215 resultados para 3-17-1
Resumo:
Stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late Maastrichtian ocean. Given mean oceanic d18Ow of -1.0 per mil, the temperature of the coolest intermediate-depth waters was 5°-7°C, that of the deepest waters was 10°C, and that of the warmest intermediate waters was 13°-15°C. The cool intermediate-depth water mass probably originated in the high-latitude Southern Ocean. The deepest waters originated at least partly in the northern Atlantic. The source region for the warmest intermediate-depth water mass is unknown. Although much of the late Maastrichtian deep water was probably preconditioned for winter sinking by low- or middle-latitude evaporation, no more than ~11% of late Maastrichtian deep water could have been directly actuated by low-latitude sea surface evaporation. At least in the southern Atlantic and Indian Oceans, heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures.
Resumo:
The majority of global ocean production and total export production is attributed to oligotrophic oceanic regions due to their vast regional expanse. However, energy transfers, food-web structures and trophic relationships in these areas remain largely unknown. Regional and vertical inter- and intra-specific differences in trophic interactions and dietary preferences of calanoid copepods were investigated in four different regions in the open eastern Atlantic Ocean (38°N to 21°S) in October/November 2012 using a combination of fatty acid (FA) and stable isotope (SI) analyses. Mean carnivory indices (CI) based on FA trophic markers generally agreed with trophic positions (TP) derived from d15N analysis. Most copepods were classified as omnivorous (CI ~0.5, TP 1.8 to ~2.5) or carnivorous (CI >=0.7, TP >=2.9). Herbivorous copepods showed typical CIs of <=0.3. Geographical differences in d15N values of epi- (200-0 m) to mesopelagic (1000-200 m) copepods reflected corresponding spatial differences in baseline d15N of particulate organic matter from the upper 100 m. In contrast, species restricted to lower meso- and bathypelagic (2000-1000 m) layers did not show this regional trend. FA compositions were species-specific without distinct intra-specific vertical or spatial variations. Differences were only observed in the southernmost region influenced by the highly productive Benguela Current. Apparently, food availability and dietary composition were widely homogeneous throughout the oligotrophic oceanic regions of the tropical and subtropical Atlantic. Four major species clusters were identified by principal component analysis based on FA compositions. Vertically migrating species clustered with epi- to mesopelagic, non-migrating species, of which only Neocalanus gracilis was moderately enriched in lipids with 16% of dry mass (DM) and stored wax esters (WE) with 37% of total lipid (TL). All other species of this cluster had low lipid contents (< 10% DM) without WE. Of these, the tropical epipelagic Undinula vulgaris showed highest portions of bacterial markers. Rhincalanus cornutus, R. nasutus and Calanoides carinatus formed three separate clusters with species-specific lipid profiles, high lipid contents (>=41% DM), mainly accumulated as WE (>=79% TL). C. carinatus and R. nasutus were primarily herbivorous with almost no bacterial input. Despite deviating feeding strategies, R. nasutus clustered with deep-dwelling, carnivorous species, which had high amounts of lipids (>=37% DM) and WE (>=54% TL). Tropical and subtropical calanoid copepods exhibited a wide variety of life strategies, characterized by specialized feeding. This allows them, together with vertical habitat partitioning, to maintain high abundance and diversity in tropical oligotrophic open oceans, where they play an essential role in the energy flux and carbon cycling.
