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Silicon (Si) isotopic compositions of marine authigenic and biogenic silica deposits are valuable proxies for reconstructing Si cycling in the Earth's oceans. Recent studies predict that pre-diatom-controlled oceans would have Si isotopic compositions of dissolved silicic acid (δ30Si DSi) that were enriched in heavier isotopes, ranging from +1.9‰ to +4.6‰, relative to NBS28 silica. This predicted range is based on calculations that assume a fractionation factor between sponges and silicic acid (Δ30Si s) in ancient (or modern) ocean waters of −3.8‰. Recently published data on sponge silicon isotopic compositions (δ30Si) and Δ30Si s , indicate that a Δ30Si s value for ancient sponges is more accurately calculated by applying corrections based on Michaelis–Menten enzyme kinetics. Predicted Δ30Si s values for pre-diatom sponges using the Michaelis–Menten enzyme kinetics corrections are −4.6 ± 0.1‰, roughly 0.9‰ lower than previous predictions. The new Δ30Si s value, applied to silicon isotopic compositions of silicified mid-Paleozoic and mid-Cenozoic coral fossils, allows for the calculation of δ30Si DSi between +2.0‰ and +2.3‰ for a Paleozoic open shelf environment. Applying the model to silicified mid-Cenozoic coral fossils, using Δ30Si values based on diatoms (−1.1‰) and sponges (−3.0 to −3.5, corresponding to DSi of 10 to 20 µM), resulted in an estimation of ocean's δ30Si DSi of +0.8 to +2.9‰. The mid-Cenozoic samples highlight the strong control of Δ30Si on the calculated values for δ30Si DSi. The results show the promise of these approaches in understanding the ocean water δ30Si DSi from Si isotope abundances measured in abiotic precipitates where DSi and Δ30Si are accurately known. [ABSTRACT FROM AUTHOR]

Belemnites were a type of cephalopod abundant in the Jurassic and Cretaceous, whose fossils have been extensively used for paleo-oceanographic studies. For this study, we analyzed 69 elements by Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS) in 15 belemnite rostra from the West Rodiles section in the Asturian Basin, Northern Spain. We aim to determine if belemnite rostra carbonate chemistry reflects changes in seawater chemistry during the Late Pliensbachian–Early Toarcian time interval and examine how belemnites can be used to trace known drivers of the Early Toarcian Oceanic Anoxic Event (T-OAE) and associated oceanographic processes. Discarding drastic intra-species effects and assuming a similar influence of growth rates, diet, and other physiological processes for all analyzed belemnite specimens and taking into consideration the sizeable analytical uncertainty, we assess if determined belemnite rostra element chemistry reflects broad and relative changes in paleo-seawater chemistry. Many determined elements are present in only ppb amounts, and their interpretation is uncertain. We found that Mg, Mn, and P increase in the interval chronocorrelative to the T-OAE. This is interpreted to have resulted from an increase in these elements' inventory in seawater due to an increase in continental weathering and fluvial runoff associated with this global event. Iron, K, and Na contents decrease upwards in the section, potentially indicating that these elements became limited and likely hampered oceanic productivity. Our study also found a correspondence between a change in the behaviour of several elements, warming, the T-OAE negative CIE, and a reduction in the diversity and size of both calcareous nannofossils and belemnites in the study area. • We study Early Toarcian seawater chemistry and T-OAE drivers. • 69 elements in 15 Spain belemnites rostra were analyzed. • Mg, Mn, and P rose due to weathering. • Fe, K, and Na declined, impacting ocean productivity and reducing nannofossil size. [ABSTRACT FROM AUTHOR]

Temporal variability of the paleo-oceanographic setting of the northern Red Sea during the last 6 Ky was deduced from high-resolution faunal results and stable isotope records of planktonic foraminifera in three short cores sediment obtained by the German R/V Meteor vessel. In general, the investigated time interval is fundamentally comparable to the present day composition and distribution of planktonic foraminifera. However, interrupted short enhanced arid phase spanning the last 4–2 Ky appears to have existed in the northern Red Sea, and resulted in elevation of salinity and somehow productivity, as hypersaline, dense surface water favored vertical mixing of the water column resulting in an increase in productivity. This paleoclimatic reconstruction is revealed from the distinct gradient in the composition and distribution of planktonic foraminifera, as well as the significant distribution trend of Globigerinoides ruber versus Globigerinoides sacculifer correlated with the stable isotope records. Starting from the last 2 Ky to the present time, less strength arid conditions relative to the previous period prevailed, reflected from a gradual decrease in surface water salinity and productivity assuming that the present water conditions and consequently current climatic conditions began to develop from that time with minor fluctuations reaching the recent conditions.

