Salinity Processes in the Upper Ocean Regional Study (SPURS): Life in the Sargasso Sea

By Eric Lindstrom

John snags a flying fish in mid flight.

There are not many places in the open ocean that get their own special name as a “sea.” Most seas are what we call marginal seas – offshoots of the major ocean basins.

The Sargasso Sea, as a vast track of the western subtropical North Atlantic Ocean is known, has a special characteristic – something noted by Portuguese sailors for centuries and even visible from space. It is the home waters of Sargassum, a genus of brown macroalgae (seaweed) that inhabit the open ocean. The sea is named after the seaweed and it seems that small clumps are nearly always within sight of the ship (we have yet to see giant mats of the stuff in the SPURS region). Anyway, the Sargasso Sea is special because of a plant. Well, it is more complicated than that!

A patch of Sargassum at the surface (Photo: Julian Shanze.)

Sargassum, up close.

Closeup of Sargassum.

In my opinion, the really cool thing about Sargassum is that each clump can be a teeming ecosystem by itself. Several varieties of fish (e.g. Sargassum fish and flying fish), crabs , and nudibranchs live in close association with the weed. Each clump is a complex island of life floating free at the surface of the deep ocean. When you are out here in the vast emptiness of the open ocean, it is just hard to imagine how this intricate web of life came to be, survived, and actually thrives. Every time I am in the Sargasso Sea, it seems such a wonder.

A flying fish.

Barnacles on French glider recovered by Knorr.

We had spectacular sunset last night and I was reminded of the old adage: “Red sky at night, sailor’s delight. Red sky in morning, sailor’s warning.” Here we are still in proximity to Hurricane Nadine and is this saying true, or is it just an old wives’ tale? Like the answer to most questions, there is a web site for that. In fact I think it may be true for us; we are well south of the hurricane weather and forecasts have good weather for in days ahead.

Sunset sen from the Knorr.

An interesting sidebar to today’s blog topic is another kind of life we have found in great abundance at our SPUR study location. It was a mystery for a few days – we were seeing lots of floating microscopic reddish dusty particles. Some said it looked a little like sawdust (but where are the trees?), and some wondered whether it was floating dust from the Sahara. Well, thank goodness for the Web again. I discovered that it’s a bloom of an important nitrogen-fixing bacterium (Trichodesmium) also known as “sea sawdust.” It certainly reinforces the idea that a key to identification is a good description!

Trichodesmium in a bucket of sea water.

A Trichodesmium bloom in the Pacific Ocean seen from space.

Trichodesmium, it turns out, just loves these sea conditions – just as much as SPURS oceanographers love the North Atlantic salinity maximum!

Tags: flying fish, NASA, oceanography, oceans, salinity, Sargasso, SPURS, Trichodesmium
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Salinity Processes in the Upper Ocean Regional Study (SPURS): All About Your Blogger

By Eric Lindstrom

Your SPURS blogger, Eric Lindstrom, discussing the Aquarius mission.

After several weeks of your following my postings from the field, I thought it would be good to tell you a little about myself. Maybe that will help explain the weird wanderings of the blog or the subject matters I choose to write about.

Let’s start at the beginning: I grew up in Seal Beach, California, very near the ocean. It seems to me like I actually grew up on the sand and in the water. So, I am pretty well infused and enthused by the seas. This has driven me toward a broad knowledge of ocean subjects. I felt that drive vindicated when National Geographic Society tapped me as senior scientific consultant (pro bono) on their first ocean atlas project.

