Percentages of sand-sized material and biogenic components in sediment core GIK12392-1

The paleo-oceanography of the southeastern North Atlantic Ocean during the last 150,000 yr has been studied using biogenous and terrigenous components of hemipelagic sediments sampled close to the northwest African continental margin. Variations of oxygen isotope ratios in shells of benthic calcareous foraminifers in two cores allow the assignment of absolute ages to these cores (in the best case at 1000 yr increments). The uncorrected bulk sedimentation rates of the longest core range from 3.4 to 7.6 cm/ 1000 yr during Interglacial conditions, and from 6.5 to 9.9 cm/1000 yr during Glacial conditions; all other cores have given results of the same order of magnitude, but with generally increasing values towards the continental edge. The distribution of sediment components allow us to make inferences about paleo-oceanographic changes in this region. Frequencies of biogenic components from benthic organisms, oxygen isotope ratios measured in benthic calcareous foraminiferal shells, the total carbonate contents of the sediment and distributions of biogenic components from planktonic organisms often fluctuate in concert. However, all fluctuations which can be attributed to changes of the bottom water masses (North Atlantic Deep Water) seem to precede by several thousand years those which can be linked to changes of the surface water mass distributions or to changes of the climate over the neighboring land masses. Late Quaternary planktonic foraminiferal assemblages in the cores from the northwest African continental margin can be defined satisfactorily in the way that distributions of assemblages found in sediment surface samples from the northeast Atlantic Ocean have been explained. The distributions of assemblages in the northwest African cores can also be used to estimate past sea surface temperatures and salinities. The downcore record of these estimates reveals two warm periods during the last 150,000 yr, the lower one corresponding to the oxygen isotope stage 5 e (equivalent to the Eemian proper in Europe), the upper one to the younger half of the Holocene. Winter surface water temperatures during oxygen isotope stages 6, 4, 3, and 2 are remarkably constant in most cores, while summer sea surface temperatures during stage 3 reach values comparable to those of the warm periods during the Late Holocene and Eemian. Estimated winter sea surface temperatures range from > 16 °C to < 11°C, the summer sea surface temperatures from > 22 °C to < 15 °C during the last 150,000 yr. Estimates of the winter sea surface salinities fluctuate between 36.6? and 35.5?, the higher values being restricted to the warm periods since the penultimate Glacial. Estimates for sea surface temperatures and salinities for two cores from the center of today's coastal upwelling region show less pronounced fluctuations than the record of the open ocean cores in the case of the station 12379 off Cape Barbas, more pronounced in the case of station 12328 off Cape Blanc. Seasonal differences between winter and summer sea surface temperatures derived from the estimated temperatures are today more pronounced in the boundary region of the ocean to the continent than further away from the continent. The differences are generally higher during warm climatic periods of the last 150,000 yr than during cooler ones. The abundance of terrigenous grains in the coarse fractions generally decreases with increasing distance from the continental edge, and also from south to north. The dominant portion of the terrigenous detritus is carried out into the ocean during the relatively cool climatic periods (stage 6, 4, later part of stage 3, stage 2 and oldest part of stage 1). The enhanced precision of dating combined with the stratigraphic resolution of these high deposition rate cores make it clear that the peaks of the terrigenous input off this part of the northwest African continental margin occur simultaneously with times of rapid sea level fluctuations resulting from large volume changes of the large Glacial ice sheets.

Detrital layer thickness in 12 varved sediment cores in Lake Mondsee and related flood events AD1976-2005

