A new planktic foraminifer transfer function for estimating pliocene—Holocene paleoceanographic conditions in the North Atlantic

Marine Micropaleontology, 16 (1990) 1-23

1

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

A New Planktic Foraminifer Transfer Function for Estimating Pliocene-Holocene Paleoceanographic Conditions in the North Atlantic HARRY J. D O W S E T T and RICHARD Z. POORE U.S. Geological Survey, 970 National Center, Reston, VA 22092 (U.S.A.) (Revised manuscript received October 6, 1989; accepted October 27, 1989)

Abstract Dowsett, H.J. and Poore, R.Z., 1990. A new planktic foraminifer transfer function for estimating Pliocene-Holocene paleoceanographic conditions in the North Atlantic. Mar. Micropaleontol., 16: 1-23. A new planktic foraminifer transfer function (GSF18) related 5 North Atlantic assemblages to winter and summer sea surface temperature. GSF18, based on recombined and simplified core top census data, preserves most environmental information and reproduces modern North Atlantic conditions with approximately the same accuracy as previous transfer functions, but can be more readily applied to faunal samples ranging in age from Pliocene to Holocene. Transfer function GSF18 has been applied to faunal data from Deep Sea Drilling Project Hole 552A to produce a 2.5 m.y. sea-surface temperature (SST) time series. Estimates show several periods between 2.3 and 4.6 Ma during which mean SST's were both several degrees warmer and several degrees cooler than modern conditions. Between 2.9 and 4.0 Ma SST was generally warmer than modern except for a 250 k.y. interval centered at 3.3 Ma. Maximum SST, with respect to modern conditions, occurred after the cool interval near 3.1 Ma when SST was approximately 3.6 ° C warmer than present conditions. Comparison of SST estimates with stable isotope data suggest that after peak warming at 3.1 Ma, there was an overall surface water cooling with concomitant build up of global ice volume, culminating in Northern Hemisphere glaciation. This event is also indicated by the presence of ice rafted detritus in 552A sediments at about 2.45 Ma.

Introduction

Multivariate statistical analysis of microfossil census data from marine and terrestrial deposits has proven to be a powerful tool for paleoclimatic and paleoceanographic studies. The most common technique used with marine microfossils is the transfer function pioneered by Imbrie and Kipp (1971), which involves factor analysis and multiple" regression to develop equations relating microfossil abundance data in modern (core-top)samples to physical parameters such as sea surface temperature (SST) and salinity. The equations are then applied to

downcore microfossil abundance data to estimate past sea-surface conditions. The transfer function approach has been widely used in paleoclimatic studies of the late Pleistocene based on planktic foraminifers, diatoms and radiolarians (Sancetta, 1979; Ruddiman and Esmay, 1986, Hays et al., 1989) and was the primary technique used in the reconstruction of global sea-surface temperatures during the last glacial maximum and the last interglacial (CLIMAP, 1981, 1984). Application of the transfer function technique to marine microfossil assemblages older than the late Pleistocene has been limited for a

2

variety of reasons. Important areas of concern include changing ecological tolerances and preferences of species as well as addition and elimination of species from fossil assemblages due to evolutionary changes and extinctions. Despite these problems a number of studies have demonstrated the usefulness and potential of the transfer function technique for quantifying oceanographic properties prior to the late Pleistocene. With regard to studies based on planktic foraminifers, Briskin an Berggren (1975) applied CLIMAP equation F13 (Kipp, 1976) in a straightforward manner to the entire Pleistocene record of tropical Atlantic core V16205. Ruddiman et al. (1986), used a modified version of F13 ( F 1 3 x 5 ) that included 5 taxonomic categories to analyze the Pleistocene record of Deep Sea Drilling Project (DSDP) Hole 607 in the mid latitude North Atlantic. The first true transfer function approach to prePleistocene foraminifer faunas involved the Pliocene of DSDP Holes 125 and 132 in the Mediterranean Sea (Thunnell, 1979a, b). Thunnell (1979a) factor analyzed counts of 24 taxonomic groups in 74 modern samples and related the resulting factors to the corresponding modern oceanographic conditions. Downcore assemblages were counted into the coretop categories by assuming that extinct Pliocene taxa were ecologically equivalent to closely related forms in the modern samples (e.g. Globigerinoides obliquus = G. ruber; Globorotalia puncticulata = Gr. inflata ). The equations developed from modern samples were then used to calculate sea-surface temperature and salinity for the Pliocene samples. Factor analysis of Miocene and Pliocene assemblages has been used to reconstruct environmental changes throughout the late Miocene-Pleistocene in the Panama basin (Keigwin, 1976) and to interpret late Miocene paleoceanography in the North Atlantic (Poore, 1981a). In both studies extinct taxa were assumed to be ecologic equivalents of closely related modern taxa and the associations of taxa delineated by factor analysis of Neogene assemblages were qualitatively

