Daily migration of marine life to and from the twilight zone to the ocean surface.
“There is a 5th dimension beyond that which is known to man.It is the middle ground between light and shadow.It is an area, which we call, the Twilight Zone.” ~Rod Serling
Like many kids growing up in the 1960’s, I eagerly anticipated every episode of a black-and-white TV series by Rod Serling, expecting to be surprised, maybe even a little scared, of the mysteries of that 5th dimension he called “The Twilight Zone.” Little did I know that decades later as an oceanographer, I’d find myself at sea with over 60 like-minded scientists on a program specifically targeting the mysteries of another twilight zone—the one in the ocean that lies just below the sunlit surface.
The WHOI EXPORTS team showed off their glow-in-the-dark ocean twilight zone t-shirts prior to departure from Seattle in August. Credit: WHOI/Ken Buesseler
What motivates us is the need to learn more about the role of the twilight zone and the animals that live there in regulating Earth’s climate. The story of how they do this actually starts at the surface, where microscopic marine algae, or phytoplankton, turn carbon dioxide in the water into organic matter via photosynthesis, much like plants on land.
This organic matter forms the base of the marine food web, which basically means that these microscopic plants serve as food for tiny marine animals called zooplankton, which are eaten by larger marine organisms and so on up to larger animals, like the fish that humans consume. Many of these animals come up from the twilight zone at night, using the cover of darkness to feed in surface waters and then disappear come daybreak. This is, in fact, the largest animal migration on Earth and happens around the globe every day, and we barely know it happens.
Phytoplankton in the form of a diatom chain. Credit: University of Rhode Island/Stephanie Anderson
But I am getting ahead of myself, because despite how appropriate Rod Serling’s description of the mysteries of “the middle ground between light and shadow” fits with what we are doing out here, peering with our instruments into the dimly lit depths, his TV show is not the origin of the name of a twilight zone in ocean sciences. In fact, at least as far back as 1915, textbooks included discussion of the “decrease in the abundance of life from the sunlit surface layers, through the twilight zone, to the zone of darkness,” as was written in College Physiography.
Getting back to this cruise, most of the carbon either sinks out of the surface ocean directly or is carried by animals back down to the twilight zone in their guts and gets excreted. All of this sinking carbon becomes food for other twilight zone animals, with less and less remaining as you go deeper. This constant rain of organic carbon is known as “marine snow,” which drifts through the twilight zone and into the deep ocean.
Who cares how much organic matter or carbon goes through the twilight zone? Well, if you are an animal living in the twilight zone, that’s your main food supply. As a human concerned with the potential for rising carbon dioxide levels in the atmosphere to disrupt our climate, it’s the quickest way you can get organic carbon to the deep ocean, effectively removing it from contact with the surface ocean and atmosphere for hundreds or thousands of years.
Simply put, without the ocean storing carbon in the deep sea, the levels of carbon dioxide in the atmosphere would be much higher than they are today. And the last time they were this high, Earth was a much different place.
The open top of a neutral-buoyancy sediment trap (NBST) showing the opening through which marine snow drifts and is then collected. Credit: UCSB/David Siegel
WHOI marine chemist Ken Buesseler (right) helps deploy a sediment trap from the research vessel Roger Revelle as part of the EXPORTS program. Credit: UCSB/Alyson Santoro
The tools I used to measure this cascade of particles carrying organic carbon to depth on this voyage include sediment traps—something like a rain gauge that captures in a tube the sinking particles that are slowly settling through the water. A second method my group uses to measure sinking particles takes advantage of a naturally occurring element called thorium-234, which is slightly radioactive and decays with a precise 24.1-day half-life. This clock allows me to calculate very precisely how much carbon is being carried from the surface through the twilight zone.
It’s far too early to share my results from this cruise, but the importance and complexity of these links between twilight zone organisms and climate should not be underestimated. Like snowfall on land, organic carbon transport to the depths varies with the seasons and locations in the oceans, but in ways we cannot predict. And it is important for us in our efforts to better understand how quickly climate will change as we keep adding more carbon dioxide to the atmosphere. This job is so complex that it takes a village out here aboard two research ships, with autonomous vehicles in the water and support teams on land and satellites above. We work together to study these carbon flows and the living organisms in the twilight zone that create what marine biologist and conservationist Rachel Carson called the “most stupendous snowfall on earth.”
