The European Gravity Field and Steady-State Ocean Circulation Explorer Satellite Mission Its Impact on Geophysics

Current knowledge of the Earth's gravity field and its geoid, as derived from various observing techniques and sources, is incomplete. Within a reasonable time, substantial improvement will come by exploiting new approaches based on spaceborne gravity observation. Among these, the European Space Agency (ESA) Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission concept has been conceived and designed taking into account multi-disciplinary research objectives in solid Earth physics, oceanography and geodesy. Based on the unique capability of a gravity gradiometer combined with satellite-to-satellite high-low tracking techniques, an accurate and detailed global model of the Earth's gravity field and its corresponding geoid will be recovered. The importance of this is demonstrated by a series of realistic simulation experiments. In particular, the quantitative impact of the new and accurate gravity field and geoid is examined in studies of tectonic composition and motion, Glaciological Isostatic Adjustment, ocean mesoscale variability, water mass transport, and unification of height systems. Improved knowledge in each of these fields will also ensure the accumulation of new understanding of past and present sea-level changes.     

Source induced vertical components in geomagnetic pulsation signals

We show how large vertical components may be induced in geomagnetic pulsation signals because of the localised nature of the source. The effect is greatest when the signal varies on a horizontal scale length which is shorter than the skin depth of the signal in the Earth. However, the horizontal scale length is also constrained to be equal or larger than the height of the ionospheric E-region (～ 120 km) as signals varying on a shorter scale are severely attenuated. Such conditions are best met by high latitude pulsations and some recent high latitude observations are explained by our results. We find that the vertical component is best correlated with the horizontal component in the direction in which the signal varies most rapidly.     

The last interglacial ocean

The final effort of the CLIMAP project was a study of the last interglaciation, a time of minimum ice volume some 122,000 yr ago coincident with the Substage 5e oxygen isotopic minimum. Based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean, last interglacial sea-surface temperatures (SST) were compared with those today. There are small SST departures in the mid-latitude North Atlantic (warmer) and the Gulf of Mexico (cooler). The eastern boundary currents of the South Atlantic and Pacific oceans are marked by large SST anomalies in individual cores, but their interpretations are precluded by no-analog problems and by discordancies among estimates from different biotic groups. In general, the last interglacial ocean was not significantly different from the modern ocean. The relative sequencing of ice decay versus oceanic warming on the Stage 6/5 oxygen isotopic transition and of ice growth versus oceanic cooling on the Stage 5e/5d transition was also studied. In most of the Southern Hemisphere, the oceanic response marked by the biotic census counts preceded (led) the global ice-volume response marked by the oxygen-isotope signal by several thousand years. The reverse pattern is evident in the North Atlantic Ocean and the Gulf of Mexico, where the oceanic response lagged that of global ice volume by several thousand years. As a result, the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years. These regional lead-lag relationships agree with those observed on other transitions and in long-term phase relationships; they cannot be explained simply as artifacts of bioturbational translations of the original signals.     

Noritic dykes of southern West Greenland: early Proterozoic boninitic magmatism

Two major swarms of early Proterozoic (ca. 2.1 Ga) basic dykes occur within the Archaean craton of southern West Greenland. One swarm comprises ophitic and sub-ophitic tholeiitic dolerites, while the other (the BN dyke swarm) constitutes mainly norites in which pyroxenes and olivine are enclosed by plagioclase oikocrysts. The close geochemical similarity between a quenched norite and the coarser-grained varieties indicates that the composition of the latter type has not been significantly modified by crystal accumulation. The BN dykes are geochemically distinctive, most having high MgO (ca. 16%), Cr and Ni contents in conjunction with relatively high SiO₂, light rare-earth (REE) and large ion lithophile (LIL) element concentrations. The texture, mineral chemistry and petrochemistry of the quenched noritic dyke all bear strong resemblances to those features in modern boninitic lavas. The BN dykes also correspond to proposed parental liquids of the Bushveld Complex and other major layered basic igneous intrusions. The two dyke swarms are petrogenetically distinct. The tholeiitic dolerites were derived from a relatively undepleted, primordial mantle while the noritic dykes originated from a metasomatized harzburgitic source. The wide-spread distribution of similar Proterozoic intrusions suggests crustal underplating by harzburgitic mantle on a world-wide scale at this time.     

