More

8.3: The Seafloor - Geosciences


The ocean surface is vast and hides an entire world underneath it. Today’s technology has allowed us to learn more about the seafloor, including both its physical properties and its effects on living organisms.

Lesson Objectives

  • Describe the obstacles to studying the seafloor and methods for doing so.
  • Describe the features of the seafloor.

Ancient myth says that Atlantis was a powerful undersea city whose warriors conquered many parts of Europe. There is little proof that such a city existed, but human fascination with the world under the oceans certainly has existed for centuries. Not much was known about the aphotic zone of the ocean until scientists developed a system modeled after the way that bats and dolphins use echolocation to navigate in the dark (Figure 14.19). Prompted by the need to find submarines during World War II, scientists learned to bounce sound waves through the ocean to detect underwater objects. The sound waves bounce back like an echo off of whatever object may be in the ocean. The distance of the object can be calculated based on the time that it takes for the sound waves to return. Finally, scientists were able to map the ocean floor.

Figure 14.19: Dolphins and whales use echolocation, a natural sonar system, to navigate the ocean.

Three main obstacles have kept us from studying the depths of the ocean: absence of light, very cold temperatures, and high pressure. As you know, light only penetrates the top 200 meters of the ocean; the depths of the ocean can be as much as 11,000 meters deep. Most places in the ocean are completely dark, which makes it impossible for humans to explore without bringing a source of light with them. Secondly, the ocean is very cold; colder than 0°C (32°F) in many places. Such cold temperatures pose significant obstacles to human exploration of the oceans. Finally, the pressure in the ocean increases tremendously as you go deeper. Scuba divers can rarely go deeper than 40 meters due to the pressure. The pressure on a diver at 40 meters would be 4 kilograms/square centimeter (60 lbs/sq in). Even though we don’t think about it, the air in our atmosphere has weight. It presses down on us with a force of about 1 kilogram per square centimeter (14.7 lbs/ sq in). In the ocean, for every 10 meters of depth, the pressure increases by nearly 1 atmosphere! Imagine the pressure at 10,000 meters; that would be 1,000 kilograms per square centimeter (14,700 lbs/sq in). Today’s submarines usually dive to only about 500 meters; to go deeper than this they must be specially designed for greater depth (Figure 14.20).

Figure 14.20: Submarines are built to withstand great pressure under the sea, up to 680 atmospheres of pressure (10,000 pounds per square inch). They still rarely dive below 400 meters.

Figure 14.21: Alvin allows for a nine hour dive for up to two people and a pilot. It was commissioned in the 1960s.

In the 19th century, explorers mapped ocean floors by painstakingly dropping a line over the side of a ship to measure ocean depths, one tiny spot at a time. SONAR, which stands for Sound Navigation And Ranging, has enabled modern researchers to map the ocean floor much more quickly and easily. Researchers send a pulse of sound down to the ocean floor and calculate the depth based on how long it takes the sound to return. Of course, some scientific research requires actually traveling to the bottom of the ocean to collect samples or directly observe the ocean floor, but this is more expensive and can be dangerous.

In the late 1950s, the bathyscaphe (deep boat) Trieste was the first manned vehicle to venture to the deepest parts of the ocean, a region of the Marianas Trench named the Challenger Deep. It was built to withstand 1.2 metric tons per square centimeter and plunged to a depth of 10,900 meters. No vehicle has carried humans again to that depth, though robotic submarines have returned to collect sediment samples from the Challenger Deep. Alvin is a submersible used by the United States for a great number of studies; it can dive up to 4,500 meters beneath the ocean surface (Figure 14.21).

In order to avoid the expense, dangers and limitations of human missions under the sea, remotely operated vehicles or ROVs, allow scientists to study the ocean’s depths by sending vehicles carrying cameras and special measuring devices. Scientists control them electronically with sophisticated operating systems (Figure 14.22).

Figure 14.22: Remotely-operated vehicles like this one allow scientists to study the seafloor.

Features of the Seafloor

Before scientists invented sonar, many people believed the ocean floor was a completely flat surface. Now we know that the seafloor is far from flat. In fact, the tallest mountains and deepest canyons are found on the ocean floor; far taller and deeper than any landforms found on the continents. The same tectonic forces that create geographical features like volcanoes and mountains on land create similar features at the bottom of the oceans.

Look at Figure 14.23. If you follow the ocean floor out from the beach at the top left, the seafloor gently slopes along the continental shelf. The sea floor then drops off steeply along the continental slope, the true edge of the continent. The smooth, flat regions that make up 40% of the ocean floor are the abyssal plain. Running through all the world’s oceans is a continuous mountain range, called the mid-ocean ridge(“submarine ridge” in Figure 14.23). The mid-ocean ridge is formed where tectonic plates are moving apart from each other, allowing magma to seep out in the space where the plates pulled apart. The mid-ocean ridge system is 80,000 kilometers in total length and mostly underwater except for a few places like Iceland. Other underwater mountains include undersea volcanoes (called seamounts), which may rise more than 1,000 meters above the ocean floor. Those that reach the surface become volcanic islands, such as the Hawaiian Islands. Deep oceanic trenchesare created where a tectonic plate dives beneath (subducts) another plate.

Figure 14.23: The seafloor is as varied a landscape as the continents.