When did I decide to become an oceanographer? I was pretty interested in the field in middle and high school. Science seemed like where I was headed. Being a good student, I was able to get into the Massachusetts Institute of Technology. There, before I finished my freshman year, I fell in love with the Earth and Planetary Sciences Department. It was a short course in astronomy that got me hooked. They really reeled me in when I realized that Earth science was just then being revolutionized by the ideas of plate tectonics and that oceanographers at MIT were bringing back the first pictures of hydrothermal vents on the mid-ocean ridges. There was not much in the way of undergraduate education in oceanography at MIT, but lots of good basic math, physics, geology, geophysics, and research opportunities. I can date myself by recalling the glorious summer of 1976, when I stayed in Boston for the bicentennial and to do my undergraduate research project on data from Lake Ontario. The lake wasn’t salty, but it was a great little laboratory for oceanography ideas! That summer truly set me on course to pursue physical oceanography as a career (and provided my first publication with Prof. John Bennett: “A simple model of Lake Ontario’s coastal boundary layer,” in Journal of Physical Oceanography, July 1977).  Most scientists remember their first publication quite fondly and I am no exception!

Graduate school at University of Washington was filled with studies and expeditions. It took me six years to get my Masters and a Doctor of Philosophy in Physical Oceanography degrees. My dissertation was on eddies in the North Atlantic Ocean. It turned out that eddies deep below the surface of the ocean can carry water across the ocean from quite distant places and arrive in the Sargasso Sea with evidence of their origins from as far afield as the Labrador Sea, the Antarctic Circumpolar Current, or the Mediterranean Sea. The idea that these origins and travels could be traced using salinity measurements was intoxicating (in a nerdy sort of a way) for a young oceanographer. I loved the data collection part of the project; being part of the right team with the right equipment in the right place at the right time to make some discovery that would move science forward. The ocean is still virtually unexplored, so every well-planned expedition has potential for great discovery. Once oceanographic expedition science is in your blood, it’s hard to give it up! I found a great opportunity for doing more expedition research by moving to Australia in 1983. The country had expanded ocean research greatly at that time due to advent of the Law of the Sea and extended Exclusive Economic Zones. Sometimes, timing is everything!

In Australia, I became engrossed in studies of the western tropical Pacific Ocean circulation and in the planning for the World Ocean Circulation Experiment (WOCE). By the end of the 1980s, the former had seen me on many expeditions near exotic tropical islands and the latter looked to be the oceanography opportunity of the 1990s. I moved back to the U.S., still working on the same projects, but with a new home base. By the mid-1990s I was the US WOCE Program Scientist in Washington, D.C. That involved organizing scientific plans, budgets, and logistics for the largest mapping of ocean waters ever undertaken, involving voyages across the globe for nearly a decade. I was bitten by the vision of global ocean observing provided by WOCE and still suffer from that fever.

Eric, giving a talk at the Consortium for Ocean Leadership.

When the opportunity arose in 1997 to lead NASA’s Physical Oceanography Program, I had the right stuff: solid experience with the ocean, ocean programs in DC, ocean researchers in general, and virtually no heritage at all with satellite oceanography (but NASA said I could learn that on the job!)

It was in my first days at NASA HQ that I began energizing NASA’s drive toward measuring ocean salinity from space. All I had to do was enable those with the knowledge and skill to realize the dream (it certainly was not a new idea) – and prove to NASA that it was both possible and useful. And here we are today. I am back out on a research vessel, doing what I love, with Aquarius, our ocean surface salinity instrument, on orbit overhead and a whole community of scientists curious about ocean salinity and the global water cycle. It’s one small victory for this man, and one giant leap for physical oceanography.

Eric, taking a break on an Argo float box after a long day of blogging at sea.

Tags: oceanography, oceans, science careers, SPURS
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Salinity Processes in the Upper Ocean Regional Study (SPURS): The Moods of Sea and Sky

By Eric Lindstrom

A beautiful day in the trade winds zone, with its typical cumulus clouds.

From the shipboard perspective, all we really see of the sea is the surface. Of course we can see into the water a short way, right close to the ship, but not very far. The horizon is 360 degrees and the great dome of sky seems endless.

Being that we are about a thousand miles from the nearest port, it is also fair to say that all we see from the ship is sea surface and sky. These are the shades of blue that I referred to in an earlier post. When this is all one has to see aside from the Knorr, our shipmates, and interesting oceanographic data (OK, we watch movies too!), it should come as no surprise that everyone becomes sensitive to the moods of the sea and sky. When you want a moment alone, the likely place to go is on deck, and there you are confronted with some new variation of the sea and sky.

