. Overview

3. What is Sea Level? Mean – Arithmetic average Mean sea level – The average sea level over a large region Mean high tide Mean sea level Mean low tide

4. Sea Level Variation Astronomical Tidal Forces Earth’s water closest to the moon is acted on more strongly by the moon’s gravity The solid Earth is pulled harder than the water on the side opposite the moon The Sun produces similar tidal forces and accounts for about 1/3 of ocean tides

5. Sea Level Variation Depth of Tampa Bay changes by 20 cm between winter and summer Primary cause is thermal expansion (water expands when it warms) Mangroves & coastal habitats must be able to handle the changing water line

6. Sea Level Variation During El Niño years, sea level along West Coast is higher than in La Niña years Higher seas caused by reduced trade winds, allows up to 8 inches of sea level rise El Niño and Multi-Year Changes Readings at Fort Point, San Francisco Depth Gauge

7. Measuring Sea Level Rise Traditional Stilling Well Pulley and Counterweight Float Mechanical device “draws” sea level on slowly rolling paper Small openings near bottom of well designed to “filter out” wave motion Sea bed Tide Gauge Benchmark Bedrock Tides and changes in sea level are measured relative to a permanent local benchmark

8. Measuring Sea Level Rise Modern Tide Gauge Station Satellite Antenna Acoustic Sensor Calibration Tube Instantaneous Water Level Pressure Gauge Data Collection Computers Tide Gauge Benchmark Computers enable in-depth analysis Data available instantly Individual waves measured

9. Measuring Sea Level Rise Modern Tide Gauge Station Housing keeps equipment dry Measures wind speed/direction Solar panels Satellite antenna sends data to Internet Computer to process and store data Acoustic sensor

10. Measuring Global Sea Level position data JASON-2 satellite GPS Range Altimeter Microwave radiometer measuring water vapor Deep ocean couldn’t be measured until about 25 years ago Satellites now measure elevation using altimetry Sea level determined by comparing measured height and GPS data

11. Causes of Sea Level Change Seepage into aquifers Circulation changes, Storm surges, Water expands as it warms

12. Summary Mean Sea Level Sea Level Variation Coastal Tide Gauge Stations Measuring Global Sea Level Causes of Sea Level Change