Lesson Summary

  • Until the development of sonar, we knew very little about the ocean floor.
  • The deep ocean is dark, very cold and has tremendous pressure from the overlying water.
  • Scuba divers can explore only to about 40 meters, while most submarines dive only to about 500 meters. Scientific research submersibles have explored the ocean’s deepest trenches, but most are designed to reach only the ocean floor.
  • Today much of our exploration of the oceans happens using sonar and remotely operated vehicles.
  • Features of the ocean include the continental shelf, slope, and rise. The ocean floor is called the abyssal plain. Below the ocean floor, there are a few small deeper areas called ocean trenches. Features rising up from the ocean floor include seamounts, volcanic islands and the mid-oceanic ridges and rises.

Review Questions

  1. What are three obstacles to studying the seafloor?
  2. The atmospheric pressure is about 1 kilogram per centimeter squared (14.7 pounds per square inch or 1 atmosphere) at sea level. About what is the pressure if you are 100 meters deep in the ocean?
  3. What invention gave people the ability to map the ocean floor?
  4. Which parts of the ocean floor would you expect there to be the greatest amount of living organisms?
  5. How much deeper did the Trieste submerge than Alvin?
  6. Compare and contrast the continental shelf and the abyssal plain.
  7. Why do you think mapping the seafloor is important to the Navy? Explain.
  8. If the mid-ocean ridge is created where the tectonic plates separate, why is a mountain range formed there?

Vocabulary

abyssal plain
The flat bottom of the ocean floor; the deep ocean floor.
continental shelf
The shallow, gradually sloping seabed around the edge of a continent. Usually less than 200 meters in depth. The continental shelf can be thought of as the submerged edge of a continent.
continental slope
The sloped bottom of the ocean that extends from the continental shelf down to the deep ocean bottom.
mid ocean ridge
Mountain range on the ocean floor where magma upwells and new ocean floor is formed.
seamount
A mountain rising from the seafloor that does not reach above the surface of the water. Usually formed from volcanoes.
trench
Deepest areas of the ocean; found where subduction takes place.

Marine Geosciences – Seafloor Processes Principal Investigator

The Monterey Bay Aquarium Research Institute (MBARI) invites qualified candidates to apply for a position as a Principal Investigator in science or engineering with a programmatic vision that advances understanding of seafloor processes and fosters the development of novel observational capabilities and/or methods. Candidate interests may span the fields of geology, geophysics, geochemistry, or interplay between abiotic and biotic systems associated within the deep-sea floor. MBARI Principal Investigators lead small research groups that collaborate with Engineering Division staff and other researchers, organize and conduct at-sea research operations, and disseminate developments and discoveries to a broad audience.

Founded in 1987 by the late David Packard, MBARI is uniquely dedicated to merging science, engineering, and marine operations for the purpose of developing state-of-the-art instruments, methods, and systems for advancing scientific research in the ocean. Principal Investigators are responsible for conceiving and executing original research programs, and for the development of technology and analytical methods. Individuals in these positions are expected to have exceptional competence in addressing important research questions in ocean science and technology. Their research program is expected to become a significant contribution towards MBARI’s primary goal of advancing ocean research and technology broadly as outlined in MBARI’s Strategic Plan and Technology Roadmap.

A Doctorate or equivalent in a scientific or engineering discipline and a minimum of 3 years demonstrated success in conducting research is required, along with a record of significant, original, and promising research contributions. Applicants at an early- to mid-career stage (equivalent to an assistant to associate professor) with a demonstrated ability to work in an interdisciplinary, team-oriented environment are encouraged to apply. The successful candidate will report directly to the Science or Engineering Division Chair.

MBARI, located in Moss Landing, California, the heart of the Monterey Bay National Marine Sanctuary, offers ready access to the open ocean and deep-sea, and embodies a balanced emphasis on science and engineering. Ongoing research programs range across autonomous and remotely operated underwater vehicle systems, control technologies, ocean physics, chemistry, geology, biology, ocean instrumentation, and information management. MBARI hosts approximately 200 employees, with shore facilities that include state-of-the-art science and engineering laboratories, manufacturing and electrical fabrication shops, and dock facilities for MBARI vessels. Our operations division supports two MBARI-owned research ships, Remotely Operated Vehicles (ROVs), a fleet of Autonomous Underwater Vehicles (AUVs), deep-sea cabled observatory, and other sea-going assets. More information about MBARI and its current research and staff is available here.

MBARI enjoys cooperative relationships with a host of neighboring academic and government institutions, including Stanford University, Hopkins Marine Station, the University of California at Santa Cruz, the Naval Postgraduate School, Moss Landing Marine Laboratories, California State University Monterey Bay, and the Monterey Bay National Marine Sanctuary, offering many opportunities for collaborative research and education. Our partnership with the Monterey Bay Aquarium also provides unique opportunities for public outreach and for engaging resource managers as well as policy makers.

Prospective applicants should send a current curriculum vita, a statement of research interests including a brief overview of current and expected future directions in relation to science, engineering, and marine operations support available at MBARI, and the names and addresses of four professional references to [email protected], or by mail to the below address, or by fax to (831) 775-1659.

MBARI, Norm Steinberg, Director of Human Resources
Job Code: Seafloor
7700 Sandholdt Road
Moss Landing, CA 95039

We are currently receiving applications for this position, which will remain open until filled. We expect to begin reviewing applications and scheduling interviews on October 1, 2021. MBARI offers a competitive compensation and benefits package consistent with peer positions at other non-profit and academic institutions.

MBARI is a non-profit, private oceanographic research institute, and an equal opportunity and affirmative action employer. MBARI considers all applicants for employment without regard to race, color, religion, sex, national origin, age, disability, or covered veteran status in accordance with applicable federal, state, and local laws.


