Ocean water levels constantly change. These predictable changes, known as tides, are a fundamental natural phenomenon that shapes coastlines and influences human interaction with marine environments. Understanding these patterns, from subtle shifts to dramatic extremes, clarifies how ocean waters behave.
The Term for the Lowest Tide
The lowest point the sea reaches daily is commonly known as “low tide” or “low water.” However, for scientific and nautical purposes, more precise terminology is used. For navigation and mapping, “Mean Lower Low Water” (MLLW) is a frequently used reference point. MLLW averages the lowest of the two daily low tides at a location over 19 years, accounting for astronomical cycles. This average provides a consistent baseline for depths on nautical charts and for predicting future tide heights, ensuring accuracy for mariners and coastal planners.
Understanding the Nature of Tides
Tides are long-period ocean waves causing the rhythmic rise and fall of sea levels along coastlines. This predictable cycle sees water levels increase to high tide and recede to low tide. Most coastal areas experience two high and two low tides within a 24-hour, 50-minute lunar day. This cyclical movement is a fundamental aspect of marine environments, influencing coastal geography and marine life.
What Causes Varying Tide Levels?
Ocean tides are primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Moon’s gravity creates water bulges on Earth’s surface, both closest to it and directly opposite. As Earth rotates, locations pass through these bulges, experiencing high tides, while areas between them have low tides.
Earth, Moon, and Sun alignment significantly influences tidal magnitude. When the Sun, Moon, and Earth align during new and full moon phases, their combined gravitational forces create “spring tides.” These result in the greatest tidal range, with exceptionally high high tides and particularly low low tides.
Conversely, during first and third quarter moon phases, the Sun and Moon are at right angles to Earth. Their gravitational pulls partially cancel, producing “neap tides” with a smaller difference between high and low water levels. Local factors like coastline shape, ocean floor topography, and water depth also modify these influences, creating unique tidal patterns in different geographical areas.
Why Lowest Tides Matter
Exceptionally low tides have practical implications for human activity and natural ecosystems. For navigation, these tides significantly impact shipping and boating, as channels can become too shallow, risking vessels running aground. Mariners use tide tables and charts, often referencing MLLW, to plan routes and avoid hazards.
In coastal ecosystems, lowest tides expose vast intertidal zones, creating temporary habitats like tide pools. This exposure allows marine life, such as shorebirds and other animals, to forage for food that is typically submerged.
For humans, these periods offer unique opportunities for recreational activities like beachcombing, clamming, or exploring usually submerged coastline areas. Scientists also study exposed marine environments and geological features during these events, gaining insights into biodiversity and coastal processes.