Marine chemistry

Marine chemistry, also known as chemical oceanography, is the study of the chemical composition of the world's oceans.

It examines how seawater interacts with the atmosphere, the seafloor, and marine organisms. This field is vital for understanding global biogeochemical cycles and ocean circulation. Scientists study how elements like carbon, nitrogen, and phosphorus move through these systems. This research helps us understand the effects of human activities like pollution and climate change. By studying these chemical processes, we can better understand the health of our entire planet.

One major focus of marine chemistry is the movement of organic matter. Dissolved Organic Matter, or DOM, is a critical part of the ocean's carbon pool. It includes molecules such as amino acids, sugars, and lipids. DOM represents about 90% of the total organic carbon in marine environments. A specific type, called Colored Dissolved Organic Matter (CDOM), makes up 20% to 70% of the ocean's carbon.

CDOM levels are higher near river outlets and lower in the open ocean. Some DOM resists degradation and can stay in the ocean for centuries, helping regulate carbon storage.

Another important component is Particulate Organic Matter, or POM. POM consists of larger organic particles like organisms, fecal pellets, and detritus. These particles settle through the water column in a process called the biological pump.

This pump transfers carbon from the surface ocean down to the deep sea. As POM sinks, bacteria decompose it, which releases nutrients and carbon dioxide. Some refractory POM reaches the ocean floor. This material can contribute to carbon sequestration over very long periods of time.

In extreme environments, life relies on unique chemical processes. Extremophiles are organisms that thrive in extreme temperature, pressure, or light conditions.

Near hydrothermal vents, many organisms use chemoautotrophy to survive. Instead of using sunlight, they use chemical compounds as energy sources. These vents enrich the water with chemicals like elemental sulfur, hydrogen, and methane. Primary producers, mostly prokaryotes, derive energy from these chemicals through redox reactions. This creates a food source for other living things in these deep-sea ecosystems.

Different metabolic pathways exist even in these harsh habitats. Some microorganisms, such as Thiomicrospira, oxidize sulfur compounds to gain energy.

In colder waters, they use oxygen as an electron acceptor. Closer to the vents, they might use nitrate instead. Other microbes perform iron-oxidation, using Fe(II) as an electron donor. This process is part of the iron-redox cycle. In sea ice, other extremophiles live in brine pockets. These pockets can have salinity up to three times higher than regular seawater. Because these organisms are often photosynthetic, they must produce antioxidants to survive hyperoxic conditions.

Geological processes also change ocean chemistry through seafloor spreading. At mid-ocean ridges, hydrothermal vents introduce iron, sulfur, and manganese into the ocean.

The rate of spreading affects the magnesium to calcium (Mg/Ca) ratio in the water. Rapid spreading rates, between 10 and 200 mm/yr, increase basalt reactions with seawater. This removes more magnesium and releases more calcium, resulting in a lower Mg/Ca ratio. A lower ratio favors the formation of calcite seas. Conversely, slow spreading leads to higher Mg/Ca ratios and aragonite seas. This chemical environment even regulates how reef-building organisms construct their skeletons.

Human activities are significantly altering these natural chemical balances. The burning of fossil fuels increases atmospheric carbon dioxide levels. This leads to ocean acidification, which can harm marine ecosystems.

Industrial pollution and land-use practices also impact ocean chemistry. Because of these changes, the international community has made restoring ocean chemistry a priority. This effort is tracked through Sustainable Development Goal 14. Scientists use many tools to monitor these shifts, including pH meters and dissolved CO2 meters.

Modern oceanographers use advanced technology to collect data.

They use CTD instruments to measure conductivity, temperature, and pressure. Autonomous Underwater Vehicles (AUVs) allow for continuous, large-scale monitoring of the ocean.

Researchers also use mass spectrometers to detect trace elements and isotopes. These tools help us understand the complex connections between the ocean, the atmosphere, and life on Earth.