Periodic Reporting for period 1 - RhodoMalta (Integrated analysis of coralline algae facies of the central Mediterranean since the Oligocene)
Periodo di rendicontazione: 2020-09-01 al 2022-08-31
The Mediterranean Sea currently hosts multiple “cold water carbonate” environments facing increasing stress from environmental change. This project is aimed at understanding how an important subset of these environments, those dominated by coralline algae, have responded to environmental change in the past and how are they responding to them now. The macro objective of this study is to understand the environmental changes in the Mediterranean across key periods in its evolution as recorded by shallow water carbonates dominated by coralline algae, with a secondary objective of understanding the behaviour and environmental record of coralline algae and their biotopes in the Anthropocene. The period of investigation entails the Late Oligocene and Late Miocene, and the Holocene - Anthropocene changes. The present will inform of past changes in nutrients, current and climate regimes in this part of the world and may provide clues on future environmental change.
Coralline algae are an important group of benthic calcifiers across a large swath of environments, from high to low latitudes and from the tidal to the mesophotic zone. Coralline algae can form long-lived structures such as rhodoliths (>100 years) and offer a high-resolution short term (annum scale) record of local oceanographic conditions. Recent (<1000 years) coralline accumulations still preserve their original high magnesium calcite (HMC) mineralogy and retain environmental information in their chemical composition. However, the low thermodynamic stability of HMC results in the loss of much of this information due to recrystallization within less than a million years. As a result, the main type of information retrieved from ancient rhodoliths, coralline crusts and grains are primarily morphological and taxonomic.
In the modern oceans it has been observed that in some cases where coral reefs have been severely affected by mortality events and/or bleaching, coralline algae have taken over or encased coral assemblage post mortality. This has occurred despite the fact that, like corals, coralline algae are susceptible to ocean acidification and water temperature increase as well as anthropogenic activities. Multiple forms of coralline algae in sublittoral settings are presently considered to be endangered habitats by the EU. This biotope is of importance to marine biodiversity, fisheries and tourism, notably to EU countries along the Mediterranean coastline. Better understanding of the short and long term behaviour of these environments is fundamental to maintaining their viability and evaluating possible mediation that might be called for in the future due to anthropogenic forcing.
Coralline algae are an important group of benthic calcifiers across a large swath of environments, from high to low latitudes and from the tidal to the mesophotic zone. Coralline algae can form long-lived structures such as rhodoliths (>100 years) and offer a high-resolution short term (annum scale) record of local oceanographic conditions. Recent (<1000 years) coralline accumulations still preserve their original high magnesium calcite (HMC) mineralogy and retain environmental information in their chemical composition. However, the low thermodynamic stability of HMC results in the loss of much of this information due to recrystallization within less than a million years. As a result, the main type of information retrieved from ancient rhodoliths, coralline crusts and grains are primarily morphological and taxonomic.
In the modern oceans it has been observed that in some cases where coral reefs have been severely affected by mortality events and/or bleaching, coralline algae have taken over or encased coral assemblage post mortality. This has occurred despite the fact that, like corals, coralline algae are susceptible to ocean acidification and water temperature increase as well as anthropogenic activities. Multiple forms of coralline algae in sublittoral settings are presently considered to be endangered habitats by the EU. This biotope is of importance to marine biodiversity, fisheries and tourism, notably to EU countries along the Mediterranean coastline. Better understanding of the short and long term behaviour of these environments is fundamental to maintaining their viability and evaluating possible mediation that might be called for in the future due to anthropogenic forcing.
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(si apre in una nuova finestra)) 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(si apre in una nuova finestra)). 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.
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(si apre in una nuova finestra)) 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(si apre in una nuova finestra)). 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.
We expect that the new data and improved mapping of the Maltese seafloor will be the base for future planning of marine infrastructure and cultural heritage. It will play an important role in marine protected area planning in European Mediterranean waters.