I don’t know if there are any episodes of The Twilight Zone to watch out here, but I do know there are many deeper mysteries we hope to unravel about the ocean’s twilight zone.
Ken Buesseler is a senior scientist at the Woods Hole Oceanographic Institution. He has been working for decades on the ocean twilight zone and its impact on Earth’s carbon cycle. He is currently on the R/V Roger Revelle as part of the Export Processes in the Ocean from Remote Sensing (EXPORTS) field campaign.
..some advice for anyone preparing for a research cruise: be flexible, be prepared (well, the best that you can be), and be excited.
“Hey Anna, want to help me make something?” asked Dr. Heather McNairof me one day. I was instantly intrigued. What were we going to make? What was it going to be used for? How were we going to put it all together? So many questions were running through my head, but I was ready to explore and learn.
This summer, I have been working in Dr. Susanne Menden-Deuer’s lab at the University of Rhode Island’s Graduate School of Oceanography as part of an National Science Foundation-funded Research Experiences for Undergraduates program called Summer Undergraduate Research Fellowship in Oceanography (SURFO). My primary focus was to understand how environmental factors, such as turbulence, affect the way microscopic marine organisms graze on other organisms. While my primary research kept me busy, I wanted to explore other areas of oceanographic research, so I offered to help in the lab any way I could.
Undergraduate Research Fellow Anna Ward measuring plankton abundances in the laboratory. Credits: University of Rhode Island/Menden-Deuer Lab
Preserved microzooplankton samples settle for microscopy analysis. Credits: University of Rhode Island/Menden-Deuer Lab
Dr. Heather McNair, a postdoctoral fellow in the Menden-Deuer Lab, explained that she was preparing for a research cruise as part of the Export Processes in the Ocean from Remote Sensing, or EXPORTS, field campaign and wanted help making a positive pressure pump, a device used to automate water sampling. I had never even heard of a positive pressure pump before, and now I was supposed to make one?! Enthusiastic and eager to begin, I put my thinking skills to the test. She showed me some of the physical pieces and explained how we wanted our end product to function and look. Okay, sounded pretty self-explanatory, put a few pieces together, and finished product—done.
Except one thing: We did not have all of the pieces, and we needed to create this device using only items available in the lab. Similar to being out at sea, you cannot simply go to the store and get what you need; you have to figure out a way to make it work given the resources available. After a lot of trial and error, we created a device that would work well at sea. Mission accomplished.
Postdoctoral Fellows Dr. Heather McNair (left), Dr. Francoise Morison (middle), and Dr. Ewelina Rubin mobilizing the R/V Roger Revelle for EXPORTS. Credits: University of Rhode Island/Menden-Deuer Lab
Unforeseen and challenging obstacles such as this are common at sea. While it might seem simple, there are many fine details involved in preparing for a cruise. Think about the average science classroom: there are various instruments and glassware, as well as other fundamental components such as water sources, sinks, safety equipment, and more. You have to think about where all of these items will go on the ship, how to secure them for the natural movements of the ship at sea, etc.
Some things are simpler, such as determining how many bottles you need for an experiment, while others are more complex, like transporting a large, expensive instrument across the country that will undergo constant motion and likely rough, stormy seas. While this process is stressful for some, it is truly one of my favorite parts of a research cruise.
Scientific equipment on the dock waiting to be loaded onto the research vessels. Credits: University of Rhode Island/Menden-Deuer Lab
No matter how prepared scientists are, unexpected things always happen at sea, including 12-foot swells sloshing up against the side of the boat. That might not seem like much for an avid surfer, but for research vessels these waves can be felt instantaneously by members. I remember my last research cruise, when we hit a wave a bit larger than I expected. I was performing an experiment and zoom, all of the bottles starting sliding across the table. Here I was trying to catch them while holding my stance. In times like these, I truly appreciated that the tables were screwed into the walls, and the boxes under tables were held in place with ratchet straps.
