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Introduction: The production of resting cysts is a key dispersal and survival strategy of many dinoflagellate species. However, little is known about the role of suspended cysts in the benthic nepheloid layer (BNL) in the initiation and decline of planktonic populations. Methods: In September 2019, sampling of the dinoflagellate cyst community at different water depths in the water column and in the bottom sediments, and studies of spatio-temporal changes in physical properties (temperature, salinity, density and suspended sediment concentration), were carried out along a landsea transect off Figueira da Foz (NW Portugal) to investigate the dinoflagellate cyst distribution and the factors (physical and biological) affecting it. A clustering analysis was used to compare the BNL and sediment cyst records with the cyst rain recorded by a sediment trap at a fixed station. Furthermore, Lagrangian particle experiments enabled simulating cyst trajectories in the BNL 5 and 10 days before sampling and assessing cross-shore, vertical and alongshore transport within the studied region. Results: A well-developed BNL was present during the survey, which covered a change from active (14th of September) to relaxed (19th of September) upwelling conditions. Organic-walled dinoflagellate cysts were dominant in all samples, although calcareous dinoflagellate cysts consistently occurred (at low abundances). High proportions of full cysts were observed in the BNL, of which a significant portion was viable as shown by excystment experiments. Moreover, BNL cyst records collected on the 19th of September along the landsea transect were similar to the sediment trap cyst record but greatly differed from sediment cyst records. The heterotrophic small spiny brown cysts (SBC) and cysts of the autotrophic yessotoxin-producer Protoceratium reticulatum notably increased during the survey, in the BNL and in the water column above. Discussion: The comparison of the BNL, surface sediment and sediment trap cyst records supported that the main origin of cysts in the BNL was the recent production in the water column. The spatial coincidences in the distribution of cysts and vegetative cells of Protoceratium reticulatum also supported that full cysts in the water column were being produced in surface waters. New data evidenced the presence of a significant reservoir of viable cysts in the BNL that have the potential to seed new planktonic blooms. Furthermore, back-track particle modelling evidenced that alongshore advection was the main physical mechanism controlling cyst dynamics in the BNL during most part of the survey period, being particularly intense in coastal stations (<100 m depth). Consequently, the sediment cyst signal is a mixture of locally and regionally produced cysts. We provide multi-disciplinary data evidencing that cysts recently formed in the photic zone can be laterally advected within the studied region through the BNL, contributing to a better understanding of the role of the BNL in cyst dynamics and tracing the seed sources of the new blooms. [ABSTRACT FROM AUTHOR]

Our understanding of dinoflagellates' present-day and past ecology is limited due to the scarcity of data on the transport of dinoflagellate cysts in oceanic environments. Previous studies have shown that lateral transport affects the source-to-sink trajectory of cysts in the very productive region off Cape Blanc (NW Africa). Unsolved questions remain, such as: how far these cysts can be advected, whether the cyst sources vary over time and whether lateral transport is a permanent feature or restricted to individual events. To fill these gaps and assess the role of nepheloid layers on the lateral transport and preservation of dinoflagellate cysts, new data on dinoflagellate cyst distributions in the water column and sediments along a land-sea transect were obtained. Samples were collected in November 2018 along a shelf break-offshore transect during intense upwelling, notably, within and between the nepheloid layers. The composition and abundance of cysts with organic walls in the water column and surface sediments were studied. Moreover, the distribution of calcareous cysts was also analysed in the water samples, using non-destructive acid-free preparation methods. The records were dominated by empty cysts, but no clear indications that these originated from local resuspension of older sediments were observed. Clustering, principal component analysis and redundant discriminant analysis were used to compare cyst assemblages in the water column and surface sediments, and environmental conditions in the upper water column. The strong similarity in species composition of water samples collected in the active upwelling region to those collected from the more onshore parts of the Benthic Nepheloid Layer (BNL), upper Intermediate Nepheloid Layer (INL) (∼1000 m depth) and lower INL (∼2200 m depth) indicated that lateral transport of cysts within these NLs occurred until about ∼110 km from the shelf break. Cyst assemblages from above and below these NLs showed significantly different taxa composition reinforcing the role of NLs in the lateral advection of cysts. In the more offshore stations, vertically similar cyst assemblages were observed in the same station, independent of the sample depth, within or between the NLs, which supported that at these stations vertical transport was the dominant process influencing cyst assemblages. Consequently, the cyst signal in sediments off Cape Blanc may be affected both by horizontal transport of allochthonous cysts and vertical deposition of locally-produced cysts, particularly in the more offshore stations (>2000 m depth). Despite lateral transport and possible species-specific preservation effects, horizontal distributions of most cyst taxa in the water column and the surface sediments could be explained to a great extent by the main environmental gradients in the upper water column. This agrees with observations made in other regions, and reinforces that dinoflagellate cysts as good proxies to reconstruct past environmental conditions in offshore environments. New data on dinoflagellate cyst distribution, transport and accumulation patterns in deep environments off Cape Blanc may be useful for interpreting past environmental signals in the region. This is particularly relevant regarding calcareous cysts, as information on their distribution and ecology is very scarce. The present work contributes to a better understanding of the dispersal patterns of dinoflagellate cysts in the deep ocean, highlighting the significant role played by nepheloid layers in this process and thus on the dinoflagellate cyst signature in deep-sea sediments. • Nepheloid layers have a key role in cyst dispersal in oceanic environments. • No evidence was found supporting local resuspension of empty cysts to the water column. • The influence of vertical and lateral transport varied along the transect. • Multivariate statistics helped in the identification of the main cyst ecological signals. • New data may help in the interpretation of sedimentary cyst records. [ABSTRACT FROM AUTHOR]

