The Ocean

Peter Letts   May 23, 2025

Ocean Health: Assessing Climate Change Impact

How does climate change affect the ocean? This article explores the ocean’s current health, the impacts of climate change, and the importance of ocean conservation.

Key Takeaways

• Ocean health is critical for global climate regulation, supporting biodiversity and marine ecosystems while influencing weather patterns and economies.

• Ocean acidification and warming, driven by increasing carbon dioxide levels, threaten marine life by disrupting ecosystems and impacting species' survival.

• Human activities, including pollution and overfishing, are significant stressors on ocean ecosystems, necessitating global conservation efforts and sustainable management practices.

Understanding the World’s Oceans

The world’s ocean is a critical component of the Earth’s surface, covering approximately three-quarters of it and containing about 97% of the planet’s water, including the Earth’s water. This immense volume of ocean water amounts to 1.335 billion cubic kilometres, making the ocean the largest ecosystem on Earth. Housing nearly a million known species, the ocean covers a treasure trove of biodiversity and natural resources essential for life, while also playing a vital role in regulating the Earth’s land mass.

The concept of the global ocean, a continuous body of salt water, has existed for eons and is divided into five principal oceans: the Pacific, Atlantic, Indian, Southern Ocean, and Arctic. These interconnected ocean basins cover about 90% of the Earth’s biosphere, providing habitat and sustenance for a vast array of marine life. The term “world’s oceans” encapsulates this unity, emphasising the interconnectedness of these large bodies of water, including the great ocean.

Recognising the oceans’ role in regulating Earth’s climate, absorbing heat and carbon dioxide, and supporting marine ecosystems is crucial. The ocean’s surface, a dynamic interface between the ocean and the atmosphere, plays a crucial role in these processes. From the ocean floor to the open ocean, each layer and area contributes to the health and functionality of the entire ocean system.

The world’s oceans, integral parts of our planet’s life-support system, influence weather patterns, support economies, and provide critical habitats for marine life. As we explore the various facets of ocean health, it becomes clear how interconnected and vital these waters are to our survival and well-being.

Ocean Chemistry and pH

The chemistry of the ocean is a delicate balance that plays a crucial role in maintaining marine ecosystems. One of the most significant aspects of ocean chemistry is its pH level, which has been steadily decreasing due to increased carbon dioxide absorption. When carbon dioxide dissolves in seawater, it forms carbonic acid, leading to higher acidity levels. This process releases hydrogen ions, increasing the ocean’s acidity.

The average pH of the ocean’s surface waters has fallen from approximately 8.1 to 8.05, indicating a significant increase in acidity. This change may seem minor, but because the pH scale is logarithmic, even a small shift can result in a substantial increase in acidity. For instance, a drop of 0.1 pH units represents about a 30% increase in acidity. This phenomenon, known as ocean acidification, poses a severe threat to marine life, particularly calcifying organisms such as shellfish and corals that rely on carbonate ions to form their shells and skeletons. The ocean’s average pH is a critical factor in understanding these changes.

Ocean acidification disrupts the availability of carbonate ions, making it difficult for organisms like pteropods and corals to build and maintain their shells. In more acidic waters, the shells of these organisms can begin to dissolve, which not only affects their survival but also has cascading effects on the entire marine food web. Fish behaviour is also impacted, as changes in ocean chemistry can alter their ability to detect predators and find suitable habitats.

The implications of these chemical changes are profound. As the ocean absorbs more carbon dioxide and becomes increasingly acidic, the health of marine ecosystems is jeopardised. Knowledge of ocean chemical properties and processes is vital for developing strategies to mitigate ocean acidification impacts and protect marine biodiversity.

The Ocean Floor and Basins

Beneath the ocean’s surface lies a diverse and complex landscape known as the ocean floor. This area, covering about 70% of the ocean areas, includes vast abyssal plains that exist at water depths exceeding 10,000 feet. These plains are some of the most extensive and flat regions on Earth, providing a habitat for various deep-sea creatures at the bottom of the ocean.

One of the most remarkable features of the ocean floor is the mid-ocean ridge, the longest mountain range on Earth, stretching over 40,000 miles. This underwater mountain range is a result of tectonic activity and plate movements, which also shape the oceanic basins. These basins cover both the oceanic and continental crust, creating a diverse topography that includes deep canyons and trenches.

Ocean trenches, such as the Mariana Trench, are among the deepest parts of the ocean, with ocean depth that can exceed 36,000 feet. These trenches are formed by the subduction of one tectonic plate beneath another, creating some of the most extreme environments on Earth. The composition of the ocean floor primarily consists of basalt and other igneous rocks, which are products of volcanic activity in deep water.

