A large igneous province is a vast lava-and-magma episode. Why can it hurt far oceans?

Answer: Global chemistry shift

Global chemistry shift ✓ — Right. The lava footprint is regional, but gases can push the atmosphere and oceans everywhere. CO2 can warm and acidify seawater; nutrient and circulation changes can help drain oxygen. That is why a rock event becomes a biology event through chemistry, not because most organisms met molten basalt.

Ash blocks local bays — Ash can damage water locally and alter sunlight after big eruptions, but a local bay mechanism is too small for a global extinction. LIP crises usually need atmosphere-ocean transmission: gases, warming, acidification, oxygen stress, and nutrient feedbacks. The geography of death outruns the geography of ash.

Heat spreads by seawater — Heat carried by seawater is not the main long-distance weapon. The lava may be regional, but gas-driven climate and chemistry travel through the whole ocean-atmosphere system. That is why organisms far from the lava can be hit by low oxygen or low pH rather than by direct thermal contact.