Miocene-Pliocene record of Pollen, charcoal and carbon isotopes of plant waxes of ODP Hole 175-1081A

Modern savannah grasslands were established during the late Miocene and Pliocene (8-3 million years ago). In the tropics, grasslands are dominated by grasses that use the C4 photosynthetic pathway, rather than the C3 pathway. The C4 pathway is better adapted to warm, dry and low-CO2 conditions, leading to suggestions that declining atmospheric CO2 levels, increasing aridity and enhanced rainfall seasonality allowed grasses using this pathway to expand during this interval. The role of fire in C4 expansion may have been underestimated. Here we use analyses of pollen, microscopic charcoal and the stable isotopic composition of plant waxes from a marine sediment core off the coast of Namibia to reconstruct the relative timing of changes in plant composition and fire activity for the late Miocene and Pliocene. We find that in southwestern Africa, the expansion of C4 grasses occurred alongside increasing aridity and enhanced fire activity. During further aridification in the Pliocene, the proportion of C4 grasses in the grasslands increased, while the grassland contracted and deserts and semi-deserts expanded. Our results are consistent with the hypothesis that ecological disturbance by fire was an essential feedback mechanism leading to the establishment of C4 grasslands in the Miocene and Pliocene.

Anelastic strain recovery and elastic properties of ODP Leg 123 oceanic basalt samples

A knowledge of rock stress is fundamental for improving our understanding of oceanic crustal mechanisms and lithospheric dynamic processes. However, direct measurements of stress in the deep oceans, and in particular stress magnitudes, have proved to be technically difficult. Anelastic strain recovery measurements were conducted on 15 basalt core samples from Sites 765 and 766 during Leg 123. Three sets of experiments were performed: anelastic strain recovery monitoring, dynamic elastic property measurements, and thermal azimuthal anisotropy observations. In addition, a range of other tests and observations were recorded to characterize each of the samples. One common feature of the experimental results and observations is that apparently no consistent orientation trend exists, either between the different measurements on each core sample or between the same sets of measurements on the various core samples. However, some evidence of correspondence between velocity anisotropy and anelastic strain recovery exists, but this is not consistent for all the core samples investigated. Thermal azimuthal anisotropy observations, although showing no conclusive correlations with the other results, were of significant interest in that they clearly exhibited anisotropic behavior. The apparent reproducibility of this behavior may point toward the possibility of rocks that retain a "memory" of their stress history, which could be exploited to derive stress orientations from archived core. Anelastic strain recovery is a relatively new technique. Because use of the method has extended to a wider range of rock types, the literature has begun to include examples of rocks that contracted with time. Strong circumstantial evidence exists to suggest that core-sample contractions result from the slow diffusion of pore fluids from a preexisting microcrack structure that permits the rock to deflate at a greater rate than the expansion caused by anelastic strain recovery. Both expansions and contractions of the Leg 123 cores were observed. The basalt cores have clearly been intersected by an abundance of preexisting fractures, some of which pass right through the samples, but many are intercepted or terminate within the rock matrix. Thus, the behavior of the core samples will be influenced not only by the properties of the rock matrix between the fractures, but also by how these macro- and micro-scale fractures mutually interact. The strain-recovery curves recorded during Leg 123 for each of the 15 basalt core samples may reflect the result of two competing time dependent processes: anelastic strain recovery and pore pressure recovery. Were these the only two processes to influence the gauge responses, then one might expect that given the additional information required, established theoretical models might be used to determine consistent stress orientations and reliable stress magnitudes. However, superimposed upon these competing processes is their respective interaction with the preexisting fractures that intersect each core. Evidence from our experiments and observations suggests that these fractures have a dominating influence on the characteristics of the recovery curves and that their effects are complex.

Toxoplasma gondii seroprevalence in ringed seals (Pusa hispida) from the Canadian Arctic

Toxoplasmosis is a significant public health threat for Inuit in the Canadian Arctic. This study aimed to investigate arctic seals as a possible food-borne source of infection. Blood samples collected from 828 seals in 7 Canadian Arctic communities from 1999 to 2006 were tested for Toxoplasma gondii antibodies using a direct agglutination test. Polymerase chain reaction (PCR) was used to detect T. gondii DNA in tissues of a subsample of seals. Associations between seal age, sex, species, diet, community and year of capture, and serological test results were investigated by logistic regression. Overall seroprevalence was 10.4% (86/828). All tissues tested were negative by PCR. In ringed seals, seroprevalence was significantly higher in juveniles than in adults (odds ratio = 2.44). Overall, seroprevalence varied amongst communities (P = 0.0119) and by capture year (P = 0.0001). Our study supports the hypothesis that consumption of raw seal meat is a significant source of infection for Inuit. This work raises many questions about the mechanism of transfer of this terrestrial parasite to the marine environment, the preponderance of infection in younger animals and the natural course of infection in seals. Further studies to address these questions are essential to fully understand the health risks for Inuit communities.

