Silicon dynamics within an intense open-ocean diatom bloom in the Pacific sector of the Southern Ocean     

Mark A. Brzezinski  David M. Nelson  Valerie M. Franck  Daniel E. Sigmon 《Deep Sea Research Part II: Topical Studies in Oceanography》2001,48(19-20)

An intense diatom bloom developed within a strong meridional silicic acid gradient across the Antarctic Polar Front at 61°S, 170°W following stratification of the water column in late October/early November 1997. The region of high diatom biomass and the silicic acid gradient propogated southward across the Seasonal Ice Zone through time, with the maximum diatom biomass tracking the center of the silicic acid gradient. High diatom biomass and high rates of silica production persisted within the silicic acid gradient until the end of January 1998 (ca. 70 d) driving the gradient over 500 km to the south of its original position at the Polar Front. The bloom consumed 30 to >40 μM Si(OH)₄ in the euphotic zone between about 60 and 66°S leaving near surface concentrations <2.5 μM and occasionally <1.0 μM in its wake. Integrated biogenic silica concentrations within the bloom averaged 410 mmol Si m⁻² (range 162–793 mmol Si m⁻²). Average integrated silica production on two consecutive cruises in December 1997 and January 1998 that sampled the bloom while it was well developed were 27.5±6.9 and 22.6±20 mmol Si m⁻² d⁻¹, respectively. Those levels of siliceous biomass and silica production are similar in magnitude to those reported for ice-edge diatom blooms in the Ross Sea, Antarctica, which is considered to be among the most productive regions in the Southern Ocean. Net silica production (production minus dissolution) in surface waters during the bloom was 16–21 mmol Si m⁻² d⁻¹, which is sufficient for diatom growth to be the cause of the southward displacement of the silicic acid gradient. A strong seasonal change in silica dissolution : silica production rate ratios was observed. Integrated silica dissolution rates in the upper 100–150 m during the low biomass period before stratification averaged 64% of integrated production. During the bloom integrated dissolution rates averaged only 23% of integrated silica production, making 77% of the opal produced available for export to depth. The bloom ended in late January apparently due to a mixing event. Dissolution : production rate ratios increased to an average of 0.67 during that period indicating a return to a predominantly regenerative system.Our observations indicate that high diatom biomass and high silica production rates previously observed in the marginal seas around Antarctica also occur in the deep ocean near the Polar Front. The bloom we observed propagated across the latitudinal band overlying the sedimentary opal belt which encircles most of Antarctica implying a role for such blooms in the formation of those sediments. Comparison of our surface silica production rates with new estimates of opal accumulation rates in the abyssal sediments of the Southern Ocean, which have been corrected for sediment focusing, indicate a burial efficiency of 4.6% for biogenic silica. That efficiency is considerably lower than previous estimates for the Southern Ocean.  相似文献   

Sand ridges off Sarasota, Florida: A complex facies boundary on a low-energy inner shelf environment     

David Twichell  Gregg Brooks  Guy Gelfenbaum  Valerie Paskevich  Brian Donahue   《Marine Geology》2003,200(1-4):243-262

The innermost shelf off Sarasota, Florida was mapped using sidescan-sonar imagery, seismic-reflection profiles, surface sediment samples, and short cores to define the transition between an onshore siliciclastic sand province and an offshore carbonate province and to identify the processes controlling the distribution of these distinctive facies. The transition between these facies is abrupt and closely tied to the morphology of the inner shelf. A series of low-relief nearly shore-normal ridges characterize the inner shelf. Stratigraphically, the ridges are separated from the underlying Pleistocene and Tertiary carbonate strata by the Holocene ravinement surface. While surficial sediment is fine to very-fine siliciclastic sand on the southeastern sides of the ridges and shell hash covers their northwestern sides, the cores of these Holocene deposits are a mixture of both of these facies. Along the southeastern edges of the ridges the facies boundary coincides with the discontinuity that separates the ridge deposits from the underlying strata. The transition from siliciclastic to carbonate sediment on the northwestern sides of the ridges is equally abrupt, but it falls along the crests of the ridges rather than at their edges. Here the facies transition lies within the Holocene deposit, and appears to be the result of sediment reworking by modern processes. This facies distribution primarily appears to result from south-flowing currents generated during winter storms that winnow the fine siliciclastic sediment from the troughs and steeper northwestern sides of the ridges. A coarse shell lag is left armoring the steeper northwestern sides of the ridges, and the fine sediment is deposited on the gentler southeastern sides of the ridges. This pronounced partitioning of the surficial sediment appears to be the result of the siliciclastic sand being winnowed and transported by these currents while the carbonate shell hash falls below the threshold of sediment movement and is left as a lag. The resulting facies boundaries on this low-energy, sediment-starved inner continental shelf are of two origins which both are tied to the remarkably subtle ridge morphology. Along the southeastern sides of the ridges the facies boundary coincides with a stratigraphic discontinuity that separates Holocene from the older deposits while the transition along the northwestern sides of the ridges is within the Holocene deposit and is the result of sediment redistribution by modern processes.  相似文献   

