Land Margin Research Articles

MEND: Political Marginalization, Repression, and Petro-Insurgency in the Niger Delta

ABSTRACT This study presents a systematic analysis of the emergence of the Movement for the Emancipation of the Niger Delta militia in Nigeria's Niger Delta. It examines the sociopolitical conditions that underpin armed conflict in the oil-rich region. The ongoing Movement for the Emancipation of the Niger Delta insurgency is a complicated conflict with varied complex dimensions that cannot be explained merely in terms of greed and grievance binary. Thus, this study departs from earlier accounts with regard to the Movement for the Emancipation of the Niger Delta. By adopting a holistic perspective to the Movement for the Emancipation of the Niger Delta it is expected that the intricate connections between land dispossession, marginalization, deprivation, political repression, and insurgency would be laid bare. Apart from this, the local, national, and global dimensions of the Movement for the Emancipation of the Niger Delta are also critically examined.

Water and energy footprints of bioenergy crop production on marginal lands

Water and energy demands associated with bioenergy crop production on marginal lands are inextricably linked with land quality and land use history. To illustrate the effect of land marginality on bioenergy crop yield and associated water and energy footprints, we analyzed seven large-scale sites (9–21 ha) converted from either Conservation Reserve Program (CRP) or conventional agricultural land use to no-till soybean for biofuel production. Unmanaged CRP grassland at the same location was used as a reference site. Sites were rated using a land marginality index (LMI) based on land capability classes, slope, soil erodibility, soil hydraulic conductivity, and soil tolerance factors extracted from a soil survey (SSURGO) database. Principal components analysis was used to develop a soil quality index (SQI) for the study sites based on 12 soil physical and chemical properties. The water and energy footprints on these sites were estimated using eddy-covariance flux techniques. Aboveground net primary productivity was inversely related to LMI and positively related to SQI. Water and energy footprints increased with LMI and decreased with SQI. The water footprints for grain, biomass and energy production were higher on lands converted from agricultural land use compared with those converted from the CRP land. The sites which were previously in the CRP had higher SQI than those under agricultural land use, showing that land management affects water footprints through soil quality effects. The analysis of biophysical characteristics of the sites in relation to water and energy use suggests that crops and management systems similar to CRP grasslands may provide a potential strategy to grow biofuels that would minimize environmental degradation while improving the productivity of marginal lands.

Composition and age of the East Antarctic Shield in eastern Wilkes Land determined by proxy from Oligocene-Pleistocene glaciomarine sediment and Beacon Supergroup sandstones, Antarctica

The Precambrian East Antarctic Shield played a central role in the tectonic evolution of Rodinia and Gondwana, as well as growth of the East Antarctic Ice Sheet, yet little is known about its ice-covered interior. Glaciogenic deposits of Oligocene-Miocene and Pleistocene age on the Wilkes Land margin include glaciomarine diamictons containing basement rock clasts and fine-grained siliciclastic detritus, which provide proxy samples of the continental basement. Rock clasts obtained by dredge (81% metamorphic, 14% igneous, and 5% sedimentary lithologies) provide petrographic, geochemical, and age information about the glacial source area. Igneous clasts with Ross orogen U-Pb zircon ages (ca. 500 Ma) include a notably old ca. 585 Ma granitoid; they and Ross-age metamorphic rocks give discrete inherited-zircon age populations of 670–780, 900–1300, 1740–2300, and >2700 Ma that reflect basement sources. Paleoproterozoic rock clasts (granitoid, charnockite gneiss, and granulite gneiss) range from ca. 1720 to 1740 Ma. Detrital zircon populations from glaciomarine sediments vary with depositional age but show common terrigenous provenance ages of 460–660, 1045–1315, 1545–1815, and 2420–2605 Ma, which overlap those from inherited zircons in the Ross granitoids. Detrital zircon ages from onshore Permian and Triassic terrestrial sedimentary rocks reveal a different provenance and indicate that the glaciogenic deposits do not contain significant second-cycle material from older interior basins. Together, these data suggest that metamorphic rock units with distinctive Neoproterozoic, Paleoproterozoic, and Archean ages dominate East Antarctic Shield basement inland from the eastern Wilkes Land margin, and that Ross-age granitoids either intruded or were derived by partial melting of this composite metamorphic basement.

