Wir untersuchen Klimawandel in der geologischen und historischen Vergangenheit und dessen Auswirkungen im unmittelbaren Lebensraum des Menschen sowie Änderungen des Erdmagnetfelds. Ein Schwerpunkt unserer Forschung sind schnelle Klimaänderungen, die sich in wenigen Jahren bis Jahrzehnten ereignet haben. Deshalb arbeiten wir mit zeitlich hochauflösenden terrestrischen Geoarchiven, wie jahresgeschichteten (warvierten) Ablagerungen in Seen und Baumringen. Ein zentraler Teil unserer Arbeit ist die Erstellung präziser Datierungen unserer Geoarchive als Grundvoraussetzung für verlässliche Rekonstruktionen von Änderungen in der Vergangenheit.
Schnelle Klimawechsel in der Vergangenheit sind natürliche Experimente, mit denen wir einen Einblick in die Ursachen und die Dynamik solcher Änderungen bekommen, um damit besser auf zukünftige Entwicklungen vorbereitet zu sein. Dazu nutzen wir Informationen aus der Struktur und chemischen Zusammensetzung von Jahresschichten (Proxidaten), die wir mit Beobachtungen heutiger Prozesse (Monitoring) abgleichen. Unsere Vision ist die Verknüpfung langer Zeitreihen aus unseren Geoarchiven mit instrumentellen Daten, um derzeitige Veränderungen in einen langfristigen Kontext stellen zu können.
Nowaczyk, N.R., Liu, J., Frank, U., Arz, H.W. (2017 online): A high-resolution paleosecular variation record from Black Sea sediments indicating fast directional changes associated with low field intensities during marine isotope stage (MIS) 4 – Earth Planet. Sci. Lett., 484, 15-29. | doi:10.1016/j.epsl.2017.12.009
Keywords: paleosecular variation, geomagnetic excursion, magnetostratigraphy, Black Sea, XRF-scanning
Abstract: A total of nine sediment cores recovered from the Archangelsky Ridge in the SE Black Sea were systematically subjected to intense paleo- and mineral magnetic analyses. Besides 16 accelerator mass spectrometry (AMS) 14C ages available for another core from this area, dating was accomplished by correlation of short-term warming events during the last glacial monitored by high-resolution X-ray fluorescence (XRF) scanning as maxima in both Ca/Ti and K/Ti ratios in Black Sea sediments to the so-called 'Dansgaard-Oeschger events' recognized from Greenland ice cores. Thus, several hiatuses could be identified in the various cores during the last glacial/interglacial cycle. Finally, core sections documenting marine isotope stage (MIS) 4 at high resolution back to 69 ka were selected for detailed analyses. At 64.5 ka, according to obtained results from Black Sea sediments, the second deepest minimum in relative paleointensity during the past 69 ka occurred, with the Laschamp geomagnetic excursion at 41 ka being associated with the lowest field intensities. The field minimum during MIS 4 is associated with large declination swings beginning about 3 ka before the minimum. While a swing to 50°E is associated with steep inclinations (50-60°) according to the coring site at 42°N, the subsequent declination swing to 30°W is associated with shallow inclinations of down to 40°. Nevertheless, these large deviations from the direction of a geocentric axial dipole field (I=61°, D=0°) still can not yet be termed as 'excursional', since latitudes of corresponding virtual geomagnetic poles (VGP) only reach down to 51.5°N (120°E) and 61.5°N (75°W), respectively. However, these VGP positions at opposite sides of the globe are linked with VGP drift rates of up to 0.2° per year in between. These extreme secular variations might be the mid-latitude expression of a geomagnetic excursion with partly reversed inclinations found at several sites much further North in Arctic marine sediments between 69°N and 81°N. Thus, the pronounced intensity minimum at 64.5 ka and described directional variations might be the effect of a weak geomagnetic field with a multi-polar geometry in the middle of MIS 4.
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