Caldensinic acid, a prenylated benzoic acid from Piper caldense

The CH(2)Cl(2) and MeOH extracts from leaves of Piper caldense were subjected to chromatographic separation procedures to afford the new prenylated benzoic acid, caldensinic acid (3-[(2`E,6`E,10`E)-11`-carboxy-3`,7`,15`-trimethylhexadeca-2`,6`,10`,14`-tetraenyl]-4,5-dihydroxybenzoic acid) whose structure was determined by spectral analysis, mainly NMR ((1)H, (13)C, HSQC, HMBC) and ESI-MS. The natural compound and derivatives displayed antifungal activity against the phytopathogenic fungi Cladosporium cladosporioides and C. sphaerospermum by direct bioautography. (C) 2009 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.

Biomarker proxies on sediment cores in the central Arctic Ocean

Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides over a distance of >350 km along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene to early Quaternary sediments close to the seafloor, allowing the retrieval of such old sediments with gravity cores. Multi-proxy biomarker analyses of these gravity cores reveal for the first time that the late Miocene central Arctic Ocean was relatively warm (4-7°C) and ice-free during summer, whereas sea ice occurred during spring and autumn/winter. A comparison of our proxy data with Miocene climate simulations seems to favour relatively high late Miocene atmospheric CO2 concentrations. These new findings from the Arctic region provide new benchmarks for groundtruthing global climate reconstructions and modeling.

Biomarker distributions and calculated sea surface temperatures from the North Pacific Ocean

In order to study the modern sea surface characteristics of the sub-polar North Pacific and the Bering Sea, i.e. sea surface temperature (SST) and sea ice cover, surface sediments recovered during the RV Sonne Expedition 202 in 2009 were analysed. To distinguish between marine and terrestrial organic carbon, hydrogen index values, long chain n-alkanes and specific sterols have been determined. The results show that in the Bering Sea, especially on the sea slope, the organic carbon source is mainly caused by high primary production. In the North Pacific, on the other hand, the organic material originates predominantly from terrestrial higher plants, probably related to dust input from Asia. SST has been reconstructed using the modified alkenone unsaturation index. Calibration from Müller et al. (1998, doi:10.1016/S0016-7037(98)00097-0) offers the most reliable estimate of mean annual temperature in the central North Pacific but does not correlate with mean annual temperature throughout the study area. In the eastern North Pacific and the Bering Sea, the Sikes et al. (1997, doi:10.1016/S0016-7037(97)00017-3) calibration seems to be more accurate and matches summer SST. The distribution of the novel sea ice proxy IP25 (highly branched C25 isoprenoid alkene) in surface sediments is in accord with the modern spring sea ice edge and shows the potential of this proxy to track past variation in sea ice cover in the study area.

Temporal and spatial LGM variability of biomarker records in the Arctic Ocean

Using the sea ice proxy IP25 and phytoplankton-derived biomarkers (brassicasterol and dinosterol) Arctic sea-ice conditions were reconstructed for Marine Isotope Stage (MIS) 3 to 1 in sediment cores from the north of Barents Sea continental margin across the Central Arctic to the Southern Mendeleev Ridge. Our results suggest more extensive sea-ice cover than present-day during MIS 3, increasing sea-ice growth during MIS 2 and decreased sea-ice cover during the last deglacial. The summer ice edge sustained north of the Barents Sea even during extremely cold (i.e., Last Glacial Maximum (LGM)) as well as warm periods (i.e., Bølling-Allerød). During the LGM, the western Svalbard margin and the northern Barents Sea margin areas were characterized by high concentrations of both IP25 and phytoplankton biomarkers, interpreted as a productive ice-edge situation, caused by the inflow of warm Atlantic Water. In contrast, the LGM high Arctic proper (north of 84°N) was covered by thick permanent sea ice throughout the year with rare break up, indicated by zero or near-zero biomarker concentrations. The spring/summer sea-ice margin significantly extended southwards to the southern Lomonosov Ridge and Mendeleev Ridge during the LGM. Our proxy reconstructions are very consistent with published model results based on the North Atlantic/Arctic Ocean Sea Ice Model (NAOSIM).

Total organic carbon, delta13C, biomarker, diatom distributions in sediment core JM11-FI-19PC

In the light of rapidly diminishing sea ice cover in the Arctic during the present atmospheric warming, it is imperative to study the distribution of sea ice in the past in relation to rapid climate change. Here we focus on glacial millennial scale climatic events (Dansgaard/Oeschger events) using the new sea ice proxy IP25 in combination with phytoplankton proxy data and quantification of diatom species in a record from the SE Norwegian Sea. We demonstrate that expansion and retreat of sea ice varied consistently in pace with the rapid climate changes 90 ka to present, and with this present the first IP25 sea ice proxy record resolving the D/O cyclicity going back in time into Marine Isotope Stage 5a. Sea ice retreated abruptly at the start of warm interstadials, but spread rapidly during the cooling phase of the interstadials and became near-perennial and perennial during cold stadials and Heinrich events, respectively. Low salinity surface water and the sea ice edge spread to the Greenland-Scotland Ridge, and during the largest Heinrich events, probably far into the Atlantic Ocean.