3.1 Response variables

3.1.1 Linear sedimentation rate

Linear sedimentation rate ( ω ) (measured in cm yr −1 ) is used here synonymously with sediment accumulation rate. Data were initially sourced from the EMODnet-Geology portal ( https://www.emodnet-geology.eu/ , last access: 5 February 2019), which provides a collation of values from the literature across European sea basins. The dataset was limited to the study site and sedimentation rates based on 210 Pb, to ensure a consistent integration timescale (Jenkins, 2018). Based on a half-life of approximately 22 years, the associated integration time is roughly 100 years (Jenkins, 2018). Data from Zuo et al. (1989) were excluded as these were deemed unreliable (de Haas et al., 1997).

The reported sedimentation rate data focussed on accumulation areas like the Norwegian Trough (Fig. 2). However, to be able to spatially predict sedimentation rates across the study site it is necessary to include data from areas of erosion and non-deposition, which predominate in the North Sea. Therefore, the data by de Haas et al. (1997) were also included. This provided less than 20 data points of zero net-sedimentation, which was still deemed insufficient. Additionally, pseudo-observations (Hengl et al., 2017) were also included. Pseudo-observations are “virtual” samples that are placed in undersampled areas and for which the value of the response variable can be assumed with high certainty. Hengl et al. (2017) cite 0 % soil OC in the top 2 m of active sand dunes as an example. Mitchell et al. (2021) placed pseudo-samples in areas of bedrock outcropping at the seabed when predicting sedimentation rates in the Baltic Sea. The placement of pseudo-observations was restricted to areas of erosion and non-deposition (based on the sedimentary environment layer, as described in Sect. 3.2), for which a sedimentation rate of 0 cm yr −1 could be assumed. The pseudo-observations were placed randomly to avoid human bias. Some of the sedimentation rate values from non-depositional areas reported by de Haas et al. (1997) and van Weering et al. (1993) appeared too high, and after a review of the 210 Pb-profiles four of them were set to 0 cm yr −1 due to low 210 Pb activities and indistinct decreases with depth. The full dataset used for subsequent modelling is shown in Fig. 2 and provided as Table S1 in the Supplement.

Figure 2Available samples on sedimentation rate (a) and OC density (b).

3.1.2 Organic carbon density

Previous studies have predicted OC content and sediment porosity separately to calculate OC stocks (Diesing et al., 2017 Lee et al., 2019 Wilson et al., 2018). Here, we first calculate OC density from concurrent measurements of OC content and sediment dry bulk densities or porosities. This has two advantages: First, there is no need to transform the response variable as would be necessary in the case of OC content reported as weight percent or fractions. Second, only one model instead of two needs to be fitted. This is advantageous as fitting two models would likely increase the uncertainty of the predictions. Initially, a wide range of data sources were accessed. Ultimately, 373 samples fulfilled the criterion of providing OC content and dry bulk density/porosity measured on the same sample. These samples were collected and measured by the Geological Survey of Norway, the Centre for Environment, Fisheries and Aquaculture Science, Bakker and Helder (1993), and de Haas et al. (1997).

OC density ρOC (kg m −3 ) was calculated from data on OC content G (g kg −1 ) and dry bulk density ρd (kg m −3 ):

If not measured, dry bulk density was calculated from porosity ϕ and the grain density ρs (2650 kg m −3 ) according to

In the majority of cases (52.8 %), the OC concentrations referred to the 0–10 cm depth interval, but other depth intervals were also present most frequently 0–1 cm (17.7 %), 0–5 cm (16.4 %), 0–0.5 cm (6.7 %), and 0–2 cm (4.6 %). It was assumed that the reported values were representative of the upper 10 cm of the sediment column. The full dataset used for subsequent modelling is shown in Fig. 2 and provided as Table S2.


8.3 Beyond Terrain Surfaces: Bathymetry

There are many other kinds of “surfaces” that methods discussed here are used to represent. They include the ocean depths (bathymetry), atmospheric surfaces in which the concept of a surface is more abstract than that for visible terrain to include any continuous mathematical “field” across which quantities can be measured (e.g., precipitation, atmospheric pressure, wind speed), and even conceptual surfaces such as population density. One example of the latter is this population density surface:

Here, we provide one example that is closest to those above, the representation of the surface under water bodies, bathymetry. The term bathymetry refers to the process and products of measuring the depth of water bodies. The U.S. Congress authorized the comprehensive mapping of the nation's coasts in 1807, and directed that the task be carried out by the federal government's first science agency, the Office of Coast Survey (OCS). That agency is now responsible for mapping some 3.4 million nautical square miles encompassed by the 12-mile territorial sea boundary, as well as the 200-mile Exclusive Economic Zone claimed by the U.S., a responsibility that entails regular revision of about 1,000 nautical charts. The coastal bathymetry data that appears on USGS topographic maps, like the one shown below, is typically compiled from OCS charts.

Early hydrographic surveys involved sampling water depths by casting overboard ropes weighted with lead and marked with depth intervals called marks and deeps. Such ropes were called leadlines for the weights that caused them to sink to the bottom. Measurements were called soundings. By the late 19th century, piano wire had replaced rope, making it possible to take soundings of thousands rather than just hundreds of fathoms (a fathom is six feet).

