P l a s t i c S e a s

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It has been called the ‘Great
Pacific Garbage Patch’, a region of the
North Pacific Ocean containing some 3
million metric tons of trash, mostly
plastic debris no larger than a grain of
rice (Lawrence 2010). And it isn’t the
only region of the ocean where plastic
accumulates in such massive quantities.
Ocean circulation drives the formation
of gyres, circular ocean current systems
that concentrate plastic and other
marine debris in their calm centres,
called convergence zones, regions
which have been dubbed, ‘the world’s
largest landfills’ (Lawrence 2010). This
special feature takes us straight into
the centre of the widening gyre as we
examine the accumulation of plastic
debris in ocean convergence zones and
discuss what, exactly, happens to
plastic at sea.
We wear it, we brush our hair
with it, and we eat with it. It is
lightweight,
durable, and inexpensive. Plastic
is everywhere…including in the
ocean. And it is no surprise. Globally,
more than 115 million metric tons of
plastic is produced annually (Whitty
2009). Approximately ten per cent of this
plastic ends up in the world’s oceans, via
sewage waste, storm drains, coastal
pollution, and flooding, while about
twenty per cent of the plastic debris that
enters the water comes directly from
ships and oil rigs (Whitty 2009). And
industrial resin pellets, also called
nurdles, the raw material used to make
plastic, comprise a staggering eleven per
cent of beach litter (Whitty 2009). Each
year, undegraded plastic kills
approximately 100 000 whales, dolphins,
manatees, and seals, about 2 million sea
birds, and an undetermined number of
sea turtles (Whitty 2009). But as the
plastic debris in the ocean starts to
degrade, the problem is just beginning.
Scientists have raised further concerns
about photodegredation, the breakdown
of plastic debris into smaller and smaller
fragments by sunlight, a process which
releases potentially toxic chemicals into
the ocean environment (Singh and
Sharma 2007).
Microplastics Are No
Small Matter
We use plastic products
everyday – After all, plastic can
be found in everything from our
cars to the television sets in our living
rooms – but most of us have probably not
thought much about what plastic is.
Plastic is a type of polymer, a large
molecule consisting of many monomers,
or repeating units of molecules
Plastic Seas 2
chemically bonded to one another in what
could be thought of as one long molecular
chain. There are many different types of
plastic and chemical composition
depends on the type of plastic (Singh and
Sharma 2007). In general, all plastics,
whether in the ocean or on dry land,
undergo degradation, the deterioration of
the physical
Oceans of Plastic1 Plastic debris collected
from Vancouver beaches during a shoreline cleanup by
Vancouver Aquarium volunteers in 2008. How quickly an
individual piece of debris degrades varies depending on
ocean conditions and chemical composition (Singh and
Sharma 2007), but, on average, plastic takes about 450
years to degrade in the ocean (Lawrence 2010) and
consumer products like these make up the vast majority
of the debris found in the world’s oceans (Lawrence
2010).
properties of a material (Singh and
Sharma). But plastic undergoes another
type of degradation, and it all has to do
with the sun. Solar ultraviolet radiation,
more commonly known as UV rays,
fragments plastic into smaller and smaller
pieces, called microplastics (Betts 2008).
Microplastics are plastic particles smaller
than five millimetres (Betts 2008), no
bigger than a grain of rice or a pencil
eraser (Lawrence 2010). Many of these
plastic particles remain afloat, but
microplastics that have a greater density
than seawater sink below the surface and
can be found in the water column and the
1 All photographs in this article are those of the article’s
author. All samples in the photographs are the property of the
Vancouver Aquarium Marine Science Centre and were
accessed by the author, with permission, as a volunteer at the
Vancouver Aquarium Marine Science Centre.
sea bed (Betts 2008). There is some
evidence that perhaps the micro
organisms responsible for the
biodegradation of other materials
accumulate on microplastics, increasing
the density of the particle and causing it
to sink (Lawrence 2010).
Cooking Up a Toxic Soup
As plastic debris breaks down
into microplastics, the plastic
polymer degrades, releasing
potentially dangerous chemicals
like bisphenol A (BPA) and polystyrene
oligomor, breakdown products of plastic,
both of which have been shown to disrupt
hormone systems and adversely affect
reproduction in living organisms (Saido
2009). Due to this fragmentation, a single
piece of plastic could remain in the ocean
for hundreds or perhaps thousands of
years (Betts 2008). This means that ocean
garbage patches are more like a toxic
soup than a mass of floating debris (Betts
2008). In fact, most of the plastic trash in
these regions is so small it is not even
visible from the deck of a ship.
Microplastics Debris collected during a surface
tow in the North Pacific Gyre. Of the approximately 3
million metric tons of debris in the gyre, about eighty per
cent are microplastics, plastic particles less than five
millimetres in size (Betts 2008).
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But don’t let its small size fool you. The
consequences of these chemicals being
released as this massive amount of tiny
plastic degrades, and how these areas of
high concentration of microplastics factor
into the equation, are yet to be fully
understood. In one recent study,
scientists looking at the thermal
degradation of polymer mixtures at the
Nihon University in Japan found that
polystyrene, a type of plastic more
commonly known as Styrofoam, degraded
to release potentially harmful monomers,
the breakdown products of plastic
polymers, at temperatures as low as
thirty degrees Celsius, a temperature
comparable to ocean surface temperature
in some regions (Saido 2009).
Considering the massive amount of
plastic accumulating in the world’s oceans
(The total mass of the debris in the North
Pacific Gyre is estimated to outnumber
the mass of plankton – those microscopic,
drifting organisms that provide a crucial
food source to larger marine organisms
like fish – in the region by six to one
(Whitty 2009)), it is probable that a
significant amount of potentially harmful
chemicals are being released into our seas
as this massive amount of plastic
continues to degrade…and degrade…and
degrade.
As it breaks down at sea debris, both
natural and synthetic materials, accumulates
in regions of the ocean due to the
organization of ocean currents. Global wind
belts influence the movement of ocean
surface currents, creating circular loops of
moving water called gyres (Trujillo 2010).
There are five major ocean gyres, located
in the Pacific, Atlantic, and Indian oceans.
And while marine debris can be found
throughout the world’s oceans, it is in
convergence zones, the regions where
currents converge or come together near
the centre of a gyre, where immense
quantities of marine debris can
accumulate. A garbage patch is a region of
the ocean with a higher than average debris
content within the upper water column
(Garbage Patches 2010). The oceanic
debris field known to many as the Great
Pacific Garbage Patch, located in the calm
centre of the North
Ocean Gyres There are five major ocean
gyres in the world: The North and South Pacific gyres, the
North and South Atlantic gyres, and the Indian Ocean
Gyre. Blue arrows indicate directionality of ocean
currents. Soure: EOSC 314, Lecture 18, M. Lipsen.
North Pacific Subtropical
Convergence Zone (STCZ) Marine
debris can accumulate in the central region, or
convergence zone, of an ocean gyre. One such gyre, the
North Pacific Gyre, contains an estimated 3 million metric
tons of debris within its convergence zone. This region is
the location of a debris field known as the Great Pacific
Garbage Patch. There exists another massive area of
debris accumulation in the North Atlantic Gyre that may
rival that of the so-called Great Pacific Garbage Patch, and
scientists predict there could be similar debris-containing
regions within other major ocean gyres as well. Source:

