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"John, Barbara"
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Ocean
The Ultimate Guide Ocean helps children aged 8+ to discover everything they need to know about the world's oceans. It includes a fully illustrated book, split into seven key sections, and text is presented as easy-to-read bullet points. Topics explored include marine life, ships and boats, ocean geography and the impact of human behaviour on this vast environment. Five colourful acetate pages, each featuring a different animal, allow you to peel back the layers to uncover more information. In addition, there are two large colour posters, one detailing ocean depths and the creatures that live in them and another focusing on coral reefs.
Book
Reestablishing a host—affiliate relationship
Co-extirpation among host–affiliate species is thought to be a leading cause of biodiversity loss worldwide. Freshwater mussels (Unionida) are at risk globally and face many threats to survival, including limited access to viable host fish required to complete their life history. We examine the relationship between the common eastern elliptio mussel (Elliptio complanata) and its migratory host fish the American eel (Anguilla rostrata), whose distribution in the Chesapeake Bay watershed is limited, in part, by dams. We examined population demographics of E. complanata across locations in the Chesapeake Bay watershed, primarily in the Susquehanna River in the absence of American eels, and conducted experimental restocking of eels to assess potential impacts on mussel recruitment. Compared to surveys completed ∼20 yr prior, E. complanata could be experiencing declines at several historically abundant sites. These sites also had extremely limited evidence of recruitment. Restoration of host fish improved recruitment, but results were not equivalent between stocking sites, indicating that host reintroduction alone may not be fully effective in reestablishing mussel populations. One site where eels were introduced (Pine Creek, Tioga County, Pennsylvania, USA) experienced an increase from 0 juveniles found during quantitative surveys prior to eel stocking to 151 (21% of individuals collected during quantitative surveys) E. complanata juveniles found four years after stocking. A second site (Buffalo Creek, Union County, Pennsylvania) experienced a more moderate increase from 2 to 7 juveniles found during 2010 and 2014 quantitative surveys, respectively. Continued examination of other potential interacting factors affecting recruitment, including water quality or habitat conditions, is necessary to target favorable sites for successful restoration.
Journal Article
Thomas Jefferson builds a library
Thomas Jefferson loved to read and collect books on almost every subject. He built his first library as a young man, and kept on building until his book collection helped to create the Library of Congress in Washington, D.C., the world's largest library.
BOOK
Three-dimensional magnetic stripes require slow cooling in fast-spread lower ocean crust
Earth’s magnetic field is recorded as oceanic crust cools, generating lineated magnetic anomalies that provide the pattern of polarity reversals for the past 160 million years
1
. In the lower (gabbroic) crust, polarity interval boundaries are proxies for isotherms that constrain cooling and hence crustal accretion. Seismic observations
2
–
4
, geospeedometry
5
–
7
and thermal modelling
8
–
10
of fast-spread crust yield conflicting interpretations of where and how heat is lost near the ridge, a sensitive indicator of processes of melt transport and crystallization within the crust. Here we show that the magnetic structure of magmatically robust fast-spread crust requires that crustal temperatures near the dike–gabbro transition remain at approximately 500 degrees Celsius for 0.1 million years. Near-bottom magnetization solutions over two areas, separated by approximately 8 kilometres, highlight subhorizontal polarity boundaries within 200 metres of the dike–gabbro transition that extend 7–8 kilometres off-axis. Oriented samples with multiple polarity components provide direct confirmation of a corresponding horizontal polarity boundary across an area approximately one kilometre wide, and indicate slow cooling over three polarity intervals. Our results are incompatible with deep hydrothermal cooling within a few kilometres of the axis
2
,
7
and instead suggest a broad, hot axial zone that extends roughly 8 kilometres off-axis in magmatically robust fast-spread ocean crust.
A record of Earth’s magnetic field constructed from near-bottom magnetization observations and oriented samples provides three-dimensional imaging of magnetic stripes in fast-spread crust, and suggests slow cooling off-axis, as opposed to deep hydrothermal cooling close to the spreading ridge.
Journal Article
Blacks of the land : Indian slavery, settler society, and the Portuguese colonial enterprise in South America
\"Beginning in the 1490s in the Caribbean, and through the slow demise of native slavery in North and South America over the eighteenth and nineteenth centuries, millions of Amerindians were subjected to enslavement, captivity, and forced labor. Indian slavery was practiced across the Americas, at one point in time or another, in jurisdictions claimed by every European power that engaged in New World colonialism. Spanish, Portuguese, Dutch, English, Scottish, French, and Russian colonists held native Americans as slaves, exerting their mastery over them and dealing in them as chattel. In parts of the United States, Mexico, and Brazil, native slavery survived the ending of European colonial claims and the formation of independent nation-states, lasting well into the nineteenth century. By that point, however, the numbers of Amerindians held as slaves in Brazil and the United States were tiny compared to the masses of African and Afro-American captives that made up the absolute majority of the populations of the two country's plantation zones. Indian slavery thus seemed a small thing-economically, socially, demographically-when set alongside African and Afro-American slavery, on the ascent through the first half of the new century in Brazil and the southern United States alike. Until recently-and for many good reasons-scholarly attention to Indian slavery has been similarly dwarfed by the volume of care and attention paid to African and Afro- American slavery in the Americas. Over the last fifteen years, however, the study of native slavery has undergone a remarkable boom among North American historians\"-- Provided by publisher.
