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This study evaluates the glycerol dialkyl glycerol tetraether (GDGT) distribution and provenance in sediments(spanning a minimum of 13.3 ka) from the St. Anna Trough (Northern Kara Sea). The site has experiencedextensive fluctuation in the delivery of river-derived organic matter (OM), caused by a eustaticchange in sea level. This is in line with the record of the concentration of the isoprenoid GDGT, crenarchaeol,produced by marine Thaumarchaota, which was low at the bottom of the core, increasing graduallyin the most shallow unit. The concentration of branched (br)GDGTs showed an opposite trend and amarked shift in distribution. The deepest sediments (>10 ka), with a distribution currently encounteredin surface sediments in front of the Yenisei River, are characterized by terrigenous brGDGTs, whereas thedistribution in the shallowest unit (<10 ka) is strongly influenced by marine, in-situ brGDGTs. During theshift from terrigenous to marine-sourced brGDGTs, there was one horizon where a pronounced shift inthe brGDGT distribution was observed and the brGDGT concentration significantly decreased. As thebrGDGTs delivered to the current Kara Sea system are derived from several sources, we postulate thata temporary change in the relative importance of the brGDGT sources happened during this interval.Both in-situ production and changing brGDGT provenance have implications for paleoclimate reconstructionusing brGDGTs. In-situ production of marine brGDGTs results in a higher reconstructed pH. However,these in-situ produced brGDGTs did not influence the reconstructed mean annual air temperature (MAT),when the MATmrs calibration was used. Changes in the relative contribution of brGDGT sub-pools wereshown, however, to influence both soil pH reconstruction and MAT reconstruction.

Bacteriohopanepolyols (BHPs) are ubiquitous bacterial membrane lipids, encountered in soils, river and marine suspended particulate matter (SPM) and sediments. Their abundance and distribution provides a direct means to identify bacterial inputs and can be used to trace soil-derived bacterial organic matter (OM) and in some cases the presence of bacterial groups and their activities in aquatic systems. We have studied the BHP distribution in the SPM of a major Siberian River (Yenisei River) that crosses a large latitudinal gradient, draining a large part of Mongolia and Siberian Russia. The Yenisei River is the main river to flow into the Kara Sea, a shelf sea of the Arctic Ocean. We show that the BHP distribution and concentration of SPM and surface sediments of the Yenisei Outflow in the Kara Sea allow to trace soil-marker BHPs and evaluate the performance of the R’soil index, a proxy developed to trace bacterial soil-derived OM. Soil-marker BHPs are present in the Yenisei River, and their concentration decreases from the Yenisei River Outflow into the offshore marine sediments. The R’soil correlates well with an independent proxy for bacterial OM, the BIT-index (r2 = 0.82) and has a moderate correlation with the d13Corg values, a bulk OM proxy for terrigenous input (r2 = 0.44). Consequently, the R’soil index performs well in the Kara Sea, strengthening its application for tracing bacterial OM in the Arctic Ocean, both in modern and downcore sediments. Furthermore, a suite of BHPs that are characteristic for methanotrophic bacteria, i.e. 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol) and 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol), is encountered in the Yenisei Outflow sediments. These components are partly sourced from terrigenous sources, but are likely also produced in-situ in the marine sediments. The distribution of the pentafunctionalized cyclitol ether BHP in the marine systems is noteworthy, and indicates that it can possibly be app

The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils has been shown to correlate with pH and mean annual air temperature. Because of this dependence brGDGTs have found an application as palaeoclimate proxies in coastal marine sediments, based on the assumption that their distribution is not altered during the transport from soils to marine systems by rivers. To study the processes acting on the brGDGT distributions, we analysed the full suite of brGDGTs, including the recently described 6-Me brGDGTs, in both the suspended particulate matter (SPM) of the Siberian Yenisei River and the SPM and sediments of its outflow in the Kara Sea. The brGDGT distribution in the SPM of the Yenisei River was fairly constant and characterized by high abundances of the 6-Me brGDGTs, reflecting their production at the neutral pH of the river water. However, the brGDGT distribution showed marked shifts in the marine system. Firstly, in the Yenisei River Mouth, the fractional abundance of the 6-Me brGDGTs decreases sharply. The brGDGT signature in the Yenisei River Mouth possibly reflects brGDGTs delivered during the spring floods that may carry a different distribution. Also, coastal cliffs were shown to contain brGDGTs and to influence especially those sites without major river inputs (e.g. Khalmyer Bay). Further removed from the river mouth, in-situ production of brGDGTs in the marine system influences the distribution. However, also the fractional abundance of the tetramethylated brGDGT Ia increases, resulting in a distribution that is distinct from in-situ produced signals at similar latitudes (Svalbard). We suggest that this shift may be caused by preferential degradation of labile (riverine in-situ produced) brGDGTs and the subsequent enrichment in less labile (soil) material. The offshore distribution indeed agrees with the brGDGT distribution encountered in a lowland peat. This implies that the offshore Kara Sea sediments possibly carry a soil-do

