Difficulty: Introductory | Prerequisites: Ocean surface currents and gyres (see companion study notes from this same lecture).
Once you understand that gyres are giant circular current systems, the next question is: what happens to everything that gets trapped inside them? This section covers two consequences. First, pollution: garbage patches form in the centres of gyres, and radiation-contaminated water from the Fukushima disaster spreads through currents. Second, temperature: currents redistribute heat unevenly, making western ocean shores warmer than eastern shores at the same latitude, which in turn shapes where marine organisms can live. Both topics rely on knowing how gyres and currents work.
Ocean gyres trap floating debris in their centres, creating garbage patches (the Great Pacific Garbage Patch is the most well known). Radiation-contaminated water from the Fukushima nuclear plant also spreads via currents, threatening marine life through direct mortality and potential DNA mutation up the food chain. Meanwhile, warm and cold currents make western ocean shores warmer and eastern shores cooler at the same latitude, which determines where temperature-sensitive organisms like corals and kelps can survive.
Great Pacific Garbage Patch (trash vortex)
A massive accumulation of floating debris, primarily plastics, trapped in the centre of the North Pacific Gyre. It is estimated to be larger than the state of Texas.
Think of it as a slow-spinning dustbin the size of an ocean basin, where currents push rubbish inward but nothing flushes it out.
Radiation-contaminated water
Water containing radioactive material, in this context from the Fukushima Daiichi nuclear plant damaged by the 2011 tsunami. Over 300 tonnes per day of contaminated water entered the ocean.
Trophic level
The position an organism occupies in a food chain. Producers (e.g. phytoplankton) are at the lowest level; top predators are at the highest. Contaminants concentrate as they move up trophic levels (bioaccumulation).
In simple terms, big fish eat contaminated small fish, so the contamination builds up the higher you go in the food web.
Sea-surface temperature (SST)
The temperature of the ocean's topmost layer. SST varies by latitude and is also influenced by warm and cold currents, making it uneven at the same latitude.
Kelp
Large, cold-water-loving brown algae that form underwater forests. They are found closer to the equator on the eastern shores of oceans, where cold currents bring cool water.
Coral
Warm-water-loving marine organisms that build reefs. They extend to higher latitudes on the western shores of oceans, where warm currents raise temperatures.
Located inside the North Pacific Gyre, between Hawaii and California.
Composed of nets, ropes, bottles, plastic bags, and miscellaneous waste.
Originally estimated at the size of Texas; likely much larger now.
The gyre's circular currents push floating debris inward toward the centre, where it accumulates.
Most of the trash stays within the gyre. Some may eventually sink to the ocean floor over centuries.
Effects on marine life are severe:
Sea turtles mistake plastic bags for jellyfish and ingest them.
Seabirds die of starvation with stomachs full of plastic (they feel full but receive no nutrition).
Some fish species are changing feeding behaviour, preferring artificial materials over natural food.
A sperm whale found dead in Spain had 17 kg of plastic (bottles, sheeting) in its stomach.
Garbage patches exist in other gyres too (e.g. North Atlantic), though the Pacific patch is the most studied.
The 2011 earthquake and tsunami damaged the Fukushima Daiichi nuclear plant.
Over 300 tonnes of radiation-contaminated water entered the ocean daily.
Effects on marine organisms:
High radiation levels kill marine organisms directly; jellyfish are among the most affected.
Surviving organisms may develop DNA mutations.
Contamination moves up the food chain through trophic levels (bioaccumulation): contaminated plankton → small fish → larger fish → top predators.
Long-term consequences are still unclear. Some terrestrial plants (tomatoes, eggplants) exposed to radiation have shown mutations, but equivalent studies in marine organisms require decades of observation.
In a simplified model, SST should be highest at the equator and decrease uniformly toward the poles. Same latitude should mean same temperature.
In reality, the western sides of oceans are warmer than the eastern sides at the same latitude.
Shanghai is warmer than California. Sydney is warmer than Chile.
This asymmetry is caused by currents:
Warm currents (e.g. North Equatorial Current, Kuroshio Current) carry tropical water to the western and northern sides of ocean basins.
Cold currents (e.g. California Current) carry polar water down the eastern side.
