remiconnesson/oceanservice-noaa-facts huggingface dataset:
# What is the Sargasso Sea?

![Illustration of sargassum and associated marine life](/facts/sargassum-healthy-ecosystem-noaa.jpg "The Sargasso Sea, located entirely within the Atlantic Ocean, is the only sea without a land boundary.")

_Illustration of sargassum and associated marine life, including fish, sea turtles, birds, and marine mammals. Sargassum is a brown algae that forms a unique and highly productive floating ecosystem on the surface of the open ocean._

The Sargasso Sea is a vast patch of ocean named for a genus of free-floating seaweed called [_Sargassum_](#). While there are many different types of algae found floating in the ocean all around world, the Sargasso Sea is unique in that it harbors species of sargassum that are 'holopelagic' — this means that the algae not only freely floats around the ocean, but it [reproduces vegetatively](#) on the high seas. Other seaweeds reproduce and begin life on the floor of the ocean.

Sargassum provides a home to an amazing variety of marine species. Turtles use sargassum mats as nurseries where hatchlings have food and shelter. Sargassum also provides essential habitat for shrimp, crab, fish, and other marine species that have adapted specifically to this floating algae. The Sargasso Sea is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark, and dolphinfish. Humpback whales annually migrate through the Sargasso Sea. Commercial fish, such as tuna, and birds also migrate through the Sargasso Sea and depend on it for food.

While all other seas in the world are defined at least in part by land boundaries, the Sargasso Sea is defined only by ocean currents. It lies within the Northern Atlantic Subtropical [Gyre](#). The Gulf Stream establishes the Sargasso Sea's western boundary, while the Sea is further defined to the north by the North Atlantic Current, to the east by the Canary Current, and to the south by the North Atlantic Equatorial Current. Since this area is defined by boundary currents, its borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.
# What are PCBs?

## PCBs, or polychlorinated biphenyls, are industrial products or chemicals.

![Contaminants](/facts/pcb.jpg "Contaminants")

PCB contamination is high in the Housatonic River and New Bedford Harbor in Massachusetts. According to the [EPA](https://www.epa.gov/pcbs/learn-about-polychlorinated-biphenyls-pcbs), PCBs belong to a broad family of human-created organic chemicals known as chlorinated hydrocarbons. PCBs were manufactured domestically from 1929 until manufacturing was banned in 1979. They have a range of toxicity and vary in consistency from thin, light-colored liquids to yellow or black waxy solids. Image credit: U.S. Fish and Wildlife Service

PCB chemicals were banned in the U.S. in 1979 because these chemicals harm human and environmental health. From the 1920s until their ban, an estimated 1.5 billion pounds of PCBs were made for things such as microscope oils, electrical insulators, capacitors, and electric appliances such as television sets or refrigerators. PCBs were also sprayed on dirt roads to keep the dust down prior to knowing some of the unintended consequences from widespread use. 

Prior to the ban in 1979, PCBs entered the air, water, and soil during manufacture and use. Wastes from the manufacturing process that contained PCBs were often placed in dump sites or landfills. Occasionally, accidental spills and leaks from these facilities or transformer fires could result in PCBs entering the environment.

PCBs can be found worldwide. In the 1960s, when initial research results were released, traces of PCBs could be detected in people and animals around the world – not only in heavily populated areas such as New York City, but also in remote areas as far as the Arctic. These findings of such widespread and persistent contamination contributed to the banning of the chemical in 1979.

PCBs can degrade or breakdown in the environment, but the process greatly depends on the chemical makeup of the PCBs. The degrading process also depends on where the PCBs are in the environment. Typically, PCBs are either broken down in the environment by sunlight or by microorganisms. Sunlight plays an important role in the breakdown of PCBs when they are in the air, shallow water, or surface soils. Microorganisms, such as bacteria, algae, or fungi, biodegrade PCBs when found in soil or sediments.

