Ocean Salinity: Ocean salinity is caused from two sources: rocks on land and underwater seeps. The rocks on land contain all sorts of minerals, and as rain falls, erosion carries these minerals away. Even the freshest rain that falls on land is still ever-so-slightly acidic, so it allows rock minerals to erode and be deposited into the ocean. The other source of salt in the ocean comes from deep down on the ocean floor in the form of hydrothermal vents. Cracks in the ocean floor allow ocean water to seep down and become heated by magma deep in the earth. Down at those levels, a series of chemical reactions occur, and the water can pick up metals and other minerals from surrounding rock. This water then is released through vents in the sea floor and into the ocean, contributing to the saline mineral concentration. The ions of chloride and sodium make up about 85 percent of all dissolved ions in the ocean. Additionally, salinity concentrations in the ocean are not always the same. Salinity is typically lower at the equator and near the poles, and typically higher at mid-latitudes. On average, salt accounts for about 35 parts per thousand parts of water. That means that 3.5 percent of the weight of ocean water is dissolved salt!
Salt Mining: Salt mining operations like this employ a simple technique of evaporation using salt ponds. Salt water is pumped into shallow ponds right near the shore, and allowed to evaporate. As the water dries up, the salt crystals are crystallized and left behind on the floor of the pond. Then, those crystals are scraped up by rakes and other machinery. These evaporation ponds typically exist in warm, arid climates that experience high evaporation rates and little rainfall.
Location: This specific salt pond site has been mining salt since 1871 (under ownership of different companies). It continues to operate as San Diego’s second-longest running business.
Logging:
Upon your visit, please send a message with:
- The name of this Earthcache and the number of people in your group.
- At the time of your visit, can you see water in the salt ponds, or are they dry?
- Use your GPS to determine where we are located in relation to the equator and the poles. Does this make sense with what you learned in the reading?
- What cause of ocean salt deposition (rocks on land or underwater seeps) do you think is occurring nearest this coastal region?
Have fun, enjoy, and post pictures if you are able to!
Sources:
https://oceanservice.noaa.gov/facts/whysalty.html
https://manoa.hawaii.edu/exploringourfluidearth/chemical/chemistry-and-seawater/salty-sea/traditional-ways-knowing-salt-harvesting
https://en.wikipedia.org/wiki/South_Bay_Salt_Works
https://hiddensandiego.net/things-to-do/places/salt-mines