Impact of pulsed Atlantic water inflow into the Alboran Basin at the time of the Zanclean flooding

The study of more than 500 single- and multichannel seismic records enabled the generation of a detailed palaeo-bathymetric map of the Messinian surface over most of the Alboran Basin, Western Mediterranean. This regional surface is characterized by several erosional features (channels, terraces and canyons) and topographic highs (structural, volcanic and diapiric in origin). The most prominent feature is the incised Zanclean Channel crossing the entire basin, its entrenchment having been associated with the opening of the Strait of Gibraltar and subsequent inflow of Atlantic waters. The incision depth of the channel is variable, suggesting local variations in the erosive capacity of the Atlantic inflow, conditioned mainly by the regional basin topography and the local presence of topographic highs. Adjacent to this channel along the Spanish and Moroccan margins, and near the Strait of Gibraltar, several submarine terraces developed at different depths suggest a pulsed flooding of the Alboran Basin. There could have been two major inflow phases of Atlantic water, one shortly before and another during the Zanclean flooding, the latter accompanied by periods of relative sea-level stillstands that enabled terrace development. Alternatively, these features were all generated during the main flooding evident and subsequent pulsed infilling of the basin.     

More than a century of bathymetric observations and present-day shallow sediment characterization in Belfast Bay, Maine, USA: implications for pockmark field longevity

Mechanisms and timescales responsible for pockmark formation and maintenance remain uncertain, especially in areas lacking extensive thermogenic fluid deposits (e.g., previously glaciated estuaries). This study characterizes seafloor activity in the Belfast Bay, Maine nearshore pockmark field using (1) three swath bathymetry datasets collected between 1999 and 2008, complemented by analyses of shallow box-core samples for radionuclide activity and undrained shear strength, and (2) historical bathymetric data (report and smooth sheets from 1872, 1947, 1948). In addition, because repeat swath bathymetry surveys are an emerging data source, we present a selected literature review of recent studies using such datasets for seafloor change analysis. This study is the first to apply the method to a pockmark field, and characterizes macro-scale (>5 m) evolution of tens of square kilometers of highly irregular seafloor. Presence/absence analysis yielded no change in pockmark frequency or distribution over a 9-year period (1999–2008). In that time pockmarks did not detectably enlarge, truncate, elongate, or combine. Historical data indicate that pockmark chains already existed in the 19th century. Despite the lack of macroscopic changes in the field, near-bed undrained shear-strength values of less than 7 kPa and scattered downcore ¹³⁷Cs signatures indicate a highly disturbed setting. Integrating these findings with independent geophysical and geochemical observations made in the pockmark field, it can be concluded that (1) large-scale sediment resuspension and dispersion related to pockmark formation and failure do not occur frequently within this field, and (2) pockmarks can persevere in a dynamic estuarine setting that exhibits minimal modern fluid venting. Although pockmarks are conventionally thought to be long-lived features maintained by a combination of fluid venting and minimal sediment accumulation, this suggests that other mechanisms may be equally active in maintaining such irregular seafloor morphology. One such mechanism could be upwelling within pockmarks induced by near-bed currents.     

Downscaling projections of climate change in Sao Tome and Principe Islands,Africa

Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work.     

Emission metrics under the 2 °C climate stabilization target

In multi-gas climate policies such as the Kyoto Protocol one has to decide how to compare the emissions of different greenhouse gases. The choice of metric could have significant implications for mitigation priorities considered under the prospective negotiations for climate mitigation agreements. Several metrics have been proposed for this task with the Global Warming Potential (GWP) being the most common. However, these metrics have not been systematically compared to each other in the context of the 2 °C climate stabilization target. Based on a single unified modeling framework, we demonstrate that metric values span a wide range, depending on the metric structure and the treatment of the time dimension. Our finding confirms the basic salient point that metrics designed to represent different aspects of the climate and socio-economic system behave differently. Our result also reflects a complex interface between science and policy surrounding metrics. Thus, it is important to select or design a metric suitable for climate stabilization based on an interaction among practitioners, policymakers, and scientists.     

Linking Cree hunters’ and scientific observations of changing inland ice and meteorological conditions in the subarctic eastern James Bay region, Canada

For the Cree First Nation communities of the eastern James Bay region in the Canadian Subarctic, local weather plays a key role in traditional subsistence activities. There is rising concern among the Cree about changes in inland ice conditions as they pose challenges to Cree livelihood, health and culture. Here we contrast Crees’ observations of inland ice conditions and long-term measurements obtained to foster interdisciplinary climate change research between scientists and Cree communities. We compiled qualitative observations of inland ice conditions and compared them with long-term measurements (> 25 years) of air temperature, precipitation and snow depth from three meteorological stations in the Cree territory. Cree hunters observed a weakening of lake ice cover (e.g., change in ice composition and structure, increased rain in winter). Trend analysis of long-term measurements showed a significant increase in mean autumn air temperature as well as in winter and autumn precipitation. By contrasting Cree hunters’ observations with climate data, we identified that an increase in fall and winter precipitation could be causing a weakening of inland ice through a change in its composition (i.e., snow ice instead of congelation ice). We conclude that Cree and scientific knowledge are complementary when investigating and understanding climate change in the Subarctic.     

