Shell growth rates of pteropod and heteropod molluscs and aragonite production in the open ocean: Implications for the marine carbonate system

Shell calcification rates of four species of euthecosomatous pteropods and two species of shelled heteropods were measured in short-term 45Ca uptake experiments. In subtropical, temperate, and subarctic waters of the North Pacific Ocean and Atlantic Ocean, animals were hand-collected by Scuba divers, captured with the use of a submersible and caught in plankton nets. Shell growth rates of pteropods ranged from 1.1 to 7.8 μg Ca deposited (mg Ca shell)−1 h−1. Heteropod growth rates ranged from 4.6 to 4.9 μg Ca deposited (mg Ca shell)−1 h−1. Aragonite production of shelled pteropods and heteropods at stations in the eastern Equatorial Pacific, North Pacific Central Water and the Tongue of the Ocean, Bahamas, was estimated using the instantaneous growth rate method. At all stations, pteropods were 3 to 9 times more abundant than heteropods and constituted 65 to 96% of aragonite production. Estimates of aragonite production ranged from 2.1 to 6.9 mg CaCO3 m−2 d−1. Using weighted averages based on two broad divisions of oceanic productivity, results were compared to reported aragonite fluxes measured with sediment traps. The data indicate that a source of alkalinity other than the dissolution of pteropod and heteropod aragonite is needed to supply the majority of a published estimate of CaCO3 dissolution in the water column of the North Pacific

Lead-210 and polonium-210 in pteropod and heteropod mollusc shells from the North Pacific: Evaluation of sample treatments and variation with shell size

Lead-210 activities in carefully cleaned size groups of pteropod and heteropod shells from the eastern equatorial Pacific were typically 0.3 dpm/g shell, similar to those reported in other biogenic calcium carbonates. However, 210Po activities were in excess of levels expected from the decay of shell-incorporated 210Pb, with (210Po/210Pb) activity ratios ranging from 20 to 28 in size-fractionated samples. Sample treatment procedures were examined using pteropod shells collected from diverse locations of the North Pacific. Possible sources of 210Po in excess of 210Pb in shells include inclusion of 210Po in the organic matrix during shell formation or adsorption of 210Po from the ambient water or nuclide-rich animal tissues. We predict that other CaCO3-precipitating organisms, including foraminifera, that have high surface/volume ratios and tissues in contact with carbonate surfaces, may also contain 210Po in excess of that supported by the decay of 210Pb. Variation in 210Pb activities measured in pteropod and heteropod shells suggests differences in the depth distributions for the species analyzed. Moreover, these results suggest ontogenetic migration in the pteropod Cavolinia longirostris. Pteropods and heteropods from regions in the equatorial Pacific were enriched 8–15 times with 210Pb relative to calcium, based on reported 210Pb activities in surface water and seawater calcium concentrations. Similarly, enrichment factors calculated for pteropod shells from the North Pacific transition zone and Subarctic Current were 13–20 times 210Pb levels in surface waters. Skeletal enrichment of 210Pb is higher in pteropods and heteropods than in corals by a factor of 3–10

The effect of phase-correlated returns and spatial smoothing on the accuracy of radar refractivity retrievals

Radar refractivity retrievals have the potential to accurately capture near-surface humidity fields from the phase change of ground clutter returns. In practice, phase changes are very noisy and the required smoothing will diminish large radial phase change gradients, leading to severe underestimates of large refractivity changes (ΔN). To mitigate this, the mean refractivity change over the field (ΔNfield) must be subtracted prior to smoothing. However, both observations and simulations indicate that highly correlated returns (e.g., when single targets straddle neighboring gates) result in underestimates of ΔNfield when pulse-pair processing is used. This may contribute to reported differences of up to 30 N units between surface observations and retrievals. This effect can be avoided if ΔNfield is estimated using a linear least squares fit to azimuthally averaged phase changes. Nevertheless, subsequent smoothing of the phase changes will still tend to diminish the all-important spatial perturbations in retrieved refractivity relative to ΔNfield; an iterative estimation approach may be required. The uncertainty in the target location within the range gate leads to additional phase noise proportional to ΔN, pulse length, and radar frequency. The use of short pulse lengths is recommended, not only to reduce this noise but to increase both the maximum detectable refractivity change and the number of suitable targets. Retrievals of refractivity fields must allow for large ΔN relative to an earlier reference field. This should be achievable for short pulses at S band, but phase noise due to target motion may prevent this at C band, while at X band even the retrieval of ΔN over shorter periods may at times be impossible