We are working in what is called the trade winds zone. It is a belt of generally east and northeast winds north of the equator and east or southeast winds south of the equator that are quite steady and global in extent (in the days of sail, one’s trade depended on using routes through these reliable wind zones). In the trades zone, we might expect relatively steady 10-15 mph winds and fair skies with broken clouds. One characteristic of the fair weather cumulus clouds in the trades is that they lean over because of wind shear in the atmosphere. The blue sky dominates the evenly scattered puffy white leaning clouds that seem to all have the same base (maybe 3,000 feet above the sea).

The trade wind cumulus clouds break up the bright shades of blue on the sea surface by casting rapidly evolving shadows across the sea. The color of the sea surface certainly depends on the light reflected from the sky (a gray sky can give the ocean a grayer look) but also depends on the intrinsic color of water, which is blue.

We had few days where there seemed to be a pink hue to the sky (especially at the low sun angles of morning and late afternoon). This is likely the result of having more Saharan dust suspended in the atmosphere. It is quite common for dust storms to carry thousands of miles out over the ocean.

Sunset in the Sargasso, with hints of Saharan dust.

The color of the water depends on the angle at which you view it and the height of the sun. One of the cool things I see in the open ocean is that when you look down into the deep waters in the middle of a sunny day there is a radiation of sunbeams seemingly coming back at you from the depths. It gives the blue ocean a kind of jewel-like quality.

Sun beams in the Sargasso Sea.

Tags: Atlantic, NASA, ocean, oceanography, salinity, SPURS
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Salinity Processes in the Upper Ocean Regional Study (SPURS): Plastic Ocean

By Eric Lindstrom

The R/V Knorr, in the beautiful Sargasso Sea.

One of the things that we worry about on the ship, as part of our daily routine, is trash. Nothing goes over the side unless it is biodegradable. We have separate trash cans for plastics, foils, and other such material that would pollute the ocean. There are cans with paper liners for food scraps and paper waste. We keep the deck clean and our eyes open for any loose cable tie or anything else that could be washed overboard. It’s our duty to pick these things up and dispose of them properly.

It may be surprising to some of you how much plastic is already in the ocean. It’s both amazing and depressing. If one stands by the ship’s rail and watches the water go by, as one wants to do in an idle moment, it is quite shocking to realize that more man-made objects can be observed than natural ones (like fish). A 2005 report from the U.N. Environment Program estimated that, on average, more than 13,000 visible pieces of plastic litter were floating on any square kilometer of ocean.

A piece of plastic debris floating near the Knorr.

Given the fact that plastic takes so long to break down, it should come as no surprise that this problem is still getting worse by the year, despite decades of effort to reduce the sources of pollution.

As a physical oceanographer, I know that the major ocean basins have gyre circulations at mid-latitude. The water moves in a great loop around the center of the ocean basins in the northern and southern hemispheres. Surface waters tend to converge toward the center of these gyres and trash of all sorts concentrates in these spots, far away from the coasts of the continents. In the North Pacific, there is the so-called “Great Garbage Patch” between California and Hawaii. Similar, but less well-known patches occupy dynamically similar regions in the other oceans. Nikolai Maximenko at University of Hawaii, a NASA-funded physical oceanographer studying the Pacific circulation, uses satellite and drifter data to understand this surface circulation in great detail. He made news with his analysis of the fate of tsunami debris from the 2011 Japan disaster.

Here in the Sargasso Sea, we have yet to see some giant patch of garbage (well, except for my desk in the upper lab!), but plastic does abound. I thought that I should testify as to my personal experience of observing so much plastic along our path. It’s more than I remember seeing 30 years ago, when I last sailed for an extended period in the Sargasso Sea. Its certainly not a scientific observation, but it reminds me that we are the creators and users of these materials and we should be the stewards of their disposal as well. So, pick up and recycle any loose plastic you see! It could wind up in the ocean.

