Spatial and seasonal evolution of dissolved oxygen and nutrients in the Southern Levantine Basin (Eastern Mediterranean Sea): chemical characterization of the water masses and inferences on the N : P ratios |
| |
| Institution: | 1. Department of Geography, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK;2. Department of Geography and Sustainable Development, School of Geography and Geosciences, University of St Andrews, St Andrews, KY16 9AL, UK;3. School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK;4. Parlamentsstraße 32, D-60385 Frankfurt, Germany;5. Paleoenvironmental Dynamics Group, Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234, D-69120, Heidelberg, Germany;6. Biodiversity and Climate Research Center (BiK-F), Senckenberganlage 25, D-60325 Frankfurt, Germany;7. Environmental Change Research Centre, Department of Geography, University College London, London, WC1E 6BT, UK;1. Department of Marine and Coastal Sciences, and Department of Earth and Planetary Sciences, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901, USA;2. Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA;3. Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI 02912, USA;4. School for Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, MA 02747, USA;1. Department of Earth Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa;2. Department of Geosciences, National Taiwan University, Taipei 106, Taiwan;3. Department of Oceanography, University of Cape Town, Rondebosch 7700, South Africa;4. Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany;5. Bermuda Institute of Ocean Sciences, St.George''s GE 01, Bermuda;6. Department of Earth System Science, University of California, Irvine, CA 92697, USA;7. Department of Geosciences, Princeton University, Princeton, NJ 08544, USA;1. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS, Sgonico, TS, Italy;2. Abdus Salam International Center for Theoretical Physics - ICTP, Trieste, Italy;3. Università degli Studi di Venezia Ca’ Foscari, Venezia, Italy;4. Centre for Marine Research and Experimentation – CMRE, La Spezia, Italy |
| |
| Abstract: | The spatial and seasonal variability of nutrients and dissolved oxygen concentrations as well as the chemical characterization of the different water masses of the Southern Levantine Basin were determined in detail. In summer, the upper 150 m of the water body was stratified and the cross basin distribution of dissolved oxygen and nutrients was fairly constant. Surficial waters were saturated with dissolved oxygen, and a shallow oxygen maximum (oversaturated) was present at about 80 m depth. Oversaturation was attributed mainly to the physical process of rapid capping and trapping of oxygen in the Atlantic water (AW) mass, with only 28% of the excess oxygen originating from biological production. Nutrient concentrations were very low and showed an increase in the intermediate levels, coupled with a decrease in oxygen. The winter cross-section distribution showed an upper mixed layer of 100 m, with dissolved oxygen and nutrient concentrations fairly constant across the basin. The concentration of nitrate was higher than in summer, while phosphate was slightly lower and silicic acid similar. In winter, the influence of the physical features (gyres) could be detected up to the surface, and in summer they were detected by the chemical properties in the 150–600 m layer. In the transition layer between the Levantine intermediate water (LIW) and the deep water (DW) (400–700 m) there was a gradual decrease in dissolved oxygen and an increase in nutrient concentrations eastwards. The DW showed no seasonal variation, only spatial variability: dissolved oxygen decreased and silicic acid increased eastwards. No differences were found in nitrate and phosphate concentrations between the DW in the western and eastern provinces, indicating the oxidation of organic matter poor in N and P.N : P ratios in the upper water masses were seasonally dependent. The largest variation was found in the Levantine surface water (LSW), from an average of 52 in winter to 5 in summer. It is hypothesized that the gradual decrease from winter to summer values was due mainly to preferential atmospheric input of N in winter and P in summer, together with biological consumption and differential regeneration of N and P. In the DW, the N : P ratios were constant throughout the year (25.2±2.7, n=567), and higher than Redfield's ratio. It was speculated that the high N : P ratio in the DW was a result of oxidation of particulate organic matter deficient in P.The winter wet atmospheric input of N provided 12% of new N to the LSW. Average new production for the Southern Levantine Basin was estimated from the new N as 4.75 g C m?2 yr?1. The dry atmospheric contribution of P was estimated to significantly increase the P pool in the LSW. Dry deposition is not evenly distributed and occurs in episodic and localized events, which may have a large effect on productivity in the short periods when deposition occurs.There have been recently reported changes in the deep thermohaline circulation of the Eastern Mediterranean, with main contribution of the Aegean Sea as a source of DW. The data presented here can serve as a reference for assessing future changes in the chemical composition of the water masses in the Southern Levantine. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