Echo sounders were introduced for deepwater surveys beginning in the 1920s. Sonar (SOund NAvigation and Ranging) technologies have revolutionized oceanography in the same way that aerial photography revolutionized topographic mapping. The seafloor topography revealed by sonar and related shipborne remote sensing techniques provided evidence that supported theories about seafloor spreading and plate tectonics.

Below is an artist's conception of an oceanographic survey vessel operating two types of sonar instruments: multibeam and side scan sonar. On the left, a multibeam instrument mounted in the ship's hull calculates ocean depths by measuring the time elapsed between the sound bursts it emits and the return of echoes from the seafloor. On the right, side scan sonar instruments are mounted on both sides of a submerged "towfish" tethered to the ship. Unlike multibeam, side scan sonar measures the strength of echoes, not their timing. Instead of depth data, therefore, side scanning produces images that resemble black-and-white photographs of the sea floor.

A detailed report of the recent bathymetric survey of Crater Lake, Oregon, USA, is published by the USGS at Crater Lake Bathymetry Survey.

Practice Quiz

Registered Penn State students should return now take the self-assessment quiz about Relief Shading, Data Sources, and Bathymetry.

You may take practice quizzes as many times as you wish. They are not scored and do not affect your grade in any way.


Coastal areas as the major sink for macro-litter

The coastal trapping of buoyant macro-litter, along with the coastal deposition of land-sourced items made of non-buoyant materials, makes the nearshore seafloor the most likely sink for macro-litter. Although there are still no consistent quantitative mass measurements across environments to scale the stocks of litter in the ocean, macro-litter density data scattered over the world support this reasoning (Fig. 5). Our analysis of macro-litter densities on the seafloor depict a sharp increasing trend from deep to shallow areas, reaching the order of one item per ten square metres on the seafloor area closest to shore, akin only to those concentrations measured along the shoreline.

Bean density plots show individual measurements per environment as dots, the median as a vertical thick line and the 10th, 25th, 75th and 90th percentiles as white lines. The graph compiles individual measurements reported in previously published reviews covering marine environments worldwide 38,49,50] . The analysis is aimed at showing order-of-magnitude differences in density of macro-litter items between environments.

Using the nearshore-seafloor reservoir to explore geographical patterns in litter composition, we noted that the prevalence of single-use items was apparent at more densely inhabited latitudes (50° N to 30° S Supplementary Fig. 7), but their proportion decreased outside this latitudinal band, where the share of fishing-related items increased. The share of single-use plastic also decreased in the socioeconomic regions with the highest gross domestic product (GDP) per capita (Fig. 6 and Supplementary Fig. 8). Both a small population and high GDP are associated with low waste inputs from land into the ocean 4 . Thereby, we found a lower fraction of single-use plastic litter relative to fishing gear in areas where lower waste loading is predicted. In addition, the persistence of litter resulting from fishing activity identifies this sector as a special target to effectively manage marine plastics globally, a proposal in line with the estimates of fishing-gear loss across the world (from 6% to 29% per year depending on gear type) 13 .

Bars show mean percentages per region the darker-coloured areas and lines around the means show the individual data outputs (n = 10,000) and the distribution beanplot, respectively. Uncertainties of results were quantified through 10,000 Monte Carlo iterations in each region. Bar colour relates to potential origin. Items above the horizontal line marks in the rankings comprise, at least, 50% of the total items identified. Only identifiable items were accounted for in the rankings high-income region (n = 247,238), East Europe and Central Asia (n = 3,123), East Asia and Pacific (n = 223,618), Latin America and the Caribbean (n = 61,900), North Africa and Middle East (n = 44,786), sub-Saharan Africa (n = 8,507) and South Asia (n = 6,711).


18.3 Sea-Floor Sediments

Except within a few kilometres of a ridge crest, where the volcanic rock is still relatively young, most parts of the sea floor are covered in sediments. This material comes from several different sources and is highly variable in composition, depending on proximity to a continent, water depth, ocean currents, biological activity, and climate. Sea-floor sediments (and sedimentary rocks) can range in thickness from a few millimetres to several tens of kilometres. Near the surface, the sea-floor sediments remain unconsolidated, but at depths of hundreds to thousands of metres (depending on the type of sediment and other factors) the sediment becomes lithified.

The various sources of sea-floor sediment can be summarized as follows:

  • Terrigenous sediment is derived from continental sources transported by rivers, wind, ocean currents, and glaciers. It is dominated by quartz, feldspar, clay minerals, iron oxides, and terrestrial organic matter.
  • Pelagic carbonate sediment is derived from organisms (e.g., foraminifera ) living in the ocean water (at various depths, but mostly near surface) that make their shells (a.k.a. tests ) out of carbonate minerals such as calcite.
  • Pelagic silica sediment is derived from marine organisms (e.g., diatoms and radiolaria ) that make their tests out of silica (microcrystalline quartz).
  • Volcanic ash and other volcanic materials are derived from both terrestrial and submarine eruptions.
  • Iron and manganese nodules form as direct precipitates from ocean-bottom water.

The distributions of some of these materials around the seas are shown in Figure 18.3.1. Terrigenous sediments predominate near the continents and within inland seas and large lakes. These sediments tend to be relatively coarse, typically containing sand and silt, but in some cases even pebbles and cobbles. Clay settles slowly in nearshore environments, but much of the clay is dispersed far from its source areas by ocean currents. Clay minerals are predominant over wide areas in the deepest parts of the ocean, and most of this clay is terrestrial in origin. Siliceous oozes (derived from radiolaria and diatoms) are common in the south polar region, along the equator in the Pacific, south of the Aleutian Islands, and within large parts of the Indian Ocean. Carbonate oozes are widely distributed in all of the oceans within equatorial and mid-latitude regions. In fact, clay settles everywhere in the oceans, but in areas where silica- and carbonate-producing organisms are prolific, they produce enough silica or carbonate sediment to dominate over clay.

