Icebergs in the North Atlantic: Modelling circulation changes and glacio-marine deposition

In order to investigate meltwater events in the North Atlantic, a simple iceberg generation, drift, and melting routine was implemented in a high-resolution OGCM. Starting from the modelled last glacial state, every 25th day cylindrical model icebergs 300 meters high were released at 32 specific points along the coasts. Icebergs launched at the Barents Shelf margin spread a light meltwater lid over the Norwegian and Greenland Seas, shutting down the deep convection and the anti-clockwise circulation in this area. Due to the constraining ocean circulation, the icebergs produce a tongue of relatively cold and fresh water extending eastward from Hudson Strait that must develop at this location, regardless of iceberg origin. From the total amount of freshwater inferred by the icebergs, the thickness of the deposited IRD could be calculated in dependance of iceberg sediment concentration. In this way, typical extent and thickness of Heinrich layers could be reproduced, running the model for 250 years of steady state with constant iceberg meltwater inflow

Assessment of trace metal contamination in a historical freshwater canal (Buckingham Canal), Chennai, India

The present study was done to assess the sources and the major processes controlling the trace metal distribution in sediments of Buckingham Canal. Based on the observed geochemical variations, the sediments are grouped as South Buckingham Canal and North Buckingham Canal sediments (SBC and NBC, respectively). SBC sediments show enrichment in Fe, Ti, Mn, Cr, V, Mo, and As concentrations, while NBC sediments show enrichment in Sn, Cu, Pb, Zn, Ni, and Hg. The calculated Chemical Index of Alteration and Chemical Index of Weathering values for all the sediments are relatively higher than the North American Shale Composite and Upper Continental Crust but similar to Post-Archaean Average Shale, and suggest a source area with moderate weathering. Overall, SBC sediments are highly enriched in Mo, Zn, Cu, and Hg (geoaccumulation index (Igeo) class 4– 6), whereas NBC sediments are enriched in Sn, Cu,Zn, and Hg (Igeo class 4–6). Cu, Ni, and Cr show higher than Effects-Range Median values and hence the biological adverse effect of these metals is 20%; Zn, which accounts for 50%, in the NBC sediments, has a more biological adverse effect than other metalsfound in these sediments. The calculated Igeo, Enrichment Factor, and Contamination Factor values indicate that Mo, Hg, Sn, Cu, and Zn are highly enriched in the Buckingham Canal sediments, suggesting the rapid urban and industrial development of Chennai MetropolitanCity have negatively influenced on the surrounding aquatic ecosystem

Nordic Seas polynyas and their role in preconditioning marine productivity during the Last Glacial Maximum.

Arctic and Antarctic polynyas are crucial sites for deep-water formation, which helps sustain global ocean circulation. During glacial times, the occurrence of polynyas proximal to expansive ice sheets in both hemispheres has been proposed to explain limited ocean ventilation and a habitat requirement for marine and higher-trophic terrestrial fauna. Nonetheless, their existence remains equivocal, not least due to the hitherto paucity of sufficiently characteristic proxy data. Here we demonstrate polynya formation in front of the NW Eurasian ice sheets during the Last Glacial Maximum (LGM), which resulted from katabatic winds blowing seaward of the ice shelves and upwelling of warm, sub-surface Atlantic water. These polynyas sustained ice-sheet build-up, ocean ventilation, and marine productivity in an otherwise glacial Arctic desert. Following the catastrophic meltwater discharge from the collapsing ice sheets at ~17.5 ka BP, polynya formation ceased, marine productivity declined dramatically, and sea ice expanded rapidly to cover the entire Nordic Seas

Coherent deglacial changes in western Atlantic Ocean circulation

Abrupt climate changes in the past have been attributed to variations in Atlantic Meridional Overturning Circulation (AMOC) strength. However, the exact timing and magnitude of past AMOC shifts remain elusive, which continues to limit our understanding of the driving mechanisms of such climate variability. Here we show a consistent signal of the 231Pa/230Th proxy that reveals a spatially coherent picture of western Atlantic circulation changes over the last deglaciation, during abrupt millennial-scale climate transitions. At the onset of deglaciation, we observe an early slowdown of circulation in the western Atlantic from around 19 to 16.5 thousand years ago (ka), consistent with the timing of accelerated Eurasian ice melting. The subsequent weakened AMOC state persists for over a millennium (~16.5–15 ka), during which time there is substantial ice rafting from the Laurentide ice sheet. This timing indicates a role for melting ice in driving a two-step AMOC slowdown, with a positive feedback sustaining continued iceberg calving and climate change during Heinrich Stadial 1

