Oceans and Furies by M. Susan Lozier
Seas and history are strewn with tales and remnants of tsunamis, cyclones, and rogue waves that defy our imagination and challenge our survival. Through millennia the ocean has been cursed for its fickleness and spite, blamed for death and destruction. The ocean, however, has a simple defense against these harsh accusations: it is simply doing the bidding of outside forces. Only when pushed is its fury unlocked.
Driven by magma currents inside Earth’s mantle, tectonic plates glide across our planet’s surface at a pace of little consequence to our daily lives. Yet for those whose curiosity is piqued by the ubiquity of seashells embedded in mountainsides thousands of miles from any sea, this movement matters. As plates creep toward or apart from one another, moving mere millimeters a year, they change the contours of our landscape, with their convergence leading to mountains and divergence leading to trenches. When plates collide under the ocean, the sea floor rises to new heights, shaking off the salty sea but keeping the seashells, sharks’ teeth, and whale bones buried in its sediment. Here is the evidence of an ocean displaced at the behest of intense heat at our planet’s core—traces of our galaxy’s birth, eons ago.
As mountains rise and fall, Earth continues its steady journey around our sun. Yet this constancy is deceiving, for as we hurtle through space, our planet wobbles and tilts and changes course ever so slightly, but enough to cause massive changes in how the sun’s heat is distributed across our globe. Due to these shifts, ice ages appear and disappear on time scales of tens of thousands of years. Glaciers advance into ocean waters, then retreat; shorelines extend inland, then withdraw; land bridges offer new routes for migrating species—including our own—and then submerge again beneath the sea. The earth wobbles and the ocean jumps.
And then there are the powerful atmospheric winds pushing surface waters this way and that, creating the system of ocean currents that mariners map and oceanographers love. The Gulf Stream, the Kuroshio, the Canary, the Benguela, and dozens of other currents owe their existence to the easterlies and westerlies that circumnavigate our planet. Fair winds are relished at sea, but when perturbed these same winds can quickly gather speed, change course, and focus their energy into the makings of a storm. The ocean has no place to hide from the fury of winds on a tear. Storm winds whip the ocean into a frothy mess, driving large waves whose energy breaks masts and bones alike. The ocean, shoved around without remorse, is cursed for this mess.
Like clockwork, the ocean labors with the tides. Driven by the gravitational attraction between the Earth, our moon, and the sun, a tidal bulge moves daily across our planet, pushing waters ashore and pulling them back in a Sisyphean endeavor. The ocean has no rest from this ebb and flow. Its toil must have inspired Mary Oliver’s poem “I Go Down to the Shore,” which describes the human desire to unburden woes when standing at the water’s edge, imagining they might be washed away with the tide. Inevitably, though, that desire is met with the indifference expressed in the poem’s closing line, “And the sea says in its lovely voice: Excuse me, I have work to do.” Please, the sea tells us, take care of your own troubles.
The ocean’s never-ending work across all these time scales is visible in our world today: mountains display seashells, ancient shorelines crisscross continents, shipwrecks litter the seafloor, a morning storm deposits flotsam and jetsam, and collapsed sandcastles mark the day’s high tide. But not all is so visible. Indeed, an ocean current—vast in scale and immensely consequential to our climate—escaped our notice until the mid-eighteenth century as it lay deep beneath the sea surface, unbeknownst to mariners skimming sunlit waters.
The tale of its discovery starts with a wooden bucket.
At the behest of the English clergyman Reverend Stephen Hales, the British sea captain Henry Ellis, aboard a slave-trading ship sailing from western Africa to the American colonies, stopped in transit to measure the temperature of the deep tropical ocean in 1751. The deep ocean at this time was largely unexplored and, as such, full of mystery if not charm. Armed with a simple wooden bucket that was fitted with valves to capture water at selected depths, and rope to lower the bucket over the side, Ellis and his crew laboriously created the first known temperature profile of the ocean.
