DIATOM ASSEMBLAGES IN COASTAL SURFACE SEDIMENTS IN SOUTHEAST OF CHINA

This study shows how modern diatom assemblages, obtained from the surface sediments of 55 deep and shallow lakes in southern Quebec and representing a gradient in trophic state and specific conductivity, can be used to reconstruct the historical water column concentrations of total phosphorus (TP) over time. Inference models were developed with the aid of regression analyses based on weighted means. The TP models demonstrate statistical performances equal to or superior to TP models developed in the past for other regions in Canada and elsewhere in the world. A reconstruction of TP values, based on fossil diatom assemblages of Lac Nairne (Charlevoix, QC), was conducted. Comparing the TP inferred values with the measured values and those estimated using export coefficients, the reliability of the model was proven. In addition, the comparison of the results obtained from reconstructions performed with two inference models (Quebec and Ontario lakes) also revealed that models predicted TP and not a collinear variable.

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Diatom fluxes in surface sediments of the Goban Spur continental margin, NE Atlantic Ocean

Journal of Micropalaeontology ◽

10.1144/jm.19.2.123 ◽

2000 ◽

Vol 19 (2) ◽

pp. 123-131 ◽

Cited By ~ 6

Author(s):

Roberto Bao ◽

Henko De Stigter ◽

Tjeerd C. E. Van Weering

Keyword(s):

North Atlantic ◽

Surface Sediments ◽

Diatom Assemblages ◽

Nepheloid Layer ◽

Continental Slopes ◽

Surface Productivity ◽

Resting Spores ◽

Ne Atlantic Ocean ◽

Upper Slope ◽

Goban Spur

Abstract. Continental slopes are presumed key areas for deposition of organic carbon exported from the shelf. Analysis of across-slope differences in diatom and silicoflagellate fluxes recorded in bottom sediments of the Goban Spur margin, a typical North Atlantic slope environment, was carried out to test if they can provide information on the magnitude of advection of material from the shelf into deeper waters. Total diatom and silicoflagellate accumulation rates showed strong across-slope differences. Minimum values are recorded at the shelf break where maximum surface productivity conditions occur while the deeper sampling stations record fluxes as high as 183×106 valves cm–2 ka–1. While high diatom fluxes show a clear correspondence with the activity of a permanent bottom nepheloid layer operating in the region, they do not correlate with productivity patterns observed in the water column. Diatom assemblages are mainly composed of Chaetoceros resting spores and Thalassionema nitzschioides (Grunow) Grunow ex Hustedt, typical indicators of spring bloom conditions in the area. The absence of clear across-slope trends in the diatom assemblages is interpreted as the effect of random mixing driven by the strong hydrodynamic regime provoked by the activity of the bottom nepheloid layer. The dominance of Chaetoceros resting spores across the slope is related to important exportation of shelf-derived production. However, due to the broad ecological tolerances of the main taxa composing the diatom assemblages, they do not allow precise estimations on the magnitude of the primary vertical flux vs. the secondary lateral flux in this slope environment. Use of the tychoplanktonic and benthic diatoms, which are restricted to the neritic realm, allows only the estimation of the minimum amount of shelf-derived diatoms reaching the slope sediments (at least 13% of the total diatom assemblage for the upper slope area of the Goban Spur). This study shows that major limitations exist for the use of diatoms preserved in surface sediments of this area as tracers of shelf-derived production transported to the continental slope.

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