Crustal structure of the hawaiian ridge near gardner pinnacles

1960 ◽  
Vol 50 (4) ◽  
pp. 563-573
Author(s):  
George G. Shor
Keyword(s):  
Crustal Structure ◽  
Seismic Refraction ◽  
Pacific Basin ◽  
The North ◽  
North Side ◽  
The Pacific ◽  
Oceanic Sediments ◽  
Hawaiian Ridge ◽  
Volcanic Islands ◽  
Mohorovičić Discontinuity

ABSTRACT A series of seismic refraction profiles has been made across a flat bank at Gardner Pinnacles (a pair of volcanic islets on the western Hawaiian Ridge) down the side of the ridge and across the adjacent deep to the floor of the Pacific basin. The ridge is composed principally of material with velocities typical of volcanic islands. The high-velocity oceanic crust, found in the oceanic areas adjacent, extends beneath the ridge and up into the center of the rise. The total crustal section is thickened and the Mohorovičić discontinuity depressed beneath the deep as well as beneath the ridge. The smooth “archipelagic apron” on the north side of the ridge has at most 20 meters of sediment over a layer with a velocity of 3 km/sec, which could be volcanic and is definitely of higher velocity than normal oceanic sediments.

Geophysical measurements in the region of the Explorer ridge off western Canada

1978 ◽  
Vol 15 (9) ◽  
pp. 1508-1525 ◽  
Author(s):  
R. D. Hyndman ◽  
G. C. Rogers ◽  
M. N. Bone ◽  
C. R. B. Lister ◽  
U. S. Wade ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Seismic Refraction ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Geothermal Heat ◽  
Juan De Fuca Plate ◽  
The North ◽  
The Pacific ◽  
Ocean Bottom Seismometers ◽  
Seismic Reflection Profiles

The region of the Explorer spreading centre off Vancouver Island, British Columbia, has been studied through a marine geophysical survey. Earthquake epicentres located by three ocean bottom seismometers confirm that the boundary between the Pacific plate and the Explorer plate (the northern extension of the Juan de Fuca plate) at present lies along the Sovanco fracture zone, the Explorer ridge, and the Dellwood Knolls. The epicentres of earthquakes in this area as determined by the onshore seismic network are found to be subject to significant errors. The ocean bottom seismometers also have been used for a detailed seismic refraction line just to the north of the Explorer spreading centre employing explosives and a large airgun as sources. A preliminary analysis of the data indicates a fairly typical crustal structure but a shallow and low velocity mantle near the ridge crest, and illustrates the value of ocean bottom seismometers in oceanic refraction studies. A new geothermal heat flux probe was employed in this study that permitted repeated 'pogostick' penetrations without raising the instrument to the surface. Six profiles with a total of 112 penetrations provided valuable data on the nature of hydrothermal circulation in the oceanic crust. Eleven standard heat probe stations provided some restraints on the poorly known age of the oceanic crust along the margin. Seismic reflection profiles using a 3.5 kHz system, a high resolution pulser profiler, and a large airgun were used as aids in the interpretation of the seismic and heat flow data.

A New Blocking Index and Its Application: Blocking Action in the Northern Hemisphere

2006 ◽  
Vol 19 (19) ◽  
pp. 4819-4839 ◽  
Author(s):  
Yina Diao ◽  
Jianping Li ◽  
Dehai Luo
Keyword(s):  
The Other ◽  
Two Dimensional ◽  
Atlantic Sector ◽  
The North ◽  
North Side ◽  
The Pacific ◽  
Different Seasons ◽  
Action Center ◽  
Blocking Event ◽  
Blocking Index

Abstract In this paper, a new two-dimensional blocking index is proposed by defining a difference between the daily 500-hPa geopotenial heights at the reference latitude and its north side. The reference latitude is determined by a composite latitude-dependent 500-hPa geopotenial height of blocking events in different seasons and sectors. The new index can take account of the duration, intensity, propagation, and spatial structure of a blocking event. Using this index, the characteristics (frequency, duration, intensity, and preferred occurrence region) of the blocking action in the North Hemisphere (NH) are investigated using a 42-yr sample of blocking events from the NCEP–NCAR reanalyses. It is found that blocking events in the NH are more frequent in the Atlantic–Europe sector than in the Pacific sector in winter and spring and autumn, but more persistent in the Atlantic–Europe sector than in the Pacific sector for all seasons. Blocking events in the Pacific sector tend to have larger amplitudes than the Atlantic counterparts. In addition, it is shown that in the NH independently occurring blocking events are most frequent, but simultaneously occurring blockings are rather rare, indicating that the blocking events in the NH should be a local phenomenon. On the other hand, a comparison with the existing indices [e.g., Tibaldi and Molteni (TM) index] indicates that in summer and autumn the new index shows similar longitudinal dependency of NH blocking events as does the TM index, but it shows two distinct action centers of blocking events in the Atlantic sector in winter and spring (in which the most frequent one is situated more westward) and an eastward blocking action center in the Pacific sector in spring and autumn, compared to the TM index. In addition, it is found that the new blocking index proposed here shows relatively low blocking frequency for all seasons compared to the TM index, especially in the Atlantic sector in spring and in the Pacific sector in winter and spring, which seems to be in agreement with the result obtained by Pelly and Hoskins using the PV–θ index.

