Distribution of suspended particulate matter at the equatorial transect in the Atlantic Ocean

A suspended particulate matter distribution against a hydrographical background was studied at the oceanographic transect across the equatorial Atlantic in the year 2000. An area of abnormally high suspended matter volume concentrations was found above the Sierra Leone Rise in the entire water column (eastern part of the transect). The suggested explanation for the anomaly is based on the ballast hypothesis whereby solid particles are incorporated as ballast into suspended biogenic aggregates, leading to increased velocities of sinking. This occurs within the Northwest African upwelling area, where the plankton exposed to the Saharan dust abundance form a significant number of aggregates, which are later transported equatorward via the Canary Current. An intermediate nepheloid layer associated with the Deep Western Boundary Current was recorded from the South American Slope at depths of 3200–3700 to 4300 m above the Para Abyssal Plain. Antarctic Bottom Water enriched in suspended matter was found mostly in the troughs at 40–41∘ W. It was detached from the bottom, coinciding with the core of the flow due to the bottom rise “dam” located up-stream. The grain size of particles along the entire transect has a polymodal distribution with 2–4 and 8–13 µm modes. The registered rise in percentage in some parts of the transect of the 7–21 µm sized particles suggests the presence of the well-known coarse mode (20–60 µm) formed by aggregation of transparent exopolymer particles (mucus).

Concentration and composition of the suspended particulate matter of the Barents sea

The results of the study of the distribution and composition of the dispersed sedimentary matter (suspended matter) in the water column of the Barents Sea were presented in the article. The distribution of suspended matter in the sea obeys the laws of circumcontinental (for surface distribution) and vertical zonality. At the same time, the absolute values of the weight and volume concentrations of the suspended matter themselves are low (on average less than 0.5 mg/l and less than 1.0 mm3/l, respectively). The highest values of all parameters of the suspended matter were found in the Pechora Sea, the most southeastern part of the Barents Sea, where the abrasion of the shores and bottom erosion, and the Pechora River runoff. Surface and bottom peaks are characteristic of the vertical distribution of the suspended matter. An intrusion of the nepheloid layer enriched in the suspended matter into the deep layers can be observed on the continental slope when the depth makes a sharp fall.

Distribution of suspended particulate matter at the equatorial transect in the Atlantic Ocean

Studied oceanographic transect across the Equatorial Atlantic is considered as a “screenshot” of suspended particulate matter distribution against a hydrographical background. The area of abnormal high suspended matter volume concentrations was found above the Sierra Leone Rise from top to bottom (eastern part of the transect). The suggested explanation for the anomaly is based on the ballast hypothesis whereby solid particles are incorporated as ballast into suspended biogenic aggregates, leading to increased velocities of sinking. This process is located within the Northwest African upwelling area since the plankton exposed to the Saharan dust abundance form a significant number of aggregates lately transported equatorward via Canary Current. The intermediate nepheloid layer associated with the Deep Western Boundary Current was recorded from the American Slope at the 3200–3700 m to the depth of 4300 m above the Para Abyssal Plain. Antarctic Bottom Water enriched in the suspended matter was found mostly in the troughs at 40–41° W. It was detached from the bottom, coinciding with the core of the flow due to the bottom rise (“dam”) located up-stream. The grain size of particles was in accordance with polymodal distribution – the 2–4 μm and the 8–13 μm modes. The registered rise in the percentage of the 7–21 μm-sized particles suggests the presence of the well-known coarse mode (20–60 μm) formed by aggregation of transparent exopolymer particles (mucus).

Monsoonal forcing of cold-water coral growth off southeastern Brazil during the past 160 kyr

