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Circulation, biogeochemistry and carbon cycling in ocean margins
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Nutrient cycling in the Eastern Mediterranean Sea: An inland sea which behaves like an ocean gyre
Monday 7th @ 1030-1050, Concert Hall
Michael Krom* , Department of Marine Biology, Haifa University, Israel
Tal Ben-Ezra, Department of Marine Biology, Haifa University, Israel
Anat Tsemel, Department of Marine Biology, Haifa University, Israel
Presenter Email: m.d.krom@leeds.ac.uk |
| The Eastern Mediterranean Sea (EMS) is a unique oceanic ecosystem. Although it is an inland sea with similar external anthropogenic nutrient supply, it behaves like a mid-oceanic gyre with very low primary productivity (PP) and nutrient concentrations, with important lateral supply of inorganic nutrients and ~25% of the PP supported by dissolved organic matter. The major reason for these unusual properties is its unusual anti-estuarine circulation. In addition the entire water column is P starved and previous studies on the pelagic system have shown that it is P limited in winter and switches to N &P limitation in summer. Almost all previous studies of nutrient distribution in the surface waters of the EMS have used frozen unfiltered samples, which have been shown to be unreliable. In this study we present experimental data to determine the sampling and analytical conditions required to obtain valid nutrient data in the ultra-oligotrophic photic zone. Based on these studies, we present the first reliable seasonal (monthly) nutrient data from both the offshore pelagic system and the first reliable data of any kind on the Israeli shelf, a region where the ultra-oligotrophic pelagic waters are modified by interactions from both the adjacent land and by recycling processes in the sediment.
The seasonal results show the nutrient succession related to winter phytoplankton bloom which demonstrate evidence of the phytoplankton succession from diatoms to pico/nanoplankton even in this nutrient starved system. Contrary to previous studies, it was concluded that the coastal system like the pelagic system, is P limited in winter and N&P co-limited in summer; in winter the nitrate in the photic zone was 0.5-1 uM while the phosphate was close to the detection limit of 2 nM, while in summer both nitrate and phosphate were at or below detection limits. The system is P starved with DOP values of ~50 nM which shows little variability implying the DOP is almost entirely refractory. Ammonia levels were generally in the low nanomolar range except for occasional peaks when nitrification was observed in the upper water column. These nutrient results will be used to constrain for the first time, the microbial biogeochemical processes in the photic zone of this ultra-oligotrophic system.
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