Productivity and upwelling changes in the Subarctic Pacific over the past five glacial cycles

The polar oceans are critical in regulating atmospheric CO₂ concentrations (pCO₂) during Pleistocene glacial cycles. However, the role of the subarctic Pacific, despite being the largest reservoir of respired carbon in the modern ocean, remains underexplored due to limited data. This study presents high-resolution export productivity records, normalized using 230Th, from the subarctic northwestern Pacific spanning the last five glacial cycles. These records reveal distinct glacial-interglacial patterns overlaid with variability driven by precession. Warm interglacial climates, coupled with high boreal summer insolation, facilitated the upwelling of nutrient-rich subsurface waters, leading to increased export productivity. Transient model simulations demonstrate that ice sheet dynamics and, to a lesser extent, precession significantly influence the strength and latitudinal shifts of the westerlies. Intensified and poleward-shifting northern westerlies during warmer intervals likely enhanced the upwelling of carbon- and nutrient-rich waters, releasing previously stored CO₂ from the subarctic Pacific into the atmosphere. These findings underscore the substantial influence of the subarctic Pacific in regulating pCO₂ variations during Pleistocene climate cycles, particularly on the precessional timescale (~20 kyr).