Resumo:
Manganese nodules research has focused on the area between the Clarion Fracture Zone to the North and the Clipperton Fracture Zone to the South where significant concentrations were found ni Ni-Cu. During the CCOP/SOPAC-IOC/IDOE International workshop on the "Geology Mineral Resources and Geophysics of the South Pacific" held in Fiji in September 1975, a working group on manganese nodules was formed by scientists from: CNEXO, Brest, the Institute of Oceanography, New Zealand, Imperial College, London and the Technical University of Aachen. A draft project was presented in July 1976 by J. Andrews, University of Hawaii and G. Pautot, Cnexo on a joint survey under the name of: "Hawaii-Tahiti Transect program". Further details were worked on in September 1976 during the International Geological Congress in Sydney with the participation of D. Cronan, Imperial College, Glasby, New Zealand Geological Survey and G. Friedrich, Aachen TU. The scientific final program was established in July 1977, planning on the participation of three research vessels: the Suroit (CNEXO), the Kana Keoki (U. of Hawaii) and the Sonne (Aachen TU). Several survey areas were selected across the Pacific Ocean (Areas A, B, C, D, E, F, G and H) with about the same crustal age (about 40 million years) and a similar water depths. Being near large fault zones, the ares would be adequate to study the influences of biological productivity, sedimentation rate and possibly volcanic activity on the formation and growth of manganese nodules. The influnece of volcanic activity study would particularly apply to area G being situated near the Marquesas Fracture Zone. The cruise from R/V Sonne started in August 1978 over areas C, D, F, G K. The R/V suroit conducted a similar expedition in 1979 over areas A, B, C, D, E, H and I. Others cruises were planned during the 1979-1980 for the R/V Kana Keoki. The present text relates the R/V Sonne Cruises SO-06/1 and SO-06/2 held within the frame work of this international cooperative project.
Resumo:
Mid-Cretaceous (Barremian-Turonian) plankton preserved in deep-sea marl, organic-rich shale, and pelagic carbonate hold an important record of how the marine biosphere responded to short- and long-term changes in the ocean-climate system. Oceanic anoxic events (OAEs) were short-lived episodes of organic carbon burial that are distinguished by their widespread distribution as discrete beds of black shale and/or pronounced carbon isotopic excursions. OAE1a in the early Aptian (~120.5 Ma) and OAE2 at the Cenomanian/Turonian boundary (~93.5 Ma) were global in their distribution and associated with heightened marine productivity. OAE1b spans the Aptian/Albian boundary (~113-109 Ma) and represents a protracted interval of dysoxia with multiple discrete black shales across parts of Tethys (including Mexico), while OAE1d developed across eastern and western Tethys and in other locales during the latest Albian (~99.5 Ma). Mineralized plankton experienced accelerated rates of speciation and extinction at or near the major Cretaceous OAEs, and strontium isotopic evidence suggests a possible link to times of rapid oceanic plateau formation and/or increased rates of ridge crest volcanism. Elevated levels of trace metals in OAE1a and OAE2 strata suggest that marine productivity may have been facilitated by increased availability of dissolved iron. The association of plankton turnover and carbon isotopic excursions with each of the major OAEs, despite the variable geographic distribution of black shale accumulation, points to widespread changes in the ocean-climate system. Ocean crust production and hydrothermal activity increased in the late Aptian. Faster spreading rates [and/or increased ridge length] drove a long-term (Albian-early Turonian) rise in sea level and CO2-induced global warming. Changes in ocean circulation, water column stratification, and nutrient partitioning lead to a reorganization of plankton community structure and widespread carbonate (chalk) deposition during the Late Cretaceous. We conclude that there were important linkages between submarine volcanism, plankton evolution, and the cycling of carbon through the marine biosphere.
Resumo:
Slow-sinking particles were sampled using the Marine Snow Catcher (MSC). For a full description of the MSC and flux calculations see Riley et al. (2012). The MSC was deployed at four depths between 50 - 650 m during four visit at Stations 1 (63°3' N 11°0' W) and three visits at Station 2 (62°5' N 2°3' W) to obtain depth profiles of slow-sinking material. The MSC was further deployed at 50 m during two visits at Station 3 (60°2' N 1°0' E). A total of 33 MSC were deployed. Slow-sinking particles were analysed for particulate organic carbon (POC), particulate inorganic carbon (PIC), biogenic silica (BSi), and Chlorophyll a (total, >10 µm).