H.J. DOWSETT AND R.Z. POORE

interpreted on the basis of the distribution of modern taxa. Multivariate statistical analyses and transfer function approaches have also been extended back in time for other microfossil groups. For example, Hays et al. (1989) used a radiolarian transfer function to obtain surface temperature estimates between 3.7 Ma and 2.4 Ma in the equatorial Pacific. Cronin and Dowsett (this volume ), have developed a transfer function for Pliocene ostracode assemblages from the Atlantic coast margin of North America. Our goal, as part of a larger project investigating global Pliocene climates, is to reconstruct North Atlantic surface marine conditions during the Pliocene. We have developed a transfer function for planktic foraminifers based on the modern CLIMAP core-top data set (Kipp, 1976) that is tailored for use with Pliocene to Holocene assemblages. We have recombined and simplified abundance data from the modern core-top data set to preserve the overriding environmental signals and allow direct comparison of Pliocene and earlier Pleistocene assemblages to modern assemblages. We factor analyzed the revised modern data base and used regresssion techniques to write a set of equations (transfer function GSF18) which relate modern physical oceanography to the faunal data. In this paper we outline the development of GSF18 and use it to delineate a record of seasurface temperatures between 2.3 and 4.6 Ma from DSDP Hole 552A in the North Atlantic Ocean.

M o d e r n core-top data Kipp (1976) developed a planktic foraminiferal data base of 191 core-top samples representing modern North Atlantic conditions for use with the CLIMAP ( 1981 ) reconstruction of the glacial North Atlantic 18,000 years ago. This data-base has since been expanded to include a total of 223 modern faunal samples from Kipp (1976), CLIMAP (1981), and unpublished data (Fig. 1). Sea-surface temperature (SST) data

NEWPLANKTICFORAMINIFERTRANSFERFUNCTION 80

TABLE I Taxonomic categories

60

Taxon 40

20

0 1 O0

80

60

40

20

0

20

Fig. 1. Map showing location of core-top samples (crosses) and DSDP Sites (numbered circles) discussed in this paper.

for winter and summer seasons for the core tops were obtained from the Oceanographic Atlas of the North Atlantic Ocean and the Oceanographic Atlas of the Polar Seas (U.S. Naval Oceanographic Office, 1958, 1967). The location, water depth and modern sea-surface temperature (SST) values for each core-top site are given in Prell {1985). For each sample, Kipp (1976) tallied the number of planktic foraminifers in each of 42 counting categories conforming to the taxonomy of Parker {1962,1967 ). Thirteen categories were found to make up < 2% of any sample and were deleted, leaving 29 categories to explain the planktic foraminiferal biogeography of the modern North Atlantic. Each of the 29 species, or counting categories, has a distinct distribution on the modern sea floor, but various groups of taxa have overall similar distributions and oceanographic significance. These groups are: Polar, Subpolar, Transitional, Subtropical, Tropical and Gyre Margin groups (Kipp, 1976). An approximate north-south transect through the Kipp data set shows patterns and trends representative of the north central Atlantic (Poore, 1981a). For example, high latitude samples are dominated by the genus Neogloboquadrina. Low latitude samples are more diverse, and generally dominated by species of Globigerinoides and warm water Globorotaliids. Intermediate latitudes show high abundances of Globigerina bul-