Historical Trends of Benthic Invertebrate Biodiversity Spanning 182 Years in a Southern New England Estuary

Benthic invertebrates support numerous ecosystem functions and services including shellfish production, energy flow to fishes, and biogeochemical cycles. The decline of marine biodiversity worldwide has raised concerns about effects on ecosystems. To examine biodiversity trends of Narragansett Bay over time, a list was compiled of all benthic invertebrate species collected from the bay since 1834. The list covers 104 studies spanning 182 years and currently holds 1214 unique taxa from 21 phyla, the majority of all animal phyla on Earth. A permuted estimator of number of species suggested there are about 300 more yet to be discovered. Widely varying sampling gear and sieve mesh sizes precluded the use of abundance data. Instead, multidimensional scaling and taxonomic distinctness were used with presence-absence data to examine biodiversity trends. The changes in community composition and decline of benthic biodiversity (p?<?0.01) since 1855 are what would be expected of a community that gradually deteriorated in the face of increasing anthropogenic stressors. Taxonomic distinctness had negative correlations (p?<?0.05) with human population in the watershed, total nitrogen inputs, and inputs of metals. This loss of benthic biodiversity has implications for ecosystem functions and services. As some of the stressors waned in the last two or three decades, following passage of environmental legislation in the 1970s, biodiversity appeared to show a partial recovery. An inventory of species, how it has changed over time, and understanding what caused those changes are important for assessing whether remediation programs are achieving improved water quality and ecosystem health.     

On inertial currents over a sloping continental shelf

Using simple mathematical models, it is shown that an equatorward flowing coastally confined eastern boundary current (or poleward flowing western boundary current) may have two conjugate forms which transport the same flux of each water type. In a slowly varying environment, these two conjugate forms coalesce at some critical latitude which depends on the flow. For lower latitudes there is no defined form. As the coalescence latitude is approached from higher latitudes, one of the two conjugate forms narrows, while the other widens. Furthermore, in the neighborhood of the critical latitude the wider form is subcritical and the narrower form is supercritical to possible long small amplitude shelf waves. It is also shown that a poleward flowing coastally confined eastern boundary current (or an equatorward flowing western boundary current) may be traced poleward to some critical latitude beyond which the possibility of a current in juxtaposition with the coast terminates. For latitudes higher than this terminating latitude the current separates from the coast.     

Bristlecone pine tree rings and volcanic eruptions over the last 5000 yr

Many years of low growth identified in a western USA regional chronology of upper forest border bristlecone pine (Pinus longaeva and Pinus aristata) over the last 5000 yr coincide with known large explosive volcanic eruptions and/or ice core signals of past eruptions. Over the last millennium the agreement between the tree-ring data and volcano/ice-core data is high: years of ring-width minima can be matched with known volcanic eruptions or ice-core volcanic signals in 86% of cases. In previous millennia, while there is substantial concurrence, the agreement decreases with increasing antiquity. Many of the bristlecone pine ring-width minima occurred at the same time as ring-width minima in high latitude trees from northwestern Siberia and/or northern Finland over the past 4000-5000 yr, suggesting climatically-effective events of at least hemispheric scale. In contrast with the ice-core records, the agreement between widely separated tree-ring records does not decrease with increasing antiquity. These data suggest specific intervals when the climate system was or was not particularly sensitive enough to volcanic forcing to affect the trees, and they augment the ice core record in a number of ways: by providing confirmation from an alternative proxy record for volcanic signals, by suggesting alternative dates for eruptions, and by adding to the list of years when volcanic events of global significance were likely, including the mid-2nd-millennium BC eruption of Thera.