Strontium measurements and sea surface temperatures of corals from Xisha Island, South China Sea

A Porites coral collected from Xisha Island, South China Sea, represents a skeleton secreted in the period from 1906 to 1994. The Sr contents of the coral vary linearly with the instrument-measured sea-surface temperature (SST), giving a Sr thermometer: SST = -1.9658 x Sr + 193.26. The reconstructed SST data show that the late 20th century was warmer (about 1°C) than the early 20th century and that two cooling (1915/1916 and 1947/1948) and three warming (1935/1936, 1960/1961, and 1976/1977) shifts occurred in the century. The temperature shifts are more pronounced for winters, implying a close effect of the west Pacific warm pool and Asian monsoon and suggesting that the former is a primary force controlling the climatic system of the region. Results of this study and previously published data indicate a close link of temperature shifts between the boreal summer and the austral winter or the boreal winter and the austral summer. The annual SST anomalies in the South China Sea and the South Pacific reveal the existence of harmonic but opposite SST variations between the two regions. On the decadal scale the comparative annual SST anomalies for the South China Sea and for the equatorial west Pacific show a similarity in temperature variations, implying that the South China Sea climate is coherent with climatic regime of the tropical west Pacific.

Methane measurements during POLARSTERN cruise ARK-XXII/2

A methane surplus relative to the atmospheric equilibrium is a frequently observed feature of ocean surface water. Despite the common fact that biological processes are responsible for its origin, the formation of methane in aerobic surface water is still poorly understood. We report on methane production in the central Arctic Ocean, which was exclusively detected in Pacific derived water but not nearby in Atlantic derived water. The two water masses are distinguished by their different nitrate to phosphate ratios. We show that methane production occurs if nitrate is depleted but phosphate is available as a P source. Apparently the low N:P ratio enhances the ability of bacteria to compete for phosphate while the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) is utilized as a C source. This was verified by experimentally induced methane production in DMSP spiked Arctic sea water. Accordingly we propose that methylated compounds may serve as precursors for methane and thermodynamic calculations show that methylotrophic methanogenesis can provide energy in aerobic environments.