Greenwich Meridian Research Articles

Anomalous precipitation signatures of the Arctic Oscillation in the time-variable gravity field by GRACE

The Arctic Oscillation (AO) controls winter climates in the Northern Hemisphere to a large extent. Positive AO brings lower/higher surface temperature and higher/lower precipitation in high/middle latitude regions, and negative AO reverses the situation. In this study, we investigate signals of anomalous precipitations caused by AO using the data of the Gravity Recovery and Climate Experiment (GRACE) satellites. Wintertime mass deviations inferred from GRACE in the high and middle (boundary ∼55N) latitude regions in Eurasia showed highly positive and negative correlations with the AO indices. This possibly reflects the northward and southward shift of the centre of winter precipitation during the positive and negative phases of AO, respectively. Wintertime mass deviations also showed positive and negative correlations with the AO indices in the northern and southern parts of Greenland, respectively, but the boundary was further to the north, say ∼75N. AO redistributes the water mass as much as ∼1000 Gt between high and middle latitude regions in the Northern Hemisphere. Such mass redistribution causes significant surface deformation by loading large enough to be observed by Global Positioning System. This also causes the shift of the Earth's rotation axis especially towards the Greenwich Meridian large enough to be detected with space geodetic techniques. AO signatures are also derived from the empirical orthogonal function (EOF) analysis, as the first leading mode of GRACE data after excluding seasonal, linear and quadratic components. The EOF analysis also demonstrates that though AO is a main contributor to bring anomalous winter precipitation in the Northern Hemisphere as a whole, in North America, however, influence of the El Niño and Southern Oscillation on the winter precipitation anomaly is larger than AO.

Regional Variation in Lytic and Lysogenic Viral Infection in the Southern Ocean and Its Contribution to Biogeochemical Cycling

Lytic and lysogenic viral infection was investigated throughout the Southern Ocean at sites spanning the sub-Antarctic zone, the Antarctic Circumpolar Current, and an Antarctic continental sea. Higher lytic virus activity was recorded in the more productive sub-Antarctic zone than in the iron-limited waters of the Antarctic Circumpolar Current during two transects. Reduced lytic viral activity in the Antarctic Circumpolar Current was combined with a shift toward lysogenic infection, probably resulting from the lower concentration of potential prokaryotic hosts. Superimposed on this variation, lytic viral production was lower in a transect completed in the Drake Passage in autumn (1.8 × 10(8) to 1.5 × 10(9) liter(-1) day(-1)) than over the Greenwich Meridian during summer (5.1 × 10(8) to 2.0 × 10(10) cells liter(-1) day(-1)), indicating that viral activity is linked to the overall seasonal fluctuations in biotic activity. Interestingly, while prokaryotic abundance was lowest in the coastal Weddell Sea, levels of bacterial and lytic viral production (4.3 × 10(8) to 1.7 × 10(10) cells liter(-1) day(-1)) in this area were similar to those of the other zones. This may explain the weak relationship between the distribution of prokaryotes and chlorophyll in the Weddell Sea, as a high turnover of prokaryotic biomass may have been stimulated by the availability of substrates in the form of viral lysate. With estimated carbon and iron releases of 0.02 to 7.5 μg liter(-1) day(-1) and 1.5 to 175.7 pg liter(-1) day(-1), respectively, viral activity in the Southern Ocean is shown to be a major contributor to satisfying the elemental requirements of microbes, notably prokaryotes in the Weddell Sea and phytoplankton in the sub-Antarctic zone.