Age models, organic analyses and major-element analyses of sediment cores on a transect of the tropical African rainbelt

The distribution of rainfall in tropical Africa is controlled by the African rainbelt**1, which oscillates on a seasonal basis. The rainbelt has varied on centennial to millennial timescales along with changes in Northern Hemisphere high-latitude climate**2, 3, 4, 5, the Atlantic meridional overturning circulation**6 and low-latitude insolation**7 over the past glacial-interglacial cycle. However, the overall dynamics of the African rainbelt remain poorly constrained and are not always consistent with a latitudinal migration**2, 4, 5, 6, as has been proposed for other regions**8, 9. Here we use terrestrially derived organic and sedimentary markers from marine sediment cores to reconstruct the distribution of vegetation, and hence rainfall, in tropical Africa during extreme climate states over the past 23,000 years. Our data indicate that rather than migrating latitudinally, the rainbelt contracted and expanded symmetrically in both hemispheres in response to changes in climate. During the Last Glacial Maximum and Heinrich Stadial 1, the rainbelt contracted relative to the late Holocene, which we attribute to a latitudinal compression of atmospheric circulation associated with lower global mean temperatures**10. Conversely, during the mid-Holocene climatic optimum, the rainbelt expanded across tropical Africa. In light of our findings, it is not clear whether the tropical rainbelt has migrated latitudinally on a global scale, as has been suggested**8,9.

Sedimentological, geochemical, micropaleontological and rock magnetic proxies of sediment core GeoB6211-2

Surface currents and sediment distribution of the SE South American upper continental margin are under influence of the South American Monsoon System (SAMS) and the Southern Westerly Wind Belt (SWWB). Both climatic systems determine the meridional position of the Subtropical Shelf Front (STSF) and probably also of the Brazil-Malvinas Confluence (BMC). We reconstruct the changing impact of the SAMS and the SWWB on sediment composition at the upper Rio Grande Cone off southern Brazil during the last 14 cal kyr combining sedimentological, geochemical, micropaleontological and rock magnetic proxies of marine sediment core GeoB 6211-2. Sharp reciprocal changes in ferri- and paramagnetic mineral content and prominent grain-size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments. Our interpretations support the assumption that the SAMS over SE South America was weaker than today during most of the Late Glacial and entire Early Holocene, while the SWWB was contracted to more southern latitudes, resembling modern austral summer-like conditions. In consequence, the STSF and the BMC were driven to more southern positions than today's, favoring the deposition of Fe-rich but weakly magnetic La Plata River silts at the Rio Grande Cone. During the Mid Holocene, the northern boundary of the SWWB migrated northward, while the STSF reached its northernmost position of the last 14 cal kyr and the BMC most likely arrived at its modern position. This shift enabled the transport of Antarctic diatoms and more strongly magnetic Argentinean shelf sands to the Rio Grande Cone, while sediment contributions from the La Plata River became less important. During the Late Holocene, the modern El Niño Southern Oscillation set in and the SAMS and the austral tradewinds intensified, causing a southward shift of the STSF to its modern position. This reinforced a significant deposition of La Plata River silts at the Rio Grande Cone. These higher magnetic silts with intermediate Fe contents mirror the modern more humid terrestrial climatic conditions over SE South America.

(Fig. 9) Pollen analysis of sediment core GIK16017-2

The improved understanding of the pollen signal in the marine sediments offshore of northwest Africa is applied to deep-sea core M 16017-2 at 21°N. Downcore fluctuations in the percentage, concentration and influx diagrams record latitudinal shifts of the main northwest African vegetation zones and characteristics of the trade winds and the African Easterly Jet. Time control is provided by 14C ages and 180 records. During the period 19,000-14,000 yr B.P. a compressed savanna belt extended between about 12 ° and 14-15°N. The Sahara had maximally expanded northward and southward under hyperarid climatic conditions. The belt with trade winds and dominant African Easterly Jet transport had not shifted latitudinally. The trade winds were strong as compared to the modern situation but around 13,000 yr B.P. the trade winds weakened. After 14,000 yr B.P. the climate became less arid south of the Sahara and a first spike of fluvial runoff is registered around 13,000 yr B.P. Fluvial runoff increased strongly around 11,000 yr B.P. and maximum runoff is recorded from about 9000-7800 yr B.P. Around 12,500 yr B.P. the savanna belt started to shift northward and became richer in woody species: it shifted about 6° of latitude, reached its northernmost position during the period of 9200-7800 yr B.P. and extended between about 16° and 24°N at that time. Tropical forest had reached its maximum expansion and the Guinea zone reached as far north as about 15°N, reflecting very humid climatic conditions south of the Sahara. North of the Sahara the climate also became more humid and Mediterranean vegetation developed rapidly. The Sahara had maximally contracted and the trade winds were weak and comparable with the present day intensity. After about 7800 yr B.P. the southern fringe of the Sahara and accordingly the savanna belt, shifted rapidly southward again.