Multi-model projections of twenty-first century North Pacific winter wave climate under the IPCC A2 scenario

A dynamical wave model implemented over the North Pacific Ocean was forced with winds from three coupled global climate models (CGCMs) run under a medium-to-high scenario for greenhouse gas emissions through the twenty-first century. The results are analyzed with respect to changes in upper quantiles of significant wave height (90th and 99th percentile H_S) during boreal winter. The three CGCMs produce surprisingly similar patterns of change in winter wave climate during the century, with waves becoming 10–15 % smaller over the lower mid-latitudes of the North Pacific, particularly in the central and western ocean. These decreases are closely associated with decreasing windspeeds along the southern flank of the main core of the westerlies. At higher latitudes, 99th percentile wave heights generally increase, though the patterns of change are less uniform than at lower latitudes. The increased wave heights at high latitudes appear to be due a variety of wind-related factors including both increased windspeeds and changes in the structure of the wind field, these varying from model to model. For one of the CGCMs, a commonly used statistical approach for estimating seasonal quantiles of H_S on the basis of seasonal mean sea level pressure (SLP) is used to develop a regression model from 60 years of twentieth century data as a training set, and then applied using twenty-first century SLP data. The statistical model reproduces the general pattern of decreasing twenty-first century wave heights south of ~40 N, but underestimates the magnitude of the changes by ~50–70 %, reflecting relatively weak coupling between sea level pressure and wave heights in the CGCM data and loss of variability in the statistically projected wave heights.     

The role of vegetation feedbacks on Greenland glaciation

The role of vegetation feedbacks for the process of ice-sheet evolution could potentially be important in realistically modeling the past and future evolution of the Greenland ice-sheet. We use a fully coupled atmosphere–ocean model to assess the response of the climate when the Greenland ice-sheet is replaced with a number of fixed vegetation types (bare soil, broadleaf and needleleaf trees, C3 and C4 grasses and shrubs) in conjunction with loaded and unloaded bedrock orography. These sensitivity experiments show that albedo changes dominate the climate response during the summer months while temperature changes during winter are attributed to altitude change and changes in atmospheric circulation over Greenland. Snow-free summers occur for all fixed vegetation types, except for high altitude eastern regions for bare soil. We perform further simulations with dynamic vegetation resulting in dominant shrub coverage over central and southern Greenland with grasses supported in the north. Ice-sheet modeling shows significant regrowth of the Greenland ice-sheet can occur for a bare soil surface type, dependent on ice-sheet model parameters, while Greenland remains almost ice-free for needleleaf tree coverage. Furthermore, a realistically vegetated Greenland can only support a small amount of ice-sheet regrowth implying multi-stability of the Greenland ice-sheet under a preindustrial climate. This study highlights the importance of considering vegetation climate ice-sheet interactions, and uncertainty in ice-sheet model parameters.     

Cyanobacteria and microcystin in the Nebraska (USA) Sand Hills Lakes before and after modern agriculture

Chlorophyll a, zeaxanthin, and pheophytin a were measured from sediment core samples from three lakes (Dewey, Island, and Two Mile Lakes) in the Nebraska Sand Hills. Pigments were extracted and identified by high performance liquid chromatography (HPLC) and used to estimate changes in the relative proportion of cyanobacteria to the algal community. The cyanobacterial toxins microcystin-LR and LA were extracted and measured using electrospray ionization liquid chromatography tandem mass spectrometry (LC/MS/MS). Microcystin-LR was found in core sections estimated to be as early as 1832, and was present in all three lake cores. Pigment and toxin data were used to determine if there were changes that occurred in the algal community structure with the onset of modernized agriculture in the region. No significant changes were found in the relative percent of cyanobacteria or chlorophyll a accumulation, indicating the frequency and intensity of cyanobacterial blooms has not changed over the last century. Despite this trend, there was a dramatic increase in microcystin-LR accumulation during the 1980s in Dewey Lake, which may be human induced.     

多粒度的人群移动模拟通用模型及其应用

人群的移动模拟应用广泛,但为不同时空尺度模拟需求开发不同的模拟系统十分困难和繁琐。该文设计了一种人群的空间移动模型(GMPM),GMPM具有多粒度特性,可应用于不同的领域,满足不同空间尺度、时间尺度的人群移动模拟需求;同时,GMPM又是一种通用开发模型原型,基于GMPM可以构造针对不同应用领域的人群空间移动模拟模型。最后,介绍了不同时空尺度人群移动模拟应用案例。