Wet-lab setup on a prior research cruise containing filtration systems tied down to the tables and carboys and boxes bungeed to the ship for safety during transport. Credits: University of Rhode Island/Menden-Deuer Lab
There are so many components to think about before going to sea in addition to the simple things, like remembering to bring a toothbrush and an extra changes of clothes. Staying organized is key. I cannot imagine trying to pack all of our equipment without the handy packing list we prepared.
But more importantly, some advice for anyone preparing for a research cruise: be flexible, be prepared (well, the best that you can be), and be excited. The thrill and excitement from performing research on a ship is extraordinary, something to truly embrace. Even if those long days and nights packing seem never-ending, just remember it will be worth it and one of the most incredible learning experiences of your life. To everyone aboard the EXPORTS cruise, fair winds and following seas. The packing is done and now you have made it to the best part—researching at sea.
The port in Seattle, Washington, from which the R/V Roger Revelle and the R/V Sally Ride embarked for the northeastern Pacific Ocean. Credits: University of Rhode Island/Menden-Deuer Lab
A mixed phytoplankton community. Credit: University of Rhode Island/Stephanie Anderson
I am Dave Siegel, aprofessor of marine scienceat the University of California, Santa Barbara. I have been working for many years to implement the Export Processes in the Ocean from Remote Sensing (EXPORTS) oceanographic campaign: a coordinated field effort to understand the interactions between life in the sea and Earth’s carbon cycle.
Last Thursday night, I watched “my baby” of a campaign sail away, as the Research VesselSally Ride left Pier 91 in Seattle for the northeastern Pacific Ocean.
While I am the science lead for EXPORTS, it’s not justmybaby—it is truly a group effort. Two teams of scientists created the EXPORTS science and implementation plans, with a lot of input from the greater oceanographic community. The result is a campaign comprising more than 50 funded NASA and NSF investigators from nearly 30 institutions and many graduate students, postdocs and technicians, all excellently supported by the masters and crews of two Scripps Institution of Oceanography’s research vessels: the R/VRoger Revelle and the R/VSally Ride.
The R/V Sally Ride, operated by the Scripps Institution of Oceanography, anchored at Pier 91 in Seattle before departing for the northeastern Pacific Ocean on Thursday, Aug. 9. Credit: NASA/Katy Mersmann
EXPORTS aims to develop a predictive understanding of the interactions of life in the sea and Earth’s carbon cycle, which is critical for quantifying the carbon storage capacity of the global ocean. The oceans are Earth’s largest active reservoir, or storage, of carbon and carbon dioxide concentrations in the atmosphere and thus helps regulate our planet’s climate. This predictive understanding of the interactions of ocean life and the carbon cycle is especially important as we are seeing that our ocean ecosystems are changing in response to changes in Earth’s physical climate. To do this we need data to test and validate these satellite-based assessments and numerical model predictions.
We are trying to tackle a super hard problem—one I believe to be a true grand challenge in Earth System Science. Our approach is simply to follow the money. For ocean ecosystems, that currency is the energy stored in phytoplankton carbon from photosynthesis. The production of phytoplankton carbon is nearly balanced by its consumption by animals called zooplankton, which in turn provide the energy for the higher trophic levels of the sea, such as fisheries and charismatic megafauna (whales, seals, sharks, and the like).
A mixed phytoplankton community. Credit: University of Rhode Island/Stephanie Anderson
The slight imbalance—roughly 10 percent of phytoplankton production globally—drives an export of organic carbon from the well-lit surface ocean into the dimly-lit twilight zone beneath. Within the twilight zone, microbes and animals of all description consume this exported organic carbon, utilizing their energy for metabolism. This export of organic carbon from the upper ocean and their consumption within the twilight zone, along with ocean circulation, shape the carbon storage capacity of the global ocean and frame the two major research questions for EXPORTS.
Constructing a field campaign to identify and quantify the flows of organic carbon through the ocean is, of course, a major challenge. Phytoplankton physiologists need to assess phytoplankton growth rates and responses to perturbations in their required nutrients (nitrogen, phosphate, silica & iron). Zooplankton grazing and the carbon cycle impacts of their daily vertical migration to the sunlit layer of the ocean from the twilight zone need to be assessed.
