Significance The equatorial Pacific is a key oceanographic region in Earth’s climate system. Biological production in this region is limited, in part, by the lack of the micronutrient iron. Atmospheric dust is a source of iron, as is upwelling of ocean waters from below. A longstanding question has been whether biological productivity has responded to variable dust supply over ice age cycles. We use geochemical proxies in three sediment cores spanning the breadth of the equatorial Pacific to show that biological productivity did not respond to dustier ice age conditions. Rather than atmospheric iron supply, we infer that ocean dynamics, linking the equatorial Pacific to nutrient supply from the Southern Ocean, played a crucial role in regulating equatorial Pacific productivity.