Low-nitrate, high-chlorophyll

Over 20% of the world s open ocean surface waters are replete in light and major nutrients (nitrate, phosphate, and silicate), yet chlorophyll and productivity values remain low. These so-called "high-nitrate low-chlorophyll" or HNLC regimes (Chisholm and Morel, 1991) include the sub-arctic North Pacific (Martin and Fitzwater, 1988 Martin et al, 1989 Miller et al, 1991), the equatorial Pacific (Murray et al, 1994 Fitzwater et al, 1996) and the southern Ocean (Martin et al.,... 

Figure 4 The major high nitrate, low chlorophyll (HNLC) regions of the ocean. The...

Three major oceanic regions (20 % of the world s open ocean) are characterized by high-nitrate and low-chlorophyll (HNLC) concentrations. The PP of the Southern Ocean (Broecker et al., 1982), the equatorial Pacific (Chavez and Barber 1987) and the Gulf of Alaska (McAllister et al. 1960) are obviously not limited by nitrate. Alternatively, as atmospheric dust loads in the Antarctic and equatorial Pacific are the lowest in the world (Prospero 1981 Uematsu et al. 1983) the importance of iron as limiting micronutrient for PP became increasingly discussed. 

Figure 16.4 Map of the North Padfic Ocean basin showing several important features of the trades biome. (A) Dynamic topography of the sea surface in dyn-cm relative to 1000 dbar based on historical hydrographic observations. Arrows show the direction of geostrophic flow. From Wyrtki (1975). (B) Sea surface distributions of chlorophyll (mg m for the Pacific Ocean in 2003 from 15°S to 65°N latitude as derived from the AQUA MODIS satellite-based sensor system (4 km resolution). Superimposed on ocean color, in white contour lines, is the mean annual surface nitrate concentration (mmol NO m ) based on the World Ocean Atlas (2001) Ocean Climate Laboratory/NODC. Areas of high NOs (and presumably NOs flux) correspond to areas that are enriched in chlorophyll as a result of net plant growth. The North Pacific trades biome is the central region of low standing stocks of plants (<0.1 mg m blue-purple areas) and low ambient NOT concentrations (<1 mmol m ).

IronEx Iron Enrichment Experiment LIDAR Light detection and ranging LNHC Low-nitrate high-chlorophyll... 

Zero or near-zero nitrate concentrations and very low phosphate concentrations have been measured in summer in the subtropical gyres of all the major oceans and in the equatorial Atlantic and Indian Oceans, implying widespread N limitation of new production [156,188]. Other parts of the ocean, such as the North Atlantic above 50°N, the Arabian Sea, and various coastal upwelling regions, have elevated nutrient concentrations (>2 pM NO ) but also support high chlorophyll concentrations (>0.5 mg m ). In contrast to both the highly productive and the nutrient depleted ocean regions mentioned earlier, some 20-40% of the... 

The biochemical mechanisms of Cd toxicity in phytoplankton are in some respects similar to those in higher plants (see Chapter 13). One of the well-known effects is that Cd can compete with essential metals for uptake sites on the cell surface. High concentration of Cd inhibits the uptake of Mn and thus causes Mn deficiency in cells at low Mn concentrations [47 9]. Similarly, Cd also inhibits Fe uptake and assimilation and thus causes Fe deficiency, as evidenced by decreases in cytochrome / to chlorophyll a ratio and nitrate reductase activity... 

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