A succession of 23 sub-millimetre to maximum 12-mm-thick, mostly flood-triggered detrital layers, deposited between 1976 and 2005, was analysed in 12 varved surface sediment cores from meso-scale peri-alpine Lake Mondsee applying microfacies and high-resolution micro X-ray fluorescence analyses. Detailed intrabasin comparison of these layers enabled identification of (i) different source areas of detrital sediments, (ii) flood-triggered sediment flux and local erosion events, and (iii) seasonal differences of suspended flood sediment distribution within the lake basin. Additional calibration of the detrital layer record with river discharge and precipitation data reveals different empirical thresholds for flood layer deposition for different parts of the basin. At proximal locations detrital layer deposition requires floods exceeding a daily discharge of 40 m**3/s, whereas at a location 2 km more distal an hourly discharge of 80 m**3/s and at least 2 days of discharge above 40 m**3/s are necessary. Furthermore, we observe a better correlation between layer thickness and flood amplitude in the depocentre than in distal and proximal areas of the basin. Although our results are partly site-specific, the applied dual calibration approach is suitable to precisely decipher flood layer formation processes and, thereby, improve the interpretation of long flood time series from lake sediments.

Pre-glacial to glacial sediment thickness grids for the Southern Pacific Margin of West Antarctica, NetCDF files

Circum-Antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions, which are important for paleo-ice sheet formation histories. By compiling old and new seismic data, we identify sequences representing pre-glacial, transitional and full glacial deposition processes along the Pacific margin of West Antarctica. The pre-glacial sediment grid depicts 1.3 to 4.0 km thick depocenters, relatively evenly distributed along the margin. The depocenters change markedly in the transitional phase at, or after, the Eocene/Oligocene boundary, when the first major ice sheets reached the shelf. Full glacial sequences, starting in the middle Miocene, indicate new depocenter formation North of the Amundsen Sea Embayment and localized eastward shifts in the Bellingshausen Sea and Antarctic Peninsula basins. Using present-day drainage paths and source areas on the continent, our calculations indicate an estimated observed total sedimentary volume of ~10 x 10**6 km**3 was eroded from West Antarctica since the separation of New Zealand in the Late Cretaceous. Of this 4.9 x 10**6 km**3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 Ma. Whereas 5.1 x 10**6 km**3 postdate the onset of glaciation, of which 2.5 x 10**6 km**3 were deposited in post mid-Miocene full glacial conditions.

(Table 1) Age determination of sediment core PC17

We have investigated glacial-interglacial differences in sea surface temperature (SST) near Hawaii using two relatively high deposition rate, shallow-water piston cores collected near Oahu, Hawaii. Modern hydrographic data show that local surface water temperatures are broadly consistent with the regional pattern of SSTs in the southern subtropical North Pacific. Past SSTs were estimated on the basis of three independently measured parameters: (1) UK'37 values of alkenones, (2) d18O of Globigerinoides ruber, and (3) assemblages of planktonic foraminifera using the modern analog technique (MAT). The two cores yield similar SST records, and if differences in the ecology of foraminifera and coccolithophores are considered, the three different approaches to estimating SSTs yield consistent results. UK'37-based temperatures, which may represent winter values at this location, were ~2.5°C colder during the Last Glacial Maximum than today, which is consistent with the February MAT estimates. The d18O-based temperature estimates, likely biased toward summer temperatures, indicate that the glacial SSTs were at least 1°C cooler than today, which is comparable to the results of MAT August estimates.

Bulk geochemical and Rock-Eval data of sediment core IKU-7430/10-U-01 (Table 1)

The late Volgian (early "Boreal" Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.

Core scans and lithologic analysis of Subglacial Lake Whillans sediment cores

The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the ice sheet. Despite considerable interest in understanding this subglacial network and its affect on ice flow, in situ observations from the ice sheet bed are exceedingly rare. Here we describe the first sediment cores recovered from an active subglacial lake. The lake, known as Subglacial Lake Whillans, is part of a broader, dynamic hydrologic network beneath the Whillans Ice Stream in West Antarctica. Even though "floods" pass through the lake, the lake floor shows no evidence of erosion or deposition by flowing water. By inference, these floods must have insufficient energy to erode or transport significant volumes of sediment coarser than silt. Consequently, water flow beneath the region is probably incapable of incising continuous channels into the bed and instead follows preexisting subglacial topography and surface slope. Sediment on the lake floor consists of till deposited during intermittent grounding of the ice stream following flood events. The fabrics within the till are weaker than those thought to develop in thick deforming beds suggesting subglacial sediment fluxes across the ice plain are currently low and unlikely to have a large stabilizing effect on the ice stream's grounding zone.