In the hydro lab aboard the R/V Roger Revelle, sampling tubes will collect water samples at varying ocean depths for analysis. Credit: NASA/Katy Mersmann
Sediment traps that catch the rain of sinking particles measure the flux of sinking carbon as well as make detailed geochemical measurements that test how well our measurements of the individual pathways reflect the large-scale mass budgets needed to build and test satellite and computational models. Optical oceanographers make ocean color measurements that link the EXPORTS datasets to NASA satellite data products. And I feel bad that I left out so many other individual research activities going on, but mentioning each of them would take up another two paragraphs!
For EXPORTS, scientists are deploying robotic explorers, like these from the Applied Physics Lab at the University of Washington. They are traveling with the ships, taking measurements at various depths. Credit: NASA/Michael Starobin
The measurements needed to constrain the various food web and export pathways as well as adequately sample the highly variable ocean environment requires technologists that can overcome these challenges. For example, the EXPORTS team includes robotics experts who build, deploy, and analyze data from an array of autonomous underwater vehicles (AUV) that sample ocean properties on time scales ranging from minute to years.
EXPORTS has also taken advantage of recent technological advances such as novel high-throughput microscopes andin situ imaging devices that take individual images of billions of phytoplankton cells as well as zooplankton and other various organic matter. These images are then analyzed using advanced machine learning techniques to provide unique views of the structure of plankton communities.
Advancements are also available from the biomolecular sciences where metagenomic and bioinformatics approaches provide complementary ways to characterize plankton communities and their metabolism. Lastly, several projects include numerical modelers who will use computational approaches to help answer EXPORTS science questions.
The first EXPORTS field deployment will be to Station P (50N 145W) in the Northeast Subarctic Pacific Ocean. Station P (or PAPA) has been sampled and resampled over many decades—from as far back as 1949, when it served as an ocean weather station. Presently, Station P is the terminus of the CanadianLine Ptransect ocean research program and is an area of focus for the National Science Foundation’sOcean Observatories Initiative project.
Last week, the R/VRoger Revelle and the R/VSally Ridesailed to Station P. Both are floating laboratories that enable our research, but they will have different missions. The R/V Roger Revelle will make detailed rate measurements and conduct a wide variety of experiments while the R/VSally Ridewill make spatial surveys around its partner ship to assess the three-dimensionality of these processes. These ship-based measurements will be supplemented by the array of AUVs. Both ships and robots will make ocean optical measurements linking the EXPORTS field data to present and future NASA ocean color satellite missions.
Graphic representation of the Northeastern Pacific Ocean deployment for EXPORTS.
EXPORTS is also planning a second field deployment in the North Atlantic Ocean in the spring of 2020 to provide contrasting data. Furthermore, NASA has supported a group of Pre-EXPORTS projects aimed at mining available, relevant data sources for use in EXPORTS synthesis analyses and to conduct modeling experiments to help plan this and the North Atlantic expeditions.
So I’m the science lead but I’m not sailing. Seems weird, but early in our planning we were worried about the coordination between all of the things going on. My job back home now is to help coordinate activities on the two ships and assist the four co-chief scientists in fouling off whatever curveballs that may come. I’m sure they will provide blog posts soon introducing themselves.
It is been a long time coming and I realized that as the R/VSally Ride was sailing away. I have been there from the start pushing this along, so I suppose it is “my baby.” I do want to thank all involved in the planning and implementation, including the program officers at NASA and NSF.
Further information about EXPORTS can be found at the NASA EXPORTS expeditionteam blogand the EXPORTSwebsite.
This week while the GLiHT crew continued collecting data over the Susitna and Tanana valleys, we focused on collecting on-the-ground data on spruce beetle infestation. Our first day out proved rainy and cold, but we pressed on, only sheltering in the car during a particularly hard spell. Aside from the occasionally torrential rain, we also dealt with clambering over downed logs nearly invisible under thick grasses and ferns, as well as waist-high patches of Devil’s club. This nasty understory shrub is covered in painful thorns tough enough to penetrate through clothing. We often found ourselves having to backtrack and find a different route to our desired tree after realizing we were wading into a sea of the spiky shrubs. As a testament to this somewhat failed effort, my legs were covered in scratches and bruises later that evening.
