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This study presents a generalised characterisation of the surface circulation over the northern shelf of the Gulf of Cadiz, based on 4 years of high-resolution satellite altimetry data from Sentinel-3A and wind model data. The altimetry-based surface zonal currents, adjusted for bottom-drag and wind effects, are compared with a generic CMEMS product and validated against in-situ ADCP measurements. The proposed altimetry product demonstrates superior performance than the CMEMS product, accurately reflecting surface circulation direction compared to in-situ measurements (r = 0.77, RMSE = 0.10 m/s, bias = 0.01 m/s). The use of the bottom-drag and wind-corrected/uncorrected altimetry product for spatiotemporal analysis of the shelf circulation revealed the distinct contributions of wind-driven and geostrophic components in different basin sectors. The results show that over the western basin, positive (eastward) surface currents were predominantly driven by westerly winds, while only occasionally, westward flows coincided with easterly winds, suggesting a higher control of the geostrophic component over the westward flows. In contrast, over the eastern basin, both eastward and westward flows were found to be primarily driven by favourable winds. Additionally, the analysis of Absolute Dynamic Topography (ADT) values along the whole basin showed the presence of ADT gradients both along-shore and cross-shore over the shelf, contributing to geostrophic flows. Finally, the seasonal analysis showed that eastward circulation tends to dominate during the spring and summer months, related to the upwelling season in the Gulf of Cadiz and associated westerly winds. Westward flows prevail during the winter months, related to easterly winds and the rebalancing of the along-shore sea level gradient during relaxed upwelling conditions. The findings demonstrate a significant improvement in the use of satellite altimetry data to study complex oceanographic dynamics in coastal areas, where both spatial and temporal variability are high. Moreover, the similarity of our results to those obtained from in-situ systems supports the use of altimetry data and publicly available wind models to support oceanographic studies in remote or resource-limited areas. [ABSTRACT FROM AUTHOR]

The establishment of many non-indigenous species is primarily controlled by propagule pressure, local environmental conditions, and biological interactions. An introduction is doomed to fail if any one of these factors is unsuitable. A few Atlantic blue crab Callinectes sapidus Rathbun, 1896 specimens have been collected along a limited stretch of the central Portuguese coast since the late 1970s, but a viable population was never detected. However, starting in 2016, a population of the Atlantic blue crab has established and expanded along the southern Portuguese coast. The objective of the present study was to provide insights into the invasion of the Atlantic blue crab in Portugal based on unpublished museum collection records and new records made by citizen scientists on the western coast and to provide a mechanistic explanation for the recent expansion based on observational oceanography data. Citizen science records along with observational oceanography data from 2019 and 2020 suggest that the southern Portugal population is expanding towards the western coast due to warmer coastal countercurrent events that form in the Gulf of Cadiz during the reproductive period of the Atlantic blue crab (summer–early fall). This oceanographic feature facilitates the transport of larvae towards the western coast of Portugal, which increases propagule pressure, while estuaries along the southwestern coast may serve as stepping stones supporting the northwards expansion of the species in tandem with increasing sea temperature. This study also highlights the value of citizen science in detecting the range expansion of invasive species over wide geographical areas. [ABSTRACT FROM AUTHOR]

Quantifying factors that influence marine predator distributions is essential to understanding the current and future change in marine biodiversity. Here, we test whether marine predator distribution relates to prey, or is better predicted by other specific habitat features. We examine the correlation between spatial distribution of three seabird species and their prey, as well as environmental proxies (oceanographic characteristics) in the Gulf of Cadiz, NE Atlantic. We modeled the at-sea distribution of Cory's shearwater, Balearic shearwater and Northern gannet, based on: (i) pelagic fish abundance according to acoustic surveys, and (ii) a forecast-model of remotely sensed environmental variables (productivity, sea surface temperature, and salinity). In general, seabird distributions were better predicted by abundance of fish than by environmental variables at the habitat scale. We obtained consistent correlations between seabird presence and the abundance of medium-sized (10–20 cm) sardines, anchovies and Mediterranean horse mackerel, providing information on their preferred prey. Additionally, oceanographic productivity variables moderately contributed to seabird distribution models, with better predictive value for the critically endangered Balearic shearwater and Northern gannet in the summer, whilst the model for Cory's shearwater's produced poorer predictions. Predator–prey combined studies may represent essential tools for an efficient ecosystem-based management of marine environments. [ABSTRACT FROM AUTHOR]