Evidence for iceberg armadas from East Antarctica in the Southern Ocean during the late Miocene and early Pliocene

Abstract Sediments from Ocean Drilling Program Site 1165 in the Indian Ocean sector of the Southern Ocean (off Prydz Bay) contain a series of layers that are rich in ice-rafted debris (IRD). Here we present evidence that IRD-rich layers at Site 1165 at 7, 4.8, and 3.5 Ma record short-lived, massive discharges of icebergs from Wilkes Land and Adelie Land, more than 1500 kilometers to the east of the depositional site. This distant source of icebergs is clearly defined by the presence of IRD hornblende grains with 40Ar/39Ar ages of 1200–1100 Ma and 1550–1500 Ma, ages that are not found on the East Antarctic continent in locations closer to Site 1165. This observation requires enormous amounts of detritus-carrying drifting icebergs, most likely in the form of large icebergs. These events probably reflect destabilization, surge, and break-up of ice streams on the Wilkes Land and Adelie Land margins of the East Antarctic Ice Sheet, in the vicinity of the low-lying Aurora and Wilkes Basins. They occurred under warming conditions, but each coast seems to have produced ice-rafting events independently, at different times. The data presented here constitute the first evidence of far-traveled icebergs from specific source areas around the East Antarctic perimeter. Launch of these icebergs may have happened during quite dramatic events, perhaps analogous to “Heinrich Events” in the North Atlantic.

A marine geophysical study of the Wilkes Land rifted continental margin, Antarctica

SUMMARY The Wilkes Land margin of East Antarctica, conjugate to the southern Australian margin, is a non-volcanic rifted margin that formed during the Late Cretaceous. During 2000–01 and 2001–02, Geoscience Australia acquired ∼10 000 line km of seismic reflection and refraction, magnetic anomaly and gravity anomaly data over the margin. We have used the seismic data to estimate the sediment thickness along the margin. The data reveal a deep (>11 km) rift basin that contains over 9 km of sediments seaward of the Totten Glacier, western Wilkes Land. The limits of oceanic and continental crust that underlies the thick post-rift and the significantly thinner pre- and syn-rift sediments are equivocal. Seismic reflection data suggest a 30–100 km wide continent–ocean transition zone (COTZ) along the margin. The COTZ extends over 400 km seaward of the shelf break off the eastern Wilkes Land/Terre Ad´ elie sector

Socio-economic drivers for UK organic pullet rearers and the implications for poultry health

1. Certified organic pullet producers were surveyed to gain a better understanding of the production environment, to identify the key constraints to organic pullet rearing and to identify factors that affected bird health. 2. Pullet rearers had been involved in organic production for between 1 and 12 years. 3. The number of pullets reared per annum ranged from 6 to 12 000 and the number of birds housed per unit from <50 to >1000. 4. The primary reason for being involved in organic production was given as ‘commercial’ with ‘environmental’ and ‘welfare’ being the next most popular categories. 5. Fewer than 50% of the respondents vaccinated their flocks and, for those that were protected, the diseases vaccinated against frequently were Newcastle disease, infectious bronchitis and Marek's disease. Annual mortality ranged from <2 to >7% with smothering accounting for 25% of all mortality. 6. Approximately 40% of respondents saw no constraints to rearing organic pullets while others identified a range of factors including capital, availability of land and inadequate margins as being the primary constraint.

Mass wasting processes in the Western Wilkes Land margin: Possible implications for East Antarctic glacial history

Multichannel seismic data collected off Western Wilkes Land (East Antarctica) reveal widespread sediment mass movement events, mainly in the form of mega debris flows deposited on the continental rise. In places, they have a seaward extent of more than 200 km and a thickness of up to 400 m. Debris flow units are commonly separated by thin deposits of well-stratified facies, interpreted as glaciomarine mixed contouritic and distal turbidite deposits, possibly with some hemipelagic sediments. These units, due to a dominant contouritic component, represent weakened layers and could then play a major role in the slope instability. Based on stratigraphic correlation with DSDP Site 268, it is suggested that slope failures in the Western Wilkes Land occurred mostly during the Miocene. Inferred high sedimentation rates, due to large amounts of sediment delivered from a temperate, wet-based ice sheet, would have constituted a key factor in the sediment failures. The distribution of mass wasting-related features appears also strongly related to the amount of meltwater discharge. The main trigger mechanism would probably have been earthquakes, enhanced by isostatic rebounds following major ice sheet retreats.

