Document kZB06ajbNOZEBZ5gxMdoL4JJ

any portion of the Greenland record over the last 700 years. If anything, the simula tion puis the neat minimum farther into the future than would . estimates based strictly on analogies with previous "cy cles." Thus, whereas the exact date of the minimum shown in the extended natural climate curve (Fig. 1) is uncertain, its oc currence in the next decade is probable. The rate of warming beyond the minimum is also open to question. As the CO, effect will dominate, the uncertainty here lies mainly in the estimates of future chemical fuel use and in the magnitude of the warm ing per unit of excess atmospheric CO,. The major point of the argument is that over the past 30 years the warming trend due to CO, has been more than countered by a natural cooling. This compensation cannot long continue both because of the rapid growth of the CO, effect and because the natural cooling will almost certainly soon bottom out. We may be in for a cli matic surprise. The onset of the era of CO,-induced warming may be much more dramatic than in the absence of natural cli matic variations. The agricultural consequences of this ensuing warming arc not obvious (neither are the implications to global sea level). A knowledge of the mean global temperature tells us little about the rainfall patterns in the chief grain-producing regions. There is little doubt, however, that this gradual warming will lead to changes in the pattern of global precipitation. Our efforts to un derstand and eventually to predict these changes must be redoubled. Wai.laceS. Broeckek Lamont-Doherty Geological Observatory and Department of Geological Sciences. Columbia University. Palisades, New York 10964 Jtrfmam awl Nmm 1. W Dantsaartl, S. i. Johnson. H. B. Clauscft, C. C. I.antway, Jr., in Late Cenoxotc Glacial Ages, K. K. furekian, Ed. (Yale Univ. Prett, New Haven. Conn . 197!). p 37; W Danagaard. S. J. Johnsen, H B Clausen, N. Oundetlmp, Medd. Grrnniand 197 (No. 2k I (1973). 2. 5. H. Schneider and W. W. Kellogg. in Chemistry of (he Lower Atmosphere. S. t. Kaaool, Ed. (Ple num, New York, 19/1), p. 203: G. Yamamoto and M Tanaka. J. Atmos. Sci. 29. 1405 (1972k R A. Bryson, Wtatherwist 21, 56 (1966k Climatic Mod ification by Air Pollution, II: The Sahelian Effect (Institute for Environmental Studies. University Qf Wisconsin. Madison. 1973k Science 194, 753 (1974k J. M. Mitcbdl Jr., m Global Effects ofEn vironmental Pollution. S. F. Singer, Ed. (Resdek, Dordrecht, Netherlands, and Sprincer-Verfaf, New York, 1968k in Man s Impact on the Climate, W. H. Matlbewa, W. W. Kellogg, G. D. Robinson, tda. (MIT Press, Cambridge, Mass., 1971k PP 133 and 167; W W. Kellogg and S. H. Schneider, Science 196, 1163 (1974k 3. S I Ruool and S. H. Schneider, Science 173, 139 (1971). 4. S. H. Schneider and R. D. Dennett. Amb4o 4, 65 (1975). 5. S. Manabe and R, T. Wethera Id, J. Atmos. Sci. 14 716(1967). 6. S. Manabe. in Mm's Impact on the Climate, W. H. Matthews. W. W. Kellogg, G. D. Robinson, Eds. (MIT Press, CimbndgtTM&u.. 1971 k p. 239; S. Manabe and R. T. Wetherald, J. Almas. Sci. 32. 3 (1975). 8 AUGUST 1975 7. S. H. Schneider,/ Atmos Sci.. m pre&a. I. C. A. EkdihL, Jr., and C D. Keeling, in Carbon and ihe Biosphere, G. M. Wood well and E. Y. Pc* can. Eds. (Technical Information Center, Office of Information Service*. US. Atomic Energy Com mission. Washington, D.C., 1973k P- 51. 9. W. S Broecker, Y.-H. Li, T.-H. Peng, in Impinge ment of Man on the Oceans, D. W Hood. Ed (Wiley, New York. 1971k p. 287. 10. B. Bolin and E Eriksson, in The Atmosphere and the Sea in Motion. Rossby Memorial Volume, B. Bolin, Ed. (Rockefeller Institute Press, New York. 1959k P 130: L. Machla, in The Changing Chem istry oj the Oceans, proceedings of the 20th Nobel Symposium, D. Dryuen and D Jagner Eds. (Wiley, New York. 1972k P 121; C. D. Keeling, in Chemistry of the Lower Atmosphere, S. \. Rasool, Ed. (Plenum, New York, 1973k chap. 6; L. Mtchta, in Carbon and the Biosphere. G M. Wood* well and E. V. Pecan. Eds. (Tethnical Infor mation Center, Office of Information Service. U.S. Atomic Energy Commission. Washington, D C . 197.5). p 2 I. R. Bacaslow and ( () kcc-lmi? ibid.,p. 86 11. United Nations, World Energy Suppitn .S wim*, (], Papers. Series J (United Nations. New York 1950 1959) 12. J. M. Muchell. And Tone Monograph 'n (UNESCO. Pans. 1963), pp 161 !!