🚨 New paper!
The waves we see at the beach only go so deep, so what shapes reefs in deeper waters? Using the cutting-edge in seafloor imaging, we're trying to figure that out and have found so far complex interactions between bottom currents and internal waves.
#WeekendReading: Innangi et al. on coralligenous algal #mesophotic #reef establishment, growth, and emergent morphologies in the central #Mediterranean #Sea.
Link: https://www.sciencedirect.com/science/article/pii/S0025322725001690
While mesophotic assemblages in the Gulf of Aqaba have been described in some detail, in the Red Sea proper, data are rare. Here we present a first report on a detached carbonate platform fragment from the Northern Red Sea off Al Wajh that stretches over a water depth range of 25 to 130 m. The assemblages observed comprise depth-typical large benthic foraminifers, crustose coralline algae, and mesophotic scleractinian corals (e.g., Leptoseris spp.). Encrusting bryozoans and foraminifers are abundant. A soft sediment cover in the deeper areas indicates the absence of strong currents. Radiocarbon ages confirm that this community is currently thriving. This example resembles the previously known occurrences of mesophotic reefs in the Gulf of Aqaba with respect to assemblage despite different oceanographic conditions. At the same time, it reminds of Cenozoic, in particular pre-Upper Miocene (i.e., before 8.5 million years ago), coral-associated assemblages, when coral bioherms preferentially occurred in mesophotic rather than euphotic settings. The present study thus contributes to improving the interpretation of those fossil bioherms with respect to their ecosystem dynamics and environmental significance.
Rising global temperatures cause widespread bleaching of shallow coral reefs but mesophotic reefs at depths over 30 metres are thought to be sheltered by cooler waters. Here, at sites in the Chagos Archipelago, the authors show bleaching of corals at depths of 90 metres, which might be due to warm surface waters being pushed deeper by the ocean’s response to the Indian Ocean Dipole.
Although ~ 20% of global carbonate production occurs on extra-tropical carbonate depositional systems, our understanding of these environments still lags behind that of tropical ones. The Maltese shelf in the central Mediterranean offers an opportunity to study in situ facies distribution and the factors controlling it in a light-dominated setting. The investigated region of the Maltese shelf visually exhibits three main depositional environments: seagrass meadows, sand flats and rhodolith and maerl beds. While visually distinctive, the grain composition of the sediments does not provide a clear differentiation of the three environments but rather a gradient. This gradient is marked by increasing grain size with water depth, a transition from green to red calcareous algae and an increase in the fraction of low magnesium calcite of total carboantes. While some of these features can be explained by changes in light availability, other factors are also in play. Baffling by seafloor vegetation and currents, storms and internal waves inducing sediment reworking appear to play important roles in governing the sediment texture and composition across the Maltese shelf. The role of seagrass meadows in regulating production and accumulation rates of carbonates appears to be of greater importance in Mediterranean C-type carbonate factories than in southern Atlantic ones and this could be an important marker to identify them in the geological record.
Dr. Or M. Bialik
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