Deuterium analysis of ice core GISP2

The Greenland Ice Sheet Project 2 (GISP2) core can enhance our understanding of the relationship between parameters measured in the ice in central Greenland and variability in the ocean, atmosphere, and cryosphere of the North Atlantic Ocean and adjacent land masses. Seasonal (summer, winter) to annual responses of dD and deuterium excess isotopic signals in the GISP2 core to the seesaw in winter temperatures between West Greenland and northern Europe from A.D. 1840 to 1970 are investigated. This seesaw represents extreme modes of the North Atlantic Oscillation, which also influences sea surface temperatures (SSTs), atmospheric pressures, geostrophic wind strength, and sea ice extents beyond the winter season. Temperature excursions inferred from the dD record during seesaw/extreme NAO mode years move in the same direction as the West Greenland side of the seesaw. Symmetry with the West Greenland side of the seesaw suggests a possible mechanism for damping in the ice core record of the lowest decadal temperatures experienced in Europe from A.D. 1500 to 1700. Seasonal and annual deuterium excess excursions during seesaw years show negative correlation with dD. This suggests an isotopic response to a SST/ land temperature seesaw. The isotopic record from GISP2 may therefore give information on both ice sheet and sea surface temperature variability. Cross-plots of dD and d show a tendency for data to be grouped according to the prevailing mode of the seesaw, but do not provide unambiguous identification of individual seesaw years. A combination of ice core and tree ring data sets may allow more confident identification of GA and GB (extreme NAO mode) years prior to 1840.

Results of bulk sediment X-ray diffraction analysis and quantification of mineral phases based on the RockJock and on the QUAX quantitative analysis

We have performed quantitative X-ray diffraction (qXRD) analysis of 157 grab or core-top samples from the western Nordic Seas between (WNS) ~57°-75°N and 5° to 45° W. The RockJock Vs6 analysis includes non-clay (20) and clay (10) mineral species in the <2 mm size fraction that sum to 100 weight %. The data matrix was reduced to 9 and 6 variables respectively by excluding minerals with low weight% and by grouping into larger groups, such as the alkali and plagioclase feldspars. Because of its potential dual origins calcite was placed outside of the sum. We initially hypothesized that a combination of regional bedrock outcrops and transport associated with drift-ice, meltwater plumes, and bottom currents would result in 6 clusters defined by "similar" mineral compositions. The hypothesis was tested by use of a fuzzy k-mean clustering algorithm and key minerals were identified by step-wise Discriminant Function Analysis. Key minerals in defining the clusters include quartz, pyroxene, muscovite, and amphibole. With 5 clusters, 87.5% of the observations are correctly classified. The geographic distributions of the five k-mean clusters compares reasonably well with the original hypothesis. The close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable at both the WNS-scale and at a more local scale in NE Greenland.

Grain size and XRD analysis on Site 162-983

The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modeling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electrosensing and laser diffraction techniques, despite issues previously raised on the low precision of electrosensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modeling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction, the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modeling meaningful current speed reconstructions can be obtained from mixed sediments.

Compilation of sedimentation rates and smear slide analysis of DSDP sites

A history of Mesozoie and Cenozoic palaeoenvironments of the North Atlantie Oeean has been developed based on a detailed analysis of the temporal and spatial distribution of major pelagie sediment facies, of hiatuses. of bulk sediment accumulation rates, and of concentrations and fluxes of the main deep-sea sediment components. The depositional history of the North Atlantic can be subdivided into three major phase: (a) Late Jurassie and Early Cretaceous phase: clastic terrigenous and biogenic pelagic sediment components accumulated rapidly under highly productive surface water masses over the entire occan basin; (b) Late Cretaceous to Early Miocene phase: relatively little terrigenous and pelagic biogenic sediment reached the North Atlantic Ocean floor, intensive hiatus formation occurred at variable rates, and wide stretches of the deep-ocean floor were covered by slowly accumulating terrigenous muds: (c) Middle Miocene to Recent phase: accumulation rates of biogenic and terrigenous deep-sea sediment components increased dramatically up to Quaternary times, rates of hiatus formation and the intensity of deep-water circulation inferred from them seem to have decreased. However, accumulation rate patterns of calcareous pelagic sediment components suggest that large scale reworking and di splacement of deep-sea sediments occurred at a variable rate over wide areas of the North Atlantic during this period.

