Depth-related and species-related patterns of Holocene reef accretion in the Caribbean and western Atlantic: A critical assessment of existing models
Reef-accretion rate was measured in 151 core intervals from 12 Caribbean and western Atlantic locations. Palaeowater depth for each core interval was determined by comparing its position to the curve of Lighty et al. (1982), based on calendar years before 1950. While the majority of the data points fell within the upper 15m of the water column, no clear depth-related pattern of reef accretion emerged. This is in sharp contrast to the widely held assumption that reef accretion will decrease exponentially with water depth at rates approximately an order of magnitude below the corresponding rates of coral growth at the same depths. Similarly, reef-accretion rates from facies dominated by branching Acropora palmate (3.83 m kyr(-1)) versus those associated with massive corals (3.07m kyr(-1)) were not significantly different (alpha = 0.05), owing to high variance across all water depths. Reef accretion showed a tendency to increase at higher rates of sea-level rise, but that relationship was also non-significant. It is proposed that the known depth-related decrease in carbonate production may be offset by a parallel drop in bioerosion. While available data generally support this hypothesis, quantitative verification must await careful measurements of both biological degradation and transport along a depth gradient. Nevertheless, bioerosion appears to not only play an important role in creating reef fabric, but to perhaps affect patterns of reef accretion as much as initial calcification. Regardless of the cause, the patterns revealed by this study fly in the face of the assumptions that underlie our most widely accepted Holocene reef models. Clearly new ones are needed that emphasize the varying contribution of biological material to what is largely a process of physical aggradation - in short reef corals grow, coral reefs accrete.
Hubbard, Dennis K. "Depth-related and species-related patterns of Holocene reef accretion in the Caribbean and western Atlantic: A critical assessment of existing models." In Perspectives in Carbonate Geology: A Tribute to the Career of Robert Nathan Ginsburg, edited by Peter K. Swart, Gregor P. Eberli, and Judith A. McKenzie. Hoboken, NJ: Wiley-Blackwell, 2009.
Special Publication 41 of the IAS.
Reef accretion, Caribbean, Holocene, Bioerosion, Sea level, Acropora