The Grounding of an Ice Shelf in the Central Arctic Ocean: A Modeling Experiment

A numerical ice sheet model was used in a first test towards evaluating the hypothesis that, during a period of large-scale glaciation, an ice shelf emanating from the Barents/Kara Seas grounded across parts of the Lomonosov Ridge to a depth of around 1000 m below present sea level (Jakobsson, 1999; Polyak et al., 2001). Despite that we not include complex ice shelf physics or grounding line mechanics in our model and treat the process of marine melting in a simple manner, our experiments are the necessary first steps toward providing a comprehensive reconstruction of the former ice-sheet/ice-shelf system in the Arctic Ocean. A series of model runs was performed where ice shelf mass balance and ice shelf strain per unit time (strain rate) were adjusted. The mass balance and shelf ice strain rate are the key model parameters that govern the flux of ice into the Arctic Ocean. Grounding on the Lomonosov Ridge was not modeled when the ice shelf strain rate was 0.005 year-1 (i.e. a free flowing ice shelf). Even with low rates (\u3c10 cm/year) of basal melting, the ice shelf thickness was always less than 100 m over the central part of the ridge. Our experiment suggests that grounding on the Lomonosov Ridge by a free-flowing ice shelf is not possible. When the strain rate in the shelf ice was reduced to zero, however, the shelf thickness increased substantially. Such conditions are likely only to have occurred during periods of large-scale glaciation if substantial stagnant and thickened sea ice was present in the ocean, buttressing the ice shelf flowing from the Barents Sea. A comprehensive study using a coupled icesheet/ shelf/sea-ice model would build on these preliminary results and have the potential to further constrain the history of circum-Arctic Ocean ice sheets

Radio-Echo Sounding Over Polar Ice Masses

Peer reviewedPublisher PD

A Modeling Experiment on the Grounding of an Ice Shelf in the Central Arctic Ocean During MIS 6

High-resolution chirp sonar subbottom profiles from the Lomonosov Ridge in the central Arctic Ocean, acquired from the Swedish icebreaker Oden in 1996, revealed large-scale erosion of the ridge crest down to depths of 1000 m below present sea level [Jakobsson, 1999]. Subsequent acoustic mapping during the SCICEX nuclear submarine expedition in 1999 showed glacial fluting at the deepest eroded areas and subparallel ice scours from 950 m water depth to the shallowest parts of the ridge crest [Polyak et al., 2001]. The directions of the mapped glaciogenic bed-forms and the redeposition of eroded material on the Amerasian side of the ridge indicate ice flow from the Barents-Kara Sea area. Core studies revealed that sediment drape the eroded areas from Marine Isotope Stage (MIS) 5.5 and, thus, it was proposed that the major erosional event took place during Marine Isotope Stage (MIS) 6 [Jakobsson et al., 2001]. Glacial geological evidence suggests strongly that the Late Saalian (MIS 6) ice sheet margin reached the shelf break of the Barents-Kara Sea [Svendsen et al. in press] and this gives us two possible ways to explain the ice erosional features on the Lomonosov Ridge. One is the grounding of a floating ice shelf and the other is the scouring from large deep tabular iceberg. Here we apply numerical ice sheet modeling to test the hypothesis that an ice shelf emanating from the Barents/Kara seas grounded across part of the Lomonsov Ridge and caused the extensive erosion down to a depth of around 1000 m below present sea level. A series of model experiments was undertaken in which the ice shelf mass balance (surface accumulation and basal melting) and ice shelf strain rates were adjusted. Grounding of the Lomonosov Ridge was not achieved when the ice shelf strain rate was 0.005 yr-1 (i.e. a free flowing ice shelf). However this model produced two interesting findings. First, with basal melt rates of up to 50 cm yr-1 an ice shelf grew from the St. Anna Trough ice stream across the section of the ridge where there is evidence for grounding. Second, even with ultra low rates of basal melting, the ice shelf thickness was always less than 200 m over the ridge. We conclude that grounding of the Lomonosov Ridge by a free-flowing ice shelf is not possible. When the strain rate was reduced to zero, however, the shelf thickness increased substantially. Such conditions are likely only to have occurred during periods of large-scale glaciation across the Eurasian Arctic such as in the Saalian, and if a substantial stagnant thickened sea ice was present in the ocean, buttressing the shelf flowing from the Barents Sea. Our results are interpreted using new techniques for dynamic 3Dvisualization

Policy making and regulation to promote entrepreneurship : procedural vs. monetary policies

The main objective of this paper is to understand under what circumstances a government should focus on procedural or monetary policies to foster entrepreneurial entry. To do this, we measure entrepreneurship by the entry density of new companies, which counts formally registered entrepreneurs only. However, we also control the effect on opportunity and necessity-driven entrepreneurship rates, which include entrepreneurs of all stages and sectors. Procedural and monetary policies are represented by time and cost to start a business respectively. The variety of control variables used in literature is approached by aggregating explanatory variables from 16 studies, resulting in 44 variables of which 8 are used in the regression analysis. For the empirical analysis, we use country and year fixed effects with country-clustered standard errors. We find a stronger positive impact for lowering cost to start a business, especially in countries with high rates of necessity-driven entrepreneurs or countries which did not belong to the lowest third in cost or time to start a business. However, the findings also suggest, that these policies do not incentivize non-entrepreneurs to engage in entrepreneurship, but rather attract informally operating entrepreneurs to register their business.O principal objetivo deste trabalho é compreender sob quais circunstâncias a administração pública deve focar em políticas procedimentais ou monetárias para fomentar novos empreendimentos. Para isso, medimos o empreendedorismo através da entrada de novas companhias no mercado, considerando apenas empreendedores formalmente registrados. Contudo, também verificamos o efeito da oportunidade e necessidade no índice de empreendedorismo, o que inclui empreendedores em todas fases e setores. Políticas procedimentais e monetárias são representadas pelo tempo e pelo custo para começar um negócio, respectivamente. A pluralidade de variáveis de controle utilizada na literatura é abordada pela conjugação de variáveis explicativas de 16 estudos, resultando em 44 variáveis, das quais 8 são utilizadas na análise de regressão. Para a análise empírica, utilizamos efeitos fixos por país e por ano com desvios-padrão agrupados em países. Encontramos um forte impacto positivo para reduzir os custos para começar um negócio, especialmente em países com alto índice de empreendedores impulsionados pela necessidade ou países que não pertenciam ao terço mais baixo de preço ou tempo para iniciar um negócio. Todavia, as conclusões também sugerem que essas políticas não incentivam não-empreendedores a se envolverem no empreendedorismo, mas sim atraem empresários que atuam informalmente no mercado a registrarem seus negócios

A revised inventory of Antarctic subglacial lakes

The locations and details of 145 Antarctic subglacial lakes are presented. The inventory is based on a former catalogue of lake-type features, which has been subsequently reanalysed, and on the results from three additional datasets. The first is from Italian radio-echo sounding (RES) of the Dome C region of East Antarctica, from which 14 new lakes are identified. These data also show that, in a number of occasions, multiple take-type reflectors thought previously to be individual lakes are in fact reflections from the same relatively large take. This reduces the former total of lake-type reflectors by six, but also adds a significant level of information to these particular lakes. The second dataset is from a Russian survey of the Dome A and Dome F regions of East Antarctica, which provides evidence of 18 new lakes and extends the coverage of the inventory considerably. The third dataset comprises three airborne RES surveys under-taken by the US in East Antarctica over the last five years, from which forty three new lakes have been identified. Reference to information on Lake Vostok, from Italian and US surveys taken in the last few years, is now included