Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)

The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75°37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607–2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice–lithosphere interactions of the Greenland Ice Sheet

A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude

Early to Middle Miocene sea-level oscillations of approximately 40-60 m estimated from far-field records1-3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth2. This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene4,5. Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72-17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution

Crescimento radicular de soja em razão da sucessão de cultivos e da compactação do solo Soybean root growth as affected by previous crop and soil compaction

O objetivo do experimento foi avaliar o crescimento radicular e produção de matéria seca da parte aérea da soja (Glycine max (L.) Merrill) cultivada após diversas espécies vegetais, em solo com diferentes níveis de compactação. O trabalho foi realizado em vasos contendo amostras de um Latossolo Vermelho, textura franco arenosa, com camada de 3,5 cm (profundidade de 15 a 18,5 cm) compactada até as densidades 1,12, 1,36 e 1,60 Mg m-3, onde cultivaram-se anteriormente aveia-preta, guandu, milheto, mucuna-preta, soja, sorgo granífero e tremoço-azul, e um tratamento sem planta (pousio). Essas espécies se desenvolveram por 37 a 39 dias, foram cortadas ao nível do solo, picadas em partes de aproximadamente 3 cm e deixadas sobre a superfície do vaso por 40 dias. Após esse período, cultivou-se a soja até 28 dias após a emergência, quando, então, as plantas foram colhidas. Foram avaliados produção de matéria seca da parte aérea e de raízes, e comprimento e diâmetro radicular da soja. O cultivo anterior com aveia-preta, guandu e milheto favoreceu o crescimento radicular da soja abaixo de camadas compactadas do solo. Independentemente do nível de compactação, o cultivo anterior com qualquer das espécies estudadas beneficiou a produção de matéria seca da parte aérea da soja.<br>This study aimed at evaluating root growth and shoot dry matter production of soybean (Glycine max (L.) Merrill) cropped after different vegetal species, in a soil with different compaction levels. The experiment was conducted in pots containing a Dark-Red Latosol (Acrortox, loamy sand), and the pots had a layer 3.5 cm (15 to 18.5 cm) thick and 15 cm deep compacted to 1.12, 1.36 and 1.60 Mg m-3. Before soybean, the pots were cropped with black oat, pigeon pea, pearl millet, black mucuna, soybean, grain sorghum and lupin, plus a treatment without plants. These species were grown for 37 to 39 days, when they were cut at soil level, prick in particles of approximately 3 cm length, and left on the soil surface for 40 days. After this, soybean was planted in the pots and was allowed to grow for 28 days after plant emergence. The soybean shoot dry matter weight, root length, diameter and dry matter were evaluated. The previous crop with black oat, pigeon pea and pearl millet favored the soybean root growth below compacted layer soil. Regardless soil compaction, the soybean shoot dry matter was favored by the previous crop