Carbonate sediments are derived from a wide range of near-surface pelagic organisms that make their shells out of carbonate (Figure 18.3.2). These tiny shells, and the even tinier fragments that form when they break into pieces, settle slowly through the water column, but they don’t necessarily make it to the bottom. While calcite is insoluble in surface water, its solubility increases with depth (and pressure) and at around 4,000 metres, the carbonate fragments dissolve. This depth, which varies with latitude and water temperature, is known as the carbonate compensation depth , or CCD. As a result, carbonate oozes are absent from the deepest parts of the ocean (deeper than 4,000 metres), but they are common in shallower areas such as the mid-Atlantic ridge, the East Pacific Rise (west of South America), along the trend of the Hawaiian/Emperor Seamounts (in the northern Pacific), and on the tops of many isolated seamounts.

Figure 18.3.2 Foraminifera from the Ambergris Caye area of Belize. Most of the shells are about 1 millimetre across.

Exercise 18.3 What type of sediment?

The diagram shows the sea floor in an area where there is abundant pelagic carbonate sediment. There is a continent within 100 kilometres of this area, to the right. What type of sediment (coarse terrigenous, clay, siliceous ooze, or carbonate ooze) would you expect at find at locations a, b, c, and d?

Figure 18.3.3 [Image Description]

All terrestrial erosion products include a small proportion of organic matter derived mostly from terrestrial plants. Tiny fragments of this material plus other organic matter from marine plants and animals accumulate in terrigenous sediments, especially within a few hundred kilometres of shore. As the sediments pile up, the deeper parts start to warm up (from geothermal heat), and bacteria get to work breaking down the contained organic matter. Because this is happening in the absence of oxygen (a.k.a. anaerobic conditions), the by-product of this metabolism is the gas methane (CH4). Methane released by the bacteria slowly bubbles upward through the sediment toward the sea floor.

At water depths of 500 metres to 1,000 metres, and at the low temperatures typical of the sea floor (close to 4°C), water and methane combine to create a substance known as methane hydrate . Within a few metres to hundreds of metres of the sea floor, the temperature is low enough for methane hydrate to be stable and hydrates accumulate within the sediment (Figure 18.3.4). Methane hydrate is flammable because when it is heated, the methane is released as a gas (Figure 18.3.4). The methane within sea-floor sediments represents an enormous reservoir of fossil fuel energy. Although energy corporations and governments are anxious to develop ways to produce and sell this methane, anyone that understands the climate-change implications of its extraction and use can see that this would be folly. As we’ll see in the discussion of climate change in Chapter 19, sea-floor methane hydrates have had significant impacts on the climate in the distant past.

Figure 18.3.4 Left: Methane hydrate within muddy sea-floor sediment from an area offshore from Oregon. Right: Methane hydrate on fire.

Image Descriptions

Figure 18.3.3 image description: A. is farthest from the continent. D is closest to the continent.

  1. A depth of 4.5 kilometres.
  2. A depth of 3.5 kilometres.
  3. A depth of 5 kilometres.
  4. A depth of 1 kilometre, close to the edge of a continent.

Media Attributions

  • Figure 18.3.1, 18.3.2, 18.3.3: © Steven Earle. CC BY.
  • Figure 18.3.4 (Left): “Gashydrat im Sediment” © Wusel007. CC BY-SA.
  • Figure 18.3.4 (Right): “Burning Gas Hydrates” by J. Pinkston and L. Stern (USGS). Public domain.

referring to sedimentary particles that originated on a continent

a single-celled protist with a shell that is typically made of CaCO3

the shell-like hard parts (either silica or carbonate) of small organisms such as radiolarian and foraminifera

photosynthetic algae that make their tests (shells) from silica

microscopic (0.1 to 0.2 millimetres) marine protozoa that produce silica shells

the depth in the ocean (typically around 4000 metres) below which carbonate minerals are soluble

processes that take place without oxygen

a combination of water ice and methane in which the methane is trapped inside “cages” in the ice


Seafloor survey finds thousands of barrels at DDT dumpsite off Los Angeles coast

UC San Diego's Research Vessel Sally Ride off the coast of Santa Catalina Island. March 2021.

An expedition led by UC San Diego’s Scripps Institution of Oceanography mapped more than 36,000 acres of seafloor between Santa Catalina Island and the Los Angeles coast in a region previously found to contain high levels of the toxic chemical DDT in sediments and the ecosystem. The survey on Research Vessel Sally Ride identified more than 27,000 targets with high confidence to be classified as a barrel, and an excess of 100,000 total debris objects on the seafloor.

“Unfortunately, the basin offshore Los Angeles had been a dumping ground for industrial waste for several decades, beginning in the 1930s. We found an extensive debris field in the wide area survey,” said Eric Terrill, chief scientist of the expedition and director of the Marine Physical Laboratory at Scripps Institution of Oceanography. “Now that we’ve mapped this area at very high resolution, we are hopeful the data will inform the development of strategies to address potential impacts from the dumping.”