Remains of molluscs were collected from the seafloor on the north-eastern margin of the Gulf of Cadiz, between 300 and 1000 m water depth, using different sampling methods (e.g. dredging, trawling and box-coring), during several deep-sea expeditions. Samples contained a suite of species which nowadays mostly occur northwards of the English Channel, together with other widespread species. Species now locally extinct in the Gulf of Cadiz and restricted to northern latitudes, which unequivocally indicate a faunal shift, include the gastropods Buccinum undatum , Colus gracilis, Liomesus ovum and Neptunea antiqua , the bivalves Arctica islandica , Chlamys islandica , Modiolus modiolus , Mya truncata and Nuculana pernula and the scaphopod Antalis entalis. These species represent "Boreal Guests" of marked palaeoclimatic significance, some of which are reported for the first time in the Gulf of Cadiz. The boreal species collected were mostly large (>5 cm) whereas smaller boreal species were extremely scarce, probably winnowed away by strong bottom currents. The pteropod Limacina retroversa , at present restricted to water masses northwards of the Iberian Peninsula but widespread in Mediterranean sediments of the last glaciation, was also recorded. Accelerator mass spectrometry (AMS) 14C dates obtained from nine specimens of molluscs ranged between 26.1 and 14.6 kyr B.P., thus confirming their attribution to a last glacial assemblage. The abundance of these molluscan remains in the present Mediterranean Outflow Water pathway could be explained if this outflow was reduced in intensity or more likely shifted to a deeper level, leaving the upper slope in contact with suitable Atlantic intermediate waters. The findings of Boreal Guests in the Gulf of Cadiz document the continuity of the faunal shift which is well-known in the Mediterranean basin. Species still living in the Gulf of Cadiz and the Alboran Sea nevertheless account for 84.6% of specimens among the larger species. • Gulf of Cadiz, in 300–1000 m depth, yielded numerous shells of boreal molluscs. • Eight arctic species locally extinct in Gulf of Cádiz document a southwards faunal shift. • 14C dates from 9 specimens ranged between 26.5 and 14.5 kyr B.P. • Our data support a deeper Mediterranean Outflow during the coldest episode. [ABSTRACT FROM AUTHOR]

A centennial scale study has been performed on the coccolith assemblage of the Integrated Ocean Drilling Program Site U1390 in the Gulf of Cadiz in order to identify changes in the surface water dynamics during the last 20 kyr. The dataset is integrated with selected planktonic foraminifer taxa and with available sedimentary and paleoceanographic proxies. The reconstructed surface water conditions controlling coccolithophores shifted from a prevailing influence of Portugal Current during the Last Glacial Maximum, to enhanced advection of subtropical water during the Holocene. Millennial to centennial-scale fluctuations are also well recorded based on abundance fluctuations of key coccolithophore taxa. During Heinrich Stadial 1 and Younger Dryas, wind/frontal-induced upwelling favored nutrient availability and productivity in surface waters, although colder temperatures during Heinrich Stadial 1 inhibited coccolithophore proliferation. Combining calcareous plankton and oxygen isotope data it was possible to highlight that Heinrich Stadial 1 has an internal variability, marked by three distinct phases. Cold and productive surface water conditions occurring during HS1a and HS1c were interrupted during HS1b by enhanced influence of the warm Azores Current at the core location, which acted in phase with increased Mediterranean Outflow Water strength. The sharpest abundance of the polar-subpolar/melt-water related taxa, observed during HS1c, suggests this was the most extreme cold climate phase in the Gulf of Cadiz during the last 20 kyr. During the Bølling-Allerød interstadial, the northward extension of the subtropical gyre, coupled with enhanced fluvial discharge, determined the increase of warm water taxa and Emiliania huxleyi large morphotype, which was able to adapt to less saline waters. During the Holocene, mainly during the last 8 kyr, over the main warming trend, coccolith assemblages display short-term fluctuations. The N ratio index together with the pattern of Gephyrocapsa oceanica , compared with a palaeo record of NAO, indicates that centennial-scale events of enhanced mixing are in phase with more arid conditions on land. This pattern is related with periods of (+) North Atlantic Oscillation leading to a prevalence of strong northerly winds and enhanced mixing during the winter season. • We examine coccolithophore variations at IODP Site U1390 in the Gulf of Cadiz. • Key planktonic foraminifera and paleoceanographic proxies are also considered. • Assemblage variations highlight millennial to centennial-scale surface water changes. • Centennial climate variability occurs during Heinrich Stadial 1. • NAO-like mode drives centennial surface water shifting in mixing/stratification. [ABSTRACT FROM AUTHOR]

