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1.
Long-term changes in summer phytoplankton communities of the open northern Baltic Sea 总被引：16，自引：0，他引：16
Sanna Suikkanen Maria Laamanen Maija Huttunen 《Estuarine, Coastal and Shelf Science》2007,71(3-4):580-592
Changes in the biomass and species composition of phytoplankton may reflect major shifts in environmental conditions. We investigated relationships between the late summer biomass of different phytoplankton taxa and environmental factors, and their long-term (1979–2003) trends in two areas of the Baltic Sea, the northern Baltic proper (NBP) and the Gulf of Finland (GF), with statistical analyses. An increasing trend was found in late summer temperature and chlorophyll a of the surface water layer (0–10 m) in both areas. There was also a significant decrease in summer salinity and an increase in winter dissolved inorganic nitrogen to phosphorus (DIN:DIP) ratio in the NBP, as well as increases in winter DIN concentrations and DIN:SiO4 ratio in the GF. Simultaneously, the biomass of chrysophytes and chlorophytes increased in both areas. In the NBP, also the biomass of dinophytes increased and that of euglenophytes decreased, whereas in the GF, cyanobacteria increased and cryptophytes decreased. Redundancy analysis (RDA) indicated that summer temperature and winter DIN concentration were the most important factors with respect to changes in the phytoplankton community structure. Thus, the phytoplankton communities seem to reflect both hydrographic changes and the ongoing eutrophication process in the northern Baltic Sea. 相似文献
2.
The Olmedo bauxite deposit occurs in the Nurra district of northwest Sardinia. It forms a stratiform horizon in Cretaceous
limestone and marl. Uplift in mid-Cretaceous had exposed recently deposited limestone to karst weathering, and a layer of
argillaceous debris accumulated on its surface and was partly converted to bauxite. Intermediate products were desiccated
marl, bauxitic argillite and argillaceous bauxite. Subsidence followed, and the bauxite was preserved by the deposition of
late Cretaceous limestone and other sediments. Uplift in Oligocene-Miocene time, with ensuing erosion, exposed the bauxite
horizon to its present configuration. Concentrations of normative minerals illustrate chemical processes and the build-up
of Al in the bauxite horizon. Plots of chemical data and correlation coefficients show that Al, Ti, Zr, Nb, Th, Cr and V were
immobile during the bauxitization process. Mass changes point to large net removal of Si, Mg and K from the system, although
some of this material and slightly mobile Al were reprecipitated in the underlying argillite and altered marl. Immobile element
ratios trace the source of the bauxite to the underlying argillaceous limestone. Al in the bauxite was accumulated from the
degradation of 25 to 50 m of the argillaceous limestone.
Received: 10 June 1996 / Accepted: 15 April 1997 相似文献
3.
Sanna HOLM Carl ALWMARK Walter ALVAREZ Birger SCHMITZ 《Meteoritics & planetary science》2011,46(12):1888-1909
Abstract– The Siljan impact structure in Sweden is the largest confirmed impact structure in Western Europe. Despite this, the structure has been poorly studied in the past, and detailed studies of shock metamorphic features in the target lithologies are missing. Here, we present the results of a detailed systematic search for shock metamorphic features in quartz grains from 73 sampled localities at Siljan. At 21 localities from an area approximately 20 km in diameter located centrally in the structure, the orientations of 2851 planar deformation feature sets in 1179 quartz grains were measured. Observations of shatter cones outside of the zone with shocked quartz extend the total shocked area to approximately 30 km in diameter. The most strongly shocked samples, recording pressures of up to 20 GPa, occur at the very central part of the structure, and locally in these samples, higher pressures causing melting conditions in the affected rocks were reached. Pressures recorded in the studied samples decrease outwards from the center of the structure, forming roughly circular envelopes around the proposed shock center. Based on the distribution pattern of shocked quartz at Siljan, the original transient cavity can be estimated at approximately 32–38 km in diameter. After correcting for erosion, we conclude that the original rim to rim diameter of the Siljan crater was somewhere in the size range 50–90 km. 相似文献
4.
