scholarly journals Comparison between Recent benthic foraminiferal faunas of the Porcupine Seabight and Western Approaches Continental Slope

1985 ◽  
Vol 4 (2) ◽  
pp. 165-183 ◽  
Author(s):  
Janice F. Weston

Abstract. Although only 1 degree of latitude apart, the South Western Approaches and Porcupine Seabight continental slopes support widely differing benthic foraminiferal faunas. The less energetic, less variable, muddier conditions of the prograding margin of the Porcupine Seabight yield foraminiferal faunas which show extremely good zonations with respect to depth and are dominated by species such as Trifarina angulosa, Gavelinopsis lobatulus and Uvigerina pygmaea. The more variable and more energetic conditions of the submarine canyons of the Western Approaches margin do not support well depth zones faunas, but assemblages which are generally dominated by more cosmopolitan and robust species, such as Cassidulina carinata, Brizalina dilatata and B.subaenariensis. Such differences may be related to factors such as a greater variability of sediment type and bottom water characteristics and a more energetic environment in the Western Approaches area.

2021 ◽  
Vol 41 (1) ◽  
Author(s):  
S. Susanth ◽  
P. John Kurian ◽  
C. M. Bijesh ◽  
D. Twinkle ◽  
Abhishek Tyagi ◽  
...  

1950 ◽  
Vol 87 (2) ◽  
pp. 102-104 ◽  
Author(s):  
K. O. Emery

AbstractThrusting along a shear plane at the continental margins may result in a temporary up-bulging of the margins above sea-level. During the time of exposure erosion by streams should have incised canyons which now, after isostatic readjustment of the margins, constitute the widely distributed submarine canyons. Known downwarped peneplains below the surface of continental shelves may have been developed on the bulged margins by long continued erosion. The margins may, thus, have served as- sources of some sediments now found on land and believed to have been derived from a seaward direction.


2020 ◽  
Author(s):  
Eugene G Morozov ◽  
Dmitry I. Frey ◽  
Roman Y. Tarakanov

Abstract We analyze measurements of bottom currents and thermohaline properties of water north of the Vema Channel with the goal to find pathway continuations of Antarctic Bottom Water flow from the Vema Channel into the Brazil Basin. The analysis is based on CTD/LADCP casts north of the Vema Channel. The flow in the deep Vema Channel consists of two branches. The deepest current flows along the bottom in the center of the channel and the other branch flows above the western wall of the channel. We found two smaller channels of the northern continuation of the deeper bottom flow. These flows become weak and almost disappear at a latitude of 25°30’S. The upper current flows at a depth of 4100-4200 m along the continental slope. We traced this current up to 24°S over a distance exceeding 250 km. This branch transports bottom water that eventually fills the deep basins of the North Atlantic.


2021 ◽  
Author(s):  
Naomi Moshe ◽  
Oded Katz ◽  
Adi Torfstein ◽  
Mor Kanari ◽  
Pere Masque ◽  
...  

<p>Submarine canyons are prominent features in continental slopes. They play an important role in sediment transport to the deep sea, as they form conduits for turbidity currents and cause landslides due their steep slopes. Such mass transport events could create geo-hazards, which compromise infrastructures along the continental slope.</p><p>Our research focuses on the Nahariya Canyon, which is part of a series of submarine canyons located along the continental slopes of the eastern Mediterranean, offshore northern Israel. This canyon is incised into the slope and does not reach the shelf. Here, we report the results from a study of two piston cores sampled in the canyon at water depths of 650m (NAC650, ~2.5m long) and 915m (NAC915, ~6m long). Chronologies were established based radiocarbon dating using slope foraminiferal shells, in addition to <sup>210</sup>Pb and OSL dating of bulk sediment. The sediments were characterized by major and trace element concentrations, mineralogy, grain size, and dead foraminiferal assemblages. We further identified the living (Rose-Bengal stained) foraminiferal species at three depths habitats (200m 650m and 915m water depth).</p><p>Our results show that both piston cores are comprised of a capping ~40 cm thick interval of fine laminated mud, deposited over the last ~150-200 years, apparently reflecting hemipelagic sedimentation. This capping interval unconformably overlays a consolidated sequence in both cores, which indicates a major sediment removal. The consolidated sequence in NAC650 is mostly homogenous and dates to the previous glacial (>140 ka), and in NAC915 the upper 70 cm of the consolidated sequence consists mud clasts dated to 27-46 ka that overlay an ‘S shape’ shear zone, which is a result of a down canyon mass wasting (debrite). Below that debrite, the sediment is mostly homogenous and dates to the last glacial (>25 ka). Broken shells of shallow benthic foraminiferal species such as Ammonia spp., Asterigerinata mamilla, Miliolids, Rosalina spp. and Sorites orbiculus are found abundantly throughout both piston-cores, varying between in-core intervals, indicating that allochthonous sediments are prevalent at those cores. Same shallow species are found also in the surface (living) assemblages, mixed with slope deep foraminiferal species. Moreover, the deep living foraminiferal shells are well preserved, in contrast to the shallow living species. Taken together, these indicate that sediment transport processes along the canyon exist to this day.</p><p>The cores suggest that the canyon is an erosive environment at least since the last glacial maximum, when the last significant mass wasting deposit is recorded. The Holocene is not represented in the records, probably due to the dominance of erosion processes, except for a thin layer of sediment deposited over the last two centuries that prevails along the entire canyon.</p>


2019 ◽  
Vol 124 (3) ◽  
pp. 1778-1794 ◽  
Author(s):  
Sarah G. Purkey ◽  
Gregory C. Johnson ◽  
Lynne D. Talley ◽  
Bernadette M. Sloyan ◽  
Susan E. Wijffels ◽  
...  

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
S. Aoki ◽  
K. Yamazaki ◽  
D. Hirano ◽  
K. Katsumata ◽  
K. Shimada ◽  
...  

Abstract The Antarctic continental margin supplies the densest bottom water to the global abyss. From the late twentieth century, an acceleration in the long-term freshening of Antarctic Bottom Waters (AABW) has been detected in the Australian-Antarctic Basin. Our latest hydrographic observations reveal that, in the late 2010s, the freshening trend has reversed broadly over the continental slope. Near-bottom salinities in 2018–2019 were higher than during 2011–2015. Along 170° E, the salinity increase between 2011 and 2018 was greater than that observed in the west. The layer thickness of the densest AABW increased during the 2010s, suggesting that the Ross Sea Bottom Water intensification was a major source of the salinity increase. Freshwater content on the continental slope decreased at a rate of 58 ± 37 Gt/a in the near-bottom layer. The decadal change is very likely due to changes in Ross Sea shelf water attributable to a decrease in meltwater from West Antarctic ice shelves for the corresponding period.


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