Tags: Atlantic, Great Garbage Patch, NASA, oceanography, plastic, pollution, salinity, SPURS
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Salinity Processes in the Upper Ocean Regional Study (SPURS): Seaglider #189 Away!

By Eric Lindstrom

We just launched the first of our autonomous vehicles – a pink Seaglider with the sexy name of #189.

The story of Seaglider 189 begins.

Underwater gliders are the longest-range autonomous undersea vehicles in the oceans by virtue of their very simple propulsion mechanism: the translation of a vertical force into an horizontal one through use of wings. Gliders adjust their buoyancy by alternately inflating and deflating a small swim bladder appended to the vehicle’s body, a mostly rigid pressure hull. A volume variation of only a couple of thousandths of the overall vehicle’s volume is enough to provide an upward or downward buoyancy force that balances a combination of lift and drag forces, resulting in forward and vertical motion, the essence of gliding. Gliders, in effect, use wings as their propellers.

About an hour away from deployment.

Once made heavy, Seagliders sink to a prescribed depth where an electric motor drives a pump to change the vehicle’s density from heavier to lighter than the surroundings, causing them to ascend. They slice through the ocean along sawtooth paths.

The fixed supply of electrical energy aboard the glider in the batteries is used for propulsion and instrument operation. At SPURS we are using gliders in somewhat opposite extremes: some of them (the Slocum gliders — more about them later) are packed with power-needy instruments that limit their mission length to a couple of weeks, while others (Seagliders) direct a greater portion of energy to propulsion and operate a less hungry suite of sensors to achieve the 7-month mission duration required by the SPURS ship schedule.

Gliders were developed to probe the oceans independently of ships. Persistence is their virtue. The Seagliders launched from R/V Knorr are meant to repeatedly survey a limited region of the ocean, every fortnight repeating a 150-nautical mile (480-kilometer) circuit to provide a four-dimensional description of the upper ocean across wide area of ocean centered on the SPURS moored array. Profiles of temperature, salinity, oxygen, chlorophyll fluorescence, and optical backscatter will be transmitted ashore at the end of dive cycles to 0.6 miles (1 km) depth, repeated about thrice daily.

A close-up of Seglider 189′s sensors.

These gliders are completely autonomous once submerged, until they make a call over the Iridium satellite network to report data collected and accept new instructions from ashore controllers that manage everything, from flight to sampling strategy. They steer toward instructed target positions by moving the battery pack to one side or the other, inducing a vehicle roll that results in a turn. They follow a calculated compass heading to approach each target and, once there, dive toward the next. Seagliders even predict the effects of currents on their progress to choose an efficient heading with which to approach the next target. Vehicle pitch is similarly controlled during flight and the nose is depressed at the sea surface to raise the trailing antenna above the waves to gather position information and communicate.

In addition to the standard suite of measurements, the SPURS Seagliders are carrying brand new temperature microstructure probes. These are intended to measure turbulence in the upper ocean over nearly 2000 km (more than 1000 nautical miles) of track through the ocean by each vehicle on each mission. The hope is that upper ocean turbulence, long exclusively measured by ship surveys, will in SPURS be extended over the course of a year in autonomous surveys. The salinity and temperature profiles collected by more conventional aboard instrumentation, together with turbulence profiles, will reveal where the ocean mixes with respect to the myriad fronts and eddies to be encountered in the SPURS region.

Members of the SPURS team, ready to deploy the Seaglider.

Getting lowered…

Free at last!

Finally, to answer the inevitable question: to what does Seaglider #189 owe its garish color? The original project engineer in Seaglider development, Jim Osse, had some paint left over from a human powered submarine contest his University of Washington team entered in Florida. He chose the hue selected by the customer ahead of him at the counter of a Seattle auto parts store, destined for a 1942 Ford Coupe (and, it turns out, a bevy of Seagliders, too): Hot Rod Pink. We are hoping that #189 stays in the pink and safely hot rods around the ocean until recovered next March!

Tags: oceanography, salinity, Seaglider, SPURS
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