A Devil’s club patch to be avoided.
Our task was to find and GPS spruce trees within the collected GLiHT imagery and record their infestation status and size so that they can later be used to develop infestation detection algorithms for aerial and satellite imagery. Spirits were running fairly low until we found a big patch of both green-stage infested trees (those that are infested with spruce beetles but have yet to show visual signs in their needles) and non-infested spruce trees. This find was especially exciting because these infested and non-infested trees were experiencing similar site and weather conditions, so differences that we detect in the GLiHT imagery will likely be due to the effects of the beetles, giving more confidence to the infestation detection algorithms that we develop.
An image captured by GLiHT as it flew over a beetle infested area. We have been working on identifying the infestation stage of spruce trees present in this imagery
On our second day the sun was shining brightly through only a few clouds, promising warmer and drier conditions for the day. We were joined by scientists from American University who were flying unmanned aerial vehicles (UAVs) over the beetle infested areas. The UAVs have visible, near-infrared, and thermal cameras mounted on them, which will provide a high resolution look at how trees respond to infestation. Together, the ground surveys, UAV flights, and GLiHT imagery provide information about infestation at broader and broader spatial resolutions, and should help to scale even further towards detecting spruce beetle infestation in satellite imagery.
A 3D image created from the UAV flights. We can see gray/brown infested trees in the middle of the patch of trees, surrounded by other healthy and green-stage infested spruce.
Professor Mike Alonzo from American University getting ready to fly a UAV with a visible and near-infrared sensor. The pool noodle X helps to post-process and correct the collected imagery
The American University team introduced us to some “field equipment” I never thought I would be using: foam pool noodles bolted together in an X formation. They are used as targets in the UAV imagery along with high-accuracy GPS points to post-process the collected imagery. A GPS point is collected at the center of the pool-noodle X, and then later the image is warped so that the center of the X (the bright pool noodles make for highly visible targets) matches the GPS’d point. This process makes sure the image is spatially accurate, and also makes for some entertaining field work.
Another objective of this field campaign is to describe the structure and biomass composition of alder and willow stands in south-central Alaska. Because alders and willows are shrub species (i.e. not trees), they are generally not monitored as frequently or intensely. Recently, however, these shrubs have been growing at much higher rates, with some stands reaching over 10 ft in height. This means there may be a lot of biomass going un-accounted for. With a combination of intensive field sampling, and correlation of that data to imagery from GLiHT and the UAVs, we can try to determine the biomass and structure of shrub stands across the region.
Because of the odd structure of alders and willows, the field sampling is particularly tricky. Each stem and large fork branching off from a main stem must be measured for diameter and length, and this process can take quite a long time and involve scrambling in and under a tangle of branches and woody debris.
An alder forest we sampled along the coast. The complicated mess of stems and branches made for a long day.
Back at “base camp” we seemed to have gained a couple new neighbors: a female moose with gangly baby in tow. We snapped photos of the pair, and while the female didn’t really seem to pay us any mind, the baby alternated between wanting to be near his mom (who was ambling up the path alongside our cabin) and being afraid of getting any closer to us.
The mom and baby moose who liked to frequent our cabins.
Fieldwork in Alaska also has the major perk of spectacular views during afternoon and evening breaks. After a particularly long day of sampling in Denali State Park, we opted to stay in the area rather than drive the long three hours back down to Anchorage and were blessed with a beautiful view of “sunset” over the Alaska Range.
We finally had clear enough skies to get a full view of Denali, and that evening got a great glimpse of an Alaskan Range sunset (at midnight).
This summer a team of scientists from NASA Goddard, American University, and the Forest Service are conducting joint field work and flights with Goddard’s LiDAR, Hyperspectral, and Thermal Imager (G-LiHT) within south-central Alaska to study the ongoing spruce beetle outbreak and develop methods for early detection of beetle infestation. The spruce beetle is an aggressive bark beetle that feeds and reproduces in the inner bark of various species of spruce trees. Currently, spruce beetles are affecting over 400,000 acres in the Matanuska-Susitna Valley, resulting in widespread mortality of spruce trees. This infestation has been ramping up over the past few years in Alaska, causing concern for both scientists and Alaskans. Data collected by G-LiHT may provide the ability to detect early stages of infestation, before they would be visible in aerial surveys conducted by the Forest Service, which would allow forest managers and scientists to better predict future infestation locations and extent.
