Table 2. Species composition of recent and glacial samples for each core (expressed as percentages). Since only eight species are reported from the total flora, the percentage values do not equal 100. Abbreviations: R, recent; G, glacial; x represents values that are less than 1 but greater than 0.5 percent. A153-146 x AlS6-4 A1‘S6-5 A164-59 x Xx A167-13 A167-14 A179-13 A1T79-17 A180-9 A180-16 A180-32 G R AI180-48 R 1 5 9 6 1 x x 2 x 1 3 5 x 3 2 2 Helico- x 3 4 Rhabdo- sphaera carteri G x x 18 x lithus leptoporus G G R 2 1 x 1 x 1 x 7 1 1 5 10 10 9 x 6 5 15 1 2 1 2 3 x 10 4 x 4 3 x 1 2 3 1 1 2 1 x x 2 RS5-36 R5-54 R5-57 R10-2 SP8-4 SP9-3 SP9-4 SP10-1 V16-200 x x 4 1 1 30 6 1 1 2 0.5 1 5 3 27 2 2 3 8 16 8 14 6 6 11 1 9 5 6 2 3 4 1 1 0.5 5 8 25 13 18 8 plotted on a map and each boundary is given the present value of the maximum temperature (isotherm), it should be possible to draw a paleoisotherm map for the glacial period. Having laid out the temperature lines for the species and interpolating between overlapping ranges, I found it possible to draw a tentative paleoisotherm map (Fig. 3). Although insufficient core coverage makes any fine adjustment of these lines impossible (a gap remains in the northwest portion of the Atlantic), two lines, the 14° and the 22°C isotherms, are established on the basis of a number of overlapping species. The addition of more core material and the mapping of other species boundaries should result in a paleoisotherm map that will be an accurate representation of the average temperature of surface water of the glacial North Atlantic. In seven species the amountoflatitudinal shift between glacial and recent is greatest along the eastern side of the Atlantic. In the three species with subtropical to transitional ranges it is a factor of 2 to 3. This distributional difference is presumably the result of the main current system in existence today and in the Wisconsin. At present the distribution of R. stylifera, H. carteri, U. tenuis, and S. pulchra is en- compassed by the northern boundary of the subtropical gyral (Gulf Stream). 8 DECEMBER 1967 1 4 1 6 1 3 R 0.5 x G 2 3 1 1 1 R G 1 1 4 3 x 2 3 4 x 2 2 2.5 x J 1 2 1 2 1 2 1 x x x 2 x 4 x 2 1 1 1 7 6 3 3 4 x 1 2 7 11 2 1 8 6 1 1 2 3 9 4 I 2 x 1 1 4 4 1 9 2 5 1 x 2 2 3 1 2 4 3 I 14 1 6 x This boundary rises from approximately 40°N latitude off North America to over 55°N latitude off Europe. This is also true for other subtropical coccolith species not included in this report. In the mid-Wisconsin the line of species presenceis relatively horizontal, running roughly parallel to the 30° latitude line with a slight southern turn along the eastern edge of the Atlantic (Fig. 3). Admittedly the core density is some- what low; nevertheless, the core coverage is sufficient to allow no more than a 5° fluctuation in latitude without a major change in azimuth of this line since it is bracketed by cores. If one compares data (Figs. sphaera mirabilis G 2 4 Um bilico- R J x 2.5 G sphaera tenuis ] 2 13 Umbello- sphaera irregularis 2 1 J A180-56 A180-72 Umbeilo- sphaera pulchra R 6 2 2 Syraco- sphaera stylifera 1 and 2), it is possible to say that the northern border of the subtropical gyral during midWisconsin time flowed along or near the 33° latitude line. From this first report, based on information gained from modern species 1 x 1 1 x 2 22 greatest shift occurring in the eastern Atlantic; (ii) that it may be possible to erect paleoisotherm maps of surface water with the use of population boundaries of Coccolithophoridae species of known temperature range as isotherms, particularly if greater core coverage can be combined with data on additional species; and (iii) that the northern boundary of the subtropical gyral, from a present position of approximately 40° latitude off North America to over 55° latitude off Europe, was displaced to a position extending from ap- proximately 30°N latitude off North America to approximately 38° off Europe. ANDREW MCINTYRE Lamont Geological Observatory, Palisades, New York References and Notes 1. D. B, Ericson, M. Ewing, G. Wollin, B. C, tion: (i) That the maximum cooling in the mid-Wisconsin resulted in a south- Heezen, Geol. Soc. Amer. 72(2) 193 (1961). . C. Emiliani, J. Geol, 63, 538 (1955). G. A. Riley, Limnol. Oceanogr. 2, 252 (1957); E. M. Hutburt, ibid. 7, 307 (1962). A. McIntyre and A. W. H. Bé, Deep-Sea Res., in press. H. G. Marshall, Limnol. Oceanogr. 11, 432 (1966). A. W. H. Bé and A. MelIntyre, Spec. Paper Geol, Soc. Amer, 82, 8 {abstr.) (1964); N. Watabe and K. M. Wilbur, Limnol. Oceanogr. 11, 567 (1966), 8. I thank A. W. H. Bé for helpful discussion and J. Imbrie, W. Broecker, A. Gordon, and C. Drake for criticism of the manuscript. Supported by National Science Foundation grant GP 4768. Lamont Geological Observatery con- of approximately 15° latitude, with the 6 September 1967 of Coccolithophoridae, it appears that coccoliths can be used for paleoecologic studies and that the application of these studies to the problem in this report has led to the following conclusions about the effect of cooling on the North Atlantic during the Wisconsin glacia- ward shift of planktonic populations wh R Cyclococco- w Coccolithus pelagicus na Core No. tribution No. 1131. 1317