scholarly journals Genesis and Evolution of Ferromanganese Crusts from the Summit of Rio Grande Rise, Southwest Atlantic Ocean

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 349 ◽  
Author(s):  
Mariana Benites ◽  
James R. Hein ◽  
Kira Mizell ◽  
Terrence Blackburn ◽  
Luigi Jovane
Keyword(s):  
Atlantic Ocean ◽  
Shallow Water ◽  
Water Column ◽  
Rio Grande ◽  
Intermediate Water ◽  
Mode Water ◽  
Southwest Atlantic ◽  
Ferromanganese Crusts ◽  
Depositional Processes ◽  
Water Depths

The Rio Grande Rise (RGR) is a large elevation in the Atlantic Ocean and known to host potential mineral resources of ferromanganese crusts (Fe–Mn), but no investigation into their general characteristics have been made in detail. Here, we investigate the chemical and mineralogical composition, growth rates and ages of initiation, and phosphatization of relatively shallow-water (650–825 m) Fe–Mn crusts dredged from the summit of RGR by using computed tomography, X-ray diffraction, 87Sr/86Sr ratios, U–Th isotopes, and various analytical techniques to determine their chemical composition. Fe–Mn crusts from RGR have two distinct generations. The older one has an estimated age of initiation around 48–55 Ma and was extensively affected by post-depositional processes under suboxic conditions resulting in phosphatization during the Miocene (from 20 to 6.8 Ma). As a result, the older generation shows characteristics of diagenetic Fe–Mn deposits, such as low Fe/Mn ratios (mean 0.52), high Mn, Ni, and Li contents and the presence of a 10 Å phyllomanganate, combined with the highest P content among crusts (up to 7.7 wt %). The younger generation is typical of hydrogenetic crusts formed under oxic conditions, with a mean Fe/Mn ratio of 0.75 and mean Co content of 0.66 wt %, and has the highest mean contents of Bi, Nb, Ni, Te, Rh, Ru, and Pt among crusts formed elsewhere. The regeneration of nutrients from local biological productivity in the water column is the main source of metals to crusts, providing mainly metals that regenerate rapidly in the water column and are made available at relatively shallow water depths (Ni, As, V, and Cd), at the expense of metals of slower regeneration (Si and Cu). Additionally, important contributions of nutrients may derive from various water masses, especially the South Atlantic Mode Water and Antarctic Intermediate Water (AAIW). Bulk Fe–Mn crusts from the summit of RGR plateau are generally depleted in metals considered of greatest economic interest in crusts like Co, REE, Mo, Te, and Zr, but are the most enriched in the critical metals Ni and Li compared to other crusts. Further investigations are warranted on Fe–Mn crusts from deeper-water depths along the RGR plateau and surrounding areas, which would less likely be affected by phosphatization.

scholarly journals Carbon and nitrogen isotope evidence for widespread presence of anoxic intermediate waters before and during the Permian-Triassic mass extinction

2021 ◽  
Author(s):  
Baojin Wu ◽  
Genming Luo ◽  
Michael M. Joachimski ◽  
Paul B. Wignall ◽  
Lidan Lei ◽  
...  
Keyword(s):  
Shallow Water ◽  
Water Column ◽  
Water Depth ◽  
Mass Extinction ◽  
Isotope Composition ◽  
Nitrogen Isotope ◽  
Intermediate Water ◽  
Negative Shift ◽  
Intermediate Waters ◽  
Direct Killing

The largest mass extinction since the advent of animals occurred during the Permian-Triassic (P-Tr) transition, ca. 252 Ma, and is commonly attributed to the eruption of the Siberian Traps large igneous province. However, the direct killing mechanism is still debated. In this study, we investigated marine redox conditions of the intermediate water column that most organisms inhabit with special attention to the time interval before the onset of the mass extinction. The carbon isotope composition of carbonate and organic carbon (δ13Ccarb and δ13Corg) as well as the nitrogen isotope composition of bulk nitrogen (δ15N) were analyzed in four P-Tr boundary sequences (Zhongli, Jianshi, Ganxi, and Chaotian sections), which record a transect from a shallow water carbonate platform to a deep water, lower ramp slope in South China. δ13Ccarb shows a distinct negative shift in all sections and displays a clear, 2−4‰, decreasing gradient accompanying an increase in water depth both before and after the mass extinction. A distinct negative shift in δ15N is observed in the shallow water Zhongli section, whereas a minor negative shift is present in the three deeper water sections. Before the mass extinction, the δ15N values from shallow water sections are higher than those from deeper waters. The low δ15N values close to 0‰ in deeper water sections suggest that microbial nitrogen fixation was the predominant source of biologically available nitrogen before the onset of the mass extinction. Thus, the water depth- dependent gradient in δ13Ccarb and δ15N suggests that an oxygen-deficient intermediate water column was already present before the mass extinction. The uniform δ15N values around 0‰ accompanying the onset of the mass extinction reveal that anoxic intermediate waters expanded into shallow waters. Meanwhile, the distinct positive shift in δ13Corg observed in upper ramp slope sections, i.e., the Jianshi and Ganxi sections, suggests that a euxinic photic zone was at least episodically present in the earliest Triassic. The temporal coincidence between the expansion of intermediate water column anoxia and the onset of the P-Tr mass extinction supports the hypothesis that marine anoxia was a direct killing mechanism.