The accumulation of barium (Ba) in marine sediments is considered to be a robust proxy for export production, although this application can be limited by uncertainty in BaSO 4 preservation and sediment mass accumulation rates. The Ba isotope compositions of marine sediments could potentially record insights into past changes in the marine Ba cycle, which should be insensitive to these limitations, enabling more robust interpretation of sedimentary Ba as a proxy. To investigate the controls on the Ba isotope compositions of marine sediments and their potential for paleo-oceanographic applications, we present the first Ba isotope compositions results for sediments, as well as overlying seawater depth profiles collected in the South Atlantic. Variations in Ba isotope compositions of the sediments predominantly reflect changes in the relative contributions of detrital and authigenic Ba sources, with open-ocean sediments constraining the isotope composition of authigenic Ba to be δ Ba 138 / 134 ≈ + 0.1 ‰ . This value is consistent with the average isotope composition inferred for sinking particulate Ba using simple mass balance models of Ba in the overlying water column and is hypothesized to reflect the removal of Ba from the upper water column with an associated isotopic fractionation of Δ Ba diss - part 138 / 134 ≈ + 0.4 to +0.5. Perturbations to upper ocean Ba cycling, due to changes in export production and the supply of Ba via upwelling, should therefore be recorded by the isotope compositions of sedimentary authigenic Ba. Such insights will help to improve the reliable application of Ba accumulation rates in marine sediments as a proxy for past changes in export production. [ABSTRACT FROM AUTHOR]

Temporal variability of the paleo-oceanographic setting of the northern Red Sea during the last 6 Ky was deduced from high-resolution faunal results and stable isotope records of planktonic foraminifera in three short cores sediment obtained by the German R/V Meteor vessel. In general, the investigated time interval is fundamentally comparable to the present day composition and distribution of planktonic foraminifera. However, interrupted short enhanced arid phase spanning the last 4–2 Ky appears to have existed in the northern Red Sea, and resulted in elevation of salinity and somehow productivity, as hypersaline, dense surface water favored vertical mixing of the water column resulting in an increase in productivity. This paleoclimatic reconstruction is revealed from the distinct gradient in the composition and distribution of planktonic foraminifera, as well as the significant distribution trend of Globigerinoides ruber versus Globigerinoides sacculifer correlated with the stable isotope records. Starting from the last 2 Ky to the present time, less strength arid conditions relative to the previous period prevailed, reflected from a gradual decrease in surface water salinity and productivity assuming that the present water conditions and consequently current climatic conditions began to develop from that time with minor fluctuations reaching the recent conditions. [ABSTRACT FROM AUTHOR]

The human colonization of Norway occurred in the Pleistocene–Holocene transition – one of the most abrupt and severe climatic shifts in human history. For 1500 years (9500–8000 bc), the whole coast was occupied by mobile, marine-oriented hunter-gatherers. This paper explores dynamic relations between human adaptation and marine environmental variations in this period. An updated record of archaeological sites and palaeo-oceanographic data suggests a correlation between marine productivity and site distribution and density. The data further demonstrate spatial and temporal differences in the environment. A cooling pulse at 9300–9200 bc (the Preboreal Oscillation) with widespread ecological consequences must have been noticeable to humans occupying Norwegian landscapes. A more gradual shift occurred around 8800 bc when the arctic climate gave way to warmer conditions: The Norwegian Atlantic current stabilized, all fjord systems became ice-free, and animal diversity increased. In the northernmost region, the impact of Atlantic water was less severe, and Polar conditions with more sea ice seem to have lingered throughout the period. Variations in the site pattern may be related to these fluctuations in the resource situation. Variations in the lithic industry, on the other hand, seem to be connected to technological choices or local traditions, rather than environmental dissimilarities. The archaeological record indicates that the lifestyle, which developed under arctic conditions, was maintained through a flexible mobility pattern and a versatile tool technology, but the Norwegian coast also provided a good base to uphold such a lifestyle. [ABSTRACT FROM PUBLISHER]