Coccolithophore high resolution (300 years) quantitative analyses have been carried out on Early Pleistocene sediment samples from Integrated Ocean Drilling Program Site U1387 retrieved in the Gulf of Cadiz. The studied interval is well constrained by the δ18O chronological frame and covers marine isotope stage (MIS) 48 to MIS 45, from 1465.9 ka to 1389.9 ka. The aim is to investigate paleoenvironmental changes during a poorly known interval of the "41 ky world" and understand how climate dynamics controlled coccolithophore abundance and variation at orbital up to millennial scale. Assemblage composition variation and Principal Component Analysis (PCA) indicate that temperature and nutrient availability are the main factors influencing coccolithophores. Precession forcing combined with hydrological and atmospheric dynamics affect changes in coccolithophore assemblage composition and abundance highlighting glacial-interglacial cycles and a millennial scale variability, which is more evident during glacials than during interglacials. Interglacial MIS 47 onset is more abrupt than MIS 45 inception in relation to a more prominent insolation maximum, which favors the sharp increase and highest abundance of warm water taxa in the early MIS 47. Short-term abundance peaks of C. pelagicus spp. pelagicus during glacials document polar-subpolar melting water influx into the Gulf of Cadiz and southward migration of the subpolar front during episodes of high volume ice-sheet in the north hemisphere and reduced Atlantic Meridional Overturning circulation. In late MIS 48 the lowest coccolithophore productivity, induced by colder and stratified surface waters, a terminal stadial has been inferred. Enhanced short-term glacial productivity is favored by higher mixing and nutrient content in surface water due to the strengthened westerly winds during +NAO- like phases. This promotes arid condition and upwelling along the studied site. The interglacial short-term coccolithophore productivity increases are associated with insolation maxima and enhanced nutrients of land origin during more humid periods led by -NAO- like phases, which induce the southward position of the westerlies and higher precipitation in the Mediterranean region and North Africa, in agreement with the contemporary sapropel occurrences in Mediterranean Sea. Our data-set suggests a connection between climate dynamics in the Gulf of Cadiz and east of Gibraltar Strait during the Early Pleistocene as well as a relationship with the north hemisphere ice-sheet dynamics. • Oceanographic dynamics is investigated at Site U1387 during Early Pleistocene • Coccolithophore assemblages are related to environmental parameters • Temperature and nutrients availability affect coccolithophore assemblages • Millennial-scale climatic variations are observed during pre-MPT glacials • Coccolithophore paleoproductivity changes are driven by NAO- like forcing [ABSTRACT FROM AUTHOR]

The Gulf of Cadiz is an extensive seepage area in the south Iberian margin (NE Atlantic) encompassing over 40 mud volcanoes (MVs) at depths ranging from 200 to 4000 m. The area has a long geologic history and a central biogeographic location with a complex circulation ensuring oceanographic connectivity with the Mediterranean Sea, equatorial and North Atlantic regions. The geodynamics of the region promotes a notorious diversity in the seep regime despite the relatively low fluxes of hydrocarbon-rich gases. We analyse quantitative samples taken during the cruises TTR14, TTR15 and MSM01-03 in seven mud volcanoes grouped into Shallow MVs (Mercator: 350 m, Kidd: 500 m, Meknès: 700 m) and Deep MVs (Captain Arutyunov: 1300 m, Carlos Ribeiro: 2200 m, Bonjardim: 3000 m, Porto: 3900 m) and two additional Reference sites (ca. 550 m). Macrofauna (retained by a 500 µm sieve) was identified to species level whenever possible. The samples yielded modest abundances (70-1567 individuals per 0.25 m²), but the local and regional number of species is among the highest ever reported for cold seeps. Among the 366 recorded species, 22 were symbiont-hosting bivalves (Thyasiridae, Vesicomyidae, Solemyidae) and tubeworms (Siboglinidae). The multivari-ate analyses supported the significant differences between Shallow and Deep MVs: The environmental conditions at the Shallow MVs make them highly permeable to the penetration of background fauna leading to high diversity of the attendant assemblages (H': 2.92-3.94; ES(100): 28.3-45.0; J: 0.685-0.881). The Deep MV assemblages showed, in general, contrasting features but were more heterogeneous (H' 1.41-3.06; ES(100): 10.5-30.5; J': 0.340-0.852) and often dominated by one or more siboglinid species. The rarefaction curves confirmed the differences in biodiversity of Deep and Shallow MVs as well as the convergence of the latter to the Reference sites. The Bray-Curtis dissimilarity demonstrated the high β -diversity of the assemblages, especially in pairwise comparisons involving samples from the Deep MVs. Diversity partitioning assessed for species richness, Hurlbert's expected number of species and Shannon-Wiener index confirmed the high β-diversity across different spatial scales (within MVs, between MVs, between Deep and Shallow MVs). We suggest that historical and contemporary factors with differential synergies at different depths contribute to the high α-, β- and γ-diversity of the mud volcano faunal assemblages in the Gulf of Cadiz. [ABSTRACT FROM AUTHOR]