This Land is Our Land: Moro Ancestral Domain and Its Implications for Peace and Development in the Southern Philippines

This paper examines land in Mindanao as both a root of conflict and a key to potential, long-term conflict resolution. It reviews the history of Moro land ownership and political dominance in the sultanates of Maguindanao and Sulu, which pre-dated Spanish and U.S. colonial rule. It looks at the Moro conflict with the Philippine government as a response to Moro land loss and marginalization, and reviews the failure of various peace agreements to resolve Moro grievances. Finally, the paper analyzes current negotiations between the Moro Islamic Liberation Front (MILF) and the Philippine government (GRP) on ancestral domain, and examines how ancestral domain could promote long-term peace and development in Mindanao.

Sedimentary processes in the Wilkes Land margin: a record of the Cenozoic East Antarctic Ice Sheet evolution

Multichannel seismic data collected off Wilkes Land (East Antarctica) reveal four main units that represent distinct phases in the evolution of the Cenozoic depositional environment. A Cretaceous synrift succession is overlain by hemipelagic and distal terrigenous sequences deposited during Phase 1. Sediment ridges and debris-flow deposits mark the transition to Phase 2. Unit 3 records the maximum sediment input from the continent and is characterized by the predominance of turbidite deposits. During Phase 4 the sediment supply from the continental margin was reduced, and draping and filling were the dominant processes on the continental rise. Unit 4 also contains the deposits of sediment wave fields and asymmetric channel-levee systems. These four units are a response to the Cenozoic evolution of the East Antarctic Ice Sheet. During Phase 1, small ice caps were formed in the innermost continental areas. The ice volume increased under temperate glacial regimes during Phases 2 and 3, when large volumes of melt-water production led to high sediment discharge to the continental rise. Change to a polar regime occurred through Phase 4, when a thick prograding wedge developed on the continental shelf and slope and the sediment transport to the rise diminished, producing general starvation conditions.

New insights into Quaternary glacial dynamic changes on the George V Land continental margin (East Antarctica)

The continental margin of the George V Land represents the seaward termination of one of the largest sub-glacial basins (the Wilkes Basin) of the East Antarctic Ice Sheet (EAIS) and hence is a potentially useful site for the investigation of the Cenozoic glacial history of Antarctica. Because the seafloor morphology relates strictly to recent glacial marine sedimentary processes, we have compiled all available echo-soundings data collected until the year 2001 and integrated the data set with satellite altimetry data. As a result, we have produced a new bathymetric map of the margin, covering an area of more than 80,000 km 2 with a spatial resolution of about 1 km. The bathymetric data have been integrated with sub-bottom profiler data with the purpose of defining sedimentary processes and their variations during the Quaternary. The continental shelf of the Wilkes Land margin is characterised by alternating banks and glacial troughs connected to sub-marine canyons that cut into the continental slope. Our study focussed on the continental rise, where asymmetrical ridges alternate with large deep-sea channels. The ridges have a long gentle eastern side and short steep western side, with axis elongated approximately in north–south direction, perpendicular to the margin. The channels represent the main sediment drainage pattern feeding the ridge depositional system found along the continental rise. The sediment is supplied to the continental shelf edge by ice sheets, and sediment gravity flows are considered the main process for sediment supply to the rise. The modern sedimentary environment of the deep margin is affected by turbiditic down-slope sediment transfer with a minor contribution from along-slope contour currents. The WEGA channel is currently affected by transport and settling of sediment through High-Salinity Shelf Water (HSSW), originating on the continental shelf. We infer that thermohaline circulation has contributed to sediment transport and deposition since the mid-Pleistocene.