[Display omitted] • A high-resolution organic matter δ13C record is present in the Upper Jurassic marine sedimentary rocks from Tibet. • An alternative to phytane- and stomatal density-based p CO 2 reconstructions is used with the carbon isotope fractionation. • Δ13C (δ13C carb -δ13C kerogen) and atmospheric p CO 2 calculation reveal a cooling event in the Early Tithonian. The Jurassic oceanographic and climatic evolution is considered to be related to the breakup of Pangaea. As a crucial component of the carbon cycle, atmospheric CO 2 concentration (p CO 2) has been postulated as a main driver for climate change during the Jurassic, and concomitant changes in paleo-oceanographic conditions occurred as a result. In this study, we present a high-resolution organic matter (kerogen) carbon isotope dataset (δ13C kerogen) from Upper Jurassic marine sedimentary rocks in the Qiangtang Basin, Tibet. The δ13C kerogen result contains a genuine record concerning the response of the eastern Tethys to exogenic carbon cycle perturbations in both marine and atmospheric reservoirs and is also consistent with the high-resolution bulk carbonate and organic matter carbon-isotope records from the Atlantic and western Tethys. The relative fractionation of carbon isotopes in organic matter vs. carbonate species, defined as Δ13C (δ13C carb -δ13C kerogen), and the secular trend of atmospheric p CO 2 over the Late Jurassic that is calculated from the high-resolution δ13C kerogen values indicate a cold Callovian-Oxfordian transition, a long-term increasing but fluctuating Kimmeridgian and a prominent early Tithonian cooling event (ETCE). The pronounced temperature plateau during the late Kimmeridgian-early Tithonian was contemporaneous with the occurrence of major magmatic events during the Late Jurassic, while the ETCE has been possibly attributed to major changes in oceanic circulation patterns. Additionally, reconstructed atmospheric p CO 2 values show very small differences to values using phytane- and stomatal density-based p CO 2 calculations, providing an alternative estimate for accurate identification of the paleoclimatic framework of this enigmatic interval in the Mesozoic. [ABSTRACT FROM AUTHOR]

Abstract: Compared to endemics, widespread species are of particular interest to retrace recent evolutionary history. These species have a large population size which provides a clearer genetic signature of past events. Moreover, their wide geographic range increases the potential occurrence of evolutionary events (expansion, divergence, etc.). Here, we used several coalescent-based methods to disentangle the evolutionary history of a widespread amphidromous goby (Sicyopterus lagocephalus), in the light of sea-level variations during the Pleistocene. Using 75 samples recovered from three biogeographic regions (Western Indian Ocean, Melanesia and Polynesia), we analysed a portion of the cytochrome b gene and confirmed three major haplogroups, each specific to a region. Furthermore, we found that: (1) the Melanesian haplogroup was the oldest while the two peripheral regions hosted daughter haplogroups; (2) two centrifugal colonisation events occurred from Melanesia to the periphery, each synchronised with periods of strong paleo-ENSO episodes; (3) the demographic contraction–expansion events were linked to Pleistocene sea-level changes; (4) Melanesia and Polynesia acted as efficient refuges during the Last Glacial Maximum. These results highlight the importance of studying widespread species to better understand the role of climate changes and paleo-oceanography on the evolution of biodiversity. [Copyright &y& Elsevier]

