Questions & explanations
1. Compare a fully protected MPA versus a multiple-use MPA in the deep sea.
A fully protected MPA, also called a no-take reserve, bans all extractive activities like fishing, mining, and drilling. This gives the ecosystem the highest level of protection and allows species to thrive. A multiple-use MPA allows some activities, such as limited fishing or mining, but restricts others to reduce damage. For example, it might permit fishing but ban bottom trawling. Fully protected MPAs are more effective at conserving biodiversity, but they are harder to enforce and may face opposition from industries. Multiple-use MPAs can be easier to establish because they allow some economic use, but they provide less protection. Both types can play a role, but fully protected areas are essential for preserving deep-sea ecosystems.
2. Explain the thermal wind relation: how does horizontal density gradient affect vertical shear?
The thermal wind relation connects changes in current speed with depth to horizontal density gradients. If there is a horizontal difference in water density (e.g., cold, dense water on one side and warm, light water on the other), then the pressure gradient changes with depth. This causes the geostrophic current to change speed or direction as you go deeper. Specifically, a horizontal density gradient creates vertical shear – meaning the current at depth is different from that at the surface. The thermal wind relation is used to estimate currents from density measurements. For example, in the ocean, cold water on the left of the current (in the Northern Hemisphere) will cause the current to increase with depth.
3. Compare the environmental impact of deep-sea mining to land-based mining.
Deep-sea mining does not require clearing forests or building roads like land mining, so it avoids some surface damage. However, deep-sea mining targets unique ecosystems that are poorly understood and may contain species found nowhere else. Land mining often produces toxic waste piles like tailings, while deep-sea mining may release fine sediment plumes that linger in the water. The deep sea has very slow natural processes, so damage from mining can last for centuries, much longer than on land. Both types cause habitat destruction and biodiversity loss, but the impacts of deep-sea mining are harder to predict and repair. Land mining can sometimes be reclaimed, but deep-sea sites may never fully recover.
4. How are deep-sea MPAs created and managed?
Deep-sea MPAs can be created by individual countries in their territorial waters (up to 200 nautical miles) or by international agreements in the High Seas. Countries often designate MPAs through their own laws, such as the United States Marine National Monuments. In the High Seas, MPAs can be established by regional fisheries organizations or by the International Seabed Authority for mining areas. Management involves rules on what activities are allowed, like no fishing or no mining, and monitoring to ensure compliance. Enforcing rules in the deep sea is difficult because of the vast distances and depth. Successful MPAs require cooperation among many nations and regular scientific surveys.
5. Compare the governance of the water column versus the seabed in the high seas.
On the high seas, the water column (the ocean water above the seabed) is governed by the principle of freedom of the seas, meaning all countries can fish, sail, and do research. However, fishing is regulated by regional fisheries management organizations. In contrast, the seabed in the Area is governed by the International Seabed Authority (ISA), which controls mineral extraction. The water column is not owned by anyone, while the seabed and its resources are common heritage. This means that mining on the seabed is more strictly regulated than fishing in the water. The difference causes challenges because activities in one zone can affect the other, for example, bottom trawling harms both.
6. Give an example of a recent international agreement related to deep-sea governance.
A recent important agreement is the Biodiversity Beyond National Jurisdiction (BBNJ) treaty, also called the High Seas Treaty, signed in 2023. This treaty aims to protect marine life in the high seas, including the deep sea. It sets rules for creating marine protected areas, doing environmental impact assessments, and sharing deep-sea genetic resources. The BBNJ treaty fills gaps in UNCLOS because UNCLOS did not specifically address biodiversity conservation. It helps countries work together to protect deep-sea ecosystems from threats like overfishing and pollution. Many nations have signed it, but it still needs enough countries to ratify it to become fully effective.
7. Compare the effects of plastic versus chemical pollution on deep-sea life.
Plastic pollution mainly causes physical harm, such as blocking the gut of animals that eat it or entangling them. It can also release toxic additives, but mostly it acts as a physical contaminant. Chemical pollution, like heavy metals and pesticides, is toxic even in tiny amounts. It can damage organs, affect reproduction, and even cause death in deep-sea animals. Metals like mercury build up in the food chain, reaching high concentrations in predators. Both types of pollution are long-lasting in the deep sea, but chemical pollution may be more directly harmful per unit. However, plastic is more visible and widespread, while chemical pollution is often invisible.
8. How can scientists tell apart changes due to Milankovitch cycles from other climate factors?
Scientists use spectral analysis to find regular, repeating cycles in sediment records that match the known orbital periods (100,000, 41,000, 23,000 years). They compare the timing of these cycles with predictions from orbital models. If the same frequencies appear across many records and align with orbital forces, it suggests Milankovitch forcing. Other factors like volcanic eruptions or tectonic changes produce irregular or longer-term patterns. Also, Milankovitch cycles affect global climate uniformly, while local factors cause regional differences. By checking multiple locations and proxies, scientists can separate orbital from non-orbital signals.
9. Compare deep-sea fishing to coastal fishing in terms of sustainability.
Coastal fishing typically targets fish that grow faster and reproduce earlier, so they can withstand more fishing pressure. Deep-sea fish are the opposite: they grow slowly, reproduce late, and have few offspring, making them much less resilient. Coastal ecosystems often recover more quickly from fishing damage because they have more sunlight and productivity. Deep-sea habitats are extremely slow to recover due to cold temperatures and low food supply. While some coastal fisheries have been managed to be sustainable, deep-sea fisheries have almost always led to overfishing. Therefore, deep-sea fishing is generally less sustainable than coastal fishing.
10. What is the United Nations Convention on the Law of the Sea (UNCLOS)?
The United Nations Convention on the Law of the Sea, or UNCLOS, is an international treaty that sets rules for how countries use the world's oceans. It was signed in 1982 and has been agreed to by many nations. UNCLOS divides the ocean into zones, such as territorial waters (up to 12 nautical miles), exclusive economic zones (up to 200 nautical miles), and the high seas beyond. It establishes countries' rights and responsibilities for things like shipping, fishing, and mining. For the deep sea, it defines the 'Area' — the seabed beyond national borders — as the 'common heritage of mankind'. UNCLOS is the main legal framework for governing the deep sea.
11. Why is the North Atlantic Gyre clockwise?
The direction of the North Atlantic Gyre is caused by the Coriolis effect and the pattern of winds. In the Northern Hemisphere, the Coriolis effect turns moving water to the right. The trade winds near the equator blow from east to west, pushing water westward. The westerlies in the mid-latitudes blow from west to east, pushing water eastward. These winds create a clockwise loop. The Gulf Stream flows north on the western side, the North Atlantic Current flows east across the top, the Canary Current flows south on the eastern side, and the North Equatorial Current flows west across the bottom. This gyre is a key driver of Atlantic circulation.
12. How does the Indian Ocean gyre differ from the Atlantic gyre?
The Indian Ocean gyre is unique because it reverses direction seasonally. In the other oceans, gyres spin the same way all year: clockwise in the Northern Hemisphere and counterclockwise in the Southern. But in the Indian Ocean, the gyre direction changes: in summer, the gyre is counterclockwise (due to southwest winds), and in winter it is clockwise (due to northeast winds). This happens because the Indian Ocean is bounded by land on the north, which changes the wind patterns. The Atlantic gyres are more stable and do not reverse. The Indian Ocean also has a smaller area north of the equator, so its circulation is dominated by monsoon winds.