Observation of manganese nodules and crusts recovered during the CHAIN 115 cruise from Nov 1973 until June 1974 in the Atlantic Ocean
Fuente:
PANGAEA
Guardado en:
| Autores principales: | , , |
|---|---|
| Formato: | Dataset Open Access |
| Lenguaje: | en |
| Publicado: |
PANGAEA
1977
|
| Materias: | |
| Acceso en línea: | |
| Etiquetas: |
Agregar Etiqueta
Sin Etiquetas, Sea el primero en etiquetar este registro!
|
| _version_ | 1867168171358683136 |
|---|---|
| author | Johnson, David A Ledbetter, Michael T Burckle, Lloyd H |
| author_facet | Johnson, David A Ledbetter, Michael T Burckle, Lloyd H |
| collection | Datos científicos de ciencias marinas y ambientales |
| contents | Investigations of piston cores from the Vema Channel and lower flanks of the Rio Grande Rise suggest the presence of episodic flow of deep and bottom water during the Late Pleistocene. Cores from below the present-day foraminiferal lysocline (at ~4000 m) contain an incomplete depositional record consisting of Mn nodules and encrustations, hemipelagic clay, displaced high-latitude diatoms, and poorly preserved heterogeneous microfossil assemblages. Cores from the depth range between 2900 m and 4000 m contain an essentially complete Late Pleistocene record, and consist of well-defined carbonate dissolution cycles with periodicities of ~100,000 years. Low carbonate content and increased dissolution correspond to glacial episodes, as interpreted by oxygen isotopic analysis of bulk foraminiferal assemblages. The absence of diagnostic high-latitude indicators (Antarctic diatoms) within the dissolution cyclss, however, suggests that AABW may not have extended to significantly shallower elevations on the lower flanks of the Rio Grande Rise during the Late Pleistocene. Therefore episodic AABW flow may not necessarily be the mechanism responsible for producing these cyclic events. This interpretation is also supported by the presence of an apparently complete Brunhes depositional record in the same cores, suggesting current velocities insufficient for significant erosion. Fluctuations in the properties and flow characteristics of another water mass, such as NADW, may be involved. The geologic evidence in core-top samples near the present-day AABW/NADW transition zone is consistent with either of two possible interpretations of the upper limit of AABW on the east flank of the channel. The foraminiferal lysocline, at ~4000 m, is near the top of the benthic thermocline and nepheloid layer, and may therefore correspond to the upper limit of relatively corrosive AABW. On the other hand, the carbonate compensation depth (CDD) at ~4250 m, which corresponds to the maximum gradient in the benthic thermocline, is characterized by rapid deposition of relatively fine-grained sediment. Such a zone of convergence and preferential sediment accumulation would be expected near the level of no motion in the AABW/NADW transition zone as a consequence of Ekman-layer veering of the mean velocity vector in the bottom boundary layer. It is possible that both of these interpretations are in part correct. The "level of no motion'' may in fact correspond to the CCD, while at the same time relatively corrosive water of Antarctic origin may mix with overlying NADW and therefore elevate the foraminifera] lysocline to depths above the level of no motion. Closely spaced observations of the hydrography and flow characteristics within the benthic thermocline will be required in order to use sediment parameters as more precise indicators of paleo-circulation. |
| format | Dataset Open Access |
| id | pangaea_https___doi_org_10_1594_PANGAEA_857913 |
| institution | PANGAEA |
| language | en |
| publishDate | 1977 |
| publisher | PANGAEA |
| record_format | pangaea |
| spellingShingle | Observation of manganese nodules and crusts recovered during the CHAIN 115 cruise from Nov 1973 until June 1974 in the Atlantic Ocean Johnson, David A Ledbetter, Michael T Burckle, Lloyd H Atlantic Ocean; CH115; CH115-11D; CH115-16D; CH115-20PC; CH115-20PG; CH115-38PC; CH115-4PC; CH115-59PC; CH115-60PC; CH115-62PC; CH115-6PG; CH115-87PC; CH115-94PG; CH115-9D; Chain; Chain115; Comment; Date/Time of event; Deposit type; Depth, bottom/max; DEPTH, sediment/rock; Depth, top/min; Description; Dredge; DRG; Elevation of event; Event label; GC; Gravity corer; Latitude of event; Longitude of event; Method/Device of event; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; PC; Piston corer; Position; Quantity of deposit; Sample ID; Sediment type; Size; Substrate type; TC; Trigger corer; Uniform resource locator/link to image Investigations of piston cores from the Vema Channel and lower flanks of the Rio Grande Rise suggest the presence of episodic flow of deep and bottom water during the Late Pleistocene. Cores from below the present-day foraminiferal lysocline (at ~4000 m) contain an incomplete depositional record consisting of Mn nodules and encrustations, hemipelagic clay, displaced high-latitude diatoms, and poorly preserved heterogeneous microfossil assemblages. Cores from the depth range between 2900 m and 4000 m contain an essentially complete Late Pleistocene record, and consist of well-defined carbonate dissolution cycles with periodicities of ~100,000 years. Low carbonate content and increased dissolution correspond to glacial episodes, as interpreted by oxygen isotopic analysis of bulk foraminiferal assemblages. The absence of diagnostic high-latitude indicators (Antarctic diatoms) within the dissolution cyclss, however, suggests that AABW may not have extended to significantly shallower elevations on the lower flanks of the Rio Grande Rise during the Late Pleistocene. Therefore episodic AABW flow may not necessarily be the mechanism responsible for producing these cyclic events. This interpretation is also supported by the presence of an apparently complete Brunhes depositional record in the same cores, suggesting current velocities insufficient for significant erosion. Fluctuations in the properties and flow characteristics of another water mass, such as NADW, may be involved. The geologic evidence in core-top samples near the present-day AABW/NADW transition zone is consistent with either of two possible interpretations of the upper limit of AABW on the east flank of the channel. The foraminiferal lysocline, at ~4000 m, is near the top of the benthic thermocline and nepheloid layer, and may therefore correspond to the upper limit of relatively corrosive AABW. On the other hand, the carbonate compensation depth (CDD) at ~4250 m, which corresponds to the maximum gradient in the benthic thermocline, is characterized by rapid deposition of relatively fine-grained sediment. Such a zone of convergence and preferential sediment accumulation would be expected near the level of no motion in the AABW/NADW transition zone as a consequence of Ekman-layer veering of the mean velocity vector in the bottom boundary layer. It is possible that both of these interpretations are in part correct. The "level of no motion'' may in fact correspond to the CCD, while at the same time relatively corrosive water of Antarctic origin may mix with overlying NADW and therefore elevate the foraminifera] lysocline to depths above the level of no motion. Closely spaced observations of the hydrography and flow characteristics within the benthic thermocline will be required in order to use sediment parameters as more precise indicators of paleo-circulation. |
| title | Observation of manganese nodules and crusts recovered during the CHAIN 115 cruise from Nov 1973 until June 1974 in the Atlantic Ocean |
| topic | Atlantic Ocean; CH115; CH115-11D; CH115-16D; CH115-20PC; CH115-20PG; CH115-38PC; CH115-4PC; CH115-59PC; CH115-60PC; CH115-62PC; CH115-6PG; CH115-87PC; CH115-94PG; CH115-9D; Chain; Chain115; Comment; Date/Time of event; Deposit type; Depth, bottom/max; DEPTH, sediment/rock; Depth, top/min; Description; Dredge; DRG; Elevation of event; Event label; GC; Gravity corer; Latitude of event; Longitude of event; Method/Device of event; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; PC; Piston corer; Position; Quantity of deposit; Sample ID; Sediment type; Size; Substrate type; TC; Trigger corer; Uniform resource locator/link to image |
| url | https://doi.org/10.1594/PANGAEA.857913 |