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| Titel |
Anti-phase seasonality and paleothermometry of G. ruber and G. trilobus upstream of the Agulhas Current |
| VerfasserIn |
Ulrike Fallet, Geert-Jan Brummer, Jens Zinke, Herman Ridderinkhof |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039641
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| Zusammenfassung |
| To infer past ocean temperatures we examined the first time-series fluxes of planktonic
foraminifera retrieved upstream of the modern Agulhas Current. Using deep-moored
sediment traps we find a distinct anti-phase response to the seasonal migration of the
Intertropical Convergence Zone (ITCZ) in the shell fluxes of common surface-dwelling G.
ruber and G. trilobus. Maximum fluxes of G. ruber occur in late austral summer (February –
March) when sea surface temperature (SST) averages 30-C. By contrast G. trilobus maxima
appear five months later in winter (June – July) at lower average SST of around 25-C when
chlorophyll a increases. Cross-correlation of the 2.5 year time-series data showed that the G.
ruber/G. trilobus ratio closely followed the seasonal cycle in SST, as did their paired δ18O
and Mg/Ca. From these results we derived five independent temperature equations
for improved paleothermometry in the southwestern Indian Ocean that specify
summer, winter and flux-weighted annual mean SST. In the boreal Indian Ocean
time-series G. ruber and G. trilobus from offshore Somalia and Oman also show
seasonality in shell flux ratios. These are shifted by about four months against southern
hemisphere values in concert with increased productivity in the Arabian Sea during
monsoon-driven coastal upwelling. We conclude that the G. ruber/G. trilobus ratio,
together with their δ18O and Mg/Ca, not only allow for seasonal paleothermometry
but also minimize a large error introduced by differential seasonal productivity. |
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