Globinerina buUoides Globigerina digitata Globigerina falconensis Globigerina rubescens, teneUus Globigerina aequilateralis calida Globigerinita glutinata Globigerinoides ruber, conglobatus Globigerinoides sacculifer Globorotalia crassaformis Globorotalia hirsuta Globorotalia inflata Globorotalia menardii, tumida Globorotalia scitula Neogloboquadrina pachyderma, "du-pac"

Neogloboquadrina dutertrei Orbulina universa Sphaeroidinella dehiscens Turborotalita quinqueloba

Maximum occurrence ( % of sample ) 54.11 4.05 23.51 15.48 16.18 34.18 85.78 46.53 8.40 9.52 44.06 67.48 9.30 100.0 38.46 19.00

8.11 33.06

loides, Globigerina falconensis, and Globorotalia inflata, all assigned to Subtropical-Subpolar assemblages by Kipp (1976). Poore (1981a) saw that grouping of species in the Kipp (1976) data set provided a viable model for interpreting late Miocene North Atlantic paleoclimatic signals. As a first step in developing our transfer function for the Pliocene to Holocene we revised the modern planktic foraminifer data into categories that retained most of the primary temperature signal but also provided a good fit to Pliocene assemblages. Our taxonomic concepts follow Parker (1962, 1967) and Blow (1969) with minor exceptions (Dowsett et al., 1988). After experimenting with a number of combinations we reduced the 29 categories of Kipp (1976) to 18 categories (Table I) with the following important groupings:

Neogloboquadrina Group We group all species of Neogloboquadrina (sinistral and dextral forms of Neogloboquadrina pachyderma and the artificial N. dutertrei-

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H.J. DOWSETTANDR.Z,POORE 15

NEOGLOBOQUADRINA GROUP

[]

[] +

80

G/obigerina rubescens G/obigerinoides re•el/us

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40

A

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25

30

I

20

10 0 100

15

20 Winter SST °C

80

60

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B

Globigerinella aequilateralis Globigerinella calida

GLOBIGERINOIDES GROUP 80

[] []

10 []

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20

,.,.,,,,~..,,,.a.~ ~.~ . ~ ~ W i ~ L r i - d m ~

10

20

30

Winter SST °C 0 100

80

60

40

20

0

20

40

Fig. 2. Maps showing the geographic distribution of the Neogloboquadrina and Globigerinoides counting categories in North Atlantic core-top samples. Contours indicate percent abundance in core-top samples.

[] +

G/oborotalia menardii G/oborota/ia tumida

3O Q) 0

[]

member of the gyre-margin assemblage representative of warmer waters surrounding the core of the North Atlantic gyre and was retained as a separate counting category. Neogloboquadrina dutertrei represents the warm end member of this genus and N. pachyderma the cold end member. In general, high latitude assemblages are dominated by the cold end members of Neogloboquadrina from the middle Miocene to Holocene time.

t[]

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N. pachyderma intergrade category of Kipp, 1976) except Neogloboquadrina dutertrei {Fig. 2 ). Neogloboquadrina dutertrei is an important

C

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10

20

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Winter SST °C

Fig. 3. Plots showing similarity in temperature preference for pairs of planktic foraminifer species grouped together in this study. (A) Globegerina rubescens and Globigerinoides tenellus. (B) GlobigerineUa aequilateralis and Globigerinella calid. (C) Globorotalia menardi and Globoro-

talia tumida.

