Carbon and nitrogen stable isotope signatures of deep-sea meiofauna follow oceanographical gradients across the Southern Ocean

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 foodweb