Phosphorus limitation of primary productivity in the eastern Mediterranean Sea

Abstract

Although NO,--is generally considered to limit primary productivity in most of the world's oceans, previous studies have suggested the Mediterranean Sea may be an exception. In this study of the southeastern Mediterranean, we found that all the POd3-was removed from the upper water column during the winter phytoplankton bloom in the core and boundary of a warm-core eddy, while measurable (0.3-0.6 PM) NO,-remained. The N: P (N0,-:P0,3-) ratio in the core and boundary of the Cyprus eddy was 27.4 and the slope of the linear portion of the N vs. P scattergram was 25.5 with a positive intercept of 0.5 PM on the NO,-axis. A similar N : P ratio (28-29), slope (21-23), and intercept (0.9-l. 1) was found for the water column across much of the southern Levantine basin. These data, taken together with the results of incubation experiments, lead us to conclude that the southeastern Mediterranean is strongly P limited. The degree of P limitation increases from west to east across the entire basin. We suggest that removal of PO,'-by adsorbtion on Fe-rich dust particles may bc an important process controlling the concentration of P in the water column.N03-is generally considered to be the master chemical variable limiting primary productivity throughout much of the ocean (Codispoti 1989). It is based principally on considerations of the N : P ratios of upwelling waters which are generally < 16 : 1 I At present: Department of Earth Science, Leeds University, Leeds L52 9JT, U.K. AcknowledgmentsThe chemical determinations of dissolved nutrients were carried out by L. Israilov. We thank U. Fiedler for technical help on-board ship; we also thank members of the Physics and Electronic department of IOLR. The data collected in September 1989 were sampled as part of a Group for Aquatic Productivity (GAP) cruise to the eddy organized by T. Berman. We thank the captain (A. Ben-Nun) and crew of the RV Shikmona. This manuscript was written while M.D.K. was on sabbatical leave at the University of Rhode Island. We thank M. E. Q. Pilson and D. Kester for the use of their facilities and for the many discussions which went into the preparation of this manuscript. We thank M. Wood for pointing out the importance of P limitation in this area and for critical reading of the manuscript by her and T. Berman. Finally we greatly appreciate the detailed comments of two reviewers, who helped us improve the quality of the final version of this manuscript.

The N:Si:P molar ratio in the Strait of Gibraltar

“…The Atlantic water entering the Mediterranean Sea is already depleted of nutrients, especially phosphate, with N:Si:P ratios similar to the deep waters of the Eastern and Western Basins. These observations are in disagreement with the conclusion by Krom et al [1991] that states that the degree of phosphorus limitation in the Mediterranean Sea increases from west to east across the entire basin. The result presented here implies that the role of the Atlantic water in the nutrient balance of the Mediterranean Sea should be reconsidered.…”

Episodic meteorological and nutrient-load events as drivers of coastal planktonic ecosystem dynamics: a time-series analysis

“…All this additional information backs the idea of a general P deficiency, which is the usual situation in the Mediterranean (e.g. Krom et al 1991), even though common criteria for limitation (Justic et al 1995) did not show a dominant limiting nutrient.…”

“…All this additional information backs the idea of a general P deficiency, which is the usual situation in the Mediterranean (e.g. Krom et al 1991), even though common criteria for limitation (Justic et al 1995) did not show a dominant limiting nutrient.An unexpected result of the present study is the strong negative relationship between total diatom biomass and Si:N ratios (r s = -0.94, p < 0.001, n = 13). This is puzzling, because there is no significant relationship with silicate or nitrogen ( Table 1).…”

Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades

“…The tendency for lower storage of P in estuarine sediments relative to freshwater sediments is probably the result of higher sulfate concentrations, leading to higher sulfate reduction rates and more sequestration of iron by sulfides. Iron sulfides are less adsorptive of phosphate than are other iron minerals (Krom and Berner 1980). Although estuarine sediments in general are less likely to adsorb and immobilize P than are lake sediments (Caraco et al 1990;Blomqvist et al 2004), the importance of this process is variable among estuaries (Sundby et al 1992;Howarth et al 1995).…”