Despite its vastness, only about 5% of the ocean floor has been mapped, making it one of the least explored areas of our planet. Organisations like the US Geological Survey (USGS) are working to map the bathymetry, or the shape of the ocean floor, to better understand this hidden world. This exploration is crucial for understanding the geological processes that shape our planet and the ecosystems that thrive in these deep and mysterious waters.

Marine Life and Biodiversity

The ocean is home to an astonishing array of marine life, with about a quarter of all eukaryotic life found in its waters. As of 2023, there are over 242,000 documented marine species, showcasing the incredible diversity and complexity of marine ecosystems. Marine life evolved approximately 3 billion years ago, long before life appeared on land, making the ocean a cradle of early life on Earth.

Coral reefs, which cover just 1% of the ocean’s area, provide habitat for about 25% of all marine species. These vibrant and diverse ecosystems are home to over 4,000 species of fish and countless other marine organisms that depend on the reefs for survival. Coral reefs are critical not only for marine biodiversity but also for supporting fisheries and tourism, which generate billions in revenue.

Deep ocean ecosystems, where sunlight cannot penetrate, rely on chemosynthesis rather than photosynthesis. Organisms such as tube worms and certain bacteria harness chemical reactions from hydrothermal vents to thrive in these dark and extreme environments. Marine species play a crucial role in maintaining the structure and function of their ecosystems, from the smallest plankton to the largest whales.

However, marine biodiversity is under threat from various factors, including ocean acidification and warming. The dissolution of pteropod shells, for example, can impact species that rely on them in the food web. The health of marine ecosystems and the ocean is intrinsically linked, and preserving this biodiversity is crucial for the stability and resilience of our planet’s life support systems.

Ocean Warming

Ocean warming, a pressing issue caused by climate change, leads to far-reaching consequences such as the acceleration of sea-level rise. From 2013 to 2021, rising levels of sea-level rise averaged 4.5 millimetres per year, a dramatic increase compared to previous decades.

Approximately 90% of global warming occurs in the ocean, making it a critical component of the Earth’s climate system. The ocean’s surface has heated between 0.68 and 1.01°C from pre-industrial times to 2011-2020, with 2024 recorded as the warmest year on record for the oceans. This warming trend has severe implications for marine ecosystems and the distribution of heat-sensitive species in the ocean.

Marine heatwaves, which have doubled in frequency, lead to extensive coral bleaching and the degradation of marine habitats. A 1.5°C increase in ocean temperature could threaten 70 to 90 per cent of coral reefs, putting thousands of marine species at risk. The last decade was the warmest for the ocean since at least the 1800s, highlighting the urgent need for action to mitigate these changes during a warm spell.

By absorbing about 23% of annual CO2 emissions from human activities, the ocean plays a crucial role in regulating the global climate. However, this absorption also contributes to ocean acidification. As ocean temperatures rise, more than half of marine species could face extinction by 2100, underscoring the importance of addressing ocean warming to protect marine biodiversity and maintain the health of our planet.

Ocean Acidification

Increased carbon dioxide levels in the atmosphere lead directly to ocean acidification. Dissolved CO2 can form carbonic acid in seawater, releasing hydrogen ions and increasing acidity. Since the industrial revolution, the average pH of surface ocean waters has decreased by 0.1 units, indicating a significant increase in acidity.

This increase in acidity poses a threat to marine organisms that rely on carbonate ions to build their shells and skeletons. Shellfish, corals, and other calcifying organisms struggle to develop in more acidic waters, with their shells beginning to dissolve. The projected future conditions of ocean acidity could lead to the dissolution of the shells of organisms such as pteropods and foraminifera.

Ocean acidification also impacts marine ecosystems by disrupting the behaviour and survival of various species. For example, increased acidity can impair the ability of fish like clownfish to detect predators, leading to higher risks of predation. Bottom-dwelling invertebrates near CO2 vents demonstrate lower survival rates due to altered pH levels in their habitats.

Rapid changes in ocean chemistry leave marine life with little time to adapt, increasing the risk of population declines and potential extinctions. Protecting marine ecosystems from the effects of ocean acidification requires urgent action to reduce carbon dioxide emissions and mitigate the impacts of climate change on our oceans.

Human Activities and the Ocean

Human activity profoundly impacts ocean health. Pollution, overfishing, and ocean acidification are major stressors threatening marine life and ecosystems. Marine pollution, caused by substances from human activities entering the ocean, leads to harmful effects on marine organisms and habitats.

