Phosphorus concentrations and accumulation rates of ODP Leg 130 sites

Little is known about the fluxes to and from the ocean during the Cenozoic of phosphorus (P), a limiting nutrient for oceanic primary productivity and organic carbon burial on geologic timescales. Previous studies have concluded that dissolved river fluxes increased worldwide during the Cenozoic and that organic carbon burial decreased relative to calcium carbonate burial and perhaps in absolute terms as well. To examine the apparent contradiction between increased river fluxes of P (assuming P fluxes behave like the others) expected to drive increased organic carbon burial and observations indicating decreased organic carbon burial, we determined P accumulation rates for equatorial Pacific sediments from Ocean Drilling Program leg 138 sites in the eastern equatorial Pacific and leg 130 sites on the Ontong Java Plateau in the western equatorial Pacific. Although there are site specific and depth dependent effects on P accumulation rates, there are important features common to the records at all sites. P accumulation rates declined from 50 to 20 Ma, showed some variability from 20 to 10 Ma, and had a substantial peak from 9 to 3 Ma centered at 5-6 Ma. These changes in P accumulation rates for the equatorial Pacific are equivalent to substantial changes in the P mass balance. However, the pattern resembles neither that of weathering flux indicators (87Sr/86Sr and Ge/Si ratios) nor that of the carbon isotope record reflecting changes in organic carbon burial rates. Although these P accumulation rate patterns need confirmation from other regions with sediment burial significant in global mass balances (e.g., the North Pacific and Southern Ocean), it appears that P weathering inputs to the ocean are decoupled from those of other elements and that further exploration is needed of the relationship between P burial and net organic carbon burial

(Table T1) Geochemical composition of ODP Site 177-1089 sediments

A primary objective of Ocean Drilling Program Leg 177 was to document changes in circulation and biogeochemical cycling on glacial/interglacial time scales across a wide latitudinal range of the south Atlantic Ocean. One of the more northerly sites drilled, Site 1089 (41°S, 10°E), is located within the present-day Subantarctic Zone, south of the Subtropical Front. The drilling site itself is located in the southern Cape Basin at a water depth of 4620 m. Pleistocene sediments at this site are dominated by interbedded carbonate and opal oozes. Initial shipboard stratigraphy identified the opal-rich sediments as deposited during glacial intervals and the carbonate-rich sediments as deposited during interglacial intervals (Gersonde, Hodell, Blum, et al., 1999, doi:10.2973/odp.proc.ir.177.1999). Postcruise isotopic stratigraphy, however, verified that this site displayed a Pacific Pleistocene sedimentation pattern with glacial intervals marked by high carbonate content (Hodell and Charles, 1999). To assess changes in biological productivity and terrigenous inputs at this site, a number of geochemical indicators were determined. Phosphorus concentrations and P/metal ratios were determined to assess changes in export production on glacial/interglacial time scales. Metal concentrations, along with elemental ratios, were used to assess terrigenous inputs. Sediment geochemistry allows us to identify changes in the lithologic component using elemental data based on Fe, Al, and Ti concentrations. Records of concentrations and ratios of biologically related elements identify changes in export production. The P and metal results are important to assess the glacial/interglacial changes in P burial and the relationships between a major nutrient such as P with metals (and possibly trace nutrients) like Fe

(Table T1) Phosphorus and metal concentrations of ODP Site 189-1171

A primary goal of Leg 189 was to evaluate Cenozoic changes in ocean circulation and the subsequent influence on climate variability (Exon, Kennett, Malone, et al., 2001, doi:10.2973/odp.proc.ir.189.2001; Exon et al., 2002, doi:10.1029/2002EO000176). Our approach is to use bulk sediment geochemical records to try to understand the influences of changing ocean circulation and climate on biogeochemical cycles and export production (e.g., Latimer and Filippelli, 2001, doi:10.1029/2000PA000586; 2002, doi:10.1016/S0031-0182(01)00493-X). Site 1171 (48°S, 149°E) is located on the South Tasman Rise at a water depth of ~2150 m. Late Paleocene to late Eocene age sediments represent shallow-water silty claystones and claystones (Exon, Kennett, Malone et al., 2001, doi:10.2973/odp.proc.ir.189.2001). A 6-m section of glauconitic sandstone to siltstone is observed in the uppermost upper Eocene and is followed by a sharp lithologic change from shallow-water siliciclastics to pelagic carbonates (Exon, Kennett, Malone, et al., 2001, doi:10.2973/odp.proc.ir.189.2001). Sediments of Oligocene age to present are predominantly nannofossil ooze or chalk. Sediment geochemistry allows us to identify changes in metal sources and terrigenous inputs using elemental data based on Fe, Al, and Ti concentrations and elemental ratios, such as Al/Ti and Fe/Ti. To assess export production, we use records of phosphorus (P) and barium (Ba) concentrations and P/metal and Ba/metal ratios, with elevated values being interpreted as higher export production

Prismatic adaptation effects on spatial representation of time in neglect patients.

