Environmental magnetism, geochemical measurements and colour reflectance of two sediment cores: GeoB4905-4 off Cameroon and GeoB4906-3 off Gabon

We combine environmental magnetism, geochemical measurements and colour reflectance to study two late Quaternary sediment cores: GeoB 4905-4 at 2° 30 N off Cameroon and GeoB 4906-3 at 0° 44 N off Gabon. This area is suitable for investigating precipitation changes over Central and West Africa because of its potential to record input of aeolian and fluvial sediments. Three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified. The magnetic signature is dominated by fine-grained magnetite, while residual haematite prevails in the reduced intervals, showing increase in concentration and fine grain size at wet intervals. Our records also show millennial-scale changes in climate during the last glacial and interglacial cycles. At the northern location, the past 5.5 ka are marked by high-frequency oscillations of Ti and colour reflectance, which suggests aeolian input and hence aridity. The southern location remains under the influence of the Intertropical Convergence Zone and thus did not register aeolian signals. The millennial-scale climatic signals indicate that drier and/or colder conditions persisted during the late Holocene and are synchronous with the 900 a climatic cycles observed in Northern Hemisphere ice core records.

Seawater carbonate chemistry, calcification rate, oxygen production, maximum quantum yield, symbiont density, chlorophyll concentration and crystal width of Halimeda macroloba, Halimeda cylindracea and Marginopora vertebralis during experiments, 2011

The effects of elevated CO2 and temperature on photosynthesis and calcification in the calcifying algae Halimeda macroloba and Halimeda cylindracea and the symbiont-bearing benthic foraminifera Marginopora vertebralis were investigated through exposure to a combination of four temperatures (28°C, 30°C, 32°C, and 34°C) and four CO2 levels (39, 61, 101, and 203 Pa; pH 8.1, 7.9, 7.7, and 7.4, respectively). Elevated CO2 caused a profound decline in photosynthetic efficiency (FV : FM), calcification, and growth in all species. After five weeks at 34°C under all CO2 levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. significantly decreased in 203 Pa, 32°C and 34°C treatments, but Chl a and Chl c2 concentration in M. vertebralis was not affected by temperature alone, with significant declines in the 61, 101, and 203 Pa treatments at 28°C. Significant decreases in FV : FM in all species were found after 5 weeks of exposure to elevated CO2 (203 Pa in all temperature treatments) and temperature (32°C and 34°C in all pH treatments). The rate of oxygen production declined at 61, 101, and 203 Pa in all temperature treatments for all species. The elevated CO2 and temperature treatments greatly reduced calcification (growth and crystal size) in M. vertebralis and, to a lesser extent, in Halimeda spp. These findings indicate that 32°C and 101 Pa CO2, are the upper limits for survival of these species on Heron Island reef, and we conclude that these species will be highly vulnerable to the predicted future climate change scenarios of elevated temperature and ocean acidification.

On the effects of circulation, sediment resuspension and biological incorporation by diatoms in an ocean model of aluminium, link to model data

The distribution of dissolved aluminium in the West Atlantic Ocean shows a mirror image with that of dissolved silicic acid, hinting at intricate interactions between the ocean cycling of Al and Si. The marine biogeochemistry of Al is of interest because of its potential impact on diatom opal remineralisation, hence Si availability. Furthermore, the dissolved Al concentration at the surface ocean has been used as a tracer for dust input, dust being the most important source of the bio-essential trace element iron to the ocean. Previously, the dissolved concentration of Al was simulated reasonably well with only a dust source, and scavenging by adsorption on settling biogenic debris as the only removal process. Here we explore the impacts of (i) a sediment source of Al in the Northern Hemisphere (especially north of ~ 40° N), (ii) the imposed velocity field, and (iii) biological incorporation of Al on the modelled Al distribution in the ocean. The sediment source clearly improves the model results, and using a different velocity field shows the importance of advection on the simulated Al distribution. Biological incorporation appears to be a potentially important removal process. However, conclusive independent data to constrain the Al / Si incorporation ratio by growing diatoms are missing. Therefore, this study does not provide a definitive answer to the question of the relative importance of Al removal by incorporation compared to removal by adsorptive scavenging.

