Trash Talking Early: Plastic "Continents" of Trash

     Plastic "continents" are not static. Based on the oceanic circulation modelling work conducted in the Pacific, the Institute de Recherche et Developpement (IRD) and the National Council for Scientific Rearch (CNRS) researchers have recently shown that there are exit currents for these areas of the sea where these piles of waste build up. This means that they are not caught in a never-ending whirlpool in the middle of the ocean, as had been previously thought. Although inappropriate given the actual estimated concentrations, this term highlights the awareness of the impact of human activity on the oceans.

.    Due to the winds on the surface of the oceans and the rotation of the earth (via the Coriolis force), huge vortexes, called "oceanic gyres," are formed in each of the five major basins: North and South Pacific, North and South Atlantic, and the Indian Ocean. These huge whirlpools slowly gather in their wake all the plastic objects and waste floating on the surface of the water, accumulating year after year.

      

      This pollution is now recognized as a global problem, representing a threat to marine biodiversity. In particular, this surface drift acts as a means of transport for the viruses and bacteria that the spread across the oceans.

      Nevertheless, these plastic "continents," as they are incorrectly christened, are not, in fact, static. The IRD and CNRS researchers have recently revealed the existence of "exit doors" leading away from these large surface current convergence zones. The scientists started by studying the oceanic circulation in the Pacific modelled with a much finer spatial resolution than that of the models generally used for this type of study (those typically used for climate research). They simulated the trajectories of several million particles, with currents defined on networks of 1/32° to 1/4° (meaning a range from a few kilometers to thirty or forty kilometers).

      The results obtained highlight currents, several hundred kilometers wide, which escape from the heart of the subtropical gyre and head eastwards instead. In addition to these currents there are physical processes such as the effects of the wind and waves, not taken into account in the models, which can also alter the trajectory and the transit time of the particles and waste.

     In the Pacific, the waste may not necessarily be trapped in the centre of the oceanic gyre and may be removed in the direction of the American coasts. Furthermore, these results are backed up by the work of the IRD's Chilean partners. They have observed an increase in the amount of waste collected on their coastlines.

     More detailed observations, modelling and analyses are needed to gain a better understanding of the ocean surface currents that regulate the slow routing of plastic waste on the surface of the seas and, in the medium-term, implement strategies for collecting and recycling all of this waste.

         I saw first-hand the dumping of all our waste aboard the Research Vessel Eastward in the Mediterranean Sea in 1978. The ship's captain laughed at me when I suggested that continual trash dumping would add up to eventually plug up the oceans. It was so devastating to see those empty cans of Spam floating in the sea.

Trash talking pre-LIV,
Steph

What Doesn't Krill Us Makes Us Stronger: Ocean Water Mixing By Tiny Organisms

        Swarms of tiny oceanic organisms known as zooplankton may have an outsized influence on their environment. New research at Stanford shows that clusters of centimeter-long individuals, each beating tiny feathered legs, can, in aggregate, create powerful currents that may mix water over hundreds of meters in depth.

     Although the work was carried out in the lab, the finding is the first to show that migrating zooplankton – or indeed any organism – can create turbulence at a scale large enough to mix the ocean’s waters. The work could alter the way ocean scientists think about global nutrient cycles like carbon, phosphate and oxygen, or even ocean currents themselves.


      A brine shrimp (below) tethered in place generates flow with its swimming motion, made visible with an overlaid time lapse of particles suspended in the water. Photo credit: Isabel Houghton.

      “Ocean dynamics are directly connected to global climate through interactions with the atmosphere,” said Dr. John Dabiri. “The fact that swimming animals could play a significant role in ocean mixing – an idea that has been almost heretical in oceanography – could therefore have consequences far beyond the immediate waters where the animals reside.”

        Dr. Dabiri, who was the senior author on the work published April 18, 2018, in Nature, added that the findings could also help scientists understand how the ocean sequesters carbon dioxide from the atmosphere and lead to updates in ocean climate models.

      “Right now a lot of our ocean climate models don’t include the effect of animals or if they do it’s as passive participants in the process,” Dabiri said.


      One of the most common zooplankton, krill are among the most abundant marine organisms and migrate daily in giant swarms, heading hundreds of meters deep by day and up to the ocean’s surface by night to feed.



      Dr. Dabiri knew that in terms of forces that drive the mixing of oceans, wind and tidal currents are thought to play the largest role. But he wondered if giant zooplankton migrations could also be involved – an idea first proposed by oceanographer Walter Munk in 1966, and since then debated but never systematically explored. {Dr. Munk, at 100 years of age, is still quite current (pun definitely intended!)}.

      Dr. Dabiri and graduate student Isabel Houghton tried to answer that question not in the ocean but in the relatively controlled environment of large water tanks in the lab. The pair worked to create flow environments that mimic the ocean with saltier water on the bottom of the tank and less salty water on the top. The resulting gradient mirrors ocean conditions that any organism would need to disrupt in order to cycle nutrients between the ocean’s surface and water deep below.

      “There’s no appreciable deep mixing of oxygen or carbon dioxide in the ocean if you can’t overcome the stabilizing influence of salinity and temperature gradients,” Dr. Koseff said.

      In the lab, the group was looking to see whether the tiny organisms they studied – mostly brine shrimp (also known as sea monkeys) as a stand-in for less lab-hardy krill – are simply churning water locally, leaving the gradient intact, or redistributing salt into a more uniform mixture. If they can mix layers in the lab, chances are they can do the same in the ocean, the group argued.

      To carry out the study, Houghton placed brine shrimp in the tank and activated laser or LED lights from either above or below, because brine shrimp are attracted to light, so they migrated toward the source. When she reversed the lights the tiny creatures scurried to the other end in a migration that lasted about 10 minutes.

      With cameras closely recording the animals’ movements, the group has been able to measure the individual water eddies surrounding each brine shrimp and the larger currents in the tank. From these, they’ve shown that turbulence from individual organisms aggregates into a much larger turbulent jet in the wake of the migration.

     What’s more, those flows were powerful enough to mix the tank’s salt gradient. “They weren’t just displacing fluid that then returned to its original location,” Houghton said. “Everything mixed irreversibly.”

     Before this work, scientists had thought that krill and other zooplankton could only create turbulence in their own size range – on the order of centimeters. That’s hardly enough to move nutrients on a meaningful scale. Now it appears that zooplankton have the capacity to mix ocean waters, at least regionally. Furthermore, Dr. Dabiri said their findings might not just apply to organisms like krill in the upper kilometer of the ocean, but also to jellyfish, squid, fish and mammals that swim even deeper, potentially churning the entire water column.

     Dr.Dabiri said his lab members need to verify their findings in the ocean, which will involve finding and following swarms of krill in locations as diverse as the California coast and frigid Antarctic waters. But if they continue to see mixing at the scales the lab work suggests, the findings could change the way ocean scientists think about the role of animals in influencing their watery environment – and potentially our climate on land.

     These ocean mixers are vastly different from the mixers we had at Smith College (or are they?)

     Did you ever order sea monkeys?
Steph