This topic will cover the basic concepts of marine chemistry, including the composition of seawater, major ions present, and the unique characteristics of the marine environment.
Introduction to Marine Chemistry
Key concepts, processes, and significance for ocean science
| Aspect | Description |
|---|---|
| Definition | The study of the chemical composition, reactions, and cycles that occur in seawater, sediments, and marine organisms. |
| Scope | - Seawater chemistry (major, minor, trace elements, gases) - Biogeochemical cycles (carbon, nitrogen, phosphorus, silica, sulfur) - Chemical oceanography (physical‑chemical interactions, water masses) - Anthropogenic impacts (pollution, acidification, eutrophication) |
| Why It Matters | Controls marine productivity, climate regulation, nutrient availability, and the health of marine ecosystems. |
| Component | Typical Concentration (average ocean) | Role |
|---|---|---|
| Water (H₂O) | ~96.5 % by mass | Solvent for all dissolved substances |
| Salts (major ions) | ~3.5 % (35 ‰) | Determines density, conductivity, and freezing point |
| Major ions | • Na⁺ 10.8 g kg⁻¹ • Mg²⁺ 1.29 g kg⁻¹ • Ca²⁺ 0.41 g kg⁻¹ • K⁺ 0.39 g kg⁻¹ • Cl⁻ 19.4 g kg⁻¹ • SO₄²⁻ 2.7 g kg⁻¹ |
Charge balance, buffering, biological functions |
| Minor & trace elements | Fe, Mn, Cu, Zn, Co, Ni, etc. (µg kg⁻¹–ng kg⁻¹) | Micronutrients, catalytic centers in enzymes |
| Dissolved gases | CO₂ (~2 mmol kg⁻¹), O₂ (~200 µmol kg⁻¹), N₂, Ar, CH₄ | Gas exchange, respiration, photosynthesis, climate feedbacks |
| Organic matter | Dissolved organic carbon (DOC) ~0.7 mmol kg⁻¹ | Carbon reservoir, substrate for microbes |
| Property | Symbol | Typical Oceanic Value | Controlling Factors |
|---|---|---|---|
| Temperature | T | -2 °C (deep polar) to 30 °C (tropics) | Solar radiation, currents |
| Salinity | S | 33–37 ‰ (practical salinity units, PSU) | Evaporation, precipitation, river input |
| Density | ρ | 1020–1030 kg m⁻³ | T, S, pressure |
| pH | — | 8.07 (average surface) | CO₂ system, buffering |
| Alkalinity | A_T | 2.3 mmol kg⁻¹ (≈2300 µeq kg⁻¹) | Bicarbonate/carbonate, borate, hydroxide |
| Partial pressure of CO₂ | pCO₂ | 380–420 µatm (surface) | Air–sea exchange, biological activity |
Note: The CO₂–carbonate system (CO₂ ↔ H₂CO₃ ↔ H