Rekonstruktion der Atlantischen Zirkulation innerhalb des letzten Glazialen Zyklus

The climate of the last 150 kyr is mainly driven by orbital forcing leading to long-lasting glacial conditions framed by the short warm periods Eemian and Holocene. To understand this climate variability it is crucial to investigate the response of the Atlantic Meridional Overturning Circulation (AMOC) on the insolation and the consequent effect it has on the climate by redistributing heat and CO2. However, the mechanisms that determine changes of the AMOC are poorly understood within the investigated time period. In this study the strength and direction of the AMOC is examined by temporal high-resolution measurements of the two proxies 231Pa/230Th and eNd from the marine sediment core ODP 1063 which is situated in the North West Atlantic. Despite the short half life of 231Pa, significant 231Pa/230Th ratios were obtained until 134 kyr which extends the so far released scope by 9 kyr. During Dansgaard-Oeschger warm events variations in the northern deep water formation and circulation dynamics are found. Further, rarely detected Heinrich cold events from the early glacial (H7, H9 and H10) are identified. It is demonstrated that the Termination II lacks a Younger Dryas-like cold event due to differences in the summer insolation. Instead to the widely perceped view of a generally shallow and weak AMOC during full glacial conditions, a reduced circulation strength associated with northern sourced water in the deep Atlantic during MIS 4 and the early MIS 3 are found. Due to the significant difference of this pattern to the so far described circulation modes, the new `intermediate mode' is defined

STIL binding to Polo-box 3 of PLK4 regulates centriole duplication

Polo-like kinases (PLK) are eukaryotic regulators of cell cycle progression, mitosis and cytokinesis; PLK4 is a master regulator of centriole duplication. Here, we demonstrate that the SCL/TAL1 interrupting locus (STIL) protein interacts via its coiled-coil region (STIL-CC) with PLK4 in vivo. STIL-CC is the first identified interaction partner of Polo-box 3 (PB3) of PLK4 and also uses a secondary interaction site in the PLK4 L1 region. Structure determination of free PLK4-PB3 and its STIL-CC complex via NMR and crystallography reveals a novel mode of Polo-box-peptide interaction mimicking coiled-coil formation. In vivo analysis of structure-guided STIL mutants reveals distinct binding modes to PLK4-PB3 and L1, as well as interplay of STIL oligomerization with PLK4 binding. We suggest that the STIL-CC/PLK4 interaction mediates PLK4 activation as well as stabilization of centriolar PLK4 and plays a key role in centriole duplication

Sedimentary protactinium / thorium and opal in sediment core MD09-3257 from Western Equatorial Atlantic

Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e. Greenland stadials). These rainfall events are recorded in MD09-3257 as peaks in ln(Ti/Ca). New sedimentary Pa/Th data indicate that mid-depth western equatorial water mass transport decreased during all of the Greenland stadials of the last 40 kyr. Using cross-wavelet transforms and spectrogram analysis, we assess the relative phase between the MD09-3257 sedimentary Pa/Th and ln(Ti/Ca) signals. We show that decreased water mass transport between a dept of ~1300 and 2300 m in the western equatorial Atlantic preceded increased rainfall over the adjacent continent by 120 to 400 y at Dansgaard-Oeschger (D-O) frequencies, and by 280 to 980 y at Heinrich-like frequencies. We suggest that the large lead of ocean circulation changes with respect to changes in tropical South American precipitation at Heinrich-like frequencies is related to the effect of a positive feedback involving iceberg discharges in the North Atlantic. In contrast, the absence of widespread ice rafted detrital layers in North Atlantic cores during D-O stadials supports the hypothesis that a feedback such as this was not triggered in the case of D-O stadials, with circulation slowdowns and subsequent changes remaining more limited during D-O stadials than Heinrich stadials