<l 13. W. Dansgaard. Tellus 16.436 (1964). 1. Merlix.it and C. Lorius. Recherche fPansi 4 (No ji (1973). 14. S. 3 Johnsen. W Dansgaard. H B Clausen ( t Langway. Jr., Mature (Lond I 235, 429 {t q 7 71 15. Conversations with Steve Schneider of the Nation al Center for Atmospheric Research were %cn helpful in straightening out questions I had with regard to varying estimates of the effects of ( <> and dust. Thu work was supported bv cormiM AT(11 -1 )2185 with the U.S Atomic tnergv i uni mission This is contribution No 224K from the Lamont-Doherly Geological Observatory 10 March 1975; revised 7 May 1975 Chlorinated Hydrocarbon Pollutants and Photosynthesis of Marine Phytoplankton: A Reassessment ^^------- _ Abstract. The chlorinated hydrocarbons DDT andffCB s (polychlorinated btphenyl^j. ubiquitous pollutants of the marine environment, have been oBseTV?tfTo~7eduic the cell division rate of marine phytoplankton, thereby indirectly reducing the total photos vnthelic carbonfixation in treated cultures. The photosynthetic capacity oj each cell was mu affected. Total marine photosynthesis will likely remain undiminished bv these com pounds, although alterations in phytoplankton communities through se/ectise toxicm could affect herbivore populations. Several persistent and ubiquitous chlori nated hydrocarbon pollutants of the ma rine environment, most notably PCB's (polychlorinated biphenyls) and DDT (1,1,1 -trichloro-2,2-bis(^-chlorophenyl)ethane), can reduce the growth rale (J. 2) and have been reported to reduce photosynthe sis (2-4) in some marine phytoplankton cultures. The decrease in carbon fixation observed in treated cultures (2-4). as mea sured by the incorporation of "C-labeled bicarbonate, could have resulted from an inhibition of the photosynthetic process it self, or it may have been due to a depressed growth rate, that is. fewer cells photosynlhesizing in treated than in control cul tures. I conducted an experiment to determine whether algal photosynthesis on a per cell basis, as well as on a per culture basis, was affected by PCB's or DDT. Tbe organochlorine concentrations used were above those found in natural waters (5); no at tempt was made to determine the toxicity of environmentally realistic concentrations of these compounds, as was done elsewhere (if). Tbe purpose of this study was to estab lish whether, in algae, photosynlhetic car bon fixation itself is inhibited or whether just growth is affected by these chemicals. The three algal species studied (7) were elected on the basis of their sensitivity to chlorinated hydrocarbons: the growth of Thaiasiiasina pseudonana and Skeletonema costatum, common marine diatoms, is affected by PCB's and DDT (I) and photosynthetic carbon fixation in cultures of Coccolithus huxleyt and the two dia toms is reportedly reduced by DD T (2. J). Culture conditions and procedures have been described elsewhere (<?). Methanolic solutions of PCB's (Aroclor 12^4) or l>[) I were injected (/) into the cell suspensions at time zero to give initial PCB concentra tions of 10 jig/liler (parts per billion) and DDT concentrations of 50 ppb in the medi um. Equal volumes of methanol were add ed to the control cultures (9). These organ ochlorine compounds, at similar concen trations (or doses per cell), have been re ported to substantially depress the net carbon fixation in monocultures of these algal species (2. J). At 4# hours. I ml of medium was removed from each tube so that cell counts could be determined (10). 0.2 tc of |"C]NaHCO, was added (//). and the cultures were incubated as bclnre for about 5 hours. The same procedure was also carried out for dark controls. The cells were then gently filtered through O K-.an Milliporc fillers and washed with filtered seawater, the radioactivity of the lilieis was counted in a liquid scintillation coun ter (Tri-Carb, Packard). The entire experi ment was repeated with the two diatom species. Table I presents the 4H-hour cell counts, photosynthetic carbon fixation per culture, and carbon uptake per ceil (a). The dark uptake of '"C, which varied with each spe cies (being 2 percent of the illuminated / pseudonana "C uptake, less than I percent with S. costatum, and 10 percent with ( huxleyi), was subtracted from the raw ' te.i DSW 031511 STLCOPCB4015473 Tabic 1 Effects of PCB's (10 ppb) and DDT (50 ppt>) on