Calcium enters the ocean primarily through three main pathways: continental weathering, hydrothermal fluid emissions, and dolomitization fluxes.
1. Continental Weathering
- Rivers and Groundwater: The most significant source of calcium is continental weathering. Rainwater, slightly acidic due to dissolved carbon dioxide, erodes rocks on land, dissolving calcium-containing minerals such as calcite and feldspar. This dissolved calcium is then carried by rivers and groundwater to the ocean. This process is influenced by factors like rainfall, temperature, and the type of rocks in a given region.
2. Hydrothermal Fluid Emissions
- Deep-Sea Vents: Hydrothermal vents, found mainly at mid-ocean ridges, release fluids that have circulated through the Earth’s crust, leaching out various elements, including calcium. These hydrothermal fluids, heated by magma, dissolve calcium from the surrounding rocks and transport it to the ocean when they are expelled at vent sites.
3. Dolomitization Fluxes
- Dolomite Formation: Dolomitization is a geochemical process where the mineral calcite (calcium carbonate) is altered to dolomite (calcium magnesium carbonate). This process can both release and consume calcium within marine sediments, impacting the calcium balance of the ocean.
In summary, the oceanic calcium concentration is influenced by a complex interplay of input sources like riverine influx and hydrothermal vents, as well as removal processes such as biogenic calcification (the formation of shells and skeletons by marine organisms) and inorganic precipitation.