As Ellis noted in his letter back to Reverend Hales, the “cold increased regularly, in proportion to the depths, till it descended to 3900 feet.” Successive draws at greater depths brought up water just as cold, which was much colder than the air temperature at that time. Having dutifully noted the measurements in his letter to Hales, Ellis turned to more practical matters, writing, “This experiment, which seem’d at first by mere food for curiosity, became in the interim very useful to us. By its means we supplied our cold bath, and cooled our wines or water at pleasure; which is vastly agreeable to us in the burning climate.”
The amenities of the ocean were not lost on these sailors.
Ellis’s letter found its way to the archives of the Royal Society of London, where it went unnoticed for decades until an American-born British scientist, Count Rumford, stumbled upon it in 1800. Rumford was puzzled as to how deep waters in the tropics could be so much colder than the temperature of the overlying atmosphere. The deep ocean in the eighteenth century was generally considered motionless. However, from this single measure of temperature, Rumford deduced the opposite. In 1800, he wrote, “It appears to me to be extremely difficult, if not quite impossible, to account for this degree of cold at the bottom of the sea in the torrid zone, on any other supposition than that of cold currents from the poles.” Rumford further reasoned that this cold current at depth “must necessarily produce a current at the surface in an opposite direction.”
With these two sentences, Rumford described the convective overturning of the ocean, popularized centuries later as the great ocean conveyor belt. This process transports cold, deep waters from polar latitudes to the tropics, as surface waters warmed by the tropical sun are transported to the polar latitudes. This quid pro quo serves us well. Without this exchange—and that provided by its fluid partner, the atmosphere—polar latitudes would be even more frozen and tropical latitudes even more sweltering.
Early in my graduate studies, I was drawn to this story.
I loved the fact that readings from a simple thermometer in a wooden bucket uncovered currents in the ocean abyss. The romance of this story inspires me still. Surface waters in the cold and frozen north take flight, so to speak, in search of warmer climes. They travel on well-worn pathways through the deep Atlantic and Pacific, thousands of meters down from our notice. Yet even in flight, even with thousands of miles under their belt, these waters remain recognizable because they carry with them what they gained from their exchange with the atmosphere: their temperature, salinity, and oxygen content. These properties provide the fingerprint of their home basin. Waters from the Labrador Sea between Canada and Greenland can be identified in the deep waters off the Florida coast, those from the Weddell Sea in Antarctica can be identified in the South Atlantic, and in the deep Pacific we find traces of waters that were once at the surface in the northern reaches of the North Atlantic. Currents are on the move.
In the 1970s, these deep waters gained another signature when oceanographers discovered measurable quantities of tritium in the deep waters of the North Atlantic. A byproduct from the nuclear bomb testing conducted by the US and the Soviet Union in the 1950s and 60s, tritium had found its way into the deep sea. Here was a visible encroachment of our human imprint. Here was proof of the deep ocean’s capacity as a reservoir for our excesses.
And then, just twenty years later, another signature was added to the ocean’s calling card. From a series of ocean expeditions in the early 1990s that stretched from the Aleutians in the North Pacific to the Southern Ocean, eastward to the Atlantic Ocean, and then northward to Iceland, oceanographers measured concentrations of anthropogenic carbon dioxide in waters as deep as 4,000 meters below the surface. Subsequent measurements and calculations have determined that about a third of the carbon dioxide released by humanity since the Industrial Revolution now resides in the ocean.
I found this sobering in the 1990s. I find it sobering still.
I was a child growing up in a town on the Ohio River when the Cuyahoga River in Cleveland caught fire in 1969. Though I didn’t understand how a waterway could catch fire, the people in Cleveland were neither confused nor surprised. The Cuyahoga had blazed about a dozen times since the late 1860s. Turns out that oil can burn.
The national outrage about this polluted river—and others just as polluted in cities across the US—is credited with the birth of the modern environmental movement and, in no small way, to the creation of the Environmental Protection Agency in 1971. And today, though pollution hotspots remain, the health of the Cuyahoga is much improved. The river burns no more.