A 322-cm-long sedimentary sequence obtained in the shallow marine basin of the Ría de Arousa—a submerged unglaciated river valley on the Atlantic margin of northwestern Iberia—was analysed using a multi-proxy approach to study how climatic and sea level changes affected the coastal ecosystems during the Last Glacial–Interglacial Transition. Past sedimentation, vegetation and marine productivities were inferred from palynological, radiocarbon, seismic and lithological data. A substantial reduction in the pollen and dinoflagellate cyst accumulation rates is observed at ∼12,700 to 11,700 cal a BP, suggesting lower marine and vegetation productivities likely as a response to the Younger Dryas cooling event. Overall, the regional vegetation changed from cold-tolerant open woodlands (Pinus sylvestris/P. nigra and Betula) dominating before ∼10,200 cal a BP to coastal wetlands and the regional spread of Quercus -dominated forests after ∼9800 cal a BP. Cluster analysis and principal component analysis allowed the identification of several small environmental oscillations, such as the 11.4 ka and 10.5 ka cooling events. After that, a conspicuous heath expansion was likely favoured by the palaeotopography, the increased precipitation and the relative sea level rise, which might have caused a profound change in the coastal configuration. Concurrently, both the dinoflagellate cyst and non-pollen palynomorph records reveal variations in the marine productivity and coastal hydrodynamics that also agree with a period of marked marine transgression, warming and increasing river flow. New sedimentary data highlight the high sensitivity of the ria's ecosystems to environmental oscillations and show a close temporal correspondence between terrestrial and marine responses to climate change. • Last Glacial-Interglacial transition on the NW Iberian coast is still poorly studied. • Ría de Arousa core is the first paleoenvironmental record of the LGIT in the region. • Multiproxy data reveal strong changes in the coastal ecosystems during the LGIT. • Younger Dryas was linked to colder conditions and lower sedimentation rates. • Quercus -dominated forests and wetland expanded in the Early Holocene. [ABSTRACT FROM AUTHOR]

Abstract New multi-proxy analyses were performed on two sedimentary sections from shallow marine ecosystems of Ría de Vigo (NW Iberia) to study the effects of the MIS-3 and early Holocene environmental variability. High-resolution data (microfossils, sedimentary facies, and geochemistry) allowed performing a comprehensive reconstruction of the main environmental changes (climate, vegetation, hydrology and sea level) that occurred during part of the MIS-3 period (57.0–38.8 cal ka BP) and the early Holocene (11.2–7.0 cal ka BP). The chronology is supported by isotopic dating and the correlation of pollen data with other regional palaeo-climatic records. Several phases characterised by increasing pollen representation of deciduous Quercus alternate with others marked by increasing representation of heliophytes that may reflect the succession of Interstadials (GI) and Stadials (GS) described in Greenland ice cores. In addition, dinoflagellate cysts and diatoms reflect conditions in the marine environment (SST and productivity). New palynological data confirms that coastal ecosystems of Atlantic Iberia were sensitive to the main climatic oscillations affecting the North Atlantic. It also suggests that pinewoods, juniper communities and mesophilous deciduous forests with Carpinus betulus L. (which shows exceptionally high pollen abundances for the MIS-3) persisted in the surroundings of Ría de Vigo until ~7500 a BP. For the first time in this region, we describe the effects of an abrupt episode of cooling that may correspond to Bond cycle 7 (10.5 ka event). Highlights • MIS-3 and early Holocene environmental variability is poorly studied at NW Iberia. • High-resolution, multi-proxy data were obtained from two sedimentary sections. • Palynological data reflect climate effects on marine productivity and vegetation. • Ría de Vigo was sensitive to the succession of GS/GI and other rapid climatic changes. • The effects of 10.5 ka event (Bond-7) are described for the first time in the region. [ABSTRACT FROM AUTHOR]

