Oceans in Motion
The magical attraction of sun, moon, and sea
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.
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.
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.
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.
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