Palynofacies analysis of sediments in the eastern Equatorial Atlantic

Analyses of the palynofacies and sporomorph thermal alteration indices (TAI) of sediments from Ocean Drilling Program (ODP) Sites 959 to 962 in the Cote d'Ivoire-Ghana Transform Margin, West Africa were undertaken to (1) determine the source and depositional conditions of the organic matter in the sediments, (2) refine a paleobathymetric curve derived from other data for Site 959, which drilled the most continuous sedimentary sequence from Pleistocene to Albian and (3) interpret the paleothermal history of the area. Twelve types of dispersed organic matter were identified: amorphous organic matter (AOM), marine palynomorphs, algae, resins, black debris, yellow-brown fragments, black-brown fragments, cuticles, plant tissue, wood, sporomorphs and fungi, The relative abundances of these organic matter components at each site were analyzed using cluster analysis, resulting in the identification of seven palynofacies assemblages at Site 959, five each at sites 960 and 961, and four at Site 962. Amorphous organic matter (which is chiefly marine derived), black debris and wood have played the most significant role in defining palynofacies assemblages. The palynofacies assemblages show some correlation with lithologic units, sediment sources and depositional environments. Previous palynofacies studies in passive margins have demonstrated that changes in the ratio of AOM to terrestrial organic matter are related primarily to proximal-distal positions of depositional environments relative to the shoreline. However, this assumption does not always hold true for a transform margin where tectonic factors play an important role in the organic matter distribution, at least in the early stages of evolution. Lithofacies, CCD paleodepths for the North Atlantic, trace fossil association, benthic foraminifera and palynofacies data were the criteria used for reconstructing a paleobathymetric curve for Site 959. A cyclicity in the organic matter distribution of the Upper Miocene to Lower Pliocene pelagic sediments could be related to fluctuations in productivity of biosiliceous and calcareous organisms, and sedimentation rates. A drastic increase in the amount of AOM and a decrease in black debris and wood in the carbonate and clastic rocks (Lithologic Unit IV) overlying the tectonized Albian sediments (Lithologic Unit V) at Sites 959 and 960 coincide with the presence of an unconformity. Qualitative color analysis of palynomorphs was undertaken for all sites, although the main focus was on Site 959 where detailed organic geochemical data were available. At Site 959, TAI values indicate an immature stage of organic maturation (<2) down to the black claystones of Lithologic Unit III at about 918.47 mbsf. Below this, samples show an increase with depth to a moderately mature stage (>2 except for the claystone samples between 1012.52 and 1036.5 mbsf, and one limestone sample at 1043.4 mbsf), reaching peak levels of 2.58 to 3.0 in the tectonized Albian sediments below the unconformity. These TAI values show a positive correlation with the Tma x values derived from Rock-Eval pyrolysis data. The highest values recorded in the basal tectonized units at all the sites (Sites 960-962 have mean values between 2.25 and 3.13) may be related to high heat flow during the intracontinental to syntransform basin stage in the region.

