A Monster of Nets: The MOCNESS

Among the net systems used by biological oceanographers, the MOCNESS ranks among the most involved and invaluable. Our MOCNESS (Multiple Opening and Closing Net and Environmental Sensing System) consists of a 1m2 metal frame with 10 stacked nets nested inside of it. The numerous nets are used to target specific depth ranges for sampling so that scientists can examine what kinds of plankton live within different layers in the ocean. The nets operate in sequence: as one net closes, the net directly above it opens. For instance, in our tows we keep the bottom net open as the net descends to 1000m, then we snap it shut, opening the next net to sample from 1000m-800m and so on. As with the Bongo, the MOCNESS filters water into a cod end, so at the end of each deployment we have 10 cod ends each full of plankton goodies!

The MOCNESS.

The top of the frame is loaded down with sensors that measure the physical environment as the net moves up and down the water column. Data are collected on temperature, salinity, oxygen, fluorescence, transmissometry and more. This allows scientists to place the different organisms in each net in a particular environmental setting. Counter to our land-based intuition, the ocean operates on 3 dimensions and more often the water above and below a single area has distinct properties and animals. In terrestrial ecosystems, a similar parallel would be a rainforest, where the canopy harbors unique fauna and light levels compared to the forest floor.

The beast of scientific innovation is also coupled with the Herculean task of deploying, operating, recovering, and maintaining the MOCNESS and later processing and analyzing the data it collects. Deploying and recovering the MOCNESS requires at least 4 scientists and a marine technician who oversees the process. It all begins with “cocking” the MOCNESS: manually pushing the nets to the top of the frame and securing them to their trip controls so that they are poised to snap shut. Next, cod ends are secured (with some help from electrical tape) and a deck check is performed to ensure all instruments are functional. One scientist remains in the electronic lab to “fly” the MOCNESS and control the software while 3 scientists and the marine tech lower the MOCNESS into the water with the A-frame.

A view of the control room while MOCNESS operations are underway.

The MOCNESS is then dropped to depth and flown for several hours, with the scientists carefully observing and noting the data relayed from the sensors and winch to ensure smooth sailing. When the MOCNESS surfaces, a team of scientists and the marine tech recover the instrument, thoroughly rinse the nets for any plankters stuck in the mesh and begin hauling the cod ends to the lab for processing. Many times nets may become ripped in the process of towing, which requires further work. This cruise we even bathed, scrubbed and soaked in vinegar all the MOCNESS nets in an attempt to remove the booger-like phytoplankton that clogs our mesh.

Recovering the MOCNESS.

Processing the MOCNESS involves each cod end being separated into different splits for preservation or analysis. The preserved splits may be placed in ethanol if the scientist wants to examine the DNA of the organisms, or in formalin if they are more interested in the shape and morphology. Another split is further separated into size classes using sieves and filters to measure biomass and isotopes back on land. Repeating this process for ten nets requires stamina and a positive attitude as we work long and odd hours. Morale boosts through fun playlists, interesting conversations and chocolate-covered treats aid in carrying us through the finish line. 

Despite the time and patience the MOCNESS demands, the excitement and mystery of opening each cod end and discovering what weird creatures we secured never gets old. Furthermore, these data provide an informative snapshot into the complex food web that sustains our coast.

-Dante Capone (Decima lab)

The Deep Cast Chronicles: Colder, Darker, Denser…Smaller

If there’s one thing you can count on as a scientist aboard a research expedition at sea, it is the infamous “Deep Cast”. This is a CTD cast that goes deeper than any other. The Deep Cast is a big deal logistically because it takes over an hour to get to its final depth (4,000m at 60m/min), is interesting scientifically because it samples very old water, and is coveted by all on board because it is the shrinking Styrofoam cast…

Everyone on board partakes in the ritual of decorating anything made of Styrofoam in preparation for the Deep Cast. Our devoted resident marine technician Caitlyn offered her battalion of rainbow sharpies (72 strong!) for us to use, and we got to work. 

Jamee Adams (Diaz lab), Anya Stajner (Decima lab), Rob Lampe (Allen lab), Clay McClure (Bowman lab), and Dante Capone (Decima lab) decorating Styrofoam and staying healthy.
Clay McLure, Dante Capone, and Dante’s creation.

Then, we strapped our creations to the CTD wrapped in layers of mesh bags, and sent the whole package down to 4,000 meters. It took over 2 hours for the CTD to travel down, down, down through layers of cold, dense, dark water, and back up to the surface.

Professors Lihini Aluwihare and Kathy Barbeau packing the cups.
Ralph Torres (Aluwihare lab) securing the mesh bags.
Marine technician Caitlyn sending the CTD down to 4,000 meters.

When the CTD came back to the surface with precious North Pacific deep water, the oldest on Earth, everything had changed. Styrofoam heads were deformed and dense, cups were shrunken, and drawings had taken on a more detailed appearance. The increase in pressure down to 4,000 meters forced the air out of the Styrofoam, and caused each piece to shrink. 

Post Deep Cast Styrofoam. 
A Styrofoam shoutout to California Current Ecosystem Long Term Ecological Research (CCE LTER)!

Aside from our treasured oceanographic samples, anyone who made a Styrofoam creation has a more personal souvenir to take home and gift to friends, family, and loved ones, or to keep for themselves as a reminder of this epic adventure. 

A family of cups.

-Jamee Adams (Diaz lab)

Finding the Upwelling Filament

You may be wondering where the ship is going on this expedition. The answer is that it is always changing! Rather than stationary sampling (Eulerian) we are sailing with one continuous water mass and observing the changes within it through time (Lagrangian). Where we are going depends on finding an upwellingfilament (a special chunk of water that is rich in nutrients) and following that chunk of water wherever it moves. 

So what is upwelling?

Upwelling begins with wind. When strong winds blow North to South along the CA coastline, a process called “Ekman transport,” causes deep water to be brought to the surface and pushed offshore. This water is cold, dense, and rich in nutrients (elements like nitrogen and phosphorous needed to make proteins and DNA). These nutrients can fuel growth of primary producers like microscopic algae. The algae is food for small animals, which become food for bigger fish, dolphins, etc—fueling a productive ecosystem! If this chunk of upwelled water moves westward offshore, we call it a “filament” and follow it with our ship.

Black arrow: Wind direction
Blue arrows: Ekman transport

In Search of a Filament!

We can predict when/where upwelling will occur by looking at wind trajectories, and satellite data.

Wind trajectories

Unfortunately, due to continuous cloud cover, we have been unable to utilize satellite data, including sea surface temperature and sea surface chlorophyll. Instead, we have relied solely on data from wind, deployed instruments, and sampling we do on the ship. When we started, we did not observe upwelling, but by Wednesday, July 21 signs of emerging upwelling were observed: a patch of relatively cold water with a high concentration of nitrogen! We can measure nutrient concentrations in the water by conducting CTD casts (see previous post) that give data that look like this:

The y-axis is depth from 0 to 100 meters, and the x-axis shows temperature, nitrogen, and fluorescence (a proxy for chlorophyll from algae). 

We continue to track the filament once we have found it, and observe the changes to the chemistry and biology as the water mass evolves.

-Monica Thukral (Allen lab)