Bulk and molecular proxies of sediment core GeoB6518-1

A 20 kyr long sediment sequence from the Congo deep sea fan (core GeoB 6518-1), one of the world's largest deep sea river fans, has been analysed for bulk and molecular proxies in order to reconstruct the marine, soil and plant organic carbon (OC) contributions to these sediments since the last glacial maximum. The bulk proxies applied, C/N ratio and d13Corg, ranged from 10 to 12.5 and from -24.5 to -21 per mill VPDB, respectively. As molecular proxies, concentrations of marine derived alkenones and terrestrial derived odd-numbered n-alkanes were used, which varied between 0.2 and 4 µg/g dry weight sediment. In addition, the branched vs. isoprenoid tetraether (BIT) index, a proxy for soil organic matter input, was used, which varied from 0.3 to 0.5 in this core. Application of binary mixing models, based on the different individual proxies, showed estimates for terrestrial OC input varying by up to 50% due to the heterogeneous nature of the OC. Application of a three end-member mixing model using the d13Corg content, the C/N ratio and the BIT index, enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary OC pool. The results show that marine OC accounts for 20% to 40% of the total OC present in the deep sea fan sediments over the last 20 kyr and that soil OC accounts for about half (45% on average) of the OC present. This suggests that soil OC represents the majority of the terrestrial OC delivered to the fan sediments. Accumulation rates of the plant and soil OC fractions over the last 20 kyr varied by a factor of up to 5, and are strongly related to sediment accumulation rates. They showed an increase starting at ca. 17 kyr BP, a decline during the Younger Dryas, peak values during the early Holocene and lower values in the late Holocene. This pattern matches with reconstructions of past central African humidity and Congo River discharge from the same core and revealed that central African precipitation patterns exert a dominant control on terrestrial OC deposition in the Congo deep sea fan. Marine OC accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions. These variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind-driven upwelling.

Pigments of sediment cores of the Northwest European Continental Margin

In the context of the European OMEX Programme this investigation focused on gradients in the biomass and activity of the small benthic size spectrum along a transect across the Goban Spur from the outer Celtic Sea into Porcupine Abyssal Plain. The effects of food pulses (seasonal, episodic) on this part of the benthic size spectrum were investigated. Sediments sampled during eight expeditions at different seasons covering a range from 200 m to 4800 m water depth were assayed with biochemical bulk measurements: determinations of chloroplastic pigment equivalents (CPE), the sum of chlorophyll a and its breakdown products, provide information concerning the input of phytodetrital matter to the seafloor; phospholipids were analyzed to estimate the total biomass of small benthic organisms (including bacteria, fungi, flagellata, protozoa and small metazoan meiofauna). A new term 'small size class biomass' (SSCB) is introduced for the biomass of the smallest size classes of sediment-inhabiting organisms; the reduction of fluorescein-di-acetate (FDA) was determined to evaluate the potential activity of ester-cleaving bacterial exoenzymes in the sediment samples. At all stations benthic biomass was predominantly composed of the small size spectrum (90% on the shelf; 97-98% in the bathyal and abyssal parts of the transect). Small size class biomass (integrated over a 10 cm sediment column) ranged from 8 g C/m**2 on the shelf to 2.1 g C/m**2 on the adjacent Porcupine Abyssal Plain, exponentially decreasing with increasing water depth. However, a correlation between water depth and SSCB, macrofauna biomass as well as metazoan meiofauna biomass exhibited a significantly flatter slope for the small size classes in comparison to the larger organisms. CPE values indicated a pronounced seasonal cycle on the shelf and upper slope with twin peaks of phytodetrital deposition in mid spring and late summer. The deeper stations seem to receive a single annual flux maximum in late summer. SSCB and heterotrophic activity are significantly correlated to the amount of sediment-bound pigments. Seasonality in pigment concentrations is clearly followed by SSCB and activity. In contrast to macro- and megafauna which integrate over larger periods (months/years), the small benthic size classes, namely bacteria and foraminifera, proved to be the most reactive potential of the benthic communities to any perturbations on short time scales (days/weeks). The small size classes, therefore, occupy a key role in early diagenetic processes.