Sedimentological and palynological analysis of sediment cores from the northeastern Vietnamese Mekong River Delta

Three radiocarbon-dated sediment cores from the northeastern Vietnamese Mekong River Delta have been analysed with a multiproxy approach (grain size, pollen and spores, macro-charcoal, carbon content) to unravel the palaeoenvironmental history of the region since the mid Holocene. During the mid-Holocene sea-level highstand a diverse, zoned and widespread mangrove belt (dominated by Rhizophora) covered the extended tidal flats. The subsequent regression and coeval delta progradation led to the rapid development of a back-mangrove community dominated by Ceriops and Bruguiera but also represented locally by e.g. Kandelia, Excoecaria and Phoenix. Along rivers this community seems to have endured even when the adjoining floodplain had already shifted to freshwater vegetation. Generally this freshwater vegetation has a strong swamp signature but locally Arecaceae, Fabaceae, Moraceae/Urticaceae and Myrsinaceae are important and mirror the geomorphological diversity of the delta plain. The macro-charcoal record implies that natural burning of vegetation occurred throughout the records, however, the occurrence of the highest amounts of macro-charcoal particles is linked with modern human activity.

Abundances of dinoflagellate cysts in sediment trap MST-9 (Appendix 1)

To study the ecology of calcareous dinoflagellates we examined the impact of the SW and NE monsoons on cyst formation using sediment trap material, collected at 1032 m water depth, off Somalia from June 1992 to February 1993. The results do not confirm the relationship between cyst production and lower nutrient concentrations, as highest cyst fluxes were recorded during late SW monsoon under the relatively nutrient-rich and less agitated conditions of mature upwelled water. Lowest cyst fluxes were found under strongly stratified, nutrient-depleted surface waters during the inter-monsoon. Although all of the studied species seem to prefer a stratified water column, an elevated concentration of nutrients appears to be necessary to maintain high cyst production. Comparison of the mean cyst flux to the sediment trap with that into the underlying surface sediments reveals a loss of 81-96%, which can be attributed to calcite dissolution. The relatively small spheres of Thoracosphaera heimii are affected more than the cysts of the other species.

Particle fluxes and in-situ particle properties measured with sediment traps and a moored camera system from 2008 - 2010 in region off Cape Blanc / NW-Africa

We compared particle data from a moored video camera system with sediment trap derived fluxes at ~1100 m depth in the highly dynamic coastal upwelling system off Cape Blanc, Mauritania. Between spring 2008 and winter 2010 the trap collected settling particles in 9-day intervals, while the camera recorded in-situ particle abundance and size-distribution every third day. Particle fluxes were highly variable (40-1200 mg m**-2 d**-1) and followed distinct seasonal patterns with peaks during spring, summer and fall. The particle flux patterns from the sediment traps correlated to the total particle volume captured by the video camera, which ranged from1 to 22 mm**3 l**-1. The measured increase in total particle volume during periods of high mass flux appeared to be better related to increases in the particle concentrations, rather than to increased average particle size. We observed events that had similar particle fluxes, but showed clear differences in particle abundance and size-distribution, and vice versa. Such observations can only be explained by shifts in the composition of the settling material, with changes both in particle density and chemical composition. For example, the input of wind-blown dust from the Sahara during September 2009 led to the formation of high numbers of comparably small particles in the water column. This suggests that, besides seasonal changes, the composition of marine particles in one region underlies episodical changes. The time between the appearance of high dust concentrations in the atmosphere and the increase lithogenic flux in the 1100 m deep trap suggested an average settling rate of 200 m d**-1, indicating a close and fast coupling between dust input and sedimentation of the material.

Major element concentration and radionuclides of equatorial Pacific deep-sea sediments

The (231Pa/230Th)xs,0 records obtained from two cores from the western (MD97-2138; 1°25'S, 146°24'E, 1900 m) and eastern (ODP Leg 138 Site 849, 0°11.59'N, 110°31.18'W, 3851 m) equatorial Pacific display similar variability over the last 85000 years, i.e. from isotopic stages 1 to 5a, with systematically higher values during the Holocene, isotopic stage 3 and isotopic stage 5a, and lower values, approaching the production rate ratio of the two isotopes (0.093), during the colder periods corresponding to isotopic stages 2 and 4. We have also measured the 230Th-normalized biogenic preserved and terrigenous fluxes, as well as major and trace elements concentrations, in both cores. The (231Pa/230Th)xs,0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial Pacific during glacial periods. The (231Pa/230Th)xs,0 variations in the western equatorial Pacific (WEP) also seem to be controlled by productivity (carbonate and/or opal). The generally high (231Pa/230Th)xs,0 ratios (>0.093) of the profile could be due to opal and/or MnO2 in the sinking particles. The profiles of (231Pa/230Th)xs,0 and 230Th-normalized fluxes indicate a decrease in exported carbonate, and possibly opal, during isotopic stages 2 and 4 in MD97-2138. Using 230Th-normalized flux, we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability.

