scholarly journals Long-term seafloor morphological changes generated by bottom trawling on the northern Catalan continental shelf (NW Mediterranean)

2021 ◽  
Author(s):  
Ruth Durán ◽  
Pere Puig ◽  
Araceli Muñoz ◽  
Claudio Lo Iacono ◽  
Jorge Guillén ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Sediment Cores ◽  
Seafloor Morphology ◽  
Bottom Trawling ◽  
Side Scan Sonar ◽  
Nw Mediterranean ◽  
High Backscatter ◽  
Sonar Images ◽  
Spanish Research

<p>The north-western Mediterranean continental margin is one of the few regions in the world where bottom trawling has been continuously practised since several decades. Among the existing trawling techniques, the one practised on this region is the "otter trawling", which has a strong impact on the seafloor morphology via scraping and ploughing, especially on muddy substrates. High-resolution multibeam bathymetry and backscatter data, side scan sonar images, sediment cores and satellite based Vessel Monitoring System (VMS) data have been integrated to investigate the impact of bottom trawling on the seafloor morphology of the northern Catalan continental shelf (NW Mediterranean). Satellite-based navigation tracks from bottom trawlers operating in the study area during 6 years (2006-2011) reveal the spatial distribution of fishing grounds and the occurrence of an intense trawling effort around the 50-60 m isobaths, since trawling is banned at shallow depths. Backscatter imagery shows a narrow (120-250 m wide) and discontinuous high backscatter facies along this depth range, extending parallel to the coastline for more than 40 km from Portbou to l’Estartit. In the bathymetric data, this high backscatter region also coincides with an abrupt change in the mean seafloor gradient (from 0.8° in the inner shelf to 0.4° in the middle shelf), or locally with a narrow (50-150 m wide) slightly depressed (0.2-0.6 m deep) channeled morphology. Side-scan sonar images display high density of trawl marks generated by fishing gears in this area. Further offshore, scattered narrower trawl hauls are also observed on the middle shelf (60-90 m deep), where they can be traced across several thousands of meters. Sediment cores retrieved from the area of high backscatter and largest trawling intensity display sediment coarsening in the upper layers (0-4 cm) caused by winnowing of finer fractions. These findings demonstrate that chronic stirring, mixing and erosion of surface sediments induced by recurrent trawling persisting over the same fishing grounds can cause long-term morphological and sedimentary changes on the continental shelf seafloor.</p><p>This study has received funding from the ABIDES (Assessment of Bottom-trawling Impacts in the Deep-sea Sediments) Spanish Research Project (CTM2015-65142-R) and the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No. 867471. Additional funds were provided by the Generalitat de Catalunya Generalitat de Catalunya (2017 SGR-663 and -1588) and by the Spanish Research Project ABRIC (RTI2018-096434-B-I00). This work is contributing to the ICM’s ‘Center of Excellence’ Severo Ochoa (CEX2019-000928-S). The authors wish to thank the Secretaría General de Pesca and Tragsa for the 2004 Espace Project dataset.</p>

Effects of bottom trawling on the Ebro continental shelf sedimentary system (NW Mediterranean)

2014 ◽  
Vol 72 ◽  
pp. 83-98 ◽  
Author(s):  
Albert Palanques ◽  
Pere Puig ◽  
Jorge Guillén ◽  
Montserrat Demestre ◽  
Jacobo Martín
Keyword(s):  
Continental Shelf ◽  
Bottom Trawling ◽  
Nw Mediterranean ◽  
Sedimentary System

scholarly journals Short-term evolution of submarine canyon head morphologies in the NW Mediterranean: Blanes and Cap de Creus canyons

2021 ◽  
Author(s):  
Cecilia Cabrera ◽  
Ruth Durán ◽  
Pere Puig ◽  
Jorge Guillén ◽  
Araceli Muñoz ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Morphological Evolution ◽  
Submarine Canyon ◽  
Small Scale ◽  
Time Interval ◽  
Shelf Water ◽  
Short Term ◽  
Seafloor Morphology ◽  
Term Evolution ◽  
Nw Mediterranean

<p>Submarine canyons are morphological features found along continental margins that play a key role channeling and connecting sediment from continental shelves to the abyssal plains. The current morphological characterization of the Blanes and Cap de Creus canyon heads, located on the Catalan continental margin (NW Mediterranean Sea), has been recently conducted during the CRIMA cruise in September 2020 using high-resolution (4 m grid size) multibeam bathymetry data. These data have been compared with a previous dataset collected in 2004 during the ESPACE project to evaluate the morphological changes during this 16-year interval. Since these canyon heads are located at shallow water depths and at short distances from the shoreline, their short-term evolution is related to the sediment dynamics on the continental shelf.</p><p>A large-scale change in the seafloor morphology was observed in the Blanes canyon head, indicating the prevalence of erosion in the western canyon rim and non-deposition in the eastern rim. In the Cap de Creus canyon head, the excavation of pre-existing erosive structures was also evidenced in the southwestern canyon rim. These changes mainly happen in the area where the shelf is narrower, which coincide with the main zone of dense water advection along the shelf and toward the canyon interior. The different small-scale morphological evolution between both canyon heads seems to be related to the local geological characteristic of the subsurface deposits of the continental shelf. The Blanes canyon head incises a succession of relict (Holocene) sediment bodies that can act as a source of erodible sediments to the canyon, mainly during strong storms. The continental shelf in the vicinity of the Cap de Creus canyon head, however, is characterized by a rocky substratum (Paleozoic) with a limited sediment coverage and numerous erosive features that evidence relative sand starvation. This creates a greater erosive resistance, although the erosive character of strong storms and major dense-shelf water cascading events occurring during the studied time interval is evident. Additionally, small changes in the shelf bedforms indicate that such high-energetic oceanographic processes also modify the fine-scale seafloor morphology.</p><p>These results reveal that both submarine canyon heads are dynamic and sensitive to oceanographic processes that enhance the erosion and transport of sediment from the shelf into the canyon, particularly during energetic storms and dense shelf water cascading events. Nevertheless, their small-scale evolution seems to be closely related to the type of geological substrate of the shelf on which they are developing.</p><p>This study has received funding from the ABRIC (RTI2018-096434-B-I00) and CRIMA (RTI2018-095770-B-I00) Spanish Research Projects, the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No. 867471 and the Generalitat de Catalunya (2017 SGR-663 and -1588). This work is contributing to the ICM’s ‘Center of Excellence’ Severo Ochoa (CEX2019-000928-S). The authors thank the Secretaría General de Pesca and Tragsa for the 2004 ESPACE Project dataset.</p>