Globigerinoides Group

Gs. conglobatus, Gs. sacculi[er and Gs. tenellus. Both Gs. ruber and Gs. conglobatus have Trop-

In the modern ocean, the genus Globigerinoides is represented by Globigerinoides ruber,

ical-Subtropical distributions and can be combined into one category with little loss of infor-

NEW PLANKTIC FORAMINIFER TRANSFER FUNCTION

mation (Fig. 2). Globigerinoides sacculi[er is retained as a separate counting category due to its importance in upwelling and gyre margin assemblages as shown by B~ and Toderlund ( 1971 ), Imbrie and Kipp {1971 ), Kipp (1976), and Prell and Hays (1976). Globigerinoides teneUus is counted with Globigerina rubescens as described below. Globigerina rubescens-Globigerinoides tenellus Group Globigerisoides tenellus is similar in all respects to Globigerina rubescens except for the development of a small supplementary aperture (Kennett and Srinivasan, 1983). We believe Gs. tenellus evolved from G. rubescens during the Pliocene. Both species have remarkably similar modern geographic distributions and temperature tolerances {Fig. 3)o Factor analysis of North Atlantic core-top samples shows little difference between these two species with respect to the 6 assemblage model of Kipp (1976). These two species have been combined into one counting category in our study to fa-

5

cilitate analysis of Pliocene samples that may not contain Gs. tenellus.

Globigerinella aequilateralis-Globigerinella calida Group Globigerinella calida probably evolved from Globigerinella aequilateralis during the Pliocene (Kennett and Srinivasan, 1983). Both species represent tropical to subtropical conditions and are combined in this study (Fig. 3). This facilitates analysis of Pliocene samples that do not contain Globigerinella calida. Globorotalia menardii Group Both Globorotalia menardii and Globorotalia tumida are warm gyre-margin species (Fig. 3) with similar geographic distributions. These species were combined for the modern data set with little loss of information. After grouping the taxa discussed above and deleting minor taxa our modern North Atlantic data base consists of the 18 categories listed in

T A B L E II Varimax assemblage description matrix Variable

Tropical

Polar

Gyreimargin

Subtropical

Subpolar

Globigerina buUoides Globigerina digitata Globigerina falconensis Globigerina rubescens, tenellus GlobigerineUa aequilateralis, calida Globigerinita glutinata Globigerinoides ruber, conglobatus Globigerinoides sacculifer Globorotalia crassaformis Globorotalia hirsuta Globorotalia inflata Globorotalia menardii, tumida Globorotalia scitula Neogloboqudrina pachyderma, " d u - p a c " Neogloboquadrina dutertrei Orbulina universa SphaeroidineUa dehiscens Turborotalita quiqueloba

- .0243 .0019 .0477 .0294 .0849 .1397 .9445 .2759 .0025 .0068 - .0237 .0038 .0023 .0152 -.0167 .0123 - .0038 .0108

.1722 .0006 - .0134 -.0004 -.0039 .1017 -.0261 .0071 .0002 - .0091 .1036 -.0147 .0080 .9659 -.0058 .0128 - .0013 .1219

.0112 .0303 - .0870 -.0152 .0287 - .0172 -.1212 .4587 .0579 - .0110 .0669 .6897 -.0103 - .0014 .5238 .0601 .0552 -.0069

.4682 .0061 .3259 .0002 .0192 .1445 .0368 -.1429 .0044 .1348 .7490 -.0089 .0765 -.1587 .0955 .0356 -.0030 -.1037

.7145 -.0013 .0214 .0063 .0225 .3770 -.0658 .0405 -.O084 -.002O -.5133 .0434 .0372 -.1409 -.0331 -.0539 .0087 .2226

Variance Cumulative variance explained

39.939 39.939

35.141 75.079

7.924 83.003

8.470 91.473

2.972 94.446

6

H.J. DOWSETTAND R.Z. POORE

Table I. Counting categories or species other than those discussed above have been mapped by Kipp (1976).

Factor analysis Following the methodology of Imbrie and

Kipp (1971) and Imbrie et al. (1973) the 18 taxonomic categories were normalized in each of 223 samples to give each sample equal weight. The CABFAC Q-mode factor analysis program of Klovan and Imbrie (1973) was used to reduce the 18 original taxonomic categories to 5 varimax factors (assemblages). Modern samTROPICAL 80

60

40

20

0 100

80

SUBTROPICAL

60

40

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GYRE MARGIN

80

60

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SUBPOLAR

POLAR

80

80

60

60

40

40

20

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0 1 O0

80

60

40

40

20

0

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80

60

40

Fig. 4. Maps showing the distribution of 5 planktic foraminifer assemblages in the North Atlantic Ocean. Contours are factor loadings from Appendix 1.

