While biblical Tarshish is accepted in most bible dictionaries to be the Greek Tartessos (Huelva, Spain), both Walter Mattfeld and Josephus say it is more likely to be Tarsus in Que/Cilicia largely because both place-names have the same consonants and once produced Ezekiel’s “silver, iron, tin, and lead”. However, it should be noted that the last “s” in “Tarsus” was a Greek ending which was never used in any Semitic language, as shown by the late 5th century BC Aramaic coins showing that, even by the Persian period, Tarzi was still not Hellenized to Tarsus. Cilicia was also not the only land that produced “silver, iron, tin, and lead” and was under Phoenician influence. The identification of Tarshish with Tarsus is therefore baseless.
The identification of Tarshish with Tartessos, however, has good basis. Tartessos, without the Greek ending “os”, would be spoken “Tartess”, very close to Semitic “Tarshish”. It also fits with Esarhaddon’s implication that Tarshish was the westernmost land he knew of, or at least was a land beyond Ionia, in his statement that “All the kings who live right in the seas, from Cyprus (mat Idanana) and Javan (mat Iaman), up to Tarshish (mat Tarsisi) submit to my feet.” The Bible itself, in Psalm 72:10 considers Tarshish to be a very distant kingdom in the style of Sheba, and in Ezekiel 27:12-14 also seems to place Tarshish to the west of Javan, due to the fact that it lists Javan/Ionia, Tubal/Taurus, Meshech/Cappadocia, and Beth-Togarmah/Armenia in order from west to east. As attested by archeology, Tartessos had strong links to Tyre, as stated of Tarshish by Exilic Isaiah and Ezekiel (https://www.tartessos.info/html/huelva_tartessos.htm). Also, Tartessos was a major producer of “silver, iron, tin, and lead”, especially silver and tin. Indeed, the sources of the River Tartessos (Rio Tinto, E. of Huelva) were, as Strabo put it, “silver sources”, which is consistent with the silver of Tarshish being mentioned in Isaiah 60:9, Jeremiah 10:9, Ezekiel 27:12. It is therefore conclusive that Semitic Tarshish and Greek Tartessos are indisputably one and the same.