Back مناطق غنية بالمغذيات فقيرة بالكلوروفيل Arabic Regions HNLC Catalan HNLC German Paradoja antártica Spanish HNLC HE Paradosso antartico Italian HNLC海域 Japanese ANBC Portuguese
High-nutrient, low-chlorophyll (HNLC) regions are regions of the ocean where the abundance of phytoplankton is low and fairly constant despite the availability of macronutrients. Phytoplankton rely on a suite of nutrients for cellular function. Macronutrients (e.g., nitrate, phosphate, silicic acid) are generally available in higher quantities in surface ocean waters, and are the typical components of common garden fertilizers. Micronutrients (e.g., iron, zinc, cobalt) are generally available in lower quantities and include trace metals. Macronutrients are typically available in millimolar concentrations, while micronutrients are generally available in micro- to nanomolar concentrations. In general, nitrogen tends to be a limiting ocean nutrient, but in HNLC regions it is never significantly depleted.[1][2] Instead, these regions tend to be limited by low concentrations of metabolizable iron.[1] Iron is a critical phytoplankton micronutrient necessary for enzyme catalysis and electron transport.[3][4]
Between the 1930s and '80s, it was hypothesized that iron is a limiting ocean micronutrient, but there were not sufficient methods reliably to detect iron in seawater to confirm this hypothesis.[5] In 1989, high concentrations of iron-rich sediments in nearshore coastal waters off the Gulf of Alaska were detected.[6] However, offshore waters had lower iron concentrations and lower productivity despite macronutrient availability for phytoplankton growth.[6] This pattern was observed in other oceanic regions and led to the naming of three major HNLC zones: the North Pacific Ocean, the Equatorial Pacific Ocean, and the Southern Ocean.[1][2]
The discovery of HNLC regions has fostered scientific debate about the ethics and efficacy of iron fertilization experiments which attempt to draw down atmospheric carbon dioxide by stimulating surface-level photosynthesis. It has also led to the development of hypotheses such as grazing control which poses that HNLC regions are formed, in part, from the grazing of phytoplankton (e.g. dinoflagellates, ciliates) by smaller organisms (e.g. protists).
- ^ a b c Lalli, C.M.; Parsons, T.R. (2004) Biological Oceanography: An Introduction (2nd Ed.) Elsevier Butterworth Heinemann, Burlington, MA, p. 55.
- ^ a b Pitchford, J.W.; Brindley, J. (1999). "Iron limitation, grazing pressure and oceanic high-nutrient-low chlorophyll (HNLC) regions". Journal of Plankton Research. 21 (3): 525–547. doi:10.1093/plankt/21.3.525.
- ^ Venables, H., and C. M. Moore (2010), Phytoplankton and light limitation in the Southern Ocean: Learning from high-nutrient, high-chlorophyll areas, J. Geophys. Res., 115, C02015, doi:10.1029/2009JC005361
- ^ Hassler, C. S.; Sinoir, M.; Clementson, L. A.; Butler, E. C. V. (2012). "Exploring the Link between Micronutrients and Phytoplankton in the Southern Ocean during the 2007 Austral Summer". Frontiers in Microbiology. 3: 202. doi:10.3389/fmicb.2012.00202. PMC 3392650. PMID 22787456.
- ^ Martin, John (1992). Primary productivity and biogeochemical cycles in the sea. Springer US. pp. 122–137.
- ^ a b Martin, John; Gordon, Michael; Fitzwater, Steve; Broenkow, William W. (1989). "VERTEX: phytoplankton/iron studies in the Gulf of Alaska". Deep Sea Research Part A: Oceanographic Research Papers. 35 (6): 649–680. Bibcode:1989DSRA...36..649M. doi:10.1016/0198-0149(89)90144-1.