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Unlock This CourseThe ocean is like a massive chemistry lab where millions of different substances mix together. Understanding the basic building blocks of matter - elements, compounds and mixtures - helps us understand how our oceans work and why changes in pH and salinity matter so much for marine life.
Key Definitions:
Seawater contains over 80 different elements! The most common ones are hydrogen and oxygen (from water molecules), sodium and chlorine (from salt), plus magnesium, calcium and potassium. These elements don't exist alone - they're usually part of compounds or ions floating in the water.
Seawater is actually a complex mixture containing water, dissolved salts, gases and tiny particles. Unlike a compound, you can separate the parts of this mixture through processes like evaporation or distillation.
The saltiness comes mainly from sodium chloride (table salt), but seawater also contains other compounds like magnesium chloride and calcium carbonate. These compounds formed when elements combined chemically, then dissolved into the ocean water over millions of years.
Makes up about 85% of ocean salt. Forms when sodium and chlorine atoms bond together chemically.
About 10% of ocean salt. Important for marine organisms to build shells and skeletons.
Used by corals, shellfish and many marine animals to build their hard parts.
Ocean pH is crucial for marine life. Normal seawater has a pH of about 8.1, making it slightly basic (alkaline). This might seem like a small number, but tiny changes in pH can have huge effects on marine ecosystems.
Many marine creatures are extremely sensitive to pH changes. When the ocean becomes more acidic (lower pH), it affects their ability to build shells, reproduce and even survive.
The Great Barrier Reef is experiencing coral bleaching partly due to ocean acidification. As the ocean absorbs more carbon dioxide from the atmosphere, it forms carbonic acid, lowering the pH. This makes it harder for corals to build their calcium carbonate skeletons, weakening the entire reef ecosystem.
Creatures like mussels, oysters and sea snails need the right pH to extract calcium and carbonate ions from seawater. Lower pH means fewer available carbonate ions, making shell-building much harder.
Salinity varies around the world's oceans, typically ranging from 32-37 parts per thousand. This variation creates different marine environments, each supporting unique communities of life.
Salinity isn't the same everywhere. Near river mouths, fresh water dilutes the seawater, creating brackish conditions. In hot, dry areas like the Red Sea, high evaporation increases salinity. These changes affect which organisms can survive in different areas.
Where rivers meet the sea. Lower salinity (5-30 ppt) creates unique mixing zones with specially adapted species.
Stable salinity around 35 ppt. Most marine organisms are adapted to these conditions.
Higher salinity (up to 40 ppt) due to high evaporation rates and low rainfall.
Human activities are changing ocean chemistry faster than ever before. Understanding elements, compounds and mixtures helps us see how pollution and climate change affect marine environments.
When we burn fossil fuels, we release carbon dioxide into the atmosphere. About 25% of this CO₂ dissolves into the ocean, where it reacts with water to form carbonic acid. This chemical reaction is lowering ocean pH worldwide.
Oyster farms in the Pacific Northwest have struggled with ocean acidification. The more acidic water dissolves young oyster shells faster than they can grow them. Farmers now monitor pH levels daily and sometimes add chemicals to buffer the water, showing how understanding chemistry helps solve real problems.
Factories release various chemical compounds into waterways. These can change local pH and salinity, creating toxic conditions for marine life. Heavy metals like mercury and lead are particularly dangerous as they don't break down naturally.
Scientists use various tools to measure pH and salinity in the ocean. Understanding whether they're measuring elements, compounds, or mixtures helps them interpret their data correctly.
pH meters detect hydrogen ion concentration, while conductivity sensors measure salinity by testing how well water conducts electricity (saltier water conducts better). These tools help scientists track changes over time and predict future conditions.
Measure hydrogen ion activity to determine acidity levels in real-time.
Measure electrical conductivity to calculate salt content accurately.
Track large-scale changes in ocean chemistry from space using colour detection.
Climate change will continue affecting ocean chemistry. Rising temperatures increase evaporation, potentially raising salinity in some areas while melting ice caps could lower it in others. Meanwhile, continued CO₂ emissions will keep pushing pH lower.
As Arctic ice melts, it adds fresh water to the ocean, lowering salinity. This affects ocean currents and the animals that depend on specific salinity levels. Polar bears aren't the only Arctic species at risk - the entire marine food web is changing as the chemical balance shifts.
Understanding ocean chemistry helps us make better decisions. Reducing CO₂ emissions slows acidification, while controlling pollution prevents harmful compounds from entering marine ecosystems. Every action that improves air and water quality helps protect our oceans' delicate chemical balance.