Leah Johnson: Physical and Chemical Properties of Ocean Water (There’s More Here Than Just Fish!) , July 26, 2015

NOAA Teacher at Sea
Leah Johnson
Aboard NOAA Ship Pisces
July 21 – August 3, 2015

Mission: Southeast Fishery – Independent Survey
Geographical Area of Cruise: Atlantic Ocean, Southeastern U.S. Coast
Date: Sunday, July 26, 2015

Weather Data from the Bridge:
Time 12:38 PM
Latitude 34.24389
Longitude -76.6625
Water Temperature 23.75 °C
Salinity –No Data-
Air Temperature 28.6 °C
Relative Humidity 68 %
Wind Speed 12.6 knots
Wind Direction 67.01 degrees
Air Pressure 1014.8 mbar

Science and Technology Log:
The primary purpose of this cruise is to survey reef fish. Our main task is to collect data pertaining to presence and number of fish species, species length frequency, and sample materials for fish age and growth. However, other types of measurements are being made as well. For example, the CTD is an instrument that measures different properties of ocean water with depth. It is deployed every time the fish traps are dropped.

CTD instrument

The CTD sits on the starboard side of the deck of NOAA Ship Pisces.

The acronym “CTD” stand for conductivity, temperature, and depth. The instruments that measure these properties are affixed to a metal cylinder called a rosette. A range of sensors can be attached depending on what needs to be measured. Additionally, containers can be attached to the frame in order to collect sea water samples at different depths. When the ship reaches the designated coordinates, the survey technician calls to the deckhands and instructs them to use the winch to lower the CTD to a designated depth, and then haul it back up.

Deckhands assist with lowering the CTD

Deckhands assist with lowering the CTD.

Below you can see a graph of the data collected earlier in the week:

CTD Data

CTD Data

The y-axis represents depth in meters. The CTD actually measures water pressure, which is then converted to depth. Pressure and depth are directly related: as depth increases, pressure increases.

There are several different properties represented on the x-axes, shown in different colors:

light green = oxygen (mg/l)
orange = conductivity (S/m)
dark green = temperature (°C)
purple = salinity (PSU, or ppt)

What do these measurements mean? As depth increases, temperature decreases. Sunlight warms the sea surface, and wind and ocean currents distribute this heat energy throughout the upper waters. Beneath this mixed layer, temperature decreases steadily with depth. In deeper water (not at this location), this rate of change decreases and the temperature of deep ocean water is nearly a constant 3 °C. Salinity refers to the concentration of dissolved salts in the water. Average ocean salinity is 35 ppt (parts per thousand), though this varies by a few parts per thousand near the surface. Increased precipitation, runoff, or melting of sea ice can decrease salinity, and evaporation and ice formation can increase salinity. Conductivity (measured in Siemens per meter) is a measure of how much current can travel through the water, and this is affected by both salinity and temperature. Finally, fish and other marine organisms require dissolved oxygen to breathe. By measuring the amount of oxygen at different levels in the water column, we can determine how much sea life can be supported in a given area. Dissolved oxygen in the ocean comes from mixing at the surface, and is also produced by photosynthetic organisms. As temperature and salinity increase, dissolved oxygen levels decrease. Additionally, temperature and salinity data can be used to determine the water density, or the mass of water per unit volume. Different fish can tolerate certain ranges of all of these chemical and physical parameters.

With respect to the fish survey, this information is important because we can monitor the conditions of the water near the ocean floor where the traps are located. For scientists who are interested in characterizing reef fish habitat, this data is a critical component of their research.

There are other ways in which this data can be used. The depth profiles of each of the chemical and physical properties at a given site can be compared to other local sites in order to identify any spatial anomalies. This is of great interest for seafloor mapping and ocean exploration cruises. For example, a change in conductivity and temperature at a site in the middle of the ocean could indicate the presence of a hydrothermal vent. Or, a decrease in salinity in a region along a coastline could indicate freshwater runoff.

Additionally, as measurements are made at similar locations over a period of time, temporal changes may be observed. This could reveal seasonal changes, or a long-term trend. Because we are observing an increase in average global temperatures and experiencing global climate change, it is critical to collect data that can be used to assess changing ocean conditions.

Personal Log:
“Will you be eating a lot of fish on the ship?” I heard this question a lot before I left for this cruise. I wondered myself. It seemed reasonable that fish would be prepared for meals because, well, we will be living at sea! On the other hand, I wondered if everyone on board would be sick to death of fish because we would be looking at them all day. As it turns out, fish is prepared for nearly every meal; however, there is often another meat option, as well as a variety of other non-meat dishes. Now we know!

ship mess

Ship mess

Did You Know?
There are many fish that make a grunting sound. When we have tubs full of tomtates in the wet lab, it sounds like a bunch of miniature pigs making snorting noises!

tomtates and nurse shark

Still from video of tomtates near a trap. A nurse shark can be seen in the background.