The expedition that ran March 10-24, was developed in collaboration with NOAA’s Office of Marine and Aviation Operations and the National Oceanographic Partnership Program. The project, part of ongoing collaboration with NOAA’s Uncrewed Systems Operations Center, tested autonomous underwater vehicle (AUV) technology to map the seafloor. As marine robotic technology continues to advance, NOAA is collaborating with Scripps to transition ocean robotics from research to operational uses.

Barrel of DDT found off the coast of Santa Catalina Island in California.
Credit: Scripps Institution of Oceanography at UC San Diego

In 2011 and 2013, UC Santa Barbara professor David Valentine discovered concentrated accumulations of DDT in the sediments in the same region, and visually confirmed 60 barrels on the seafloor. Scientists are also finding high levels of DDT in marine mammals including dolphins and sea lions, with exposure to PCBs and DDT linked to the development of cancer in sea lions. Reporting on this issue by the Los Angeles Times noted that shipping logs from a disposal company supporting Montrose Chemical Corp. of California, a DDT-producing company, show that 2,000 barrels of DDT-laced sludge could have potentially been dumped each month from 1947 to 1961 into a designated dumpsite. In addition to Montrose, logs from other entities show that many other industrial companies in Southern California used this basin as a dumping ground until 1972, when the Marine Protection, Research and Sanctuaries Act, also known as the Ocean Dumping Act, was enacted.

Barrels and targets of interest were found in nearly all areas of the 36,000 acres surveyed and extended beyond dumpsite limits, which is roughly 12 miles offshore Los Angeles, and eight miles from Catalina Island. The 27,000 targets identified with confidence to be barrels had stronger brightness in their acoustic signal and distinct geometry in the shape of the image. The other objects identified also showed these signals, however not as bright or distinct which could be due to how deep they were deposited in the sediments, or deterioration of the material. There were also patterns that indicate how the barrels were dumped.

“There are several distinct track-line patterns in the surveyed area, suggesting that the dumping was repeatedly done from an underway platform such as a moving ship or barge. Some of those lines are as long as 11 miles and approach state waters,” said Terrill. “While our mapping sonars cannot measure the contents inside the barrels, the target locations are consistent with the previously identified dumpsite and extend much further than we expected.”

The expedition included a team of 31 scientists, engineers, and crew conducting 24-hour, around-the-clock operations to deploy two AUVs used for the expedition from R/V Sally Ride. The research vessel is one of the most technologically-advanced vessels in the U.S. Academic Research Fleet, and is owned by the Office of Naval Research and operated by Scripps on behalf of the U.S. research community. The search entailed work at depths up to 900 meters (3,000 feet), in what is considered a semi-abyssal, steep seafloor between Catalina and Los Angeles. The two AUVs, the REMUS 6000, capable of working up to depths of 6,000 meters (19,600 feet), and Bluefin, capable of depths up to 1,500 meters (4,900 feet), were deployed to work in tandem to map the seabed at a high resolution.

Scripps researchers aboard the Research Vessel Sally Ride using the REMUS 6000 and Bluefin autonomous underwater vehicles (AUVs) to survey the seafloor for discarded barrels near Santa Catalina Island. March 2021.
Credit: Scripps Institution of Oceanography at UC San Diego

The robots adjust to changes in the topography flying at a constant 20 meters (65 feet) above the seafloor, using high frequency side-scan sonar to send signals 150 meters (490 feet) on each side of the vehicle. The continuous echo-location of these signals reflecting from the seafloor creates images of the bottom and the objects resting there. Scanning the seabed at a rate of 0.75 square kilometers per hour—roughly the size of 140 football fields—the sonar data can be used to detect objects, characterize seafloor habitat or map hazards. Sonar settings for this expedition were tuned to detect objects as small as a coffee cup.

The ability to operate in deep waters for long duration and survey large areas at very high resolution is what enabled a wide area survey of this magnitude. Underwater acoustics were also used to broadcast GPS signals from the research vessel to the AUVs, so that they could be tracked with high precision through each deployment.

Topside, the science team would recharge the instruments, and offload sonar imagery to analyze data. More than 100 gigabytes of sonar data were captured during the expedition.

Since the expedition, researchers have been analyzing the acoustic imaging data of this complex site. Typically, manually counting the targets is the approach taken with side-scan sonar processing, but this approach was not feasible given the size and extent of the survey area. An automated process was used, perhaps the first time automated approaches have been done at this scale, said Terrill. The 60 barrels confirmed by Valentine in 2011 and 2013 served as a reference point for validating detection algorithms that were developed to find barrels.

“The data from the Valentine expedition were used to ground-truth our algorithms,” said Sophia Merrifield, a researcher at Scripps who has been leading the data analytics after R/V Sally Ride returned to shore. “Location, size and acoustic brightness are tracked for each target detected and used to characterize patterns and densities of the debris field.”

Research vessel Sally Ride oversaw the underwater survey, continuously broadcasting underwater GPS signals to the autonomous underwater vehicles so that the vehicles and their sonar mapping data were highly accurate on the seabed. Crews remained in communication with shore using satellite data links, and were able to share data with scientists who remained on shore.
Credit: Scripps Institution of Oceanography at UC San Diego

Terrill’s team is now working to finalize the release of the sonar data, which they hope will serve as a catalyst for an action plan and additional research endeavors to understand environmental impacts.

There is a lot to be understood towards how DDT is impacting our environment and marine food webs, according to Scripps chemical oceanographer and professor of geosciences Lihini Aluwihare, who in 2015 co-authored a study that found high abundance of DDT and other man-made chemicals in the blubber of Bottlenose Dolphins that died of natural causes.

