Modeling calcification periods of <i>Cytheridella ilosvayi</i> from Florida based on isotopic signatures and hydrological data
The isotopic signatures of ostracod shells are the result of the temperature and composition of their host water and the phenology and ecology of the target species. Investigations addressing the influence of site-specific environmental variations on the isotopic ranges of ostracod shells are sti...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-11-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/4927/2017/bg-14-4927-2017.pdf |
| Summary: | The isotopic signatures of ostracod shells are the result of the temperature
and composition of their host water and the phenology and ecology of the
target species. Investigations addressing the influence of site-specific
environmental variations on the isotopic ranges of ostracod shells are still
rare but can provide important information on habitat-dependent variations
and may signify a seasonally restricted timing of calcification periods. Here
we present isotopic signatures (<i>δ</i><sup>18</sup>O<sub>ostr</sub>, <i>δ</i><sup>13</sup>C<sub>ostr</sub>) of living <i>Cytheridella ilosvayi</i> (Ostracoda)
and physical, chemical, and isotopic (<i>δ</i>D,
<i>δ</i><sup>18</sup>O<sub>water</sub>, <i>δ</i><sup>13</sup>C<sub>DIC</sub>) compositions
of 14 freshwater habitats (rivers, lakes, canals, marshes, sinkholes) in
South Florida from winter 2013 and summer 2014. We also present instrumental
data of river temperatures and <i>δ</i><sup>18</sup>O of precipitation
(<i>δ</i><sup>18</sup>O<sub>prec</sub>) from this region. The physicochemical and
isotopic compositions of the selected sites characterize the different
habitats and show the influence of the source water, biological activity, and
duration of exposure to the surface. Mean <i>δ</i><sup>18</sup>O<sub>ostr</sub> and
<i>δ</i><sup>13</sup>C<sub>ostr</sub> signatures of <i>C. ilosvayi</i> shells
correlate well with the isotopic composition of their host waters.
Within-sample variabilities in repeated isotopic measurements of single
ostracod shells reflect habitat-dependent ranges. The similarly high range of
ostracod <i>δ</i><sup>18</sup>O in rivers and one marsh sample indicates that both
temperature and <i>δ</i><sup>18</sup>O<sub>prec</sub> are responsible for their
variation in the whole study area. Rivers and canals, which are predominantly
influenced by the input and mixing of inorganic carbon from the catchment,
show smaller <i>δ</i><sup>13</sup>C<sub>ostr</sub> ranges than the marsh dominated
by local fluctuations in biological activities.
<br><br>
Based on these observations, background data of water temperatures and
<i>δ</i><sup>18</sup>O<sub>prec</sub> were used to calculate monthly <i>δ</i><sup>18</sup>O
variations in a theoretical calcite formed in rivers in Florida assuming a
direct reaction on precipitation changes. The calculated values showed a high
variation coupled with low mean values during the summer wet season, while
during the winter dry season the variation remains small and mean values
increased. Inferred configurations were used to approximate possible
calcification periods of <i>C. ilosvayi</i>. For a plausible calcification period, mean values
and ranges of <i>δ</i><sup>18</sup>O<sub>ostr</sub> had to be equal to the theoretical
calcite with a slight positive offset (vital effect). The applied model
suggests a seasonal calcification period of <i>C. ilosvayi</i> in early spring that is
probably coupled to the hydrologic cycle of Florida. |
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| ISSN: | 1726-4170 1726-4189 |