Daniel Rivera, Day 2, First Day Out At Sea, Jul7 17, 2014

NOAA Teacher at Sea

Daniel Rivera

Aboard the Ship R/V Fulmar

July 16-24, 2014 

 

Mission: Water conductivity, temperature, and depth (CTD) readings; marine bird and mammal counts

Geographical Area: Gulf of the Farallones and Cordell Bank National Marine Sanctuaries; Sonoma County Coast, Pacific Ocean

Dates: July 17, 2014

 

Weather Data from the bridge: Wind speed variable, less than 10 knots; wind waves less than 2 feet; visibility about 3 km, temperature range from 57-66 F

 

Science and Technology Log: During our week long cruise we take CTD readings with the CTD device and record marine bird and mammal sightings from the Gulf of the Farallones and Cordell Bank Marine Sanctuaries, marine protected areas (MPA) off the northern coast of California. CTD readings tell us the levels of salinity of the water and the temperature of the water, and the depth at which these two conditions exists, along with the number of marine birds and mammals in the area, can tell scientists a lot about the health of the ocean. The scientist aboard the R/V Fulmar are looking for correlations between the number of birds and mammals along the transects and the CTD readings. Are conditions changing, staying the same? Has any kind of natural or manmade disaster affected the numbers?

Today’s mission was extra special because these two MPAs are currently undergoing a proposed expansion, and for the first time the science team took samples from this proposed expansion area. The transect lines covered today were 14, 13, and N13.

An expansion of these two MPAs would increase the area allotted to the protection and preservation of our coastal waters and, by extension, marine life within those waters. The reason behind the expansion of the MPAs is due to the upwelling that starts north of the current MPA, at a spot along the coast called Point Arena. The large amount of upwelling that begins at Point Arena eventually moves down the coast with the California Current, creating the spectacular assortment of rich life that exists in the Gulf of the Farrallones and the Cordell Bank Sanctuaries. By protecting the starting point of the massive upwelling, we are ensuring the protection of the explosion of life that continues along California Current. 

 

Personal Log: Todays begins with my alarm clock going off at 5:30 am. Why so early? Because we leave port no later than 7am, and with 11 people on board one ship, I don’t want to be the last one in line for the bathroom. Plus I like to have coffee in the morning. And I’m a little nervous because it’s my first day at sea. Any one of these excuses work. 

Once everybody’s is up and ready to go, my first task is go over emergency procedures with Dave Benet, the mate of the ship. We go through the safety protocols and when done I don the immersion suit, which looks like a giant red gumby suit and leaves you with as much dexterity as do ski mittens. I’m told it will keep you warm in the water if you manage to zip it up before you hit the water; I do not want to test out this theory, so I take Dave’s word.

This gumby-looking outfit, called an immersion suit, will keep you afloat and warm if you happen to abandon ship.

This gumby-looking outfit, called an immersion suit, will keep you afloat and warm if you happen to abandon ship.

As we head out to sea and towards out first transect, everybody is excited that the water and weather are calm; very little to no wind, glass-like water, no waves. This is a treat for all on board because during the last cruise the waves were so bad that the boat had to return to shore because it was too dangerous to be out at sea.

The first task of the day is on the top deck, where scientists monitor the marine birds and mammals within the transect line. As birds and mammals are spotted along the transect, data is collected about each organism. Among this data is type of organism, the direction of travel, the sex (if known), age (if known), the behavior, and location of the organism. There is one spotter for birds and two spotters for mammals, and as each organism is spotted, a series of numbers and names is called out to the recorder, the scientist who inputs the data into a log on a laptop. Today is mild, weather-wise, so the crew calls out the information and logs it in as the boat gently sways back and forth along the transect; last month I would’ve seen the same crew holding on for dear life, trying to keep in their meals, while still recording the data. 

Because I’m not trained on how to spot birds and mammals, my task while on board is to assist with CTD and plankton net deployment. Along predetermined spots along the transect the boat stops and we drop the CTD to about 5 meters above the seafloor. Our first CTD reading had us at 200 meters to the bottom, so we sent the CTD down to 195 meters below. Once it hits 195 meters we immediately bring it back up and secure the device back to the boat. After that we then launch the hoop net, which is a big plankton net that is dragged behind the boat till a depth of 50 meters. Once it’s down to 50 meters, we then bring the net back up to the boat, empty the contents into a jar, and add preserving agent to bring the samples back to the lab. Once at the lab the plankton samples are counted and recorded, giving us a picture of the biological activity in that particular area of the transect.

The CTD is deployed down to a depth that is 5 meters above the surface and collects conductivity, temperature, and depth data.

The CTD is deployed down to a depth that is 5 meters above the surface and collects conductivity, temperature, and depth data.

The handling of the hoop net and CTD take practice to properly deploy, and the parameters of the deployment have to be very exact or else we risk losing the very costly tools. If the measurements for depth are not accurate, the CTD could hit the bottom of the ocean, causing damage to the CTD. We could also risk snagging and losing the hoop net if it is dragged along the bottom, so these measurements are doubled- and triple-checked by the captain and the scientists to avoid costly mistakes. 

Did you know? Just as there are hotspots of magma flow on land, there are hot spots of life at sea. The transect lines monitored aboard the R/V Fulmar help to pinpoint these hotspots of sea-life activity. 

Question of the Day? What does the acronym MPA stand for? Provide 2 examples of MPAs.

New Term/Phrase/Word: CTD; hoop net.

Something to Think About: The more you eat while on a cruise, the less seasick you will become, which is counterintuitive.

Challenge Yourself: How might wind waves affect the efficiency of a cruise?