TM/ETM+/LDCM Images for Studying Land Surface Temperature (LST) Interplay with Impervious Surfaces Changes over Time Within the Douala Metropolis,Cameroon     

Salomon Cesar Nguemhe Fils  Mumbfu Ernestine Mimba  Jean Guy Dzana  Joachim Etouna  Patrick Valerie Mounoumeck  Mustapha Hakdaoui 《Journal of the Indian Society of Remote Sensing》2018,46(1):131-143

Douala, the most important metropolis of Cameroon, is a sub-Saharan wet coastal environment of which the anarchic urbanization is a socio-economic and environmental problem, significantly influencing the local climate. In this study, three Landsat images from 1986 (TM), 2007 (ETM+) and 2016 (LDCM), were utilized to investigate the effect of this urbanization on the increasing land surface temperature (LST) between these dates. Thus, the urban indices (UI), determined from the Landsat Visible and NIR channels were used to identify impervious areas (Urban Fabric and bare soil) of urban area. It has been shown from the UI images that, impervious areas have been increased from 1986 to 2016. The LST images derived have a continual expansion of zones and points of heat throughout these dates. The correlation analysis of LST and UI, at the pixel-scale, indicated the positive relationship between these parameters, which could show a real impact of urbanization on the increasing temperature in the area. These correlations are fairly low in 1986 (maximum R-square value is about 0.35) and in 2007 (maximum R-square value is about 0.44. In 2016, a high positive correlation (maximum R-square value is about 0.77) confirm that, the impervious areas strengthen the temperature and the Urban Heat Island effect in Douala urban zone. Overall, the earth observation images and the geographic information system techniques were effective approaches for aiming at environment monitoring and analyzing urban growth patterns and evaluating their impacts on urban climates.  相似文献   

Relative current effect on short wave growth     

Guimarães  Pedro Veras  Ardhuin  Fabrice  Perignon  Yves  Benetazzo  Alvise  Bouin  Marie-Noëlle  Garnier  Valerie  Redelsperger  Jean-Luc  Accensi  Mickael  Thomson  Jim 《Ocean Dynamics》2022,72(8):621-639

Ocean Dynamics - Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and...  相似文献   

The family of planar periodic orbits generated by the equal-mass four-body Schubart interplay orbit     

Valerie Chopovda  Winston L. Sweatman 《Celestial Mechanics and Dynamical Astronomy》2018,130(5):39

We locate members of a one-parameter family of equal-mass four-body periodic orbits in the plane. The family begins and ends with the rectilinear four-body equal-mass Schubart interplay orbit and passes through a double choreography orbit. The first-order stability of these orbits is computed. Some members of this symmetric family are stable to symmetric perturbations; however, they are unstable when all perturbations are allowed.  相似文献   

Towards climate adaptation and coastal governance in Ireland: Integrated architecture for effective management?     

Maria Falaleeva  Cathal O'Mahony  Stefan Gray  Margaret Desmond  Jeremy Gault  Valerie Cummins 《Marine Policy》2011

Coastal environments are susceptible to a range of impacts arising from medium and long-term climate change. However, as Ireland's population and industrial centres are concentrated in coastal locations, Ireland's coastal communities will be particularly vulnerable to the impacts of climate change. Therefore, making the best use of existing knowledge to inform the establishment of governance structures capable of facilitating the measures and actions which may soon be required is a national imperative. Coastal communities worldwide have turned to integrated coastal zone management (ICZM) as a process to deliver sustainable development. This paper explores how experience gained from ICZM implementation can be harnessed to inform the development and implementation of climate adaptation policies, with a particular focus on the coastal zone. Using the principles and conceptual basis of Earth System Governance – an emerging approach to analyse complexity of governance under global environmental change – the paper maps the architecture of ICZM and climate governance in Ireland. The research identifies the main barriers to, and opportunities for, integrated application of the two policy domains. Barriers include the fragmentation of governance structures and responsibilities of key stakeholders, a lack of coordinated support for ICZM implementation at the national level, and a relatively weak awareness of the specifics of adaptation at the local level. Opportunities include the availability of expertise gathered from phases of ICZM implementation in Ireland, which encompasses mechanisms for science-policy integration, and invaluable experience of stakeholder participation and interaction. Current political and scientific support at national and EU levels give an additional impetus to climate research and actions which may bring additional opportunities and resources to coastal governance in Ireland.  相似文献   

