Enhanced direct ventilation in the subarctic Pacific Ocean during 3.5–2.73 Ma: New evidence of elemental results from ODP Site 882

Abstract

Ocean ventilation change in the subarctic Pacific Ocean is critical for regulating nutrients, heating, and ocean–atmosphere CO2 exchange. Debate continues over whether direct ventilation in the subarctic Pacific Ocean has reached the deep/bottom oceans on different time scales over the last millions of years. Here, we studied the main and trace elements, including Si, Ca, Ba, Zn, Zr, and Rb, and stable nitrogen isotope signals between 5.5 and 2.5 Ma at Ocean Drilling Program (ODP) Site 882. Our results revealed that weakening of deep/bottom water circulation after 3.5 Ma at ODP Site 882 was strongly linked to slowdown of deep/bottom water ventilation in the Atlantic and Southern Ocean. Element results indicated increase in oxygen content between ~3.5 and 2.73 Ma, supporting the suggestion of North Pacific Deep Water formation. Surface vertical mixing strength varied over a long cycle of ~400 kyr during the Early- to Mid-Pliocene in the northwest subarctic Pacific Ocean, which was linked to sea surface temperature gradient between low- and high- latitude regions caused by solar radiation differences regulated by changes in the Earth's orbital eccentricity.