Book
On the occurrence, trace element geochemistry, and crystallization history of zircon from in situ ocean lithosphere
We characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite, evolved gabbro, and metamorphosed ultramafic host-rocks collected along present-day slow and ultraslow spreading mid-ocean ridges (MORs). The geochemistry of 267 zircon grains was measured by sensitive high-resolution ion microprobe-reverse geometry at the USGS-Stanford Ion Microprobe facility. Three types of zircon are recognized based on texture and geochemistry. Most ocean crustal zircons resemble young magmatic zircon from other crustal settings, occurring as pristine, colorless euhedral (Type 1) or subhedral to anhedral (Type 2) grains. In these grains, Hf and most trace elements vary systematically with Ti, typically becoming enriched with falling Ti-in-zircon temperature. Ti-in-zircon temperatures range from 1,040 to 660°C (corrected for
a
TiO2
≈ 0.7,
a
SiO2
≈ 1.0, pressure ≈ 2 kbar); intra-sample variation is typically ~60–150°C. Decreasing Ti correlates with enrichment in Hf to ~2 wt%, while additional Hf-enrichment occurs at relatively constant temperature. Trends between Ti and U, Y, REE, and Eu/Eu* exhibit a similar inflection, which may denote the onset of eutectic crystallization; the inflection is well-defined by zircons from plagiogranite and implies solidus temperatures of ~680–740°C. A third type of zircon is defined as being porous and colored with chaotic CL zoning, and occurs in ~25% of rock samples studied. These features, along with high measured La, Cl, S, Ca, and Fe, and low (Sm/La)
N
ratios are suggestive of interaction with aqueous fluids. Non-porous, luminescent CL overgrowth rims on porous grains record uniform temperatures averaging 615 ± 26°C (2SD,
n
= 7), implying zircon formation below the wet-granite solidus and under water-saturated conditions. Zircon geochemistry reflects, in part, source region; elevated HREE coupled with low U concentrations allow effective discrimination of ~80% of zircon formed at modern MORs from zircon in continental crust. The geochemistry and textural observations reported here serve as an important database for comparison with detrital, xenocrystic, and metamorphosed mafic rock-hosted zircon populations to evaluate provenance.
Journal Article
Primitive layered gabbros from fast-spreading lower oceanic crust
Drilling by the Integrated Ocean Drilling Program has recovered primitive, modally layered, orthopyroxene-bearing cumulate rocks from the lower plutonic crust formed at a fast-spreading ridge, leading to a better-constrained estimate of the bulk composition of fast-spreading oceanic crust.
Crust formation at a fast-spreading ridge
Kathryn Gillis
et al
. report cored intervals from the lower plutonic crust formed at a fast-spreading ridge, sampled at the Hess Deep rift in the equatorial Pacific Ocean. They find spectacular centimetre-scale modally layered rocks, some of which have a strong layering-parallel foliation, confirming a long-held paradigm that such rocks are a key constituent of the lower ocean crust formed at fast-spreading ridges. Geochemical analysis of these primitive lower plutonics, in combination with previous geochemical data for shallow-level plutonics, sheeted dikes and lavas, provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust to date.
Three-quarters of the oceanic crust formed at fast-spreading ridges is composed of plutonic rocks whose mineral assemblages, textures and compositions record the history of melt transport and crystallization between the mantle and the sea floor. Despite the importance of these rocks, sampling them
in situ
is extremely challenging owing to the overlying dykes and lavas. This means that models for understanding the formation of the lower crust are based largely on geophysical studies
1
and ancient analogues (ophiolites)
2
,
3
,
4
,
5
that did not form at typical mid-ocean ridges. Here we describe cored intervals of primitive, modally layered gabbroic rocks from the lower plutonic crust formed at a fast-spreading ridge, sampled by the Integrated Ocean Drilling Program at the Hess Deep rift. Centimetre-scale, modally layered rocks, some of which have a strong layering-parallel foliation, confirm a long-held belief that such rocks are a key constituent of the lower oceanic crust formed at fast-spreading ridges
3
,
6
. Geochemical analysis of these primitive lower plutonic rocks—in combination with previous geochemical data for shallow-level plutonic rocks, sheeted dykes and lavas—provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust so far. Simple crystallization models using this bulk crustal composition as the parental melt accurately predict the bulk composition of both the lavas and the plutonic rocks. However, the recovered plutonic rocks show early crystallization of orthopyroxene, which is not predicted by current models of melt extraction from the mantle
7
and mid-ocean-ridge basalt differentiation
8
,
9
. The simplest explanation of this observation is that compositionally diverse melts are extracted from the mantle and partly crystallize before mixing to produce the more homogeneous magmas that erupt.
Journal Article
Strain localization along the Atlantis Bank oceanic detachment fault system, Southwest Indian Ridge
Microstructural observations and mineral thermometry from in situ samples collected from the Atlantis Bank oceanic core complex (SW Indian Ridge) indicate that detachment faulting was initiated under hypersolidus conditions in the ductile regime and continued through subgreenschist temperatures through the ductile, semibrittle, and brittle regimes as strain localized along the exposed, now subhorizontal fault surface. Ductile, semibrittle, and brittle fabrics are developed within dominantly gabbroic rocks. Footwall rocks exhibit crystal plastic fabrics distributed over a structural thickness up to 400 m below the denuded fault surface exposed at the seafloor, whereas semibrittle and brittle fabrics are concentrated in the 80 and 30 m immediately below the principal slip surface of the detachment fault, respectively. Sample fabrics suggest that strain localization was achieved by dynamic recrystallization of plagioclase at temperatures between 910°C and 650°C, by amphibole‐accommodated dissolution‐precipitation creep at temperatures ∼750°C–450°C, by chlorite‐accommodated reaction softening at temperatures ∼450°C–300°C, and by brittle fracturing and cataclasis at temperatures <300°C.
Journal Article