scholarly journals Rapid acidification of mode and intermediate waters in the southwest Atlantic Ocean

2014 ◽  
Vol 11 (5) ◽  
pp. 6755-6792
Author(s):  
L. A. Salt ◽  
S. M. A. C. van Heuven ◽  
M. E. Claus ◽  
E. M. Jones ◽  
H. J. W. de Baar
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Buffering Capacity ◽  
Intermediate Water ◽  
Mode Water ◽  
Maximum Increase ◽  
Southwest Atlantic ◽  
Subantarctic Mode Water ◽  
Anthropogenic Component ◽  
Rate Of Increase ◽  
Total Pool

Abstract. Observations along the southwest Atlantic WOCE A17 line made during the Dutch GEOTRACES-NL program (2010–2011) were compared with historical data from 1994 to quantify the changes in the anthropogenic component of the total pool of dissolved inorganic carbon (ΔCant). Application of the extended Multi Linear Regression (eMLR) method shows that the ΔCant from 1994 to 2011 has largely remained confined to the upper 1000 dbar. The greatest changes occur in the upper 200 dbar in the SubAntarctic Zone (SAZ), where a maximum increase of 37 μmol kg−1 is found. South Atlantic Central Water (SACW) experienced the highest rate of increase in Cant, at 0.99 ± 0.14 μmol kg−1 yr−1, resulting in a rate of decrease in pH of −0.0016 yr−1. The highest rates of acidification relative to ΔCant, however, were found in SubAntarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). The low buffering capacity of SAMW and AAIW combined with their relatively high rates of Cant increase of 0.53 ± 0.11 μmol kg−1 yr−1 and 0.36 ± 0.06 μmol kg−1 yr−1, respectively, will lead to rapid acidification in the SAZ and simultaneously reduce the chemical buffering capacity of this significant CO2 sink.

A New Algorithm for Finding Mixed Layer Depths with Applications to Argo Data and Subantarctic Mode Water Formation*

2009 ◽  
Vol 26 (9) ◽  
pp. 1920-1939 ◽  
Author(s):  
James Holte ◽  
Lynne Talley
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Gradient Methods ◽  
Temperature Threshold ◽  
Intermediate Water ◽  
Mode Water ◽  
Southwest Atlantic ◽  
Argo Data ◽  
Southeastern Pacific ◽  
Subantarctic Mode Water

Abstract A new hybrid method for finding the mixed layer depth (MLD) of individual ocean profiles models the general shape of each profile, searches for physical features in the profile, and calculates threshold and gradient MLDs to assemble a suite of possible MLD values. It then analyzes the patterns in the suite to select a final MLD estimate. The new algorithm is provided in online supplemental materials. Developed using profiles from all oceans, the algorithm is compared to threshold methods that use the C. de Boyer Montégut et al. criteria and to gradient methods using 13 601 Argo profiles from the southeast Pacific and southwest Atlantic Oceans. In general, the threshold methods find deeper MLDs than the new algorithm and the gradient methods produce more anomalous MLDs than the new algorithm. When constrained to using only temperature profiles, the algorithm offers a clear improvement over the temperature threshold and gradient methods; the new temperature algorithm MLDs more closely approximate the density algorithm MLDs than the temperature threshold and gradient MLDs. The algorithm is applied to profiles from a formation region of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). The density algorithm finds that the deepest MLDs in this region routinely reach 500 dbar and occur north of the A. H. Orsi et al. mean Subantarctic Front in the southeastern Pacific Ocean. The deepest MLDs typically occur in August and September and are congruent with the subsurface salinity minimum, a signature of AAIW.

Miocene phosphatization of rocks from the summit of Rio Grande Rise, Southwest Atlantic Ocean

2021 ◽  
Author(s):  
Mariana Benites ◽  
James R. Hein ◽  
Kira Mizell ◽  
Luigi Jovane
Keyword(s):  
Atlantic Ocean ◽  
Rio Grande ◽  
Southwest Atlantic

Contourites and Gravitites on the Rio Grande Rise, Southwest Atlantic Ocean (Seismoacoustic Data)

2020 ◽  
Vol 55 (3) ◽  
pp. 165-176 ◽  
Author(s):  
O. V. Levchenko ◽  
D. G. Borisov ◽  
N. V. Libina
Keyword(s):  
Atlantic Ocean ◽  
Rio Grande ◽  
Southwest Atlantic

scholarly journals Diet and feeding behavior of Kyphosus spp. (Kyphosidae) in a Brazilian subtropical reef

2006 ◽  
Vol 49 (4) ◽  
pp. 623-629 ◽  
Author(s):  
Renato Azevedo Matias Silvano ◽  
Arthur Ziggiatti Güth
Keyword(s):  
Atlantic Ocean ◽  
Feeding Behavior ◽  
Water Column ◽  
First Record ◽  
Calanoid Copepods ◽  
Southwest Atlantic ◽  
Substrate Use

The present study analyzed and compared diet and feeding behavior (substrate use, position in water column, interactions with other fishes) of Kyphosus spp. (sea chubs) in a Brazilian subtropical reef. Juveniles (< 160 mm) of Kyphosus incisor consumed both algae and invertebrates, which were mainly calanoid copepods. Juvenile and small adults of also observed foraging in the water column. We thus provide the first record of omnivory for Kyphosids in the southwest Atlantic Ocean.

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