Tides are the periodic rise and fall of large bodies of water (oceans, seas, and some large lakes) on Earth. In Turkish, they are referred to as med (rise in water level) and cezir (fall in water level). Tides are primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun on Earth.

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Physical Mechanism

The Moon's Gravitational Effect

The Moon is the closest celestial body to Earth, and due to this proximity, it exerts a significant gravitational pull on the waters of Earth. The Moon's gravitational force pulls water masses toward itself on the side of Earth closest to it, causing the sea level to rise; this rise is called “high tide.” However, this phenomenon is not limited to the side facing the Moon. The Earth rotates around a common center of mass (barycenter) with the Moon. The centrifugal force resulting from this rotational movement causes a second bulge on the surface opposite the Moon. Thus, two different regions on Earth experience high tide at the same time: one facing the Moon and the other on the opposite side. In the areas in between, the water recedes, causing low tide.

The Sun's Contribution

Although the Sun is much larger in mass than the Moon, its gravitational effect on Earth is weaker than that of the Moon because it is much farther away. Nevertheless, its effect cannot be completely ignored. Approximately 30% to 40% of tidal events are caused by the Sun's gravitational pull. During the new moon and full moon phases, when the Moon and Sun are aligned, their gravitational forces combine to create a stronger effect, known as a “spring tide.” During the first and last quarters, when the Moon and Sun are at right angles, the gravitational forces partially balance each other, creating a weaker tidal difference, known as a “neap tide.”

Earth's Rotation and the Response of Water Masses

The Earth's rotation around its own axis plays a decisive role in the timing of the tidal phenomenon. While the Earth completes a full rotation every 24 hours, the Moon returns to the same position in approximately 24 hours and 50 minutes. Therefore, the same type of tide occurs approximately 50 minutes later each day. As the Earth rotates, water masses attempt to remain stationary, causing tidal bulges to shift and circulate across the Earth's surface. This rotational movement demonstrates that tides are not merely a gravitational phenomenon but also a dynamic process tied to rotation.

The Flexibility of the Hydrosphere and Geographical Factors

The effect of tides is accentuated by the fact that water masses on the Earth's surface are not rigid but fluid and flexible. The hydrosphere, i.e., the water mass in oceans and seas, responds to the influence of celestial bodies while being affected by landforms, continental margins, and seabed topography. Factors such as the shape of the bay, the width of the continental shelf, and the depth of the ocean directly affect the intensity and timing of the tide. For example, in Fundy Bay in Canada, the narrowing and shallowing of the coastal geometry can cause the tide level to reach up to 16 meters. In contrast, in semi-enclosed seas like the Black Sea, where connection to the open ocean is limited, the tidal range remains between 30–50 cm.

Types of Tides

The types and timing of tides vary depending on the Moon's movement around the Earth and the position of the Sun. This variation causes different types of tides to form, depending on how the gravitational forces combine or oppose each other. When the Moon and Sun are aligned in the same direction (this occurs during the new moon or full moon phases), the gravitational forces combine to create a stronger overall effect. During this time, the rise in sea level reaches its highest point, while the fall reaches its deepest point. In this type of tide, the difference between high and low tide reaches its maximum. The sea water advances further toward the shore and then recedes with a much larger volume. This phenomenon is commonly referred to as a “high tide” or “rising waters” and is scientifically termed a “spring tide.” The term “spring” here does not refer to the season but rather to “jumping” or “rising.”

Conversely, when the Moon is in its first or last quarter phases, meaning when the Moon and Sun are approximately 90 degrees apart in the sky, the gravitational forces partially balance each other out. This state of equilibrium results in less intense changes in the sea surface. While the rise (high tide) occurs more moderately, the fall (low tide) also remains limited. Such tides are less pronounced and indicate the times when the difference between high and low tides is minimal. In scientific literature, this type of tide is defined as a “weak tide” or “neap tide.” During weak tides, especially in inland seas and bays, the tide is almost imperceptible.

in 24 hours, the Moon's rotation around the Earth takes 24 hours and 50 minutes. Due to this difference, the tidal events that occur each day are delayed by approximately 50 minutes compared to the previous day. In other words, every day the sea water rises and falls a little later than the previous day. Based on this astronomical pattern, there are generally two high tides (high tide) and two low tides (low tide) every 24 hours. However, this cycle shows constant small deviations throughout the year depending on the position and phase of the Moon. Especially during spring and autumn, when the Moon is closest to Earth, tidal events can be more intense.

Geographical Effects and Differences

The intensity and effect of tidal events vary greatly depending on geographical location on Earth. The tidal effect is extremely pronounced on open ocean coasts, where sea levels change visibly with daily cycles. One of the most striking examples of this is Canada's Bay of Fundy. In this bay, the difference in sea level between high and low tide can reach up to 16 meters due to the influence of the terrain. Such high tidal range directly affects both the coastal morphology and the composition of the ecosystem in the region.

In contrast, the tidal effect is quite limited in closed or semi-closed seas. In countries like Türkiye, which are surrounded by seas on three sides, most of these seas are semi-closed in nature, and tidal range remains at very low levels. For example, in inland seas such as the Black Sea, Mediterranean Sea, and Aegean Sea, the tidal difference typically ranges between 30 and 50 centimeters. While this difference is an important factor to consider in terms of coastal structures and maritime activities, it has much lower effects compared to examples in open oceans. Therefore, the ecological and economic impacts of tidal phenomena in such inland seas are more limited, and their effects may be difficult to notice in daily life.

Some narrow straits and passages, however, become areas where the effects of tides are intensified as a result of their geographical structure. In such regions, the rapid changes in direction and level of tides can lead to the formation of strong and directional currents. These currents can gain significant speed, especially in areas where the seabed has a steep slope. These tidal currents present both opportunities and risks for maritime transportation, as ship passages can be affected by these rapid water movements. Additionally, these regions are being evaluated for tidal energy production, with some countries utilizing turbine systems installed in narrow passages to generate electricity from the kinetic energy of the tides.