Diatom‐based reconstruction of summer sea‐surface salinity in the South China Sea over the last 15 000 years

We present a new reconstruction of summer sea‐surface salinity (SSS) over the past 15 000 years based on a diatom record from piston core 17940, located on the northern slope of the South China Sea (SCS). The reconstructed diatom‐based summer SSS values for the modern period are in accord with instrumental observations of summer SSS in the area. Here, the modern summer SSS is primarily controlled by river runoff, in particular from the Pearl River. The reconstruction presented in this study shows that the summer SSS varied between 33.3 and 34.2 psu over the past 15 000 years. The long‐term summer SSS trend closely followed the trend of the orbitally controlled solar insolation at 20°N, suggesting that orbital forcing was the dominant driver of changes in summer SSS in this area. Comparisons to speleothem δ¹⁸O data and studies of surface hydrography in the region suggest that changes in solar insolation affected the summer SSS through changes in the East Asian Monsoon and sea‐level changes associated with the last deglaciation. Univariate spectral analyses indicate that centennial‐scale oscillatory variations in summer SSS were superimposed on the long‐term trend. During the deglacial period (c. 12 000–9000 cal. a BP), the dominant periodicity was centred around 230–250 years, whereas a ～350‐year oscillation dominated in the period 2200–4500 cal. a BP. The balance of evidence suggests that these centennial‐scale changes in summer SSS may have been driven by solar‐induced changes in the East Asian Monsoon, but further evidence is needed to firmly establish this relationship.     

Discriminant Analysis for Compositional Data Incorporating Cell-Wise Uncertainties

Mathematical Geosciences - In the geosciences it is still uncommon to include measurement uncertainties into statistical methods such as discriminant analysis, but, especially for trace elements,...     

Paleocene alkaline volcanism in the Nares Strait region: evidence from volcanic pebbles

Paleogene sediments in fault-bounded basins on Judge Daly Promontory, northeast Ellesmere Island, Canadian High Arctic, are rich in volcanogenic material. Volcanic pebbles within the Cape Back basin near Nares Strait were studied for their petrography, geochemistry, Sr and Nd isotopes, and geochronology to identify and characterize their parent rock. The pebbles are derived from lava flows and ignimbrites of a continental rift-related, strongly differentiated, highly incompatible element enriched, alkaline volcanic suite, the proposed Nares Strait volcanic suite, which is distinct from other alkaline volcanic suites on the northern coasts of Ellesmere Island and Greenland. ⁴⁰Ar/³⁹Ar amphibole and alkali feldspar ages indicate that volcanism was active around 61–58 Ma and was probably contemporaneous with sedimentation resulting in Middle to Late Paleocene age for deposition within the Cape Back basin and the other Paleogene basins on Judge Daly Promontory.     

Determination of the submerged macrophyte coverage of greifswalder bodden

The extent to which a water body can support submerged macrophytic vegetation provides an indicator of its degree of eutrophication. Regular, quantitative assessment of macrophyte populations enables changes in the trophic state of the system to be observed. A combination of aerial photography and underwater videography has proved to be an efficient method for calculating macrophyte coverage of large coastal areas.     

A sensitive and rapid method for analysis of dissolved mono- and polysaccharides in seawater

A spectrophotometric method is described for the determination of dissolved mono- and polysaccharides in seawater. It is based upon the well known alkaline ferricyanide reaction, but uses the reagent 2,4,6-tripyridyl-s-triazine (TPTZ) to give a strongly colored complex with the reduced iron. The method has been tested on model carbohydrates and other compounds, and also on natural samples of coastal and oceanic waters. Total carbohydrate content of the natural samples ranged from 5.2 to 25.1 μmol glucose-Cl⁻¹. The coefficient of variation was typically below 6% for values near 17 μmol Cl⁻¹ and approximately 10% for values near 3.5 μmol Cl⁻¹.     

Lipids in selected abyssal benthopelagic animals: links to the epipelagic zone?