Response of a natural phytoplankton community from the Qingdao coast (Yellow Sea, China) to variable CO2 levels over a short-term incubation experiment

Since marine phytoplankton play a vital role in stabilizing earth's climate by removing significant amount of atmospheric CO2, their responses to increasing CO2 levels are indeed vital to address. The responses of a natural phytoplankton community from the Qingdao coast (NW Yellow Sea, China) was studied under different CO2 levels in microcosms. HPLC pigment analysis revealed the presence of diatoms as a dominant microalgal group; however, members of chlorophytes, prasinophytes, cryptophytes and cyanophytes were also present. delta 13CPOM values indicated that the phytoplankton community probably utilized bicarbonate ions as dissolved inorganic carbon source through a carbon concentration mechanism (CCM) under low CO2 levels, and diffusive CO2 uptake increased upon the increase of external CO2 levels. Although, considerable increase in phytoplankton biomass was noticed in all CO2 treatments, CO2-induced effects were absent. Higher net nitrogen uptake under low CO2 levels could be related to the synthesis of CCM components. Flow cytometry analysis showed slight reduction in the abundance of Synechococcus and pico-eukaryotes under the high CO2 treatments. Diatoms did not show any negative impact in response to increasing CO2 levels; however, chlorophytes revealed a reverse tend. Heterotrophic bacterial count enhanced with increasing CO2 levels and indicated higher abundance of labile organic carbon. Thus, the present study indicates that any change in dissolved CO2 concentrations in this area may affect phytoplankton physiology and community structure and needs further long-term study.

Grain size analysis of ODP Site 162-984

Past changes in the freshwater balance of the surface North Atlantic Ocean are thought to have influenced the rate of deep-water formation, and consequently climate (Broecker and Denton, 1989, doi:10.1016/0016-7037(89)90123-3; Manabe and Stouffer, 1996; doi:10.1038/378165a0). Although water-mass proxies are generally consistent with an impact of freshwater input on meridional overturning circulation (Boyle and Keigwin, 1987, doi:10.1038/330035a0), there has been little dynamic evidence to support this linkage. Here we present a 25,000 year record of variations in sediment grain size from south of Iceland, which indicates vigorous bottom-water currents during both the last glacial maximum and the Holocene period. Together with reconstructions of North Atlantic water-mass distribution, vigorous bottom currents suggest a shorter residence time of northern-source waters during the last glacial maximum, relative to the Holocene period. The most significant reductions in flow strength occur during periods that have been associated with freshening of the surface North Atlantic. The short-term deglacial oscillations in bottom current strength are closely coupled to changes in Greenland air temperature, with a minimum during the Younger Dryas cold reversal and a maximum at the time of rapid warming at the onset of the Holocene. Our results support a strong connection between ocean circulation and rapid climate change.

Geochemical analysis of surface sediments from the ocean floor and from sea ice in the northern Atlantic and Arctic Oceans

Barium in marine terrigenous surface sediments of the European Nordic Seas is analysed to evaluate its potential as palaeoproductivity proxy. Biogenic Ba is calculated from Ba and Al data using a conventional approach. For the determination of appropriate detrital Ba/Al ratios a compilation of Ba and Al analyses in rocks and soils of the catchments surrounding the Nordic Seas is presented. The resulting average detrital Ba/Al ratio of 0.0070 is similar to global crustal average values. In the southern Nordic Seas the high input of basaltic material with a low Ba/Al ratio is evident from high values of magnetic susceptibility and low Al/Ti ratios. Most of the Ba in the marine surface sediments is of terrigenous and not of biogenic origin. Variability in the lithogenic composition has been considered by the application of regionally varying Ba/Al ratios. The biogenic Ba values are comparable with those observed in the central Arctic Ocean, they are lower than in other oceanic regions. Biogenic Ba values are correlated with other productivity proxies and with oceanographic data for a validation of the applicability in paleoceanography. In the Iceland Sea and partly in the marginal sea-ice zone of the Greenland Sea elevated values of biogenic Ba indicate seasonal phytoplankton blooms. In both areas paleoproductivities may be reconstructed based on Ba and Al data of sediment cores.

