The origin of modern agglutinated foraminiferal assemblages: evidence from a stratified fjord

Murray, J.W., Alve, E. and Cundy, A.B. (2003) The origin of modern agglutinated foraminiferal assemblages: evidence from a stratified fjord Estuarine coastal and shelf science, 58 (3). pp. 677-697. ISSN 0272-7714

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Abstract

Loch Etive, a silled 145 m deep fjord on the Scottish west coast, provides an example of modern benthic foraminiferal assemblages at intermediate depths (i.e., below the intertidal zone and above the CCD) consisting almost exclusively of organic-cemented agglutinated forms. Since such faunas from intermediate depths are rare in modern oceans but relatively common in the fossil record, the present study allows new insights into one kind of ancient environment for which there are few modern analogues. The strong dominance of agglutinated forms (both living and in some dead assemblages of foraminifera to the exclusion of calcareous taxa) is attributed to the unusual oceanographic conditions. These include a combination of restricted deep-water renewals and strong influence of freshwater which drains through large areas (relative to the size of the loch) of vegetated land. The result is calm bottom water conditions with commonly occurring oxygen depletion (although not anoxic), brackish water throughout the water column (salinity 28 in the deeper parts), and organic-rich (mostly terrestrially derived) sediments with geochemical properties, which, to a much larger degree than open marine ones, are controlled by local input. This environment supports low abundance and low diversity live assemblages, mainly restricted to the surface 1 cm of sediment. The dead assemblages show similar faunal characteristics, but the calcareous components are, due to carbonate dissolution, even more reduced. One of the calcareous species in Loch Etive is Elphidium albiumbilicatum. Its occurrence is the first record in British waters and it matches the previously suggested southern limit of its distribution. Analysis of a 90 cm long core representing sediments deposited over the past two centuries shows the presence of a calcareous dominated assemblage, including more marine species, with a higher diversity, in the lower part. This suggests that Loch Etive is in the process of going from a marine, to a more terrestrial dominated environment. The relatively high sedimentation rate (0.5 cm per yr), the apparent lack of smearing through bioturbation, and the presence of faunal changes in response to reduced marine influence over the past centuries, shows that Loch Etive has a good potential for performing high-resolution climatic studies.

Item Type:Journal article
Uncontrolled Keywords:agglutinated foraminifera; Loch Etive; fjord; oxygen depletion; carbonate dissolution; climatic history
Subjects:F000 Physical Sciences > F600 Geology
H000 Engineering > H200 Civil Engineering > H220 Environmental Engineering
DOI (a stable link to the resource):10.1016/S0272-7714(03)00179-3
Faculties:Faculty of Science and Engineering > School of Environment and Technology > Applied Geosciences
Faculty of Science and Engineering > School of Environment and Technology > Ecology, Landscape and Pollution Management
Faculty of Science and Engineering > School of Environment and Technology
ID Code:150
Deposited By:editor environment
Deposited On:06 Oct 2006
Last Modified:04 May 2012 08:35

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