Variation characteristics of ocean sediment Fe levels and their relationship with grain sizes in culture areas over a long period

Iron (Fe) is an essential component for marine ecosystems, and it is related to the growth of phytoplankton communities and environmental evolution in coastal area. However, the effect of aquaculture activities on sediment Fe levels is not well studied. Fe levels and grain sizes are determined in two cores (respectively Core C in the culture area and Core A in the control area) in Sishili Bay to reveal the influence of cultivation on sediment Fe levels over an extended period. The sediment Fe levels are distinguished in the upper sections (culture period) but equal in the lower sections (non-culture period) of the two cores. The core C has the same Fe levels as Core A before 1950s (non-culture period). However, the sediment Fe levels of Core C increased during 1950s–1970s (the algae culture period) and decreased after the 1970s (shellfish culture period) compared with Core A, indicating the algae and shellfish culture impose opposite effects on sediment Fe levels. Similarly, sediment grain sizes are observed to be finer during the algae culture period but coarser during the shellfish culture period, and the variation of sediment grain sizes because of culture activities is the important factor affecting sediment Fe levels. The slowing down of ocean current due to algae culture causes finer particles and higher Fe levels in sediment. However, during the shellfish culture period, bio-deposition and re-suspension play major roles in coarsening sediment particles and decreasing sediment Fe levels.

MOSAIC (Modern Ocean Sediment Archive and Inventory of Carbon): a (radio)carbon-centric database for seafloor surficial sediments

Mapping the biogeochemical characteristics of surficial ocean sediments is crucial for advancing our understanding of global element cycling, as well as for assessment of the potential footprint of environmental change. Despite their importance as long-term repositories for biogenic materials produced in the ocean and delivered from the continents, biogeochemical signatures in ocean sediments remain poorly delineated. Here, we introduce MOSAIC (Modern Ocean Sediment Archive and Inventory of Carbon; https://doi.org/10.5168/mosaic019.1, http://mosaic.ethz.ch/, last access: 1 March 2021; Van der Voort et al., 2019), a (radio)carbon-centric database that seeks to address this information void. The goal of this nascent database is to provide a platform for development of regional-to-global-scale perspectives on the source, abundance and composition of organic matter in marine surface sediments and to explore links between spatial variability in these characteristics and biological and depositional processes. The database has a continental margin-centric focus given both the importance and complexity of continental margins as sites of organic matter burial. It places emphasis on radiocarbon as an underutilized yet powerful tracer and chronometer of carbon cycle processes, with a view to complementing radiocarbon databases for other Earth system compartments. The database infrastructure and interactive web application are openly accessible and designed to facilitate further expansion of the database. Examples are presented to illustrate large-scale variabilities in bulk carbon properties that emerge from the present data compilation.

Iron colloids dominate sedimentary supply to the ocean interior

Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a “rusty source”) that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.

Image Recognition Technology in Texture Identification of Marine Sediment Sonar Image

Through the recognition of ocean sediment sonar images, the texture in the image can be classified, which provides an important basis for the classification of ocean sediment. Aiming at the problems of low efficiency, waste of human resources, and low accuracy in the traditional manual side-scan sonar image discrimination, this paper studies the application of image recognition technology in sonar image substrate texture discrimination, which is popular in many fields. At the same time, considering the scale complexity, diversity, multisources, and small sample characteristics of the marine sediment sonar image texture, the transfer learning is introduced into the image recognition, and the K-means clustering algorithm is used to reset the prior frame parameters to improve the speed and accuracy of image recognition. Through the experimental comparison between the original model and the new model based on transfer learning, the AP (average precision) value of the yolov3 model based on transfer learning can reach 84.39%, which is 0.97% higher than that of the original model, with considerable accuracy and room for improvement; it takes less than 0.2 seconds. This shows the applicability and development of image recognition technology in texture discrimination of bottom sonar images.

Muricauda sediminis sp. nov., isolated from western Pacific Ocean sediment

A Gram-stain-negative bacterium, designated strain 40Bstr401T, was isolated from a sediment sample collected from the western Pacific Ocean. Analysis of its 16S rRNA gene sequence revealed that strain 40Bstr401T belongs to the genus Muricauda and is closely related to type strains Muricauda antarctica Ar-22T (98.2 %), Muricauda taeanensis 105T (98.2 %) and Muricauda beolgyonensis BB-My12T (97.4 %). The average nucleotide identity values for 40Bstr401T with M. antarctica Ar-22T and M. taeanensis 105T are 79.3 % and 78.8 %, respectively. The in silico DNA–DNA hybridization values between strain 40Bstr401T and M. antarctica Ar-22T and M. taeanensis 105T are 26.7 and 26.6 %, respectively. The major isoprenoid quinone of 40Bstr401T is MK-6, and iso-C17 : 0 3-OH and iso-C15 : 0 are the dominant cellular fatty acids. The major polar lipids are phosphatidylethanolamine, four unidentified amino lipids and two unidentified lipids. The G+C content of the genomic DNA is 42.9 mol%. Its phylogenetic distinctiveness and chemotaxonomic differences, together with the phenotypic properties observed in this study, indicate that strain 40Bstr401T can be differentiated from closely related species. Therefore, we propose strain 40Bstr401T represents a novel species in the genus Muricauda , for which the name Muricauda sediminis sp. nov. is suggested. The type strain is 40Bstr401T (=MCCC 1K04568T=KCTC 82139T).

Decadal climate sensitivity of contouritic sedimentation in a dynamically coupled ice-ocean-sediment model of the Pan-Arctic region

<p>Ocean sediment drifts contain important information about past bottom currents but a direct link from the study of sedimentary archives to ocean dynamics is not always possible. To close this gap for the North Atlantic, we set up a  new coupled Ice-Ocean-Sediment Model of the entire Pan-Arctic region. In order to evaluate the potential dynamics of the model, we conducted decadal sensitivity experiments. In our model contouritic sedimentation shows a significant sensitivity towards climate variability for most of the contourite drift locations in the model domain. We observe a general decrease of sedimentation rates during warm conditions with decreasing atmospheric and oceanic gradients and an extensive increase of sedimentation rates during cold conditions with respective increased gradients. We can relate these results to changes in the dominant bottom circulation supplying deep water masses to the contourite sites under different climate conditions. A better understanding of northern deep water pathways in the Atlantic Meridional Overturning Circulation (AMOC) is crucial for evaluating possible consequences of climate change in the ocean.</p>