Bollons Seamount and early New Zealand–Antarctic seafloor spreading

Magnetic anomaly, swath bathymetry and gravity data from the southern Chatham Rise to Bollons Seamount region reveal a history of Cretaceous seafloor spreading in the mouth of the Bounty Trough starting at ∼85 Ma followed by spreading ridge jumps back to the Marie Byrd Land Margin at 83.7 and 78.5 Ma. The latter ridge jump accompanied the rifting of the Bollons Seamount from the Marie Byrd Land margin. Interpreted magnetic anomalies indicate a pattern of highly asymmetric spreading prior to 78 Ma that varied in bias along the margin on a ∼100 km length scale. Crustal thickening within the ∼50 km Bollons Gap linking the Bollons Seamount to the Campbell Plateau is interpreted to be due to excess volcanism associated with the initial rifting–seafloor spreading process and possible thinned continental crust. The elevated 200 km long segment of Antipodes Fracture Zone southeast of Bollons Seamount has been exposed to varying styles of ridge end volcanism and possible normal compression associated with the development during chron 32n.2n of a triple junction at its southeastern limit marking the Bellingshausen‐Marie Byrd Land plate boundary.

Interplay of turbidite and contourite deposition along the Cosmonaut Sea/Enderby Land margin, East Antarctica

Multichannel seismic reflection data from the Cosmonaut Sea margin of East Antarctica have been interpreted in terms of depositional processes on the continental rise. A major sediment lens is present below the upper continental rise along the entire Cosmonaut Sea margin. The lens probably consists of sediments supplied from the shelf and slope, being constantly reworked by westward flowing bottom currents redepositing the sediments into a large-scale plastered drift deposit prior to the main glacigenic input along the margin. High-relief elongated and sometimes semicircular depositional structures are found on the upper continental rise, stratigraphically above the regional sediment lens, and were mainly deposited by the action of closely spaced turbidity currents. On the lower continental rise, large-scale sediment bodies extend perpendicular to the continental margin and were deposited as a result of down-slope turbidity transport and westward flowing bottom currents. The elongated sediment mounds on the upper and lower continental rise were deposited after initiation of glacigenic input to the slope and rise.

Cenozoic ice sheet history from East Antarctic Wilkes Land continental margin sediments

The long-term history of glaciation along the East Antarctic Wilkes Land margin, from the time of the first arrival of the ice sheet to the margin, through the significant periods of Cenozoic climate change is inferred using an integrated geophysical and geological approach. We postulate that the first arrival of the ice sheet to the Wilkes Land margin resulted in the development of a large unconformity (WL-U3) between 33.42 and 30 Ma during the early Oligocene cooling climate trend. Above WL-U3, substantial margin progradation takes place with early glacial strata (e.g., outwash deposits) deposited as low-angle prograding foresets by temperate glaciers. The change in geometry of the prograding wedge across unconformity WL-U8 is interpreted to represent the transition, at the end of the middle Miocene “climatic optimum” (14–10 Ma), from a subpolar regime with dynamic ice sheets (i.e., ice sheets come and go) to a regime with persistent but oscillatory ice sheets. The steep foresets above WL-U8 likely consist of ice proximal sediments (i.e., water-lain till and debris flows) deposited when grounded ice-sheets extended into the shelf. On the continental rise, shelf progradation above WL-U3 results in an up-section increase in the energy of the depositional environment (i.e., seismic facies indicative of more proximal turbidite and of bottom contour current deposition from the deposition of the lower WL-S5 sequence to WL-S7). Maximum rates of sediment delivery to the rise occur during the development of sequences WL-S6 and WL-S7, which we infer to be of middle Miocene age. During deposition of the two uppermost sequences, WL-S8 and WL-S9, there is a marked decrease in the sediment supply to the lower continental rise and a shift in the depocenters to more proximal areas of the margin. We believe WL-S8 records sedimentation during the final transition from a dynamic to a persistent but oscillatory ice sheet in this margin (14–10 Ma). Sequence WL-S9 forms under a polar regime during the Pliocene–Pleistocene, when most sediment delivered to the margin is trapped in the outer shelf and slope-forming steep prograding wedges. During the warmer but still polar, Holocene, biogenic sediment accumulates quickly in deep inner-shelf basins during the high-stand intervals. These sediments contain an ultrahigh resolution (annual to millennial) record of climate variability. Validation of our inferences about the nature and timing of Wilkes Land glacial sequences can be achieved by deep sampling (i.e., using IODP-type techniques). The most complete record of the long-term history of glaciation in this margin can be obtained by sampling both (1) the shelf, which contains the direct (presence or no presence of ice) but low-resolution record of glaciation, and (2) the rise, which contains the distal (cold vs. warm) but more complete record of glaciation. The Wilkes Land margin is the only known Antarctic margin where the presumed “onset” of glaciation unconformity (WL-U3) can be traced from shelf to the abyssal plain, allowing links between the proximal and the distal records of glaciation to be established. Additionally, the eastern segment of the Wilkes Land margin may be more sensitive to climate change because the East Antarctic Ice Sheet (EAIS) is grounded below sea level. Therefore, the Wilkes Land margin is not only an ideal location to obtain the long-term EAIS history but also to obtain the shorter-term record of ice sheet fluctuations at times that the East Antarctic Ice Sheet is thought to have been more stable (after 15 Ma-recent).

