Amino acids from ODP Holes 117-722B and 177-724C

Sedimentary d15N records are valuable archives of ocean history but they are often modified during early diagenesis. Here we quantify the effect of early diagenetic enrichment on sedimentary N-isotope composition in order to obtain the pristine signal of reactive N assimilated in the euphotic zone. This is possible by using paired data of d15N and amino acid composition of sediment samples, which can be applied to estimate the degree of organic matter degradation. We determined d15N and amino acid composition in coeval sediments from Ocean Drilling Program (ODP) Hole 772 B in the central Arabian Sea and from Hole 724 C situated on the Oman Margin in the western Arabian Sea coastal upwelling area. The records span the last 130 kyr and include two glacial-interglacial cycles. These new data are used in conjunction with data available for surface sediments that cover a wide range of organic matter degradation states, and with other cores from the northern and eastern Arabian Sea to explore spatial variations in the isotopic signal. In order to reconstruct pristine N values we apply the relationship between organic matter degradation and 15N enrichment in surface sediments to correct the core records for early diagenetic enrichment. Reconstructed d15N values suggest a significant role of N2-fixation during glacial stages. An evaluation of two preservation indices based on amino acid composition (Reactivity Index, RI; Jennerjahn and Ittekkot, 1997; and the Degradation Index, DI; Dauwe et al., 1999) in both recent sediments and core samples suggests that the RI is more suitable than the DI in correcting Arabian Sea d15N records for early diagenetic enrichment.

Amino acids in the interstitial waters from ODP Hole 113-695A

Site 695 lies on the southeast margin of the South Orkney microcontinent on the northern margin of the Weddell Sea, at 62°23.48'S, 43°27.10'W in 1305 m water depth. The inorganic properties of interstitial waters at this site, including sulfate reduction, biogenic methane production, and high concentrations of ammonia and phosphate, imply high microbial activity. However, no clear relationship between amino acid composition and concentration and the type of microbial activity (e.g., sulfate reduction or methane production) can be identified. The THAA (total hydrolyzable amino acids) values range between 2.45 and 17.31 µmol/L, averaging 7.14 µmol/L. The mean concentrations and relative abundance values of acidic, basic, neutral, aromatic, and sulfur-containing amino acids are 1.34 (18%), 1.09 (15%), 3.93 (54%), 0.50 (8%), and 0.02 (0%) µmol/L, respectively. Glycine is the most abundant amino acid residue, with serine, glutamic acid, and ornithine next. The DFAA (dissolved free amino acids) values range from 0.10 to 12.73 µmol/L, averaging 4.07 µmol/L. The acidic, basic, neutral, aromatic, and sulfurcontaining amino acids are on average 0.21, 0.79, 2.56, 0.41, and 0.01 µmol/L, respectively. The relative abundances of acidic, basic, neutral, and aromatic amino acids average 4%, 18%, 58%, and 15%, respectively. Predominance of DFAA over DCAA (dissolved combined amino acids) in interstitial waters of Lithologic Units I and II is contrary to the predominance of DCAA over DFAA in other interstitial waters and seawater. The comparison of amino acid compositions between DCAA and siliceous plankton suggests that the DCAA in interstitial waters originally comes from amino acids derived from siliceous plankton. However, other sources which are much enriched in glutamic acid contribute to the DCAA composition.

Using the critical salinity (Scrit) concept to predict invasion potential of the anemone Diadumene lineata in the Baltic Sea

It is widely assumed that the ability of an introduced species to acclimate to local environmental conditions determines its invasion success. The sea anemone Diadumene lineata is a cosmopolitan invader and shows extreme physiological tolerances. It was recently discovered in Kiel Fjord (Western Baltic Sea), although the brackish conditions in this area are physiologically challenging for most marine organisms. This study investigated salinity tolerance in D. lineata specimens from Kiel Fjord in order to assess potential geographical range expansion of the species in the Baltic Sea. In laboratory growth assays, we quantified biomass change and asexual reproduction rates under various salinity regimes (34: North Sea, 24: Kattegat, 14: Kiel Fjord, 7: Baltic Proper). Furthermore, we used 1H-NMR-based metabolomics to analyse intracellular osmolyte dynamics. Within 4 weeks D. lineata exhibited a 5-fold population growth through asexual reproduction at high salinities (34 and 24). Biomass increase under these conditions was significantly higher (69%) than at a salinity of 14. At a salinity of 7, anemones ceased to reproduce asexually, their biomass decreased and metabolic depression was observed. Five main intracellular osmolytes were identified to be regulated in response to salinity change, with osmolyte depletion at a salinity of 7. We postulate that depletion of intracellular osmolytes defines a critical salinity (Scrit) that determines loss of fitness. Our results indicate that D. lineata has the potential to invade the Kattegat and Skagerrak regions with salinity >10. However, salinities of the Baltic Proper (salinity <8) currently seem to constitute a physiological limit for the species.