To obtain a perspective of changes occurring
in the marine environment it is essential to
study an area over a long time span. Doing so
might also facilitate the understanding of the
mechanisms and processes that govern a
certain marine setting. In this thesis, changes
in the pelagic and benthic environment during
the last c. 200 years have been investigated in
two fjords on the Swedish west coast, Koljö
Fjord and Gullmar Fjord; this was done using
the sediment record and its content of
biological and sedimentological markers,
so-called proxies. Further, with the use of
hydrographic and meteorological data, this
thesis establishes relationships between
climatic variations and these changes in the
benthic environment. In particular, climate and
variations in climate are important factors
behind low oxygen conditions in the deep
water in Koljö Fjord. Furthermore, with the use
of benthic foraminifera as indicators, this
thesis demonstrates that the deep water in
Koljö Fjord has been a varying but harsh
environment for benthic life for at least 170
years. In contrast, the surface water
environment in Koljö Fjord has experienced
one substantial change over the same time.
The composition and abundances of
dinoflagellate cysts and diatoms changed
markedly in the late 1930s to early 1940s.
This change occurred at the same time as
engineering works were undertaken at one of
the shallow entrances of the fjord. The
differences in surface-water exchange due to
the engineering work are estimated, and
these results suggest that relatively small
changes in topography can cause changes in
the surface water environment large enough
to affect the phytoplankton community. To
examine how phytoplankton blooms affect the
carbon isotopic composition in foraminifera,
analyses from a seasonal study were
performed on living Stainforthia fusiformis
from Havstens and Gullmar Fjord. A marked
decrease in the d13C was noted after
phytodetritus input.

The benthic environment in the deep Gullmar
Fjord has experienced rather stable
conditions over the last 90 years. From
stratigraphical studies, using benthic
foraminifera, a major faunal change is noted.
The change occurred in the late 1970s to early
1980s when the fauna changed from a
common Skagerrak–Kattegat fauna to a fauna
dominated by the low-oxygen-tolerant species,
S. fusiformis. By using stable isotopes, it is
shown that S. fusiformis did not inhabit the
deepest part of the fjord before the late 1970s.
This shift occurred in connection with the first
(1979/1980) of several, recent low-oxygen
events in the fjord. These low-oxygen events
have occurred, in general, when the winter
climate has been more maritime, with more
frequent westerly and south-westerly winds, a
wind situation that suppress deep-water
exchanges. This demonstrates the large effect
climate may have on hydrography and thereby
on the benthic environment.
E-mail: helo@oce.gu.se