three species of marine algae: growth was measured in terms of cell density at 4K hours ihe cat bon uptake per culture was measured after 5 hours of incubation, and the carbon uptake (a) has the units cpm per 190.000 cells per hour Numhcs are the means of four replicate cultures and are shown with their 95 percent confidence intervals (16). Single classification analysts of variance 116) indicated that growth and carbon uptake per culture by treated cells differed from control cultures for T pseudonana (P < .025) and for 5 cosiaium (P ^ Ool) but uptake per cell in treated cultures did not significantly differ from control culture values for either species. Control C huxleyt cultures did noi sig nificantly differ from treated cultures for growth, carbon uptake per culture, or carbon uptake per cell. Species T reatment Cells per milliliter (x 10*) Mean % Control '*C uptake per culture (cpm/19 ml) Mean % Control l4C uptake per cell (") Mean % Control '*C uptjke pc1 cell (repeat) (lV control) T pseudonana Control 10.76 0.89 100 1034 226 100 15.71 3.73 too T pseudonana PCB's 6.77 1.94 63 538 180 52 13.49 1.43 86 T pseudonana DDT 3.18 1.74 30 295 106 28 16.37 3.63 104 S. cosiaium Control 22.78 4.13 100 6584 1494 100 44.39 4.38 100 S cosiaium DD1 4.17 0.52 18 1074 J47 16 45 86 14.26 103 C huxleyi Conirol 3.28 1 30 100 404 93 100 23.22 8.09 too C huxleyi PCB's 3 17 0.64 97 403 * 187 100 23.10 efc 5.44 99 C. hL.\}e\ i DDT 2.88 1.04 88 376 .t 76 93 24.55 5.18 106 100 104 102 100 94 counts to give the net values shown in Table I. Because dilferential growth rates during incubation could cause inaccurate estimates of carbon fixation per cell, a was determined by considering the specific ex ponential growth rate of each culture: o- --------- C--------[(N/W- 1)J (I) where C denotes the radioactive counts per minute (cpm) per 19 ml of culture. N is the cell density at 48 hours, r is the growth rate in cell divisions per hour (12), C denotes the incubation time with the '*C-labeled bi carbonate, and a is the carbon uptake rate per cell (in units of cpm per cell per hour) (IDThe total photosynthesis in cultures of T. pseudonana and S. costatum was re duced by the chlorinated hydrocarbons, confirming earlier results (2, 1). Carbon fixation per T. pseudonana culture was di minished 48 percent by the PCB's and 72 percent by the DDT. but growth was also diminished in the treated cultures. The "C uptake per cell (Table I), a direct assess ment of the pholosynthctic response of the cells to the organochlorine compounds, was unaffected by the chemicals. Thus, what appears to be 72 percent inhibition of T. pseudonana'^ photosynthesis and 84 percent of 5. cosiaium's photosynthesis by DDT is merely a reflection of growth inhi bition by this compound, rather than of photosynlhelic inhibition per se. These re sults. confirmed in the repeat experiment ( Table I), might explain earlier work (2-4) which showed a reduction in the incorpora tion of '`C-labeled bicarbonate per culture by these compounds. The growth and photosynthesis of C. huxleyi were not af fected by either chemical, in contrast with past findings (J). Skelelonema cosiaium was killed by the PCB's; both growth and photosynthesis stopped, and the integrity of the cells was completely disrupted. No other morphological differences between treated and control culture cells were ob served under the light microscope. 4*4 The pholosynthctic decline in treated cultures was thus due to reduced cell divi sion rales. The mechanism by which the chlorinated hydrocarbons affect diatom growth is as yet unclear, although recent studies with T. pseudonana suggest that PCB's may inhibit membrane-bound en zymes involved in nitrogen metabolism (14). Although total photosynthesis in the diatom monocultures was reduced by the PCB's and DDT. pholosynthctic carbon fixation in nature would likely remain unaffected by these compounds, even if present at concentrations many times the current environmental levels. Resistant au totrophs would probably replace sensitive species, as demonstrated in mixed cultures of marine phytoplankton with low (6) and high (IS) concentrations of PCB's and DDT. Alterations in the species compo sition of phytoplankton communities, caused by persistent pollutants, such as the chlorinated hydrocarbons, could result in deleterious effects on marine ecosystems if the resistant species that become dominant were an inferior food source for the resi dent herbivores. The most likely con sequences of chlorinated hydrocarbon pol lution for (he lower marine food web would therefore stem from qualitative, not quantitative, changes in the herbivores' food supply. Nicholas S. Fisher Woods Hole Oceanographic Institution. Woods Hole, Massachusetts 02541 Rtftrnm ia4 Note* 1. J. L. Mosser et ai., Science 175. |9l (1972). 