RhodoMalta was set up to study the modern and ancient coralline-rich deposits in and around Malta. As such, work on the project was split between work at sea on the modern seafloor and onshore on outcrops. The ancient units reflect a high pCO2 world and set up an analogue to the possible future state of the system currently active on the seafloor.
Modern Seafloor
Within the scope of the project, a high-resolution survey of the seafloor in Maltese waters was carried out. In this survey, we collected sediment samples from the sea floor and carried out detailed imaging using acoustic tools and remotely operated underwater robots.
This survey allowed us to identify hundreds of small, previously unknown, features on the seafloor, which we were able to verify to be biogenic mounds. These biogenic mounds are constructed by multiple biological groups characteristic of the Mediterranean. Each mound is only a few m in size, and they are concentrated in specific depths. These depths’ preference appears to be related to reefs which inhabit these locations during lower sea levels of the glacial cycle. This high density of mounds is not common and makes them a special habitat. However, the high-resolution data also revealed intense trolling activity near the mounds with possible damage to individual mounds due to trolling activity. Detailed descriptions of these features have been published in Frontiers in Marine Sciences (
https://www.frontiersin.org/articles/10.3389/fmars.2022.803687/full(s’ouvre dans une nouvelle fenêtre)) and subsequently, been covered by the local media outlets as well (
https://timesofmalta.com/articles/view/scientists-discover-marsascala-coral-mound-area-10-times-the-size-of.910653(s’ouvre dans une nouvelle fenêtre)). Recommendations for protection and policy change needed for the protection of these mounds have been made to the relevant agencies in the Maltese government.
In the scope of the project’s secondment two extra Mediterranean coralline-rich settings, in the Indian and the Pacific oceans, have been explored.
Ancient outcrops
The onshore work in Malta was focused on two main units: the Late Miocene Upper Coralline Limestone (UCL) and the Late Oligocene Lower Coralline Limestone (LCL). These units are exposed across the Maltese archipelago.
UCL
The UCL was deposited between the late Tortonian and the early Messinian and was likely terminated by palaeoceanographic events related to the Messinian Salinity Crisis. The UCL is a shallow-water carbonate unit can be used to trace palaeoenvironmental changes atop the sill between the Eastern and Western Mediterranean. In the scope of RhodoMalta extensive field surveys were carried out, and analysis of the depositional environment within the UCL in Malta, are combined with recently acquired multichannel seismic reflection profiles between Malta and Gozo, to reconstruct the depositional sequence in the Malta Plateau during the late Miocene. The UCL consists of multiple coralline and larger benthic foraminifera dominated facies, extending from subtidal to intertidal environments. These accumulated in two depositional cycles observed in both outcrop and seismic reflection data. These were deposited above a deep-water unit and are indicative of a preceding uplift phase followed by filling of the accommodation space through the deposition of the UCL in shallow marine depths. The presence of this highly elevated sill during the late Miocene could have restricted circulation to the eastern basin.
LCL
The low latitude circum global current (LLCGC) was a powerful zonal current, going through the Tethyan realm, connecting the world ocean during most of the Cenozoic. The flow of this current through the Tethyan realm had a role in the development of the prevalent carbonate platform which existed there through this period. The intensity of the LLCGC had significant impact on the production of shallow water carbonates, such as the ones in Malta. During the late Oligocene, the Maltese archipelago was an extensive, well developed, carbonate platform in the central Mediterranean, then the Mediterranean Tethys. Work done as part of the RhodoMalta project found that the production of the LCL appears to have been distributed with multiple production centers until its demise. The findings of the RhodoMalta project favor organographic control on that ddemise as new evidence accumulated now indicate significant modulation of the LLCGC at that time.
