Long chain 1,13- and 1,15-diols in surface sediments ans SST reconstruction for sediment core GeoB6518-1

Although commonly reported in marine and freshwater environments, little is known about the biological sources of long chain alkyl 1,13- and 1,15-diols, and factors controlling their distributions. Here we analyzed the occurrence and distribution of these lipids in a comprehensive set of marine surface sediments and compare their distributions with environmental conditions like sea surface temperature (SST), salinity and nutrient concentrations. Fractional abundances of the C28 1,13-, C30 1,13- and C30 1,15-diols show a strong correlation with SST and based on these results, we propose the Long chain Diol Index (LDI), which expresses the C30 1,15-diol abundance relative to those of C28 1,13-, C30 1,13- and C30 1,15-diols. The LDI shows a strong linear correlation with SST (LDI = 0.033 × SST + 0.095; R2 = 0.969, n = 162) over a temperature range of -3 to 27 °C. Long chain diol distributions in sediments from the South Atlantic close to the Congo River outflow (West Africa) provided a 43 kyr LDI SST record. This record reflects several known climatic events and shows similarities with an alkenone-derived SST record obtained using the same suite of sediments, both in trend and in terms of absolute SST. This confirms the potential of the LDI as a proxy for palaeo-SST reconstruction.

Nd isotope data for planktonic foraminifera from within and around sapropels S1 and S5 from ODP Site 160-967

The development of widespread anoxic conditions in the deep oceans is evidenced by the accumulation and preservation of organic-carbon-rich sediments, but its precise cause remains controversial. The two most popular hypotheses involve (1) circulation-induced increased stratification resulting in reduced oxygenation of deep waters or (2) enhanced productivity in the surface ocean, increasing the raining down of organic matter and overwhelming the oxic remineralization potential of the deep ocean. In the periodic development of deep-water anoxia in the Pliocene-Pleistocene Mediterranean Sea, increased riverine runoff has been implicated both as a source for nutrients that fuel enhanced photic-zone productivity and a source of a less dense freshwater cap leading to reduced circulation, basin-wide stagnation, and deep-water oxygen starvation. Monsoon-driven increases in Nile River discharge and increased regional precipitation due to enhanced westerly activity-two mechanisms that represent fundamentally different climatic driving forces-have both been suggested as causes of the altered freshwater balance. Here we present data that confirm a distinctive neodymium (Nd) isotope signature for the Nile River relative to the Eastern Mediterranean-providing a new tracer of enhanced Nile outflow into the Mediterranean in the past. We further present Nd isotope data for planktonic foraminifera that suggest a clear increase in Nile discharge during the central intense period of two recent anoxic events. Our data also suggest, however, that other regional freshwater sources were more important at the beginning and end of the anoxic events. Taken at face value, the data appear to imply a temporal link between peaks in Nile discharge and enhanced westerly activity.

X-ray fluorescence (XRF) scannings and grain size analysis at sites in the Gulf of Cádiz

Contourites in the Gulf of Cádiz preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 5.3 Ma. In our study we investigate the potential of geochemical data obtained by XRF scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled through contourite deposits in the northern Gulf of Cadiz: Site U1387, which is bathed by the upper MOW core, and Site U1389, located more proximal to the Straits of Gibraltar. The lack of major downslope transport at both locations during the Pleistocene makes them ideal locations for the purpose of our study. The results indicate that the Zr/Al ratio, representing the relative enrichment of heavy minerals (zircon) over less dense alumosilicates under strong bottom current flow, is the most useful indicator for a semi-quantitative assessment of current strength. While most elements are biased by current-related processes, the bromine record, representing organic content, preserves the most pristine climate signal rather independent of grain size changes. Hence, Br can be used for chronostratigraphy and site-to-site correlation in addition to stable isotope stratigraphy. Based on these findings we reconstructed MOW variability for Marine Isotope Stages 1-5 using the Zr/Al ratio from Site U1387. The results reveal abrupt, millennial-scale variations of MOW strength during Greenland Stadials (GS) and Interstadials (GI) with strong MOW during GS and glacial Terminations and a complex behavior during Heinrich Stadials. Millennial-scale variability persisting during periods of poorly expressed GS/GI cyclicities implies a strong internal oscillation of the Mediterranean/North Atlantic climate system.