Cold-water corals (CWCs) constitute important deep-water ecosystems that are under increasing environmental pressure due to ocean acidification and global warming. The sensitivity of these deep-water ecosystems to environmental change is demonstrated by abundant paleorecords drilled through CWC mounds that reveal characteristic alterations between rapid formation and dormant or erosive phases. Previous studies have identified several central parameters for driving or inhibiting CWC growth such as food supply, oxygenation, and the carbon saturation state of bottom water, yet there are still large uncertainties about the relative importance of the different environmental parameters. To advance this debate we have performed a multiproxy study on a sediment core retrieved from the 25 m high Bowie Mound, located at 866 m water depth on the continental slope off southeastern Brazil, a structure built up mainly by the CWC Solenosmilia variabilis. Our results indicate a multifactorial control on CWC growth at Bowie Mound during the past ∼ 160 kyr, which reveals distinct formation pulses during northern high-latitude glacial cold events (Heinrich stadials, HSs) largely associated with anomalously strong monsoonal rainfall over the continent. The ensuing enhanced runoff elevated the terrigenous nutrient and organic-matter supply to the continental margin and likely boosted marine productivity. The dispersal of food particles towards the CWC colonies during HSs was facilitated by the highly dynamic hydraulic conditions along the continental slope that prevailed throughout glacial periods. These conditions caused the emplacement of a pronounced nepheloid layer above Bowie Mound, thereby aiding the concentration and along-slope dispersal of organic matter. Our study thus emphasizes the impact of continental climate variability on a highly vulnerable deep-marine ecosystem.

Particulate rare earth element behavior in the North Atlantic (GEOVIDE cruise)

Particulate concentrations of the 14 Rare Earth Elements (PREE), yttrium, and 232-thorium were measured in 200 samples collected in the epipelagic (ca. 0–200 m) and mesopelagic (ca. 200–1500 m) zones of the North Atlantic during the GEOVIDE cruise (May/June 2014, R/V Pourquoi Pas?, GEOTRACES GA01), providing the most detailed snapshot of the PREE distribution in the North Atlantic so far. Concentrations of particulate cerium (PCe) varied between 0.2 and 16 pmol L−1, while particulate neodymium (PNd) concentrations ranged between 0.1 and 6.1 pmol L−1. Particulate ytterbium (PYb) concentrations ranged between 0.01 and 0.50 pmol L−1. In addition, this study showed that PREE distributions were also controlled by the biological production in the upper sunlit ocean and by remineralization processes in the mesopelagic area. Low surface concentrations combined with normalized PREE patterns displaying a negative Ce anomaly and HREE enrichments pointed to freshly formed biogenic particles imprinting the seawater signature. A significant relationship between biogenic silica (BSi) and PHREE was also observed in the Labrador and Irminger seas, due to the occurrence of strong diatom blooms at the sampling time. In order to identify dissolved-particulate processes independent of the ionic radius, we used PHo∕PY ratios and showed that absorption processes were predominant in the upper ocean, while adsorption processes dominated at deeper depths. This study highlighted different lithogenic fractions of PREE and dispersion depending on the shelf: off the Iberian margin, up to 100 % of the PREE were determined to have a lithogenic origin. This lithogenic input spread westward along an intermediate nepheloid layer (INL), following isopycnals up to 1700 km away from the margin. In contrast, along the Greenland and Newfoundland margins, the circulation maintained lithogenic inputs of PREE along the coasts.

Challenges of Measuring Abyssal Temperature and Salinity at the Kuroshio Extension Observatory

The deep ocean is severely undersampled. Whereas shipboard measurements provide irregular spatial and temporal records, moored records establish deep ocean high-resolution time series, but only at limited locations. Here, highlights and challenges of measuring abyssal temperature and salinity on the Kuroshio Extension Observatory (KEO) mooring (32.3°N, 144.6°E) from 2013 to 2019 are described. Using alternating SeaBird 37-SMP instruments on annual deployments, an apparent fresh drift of 0.03–0.06 psu was observed, with each newly deployed sensor returning to historical norms near 34.685 psu. Recurrent salinity discontinuities were pronounced between the termination of each deployment and the initiation of the next, yet consistent pre- and postdeployment calibrations suggested the freshening was “real.” Because abyssal salinities do not vary by 0.03–0.06 psu between deployment locations, the contradictory salinities during mooring overlap pointed toward a sensor issue that self-corrects prior to postcalibration. A persistent nepheloid layer, unique to KEO and characterized by murky, sediment-filled water, is likely responsible for sediment accretion in the conductivity cell. As sediment (or biofouling) increasingly clogs the instrument, salinity drifts toward a fresh bias. During ascent, the cell is flushed, clearing the clogged instrument. In contrast to salinity, deep ocean temperatures appear to increase from 2013 to 2017 by 0.0059°C, whereas a comparison with historical deep temperature measurements does not support a secular temperature increase in the region. It is suggested that decadal or interannual variability associated with the Kuroshio Extension may have an imprint on deep temperatures. Recommendations are discussed for future abyssal temperature and salinity measurements.