Global literary refractions: Reading Pascale Casanova's The World Republic of Letters in the post-Cold War era

This article critically examines Pascale Casanova's recent theorization of the world literary space from the point of view of postcolonial and especially post-Cold War debates on global literary comparativism. It investigates whether her Bourdieu-derived ‘field’ approach, with its overwhelming conceptual dependence on ‘market’ and ‘nation’ metaphors, equips her to make valid qualitative judgements on vast swathes of ‘non-European’ and ‘transnational’ literary spaces. In annexing all literatures of the non-European, postcolonial world to a historiography of European literatures, Casanova's book, this article argues, is not well positioned to theorize contemporary forms of literary ‘worldling’ where Europe is but one node among many others and scarcely the ‘Greenwich Meridian’ of literary taste. Finally, the article discusses alternative ways of studying world literary spaces and histories that have emerged in recent years, especially in the works of David Damrosch and Franco Moretti. In the process, it also weaves in aspects of a post-1989 Anglophone world literature project the theoretical and geopolitical assumptions of which are in quite some tension with those of Casanova's book.

Phytoplankton production characteristics in the southern Atlantic and the Atlantic sector of the Southern Ocean in the austral summer of 2009–2010

In December-January of 2010 the spatial distribution of the phytoplankton production charac� teristics was studied along transects in the vicinity of the Greenwich meridian (I) and in the Drake Passage (II). On transect I, the surface chlorophyll a concentration and primary production varied from 0.11 up to 3.57 mg/m 3 and from 4.38 up to 37.47 mgC/m 3 per day, respectively. The chlorophyll a in the photosynthetic layer and the integrated primary production varied from 10.7 up to 66.1 mg/m 2 and from 83 to 646 mgC/m 2 per day, respectively. On transect II in the surface layer, the chlorophyll a concentration changed within the range of 0.09-1.02 mg/m 3 and the primary production ranged from 2.08 to 9.49 mgC/m 3 . The integrated val� ues ranged from 6.32 to 38.29 mg/m 2 and from 41 to 221 mgC/m 2 per day, respectively. The moderate means of themaximum quantum yield (Fv/Fm) on transects I and II (0.41 and 0.35, respectively) testify to the low activity of the phytoplankton's photosynthetic apparatus. The studied water areas in the Southern Ocean dif� fered both in the phytoplankton biomass expressed in the chlorophyll a concentration values and in the con� ditions of the primary production formation.

Mid‐century effects of Climate Change on African monsoon dynamics using the A1B emission scenario

AbstractFuture climate changes in African regions are model‐dependent and there is no consensus regarding Sahelian rainfall by the end of this century. Using 12 atmosphere‐ocean global climate models of the third Coupled Model Intercomparison Project (CMIP3) we propose a multi‐model (MM) analysis contrasting the 1960–1999 period (20c3m integration) and the 2031–2070 period (A1B emission scenario). The analyses are based on MM response but also on the ‘one model‐one vote’ concept to give the same weight to each model. The results show robust signals in the rainfall response, i.e., increasing (decreasing) amounts in central (western) Sahel associated with specific changes in atmospheric dynamics. The rainfall excesses expected in central Sahel are mainly linked to an enhancement of the northern Hadley‐type cell and probably to its northward shift. At low‐levels increasing temperature and evaporation strengthen the monsoon flux. Rainfall deficits predicted westward are due to a reinforcement of the African Easterly Jet and to anomalies in the zonal circulation between the Indian and the Atlantic Oceans, favouring air subsidence and moisture export outside the region. The weakening of the meridional circulation is also able to prevent rainfall amounts in the western part of the Sahel. More generally, these analyses show that in future works the Sahel region must not be considered as one consistent region but as two separate areas, both sides of the Greenwich meridian. The authors propose to consider this feature in the next Fifth Assessment cycle (AR5) in order to better understand the impacts of the climate change on West Africa. Copyright © 2012 Royal Meteorological Society