Carl ALWMARK Birger SCHMITZ Sanna HOLM Federica MARONE Marco STAMPANONI 《Meteoritics & planetary science》2011,46(8):1071-1081
Abstract– A method is described for imaging in 3‐D the interiors of meteoritic chromite grains and their inclusions using synchrotron radiation X‐ray tomographic microscopy. In ordinary chondrites, chromite is the only common mineral that survives long‐term weathering on Earth. Information about the silicate matrix of the original meteorite, however, can be derived from mineral inclusions preserved in the protecting chromite. The inclusions are crucial in the classification of fossil meteorites as well as sediment‐dispersed chromite grains from decomposed meteorites and larger impacts, as these are used for characterizing the past influx of material to Earth, but have previously been difficult to locate. The method is non‐destructive and time efficient for locating inclusions. The method allowed quantitative and morphological studies of both host chromite grains and inclusions in three dimensions. The study of 385 chromite grains from eight chondrites (H4–6, L4–6, LL4, LL6) reveals that inclusions are abundant and equally common in all samples. Almost two‐thirds of all chromite grains contain inclusions, regardless of group and type. The study also shows that the size of the inclusions and the host chromite grains, as well as the number of inclusions, within the host chromite grains vary with petrographic type. Thus, the petrographic type of the host of a suite of chromite grains can be determined based solely on inclusion content. The study also revealed that the amount of fractures in the host chromite can be correlated to previously assigned shock stages for the various chondrites. The study has thus shown that the features and inclusions of fossil chromite grains can give similar information about a former host meteorite as do studies of an unweathered whole meteorite, meaning that this technique is essential in the studies of ancient meteorite flux to Earth. 相似文献
5.
Combining shock barometry with numerical modeling: Insights into complex crater formation—The example of the Siljan impact structure (Sweden) 
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下载免费PDF全文 Sanna Holm‐Alwmark Auriol S. P. Rae Ludovic Ferrière Carl Alwmark Gareth S. Collins 《Meteoritics & planetary science》2017,52(12):2521-2549
Siljan, central Sweden, is the largest known impact structure in Europe. It was formed at about 380 Ma, in the late Devonian period. The structure has been heavily eroded to a level originally located underneath the crater floor, and to date, important questions about the original size and morphology of Siljan remain unanswered. Here we present the results of a shock barometry study of quartz‐bearing surface and drill core samples combined with numerical modeling using iSALE. The investigated 13 bedrock granitoid samples show that the recorded shock pressure decreases with increasing depth from 15 to 20 GPa near the (present) surface, to 10–15 GPa at 600 m depth. A best‐fit model that is consistent with observational constraints relating to the present size of the structure, the location of the downfaulted sediments, and the observed surface and vertical shock barometry profiles is presented. The best‐fit model results in a final crater (rim‐to‐rim) diameter of ~65 km. According to our simulations, the original Siljan impact structure would have been a peak‐ring crater. Siljan was formed in a mixed target of Paleozoic sedimentary rocks overlaying crystalline basement. Our modeling suggests that, at the time of impact, the sedimentary sequence was approximately 3 km thick. Since then, there has been around 4 km of erosion of the structure. 相似文献
6.
7.
Sanna Vaalgamaa Eloni Sonninen Atte Korhola Kaarina Weckström 《Journal of Paleolimnology》2013,50(2):191-206
We studied the potential for using stable carbon and nitrogen isotope ratios in sediment profiles to trace external nutrient sources and eutrophication at four coastal sites in the Baltic Sea. The sites are characterized by various present and past activities in their catchments, including residential development, sugar processing, agriculture and fish farming. Radiometrically dated sediment cores were analysed for nutrient isotope ratios, organic carbon and total nitrogen. Background information was collected from historical sources, literature and water monitoring data. Despite the multiple organic enrichment sources, it was possible to identify individual sources and processes in the sediment profiles using stable isotope analysis of bulk sediment. The largest changes in δ15N values were seen at sites receiving urban wastewaters. The site that received effluents from a sugar cane (C4-plant) refinery in the past showed a clear effect on δ13C values compared to the site that received wastewater from a sugar beet (C3-plant) factory. Fish farming produced detectable, albeit minor changes in the sediment profile. Slightly lower δ13C values reflected the influence of fish feed and fish metabolism, and higher δ15N values likely indicated the influence of increased sediment denitrification. The land-sea connection via river discharge was observable in the overall δ13C levels of the sediment cores. Our results suggest that temporal changes in sources of organic matter enrichment can be detected in well-dated coastal sediment cores using nutrient stable isotope analyses, even at sites subjected to multiple impacts. There is not, however, a simple relationship between sediment stable isotope profiles and the eutrophication history of our study sites. 相似文献
8.
The Paris Agreement and the Sustainable Development Goals (SDGs) set ambitious targets for environmental, economic and social progress. Climate change mitigation policies play a central role in this process. To maximize the benefits and minimize the negative effects of climate change mitigation policies, policymakers need to be aware of the indirect and often complex social and inequality impacts that these policies may have and the pathways through which these impacts emerge. Better understanding of the distributional and inequality impacts is important to avoid negative social and distributional outcomes as countries ratchet up their climate policy ambition in the post-Paris context. This paper synthesizes evidence from the existing literature on social co-impacts of climate change mitigation policy and their implications for inequality. The analysis shows that most policies are linked to both co-benefits and adverse side-effects, and can compound or lessen inequalities depending on contextual factors, policy design and policy implementation. The risk of negative outcomes is greater in contexts characterized by high levels of poverty, corruption and economic and social inequalities, and where limited action is taken to identify and mitigate potentially adverse side-effects.