Analysis of Atlantic SST Variability Factoring Interbasin Links and the Secular Trend: Clarified Structure of the Atlantic Multidecadal Oscillation

2009 ◽  
Vol 22 (15) ◽  
pp. 4228-4240 ◽  
Author(s):  
Bin Guan ◽  
Sumant Nigam
Keyword(s):  
Atlantic Multidecadal Oscillation ◽  
Single Step ◽  
Secular Change ◽  
Pacific Basin ◽  
The North ◽  
Mature Phase ◽  
Sst Variability ◽  
The Pacific ◽  
Leading Mode ◽  
Simultaneous Loss

Abstract Atlantic SST variability in the twentieth century is analyzed factoring the influence of natural SST variability in the Pacific basin and the secular change in global SSTs. The tropical and northern extratropical basins are analyzed together using the extended EOF technique, which permits extraction of the interannual and multidecadal modes in the pan-Atlantic basin in a single step. The leading mode of Pacific-uninfluenced SST variability is a multidecadal oscillation focused in the extratropical basin, with a period of ∼70 yr. The mode differs from the conventional Atlantic multidecadal oscillation (AMO) in the near quiescence of the tropical–subtropical basin, highlighting the significant influence of the Pacific basin on this region in conventional analysis; as much as 45% of the regional variance resulting from the conventional AMO is due to this influence. The second and third modes capture the growth (east-to-west development) and decay (near-simultaneous loss of amplitudes) of interannual SST variability in the eastern tropical Atlantic. A nominal 4-yr evolution cycle is identified, but phase transitions are irregular. The fourth mode describes a north–south tripole with the mature-phase structure resembling the North Atlantic Oscillation’s (NAO’s) SST footprint in winter. The mode lags the NAO by two seasons. Modal evolution involves eastward extension of the main lobe (centered near the separation of the Gulf Stream) along with shrinkage of the oppositely signed two side lobes.

The Structure of the Pacific Basin

1934 ◽  
Vol 71 (7) ◽  
pp. 289-302 ◽  
Author(s):  
L. J. Chubb
Keyword(s):  
Pacific Basin ◽  
The Pacific ◽  
Volcanic Islands

Since the return of the St. George Expedition from the Pacific in 1925, a series of nine papers (2–8, 26, 27), describing the geology of most of the volcanic islands visited, has been published, and it is now possible to co-ordinate the results already arrived at, and to use them in an attempt to throw light on the structure of the Pacific basin.

scholarly journals The crustal structure of the Northeast Greenland continental shelf across the extension of the West Jan Mayen Fracture Zone

2020 ◽  
Author(s):  
Thomas Funck ◽  
Andreas Skifter Madsen ◽  
Christian Berndt ◽  
Anke Dannowski ◽  
Dieter Franke ◽  
...  
Keyword(s):  
Continental Margin ◽  
Crustal Structure ◽  
Fracture Zone ◽  
Seismic Refraction ◽  
Moho Depth ◽  
Gravity Modeling ◽  
The South ◽  
The West ◽  
The North ◽  
Lower Crustal

<p>Between August and October 2017, the German research vessel Maria S. Merian acquired geophysical data along the Northeast Greenland continental margin during its cruise MSM-67. This included seismic reflection and wide-angle/refraction data as well as potential field data. In comparison to the conjugate mid-Norwegian margins, the Northeast Greenland continental margin is less well studied. Hence, one of the key objectives of the expedition was to improve the understanding of the opening of the Northeast Atlantic Ocean and the evolution of the conjugate margin pair. One particular goal of the experiment was the mapping of the lateral extent of magmatism associated with the opening and how this relates to margin segmentation.</p><p>Seismic refraction line BGR17-2R2 runs on the shelf and parallel to the coast of NE Greenland. It crosses the landward extension of the West Jan Mayen Fracture Zone that separates the seafloor spreading along the Mohn’s Ridge in the north from the Kolbeinsey Ridge in the south. A total of 29 ocean bottom seismometers (OBS) equipped with a hydrophone and three-component geophones were deployed along the 235-km-long line. The seismic source was a G-gun array with a total volume of 4840 cubic inches (79.3 L) fired every 60 s. In the central and northern part of the line, two older seismic refraction profiles are crossed (lines AWI2003-500 and 400, respectively), which run perpendicular to the margin and can be used for lateral correlation of the crustal structure.</p><p>For the initial analysis, a velocity model was developed by forward and inverse modeling of travel times using the program RAYINVR. Later, a travel time tomography was carried out employing the code Tomo2D and performing a Monte Carlo analysis with 100 inversions from which an average model was calculated. The models show a 1-to 3-km-thick sedimentary column with velocities ranging from 1.6 to 4.0 km/s. In the central and northern part, a 1-km-thick layer with velocities around 4.6 km/s is underlying the sediments and is interpreted to consist of volcanic material. Below and extending along the entire length of the line, velocities of 5.6 km/s are observed in a layer that is ~2 km thick. The crystalline basement has a depth around 5 km with higher velocities in the north (6.5 km/s) than in the south (6.3 km/s). High lower crustal velocities (>7.2 km/s) are observed along the entire line and either indicate magmatic underplating or lower crustal sill intrusions. The Moho depth is seismically constrained along the central part of the line where it is 30 km. Gravity modeling suggest a depth of 35 and 27 km at the southern and northern limit of the profile, respectively. Within the zone of the landward extension of the West Jan Mayen Fracture Zone, a decrease in mid-crustal velocities by 0.2 km/s is observed. Slightly to the north of the fracture zone, a 50-km-wide zone with increased mid-and lower crustal velocities may indicate an igneous center in an area where the upper volcanic layer is shallowest.</p>