LUCIAN AND THE GREAT MOON HOAX OF 1835

The science of astronomy has had a long and distinguished history at the Cape of Good Hope (hereafter referred to as “the Cape”). This is no accident, since Cape Town was for many years (since 1652, in fact) the only fortified and inhabited European settlement in the southern hemisphere. Thus when astronomers in The Netherlands, France, and England turned their attention to mapping the southern skies it was to the Cape that they brought their instruments. In addition, the mother city of South Africa is only about eighteen degrees east of the Greenwich meridian in London, so that observations of the skies in London and Cape Town could be made from approximately the same longitude. In the eighteenth and nineteenth centuries, star-gazing was not merely a matter of academic interest; on it depended the accuracy of navigational aids used by the merchant and naval shipping of these and other nations. The interest shown in Cape Town by the British astronomical community is also evident from the construction of the Royal Observatory at the Cape in 1820 by the Admiralty. This observatory was intended to be the counterpart of the Greenwich Observatory in London (Evans 1981a:196; Warner 1995). In addition to this interest in navigational accuracy, the invention of the refracting telescope at the beginning of the seventeenth century provided the means for scientists to make star-maps of the southern skies more accurate and complete. The Dutch astronomer, Peter Kolbe, was sent to the Cape in 1705, and in 1751 a Frenchman, the Abbe De La Caille, also arrived there for this purpose (McIntyre 1951:3-5; De La Caille 1763b). The latter was considerably more successful than the former; he added 9766 stars and 42 nebulae to the celestial catalogue (De La Caille 1763a). Among other things he determined the distance between his Cape observatory in Strand Street and the moon (De La Caille 1751).

Higher precision estimates of regional polar warming by ensemble regression of climate model projections

This study presents projections of twenty-first century wintertime surface temperature changes over the high-latitude regions based on the third Coupled Model Inter-comparison Project (CMIP3) multi-model ensemble. The state-dependence of the climate change response on the present day mean state is captured using a simple yet robust ensemble linear regression model. The ensemble regression approach gives different and more precise estimated mean responses compared to the ensemble mean approach. Over the Arctic in January, ensemble regression gives less warming than the ensemble mean along the boundary between sea ice and open ocean (sea ice edge). Most notably, the results show 3 °C less warming over the Barents Sea (~7 °C compared to ~10 °C). In addition, the ensemble regression method gives projections that are 30 % more precise over the Sea of Okhostk, Bering Sea and Labrador Sea. For the Antarctic in winter (July) the ensemble regression method gives 2 °C more warming over the Southern Ocean close to the Greenwich Meridian (~7 °C compared to ~5 °C). Projection uncertainty was almost half that of the ensemble mean uncertainty over the Southern Ocean between 30° W to 90° E and 30 % less over the northern Antarctic Peninsula. The ensemble regression model avoids the need for explicit ad hoc weighting of models and exploits the whole ensemble to objectively identify overly influential outlier models. Bootstrap resampling shows that maximum precision over the Southern Ocean can be obtained with ensembles having as few as only six climate models.

Distribution and feeding of chaetognaths in the epipelagic zone of the Lazarev Sea (Antarctica) during austral summer

This study seeks to determine the effects of local hydrography on the distribution, abundance and feeding of chaetognaths in the Lazarev Sea, an area strongly controlled by physical processes which has been held responsible for initiating the Weddell Polynya. Zooplankton samples were taken at 39 stations on four transects located between 6°W and 3°E and from 60°S to 70°S between surface and 350 m. The dominant species, Eukrohnia hamata, accounted for 86.5% of all chaetognaths, followed by Sagitta gazellae (8.1%) and Sagitta marri (5.4%). These three species showed distinct vertical and horizontal distribution patterns. While E. hamata and S. marri had maximum abundances below 250 m depth, S. gazellae showed a narrow distribution band in the upper 150 m depth. The distribution pattern was strongly modified at the Greenwich meridian with an upward transport of a high abundance of deep dwelling organisms (S. marri and E. hamata) and a displacement of S. gazellae to the surface, likely coupled with the rise of the warm, saline halo around the Maud Rise. Small copepods were the main prey of all three chaetognath species. Feeding rates (FR) varied among species and depth. Sagitta marri showed the highest FR with 0.38 prey d−1, followed by S. gazellae and E. hamata (0.22 and 0.07 prey d−1). Feeding rates were usually highest in the 25–80-m stratum. Size distribution and maturity of E. hamata revealed a dominance of small and immature organisms along all depths and stations, suggesting that this area might be acting as an important source of recently spawned organisms to the surface.