“The uniquely high body burden of DDT in top predators feeding in Southern California waters has been known for some time. The extent of the dumping ground helps to explain some of these previous observations,” said Aluwihare, who was not part of the survey expedition. “These results also raise questions about the continued exposure and potential impacts on marine mammal health, especially in light of how DDT has been shown to have multi-generational impacts in humans. How this vast quantity of DDT in sediments has been transformed by seafloor communities over time, and the pathways by which DDT and its degraded products enter the water column food web are questions that remain to be explored.”


The Institute for Creation Research


The two previous articles in this series demonstrated problems with the old-earth timescales that secular scientists have assigned to deep seafloor sediments and ice cores. 1,2 This article presents a positive argument for the youthfulness of the seafloor sediments&mdashan argument that has ominous implications for the vast ages assigned to the high-latitude ice sheets.

Dating Seafloor Sediments: Secular vs. Creation Thinking

At today&rsquos &ldquoslow and gradual&rdquo rates, it can take a thousand years for just a couple of centimeters of sediment to be deposited on the ocean floor. Because these sediment layers can be many hundreds of meters thick, and because it&rsquos assumed that sedimentation rates have always been slow, secular scientists believe the sediment deposition required many millions of years.

Secular scientists assign ages to these layers by using the astronomical or Milankovitch hypothesis of ice ages to interpret chemical clues within the seafloor sediments. This theory simply accepts as a given the idea of &ldquodeep time&rdquo&mdashmillions of years. A previous article discussed some of the problems with the Milankovitch hypothesis. 1

Although creation scientists reject the millions of years that secular scientists have assigned to the seafloor sediments, they do agree that their deposition has been slow and gradual for at least the last few thousand years. But even a few thousand years of slow deposition could only account for a tiny fraction of the total sediments on the ocean floor. How, then, can creation scientists explain the great thickness of these sediments? Objects called manganese nodules found on the floors of the Pacific, Atlantic, and Indian Oceans provide a significant clue.

Manganese Nodules

Manganese nodules are typically potato-size concretions found scattered on the ocean floor (Figure 1). Composed of manganese and other metals such as iron, nickel, and copper, these nodules form as a result of the accumulation of chemicals onto a nucleus. These chemicals originate in seawater or within water trapped between the sediment grains below the sea floor. In both cases, the end result is the formation of metallic pellets near the surface of the ocean floor. Manganese and iron extruded from underwater volcanoes can also contribute to nodule growth, as can the presence of algae and bacteria. 3,4 Nodule growth is thought to cease once the nodules become buried beneath more than a few centimeters of sediment. 5,6 Based on radioisotope dating methods, secular scientists estimate that these nodules typically grow at the exceptionally slow rate of only a few millimeters per million years. 3

Manganese Mystery

Manganese nodules puzzle secular scientists because most are found in just the uppermost 50 centimeters (

20 inches) of sediment, although some are found at greater depths. 3,5,6

Why are nodules generally missing from the deeper seafloor sediments? If the present really is the &ldquokey to the past,&rdquo one would expect nodules to be found at all depths within the seafloor sediments. After surveying manganese nodule data from the Deep Sea Drilling Project, one secular geologist observed, &ldquoThe major question arising from this survey is why nodules occur in such paucity at depth in the sediment column.&rdquo 5

Some scientists have speculated that this scarcity of deep nodules can be explained by chemical dissolution of the nodules after burial. However, this proposal is problematic for at least two reasons. First, some nodules have been found at great depths, although this is relatively rare. 5 Second, buried nodules do not exhibit any clear trends in chemical composition with depth, as one might expect if they were in various stages of dissolving, suggesting that &ldquoburied nodules neither grow nor dissolve after their burial in the sediment column.&rdquo 6

But if nodules don&rsquot dissolve after burial, then their absence in the deep sediments implies that nodules simply were not being formed when the deeper sediments were deposited. Secular scientists have suggested possible explanations for this, 5 but these proposals tacitly acknowledge that past conditions were significantly different than those of today, and this violates uniformitarian assumptions. In the case of manganese nodules, the present is definitely not &ldquothe key to the past&rdquo!

Creation Explanation

Creation scientists have an extremely straightforward and logical explanation for the rarity of manganese nodules within the deep seafloor sediments: Since nodule growth is apparently possible only at the surface or below a shallow layer of sediment, the absence of nodules in the deeper sediments implies that these deeper sediments were simply deposited too rapidly for nodules to form and grow. 7 This is consistent with the proposal of creation scientist Dr. Larry Vardiman that the deposition of seafloor sediments was initially very rapid during and shortly after the Genesis Flood but then decreased to the slow and gradual rates we observe today (Figure 2). 8

This argument is strengthened by the fact that secular scientists seem to have seriously underestimated the true rates of nodule growth. Although growth rates can vary considerably due to a number of factors, nodules have consistently been observed growing at rates hundreds of thousands of times faster than the slow rates calculated from radioisotope dating methods. 4,9,10 This implies that deposition of the deeper sediments would had to have been even more rapid in order to prevent the formation of nodules at these faster growth rates. Moreover, this glaring discrepancy between the calculated and observed rates of nodule growth is just one more indication that there are serious problems inherent in radioisotope dating methods. 11

Planation Surfaces

If most of the seafloor sediments were rapidly dumped into the ocean basins, then one might expect additional geological clues to fit this interpretation of the data. Is this the case?

