Location: North Pacific
Dates: June 25 – July 15, 2017
Biological Oceanographer, Sonya Dyhrman’s team is embarking on a research cruise off Hawaii as part of the Simons Collaboration on Ocean Processes and Ecology (SCOPE) on the R/V Kilo Moana June 25-July 15. Gwenn Hennon, and Matthew Harke will be at sea for nearly three weeks with logistical support from Sheean Haley back on shore. The cruise will be in the North Pacific, near the Hawaiian Islands where ocean currents create swirling features with diameters five times the length of Manhattan, called mesoscale eddies. The aim is to identify how mesoscale eddies shape the microbial ecosystem of the North Pacific Subtropical Gyre. Microbes perform the most important functions in the ocean from phytoplankton that fix carbon to bacteria that recycle scarce resources necessary for all life. Eddies alter these dynamics by bringing nutrient rich deep water up or pushing it down away from the sunlit surface. The Dyhrman team will be focused on experiments to understand how the upwelling of deep water, competition, and cooperation between microbes controls the growth of phytoplankton.
By Gwenn M. M. Hennon
The microscopic organisms that make up ocean ecosystems are invisible to the naked–eye, yet they are responsible for producing half the oxygen we breathe, and for sustaining all the world’s fisheries. Now, nearing the end of our three-week cruise of the North Pacific off Hawaii, we are working to understand how these tiny bacteria connect and communicate with one another.
We know bacteria have the ability to sense and respond to an unknown number of chemical signals, but we think it may be tens to hundreds. A few signals we know from lab experiments include quorum sensing molecules. Quorum sensing molecules are released by other bacteria to change the way cells behave when they have reached a sufficient density, or quorum. We know from previous work in the Dyhrman lab and the Van Mooy lab that quorum signaling is important in the bacteria communities that surround a particularly large and important
cyanobacterium, Trichodesmium. Tricho, as it is affectionately referred to, fixes large quantities of nitrogen fertilizer directly from nitrogen gas ( see my post: http://bit.ly/2udAf6F ). The bacteria surrounding Tricho, or its microbiome can greatly affect the rates of nitrogen fixation in ways we do not yet fully understand. Nitrogen fixation is one of the most important biochemical processes on earth and in the oceans. In ocean ecosystems, it enables microorganisms to grow even when other nutrients, such as nitrate and ammonium, are scarce.
We would like to understand which bacteria are actively recruited to colonize Tricho and other large cells, and how chemical signaling impacts this process. To do this, we created a trap for bacteria using new techniques pioneered by our collaborator Otto Cordero. From scratch, we made microscopic beads embedded with phytoplankton cell extract and magnetic particles that allow us to pull the beads out of solution, separating them from the seawater and free-living cells. Inside the bottle I’m holding (see photo) are thousands of these tiny beads mixed with ocean bacteria. Over the past few weeks, we have mixed natural bacteria found in the surface ocean with different mixtures of chemical signals and phytoplankton-flavored beads. After we take our samples back to the lab, we can use DNA sequencing as a kind of universal barcode to identify the bacteria caught in our trap.
I can’t wait to see what we will discover from these experiments, which give us new tools to eavesdrop on the conversation among marine bacteria. Understanding how bacteria communicate through signals is an important challenge for predicting the future of the ocean’s complex microbial ecosystem.
By Gwenn Hennon
As far as I can see from the ship to the horizon there is nothing but deep blue sea. Not a single ship has passed within sight since we left the north shore of Oahu. We are only a day’s steam away from the Hawaiian Islands, yet in the vast Pacific Ocean we could go weeks without seeing another ship. The ship is nothing more than a tiny speck on a massive blue marble. This is one of the dwindling places on earth where I feel truly alone with my thoughts.
The sea is a deep blue, so clear that you might think it was devoid of life. We have seen only a few seabirds circling the ship and playing in the air currents we generate. We haven’t seen any whales or sharks, only an occasional flying fish taking to the air in front of our bow wake. In this apparent desert, microbial life is king. Microbes here can persist off of little more than sunlight and gasses in the air. Marine microbes are expert recyclers, rapidly scavenging the precious little nitrogen and phosphorous fertilizers in the surface ocean. Some of these microbes can even take nitrogen directly from the air to use as fertilizer. Chemists figured out how to make fertilizer from nitrogen gas by using incredible heat and pressure, but these microbes can do it at ambient temperature and pressure. Billions of years of evolution has given these tiny cells better technology than the accumulated efforts of every chemist in the history of humanity (I note with more than a little envy as a
Very little gets wasted in this hyper-efficient ecosystem, but a little waste is inevitable. Some of these microbes die, killed by viruses or damaged by UV rays. Instead of being recycled or passed up the food chain a tiny fraction of them will sink into the deep. A slow rain of this waste falls from the surface ocean into the perpetually
dark “twilight zone” of ocean. Carried down with this waste is carbon, nitrogen and phosphorous from the surface. At depth, these elements are released by yet more microbes, munching away on the pieces of the dead and dying cells. About three miles directly below us on the sea floor a very small fraction of this waste will be buried in sediments and preserved for millions of years. In the enormous warehouse of sediment cores drilled from the ocean floor in Lamont-Doherty Earth Observatory, I have seen first-hand how the remains of ancient microbes allow researchers to look into the deep past.
