Chronology of sedimentation in Colesbukta, Spitsbergen (Svalbard Archipelago): the results of the 2018 expedition

This paper presents results of a study of sedimentation in Colesbukta (Isfjorden, Spitsbergen), a typical example of sedimentation in a shallow bay of the Svalbard Archipelago. We have examined sediment samples from several cores collected in Colesbukta in May 2018. To meet the goals of this study, geomorphological features of the Colesbukta catchment area have been identified and described. The lithological characteristics of bottom sediments from the study area have been described and their spatial and temporal changes analyzed. The chronology of sedimentation has been reconstructed by 210Pb and 137Cs. We have calculated sedimentation rates in Colesbukta and their temporal dynamics over the several latest decades. According to our estimations, the sedimentation rate has increased by 2–4 times compared to the middle of the 20th century and ranges from 0.2 to 0.46 mm/year depending on the individual conditions of sedimentation in each part of the bay. Climatic fluctuations are shown to have a direct impact on sedimentation processes in Colesbukta. We have revealed that on the periphery of the studied area the rate of sedimentation better depends on the temperature regime while in its central part it is rather a result of the amount of atmospheric precipitation.

Sponge contribution to the silicon cycle of a diatom-rich shallow bay

In coastal systems, planktonic and benthic silicifiers compete for the pool of dissolved silicon, a nutrient required to make their skeletons. The contribution of planktonic diatoms to the cycling of silicon in coastal systems is often well characterized, while that of benthic silicifiers such as sponges has rarely been quantified. Herein, silicon fluxes and stocks are quantified for the sponge fauna in the benthic communities of the Bay of Brest (France). A total of 45 siliceous sponge species living in the Bay account for a silicon standing stock of 1215 tons, while that of diatoms is only 27 tons. The silicon reservoir accumulated as sponge skeletons in the superficial sediments of the Bay rises to 1775 tons, while that of diatom skeletons is only 248 tons. These comparatively large stocks of sponge silicon were estimated to cycle two orders of magnitude slower than the diatom stocks. Sponge silicon stocks need years to decades to be renewed, while diatom turnover lasts only days. Although the sponge monitoring over the last 6 years indicates no major changes of the sponge stocks, our results do not allow to conclude if the silicon sponge budget of the Bay is at steady state, and potential scenarios are discussed. The findings buttress the idea that sponges and diatoms play contrasting roles in the marine silicon cycle. The budgets of these silicon major users need to be integrated and their connections revealed, if we aim to reach a full understanding of the silicon cycling in coastal ecosystems.

Measurements of Enhanced Near-Surface Turbulence under Windrows

Observations of waves, winds, turbulence, and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of Rimouski, Québec. Water velocities measured from a forward-looking pulse-coherent ADCP mounted on a small zodiac show spanwise (cross-windrow) convergence, streamwise (downwind) velocity enhancement, and downwelling in the windrows, consistent with the view that windrows are the result of counterrotating pairs of wind-aligned vortices. The spacing of windrows, measured with acoustic backscatter and with surface imagery, was measured to be approximately twice the water depth, which suggests an aspect ratio of 1. The magnitude and vertical distribution of turbulence measured from the ADCP are consistent with a previous scaling and observations of near-surface turbulence under breaking waves, with dissipation rates larger and decaying faster vertically than what is expected from a shear-driven boundary layer. Measurements of dissipation rate are partitioned to within, and outside of the windrow convergence zones, and measurements inside the convergence zones are found to be nearly an order of magnitude larger than those outside with similar vertical structure. A ratio of time scales suggests that turbulence likely dissipates before it can be advected horizontally into convergences, but the advection of wave energy into convergences may elevate the surface flux of TKE and could explain the elevated turbulence in the windrows. These results add to a limited number of conflicting observations of turbulence variability due to windrows, which may modify gas flux, and heat and momentum transport in the surface boundary layer.

Carbon-isotope stratigraphy of the SPICE event (Upper Cambrian) in eastern Laurentia: implications for global correlation and a potential reference section

The δ13C profile from the lower interval of the Martin Point section in western Newfoundland (Canada) spans the Upper Cambrian (uppermost Franconian – lowermost Trempealeauan). The investigated interval (∼110 m) is a part of the Green Point Formation of the Cow Head Group and consists of the upper part of the Tucker Cove Member (topmost part of the Shallow Bay Formation) and the lowermost part of the Martin Point Member (bottom of the Green Point Formation). It is formed of rhythmites of marine carbonates alternating with shales and minor conglomeratic interbeds. Multiscreening petrographic and geochemical techniques have been utilized to evaluate the preservation of the investigated lime mudstones. The δ13C and δ18O values of the sampled micrites (−4.8 ‰ to +1.0 ‰ VPDB and −8.2 ‰ to −5.3 ‰ VPDB, respectively) have insignificant correlation (R2= 0.01), as similarly do the δ13C values with their Sr counterparts (R2= 0.07), which supports the preservation of at least near-primary δ13C signatures that can be utilized to construct a reliable high-resolution carbon-isotope profile for global correlations. The δ13C profile exhibits two main negative excursions: a lower excursion (∼4 ‰) that reaches its maximum at the bottom of the section and an upper narrow excursion (∼6 ‰) immediately above the boundary of the Tucker Cove/Martin Point members (Shallow Bay Formation – Green Point Formation boundary). The lower excursion may be correlated with the global SPICE event, whereas the upper excursion may match with a post-SPICE event that has been also recognized in profiles of equivalent sections on different palaeocontinents.

Pseudocryptic species of the Middle Cambrian trilobite Eodiscus Hartt, in Walcott, 1884, from Avalonian and Laurentian Newfoundland

Two species of the Middle Cambrian trilobite Eodiscus Hartt, in Walcott, 1884, E. punctatus (Salter, 1864) and E. scanicus (Linnarsson, 1883), have been reported from several paleocontinents. However, in their respective type areas of Avalonian Britain and Baltica (Sweden), both species are poorly documented from moulds preserved in siliciclastic mudstone that are variably compacted and distorted. Moreover, variation in such characters as surface sculpture between putative occurrences suggests that widespread use of these names may mask species differentiation within and between paleocontinents. Detailed examination of Eodiscus sclerites that are exquisitely preserved in full relief in limestone from the Manuels River Formation of Avalonian Newfoundland and the Shallow Bay Formation of Laurentian Newfoundland demonstrates the presence of multiple species that are distinct from both E. punctatus and E. scanicus. We interpret them as a group of pseudocryptic species that are comparable to groups that are now identified routinely among modern invertebrates. New species are E. confossus, E. tuberculus, and E. coloholcus. At the current state of knowledge, E. punctatus and E. scanicus are best restricted to their respective types.

Initial observations of the shallow geology in Tannis Bugt, Skagerrak, Denmark

During August 2017, as part of the habitat mapping of Natura2000 areas, a geophysical survey of a large area within the Skagerrak was undertaken by the Geological Survey of Denmark and Greenland. In this article, we use the acquired data to discuss the geology of Tannis Bugt (Fig. 1), a large shallow bay at the north-west coast of Vendsyssel. The bay extends 40 km between Hirtshals in the west and Skagen in the east forming the northern-most Danish Skagerrak coast.