Estimating long-term soil respiration rates from carbon isotopes occluded in gibbsite

Carbon occluded in the soil gibbsite crystal structure at the Panola Mountain Research Watershed, Georgia, U.S. is presumed to be in isotopic equilibrium with the CO₂ respired from soil organics by microbes and plant roots. Fitting of the stable carbon isotopic data to a Fickian diffusion-based depth function results in an estimate of 47 gC m⁻² y⁻¹ for the long-term soil respiration rate. A numerical model that includes depth-dependent production and diffusion terms results in estimates of 28-12 gC m⁻² y⁻¹. These values range from 15 to 50 times less than the average of modern values for mixed deciduous forests in wet temperate climates. This disparity has several implications for our understanding of the geologic record of climate change, which include: (1) evidence for a cooler and seasonally drier climate during the mid-Holocene in the southeastern U.S., or (2) fluxes of carbon from the soil pool as recorded by soil mineral proxies (i.e., long-term soil respiration rates) under estimate atmosphere annual carbon flux measurements (i.e., short-term measures), and (3) the need to refine soil respiration models used to relate paleosol stable carbon isotopic measurements to paleo-atmospheric estimates.     

A multi-proxy lacustrine record of Holocene climate change on northeastern Baffin Island, Arctic Canada

Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomid-inferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5°C warmer than historic summer temperatures from 10,000 to 8500 cal yr B.P. Following rapid cooling 8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern Canada. However, the lacustrine proxies in Lake CF3 apparently responded to insolation-driven warmth, despite the proximity of Lake CF3 to the Laurentide Ice Sheet and its meltwater. The magnitude and timing of the Holocene thermal maximum at Lake CF3 indicate that temperatures and environmental conditions at this site are highly sensitive to changes in radiative forcing.     

A comparison of permafrost prediction models along a section of Trail Ridge Road, Rocky Mountain National Park, Colorado, USA

The distribution of mountain permafrost along Trail Ridge Road (TRR) in Rocky Mountain National Park, Colorado, was modeled using ‘frost numbers’ and a ‘temperature of permafrost model’ (TTOP) in order to assess the accuracy of prediction models. The TTOP model is based on regional observations of air temperature and heat transfer functions involving vegetation, soil, and snow; whereas the frost number model is based on site-specific ratios of ground temperature measurements of frozen and thawed degree-days. Thirty HOBO© temperature data loggers were installed near the surface as well as at depth (30 to 85 cm). From mid-July 2008 to 2010, the mean annual soil temperature (MAST) for all surface sites was − 1.5 °C. Frost numbers averaged 0.56; TTOP averaged − 1.8 °C. The MAST was colder on western-facing slopes at high elevations. Surface and deeper probes had similar MASTs; however, deeper probes had less daily and seasonal variation. Another model developed at the regional scale based on proxy indicators of permafrost (rock glaciers and land cover) classified 5.1 km² of permafrost within the study area, whereas co-kriging interpolations of frost numbers and TTOP data indicated 2.0 km² and 4.6 km² of permafrost, respectively. Only 0.8 km² were common among all three models. Three boreholes drilled within 2 m of TRR indicate that permafrost does not exist at these locations despite each borehole being classified as containing permafrost by at least one model. Addressing model uncertainty is important because nutrients stored within frozen or frost-affected soils can be released and impact alpine water bodies. The uncertainty also exposes two fundamental problems: empirical models designed for high latitudes are not necessarily applicable to mountain permafrost, and the presence of mountain permafrost in the alpine tundra of the Colorado Front Range has not been validated.     

The level and nature of sustainability for clusters of abandoned limestone quarries in the southern Palestinian West Bank

