Volatile retention from cometary impacts on the Moon

Impacts of comets and asteroids play an important role in volatile delivery on the Moon. We use a novel method for tracking vapor masses that reach escape velocity in hydrocode simulations of cometary impacts to explore the effects of volatile retention. We model impacts on the Moon to find the mass of vapor plume gravitationally trapped on the Moon as a function of impact velocity. We apply this result to the impactor velocity distribution and find that the total impactor mass retained on the Moon is approximately 6.5% of the impactor mass flux. Making reasonable assumptions about water content of comets and the comet size-frequency distribution, we derive a water flux for the Moon. After accounting for migration and stability of water ice at the poles, we estimate a total 1.3×10⁸-4.3×10⁹ metric tons of water is delivered to the Moon and remains stable at the poles over 1 Ga. A factor of 30 uncertainty in the estimated cometary impact flux is primarily responsible for this large range of values. The calculated mass of water is sufficient to account for the neutron fluxes poleward of 75° observed by Lunar Prospector. A similar analysis for water delivery to the Moon via asteroid impacts shows that asteroids provide six times more water mass via impacts than comets.     

The role of palaeolimnology in assessing eutrophication and its impact on lakes

Eutrophication is perhaps the most pervasive form of pollution. Here we first review its effects on lake ecosystems based largely on modern ecological investigation. The longer time scale afforded by palaeolimnological investigation has seen an increase in the number of the publications since 1990 with a disproportionate increase in citations demonstrating the increasing use and usefulness of palaeolimnology to help understand lakes ecosystems and their response to eutrophication. We summarise briefly the history and origins of palaeolimnological investigation into eutrophication and its impacts in lakes. Then we review quantitative and qualitative palaeolimnological methods for tracking change in nutrient concentrations, algal community and abundance, macrophyte community composition and abundance and zooplanktivorous fish density. The usefulness of stable isotope analysis on sediment organic matter to track eutrophication is assessed and alternative methods discussed. A current challenge is to determine the effects of recent climate change on lake ecosystems. The impacts of climate change and eutrophication on the ecology of lakes have many similarities making it difficult to disentangle the impact of one from the other, in particular where the eutrophication impacts are greatest. We review a number of recent palaeolimnological studies, in particular those integrating long term monitoring data, which have gone some way to identifying when nutrients or climate may be having the greatest impact. Finally, we discuss possible future directions for the discipline, such as the greater integration of studies of evolutionary change using molecular techniques.     

On the consequences of a long-term perspective for coastal management

The potential impacts of climate change on coastal zones combined with the ever increasing number of people living in these areas, motivate a more long-term perspective in coastal management. To explore whether such a perspective raises the need for developing coastal management strategies at larger spatial scales, this paper presents a case study for the dune-protected Holland coast. Long-term (200 years) coastal management strategies are set-up at different levels of spatial aggregation, accounting for specific characteristics of the coast itself and for types of land use in the hinterland. Using a combination of multi-criteria analysis and cost-benefit analysis the new coastal management strategies are compared to the long-term continuation of present coastal management practice. It appears that the large uncertainties that inevitably accompany a long-term perspective do not preclude the comparison of long-term coastal management strategies. Additionally, it appears that a long-term perspective favors solutions for coastal defense enhancement that are more spatially extended and alongshore uniform than those emerging from continuing today's coastal management practice for two centuries.     

A paleolimnological record of rainfall and drought from East Java, Indonesia during the last 1,400?years

Variations in the location and strength of convection in the Western Pacific Warm Pool (WPWP) have a profound impact on the distribution and amount of global rainfall. Much of the variability in WPWP convection is attributed to variations in the El Ni?o-Southern Oscillation, for which the long-term trends and forcing mechanisms remain poorly understood. Despite the importance of WPWP convection to global climate change, we have very few paleohydrological reconstructions from the region. Here we present a new paleolimnologic and paleohydrologic record spanning the past 1,400 years using a multi-proxy dataset from Lake Logung, located in East Java, Indonesia that provides insights into centennial-scale trends in warm pool hydrology. Organic matter δ¹³C data indicate that East Java became wetter over the last millennium until ca. 1800 Common Era (CE), consistent with evidence for the southward migration of the Intertropical Convergence Zone (ITCZ) during this time. Superimposed on this long-term trend are four decade- to century-scale droughts, inferred from organic matter δ¹³C and calcite abundance data. They are centered at 1030, 1550, 1830, and 1996 CE. The three more recent droughts correlate with hydrologic anomalies documented in other proxy records from the WPWP region on both sides of the equator, and the two most recent droughts correlate in time with historically documented periods of multiple, intense El Ni?o events. Thus, our record provides strong evidence that century-scale hydrologic variability in this region relates to changes in the Walker Circulation. Human activity within the lake catchment is apparent since 1860 CE.