Dynamic Planet/Oceanography

Oceanography was the topic of Dynamic Planet for the 2007 and 2008 seasons, and is once again the focus for the 2015 season.

Overview

During the 2015 season, this event will focus on physical and geological oceanography. Physical oceanography is primarily concerned with the ocean as a physical system in which principles like conservation of mass, energy, momentum and spin play a huge role in determining what you see. Geological oceanography looks at the rocks and sediments on the ocean bottom and margins and tries to infer how that got that way and what that tells us about the history of the earth.

The Competition

The competition consists of a test covering the geological and physical aspects of the ocean. Usually this test will be presented in stations, which competitors will rotate from after a certain period of time. To be successful, competitors should possess a mix of practical and theoretical skills. Practical skills should involve knowing how to read plots and graphs, particularly line plots, scatterplots, and contour plots. Theoretical skills should include an understanding of the Coriolis force, surface waves, and how the ocean interacts with the atmosphere. You should also study ocean geography.

In 2015, each team may bring 4 double-sided note sheets. In addition, each student can bring any type of calculator.

Plate Tectonics

Plate tectonics is a theory that describes the large-scale movement of the Earth's lithosphere. The lithosphere is divided into tectonic plates, and where they meet, they interact by either converging (known as a convergent plate boundary), diverging (known as a divergent plate boundary), or sliding next to each other in opposite directions (known as a transform plate boundary).

These interactions may be further defined by the composition of the two lithospheric plates at the boundary. Continental crust is composed primarily of granitic rocks while oceanic crust is comprised primarily of basaltic rocks. As a result, oceanic crust has a higher density than continental crust. Oceanic crust is generally 2.9 grams per cubic centimeter as opposed to continental crust, which is generally 2.7 grams per cubic centimeter. In addition, continental crust is thicker than oceanic crust.

Reef Formation

A volcanic island is formed by tectonic activity and the shores are warm where coral can grow.

Fringing Reef

The coral starts forming because their attracted to the heat from the hydrothermal vents. Soon more animals move in creating a coral reef. This reef fringes of the island hence the name "Fringing Reef".

Barrier Reef

The reef continues to grow, but the volcanic island starts to eroded away leaving a stub of island left. Yet it is warm enough for the coral to grow and the coral continues almost creating something along the lines of a barrier.

Atoll Reef

The island has disappeared completely only leaving traces of the once island. The coral still remains and where the island was is now a lagoon.

Oceanic Circulation

Thermohaline Circulation

The term thermohaline circulation refers to the part of the large-scale ocean circulation that is thought to be driven by global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives from "thermo-", referring to temperature, and "-haline", referring to salt content. These factors together determine the density of sea water. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is used to refer to the meridional overturning circulation (often abbreviated as MOC).

El Niño Southern Oscillation

El Niño is a very important oceanographic phenomenon. El Niño and La Niña are officially defined as sustained sea surface temperature anomalies of magnitude greater than 0.5°C across the central tropical Pacific Ocean. When the condition is met for a period of less than five months, it is classified as El Niño or La Niña conditions; if the anomaly persists for five months or longer, it is classified as an El Niño or La Niña episode. Historically, it has occurred at irregular intervals of 2-7 years and has usually lasted one or two years. Under normal conditions, there is the Walker circulation cell and rain and warm water is at the Southeast Asia side of the Pacific. There is upwelling near South America with cold water.

El Niño

El Niño occurs when the trade winds weaken and warm water from Southeast Asia go to West Pacific and there is no more upwelling and there is more rain. The Walker circulation cell has been broken and the trade winds reverse.

The first signs of an El Niño are:

1. Rise in air pressure over the Indian Ocean, Indonesia, and Australia 2. Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean 3. Trade winds in the south Pacific weaken or head east 4. Warm air rises near Peru, causing rain in the northern Peruvian deserts 5. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.

El Niño's warm current of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current, also known as the Peru Current, which support great populations of food fish. In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Niño conditions last for many months, more extensive ocean warming occurs and its economic impact to local fishing for an international market can be serious. During non-El Niño conditions, the Walker circulation is seen at the surface as easterly trade winds, which move water and air warmed by the sun towards the west. This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient-rich cold water to the surface, increasing fishing stocks. The western side of the equatorial Pacific is characterized by warm, wet low-pressure weather as the collected moisture is dumped in the form of typhoons and thunderstorms. The ocean is some 60 cm higher in the western Pacific as the result of this motion.

La Niña

In the Pacific, La Niña is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the same area. Atlantic tropical cyclone activity is generally enhanced during La Niña. The La Niña condition often follows the El Niño, especially when the latter is strong.

Table with La Niña and El Niño Effects

La Niña and El Niño Effects

El Niño	La Niña
Strong Equatorial Counter-Current	Strong Peruvian Current
Wetter than Average Winter over Florida	Higher Sea Level in the West Pacific
Pronounced Ridge in Polar Jet over Western North America	Stronger than Normal Subtropical Highs in Pacific
Drier than Average over Indonesia and Australia	Increased Snowfall in the North Western U.S.
Large-Scale Warming of Pacific	Oceanic Cooling of the Pacific

2016 Topics

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Meteorological Concepts

Atmospheric Circulation

Prevailing Winds

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Reference

Tips

• An important aspect of this event (and Dynamic Planet topics in general) is understanding how to read a map. Reading maps is discussed in great detail in Road Scholar and Meteorology.
• For more information, see the Oceanography notes page.

Links

A good starting resource

NOAA Education Resources for Science Olympiad