Abstract: This study investigates the environmental and biological controls on trace element partitioning and stable isotope composition of modern giant long-lived bivalves (Tridacna gigas) with the aim to use these archives for paleoclimatic reconstructions. Firstly, the intra-shell variability is studied by measuring time equivalent profiles in the different shell layers characterised by different growth rates. Secondly, the inter-site variability is studied by comparing profiles derived from three modern specimens collected in sites across the Indo-Pacific region characterised by different ranges of temperature and productivity. These results show that δ18O profiles are highly reproducible across the shell regardless of significantly different growth rates. Shell δ18O is primarily controlled by water δ18O and temperature. Comparison of intra shell Mg/Ca profiles shows a clear and systematic partitioning where inner layer Mg/Ca values are a least 2–3 times higher than outer layer and hinge areas. Inner layer Mg/Ca shows seasonal oscillations but superimposed on an ontogenetic trend with increasing values and increasing amplitude Mg/Ca oscillations with age. The Sr/Ca profiles do not show clear reproducible seasonal trends in the different shell zones. It is concluded that Mg/Ca and Sr/Ca profiles appear to reflect a combination of biological and environmental controls that will need to be disentangled before using these proxies in paleoclimatic studies. Finally, intra shell Ba/Ca profiles are reproducible in great detail for all modern specimens studied. Inter-site comparison shows that the amplitude and the timing of the Ba/Ca peaks appear to reflect the timing and the amplitude of the chlorophyll peaks associated with phytoplankton blooms at each locality making this tracer a potential paleoproductivity indicator. [Copyright &y& Elsevier]

Abstract: We investigate the redox-sensitive isotope system of molybdenum (Mo) in marine carbonates to evaluate their potential as archive of the Mo isotopic composition of coeval seawater. We present Mo isotope data (δ 98/95Mo) of modern skeletal and non-skeletal carbonates as well as a variety of precipitates from the mid and late Carboniferous. The external reproducibility is determined by repeated analyses of two commercially available carbonate standards. The resulting uncertainty of the low concentration samples is ±0.1‰ (2σ). Analysis of modern ooid sands from the Bahamas shows a consistently heavy Mo isotopic composition (δ 98/95Mo between 2 and 2.2‰), approaching modern mean seawater values (δ 98/95Mo=2.3‰±0.1‰ (2σ)). This suggests that isotope fractionation during Mo uptake into non-skeletal carbonate precipitates is small. In contrast, modern skeletal carbonates show variable isotopic compositions (0.1 to 2.2‰) which suggests a biologically controlled fractionation process. The varying Mo signatures found in Carboniferous cement phases point to a strong response to local changes in fluid composition from which they precipitated. Overall, we recognized three important factors to cause an offset relative to ocean water: Mo derived from skeletal components, input of detrital Mo and admixture of light, hydroxide derived Mo via diagenetic fluids. All of these factors cause a lighter Mo isotopic composition relative to seawater. Due to the apparent small isotope fractionation during Mo uptake into non-skeletal carbonates, their δ 98/95Mo closely reflects the ambient fluid composition. From these results we conclude that carbonates represent a promising new tool to characterize the water mass Mo isotopic composition of marine paleo-environments. [Copyright &y& Elsevier]

Abstract: Deep-sea corals are a new tool in paleoceanography with the potential to provide century long records of deep ocean change at sub-decadal resolution. Complicating the reconstruction of past deep-sea temperatures, Mg/Ca and Sr/Ca paleothermometers in corals are also influenced by non-environmental factors, termed vital effects. To determine the magnitude, pattern and mechanism of vital effects we measure detailed collocated Sr/Ca and Mg/Ca ratios, using a combination of micromilling and isotope-dilution ICP-MS across skeletal features in recent samples of Desmophyllum dianthus, a scleractinian coral that grows in the near constant environment of the deep-sea. Sr/Ca variability across skeletal features is less than 5% (2σ relative standard deviation) and variability of Sr/Ca within the optically dense central band, composed of small and irregular aragonite crystals, is significantly less than the surrounding skeleton. The mean Sr/Ca of the central band, 10.6±0.1 mmol/mol (2σ standard error), and that of the surrounding skeleton, 10.58±0.09 mmol/mol, are statistically similar, and agree well with the inorganic aragonite Sr/Ca-temperature relationship at the temperature of coral growth. In the central band, Mg/Ca is greater than 3 mmol/mol, more than twice that of the surrounding skeleton, a general result observed in the relative Mg/Ca ratios of D. dianthus collected from separate oceanographic locations. This large vital effect corresponds to a ∼10 °C signal, when calibrated via surface coral Mg/Ca-temperature relationships, and has the potential to complicate paleoreconstructions. Outside the central band, Mg/Ca ratios increase with decreasing Sr/Ca. We explain the correlated behavior of Mg/Ca and Sr/Ca outside the central band by Rayleigh fractionation from a closed pool, an explanation that has been proposed elsewhere, but which is tested in this study by a simple and general relationship. We constrain the initial solution and effective partition coefficients for a Rayleigh process consistent with our accurate Metal/Ca measurements. A process other than Rayleigh fractionation influences Mg in the central band and our data constrain a number of possible mechanisms for the precipitation of this aragonite. Understanding the process affecting tracer behavior during coral biomineralization can help us better interpret paleoproxies in biogenic carbonates and lead to an improved deep-sea paleothermometer. [Copyright &y& Elsevier]

