Analytical Exploration of the Depths of Ocean Chemistry

By Rebecca Ingle, Ph.DReviewed by Danielle Ellis, B.Sc.

Over 79 % of our Earth’s surface is covered by oceans, and the oceans play a critical role in the regulation of our climate and atmosphere.¹ The oceans act as both a carbon dioxide and heat sink^2, and therefore, understanding the chemical composition of the ocean and its evolution is a critical part of environmental research.

There are a number of analytical techniques that are utilized in ocean chemistry, including spectrophotometry, hyphenated mass spectrometry techniques such as proton-transfer reaction mass spectrometry (PTR-MS), and variations of these and other analytical techniques, for performing flow analysis.^3,4

Such methods provide a means of quantitative and qualitative analysis of the composition of seawater. However, each has different strengths and weaknesses with the profiles of chemicals that can be detected and their sensitivities.  

Key Analytical Techniques in Studying Ocean Chemistry

With ocean chemistry analysis, it can be advantageous to make flow measurements rather than batch measurements. Flow analysis is where the chemical analysis is performed over a flowing stream of water, often obtaining results in real-time. Batch analysis relies on a sample being taken and then analyzed by offline instrumentation – often back in a laboratory setting.

While offline laboratory techniques often boast better limits of detection for trace elements, the ability to monitor changing ocean conditions in situ can be very advantageous for ocean monitoring studies.³ Ocean chemistry studies always rely on some sampling step.

Still, for pollution and other kinds of tracer studies, it can be advantageous to be able to set up remote monitoring stations rather than needing to make multiple exhibitions to collect and return samples from the field.

Techniques such as PTR-MS, gas-chromatography mass spectrometry (GC-MS) and liquid chromatography mass spectrometry (LC-MS) are particularly well-suited to the study of organic volatile compounds in both the atmosphere and seawater.⁵ These family of methods have a high information content, as particular masses or chromatographic peaks can be selected for further analysis, and sample preparation procedures like preconcentration can be used to detect even very low concentrations of such chemical species.

There are a large number and variety of ionic compounds in seawater, from salts such as sodium chloride to a variety of metal ions that can arise either from external pollution or as part of the natural ocean chemical cycles.⁶ Ion chromatography is often a popular choice for such studies as well as it is also compatible with the detection of a very large variety of chemical species.

Investigating Marine Life Through Chemical Analysis

The health of the marine ecosystem is strongly related to the local chemistry. For marine life to thrive, there cannot be an excess of pollutants, and much be sufficient nutrients in the water to support the ecosystem. In turn, the local marine life also has a direct impact on the local chemistry of the ocean water, and profiling the water for certain metabolites can be a way of screening for which local species are present or even for discovering the presence of new species.⁷

The Role of Ocean Chemistry in Climate Change and Environmental Health

The ocean has a number of roles to play in climate change and the overall environmental health of our planet. Many scientists and researchers try to model changing ocean conditions and their effect on other environmental systems, such as the atmosphere, to understand better how the ocean's chemistry may change as a result of climate change or what impact changing ocean chemistry may have.

Many scientists are now strongly advocating that ocean management becomes a key focus in future sustainability discussions⁸ as changing ocean chemistry, such as the acidification of ocean water due to higher levels of dissolved carbon dioxide forming carbonates in the water, can form disastrous feedback loops for marine life. Changing ocean currents due to increased melting of freshwaters also has a direct impact on the atmospheric conditions, affecting climate and water.  

Commercial Applications of Ocean Chemistry Research

The complexity and vastness of the ocean and its chemistry have driven a huge amount of commercial technological development in terms of instrumentation for the analysis of seawater and remote sensing platforms that are often able to operate in challenging and highly variable environmental conditions.

Ocean chemistry is also exploited as a means of trying to locate new sites for exploitation in oil, gas, and mineral mining. Often polymetallic nodules are formed on the ocean floor when valuable metals are present in a region, and spectroscopic analysis and imaging of those nodes can help pinpoint regions where there may be sufficient reserves for further exploitation.⁹

Challenges and Future Directions in Ocean Chemistry Research

The ocean is an inherently challenging chemical environment for measurement due to the harsh and corrosive nature of seawater itself and the need to develop measurement devices that can both withstand this and be deployed and maintained in often highly remote and inaccessible areas.

The need for greater ocean chemistry monitoring will only increase with the increasing impact of climate change as destabilizing systems require more frequent and closely spaced measurements to capture the behavior that current models do not describe well. Pollutants, in particular microplastics, are another highly active area of research, and researchers are trying to find ways to preserve marine ecosystems, including fish and coral reefs.