Abstract: The 14C content of marine shells can be used as a proxy for past coastal upwelling intensity. The Iberian coast of the Gulf of Cadiz can be divided in two regions with different oceanographic conditions: the southern Portuguese coast with an active upwelling, influenced by the Northeastern Atlantic circulation, and the southwestern Andalusian coast where, due to its configuration, a wind-driven coastal upwelling is absent. Because these oceanographic conditions ΔR, a parameter that quantifies the marine reservoir effect, has positive values with a weighted mean of 65±20 14Cyr (southern Portuguese coast) or negative values with a weighted mean of −135±20 14Cyr (Andalusian coast). Nevertheless, between 4400 BP and 4000 BP ΔR values are strongly positive, suggesting a very strong upwelling existed in the entire region of the Gulf of Cadiz. This does not reflect wind-driven processes, but probably an eastward extension of the Azores Front, which is characterized by locally intense upwelling, along the Azores Current that penetrated into the Gulf of Cadiz. The study highlights the importance of using appropriate calibration methods when developing 14C chronologies from the Gulf of Cadiz, as well as the potential of ΔR for reconstructing palaeoceanographic conditions. [Copyright &y& Elsevier]

Over the past decades, the northern Gulf of Cadiz has been the focus of a wide range of late Quaternary seismic and sequence stratigraphic studies, either addressing the slope contourite depositional system (CDS), or the development of the continental shelf. Yet, high-resolution seismic data bridging between these domains and age information have remained sparse. This study, based on new high-resolution reflection seismic profiles calibrated to IODP Expedition 339 sites U1386/U1387, now presents an updated stratigraphic framework, that integrates (for the first time) the late Quaternary records of the northern Gulf of Cadiz middle slope to shelf off the Guadiana River. Seismic stratigraphic analysis of the stacking, depocenter distribution, stratal architecture and facies of the seismic (sub-)units reveals the influence of ~100 kyr sea-level variations paced by Milankovitch (eccentricity) cycles, tectonics (manifesting as two pulses of uplift and margin progradation), sediment supply and bottom current activity. This work furthermore contributes to the application and understanding of high-resolution, late Quaternary sequence stratigraphy. Firstly, the proposed sequence stratigraphic interpretation shows that adaptations to the basic models are required to integrate the shelf and slope record, and to account for the presence of a significant alongslope (bottom current-controlled) component. Secondly, the results confirm that the sequences are dominantly composed of regressive deposits, whereas the preservation of transgressive to highstand deposits is more irregular. Significantly, the common assumption that successive major glacial lowstands are consistently recorded as well-marked, shelf-wide erosional unconformities, is demonstrated to be occasionally invalid, as tectonics can obliterate this one-to-one relationship. • A revised late Quaternary stratigraphic framework for the northern Gulf of Cadiz shelf to middle slope is presented. • Age information is provided through the calibration to IODP Expedition 339 sites U1386 and U1387. • The development of the margin is mainly governed by ~100 kyr sea-level cycles, tectonics, oceanography and sediment supply. • Conceptual implications concern e.g. the relation between glacial lowstands and sequence boundary preservation on the shelf. [ABSTRACT FROM AUTHOR]