(Table 2) Age determination of sediment cores MD95-2002 and MD03-2692

We have compiled results obtained from four high sedimentation rate hemipelagic sequences from the Celtic sector of the NW European margin (NE Atlantic) to investigate the paleoceanographic and paleoclimatic evolution of the area over the last few climatic cycles. We focus on periods characteristic of deglacial transitions. We adopt a multiproxy sedimentological, geochemical, and micropaleontological approach, applying a sampling resolution down to ten microns for specific intervals. The investigation demonstrates the relationships between the Bay of Biscay hydrography and the glacial/deglacial history of both the proximal British-Irish Ice Sheet (BIIS) and the western European continent. We identify recurrent phases of laminae deposition concurrent with major BIIS deglacial episodes in all the studied cores. Evidence for abrupt freshwater discharges into the open ocean highlights the influence of such events at a regional scale. We discuss their impact at a global scale considering the present and past key location of the Bay of Biscay versus the Atlantic Meridional Overturning Circulation (AMOC).

Enviromagnetic, major element, and grain-size analyses of surface sediment samples along the continental margin between East Brazil and Patagonia

Continental margin sediments of SE South America originate from various terrestrial sources, each conveying specific magnetic and element signatures. Here, we aim to identify the sources and transport characteristics of shelf and slope sediments deposited between East Brazil and Patagonia (20°-48°S) using enviromagnetic, major element, and grain-size data. A set of five source-indicative parameters (i.e., chi-fd%, ARM/IRM, S0.3T, SIRM/Fe and Fe/K) of 25 surface samples (16-1805 m water depth) was analyzed by fuzzy c-means clustering and non-linear mapping to depict and unmix sediment-province characteristics. This multivariate approach yields three regionally coherent sediment provinces with petrologically and climatically distinct source regions. The southernmost province is entirely restricted to the slope off the Argentinean Pampas and has been identified as relict Andean-sourced sands with coarse unaltered magnetite. The direct transport to the slope was enabled by Rio Colorado and Rio Negro meltwaters during glacial and deglacial phases of low sea level. The adjacent shelf province consists of coastal loessoidal sands (highest hematite and goethite proportions) delivered from the Argentinean Pampas by wave erosion and westerly winds. The northernmost province includes the Plata mudbelt and Rio Grande Cone. It contains tropically weathered clayey silts from the La Plata Drainage Basin with pronounced proportions of fine magnetite, which were distributed up to ~24° S by the Brazilian Coastal Current and admixed to coarser relict sediments of Pampean loessoidal origin. Grain-size analyses of all samples showed that sediment fractionation during transport and deposition had little impact on magnetic and element source characteristics. This study corroborates the high potential of the chosen approach to access sediment origin in regions with contrasting sediment sources, complex transport dynamics, and large grain-size variability.

Table 1. Concentration of rare earth elements in ferromanganese nodule (crust), sediment and rock of the South China Sea

Based on the X-ray fluorescence spectrum analysis of 15 rare earth elements in 6 ferromanganese nodu1es and 5 ferro mangane se crusts from the South China Sea, their abundances, distribution patterns, sources and relationships with associated elements are discussed in detail in this paper. The results show that: 1) The average abundance of rare earth elements in ferromanganese nodu1es and crusts is 1. 625 g/kg and 2. 167 g/kg respectively, which is 1-2 tim es , 5-6 times and 15-20 times higher than that in the Pacific, in the sediments of the North Pacific and the South China Sea, respectively; 2) The distribution patterns of rare earth elements standardized by the globular aerolite in ferro mangane se nodules and crusts are basically similar, that is, Ce is positively abnormal and Eu is in deficit slightly; 3) The relationships between rare earth elements and associated elements, sediments and rocks show that the source of rare earth elements in ferromanganese nodules and crusts have mainly come from slow deposition caused by weathering and leaching of medium acidic rock of the South China Sea.

