Primary productivity oceans

Passive satellite measurements of reflected intensity at visible wavelengths allow mapping of ocean color. Ocean color is dominated by the amount of chlorophyll and phaeopigments present, which in turn can be related to primary productivity. Ocean color is also an important indicator of the presence or absence of nutrients and various physical oceanographic phenomena. 

Comparison with other Studies. How do the results of our investigation compare with similar studies Our results corroborate the data provided in a similar study of the effect of UV-B on primary productivity in the southeastern Pacific Ocean (35). In the latter study, it was noted that enhanced UV-B radiation caused significant decreases in the productivity of surface and deep samples. Compared to ambient, primary productivity decreased with increasing doses of UV-B. In another study in which in situ experiments using natural Antarctic phytoplankton populations, it was noted that incident solar radiation significantly depressed photosynthetic rates in the upper 10-15 meters of the water column (36). It was also found that the spectral region between 305 and 350 nm was responsible for approximately 75 percent of the overall inhibitory effect. 

The quantity of primary production that is exported from the upper ocean is said to be equivalent to new production (18, 19) New primary production is that associated with allocthonous nutrients (i.e., those upwelled or mixed into the euphotic zone or input via rivers and rain). In order for steady state to be maintained, an equivalent flux out of the euphotic zone is required. Earlier studies (19) suggested that sediment-trap measurements of particulate organic carbon (POC) flux were equivalent to new primary production however, recently it has become clear that these measurements probably represent only a... 

Fig. 10-14 Approximate geographical distibution of primary productivity in the oceans (g C/m per year).

Sediment trap studies in the open ocean show that the flux of organic carbon at any depth is directly proportional to the rate of primary productivity in the surface water and inversely proportional to the depth of the water column (Suess, 1980) ... 

Fig. 10-15 Organic carbon fluxes with depth in the water column normalized to mean annual primary production rates at the sites of sediment trap deployment. The undulating line indicates the base of the euphotic zone the horizontal error bars reflect variations in mean annual productivity as well as replicate flux measurements during the same season or over several seasons vertical error bars are depth ranges of several sediment trap deployments and uncertainities in the exact depth location. (Reproduced with permission from E. Suess (1980). Particulate organic carbon flux in the oceans - surface productivity and oxygen utilization, Nature 288 260-263, Macmillan Magazines.)...

This discussion suggests a rapid and relatively direct transport of organic material vertically through the ocean water column. However, this transport is not efficient and under "average" ocean conditions (primary productivity = 100 g C/m per year and water... 

Oceanic surface waters are efficiently stripped of nutrients by phytoplankton. If phytoplankton biomass was not reconverted into simple dissolved nutrients, the entire marine water column would be depleted in nutrients and growth would stop. But as we saw from the carbon balance presented earlier, more than 90% of the primary productivity is released back to the water column as a reverse RKR equation. This reverse reaction is called remineralization and is due to respiration. An important point is that while production via photosynthesis can only occur in surface waters, the remineralization by heterotrophic organisms can occur over the entire water column and in the underlying sediments. 

Falkowski, P. G., Barber, R. T. and Smetacek, V. (1998). Biogeochemical controls and feedbacks on ocean primary production. Science 281, 200-206. 

Field, C. B., Behrenfeld, M. J., Randerson, J. T. and Falkowski, P. (1998). Primary production of the biosphere Integrating terrestrial and oceanic components. Science 281,237-240. 

Platt, T. and Sathyendranth, S. (1988). Oceanic primary production Estimation by remote sensing at local and regional scales. Science 241,1613-1620. 

The subsequent fate of the assimilated carbon depends on which biomass constituent the atom enters. Leaves, twigs, and the like enter litterfall, and decompose and recycle the carbon to the atmosphere within a few years, whereas carbon in stemwood has a turnover time counted in decades. In a steady-state ecosystem the net primary production is balanced by the total heterotrophic respiration plus other outputs. Non-respiratory outputs to be considered are fires and transport of organic material to the oceans. Fires mobilize about 5 Pg C/yr (Baes et ai, 1976 Crutzen and Andreae, 1990), most of which is converted to CO2. Since bacterial het-erotrophs are unable to oxidize elemental carbon, the production rate of pyroligneous graphite, a product of incomplete combustion (like forest fires), is an interesting quantity to assess. The inability of the biota to degrade elemental carbon puts carbon into a reservoir that is effectively isolated from the atmosphere and oceans. Seiler and Crutzen (1980) estimate the production rate of graphite to be 1 Pg C/yr. 

The two prime mechanisms of carbon transport within the ocean are downward biogenic detrital rain from the photic zone to the deeper oceans and advection by ocean currents of dissolved carbon species. The detrital rain creates inhomogeneities of nutrients illustrated by the characteristic alkalinity profiles (Fig. 11-9). The amount of carbon leaving the photic zone as sinking particles should not be interpreted as the net primary production of the surface oceans since most of the organic carbon is recycled... 

As reactive P is transported through the terrestrial system, it is assimilated into plants and subsequently into the rest of the biosphere (2). Although many elements are required for plant life, in many ecosystems P is the least available and, therefore, limits overall primary production (Schindler, 1977 Smith et al., 1986). Thus, in many instances the availability of P influences or controls the cycling of other bioactive elements. When organisms die, the organic P compounds decompose and the P is released back into the soil-water system. This cycle of uptake and release may be repeated numerous times as P makes its way to the oceans. 

The present average PO4 concentration of deep ocean water is 2.2 /rmol/kg. When a parcel of deep water is transported to the photic zone, this POi is completely incorporated into plants. Note that this assumes that net primary productivity is not limited by the availability of other micronutrients. In shortterm laboratory studies, this assumption is clearly not true in that it has been demonstrated... 

Van Cappellen, P. and Ingall, E. D. (1994). Benthic phosphorus regeneration, net primary production, and ocean anoxia A model of the coupled marine biogeochemical cycles of carbon and phosphoms. Paleoceanography 9,677-692. 

Antoine, D., Andre, J.-M., and Morel, A. (1996). Oceanic primary production, 2. Estimation at global scale from satellite (coastal zone color scanner) chlorophyll. Global Biogeochem. Cycles 10, 57-70. 

Sarntheim, M., Winn, K., Duplessey, J.-C. and Fontugne, M.R. 1988 Global variations of surface ocean primary productivity in low and mid latitudes influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years. Paleoceanography 3 361-399. 

The fluxes of POC determined by the " Th method applied to the world s oceans are summarized in Table 1. Where possible we have tabulated the ratio of Th-derived POC export to independent estimates of primary production. As noted above, this ratio, termed the 77i ratio (Buesseler 1998), is important in the euphotic zone carbon balance as it represents the leakage of POC out of the euphotic zone (The ThE ratio is so named to evoke the e ratio, which is defined as the ratio of POC flux measured with sediment traps to primary production). 

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