Map showing bottom topography of the Pacific Continental Margin, Cape Mendocino to Point Conception

AbstractThe Antarctic Peninsula contains a record of continental-margin volcanism extending from Jurassic to Recent times. Subduction of the Pacific oceanic lithosphere beneath the continental margin developed after Late Jurassic volcanism in Alexander Island that was related to extension of the continental margin. Mesozoic ocean-floor basalts emplaced within the Alexander Island accretionary complex have compositions derived from Pacific mantle. The Antarctic Peninsula volcanic arc was active from about Early Cretaceous times until the Early Miocene. It was affected by hydrothermal alteration, and by regional and contact metamorphism generally of zeolite to prehnite–pumpellyite facies. Distinct geochemical groups recognized within the volcanic rocks suggest varied magma generation processes related to changes in subduction dynamics. The four groups are: calc-alkaline, high-Mg andesitic, adakitic and high-Zr, the last two being described in this arc for the first time. The dominant calc-alkaline group ranges from primitive mafic magmas to rhyolite, and from low- to high-K in composition, and was generated from a mantle wedge with variable depletion. The high-Mg and adakitic rocks indicate periods of melting of the subducting slab and variable equilibration of the melts with mantle. The high-Zr group is interpreted as peralkaline and may have been related to extension of the arc.

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A Series of Zonal Jets Embedded in the Broad Zonal Flows in the Pacific Obtained in Eddy-Permitting Ocean General Circulation Models

Journal of Physical Oceanography ◽

10.1175/jpo2698.1 ◽

2005 ◽

Vol 35 (4) ◽

pp. 474-488 ◽

Cited By ~ 86

Author(s):

Hideyuki Nakano ◽

Hiroyasu Hasumi

Keyword(s):

General Circulation ◽

Bottom Topography ◽

Zonal Flow ◽

General Circulation Models ◽

Wind Forcing ◽

Zonal Flows ◽

Zonal Jets ◽

The Pacific ◽

Ocean General Circulation Models ◽

Ocean General Circulation

Abstract A series of zonal currents in the Pacific Ocean is investigated using eddy-permitting ocean general circulation models. The zonal currents in the subsurface are classified into two parts: one is a series of broad zonal flows that has the meridional pattern slanting poleward with increasing depth and the other is finescale zonal jets with the meridional scale of 3°–5° formed in each broad zonal flow. The basic pattern for the broad zonal flows is similar between the coarse-resolution model and the eddy-permitting model and is thought to be the response to the wind forcing. A part of the zonal jets embedded in each zonal flow is explained by the anomalous local wind forcing. Most of them, however, seem to be mainly created by the rectification of turbulent processes on a β plane (the Rhines effect), and zonal jets in this study have common features with the zonally elongated flows obtained in previous modeling studies conducted in idealized basins. The position of zonal jets is not stable when the ocean floor is flat, whereas it oscillates only within a few degrees under realistic bottom topography.

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Morphological variation in the Pacific sand dollar Dendraster excentricus

Canadian Journal of Zoology ◽

10.1139/z95-066 ◽

1995 ◽

Vol 73 (3) ◽

pp. 576-583

Author(s):

Raymond K. Nakamura

Keyword(s):

Principal Component Analysis ◽

Principal Components ◽

Morphological Variation ◽

Correlation Matrix ◽

Principal Component ◽

Sand Dollar ◽

Coastal Habitats ◽

Point Conception ◽

The Pacific ◽

Dendraster Excentricus

Correlations between latitude, habitat, and morphology in the Pacific sand dollar Dendraster excentricus were identified with principal component analysis. Twenty-two lengths were measured on the oral and aboral surfaces of 615 specimens from 31 sites. Samples were divided at latitude 34°30′N (Point Conception) and into bay and coastal habitats by relative wave exposure. Principal components (PC) were estimated from a correlation matrix of sample means of log-transformed measurements. PC1 accounted for 90% of the variance and was a measure of overall size. All 22 PC1 coefficients were positive and differed significantly from 0, according to a jackknifing test. PC1 differed significantly with latitude (ANOVA, p < 0.01) but not habitat. Southern populations tended to be smaller. PC2 accounted for 5% of the variance and described overall shape. Of the 22 variables, 13 had significant coefficients that varied in sign. PC2 varied significantly with habitat (ANOVA, p < 0.05) but not latitude. In coastal populations, the peristome and petaloids tended to be more posteriorly positioned and the food grooves were branched more peripherally. These features correspond to the greater tendency for coastal specimens to use their posterior end to suspension feed.

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