Stable carbon and oxygen isotope compositions of Eocene benthic foraminifera from ODP Site 207-1258

'Hyperthermals' are intervals of rapid, pronounced global warming known from six episodes within the Palaeocene and Eocene epochs (~65-34 million years (Myr) ago) (Zachos et al., 2005, doi:10.1126/science.1109004; 2008, doi:10.1038/nature06588; Roehl et al., 2007, doi:10.1029/2007GC001784; Thomas et al., 2000; Cramer et al., 2003, doi:10.1029/2003PA000909; Lourens et al., 2005, doi:10.1038/nature03814; Petrizzo, 2005, doi:10.2973/odp.proc.sr.198.102.2005; Sexton et al., 2006, doi:10.1029/2005PA001253; Westerhold et al., 2007, doi:10.1029/2006PA001322; Edgar et al., 2007, doi:10.1038/nature06053; Nicolo et al., 2007, doi:10.1130/G23648A.1; Quillévéré et al., 2008, doi:10.1016/j.epsl.2007.10.040; Stap et al., 2010, doi:10.1130/G30777.1). The most extreme hyperthermal was the 170 thousand year (kyr) interval (Roehl et al., 2007) of 5-7 °C global warming (Zachos et al., 2008) during the Palaeocene-Eocene Thermal Maximum (PETM, 56 Myr ago). The PETM is widely attributed to massive release of greenhouse gases from buried sedimentary carbon reservoirs (Zachos et al., 2005; 2008; Lourenbs et al., 2005; Nicolo et al., 2007; Dickens et al., 1995, doi:10.1029/95PA02087; Dickens, 2000; 2003, doi:10.1016/S0012-821X(03)00325-X; Panchuk et al., 2008, doi:10.1130/G24474A.1) and other, comparatively modest, hyperthermals have also been linked to the release of sedimentary carbon (Zachos et al., 2008, Lourens et al., 2005; Nicolo et al., 2007; Dickens, 2003; Panchuk et al., 2003). Here we show, using new 2.4-Myr-long Eocene deep ocean records, that the comparatively modest hyperthermals are much more numerous than previously documented, paced by the eccentricity of Earth's orbit and have shorter durations (~40 kyr) and more rapid recovery phases than the PETM. These findings point to the operation of fundamentally different forcing and feedback mechanisms than for the PETM, involving redistribution of carbon among Earth's readily exchangeable surface reservoirs rather than carbon exhumation from, and subsequent burial back into, the sedimentary reservoir. Specifically, we interpret our records to indicate repeated, large-scale releases of dissolved organic carbon (at least 1,600 gigatonnes) from the ocean by ventilation (strengthened oxidation) of the ocean interior. The rapid recovery of the carbon cycle following each Eocene hyperthermal strongly suggests that carbon was resequestered by the ocean, rather than the much slower process of silicate rock weathering proposed for the PETM (Zachos et al., 2005; 2003). Our findings suggest that these pronounced climate warming events were driven not by repeated releases of carbon from buried sedimentary sources (Zachos et al., 2008, Lourens et al., 2005; Nicolo et al., 2007; Dickens, 2003; Panchuk et al., 2003) but, rather, by patterns of surficial carbon redistribution familiar from younger intervals of Earth history.

(Table 1) Age determination of sediment cores OCE205-2-100GGGC and KNR166-2-31

Benthic foraminiferal Cd/Ca from a Florida Current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the Atlantic meridional overturning circulation (AMOC). Cd seawater estimates (CdW) indicate that intermediate-depth southern source waters crossed the equator and contributed to the Florida Current during the Bølling-Allerød warm period of the last deglaciation, consistent with evidence of only a modest AMOC reduction compared to today. The CdW estimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate-depth southern source waters within the Florida Current during the Younger Dryas, a deglacial cold event characterized by a weak North Atlantic AMOC. Our results reveal a close correspondence between the northward penetration of intermediate-depth southern source waters and the influence of North Atlantic Deep Water, suggesting a possible link between intermediate-depth southern source waters and the strength of the Atlantic AMOC.

Gletscherstände des Vernagtferner 1889-1969

The Vernagtferner in the Ötztaler Alps (Tirol) has been mapped after terrestrial-photogrammetric surveying by Sebastian Finsterwalder in 1889, Otto von Gruber in 1912, and Heinrich Schatz in 1938. The new, four-colored map in the scale 1: 10.000 enclosed in this issue was composed from aerial photographs of 1969. It was conceived as topographicaI map with additional geodetic and glaciological content. The methods of survey are explained and the means of cartographic representation are discussed.

Der Vernagt-Ferner im Jahre 1889 (facsimile)

Problems resulting from mapping of glaciers with traditional techniques motivated Sebastian Finsterwalder to apply the planetable-photogrammetry to a survey of Vernagt- and Guslarferner (Ötztal Alps, Austria) in 1888/ 1889. The result of this photogrammetric survey was the map "Der Vernagt-Ferner im Jahre 1889", which had been published in four colours. This is the first map of an entire glacier in the large scale 1: 10.000 with a high accuracy. Since this remarkable map of Vernagt- and Guslarferner is almost not available a facsimile-reprint had been produced.