Carbonate, organic carbon and nitrogen, bitumen and rock-eval pyrolysis at DSDP Leg 79 Holes

The lipids and kerogens of 15 sediment samples from Site 547 (ranging from Pleistocene to Early Jurassic/Triassic) and 4 from Site 545 (Cretaceous) have been analyzed. A strong terrestrial contribution of organic matter was found, and significant autochthonous inputs were also present, especially at Site 545. Both strongly reduced and highly oxidized sediments have been found in the Cenozoic and Jurassic samples of Site 547. On the contrary, all the Cretaceous sections of Sites 547 and 545 are anoxic. Sediments from anoxic paleoenvironments are immature and have a high content of sterenes, diasterenes, steradienes, hopenes, and ßß hopanes. Samples from oxic paleoenvironments are mainly mature and their content of hopenes and steriod structures is below the detection level. Nevertheless, their hopane distributions have the immature ßß homologs as the predominant molecular markers. For Site 545 the most abundant molecular markers are ring A monoaromatic steranes, and their presence is attributed to microbial and chemical transformations during early diagenesis.

Molecular dissolved organic matter composition in lakes across Sweden as relative intensities of FT-ICR-MS peaks and PARAFAC components and optical indices

Whether intrinsic molecular properties or extrinsic factors such as environmental conditions control the decomposition of natural organic matter across soil, marine and freshwater systems has been subject to debate. Comprehensive evaluations of the controls that molecular structure exerts on organic matter's persistence in the environment have been precluded by organic matter's extreme complexity. Here we examine dissolved organic matter from 109 Swedish lakes using ultrahigh-resolution mass spectrometry and optical spectroscopy to investigate the constraints on its persistence in the environment. We find that degradation processes preferentially remove oxidized, aromatic compounds, whereas reduced, aliphatic and N-containing compounds are either resistant to degradation or tightly cycled and thus persist in aquatic systems. The patterns we observe for individual molecules are consistent with our measurements of emergent bulk characteristics of organic matter at wide geographic and temporal scales, as reflected by optical properties. We conclude that intrinsic molecular properties are an important control of overall organic matter reactivity.

(Table 2) Vertical distribution of particulate matter and its organic and mineral components in waters of the Tropical Atlantic in November 1984

Results of multiyear investigation of distribution and composition of suspended matter in waters off the northwest coast of Africa are presented. Large-scale circulation, upwelling, river runoff, and aeolian deposition affect distribution and evolution of biochemical composition of particulate matter. Concentrations of organic carbon, nitrogen, chlorophyll, phytoplankton and trace metals in the particulate matter are determined. Ratios of these components exhibit seasonal variations.

Interactive effects of light, nitrogen source, and carbon dioxide on energy metabolism in the diatom Thalassiosira pseudonana

Due to the ongoing effects of climate change, phytoplankton are likely to experience enhanced irradiance, more reduced nitrogen, and increased water acidity in the future ocean. Here, we used Thalassiosira pseudonana as a model organism to examine how phytoplankton adjust energy production and expenditure to cope with these multiple, interrelated environmental factors. Following acclimation to a matrix of irradiance, nitrogen source, and CO2 levels, the diatom's energy production and expenditures were quantified and incorporated into an energetic budget to predict how photosynthesis was affected by growth conditions. Increased light intensity and a shift from inline image to inline image led to increased energy generation, through higher rates of light capture at high light and greater investment in photosynthetic proteins when grown on inline image. Secondary energetic expenditures were adjusted modestly at different culture conditions, except that inline image utilization was systematically reduced by increasing pCO2. The subsequent changes in element stoichiometry, biochemical composition, and release of dissolved organic compounds may have important implications for marine biogeochemical cycles. The predicted effects of changing environmental conditions on photosynthesis, made using an energetic budget, were in good agreement with observations at low light, when energy is clearly limiting, but the energetic budget over-predicts the response to inline image at high light, which might be due to relief of energetic limitations and/or increased percentage of inactive photosystem II at high light. Taken together, our study demonstrates that energetic budgets offered significant insight into the response of phytoplankton energy metabolism to the changing environment and did a reasonable job predicting them.

