Marine Science HW's

A tidal bore may occur under which condition?

A confining river mouth that forces the tide wave to move toward land at high speeds

What is amphidromic point?

An amphidromic point is a "no-tide" point for a specific tidal constituent in an ocean region, around which the tidal waves rotate. An amphidromic point and associated tidal waves define a tidal system. So-called "no tide" is referred to the zero tidal range b/c the tidal crests and troughs cancel each other out @ these points; in fact, tidal currents are these locations can be quite strong.

What water mass is the densest in the world ocean?

Antarctic Bottom Water

Based on the following illustration of M2 tidal system(color lines are the co-phase lines, and blue lines are co-amplitude lines) in the NorthAtlantic Ocean, how long does the high tide at New York lag behind Brest? What is theapproximate M2 tidal amplitude in New York? (note black bold arrows highlight the rotation direction of the tidal wave; they are not part of the contour)

Based on this illustration, NY on the co-phase line @ 12 hr while Brest is located @ 4 hr co-phase line. There the time NY reaching high tide is about 8 hrs later than in Brest, and the M2 amplitude is about 1 m.

What major phenomenon happened in the equatorial Pacific during El Nino?

During La Nina term-25(NORMAL) phase, surface winds across most of the tropical Pacific move from east to west. The trade winds blow from high-pressure area over the eastern Pacific to the stable low-pressure area over the western Pacific. The trade wings drag huge quantities of water westward (westward equatorial currents) along the ocean's surface on each side of the equator.

Briefly explain why there are Spring and Neap tides?

During Spring tides, one observes highest high tide and lowest low tide for the month. The reason for this is the gravitational forces due to moon and sun are combined to maximum extent (Maximum moon effect is located @ same place as Maximum sun effect) during these situations. During Neap tides, one observes lowest high tide and highest low tides for the month. The reason for that is the gravitational forces due to sun and moon are largely out of place (The locations experiencing strongest moon effect are different from locations w/ strongest sun effect) during these situations.

How do Ekman Spiral and Ekman Transport work?

Ekman Spiral: The currents at layer immediately below the surface rotates clockwise further to the right but the current speed decreases @ the same time. This phenomenon occurs continuously to deeper layers, leading to a vertical spiraling profile of currents w/ clockwise rotating angle and decreasing current speed. At certain depths, the direction of currents is opposite to the surface winds. Altogether, this current profile is referred to as Ekman Spiral Ekman Transport: Specifically, this is the depth-integrated transport of wind-driven currents from surface to the bottom of the Ekman spiral. In the Northern Hemisphere, Ekman transport is 90° to the right of the wind direction due to Coriolis effects.

What are Ekman Spiral and Ekman Transport?

Ekman spiral is referred to the vertical spiraling profile of wind-driven surface currents. In northern hemisphere, wind-driven currents @ ocean surface (depth 0) are flowing 45° to the right of surface winds direction due to Coriolis effect. The Ekman transport is defined as total volume transport of waters by currents driven by surface winds.

What is El Nino?

El Nino refers to an abnormal oceanographic period in the equatorial Pacific.

The flow of water around the periphery of an ocean basin driven by winds and the Coriolis effect is called a(n)_____.

Gyre

What is relationship b/w heights of tides and the amphidromic point?

Heights increase w/ distance from the amphidromic point

What are high tides and low tides?

High tides refer to tidal state (time, water level, tidal currents, etc.) when the water level @ a particular location is @ its highest point during on tidal cycle. Low tides refer to the tidal state when the water level is @ its lowest point.

What phenomena are happening in the equatorial Pacific during El Nino? (cont.)

However- for reasons that are still unclear; these pressure areas change places @ irregular intervals of roughly 2-7 years; high pressure builds in western Pacific, and low pressure dominates in eastern Pacific. Winds across the tropical Pacific then reverse direction and blow from west to east-the trade winds weaken or reverse. This change is atmospheric pressure (and thus in wind direction) is called Southern Oscillation, but as the winds weaken or reverse, these equatorial currents crawl to a stop or become eastward. Warm water that has accumulated @ the western side of the Pacific can move to the east along the equator toward the coasts of Central and South America. This results in significant sea level rise (~100cm) in the eastern equatorial Pacific. The eastward-moving warm water usually arrives near the South American coast around Christmas time and the current was given the name El Nino. An El Nino event typically lasts about a year, but some have persisted for more than three years!

What is true of density, salinity, and temperature?

Many combinations of temperature and salinity can yield the same density.

What water mass is most saline in the world ocean?

Mediterranean Deep Water

When do tidal currents reach their maximum velocity?

Midway b/w high and low tide

Equitorial upwelling occurs worldwide! but where is it most pronounced?

Pacific Ocean

What type of tidal pattern exists on the coast of the United States, which experiences two high tides and two low tides of similar heights every day?

Semidiurnal (Semidiurnal mixed is OK answer)

High or low tidal currents that change direction result in ______.

Slack water

What are Spring and Neap tides?

Spring tides are strongest tides @ a particular location, may experience each month during the new or full moon when the moon, sun, and earth line up in a straight line. Neap tides are the weakest tides a particular location may experience during the first and third quarter of the month when moon, sun and earth form a right angle.

Briefly explain why there are high tides and low tides?

The occurrence of high tides and low tides are due to the earth rotation relative to moon's position. When a specific location on earth is directly under the moon, waters are subject to the strongest pull from the moon. Therefore, tidal elevation is @ it's higest point; i.e. high tides. When the same location rotates away, water level drops. When that location is @ 90° angle away from connection line b/w earth and moon's mass centers, waters being pulled away due to moon attraction, and the water level is @ it's lowest point, i.e. low tides. Sun's attraction can similarly produce high and low tides, the patterns can become quite complicated when both sun and moon's effects are considered.

Which currents are the slow, deep currents that affect seawater beneath the pycnocline?

Thermohaline

The trade winds and westerlies drive what geostrophic currents?

Transverse currents

What are Upwellings and Downwellings?

Upwelling refers to upward vertical movement of oceanic waters. Downwelling is the opposite (Downward vertical movement of oceanic waters).

The fastest & deepest geostrophic currents are______.

Western Boundary Currents (WBC)

Using U.S. west coast (e.g. California); as an example, briefly describe coastal upwelling processes.

Wind blowing parallel to shore can cause coastal upwelling or downwelling. For EX: if northerly winds blowing along the west coast (e.g. California) in the Northern Hemisphere, the friction of the wind blowing along the ocean surface causes water to begin moving. Coriolis effect deflects it to the right (toward Northern Hemisphere), and the resultant Ekman transport moves water offshore. Coastal upwelling occurs when this surface water is replaced by subsurface cold water rising to the surface along the shore, b/c new surface water is often rich in nutrients, prolonged wind can result in increased biological productivity.