A Protocol for the Determination of the Rare Earth Elements at Picomole Level in Rocks by ICP-MS: Results on Geological Reference Materials USGS PCC-1 and DTS-1     

Valerie Olive  Rob M. Ellam  Lyn Wilson 《Geostandards and Geoanalytical Research》2001,25(2-3):219-228

Rare earth element analyses are widely used in geology, environmental science and archaeology. Over the past decade inductively coupled plasma-mass spectrometry has become an important source of rare earth data on geological material. However, ICP-MS analysis of rock samples without pre-concentration can be problematic because of complex sample matrices that can generate significant molecular isobaric interferences on rare earth peaks and which need to be corrected. Such problems are exacerbated for ultramafic rocks because the low levels of rare earth elements demand more concentrated solutions in order to maintain signals above background levels. These high solid loads result in intra-run changes in instrument sensitivity which need to be monitored. Pre-concentration chemistries have been developed in order to avoid high solid loads but these are time-consuming and must offer quantitative recoveries or use a yield tracer. Here, we describe an alternative method for rare earth element analysis by ICP-MS, which involves no pre-concentration and is, therefore, able to deliver data rapidly. Our approach is to apply an external correction procedure, based on the analysis of a reference material closely matched in composition to the unknown samples, which allows correction for both interferences and variations in instrument sensitivity. Testing this method, we obtained accurate rare earth element results for basaltic rocks with a precision of about 2% (1s). We demonstrate that the method is also applicable to ultramafic rocks with abundances at ultra-trace (ng g⁻¹) level and present data for twelve separate dissolutions of the peridotite USGS PCC-1 and four separate dissolutions of the dunite DTS-1 reference materials. The repeatability of the data is between 3% and 9% (1s).  相似文献   

The uses of social and environmental health indicators in monitoring the effects of climate change     

Valerie A. Brown 《Climatic change》1993,25(3-4):389-403

This paper argues that information collected in the field of Public Health has the potential to provide a valuable contribution to the forecasting and evaluation of the impact of climate change. The well-developed sets of social and environmental health data collected to monitor the health of human populations could also offer sensitive indicators of the effects and potential effects of climate change. City collections of public health data and general demographic information are reviewed as examples of the availability of such monitoring systems.The interests of those monitoring climate change and those monitoring health march together in other ways as well. Changes in radiation, rainfall and temperature will change food and building safety levels, as well as waste disposal capacity. People who are on the poverty line or ill, or both, have little opportunity to respond to such changes, or the strategies designed to control them. Since the Canadian Lalonde Report of 1974, health services have increasingly linked their social and physical health information to environmental data. Coordinated planning using a multidisciplinary data base and responses to change which give due regard to equity are both central considerations in responding to changes in the environment as well as to risks to human health.  相似文献   

The new fisheries multibeam echosounder ME70: description and expected contribution to fisheries research   总被引：1，自引：0，他引：1  

Trenkel  Verena M.; Mazauric  Valerie; Berger  Laurent 《ICES Journal of Marine Science》2008,65(4):645-655

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The morphological development of alpine valley heads in the Antarctic Peninsula     

Valerie M. Haynes 《地球表面变化过程与地形》1998,23(1):53-67

Glaciation has continued in Antarctica for longer than anywhere else on Earth, so the long-term development of glaciated landforms can be investigated. Complex alpine valley heads up to 36 km wide are found in the Antarctic Peninsula. The largest of these may represent an advanced stage of alpine glaciation, having evolved from the earliest corries which could have developed around the early Oligocene. This study is based on a morphometric analysis of the plan form of 1680 alpine valley heads. This is a much larger sample than used by any previous study. Skewed distributions of dimensional properties (width, length and area) suggest that small corries are continually being added to the population, as older ones are enlarged and some eliminated by coalescence and ice sheet erosion. Very large features are found only in parts of Graham Land and Alexander Island, where lack of high-level ice sheet erosion has allowed the forms of mountain glaciation to dominate the landscape. The attainment of an equilibrium planform shape is suggested by the persistence of an equidimensional form, the development of characteristic or limiting values of other morphometric properties, e.g. planform closure and basin order, and by the intercorrelation of morphometric properties. A combination of branching and coalescence is fundamental in the development of corries. The latter results both in widening, which counteracts the tendency towards lengthening observed by other workers, and also in a limit to basin complexity. © 1998 John Wiley & Sons, Ltd.  相似文献