Because PCBs exist in sediments, scientists need to determine if it is better to dredge and remove contaminated sediments from waterways or if it is safer to leave the sediments in place and cover with clean sediments, allowing them to naturally biodegrade. A cap or barrier can also be placed over contaminated sediments to prevent them from entering the environment. There are environmental, human health, and financial concerns with all of these alternatives.
# How did the Hawaiian Islands form?

## The Hawaiian Islands were formed by volcanic activity.

![A bathymetric map of Kachemak Bay, Alaska](/facts/hawaii.jpg "A bathymetric map of Kachemak Bay, Alaska")

The Hawaiian Emperor seamount chain is a well-known example of a large seamount and island chain created by hot-spot volcanism. Each island or submerged seamount in the chain is successively older toward the northwest. Near Hawaii, the age progression from island to island can be used to calculate the motion of the Pacific Oceanic plate toward the northwest. The youngest seamount of the Hawaiian chain is Loihi, which presently is erupting from its summit at a depth of 1000 meters. _Image courtesy of U.S. Geological Survey._

The Earth’s outer crust is made up of a series of tectonic plates that move over the surface of the planet. In areas where the plates come together, sometimes volcanoes will form. Volcanoes can also form in the middle of a plate, where magma rises upward until it erupts on the seafloor, at what is called a “hot spot.”

The Hawaiian Islands were formed by such a hot spot occurring in the middle of the Pacific Plate. While the hot spot itself is fixed, the plate is moving. So, as the plate moved over the hot spot, the string of islands that make up the Hawaiian Island chain were formed.

The Hawaiian Islands form an archipelago that extends over a vast area of the North Pacific Ocean. The archipelago is made up of 132 islands, atolls, reefs, shallow banks, shoals, and seamounts stretching over 1,500 miles from the island of Hawaii in the southeast to Kure Atoll in the northwest.
# What is the difference between land cover and land use?

## Land cover indicates the physical land type such as forest or open water whereas land use documents how people are using the land

![description of image](/facts/lclu1.jpg "short caption")

By comparing land cover data and maps over a period of time, coastal managers can document land use trends and changes.

Land cover data documents how much of a region is covered by forests, wetlands, impervious surfaces, agriculture, and other land and water types. Water types include wetlands or open water. Land use shows how people use the landscape – whether for development, conservation, or mixed uses. The different types of land cover can be managed or used quite differently.

Land cover can be determined by analyzing satellite and aerial imagery. Land use cannot be determined from satellite imagery. Land cover maps provide information to help managers best understand the current landscape. To see change over time, land cover maps for several different years are needed. With this information, managers can evaluate past management decisions as well as gain insight into the possible effects of their current decisions before they are implemented.

Coastal managers use land cover data and maps to better understand the impacts of natural phenomena and human use of the landscape. Maps can help managers assess urban growth, model water quality issues, predict and assess impacts from floods and storm surges, track wetland losses and potential impacts from sea level rise, prioritize areas for conservation efforts, and compare land cover changes with effects in the environment or to connections in socioeconomic changes such as increasing population.
# Do the Great Lakes have tides?

## Water levels in the Great Lakes change primarily because of meteorological effects.

![View of the Holland, Michigan water level and meteorological station, located at the entrance to Macatawa Bay. Historic water level data has been collected in this vicinity since 1894](/facts/gltides.jpg "Do the Great Lakes have tides?")

View of the Holland, Michigan water level and meteorological station, located at the entrance to Macatawa Bay. Historic water level data has been collected in this vicinity since 1894.

True tides—changes in water level caused by the gravitational forces of the sun and moon—do occur in a semi-diurnal (twice daily) pattern on the Great Lakes. Studies indicate that the Great Lakes spring tide, the largest tides caused by the combined forces of the sun and moon, is less than five centimeters in height. These minor variations are masked by the greater fluctuations in lake levels produced by wind and barometric pressure changes. 

Consequently, the Great Lakes are considered to be non-tidal.