Nitrogen isotopic and opal record of sediments in the Gulf of California

High-resolution records of the nitrogen isotopic composition of organic matter (d15Norg), opal content, and opal accumulation rates from the central Gulf of California reveal large and abrupt variations during deglaciation and gradual Holocene changes coincident with climatic changes recorded in the North Atlantic. Homogenous sediments with relatively low d15Norg values and low opal content were deposited at the end of the last glacial period, during the Younger-Dryas event, and during the middle to late Holocene. In contrast, laminated sediments deposited in the two deglacial stages are characterized by very high d15Norg values (>14 per mil) and opal accumulation rates (29-41 mg/cm**2/yr). Abrupt shifts in d15Norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling, vertical mixing, and/or the latitudinal position of the Intertropical Convergence Zone.

Carbon and Nitrogen concentrations and isotopic composition of ODP Site 170-1040 and Leg 205 sites

We determined the C and N concentrations and isotopic compositions of sediments in the prism sampled during Ocean Drilling Program Legs 170 and 205 offshore Costa Rica, with the goals of evaluating sediment sources and extents of diagenesis and identifying any effects of infiltrating fluids on the sedimentary C and N. The sediments from Leg 170 Site 1040 contain 0.85-1.96 wt% total organic carbon (TOC) with Vienna Peedee belemnite (VPDB) d13CVPDB from -26.3 per mil to -22.5 per mil, and 832-2221 ppm total nitrogen (TN) with d15Nair from +3.5 per mil to +6.6 per mil. Sediment TN concentrations and d15N values show dramatic downhole increases within the uppermost 130 m of the section and more gradual downhole decreases from 130 meters below seafloor (mbsf) to the base of the décollement at ~370 mbsf. Concentrations and isotopic compositions of TOC are relatively uniform within the entire section, showing some minor perturbation within the décollement zone. In the uppermost 100 m, upsection increases in TN concentrations at constant TOC concentrations produce significant increases in atomic TOC/TN ratios from ~8 to ~18. Carbonate (calcite) contents in the wedge sediments are generally low (<4 wt%), but the d13C and Vienna standard mean ocean water (VSMOW) d18OVSMOW values vary significantly from -26.1 per mil to +4.1 per mil and from +30.0 per mil to +35.3 per mil, respectively. Concentrations and isotopic compositions of TOC and TN for sediments from Leg 205 Sites 1254 and 1255 overlap well with C-N data for sediments from the same depth intervals obtained during Leg 170 at Site 1040.

Lipid, carbon and nitrogen content and fatty acid composition of Temora longicornis females and different food species during the experiment

Temora longicornis, a dominant calanoid copepod species in the North Sea, is characterised by low lipid reserves and high biomass turnover rates. To survive and reproduce successfully, this species needs continuous food supply and thus requires a highly flexible digestive system to exploit various food sources. Information on the capacity of digestive enzymes is scarce and therefore the aim of our study was to investigate the enzymatic capability to respond to quickly changing nutritional conditions. We conducted two feeding experiments with female T. longicornis from the southern North Sea off Helgoland. In the first experiment in 2005, we tested how digestive enzyme activities and enzyme patterns as revealed by substrate SDS-PAGE (sodium dodecylsulfate polyacrylamide gel electrophoresis) responded to changes in food composition. Females were incubated for three days fed ad libitum with either the heterotrophic dinoflagellate Oxyrrhis marina or the diatom Thalassiosira weissflogii. At the beginning and at the end of the experiment, copepods were deep-frozen for analyses. The lipolytic enzyme activity did not change over the course of the experiment but the enzyme patterns did, indicating a distinct diet-induced response. In a second experiment in 2008, we therefore focused on the enzyme patterns, testing how fast changes occur and whether feeding on the same algal species leads to similar patterns. In this experiment, we kept the females for 4 days at surplus food while changing the algal food species daily. At day 1, copepods were offered O. marina. On day 2, females received the cryptophycean Rhodomonas baltica followed by T. weissflogii on day 3. On day 4 copepods were again fed with O. marina. Each day, copepods were frozen for analysis by means of substrate SDS-PAGE. This showed that within 24 h new digestive enzymes appeared on the electrophoresis gels while others disappeared with the introduction of a new food species, and that the patterns were similar on day 1 and 4, when females were fed with O. marina. In addition, we monitored the fatty acid compositions of the copepods, and this indicated that specific algal fatty acids were quickly incorporated. With such short time lags between substrate availability and enzyme response, T. longicornis can successfully exploit short-term food sources and is thus well adapted to changes in food availability, as they often occur in its natural environment due seasonal variations in phyto- and microzooplankton distribution.