2. D. W. Menzel, J. Anderson. A. Randtke, ibid. 147, 1724 (1970). 3. C. F Wumer. Jr., ibid 159. 1474 (1964). 4. E. J Luard, Phycologio 12, 29(1973); S. A. Moor* nd R. C. Harris*, NaturtfLond.) 244. 336(1972); Mar. Potlui. flu//. 5, 174 (1974). 5. G. R. Harvey. W G. Steinhauer. J. M. Teal, Sdence 190, 643 (1973); P. C. Olofli L. J. Albright, S Y. Saeio. Can. J. Microbiol. It. 1393 (1972k T. T. SchmidL R- W. Risebrough, F. Cress, Bull En viron Contam Toxicot. 6. 235 (1971); G. D. Veilb and G. F. Lee, Water Res. 5. 1107(1971). 6. N. S. Fisher ex at , Microb Ecoi I. 39 (1974); N. S. Fisher, ihesti, State University of New York, Stony Brook (1974), 7. Clone* M3H" of T. pseudonana, "Skel" of5 cojro* turn, and "BT-6" of C. huxleyi e obtained Irom R. R. L. GuiHard. Wood* Hole Occanograpnu. In itilulton culture collection All culture* were j enic and were tn their exponential phase ol growth 8. N. S. Fisher. L. B. Graham. E ) Carpenter ( \ Wurster, Nature Hond.l 241. 548 (197.0 tqual cell densities (KV/ml) were assured at lime reru for each culture tube by first inoculating the medi um in a sterile flask, vigorously wtrnng io form j uniform cell suspension, and ascepdcallv dis pensing 20 mi fwr lube (25-ml capacity) Hicte were four replicate tube* per treatment 9 Methanol was shown in preliminary experiment* to have no effect on photosynthesis or growth 7 be concentrations and purity of ihe chlorinated hvdrocarbon stocks were checked by electron-i.jplure gas chromatography (J) The PCD concentra tion was lower than its reported volubility limit I to 2 mg/liler--m seawater (V iiko. flu// finvi ron. Conlem. Toxicol 5, 279 <|970)|, whereas ihe DDT concentration exceeded 1.2 ppb. its solubility m water (F. Acree. M Beroza. M C Bowman. AgriC- Food Chem. II. 278 < IQ63>| However. DDT at concentrations exceeding its soiubilm m water can affect algal growth in a dose-response manner (/. 2). either by influencing growth m (he undissolvod state or by being rapidly jnd vimujIIv completely incorporated into the cells, m which case it would not crystallize in ihe medium Experimental evidence supports the latter ex planation (A. Sddergren. Oikos 19, 12b (t968)| 10. A Speirs-Levy eosinophil counter (hemacytom eter) was used. 11. The (,4C)NaHCOi was dissolved in stenie distilled water, pH 9.5, and filtered through a 0 22- t*m Millipor* filter before use. A syringe ii used to add 0.2 mJ per culture. 12. The value of r was calculated according to ihe method of R W fcppley and J D H Strickland (in Advances in Microbiology oj (hr Sra. M R Droop and E. J. F. Wood. Eds ( Academic Press, London. 1968), vol. I. p. 23). 13. In Eq. I it is assumed that >n each culture. "C up take is dependent on the number of ceils, that the uptake rate per cell remained constant, jnd mat growth proceeded at a constant rale, r (The elapsed lime of the enure experiment was shorter than the exponential growth phase of the-* aigje. given the same initial conditions (/) | Under these assumptions. JC/dl - aNt "'dt for /> 48; integrating, we obtain C - aN f eril 4,liit-[aN(r)[e" It 4 where T is the time at the end of the experiment for each replicate and t' m T 48 14. N. S. Fisher. R. R. L. Guillard. C F Wurster. pa per presented at the American Chemical Society meeting. Philadelphia, 1975. N. S. Fisher and l S Murphy, in preparation 15. J. L. Mosier, N. S. Fiiher, C. F. Wurster. Science 174. 533(1972). 16. R. R. Sokal and F J, Rohlf, Biometry (Freeman San Francisco, 1969). 17. Supported by Ihe Sarah Mellon Scatfe Founda tion. j thank B L. Dempsey and A C Collins tor laboratory assistance. S. w. Watson and G R Harvey for use of their equipment, and V T Bow en. J. W Farrington. W k. Smith. D W Spencer, and C F Wurster for suggestions and criticisms Woods Hole Oceanographic (monition Contribu tion No. 3526. 26 March 1975; revised 21 May 1975 SCIENCE. VOL IHU DSW 031512 STLCOPCB4015474