Abstract: Strontium isotope ratios of the HCL-insoluble residue (“ISR”) and foraminifera of cores from the Red Sea and Gulf of Aden are used to monitor effects of hydrothermal, fluvial and desert dust transport to these regions during the past ∼0.5 Ma. While the Gulf of Aden was open-ocean, during low glacial sea levels the Red Sea was a semi-isolated basin, allowing the possibility to study the effects regional versus global inputs during glacial–interglacial cycles. The ISR from the Gulf of Aden and the Red Sea display different ranges of 87Sr/86Sr ratios of 0.7085–0.7107 and 0.7062–0.7085, respectively. These reflect mixtures between three components: granitic, hydrothermal and loess strontium with representative 87Sr/86Sr of ∼0.711; ∼0.706 and ∼0.7085, respectively. Gulf of Aden ISR represent mixtures of the loess and “granitic” sources, while Red Sea ISR are mixtures of the loess and sea floor “hydrothermal” sources. In the Gulf of Aden, loess sources dominate during glacials, indicating intensification of the NE moonsonal wind regime, and granitic sources dominate during interglacials, reflecting wetter conditions related to an enhanced regional SW monsoon. Red Sea ISR show no clear glacial–interglacial distinction, but display a general temporal increase in 87Sr/86Sr ratios over the past 380 ka toward loess-like values, indicating increasing loess contributions toward the present day. The ranges of ISR 87Sr/86Sr ratios in the Red Sea and the Gulf of Aden were distinct prior to the last glacial period (<60 ka), when they converge at loess values. The increasing loess signal may be due to increasing aridity in the dust source regions, or increasing accumulation and availability of loess with progressive glacial cycles. Superimposed on the Red Sea general trend are shifts to higher 87Sr/86Sr ratios following major climate transitions (at ∼10, ∼80, ∼130, ∼190, ∼240 and ∼330 ka BP) that coincide with sapropel episodes in the Eastern Mediterranean, which originated from the African monsoonal system and indicate enhanced wetness in the desert belt. 87Sr/86Sr ratios of foraminifera show a very narrow range from 0.70912 to 0.70917 over 530 ka, and in most samples are consistent with the contemporaneous global ocean. In the Red Sea, foraminifera and pteropods show slightly more variability than the Gulf of Aden. A few Red Sea samples fall slightly above the seawater trend (in Marine Isotope Stages 5 and 9) and below (during the last deglaciation), suggesting local effects that occurred when the flow of surface ocean water from the Gulf of Aden to the Red Sea was limited and the Red Sea behaved like an “amplifier basin”. [Copyright &y& Elsevier]

We present Fe isotope compositions for magnetite crystals from >3.7 Ga banded iron formation (BIF) from the Isua Greenstone Belt and younger, spatially related pyrite obtained in situ by secondary ion mass spectrometry (SIMS). Across a distance of several millimeters, individual magnetite crystals of BIF show δ56Fe values up to 2‰, and within single magnetiterich layers, there is a >2‰ range in δ56Fe. The highest positive δ56Fe values are consistent with those predicted by the equilibrium fractionation factor for oxidation of ferrous to ferric Fe in aqueous solution at a likely Early Archean ocean temperature of ∼70 °C, and further suggest that subsequent precipitation of ferric oxides was sufficiently slow that kinetic fractionation effects were minimal. These high values also imply that the supply of oxidant was limited. Heterogeneity in δ56Fe values is attributed to diagenetic reactions occurring in limited-volume pore waters, isolated from the bulk ocean (δ56Fe = 0‰), with development of isotope reservoir effects. Secondary pyrite in BIF and a conglomerate also show a distinct enrichment in heavy Fe isotopes, interpreted as redistribution and/or fractionation during postformational events. [ABSTRACT FROM AUTHOR]

