Chemical and mineral compositions of sediments from ODP Site 127-797

In order to reconstruct past variations in the aeolian dust (Kosa) contribution to the Japan Sea, and to establish a direct link between terrestrial and marine climatic records, we have applied statistical procedures to distinguish and quantify detrital subcomponents within the detrital fraction of the late Quaternary hemipelagic sediments in the Japan Sea. Q-mode factor analysis with varimax and oblique rotation of the factors followed by multiple-regression analysis between mineral composition and factor loadings was conducted using six ''detrital'' elements. Four detrital subcomponents were defined, which are attributed to Kosa derived from ''typical'' loess, Kosa from ''weathered'' loess, and fine and coarse arc-derived detritus, respectively, based on comparisons with the chemical and mineral compositions of probable source materials. Using these detrital subcomponents, the variation in Kosa fraction was reconstructed for the last 200 ky. The results reveal millennial-scale as well as glacial-interglacial scale variations in Kosa contribution. Especially, millennial-scale variability of Kosa contribution suggests the presence of high frequency variation in summer monsoon precipitation in the central to east Asia during the last 200 ky.

Sedimentology and geochemistry of ODP Site 184-1144

We analyzed sediment from Ocean Drilling Program (ODP) Site 1144 in the northern South China Sea to examine the weathering response of SE Asia to the strengthening of the East Asian Monsoon (EAM) since 14 ka. Our high-resolution record highlights the decoupling between continental chemical weathering, physical erosion and summer monsoon intensity. Mass accumulation rates, Ti/Ca, K/Rb, hematite/goethite and 87Sr/86Sr show sharp excursions from 11 to 8 ka, peaking at 10 ka. Clay minerals show a shorter-lived response with a higher kaolinite/(illite + chlorite) ratio at 10.7-9.5 ka. However, not all proxies show a clear response to environmental changes. Magnetic susceptibility rises sharply between 12 and 11 ka. Grain-size becomes finer from 14 to 10 ka and then coarsens until ~7 ka, but is probably controlled by bottom current flow and sealevel. Sr and Nd isotopes show that material is dominantly eroded from Taiwan with a lesser flux from Luzon, while clay mineralogy suggests that the primary sources during the Early Holocene were reworked via the shelf in the Taiwan Strait, rather than directly from Taiwan. Erosion was enhanced during monsoon strengthening and caused reworking of chemically weathered Pleistocene sediment largely from the now flooded Taiwan Strait, which was transgressed by ~8 ka, cutting off supply to the deep-water slope. None of the proxies shows an erosional response lasting until ~6 ka, when speleothem oxygen isotope records indicate the start of monsoon weakening. Although more weathered sediments were deposited from 11 to 8 ka when the monsoon was strong these are reworked and represent more weathering during the last glacial maximum (LGM) when the summer monsoon was weaker but the shelves were exposed.

Mineralogy at DSDP Site 82-558 and Hole 82-563

Downhole bulk-sample and clay-mineral analytical results for Sites 558 and 563 are presented in this chapter. These results show a Tertiary climatic and hydrologic evolution similar to that at other DSDP drill sites in the northeastern Atlantic Ocean (Sites 398, 403-406, 548-550, 552-555). The sediments recovered at both sites are primarily calcareous and chalky oozes characterized by >90% carbonate and minor quartz and plagioclase feldspar. Clay minerals smectite, kaolinite, illite, and chlorite are present throughout the cores; upsection, illite increases at the expense of smectite. The clay mineralogy suggests climatic cooling and increased ocean circulation during the Miocene. Intervals rich in very fine grained (<2 µm) quartz suggest times of increased eolian input. This could have resulted from development, during Oligocene and late Miocene time, of an arid, desertlike sediment provenance that lasted until the present day.

Clay mineralogy of ODP Site 131-808 sediments

Drill core recovered at Ocean Drilling Program Site 808 (Leg 131) proves that the wedge of trench sediment within the central region of the Nankai Trough comprises approximately 600 m of hemipelagic mud, sandy turbidites, and silty turbidites. The stratigraphic succession thickens and coarsens upward, with hemipelagic muds and volcanic-ash layers of the Shikoku Basin overlain by silty and sandy trench-wedge deposits. Past investigations of clay mineralogy and sand petrography within this region have led to the hypothesis that most of the detritus in the Nankai Trough was derived from the Izu-Honshu collision zone and transported southwestward via axial turbidity currents. Shipboard analyses of paleocurrent indicators, on the other hand, show that most of the ripple cross-laminae within silty turbidites of the outer marginal trench-wedge facies are inclined to the north and northwest; thus, many of the turbidity currents reflected off the seaward slope of the trench rather than moving straight down the trench axis. Shore-based analyses of detrital clay minerals demonstrate that the hemipelagic muds and matrix materials within sandy and silty turbidites are all enriched in illite; chlorite is the second-most abundant clay mineral, followed by smectite. In general, the relative mineral percentages change relatively little as a function of depth, and the hemipelagic clay-mineral population is virtually identical to the turbidite-matrix population. Comparisons between different size fractions (<2 µm and 2-6 µm) show modest amounts of mineral partitioning, with chlorite content increasing in the coarser fraction and smectite increasing in the finer fraction. Values of illite crystallinity index are consistent with conditions of advanced anchimetamorphism and epimetamorphism within the source region. Of the three mica polytypes detected, the 2M1 variety dominates over the 1M and 1Md polytypes; these data are consistent with values of illite crystallinity. Measurements of mica bo lattice spacing show that the detrital illite particles were eroded from a zone of intermediate-pressure metamorphism. Collectively, these data provide an excellent match with the lithologic and metamorphic character of the Izu-Honshu collision zone. Data from Leg 131, therefore, confirm the earlier interpretations of detrital provenance. The regional pattern of sediment dispersal is dominated by a combination of southwest-directed axial turbidity currents, radial expansion of the axial flows, oblique movement of suspended clouds onto and beyond the seaward slope of the Nankai Trough, and flow reflection back toward the trench axis.