Silicon pool dynamics and biogenic silica export in the Southern Ocean inferred from Si-isotopes

Abstract. Silicon isotopic signatures (δ30Si) of water column silicic acid (Si(OH)4) were measured in the Southern Ocean, along a meridional transect from South Africa (Subtropical Zone) down to 57° S (northern Weddell Gyre). This provides the first reported data of a summer transect across the whole Antarctic Circumpolar Current (ACC). δ30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional water transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determine different mixing interfaces: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the δ30Si alteration of the mixing products and with the exception of AASW, all mixing interfaces have a highly Si-depleted mixed layer end-member. These processes deplete the silicic acid AASW concentration northward, across the different interfaces, without significantly changing the AASW δ30Si composition. By comparing our new results with a previous study in the Australian sector we show that during the circumpolar transport of the ACC eastward, the δ30Si composition of the silicic acid pools is getting slightly, but significantly lighter from the Atlantic to the Australian sectors. This results either from the dissolution of biogenic silica in the deeper layers and/or from an isopycnal mixing with the deep water masses in the different oceanic basins: North Atlantic Deep Water in the Atlantic, and Indian Ocean deep water in the Indo-Australian sector. This isotopic trend is further transmitted to the subsurface waters, representing mixing interfaces between the surface and deeper layers. Through the use of δ30Si constraints, net biogenic silica production (representative of annual export), at the Greenwich Meridian is estimated to be 5.2 ± 1.3 and 1.1 ± 0.3 mol Si m−2 for the Antarctic Zone and Polar Front Zone, respectively. This is in good agreement with previous estimations. Furthermore, summertime Si-supply into the mixed layer of both zones, via vertical mixing, is estimated to be 1.6 ± 0.4 and 0.1 ± 0.5 mol Si m−2, respectively.

Solar time, legal time, time in use

The International Conference held in 1884 at Washington defined a universal time as the mean solar time at the Greenwich meridian (GMT). Now, the Universal Time, version UT1, is strictly defined as proportional to the angle of rotation of the Earth in space. In this evolution, the departure of UT1 from GMT does not exceed one or two seconds. This is quite negligible when compared with the departure between the solar time and the legal time of citizens, which may exceed two hours without raising protests.

Variations of Winter Water properties and sea ice along the Greenwich meridian on decadal time scales

Sea–ice ocean interaction processes are of significant influence on the water mass formation in the Weddell gyre. On the basis of data obtained between 1984 and 2008 from eight repeat hydrographic sections, moored instruments and profiling floats in the Weddell gyre on the Greenwich meridian – almost all of them collected with R.V. Polarstern – we identified variations in the properties of the Winter Water and the sea ice draft. In the Winter Water the salinity was relatively low throughout the 1990s (with a minimum in 1992) and a maximum was observed in 2003. Observations of sea ice draft by moored upward looking sonars are available from 1996 onwards. In the southern part of the transect they display variations on a decadal time scale with a minimum in sea-ice thickness in 1998 and an increase since then. Salinity variations in the Winter Water layer cannot be explained only by variations in sea-ice formation and variable entrainment of underlying Warm Deep Water, but lateral advection of water and sea ice needs to be taken into account as well. Potential sources are melt water from the ice shelves in the western Weddell Sea or transport of water of low salinity entering the Weddell gyre from the east. Accompanying variations of the properties of Warm Deep Water are discussed in detail in a companion paper ( Fahrbach et al., 2011).

