Thibodeau,B., de Vernal,A. and Mucci,A.(2006): Recent eutrophication and consequent hypoxia in the bottom waters of the Lower St. Lawrence Estuary: Micropaleontological and geochemical evidence. Marine Geology, 231, 37-50.

『下部セントローレンス川河口の底流における最近の富栄養化とそれに引き続く酸欠化：微古生物学的および地球化学的証拠』

『Abstract
　Micropaleontological and geochemical analyses were carried out on two sediment box cores (AH00-2220 and CR02-23) recovered in the Lower St. Lawrence Estuary (LSLE) in order to document recent temporal variations of primary productivity and carbon fluxes to the bottom waters. These reveal a ten-fold increase in the accumulation rate of dinoflagellate cysts and benthic foraminifera in the sediment over the last four decades which can be interpreted as a recent increase in pelagic and benthic production. Furthermore, the appearance of the benthic foraminiferal species Brizalina subaenariensis and Bulimina exilis, which are tolerant of low oxygen concentrations and high organic fluxes, in the upper 20 cm of the cores, may reflect significant changes in bottom water conditions over the last 40 yrs. Variations in the microfossil abundances in core AH00-2220 are strongly correlated with an increase in organic carbon (OC) content (from 1.1 to 1.6％) and to a shift in the isotopic signature of the latter (δ13CORG from -24.8 to -24.0‰). Similarly, a concomitant decrease in the CORG:N ratio (from 15 to 12), an increase in organic carbon content (from 1.3 to 1.9％) and an increase δ13CORG (from -24.5 to -23.5‰) were observed in core CR02-23, all of which suggest an enhanced accumulation of marine over terrestrial OC in the LSLE. Our results imply that a significant increase in marine productivity in the LSLE occurred since the 1960's.

Keywords: Lower St. Lawrence Estuary; eutrophication; hypoxia; dinoflagellate cysts; benthic foraminifera; geochemistry

1. Introduction
2. Study area
　2.1. Water masses
　2.2. The oxygen balance
　2.3. Land use history
3. Materials and methods
　3.1. Coring sites and on-board sampling
　3.2. Chronology and accumulations rates
　3.3. Micropaleontological analyses
　　3.3.1. Palynomorphs
　　3.3.2. Benthic foraminiferal tests
　3.4. Carbon analyses (TOC/TIC, δ13C, C:N)
　3.5. Microfossil accumulation rate estimates
4. Results
　4.1. Core AH00-2220
　　4.1.1. Excess 210Pb, 137Cs activity and sedimentation rates
　　4.1.2. Dinocyst assemblages
　　4.1.3. Benthic foraminiferal assemblages
　　4.1.4. Geochemistry
　4.2. Core CR02-23
　　4.2.1. Chronology
　　4.2.2. Palynology
　　4.2.3. Benthic foraminiferal assemblages
　　4.2.4. Geochemistry
5. Discussion
　5.1. Chronology of cores
　5.2. Organic matter flux
　5.3. Primary productivity
　5.4. Dissolved oxygen concentration
6. Conclusions
Acknowledgement
References

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