NO A A PROFESSIONAL PAPER U 



The large dinoflagellate, Ceratium tripos, dominated 

 the total particulate organic carbon loading in 1976. The 

 1976 population growth was a biochemical phenomenon 

 of great significance, which, at least in 1976, exhibited a 

 much larger annual fluctuation than nutrient and carbon 

 loadings. Significantly, initial development of the C tripos 

 bloom "involved processes operative on spatial scales on 

 the order of the continental shelf and time scales on the 

 order of months to years" (ch. 9, pi. 1). The initial causes 

 of this bloom are unknown, but the bloom apparently 

 originated around January 1976 throughout the entire 

 Bight and beyond (ch. 9, pt. 1). Thus, at least initially, 

 the buildup of the C. tripos population may have been 

 responding to the same atmospheric and oceanic factors 

 leading to prolonged, intense stratification and reduced 

 flushing in summer 1976. These physical factors need not 

 have been strikingly exceptional to trigger the substantial 

 bloom of C tripos. 



The later aggregation (during April through June) of 

 very dense C. tripos accumulations near the base of the 

 pycnocline off New Jersey may be explained in physical 

 terms and as biochemical processes, both of which may 

 have contributed. The evidence for and against physical 

 aggregation by two-layered thermohaline circulation is 

 summarized by Malone (ch. 9, pt. 1) and Mayer et al. 

 (ch. 7). Five stations located from 50 to IIU km off New 

 Jersey indicate an average westward current component 

 of 34 km/mo. (1.3 cm/s) from April through June 1976. 

 This amount of westward displacement beneath the pyc- 

 nocline contributed to the observed C. tripos aggregation. 



Possibly the inshore increase of Ceratium numbers also 

 resulted in part from faster reproductive rates beneath the 

 higher concentrations of particulate organic carbon in in- 

 shore waters. Some species of Ceratium are known to 

 assimilate particulate material, and there is evidence that 

 C. tripos also has this mode of nutrition (ch. 10). Most of 

 the C. tripos population within 20 km of New Jersey was 

 at depths where light was inadequate to maintain the pop- 

 ulation photosynthetically. The population increase in 

 April through June in this region may have been partially 

 due to faster growth rates than were possible offshore, 

 because of the more concentrated organic particulates in- 

 shore. Although both the physical and biochemical hy- 

 potheses for the exceptional C. tripos buildup are plau- 

 sible, there is no evidence as to their relative significance. 



Assuming no photosynthesis below the pycnocline, the 

 respiration of Ceratium would have utilized very signifi- 

 cant quantities of water column oxygen (ch. 9, pt. 1). The 

 quantity respired by C. tripos was estimated at 0.37 ml 

 Oi/l/d in the Apex and coastal waters of New Jersey. This 

 is about 12 times the rate of oxygen uptake by benthic 

 respiration estimated by Thomas et al. (1976), and more 

 than twice the rate of estimated oxygen usage in the Apex 

 and New Jersey coastal waters from May 18 to June 29, 

 1976 (ch. 8). In addition to the respiration of C. tripos. 



the decay of this population must have placed a substantial 

 demand on oxygen beneath the pycnocline. Oxidation of 

 the C. tripos biomass over 60 days was estimated to require 

 0.16 ml 0;/l/d (ch. 16), the same as the rate of oxygen 

 usage beneath the pycnocline estimated by Han et al. (ch. 

 8). Dead C. tripos cells are large enough to sink very 

 rapidly and were not completely oxidized within the water 

 column, but the remaining detritus apparently decayed 

 rapidly on the sediment surface (ch. 10). 



The remainder of the particulate organic carbon (POC) — 

 apart from C. tripos — also contributed to oxygen deple- 

 tion in 1976 and in each summer/autumn season. Malone 

 (ch. 9, pt. 1) indicates that C. tripos accounted for 64 

 percent of the POC by April 1976 and that the rest of the 

 phytoplankton bloom was apparently typical of that ob- 

 served in previous years. 



The average input rate of POC to the bottom layer has 

 not been estimated; however, the average sinking rate of 

 nannoplankton in the Bight is within the range of to 2 

 m/d (Malone and Chervin 1979). The typical summer load- 

 ing of POC to bottom waters is very sensitive to the actual 

 average sinking rate of POC exclusive of C. tripos. If these 

 particles, at an average summer concentration of 1.1 g C/ 

 m' (ch. 9, pt. 1) sink 1 m/d, then 66 g C/m^ would be 

 introduced through the pycnocline during the 60-day pe- 

 riod used in the above calculations. Oxidation of this POC 

 alone would require 5.4 ml OJl/d or more than 30 times 

 the oxygen utilization rate estimated by Han et al. (ch. 

 8). There are, almost certainly, several spatial and tem- 

 poral discontinuities in any particular summer/autumn 

 season that cause departures from this calculation. For 

 instance, POC tends to accumulate at the pycnocline and 

 is perhaps thereupon grazed intensively; not all the po- 

 tential BOD represented in POC beneath the pycnocline 

 is oxidized before being eaten or flushed from the region 

 of oxygen depletion. Additional complicating factors 

 could be postulated, most of which would tend to minimize 

 the actual oxygen demand of the POC. If these factors are 

 not too influential, POC exclusive of C. tripos cannot be 

 dismissed as an insignificant BOD loading. This is true 

 even if much slower sinking rates are presumed. 



If the average POC sinking rate (excluding Ceratium) 

 is 0.1 m/d, the resulting BOD would still require more 

 than three times the estimate of oxygen used — an amount 

 equal to that attributed to C. tripos respiration and decay 

 by Malone (ch. 9, pt. 1). Even assuming no replenishment 

 of this residual POC in bottom waters, the quantities nor- 

 mally present would require more than half the estimated 

 oxygen consumed, and 17 percent of that attributed to C. 

 tripos. Despite the very imprecise knowledge of POC re- 

 plenishment rates and its actual fates beneath the pyc- 

 nocline, the subpycnocline oxygen demand of nanno- 

 plankton and detritus would seem to be of the order 

 contributed by C. tripos in 1976, and perhaps more. 



Oxidation of dissolved organic matter may also be very 



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