Structural group composition of low-polarity organic matter dissolved in waters of the Northwest Indian Ocean and the Red Sea

Data on amounts of various functional groups, i.e. aldehyde, acid, ester, alcohol, thiol and aromatic groups in several fractions of low-polarity dissolved organic matter are presented. An assumption that this organic matter is part of the lipid fraction is not confirmed. Amount of aromatic compounds in waters of the Northwest Indian Ocean is estimated to be about 1000 times higher than quantity of aromatic hydrocarbons discharged into the ocean each year in petroleum and petroleum products.

Organic matter preservation in turbidites on the Madeira Abyssal Plain

Oxidized intervals of five organic-rich Madeira Abyssal Plain (MAP) turbidites deposited during the Miocene, Pliocene, and Pleistocene all displayed comparable major loss of total organic carbon (TOC) (84 ± 3.1%) accompanied by a negative isotopic (d13C) shift ranging from -0.3 to -2.9 per mil. Major but significantly lower loss of total nitrogen (Ntot, 61 ± 7.1%) also occurred, leading to a decrease in TOC relative to Ntot (C/Ntot) and a +1.3 to 2.7 per mil Ntot isotopic (d15N) shift. Compound specific isotopic measurements on plant wax n-alkanes indicate the terrestrial organic component in the unoxidized deposits is 13C-enriched owing to significant C4 contribution. Selective preservation of terrestrial relative to marine organic carbon could account for the d13C behavior of TOC upon oxidation but only if a 13C-depleted component of the bulk terrestrial signal is selectively preserved in the process. Although the C/Ntot decrease and positive d15N shift seems inconsistent with selective terrestrial organic preservation, results from analysis of a Modern eolian dust sample collected in the vicinity indicate these observations are compatible. Regardless of the specific explanation for these isotopic observations, however, our findings provide evidence that paleoreconstruction of properties such as pCO2 using the d13C of TOC is a goal fraught with uncertainty whether or not the marine sedimentary record considered is 'contaminated' with significant terrestrial input. Nonetheless, despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation, intensive organic geochemical proxies such as the alkenone unsaturation index, UK'37, appear resistant to change and thereby retain their paleoceanographic promise.

(Table 1) Tree age, post fire stand age, and soil organic matter thickness in the western Quebec black spruce boreal ecosystem

The observed long-term decrease in the regional fire activity of Eastern Canada results in excessive accumulation of organic layer on the forest floor of coniferous forests, which may affect climate-growth relationships in canopy trees. To test this hypothesis, we related tree-ring chronologies of black spruce (Picea mariana (Mill.) B.S.P.) to soil organic layer (SOL) depth at the stand scale in the lowland forests of Quebec's Clay Belt. Late-winter and early-spring temperatures and temperature at the end of the previous year's growing season were the major monthly level environmental controls of spruce growth. The effect of SOL on climate-growth relationships was moderate and reversed the association between tree growth and summer aridity from a negative to a positive relationship: trees growing on thin organic layers were thus negatively affected by drought, whereas it was the opposite for sites with deep (>20-30 cm) organic layers. This indicates the development of wetter conditions on sites with thicker SOL. Deep SOL were also associated with an increased frequency of negative growth anomalies (pointer years) in tree-ring chronologies. Our results emphasize the presence of nonlinear growth responses to SOL accumulation, suggesting 20-30 cm as a provisional threshold with respect to the effects of SOL on the climate-growth relationship. Given the current climatic conditions characterized by generally low-fire activity and a trend toward accumulation of SOL, the importance of SOL effects in the black spruce ecosystem is expected to increase in the future.

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.

Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone

Oxygen minimum zones are expanding globally, and at present account for around 20-40% of oceanic nitrogen loss. Heterotrophic denitrification and anammox-anaerobic ammonium oxidation with nitrite-are responsible for most nitrogen loss in these low-oxygen waters. Anammox is particularly significant in the eastern tropical South Pacific, one of the largest oxygen minimum zones globally. However, the factors that regulate anammox-driven nitrogen loss have remained unclear. Here, we present a comprehensive nitrogen budget for the eastern tropical South Pacific oxygen minimum zone, using measurements of nutrient concentrations, experimentally determined rates of nitrogen transformation and a numerical model of export production. Anammox was the dominant mode of nitrogen loss at the time of sampling. Rates of anammox, and related nitrogen transformations, were greatest in the productive shelf waters, and tailed off with distance from the coast. Within the shelf region, anammox activity peaked in both upper and bottom waters. Overall, rates of nitrogen transformation, including anammox, were strongly correlated with the export of organic matter. We suggest that the sinking of organic matter, and thus the release of ammonium into the water column, together with benthic ammonium release, fuel nitrogen loss from oxygen minimum zones.