Warming of deep and abyssal water masses along the Greenwich meridian on decadal time scales: The Weddell gyre as a heat buffer

The Southern Ocean renders a significant contribution to the global overturning system through the formation of deep and bottom waters. The Weddell Sea is one of the most prominent regions in this respect. Data obtained between 1984 and 2008 from eight repeat hydrographic sections, moored instruments and profiling floats in the Weddell gyre on the Greenwich meridian – almost all of them collected with RV Polarstern – were used to identify variations in the Weddell system. Fluctuations in the water mass properties were detected in the Warm Deep Water, with a temperature maximum in the 1990s and a minimum in 2005, but also significant variations occurred in the Weddell Sea Deep and Bottom Waters, whereas the Warm Deep Water is dominated by decadal variations; the average temperature and salinity of the whole water column is subject to a positive trend over 24 years. The variations of the water mass properties are induced by variations of the inflow of Circumpolar Deep Water at the boundary. Due to asymmetric wind forcing at the northern and the southern limb of the gyre, variable in- and outflows occur at the open boundaries. Internal processes redistribute heat and salt in the gyre resulting in a long-term increase of the temperature and salinity in the whole water column. The transfer of heat to deeper layers assigns to the Weddell gyre the role of a buffer, with potential impact on the global climate.

The biogeochemical cycle of dissolved cobalt in the Atlantic and the Southern Ocean south off the coast of South Africa

The spatial distribution, biogeochemical cycle and external sources of dissolved cobalt (DCo) were investigated in the southeastern Atlantic and the Southern Ocean between 33°58′S and 57°33′S along the Greenwich Meridian during the austral summer 2008 in the framework of the International Polar Year. DCo concentrations were measured by flow-injection analysis and chemiluminescence detection in filtered (0.2 μm), acidified and UV-digested samples at 12 deep stations in order to resolve the several biogeochemical provinces of the Antarctic Circumpolar Current and to assess the vertical and frontal structures in the Atlantic sector of the Southern Ocean. We measured DCo ranging from 5.73 ± 1.15 pM to 72.9 ± 4.51 pM. The distribution of DCo was nutrient-like in surface waters of the subtropical domain with low concentrations in the euphotic layer due to biological uptake. The biological utilization of dissolved cobalt was proportional to that of phosphate in the subtropical domain with a DCo:HPO 4 2− depletion ratio of ~ 44 μM M −1. In deeper waters the distribution indicated remineralization of DCo and inputs from the margins of South Africa with lateral advection of enriched intermediate and deep waters to the southeastern Atlantic Ocean. In contrast the vertical distribution of DCo changed southward, from a nutrient-like distribution in the subtropical domain to scavenged-type behavior in the domain of the Antarctic Circumpolar Current and conservative distribution in the Weddell Gyre. There the cycle of DCo featured low biological removal by Antarctic diatoms with input to surface waters by snow, removal in oxygenated surface waters, and dissolution and stabilization in the low-oxygenated Upper Circumpolar Deep Waters. DCo distributions and physical hydro-dynamics features also suggest inputs from the Drake Passage and the southwestern Atlantic to the 0° meridian along the eastward flow of the Antarctic Circumpolar Current. Bottom enrichment of DCo in the Antarctic Bottom Waters was also evident, together with increasing water-mass pathway and aging, possibly due to sediment resuspension and/or mixing with North Atlantic Deep waters in the Cape Basin. Overall atmospheric input of soluble Co by dry aerosols to the surface waters was low but higher in the ACC domain than in the northern part of the section. At the highest latitudes, it is possible that snowfall could be a source of DCo to surface waters. Tentative budgets for DCo in the mixed layer of the subtropical and the ACC domains have been constructed for each biogeochemical region encountered during the cruise. The estimated DCo uptake flux was found to be the dominant cobalt flux along the section. This flux decreases southward, which is consistent with the observations that DCo shows a southward transition from nutrient-like towards conservative distribution in the mixed layer.

