Volcanoes emit chlorine and all the other halides. Remember the inventor of the DDT claims he obtained the chlorine gas as he was walking up Mt. St. Helen's.

Natural Chlorination of Marine Organic Matter

Alessandra C. Leri et al.. August 2015 Photon Sciences Department Brookhaven National Laboratory.

Abstract:

Chloride, Cl- , is the most abundant solute in seawater, amounting to 55% of ions by weight. Cl- is more difficult to oxidize than bromide, and marine halogenating enzymes tend to be bromoperoxidases2 that are incapable of forming organochlorines. Consequently, most halogenated natural products identified in the marine environment are organobromines3 . Known exceptions include small quantities of volatile chlorocarbons emitted by marine algae and dissolved

chlorinated benzoic acids. We report here high concentrations (180-700 mg·kg-1 ) of organochlorine in particulate organic matter from deep-water sediment traps, the first evidence of natural organochlorine in marine organic detritus. X-ray spectromicroscopic imaging revealed that this organochlorine exists in two fractions, with sparse hotspots of aliphatic compounds against a diffuse background of aromatic organochlorine. Examining fresh phytoplankton as potential biogenic sources, we measured high aliphatic organochlorine in particulate material from E. huxleyi and Pavlova sp. We also studied abiotic chlorination, finding that algal detritus serves as suitable substrate for photochemical and Fenton-like processes to incorporate Cl at levels up to several g·kg-1 . These findings provide the first evidence of significant transformations of marine Cl- to non-volatile organochlorine via biological and/or abiotic pathways, elucidating a new oceanic sink for this relatively unreactive element.

Sodium is contained in the most widespread silicate in the crust plagioclase. After decomposition by chemical weathering the albitic part of the s.s.s. contributes the majority of Na to the seawater. Chlorine may have derived from subaerial and subaquatic magmatic exhalations and the decomposition of micaceous sheetsilicates which also are subjected to chemical weathering.

(See also previous thread: Where does sodium and chloride of seawater come from ?)

H.G.Dill

Dear all: yes, chlorine is a magmatic volatile, and it is exhaled in subaerial and subaquatic vents. Some Chilean volcanoes have hot springs which contain HCl (Río Vinagre). But, chlorine, and sodium, are also present in at least two more common silicates: sodalite, and scapolite, especially in marialite. Surely these minerals are not as abundant as plagioclase, but can contribute both Na and Cl to the drainage that goes to the oceans. This recalls us the John Hutton method to calculate the age of the Earth comparing the salinities of world rivers with that of the ocean, he obtained the "unbelievable" result of 120 Ma, which at that time, was considered outrageous. The "mistake" he made was precisely not having accounted for both important sources and sinks of salt in the oceans: black-smokers and fumalores, and evaporite basins; also the incorporation of Cl and Na in pelagic clays should have been taken into account. So his calculations gave an age far too young for the planet...

Regards, Sebastian.

Although it is correct that the primary sources of Na and Cl are weathering of primary silicate crust and subaerial and subaquatic magmatic exhalations, it is important to bear in mind that these elements/ions make up significantly soluble compounds under high water activity and under surface conditions. For this reason, their concentration is significantly high in seawater, as compared to other major cations and anions in solution. That is, they accumulate as a result of the aforementioned processes, and very concentrated/supersaturated solutions are required for removal these elements from solution.

interesting to note the conservative property of salinity. Since it's origin is from weathering, the relative proportion of salt remains. this is because salt is also being lost, as in the construction of evaporites, etc., to the same extent that it enters more into the system. .