(Fig. 9) Pollen analysis of sediment core GIK16017-2

The improved understanding of the pollen signal in the marine sediments offshore of northwest Africa is applied to deep-sea core M 16017-2 at 21°N. Downcore fluctuations in the percentage, concentration and influx diagrams record latitudinal shifts of the main northwest African vegetation zones and characteristics of the trade winds and the African Easterly Jet. Time control is provided by 14C ages and 180 records. During the period 19,000-14,000 yr B.P. a compressed savanna belt extended between about 12 ° and 14-15°N. The Sahara had maximally expanded northward and southward under hyperarid climatic conditions. The belt with trade winds and dominant African Easterly Jet transport had not shifted latitudinally. The trade winds were strong as compared to the modern situation but around 13,000 yr B.P. the trade winds weakened. After 14,000 yr B.P. the climate became less arid south of the Sahara and a first spike of fluvial runoff is registered around 13,000 yr B.P. Fluvial runoff increased strongly around 11,000 yr B.P. and maximum runoff is recorded from about 9000-7800 yr B.P. Around 12,500 yr B.P. the savanna belt started to shift northward and became richer in woody species: it shifted about 6° of latitude, reached its northernmost position during the period of 9200-7800 yr B.P. and extended between about 16° and 24°N at that time. Tropical forest had reached its maximum expansion and the Guinea zone reached as far north as about 15°N, reflecting very humid climatic conditions south of the Sahara. North of the Sahara the climate also became more humid and Mediterranean vegetation developed rapidly. The Sahara had maximally contracted and the trade winds were weak and comparable with the present day intensity. After about 7800 yr B.P. the southern fringe of the Sahara and accordingly the savanna belt, shifted rapidly southward again.

Uvigerina spp. minor element and derived d18Oseawater records over the Mid-Pleistocene Transition (500-1500 kyr), DSDP Hole 94-607

During the Mid-Pleistocene Transition (MPT), the dominant glacial-interglacial cyclicity as inferred from the marine d18O records of benthic foraminifera (d18Obenthic) changed from 41 kyr to 100 kyr years in the absence of a comparable change in orbital forcing. Currently, only two Mg/Ca-derived, high-resolution bottom water temperature (BWT) records exist that can be used with d18Obenthic records to separate temperature and ice volume signals over the Pleistocene. However, these two BWT records suggest a different pattern of climate change occurred over the MPT-a record from North Atlantic DSDP Site 607 suggests BWT decreased with no long-term trend in ice volume over the MPT, while South Pacific ODP Site 1123 suggests that BWT has been relatively stable over the last 1.5 Myr but that there was an abrupt increase in ice volume at ~900 kyr. In this paper we attempt to reconcile these two views of climate change across the MPT. Specifically, we investigated the suggestion that the secular BWT trend obtained from Mg/Ca measurements on Cibicidoides wuellerstorfi and Oridorsalis umbonatus species from N. Atlantic Site 607 is biased by the possible influence of D[CO3]2- on Mg/Ca values in these species by generating a low-resolution BWT record using Uvigerina spp., a genus whose Mg/Ca values are not thought to be influenced by D[CO3]2-. We find a long-term BWT cooling of ~2-3°C occurred from 1500 to ~500 kyr in the N. Atlantic, consistent with the previously generated C. wuellerstorfi and O. umbonatus BWT record. We also find that changes in ocean circulation likely influenced d18Obenthic, BWT, and d18Oseawater records across the MPT. N. Atlantic BWT cooling starting at ~1.2 Ma, presumably driven by high-latitude cooling, may have been a necessary precursor to a threshold response in climate-ice sheet behavior at ~900 ka. At that point, a modest increase in ice volume and thermohaline reorganization may have caused enhanced sensitivity to the 100 kyr orbital cycle.

Fig. 2. Lithology, water and total carbon content, cumulative grain-size distribution, and quartz, feldspar, and mica contents of core sequence Lz1013 from south-western Beaver Lake

A 100 cm long sediment sequence was recovered from Beaver Lake in Amery Oasis, East Antarctica, using gravity and piston corers. Sedimentological and mineralogical analyses and the absence of micro and macrofossils indicate that the sediments at the base of the sequence formed under glacial conditions, probably prior to c. 12 500 cal. yr BP. The sediments between c. 81 and 31 cm depth probably formed under subaerial conditions, indicating that isostatic uplift since deglaciation has been substantially less than eustatic sea-level rise and that large areas of the present-day floor of Beaver Lake must have been subaerially exposed following deglaciation. The upper 31 cm of the sediment sequence were deposited under glaciomarine conditions similar to those of today, supporting geomorphic observations that the Holocene was a period of relative sea-level highstand in Amery Oasis.

Biochemical investigation of multicorer sediment profile PS74/108-2

To detect and track the impact of large-scale environmental changes in a the transition zone between the northern North Atlantic and the central Arctic Ocean, and to determine experimentally the factors controlling deep-sea biodiversity, the Alfred- Wegener-Institute for Polar and Marine Research (AWI) established the deep-sea long-term observatory HAUSGARTEN, which constitutes the first, and until now only open-ocean long-term station in a polar region. Virtually undisturbed sediment samples have been taken using a video-guided multiple corer (MUC) at 13 HAUSGARTEN stations along a bathymetric (1,000 - 4,000 m water depth) and a latitudinal transect in 2,500 m water depth as well as two stations at 230 and 1,200 m water depth within the framework of the KONGHAU project. Various biogenic sediment compounds were analyzed to estimate the input of organic matter from phytodetritus sedimentation, benthic activities (e.g. bacterial exoenzymatic activity), and the total biomass of the smallest sediment-inhabiting organisms (size range: bacteria to meiofauna).

Biochemical investigation of multicorer sediment profile PS74/116-2

To detect and track the impact of large-scale environmental changes in a the transition zone between the northern North Atlantic and the central Arctic Ocean, and to determine experimentally the factors controlling deep-sea biodiversity, the Alfred- Wegener-Institute for Polar and Marine Research (AWI) established the deep-sea long-term observatory HAUSGARTEN, which constitutes the first, and until now only open-ocean long-term station in a polar region. Virtually undisturbed sediment samples have been taken using a video-guided multiple corer (MUC) at 13 HAUSGARTEN stations along a bathymetric (1,000 - 4,000 m water depth) and a latitudinal transect in 2,500 m water depth as well as two stations at 230 and 1,200 m water depth within the framework of the KONGHAU project. Various biogenic sediment compounds were analyzed to estimate the input of organic matter from phytodetritus sedimentation, benthic activities (e.g. bacterial exoenzymatic activity), and the total biomass of the smallest sediment-inhabiting organisms (size range: bacteria to meiofauna).