Given the record number of shark sightings and attacks off Southern California this spring, it’s about time we had a shark encounter of our own out here! Unfortunately, yesterday marked the first shark-related casualty of the trip: an autonomous carbon flux explorer (CFE) from Jim Bishop’s group at UC Berkeley.
The CFE was scheduled to surface and be recovered by the ship yesterday afternoon. Around 4:30 p.m., as we neared the bobbing blue cylinder of the CFE, a dark fin appeared on the horizon. It circled a couple of times and then chomped down on the CFE, killing the instrument’s signal and any hope for its recovery. We think the shark was a short-fin mako, but we now know for a fact that CFEs resemble seals bobbing at the surface.
Fortunately Bishop’s team (which also consists of technician Todd Wood, graduate student Hannah Bourne, and undergraduate assistant Sylvia Targ) has three other CFEs that they will continue to deploy for Cycle 4. CFEs capture and image subsets of sinking particles in the ocean, as a way to determine how much carbon is transported below the ocean’s surface and what kinds of fecal pellets and detrital fluff dominate production. This information helps quantify the ultimate fates of surface-produced phytoplankton carbon and particles, which are important components of the ocean’s essential role as a sink for atmospherically-produced carbon.
Yesterday we completed our second cross-sectional transect of the upwelling filament we have been studying. This transect complemented the four-day ‘cycle’ we just finished. During cycles, we pick a parcel of ocean water, deploy drifting instruments, and follow those instruments (and the water) for several days, sampling as we go. For transects, we use satellite images of sea surface temperature and phytoplankton chlorophyll to determine the overall extent of the filament, and then draw a line through it and sample along that. Ideally, the midpoint of the line captures the core salty, upwelled, and (presumably) high-productivity waters of the filament, while the endpoints capture lower-productivity waters on either side.
Transects are fast-paced, all-night-through-afternoon affairs. This one encompassed a broad section of the filament, which meant 11 sampling stations spaced 5 nautical miles, or about 45 minutes, apart. So by the time we finished collecting water and processing plankton nets from one station, we turned around and sample at the next station.
Our sampling produced successful and very interesting results! The central (core filament) part of the transect showed cooler temperatures and elevated salinity and fluorescence, consistent with the waters that we measured in Cycle 1, closer to the coast at the newly-upwelled origins of the filament. Plankton samples captured green, phytoplankton-rich waters across the filament, with a notable drop-off to very blue water and reduced biomass at our last station (outside of the filament).
We have moved farther west for Cycle 3, to sample the narrow leading tip of the filament – presumably the initial upwelled waters that have since evolved biologically as they have been transported away from shore. We are still seeing lots of big diatoms (a type of phytoplankton that indicates highly-productive waters), but they are mostly dying and sinking, suggesting that they have already bloomed and run their course. The fact that we are finding them offshore provides evidence for exactly the questions we are out here to explore: how much are nearshore upwelling blooms transported offshore, and what does that mean for the ecosystem?
Today we did our first deep CTD cast of the cruise, to 3500 meters below the ocean surface (over 10,000 ft). In addition to sampling important water column properties, we entrusted the CTD with a precious task: transporting decorated Styrofoam cups! No, we didn’t release Styrofoam into the ocean to perpetuate the global marine debris problem; Styrofoam cups make great cruise mementos and oceanographic teaching props!
Since pressure increases with water depth (more water weight sits above something at 3500 meters than at 10 meters depth), and since Styrofoam is compressible, sending cups down into the ocean squeezes them to less than a quarter of their normal size at the surface. This makes them hardly useful for drinking out of, but great for demonstrating how much pressure a fish must adapt to in order to live several thousand meters below the surface.
Our scientific impetus for conducting deep CTD casts is to measure dissolved organic carbon (DOC) in the deep water column. DOC is released into surface waters by animals that produce or take up carbon and then extrude it in dissolved form – usually from phytoplankton that release DOC as they die, or from zooplankton regurgitating bits of carbon as they feed. The pool of DOC in the ocean is similar to the amount of carbon dioxide in the atmosphere, making DOC an important component of the ocean and global carbon cycle.
Brandon Stephens, a Ph.D. candidate in Lihini Aluwihare’s lab at Scripps, is interested in isolating a carbon component known as ‘refractory’ DOC, which is the unpalatable and therefore very old component of organic carbon in the ocean (nothing wants to eat it, so it just cycles around for thousands of years). Stephens is interested in aging DOC and determining the distinct composition of the pool in the California Current System. He also uses deep DOC as a baseline reference for the upper ocean DOC values that he measures during the cruise. His findings suggest, among other things, that deep DOC in the California Current is some of the most carbon-depleted in the world. The ocean in our backyard continues to surprise us!