The question of how sustainable a mining site is at the end of its operational life has been somewhat unanswered. The fundamental problem has been how to evaluate the sustainability of a mining site once operations cease and is abandoned. Environmental Impact Assessment (EIA) is certainly a way to evaluate sustainability of such sites, but only through inference and subjective evaluation. This is because the topic of sustainability still hotly debated, and is predominantly focussed on an anthropocentric approach. Even with quantitative-based EIAs, the question is how to directly evaluate sustainability from the data available using a consistent quantitative approach rather than on a case-by-case basis or subjective evaluation.However, by using the ideas and concepts concerning the coupled relationship between the environment and humans prevalent in sustainability science, the question of what is and how to evaluate sustainability has become capable of being answered. Based on previous work of the author in the development and application of a mathematical model of sustainability, the paper applies the model to the results of a quantitative EIA evaluation for nine clusters of abandoned limestone quarries located in the southern Palestinian West Bank.The results indicate that seven of the nine clusters were deemed to be unsustainable, whilst the other two clusters were considered as sustainable at a very weak level only. The results are discussed within the broader context of the coupled environment-human system using one of the supporting frameworks for the development and application of the mathematical model of sustainability: Earth System Analysis. Within this context, the discussion indicates the fact that unmanaged impacts by humans has created the situation for unsustainability to occur. The paper therefore provides for the clearest indication yet of the nature of sustainability at the end of the mining operational life-cycle without an effective and proper management strategy or policies.     

Leaf wax δ2H and varve-thickness climate proxies from proglacial lake sediments, Baffin Island, Arctic Canada

We present a multiproxy paleoclimate record using leaf wax hydrogen isotopes (??²H_wax) and varve thickness from Arctic proglacial lake sediments. We also provide one of the first evaluations of the utility of ??²H_wax as a paleoclimate proxy in Arctic proglacial lakes. We compare varve thickness and ??²H_wax at sub-decadal resolution from 1948 to 2004 AD, and at sub-centennial resolution from 1450 to 2004 AD. Varve thickness and ??²H_wax both contain large interannual variability and are anti-correlated during the late twentieth century, suggesting that both proxies respond rapidly, but by different mechanisms, to catchment-scale forcings. At longer time scales, varve thickness exhibits a strong response to Little Ice Age cooling (1661?C1827 AD in this record) but does not show evidence for twentieth century warming recorded throughout the Arctic. ??²H_wax does record regional-scale temperature changes, with more ²H-depleted values during the Little Ice Age and an abrupt change to more ²H-enriched values in the twentieth century. This corresponds well with a recent Arctic-wide temperature reconstruction in which the seventeenth century is the coldest interval, and the twentieth century is the warmest interval. Our results suggest that ??²H_wax is a promising proxy that can be applied at high resolution in proglacial Arctic lakes.     

Thermal evolution of Kuiper belt objects, with implications for cryovolcanism

We investigate the internal thermal evolution of Kuiper belt objects (KBOs), small (radii <1000 km), icy (mean densities ) bodies orbiting beyond Neptune, focusing on Pluto's moon Charon in particular. Our calculations are time-dependent and account for differentiation. We review evidence for ammonia hydrates in the ices of KBOs, and include their effects on the thermal evolution. A key finding is that the production of the first melt, at the melting point of ammonia dihydrate, ≈176 K, triggers differentiation of rock and ice. The resulting structure comprises a rocky core surrounded by liquids and ice, enclosed within a >100-km thick undifferentiated crust of rock and ice. This structure is especially conducive to the retention of subsurface liquid, and bodies the size of Charon or larger (radii >600 km) are predicted to retain some subsurface liquid to the present day. We discuss the possibility that this liquid can be brought to the surface rapidly via self-propagating cracks. We conclude that cryovolcanism is a viable process expected to affect the surfaces of large KBOs including Charon.     

