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| Registros recuperados: 10 | |
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| Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf. |
| Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was... |
| Tipo: Text |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00497/60842/64285.pdf |
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| Caniupan, Magaly; Lamy, Frank; Lange, Carina B.; Kaiser, Jerome; Kilian, Rolf; Arz, Helge W.; Leon, Tania; Mollenhauer, Gesine; Sandoval, Susana; De Pol-holz, Ricardo; Pantoja, Silvio; Wellner, Julia; Tiedemann, Ralf. |
| Here we provide three new Holocene (11-0 cal ka BP) alkenone-derived sea surface temperature (SST) records from the southernmost Chilean fjord region (50-53 degrees S). SST estimates may be biased towards summer temperature in this region, as revealed by a large set of surface sediments. The Holocene records show consistently warmer than present-day SSTs except for the past similar to 0.6 cal ka BP. However, they do not exhibit an early Holocene temperature optimum as registered further north off Chile and in Antarctica. This may have resulted from a combination of factors including decreased inflow of warmer open marine waters due to lower sea-level stands, enhanced advection of colder and fresher inner fjord waters, and stronger westerly winds. During... |
| Tipo: Text |
Palavras-chave: Holocene; Alkenones; Sea-surface temperature; Fjords; Chile. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00290/40088/39292.pdf |
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| Rippert, Nadine; Max, Lars; Mackensen, Andreas; Cacho, Isabel; Povea, Patricia; Tiedemann, Ralf. |
| The eastern equatorial Pacific (EEP) is a key area to understand past oceanic processes that control atmospheric CO2 concentrations. Many studies argue for higher nutrient concentrations by enhanced nutrient transfer via Southern Ocean Intermediate Water (SOIW) to the low-latitude Pacific during glacials. Recent studies, however, argue against SOIW as the primary nutrient source, at least during early Marine Isotope Stage 2 (MIS 2), as proxy data indicate that nutrients are better utilized in the Southern Ocean under glacial conditions. New results from the subarctic Pacific suggest that enhanced convection of nutrient-rich Glacial North Pacific Intermediate Water (GNPIW) contributes to changes in nutrient concentrations in equatorial subthermocline water... |
| Tipo: Text |
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| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00497/60825/64592.pdf |
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| Max, Lars; Riethdorf, Jan-rainer; Tiedemann, Ralf; Smirnova, Maria; Lembke-jene, Lester; Fahl, Kirsten; Nuernberg, Dirk; Matul, Alexander; Mollenhauer, Gesine. |
| Past changes in North Pacific sea surface temperatures and sea-ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the North Atlantic. Here, we present new alkenone-based sea surface temperature records from the subarctic northwest Pacific and its marginal seas (Bering Sea and Sea of Okhotsk) for the time interval of the last 15 kyr, indicating millennial-scale sea surface temperature fluctuations similar to short-term deglacial climate oscillations known from Greenland ice core records. Past changes in sea-ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the IP25 biomarker related to sea-ice diatoms. The... |
| Tipo: Text |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00265/37630/36988.pdf |
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| Meyer, Vera D.; Max, Lars; Hefter, Jens; Tiedemann, Ralf; Mollenhauer, Gesine. |
| It has been proposed that North Pacific sea surface temperature (SST) evolution was intimately linked to North Atlantic climate oscillations during the last glacial-interglacial transition. However, during the early deglaciation and the Last Glacial Maximum, the SST development in the subarctic northwest Pacific and the Bering Sea is poorly constrained as most existing deglacial SST records are based on alkenone paleothermometry, which is limited prior to 15ka B.P. in the subarctic North Pacific realm. By applying the TEX86L temperature proxy we obtain glacial-Holocene-SST records for the marginal northwest Pacific and the Western Bering Sea. Our TEX86L-based records and existing alkenone data suggest that during the past 15.5ka, SSTs in the northwest... |
| Tipo: Text |
Palavras-chave: TEX86L; Surface circulation; Northwest Pacific; Bering Sea; Deglaciation. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00421/53231/54786.pdf |
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| Ronge, Thomas A.; Steph, Silke; Tiedemann, Ralf; Prange, Matthias; Merkel, Ute; Nuernberg, Dirk; Kuhn, Gerhard. |
| Glacial/interglacial changes in Southern Ocean's air-sea gas exchange have been considered as important mechanisms contributing to the glacial/interglacial variability in atmospheric CO2. Hence, understanding past variability in Southern Ocean intermediate to deep water chemistry and circulation is fundamental to constrain the role of these processes on modulating glacial/interglacial changes in the global carbon cycle. Our study focused on the glacial/interglacial variability in the vertical extent of southwest Pacific Antarctic Intermediate Water (AAIW). We compared carbon and oxygen isotope records from epibenthic foraminifera of sediment cores bathed in modern AAIW and Upper Circumpolar Deep Water (UCDW; 943–2066 m water depth) to monitor changes in... |
| Tipo: Text |
Palavras-chave: AAIW; UCDW; SW-Pacific; Stable isotopes. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00294/40568/39465.pdf |
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| Lamy, Frank; Arz, Helge W.; Kilianc, Rolf; Lange, Carina B.; Lembke-jene, Lester; Wengler, Marc; Kaiser, Jerome; Baeza-urrea, Oscar; Hall, Ian R.; Harada, Naomi; Tiedemann, Ralf. |
| The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total... |
| Tipo: Text |
Palavras-chave: Paleoceanography; Drake Passage; Antarctic Circumpolar Current; Glacial-interglacial changes; Sedimentology. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00351/46233/46119.pdf |
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| Ho, Sze Ling; Mollenhauer, Gesine; Lamy, Frank; Martinez-garcia, Alfredo; Mohtadi, Mahyar; Gersonde, Rainer; Hebbeln, Dierk; Nunez-ricardo, Samuel; Rosell-mele, Antoni; Tiedemann, Ralf. |
| In spite of the important role played by the Southern Ocean in global climate, the few existing paleoceanographic records in the east Pacific sector do not extend beyond one glacial-interglacial cycle, hindering circumpolar comparison of past sea surface temperature (SST) evolution in the Southern Ocean. Here we present three alkenone-based Pleistocene SST records from the subantarctic and subtropical Pacific. We use a regional core top calibration data set to constrain the choice of calibrations for paleo SST estimation. Our core top data confirm that the alkenone-based U-37(K) and U-37(K') values correlate linearly with the SST, in a similar fashion as the most commonly used laboratory culture-based calibrations even at low temperatures (down to similar... |
| Tipo: Text |
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| Ano: 2012 |
URL: https://archimer.ifremer.fr/doc/00265/37610/36990.pdf |
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| Riethdorf, Jan-rainer; Max, Lars; Nuernberg, Dirk; Lembke-jene, Lester; Tiedemann, Ralf. |
| Based on models and proxy data, it has been proposed that salinity-driven stratification weakened in the subarctic North Pacific during the last deglaciation, which potentially contributed to the deglacial rise in atmospheric carbon dioxide. We present high-resolution subsurface temperature (T-Mg/Ca) and subsurface salinity-approximating (delta O-18(ivc-sw)) records across the last 20,000 years from the subarctic North Pacific and its marginal seas, derived from combined stable oxygen isotopes and Mg/Ca ratios of the planktonic foraminiferal species Neogloboquadrina pachyderma (sin.). Our results indicate regionally differing changes of subsurface conditions. During the Heinrich Stadial 1 and the Younger Dryas cold phases, our sites were subject to reduced... |
| Tipo: Text |
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| Ano: 2013 |
URL: https://archimer.ifremer.fr/doc/00262/37307/35719.pdf |
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| Registros recuperados: 10 | |
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