June isn’t just a great month for chasing ocean filaments – it’s also a popular birthday month on our Process Cruise! In the past week, we have had three birthdays: Stephanie, Ben, and Cynthia (all, coincidentally, grad students or volunteers in Mark Ohman’s lab).
The science never stops – Ben started his birthday by deploying a midnight MOCNESS tow, and Stephanie and Cynthia each wrangled several Bongo tows and plankton preservationists to celebrate their days – but the chefs baked each of them a birthday cake, and we didn’t let them escape dinner without several rounds of birthday singing. Being at sea is definitely a memorable way to celebrate!
When you’ve spent a long time immersed in the world of oceanography, it’s easy to forget that not everyone speaks your lingo in their daily lives. Someone outside of the ship might be surprised to hear us casually mention a monster onboard: the MOCNESS! Fortunately this is one beast we can (mostly) control. The MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) is a set of ten nets that can be closed at discrete depths, allowing us to sample and compare planktonic organisms from up to ten different parts of the water column. The MOCNESS also has environmental sensors (temperature, salinity, and fluorescence) which collect concurrent physical water measurements to produce a whole picture of the slice of ocean we sample.
Discrete-depth sampling helps us determine things like: how often and far plankton taxa move up and down in the water column throughout the day (many plankton undergo a daily cycle of vertical migration hundreds of meters up and down), whether certain types of plankton prefer specific water depths, and how plankton distributions change in high- versus low-productivity water masses. In the context of our current cruise to study a newly-upwelled, high-productivity filament off central California, the MOCNESS can also cue us in to how water column distributions change between nearshore and offshore waters, and within the filament as it evolves through time.
This afternoon’s MOCNESS brought up mainly euphausiids (krill) and a few mall fishes, but stay tuned for exciting hauls, especially from the night tows! We are halfway through our second cycle, which means we have two more MOCNESS tows for this round (one tonight, one tomorrow afternoon), along with the usual CTDs, Bongo net tows, and various drifter deployments. After a few brushes with the Navy’s missile testing schedule, we have been cleared to keep tracking our filament. Science stands strong!
It’s easy to lose track of days at sea, with our constant stream of science and ever-blue horizon. But in some ways, life on the ship is just like a summer afternoon on land: when you smell the barbeque firing up, you know it’s Sunday – steak night!
On Sunday evenings (and occasionally other days), the crew will set up a charcoal barbeque on the upper decks and flip steaks and asparagus. It’s a little slice of summer grilling in the park – as long as it doesn’t set off the fire alarms!
In other news, we have finished our first three-day cycle and are now transitting farther offshore to sample the core of our filament. Tonight we will deploy the MVP to survey the area, and will then begin our second cycle. We’ll see if our samples will be as full of green algae as in our first cycle, or if we run into a bloom of something new!
Last night we ramped up our sampling in earnest with a marathon cross-filament transect. A beautiful filament of cold, newly-upwelled water emerged off the coast of Morro Bay, California, a few days ago, giving us the perfect feature to begin our first sampling sequence.
We started the transect yesterday evening, just in time to catch a pod of whales and flocks of seabirds feeding off the stern – a sure sign that we were in high-productivity waters! Everyone worked through the night to deploy a rapid-fire 11 rounds of CTDs, trace metal water-sampling, and vertical Bongo net tows as we cut a straight line across the filament. We had several new people who had never done this work, but everyone rapidly got up to speed in the flurry of water sampling, filtering, and zooplankton processing. This transect will give us valuable information on the relative productivity within the filament compared to the surrounding waters. Time and data analysis will tell all, but at first glance we saw very green, high-chlorophyll waters (indicating high phytoplankton productivity) and lots of pyrosomes and jellyfish in the plankton samples.
Tonight we begin the second half of this sequence: a four-day cycle in which we deploy various instruments and follow them as they drift for several days in a parcel of ocean water. One piece of equipment is sediment traps, which capture sediments and organic particles as they sink through the water column. Another piece is an in situ incubator that holds phytoplankton as it floats through the ocean, allowing them to grow under real ocean temperature and light conditions. We will retrieve the arrays at the end of four days, but in the meantime, we will be deploying plankton nets and CTDs several times a day. All of this information will help us understand the evolution of the filament of upwelled water as it evolves over time.
When I tell people that I’m going out to sea, they usually ask: “How big is the ship you’ll be on?” When I tell them (something in the 200 ft range), their response is “I have no idea how big that is, but how do you spend a month at sea on a tiny boat without going crazy?”
