Oceanography - Chapter 3 - Studying the Ocean

Why does visible light easily pass through the atm and not water?

Visible light passes through air more easily than water because air is much less dense, so there are fewer molecules for the light to interact with.

In water, light is more likely to be absorbed or scattered by water molecules and particles, so its intensity decreases quickly with depth.

Why do open oceans have greater light penetration than costal waters?

Costal waters are more turbid with suspended sediments

Scientists use what to “see underwater”?

Sound waves ; and the speed of sound is affected my temperature and pressure

What are some constraints of studying the oceans?

• Very deep

• High Pressure

• Salt water is corrosive

• Unstable conditions on ocean surface

• All this culminates to it being very expensive

  • One deep sample could cost $10,000-$70,000

pressurized environments

• In space = 0 atm pressure

• Earths surface = 1 atm pressure

• Oceans = Pressure increases 1 atm every 10m depth

Problems with working in salt water

• Can conduct electricity and cause short circuiting of equipment

• Corrosive to metals

• Allows for bacteria and biofilm to collect, fouling the equipment, and attracting other organisms

Bathymetry

the measurement and mapping of the depth and shape of the ocean floor.

Think of it as topography, but underwater:

Depth Sounding

• Depth soundings using a lead line

  • However time, weight, wind/current, and slack of the line can make this method difficult

  • It’s not really done like this anymore in favor of echo sounding

Methods of measuring bathymetry

• Depth Sounding

• Echo Sounders

  • Multibean sonar

Echo Sounding

• Instead of using a lead line, a sonar is attached to the bottom of the boat.

• Sonar - emits sound waves a detects the echo returning

• Continuous data being collected under a moving ship

• This is the modern standard

What is multibeam sonar?

A sonar system that sends multiple sound beams over a wide area of the seafloor, allowing scientists to create detailed bathymetric maps much faster than traditional single-beam echo sounding.

Seafloor sediments

are basically layers of material that accumulate on the ocean floor over time. This matters because those layers can act like a historical record of the ocean and Earth.

Methods of collection seafloor sediment samples:

• grab samplers

• Box corers

• Gravity cores

• Drilling Ships

• Dredges

• Seismic sound (no actual sediment, just data)

Grab samplers

claw devices that are lowered to the seafloor and grab a small sample of surface sediment.

Box corers

are another tool used to collect seafloor sediment, but they remove a relatively large, intact block of the upper sediment

Gravity Cores

is a tool used to collect deeper seafloor sediment cores. Your presentation says these cores can be about 2–50 meters deep.

It works by using gravity and the corer's weight to drive a long tube down into the seafloor sediment. When it's pulled back up, the tube contains a vertical column—or core—of sediment

Drilling ships

• Ships used to collect the deepest seafloor sediments that are even older in time

• 100s - 1000s of meters of cores

Dredges

is essentially dragged along the bottom, where it scrapes/scoops up rocky material, which is then brought back to the ship for study.

Seismic Sound Profiling

A technique that uses sound waves reflected from sediment layers beneath the seafloor to study their structure, especially where physical sediment cores aren't available

Niskin and Van Dorn bottles

are devices used to collect water samples from specific depths in the ocean so the water can be brought back for lab-based chemical and physical analysis

CTD

An instrument that continuously measures conductivity, temperature, and depth through the water column, helping identify differences between water layers. It can also measure O₂, pH, turbidity, and fluorescence.

Measuring Currents

• Measure speed and direction

• For large scale currents, there can be indirect measurements

  • Model these large currents for sal and temp distributions

• For small currents, we can get more specific direct measurements using passive samplers or current meters

Types of passive samplers

• Drifters

• Drogues

passive devices are used to measure ocean currents, particularly their speed and direction

Drifter passive sampler

• they float on the surface and measure surface currents

Drogues passive sampler

• use a tether parachute beneath the surface, and weights, to measure deeper currents

Current Meters

Instruments held at fixed positions that measure the speed and direction of water moving past them, often at different depths.

• Can be deployed at different depths

Accoustic Current meters

A device that measures water movement using sound waves reflected off moving particles. It uses the Doppler effect to determine current movement.

Doppler Affect

pitch increases as particles move closer to the meter

Acoustic Tomography

A method that uses an array of sound sources and receivers over hundreds of kilometers to study large-scale ocean conditions

Challenges of biological oceanography

• Ocean life moves in three dimensions

• Large range in body size

• Many mobile species

• Fragile species

• Deep sea species cannot survive being brough to the surface

Types of nets used to catch biological samples

• Otter trawl

• Purse Seine

• Plankton Net

• Drift net

Types of Autonomous Under Water Vehicles (AUVs)

• Argo floats

• Gliders (look like a plane drone)

Satalite Data

• Can survey in days, not years

• Observe daily, yearly, and long term changes

• Limited to only surface water data

• Monitors weather, currents, waves, temp/salinity, sediment plumes, plankton etc