Horizontal profiles of longwave and shortwave radiation components over sea ice near Barrow, Alaska during the 2011 melt

An integrated instrument package for measuring and understanding the surface radiation budget of sea ice is presented, along with results from its first deployment. The setup simultaneously measures broadband fluxes of upwelling and downwelling terrestrial and solar radiation (four components separately), spectral fluxes of incident and reflected solar radiation, and supporting data such as air temperature and humidity, surface temperature, and location (GPS), in addition to photographing the sky and observed surface during each measurement. The instruments are mounted on a small sled, allowing measurements of the radiation budget to be made at many locations in the study area to see the effect of small-scale surface processes on the large-scale radiation budget. Such observations have many applications, from calibration and validation of remote sensing products to improving our understanding of surface processes that affect atmosphere-snow-ice interactions and drive feedbacks, ultimately leading to the potential to improve climate modelling of ice-covered regions of the ocean. The photographs, spectral data, and other observations allow for improved analysis of the broadband data. An example of this is shown by using the observations made during a partly cloudy day, which show erratic variations due to passing clouds, and creating a careful estimate of what the radiation budget along the observed line would have been under uniform sky conditions, clear or overcast. Other data from the setup's first deployment, in June 2011 on fast ice near Point Barrow, Alaska, are also shown; these illustrate the rapid changes of the radiation budget during a cold period that led to refreezing and new snow well into the melt season.

Sulphur and iron species in Dvurechenskii mud volcano sediments

The deep Black Sea is known to be depleted in electron-acceptors for sulphide oxidation. This study on depth distributions of sulphur species (S(II), S(0),S(n)**2-,S2O3**2-,SO3**2-,SO4**2-) in the Dvurechenskii mud volcano, a cold seep situated in the permanently anoxic eastern Black Sea basin (Sorokin Trough, 2060 m water depth), showed remarkable concentrations of sulphide oxidation products. Sulphite concentrations of up to 11 µmol L**1-, thiosulphate concentrations of up to 22 µmol L**1-, zero-valent sulphur concentrations of up to 150 µmol L**1- and up to five polysulphide species were measured in the upper 20 cm of the sediment. Electron-acceptors found to be available in the Dvurechenskii mud volcano (DMV) for the oxidation of hydrogen sulphide to sulphide oxidation intermediates are iron-minerals, and probably also reactive manganese phases. Up to 60 µmol g**1- of reactive iron-minerals and up to 170 µmol L**1- dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow. Thus, the source for the oxidative power in the DMV are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments, leading to the formation of various sulphur intermediates in comparably high concentrations. Another possible source of sulphide oxidation intermediates in DMV sediments could be the formation of zero-valent sulphur by sulphate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero-valent sulphur. Sulphide oxidation intermediates, which are produced by these processes, do not reach thermodynamic equilibrium with rhombic sulphur, especially close to the active center of the DMV due to a short equilibration time. Thus, mud volcano sediments, such as in the DMV, can provide oxidizing niches even in a highly reduced environment like the abyssal part of the Black Sea.

Plio-Pleistocene Mg/Ca and TEX86 sea surface temperature records of ODP Sites 184-1143 and 165-999,

The western warm pools of the Atlantic and Pacific oceans are a critical source of heat and moisture for the tropical climate system. Over the past five million years, global mean temperatures have cooled by 3-4 °C. Yet, current reconstructions of sea surface temperatures indicate that temperature in the warm pools has remained stable during this time. This stability has been used to suggest that tropical sea-surface temperatures are controlled by some sort of thermostat-like regulation. Here we reconstruct sea surface temperatures in the South China Sea, Caribbean Sea and western equatorial Pacific Ocean for the past five million years, using a combination of the Mg/Ca, TEXH86-and Uk'37 surface temperature proxies. Our data indicate that during the period of Pliocene warmth from about 5 to 2.6 million years ago, the western Pacific and western Atlantic warm pools were about 2 °C warmer than today. We suggest that the apparent lack of warming seen in the previous reconstructions was an artefact of low seawater Mg/Ca ratios in the Pliocene oceans. Taking this bias into account, our data indicate that tropical sea surface temperatures did change in conjunction with global mean temperatures. We therefore conclude that the temperature of the warm pools of the equatorial oceans during the Pliocene was not limited by a thermostat-like mechanism.

Geochemistry of ODP Sites 123-765 and 123-766

The sediments of the Argo and Gascoyne abyssal plains are generally lean in organic matter, are immature, and contain hydrocarbons trapped during sediment deposition rather than those generated during sediment catagenesis. TOC concentrations in the Argo Abyssal Plain Cenozoic sediments are 0.5 wt%, and organic matter appears to be from mixed marine and reworked, degraded, organic matter sources, with the latter being contributed by turbidity flows from the nearby continental margin. TOC concentrations within the Cenozoic sediments of the Gascoyne Abyssal Plain are mostly undetectable (<0.1 wt%). Biomarker distributions determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GCMS) indicate that organic matter extracted from the Lower Cretaceous sediments from both sites is predominantly marine with varying contributions from terrestrial organic matter. The specific marine biomarker, 24-n-propylcholestane is in relatively high abundance in all samples. In addition, the relatively high abundance of the 4-methylsteranes with the 23,24-dimethyl side chain (in all samples) indicates significant dinoflagellate contributions and marine organic matter. The ratios of n-C27/n-C17 reflect relative contributions of marine vs. terrestrial organic matter. TOC, while generally low at Argo, is relatively high near the Barremian/Aptian boundary (one sample has a TOC of 5.1 wt%) and the Aptian/Albian boundary (up to 1.3 wt% TOC), and two samples from the Barremian and Aptian sections contain relatively high proportions of terrestrial organic carbon. TOC values in the Lower Cretaceous sediments from Gascoyne Abyssal Plain are low (<0.1 wt%) near the Aptian/Barremian boundary. TOC values are higher in older sediments, with maxima in the upper Barremian (1.02 wt%), the Barremian/Hauterivian (0.6 wt%), and Valanginian (1.8 wt%). Sediments from the upper Barremian contain higher amounts of terrestrial organic carbon than older sediments.