scholarly journals Major processes of the dissolved cobalt cycle in the North and equatorial Pacific Ocean

2021 ◽  
Author(s):  
Rebecca Chmiel ◽  
Nathan Lanning ◽  
Allison Laubach ◽  
Jong-Mi Lee ◽  
Jessica Fitzsimmons ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
Thermohaline Circulation ◽  
Equatorial Pacific ◽  
Biogeochemical Model ◽  
Pacific Basin ◽  
Equatorial Pacific Ocean ◽  
Oxygen Minimum Zones ◽  
The North ◽  
The Pacific

Abstract. Over the past decade, the GEOTRACES and wider trace metal geochemical community have made substantial contributions towards constraining the marine cobalt (Co) cycle and its major biogeochemical processes. However, few Co speciation studies have been conducted in the North and equatorial Pacific Ocean, a vast portion of the world’s oceans by volume and an important endmember of deep thermohaline circulation. Dissolved Co (dCo) samples, including total dissolved and labile Co, were measured at-sea during the GEOTRACES Pacific meridional transect (GP15) along the 152° W longitudinal from 56° N to 20° S. Along this transect, upper ocean dCo was linearly correlated to dissolved phosphate (slope = 82 ± 2 µM:M) due to phytoplankton uptake and remineralization. As depth increased, dCo concentrations became increasingly decoupled from phosphate concentrations due to co-scavenging with manganese oxide particles in the mesopelagic. The transect revealed an organically-bound coastal source of dCo to the Alaskan Stream associated with low salinity waters. An intermediate-depth hydrothermal flux of dCo was observed off the Hawaiian coast at the Loihi Seamount, and the elevated dCo was correlated to estimated xs3He at and above the vent site; however, the Loihi Seamount likely did not represent a major source of Co to the Pacific basin. Elevated concentrations of dCo within oxygen minimum zones (OMZs) in the equatorial North and South Pacific were consistent with the suppression of oxidative scavenging, and we estimate that future deoxygenation could increase the OMZ dCo inventory by 13–28 % over the next century. In North Pacific Deep Water (NPDW), a fraction of elevated ligand-bound dCo appeared protected from scavenging by the high biogenic particle flux in the North Pacific basin. This finding is counter to previous expectations of low dCo concentrations in the deep Pacific due to scavenging over thermohaline circulation. Compared to a Co global biogeochemical model, the observed transect displayed more extreme inventories and fluxes of dCo than predicted by the model, suggesting a highly dynamic Pacific Co cycle.

A discussion concerning the floor of the northwest Indian Ocean - Crustal structure between Kenya and the Seychelles

1966 ◽  
Vol 259 (1099) ◽  
pp. 240-261 ◽  
Keyword(s):  
Indian Ocean ◽  
Gravity Anomaly ◽  
Crustal Structure ◽  
Seismic Refraction ◽  
Crustal Layer ◽  
African Coast ◽  
Mohorovičić Discontinuity

A series of seismic refraction profiles has been shot between Kenya and the Seychelles Bank and in the neighbourhood of the Bank itself. Thick sediments have been observed for 300 to 400 km from the African coast. Near Kenya, great thicknesses of material of about 4.8 km/s velocity match closely the 9 to 10 km of Karroo beds expected on the coast at Lamu. The Mohorovicic discontinuity has been traced from 100 km off the African coast to the Seychelles Bank. West of the Bank the mantle is unusually shallow, rising to only 8.5 km below the surface, and the 6.8 km/s crustal layer unusually thin or absent. The absence of a gravity anomaly associated with this very shallow mantle raises a problem which has yet to be resolved.

Sign in / Sign up

Export Citation Format

Share Document