Abstract: The restricted exchange of water with the Indian Ocean makes the Red Sea extremely sensitive to global oceanographic changes, such as sea-level variations linked with Quaternary climate change. The 120 m global sea level lowering during the last glacial maximum caused great reduction in water exchange with the open ocean. At that time, salinities reached 50‰, and were beyond the tolerance of planktonic foraminifera. Some topographic depressions located on the Red Sea axial zone are the centre of hydrothermal activity. They are filled with hot brines and contain metalliferous sediments. We studied three sediment cores in the axial part of the Red Sea, one from the metal-rich Suakin Deep depression, and two cores sampled outside any deep, at two different depths. The sediment of the core located in the anoxic brine-filled Suakin Deep contained no benthic foraminifera, indicating the deep was filled by a brine pool during the recovered period of marine isotopic stages 1, 2, and 3. The distribution of benthic foraminifera in the two other cores indicates that Red Sea waters were saltier during stage 2 and 3 than today, and that at 2000 m depth, Red Sea waters were anoxic during stage 2 and dysoxic during stage 3. Profiles of Fe, Mn, and Zn indicate that the sedimentary flux of metals was higher during stage 1 than during stage 2 in hydrothermal brine-filled deeps. In contrast, the sedimentary flux of metal in cores outside the anoxic depressions was higher during stage 2. The shape of the metal profiles can be attributed to hydrological changes that induced variations of redox conditions in water column during isotopic stage 1, 2, and 3. During interglacial periods, metals dissolved in anoxic brines precipitated at the redox boundary that corresponded to the brine–seawater interface, so that metals precipitated only in the deeps. During glacial period, the deep water was anoxic, and the redox boundary was located above the brine–seawater interface. Therefore, the hydrothermal metals could diffuse into the anoxic deep Red Sea water and be precipitated over a large area. This interpretation suggests that the observed variations of metal concentrations are not only related to fluctuations of the hydrothermal fluid discharge, but also to the varying redox conditions in the deep Red Sea water. [Copyright &y& Elsevier]

The response of coccolithophore assemblages to short-term millennial and centennial climatic changes over the last 50 kyr is studied in core M39029-7 from the Gulf of Cadiz (Atlantic Ocean) and core MD95-2043 from the Alboran Sea (Western Mediterranean Sea). The nannoplankton data are compared with oxygen isotopes, U37k′-SST and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short-term climatic changes. Coccolithophores indicate that Heinrich events (HE) were characterised by the presence of cold, low salinity and turbid water masses on both sides of the Strait of Gibraltar. High abundances of the Lower Photic Zone (LPZ) species Florisphaera profunda in the Gulf of Cadiz synchronous with HE are interpreted as being an evidence of upper water-column stratification on the Atlantic side. These episodes coincided with input of terrigenous material, especially during H2. Surface waters during Dansgaard-Oeschger (DO) Stadials were also cold and turbid, while most of DO Interstadials were characterised by warm-water flora. The increase in small placoliths (small Gephyrocapsa and Emiliania huxleyi (<4 μm)) reveals a higher coccolithophore production during DO Interstadials and the Holocene. Conversely, HE and most of DO Stadials show peaks of E. huxleyi (>4 μm), which is considered here as a cold-water indicator. The sharp decrease in large specimens of E. huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks—at least approximately—the deglaciation and the beginning of the Holocene. Peaks of F. profunda are observed during Termination 1 (T1) in the Alboran Sea. They are isochronous with the “Organic-Rich Layer 1” recognised in the Western Mediterranean. In this interval, the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation. Quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the Alboran Sea than in the Gulf of Cadiz during the Holocene. [Copyright &y& Elsevier]