(Table 2) Seasonal flux data and percentages of major bulk components of total flux at the mesotrophic sediment trap site CB from 1988 - 2012

A more than two-decadal sediment trap record from the Eastern Boundary Upwelling Ecosystem (EBUE) off Cape Blanc, Mauritania, is analysed with respect to deep ocean mass fluxes, flux components and their variability on seasonal to decadal timescales. The total mass flux revealed interannual fluctuations which were superimposed by fluctuations on decadal timescales. High winter fluxes of biogenic silica (BSi), used as a measure of marine production (mostly by diatoms) largely correspond to a positive North Atlantic Oscillation (NAO) index (December-March). However, this relationship is weak. The highest positive BSi anomaly was in winter 2004-2005 when the NAO was in a neutral state. More episodic BSi sedimentation events occurred in several summer seasons between 2001 and 2005, when the previous winter NAO was neutral or even negative. We suggest that distinct dust outbreaks and deposition in the surface ocean in winter and occasionally in summer/autumn enhanced particle sedimentation and carbon export on short timescales via the ballasting effect. Episodic perturbations of the marine carbon cycle by dust outbreaks (e.g. in 2005) might have weakened the relationships between fluxes and large-scale climatic oscillations. As phytoplankton biomass is high throughout the year, any dry (in winter) or wet (in summer) deposition of fine-grained dust particles is assumed to enhance the efficiency of the biological pump by incorporating dust into dense and fast settling organic-rich aggregates. A good correspondence between BSi and dust fluxes was observed for the dusty year 2005, following a period of rather dry conditions in the Sahara/Sahel region. Large changes of all bulk fluxes occurred during the strongest El Niño-Southern Oscillation (ENSO) in 1997-1999 where low fluxes were obtained for almost 1 year during the warm El Niño and high fluxes in the following cold La Niña phase. For decadal timescales, Bakun (1990) suggested an intensification of coastal upwelling due to increased winds (''Bakun upwelling intensification hypothesis''; Cropper et al., 2014) and global climate change. We did not observe an increase of any flux component off Cape Blanc during the past 2 and a half decades which might support this. Furthermore, fluxes of mineral dust did not show any positive or negative trends over time which might suggest enhanced desertification or ''Saharan greening'' during the last few decades.

Sediment Budget for Cane Land on the Lower Herbert River Floodplain, North Queensland, Australia

