192
Fischer et al.
Due to rapid dissolution of their aragonitic shells,
preservation in the sediments ofthe ocean is limited to topographic elevations, marginal seas (e.g.
Persian Gulf, Red Sea) and tropical shallow oceanic areas. Pteropods in the sediment may occur
as layers, pavements (Price et aI. 1985) or as minor components in hemipelagic environments above
the ACD (Aragonite Compensation Depth).
Pteropod-rich layers, e.g. off northwest Africa
concur with post-glacial warming pulses as has
been shown by Sarnthein et aI. (1982). Distinct
periods of aragonite preservation during the last
16,000 years were also observed in the North
Atlantic coinciding with periods of climatic change,
e.g. at terminations lA, 1 Band 1 C (Ganssen et aI.
1991). Mostly monospecific layers were encountered at depths between 2700 and 3100 m and often showed intense Fe/Mn coatings, probably favouring the preservation of aragonite. Applying 14C
AMS, Ganssen et aI. (1991) interpreted these layers as lag deposits.
Besides water temperature, other factors affect
the temporal and spatial distribution of pteropods in
marginal seas. In the Red Sea, for example,
monospecific assemblages during glacial maxima
characterize periods of high salinity conditions in
highly productive surface waters (Almogi-Labin
1982). In the Central Red Sea, downcore variations
in the abundance of epipelagic, non-migratory species occurring in the mixed-layer (0-100 m) and
mesopelagic (=diel migratory) pteropods were used
to trace fluctuations in the nature and depth of the
oxycline (Almogi-Labin et al. 1991). There,
epipelagic species dominated during glacial isotope
stages when a highly stratified water column associated with a low oxygen content in intermediate
waters prevailed. In contrast, the present-day situation with mesopelagic species comprising 75% of
the assemblage is characterized by an improved
ventilation of the intermediate water masses
(Almogi-LabinetaI. 1991).
Oxygen and carbon isotope compositions ofthe
aragonitic shells of pteropods have been reported
by several workers (e.g. Hoefs and Samthein 1971;
Price et al. 1985; Grossman and Ku 1986;
Grossman et al. 1986; Meinecke and Wefer 1990;
Fabry and Deuser 1992; Kalberer et al. 1993;
Jasper and Deuser 1993; Almogi-Labinet al. 1991;
Hemleben et al. 1996). Analyzing the oxygen isotope composition offive pteropod species collected
during a 14-month time-series of sediment traps,
Fabry and Deuser (1992) tested the utility of
pteropods as skeletal records of water temperature
and salinity (see also Hoefs and Sarnthein 1971;
Kalberer et al. 1993). Many species are diel vertical migrators, often migrating over several hundred
meters ofthe water column (Be and Gillmer 1977),
and are therefore exposed to a wide range of temperatures and salinity. However, these studies
showed that the estimated depth of calcification
matches the upper parts of the species' diel vertical ranges where the populations occur only at night.
The four species studied by Fabry and Deuser
(1992) showed a clear response to the seasonal
variation in temperature and salinity which occurs
only in waters near the surface. Fabry and Deuser
(1992) suggested that the mesopelagic Limacina
inflata forms most of its shell at approximately
50 m, whereas the mesopelagic Clio pyramidata
at about 75 m water depth. On a diel cycle, these
species migrate between 50 and 350 m (Wormuth
1981), and between 50 and 950 m water depth (Van
der SpoeI1973), respectively. Vital effects on the
oxygen isotope composition of pteropods appear to
be of minor importance (Jasper and Deuser 1993).
Fabry and Deuser (1992) estimated deviations from
equilibrium for several species in the range of only
0.1 to 0.3%0.
Despitc a few numbers of pteropod studies already performed, the potential ofthese organisms
for paleoceanographic studies has not yet been fully
explored, and they rarely have been employed for
paleoceanographic interpretations, or for sediment
core stratigraphy, except at a few sites in particular areas (e.g. the Red Sea; Almogi-Labin 1982;
Almogi-Labin et al. 1991, and references therein;
Hemleben et al. 1996). For instance, quantitative
studies ofthe stable oxygen isotopes of planktonic
foraminifera and pteropoda from the Central Red
Sea revealed salinity estimations of53-55%0 for the
Last Glacial Maximum (Hemleben et al. 1996).
As pteropods also construct larger shells
(> I cm size) and are assumed by some authors to
have maximal life-times of about one year (Van der
Spoel1973; Wells 1976), they may provide, in contrast to planktonic foraminifera, an annual mean
Fischer et al.
