Consequences of change and variability in sea ice on marine ecosystem and biogeochemical processes during the 2007–2008 Canadian International Polar Year program     

David G. Barber  Matthew G. Asplin  Tim N. Papakyriakou  Lisa Miller  Brent G. T. Else  John Iacozza  C. J. Mundy  M. Gosslin  Natalie C. Asselin  Steve Ferguson  Jennifer V. Lukovich  Gary A. Stern  Ashley Gaden  Monika Pu?ko  N.-X. Geilfus  Fei Wang 《Climatic change》2012,115(1):135-159

Change and variability in the timing and magnitude of sea ice geophysical and thermodynamic state have consequences on many aspects of the arctic marine system. The changes in both the geophysical and thermodynamic state, and in particular the timing of the development of these states, have consequences throughout the marine system. In this paper we review the ??consequences?? of change in sea ice state on primary productivity, marine mammal habitats, and sea ice as a medium for storage and transport of contaminants and carbon exchange across the ocean-sea-ice-atmosphere interface based upon results from the International Polar Year. Pertinent results include: 1) conditions along ice edges can bring deep nutrient-rich ??pacific?? waters into nutrient-poor surface waters along the arctic coast, affecting local food webs; 2) both sea ice thermodynamic and dynamic processes ultimately affect ringed seal/polar bear habitats by controlling the timing, location and amount of surface deformation required for ringed seal and polar bear preferred habitat 3) the ice edges bordering open waters of flaw leads are areas of high biological production and are observed to be important beluga habitat. 4) exchange of climate-active gases, including CO₂, is extremely active in sea ice environments, and the overall question of whether the Arctic Ocean is (or will be) a source or sink for CO₂ will be dependent on the balance of competing climate-change feedbacks.  相似文献   

Preparing for climate change in Washington State     

Lara C. Whitely Binder  Jennifer Krencicki Barcelos  Derek B. Booth  Meriel Darzen  Marketa McGuire Elsner  Richard Fenske  Thomas F. Graham  Alan F. Hamlet  John Hodges-Howell  J. Elizabeth Jackson  Catherine Karr  Patrick W. Keys  Jeremy S. Littell  Nathan Mantua  Jennifer Marlow  Don McKenzie  Michael Robinson-Dorn  Eric A. Rosenberg  Claudio O. Stöckle  Julie A. Vano 《Climatic change》2010,102(1-2):351-376

Climate change is expected to bring potentially significant changes to Washington State’s natural, institutional, cultural, and economic landscape. Addressing climate change impacts will require a sustained commitment to integrating climate information into the day-to-day governance and management of infrastructure, programs, and services that may be affected by climate change. This paper discusses fundamental concepts for planning for climate change and identifies options for adapting to the climate impacts evaluated in the Washington Climate Change Impacts Assessment. Additionally, the paper highlights potential avenues for increasing flexibility in the policies and regulations used to govern human and natural systems in Washington.  相似文献   

Uranium diagenesis in sediments underlying bottom waters with high oxygen content     

Jennifer L. Morford  William R. Martin 《Geochimica et cosmochimica acta》2009,73(10):2920-7276