scholarly journals Optimizing the Sediment Classification of Small Side-Scan Sonar Images Based on Deep Learning

IEEE Access ◽  
2021 ◽  
Vol 9 ◽  
pp. 29416-29428
Author(s):  
Xiaoming Qin ◽  
Xiaowen Luo ◽  
Ziyin Wu ◽  
Jihong Shang
Keyword(s):  
Deep Learning ◽  
Side Scan Sonar ◽  
Sediment Classification ◽  
Sonar Images ◽  
Small Side

scholarly journals Vulnerability of the North Water ecosystem to climate change

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sofia Ribeiro ◽  
Audrey Limoges ◽  
Guillaume Massé ◽  
Kasper L. Johansen ◽  
William Colgan ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Late Holocene ◽  
Sediment Cores ◽  
Arctic Ecosystems ◽  
Little Auk ◽  
The North ◽  
Water Ecosystem ◽  
North Water

AbstractHigh Arctic ecosystems and Indigenous livelihoods are tightly linked and exposed to climate change, yet assessing their sensitivity requires a long-term perspective. Here, we assess the vulnerability of the North Water polynya, a unique seaice ecosystem that sustains the world’s northernmost Inuit communities and several keystone Arctic species. We reconstruct mid-to-late Holocene changes in sea ice, marine primary production, and little auk colony dynamics through multi-proxy analysis of marine and lake sediment cores. Our results suggest a productive ecosystem by 4400–4200 cal yrs b2k coincident with the arrival of the first humans in Greenland. Climate forcing during the late Holocene, leading to periods of polynya instability and marine productivity decline, is strikingly coeval with the human abandonment of Greenland from c. 2200–1200 cal yrs b2k. Our long-term perspective highlights the future decline of the North Water ecosystem, due to climate warming and changing sea-ice conditions, as an important climate change risk.

scholarly journals Energy transformations and dissipation of nonlinear internal waves over New Jersey's continental shelf

2010 ◽  
Vol 17 (4) ◽  
pp. 345-360 ◽  
Author(s):  
E. L. Shroyer ◽  
J. N. Moum ◽  
J. D. Nash
Keyword(s):  
Continental Shelf ◽  
Internal Waves ◽  
Turbulent Mixing ◽  
Internal Tide ◽  
Flux Divergence ◽  
Wave Interactions ◽  
Nonlinear Internal Waves ◽  
Dissipative Loss ◽  
Peak Energy

Abstract. The energetics of large amplitude, high-frequency nonlinear internal waves (NLIWs) observed over the New Jersey continental shelf are summarized from ship and mooring data acquired in August 2006. NLIW energy was typically on the order of 105 Jm−1, and the wave dissipative loss was near 50 W m−1. However, wave energies (dissipations) were ~10 (~2) times greater than these values during a particular week-long period. In general, the leading waves in a packet grew in energy across the outer shelf, reached peak values near 40 km inshore of the shelf break, and then lost energy to turbulent mixing. Wave growth was attributed to the bore-like nature of the internal tide, as wave groups that exhibited larger long-term (lasting for a few hours) displacements of the pycnocline offshore typically had greater energy inshore. For ship-observed NLIWs, the average dissipative loss over the region of decay scaled with the peak energy in waves; extending this scaling to mooring data produces estimates of NLIW dissipative loss consistent with those made using the flux divergence of wave energy. The decay time scale of the NLIWs was approximately 12 h corresponding to a length scale of 35 km (O(100) wavelengths). Imposed on these larger scale energetic trends, were short, rapid exchanges associated with wave interactions and shoaling on a localized topographic rise. Both of these events resulted in the onset of shear instabilities and large energy loss to turbulent mixing.

scholarly journals Estimation of long-term Ph changes in lakes of the Caucasus using a bioindication method based on diatomaceous analysis

2019 ◽  
Vol 46 (1) ◽  
pp. 51-57 ◽  
Author(s):  
L. V. Razumovskii ◽  
V. L. Razumovskii
Keyword(s):  
Sediment Cores ◽  
Western Caucasus ◽  
Small Lakes ◽  
The Caucasus ◽  
Ph Values ◽  
Long Term Changes ◽  
The Western Caucasus ◽  
Central Caucasus ◽  
Hydrological Parameter

To analyze processes that may lead to long-term changes in pH, lake sediments from five small lakes in the Western and Central Caucasus were studied according to diatomaceous complexes from sediment cores. A proprietary principle of hydrological parameter unification was used to reconstruct numerical pH values. In isotopic dating experiments, a series of numerical pH values for 2000–130 years were generated for the lakes. These data indicate an absence of noticeable changes in pH in the lakes of the Western Caucasus and alkalization processes in the lakes of the Central Caucasus.

Sign in / Sign up

Export Citation Format

Share Document