The interpretation of fen carr pollen diagrams: pollen–vegetation relationships within the fen carr

Sediments deposited in fen carr environments are frequently used in pollen-based reconstructions of vegetation history, although few studies of modern pollen–vegetation relationships in fen carr have been undertaken to aid the interpretation of fossil assemblages. It is often assumed that the wetland pollen signal will reflect the overall composition of the fen carr system although, given the closed canopy context, it may actually be dominated by local vegetation elements. This paper seeks to determine whether the vegetation heterogeneity within a modern fen carr is reflected in the pollen signal of the wetland taxa. Vegetation composition was recorded around a series of moss polster sample points at Calthorpe and Wheatfen, two areas of fen carr in the Norfolk Broadland, UK. The spatial interrelationship between the wetland components of the vegetation and their palynological equivalents in the moss polster pollen assemblages is explored through trend surfaces and a correlation based statistical test (the Mantel Test). The representation of the major vegetation components in the pollen record is highly variable. Values for Alnus glutinosa, a dominant canopy species, range from 5.3% to 73% of total land pollen (TLP) at Calthorpe and 2.5–61% TLP at Wheatfen. In part, this variation reflects the enhanced input of pollen from dry land sources close to the wetland edge although the variation recorded at points equidistant from the dry land margin suggests that other processes are also influential. The strongest positive associations in the Mantel Test are for under-storey and ground flora elements that are poorly represented in the pollen record. Taxa for which there is no association include those with few vegetation occurrences and those for which a large proportion of the pollen appears to have been derived from outside the study areas. We conclude that modern pollen samples collected from fen carr broadly reflect the vegetation composition of the study areas. However, the input of pollen from fen carr species is spatially inconsistent. Differences between the sample points can be attributed to the distribution and pollination biology of the under-storey and ground flora elements and the structure of the vegetation around sites. The results caution against assuming that changes in the pollen representation of wetland taxa, in fossil sequences constructed from fen carr deposits, necessarily reflect changes in the overall composition of the community.

Characteristics of the Composite Metallogenic System along the Jilin Paleocontinental Margin and the Evolution of Continental Dynamic Regimes

Abstract In view of the existing problems about the metallogenic epoch and origin of the complex along the Jilin paleocontinental margin, we propose the composite metallogenic system of the Jilin old land, based on the theory of metallogeny and from the continental dynamics and comprehensive analysis on the metallogenic characteristics. Its scientific theory is demonstrated by the following aspects: (1) Screening and analysis of the multi‐stage superimposition and sequences. The composite ore‐forming system consists mainly of three types: the divergent‐type epicontinental metallogenic system on the southern margin, the convergent‐type epicontinental metallogenic system on the northern margin and the strike‐slip‐type epicontinental metallogenic system on the northeastern margin. Their major metallogenic epochs are Archean‐Proterozoic, Variscan and Yanshanian respectively. (2) Comprehensive analysis of the genetic relations of the complicated deposits. The above‐mentioned three types all indicate a consanguinity among granites, vein rocks and gold deposits, correspondence with geochemical elements, and unicity showing the same activities of mantlederived fluids and multi‐source origin of ore‐forming substances. (3) As to the mechanisms for mineral concentration, in addition to the sources, we also focus on the co‐actions of permeability, vibration, gas‐liquid state alternation and abrupt changes of flow velocity during the movement of ore‐forming liquids, as well as the extraction and communication of multi‐sequence circulating liquids. (4) It is helpful for establishing the relationship between metallogeny and the evolution of continental dynamic regimes, i.e., the ore‐controlling correlations between the ore‐forming elements‐metallogenic series‐metallogenic systems‐composite metallogenic system and ore‐controlling structural features (stratabound, primary and branching types)‐regional faulting or secondary continental extension and collision‐transformation of different continental dynamic types (divergent, convergent and strike‐slip)‐the evolution process of the whole old land for the Jilin old land margin. All these are helpful for further researches on the continental metallogenic dynamics.