So how big does the 277 ft Revelle (the largest ship in the Scripps fleet) actually feel? Here’s one useful way to think about it: At home, if you wake up in the middle of the night and want a snack, how many doors and staircases do you have to go through to get to your kitchen? Probably not more than one or two of each. The Revelle has seven decks (levels) and two main internal stairwells (not to mention 2-3 outside staircases between each deck). The ship is also very compartmentalized to conserve air conditioning and contain potential fires, which means that the main hallway alone is divided into five separate sections. Most of the science staterooms are on the lower deck, which means that a midnight trip to the mess deck (kitchen) entails climbing two levels of stairs and going through five doors. Heavy metal doors. Sometimes tilted sideways in the waves. That part of being at sea could make me go crazy.
Even basic science tasks involve a lot of transit. Getting from the from the back deck, where we do most of our sampling, all the way forward to the main lab can involve four doors and a lengthy hallway, which starts to add up when you’re carrying awkward sample bottles. And with five separate labs plus cold rooms and storage spaces, it’s easy to lose your fellow scientists in the maze!
That doesn’t even include trips up to the bridge, which is the uppermost level where the captain and mates steer the ship and the rest of us spot whales in our sporadic free time, or down to the laundry room, which is an essential destination on a month-long voyage. If you were putting your clothes in the dryer after dinner and suddenly realized that you absolutely must go straight up to the bridge to catch the sunset, you would have to sprint up seven levels and open more doors than I can count. If you forgot your binoculars for whale-watching, you would have to do the whole thing again (or borrow from the bridge). Fortunately the sun doesn’t set until after 8 p.m. these days.
We are grateful for all of the space, though, especially the large labs that allow us to spread out our extensive sampling equipment without bumping elbows. We will be finishing our SeaSoar transects tomorrow morning, after which we will head into Santa Barbara to drop off and pick up several people, before heading back out to sea to begin deploying instruments and sampling. Stay tuned for lots of exciting science!
“Sally saw the SeaSoar near the sea surface over the seamount…” – The ‘6 o’clock News’ SeaSoar watch (Sara Rivera, Lauren Manck, Cynthia Martinson).
One of the funnest parts of oceanography is getting to play with high-tech instruments that help us collect data about the sea around us. Yesterday we deployed something that looks like a yellow toy airplane – the SeaSoar!
The SeaSoar is a winged torpedo-like instrument that we tow behind the ship to collect a 3D profile of the water column. The instrument ‘soars’ up and down between the surface and 260 m deep in a yo-yo-like pattern, recording water temperature, salinity, oxygen, chlorophyll fluorescence from phytoplankton, and water clarity.
Our goal during this cruise is to sample and track the evolution of a filament of cold, newly-upwelled water that has developed along the Central California coast, extending out into the California Current System. Filaments like the one we are tracking are common upwelling features along our coast, and can be important conduits for moving nutrients, plankton, fish larvae, and other organic matter into offshore waters. The SeaSoar measurements help us characterize the subsurface picture of the filament.
Our SeaSoar path is a radiator-like grid pattern that traverses up and down between Pt. Conception and Monterey Bay, which means that today’s upwind leg to Monterey brought plenty of large swells, sea spray, and rocking ship decks. The SeaSoar has to be monitored via computer full-time, so our army of grad students and volunteers has been busy standing watch and composing sea limericks. We are all in good spirits after some evening whale-watching and a beautiful sunset – along with a great first day of data!
The SeaSoar saga will be continued by The 6 o’clock News tomorrow…
After much land preparation and several hectic days of ship loading, we finally headed out to sea yesterday on our 2017 CCE-LTER Process Cruise! Our trip out of San Diego Harbor and up to the Channel Islands has been smooth and sunny, allowing us to get our feet under us as we navigate the maze of tunnels and hallways on the 277-ft (aka huge!) R/V Roger Revelle, as well as to test-deploy some of the instruments we will use on our cruise.
Some of today’s tests included: two types of CTDs, which measure water column properties (temperature, salinity, clarity, nitrate levels, chlorophyll fluorescence); two types of plankton nets; and a Moving Vessel Profiler (MVP), a fish-shaped metal instrument that we tow behind the ship to get a 3D profile of the ocean by measuring similar characteristics to CTDs.
This Process Cruise marks the beginning of Phase III of the CCE-LTER program. This phase focuses on cross-shore fluxes in the Central and Southern California Current, which means we are interested in how water masses change and evolve as they move from coastal upwelling regions out away from shore.
Our cruise is a collaboration between multiple groups, with representatives from the Ohman, Landry, Barbeau, Aluwihare, Allen and Goericke labs at Scripps Institution of Oceanography, the Bishop lab at UC Berkeley, and the Stukel lab at Florida State University. We also have several enthusiastic volunteers, some of whom are at sea for the first time. We look forward to learning from each other and working with the ship’s excellent crew to collect valuable science!