Organic-walled dinoflagellate cyst assemblages were analysed in 31 surface sediment samples from the Ría de Vigo (NW Iberia) to obtain supporting evidence for the interpretation of past environmental signals from sediment cores. Complementarily, the totals of pollen (and pollen from riparian taxa), foraminiferal linings and freshwater algae were also considered to test their value as (palaeo)environmental indicators in fluvio-marine sedimentary environments. Abundances of foraminiferal linings gradually increased towards the ría's mouth, which supports its use as a proxy to infer the degree of marine influence in the sediment record. The ratio of dinoflagellate cysts to pollen and spores (D/P) increased with distance to the main river's mouth (and water depth) in the inner (< 7 m water depth) and the outer (> 20 m) parts of the ría. Total pollen concentrations decreased with water depth in the outer part but did not show any clear trend in the rest of the ría. No clear pattern in the distributions of pollen from riparian plants and spores from freshwater microalgae was detected. Multivariate analyses (clustering and RDA) performed on dinoflagellate cyst records and environmental data reflected a marked inshore-offshore distribution pattern mainly controlled by a fluvio-marine environmental gradient. Increasing abundances of cysts of Gymnodinium species and heterotrophic cysts as well as higher cyst diversity characterised the deeper environments of the outer ría. These observations suggest a relationship with increased shelf influence and are compatible with the heterotroph upwelling signal described in previous works. A very different cyst association with a predominance of autotrophic cysts characterised the intermediate and inner parts of ría, where exceptionally high cyst abundances of Lingulodinium polyedra (∼ 56–99% and ∼ 200–114,000 cysts.g−1) were reported. Abundances of cysts of L. polyedra positively correlated with shallower and higher river-influenced environments characterised by higher sea-surface temperature. Our results agree with previous studies and reinforce the value of this species as an indicator of warmer and stratified conditions. Moreover, cysts of L. polyedra positively correlated with winter sea-surface nitrate contents, which is compatible with the nutrient enrichment signal (natural or anthropogenic) that has already been described in other deep and stratified estuarine environments and is consistent with historical cyst records obtained in the Ría de Vigo. However, further research is needed to disentangle the nutrient enrichment signal from the influence of other environmental factors. • Modern dinoflagellate cyst assemblages in coastal environments of NW Iberia. • The distribution of dinoflagellate cysts was controlled by a fluvio-marine gradient. • Cyst records were compared to environmental data using multivariate statistics. • Cysts of Gymnodinium spp. was related to increasing oceanic influence in the Ría de Vigo. • Cysts of Lingulodinium polyedra increased in the inner ría with higher river inputs. [ABSTRACT FROM AUTHOR]

The coastal lagoon-beach complex at the Cíes Islands located at the opening of the Ría de Vigo (NW Iberia) is an important ecosystem currently threatened by anthropogenic impacts and climate variations. We used multiproxy marine sediment analyses to reconstruct the millennial environmental dynamics of this insular system and, in particular, the recent history of its coastal lagoon. Geophysical surveys were used to obtain bathymetry and identify the major sedimentary units of its closest submarine basin as well as their sediment sources. Core samples were taken in the middle and distal parts of the sedimentary body, where several prograding sedimentary units are thinner, allowing continuous sampling of the facies. Lithological, textural, elemental and chronological analyses were carried out on two cores. The detailed palynological studies on one of the cores included the analyses of the pollen, non-pollen palynomorphs and dinocysts dating back three millennia. Our results revealed noticeable environmental changes affecting this area during the last 3000 years, due mainly to changing climate and oceanic conditions but also to the impact of historic human occupation of the islands. Several cold events (the 2.8 ka BP event and the Little Ice Age) characterized by enhanced upwelling alternated with warmer stormy periods of prevailing downwelling conditions in the ria. These circumstances altered the balance amongst the lacustrine, marsh, dune and lagoon systems, opening ephemeral inlets and modifying the trophic stage of the shallow waters surrounding the archipelago. Here we provide a background of the human and climatic impacts affecting these highly sensitive habitats, which may serve to improve their future management strategies. [ABSTRACT FROM AUTHOR]