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The SW coast of the Iberian Peninsula experiences a lack of palaeoenvironmental and archaeological data. With the aim to fill this gap, we contribute with a new palynological and geochemical dataset obtained from a sediment core drilled in the continental shelf of the Algarve coast. Archaeological data have been correlated with our multi-proxy dataset to understand how human groups adapted to environmental changes during the Early-Mid Holocene, with special focus on the Mesolithic to Neolithic transition. Vegetation trends indicate warm conditions at the onset of the Holocene followed by increased moisture and forest development ca. 10–7 ka BP, after which woodlands are progressively replaced by heaths. Peaks of aridity were identified at 8.2 and 7. 5 ka BP. Compositional, textural, redox state, and weathering of source area geochemical proxies indicates abrupt palaeoceanographic modifications and gradual terrestrial changes at 8.2 ka BP, while the 7.5 ka BP event mirrors a decrease in land moisture availability. Mesolithic sites are mainly composed of seasonal camps with direct access to the coast for the exploitation of local resources. This pattern extends into the Early Neolithic, when these sites coexist with seasonal and permanent occupations located in inland areas near rivers. Changes in settlement patterns and dietary habits may be influenced by changes in coastal environments caused by the sea-level rise and the impact of the 8.2 and 7.5 ka BP climate events. [ABSTRACT FROM AUTHOR]

Since the catastrophic impact of the 1755 Lisbon tsunami, tsunami exposure of the Portuguese coast is well known. However, due to the limited accuracy of historical records and poor preservation of geological onshore archives, significant uncertainties remain regarding the recurrence patterns of large tsunamis [1]. Offshore tsunami deposits, which as yet have been poorly investigated, may help to fill existing knowledge gaps in the regional tsunami history. New evidence from the Algarve shelf, which includes sediments of a potential predecessor of the 1755 tsunami, has been identified during METEOR cruise M152 [2]. In this study, quartz and feldspar luminescence dating was applied to the silt- and sand fraction of tsunami backwash and shelf deposits recovered during this cruise, with the aim to improve understanding of magnitude-frequency patterns by providing new information on chronology and transport dynamics. Since this is a seminal application of luminescence dating to offshore tsunami deposits, dating accuracy for different minerals, signals, aliquot sizes and grain-size factions was evaluated against a correlative radiocarbon chronology. Linear regression yielded smallest residuals for single-grain quartz and feldspar IRSL ages, while those of multi-grain ages were significantly larger. The associated quartz and feldspar single-grain chronologies show overall good agreement with radiocarbon ages for the same cores and, when combined with Bayesian deposition models [3], support evidence of tsunami backwash associated with the 1755 tsunami and a prehistoric event that, according to the radiocarbon-based age-depth model, took place 3600±600 years BP. Luminescence-based tracers for signal resetting in different minerals and grain-size fractions, offer new insights into sediment transport during tsunami backwash on the investigated shelf sections: (i) offshore sediment transport during the 1755 tsunami was characterised by significant spatial variability between sediments derived from local sources that were transported as gravity currents, and sediments derived from a mixture of sediment sources that were partly transported in suspension over larger distances; (ii) when comparing sediments of the 1755 tsunami and the prehistoric event in the same sediment core, incomplete signal resetting of most sand and silt grains in the palaeo-event indicates a mixture of more local sediment sources mainly transported as bedload; and (iii) varying degrees of signal resetting within the sand layer of the palaeo-event point to a successive shift towards sediment sources with better prebleaching. [ABSTRACT FROM AUTHOR]

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]

The RV Meteor M152 expedition mapped and sampled two transects perpendicular to the south coast of the Algarve, off Portugal, in water depths from 60 to 800 meters. The special focus was on the areas to the east of Portimão and the west of Sagres/Martinhal transects, close to the famous Martinhal, Boca do Rio and Salgados AD 1755 onshore sedimentary imprints. This part of the coast was heavily affected by tsunami inundation exactly 263 years ago on All Saints Day 1755 following a strong earthquake offshore. Shortly after the earthquake a tsunami hit the Portuguese coastline. It was one of the most consequential and impressive natural hazards ever reported destroying the Portuguese capital and many villages were destroyed along the south Portuguese coast, with the exception of Faro that was sheltered by sandbanks, whereas in Lagos the waves overtopped the city walls. Deposits of the Lisbon 1755 tsunami have been well studied along the southern Portuguese coast, but the impact of backwash, the retreating flood into the sea has not been well understood and studied. To date, very scarce information on backwash deposits is available from other areas, so this is unknown terrain, especially in these water depths. We focus on the following scientific questions: Do we find variations in thickness and sediment composition, distribution and preservation of the tsunami layer? What effects on benthic life after tsunami deposition can be observed? Can we develop a tool for the identification of historic and prehistoric tsunami deposits on the inner shelf? Can we detect predecessor events along the Algarve coast, and obtain information about timing, frequency and magnitude of these natural hazards thus extending the time-window of observation?We collected pre- and post-tsunami deposits (the background sedimentation) along the transects for comparison, e.g. of the benthic life and its resilience. Other proxies such as geochemistry and physical properties are analyzed as well. Radiocarbon and OSL dating methods are used for establishing a geochronological framework and to estimate ages of preceding events identified macroscopically in the sediment cores. Overall, the lithostratigraphic column can be characterized as a silty-dominated sequence, likely reaching the Younger Dryas. More importantly, we detected a gravelly high-energy layer at a depth of approx. 16-25 cm depth in many cores, characterized by an erosive base, shell debris and well-rounded extra-clasts of fluvial origin. A surprising finding was a second medium to coarse sand layer at depths of around 150-180 cm with clear indications of a high-energy depositional environment (e.g. sharp erosional base, mineralogical diversified composition, macrofossil diversity, etc.). Both of the layers are found within cores of the two transects; they are preliminarily interpreted as two events, the upper is regarded as deposits of the 1755 event, whereas the lower dates younger than 4000 yrs BP. [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]