Nathan Pierantoni, Tuesday 4.5.11

NOAA Teacher at Sea: Nathan Pierantoni

University of Miami Ship R/V Walton Smith

South Florida Bimonthly Hydrographic Survey

Florida Bay

Tuesday, April 5 2011

Weather Data from the Bridge

1400 hrs Local Time

Barometric pressure = 1014 Millibars

80 F

94% Humidity

Visibility = good

Wind S 14 knots

Science and Technology Log

Its Tuesday evening and I am finally taking the opportunity to organize my thoughts. The ship has been a whirlwind of activity since Sunday evening when scientists and crew began arriving and preparing for this 5-day research cruise to the Florida Keys and the Florida Bay. I have done my best to learn as much as I can in my time aboard the Walton Smith. The science that is being conducted on this cruise falls into three different areas of oceanography: physical oceanography, ocean chemistry, and marine biology. At all times there are scientists doing the fieldwork necessary to answer questions in these areas of science. In this log I will discuss the physical oceanography that is being conducted by Nelson Melo, a physical oceanographer, and our mission’s chief scientist.

Nelson is the leader when it comes to the organization and coordination of all of the work aboard the ship. Nelson is thoughtful and helpful, and has provided me with all of the information I need to make sense of the myriad of activities going on aboard our ship. Nelson Works for NOAA, and has multiple degrees in areas of physics ranging from nuclear physics to solid state transistors. He holds a PhD in Oceanography and is passionate about protecting and preserving the ocean. Originally from Cuba, he came to the United States 8 years ago.

Nelson’s work involves the synthesis of remote sensing data that is being shot from space via satellite with corollary data that he is working to collect from our ship as we pass through waters of the Florida Bay. For example, as the ship moves from one location to the next, the water might appear green or deep blue. These color changes are also visible from space and are being collected via satellite. The satellites used to collect this data are scanning the sea and creating multispectral images which, when processed and combined, appear like a color photograph of the ocean. These colors change as the conditions in the ocean change, and can be used to tell scientists about the health of the ocean. From the ship, we are moving throughout the Florida bay in order to sample many different parameters of water quality. One of them is chlorophyll. Nelson is most interested in the amount of chlorophyll in the water, because it serves as an indicator for the autotrophic life in the water column. Put simply, the presence or absence of chlorophyll in the water is valuable scientific information as it relates to many areas of study for ecologists, marine biologists and nearly every scientist who studies the ocean. As we collect water samples from different locations throughout the cruise, Nelson is using a sensor to measure the light as it appears at different depths of water. Today we were in about 7 m of water, and while the chemistry team sampled chlorophyll levels at different depths of water, Nelson put a photosensitive device over the side of the ship and slowly lowered it to the bottom. This device captured the intensity of light as it moved from the surface to the bottom, and all of the data was recorded on his computer. Then, he graphed his results. With the chlorophyll levels that the chemistry department has collected and the information from his submersible, as well as other parameters such as water current, salinity, and temperature he and many other scientists from the University of South Florida will work toward building an algorithm that will allow scientists in the future to use remote sensing from satellites to measure water parameters from space.

In fact, this work is already being done and oceanographers already have the tools to do this very accurately for offshore waters where there is less distortion from the reflection of the bottom or noise from particles in suspension due to shore currents or dissolved organic materials. Nelson is part of a team of scientists that is fine -tuning the algorithms used to measure water parameters from space that is more accurate for inshore waters.

Personal Log

Wow! Its been a busy couple of days!!! There is so much going on its kind of hard to know where to begin. The thing that I think I most appreciate right now is just how hard everyone is working. There hasn’t been much time to ‘mingle’, because everyone on the ship has a job to do, and it’s a full time operation. I think this is mostly due to the fact that this cruise it in relatively shallow waters, with many stops in close proximity to one another. And the ‘stops’ aren’t even really stops; they are simply the places where we slow down enough to do a CTD (which I’ll explain in a chemistry log tomorrow) or to do a net tow or to run the submersible photometer. Other than that, there is recording, chemistry, data analysis, and preparation for the next station to be done during transit times. The ship just keeps on following our prescribed cruise plan, from station to station, and if there is work to do during mealtime then everyone finishes their work before they get to eat. And the boat is divided into day shifts and night shifts for the science crew, and 6 hour on and off shifts for the ships crew. I appreciate that Nelson is packing in as much science as he can into this operation, because its obvious that great amounts of resources are going into these studies. I feel very lucky to get the opportunity to participate in this operation!

It is too bad that there are some other members of this cruise who I will not get to know as well, simply because they are asleep while I am awake. The ship is the most lively during the shift changes, when everyone is up for a meal of to catch each other up on the progress we had made during the day.

A special note to my classes:

Keep writing on the blog with questions, and I will keep catching opportunities to answer them, to upload pictures, and to go into more depth tomorrow about the chemistry and biology that are going on on the ship!

Here is the machine that Dr. Nelson uses to take his measurements, the PRR 2600.

PRR 2600
PRR 2600

Here is a shot off of Dr. Melo’s computer, it is recently acquired satellite data measuring the light specra from the earth. Notice the curvature at the left hand side of the screen, that is how the satellite sees the earth.

Dr Melo's computer
Dr Melo's computer

Here is the PRR 2600 at the surface of the water.