Reef reconstruction after extinction events of the latest ordovician in the Yangtze platform, South China

Early Silurian reef reconstruction on the Yangtze Platform, in the northern part of the South China Block, is preceded by a combination of regional and global processes. During most of Ashgill time (Late Ordovician), the area was dominated by Wufeng Formation deep water graptolitic black shales. Reefs largely disappeard in the middle of the Ashgill Stage, from the northwestern margin of Cathaysian Land (southeastern South China Block), in advance of the Late Ordovician glaciation and mass extinction, due to regional sea-level changes and regional uplift, unrelated to the mass extinction itselt. Late Ordovician microbial mudmound occurrence is also found in the western margin of the Yangtze Platform, its age corresponding to theDicellograptus complexus graptolite biozone of pre-extinction time. On the Yangtze Platform, a thin, non-reef-bearing carbonate, the Kuanyinchiao Formation (=Nancheng Formation in some sites), thickness generally no more than 1m, occurs near several landmasses as a result of Hirnantian regression. Reappearance of the earliest Silurian carbonates consisting of rare skeletal lenses in the upper part of Lungmachi Formation, are correlated to theacensus graptolite biozone, early Rhuddanian of Shiqian, northeastern Guizhou, near Qianzhong Land. Carbonate sediments gradually developed into beds rich in brachiopods and crinoids in the lower part of Xiangshuyuan Formation, middle Rhuddanian. In the middle part of Xiangshuyan Formation, biostromes, containing abundant and high diversity benthic faunas such as corals, crinoids and brachiopods, show beginnings of reconstruction of reef facies. Substantial reef recovery occurred in the upper part of Xiangshuyuan Formation, lower Aeronian, as small patch reefs and biostromes. During the late Aeronian, carbonate sediments, especially reefs and reef-related facies, expanded on the upper Yangtze Platform, and radiation of reefs occurred in Ningqiang Formation, upper Telychian. The long period of reef recovery, taking several million years, remains difficult to explain, because redistribution of any refugia faunas would be expected to take place soon after the extinction. Reefs and reef-related facies subsequently declined after Telychian time due to regional uplift of the major portion of the Yangtze Platform. Carbonate facies are therefore uncommon in South China during the rest of Silurian time.

Erratum to “Sediment distribution and sedimentary processes across the Antarctic Wilkes Land margin during the Quaternary” [Deep-Sea Research II 50 (2003) 1481–1508

Erratum to “Sediment distribution and sedimentary processes across the Antarctic Wilkes Land margin during the Quaternary” [Deep-Sea Research II 50 (2003) 1481–1508

Sediment distribution and sedimentary processes across the Antarctic Wilkes Land margin during the Quaternary

The study of existing cores collected across the Wilkes Land margin provides us with a better understanding of the sediment distribution and processes across this margin during the Holocene, and during Pleistocene glacial and interglacial cycles. Holocene depositional rates are high in deep (>1000 m) inner-shelf basins where diatomaceous ooze is deposited at estimated minimum sedimentation rates ranging from 40 to 60 cm/kyr. In the shelf troughs, Holocene sediment has a patchy distribution or is totally absent. This is also the case on the shelf banks due to differential deposition because of the irregular relief of the continental shelf and the erosion and redistribution by bottom currents. Pleistocene interglacial sedimentation is well represented in sediment from the continental rise and is dominated by hemipelagic deposition of massive mud with the highest biogenic content (as indicated by %opal) and with a high abundance of clasts (IRD). During the Pleistocene glacial cycles, diamictons were deposited in the continental-shelf troughs and on the banks. Reworking (e.g., by bottom currents) and remobilization (e.g., gravity flows) of these diamictons is a common process along the shallow continental-shelf banks. On the continental slope and the continental rise, gravity flows are one of the most important sedimentary processes. Sediment from continental-slope cores, with a texture that greatly resembles the diamictons on the shelf, is interpreted to represent either part of a slump block or the start of a debris flow. Downslope, crudely stratified to laminated intervals represent the transition between an end member of a debris flow and a turbidity flow. Some of the laminated intervals in cores from the continental rise represent sediment deposited from a turbidity flow. Ages obtained from cores further support that slumps and gravity flows are dominant processes in this margin, because numerous hiatuses apparently are present in cores from the base of the slope. One of these cores extends into the Miocene. Elsewhere on the continental rise, massive and laminated sediments in cores of similar length record near-continuous Pleistocene sedimentation. r 2003 Elsevier Science Ltd. All rights reserved.