NEW PLANKTIC FORAMINIFER TRANSFER FUNCTION

ples can then be expressed as proportions of assemblages. The contributions of each of the factors (interpreted to be Tropical, Subtropical, Subpolar, Polar and Gyre margin assemblages) to each of the modern samples as well as sample communalities are given in the factor loading matrix, Appendix 1. The 5 factor model accounts for more than 94% of the original North Atlantic data. The relative importance of each of the 18 counting categories to each factor are presented in the factor score matrix (Table II). The most important counting categories in the Tropical assemblage are the Globigerinoides group and Gs. sacculifer followed in order by Globigerinitaglutinata and the GlobigerineUa group. As expected, the Polar assemblage is quantitatively dominated by the Neogloboquadrina group. In contrast to Kipp (1976), we do not discriminate an assemblage transitional between the Subtropical and Subpolar assemblage. Therefore some of the species we use to characterize our Subtropical assemblage are used by other authors to define a transitional assemblage. The Subpolar assemblage has important contributions from Globigerina buUoides, Globigerinita glutinata and Turborotalita quinqueloba. The Subtropical assemblage has Globorotalia inflata as a dominant species followed by lesser contributions from Globigerina bulloides and Globigerina falconensis. Finally, the Gyre-margin assemblage is dominated by the Globorotalia menardii group, Neogloboquadrinadutertrei and

Globigerinoides sacculifer. The geographic distribution of these varimax factors (assemblages) is shown in Fig. 4. The tropical assemblage is most developed in the low latitude areas of the North Atlantic, specifically in the Caribbean and western tropical areas. The importance of the Tropical assemblage in the tropical areas off northwest Africa and subtropical area off the northeastern U.S.Newfoundland decreases and is replaced by the Gyre-margin fauna which thrives in these upwelling areas of the ascending and descending

7

limbs of the North Atlantic gyre. The Gyremargin assemblage is noticeably absent from the central regions of the gyre. In these areas, the Subtropical assemblage, centered at approximately 40 ° North latitude, dominates, with the Subpolar assemblage immediately to the North. The Polar assemblage is generally dominant at high latitude North Atlantic sites. One exception to this generality is the area immediately adjacent to northwest Africa where the Polar assemblage is weakly developed in a southward direction to a latitude of 20 °N. This is an artifact of our grouping the artificial Neo-

globoquadrina dutertrei-Neogloboquadrina pachyderma intergrade category (du-pac) with Neogloboquadrina pachyderma to form our "cold" Neogloboquadrina group. The du-pac category is abundant in this region and therefore our Polar assemblage maps into this area. D e r i v a t i o n of t r a n s f e r f u n c t i o n G S F 1 8 Transfer functions are sets of equations which relate physical oceanographic parameters to faunal data. Transfer function F13 (Kipp, 1976) contained 16 equations estimating temperature and salinity at surface and 100 m depth. Transfer function GSF18, derived in this study, is a set of two equations which relate the 5 varimax assemblages derived from the factor analysis of the revised modern core-top data to winter and summer sea-surface temperature. Standard multiple regression techniques have been applied to write paleoecological equations of the form Yest =B2ctKTko where Yest=the paleoecological estimates, B2ct = the cross product matrix formed by arranging the varimax factors, their squares and cross products into a matrix, K=a vector of regression coefficients corresponding to the columns of B 2ct and ko is the intercept of the equation.