I would love to take solace in the story of the Cuyahoga, but human impact on rivers is one thing, while human impact on oceans is something else entirely. While the ocean is not aflame, those elevated levels of carbon dioxide are slowly and inexorably increasing ocean acidity. A slow burn, if you like.
Rising acidity, coupled with ocean warming and the deoxygenation that warming brings, unduly stresses marine species and the entire ocean ecosystem. These waters are accommodating our excesses, even at their own expense. As with the gravitational pull of our moon and sun, we are an undeniable force that the ocean must now reckon with. We have, in effect, given it more work to do.
That reckoning extends beyond ocean chemistry and biology. As our climate warms, ocean temperatures are climbing, sea ice and glaciers are melting, and sea levels are rising. As if that were not enough, ocean warming and ice melt put the overturning at risk of slowing down. And if the overturning slows, we can expect major disruptions to weather and climate patterns—such as stronger hurricanes and more extreme precipitation. In short, we can expect the fury of the ocean to further unfold.
How this story ends for the ocean—and for us—we do not yet know. You see, all these ocean changes—the warming, ice melt, sea level rise, increasing acidity, and an overturning circulation at risk—are due to the rising levels of carbon dioxide in our atmosphere. And so, if we want any chance of a Cuyahoga ending, there is just one choice: we must unburden the atmosphere of this greenhouse gas. That challenge is daunting, but the consequences of inaction are even more so.
In my study of the ocean, I am keenly aware of these physical, chemical, and biological changes. Yet, as time goes on, the most disconcerting change to me is the change in the human relationship to the ocean. For ages, humankind has veered between fearing and revering the ocean. We have been vulnerable to its power and just as vulnerable to its majesty.
Yet now, the tides have turned: the ocean is vulnerable to our power. We now speak of stewarding rather than fearing the ocean. We now speak of saving the ocean. How or when that salvation comes, I am not sure, but I still have faith that it will. All we need is for our courage to unfold here at the precipice of a sea change in our world.
References
Broecker, Wallace S. “The Great Ocean Conveyor.” Oceanography 4, no. 2 (1991): 79–89. https://doi.org/10.5670/oceanog.1991.07.
Lozier, M. Susan. “Overturning Assumptions: Past, Present and Future Concerns about the Ocean’s Circulation.” Oceanography 28, no. 2 (2015): 240–51. https://doi.org/10.5670/oceanog.2015.50.
Oliver, Mary. A Thousand Mornings: Poems by Mary Oliver. New York: Penguin Press, 2012.
Rumford, Benjamin (Count of). “The Propagation of Heat in Fluids” (Essay VII). In Essays, Political, Economical, and Philosophical: A New Edition, vol. 2, 197–386. London: Printed by A. Strahan for T. Cadell et al., 1800.
Sarmiento, Jorge L., and Nicolas Gruber. “Sinks for Anthropogenic Carbon.” Physics Today 55, no. 8 (2002): 30–36. http://dx.doi.org/10.1063/1.1510279.
Warren, Bruce A. “Deep Circulation of the World Ocean.” In Evolution of Physical Oceanography: Scientific Surveys in Honor of Henry Stommel, edited by B. A. Warren and C. Wunsch, 6–41. Cambridge, MA: MIT Press, 1981.
M. Susan Lozier was raised in southern Indiana alongside the Ohio River but somehow found herself studying the salty seas in graduate school at the University of Washington. While the majesty of the ocean has inspired her study of ocean circulation for over three decades, the need to understand how ocean circulation plays a role in our changing climate adds agency and urgency to her study. Though prone to seasickness, she has found herself on research cruises in the South Pacific, North Atlantic, the Labrador Sea, and the Inner Passage off the western Canadian coast. In her other day job, she is the Dean of the College of Sciences at Georgia Tech. Her work as an educator, researcher, and leader in the ocean sciences community has been recognized with numerous awards and honors. Most recently, she was inducted into the American Academy of Arts and Sciences. She has published widely in scientific journals.