Invasive Alien Plant Species in Nigeria and Their Effects on Biodiversity Conservation

With very scanty information on invasive alien species (IAS) in Nigeria, this study was conducted to identify the invasive species in the field gene bank of the National Centre for Genetic Resources and Biotechnology (NACGRAB), Ibadan, Nigeria, on the latitude 7° 22′ north of the equator and longitude 3° 50′ east of the Greenwich Meridian, and also to assess the level of the species' disturbance to the conserved native plants in the protected area. This study involved sampling of the field gene bank and an on-site assessment and identification of the species and their effects on the indigenous plants established in the field for conservation. Twenty-five invasive plant species were identified, across 16 plant families, of which 14 were herbs, followed by vines, shrubs, and trees, all of which are presently estimated to occupy about 18% of the gene bank. The effects of IAS on the indigenous plants conserved in the field gene bank range from competition for space and nutrients and alteration of the tree canopies (thereby affecting the microclimatic conditions in the lower strata) to obstruction of the plants' reception of sunlight (which could thereby reduce the potential yield of the fruit trees in the gene bank. The paper also discusses the effects of IAS on biodiversity conservation in Nigeria. Human disturbance was observed as the major factor responsible for the spread of these IAS in the gene bank. The paper concludes by advocating stricter screening measures before introducing new plants into the country, capacity building on the early detection and management of IAS in protected areas for the technical staff, biological control, and exchange of technical information among concerned countries.

Diversity and distribution of Polychaeta in deep Antarctic and Subantarctic waters along the Greenwich meridian

In the course of the ANDEEP-SYSTCO project, during the ANT XXIV-2 expedition in austral summer 2007/2008, the diversity and composition of the Polychaeta of the Antarctic deep-sea and adjacent South Atlantic basins were analyzed. A total of 847 individuals of 31 families were found belonging to 86 different species. Calculation of diversity (Shannon-Wiener Index, Pielou's Evenness) and the general species composition of Polychaeta showed patterns typical for the deep sea, with high species richness and low abundances. Lowest diversity was found in the Agulhas Basin in over 4000 m water depth. Lowest Evenness was found on top of Maud Rise where one-third of all Polychaeta belonged to one species. Cluster analyses resulted in higher affinities of Maud Rise to the Agulhas Basin than to the Antarctic continental slope. Explanations are sought in similarities of environmental factors (e.g., sediment, food input).

Variability of the Southern Ocean fronts at the Greenwich Meridian

Maps of Absolute Dynamic Topography (MADT) at the Greenwich Meridian are used to identify the locations and gradients of the various fronts in the Southern Ocean (Subtropical Front, Sub-Antarctic Front, Antarctic Polar Front, Southern ACC Front, and Southern Boundary of the ACC). It is found that the frontal gradients in Sea Surface Height (SSH) used to determine these fronts are consistent with those determined from hydrographic data. A strong relationship was found to exist between the position of all the fronts and the gradients of SSH except for the Southern Boundary (SBdy) front. Substantial seasonality and interannual variability in the frontal positions is found. All the fronts except the Antarctic Polar Front (APF) show a poleward tendency in position over the last 15-years. Using the MADT-derived frontal positions, the meridional zones between the fronts are examined and the mean zonal sea surface temperature (SST) is used to consider the surface variability in these frontal zones. In addition to the strong seasonality and interannual variability in the SST of these frontal zones, there is also a tendency towards warming (cooling) of the Sub-Antarctic and Antarctic Polar Zones (Southern Boundary Zone). The tendencies in the frontal positions are consistent with a warming in the Southern Ocean except near the APF and the Southern ACC Front (SACCF).

Biodiversity and conservation of plant genetic resources in the Field Genebank of the National Centre for Genetic Resources and Biotechnology, Ibadan, Nigeria.