Plastic pollution is significant, with millions of tons of waste entering the ocean each year. This pollution affects marine life, from the smallest plankton to the largest whales, and can lead to the ingestion and entanglement of marine animals. Overfishing also poses a severe threat to marine ecosystems, leading to resource depletion and disrupting food webs. Additionally, marine debris can exacerbate these issues, further impacting the health of our oceans.

Coral reefs support fisheries and tourism, generate billions in revenue, and are essential for the economic well-being of many coastal communities. The medicinal compounds derived from coral reef organisms are being explored for treatments, highlighting the importance of preserving these ecosystems.

Efforts to reduce marine litter and manage resources sustainably are critical for protecting ocean health. Initiatives like the Pacific Ocean Litter Project and the Enhancing Pacific Ocean Governance project empower nations to tackle marine pollution and promote sustainable practices. Regional Fisheries Management Organizations (RFMOs) play a vital role in international fisheries conservation efforts, ensuring the sustainable use of marine resources.

Protecting Our Oceans

Protecting our oceans is crucial for sustaining marine biodiversity and ensuring the health of our planet. Global efforts to conserve ocean resources are essential for sustainable management and the restoration of marine ecosystems. One such initiative is the Coral Triangle Initiative, which aims to enhance marine conservation across six Southeast Asian countries.

Australia has committed substantial funding to support the Coral Triangle Initiative’s Regional Secretariat, emphasising the importance of international collaboration in marine conservation. The creation and enforcement of marine protected areas (MPAs) is a key measure for safeguarding ocean ecosystems. The High Seas Treaty, signed in March 2023, aims to create MPAs in international waters and protect 30% of the oceans by 2030.

The Torres Strait Treaty focuses on protecting the cultural practices of Indigenous peoples while conserving marine habitats in the region. Australia also participates in the Convention on International Trade in Endangered Species, regulating the trade of endangered marine species. These efforts highlight the importance of international cooperation and sustainable management in protecting our oceans.

Instruments and Methods of Ocean Study

Understanding and protecting our oceans require advanced tools and methods to study their complex systems. Argo floats are a key component of the ocean observing system, collecting data on temperature and salinity from the upper 2,000 meters of the ocean. Since its inception, the Argo program has deployed over 15,000 floats and gathered more than 2 million temperature and salinity profiles.

CTDs, which measure conductivity, temperature, and depth, are essential for understanding the physical properties of ocean water. They provide valuable data on ocean conditions, aiding scientists in monitoring changes in the ocean’s chemistry and temperature.

Satellite monitoring offers comprehensive coverage of oceanic changes, aiding in the analysis of global sea surface temperatures and ocean currents. Various instruments, including Argo floats, CTDs, and satellite monitoring, are employed by scientists to study the ocean.

These tools are crucial for gathering data and understanding the impacts of climate change on the oceans. Ocean science plays a vital role in developing strategies to protect marine ecosystems and mitigate the effects of climate change.

Summary

In summary, our oceans are facing unprecedented challenges due to climate change, human activities, and environmental degradation. Ocean warming, acidification, and pollution are threatening marine biodiversity and the health of our planet. However, global efforts to protect and conserve ocean resources offer hope for the future. By understanding the science behind these changes and taking action to mitigate their impacts, we can work towards a sustainable and healthy ocean for generations to come.

Frequently Asked Questions

How does ocean acidification impact marine life?

Ocean acidification significantly impacts marine life by disrupting carbonate ion availability, crucial for shell and skeleton formation in calcifying organisms such as shellfish and corals. This challenge threatens their survival and destabilises the entire marine food web.

What are the primary causes of ocean warming?

Ocean warming is primarily driven by human-induced climate change, as the oceans absorb approximately 90% of the excess heat from global warming, resulting in rising sea temperatures and severe impacts on marine ecosystems. It is crucial to address this issue to protect our oceans and biodiversity.

Why is the ocean floor less explored than outer space?

The ocean floor remains less explored than outer space, primarily due to its challenging conditions and vast depths, with only about 5% mapped. Advanced technology and significant resources are necessary for exploration, making it a more daunting task than venturing into space.

What are marine protected areas (MPAs), and why are they important?

Marine protected areas (MPAs) are crucial for safeguarding marine ecosystems by regulating human activities, which in turn support biodiversity and sustainable fisheries. Their establishment is vital in the global initiative to conserve 30% of the oceans by 2030.

How do human activities contribute to marine pollution?

Human activities significantly contribute to marine pollution via plastic waste, chemical runoff, and oil spills, with millions of tons of plastic entering the ocean annually, harming marine ecosystems. Effective waste management and sustainable practices are essential to mitigate this issue.