Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific, POLARSTERN cruise ANT-XXVI/2

Since the inception of the international GEOTRACES program, studies investigating the distribution of trace elements and their isotopes in the global ocean have significantly increased. In spite of this large-scale effort, the distribution of neodymium isotopes (143Nd/144Nd) and concentrations ([Nd]) in the high latitude south Pacific is still understudied. Here we report dissolved Nd isotopes and concentrations from 11 vertical water column profiles from the south Pacific between South America and New Zealand. Results suggest that Ross Sea Bottom Water (RSBW) is represented by an epsilon-Nd value of ~ -7, and is thus more radiogenic than Circumpolar Deep Water (epsilon-Nd ~ -8). RSBW and its characteristic epsilon-Nd signature can be traced far into the SE Pacific until progressive mixing with ambient Lower Circumpolar Deep water (LCDW) dilutes this signal north of the Antarctic Polar Front (APF). The SW-NE trending Pacific-Antarctic Ridge restricts the advection of RSBW into the SW Pacific, where bottom water density, salinity, and epsilon-Nd values of -9 indicate the presence of bottom waters of an origin different from the Ross Sea. Neodymium concentrations show low surface concentrations and a linear increase with depth north of the Polar Front. South of the APF, surface [Nd] is high and increases with depth but remains almost constant below ~1000 m. This vertical and spatial [Nd] pattern follows the southward shoaling density surfaces of the Southern Ocean frontal system and hence suggests supply of Nd to the upper ocean through upwelling of Nd-rich deep water. Low particle abundance dominated by reduced opal production and seasonal sea ice cover likely contributes to the maintenance of the high upper ocean [Nd] south of the APF. The reported data highlights the use of Nd isotopes as a water mass tracer in the Southern Ocean, with the potential for paleocenaographic reconstructions, and contributes to an improved understanding of Nd biogeochemistry.

Physical oceanography during Nathaniel B. Palmer cruises NBP06-01 and NBP06-08 to the Ross Sea

We calculate net community production (NCP) during summer 2005-2006 and spring 2006 in the Ross Sea using multiple approaches to determine the magnitude and consistency of rates. Water column carbon and nutrient inventories and surface ocean O2/Ar data are compared to satellite-derived primary productivity (PP) estimates and 14C uptake experiments. In spring, NCP was related to stratification proximal to upper ocean fronts. In summer, the most intense C drawdown was in shallow mixed layers affected by ice melt; depth-integrated C drawdown, however, increased with mixing depth. Delta O2/Ar-based methods, relying on gas exchange reconstructions, underestimate NCP due to seasonal variations in surface Delta O2/Ar and NCP rates. Mixed layer Delta O2/Ar requires approximately 60 days to reach steady state, starting from early spring. Additionally, cold temperatures prolong the sensitivity of gas exchange reconstructions to past NCP variability. Complex vertical structure, in addition to the seasonal cycle, affects interpretations of surface-based observations, including those made from satellites. During both spring and summer, substantial fractions of NCP were below the mixed layer. Satellite-derived estimates tended to overestimate PP relative to 14C-based estimates, most severely in locations of stronger upper water column stratification. Biases notwithstanding, NCP-PP comparisons indicated that community respiration was of similar magnitude to NCP. We observed that a substantial portion of NCP remained as suspended particulate matter in the upper water column, demonstrating a lag between production and export. Resolving the dynamic physical processes that structure variance in NCP and its fate will enhance the understanding of the carbon cycling in highly productive Antarctic environments.

Benthic freshwater diatom abundance in streams and seepage areas of northern James Ross Island between 2004-2009

Background and aim - The non-marine diatom communities in the Antarctic Region are characterized by a typical species composition, in close relationship with their environment. Despite the growing interest, the diatom flora of James Ross Island is only poorly known. The present paper discusses the diversity of limnoterrestrial diatoms on this island: seepages and streams. Methods - The diatom flora of 53 samples taken on the eastern side of the Ulu peninsula on James Ross Island has been studied using light and scanning electron microscopy. Key results - A total of 69 diatom taxa belonging to 26 genera have been observed. The genera Luticola, Diadesmis, Muelleria and Pinnularia dominated the species composition. The flora shows an interesting mixture of cosmopolitan and Antarctic species containing several species reaching on James Ross Island their most northern distribution in the Antarctic Region. The taxonomical position of one widespread Antarctic species, Psammothidium papilio (D.E.Kellogg, Stuiver, T.B.Kellogg & Denton) Kopalova & Van de Vijver comb. nov., is corrected. Conclusions - The limnoterrestrial diatom flora of James Ross Island has a rather low number of species, of which a large proportion shows a restricted Antarctic distribution.