Biogenic and terrigeneous components in ODP Leg 108 holes

Five Ocean Drilling Program sites (657-661), which form a north-south transect off the western periphery of the Sahara, were selected to measure the long-term history of Saharan/Sahelian dust flux and fluvial sediment discharge and the fluxes of marine CaCO3 and opal over the last 8 m.y. Sites 658 and 659 served for high-resolution studies, and Sites 657, 660, and 661 for insights into the spatial patterns of dust flux. The nearshore mean flux of opal off Cap Blanc (21 °N) showed an abrupt increase about 3 Ma that appears to reflect the main onset of coastal upwelling fertility and enhanced trade winds. At the same time, the input of river-borne clay strongly decreased, suggesting a dry up of the central Saharan rivers. Later, marked short-lived spikes of clay and opal may indicate ongoing ephemeral pulses of fluvial runoff linked to peak interglacial stages. Given the zonal dust discharge centered near 18 °N at Site 659, the aridification of the south Sahara and Sahel increased in several steps: at 4.6, 4.3, and especially at 4.0, 3.6, and 2.1 Ma, and again, at 0.8 Ma. The late Miocene and earliest Pliocene were humid. Although the central and north Saharan climate appears to be linked to the glaciation history of the Northern Hemisphere, the long-term aridification further south followed a different schedule. The spatial distribution of quartz accumulation suggests that the dust outbreaks linked to the Intertropical Convergence Zone during summer did not shift in latitude back to 4.0 Ma, at least. The short-term variations of dust output over the last 0.5 m.y. followed orbital scale pulses with a strong precessional signal, showing a link of Sahelian humidity changes to the variation of sea-surface temperature and evaporation in the tropical Atlantic.

Concentrations and accumulation rates of chemical elements and sediment components in sediments of central equatorial Pacific, DSDP data

Accumulation rates of Mg, Al, Si, Mn, Fe, Ni, Cu, Zn, opal, and calcium carbonate have been calculated from their concentrations in samples from equatorial Deep Sea Drilling Project sites. Maps of element accumulation rates and of Q-mode factors derived from raw data indicate that the flux of trace metals to equatorial Pacific sediments has varied markedly through time and space in response to changes in the relative and absolute influence of several depositional influences: biogenic, detrital, authigenic, and hydrothermal sedimentation. Biologically derived material dominates the sediment of the equatorial Pacific. The distributions of Cu and Zn are most influenced by surface-water biological activity, but Ni, Al, Fe, and Mn are also incorporated into biological material. All of these elements have equatorial accumulation maxima similar to those of opal and calcium carbonate at times during the past 50 m.y. Detritus distributed by trade winds and equatorial surface circulation contributes Al, non-biogenic Si, Fe, and Mg to the region. Detrital sediment is most important in areas with a small supply of biogenic debris and low bulk-accumulation rates. Al accumulation generally increases toward the north and east, indicating its continental source and distribution by the northeast trade winds. Maxima in biological productivity during middle Eocene and latest Miocene to early Pliocene time and concomitant well-developed surface circulation contributed toward temporal maxima in the accumulation rates of Cu, Zn, Ni, and Al in sediments of those ages. Authigenic material is also important only where bulk-sediment accumulation rates are low. Ni, Cu, Zn, and sometimes Mn are associated with this sediment. Fe is almost entirely of hydrothermal origin. Mn is primarily hydrothermal, but some is probably scavenged from sea water by amorphous iron hydroxide floes along with other elements concentrated in hydrothermal sediments, Ni, Cu, and Zn. During the past 50 m.y. all of these elements accumulated over the East Pacific Rise at rates nearly an order of magnitude higher than those at non-rise-crest sites. In addition, factor analysis indicates that some of this material is carried substantial distances to the west of the rise crest. Accumulation rates of Fe in basal metalliferous sediments indicate that the hydrothermal activity that supplied amorphous Fe oxides to the East Pacific Rise areas was most intense during middle Eocene and late Miocene to early Pliocene time.