Due to rapid dissolution of their aragonitic shells,
preservation in the sediments ofthe ocean is limited to topographic elevations, marginal seas (e.g.
Persian Gulf, Red Sea) and tropical shallow oceanic areas. Pteropods in the sediment may occur
as layers, pavements (Price et aI. 1985) or as minor components in hemipelagic environments above
the ACD (Aragonite Compensation Depth).
Pteropod-rich layers, e.g. off northwest Africa
concur with post-glacial warming pulses as has
been shown by Sarnthein et aI. (1982). Distinct
periods of aragonite preservation during the last
16,000 years were also observed in the North
Atlantic coinciding with periods of climatic change,
e.g. at terminations lA, 1 Band 1 C (Ganssen et aI.
1991). Mostly monospecific layers were encountered at depths between 2700 and 3100 m and often showed intense Fe/Mn coatings, probably favouring the preservation of aragonite. Applying 14C
AMS, Ganssen et aI. (1991) interpreted these layers as lag deposits.
Besides water temperature, other factors affect
the temporal and spatial distribution of pteropods in
marginal seas. In the Red Sea, for example,
monospecific assemblages during glacial maxima
characterize periods of high salinity conditions in
highly productive surface waters (Almogi-Labin
1982). In the Central Red Sea, downcore variations
in the abundance of epipelagic, non-migratory species occurring in the mixed-layer (0-100 m) and
mesopelagic (=diel migratory) pteropods were used
to trace fluctuations in the nature and depth of the
oxycline (Almogi-Labin et al. 1991). There,
epipelagic species dominated during glacial isotope
stages when a highly stratified water column associated with a low oxygen content in intermediate
waters prevailed. In contrast, the present-day situation with mesopelagic species comprising 75% of
the assemblage is characterized by an improved
ventilation of the intermediate water masses
(Almogi-LabinetaI. 1991).
Oxygen and carbon isotope compositions ofthe
aragonitic shells of pteropods have been reported
by several workers (e.g. Hoefs and Samthein 1971;
Price et al. 1985; Grossman and Ku 1986;
Grossman et al. 1986; Meinecke and Wefer 1990;
Fabry and Deuser 1992; Kalberer et al. 1993;
Jasper and Deuser 1993; Almogi-Labinet al. 1991;
Hemleben et al. 1996). Analyzing the oxygen isotope composition offive pteropod species collected
during a 14-month time-series of sediment traps,
Fabry and Deuser (1992) tested the utility of
pteropods as skeletal records of water temperature
and salinity (see also Hoefs and Sarnthein 1971;
Kalberer et al. 1993). Many species are diel vertical migrators, often migrating over several hundred
meters ofthe water column (Be and Gillmer 1977),
and are therefore exposed to a wide range of temperatures and salinity. However, these studies
showed that the estimated depth of calcification
matches the upper parts of the species' diel vertical ranges where the populations occur only at night.
The four species studied by Fabry and Deuser
(1992) showed a clear response to the seasonal
variation in temperature and salinity which occurs
only in waters near the surface. Fabry and Deuser
(1992) suggested that the mesopelagic Limacina
inflata forms most of its shell at approximately
50 m, whereas the mesopelagic Clio pyramidata
at about 75 m water depth. On a diel cycle, these
species migrate between 50 and 350 m (Wormuth
1981), and between 50 and 950 m water depth (Van
der SpoeI1973), respectively. Vital effects on the
oxygen isotope composition of pteropods appear to
be of minor importance (Jasper and Deuser 1993).
Fabry and Deuser (1992) estimated deviations from
equilibrium for several species in the range of only
0.1 to 0.3%0.
Despitc a few numbers of pteropod studies already performed, the potential ofthese organisms
for paleoceanographic studies has not yet been fully
explored, and they rarely have been employed for
paleoceanographic interpretations, or for sediment
core stratigraphy, except at a few sites in particular areas (e.g. the Red Sea; Almogi-Labin 1982;
Almogi-Labin et al. 1991, and references therein;
Hemleben et al. 1996). For instance, quantitative
studies ofthe stable oxygen isotopes of planktonic
foraminifera and pteropoda from the Central Red
Sea revealed salinity estimations of53-55%0 for the
Last Glacial Maximum (Hemleben et al. 1996).
As pteropods also construct larger shells
(> I cm size) and are assumed by some authors to
have maximal life-times of about one year (Van der
Spoel1973; Wells 1976), they may provide, in contrast to planktonic foraminifera, an annual mean