Impact of strong deep ocean stratification on the glacial carbon cycle

During the Last Glacial Maximum, the climate was substantially colder and the carbon cycle was clearly different from the late Holocene. According to proxy data deep oceanic δ13C was very low, and the atmospheric CO2 concentration also reduced. Several mechanisms have been proposed to explain these changes, but none can fully explain the data, especially the very low deep ocean δ13C values. Oceanic core data show that the deep ocean was very cold and salty, which would lead to enhanced deep ocean stratification. We show that such an enhanced stratification in the coupled climate model CLIMBER-2 helps get very low deep oceanic δ13C values. Indeed the simulated δ13C reaches values as low as −0.8‰ in line with proxy data evidences. Moreover it increases the oceanic carbon reservoir leading to a small, yet robust, atmospheric CO2 drop of approximately 10 ppm.

Thermobaric control of gravitational potential energy generation by diapycnal mixing in the deep ocean

Sources and sinks of gravitational potential energy (GPE) play a rate-limiting role in the large scale ocean circulation. A key source is turbulent diapycnal mixing, whereby irre- versible mixing across isoneutral surfaces is enhanced by turbulent straining of these surfaces. This has motivated international observational efforts to map diapycnal mixing in the global ocean. However, in order to accurately relate the GPE supplied to the large scale circulation by diapycnal mixing to the mixing energy source, it is first necessary to determine the ratio, ξ , of the GPE generation rate to the available potential energy dissipation rate associated with turbulent mixing. Here, the link between GPE and hydro- static pressure is used to derive the GPE budget for a com- pressible ocean with a nonlinear equation of state. The role of diapycnal mixing is isolated and from this a global cli- matological distribution of ξ is calculated. It is shown that, for a given source of mixing energy, typically three times as much GPE is generated if the mixing takes place in bottom waters rather than in the pycnocline. This is due to GPE destruction by cabbelling in the pycnocline, as opposed to thermobaric enhancement of GPE generation by diapycnal mixing in the deep ocean.

In at the Deep End. Impressions of farming in a year gaining experience: 1952-3; 1978-85

The book describes a wide variety of students’ experiences in their practical year prior to entering University to study BSc Agriculture. Until comparatively recently it was the normal requirement for all such students, whether or not they already had home farming experience, to gain a full year’s experience of practical agriculture – and to write a report thereon. This record of 41 students’ reports of the pre-entry year begins with Paul’s own experience in the early 1950s before 41 reports from 30 or more years ago. The essays provide compelling and fascinating stories, well-articulated with clear acknowledgement for most part of the humanity and the warmth with which each student was treated by farmers and farm workers alike, despite the difference in both age and experience (considerable!). [This summary is an extract from the full overview which is archived here together with the book.]

Simulated last glacial maximum D14Catm and the deep glacial ocean carbon reservoir

∆14Catm has been estimated as 420 ± 80‰ (IntCal09) during the Last Glacial Maximum (LGM) compared to preindustrial times (0‰), but mechanisms explaining this difference are not yet resolved. ∆14Catm is a function of both cosmogenic production in the high atmosphere and of carbon cycling and partitioning in the Earth system. 10Be-based reconstructions show a contribution of the cosmogenic production term of only 200 ± 200‰ in the LGM. The remaining 220‰ have thus to be explained by changes in the carbon cycle. Recently, Bouttes et al. (2010, 2011) proposed to explain most of the difference in pCO2atm and δ13C between glacial and interglacial times as a result of brine-induced ocean stratification in the Southern Ocean. This mechanism involves the formation of very saline water masses that contribute to high carbon storage in the deep ocean. During glacial times, the sinking of brines is enhanced and more carbon is stored in the deep ocean, lowering pCO2atm. Moreover, the sinking of brines induces increased stratification in the Southern Ocean, which keeps the deep ocean well isolated from the surface. Such an isolated ocean reservoir would be characterized by a low ∆14C signature. Evidence of such 14C-depleted deep waters during the LGM has recently been found in the Southern Ocean (Skinner et al. 2010). The degassing of this carbon with low ∆14C would then reduce ∆14Catm throughout the deglaciation. We have further developed the CLIMBER-2 model to include a cosmogenic production of 14C as well as an interactive atmospheric 14C reservoir. We investigate the role of both the sinking of brine and cosmogenic production, alongside iron fertilization mechanisms, to explain changes in ∆14Catm during the last deglaciation. In our simulations, not only is the sinking of brine mechanism consistent with past ∆14C data, but it also explains most of the differences in pCO2atm and ∆14Catm between the LGM and preindustrial times. Finally, this study represents the first time to our knowledge that a model experiment explains glacial-interglacial differences in pCO2atm, δ13C, and ∆14C together with a coherent LGM climate.