We measured U in sediments (both pore waters and solid phase) from three locations on the middle Atlantic Bight (MAB) from the eastern margin of the United States: a northern location on the continental shelf off Massachusetts (OC426, 75 m water depth), and two southern locations off North Carolina (EN433-1, 647 m water depth and EN433-2, 2648 m water depth). These sediments underlie high oxygen bottom waters (250-270 μM), but become reducing below the sediment-water interface due to the relatively high organic carbon oxidation rates in sediments (EN433-1: 212 μmol C/cm²/y; OC426: 120 ± 10 μmol C/cm²/y; EN433-2: 33 μmol C/cm²/y). Pore water oxygen goes to zero by 1.4-1.5 cm at EN433-1 and OC426 and slightly deeper oxygen penetration depths were measured at EN433-2 (∼4 cm).All of the pore water profiles show removal of U from pore waters. Calculated pore water fluxes are greatest at EN433-1 (0.66 ± 0.08 nmol/cm²/y) and less at EN433-2 and OC426 (0.24 ± 0.05 and 0.13 ± 0.05 nmol/cm²/y, respectively). Solid phase profiles show authigenic U enrichment in sediments from all three locations. The average authigenic U concentrations are greater at EN433-1 and OC426 (5.8 ± 0.7 nmol/g and 5.4 ± 0.2 nmol/g, respectively) relative to EN433-2 (4.1 ± 0.8 nmol/g). This progression is consistent with their relative ordering of ‘reduction intensity’, with greatest reducing conditions in sediments from EN433-1, less at OC426 and least at EN433-2. The authigenic U accumulation rate is largest at EN433-1 (0.47 ± 0.05 nmol/cm²/y), but the average among the three sites on the MAB is ∼0.2 nmol/cm²/y. Pore water profiles suggest diffusive fluxes across the sediment-water interface that are 1.4-1.7 times greater than authigenic accumulation rates at EN433-1 and EN433-2. These differences are consistent with oxidation and loss of U from the solid phase via irrigation and/or bioturbation, which may compromise the sequestration of U in continental margin sediments that underlie bottom waters with high oxygen concentrations.Previous literature compilations that include data exclusively from locations where [O₂]_bw < 150 μM suggest compelling correlations between authigenic U accumulation and organic carbon flux to sediments or organic carbon burial rate. Sediments that underlie waters with high [O₂]_bw have lower authigenic U accumulation rates than would be predicted from relationships developed from results that include locations where [O₂]_bw < 150 μM.  相似文献   

The pulsating DA white dwarf star EC 14012−1446: results from four epochs of time-resolved photometry     

G. Handler  E. Romero-Colmenero  J. L. Provencal  K. Sanchawala  M. A. Wood  I. Silver  W.-P. Chen 《Monthly notices of the Royal Astronomical Society》2008,388(3):1444-1456

The pulsating DA white dwarfs are the coolest degenerate stars that undergo self-driven oscillations. Understanding their interior structure will help us to understand the previous evolution of the star. To this end, we report the analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA white dwarf star EC 14012−1446 acquired during four observing epochs in three different years, including a coordinated three-site campaign. A total of 19 independent frequencies in the star's light variations together with 148 combination signals up to fifth order could be detected. We are unable to obtain the period spacing of the normal modes and therefore a mass estimate of the star, but we infer a fairly short rotation period of  0.61 ±0.03 d  , assuming the rotationally split modes are  ℓ= 1  . The pulsation modes of the star undergo amplitude and frequency variations, in the sense that modes with higher radial overtone show more pronounced variability and that amplitude changes are always accompanied by frequency variations. Most of the second-order combination frequencies detected have amplitudes that are a function of their parent mode amplitudes, but we found a few cases of possible resonantly excited modes. We point out the complications in the analysis and interpretation of data sets of pulsating white dwarfs that are affected by combination frequencies of the form   f _A + f _B − f _C   intruding into the frequency range of the independent modes.  相似文献   

Southern high latitude climate variability in the Late Cretaceous greenhouse world     

Stephen J. Gallagher  Barbara E. Wagstaff  Jennifer G. Baird  Malcolm W. Wallace  Chung Leong Li 《Global and Planetary Change》2008,60(3-4):351-364

A palynological study of oil exploration wells in the Gippsland Basin southeastern Australia has provided a record of southern high latitude climate variability for the last 12 million years of the Cretaceous greenhouse world. During this time, the vegetation was dominated by a cool to temperate flora of Podocarpaceae, Proteaceae and Nothofagidites spp. at a latitude of 60°S. Milankovitch forced cyclic alternations from drier to wetter climatic periods caused vegetation variability from 72 to 77 Ma. This climate change was probably related to the waxing and waning of ephemeral (100 ky) small ice sheets in Antarctica during times of insolation minima and maxima. Drying and cooling after 72 Ma culminated from 68 to 66 Ma, mirroring trends in global δ¹⁸O data. Quantitative palynofloral analyses have the potential to provide realistic proxies for small-scale climate variability in the predominantly ice-free Late Cretaceous.  相似文献   