Очистка водных сред от микробиологических загрязнений с использованием адсорбентов на основе газобетона

Объект исследования: газобетон (ГОСТ 25485-89), штамм бактерий E. coli ATCC-25922. Цель работы: оценка эффективности использования газобетона для очистки водных сред от микробиологических загрязнений. В процессе исследования проводились оценка гидродинамического сопротивления, определение фильтрующей способности сорбентов в отношении бактерий E. Coli. В результате исследования получены оптимальные фракции сорбента, определены физико-химические характеристики и сорбционные свойства сорбентов. Область применения: водоочистка и водоподготовка в различных отраслях промышленности.Subject of research: aerated concrete (State Standard 25485-89), a strain of the bacteria E. coli ATCC-25922. The main goal of this study was investigation of sorbent on the basis of the aerated concrete for water purification. The study assesses the hydrodynamic resistance, determining the ability of the filter sorbents against the bacteria E. Coli. The research obtained the optimal fraction of the sorbent, determined physico-chemical characteristics and sorption properties of the sorbents. Applications: water purification and water conditioning in various industries

Evaluation of data-based estimates of anthropogenic carbon in the Arctic Ocean

The Arctic Ocean is particularly vulnerable to ocean acidification, a process that is mainly driven by the uptake of anthropogenic carbon (Cant) from the atmosphere. Although Cant concentrations cannot be measured directly in the ocean, they have been estimated using data-based methods such as the transient time distribution (TTD) approach, which characterizes the ventilation of water masses with inert transient tracers, such as CFC-12. Here, we evaluate the TTD approach in the Arctic Ocean using an eddying ocean model as a test bed. When the TTD approach is applied to simulated CFC-12 in that model, it underestimates the same model's directly simulated Cant concentrations by up to 12%, a bias that stems from its idealized assumption of gas equilibrium between atmosphere and surface water, both for CFC-12 and anthropogenic CO2. Unlike the idealized assumption, the simulated partial pressure of CFC-12 (pCFC-12) in Arctic surface waters is undersaturated relative to that in the atmosphere in regions and times of deep-water formation, while the simulated equivalent for Cant is supersaturated. After accounting for the TTD approach's negative bias, the total amount of Cant in the Arctic Ocean in 2005 increases by 8% to 3.3 ± 0.3 Pg C. By combining the adjusted TTD approach with scenarios of future atmospheric CO2, it is estimated that all Arctic waters, from surface to depth, would become corrosive to aragonite by the middle of the next century even if atmospheric CO2 could be stabilized at 540 ppm

Ocean Acidification: The Other CO\u3csub\u3e2\u3c/sub\u3e Problem?

Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions. Republished with permission from 1 Ann. Rev. Mar. Sci. 169 (2009)

Theory and observations of ice particle evolution in cirrus using Doppler radar: evidence for aggregation

Vertically pointing Doppler radar has been used to study the evolution of ice particles as they sediment through a cirrus cloud. The measured Doppler fall speeds, together with radar-derived estimates for the altitude of cloud top, are used to estimate a characteristic fall time tc for the `average' ice particle. The change in radar reflectivity Z is studied as a function of tc, and is found to increase exponentially with fall time. We use the idea of dynamically scaling particle size distributions to show that this behaviour implies exponential growth of the average particle size, and argue that this exponential growth is a signature of ice crystal aggregation.Comment: accepted to Geophysical Research Letter