(Table 2) Age model of ODP Site 184-1146

Orbital tuning of benthic d18O is a common approach for assigning ages to ocean sediment records. Similar environmental forcing of the northern South China Sea and the southeast Asian cave regions allows for transfer of the speleothem d18O radiometric chronology to the planktonic and benthic d18O records from Ocean Drilling Program Site 1146, yielding a new chronology with 41 radiometrically calibrated datums, spanning the past 350 kyr. This approach also provides for an independent assessment of the accuracy of the orbitally tuned benthic d18O chronology for the last 350 kyr. The largest differences relative to the latest chronology occur in marine isotope stages (MIS) 5.4, 5.5, 6, 7, and 9.3. Prominent suborbital-scale structure believed to be global in nature is identified within MIS 5.4 and MIS 7.2. On the basis of the radiometrically calibrated chronology, the time constant of the ice sheet is found to be 5.4 kyr at the precession band (light d18O lags precession minima by -55.4°) and 10.4 kyr at the obliquity band (light d18O lags obliquity maxima by 57.4°). These values are significantly shorter than the single 17 kyr time constant originally estimated by Imbrie et al. (1984), based primarily on the timing of terminations I and II and the 15 kyr time constant used by Lisiecki and Raymo (2005, doi:10.1029/2004PA001071).

Investigations on sediment coring site PS1823 in the Riiser-Larsen Sea, Southern Ocean

Physical and sedimentological investigations were carried out on a 14 m long gravity core and a 0.5 m long box core from 4440 m water depth off Queen Maud Land, East-Antarctica. Strongly bioturbated hemipelagic muds of predominantly terrigenous origin and a very small biogenic part build up the 'Normal-Facies'. Several sandy to silty layers are inserted in the 'Normal-Facies'. These layers are seperated by lithology, structure and the investigated parameters of this study and are interpreted as turbidites. The source area for the turbidity currents is supposed to be at the uppermost continental margin, close to the shelf break and there is evidenee for this gravity transport within the erosive Ritscher-Canyon, which extends close to the core position. The distribution of biogenic components indicates an age of 1.3 million years or more, with an average sedimentation rate of about 1 cm/1000 years. Early diagenetic proeesses caused water loss by compaction, errosion and dissolution of biogenic components and precipitation and recrystallization of manganese micronodules. Cyclic fluctuations of the sediment-parameters within the 'Normal-Facies' enable the distinction of a 'Glazial'- and an 'Interglazial'-Facies. The 'Glazial'-Facies reflects glacial sedimentary conditions and shows a dark olive gray colour, high susceptibility, low silt/clay-ratios, only a few biogenic components and the regular occurence of interrelated turbidite layers. In contrast, the 'Interglazial'-Facies is dominated by a light olive or olive-brown colour, low susceptibility, high silt/clay-ratios and an increased number of biogenic components. This facies corresponds to interglacial conditions. Three main processes are supposed to have been responsible for the observed facies changes: (1) the bottom water mass circulation, (2) the gravity transport by turbidity currents and (3) the biogenic surface production. These processes are related to the quaternary climatic changes. The extension of the ice shelves directed the gravity transport to the deep sea and the formation of Antarctic Bottom Water, which in turn influenced the silt/clay-ratios in the sediment record. Fluctuations in sea ice coverage controlled the biogenic surface production.

Location and ages of terrestrial peatlands located on continental shelves and in coastal sediments

This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

Calcareous nannofossils and C37 alkenones at ODP Site 162-982

During the late Pliocene (~3 to 2.5 Ma), oceanic records of opal and C37 alkenone accumulation from around the world show a secular shift towards lower values in the high latitudes and higher values in the low and mid latitudes. These shifts are broadly coincident with the intensification of northern hemisphere glaciation and are suggestive of changes in export productivity, with potential implications for Pliocene atmospheric carbon dioxide concentrations. The interpretation of a global latitudinal shift in productivity, however, requires testing because of the potential uncertainties associated with site to site comparisons of records that can be influenced by highly nonlinear processes associated with production, export, and preservation. Here, we assess the inferred Pliocene latitudinal productivity shift interpretation by presenting new records of C37 alkenone accumulation from Ocean Drilling Program (ODP) Site 982 in the North Atlantic and biotic assemblages (calcareous nannoplankton) from this site and ODP Site 846 in the eastern tropical Pacific. Our results corroborate the interpretation of C37 alkenone accumulation as a proxy for gross export productivity at these sites, indicating that large-scale productivity decreases at high latitudes and increases at tropical sites are recorded robustly. We conclude that the intensification of northern hemisphere glaciation during the late Pliocene was associated with a profound reorganisation of ocean biogeochemistry.