Cover crops and precipitation influence soluble reactive phosphorus losses via tile drain discharge in an agricultural watershed     

Matt T. Trentman  Jennifer L. Tank  Todd V. Royer  Shannon L. Speir  Ursula H. Mahl  Lienne R. Sethna 《水文研究》2020,34(23):4446-4458

Subsurface tile drainage speeds water removal from agricultural fields that are historically prone to flooding. While managed drainage systems improve crop yields, they can also contribute tothe eutrophication of downstream ecosystems, as tile-drained systems are conduits for nutrients to adjacent waterways. The changing climate of the Midwestern US has already altered precipitation regimes which will likely continue into the future, with unknown effects on tile drain water and nutrient loss to waterways. Adding vegetative cover (i.e., as winter cover crops) is one approach that can retain water and nutrients on fields to minimize export via tile drains. In the current study, we evaluate the effect of cover crops on tile drain discharge and soluble reactive phosphorus (SRP) loads using bi-monthly measurements from 43 unique tile outlets draining fields with or without cover crops in two watersheds in northern Indiana. Using four water years of data (n = 844 measurements), we examined the role of short-term antecedent precipitation conditions and variation in soil biogeochemistry in mediating the effect of cover crops on tile drain flow and SRP loads. We observed significant effects of cover crops on both tile drain discharge and SRP loads, but these results were season and watershed specific. Cover crop effects were identified only in spring, where their presence reduced tile drain discharge in both watersheds and SRP loads in one watershed. Varying effects on SRP loads between watersheds were attributed to different soil biogeochemical characteristics, where soils with lower bioavailable P and higher P sorption capacity were less likely to have a cover crop effect. Antecedent precipitation was important in spring, and cover crop differences were still evident during periods of wet and dry antecedent precipitation conditions. Overall, we show that cover crops have the potential to significantly decrease spring tile drain P export, and these effects are resilient to a wide range of precipitation conditions.  相似文献   

Watershed-scale vegetation,water quantity,and water quality responses to wildfire in the southern Appalachian mountain region,United States     

Peter V. Caldwell  Katherine J. Elliott  Ning Liu  James M. Vose  David R. Zietlow  Jennifer D. Knoepp 《水文研究》2020,34(26):5188-5209

Wildfires are landscape scale disturbances that can significantly affect hydrologic processes such as runoff generation and sediment and nutrient transport to streams. In Fall 2016, multiple large drought-related wildfires burned forests across the southern Appalachian Mountains. Immediately after the fires, we identified and instrumented eight 28.4–344 ha watersheds (four burned and four unburned) to measure vegetation, soil, water quantity, and water quality responses over the following two years. Within burned watersheds, plots varied in burn severity with up to 100% tree mortality and soil O-horizon loss. Watershed scale high burn severity extent ranged from 5% to 65% of total watershed area. Water quantity and quality responses among burned watersheds were closely related to the high burn severity extent. Total water yield (Q) was up to 39% greater in burned watersheds than unburned reference watersheds. Total suspended solids (TSS) concentration during storm events were up to 168 times greater in samples collected from the most severely burned watershed than from a corresponding unburned reference watershed, suggesting that there was elevated risk of localized erosion and sedimentation of streams. NO₃-N concentration, export, and concentration dependence on streamflow were greater in burned watersheds and increased with increasing high burn severity extent. Mean NO₃-N concentration in the most severely burned watershed increased from 0.087 mg L⁻¹ in the first year to 0.363 mg L⁻¹ (+317%) in the second year. These results suggest that the 2016 wildfires degraded forest condition, increased Q, and had negative effects on water quality particularly during storm events.  相似文献   

Extracting drainage networks and their connectivity using LiDAR data          下载免费PDF全文

Jennifer Roelens  Ine Rosier  Stefaan Dondeyne  Jos Van Orshoven  Jan Diels 《水文研究》2018,32(8):1026-1037