Across every continent, we observe flat or nearly flat erosional surfaces that extend for many miles. These erosional plains are known as planation surfaces (Figure 3). 12

Each planation surface marks a very specific event in time and therefore allows insight into the geological history of that area. These surfaces are especially important since they are observed on a global scale. The deepest global planation surface is called the Great Unconformity.

In many places around the world, the Great Unconformity resides at the Cambrian-Precambrian boundary. Uniformitarians believe this surface, and others like it, formed as the sea level slowly rose, invading (transgressing) the land and forming a broad zone of coastal erosion. Their explanation for the formation of this global surface is problematic and falls outside traditional uniformitarian thought. 13

Secular geologists have identified at least five other global planation surfaces that were supposedly formed as oceans slowly flooded the continents and later drained off in cyclic succession. Secular scientists believe these planation surfaces define the tops and bottoms of what are termed megasequences. The Great Unconformity is, in fact, the base of the first of these megasequences, known as the Sauk sequence. The upper erosional boundaries of each megasequence are believed to have been created as each new megasequence, during its deposition, eroded the top of the previous sequence. These megasequence-bounding erosional surfaces, like the Great Unconformity, have been traced across the globe and yet the mechanism of their formation continues to perplex secular scientists. 12 This is because modern erosion creates V-shape stream channels across all exposed land it does not create planar surfaces. So if no modern geologic process can account for the creation of flat planation surfaces, then how did they form?

Source of the Sediment: The Genesis Flood

The answer requires a unique global erosional event: the Genesis Flood. At the start of the Flood, we would expect the formation of a vast erosional plain like the Great Unconformity as immense tsunami-like waves swept across the continents, stripping away soil in a matter of hours or days.

As the Flood progressed, the water oscillated, retreated, and advanced in cycles, resulting in the formation of additional megasequences and their associated planation surfaces. Thus, these erosional episodes (planation surfaces) between megasequences do not represent millions of years but merely brief hiatuses as the floodwaters surged.

At the end of the Flood, the newly formed ocean crust cooled and subsided, deepening the ocean basins and lowering sea levels worldwide. This caused the floodwaters to recede on a vast scale, likely as massive sheets of rapidly moving water drained off the continents. 14 &ldquoAnd the waters receded continually from the earth. At the end of the hundred and fifty days the water decreased&rdquo (Genesis 8:3).

It should also be noted that the warm, mineral-rich oceans during and after the Flood would also have greatly stimulated the growth of phytoplankton, likely resulting in many algal blooms. Since zooplankton (such as foraminifera and diatoms) can feed on phytoplankton, it&rsquos likely that they too greatly increased in number, and their abundant remains would also have contributed to the accumulating sediments during the post-Flood period. 15

Evidence for Rapid Erosion

In some cases, inclined strata of varying hardness on the continents have been beveled flat (Figure 4). This is consistent with catastrophic erosion by rapidly moving sheets of water but inconsistent with slow and gradual erosion over long periods of time. 12 Such catastrophic sheet erosion would have dumped enormous quantities of sediment into the ocean basins in a short amount of time. The scarcity of manganese nodules in the deeper seafloor sediments is consistent with this rapid deposition, and their abundance in the upper seafloor sediments is consistent with a gradual decrease in sedimentation rates in the millennia after the Flood.

Implications for the Seafloor Sediment and Ice Cores

But such rapid deposition invalidates the timescales that secular scientists have assigned to the deep seafloor sediments because these sediments are assumed to have been deposited slowly and gradually&mdashnot catastrophically&mdashover many millions of years. Moreover, it also invalidates the age scales that have been assigned to the deep ice cores from Greenland and Antarctica since these age scales are ultimately tied&mdashvia a complex network of circular reasoning&mdashto the dates that have been assigned to the seafloor sediments! 1,16

Hence, the Bible&rsquos true history of a global flood and a young earth enables us to make far better sense of the seafloor sediment and erosional data than can uniformitarian, old-Earth assumptions and speculations. The evidence points to a young earth!

Click here to read &ldquoIce Cores, Seafloor Sediments, and the Age of the Earth, Part 1.&rdquo

Click here to read &ldquoIce Cores, Seafloor Sediments, and the Age of the Earth, Part 2.&rdquo


Author information

Affiliations

Center for Marine Biodiversity and Conservation and Integrative Oceanography Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA

Department of Life Sciences, Natural History Museum, London, UK

Independent Consultant, London, UK

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

Contributions

L.A.L. initially conceived the manuscript and developed the figures and tables. L.A.L., D.J.A. and H.L. wrote the manuscript together.

Corresponding authors


Unmapped Areas of the Seafloor

I had a little bit of orientation problems on that one.

But really cool! There's so much to explore still on our own planet!

I had to look at it for awhile for my mind to eventually make sense of it. Zooming in helped

You can see the search zone for mh370 off the west coast of Australia. They actually mapped quite a large area as a result of the search.

Came here to say this. Crazy huh!

I’m guessing this doesn’t include classified data like us navy or others have. Bathymetric data is extremely important for submarines.

"in detail" being the key word in the description too. We have coarse data for pretty much all of it.

I don't know how many military subs are traveling along the sea floor, but I'm sure that the major navies of the world have some pretty good secret maps.

This is some true map porn. So often, we get simple colored states with statistics. While interesting sometimes, I don't spend a lot of time looking at them. This, on the other hand, from the projection to the data displayed to the detail is a fascinating map.


Watch the video: QUEST-CE QUE LES GÉOSCIENCES? (September 2021).