Oceans in Motion

The magical attraction of sun, moon, and sea

Oceans in Motion - Tides

Photo by Anna Strumillo

Our oceans are constantly on the move. The gravitational pull of the sun and the moon and rotation of the earth set in motion the circulation of the earth’s waters. Where and how these waters move is also driven by the interaction of wind, waves, tides, currents, and the contours of the shoreline and ocean floor.

This constant movement of water blends and balances salty ocean and fresh mainland waters. It mixes deep, cold waters with warmer surface ones. In the process, it circulates nutrients, larvae, and reproductive cells that nourish sea life and support lifecycles.

Moving oceans exchange heat and gases with the atmosphere, influencing climate and coastal ecosystems. Warming oceans threaten many species and alter weather patterns. Also, as ocean water absorbs carbon dioxide, it becomes more acidic, challenging the delicate chemical balance of the marine ecosystem.

Waves

Oceans in Motion

Photo by B. Monginoux

Wind is the most common cause of waves, dragging seawater along as it blows across the surface. The wind’s speed and its duration and distance over the water contribute to the size of the waves. In contrast, tsunami waves are caused by underwater seismic activity.

Tides

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Courtesy National Oceanic & Atmospheric Administration

Tidal patterns differ around the globe. A daily cycle of one high tide and one low tide is called a diurnal tide. Two high and two low tides daily - of constant heights - are called semi-diurnal tides. When these tide heights differ, as in Fidalgo Bay, the pattern is called mixed semi-diurnal tides.

Currents

Oceans in Motion - Currents

Courtesy NASA Goddard Space Flight Center - View the animation

Currents are continuous, horizontal ocean movements that circulate water and heat around the globe. Wind, water density, and tides set currents in motion. Coastal and sea floor topography influence their location, direction, and speed. Narrow channels between islands magnify local currents.

Upwelling

Oceans in Motion - Upwelling

Illustration courtesy National Oceanic & Atmospheric Administration

When northerly winds drive surface water offshore, cold deep water circulates to the surface, delivering vital nutrients to sea life concentrated in the upper layers. In the Northwest, these upwelling currents create one of the world’s richest ecosystems and most highly productive fisheries.

Top of page photo by Eric Veland

Information on this Trail Tales website was prepared under funding from the Washington State Department of Ecology’s Public Participation Grant Program. While the information was reviewed for grant consistency and accuracy of project references, this does not necessarily constitute endorsement by the Department.

Learn more about Ecology’s Anacortes Baywide Cleanup

Photo credits: Anacortes History Museum, Washington state Dept. of Ecology, Samish Indian Nation and others, as noted. Illustrations by Linda Feltner.

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icon-exclamationIt’s a fact!

The Bay of Fundy in Nova Scotia, Canada, has the world’s largest tidal range, with a peak of about 48 feet between high and low tides. Our largest local tidal range is around 12 feet. View live Guemes Channel tide chart.

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Tides are extended waves caused by the gravitational pull of the sun and the moon on earth’s oceans. This pull creates “bulges” (high tides) on the sides of the earth closest and farthest from the moon, with low tides in between. When the sun, moon, and earth are aligned during the new and full moons, the pull is strongest and the range between high and low tides is greatest.

How Raven Made the Tide

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Not all explanations of how tides work are based on astronomical phenomena. In fact, indigenous peoples of the Pacific Northwest have a legend that offers a very interesting competing theory.
 
Coast Salish traditions are rich with stories of Raven, an important cultural symbol and character in many important legends. Raven had two spirits, one the creator and the other the mischievous trickster. Raven could devise ways of dealing with the chaotic natural world, taming it for the benefit of mankind. These abilities are demonstrated in this fanciful legend, shared at this Birdnote website link, which tells the story of how Raven was responsible for setting the tides in motion.