Distribution of suspended particulate matter in the Barents Sea in late winter 2019

Arctic summer and winter sea-ice extent is continuously declining as a result of climate change, affecting the hydrography and biogeochemical cycles on the seasonally ice-free Eurasian Shelves. The prolongation of the open-water season causes higher sediment resuspension and coastal erosion due to larger wind fetch and wave heights. This impacts the optical properties of the water column and hence biological productivity in this region. During “Transarktika-2019” leg 1 in late winter 2019, a comprehensive dataset of and optical data was collected throughout the central and northern Barents Sea. Combining suspended particulate matter concentrations obtained from water samples and optical data revealed a pronounced bottom nepheloid layer on the Barents Sea shelf even under ice-covered conditions. Moreover, the data indicate that the Franz Viktoria Trough could be a major pathway for sediment transport into the Eurasian Basin. Therefore, to link changes in sediment distribution and its impact on the ecosystem under a warming climate, further studies of sediment dynamics are required, particularly during winter.

Monsoonal forcing controlled cold water coral growth off south-eastern Brazil during the past 160 kyrs

Cold-water corals (CWC) constitute important deep-water ecosystems that are increasingly under environmental pressure due to ocean acidification and global warming. The sensitivity of these deep-water ecosystems to environmental change is demonstrated by abundant paleo-records drilled through CWC mounds that reveal a characteristic alteration between rapid formation and dormant or erosive phases. Previous studies have identified several parameters such as food supply, oxygenation, and carbon saturation state of bottom water as central for driving or inhibiting CWC growth, yet there is still a large uncertainty about the relative importance of the different environmental parameters. To advance this debate we have performed a multi-proxy study on a sediment core retrieved from the 25 m high Bowie Mound, located in 866 m water depth on the continental slope off south-eastern Brazil, a structure built up mainly by the CWC Solenosmilia variabilis. Our results indicate a multi-factorial control on CWC growth and mound formation at Bowie Mound during the past ~160 kyrs, which reveals distinct formation pulses during glacial high northern latitude cold events (Heinrich Stadials, HS) largely associated with anomalous continental wet periods. The ensuing enhanced run-off elevated the terrigenous nutrient and organic matter supply to the continental margin, and might have boosted marine productivity. The dispersal of food particles towards the CWC colonies during HS was facilitated by the highly dynamic hydraulic conditions along the continental slope that prevailed throughout glacial periods. These conditions caused the emplacement of a pronounced nepheloid layer above Bowie Mound aiding the concentration and along-slope dispersal of organic matter. Our study thus demonstrates a yet unrecognized impact of continental climate variability on a highly vulnerable deep-marine ecosystem.

Exceptional preservation of two new early rossellid sponges: the dominant species in the Hirnantian (Late Ordovician) Anji Biota of China

The Anji Biota of Zhejiang Province, South China, is an exceptionally preserved, sponge-dominated fauna from the latest Ordovician interval, representing a deep-water environment and containing more than 100 sponge species. Herein a complex of two common species that together dominate the deepest-water sponge assemblages within the sequence are described: Shouzhispongia coronata gen. et sp. nov. and Shouzhispongia prodigia gen. et sp. nov. The complex taphonomic pathway for sponge preservation is critical to interpretation of the fossils: prostalial hypodermal pentactins (a unique character of the hexactinellid family Rossellidae) were originally present and are locally visible, but many have been lost taphonomically because spicules are primarily preserved as moulds within soft tissues. The choanosomal skeleton is composed dominantly of very small hexactins and other triaxon spicules rather than diactins, suggesting an early branching position within the family stem group. Despite their abundance in the Anji Biota, and superficial similarity to certain extant rossellid genera such as Bathydorus, no closely similar sponges have yet been described. This highlights the extremely incomplete fossil record of truly deep-water ecosystems. Preservational alignment patterns of the sponges on bedding planes support previous ideas of nepheloid-layer collapse as the primary burial mechanism.