This study was conducted to determine the biodiversity of the plant collections at the National Field Genebank at the National Centre for Genetic Resources and Biotechnology (NACGRAB), with the view of evaluating the conservation strategy of the ex situconservation of recalciterant crops in the genebank for effective conservation and sustainable utilization. The results reveal that three hundred and sixty-one plants were identified in the field gene bank, spread across ninety-six plant families. The studies further show that the family Caesalpiniaceae has the highest number (20) of represented plant species; followed by Euphorbiaceae and Rubiaceae, each having nineteen representative plant species each. The location of the National Field Genebank at NACGRAB in Ibadan, on the latitude 7° 22’ North of the equator and longitude 3° 50’ East of the Greenwich Meridian, was found to have a positive effect on the adaptability of the plants collected from various different ecological and geographical zones of the country, since it was observed that Ibadan has a somewhat transitory climate between the moist tropical forests and the dry savanna regions of the country, both extreme zones being the natural habitats of some of the plant germplasms in the Field Genebank. The advantage of ex situ live collections overin situ conservation in terms of protection of the collections in Nigeria was also stressed. The need to establish more ex situ live collections in the different climatic zones of the Country to facilitate more conservation activities is also emphasized. Some of the endangered and endemic plant species yet to be collected and conserved are enumerated, so as to receive attention from conservation scientists in Nigeria. Key words: Biodiversity, conservation, NACGRAB, Ibadan.

A comparative analysis of three different MODIS NDVI datasets for Alaska and adjacent Canada

Moderate Resolution Imaging Spectroradiometer (MODIS) data offer great potential for monitoring vegetation dynamics in Alaska. However, certain MODIS image quality issues, such as geometric distortion, have been analyzed and documented in high latitudes and regions distant from the Greenwich Meridian. To improve MODIS data usability, the Canada Centre for Remote Sensing (CCRS) developed a seven-band reflectance dataset (10 day composite) at 250 m resolution for Canada and North America. More recently, the US Geological Survey Earth Resources Observation and Science Center produced an eMODIS dataset that includes a 7 day composite of normalized difference vegetation index (NDVI) and surface reflectance data at 250 m, 500 m, and 1 km resolutions for the conterminous United States and Alaska. Although these two datasets are based on the same MODIS level 1B data as those of the standard MODIS products, they are processed to improve their use in high-latitude regions. In this study, we conducted a comparative analysis of the standard MODIS, CCRS MODIS, and eMODIS Alaska 250 m NDVI products using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images as a reference source. CCRS MODIS and eMODIS Alaska NDVI images have significantly improved geometric features over those of the standard MODIS product. Pixel-by-pixel comparisons of the MODIS datasets indicated that all retained the original MODIS radiometric characteristics, but considerable mismatches at the pixel level were found due to geometric distortions caused by resampling. All three MODIS datasets agreed well as images were degraded to 5 or 10 km resolution.

Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea, Antarctica

Ten-month time series of mean volume backscattering strength (MVBS) and vertical velocity obtained from three moored acoustic Doppler current profilers (ADCPs) deployed from February until December 2005 at 64°S, 66.5°S and 69°S along the Greenwich Meridian were used to analyse the diel vertical zooplankton migration (DVM) and its seasonality and regional variability in the Lazarev Sea. The estimated MVBS exhibited distinct patterns of DVM at all three mooring sites. Between February and October, the timing of the DVM and the residence time of zooplankton at depth were clearly governed by the day–night rhythm. Mean daily cycles of the ADCP-derived vertical velocity were calculated for successive months and showed maximum ascent and descent velocities of 16 and –15 mm s −1. However, a change of the MVBS pattern occurred in late spring/early austral summer (October/November), when the zooplankton communities ceased their synchronous vertical migration at all three mooring sites. Elevated MVBS values were then concentrated in the uppermost layers (<50 m) at 66.5°S. This period coincided with the decay of sea ice coverage at 64°S and 66.5°S between early November and mid-December. Elevated chlorophyll concentrations, which were measured at the end of the deployment, extended from 67°S to 65°S and indicated a phytoplankton bloom in the upper 50 m. Thus, we propose that the increased food supply associated with an ice edge bloom caused the zooplankton communities to cease their DVM in favour of feeding.

O SIGNO DO POETA

This is a semiotic analysis of the poem "Greenwich Meridian Time", exploring the non-verbal components as regards symbolic terms presentation. We try to show that the good visual poem should be based on tradition, which goes bach to the beginning of the esoteric Sciences, especially the mandala, the cabala and the alchemy.