Mangrove expansion at poleward range limits in North and South America: Late-Holocene climate variability or anthropocene global warming?

•American mangroves reached their current range limits after the Industrial Era.•An over four-fold increase in mangrove cover was recorded after the 21st century.•Mangrove expansion at the boreal range limit is accelerated by warmer winters.•Mangrove expansion at the austral range limit is governed by habitat availability. Mangroves are expanding poleward in North and South America, but it is unclear whether such ecotonal-shift is an Industrial-Era phenomenon, or a recurring occurrence tied to Holocene climate variability. Our multi-proxy and remote sensing data from the U.S. Gulf Coast and southeastern Brazil suggest that the Industrial Era is the first time throughout the Holocene when mangroves were able to extend their distributions to the current boreal and austral range limits. A mangrove expansion of ∼1.3 ha (from 0.002 to 1.33 ha), 103 ha (from 23 to 126 ha), and 1.42 ha (from 0.39 to 1.81 ha) are documented at Bolivar Flats (Texas, U.S.A.), Mississippi River Delta (Louisiana, U.S.A.), and Apalachicola (Florida, U.S.A.), respectively, since the early 2000s, suggesting that mangrove expansion in North America is a 21st -century phenomenon and likely governed by warming winters. In contrast, the relatively slow mangrove expansion (from 96.1 to 106 ha between 2003 and 2019) at the austral range limit is controlled primarily by available habitats with suitable salinity and sediment substrate.