Growing at the limit: Reef growth sensitivity to climate and oceanographic changes in the South Western Atlantic

Whilst the impacts of climatic and oceanographic change on lower latitude reefs are increasingly well documented, our understanding of how reef-building has fluctuated in higher latitude settings remains limited. Here, we explore the timing and longevity of reef-building through the mid- to late Holocene in the most southerly known reef (24 degrees S) in the Western Atlantic. Reef core data show that reef growth was driven by a single coral species, Madracis decactis, and occurred over two phases since similar to 6000 calibrated (cal.) yr B.P.. These records further indicate that there was a clear growth hiatus from similar to 5500 to 2500 cal. yr B.P., and that there is no evidence of reef accretion on the Queimada Grande Reef (QGR) over the past 2000 yrs. It thus presently exists as a submerged senescent structure colonized largely by non-reef building organisms. Integration of these growth data with those from sites further north (18 degrees S and 21 degrees S) suggests that Intertropical Convergence Zone (ITCZ), South Westerlies Winds (SWW) and El Nino-Southern Oscillation (ENSO) variability and shifts during the Holocene drove changes in the position of the Brazil-Falklands/Malvinas Confluence (BFMC), and that this has had a strong regional influence on the timing and longevity of reef growth. Our results add new evidence to the idea that reef growth in marginal settings can rapidly turn-on or -off according to regional environmental changes, and thus are of relevance for predicting high latitude reef growth potential under climate change.

Automated summary

The study explores the timing and longevity of reef-building in the southernmost known reef in the Western Atlantic, revealing that reef growth was primarily driven by a single coral species and had two distinct phases since approximately 6000 years ago. It also indicates a growth hiatus from around 5500 to 2500 years ago, with no reef accretion in the past 2000 years, suggesting that regional environmental changes can rapidly impact high latitude reef growth potential.