PRR 2600 in the water
PRR 2600 in the water

This is data from the ship. Notice duplicate measurements for parameters such as temp and salinity, and notice four sig figs. Those are real measurements, to a 10,000th of a degree!

data from the ship
Data from the Ship

Here is a shot of Dr Melo and with his submersible. He is slowly lowering the machine to the bottom while it takes accurate measurements of the light from the sun. At different depths the spectra of light change, and the amount that they change is related to the amounts of chlorophyll and other water parameters. This type of information from near-shore locations is what scientists will use to build accurate algorithms for interpreting future remote sensing data.

Dr. Melo lowering his Submersible
Dr. Melo lowering his Submersible

Robert Lovely, April 4, 2008

NOAA Teacher at Sea
Robert Lovely
Onboard NOAA Ship Gordon Gunter
March 31 – April 12, 2008

Mission: Reef Fish Ecological Survey
Geographical area of cruise: Pulley Ridge and the West Florida Shelf, Gulf of Mexico
Date: April 4, 2008

A “rosette” is used to hold the instrumentation for the CTD.  Here we see the rosette being lowered down into the water column by way of a crane mounted on the GORDON GUNTER.
A “rosette” is used to hold the instrumentation for the CTD. Here it is lowered down into the water by way of a crane.

Weather Data from the Bridge 
Visibility:  12 miles
Wind Direction:  150° (SE)
Wind Speed:  18 knots
Sea Wave Height:  2-3 foot
Swell Wave Height:  1-2 foot
Seawater Temp: 24.4 degrees C.
Present Weather:  Clear

Science and Technology Log 

We begin and end each day by making a CTD profile of the water column at our sampling site.  CTD refers to conductivity, temperature, and depth, but other parameters, such as dissolved oxygen (DO), also may be measured.  Conductivity is an expression of salinity, which at our location on Pulley Ridge is pretty uniform throughout the water column.  As we see from the graph below, however, both DO and water temperature do vary with depth. Temperature is uniform in the top layer of water and then begins to drop steadily with increasing depth from about 20 meters down.  This portion of the water column, where temperature declines rapidly with depth, is called the thermocline.  The temperature profile on our graph shows that a subtle thermocline extends nearly to the bottom at Pulley Ridge. This may help explain why certain shallow-water organisms are able to survive in this relatively deep water. In other locations the same depth may be well below the thermocline and therefore in water too cold for shallow-water species to live.

Above is a graph of the CTD profiles generated at Pulley Ridge on April 4, 2008.  Software linked to the CTD instrumentation on the rosette generates salinity, temperature, depth and oxygen profiles of the water column.  Note that the double lines on the graph result from the roundtrip made by the rosette down to the bottom and back.
Graph of the CTD profiles from Pulley Ridge. Software linked to the CTD instrumentation on the rosette generates salinity, temperature, depth and oxygen profiles of the water. The double lines on the graph result from the roundtrip down to the bottom and back.

Dissolved oxygen is normally high at the surface due to the mixing effect of wave action. But oxygen concentrations can be high in the deeper thermocline as well simply because cold water can hold more oxygen than warm water.  Our graph above illustrates this relationship by exhibiting an increase in dissolved oxygen concentrations at depths between 20-45 meters.

This remotely operated vehicle (ROV) carries both a video camera and a still camera.  The yellow umbilical shown in the foreground supplies power and control signals from the GORDON GUNTER.
This remotely operated vehicle (ROV) carries both a video camera and a still camera. The yellow umbilical shown in the foreground supplies power and control signals

Marine scientists employ different types of underwater vehicles to collect data on deep coral reefs, and the different vehicle types may seem a bit confusing at first.  Three important underwater vehicles are Submersibles, AUVs, and ROVs.  Submersibles typically refer to human-occupied vehicles, where a pilot climbs inside and drives the vehicle around like a small submarine.  The most famous example is Alvin, a submarine operated by the Woods Hole Oceanographic Institution. AUVs, in contrast, are Autonomous Underwater Vehicles that are programmed to perform specific functions, such as bathymetric mapping.  AUVs are robotic— they are completely independent, having no wires to the surface.  Finally, ROVs are Remotely Operated Vehicles, which are tethered to the ship by means of a cable and umbilical.  The ROV captures video and still images, and is driven by a pilot from a control room onboard the ship.  While utilizing bathymetric charts created during earlier cruises, our mission on Pulley Ridge and the West Florida Shelf employs only the ROV.

Rob finds out that it’s interesting, but difficult, driving the ROV.
Rob finds out that it’s interesting, but difficult, driving the ROV.

Today we made three video transects (dives) with the ROV, each lasting about two hours.  Each dive followed a predetermined course, as we began working our way north along Pulley Ridge.  The depth of our dives normally ranged between 200-230 feet, with the ROV gliding about three feet above the reef. The ship towed the ROV at speeds that typically ranged from .5 to 1.3 knots.  However, because of the slack in the tether, the ROV itself had a remarkable range of speeds. In fact, skilled pilots can bring the ROV to a dead stop (while the ship continues to move) in order to pause for nice steady close-up shots of bottom organisms.  I was very impressed by this flexibility of motion and the freedom it offered the pilot to search around the reef for organisms hiding in nooks and crannies.

Personal Log 

I was given the opportunity to take the helm of the ROV during one of our video transects. I found this experience to be fun and somewhat akin to playing a video game.  However, I also found driving the ROV to be much more difficult than it looks.  It gave me a greater appreciation for the skill of our veteran pilots, Lance Horn and Glenn Taylor.