http://marinedebris.noaa.gov/info/patch.html

Plastic Seas 4
Pacific Gyre, in a region called the North
Pacific Subtropical Convergence Zone
(STCZ) is one of these areas of
accumulation. Estimates on the size of the
patch range from the size of the state of
California right up to a mega patch bigger
than the continental United States. It is
difficult to obtain an accurate estimate of
the patch’s size because it is not a solid
mass of debris, but rather a region of the
ocean that acts like a vortex, sucking up
trash from Asia and the United States and
trapping it within.
But how do the planet’s wind
currents create these enormous trashtrapping
loops in the sea? The simple
answer to this complex question begins
with something called the Coriolis effect.
Our roughly spherical planet is constantly
spinning eastwardly, completing one full
spin during each twenty-four hour day.
And the surface velocity is different,
depending where you are on the globe.
Earth is a sphere, meaning it has the
greatest circumference at the middle, at
the Equator, and the smallest
circumference at – you guessed it – the
poles. Let’s review the classic Coriolis
example: Imagine you are standing on the
Equator, shooting a projectile toward the
North Pole. Will the projectile land east or
west of your intended target? It will land
to the east, or to the right of your
intended target. This is because at the
Equator the projectile is moving eastward
faster than its target, the North Pole. If the
projectile were fired from the North Pole
to the Equator it again deflects to the
right. This makes sense – The target is
located on the Equator and the Equator
moves eastward more quickly than the
pole, so the target moved eastward before
the projectile could reach it. In the
southern hemisphere, the opposite is true
and the projectile deflects to the left. The
Coriolis effect is the deflection of the
intended path of an object that is moving
within a rotating coordinate system
(Coriolis Effect). Put simply, the Earth is a
spinning sphere and an object traveling in
the north to south direction will undergo
deflection to the right in the northern
hemisphere and to the left in the southern
hemisphere.
Coriolis Deflection The Earth is a
sphere that rotates eastwardly (counter clockwise). The
circumference of the Earth is largest at the Equator and
smallest at the poles. This means that the Equator travels
farther than the poles in the same amount of time. In
other words, the whole Earth is moving at the same
velocity, but the surface speed is greater at the Equator.
An object originating from the North Pole traveling
toward the Equator is deflected to the right because the
target on the Equator moves eastward before the
projectile, which is traveling more slowly at the pole,
reaches it (Coriolis Effect). The opposite is true in the
southern hemisphere, where objects deflect to the left.
Source:

