Excerpt in question: "Figure 4.1. Major ions in seawater. Note that ‰ means "parts per thousand" and % indicates "parts per hundred." Therefore 3.5% equals 35 ‰."

‰ is the "per mille sign" symbol, as described by the Unicode standard. The local voices pronounce "‰" as "per thousand". Meanwhile, the standard (and possibly premium) voices just ignore it entirely.