High-resolution mapping reveals seafloor sediment patterns that influence biodiversity
A new study with participation from MARE, "Occurrence and morphometric analysis of sorted bedforms on the Alentejo continental shelf, Southwestern Portugal," has been published in the International Journal of Earth Sciences.
Researchers João Noiva (IPMA), Pedro Brito (IPMA), Marcos Rosa (IPMA), Carlos Ribeiro (IPMA, MARE|ARNET) and Pedro Terrinha (Instituto Dom Luiz) showed that high-resolution mapping can reveal seafloor sediment patterns and histories, with significant impacts on biological diversity.
The research team combined more traditional and advanced methods to map sediment deposits along the Portuguese continental shelf. Sediment sampling was carried out using an irregular grid, but it was the acoustic data survey, using a multibeam echosounder system, that produced detailed images of the seafloor, between 5 and 250 metres deep. Sampling was further complemented by a high-resolution seismic system, revealing layers of sediment accumulated over time down to 150 metres in depth.
The use of acoustic data revealed a surprising, high-resolution characterisation of sediment facies. The acoustic backscatter signature effectively distinguishes highly reflective lithologies (gravel/coarse sand) from low-reflectivity deposits (fine sand/silt) (fig. right). These patterns reflect grain-size segregation controlled by the Holocene marine transgression, evidencing the paleogeographic evolution and active depositional dynamics since 8,500 years BP (Before Present).
The Portuguese continental shelf is morphologically defined between the coastline and the shelf break, located between 120 and 200 metres deep. The distribution of detrital sediments (predominantly sands and gravels) provides information on the preferential location of marine ecosystems, the load-bearing capacity of the substrate for offshore wind infrastructure, the current hydrodynamic regime, erosion/accretion sediment balances, and sea-level evolution during the Quaternary.
This study is the result of a joint effort between IPMA, University of Évora, Instituto Dom Luiz and MARE|ARNET, funded by the MINEPLAT project, Determination of mineral resource potential on the Alentejo continental shelf and the natural constraints imposed by the Plio-Quaternary uplift of the continental margin (ALT20-03-0145-FEDER-000013), co-financed by Alentejo 2020 / Portugal 2020.
Text: Patrícia Chaves