Abstract Aim To evaluate the state of knowledge about the biogeography of Brazilian reef fishes and propose processes that lead to the observed distribution patterns. Location The tropical western Atlantic. Methods The geological history of the Amazon barrier was obtained from the literature, and its potential influence on speciation of reef fishes was analysed. Species distributions were analysed based on literature records and material deposited at Brazilian and American collections. Results Recent estimates indicate that about 12% of the Brazilian reef fish species are endemic, and most ichthyologists agree that this endemism is generated by the barrier formed by the freshwater and sediment discharge of large rivers in north-eastern South America, mainly the Amazon, Orinoco and their tributaries. However, little is known about the dynamics of this barrier, and recent studies have demonstrated that it can be crossed through deep sponge bottoms on the outer continental shelf off north-eastern South America. Moreover, the recent discovery of species regarded as Brazilian endemics in the extreme southern Caribbean is showing that the Amazon barrier is weaker than previously thought. Main conclusions The Amazon freshwater and sediment outflow is a strong barrier to shallow water reef fish and other organisms, and it is probably responsible for most of the endemism found in Brazilian coastal habitats. However, sea-level fluctuations influence the effectiveness of such barrier and may play a large role in the generation of diversity in the western tropical Atlantic. Alternatively, larval exchange between Brazil and the Caribbean is small but constant, and contrasting selection pressures in divergent environments (continental Brazil vs. insular Caribbean) may be the central force driving speciation. [ABSTRACT FROM AUTHOR]

The use of the Nd isotope composition of planktic foraminifera as a proxy for sea surface water is based on the assumption that Nd is incorporated during initial calcification and preserved after foraminifera death, subsequent transport through the water column and storage in the sediment pile. To test this assumption Nd concentrations are reported from foraminiferal tests collected from 20 to 3045 m depth (multinets and sediment traps) from offshore Somalia and in the Somali Basin of the Indian Ocean. Nd partition coefficients calculated for two species Globigerinoides ruber and Globigerina bulloides sampled in the uppermost water column (100 m) are 16–52. The measured Nd/Ca ratio of living foraminifera is ∼8 nmol/mol, which is 8–190 times lower than reported in cleaned foraminifera from sediment cores (61–1500 nmol/mol). Moreover, the Nd content of foraminiferal tests varies markedly within the water column (8–220 nmol/mol Ca) recording a positive correlation with Mn content (r2=0.91). The observed changes in the Nd concentration after foraminiferal death appear to reflect Nd addition from deeper in the water column and imply a major disturbance of the primary Nd isotope composition formed at the surface. The high Nd/Ca reported for cleaned foraminifera from sediment cores are interpreted to be a consequence of current cleaning techniques. Although cleaning successfully removes organics and secondary Mn coatings into solution any released rare earth elements (REE) are subsequently re-adsorbed onto the calcite. Cleaning removes elements with a 2+ valency state into solution (e.g. Cd and Mn) but more reactive elements with higher valency states (e.g. REE3+, Th4+) are re-absorbed onto residual carbonate. It is concluded that, although foraminifera clearly record temporal variations in Nd isotope composition, the relationship between these variations and changes in the sea surface Nd isotope composition has yet to be established unambiguously. Further work is required to rule out the possibility that the Nd in foraminifera represents a mixed signal derived from surface sediments and bottom and pore waters. [Copyright &y& Elsevier]

Environmental variables such as temperature and salinity cannot be directly measured for the past. Such variables do, however, influence the chemistry and biology of the marine sedimentary record in a measurable way. Reconstructing the past environment is therefore possible by ‘proxy’. Such proxy reconstruction uses chemical and biological observations to assess two aspects of Earth’s climate system – the physics of ocean–atmosphere circulation, and the chemistry of the carbon cycle. Early proxies made use of faunal assemblages, stable isotope fractionation of oxygen and carbon, and the degree of saturation of biogenically produced organic molecules. These well-established tools have been complemented by many new proxies. For reconstruction of the physical environment, these include proxies for ocean temperature (Mg/Ca, Sr/Ca, δ44Ca) and ocean circulation (Cd/Ca, radiogenic isotopes, 14C, sortable silt). For reconstruction of the carbon cycle, they include proxies for ocean productivity (231Pa/230Th, U concentration); nutrient utilization (Cd/Ca, δ15N, δ30Si); alkalinity (Ba/Ca); pH (δ11B); carbonate ion concentration (foraminiferal weight, Zn/Ca); and atmospheric CO2 (δ11B, δ13C). These proxies provide a better understanding of past climate, and allow climate–model sensitivity to be tested, thereby improving our ability to predict future climate change. Proxy research still faces challenges, however, as some environmental variables cannot be reconstructed and as the underlying chemistry and biology of most proxies is not well understood. Few proxies have been applied to pre-Pleistocene times – another challenge for future research. Only by solving such challenges will proxies provide a full understanding of the range of possible climate variability on Earth and of the mechanisms causing this variability. [Copyright &y& Elsevier]

