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Seasonal study of delta O-18 and delta C-13 in living (stained) benthic foraminifera from two Swedish fjords

Journal article
Authors Helena L. Filipsson
Kjell Nordberg
Mikael Gustafsson
Published in Marine Micropaleontology
Volume 53
Issue 1-2
Pages 159-172
ISSN 0377-8398
Publication year 2004
Published at Department of Earth Sciences
Pages 159-172
Language en
Links dx.doi.org/10.1016/j.marmicro.2004....
Keywords benthic foraminifera, stable isotopes, phytoplankton, seasonal variations, fjords, skagerrak, o-18 isotopic disequilibrium, west-coast, gullmar fjord, biological carbonates, oxygen concentrations, british-columbia, vancouver-island, havstens-fjord, koljo-fjord, celtic sea
Subject categories Earth and Related Environmental Sciences

Abstract

In a previous 16-month seasonal study on living (stained) benthic foraminifera from two fjords on the Swedish west coast, it was reported that foraminifera proliferated in response to phytodetritus input; the strongest response came from the opportunistic species Stainforthia fusiformis. In this study, our objective was to find out if that phytodetritus input resulted in a change in the carbon isotopic composition of the foraminiferal tests. We also wanted to examine if variations in salinity and temperature (due to seasonality or deep-water exchanges) were reflected in the delta(18)O values. From S. fusiformis that were obtained from the Havstens Fjord (20 m) and the Gullmar Fjord (119 m) during the 16-month study, we developed a time series of delta(18)O and delta(13)C. After the spring blooms in the Havstens and the Gullmar Fjord, decreases of about 0.2parts per thousand to 0.3parts per thousand in the foraminiferal delta(13)C values were noted; in the Gullmar Fjord after the autumn blooms, decreases of the same order were also noted. Comparing the Havstens and the Gullmar Fjord, we found a 1parts per thousand difference in both delta(13)C and delta(18)O; we attribute this to hydrographic differences between the two fjords. Using calculated values of delta(18)O, together with the measured ones, we noticed that S. fusiformis in the Gullmar Fjord seems to calcify close to equilibrium with respect to the oxygen isotopes. During autumn, water temperatures were relatively high in the Havstens Fjord, and foraminiferal abundance in the fjord was also high after a phytodetritus input; but, the measured delta(18)O values do not reflect these higher temperatures. This apparently contradictory combination of results might be explained by a varying delta(18)O composition of the water during the year, which counterbalances the temperature effect. (C) 2004 Published by Elsevier B.V.

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