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| Titel |
Characterization of Tahiti water samples with respect to carbonate dissolution, nutrient content and end-member modeling |
| VerfasserIn |
J. Hoffmann, M. Koelling, T. Pichler |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028869
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| Zusammenfassung |
| As part of the EuroMARC project CHECREEF this project investigates the influence of
freshwater on the internal and external structure of coral reefs around Tahiti. In 2007
approximately 70 water samples, including surface water, groundwater, seawater and
brackish water samples, were collected and analyzed for major elements, nutrients and stable
isotopes.
The amount of total dissolved solids (TDS) in the freshwater samples is very low
(conductivity ranged between 10-460 μS), which is due to the high amount of precipitation
(up to 8500 mma-1) and the low residence times in the aquifer prior to discharge from
onland springs or as submarine groundwater discharge (SGD). SGD is likely on Tahiti
because of the high hydraulic gradient, which is a result of the islands internal structure
and its steep relief. All freshwater samples were undersaturated with respect to
aragonite/calcite and therefore could potentially dissolve the reef carbonates offshore
Tahiti. Based on a simple water balance calculation, which employs climatic data of
Tahiti and surface water runoff, we can estimate the potential amount of submarine
groundwater discharge (SGD). Assuming chemical equilibrium, the maximum
quantity of Ca-carbonates, which could be dissolved can be calculated with the
geochemical program PHREEQC. This data in conjunction with an estimate of
SGD allows us to estimate the potential amount of dissolved carbonate rocks due to
SGD.
A second modeling approach is end-member water mixing along different freshwater
pathways discharging into the ocean. We can track the pathways and the mixing amount
using stable isotope data and conservative tracers like sodium and chloride. These findings
shed light on, whether the dissolved compounds behave conservative according to mixing or
if there are other processes that influence the dissolved content of the water sample. |
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