8

H.J. DOWSE'IT AND R.Z. POORE

6

T A B L E III =:

ILl

4:

Coefficients of terms and intercept of equation GSF18, multiple correlation coefficients and standard e r r o r s of estimate for winter and summer seasons

++ +

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TEMPs

om

Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor Factor

1 (Tropical) 2 (Polar) 3 (Gyre M a r g i n ) 4 (Subtropical) 5 (Subpolar) 1X Factor 2 1 X Factor 3 1 X Factor 4 1 × Factor 5 2 X Factor 3 2 XFactor 4 2 X Factor 5 3 X Factor 4 3 X Factor 5 4 X Factor 5 1 squared 2 squared 3 squared 4 squared 5 squared

Intercept

0.96 1.47

1.36

23.88 -31.44 24.43 15.78 3.23 18.56 - 16.65 - 28.44 1.56 - 2.40 0.54 - 3.14 -9.85 9.17 - 7.51 - 13.80 22.99 - 14.54 -5.98 -6.03 13.92

23.43 -28.28 19.42 28.32 8.77 7.11 - 16•99 - 26.69 2.16 24.74 -8.11 - 14.49 - 13.67 0.67 - 5.50 - 14.09 21.79 - 11.48 - 10.42 -7.15 17.70

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The statistics of GSF18 are given in Table III. The multiple correlation coefficients for winter and summer SST are slightly lower than those of F13. Analysis of the residuals (measured as observed SST minus estimated SST) of GSF18 show that they are generally randomly distributed with respect to observed temperature with a tendency toward warmer estimates at the coldest samples (Fig. 5). Plots of F13 residuals indicate similar distributions (Fig. 5). The standard error of estimate for winter temperatures ( 1.47 oC ) is higher and for summer temperatures (1.36 oC) is lower than the standard errors for equation F13 (1.16°C and 1.38°C respectively). Figure 6 compares observed winter temperature with the estimated winter temperatures produced by GSF18

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Fig. 5. Plots of residuals (observed minus estimated) for summer and winter seasons from equations GSF18 and F13.

(this paper) and F13 (Kipp, 1976)• In general, transfer function GSF18 reproduces modern conditions with almost the same accuracy as F13 of Kipp (1976). The major difference between the equations is that GSF18, with its

9

NEW PLANKTIC FORAMINIFER TRANSFER FUNCTION

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Chronology

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been shown to be very sensitive to climate change during the Pleistocene (e.g. Ruddiman and McIntyre, 1976) and Site 552 is ideally located to record the evolution of late Neogene climate and associated paleoceanographic changes in the North Atlantic. The Pliocene section of Hole 552A investigated includes approximately 55 m of nannofossil and nannofossil-foraminifer oozes from cores 9-20; 154 samples were selected from this interval for total faunal analysis. The tops of cores 11 and 12 and all of core 13 were found to be disturbed and contaminated and were deleted from the present study.

30

F13 W I N T E R S S T ( ° C )

Fig. 6. Scatter plots showing similarity between observed and GSF18 and F13 predicted winter temperatures for 223 North Atlantic core-top samples.

simplified taxonomic groupings, can be more readily applied to faunal samples ranging in age from early Pliocene to Holocene. DSDP Hole 552A

DSDP Hole 552A is located near the margin of the Hatton-Rockall Basin, just west of Edoras Bank, in 2301 meters of water (Fig. 1). Hydraulic piston coring at this hole recovered 182.98 m of sediment (nominal recovery is 99.7% ) ranging in age from middle Eocene to Pleistocene. This area of the North Atlantic has

Table IV lists paleomagnetic reversal and other data used to produce an age model for Hole 552A (Zimmerman et al., 1985). Several workers (Raymo et al., 1989; Curry and Miller, in press) have determined that a hiatus exists between cores 9 and 10 at Hole 552A with a duration between 130 and 300 k.y. We follow the estimates of Curry and Miller (in press) and extrapolate the sedimentation rate between the top of the Olduvai and Matuyama-Gauss boundary to the base of core 9 to arrive at an age of 2.53 Ma for the 9/10 core break. The age at the top of core 10 is estimated at 2.71 Ma by extrapolating the same sedimentation rate upward from the base of the Kaena subchron. There is undoubtably material missing at most core breaks at 552A but without offset drilling TABLE IV Geomagnetic reversals used for age model construction Event

Depth (m)

Age (Ma)

Base JaramiUo subchron Top Olduvai subchron Top Gauss chron Bottom Core 9 Top Core 10 Base Kaena subchron Base Gauss chron