Age determination of sediment cores from the Panama Basin

High-resolution percent Corg and delta18Oforam records obtained from Panama Basin core Atlantis II 54-25PC and additional data from nearby core P7 show that enhanced burial of organic carbon has characterized every major glacial period for the last 500 kyr in that area. Both Corg concentration and mass accumulation rate profiles exhibit a sawtooth pattern with maxima occurring typically in the later stages of glacial periods. Comparison with dust records suggests that the carbon accumulation rate profile reflects both the upwelling history and a variable rate of iron input during the late Quaternary. The sawtooth character may derive from increased wind velocities and rates of upwelling during glacials which are indirectly related to ice volume (Sarnthein et al., 1988). The rapid decline in export production at the end of glacials in the equatorial Pacific may be attributed to the retreat of ice sheets (thus reduced wind velocities and upwelling) coupled with a coincident decline in atmospheric dust load and/or delivery rate. The Corg accumulation rate profiles do not correlate well with atmospheric CO2 records. For example, atmospheric CO2 was already at a minimum 40 kyr ago when production in the Panama Basin began increasing dramatically, commensurate with an increase in global dust levels. Using the relationship between the degree of photosynthetic fractionation and the concentration of free CO2 in the surface ocean postulated by Popp et al. (1989), delta13Corg measurements made on core P7 show that Panama Basin surface waters have been supplying CO2 to the atmosphere continually for at least the last 50 kyr. There is no evidence for a flux of CO2 into the surface ocean in this area at any time during this period despite the higher production. If the Panama Basin cores are representative of the eastern and central equatorial Pacific, then these observations weaken the influence on CO2 drawdown postulated for increased glacial productivity at low latitudes.

Index properties, calcium carbonate content and opal concentration of ODP Core 167-1016B-17H sediments

Physical properties measurements provide a relatively inexpensive and fast way to obtain high-resolution estimates of the variations in sedimentological properties. To better resolve the validity and cause of the geophysical signals measured by the Ocean Drilling Program (ODP) shipboard multisensor track (MST) instruments, 223 x 10 cm**3 core samples were collected at 4 cm intervals in Core 167-1016B-17H at the California Margin Conception Transect for the measurements of index properties, carbonate content, and opal content. This core was chosen because hole-to-hole stratigraphic correlation of MST data suggested that Core 17H corresponds to a depth interval that displays the greatest range of amplitude of many physical properties.

Major, trace and rare earth element concentration of ODP Site 210-1277 basalts, Newfoundland margin

Drilling of the distal Newfoundland margin at Ocean Drilling Program Site 1277 recovered part of the transition between exhumed sub-continental mantle lithosphere and normal mid-ocean-ridge basalt (N-MORB) volcanism perhaps related to the initiation of seafloor spreading, which may have occurred near the Aptian/Albian boundary, coincident with the final separation of subcontinental mantle lithosphere. Subcontinental mantle lithosphere was recovered near the crest of a basement high, the Mauzy Ridge. This ridge lies near magnetic Anomaly M1 and is inferred to be of Barremian age. The recovered section is dominated by serpentinized spinel harzburgite, with subordinate dunite and minor gabbroic intrusives, and it includes inferred high-temperature ductile shear zones. The serpentinite is capped by foliated gabbro cataclasite that is interpreted as the product of a major seafloor extensional detachment. The serpentinized harzburgite beneath is highly depleted subcontinental mantle lithosphere that was exhumed to create new seafloor within the ocean-continent transition zone. After inferred removal of overlying brittle crust, the detachment was eroded, producing multiple mass flows that were dominated by clasts of serpentinite and gabbro in a lithoclastic and calcareous matrix. Basaltic lavas were erupted spasmodically, mainly as sheet flows, with subordinate lava breccia, hyaloclastite, and possible pillow lava. The sedimentary-volcanic succession and the exhumed mantle lithosphere experienced later high-angle extensional fracturing and probably faulting. Extensional fissures opened incrementally and were filled with silt-sized carbonate, basalt-derived clastic sediment, and hyaloclastite, forming neptunian dykes and geopetal structures. Chemical analysis of representative basalts for major elements and trace elements were made using a high-precision, high-accuracy X-ray fluorescence method (utilizing increased count times) and by whole-rock inductively coupled plasma-mass spectrometry that yielded additional evidence for rare earth elements. The analyses indicate N-MORB to slightly enriched compositions. The MORB was produced by relatively high degree melting of a fertile mantle source that differed strongly from the cored serpentinized peridotites. The basalts exhibit a distinct negative Nb anomaly on MORB-normalized plots that can be explained by prior extraction of melt from upper mantle that had previously been affected by subduction, possibly during closure of the Iapetus or Rheic oceans. In the proposed interpretation, mantle lithosphere was exhumed to the seafloor and experienced mass wasting to form serpentinite-rich mass flows. The interbedded MORB records the beginning of a transition to "normal" seafloor spreading. This interpretation takes into account drilling results from the Iberia-Galicia margin and the Jurassic Alps-Apennines.

