Biogenic Sediments and Their Paleoceanographic Implication in West Pacific Warm Pool during the Pleistocene

Primary productivity has played an important role in the global carbon cycle during the Quaternary. The average Corg/N ratio was 7.0 from the core MD97-2140 in the West Pacific Warm Pool （WPWP） over the last 1 755 ka, which indicates a main contribution of marine organic carbon to the organic matter in the sediments. Large fluctuations in mass accumulation rates （MARs） of biogenics and lithogenics from this core since the marine isotope stage （MIS） 6 reflected the moderate variability in oceanographic condition, while tittle fluctuations in MAR-biogenics and -lithogenics from the MIS 59 to MIS 7 implied the relatively stable and uniform oceanographic condition, although the sea surface temperatures （SSTs） probably fluctuated by ca. 5 ℃. MAR-organic since the MIS 6 increased evidently during the glacial periods, which ascribed to terrestrial inputs, including lithogenic matter and dissolved nutrient, which also contribute to stimulating primary productivity. The results compared among the four cores in the WPWP since the MIS 9 indicate that in the western sector with the shallow thermocline, high primary productivity during the glacial periods was controlled by wind-induced surface water mixing, upwelling, and terrestrial inputs, while in the central and eastern sectors, the little different medium to low productivity might have been made by more intense upweil- ing driven by strong winds because the thicker warm surface water pool and the deeper thermocline prevented nutrient-bearing water from upwelling to upper water column even during the glacial times.

Sedimentary Organic Matter Characterization on a Tropical Continental Shelf in Northeastern Brazil

In continental shelf areas works where the focus is Geochemistry are widely relevant, due to the vast complexity and uses of these relief features (social, environmental and economic). On the Brazilian Northeast tropical shelves, with emphasis on the Pernambuco Continental Shelf (PCS), the published studies are limited and have aimed at portions closer to the coastline. The objective of the present work is the description of the characteristics and origin of sedimentary organic matter (SOM) in the inner and middle Pernambuco shelf, defining and classifying the local geochemical sedimentary facies. The sampling stations (136) were collected in the study area, and the grain-size, contents of total organic matter (TOM), calcium carbonate (CaCO3) were analyzed. The samples were processed in an elemental analyzer coupled with a mass spectrometer after the elimination of calcium carbonate. The obtained data were the grain-size, TOM, CaCO3, elemental (C, N) and the stable isotopic ratios of δ13C e δ15N of SOM. Based on the measured values of carbon and nitrogen, the C/N ratio, associated to δ13C e δ15N, is observed that in the PCS predominates an organic matter of marine origin along its entire length: C < 1%, N < 1%, C/N < 5, δ13C > -21 PDB e δ15N > 8Ar. The PCS presents patches of continental origin SOM, associated to the coastal zones adjacent to estuarine systems mouths and covering the paleochannels, which may indicate that this material was carried from the coastal rivers to the offshore areas, possibly by the paleo-valleys that also act as traps of fine sediments and SOM. The statistical analysis indicates the existence of 6 different sedimentary facies and a prevalence of one of them, characterized by poorly-sorted bioclastic sandy-gravel, with low to medium organic contents of marine origin. This indicates that the coastal sedimentary material contributions are low and the local cover is autochthonous of biogenic origin, and deposited according to the surficial topography, morphosedimentary processes and meteoceanographycal conditionings of the study area, typical of moderate hydrodynamic energy environments.

Distribution and contamination of metals and biogenic elements in sediments from Zhifu Bay of the Yellow Sea,China

Metals and biogenic elements were analyzed from surface sediments of sixteen stations and a 32 cm core collected from Zhifu Bay in July 2009.High concentrations of biogenic silica（BSi）reflected the high diatom productivity in the Bay.Meanwhile,total organic carbon（TOC）in Zhifu Bay was mainly from terrestrial sources.All metals were lower than the marine sediment quality guidelines.Based on the vertical profiles of biogenic elements,there was a clear increase of TOC,total nitrogen（TN）,and total phosphate（TP）between1985 and 2000.TN concentrations decreased after the start of the operation of the sewage treatment plant in 1998;however TOC and BSi remained at high levels.Metal concentrations showed a general increase from the bottom to the top of the core.Most anthropogenic metals reached a maximum during 1996 and 2000,and decreased after the startup of the sewage plant;however,they have increased again recently.The results from correlation analysis and principal component analysis show that industrial pollution is the main source of Cd,Cr,Cu,Ni,Pb and Zn contamination in Zhifu Bay,and Yantai Port and ship transportation also contribute a lot to Cd,Cu,Hg,and Pb pollution.