Abstract
Drilling of the eastern Brazilian continental shelf in the 1980’s identified several main factors controlling Holocene reef growth in the South Atlantic. However, this model is limited by few fossil reef cores, sparse uncalibrated dates (< 10) and basic sedimentary and coralgal descriptions. Here we integrate 62 recently published C14-AMS ages with newly defined coralgal assemblages, sedimentary facies and lateral progradation rates from several transects in the Abrolhos Continental Shelf (ACS) and Anchieta reef, Eastern Brazil. The progression of reef flat development across the ACS reefs varies through time, influencing the timing at which each reef shifts from a juvenile to senile state. This has produced a range of reef evolutionary states not previously identified in the South Atlantic. This difference in timing is likely controlled by: (1) the availability of antecedent substrate and (2) inimical conditions created during the initial transgression ~ 8–10 thousands of years ago (ka), causing spatial and temporal delays in reef turn on. We suggest that weak hydrodynamic energy and unique mushroom-shaped morphology of the ACS reefs are responsible for the lack of discernible progradation direction, whilst high sedimentation and increased tolerance to adverse conditions produced the rapid progradation rates (762.5–1909 m/ky). Finally, following a reef flat hiatus from ~ 3.7–2.5 ka we show a distinct shift in the dominant reef assemblage from Mussissmilia to more stress-tolerant Siderastrea in the ACS reefs, as well as declining reef growth at Anchieta. Falling sea levels combined with increased precipitation and higher sediment flux from regional climatic mechanisms likely created inimical conditions responsible for the observed shifts. Our results demonstrate that even though the health of these reefs has fluctuated through cycles independent of anthropogenic impacts, they are particularly sensitive to deteriorating water quality, as is currently observed due to large-scale deforestation, industrial uses, and recent mining disasters in the region.
Original language | English |
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Pages (from-to) | 1321-1337 |
Number of pages | 17 |
Journal | Coral Reefs |
Volume | 40 |
Issue number | 4 |
DOIs | |
Publication status | Published - Aug 2021 |