Sedimentary climate indicators of sediment core MD08-3167 and GeoB1711-4, southwestern Africa

The past climate evolution of southwestern Africa is poorly understood and interpretations of past hydrological changes are sometimes contradictory. Here we present a record of leaf-wax dD and View the MathML source taken from a marine sediment core at 23°S off the coast of Namibia to reconstruct the hydrology and C3 versus C4 vegetation of southwestern Africa over the last 140 000 years (140 ka). We find lower leaf-wax dD and higher View the MathML source (more C4 grasses), which we interpret to indicate wetter Southern Hemisphere (SH) summer conditions and increased seasonality, during SH insolation maxima relative to minima and during the last glacial period relative to the Holocene and the last interglacial period. Nonetheless, the dominance of C4 grasses throughout the record indicates that the wet season remained brief and that this region has remained semi-arid. Our data suggest that past precipitation increases were derived from the tropics rather than from the winter westerlies. Comparison with a record from the Congo Basin indicates that hydroclimate in southwestern Africa has evolved in antiphase with that of central Africa over the last 140 ka.

Graphs of experimental results given in concentration of trace metals versus time in days

The impact of CO2 leakage on solubility and distribution of trace metals in seawater and sediment has been studied in lab scale chambers. Seven metals (Al, Cr, Ni, Pb, Cd, Cu, and Zn) were investigated in membrane-filtered seawater samples, and DGT samplers were deployed in water and sediment during the experiment. During the first phase (16 days), "dissolved" (<0.2 µm) concentrations of all elements increased substantially in the water. The increase in dissolved fractions of Al, Cr, Ni, Cu, Zn, Cd and Pb in the CO2 seepage chamber was respectively 5.1, 3.8, 4.5, 3.2, 1.4, 2.3 and 1.3 times higher than the dissolved concentrations of these metals in the control. During the second phase of the experiment (10 days) with the same sediment but replenished seawater, the dissolved fractions of Al, Cr, Cd, and Zn were partly removed from the water column in the CO2 chamber. DNi and DCu still increased but at reduced rates, while DPb increased faster than that was observed during the first phase. DGT-labile fractions (MeDGT) of all metals increased substantially during the first phase of CO2 seepage. DGT-labile fractions of Al, Cr, Ni, Cu, Zn, Cd and Pb were respectively 7.9, 2.0, 3.6, 1.7, 2.1, 1.9 and 2.3 times higher in the CO2 chamber than that of in the control chamber. AlDGT, CrDGT, NiDGT, and PbDGT continued to increase during the second phase of the experiment. There was no change in CdDGT during the second phase, while CuDGT and ZnDGT decreased by 30% and 25%, respectively in the CO2 chamber. In the sediment pore water, DGT labile fractions of all the seven elements increased substantially in the CO2 chamber. Our results show that CO2 leakage affected the solubility, particle reactivity and transformation rates of the studied metals in sediment and at the sediment-water interface. The metal species released due to CO2 acidification may have sufficiently long residence time in the seawater to affect bioavailability and toxicity of the metals to biota.

Concentrations of dinoflagellate cysts in the surface layer of bottom sediment from the White Sea

Dinoflagellate cysts were studied in 42 samples from surface sediments of the White Sea. Total concentration of dinocysts varies from single cysts to 25000 cyst/g of dry sediments, which reflects biological productivity in White Sea waters and regional particular features of sedimentation processes. The highest concentrations are observed in silts; they are related to the regions of propagation of highly productive Barents Sea waters in the White Sea. Generally, spatial distribution of dinocyst species in the surface sediments corresponds to distribution of the major types of water masses in the White Sea. Cysts of relatively warm-water species (Operculodinium centrocarpum, Spiniferites sp.) of North Atlantic origin that dominate in the sediments indicate an intensive intrusion of Barents Sea water masses to the White Sea along with hydrological dwelling conditions in the White Sea favorable for development of these species during their vegetation period. The cold-water dinocyst assemblage (Islandinium minutum, Polykrikos sp.) is rather strictly confined to inner parts of shallow-water bays, firstly, those adjacent to the Onega and Severnaya Dvina river mouths.