Harmful Elements in Estuarine and Coastal Systems

Estuaries and coastal zones are dynamic transitional systems which provide many economic and ecological benefits to humans, but also are an ideal habitat for other organisms as well. These areas are becoming contaminated by various anthropogenic activities due to a quick economic growth and urbanization. This chapter explores the sources, chemical speciation, sediment accumulation and removal mechanisms of the harmful elements in estuarine and coastal seawaters. It also describes the effects of toxic elements on aquatic flora and fauna. Finally, the toxic element pollution of the Venice Lagoon, a transitional water body located in the northeastern part of Italy, is discussed as a case study, by presenting the procedures adopted to measure the extent of the pollution, the impacts on organisms and the restoration activities

Pb, Zn, Cs, Sc and rare earth elements as tracers of the Loire and Gironde particles on the Biscay shelf (SW France)

The western Atlantic continental margin of the Bay of Biscay is characterised by a combined macro-tidal and a high energy environment. These conditions are responsible for the essentially sandy sedimentary cover along with well-defined fine deposit zones observed on the shelf. The main continental sources are the Loire, Gironde and Adour Rivers. It is estimated that 2.4 to 2.5 million tons of fine sediments are supplied annually to the ocean from these rivers of the French Atlantic coast. The Gironde and the Loire contribute with 84 % and the Gironde with 60 % of this amount. Previous studies of the distribution of the clay mineral assemblages and of oligo-elements have distinguished two provinces (north and south Biscay areas) according to these riverine sources. The use of an inductively coupled plasma-mass spectrometry (ICP-MS) technique allowed us to analyse both heavy metals and rare earth elements (REE), thus permitting an effective characterisation of continental sources. On the basis of these results, it has been possible to better identify the respective contributions of the Loire and the Gironde Rivers to the fine-grained sedimentation on the inner shelf.La marge continentale ouest-atlantique est un domaine macro-tidal à haut niveau d'énergie. Cette dynamique forte a mis en place sur la plate-forme du Golfe de Gascogne une couverture sédimentaire essentiellement sableuse et des zones de dépôts fins bien circonscrites. Les principales sources continentales sont la Loire, la Gironde et l'Adour. On estime que 2,4 à 2,5 millions de tonnes de sédiments fins sont issus chaque année de ces fleuves. La Gironde et la Loire contribuent pour 84 % à cet apport et la Gironde, à elle seule, pour 60 %. Des études antérieures fondées sur la répartition des cortèges de minéraux argileux ou sur celle des éléments traces ont mis en évidence des domaines nord et sud-Gascogne. L'utilisation de techniques d'analyses multi-élémentaires telles que l'ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) dosant également les terres rares, a permis une meilleure caractérisation des sources continentales girondine et ligérienne. Ces résultats permettent de préciser les domaines d'influence respectifs de la Loire et de la Gironde dans la sédimentation fine actuelle sur la plate-forme interne

Volcanic layers in Antarctic (Vostok) ice cores: Source identification and atmospheric implications

Fifteen visible volcanic ash layers (tephra) from Vostok ice cores have been analyzed for major elements, trace elements, and Sr and Nd isotope composition. Comparison of their geochemical signatures to lava composition from the inventory of Antarctic and subantarctic volcanoes, which have been active over the last 0.5 million years, indicates that nine layers originate from activity of the South Sandwich volcanic arc, three from southern South America, one from the Antarctic Peninsula (Bransfield Strait), and one from West Antarctica (Marie Byrd Land province). The large size of the tephra (up to 50 mum) requires rapid atmospheric transfer from the volcanic centers to East Antarctica. Rapid tropospheric transport from the southwestern Atlantic, penetrating East Antarctica, therefore predominates during the period studied, whether in glacial or interglacial climatic mode. In spite of the low frequency of occurrence of visible tephra layers in Vostok core (one event every 20 kyr), the overall atmospheric pathway of these ash events appears consistent with the almost continuous advection of continental dust from South America

Patagonian origin of glacial dust deposited in East Antarctica (Vostok and Dome C) during glacial stages 2, 4 and 6

The source area of continental dust deposited at both Vostok and Dome C sites (East Antarctica) during the glacial stages (stage 2: similar to 18 ka (Last Glacial Maximum), stage 4: similar to 60 ka and stage 6: similar to 160 ka) of the last two climatic cycles has remained constant. The isotopic composition (Sr-87/Sr-86 and Nd-143/Nd-114) of the ice-core dust has been compared with the isotopic composition of the potential source areas: Antarctica, New Zealand, Southern Africa, Australia and South America. This comparison reveals the southern South American provenance of the dust for all three glacial periods, as has already been shown for the LGM [1], We show that the Patagonian loess and the marine shelf sediments from the Argentine continental shelf, which was variably emerged during glacial periods, display different isotopic compositions and that the composition of the Patagonian loess best matches the signature of the ice-core dust, The identification of the Patagonian region as the source of the windblown dust deposited over East Antarctica during all the latest glacial periods permits a better understanding of paleo-atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models