20.10 32.10 43.20 43.99 44.00 47.80 56.60

0.98 1.66 2.47 2.53 2.71 2.99 3.40

10

of an adjacent hole we cannot readily determine the duration of these gaps. Beyond the base of the Gauss chron we use one biostratigraphic control point, the last appearance of Discoaster quinqueramus at 125.90 m subbottom to constrain the lower part of our record. This last appearance is generally accepted to have taken place at 5.6 Ma (Berggren et al., 1985). The presence of primitive Globorotalia margaritae in core 20 samples and the first appearance of Globorotalia puncticulata at 91.00 m subbottom (core 19, section 3) support an early Pliocene age for the lowest segment of our time series.

Faunal data One hundred and fifty four 10cc samples (mean spacing 15 k.y.) from cores 9-20 were processed using low temperature (isotope) procedures. Sediment samples were dried in an oven at _<50 ° C and dissaggregated with warm tap water and about 2 ml of dilute calgon solution. After agitation the samples were washed through a 63tt sieve and dried in an oven at _<50°C. Some samples required additional treatments with about 10 ml of 10% H202 added to the wash in order to obtain clean specimens. A split of 300-350 planktic foraminifer specimens was obtained from the > 149 # size fraction using a Carpco sample splitter. Specimens were identified, sorted and glued to a standard 60 square micropaleontological slide. Raw faunal data from Hole 552A are listed in Appendix 2 along with the taxa included in the various counting categories. In general our taxonomic concepts follow those of Parker (1962; 1967) and Blow (1969) (See also Dowsett et al., 1988). To apply GSF18 to the planktic foraminiferal assemblages observed throughout Site 552A the raw faunal data were grouped like the core top data. However, fossil samples present additional problems which need to be addressed. First, taxa are encountered in Pliocene sediments which are now extinct and therefore are not explicitly included in the core-top data

H.J. DOWSETT AND R.Z. POORE

set. Examples include Globigerinoides obliquus,

Globigerina woodi, Neogloboquadrina atlantica, Globorotalia puncticulata, Globorotalia margaritae and SphaeroidineUopsis species. Unless contradicted by other data, we make the assumption that closely related taxa {ancestordescendent pairs ), have similar ecological needs and preferences. Based on this assumption, we follow previous workers in grouping Globigerinoides obliquus with Gs. ruber, Globorotalia puncticulata with Gr. inflata, SphaeroidineUops/s species with Sphaeroidinella dehiscens and Globorotalia margaritae with Gr. hirsuta (Thunnell, 1979a,b; Keigwin, 1976). We judge that Neogloboquadrina atlantica is best grouped with modern N. pachyderma and the artificial "du-pac" category. Studies of the North Atlantic Pliocene demonstrate that N. atlantica is the dominant form in high latitudes whereas it is absent or very rate in mid to low latitudes (Poore and Berggren, 1975; Poore, 1981b; Raymo et al., 1986). Neogloboquadrina acostaensis, N. humerosa and N. continuosa are equated with modern N. dutertrei. Thus, as in the modern grouping, our Pliocene census data contains a "cool" and a "warm" Neogloboquadrina category. Down core plots of per cent values of several of the dominant counting categories in Hole 552A assemblages are shown in Fig. 7.

Sea-surface temperature estimates As outlined above, downcore faunal census data from Site 552A are transformed into the modern core-top counting categories and hence downcore factors via a parafactor computation. Oceanographic estimates are then obtained via transfer function GSF18. These down core factors (Fig. 8) provide a quantitative picture of the assemblage composition of each sample in the 552A time series. Hole 552A communalities range from 0.869 to 0.994 with a mean of 0.955 suggesting that GSF18 does an adequate job of explaining the variability observed at this site throughout the Pliocene. The resulting winter

Ii

NEW PLANKTICFORAMINIFERTRANSFERFUNCTION "Warm .

G. bulloldes 0

10

20

30

40

G. glutinata

Gr. puncticulata 50 0

10

20

30

40

50 0

5

10

15

.

.

.

