Hydrodynamic and Sediment Transport Patterns in the Minho and Douro Estuaries (NW Portugal) Based on ADCP Monitoring Data: Part 1-Tidal Sediment Exchanges

The tidal variability of the Minho and Douro lower estuaries (NW Portugal) water column structure was assessed at the semi-diurnal and fortnightly time scales under two contrasting seasonal river flow scenarios during the summer of 2005 and winter of 2006. Sediment fluxes inferred from calibrated ADCP acoustic backscatter revealed that, during spring tides and low runoff conditions, both estuaries act as sinks instead of sources of sediments into the inner shelf. Sediment export occurred during neaps, in both estuaries, when the river flow values were high enough to counteract the effect of the entering flood. No evidence of coarse sediment export into the inner shelf that would eventually nourish the littoral system could be inferred from these datasets.

Estimating the Absolute Salinity of Chinese offshore waters using nutrients and inorganic carbon data

In June 2009, the Intergovernmental Oceanographic Commission of UNESCO released The international thermodynamic equation of seawater – 2010 (TEOS-10 for short; IOC et al., 2010) to define, describe and calculate the thermodynamic properties of seawater. Compared to the Equation of State-1980 (EOS-80 for short), the most obvious change with TEOS-10 is the use of Absolute Salinity as salinity argument, replacing the Practical Salinity used in the oceanographic community for 30 years. Due to the lack of observational data, the applicability of the potentially increased accuracy in Absolute Salinity algorithms for coastal and semi-enclosed seas is not very clear to date. Here, we discuss the magnitude, distribution characteristics, and formation mechanism of Absolute Salinity and Absolute Salinity Anomaly in Chinese shelf waters, based on the Marine Integrated Investigation and Evaluation Project of the China Sea and other relevant data. The Absolute Salinity SA ranges from 0.1 to 34.66 g kg−1. Instead of silicate, the main composition anomaly in the open sea, CaCO3 originating from terrestrial input and re-dissolution of shelf sediment is most likely the main composition anomaly relative to SSW and the primary contributor to the Absolute Salinity Anomaly δSA. Finally, relevant suggestions are proposed for the accurate measurement and expression of Absolute Salinity of the China offshore waters.

Influence of the “Great Acceleration” of the Anthropocene on the fluxes of trace elements in sediments of the Santos and São Vicente estuarine system, southeastern Brazil

The worldwide evidence of human activities on the environment led the scientific community to recognize a new geologic time unit known as the Anthropocene. Since the twentieth century, the estuaries have been largely impacted by urbanization and industrialization needs driven by population and economic growth. To assess the contamination, provenance, and fluxes of trace elements (As, Cr, Cu, Ni, Pb, Sc, V and Zn) over the last century, a geochemical and chemometric technique was employed in sediment cores of the Santos and São Vicente Estuarine System (SSVES), an industrial and port region of international importance. The results indicated low contamination, with the highest enrichment factors (EF) for Cu (EF = 3.1), Pb (EF = 2.7), Zn (EF = 2.4) and As (EF = 2.3) found next to the harbor area. The Pre-industrial records confirm the relatively high concentrations of As and its naturally enriched occurrence on the Brazilian shelf. Sediment accumulation rates and trace element fluxes showed a general increase over the years, since the early 1960s, associated with the “Great Acceleration” of the mid-twentieth century. These alterations are human-induced and include urbanization and industrialization. Nonetheless, as the contents and enrichment of trace elements indicate that the region is not severely polluted, we hypothesize that the contamination in the SSVES is likely related to the drainage and erosion of the urbanized adjacent area, rather than direct disposal of inorganic contaminants from the industrial activity.

Monitoring inner shelf sediment transport using fluorescent sand tracers: an example from the south coast of Portugal

<p>The continuous need for beach nourishment requires a detailed understanding of the sediment transport characteristics at the shelf borrow sites, to assess their recovery rate and to evaluate the long-term sustainability of these operations. </p><p>The main objective of this work is to assess sediment transport conditions at an inner shelf borrow site exploited to nourish a beach located at the updrift boundary of the same sedimentary cell (Belharucas, Albufeira, south coast of Portugal).</p><p>The work is supported by a sand tracer experiment, where 600 kg of coated sand with fluorescent ink was deposited (August 2020) by divers at 11 m depth (referred to the mean sea level). Periodic sediment sampling using a Van Veen grab was performed using an adaptative sampling grid that accounted for tracer’s dispersion trough time. The samples were washed and dried in laboratory and tagged particles were automatically identified using an automated image analysis procedure based on ultraviolet lighting.</p><p>Preliminary results show that sediment transport is dominated by a eastward component,probably related with the energetic events from the SW. Ongoing work relates the tracer’s displacement with ADCP (wave and current) data measured nearby the borrow site during the experiment.</p><p> </p><p>The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL and ECOEXA project (MAR-01.04.02-FEAMP-0016).</p><p> </p><p> </p>

Holocene variability of the northeastern Laurentide Ice Sheet in the Clyde Inlet area, western Baffin Bay, from radiogenic isotope records in marine sediments