Processing of temporal information may require the use of spatial attention to represent time along a mental time line. We used prismatic adaptation (PA) to explore the contribution of spatial attention to the spatial representation of time in right brain damaged patients with and without neglect of left space and in age-matched healthy controls.Right brain damaged patients presented time underestimation deficits, that were significantly greater in patients with neglect than in patients without neglect. PA inducing leftward attentional deviation reduced time underestimation deficit in patients with neglect.The results support the hypothesis that a right hemispheric network has a role, per se, in time perception. Moreover, they suggest that right hemisphere is important in time perception for its control of spatial attention, engaged in spatial representation of time. Procedures that ameliorate left spatial deficits could also be useful for modulating temporal deficits in right brain damaged patients with neglect

Surface water dynamics and phytoplankton communities during deposition of cyclic late Messinian sapropel sequences in the western Mediterranean

Distinctive precession-scale sapropel/marl sequences of late Messinian age are found in several outcrops bordering the western Mediterranean. To examine the roles of stratification and productivity in driving this cyclic sedimentation, we performed a high resolution analysis of calcareous nannofossil assemblages through four orbital sequences (composed of sapropel/marl/ diatomite/marl) from the Sorbas basin in southern Spain. This effort also involved a detailed comparison between calcareous nannofossil abundances and other micropaleontological, sedimentological and geochemical proxies to further understand the behaviour of some taxa. For this period, fluctuations in the depth and gradient of the pycnocline, and the distribution and remobilization of nutrients seem to be the main factors controlling the calcareous nannoplankton assemblages, with temperature of secondary importance. In the sapropels, the warm-oligotrophic genus Sphenolithus and Discoaster are abundant. Especially significant is the progressive increase towards the top of Discoaster pentaradiatus, indicator of severe oligotrophic (deep pycnocline) conditions. At the top of the sapropels, peaks in Reticulofenestra rotaria are interpreted here as the result of an increase of surface water temperatures, although decreasing salinity may also play a role. Small Reticulofenestra ( 5 μm) are more frequent in diatomites even considering conditions of extreme mixing and eutrophication occurred in the basin. Umbilicosphaera jafari peaks just after diatomites, replacing small Reticulofenestra, probably as a response to an increase in salinity and/or nutrient limitation. Species such as Coccolithus pelagicus and Helicosphaera carteri are abundant at the top of the diatomites and in the overlying marls, indicating relatively mesotrophic and cool water conditions. This succession shows similar characteristics in the four studied cycles, allowing us to interpret surface water dynamics in this region on orbital time scales. The top of the sapropel represents a warm, low salinity and well stratified episode under a situation of maximum insolation. A well developed pycnocline and oligotrophic conditions (moderate production of calcareous phytoplankton) coinciding with anoxic conditions at the bottom enhance the preservation of organic matter, and consequently generate a sapropel. Diatomites are deposited under a situation of unstable pycnocline that produce an increase in productivity in surface waters. Diatoms significantly deplete limiting nutrients, and consequently calcareous nannofossils start to be dominant again in the water column as result of a progressive stabilization of the pycnocline. © 2005 Elsevier B.V. All rights reserved.Research grants REN2003-08642-C02-02 CLI, BTE 2002-04670 (Ministerio de Educación y Ciencia) and Junta de Castilla y León SA088/04 supported this study.Peer Reviewe

A Sediment-Nutrient-Oxygen Feedback Responsible for Productivity Variations in Late Miocene Sapropel Sequences of the Western Mediterranean

Cyclic sediments observed throughout the Mediterranean during the Late Miocene have been related to precessional forcing of ocean stratification. Individual couplets, typically 2-m-thick sequences of sapropels and diatom-rich marls, can be reliably traced from western Spain to Crete, and were formed in restricted marginal basins. Micropaleontological evidence indicates paradoxically that the organic carbon-rich sapropels were formed under low productivity conditions marked by surface water stratification and deep anoxia, whereas the diatom-rich marls were formed under high productivity conditions marked by upwelling. Here we present geochemical evidence, mainly from detailed phosphorus determinations and paleo-redox proxies, indicating that a sediment–nutrient–oxygen feedback (herein dubbed the SNO Effect) is in part responsible for driving the observed productivity variations. During stratification, anoxic conditions in these basins cause the release of the limiting nutrient phosphorus from reducible oxide phases in the sediments. Basin stagnation causes the buildup of phosphorus below the photic zone. Subsequent overturn driven by precessionally-driven winds injects phosphorus-rich bottom waters into the photic zone. The biotic response to this overturn is high productivity in marls directly overlying the sapropels culminating in diatom mat formation. Exhaustion of the stored excess phosphorus results in lower productivity marls, which grade back into sapropels due to lower wind stresses and the return of stagnant basin conditions. These findings indicate that the SNO Effect may in part be responsible for precessional-scale productivity variations observed in parts of the Mediterranean, and perhaps present in other restricted ocean basins, like the Miocene Monterey Formation and the modern Santa Barbara Basin.We thank the donors of the Petroleum Research Fund,administered by the American Chemical Society,the US National Science Foundation (Grant OCE9711957 to G.M.F.),the Fulbright Organization,and the DGCYES project PB98^0288 for support of this research.Peer Reviewe