Size variations in Globigerina bulloides dOrbigny as a G. … · 2011-05-06 · Size variations in Globigerina bulloides dOrbigny as a Quaternary paleoclimatic index in the southern

Size variations in Globigerinabulloides d'Orbigny as a

Quaternary paleoclimatic indexin the southern ocean

BJORN A. MALMGREN and JAMES P. KENNETTGraduate School of Oceanography

University of Rhode IslandKingston, Rhode Island 02881

Malmgren and Kennett (1976) show that averagetest size and coiling direction in modern assem-blages (surface sediments of USNS Eltanin cores)of the planktonic foraminifera Globigerina bulloidesd'Orbigny show clear relationships with the distri-butions of southern subtropical to northern antarc-tic waters of the southern Indian Ocean (300 to53°S.). The species attains largest test sizes in coolerwaters (average widths of about 350 microns) anddecreases gradually in size with increasing surface-water temperature (to a minimum average of about210 microns). Highest percentages of sinistrallycoiled forms (about 70 percent) occur in coolerwaters decreasing to about 55 percent sinistral coil-ing in warmer waters. We are studying G. bulloidesin late Quaternary Eltanin cores from subantarcticwaters to determine if average test size and coilingdirection changes parallel paleotemperature curvesestablished using other methods. The other meth-ods include those based on frequency variations insingle species or groups of species, coiling direc-tions, and oxygen isotopic variations.

MEAN TEST SIZE

OF G. BULLOIDES

(IN MICRONS)

Study of one core is complete (Eltanin 48-22A;39.900S. 85.41 0E.; water depth 3,378 meters). Theresult indicates that mean test size variations in G.bulloides closely follow paleotemperature variations(figure). The size oscillations show a significantoverall correlation (r=0.65) with paleotemperaturecurves based on coiling ratios of the planktonic spe-cies Neogloboquadrina pachyderma and factor analysisof entire planktonic foraminiferal assemblages(figure). Three major climatic coolings are markedby large average mean sizes (between about 280 and315 microns), and four major warming episodes arereflected by small mean sizes (between about 235and 280 microns).

Coiling direction of G. bulloides does not showany relationship to the paleotemperature curvesdespite relationships exhibited between tempera-ture and coiling direction in surface sediments.

In Recent assemblages a correlation also existsbetween test size and percentages of G. bulloides,with highest frequencies generally being found insouthern subantarctic waters. It is therefore pos-sible that water temperature itself is not the primaryfactor controlling test size, but that largest growthoccurs in the optimum environmental conditionsfor this species (as indicated by highest frequen-cies). The observed correlation between test sizeand water temperature may thus be a secondaryconsequence of the relationship between watertemperature and percentages of G. bulloides in thearea of study. Agreement between optimum adap-tation and optimum growth environments in G.bulloides would be in accordance with a generalmodel for the growth of planktonic foraminiferaproposed by Hecht (1976).

We thank Douglas Williams for allowing us to use

% SINISTRAL N. PACHYDERMA TOTAL FAUNA CURVE

320 300 280 260240605040302010-60 -40-2002040

00

200

300

400

50C

LOC

70C

Variation in mean test sizeof Globigerina bulloldes inUSNS Eltanin core 48-22A(39.90°S. 85.41°E.) fromthe southern Indian Ocean(close to the SubtropicalConvergence) compared topaleotemperature curvesderived from coiling ratiosofNeogloboquadrinapachyderma and factoranalysis of total planktonicforaminiferal assemblages(from Williams, in press).Size curve is significantlycorrelated (r=0.65) withpaleotemperature curves.

September 1976 177

his oxygen isotope data and coiling directions ofN. pachyderma from core 48-22A. This research wassupported by National Science Foundation grantDPP 75-15511.

References

Hecht, A. D. 1976. Size variations in planktonic foraminifera:implications for quantitative paleoclimatic analysis. Science,192: 1330-1332.

Malmgren, B., and Kennett, J . P. 1976. Biometric analysis ofphenotypic variation in Recent Globigerina bulloides d'Orbignyin the southern Indian Ocean. Marine Micropaleontology, 1:3-25.

Williams, D. F. In press. Late Quaternary migrations of theSubtropical Convergence and Polar Front in the southeastIndian Ocean. Marine Micropaleontology, 1.

Morphologic variations inHannaites, a Paleogene

silicoflagellate

YORK T. MANDRASan Francisco State University

San Francisco, California 94132and

California Academy of Sciences

A. L. BRIGGERCalifornia Academy of Sciences

San Francisco, California 94118

HIGHOOHI MANDRA8 Bucareli Drive

San Francisco, Ca4fornia 94132

DAVID PIERCEBiogeology Clean Laboratory

University of Cal[ornia, Santa BarbaraSanta Barbara, California 93106

We have continued our studies of surface ultra-structure and morphology of Hannaites (Mandra

*Illustrations are stereograms. All stereograms have onespecimen at 0° and the second at 8° tilt, except figures 9a and9b, which were 34° and 42° tilt. In all cases the acceleratingvoltage was 25 kilovolts. Bar scales = 10 microns.

et al., 1975). In this paper the following are illus-trated and described for the first time: three- andfive-sided Hannaites (figures 1, 5, and 6*) and grossmorphology of new four-sided specimens (figures2, 3, and 4). Also, a correlation is presented betweensome morphologic terms of earlier workers and ourcurrent terms for surface morphology and ultra-structural detail (figures 7, 8, and 9) as describedin 1975.

The three levels of morphology reported in 1975for the four-sided Hannaites are also present in thethree- and five-sided Hannaites. It now appears thatthese three levels of morphology are present inmany, but not all, silicoflagellates of other genera.Similarly, three- and five-sided forms also have:surface morphology with reticulations and "flowlines" (figure 8) and ultrastructural morphologywith nanodivides, nanopeaks, and nanovalleys(figures 7, 8, and 9).

The gross morphology of Hannaites includesthree-, four-, and five-sided forms that have a basalring and an apical bridge system comparable to theapical system and basal ring of the genus Dictyocha.However, the protuberances (swellings) of Hannai-tes distinguish it from Dictyocha. Our prior paperson Hannaites report the protuberances only at thecorners of specimens. Here we illustrate (figure 2)a specimen having protuberances not only at eachof the four corners but also in the middle of threesides of the four-sided basal ring. These midsideprotuberances are at three of the four apicalbridge-to-basal-ring intersections. Therefore, thisfour-sided Hannaites has seven protuberances.

In most specimens two tubes radiate from eachcorner protuberance, either in or nearly in theplane of the basal ring. These two corner radiat-ing tubes are oriented about 45° to 900 to eachother. There are exceptions, one of which is a speci-men with one corner protuberance having threeradiating tubes (figure 3). Protuberances on thesides have three radiating tubes because they jointhe basal ring to the apical system. In plan view(figure 2), these tubes are usually oriented at about00, 90°, 180°. The apical tube is always inclinedto the plane of the basal ring. Usually two tubesradiate from an area close to the equatorial (basalring) plane of the protuberances. However, someprotuberances with three radiating tubes havetubes almost tangential to the sphere-like swelling(figure 2, left central protuberance).

Figure 4 illustrates a four-sided Hannaites withbasal ring tubes that do not meet at one corner. Instereo one sees that these tubes are displaced fromeach other normal to the page. The terminal partsof these two tubes have small, clublike swellings atthe corner region, and the two tubes apparently justmiss forming a corner protuberance. The adjacentcorner protuberance to the right has clear-cut lobes

178 ANTARCTIC JOURNAL