# Ocean freshening near the end of the Mesozoic

## TL;DR

This study shows that changes in ocean gateways near the end of the Mesozoic altered global ocean salinity and circulation, reshaping climate patterns.

## Contribution

The study identifies how combined changes in Arctic and Central American gateways caused ocean freshening and altered global climate dynamics.

## Key findings

- Central American Seaway shoaling reorganized ocean currents.
- Arctic gateway restrictions caused Arctic Ocean surface freshening and low-salinity water outflow.
- Combined gateway changes led to increased water mass stratification in multiple regions.

## Abstract

Paleogeographic changes have significantly shaped ocean circulation and climate dynamics throughout Earth’s history. This study integrates geological proxies with climate simulations to assess how ocean gateway evolution influenced ocean salinity near the end of the Mesozoic (~66 Ma). Our modeling results demonstrate that 1) Central American Seaway shoaling reorganizes ocean currents, and 2) Arctic marine gateway restrictions, confining Arctic–Global Ocean exchange exclusively to the Greenland–Norwegian Seaway, drive Arctic Ocean surface freshening and southward outflow of buoyant, low-salinity waters. However, only the combined effect of these two factors leads to both Arctic freshening and increased water mass stratification in the Greenland–Norwegian Seaway, proto-North Atlantic, and the Western Tethys. This scenario aligns with Maastrichtian palynological, micropaleontological, and geochemical records from high- and low-latitude sites. Our findings highlight the profound impact of these latest Cretaceous paleogeographic reconfigurations in altering global salinity patterns, underscoring their role as key drivers of global climate dynamics.

This study shows that changes in ocean gateways near the end of the Mesozoic (~66 Ma) altered global ocean salinity and circulation, reshaping climate patterns through combined reconfigurations in the Arctic and Central American regions.