In the next few days, the MESOSCOPE team will set traps to collect freshly sinking material. Our estimates of how much carbon and other elements sink out of the surface ocean every year are still very uncertain. We do not yet understand the factors that allow particles to sink out and escape the gauntlet of scavengers. Carbon carried to depths by dead microbes is estimated to be on the same order of magnitude as the yearly global emissions from fossil fuel burning. So far, the ocean has absorbed about half of the carbon dioxide emitted into the atmosphere from human activity, but we can’t yet predict how the equation might change in the future.
Standing on the back deck of the Kilo Moana, the deep blue sea makes me feel both insignificantly small and reminds me of the power of microbial life to shape our planet. In a million years how many atoms of carbon from my exhaled breath or from the smoke stack of the Kilo Moana will be trapped in deep sea sediments? Not sure I could calculate that yet… but give me some time.
By Gwenn Hennon and Matthew Harke
For the past few days, we have been loading the gear and setting up our lab on the R/V Kilo Moana. We have to secure everything down to the benches to prevent equipment from falling and being damaged in rough seas.
Yesterday, we set sail at 8am, rounded the Island of O’ahu, and headed north into the blue waters of the North Pacific Subtropical Gyre. We are currently in transit, but this gives us time to test equipment and make sure everything is in order by the time we reach our first station. It also gives us time to help with the many shipboard operations. After a hearty breakfast of eggs, bacon, tater tots, and coffee, we had the opportunity to help deploy a “towfish” from a boom extending out 15 meters off the starboard side of the boat. Since this was the first deployment of its kind on this vessel, there were a lot of hands to help. Matt is the guy in the blue hard hat.
A towfish is a device which looks like a torpedo. The towfish is tethered to the boat and lowered into the water with the boom. It then “swims” through the water while the ship is under way, allowing us to take continuous samples. The team is trying to collect trace metal samples, and so they attached a trace metal-clean hose to the towfish to pump water as far from the ship as possible.
One difficulty with working on a large steel ship is that it “leaks” a lot of iron (as well as other metals) into the water. If you care about measuring iron levels in the water, you need to find a way to get away from the ship, and this method seems to do the trick. After a successful deployment and refueling at lunch, we also helped deploy and recover an underway CTD off the stern of the vessel. CTD stands for conductivity, temperature, and depth. This device allows us to profile the eddy as we transit across, giving us an in-depth look at the physical structure of the eddy. This will allow us to more accurately target water features when we stop to collect water later on. Each deployment lasts around 15 minutes and involves dropping the underway CTD off the back of the boat, letting it sink to 300 meters, reeling it in, resetting it, and then redeploying it. All of this is done while the ship is moving at about 8 knots. This will go on for the next day or so, as it takes a few days to traverse an eddy.
By Gwenn Hennon
As I kissed my 1-year-old son goodbye this morning at daycare it seemed like any other day. Yet as I dropped him off, I knew that I wouldn’t see him again for almost four weeks. I will be returning just in time for his second birthday. My heart aches knowing that he will likely be calling for me as my husband gets him ready for bed tonight, not understanding why I can’t be there to read him a story and kiss him goodnight.
Don’t get me wrong, I love my job! I love that as a biological oceanographer I get to go to sea off the Hawaiian Islands to study how ocean life is shaped by swirling 60-mile-wide currents. The microscopic organisms that make up ocean ecosystems are invisible to the naked-eye, yet they are responsible for producing half the oxygen we breathe and sustaining all the world’s fisheries.
Scientists like myself are in a race against time to understand the fundamental drivers of ocean ecosystems before climate change pushes them towards a new unknown state. State-of-the-art models predict that warming, ocean acidification, and changes in ocean currents predicted for the year 2100 will have big impacts on the structure of the microbial ecosystem. These changes have large potential consequences for carbon sequestration and the rate of climate change, as well as the security of the world’s food supply. 2100 may seem like a long time off, but it’s likely that my son will be alive to see it. When he is 85 years old, what will he make of the world we have left for him? Did we accurately predict changes to the ocean ecosystem? Did we do enough to avert an ecological disaster?
Because no one has invented a time machine, we have to make do with our current best guesses. Unfortunately, our picture of the ocean ecosystem is far from complete, making it difficult to predict the future. As I board my flight for Honolulu, I’m grateful for the opportunity to fit a few more puzzle pieces into the big picture of how the ocean ecosystem functions. Every scientist and crew member participating in this research cruise will make sacrifices, leaving behind family and friends, and working round the clock in an effort to gather new data to understand ocean processes. Wish us luck for a successful trip!