Physical oceanography during UPAT cruise to the Amvrakikos Gulf, August 2009

Oceanographic research in the Amvrakikos Gulf in Western Greece, a semi-enclosed embayment isolated from the Ionian Sea by a narrow, shallow sill, has shown that it is characterised by a fjord-like oceanographic regime. The Gulf is characterised by a well-stratified two layer structure in the water column made up of a surface layer and a bottom layer that are separated by a strong pycnocline. At the entrance over the sill, there is a brackish water outflow in the surface water and a saline water inflow in the near-bed region. This morphology and water circulation pattern makes the Amvrakikos Gulf the only Mediterranean Sea fjord. The investigations have also shown that the surface layer is well oxygenated, whereas in the pycnocline, the dissolved oxygen (DO) declines sharply and finally attains a value of zero, thus dividing the water column into oxic, dysoxic and anoxic environments. At the dysoxic/anoxic interface, at a depth of approximately 35 m, a sharp redox cline develops with Eh values between 0 and 120 mV occurring above and values between 0 and -250 mV occurring below, where oxic and anoxic biochemical processes prevail, respectively. On the seafloor underneath the anoxic waters, a black silt layer and a white mat cover resembling Beggiatoa-like cells are formed. The dysoxic/anoxic conditions appeared during the last 20 to 30 years and have been caused by the excessive use of fertilisers, the increase in animal stocks, intensive fish farming and domestic effluents. The inflicted dysoxia/anoxia has resulted in habitat loss on the seafloor over an area that makes up just over 50% of the total Gulf area and approximately 28% of the total water volume. Furthermore, anoxia is also considered to have been responsible for the sudden fish mortality which occurred in aquaculture rafts in the Gulf in February 2008. Therefore, anoxic conditions can be considered to be a potential hazard to the ecosystem and to the present thriving fishing and mariculture industry in the Gulf.

Lacustrine sediments from two setions in northern Greece

We investigated two lignite quarries in northern Greece for orbital and suborbital climate variability. Sections Lava and Vegora are located at the southern and northern boundaries of the Ptolemais Basin, a northwest southeast elongated intramontane basin that contains Upper Miocene to Lower Pliocene lacustrine sediments. Sediments show cyclic alterations of marl-rich (light), and coal-rich or clay-rich (dark) strata on a decimeter to meter scale. First, we established low-resolution ground-truth stratigraphy based on paleomagnetics and biostratigraphy. Accordingly, the lower 67 m and 65 m that were investigated in both sections Vegora and Lava, respectively, belong to the Upper Miocene and cover a time period of 6.85 to 6.57 and 6.46 to 5.98 Ma at sedimentation rates of roughly 14 and 22 cm/ka. In order to obtain a robust and high-resolution chronology, we then tuned carbonate minima (low L* values; high magnetic susceptibility values) to insolation minima. Besides the known dominance of orbital precession and eccentricity, we detected a robust hemi-precessional cycle in most parameters, most likely indicative for monsoonal influence on climate. Moreover, the insolation-forced time series indicate a number of millennial-scale frequencies that are statistically significant with dominant periods of 1.5-8 kyr. Evolutionary spectral analysis indicates that millennial-scale climate variability documented for the Ptolemais Basin resembles the one that is preserved in ice-core records of Greenland. Most cycles show durations of several tens of thousands of years before they diminish or cease. This is surprising because the generally argued cause for Late Quaternary millennial-scale variability is associated with the presence of large ice sheets, which cannot be the case for the Upper Miocene. Possible explanations maybe a direct response to solar forcing, an influence on the formation of North Atlantic Deep Water through the outflow of high-salinity water, or an atmospheric link to the North Atlantic Oscillation.

Water temperature reconstruction for Terminations I and II of sediment core MD01-2378

We present centennial records of sea surface and upper thermocline temperatures in Core MD01-2378 from the Timor Sea, which provide new insights into the variability of the Indonesian outflow across the last two glacial terminations. Mg/Ca in Globigerinoides ruber (white s. s.) indicates an overall increase of 3.2 °C in sea surface temperature (SST) over Termination I. Following an early Holocene plateau at 11.3-6.4 ka, SSTs cooled by 0.6 °C during the middle to late Holocene (6.4-0.7 ka). The early Holocene warming occurred in phase with increasing northern hemisphere summer insolation, coinciding with northward displacement of the Intertropical Convergence Zone, enhanced boreal summer monsoon and expansion of the Indo-Pacific Warm Pool. Thermocline temperatures (Pulleniatina obliquiloculata Mg/Ca) gradually decreased from 24.5 to 21.5 °C since 10.3 ka, reflecting intensification of a cool thermocline throughflow. The vertical structure of the upper ocean in the Timor Sea evolved in similar fashion during the Holocene and MIS5e, although the duration of SST plateaux differed (11.3 to 6.4 ka in Termination I and from 129 to 119 ka in Termination II), which was probably due to the more intense northern hemisphere summer insolation during MIS 5e. During both terminations, SST increased simultaneously in the southern high latitudes and the tropical eastern Indian Ocean, suggesting virtually instantaneous atmospheric climate feedbacks between the high and low latitudes.