Land use in the river catchments of tropical North Queensland appears to have increased the export of sediment and nutrients to the coast. Although evidence of harmful effect of sediment on coastal and riverine ecosystems is limited, there is a growing concern about its possible negative impacts. Sugarcane cultivation on the floodplains of the tropical North Queensland river catchments is thought to be an important source of excess sediment in the river drainage systems. Minimum-tillage, trash blanket harvesting has been shown to reduce erosion from sloping sugarcane fields, but in the strongly modified floodplain landscape other elements (e.g. drains, water furrows and headlands) could still be important sediment sources. The main objectives of this thesis are to quantify the amount of sediment coming from low-lying cane land and identify the important sediment sources in the landscape. The results of this thesis enable sugarcane farmers to take targeted measures for further reduction of the export of sediment and nutrients. Sediment budgets provide a useful approach to identify and quantify potential sediment sources. For this study a sediment budget is calculated for a part of the Ripple Creek catchment, which is a sub-catchment of the Lower Herbert River. The input of sediment from all potential sources in cane land and the storage of sediment within the catchment have been quantified and compared with the output of sediment from the catchment. Input from, and storage on headlands, main drains, minor drains and water furrows, was estimated from erosion pin and surface profile measurements. Input from forested upland, input from fields and the output at the outlet of the catchment was estimated with discharge data from gauged streams and flumes. Data for the sediment budget were collected during two ‘wet’-seasons: 1999-2000 and 2000-2001. The results of the sediment budget indicate that this tropical floodplain area is a net source of sediment. Plant cane fields, which do not have a protective trash cover, were the largest net source of sediment during the 1999-2000 season. Sediment input from water furrows was higher, but there was also considerable storage of sediment in this landscape element. Headlands tend to act as sinks. The source or sink function of drains is less clear, but seems to depend on their shape and vegetation cover. An important problem in this study is the high uncertainty in the estimates of the sediment budget components and is, for example, likely to be the cause of the imbalance in the sediment budget. High uncertainties have particularly affected the results from the 20002001 season. The main source of uncertainty is spatial variation in the erosion and deposition processes. Uncertainty has to be taken into consideration when interpreting the budget results. The observation of a floodplain as sediment source contradicts the general understanding that floodplains are areas of sediment storage within river catchments. A second objective of this thesis was therefore to provide an answer to the question: how can floodplains in the tropical North Queensland catchments can be a source of sediment? In geomorphic literature various factors have been pointed out, that could control floodplain erosion processes. However, their importance is not 'uniquely identified'. Among the most apparent factors are the stream power of the floodwater and the resistance of the floodplain surface both through its sedimentary composition and the vegetation cover. If the cultivated floodplains of the North Queensland catchments are considered in the light of these factors, there is a justified reason to expect them to be a sediment source. Cultivation has lowered the resistance of their surface; increased drainage has increased the drainage velocity and flood control structures have altered flooding patterns. For the Ripple Creek floodplain four qualitative scenarios have been developed that describe erosion and deposition under different flow conditions. Two of these scenarios were experienced during the budget study, involving runoff from local hillslopes and heavy rainfall, which caused floodplain erosion. In the longer term larger flood events, involving floodwater from the Herbert River, may lead to different erosion and deposition processes. The present study has shown that the tropical floodplain of the Herbert River catchment can be a source of sediment under particular flow conditions. It has also shown which elements in the sugarcane landscape are the most important sediment sources under these conditions. This understanding will enable sugarcane farmers to further reduce sediment export from cane land and prevent the negative impact this may have on the North Queensland coastal ecosystems.

The interplay between tectonics, sediment dynamics and gateways evolution in the Danube system from the Pannonian Basin to the western Black Sea

Understanding the natural evolution of a river–delta–sea system is important to develop a strong scientific basis for efficient integrated management plans. The distribution of sediment fluxes is linked with the natural connection between sediment source areas situated in uplifting mountain chains and deposition in plains, deltas and, ultimately, in the capturing oceans and seas. The Danube River–western Black Sea is one of the most active European systems in terms of sediment re-distribution that poses significant societal challenges. We aim to derive the tectonic and sedimentological background of human-induced changes in this system and discuss their interplay. This is obtained by analysing the tectonic and associated vertical movements, the evolution of relevant basins and the key events affecting sediment routing and deposition. The analysis of the main source and sink areas is focused in particular on the Miocene evolution of the Carpatho-Balkanides, Dinarides and their sedimentary basins including the western Black Sea. The vertical movements of mountains chains created the main moments of basin connectivity observed in the Danube system. Their timing and effects are observed in sediments deposited in the vicinity of gateways, such as the transition between the Pannonian/Transylvanian and Dacian basins and between the Dacian Basin and western Black Sea. The results demonstrate the importance of understanding threshold conditions driving rapid basins connectivity changes superposed over the longer time scale of tectonic-induced vertical movements associated with background erosion and sedimentation. The spatial and temporal scale of such processes is contrastingly different and challenging. The long-term patterns interact with recent or anthropogenic induced modifications in the natural system and may result in rapid changes at threshold conditions that can be quantified and predicted. Their understanding is critical because of frequent occurrence during orogenic evolution, as commonly observed in the Mediterranean area and discussed elsewhere.