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| Kienast, M.; Lehmann, M. F.; Timmermann, A.; Galbraith, E.; Bolliet, T.; Holboum, A.; Normandeau, C.; Laj, C.. |
| Sedimentary delta(15)N records from the oligotrophic western equatorial Pacific (WEP) off Mindanao show that late Holocene sedimentary delta(15)N is substantially lower than that of the early Holocene, following a gradual >3 parts per thousand decrease that occurred between 7 and 3 kyrs ago. Analyses of modem day nitrate isotope profiles from the same region indicate the sensitivity of the WEP N pools towards (1) the advection of (15)N-enriched nitrate from the Eastern Equatorial Pacific (EEP) by the North Equatorial Current (NEC) and the Mindanao Current in subsurface waters and, (2) at shallow depths, the input of new and (15)N-depleted nitrate through N, fixation. We suggest that the Holocene decrease in sedimentary delta(15)N reflects a diminished... |
| Tipo: Text |
Palavras-chave: Tropical Pacific; El Nino; Surface temperature; Fresh water; Nitrate; Mindanao; Ocean; Variability; Holocene; Seawater. |
| Ano: 2008 |
URL: https://archimer.ifremer.fr/doc/00207/31843/30257.pdf |
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| Menviel, L.; Timmermann, A.; Friedrich, T.; England, M. H.. |
| Millennial-scale variability associated with Dansgaard-Oeschger events is arguably one of the most puzzling climate phenomena ever discovered in paleoclimate archives. Here, we set out to elucidate the underlying dynamics by conducting a transient global hindcast simulation with a 3-D intermediate complexity earth system model covering the period 50 to 30 ka BP. The model is forced by time-varying external boundary conditions (greenhouse gases, orbital forcing, and ice-sheet orography and albedo) and anomalous North Atlantic freshwater fluxes, which mimic the effects of changing northern hemispheric ice volume on millennial timescales. Together these forcings generate a realistic global climate trajectory, as demonstrated by an extensive model/paleo data... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00274/38487/36951.pdf |
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| Friedrich, T.; Timmermann, A.. |
| Ratios of oxygen isotope values obtained from foraminiferal calcite are one of the most established paleoceanographic proxies. They are used in the context of estimating variations in ice volume, ocean temperature, and salinity and provide a means to date marine sediment cores across different ocean basins. Our study addresses the question how the delta O-18 of the deglacial meltwater signal propagates into the interior ocean, when large-scale millennial-scale reorganizations of the Atlantic Meridional Overturning Circulation ( AMOC) are present. Analyzing a series of idealized tracer-injection experiments conducted with an earth system model, we find that a substantial weakening of the AMOC leads to a massive delay in the export of the glacioeustatic... |
| Tipo: Text |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00265/37629/36894.pdf |
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| Friedrich, T.; Timmermann, A.; Stichel, T.; Pahnke, K.. |
| Over the past decade, records of the seawater neodymium isotopic composition (epsilon(Nd)) have become a widely used proxy to reconstruct changes in ocean circulation. Our study investigates the transient response of epsilon(Nd) to large-scale ocean circulation changes using an Earth system model of intermediate complexity. It is shown that a weakening of the North Atlantic Deep Water formation results in positive epsilon(Nd) anomalies in the Atlantic and the Pacific below 1000m water depth whereas variations in Antarctic Bottom Water production generate a Pacific-Atlantic dipole pattern of deep ocean epsilon(Nd) changes. Further experiments explore which ocean regions are suitable to record the temporal evolution of the overturning in the North Atlantic... |
| Tipo: Text |
Palavras-chave: Neodymium; Ocean circulation; Meridional overturning; Ocean modeling; Reconstruction. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00289/40055/39405.pdf |
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| Tachikawa, K.; Timmermann, A.; Vidal, Lucas; Sonzogni, C.; Timm, O. E.. |
| The western Pacific warm pool (WPWP) is an important heat source for the atmospheric circulation and influences climate conditions worldwide. Understanding its sensitivity to past radiative perturbations may help better contextualize the magnitudes and patterns of current and projected tropical climate change. Here we present a new Mg/Ca-based sea surface temperature (SST) reconstruction over the past 400 kyr from the Bismarck Sea, off Papua New Guinea, along with results from a transient earth system model simulation. Our results document the primary influence of CO2 forcing on glacial/interglacial WPWP SSTs and secondary effects due to changes in wind-driven tropical boundary currents. In addition to the SST, deep ocean temperature reconstructions from... |
| Tipo: Text |
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| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00274/38504/37010.pdf |
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