Organic geochemistry of Cretaceous black shales at DSDP Hole 75-530A

Five-hundred ten meters of Cretaceous sediments were drilled north of the Walvis escarpment in Hole 530A during Leg 75. An immature stage of evolution for organic matter can be assigned to all the samples studied. Black shales are interbedded with red and green claystone in the bottom sedimentary unit, Unit 8, which is of Coniacian to late Albian age. The richest organic carbon contents and petroleum potentials occur in the black shales. Detrital organic matter is present throughout the various members of a sequence, mixed with largely oxidized organic matter in the gray and green claystone or marlstone members on both sides. Detrital organic matter also characterizes the black streaks observed in the claystones. Vertical discontinuities in organic matter distribution are assigned to slumping. Several types of black shales can be identified, according to their content of detrital organic matter, the more detrital black levels corresponding to the Albian-Cenomanian period. Cyclic variations of organic matter observed for a sequence can occur for a set of sequences and even for some consecutive sets of sequences. Climatic factors are proposed to account for the cyclic sedimentation and distribution of organic matter for every sequence that includes a black bed.

Geochemical characterization of black shales from the Tarfaya Basin

Organic geochemical and petrological investigations were carried out on Cenomanian/Turonian black shales from three sample sites in the Tarfaya Basin (SW Morocco) to characterize the sedimentary organic matter. These black shales have a variable bulk and molecular geochemical composition reflecting changes in the quantity and quality of the organic matter. High TOC contents (up to 18wt%) and hydrogen indices between 400 and 800 (mgHC/gTOC) indicate hydrogen-rich organic matter (Type I-II kerogen) which qualifies these laminated black shale sequences as excellent oil-prone source rocks. Low Tmax values obtained from Rock-Eval pyrolysis (404-425 MC) confirm an immature to early mature level of thermal maturation. Organic petrological studies indicate that the kerogen is almost entirely composed of bituminite particles. These unstructured organic aggregates were most probably formed by intensive restructuring of labile biopolymers (lipids and/or carbohydrates), with the incorporation of sulphur into the kerogen during early diagenesis. Total lipid analyses performed after desulphurization of the total extract shows that the biomarkers mostly comprise short-chain n-alkanes (C16-C22) and long-chain (C25-C35) n-alkanes with no obvious odd-over-even predominance, together with steranes, hopanoids and acyclic isoprenoids. The presence of isorenieratane derivatives originating from green sulphur bacteria indicates that dissolved sulphide had reached the photic zone at shallow water depths (~100m) during times of deposition. These conditions probably favoured intensive sulphurization of the organic matter. Flash pyrolysis GC-MS analysis of the kerogen indicates the aliphatic nature of the bulk organic carbon. The vast majority of pyrolysis products are sulphur-containing components such as alkylthiophenes, alkenylthiophenes and alkybenzothiophenes. Abundant sulphurization of the Tarfaya Basin kerogen resulted from excess sulphide and metabolizable organic matter combined with a limited availability of iron during early diagenesis. The observed variability in the intensity of OM sulphurization may be attributed to sea level-driven fluctuations in the palaeoenvironment during sedimentation.

Organic carbon accumulation in the equatorial Atlantic

Organic geochemical records of the last 940 kyr are presented for equatorial Atlantic Ocean Drilling Program (ODP) sites 663 and 664 and discussed with regard to the development of ocean productivity and African paleoclimate. Proportions of marine and terrigenous organic matter (OM) are estimated from elemental, pyrolytic, isotopic, and petrologic data. Spectral analyses reveal a strong power at the eccentricity and obliquity band, indicating a close response of tropical organic sedimentation to the climatic evolution at high latitudes. The orbital covariance of organic carbon with biogenous opal and terrigenous records favor that glacially enhanced dust supply and surface water mixing were primary controls for deposition of organic carbon. Wind-borne supply of terrigenous OM contributes 26 to 55% and 0 to 39% to the bulk OM based on microscopic and isotopic records, respectively. Admixture of C4 plant matter was approximated to contribute up to 16% to the bulk organic fraction during peak glacial conditions.

Investigations of Cretaceous and Tertiary kerogens in sediments of ODP Leg 113 holes

Seventy-one samples from nine sites were analyzed for total organic carbon (TOC). Fifty-six samples, containing 0.2% or more TOC, were evaluated by Rock-Eval to assess the nature of their kerogen and its petroleum source potential. Visual kerogen studies were carried out. Petroleum potential was encountered only in Valanginian calcareous claystones at Hole 692B close to the margin of Dronning Maud Land. A section of 44.7 m was penetrated. The unit possesses a revised mean TOC of 9.8% and petroleum potential of 43.2 kg/Mg, relatively high values in comparison to other Cretaceous anoxic oceanic sections and the totality of petroleum source rocks. At Sites 689 and 690, extremely low TOC levels, mean 0.07%, preclude kerogen analysis. Kerogens in Eocene to Pliocene sediments of the central and western Weddell Sea (Sites 694, 695, 696, and 697) are similar everywhere, largely comprising brown to black, granular, amorphous material of high rank, and generally possessing several reflectance populations of vitrinite particles. The latter are interpreted as indicative of the recycling of sediments of a variety of levels of thermal maturity.