Water levels in the Great Lakes have long-term, annual, and short-term variations. Long-term variations depend on precipitation and water storage over many years. Annual variations occur with the changing seasons. There is an annual high in the late spring and low in the winter. These changes occur at a rate that can be measured in feet per month.

Wind and weather conditions on the Great Lakes may create a [seiche](seiche.html), an oscillating wave which can be several feet high. In many of the Great Lakes, the time period between the “high” and “low” of a seiche may be between four and seven hours. As this is very similar to the six-hour time period of the tides on the ocean, it is frequently mistaken for a tide.
# What ocean basin has the most corals?

## What is a marine national monument?

## Similar to national marine sanctuaries, marine national monuments are designated to protect areas of the marine environment.

![coral and ulua](/facts/marine-monument.jpg "Coral reef")

Coral and Ulua found in the Papahānaumokuākea Marine National Monument. Coral reefs found in Papahānaumokuākea are home to over 7,000 marine species, one quarter of which are found only in the Hawaiian Archipelago.

Marine monuments and national marine sanctuaries are both types of marine protected areas. The main difference between national marine sanctuaries and marine national monuments is the designation process and the laws under which they are established. Sanctuaries are designated by NOAA or Congress and are managed by NOAA using the National Marine Sanctuaries Act (NMSA). The NMSA requires extensive public process, local community engagement, stakeholder involvement, and citizen participation, both prior to and following designation.

The Office of National Marine Sanctuaries serves as the trustee for a network of underwater parks in marine and Great Lakes waters from Washington state to the Florida Keys, and from Lake Huron to American Samoa. This network includes a growing number of national marine sanctuaries and Papahānaumokuākea and Rose Atoll marine national monuments.
# What is ecosystem science?

## Ecosystem science is the study of inter-relationships among the living organisms, physical features, bio-chemical processes, natural phenomena, and human activities in ecological communities.

![ecosystem](/facts/eco-science.jpg "ecosystem")

Within any given area, living and nonliving interact with each other. Together, these things form an ecosystem. Because all of the elements within an ecosystem are interrelated, these systems can be quite complex. All ecosystems must maintain a delicate balance between all of their members in order to thrive. Human interference and extreme natural events can tip this balance and threaten an ecosystem's health.

An ecosystem is an ecological community comprised of biological, physical, and chemical components, considered as a unit.

NOS scientists monitor, research, and study ecosystem science on many levels. They may monitor entire ecosystems or they may study the chemistry of a single microbe. This wide range of data is collected into combined assessments that describe current ecosystem health, predict the future state of an ecosystem, and evaluate different management strategies that may improve the health of an ecosystem.

NOS focuses its efforts on ecosystems that are given importance by legislative and executive orders. These areas include coral reefs, estuaries, [national marine sanctuaries](http://sanctuaries.noaa.gov/), [national estuarine research reserves](https://coast.noaa.gov/nerrs/), and other ocean ecosystems. The areas are observed and studied to determine how they are affected by human actions. Strategies are then formed in order to best protect these valuable ecosystems in order to keep them safe and healthy.
# What is a hydrothermal vent?

## Hydrothermal vents form at locations where **seawater** meets **magma**.

![A venting black smoker emits jets of particle-laden fluids.](/facts/vents2.jpg "A hydrothermal vent forms when seawater meets hot magma")

A venting black smoker emits jets of particle-laden fluids. The particles are predominantly very fine-grained sulfide minerals formed when the hot hydrothermal fluids mix with near-freezing seawater. These minerals solidify as they cool, forming chimney-like structures. “Black smokers” are chimneys formed from deposits of iron sulfide, which is black. “White smokers” are chimneys formed from deposits of barium, calcium, and silicon, which are white.

[Underwater volcanoes](volcanoes.html) at [spreading ridges and convergent plate boundaries](/facts/midoceanridge.html) produce hot springs known as hydrothermal vents.