Soil-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs) in marine river fan sediments have a potential use for determining changes in the mean annual temperature (MAT) and pH of the river watershed soils. Prior to their incorporation in marine sediments, the compounds are transported to the marine system by rivers. However, emerging evidence suggests that the brGDGTs in freshwater systems can be derived from both soil run-off and in situ production. The production of brGDGTs in the river system can complicate the interpretation of the brGDGT signal delivered to the marine system. Therefore, we studied the distribution of brGDGT lipids in suspended particulate matter (SPM) of the Yenisei River. Chromatographic improvements allowed quantification of the recently described hexamethylated brGDGT isomer, characterized by having two methyl groups at the 6/6 ' instead of the 5/5 ' positions, in an environmental dataset for the first time. This novel compound was the most abundant brGDGT in SPM from the Yenisei. Its fractional abundance correlated well with that of the 6-methyl isomer of the hexamethylated brGDGT that contains one cyclopentane moiety. The Yenisei River watershed is characterized by large differences in MAT (>11 degrees C) as it spans a large latitudinal range (46-73 degrees N), which would be expected to be reflected in brGDGT distributions of its soils. However, the brGDGT distributions in its SPM show little variation. Furthermore, the reconstructed pH values are high compared to the watershed soil pH. We, therefore, hypothesize that the brGDGTs in the Yenisei River SPM are predominantly produced in situ and not primarily derived from erosion of soil. This accounts for the absence of a change in the temperature signal, as the river water temperature is more stable. Using a lake calibration, the reconstructed temperature values agree with the mean summer temperatures (MST) recorded. The brGDGTs delivered to the sea by the Yenisei River during

In addition to the two new hydrothermal fields Krasnov (l6 degrees 38' N) and Ashadze (13 degrees N) discovered in 2003-2004, some later discoveries were made in the Northern Equatorial segment of the Mid-Atlantic Ridge (MAR). Two new major seafloor massive sulfide (SMS) deposits: Semyenov (13 degrees 31' N) and Zenith-Victory (20 degrees 08' N), as well as the now extended Puy des Folles hydrothermal field (20 degrees 30.5' N), provide enough data to make conclusions about the general characteristics of SMS deposits in the northern equatorial MAR environment. Parameters of SMS deposits, such as their distribution, geological setting, morphology, composition and age, are discussed in this paper. A majority of studied SMS deposits (Ashadze, Logatchev, Semyenov) are associated with uplifted lower crust and mantle rocks (oceanic core complex, or OCC) at the MAR segments with asymmetric mode of accretion. OCC is tectonically uplifted along with detachment faults, which exhume deep-seated rocks onto the seafloor. Detachment faults, in turn, could be the conduits for the circulation of seawater and discharge of hydrothermal fluids. Gabbro-peridotite hosted deposits are characterized by high concentrations of copper, gold and cobalt. The relationship between the size of the deposits and their age is documented.

Two new hydrothermal fields have been discovered in the rift of the mid-Atlantic ridge at 13 degrees N (Ashadze) and 16 degrees 38 min. N (Krasnov). The Ashadze field consists of a cluster of active hydrothermal sites associated with ultramafic rocks and located at the greatest depth (4 200 m) in the ocean. By contrast, the Krasnov field consists of inactive sulphide mounds hosted in basalts. The Krasnov field is the largest hydrothermal deposit (17 400 000 t) so far discovered on the mid-Atlantic ridge, with iron sulphide as the principal mineral type, whereas Cu-Zn sulphides are the major minerals in the Ashadze deposits, which are also enriched in gold and several other metals., Two new hydrothermal fields have been discovered in the rift of the mid-Atlantic ridge at 13 degrees N (Ashadze) and 16 degrees 38 min. N (Krasnov). The Ashadze field consists of a cluster of active hydrothermal sites associated with ultramafic rocks and located at the greatest depth (4 200 m) in the ocean. By contrast, the Krasnov field consists of inactive sulphide mounds hosted in basalts. The Krasnov field is the largest hydrothermal deposit (17 400 000 t) so far discovered on the mid-Atlantic ridge, with iron sulphide as the principal mineral type, whereas Cu-Zn sulphides are the major minerals in the Ashadze deposits, which are also enriched in gold and several other metals.

The characteristics of the deposits are discussed such as their distribution, geological setting, morphology, composition and age based on data for the two hydrothermal fields, Krasnov and Ashadze, which were discovered in 2003-2004, and later discoveries including two new major seafloor massive sulphide deposits at Semyenov and Zenith-Victory and the now extended Puy des Folles hydrothermal field. Most of the deposits, including Ashadze, Logatchev and Semyenov, are associated with uplifted lower crust and mantle rocks (oceanic core complex, OCC) at the mid- Atlantic ridge segments with an asymmetric mode of accretion. The OCC is tectonically uplifted along with detachment faults, which exhume deep- seated rocks on to the seafloor. Detachment faults may in turn be the conduits for the circulation of seawater and discharge of hydrothermal fluids. Gabbro-peridotite hosted deposits are characterised by high concentrations of Cu, Au and Co. The relationship between the size of the deposits and their age is considered with reference to exploration criteria., The characteristics of the deposits are discussed such as their distribution, geological setting, morphology, composition and age based on data for the two hydrothermal fields, Krasnov and Ashadze, which were discovered in 2003-2004, and later discoveries including two new major seafloor massive sulphide deposits at Semyenov and Zenith-Victory and the now extended Puy des Folles hydrothermal field. Most of the deposits, including Ashadze, Logatchev and Semyenov, are associated with uplifted lower crust and mantle rocks (oceanic core complex, OCC) at the mid- Atlantic ridge segments with an asymmetric mode of accretion. The OCC is tectonically uplifted along with detachment faults, which exhume deep- seated rocks on to the seafloor. Detachment faults may in turn be the conduits for the circulation of seawater and discharge of hydrothermal fluids. Gabbro-peridotite hosted deposits are characterised by high concentrations of Cu, Au and Co. The relationship between the size of the deposits and their age is considered with reference to exploration criteria.