As we pass over the Susitna Valley we can see how far this outbreak has spread. The red-brown and gray trees have been infested for several years. Some of the green trees may be the early stages of spruce beetle infestation.
This past week we have been flying with G-LiHT and visiting areas where G-LiHT data was collected to identify and GPS trees infested with spruce beetles. The infested trees can later be located and analyzed within the collected imagery. This summer, the G-LiHT instrument is flying on a King Air A90. The pilots have to maintain an altitude of 1,100 feet for the best imagery, and this makes for quite an exciting ride over the various mountain ranges in Alaska. The swoops and dives the plane makes as it follows the terrain feel more like a roller coaster than a plane ride.
Our pilot Justice Pousson (on the wing) and co-pilot Sam Wilson (behind the propeller) work on the King Air A90 before take-off.
Outside the windows we get a full view of Alaskan landscape. We pass over the jagged peaks of the Talkeetnas into rolling spruce forests. From up here we can really see the extent of the beetle outbreak. Tendrils of red-brown and gray trees climb northward up the Matanuska-Susitna Valley. The red trees have likely been infested for over a year, and these needles will after three years turn gray and eventually fall off the tree. Though there are still some green spruce that we can see from the plane, there’s a good possibility that many of them are in fact already infested, as infested spruce trees generally maintain green needles for at least a year. The aerial Forest Service surveys can detect trees that have red or gray needles, but detecting trees that have only been infested for one year currently requires on-the-ground inspection of tree trunks. We are hoping these flights with G-LiHT will provide the imagery required to develop algorithms for green-stage detection.
The G-LiHT instrument in the back of the plane. It includes a 3 cm camera and a hyperspectral, thermal, LiDAR, and solar-induced fluorescence sensor.
The computer used to operate G-LiHT during flights. We have to make sure we turn on and off all the sensors at the right times.
The weather sometimes prevents us from completing all of that day’s planned flight lines. On Thursday we had hoped the clouds that had been hanging low over the Chugach Mountains would dissipate as the day wore on, but we ended up having to turn back after only a few flight lines were collected. While this was disappointing, on the way back to the airport we got a spectacular view of Denali rising above the clouds.
As we transited home we got a great view of Denali to the west.
Earlier this week we drove north from our base at Alaska Pacific University in Anchorage towards Denali State Park, armed with a Trimble GPS, DBH tape, and plenty of bear spray. We stopped off where G-LiHT had flown overhead the previous week and found trees to GPS. As we made our way around moose droppings and hoped not to come upon any bears, we picked out the infested from the healthy spruce trees and measured their position and size. We can identify the infested trees by the characteristic globs of pitch-out sap running down the trees’ trunks as well as red-brown dust along the bark crevices and at the base of the tree. The sap is a defense mechanism used by the trees to trap and kill the attacking beetles. Young, healthy trees are usually successful at fending off these attackers, however older or more stressed trees often succumb to the beetles’ offensive. Swarming pheromones given off by the beetles attract others in a “mass attack” which can overwhelm the defenses of even the more vigorous trees. This snowballing effect of more and more beetles attacking more and more trees, which then leads to more beetles reproducing and attacking in subsequent years is the mechanism behind the growing spruce beetle outbreaks.
Back at the cabins where we are staying we relax by a campfire and grill steaks, veggies, and salmon. I’m still trying to get used to the sunrise and sunset times in Alaska. With a sunrise time of 4:50am and a sunset time of 11:20pm, it barely gets dark at all. On the plus side this allows us to stay out later in the field collecting data without having to worry about daylight hours. On the down side it makes it pretty difficult to discern the time of day (or when you should probably head to bed…).
Our campfire (note: it was 9pm when I took this picture).
Next week we have more plans for field work, including flights with some unmanned aerial vehicles to collect data over the infestation areas. Also on my to-do list: more moose and other wildlife sightings!