Calcite saturation and yield and Mg/Ca, Mn/Ca, Al/Ca, Fe/Ca for four species of planktic foraminifera cleaned using Mg-cleaning and Cd-cleaning methods

Four species of planktic foraminifera from core-tops spanning a depth transect on the Ontong Java Plateau were prepared for Mg/Ca analysis both with (Cd-cleaning) and without (Mg-cleaning) a reductive cleaning step. Reductive cleaning caused etching of foraminiferal calcite, focused on Mg-rich inner calcite, even on tests which had already been partially dissolved at the seafloor. Despite corrosion, there was no difference in Mg/Ca of Pulleniatina obliquiloculata between cleaning methods. Reductive cleaning decreased Mg/Ca by an average (all depths) of ~ 4% for Globigerinoides ruber white and ~ 10% for Neogloboquadrina dutertrei. Mg/Ca of Globigerinoides sacculifer (above the calcite saturation horizon only) was 5% lower after reductive cleaning. The decrease in Mg/Ca due to reductive cleaning appeared insensitive to preservation state for G. ruber, N. dutertrei and P. obliquiloculata. Mg/Ca of Cd-cleaned G. sacculifer appeared less sensitive to dissolution than that of Mg-cleaned. Mg-cleaning is adequate, but SEM and contaminants (Al/Ca, Fe/Ca and Mn/Ca) show that Cd-cleaning is more effective for porous species. A second aspect of the study addressed sample loss during cleaning. Lower yield after Cd-cleaning for G. ruber, G. sacculifer and N. dutertrei confirmed this to be the more aggressive method. Strongest correlations between yield and Delta[CO3^2-] in core-top samples were for Cd-cleaned G. ruber (r = 0.88, p = 0.020) and Cd-cleaned P. obliquiloculata (r = 0.68, p = 0.030). In a down-core record (WIND28K) correlation, r, between yield values > 30% and dissolution index, XDX, was -0.61 (p = 0.002). Where cleaning yield < 30% most Mg-cleaned Mg/Ca values were biased by dissolution.

Biogenic and terrigeneous components in Pliocene-Pleistocene sediments of the equatorial Atlantic

High-resolution analyses of sediments at equatorial Atlantic Sites 662, 663, and 664 define the accumulation rates of biogenically produced CaC03 and opal and of eolian dust from North Africa over the last 3.7 m.y. The mean flux of opal increased abruptly by 60%-70% near 2.5 Ma (2.65 to 2.3 Ma), reflecting pulses of increased opal productivity along the equator due mainly to increased upwelling. The mean winter-plume dust influx from Sahelian and Saharan Africa also increased at this time by between 35% and 75%, following smaller increases earlier in the late Pliocene. The increased opal flux implies a stronger zonal component of the southern trade winds in Southern Hemisphere winter. Consistent with this wind configuration, the stronger dust flux suggests a weaker southwesterly monsoonal flow into Africa in Northern Hemisphere summer, thus increasing Sahelian aridity and winter-plume dust fluxes. Dust fluxes to the equator may possibly have also been enhanced by stronger Northern Hemisphere winter trade winds and a more southerly position of the Intertropical Convergence Zone over Africa. These late Pliocene biogenic and terrigenous flux changes coincided with the appearance of Northern Hemisphere ice sheets, implying an ultimate causal link. The immediate control on changes in tropical circulation may, however, have been changes in the Atlantic sector of the Southern Ocean. A steady background trend of increasing winter-plume dust flux occurred from the late Pliocene until the middle Pleistocene. This may reflect a progressive, tectonically induced aridification of northern and eastern Africa because of the gradual uplift of the Tibetan Plateau.