Policies, measures, and models geared towards flood prevention and managing surface waters benefit from high quality data on the presence and characteristics of drainage ditches. As a cost and labour effective alternative for acquiring such data through field surveys, we propose a method (a) to extract vector data representing ditch drainage networks based on local morphologic features derived from high resolution digital elevation models (DEM) and (b) to identify possible connections in the ditch network by calculating a probability of the connectivity using a logistic regression where the predictor variables are characteristics of the ditch centre lines or derived from the DEM. Using Light Detection and Ranging (LiDAR) derived DEMs with a 1 m resolution, the method was developed and tested for a mixed agricultural residential area in north‐eastern Belgium. The derived ditch segments had an error of omission of 8% and an error of commission of 5%. The original positional accuracy of the centre lines of the extracted ditches was 0.6 m and could be improved to 0.4 m by shifting each vertex to the position of the lowest LiDAR point located within a radius equal to the spatial resolution of the used DEM. About 69% of the false disconnections in the network were identified and corrected leading to a reduction of the unconnected parts of the ditch network by 71%. The extracted and connected network approximated the reference ditch network fairly well.  相似文献   

Cities within cities: intra-urban comparison of infrastructure in Mumbai,Delhi and Cape Town     

Colin McFarlane  Jonathan Silver  Yaffa Truelove 《Urban geography》2017,38(9):1393-1417

Comparison is now taken as vital to the constitution of knowledge about cities and urbanism. However, debate on comparative urbanism has been far more attentive to the merits of comparisons between cities than it has been to the potential and challenges of comparisons within cities—to what we call “Intra-Urban Comparison” (IUC). We argue that a focus on the diverse forms of urbanism located within cities may generate critical knowledge for both intra- and inter-urban comparative projects. IUCs highlight the diversity inherent in the category “city,” revealing dimensions of the urban that are central to how cities work and are experienced. We mobilise fieldwork within three cities: Mumbai, Delhi and Cape Town, and consider both how these cities have been historically understood as different urban worlds within a city, and discuss key findings from IUCs we have conducted on infrastructures. We find that IUCs can enhance comparative work both within and between cities: reconceptualising urban politics; attending to the varied and contradictory trajectories of urban life; and bringing visibility to the diverse routes through which progressive change can occur.  相似文献   

Stable carbon isotopes (δ<Superscript>13</Superscript>C) of total organic carbon and long-chain <Emphasis Type="Italic">n</Emphasis>-alkanes as proxies for climate and environmental change in a sediment core from Lake Petén-Itzá, Guatemala     

Jennifer L. Mays  Mark Brenner  Jason H. Curtis  Kathryn V. Curtis  David A. Hodell  Alex Correa-Metrio  Jaime Escobar  Andrea L. Dutton  Andrew R. Zimmerman  Thomas P. Guilderson 《Journal of Paleolimnology》2017,57(4):307-319

Sediment core PI-6 from Lake Petén Itzá, Guatemala, possesses an ~85-ka record of climate and environmental change from lowland Central America. Variations in sediment lithology suggest large and abrupt changes in precipitation during the last glacial and deglacial periods, and into the early Holocene. We measured stable carbon isotope ratios of total organic carbon and long-chain n-alkanes from the core, the latter representing a largely allochthonous (terrestrial) source of organic matter, to reveal past shifts in the relative proportion of C₃–C₄ terrestrial biomass. We sought to test whether stable carbon isotope results were consistent with other paleoclimate proxies measured in the PI-6 core, and if extraction and isotope analysis of n-alkanes is warranted. The largest δ¹³C variations are associated with Heinrich Events. Carbon isotope values in sediments deposited during the last glacial maximum indicate moderate precipitation with little fluctuation. The deglacial was a period of pronounced climate variability, e.g. a relatively warm and moist Bølling–Allerød, but a cool and dry Younger Dryas. Arid periods of the deglacial were inferred from samples with high δ¹³C values in total organic carbon, which reflect times of greater proportions of C₄ plants. These inferences are supported by stable isotope measurements on ostracod shells and relative abundance of grass pollen from the same depths in core PI-6. Similar trends in carbon stable isotopes measured on bulk organic carbon and n-alkanes suggest that carbon isotope measures on bulk organic carbon in sediments from this lake are sufficient to infer past climate-driven shifts in local vegetation.  相似文献