Scientists first discovered hydrothermal vents in 1977 while exploring an oceanic spreading ridge near the Galapagos Islands. To their amazement, the scientists also found that the hydrothermal vents were surrounded by large numbers of [organisms](/facts/extremophile.html) that had never been seen before. These biological communities depend upon chemical processes that result from the interaction of seawater and hot magma associated with underwater volcanoes.

Hydrothermal vents are the result of seawater percolating down through fissures in the ocean crust in the vicinity of spreading centers or subduction zones (places on Earth where two tectonic plates move away or towards one another). The cold seawater is heated by hot magma and reemerges to form the vents. Seawater in hydrothermal vents may reach temperatures of over 700° Fahrenheit.

Hot seawater in hydrothermal vents does not boil because of the extreme pressure at the depths where the vents are formed.
# What is geodesy?

![Geodesy is the science of accurately measuring and understanding three fundamental properites of the Earth](/facts/geodesy.jpg)

_Geodesy is the science of accurately measuring and understanding three fundamental properites of the Earth._

Many organizations use geodesy to map the U.S. shoreline, determine land boundaries, and improve transportation and navigation safety. To measure points on the Earth’s surface, geodesists assign coordinates (similar to a unique address) to points all over the Earth. In the past, geodesists determined the coordinates of points by using Earth-based surveying tools to measure the distances between points. Today, geodesists use space-based tools like the Global Positioning System (GPS) to measure points on the Earth’s surface.

Geodesists must accurately define the coordinates of points on the surface of the Earth in a consistent manner. A set of accurately measured points is the basis for the National Spatial Reference System, which allows different kinds of maps to be consistent with one another.

To measure the Earth, geodesists build simple mathematical models of the Earth which capture the largest, most obvious features. Geodesists have adopted the ellipsoid as the most basic model of the Earth. Because the ellipsoid is based on a very simple mathematical model, it can be completely smooth and does not include any mountains or valleys. When additional detail of the Earth is needed, geodesists use the [geoid](/facts/geoid.html). A geoid has a shape very similar to global mean sea level, but this exists over the whole globe, not just over the oceans.
# What is an archipelago?

##### **Did you know?**

_Archipelagos are sometimes defined by political boundaries. The Gulf Archipelago off the Pacific Coast forms part of a larger archipelago that geologically includes Washington State’s San Juan Islands. While the Gulf Archipelago and San Juan Islands are geologically related, they are not technically included in the same archipelago due to manmade geopolitical borders._

Did you know? - *Archipelagos are sometimes defined by political boundaries. The Gulf Archipelago off the Pacific Coast forms part of a larger archipelago that geologically includes Washington State’s San Juan Islands. While the Gulf Archipelago and San Juan Islands are geologically related, they are not technically included in the same archipelago due to manmade geopolitical borders.*
# What are the Totten Beacons?

## These 19th-century **aids to navigation** are protected **historical** resources.

![Beacon pile in proximity to American Shoal lighthouse, completed 1880. Photo credit: M. Lawrence.](/facts/totten-beacon.jpg)

The rusty remnants of a Totten Beacon (foreground) located near American Shoal lighthouse. Photo credit: M. Lawrence.

[![Main beacon pile centered among three significantly shorter support posts. Photo credit: M. Lawrence.](totten-american-shoal.jpg)](http://floridakeys.noaa.gov/historic-navigation-aids/inventory/beacon_b.html)

Main beacon pile centered among three significantly shorter support posts. Photo credit: M. Lawrence.

![](/bootstrap/img/shadow1.png)

In 1513, Spanish explorer Ponce de León sailed into the strong currents of the Florida Straits. Little did he know that within a few years, these uncharted waters, which feed into the Gulf Stream, would become a major international shipping route to and from Europe and the New World.

As Europeans explored and colonized the Americas, they took advantage of the Florida Straits' winds and currents. The winds changed direction often, however, easily pounding countless vessels against miles of treacherous submerged coral reefs off the southern Florida coast.