Cold-loving organisms (e.g. kelp): Found closer to the equator on the eastern shores of oceans, where cold currents bring cooler water (e.g. west Africa, California).
Warm-loving organisms (e.g. corals): Extend to higher latitudes on the western shores of oceans, where warm currents raise temperatures (e.g. Florida, Indonesia, southern Japan).
The exam will ask you to explain these distribution patterns using currents. The logic: identify which current affects that shore → state whether it is warm or cold → connect to the organism's temperature preference.
"The Great Pacific Garbage Patch is a visible island of trash you could stand on." It is not a solid mass. Much of it is microplastics and dispersed debris spread over a vast area. You would not see a distinct boundary from a boat.
"Garbage patches only affect organisms inside them." Marine animals encounter debris at the edges and throughout the gyre. Plastics also break down into microplastics that enter the food chain far from the patch itself.
"Sea-surface temperature depends only on latitude." Currents make western ocean shores significantly warmer than eastern shores at the same latitude. Latitude alone is not enough to predict SST.
"Kelps live only in polar waters." Kelps can be found surprisingly close to the equator on eastern ocean shores, because cold currents bring the cool water they need.
⚠️ The lecturer states directly that you will be asked to use currents to explain organism distribution. Practise explaining why corals extend to high latitudes on western shores and kelps reach low latitudes on eastern shores.
⚠️ Know why western ocean shores are warmer than eastern shores at the same latitude (warm currents like Kuroshio flow poleward on the western side; cold currents like the California Current flow equatorward on the eastern side).
⚠️ Understand that garbage patches form inside gyres because the circular currents trap floating debris in the centre.
⚠️ Be able to explain how radiation or pollutants move up the food chain through trophic levels (bioaccumulation).
True or false: The Great Pacific Garbage Patch is located inside the South Pacific Gyre. (False, it is inside the North Pacific Gyre.)
Fill in the blank: Western ocean shores are ______ than eastern shores at the same latitude. (warmer)
True or false: Cold-loving organisms like kelps are found closest to the equator on the western shores of oceans. (False, they are found on the eastern shores, where cold currents flow.)
Fill in the blank: Contaminants concentrate as they move up ______ levels in the food chain. (trophic)
True or false: The Fukushima nuclear plant released over 300 tonnes of contaminated water per day into the ocean after the 2011 earthquake. (True)
Q: Why does the Great Pacific Garbage Patch form where it does?
A: It sits in the centre of the North Pacific Gyre. The circular currents of the gyre push floating debris inward, where it accumulates because there is no mechanism to flush it out.
Q: Explain why warm-loving organisms like corals extend to higher latitudes on the western shores of oceans.
A: Warm currents (e.g. the Kuroshio Current in the Pacific, the Gulf Stream in the Atlantic) carry tropical water poleward along the western side of the ocean basin. This raises sea-surface temperatures at those latitudes, allowing corals to survive further from the equator than they could on the eastern side.
Q: Why are cold-loving organisms like kelps found closest to the equator on the eastern shores of oceans?
A: Cold currents (e.g. the California Current) flow equatorward along the eastern side of ocean basins, bringing cool water to relatively low latitudes. This creates conditions suitable for kelp closer to the equator than would otherwise be possible.
Q: How does radiation-contaminated water from the Fukushima plant affect marine ecosystems?
A: High radiation kills marine organisms directly (jellyfish are especially affected). Surviving organisms may develop DNA mutations. Contamination also bioaccumulates up the food chain: organisms at higher trophic levels (e.g. finfish that eat contaminated plankton) carry higher concentrations of radiation.
Q: If sea-surface temperature depended only on latitude, what pattern would you expect? How does reality differ, and why?
A: You would expect SST to be highest at the equator and decrease evenly toward both poles, with identical temperatures at the same latitude. In reality, western ocean shores are warmer than eastern shores at the same latitude, because warm currents carry tropical water poleward on the western side while cold currents bring polar water equatorward on the eastern side.
The garbage patch and SST material builds directly on the gyre and current concepts from the companion study notes. Bioaccumulation of contaminants connects to ecology and food-web topics later in the course. The distribution of corals and kelps ties into reef ecology, biodiversity, and climate-change modules (as SST rises, these distributions will shift). Understanding the east-west temperature asymmetry will also be relevant when studying upwelling zones and their productivity.
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