The hidden organic carbon in deep mineral soils

Aims Current estimates of soil organic carbon (SOC) are based largely on surficial measurements to depths of 0.3 to 1 m. Many of the world’s soils greatly exceed 1 m depth and there are numerous reports of biological activity to depths of many metres. Although SOC storage to depths of up to 8 m has been previously reported, the extent to which SOC is stored at deeper depths in soil profiles is currently unknown. This paper aims to provide the first detailed analysis of these previously unreported stores of SOC. Methods Soils from five sites in the deeply weathered regolith in the Yilgarn Craton of south-western Australia were sampled and analysed for total organic carbon by combustion chromatography. These soils ranged between 5 and 38 m (mean 21 m) depth to bedrock and had been either recently reforested with Pinus pinaster or were under agriculture. Sites had a mean annual rainfall of between 399 and 583 mm yr−1. Results The mean SOC concentration across all sites was 2.30 ± 0.26 % (s.e.), 0.41 ± 0.05 % and 0.23 ± 0.04 % in the surface 0.1, 0.1–0.5 and 0.5 to 1.0 m increments, respectively. The mean value between 1 and 5 m was 0.12 ± 0.01 %, whereas between 5 and 35 m the values decreased from 0.04 ± 0.002 % to 0.03 ± 0.003 %. Mean SOC mass densities for each of the five locations varied from 21.8–37.5 kg C m−2, and were in toto two to five times greater than would be reported with sampling to a depth of 0.5 m. Conclusions This finding may have major implications for estimates of global carbon storage and modelling of the potential global impacts of climate change and land-use change on carbon cycles. The paper demonstrates the need for a reassessment of the current arbitrary shallow soil sampling depths for assessing carbon stocks, a revision of global SOC estimates and elucidation of the composition and fate of deep carbon in response to land use and climate change

Commensalism in an agroecosystem: hydraulic redistribution by deep-rooted legumes improves survival of a droughted shallow-rooted legume companion

We investigated commensalism of water use among annual shallow-rooted and perennial deep-rooted pasture legumes by examining the effect of hydraulic lift by Cullen pallidum (N.T.Burb.) J.W.Grimes and Medicago sativa on growth, survival and nutrient uptake of Trifolium subterraneum L. A vertically split-root design allowed separate control of soil water in top and bottom soil. Thirty-five days after watering ceased in the top tube, but soil remained at field capacity in the bottom tube, an increase in shallow soil water content by hydraulic lift was 5.6 and 5.9 g kg−1 soil overnight for C. pallidum and M. sativa, respectively. Trifolium subterraneum in this treatment maintained higher leaf water potentials (with M. sativa) or exhibited a slower decline (with C. pallidum) than without companion perennial plants; and shoot biomass of T. subterraneum was 56% (with C. pallidum) and 67% (with M. sativa) of that when both top and bottom tubes were at field capacity. Uptake of rubidium (a potassium analog) and phosphorus by T. subterraneum was not facilitated by hydraulic lift. Interestingly, phosphorus content was threefold greater, and shoot biomass 1.5–3.3-fold greater when T. subterraneum was interplanted with C. pallidum compared with M. sativa, although dry weight of C. pallidum was much greater than that of M. sativa. This study showed that interplanting with deep-rooted perennial legumes has benefited the survival of T. subterraneum.

A comparative study of the characteristics of French Fries produced by deep fat frying and air frying

Air frying is being projected as an alternative to deep fat frying for producing snacks such as French Fries. In air frying, the raw potato sections are essentially heated in hot air containing fine oil droplets, which dehydrates the potato and attempts to impart the characteristics of traditionally produced French fries, but with a substantially lower level of fat absorbed in the product. The aim of this research is to compare: 1) the process dynamics of air frying with conventional deep fat frying under otherwise similar operating conditions, and 2) the products formed by the two processes in terms of color, texture, microstructure, calorimetric properties and sensory characteristics Although, air frying produced products with a substantially lower fat content but with similar moisture contents and color characteristics, it required much longer processing times, typically 21 minutes in relation to 9 minutes in the case of deep fat frying. The slower evolution of temperature also resulted in lower rates of moisture loss and color development reactions. DSC studies revealed that the extent of starch gelatinization was also lower in the case of air fried product. In addition, the two types of frying also resulted in products having significantly different texture and sensory characteristics.

Planning in the face of ‘deep divisions’: a view from Beirut, Lebanon

This article discusses planning in the global South-East while focusing on the specific context of social divides, political turmoil and conflict situations. The article proposes a five-way framework based on political science and planning to theory to analyse such contexts. The article explores the case of Beirut, Lebanon that has undergone several episodes of internal and external conflicts resulting in a society splintered along sectarianism. Three Two case studies of open urban spaces and their public activities are analysed using the five-way framework The discussion indicates how economic liberalism that is prevalent in countries of the South-East, along with place-based identities, interest-based identities, consensus orientated processes and institutionalism might facilitate a cultivation of deep values away from a narrowly constructed identity. The article argues that planners should understand the options for positive action that aim to bridge deep divisions and suggests that the five-way framework provides a reference for contextualising in different ways to suit particular contexts. Therefore, the framework is not necessarily restricted to the South-East but could be applicable to any context which manifests deep divisions.