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The present-day human footprint is traceable in all environments. Growing urban centers, tourism, agricultural and industrial activities in combination with fishery, aquacultures and intense naval traffic, result in a large output of pollutants onto coastal regions. The Algarve shelf (Portugal) is one exemplary highly affected coastal system. With this study the contemporary pollution was followed in eighteen offshore surface sediment samples. Heavy metals (e.g., Cr, Pb, Cu, Hg) and organic contaminants, such as linear alkylbenzenes, dichlorodiphenyltrichloroethane metabolites, polycyclic aromatic hydrocarbons, and hopanes, have been identified and quantified, that pose hazardous effects on the marine environment and biota. This study correlates spatial distribution patterns with the pollutant composition, potential sources and pathways, each sample's grain size, and local influences, such as discharging river systems and ocean currents. This study presents a blueprint-study that allows the methodological adaption to new shelf systems with regionally different ocean current-driven distribution patterns of anthropogenic pollutants. • Blueprint-study of the contemporary pollution and pollutant pathways in shelf systems • Algarve shelf is polluted by inorganic heavy metals (Pb, Cr, Ni) and organic contaminants (PAHs, LABs, DDX) • Spatial concentration linked to sources, river discharge, ocean currents and accumulation-control factors • Difference in distribution and accumulation mechanisms for heavy metals and organic pollutants [ABSTRACT FROM AUTHOR]

In 1755 CE, a strong earthquake followed by a transatlantic tsunami destroyed large coastal areas; it also left its sedimentary imprints in the Boca do Rio valley (western Algarve, Portugal). This tsunami layer is very well preserved and has been analysed in several studies. Deposits of preceding extreme wave events, however, have rarely been described for the entire Algarve coast. In this study, we present a multiproxy analysis of seven sediment cores from the Boca do Rio region, organized in two crossing transects, one parallel and the other perpendicular to the coastline. The geochronological framework has been established by combining radiocarbon and optically stimulated luminescence dating with sedimentological and geochemical analyses (XRF, C/N, magnetic susceptibility, granulometry, micropalaeontology), and covers the palaeogeographical evolution of that area for the last four millennia. As expected, the 1755 CE tsunami was easily identified at all coring sites, as a sandwiched stratum between fine-grained alluvium. This event layer presents several tsunami characteristics, such as erosive basal contact, rip-up clasts, a fining-upward sequence, and a mud cap. At one coring site, a second extreme wave event layer of marine origin was detected within floodplain deposits, due to its granulometric, XRF, magnetic susceptibility and micropalaeontological properties. It is stratigraphically located below the 1755 CE Lisbon tsunami layer and can be associated with another yet undocumented extreme wave event, most likely dating to the mid or late 1st millennium CE. • First study identifying a second event layer in Boca do Río • Palaeoenvironmental evolution since the younger Holocene • Multi-proxy analysis including dating, sedimentology, geochemistry and palaeontology • Environmental and natural hazards affecting Roman production sites (1st–5th century CE) [ABSTRACT FROM AUTHOR]

The well-known 1755 CE Lisbon tsunami caused widespread destruction along the Iberian and northern Moroccan coastlines. Being affected by the powerful 1755 CE Lisbon tsunami, the southwestern Algarve shelf provides environments for detecting offshore tsunami imprints. Our multidisciplinary investigations (hydroacoustics, sedimentology, geochemistry, radiocarbon dating) of the Holocene sediments have revealed tsunami deposits linked to this tsunami and a ca. 3600 cal yr BP event. The latter event is until now unidentified in Portugal. Both event deposits contrast with the background shelf sedimentation by their coarser grain size, element composition, internal structure, and erosive base, making them discernible in the sub-bottom data and cores. Especially the ca. 3600 cal yr BP deposit is exceptionally well-preserved at one of the coring sites. The clear differentiation into several sections enables further insights into offshore tsunami transport and depositional processes. This study demonstrates that the record and preservation of tsunami deposits were possible on the Algarve shelf in specific locations sheltered from possible alterations. Our findings extend the tsunami catalogs of Portugal with a previously unknown tsunami dated to ca. 3600 cal yr BP. • Offshore tsunami deposits of the 1755 CE Lisbon and a previously unknown tsunami • The ca. 3600 cal yr BP tsunami extends the Portuguese tsunami catalog. • Characteristics of offshore tsunami deposits are strongly site-specific. • Tsunami backwash can transport sediments as grain or debris flows. [ABSTRACT FROM AUTHOR]