<p>The reconstruction of late glacial ice sheet fluctuations helps understanding and modelling the local glacio-isostatic adjustment as well as global eustatic changes. From this viewpoint, the large-scale spatial and temporal variations of the Fox Basin-Baffin Island ice dome (NE Laurentide Ice Sheet, Canada) have been well documented. However, high frequency Holocene fluctuations and final decay of it are still poorly documented. We have thus investigated the behaviour of one of its eastern outlet glaciers in the Clyde Inlet fjord, northeastern Baffin Island. The reconstruction of ice sheet margin fluctuation is based on the radiogenic isotope composition (Sr-Pb-Nd) and mineral assemblage of detrital sediments in two marine cores raised within and off the Clyde Inlet (GeoB22346-3, Clyde Inlet head; GeoB22357-3, adjacent continental shelf). Radiogenic isotope ratios and bulk mineral assemblages from such sites are imprints of bedrock erosion along the active ice margin, as well as along ice-streams and subglacial drainage patterns. They may thus be used for the reconstruction of spatial and temporal variations in meltwater discharge into Baffin Bay and of the position of the active margin fluctuations inland. The location of the two sediment cores also informs on the traceability of radiogenic isotope signals from proximal to more distal areas of sediment deposition. Changes in mineralogical and radiogenic isotope compositions at the proximal core site suggest ice margin and drainage fluctuations rather than a constant retreat throughout the Holocene. Shelf sediment provenances are dominated by relatively homogenized Baffin Island inputs during the mid to late Holocene, but record a slightly offshore ice margin position from the late Pleistocene to the early Holocene.</p>

Estimating the Absolute Salinity of China Sea Using Nutrients and Inorganic Carbon Data

In June 2009, the Intergovernmental Oceanographic Commission of UNESCO released the international thermodynamic equation of seawater – 2010 (TEOS-10 for short) to define, describe and calculate the thermodynamic properties of seawater. Compared to the Equation of State-1980 (EOS-80 for short), the most obvious change with TEOS-10 is the use of Absolute Salinity as salinity argument, replacing the Practical Salinity used in the oceanographic community for 30 years. Due to the lack of observational data, the applicability of the potentially increased accuracy in Absolute Salinity algorithms for coastal and semi-enclosed seas is not very clear to date. Here, we discuss the magnitude, distribution characteristics and formation mechanism of Absolute Salinity and Salinity Anomaly in Chinese shelf waters, based on the Marine Integrated Investigation and Evaluation Project of China Offshore and other relevant data. The Absolute Salinity SA ranges from 0.1 to 34.66 g·kg−1. Instead of silicate, CaCO3 originating from terrestrial input and re-dissolution of shelf sediment is most likely the main composition anomaly relative to SSW and the primary contributor to the Absolute Salinity Anomaly δSA. Finally, relevant suggestions are proposed for the accurate measurement and expression of Absolute Salinity of the China offshore.

Influence of incoming plate relief on overriding plate deformation and earthquake nucleation: Cocos Ridge subduction (Costa Rica)

<p>We present a 2D p-wave velocity (Vp) model and a coincident multichannel seismic reflection profile mapping the structure of the southern Costa Rica margin and incoming Cocos Ridge. The seismic profiles image the ocean and overriding plates from the trench across the entire offshore margin, including the structures involved in the 2002 Mw6.4 Osa earthquake. The overriding plate consists of three domains: Domain I at the margin front displays thin-skinned deformation of an imbricated-thrust system composed of fractured rocks with relatively low Vp. Domain II under the middle continental shelf is comparatively less fractured, showing ~15 km long landward-dipping reflection packages and discrete active deformation of the shelf sediment and seafloor. Domain III in the inner shelf is little fractured and appears to be dominated by elastic deformation, with inactive structures of an extensional basin consisting of tilted blocks overlain by ~2 km-thick gently landward-dipping strata. The velocity structure supports the argument that the bulk of the margin is highly consolidated rock possibly similar to outcrops in the Osa Peninsula. Thick-skinned tectonics probably causes the uplift of Domains II and III. The incoming oceanic plate shows crustal thickness variations from ~14 km at the trench (Cocos Ridge) to 6-7 km beneath the continental shelf. We combine (1) inter-plate geometry and velocity-derived fracturing degree at the base of the overriding plate, (2) tectonic stresses and brittle strain above the inter-plate boundary extracted from 3D numerical models, and (3) earthquake locations, to investigate potential relationships between structure and earthquake generation. The 2002 Osa earthquake and its aftershocks appear to have nucleated at the leading flank of two subducting seamounts, coinciding with the area of highest tectonic overpressure in numerical models. Both estimated rock fracturing and modelled brittle strain, steadily increase from the leading flank of the subducting seamounts to their top, which we interpret to reflect the progressive damage caused by the incoming plate relief. Therefore, the analysis supports a spatial and temporal relationship between subducting seamount location, upper plate fracturing, brittle strain, tectonic overpressure, and earthquake nucleation.</p>