Sea surface temperature estimates and alkenone C37:4 abundances in ODP Site 145-882 and 177-1090

The cold upwelling 'tongue' of the eastern equatorial Pacific is a central energetic feature of the ocean, dominating both the mean state and temporal variability of climate in the tropics and beyond. Recent evidence for the development of the modern cold tongue during the Pliocene-Pleistocene transition has been explained as the result of extratropical cooling that drove a shoaling of the thermocline. We have found that the sub-Antarctic and sub-Arctic regions underwent substantial cooling nearly synchronous to the cold tongue development, thereby providing support for this hypothesis. In addition, we show that sub-Antarctic climate changed in its response to Earth's orbital variations, from a subtropical to a subpolar pattern, as expected if cooling shrank the warm-water sphere of the ocean and thus contracted the subtropical gyres.

Multi-proxy record of planktonic and benthic foraminiferal d18O, and Mg/Ca-derived surface and lower thermocline temperatures in sediment core SO18471 (GIK18471), Timor Sea

Paleostudies of the Indonesian Throughflow (ITF) are largely based on temperature and salinity reconstructions of its near surface component, whereas the variability of its lower thermocline flow has rarely been investigated. We present a multi-proxy record of planktonic and benthic foraminiferal d18O, Mg/Ca-derived surface and lower thermocline temperatures, X-ray fluorescence (XRF)-derived runoff and sediment winnowing for the past 130 ka in marine sediment core SO18471. Core SO18471, retrieved from a water depth of 485 m at the southern edge of the Timor Strait close to the Sahul Shelf, sits in a strategic position to reconstruct variations in both the ITF surface and lower thermocline flow as well as to investigate hydrological changes related to monsoon variability and shelf dynamics over time. Sediment winnowing demonstrates that the ITF thermocline flow intensified during MIS 5d-a and MIS 1. In contrast during MIS 5e, winnowing was reduced and terrigenous input increased suggesting intensification of the local wet monsoon and a weaker ITF. Lower thermocline warming during globally cold periods (MIS 4 - MIS 2) appears to be related to a weaker and contracted thermocline ITF and advection of warm and salty Indian Ocean waters.

(Table 1) Hydrocarbon gas composition of sediment and gas hydrate collected in video-guided grabs from Chapopote

In the Campeche Knolls, in the southern Gulf of Mexico, lava-like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level. Chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt, which chilled and contracted after discharge. The site also includes oil seeps, gas hydrate deposits, locally anoxic sediments, and slabs of authigenic carbonate. Asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the Gulf of Mexico.

(Table S1) Age determination ofs ediment cores of the Azores Current System

In order to test the sensitivity of marine primary productivity in the midlatitude open ocean North Atlantic to changes in the Atlantic Meridional Overturning Circulation (AMOC), we investigated two spliced sediment cores from a site south of the Azores Islands at the northern rim of the North Atlantic subtropical gyre. For this purpose we analyzed coccolithophore assemblages, diatom abundances, alkenones and conducted X-ray fluorescence (XRF) core scanning. During times of reduced AMOC, especially during Heinrich event 1 (H1) and the Younger Dryas, we observe a strong increase in productivity as evidenced by high coccolith accumulation rates, high alkenone concentrations/accumulation rates, high Ba/Ti-ratios, high abundances of diatoms and low abundances ofF. profunda. The increased productivity is partly caused by a more southern position of the Azores Front (AzF), and hence by a less northward extension of the subtropical gyre, as deduced from high abundances of the temperate coccolithophore species G. muellerae and low abundances of subtropical species (Oolithotus spp., Umbellosphaera spp., Umbilicosphaeraspp.). However, to explain the full range of the observed productivity increase, other factors like increased westerly winds and advection of nutrient-rich surface waters have also to be considered. Because this pattern can also be observed in other sediment cores from the midlatitude North Atlantic, we propose that during times of reduced AMOC there has been a band of strongly increased productivity across the North Atlantic at the northern rim of the contracted subtropical gyre, which partly counteracts the decreased organic carbon pump in the high northern latitudes.

Annotated record of the detailed examination of Mn deposits on the coral banks of the continental shelf in the south-western coastal area of the Gulf of Mexico off Texas

During U.S. Department of Interior, Bureau of Land Management (BLM) public hearings held in 1973, 1974 and 1975 prior to Texas Outer Continental Shelf (OCS) oil and gas lease sales, concern was expressed by the National Marine Fisheries Service, scientists from Texas A&M and the University of Texas and private citizens over the possible environmental impact of oil and gas drilling and production operations on coral reefs and fishing banks in or adjacent to lease blocks to be sold. As a result, certain restrictive regulations concerning drilling operations in the vicinity of the well documented coral reefs and biostromal communities at the East and West Flower Gardens were established by BLM, and Signal Oil Company was required to provide a biological and geological baseline study of the less well known Stetson Bank before a drilling permit could be issued. Considering the almost total lack of knowledge of the geology and biotic communities associated with the South Texas OCS banks lying in or near lease blocks to be offered for sale in 1975, BLM contracted with Texas A&M University to provide the biological and geological baseline information required to facilitate judgments as to the extent and nature of restrictive regulations on drilling near these banks which might be required to insure their protection. In pursuit of this, scientists from Texas A&M University were to direct their attention toward assessments of ground fish populations, unique biological and geological features, substratum type and distribution, and the biotic and geologic relationships between these banks and those farther north.