Ocean Exploration Program Research Articles

The origin of the Musicians Seamount Province and its inferences for Late Cretaceous Pacific Plate Motion

Linear chains of seamounts, sourced from mantle plume processes, have the potential to refine plate motion models because the hotspot remains fixed relative to the moving lithospheric plate. However, to define plate motion, consistent seamount age progression and geometry are required. Some seamount chains, such as the Musician Seamount Province (MSP), have complex geometries and age distributions, which complicates calibrating plate motion. The MSP resides northwest of the Hawaiian Islands and is composed of seamounts and volcanic elongated ridges (VERs) that cover ∼420,000 km2 of Pacific seafloor. Here we provide new 40Ar/39Ar age determinations for a series of lava flows recovered from the MSP during expedition EX1708 of the National Oceanic and Atmospheric Administration's Ocean Exploration program. The MSP was built by four distinct volcanic processes: (1) age-progressive hotspot volcanism associated with the Euterpe Plume (ca. 98–79 Ma). (2) VER formation from plume-ridge channelization (ca. 97–94 Ma; 86–79 Ma) where the VERs only form when the hotspot is within ∼600 km of the ridge. (3) Eocene volcanism driven by extension during the ca. 50 Ma change in Pacific rotation poles (ca. 54–47 Ma). (4) Some near-ridge shear-driven upwelling or diffuse extensional volcanism that preceded the southern MSP lithosphere overriding the plume (ca. 86–84 Ma). By filtering lava flows with only robust statistically concordant 40Ar/39Ar age determinations as well as geologic setting, we develop a dataset of samples valuable for constraining Pacific plate motion. A local plate velocity of 42 ± 9 km/Ma for the 98–81 Ma time frame is calculated. Furthermore, the seamount track indicates that large shifts in Pacific rotation pole locations are required prior to 98 Ma and at ca. 81 Ma.

Primary and new production in the deep Canada Basin during summer 2002

The NOAA Ocean Exploration program provided the opportunity to measure the carbon and nitrogen productivity across the Canada Basin. This research examined the major environmental factors limiting the levels of primary production and possible future climate change on the ecosystems. The vertical distributions of the carbon and nitrogen uptakes of phytoplankton had similar patterns as their respective biomass concentrations which were low at the surface and highest in the chlorophyll-maximum layer. The annual carbon and new production rates of phytoplankton in the Canada Basin were about 5 and 1 g C m−2, respectively. Nutrients were determined to be a main limiting factor at the surface, whereas light may be a major factor limiting phytoplankton productivity in the chlorophyll-maximum layer for open waters. The bottom surface of the ice has a low specific uptake and productivity of phytoplankton, indicating that photosynthetic activity might be controlled by both light and nutrients.

Ocean sediment care data available

Paleontological and geochemical data from 635 cores are available through the National Geophysical and Solar‐Terrestrial Data Center Climap study, part of the International Decade of Ocean Exploration program funded by the National Science Foundation. Collection and analysis of ocean sediment core data for Climap are carried out by several major U.S. universities as well as foreign institutions. By describing and defining climatic change and patterns of change over the last million years, as recorded in marine sediments, and by comparing these observations to computer models, Climap scientists expect to better understand the mechanisms of transitions between temperate and ice ages.

U.S. contribution to Southern Ocean dynamics

United States activity in general circulation problems in the Southern Ocean has recently been increasing rapidly. The data base collected through the Eltanin program through 1972, the promise of increased meteorological coverage by FGGE in 1978, and the development of long‐term current meter technology have led to the establishment of the U.S. component of the International Southern Ocean Studies, an International Decade of Ocean Exploration program sponsored by the National Science Foundation (1973). This program io designed to study the structure and long‐term variations in the current systems of the Southern Ocean; the first year‐long array of current meters was placed in the Drake Passage in January 1975. First studies on the problem of winter formation of antarctic bottom water (AABW) under ISOS began in September 1974; these will continue in order to determine the feasibility of monitoring such production (see below for further field studies on AABW).

Continental Margin Off Western Africa: Angola to Sierra Leone

About 30,750 line-km of geophysical traverses (seismic reflection and refraction, magnetics, and gravity) were made in the Gulf of Guinea and vicinity aboard R/V Atlantis II during 1972 and 1973 as part of the International Decade of Ocean Exploration program. These traverses, supplemented by about 50,000 line-km of previous ones by other ships, provide a basis for mapping and understanding the geologic structure, history, and origin of the region. The deep indentation of the outline of western Africa is paralleled by a similar bend of the Mid-Atlantic Ridge and by the prominent bulge of northeastern Brazil. These sharp bends are the result of left-lateral offsets by many transform faults in a belt of equatorial fracture zones. Some of the fracture zones continue eastward and intersect the entire length of the east-west coast of the Gulf of Guinea and penetrate the continent at the Benue trough or graben. The valleys of the fracture zones have been sites of sediment deposition, whereas the ridges have served as dams that force the sediment to move westward. Where enormous quantities of sediment have been delivered to the ocean by the Niger-Benue Rivers, a large delta has deeply buried the irregular topography of the fracture zones. In this entire belt of fractured ocean floor the structure, physiography, and stratigraphy have been controlled by lateral movement, or translation, of the ocean floor with respect to the continent. In contrast, the regions southeast and northwest of the belt of equatorial fractures have fewer large fracture zones, smoother topography, and simpler sediment wedges. These two regions owe their origin to simple divergence during sea-floor spreading, when new oceanic basement added at the Mid-Atlantic Ridge increased the distances between the African continent, the Mid-Atlantic Ridge, and the American continents. Deposition of sediments along the margins of the originally narrow Atlantic Ocean was dominated early by coarse-grained and largely nonmarine sediments. South of the Gulf of Guinea these deposits were followed by evaporites as products of restricted water circulation in a long narrow arm of the ocean. There was little flow of water across the equator because of the sliding-v lve nature of the region of translation between the two regions of divergence. As spreading continued, the ocean widened, and thick prisms of marine sediments were deposited on the continental margins. Large deltas in western Africa first began at the south, with the now submerged deltas of the Orange and the Congo Rivers being chiefly Mesozoic in age and having no present coastal projection. The Niger delta farther north is mostly Cenozoic in age. Petroleum prospects appear to be far greater in the Niger delta and the region of divergence south of it than in the entire region west of the delta. The favorable continental margin contains thicker sediments, large ancient and modern deltas, and salt and mud diapirs. End_Page 2209------------------------------