A detailed study of the lipids of selected zooplankton species and scavenging amphipods in the near-bottom water layer (15–100 m above bottom, mab) was carried out at the BENGAL site in late summer 1998. Copepoda were the main contributors to the zooplankton, comprising 75% of the total abundance, followed by Ostracoda and Chaetognatha. Calanoid copepods of the family Metridinidae were predominant and accounted for more than 50% of all copepods.Two types of storage lipids were distinguished: triacylglycerols and wax esters. Ostracoda and the polychaete Vanadis sp. stored exclusively triacylglycerols whilst the bulk of the Copepoda accumulated wax esters, with the exception of the family Aetideidae. In the amphipods both lipid classes were found: Eurythenes gryllus stored wax esters and Paralicella spp. and Orchomene sp. triacylglycerols.The fatty acid composition was characterized by a high level of monounsaturated 18:1 (n—9), which is described as characteristic for animals living in the deeper layers of the water column, and to a lesser degree by 16:1 (n—7) and 20:5 (n—3), which are typical components of diatom lipids, and 22:6 (n—3), typical of dinoflagellates. The ratio of 18:1 (n—9):18:1 (n—7) fatty acids was between 5 and 10 in the copepods and indicates a carnivorous/omnivorous feeding behaviour in this group, whereas the higher ratios of 8–18 in the amphipods confirm their necrophagy. The fatty alcohols of the animals storing wax esters were dominated by the monounsaturated isomers 18:1 (n—9) and 18:1 (n—7).The predominance of wax esters as storage lipids in the deep-sea copepods indicates a strong seasonality in the availability of food. This is supported by the high levels of 16:1 (n—7), 20:5 (n—3) and 22:6 (n—3) fatty acids, which point to there being a direct link between the surface primary production and deep-sea copepods, probably via the rapid deposition of phytodetritus.     

A diatom‐based reconstruction of summer sea‐surface salinity in the Southern Okinawa Trough,East China Sea,over the last millennium

A high‐resolution diatom record from site MD05‐2908 in the Southern Okinawa Trough, East China Sea, reveals pronounced multidecadal‐ to centennial‐scale palaeoceanographic changes throughout the last millennium. Summer sea‐surface salinity (SSS) was reconstructed using a weighted averaging partial least squares diatom‐based training set. The reconstructed SSS shows slightly decreasing values during the period AD 905–1930 with considerable fluctuations superimposed on this general trend. Relatively high‐salinity conditions during the interval AD 905–1450 probably suggest a low flood frequency in north‐eastern Taiwan. Furthermore, the high SSS values are associated with a strong and stable influence of the Kuroshio Current on the Southern Okinawa Trough during the Medieval Climate Anomaly. The period AD 1450–1930 is characterized by three low‐salinity intervals (AD 1450–1500, AD 1625–1725 and AD 1770–1880) separated by periods of relatively high salinity. The low SSS intervals indicate increased freshwater discharge into the Southern Okinawa Trough during the Little Ice Age, probably as a result of higher flood frequencies in north‐eastern Taiwan. Spectral and wavelet analyses suggest that this pattern was linked to multidecadal variations in summer SSS, presumably associated with the Pacific Decadal Oscillation. Copyright © 2012 John Wiley & Sons, Ltd.     

Exotic pollen as an indicator of variable atmospheric circulation over the Labrador Sea region during the mid to late Holocene

Variability in the abundance of exotic (non‐native) pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation, but the difficulty of gaining sufficient total exotic pollen and the incomplete understanding of atmospheric pollen transport patterns has hindered its application. In light of recent advances in the study of pollen transport, we present an exotic pollen record from two fjord sediment cores taken from the west (Placentia Bay, Newfoundland) and east (Narsaq Sund, Greenland) Labrador Sea as a basis for studying variations in regional atmospheric circulation. The two cores cover the last ca. 5500 years and indicate a shift in dominant spring/summer air masses at ca. 2000 (southern Greenland) and 3000 cal a BP (Newfoundland) transporting reduced concentrations of pollen from southerly and south‐westerly vegetation zones. This may suggest a shift away from more dominantly zonal atmospheric circulation (a feature of positive North Atlantic Oscillation years) to more frequent meridional circulation. These results support sea ice/sea‐surface temperature proxy reconstructions from Newfoundland, investigated as part of the same project, which also suggest increased winter atmospheric circulation during the early part of the time period studied. In this region, more positive North Atlantic Oscillation years, and therefore more zonal atmospheric circulation, are associated with increased atmospheric circulation in both the winter and the summer seasons. Copyright © 2011 John Wiley & Sons, Ltd.