Seasonal variations in the speciation of dissolved iodine in the Chesapeake Bay

The speciation of dissolved iodine and the distributions of the iodine species in the deep Chesapeake Bay underwent seasonal variations in response to changes in the prevailing redox condition. In the deep water, the ratios of iodate to iodide and iodate to inorganic iodine decreased progressively from the Winter through the Summer as the deep water became more poorly oxygenated before they rebounded in the Fall when the deep water became re-oxygenated again. The composition of the surface water followed the same trend. However, in this case, the higher biological activities in the Spring and the Summer could also have enhanced the biologically mediated reduction of iodate to iodide by phytoplankton and contributed to the lower ratios found during those seasons. Superimposed on this redox cycle was a cycle of input and removal of dissolved iodine probably as a result of the interactions between the water column and the underlying sediments. Iodine was added to the Bay during the Summer when the deep water was more reducing and removed from the Bay in the Fall when the deep water became re-oxygenated. A third cycle was the inter-conversion between inorganic iodine and ‘dissolved organic iodine’, or ‘‘DOI’’. The conversion of inorganic iodine to ‘DOI’ was more prevalent in the Spring. As a result of these biogeochemical reactions in the Bay, during exchanges between the Bay and the North Atlantic, iodate-rich and ‘DOI’-poor water was imported into the Bay while iodide- and ‘DOI’-rich water was exported to the Atlantic. The export of iodide from these geochemically reactive systems along the land margins contributes to the enrichment of iodide in the surface open oceans.

Upper mantle seismic anisotropy beneath Antarctica and the Scotia Sea region

Recent investigations on shear wave splitting from recordings of permanent and temporary Antarctic seismological stations have lead to a greater understanding of the upper mantle dynamics of the Scotia Sea region and the continental margin in the eastern Weddell Sea in terms of their tectonic evolution. The analysis of shear wave splitting from teleseismic core (SKS, SKKS, PKS) and direct S waves reveals the seismic anisotropy and the strain field of the upper mantle. Similar to the Caribbean, anisotropy structures in the Antarctic Peninsula and Scotia Sea regions are assumed to be influenced by mantle flows in easterly directions around the subducting Nazca plate. In general, anisotropy polarization directions in the Scotia Sea do not contradict this hypothesis, with polarizations oriented nearly E-W and therefore aligning with the suggested mantle flow patterns. Anisotropy strengths decrease from delay times of δt=1.8s (PMSA, Palmer Station) in the west towards the east with delay times of δt=0.3s beneath HOPE (South Georgia) and CAND (Candlemas, South Sandwich Islands). Nevertheless, a lithospheric and therefore fossil origin cannot be ruled out. Only the exceptionally high delay times at PMSA probably originate in part from recent asthenospheric flow around the subduction slab of the former Phoenix Plate beneath the northwestern margin of the Antarctic Peninsula. The continental margin of western Dronning Maud and Coats Land plays a crucial role in understanding the early processes during the break-up of Gondwana. Upper mantle seismic anisotropy with delay times well over δt=1s in this region gives new constraints on ancient deformation processes during break-up and former episodes. Two-layer modelling reveals Archaean anisotropy in the upper layer corresponding well to polarization directions of the South African Kaapvaal Craton. Lower layer anisotropy is assumed to have been created during early Gondwana rifting stages.