Bulk sediment parameters and coarse-fraction analysis of ODP Leg 178 holes

The area west of the Antarctic Peninsula is a key region for studying and understanding the history of glaciation in the southern high latitudes during the Neogene with respect to variations of the western Antarctic continental ice sheet, variable sea-ice cover, induced eustatic sea level change, as well as consequences for the global climatic system (Barker, Camerlenghi, Acton, et al., 1999). Sites 1095, 1096, and 1101 were drilled on sediment drifts forming the continental rise to examine the nature and composition of sediments deposited under the influence of the Antarctic Peninsula ice sheet, which has repeatedly advanced to the shelf edge and subsequently released glacially eroded material on the continental shelf and slope (Barker et al., 1999). Mass gravity processes on the slope are responsible for downslope sediment transport by turbidity currents within a channel system between the drifts. Furthermore, bottom currents redistribute the sediments, which leads to final build up of drift bodies (Rebesco et al., 1998). The high-resolution sedimentary sequences on the continental rise can be used to document the variability of continental glaciation and, therefore, allow us to assess the main factors that control the sediment transport and the depositional processes during glaciation periods and their relationship to glacio-eustatic sea level changes. Site 1095 lies in 3840 m of water in a distal position on the northwestern lower flank of Drift 7, whereas Site 1096 lies in 3152 m of water in a more proximal position within Drift 7. Site 1101 is located at 3509 m water depth on the northwestern flank of Drift 4. All three sites have high sedimentation rates. The oldest sediments were recovered at Site 1095 (late Miocene; 9.7 Ma), whereas sediments of Pliocene age were recovered at Site 1096 (4.7 Ma) and at Site 1101 (3.5 Ma). The purpose of this work is to provide a data set of bulk sediment parameters such as CaCO3, total organic carbon (TOC), and coarse-fraction mass percentage (>63 µm) measured on the sediments collected from the continental rise of the western Antarctic Peninsula (Holes 1095A, 1095B, 1096A, 1096B, 1096C, and 1101A). This information can be used to understand the complex depositional processes and their implication for variations in the climatic system of the western Pacific Antarctic margin since 9.7 Ma (late Miocene). Coarse-fraction particles (125-500 µm) from the late Pliocene and Pleistocene (4.0 Ma to recent) sediments recovered from Hole 1095A were microscopically analyzed to gather more detailed information about their variability and composition through time. These data can yield information about changes in potential source regions of the glacially eroded material that has been transported during repeated periods of ice-sheet movements on the shelf.

Geochemical analysis at ODP Site 207-1259 from the Demerara Rise in the western equatorial Atlantic

Organic carbon-rich shales deposited during the Coniacian-Santonian Oceanic Anoxic Event 3 were drilled during ODP Leg 207 at Demerara Rise. We present integrated high-resolution geochemical records of core intervals from ODP Sites 1259 and 1261 both from nannofossil biozone CC14. Our results reveal systematic variations in marine and detrital sediment contribution, depositional processes, and bottom water redox conditions during black shale formation at two locations on Demerara Rise in different paleo-water depths. A combination of redox proxies (Fe/S, P/Al, C/P, redox-sensitive/sulfide-forming trace metals Mn, Cd, Mo, Ni, V, Zn) and other analytical approaches (bulk sediment composition, P speciation, electron microscopy, X-ray diffraction) evidence anoxic to sulfidic bottom water and sediment conditions throughout the deposition of black shale. These extreme redox conditions persisted and were periodically punctuated by short-termed periods with less reducing bottom waters irrespective of paleo-water depth. Sediment supply at both sites was generally dominated by marine material (carbonate, organic matter, opal) although relationships of detrital proxies as well as glauconitic horizons support some influence of turbidites, winnowing bottom currents and/or variable detritus sources, along with less reducing bottom water at the proposed shallower location (ODP Site 1259). At Site 1261, located at greater paleo-depth, redox fluctuations were more regular, and steady hemipelagic sedimentation sustained the development of mostly undisturbed lamination in the sedimentary record. Strong similarities of the studied deposits exist with the stratigraphic older Cenomanian-Turonian OAE2 black shale sections at Demerara Rise, suggesting that the primary mechanisms controlling continental supply and ocean redox state were time-invariant and kept the western equatorial Atlantic margin widely anoxic over millions of years.