How Does Plastic Travel in the Ocean

Map of ocean currents - (Pidwirny, 2006)

In 2017, scientists estimated that there was roughly 100 million tons of plastic in our oceans, with this figure constantly on the rise. The plastics are constantly circulating the globe via ocean currents which is the movement of sea water between locations, in a similar way to a conveyor belt, that are generated by a range of forces that change regionally including wind speed and force as well temperature difference. This has led to large accumulations, particularly of microplastic, specific areas of the ocean with the most well-known being the Great Pacific Garbage Patch. All the mentioned factors (plus many more) mean that rubbish from my university in Plymouth could end up polluting the Great Barrier Reef.

Ocean currents are defined as “a horizontal flow of water through the ocean” (according to the freedictionary.com) that redistributes heat from the sun through the globe. The movements that generate the currents are often seasonal and affected by a range of factors including:
• Differences in temperature
• Wind direction and speed
• Gravitational pull from moon and sun
• Rise and fall of the tides
• Salinity
• Atmospheric pressure

The global system of ocean currents has an important role within a range of ecosystems as well as the global climate. Ocean currents carry heat from tropical regions and transports and redistributes this heat away from the equator to warm coastal areas, making land more habitable and increasing soil fertility. They also have an impact on the weather as warmer water has a higher rate of evaporation, resulting in heavier rainfall in tropical regions which allows the tropical rainforests to have the heavy rainfall and humidity it is known for. This is what gives these rainforests the fertile soil that allows the beautiful tropical plants to grow. Currents also increase the biodiversity in the photic zone (or the top layer of the ocean) as upwelling occurs that bring nutrients to the surface. This allows phytoplankton to grow and increase in population that increase oxygen levels and provide more food for the primary consumers in the food chain. Needless to say this has a knock on effect and affects higher trophic levels within the ecosystem.

The global transport of plastics via ocean currents has created ‘rubbish hotspots’ such as the Great Pacific Garbage Patch. Despite public belief, the Great Pacific Garbage Patch is not a large mound of debris in the middle of the pacific like the name suggests and it is not even visible by satellite. The other name the Pacific Trash Vortex describes the area much better as it is a gyre containing high concentrations of marine litter and chemicals that circulate the North Pacific Ocean. With 1.9 million pieces of microplastic per square mile, the risk to the ecosystem in this area is huge and as 70% of all litter in the ocean sink to the floor the unseen impacts may be even greater than expected. The North Pacific Gyre keeps the debris circulating the North Pacific Ocean and creates convergence zones that are the natural gathering points within the ocean current system. In the case of the North Pacific, the two largest convergence zones are the western Garbage Patch and the eastern Garbage Patch (shown below). The constant movement of the gyre means that the microplastic and other marine debris remains trapped within the North Pacific ecosystem, amplifying the damage even more.

A map showing the North Pacific Garbage patch, (NOAA - Response and Restoration, 2013)

As the amount of plastic within our oceans continues to rise, we could be seeing more gatherings of plastics like the pacific garbage patch as it is transported globally and deposited by ocean currents. This has a huge impact on biodiversity in these areas and have been ingested by species, particularly seas turtles, as well as entangling others. With 17% or all threatened marine species being affected by plastic in our oceans, we need to be more aware that plastic does travel within our oceans and dropping a plastic bottle on your local beach could impact the Great Barrier Reef or be ingested by the endangered Leatherback turtle. 

References -

• Krieger, A. (2016, Febuary 7). What will it take to get plastics out of the ocean? Vox: https://www.vox.com/2016/2/7/10928788/ocean-plastic-pollution-solutions
• National Geographic. (2014, September 19). Great Pacific Garbage Patch.  https://www.nationalgeographic.org/encyclopedia/great-pacific-garbage-patch/
• NOAA - Response and Restoration. (2013, Febuary 7th). How Big Is the "Great Pacific Garbage Patch"? Science vs. Myth. Office of Response and Restoration: https://response.restoration.noaa.gov/about/media/how-big-great-pacific-garbage-patch-science-vs-myth.html
• Pidwirny, M. (2006). Surface and Subsurface Ocean Currents: Ocean Current Map. Retrieved from Fundamentals of Physical Geography: http://www.physicalgeography.net/fundamentals/8q_1.html
• Sea Turtle Conservancy. (2017). Information About Sea Turtles: Threats from Marine Debris. Sea Turtle Conservancy: https://conserveturtles.org/information-sea-turtles-threats-marine-debris/