As The Meltdown ( El Deshielo ) begins, vintage news footage reveals the strange-but-true sight of something being lifted out of a frosty sea. It’s a huge chunk of an Antarctic iceberg, on its way to becoming the centerpiece of Chile’s pavilion at the 1992 world’s fair. As a symbol of national ingenuity and know-how, the frosty specimen is kind of out-there. And yet, for a country emerging from 17 years of military rule and determined to redefine itself, it represents an understandable leap of faith. It’s also an apt starting point for a movie in which submerged things come to light, if only briefly — a coming-of-age story where the key lesson is to keep what you know to yourself. Manuela Martelli’s well-received debut, 1976 (aka Chile ’76 ), a selection of the 2022 Directors’ Fortnight, took place during Chile’s Pinochet era. The writer-director sets her sophomore feature barely two years after the country shook off the despot’s iron grip.…