Planktonic foraminifera Mg/Ca-based temperatures and planktonic foraminiferal cenus counts of core GeoB10065-7 (Lombok Basin, Indonesia)

Modern variability in upwelling off southern Indonesia is strongly controlled by the Australian-Indonesian monsoon and the El Niño-Southern Oscillation, but multi-decadal to centennial-scale variations are less clear. We present high-resolution records of upper water column temperature, thermal gradient and relative abundances of mixed layer- and thermocline-dwelling planktonic foraminiferal species off southern Indonesia for the past two millennia that we use as proxies for upwelling variability. We find that upwelling was generally strong during the Little Ice Age (LIA) and weak during the Medieval Warm Period (MWP) and the Roman Warm Period (RWP). Upwelling is significantly anti-correlated to East Asian summer monsoonal rainfall and the zonal equatorial Pacific temperature gradient. We suggest that changes in the background state of the tropical Pacific may have substantially contributed to the centennial-scale upwelling trends observed in our records. Our results implicate the prevalence of an El Niño-like mean state during the LIA and a La Niña-like mean state during the MWP and the RWP.

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.

Air temperatures in Eismitte and during Wegeners sledging

Einer kalten Bodenschicht entspricht eine niedrige Temperatur der freien Atmosphäre. Eine Kälteperiode an der Oberfläche wie die von Ende Oktober bis Mitte November 1930 wird also wahrscheinlich Hand in Hand gegangen sein mit einer niedrigen Temperatur im größten Teil der grönländischen Troposphäre, und die Ansammlung solcher hochreichender Kaltluft im Raum von Grönland kann zu kräftigen Ausbrüchen kalter Luft von dort führen. Die neueren Expeditionen, die die Pläne Alfred Wegeners zur Erforschung des Inlandeises und seiner Atmosphäre weitergeführt haben, beantworten uns also die Fragen, zu deren Lösung Alfred Wegener vor einem Vierteljahrhundert sein Leben geopfert hat.

Calculated sea surface temperatures of two sediment cores

The reconstruction of ocean history employs a large variety of methods with origins in the biological, chemical, and physical sciences, and uses modern statistical techniques for the interpretation of extensive and complex data sets. Various sediment properties deliver useful information for reconstructing environmental parameters. Those properties that have a close relationship to environmental parameters are called ''proxy variables'' (''proxies'' for short). Proxies are measurable descriptors for desired (but unobservable) variables. Surface water temperature is probably the most important parameter for describing the conditions of past oceans and is crucial for climate modelling. Proxies for temperature are: abundance of microfossils dwelling in surface waters, oxygen isotope composition of planktic foraminifers, the ratio of magnesium or strontium to calcium in calcareous shells or the ratio of certain organic molecules (e.g. alkenones produced by coccolithophorids). Surface water salinity, which is important in modelling of ocean circulation, is much more difficult to reconstruct. At present there is no established method for a direct determination of this parameter. Measurements associated with the paleochemistry of bottom waters to reconstruct bottom water age and flow are made on benthic foraminifers, ostracodes, and deep-sea corals. Important geochemical tracers are d13C and Cd/Ca ratios. When using benthic foraminifers, knowledge of the sediment depth habitat of species is crucial. Reconstructions of productivity patterns are of great interest because of important links to current patterns, mixing of water masses, wind, the global carbon cycle, and biogeography. Productivity is reflected in the flux of carbon into the sediment. There are a number of fluxes other than those of organic carbon that can be useful in assessing productivity fluctuations. Among others, carbonate and opal flux have been used, as well as particulate barite. Furthermore, microfossil assemblages contain clues to the intensity of production as some species occur preferentially in high-productivity regions while others avoid these. One marker for the fertility of sub-surface waters (that is, nutrient availability) is the carbon isotope ratio within that water (13C/12C, expressed as d13C). Carbon isotope ratios in today's ocean are negatively correlated with nitrate and phosphate contents. Another tracer of phosphate content in ocean waters is the Cd/Ca ratio. The correlation between this ratio and phosphate concentrations is quite well documented. A rather new development to obtain clues on ocean fertility (nitrate utilization) is the analysis of the 15N/14N ratio in organic matter. The fractionation dynamics are analogous to those of carbon isotopes. These various ratios are captured within the organisms growing within the tagged water. A number of reconstructions of the partial pressure of CO2 have been attempted using d13C differences between planktic and benthic foraminifers and d13C values of bulk organic material or individual organic components. To define the carbon system in sea water, two elements of the system have to be known in addition to temperature. These can be any combination of total CO2 , alkalinity, or pH. To reconstruct pH, the boron isotope composition of carbonates has been used. Ba patterns have been used to infer the distribution of alkalinity in past oceans. Information relating to atmospheric circulationand climate is transported to the ocean by wind or rivers, in the form of minerals or as plant andanimal remains. The most useful tracers in this respect are silt-sized particles and pollen.