http://abyss.uoregon.edu/~js/glossary/coriolis_effect.ht

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Plastic Seas 5
Going Beneath the
Waves: Ekman Transport
The Coriolis effect influences
motion over the surface of the
Earth, and the prevailing winds
that drive ocean surface currents are no
exception. It works like this: About two
percent of the wind speed is transferred
to water at the surface. For example, a
fifty knot wind (equivalent to about 92
km/h) produces a surface current of
about 2 km/h. This current moves away
from the wind source. This concept is a
familiar one – Simply blow on the surface
of the water in your bathtub and the
water moves away from you (the wind
source).
The Formation of An Ocean Gyre
Water in the northern hemisphere is deflected to the right
of the wind source due to the Coriolis effect, resulting in a
net transport of surface water ninety degrees to the right
of the wind direction. The water continues in the counter
clockwise direction, forming a circular loop of moving
water called a gyre. Soure: EOSC 314, Lecture 18, M.
Lipsen.
But it works a little differently in the
ocean than it does in the bath tub. And to
look at ocean surface currents we start by
looking at what goes on beneath the
waves. for these purposes, the ocean
surface can be defined as the depth to
which the wind penetrates (which is
usually about one hundred meters). We
know that as the planet spins there is
deflection to the right (in the northern
hemisphere) and to the left (in the
southern hemisphere). But this also
occurs in the ocean, where there is a
deflection of about ninety degrees to the
right of the wind direction, a concept
called Ekman Transport. To understand
what Ekman Transport means think of
the ocean not as one big pool of deep
water, but as layers of water piled on top
of one another. Waves transfer kinetic
energy from the wind to the surface water
by the force of friction. Due to the Coriolis
effect, each layer of water is deflected (to
the right in the northern hemisphere and
to the left in the southern hemisphere) at
a greater angle to the wind source than
the layer on top of it, creating a spiral of
sea water. The result is a ninety degree
net transport, or total movement, of the
surface water relative to the direction of
the wind. And it is this spiralling
behaviour, called the Ekman Spiral, which
is caused by Coriolis deflection, that are
responsible for the creation of Earth’s
major ocean gyres.
Ekman Spiral Energy is transferred from the
top of the surface water to the subsurface water with
Coriolis deflection. Each subsequent layer of surface
water is deflected at a greater angle to the direction of the
wind for a net transport of ninety degrees to the right
(left) of the wind direction in the northern hemisphere
(southern hemisphere). Soure: EOSC 314, Lecture 18, M.
Lipsen.
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Hilly Mounds of Seawater
Hold a Mountain of Trash
The movement of surface
water perpendicular to the
prevailing winds pushes
water toward the middle of
the ocean basins, resulting in
mounds. And a mound is just that – a
whole pile of seawater. And if you find
yourself reminiscing of your childhood
days in the sandbox, piling up sand into
great big hilly mounds, you are not very
far off the mark. If you think of the sand
as seawater, this is essentially what wind
does to surface water – it piles it up. And
these piles of water are actually at a
higher elevation than the surrounding
surface water, just like the mounds in
your sandbox. When surface water in the
northern hemisphere is directed ninety
degrees to the right of the wind direction,
the water is moved in the counter
clockwise direction. And surface water in
the southern hemisphere, which is
deflected to the left, is pushed in the
clockwise direction. Surface currents flow
Mounds of Seawater Ocean
surface water is deflected (red arrows)
perpendicular to the prevailing winds (yellow
arrows). Westerlies cause surface water to
move in the opposite direction of the surface
water being moved by the trade winds, causing
the surface water to pile up in the middle of
ocean basins in regions called mounds. These
are the locations of ocean gyres, where debris
accumulates in ‘ocean landfills.’ Soure: EOSC
314, Lecture 18, M. Lipsen.
around these mounds, traveling counter
clockwise in the northern hemisphere
and clockwise in the southern
hemisphere as they gather the world’s
trash in their vast centres.
Talking Trash
It spans an immense area
and it certainly does contain
an incredible amount of
trash, but the term ‘garbage patch’ is
misleading. There are no islands of
garbage the size of the state of Texas, no
rafts of ocean-faring plastic thick enough
to walk across, no floating landfills in the
middle of the Pacific ocean…at least not in
the traditional sense of the term
(Lawrence 2010). What we do know is
that debris becomes concentrated in
regions of the ocean, such as the North
Pacific Gyre, due to the movement of
ocean surface currents, which are subject
to Earth’s wind currents. But what is not
yet fully understood is how the many
different types of plastic degrade in the
ocean, or even what impact this long
degradation process will have on the
ocean environment in years to come
(Betts 2008).
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