Paired benthic Cd/Ca and δ13C records have been generated along core M35003 in the western tropical Atlantic. Decreased glacial water column dissolved cadmium (Cdw) and increased benthic δ13C indicate enhanced ventilation with nutrient-deplete intermediate waters, in line with similar inferences from other North Atlantic mid-depth records. An abrupt early deglacial δ13C collapse that is associated with a marked positive Cdw anomaly indicates a transient collapse of mid-depth ventilation from North Atlantic sources, conceivably in conjunction with the H1 meltwater anomaly. The Cdw record displays fine-scale fluctuations that mimic the Greenland Dansgaard/Oeschger (D/O) cycles and show decreased Cdw during stadials. This pattern is opposite to Cdw variations in a deep water record from Bermuda Rise that display increased Cdw concentrations during stadials. The divergent pattern between mid-depth and deep water Cdw records indicates millennial-scale switches between deep and shallow convection in the glacial North Atlantic, at the pace of the D/O climatic cycles. Several high-amplitude anomalies occur in the Cdw record that reach levels similar to those observed today in the North Pacific. While a substantial nutrient increase in the mid-depth North Atlantic cannot be ruled out during these events, changes of pore water chemistry and Cd/P fractionation during biological uptake offer alternative scenarios to explain the peak Cdw maxima. [Copyright &y& Elsevier]

We have generated benthic foraminiferal Mg/Ca records from eastern tropical Atlantic core M16772 (3.9 km) and eastern tropical Pacific core TR163-31P (3.2 km) to assess the potential for using benthic Mg-paleothermometry to reconstruct Quaternary bottom water temperature histories. Variations in Mg/Ca records from both the Atlantic and Pacific show a significant correlation with climatic oscillations of the last 330 kyr. Shell Mg/Ca peaks during interglacial episodes, with marine isotope stage (MIS) 5e Mg/Ca nearly matching Holocene values in both cores. Lower Mg/Ca values occur during glacial intervals. To estimate temperatures from downcore Mg/Ca, we have augmented the published Cibicidoides sp. Mg/Ca–temperature dataset [Rosenthal et al., Geochim. Cosmochim. Acta 61 (1997) 3633–3643] with new data to include the temperature range of deep waters. Applying the 10.9% change in Mg/Ca per °C defined by the expanded calibration to the deep Atlantic data implies glacial–interglacial shifts in deep water temperature of 2–4°C over the last 300 kyr. Temperature estimates are comparable to deep Atlantic temperature changes proposed by Labeyrie et al. [Nature 327 (1987) 477–482]. There is greater uncertainty in deriving temperatures from the tropical Pacific core due to a limited Uvigerina spp. core top calibration set; however, glacial–interglacial temperature oscillations appear to be on the order of 2–3°C. In addition, core TR163-31P records clear millennial-scale Mg/Ca and δ18O oscillations in MIS 3 corresponding to temperature fluctuations of >0.5°C. Additional calibration studies are needed to address potential secondary effects on Mg/Ca. [Copyright &y& Elsevier]

We developed a plate tectonic model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean spreading rates and major tectonic and magmatic events. Plates were constructed through time by adding/removing oceanic material, symbolized by synthetic isochrons, to major continents and terranes. Driving forces like slab pull and slab buoyancy were used to constrain the evolution of paleo-oceanic domains. This approach offers good control of sea-floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained, due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean–Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys–Atlantic domain versus the NeoTethys domain. [Copyright &y& Elsevier]