Key policy insights
The risk of adverse social outcomes associated with climate change mitigation policies, including worsening inequality, increases as countries ratchet up their ambition to meet the Paris Agreement targets. Many policies that have so far only been piloted will need to be up-scaled.
Negative inequality impacts of climate policies can be mitigated (and possibly even prevented), but this requires conscious effort, careful planning and multi-stakeholder engagement. Best results can be achieved when potential inequality impacts are taken into consideration in all stages of policy making, including policy planning, development and implementation.
Climate change mitigation policies should take a pro-poor approach that, in best case scenarios, can also lead to a reduction of existing inequalities.
9.
This study examines the variability of the monthly average significant wave height (SWH) field in the Mediterranean Sea, in
the period 1958–2001. The analysed data are provided by simulations carried out using the WAM model (WAMDI group, 1988) forced
by the wind fields of the ERA-40 (ECMWF Re-Analysis). Comparison with buoy observations, satellite data, and simulations forced
by higher resolution wind fields shows that, though results underestimate the actual SWH, they provide a reliable representation
of its real space and time variability. Principal component analysis (PCA) shows that the annual cycle is characterised by
two main empirical orthogonal functions (EOF) patterns. Most inter-monthly variability is associated with the first EOF, whose
positive/negative phase is due to the action of Mistral/Etesian wind regimes. The second EOF is related to the action of southerly
winds (Libeccio and Sirocco). The annual cycle presents two main seasons, winter and summer characterised, the first, by the
prevalence of eastwards and southeastwards propagating waves all over the basin, and the second, by high southwards propagating
waves in the Aegean Sea and Levantin Basin. Spring and fall are transitional seasons, characterised by northwards and northeastwards
propagating waves, associated to an intense meridional atmospheric circulation, and by attenuation and amplification, respectively,
of the action of Mistral. These wave field variability patterns are associated with consistent sea level pressure (SLP) and
surface wind field structures. The intensity of the SWH field shows large inter-annual and inter-decadal variability and a
statistically significant decreasing trend of mean winter values. The winter average SWH is anti-correlated with the winter
NAO (North Atlantic Oscillation) index, which shows a correspondingly increasing trend. During summer, a minor component of
the wave field inter-annual variability (associated to the second EOF) presents a statistically significant correlation with
the Indian Monsoon reflecting its influence on the meridional Mediterranean circulation. However, the SLP patterns associated
with the SWH inter-annual variability reveal structures different from NAO and Monsoon circulation. In fact, wave field variability
is conditioned by regional storminess in combination with the effect of fetch. The latter is likely to be the most important.
Therefore, the inter-annual variability of the mean SWH is associated to SLP patterns, which present their most intense features
above or close to Mediterranean region, where they are most effective for wave generation.
相似文献
| P. LionelloEmail: |
10.
Sebastián Tomás Sánchez Gómez Jens Ormö Carl Alwmark Sanna Holm-Alwmark Gabriel Zachén Robert Lilljequist Juan Antonio Sánchez Garrido 《Meteoritics & planetary science》2023,58(10):1512-1539
The Tabernas–Alhabia Basin is a structural depression situated in the province of Almería, southeastern Spain. The basin is filled with Neogene, Pliocene, and Pleistocene sediments resting discordantly on a Paleozoic metamorphic basement. During the marine Tortonian sedimentation, a bed of breccia (Gordo megabed) was formed. It consists of rotated sedimentary megablocks commonly capped and/or surrounded by a polymict breccia composed mainly of up to dm-sized clasts of the crystalline (schist) basement. Previous work has suggested the bed to be a seismite corresponding to events induced by earthquakes. Here, we link the formation of the Gordo megabed with an ∼5 km wide, rimmed depression with exposed breccias on the northern flank of the Sierra de Gádor mountain. This semicircular structure, developed in mainly schists and dolostone of the basement, is delimited to the W, S, and E by an up to 350 m high escarpment with overturned stratigraphy. Toward the north, this crater-like structure opens toward the Gordo megabed of the Tabernas Basin. In the southern sector, the overturned strata transform outward for into a blocky allochthonous breccia with decreasing thickness and clast size. In the interior of the structure, there are occurrences of graded breccia and arenite superposed on a blocky, autochthonous breccia. Based on the presence of mineralogical shock metamorphic evidence, potential shatter cones, and a high Ir anomaly (∼500 ppb) as well as the position of the structure near the town of Alhama de Almería, we propose to call it the Alhama de Almería impact structure. 相似文献