ALBERT

Description: Carbon (d13C) and nitrogen (d15N) stable isotope values of deep-sea benthic copepods, nematodes, and sediments were determined along a latitudinal transect covering bathyal and abyssal depths in the Southern Ocean and the Weddell Sea (49�S–70�S). This is the first time geographical patterns in stable isotope composition including d15N are reported for deep-sea meiofauna. In agreement with previous findings on isotopic patterns of sea-surface organic matter, the deep-sea meiofauna d13C values gradually declined with latitude. In the nematodes, d15N values were depleting southwards and followed the known gradients of increasing nitrate concentrations with decreasing d15N values available to primary producers in the surface waters. Differences in productivity, water depth, and degradation state of the organic matter at the seafloor along the transect did not influence the southwards declining trend observed in the stable isotope values of the deep-sea meiofauna. The most depleted 13C values were detected in the communities of Maud Rise. The southernmost Lazarev Sea station was an expected exception to this trend: its long-lasting sea-ice cover and a primary production dominated by 13C-enriched ice algae may have lead to the heavier isotopic signatures that were encountered in the organisms and sediments at 70�S. It is suggested that the bulk of benthic meiofauna mainly feeds on degraded organic matter, a food source that is continuously available throughout the year, because only small differences of sediment d13C and the values for meiofauna were detected. The isotopic composition of consumers such as copepods and nematodes are a combination of geographical conditions and the organisms’ position in the food web. Hence, the comparison of stable isotope values of deep-sea meiofauna over a wide geographical range yields basic information for detailed follow-up studies on Antarctic meiofauna foodwebs

Description: Carbon (δ13C) and nitrogen (δ15N) stable isotope values of deep-sea benthic copepods, nematodes, and sediments were determined along a latitudinal transect covering bathyal and abyssal depths in the Southern Ocean and the Weddell Sea (49° S to 70° S). This is the first time geographically interpretable stable isotope data including δ15N are presented for deep-sea meiofauna. In agreement with previous findings on isotopic patterns of sea-surface organic matter, the deep-sea meiofauna δ13C and δ15N values gradually declined with latitude. The southernmost Lazarev Sea station was an exception to this trend. A long-lasting sea-ice cover and a primary production dominated by 13Cenriched ice algae lead to isotopic signals that were heavier than expected for this latitude. The greatest 13C depletions were found in the communities of Maud Rise. Compared to the Weddell Sea and the Lazarev Sea, this seamount region is first free of ice and thus earlier and longer under influence of the isotopically lighter water column diatoms. The prevailing oceanographic conditions additionally favor an enhanced transportation velocity of surface POM to the seafloor at Maud Rise. Generally small offsets between calculated surface δ13CPOM values and the deep-sea organisms suggested a strong bentho-pelagic coupling. Benthic copepods and nematodes seem to be primary or secondary consumers of planktonic detritus. Meiofauna individual numbers and community composition did not differ distinctly along the transect spanning a distance of 2400 km and covering a range of 3400 m water depth. This observation can be attributed to the overall low and patchy organic C fluxes to the seafloor