The geology of Hotei Regio, Titan: Correlation of Cassini VIMS and RADAR

Joint Cassini VIMS and RADAR SAR data of ∼700-km-wide Hotei Regio reveal a rich collection of geological features that correlate between the two sets of images. The degree of correlation is greater than anywhere else seen on Titan. Central to Hotei Regio is a basin filled with cryovolcanic flows that are anomalously bright in VIMS data (in particular at 5 μm) and quite variable in roughness in SAR. The edges of the flows are dark in SAR data and appear to overrun a VIMS-bright substrate. SAR-stereo topography shows the flows to be viscous, 100-200 m thick. On its southern edge the basin is ringed by higher (∼1 km) mountainous terrain. The mountains show mixed texture in SAR data: some regions are extremely rough, exhibit low and spectrally neutral albedo in VIMS data and may be partly coated with darker hydrocarbons. Around the southern margin of Hotei Regio, the SAR image shows several large, dendritic, radar-bright channels that flow down from the mountainous terrain and terminate in dark blue patches, seen in VIMS images, whose infrared color is consistent with enrichment in water ice. The patches are in depressions that we interpret to be filled with fluvial deposits eroded and transported by liquid methane in the channels. In the VIMS images the dark blue patches are encased in a latticework of lighter bands that we suggest to demark a set of circumferential and radial fault systems bounding structural depressions. Conceivably the circular features are tectonic structures that are remnant from an ancient impact structure. We suggest that impact-generated structures may have simply served as zones of weakness; no direct causal connection, such as impact-induced volcanism, is implied. We also speculate that two large dark features lying on the northern margin of Hotei Regio could be calderas. In summary the preservation of such a broad suite of VIMS infrared color variations and the detailed correlation with features in the SAR image and SAR topography evidence a complex set of geological processes (pluvial, fluvial, tectonic, cryovolcanic, impact) that have likely remained active up to very recent geological time (<10⁴ year). That the cryovolcanic flows are excessively bright in the infrared, particularly at 5 μm, might signal ongoing geological activity. One study [Nelson, R.M., and 28 colleagues, 2009. Icarus 199, 429-441] reported significant 2-μm albedo changes in VIMS data for Hotei Arcus acquired between 2004 and 2006, that were interpreted as evidence for such activity. However in our review of that work, we do not agree that such evidence has yet been found.     

An architecture for government action on adaptation to climate change. An editorial comment

An architecture of government adaptation programs is presented. Components include leadership, institutional organization, stakeholder involvement, climate change information, appropriate use of decision analysis techniques, explicit consideration of barriers to adaptation, funding for adaptation, technology development and diffusion, and adaptation research. This architecture is a useful heuristic for identifying, evaluating, and reevaluating the needs of decision makers as they improve management of climate-sensitive resources in a changing environment.     

Understanding uncertainty in future projections for the tropical Atlantic: relationships with the unforced climate

Through its control on the marine ITCZ, future changes in the tropical Atlantic meridional sea-surface temperature gradient (TAG) could have important impacts, on regional to global scales. We study the inter-model spread of projected TAG trends in response to increasing CO₂, using results from 19 coupled GCMs which took part in the IPCC fourth assessment. Some models project substantial changes, with the smallest changes being in boreal autumn. There is substantial uncertainty, with no consistency even in the sign of change, and an ensemble mean close to zero. However, a strong statistical relationship is found between the simulated magnitudes of TAG trends and unforced TAG variability. Models with larger unforced variability in December–February show larger magnitude trends. We speculate that this relationship may be due to an underlying system of feedbacks whose strength varies considerably from model to model (the unforced variability ranges by a factor of 3 amongst these models, and the models exhibit large differences in mean state). We present evidence from further analysis and the literature to suggest which physical mechanisms may be involved. In particular, models projecting larger(smaller) magnitude TAG trends have larger(smaller) SST variability and cooler(warmer) mean SST in not just the Atlantic, but all three tropical/sub-tropical oceans, especially in the southern hemisphere near eastern coasts. These results could assist efforts to understand model errors in present and future tropical climate, and to develop observational constraints on future tropical projections.     

The East Asian monsoon during MIS 2 expressed in a speleothem δO record from Jintanwan Cave, Hunan, China

Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ¹⁸O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∼29.5 to 14.7 ka and from ∼12.9 to 11.0 ka. At the time of the last glacial maximum (LGM), the East Asian summer monsoon weakened and then strengthened in response to changes in Northern Hemisphere insolation. As the ice sheets retreated the East Asian summer monsoon weakened, especially during Heinrich event H1, when atmospheric and oceanic teleconnections transferred the climatic changes around the North Atlantic to the monsoonal regions of Eastern Asia. A depositional hiatus between ∼14.7 and 12.9 ka leaves the deglacial record incomplete, but an abrupt shift in δ¹⁸O values at ∼11.5 ka marks the end of the Younger Dryas and the transition into the Holocene. Comparisons of the J1 record to other Chinese speleothem records indicate synchronous climatic changes throughout monsoonal China. Further comparisons to a speleothem record from western Asia (Socotra Island) and to Greenland ice cores support hemispherical-scale paleoclimatic change. Spectral and wavelet analyses reveal centennial- and decadal-scale periodicities that correspond to solar frequencies and to oscillations in atmospheric and oceanic circulation.