By 1852, Lieutenant James Totten, the U.S. Army's assistant to the [Coast Survey](https://nauticalcharts.noaa.gov/about/history-of-coast-survey.html), had installed 15 wooden signal poles in the reefs to [create more accurate charts](https://celebrating200years.noaa.gov/foundations/nautical_charts/welcome.html#begins) of the Florida Keys. Local mariners quickly recognized that the poles themselves helped them safely navigate the reefs, and by 1855, Totten and his team installed a second generation of 16 poles using a more permanent material—iron. The "beacons" each displayed a letter, starting with "A" and ending with "P." Today, remnants of Totten Beacons are protected as historical resources by the [Florida Keys National Marine Sanctuary](http://floridakeys.noaa.gov/) (FKNMS).

Today, [GPS](/facts/gps.html) and sophisticated electronic navigation systems along with lighted navigational aids, buoys, radar beacons, and other visual aids maintained by the U.S. Coast Guard help warn mariners of dangerous coral reefs and shoals. FKNMS installs and maintains more than 700 buoys for resource management purposes. [Mooring buoys](http://floridakeys.noaa.gov/mbuoy/howto.html), which are round with a blue stripe, make it possible for a vessel to linger on a reef without using an anchor and potentially damaging fragile marine resources. Round yellow regulatory buoys in the sanctuary mark areas which have specific regulations, while cylindrical white buoys delineate special zones.
# What is GRAV-D?

![The pilot and co-pilot of a Navy-owned King Air aircraft prepare for takeoff on a data collection flight with GRAV-D instruments (fore and mid-ground) and a GRAV-D operator as their payload.](/facts/grav-d.jpg "The pilot and co-pilot of a Navy-owned King Air aircraft prepare for takeoff on a data collection flight with GRAV-D instruments (fore and mid-ground) and a GRAV-D operator as their payload.")

_The pilot and co-pilot of a Navy-owned King Air aircraft prepare for takeoff on a data collection flight with GRAV-D instruments (fore and mid-ground) and a GRAV-D operator as their payload._

So, what does that mean? First, to define a couple of terms: _Gravity_ is the force that causes objects to fall to, and stay on, the ground. _[Datums](https://oceanservice.noaa.gov/facts/datum.html)_ are the basis for all geodetic survey work, and _vertical datums_ are used to measure land elevations and water depths.

![Map of variations in Earth's gravity as measured by the GRAV-D airborne instruments over Lake Michigan and surrounding states.](/facts/grav-d-map.jpg "Map of variations in Earth's gravity as measured by the GRAV-D airborne instruments over Lake Michigan and surrounding states.")

_Map of variations in Earth's gravity as measured by the GRAV-D airborne instruments over Lake Michigan and surrounding states." title="Map of variations in Earth's gravity as measured by the GRAV-D airborne instruments over Lake Michigan and surrounding states._

The vertical datum is determined, or "realized," through a collection of specific points on the Earth with known heights. In 2007, NOAA’s [National Geodetic Survey](http://www.ngs.noaa.gov/) began a 15-year project to redefine the datum based on gravity measurements.

GRAV-D measures and monitors Earth’s gravity field to support the [geoid](https://oceanservice.noaa.gov/facts/geoid.html)—a model of roughly global mean sea level used to measure precise surface elevations—so that it may serve as the “zero reference surface” for all heights in the nation. Accurate heights are critical to many scientific endeavors, but are particularly important for protecting low-lying coastal ecosystems.

Variations in the size, shape, and mass distribution of the Earth cause slight variations in the “strength” of gravity’s pull. GRAV-D measures gravity from an aircraft and those data are combined with satellite and surface gravity measurements to create the geoid. When the project is completed in 2022, the geoid will be applied to satellite position measurements like GPS to obtain extremely accurate heights (to within 2 cm where possible).

It is estimated that GRAV-D will provide $4.8 billion in socioeconomic benefits to the United States through improved floodplain mapping, coastal resource management, construction, agriculture, and emergency evacuation planning.