Age determination of sediment core SO75-26KL, Portuguese margin

A benthic isotope record has been measured for core SO75-26KL from the upper Portuguese margin (1099 m water depth) to monitor the response of thermohaline overturn in the North Atlantic during Heinrich events. Evaluating benthic delta18O in TS diagrams in conjunction with equilibrium deltac fractionation implies that advection of Mediterranean outflow water (MOW) to the upper Portuguese margin was significantly reduced during the last glacial (< 15% compared to 30% today). The benthic isotope record along core SO75-26KL therefore primarily monitors variability of glacial North Atlantic conveyor circulation. The 14C-accelerator mass spectrometry ages of 13.54±.07 and 20.46±.12 ka for two ice-rafted detritus (IRD) layers in the upper core section and an interpolated age of 36.1 ka for a third IRD layer deeper in the core are in the range of published 14C ages for Heinrich events H1, H2, and H4. Marked depletion of benthic delta13C by 0.7-1.1 per mil during the Heinrich events suggests reduced thermohaline overturn in the North Atlantic during these events. Close similarity between meltwater patterns (inferred from planktonic delta18O) at Site 609 and ventilation patterns (inferred from benthic delta13C) in core SO75-26KL implies coupling between thermohaline overturn and surface forcing, as is also suggested by ocean circulation models. Benthic delta13C starts to decrease 1.5-2.5 kyr before Heinrich events Hl and H4, fully increased values are reached 1.5-3 kyr after the events, indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor's full strength well after the events. Benthic delta13C changes in the course of the Heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation, a distinct feature of thermohaline instability in numerical models. Inferrred gradual spin-up of thermohaline circulation after Hl and H4 is in contrast to abrupt wanning in the North Atlantic region that is indicated by sudden increases in Greenland ice core delta18O and in marine faunal records from the northern North Atlantic. From this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the Greenland ice core record.

Age determination of sediment cores close to the Strait of Gibralta

A suit of sediment cores close to and south of the Strait of Gibraltar (12°-36°N, 500-2800 m water depth) were analyzed for stable isotopes in epibenthic foraminifers Cibicidoides wuellerstorfi and Planulina ariminensis. During peak glacial times, the data exhibit higher delta13C values of up to 1.6 per mil at intermediate depths near the Strait of Gibraltar (36°N). The values decrease to the south as evidenced by our data, but also to the north as revealed by data of intermediate depth cores north of 38°N (in Duplessy et al. (1987)). Thus, the distribution pattern of delta13C provides crucial evidence for an increased influence of nutrient depleted Mediterranean Outflow Water (MOW) on the glacial northeast Atlantic hydrography. During oxygen isotope Terminations I and II, the meridional carbon isotope gradient indicates a significantly decreased but still active MOW. As deduced from the delta18O fluctuations, the temperatures of the MOW in the Atlantic were lower during glacial times by as much as 5°C. During glacial times and during Termination I the maximum delta13C values of the MOW correlate with minimum values of the North Atlantic Deep Water (NADW) and vice versa. This inverse response to climatic change of the carbon isotope signals of both water masses indicates, that the supply of saline MOW to the north Atlantic may be less important for the formation of NADW than previously assumed.

Ingestion rate and egg production of copepods collected in the upper 20m in the eastern Mediterranean Sea in April 2008 during SES_GR2

The ingestion on ciliates and phytoplankton dataset is based on samples taken during October 2008 in Northern Aegean Sea, the area influenced by the Black Sea water outflow. A Lagrangian experiment was established and copepod ingestion was estimated from experiments performed at stations according to the different positions of drifters during the cruise. Copepods for the experiments were obtained with slow non-quantitative tows from the upper 20 m layer of the water column using 200 µm mesh size nets fitted with a large non-filtering cod end. For the grazing experiments we used the following copepod species: Clausocalanus furcatus, and Temoraa stylifera according to the relevant reference (Bamstedt et al. 2000). Copepod clearance rates on ciliates were calculated according to Frost equations (Frost 1972). Ingestion rates were calculated by multiplying clearance rates by the initial standing stocks (Bamstedt et al. 2000). The egg production dataset is based on samples taken during October 2008 in Northern Aegean Sea, the area influenced by the Black Sea water outflow. A Lagrangian experiment was established and copepod egg production was estimated from experiments performed at stations according to the different positions of drifters during the cruise. Egg production rates of the dominant calanoid copepods were determined by incubation of fertilised females (eggs female/day) collected in the 0-20m layer. Copepod egg production was measured for the copepods Clausocalanus furcatus, Temora stylifera. On board experiments for the estimation of copepod egg production were taken place. For the estimation of copepod production (mgC/m**2/day), lengths (copepods and eggs) were converted to body carbon (Hopcroft et al., 1998) and production was estimated from biomass and weight-specific egg production rates, by assuming that those rates are representative for juvenile specific growth rates (Berggreen et al., 1988).

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.