Language selection

Government of Canada / Gouvernement du Canada

Search

Plankton electronics and instrumentation laboratory

Learn about the equipment we use to sample the ocean.

On this page

CTD Rosette water sampling instrument

The CTD Rosette measures the conductivity, temperature and pressure, and depth of seawater, which explains the acronym.

The CTD often has additional channels to accept data collection from other sensors. The Rosette unit is a series of sample bottles that can be closed at any depth. The water from that depth is then brought to the surface for analysis.

As the CTD Rosette goes through the water column, it sends information up to be displayed on the shipboard computer.

We use several different CTD sensors to measure different ocean properties.

Conductivity

Higher salinity (saltier) water is related to the electrical conduction in water. We don't measure salinity directly. Instead, we measure conductivity and convert to salinity using a mathematical formula.

In the northeast Pacific, salinity usually increases with depth. In other areas, salinity may decrease with depth due to colder fresh water existing under warmer saline water.

Temperature

We record temperature in degrees Celcius. We usually find higher temperatures at the sea surface, since sunlight and air will warm the water in the summer. During the winter, the air will cool the surface layer. Temperatures generally decrease with depth.

Depth

We measure depth as a pressure increase within a fluid-filled container. Each 10-metre increase in depth is approximately equivalent to 1 atmosphere of pressure.

Most of our casts are to 500 metres, water depth permitting.

Light transmission in water column

We measure water clarity by sending a beam of light through water and detecting how much of the light is received at an endpoint. Less light arriving at the end means the water contains more phytoplankton and/or sediment.

Light from surface

Phytoplankton and zooplankton are affected by how deep sunlight can get in the ocean water.

Twilight (depth of complete darkness) occurs around 125 metres on a sunny day.

Fluorometry

Phytoplankton contain the chemical chlorophyll, which fluoresces, or glows, when we shine a specific wavelength of light on it. The amount of light we detect is a direct measurement of the amount of phytoplankton in the water.

The irregularity in transmission and fluoresence at about 15 metres is at the depth of maximum nutrient levels and the presence of phytoplankton using these nutrients. The phytoplankton have exhausted the nutrients in the upper 15 metres and will continue to move down in the water column as the nutrients are depleted. Storms and wave action (and other processes) will mix the upper water column and stir the nutrients up again.

Water bottle sampling

We take samples from bottles to test for:

Sampling the water from various depths on the CTD Rosette gives us an insight into various chemical and phytological (relating to plants) properties, including:

Ocean drifter

The drifter follows a body of water over a time period.

Echosounder

An echosounder sends a short pulse of sound at a given frequency into the water from a transducer (underwater speaker) mounted on a ship. Fish or plankton in the water column will reflect the sound pulse. This is because they have different relative densities to the water column, due to swim bladders or oily body composition.

We receive the reflected pulse and:

The intensity of the return signal is measured as a voltage (intensity proportional to voltage) and converted to a relative biomass.

We use a scientific echosounder running at 100 kilohertz to detect plankton down to about 7 millimetres in length.

Environmental sampling net

The Bedford Institute of Oceanography, Net Environmental Sampling System (BIONESS) is a series of 9 nets. From a shipboard computer connecting to the BIONESS via a cable we're able to open and close the nets in sequence to sample various depths.

We tow the BIONESS nets obliquely (diagonally) through the water at given depths. A CTD unit is attached to the frame of the BIONESS to display:

We use our BIONESS in combination with a scientific echosounder to strategically sample locations of high biomass within the water column.

A flowmeter on the mouth of the BIONESS gives us an estimate of the amount of water sampled per net. We preserve any animals captured within each net in formalin (a solution of formaldehyde and water) for later species composition and biomass estimates. The BIONESS serves as one way to calibrate acoustic return with actual biomass.

Bongo net

Bongo nets provide a vertical sample of the zooplankton from a depth to the surface.

The bongo net is made of 2 identical nets that can be towed either vertically or obliquely (diagonally). Bongo nets give us an idea of what plankton exists within a certain depth range, such as from 250 metres to the surface. We lower the nets to a certain depth and quickly bring them to the surface at a rate of 1 metre per second.

All the plankton on the net sides are washed down into a cod end, which is a small bucket at the bottom of the net. One net sample is preserved in formalin for later analysis. The other sample is frozen and can serve as a duplicate if needed. Often, we'll use the formalin-preserved sample to conduct species analysis and then calculate the biomass captured using the frozen sample.

Our bongo nets rarely catch any animals larger than shrimp or juvenile fish larvae (around 30 millimetres) since they can avoid the nets. Our nets use a 236 micrometres (0.236 millimetres) mesh.

Epibenthic sled net sampler

We use the epibenthic sled net to sample zooplankton just above the sea floor. When the net hits the floor of the ocean it opens a door at the front of the net. The sled runs along the sea bottom and captures any zooplankton around 1 metre above the sea floor.

Often other animals get into the net as well, including:

We return all non-zooplankton to the ocean.

Date modified: