Observation of manganese nodules and crusts recovered during the CHAIN 115 cruise from Nov 1973 until June 1974 in the Atlantic Ocean

• Main Authors: Johnson, David A, Ledbetter, Michael T, Burckle, Lloyd H
• Format: Dataset
• Language: English
• Published: PANGAEA 1977
• Subjects: 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; sediment/rock; 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; Antarctic; Antarc*; NADW
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.857913; https://doi.org/10.1594/PANGAEA.857913

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 ...