Cold"

Neogloboquadrina Neogloboquadrina 20 0

10

20

30 20 30 40 50 60 70 80

2.0

25

~"

3.0

U.I (3 3,5

4,0

!!!!!

4.5

5,0

Fig. 7. Down core abundances ( % ) of important planktic foraminiferal taxa at Hole 552A. Gray band indicates position of inferred hiatus.

and summer sea surface temperature estimates are given in Fig. 9. Comparison of down core abundance data (Fig. 7) and temperature estimates (Fig. 9) indicates that Neogloboquadrina, Globigerina bulloides and Globorotaliapuncticulata strongly influence the temperature estimates. We are concerned with potential problems in separating the Neogloboquadrina. Small specimens of Neogloboquadrina atlantica can be confused with compact variants of Globigerina bulloides. In addition, separation of Neogloboquadrina acostaensis and N. continuosa from "du-pac" was difficult in some samples. Therefore, we conducted several sensitivity tests to determine the impact of taxonomic problems or operator error on the SST estimates. We ran GSF18 on the 552A data with 10% of the Globigerina bulloides reassigned to Neoglo-

boquadrina atIantica and found that these changes amounted to less than 0.25 °C cooling in both seasons (Table V). With regard to potential problems with Neogloboquadrina acostaensis and N. continuosa we made two tests: first, we investigated the possibility that as many as 50% of the specimens identified as Neogloboquadrina acostaensis or N. continuosa were actually "du-pac" (alternatively, we estimated the impact of reassigning 20% of our "dupac" category to N. acostaensis. The results of these tests are in Table V and show significant changes in some samples with summer SST being the most sensitive. These results indicate the need for a more rigorous definition of the Pliocene "du-pac" morphology. We anticipate developing a larger geographic data set to develop such a definition. Because of the potential problems with the "du-pac") category, we

12

H.J. D O W S E T T A N D R.Z. P O O R E

FACTOR 1 TROPICAL -0.5 20

0

..........

FACTOR 2 POLAR 0.50,0

0.5

i .........

FACTOR 3 GYRE MARGIN 1.00.0

0.5

FACTOR 4 SUBTROPICAL 1.0 -1

0

FACTOR 5 SUBPOLAR -1

0

i[----11

25

3.0

I.LI 0 35"

4.0"

. . . . . . . . . . . . . . . . . . . . .

4.5-

50

Fig. 8. Down core variation in factor loadings for Tropical, Polar, Gyre-margin, Subtropical, and Subpolar assemblages at Hole 552A. Gray band indicates position of inferred hiatus.

place greater confidence in our estimates of winter SST than our summer SST estimates. Sea-surface temperature estimates derived from Site 552 (Fig. 9) show several major features between 4.6 Ma. and 2.3 Ma. There are periods during which mean sea-surface temperatures were several degrees warmer and other periods several degrees cooler than modern conditions. The warm intervals are of particular interest to us. Reconstructions of the last interglacial (isotope stage 5e) indicate that seasurface temperatures in this area of the North Atlantic were essentially the same as modern conditions (CLIMAP, 1984). Thus, our SST estimates identify intervals within the Pliocene that were substantially warmer than modern isotope stage 5e and, judging from isotopic records, any other Pleistocene interglacial. Between 4.6 and 4.0 Ma SST estimates are

characterized by low amplitude and low frequency oscillations. Mean winter SST (6° C) was 3.0 oC cooler than modern. At 4.0 Ma, temperatures warmed significantly and remained elevated until about 3.4 Ma. Fluctuations about the mean were small from 4.0 to 3.8 Ma and then became more pronounced towards the end of the warm interval. Mean winter SST was about 2.0°C warmer than modern values during this interval. A marked cool interval is seen between 3.4 and 3.2 Ma. Winter SST returned to levels seen prior to 4.0 Ma, but the amplitude of variation about the mean is greater. The end of the cooling event is marked by another sharp temperature increase to a peak at about 3.1 Ma. Mean winter SST at the peak warming were about 3.5°C warmer than modern. The temperature record after 3.1 Ma shows a trend towards cooler conditions with high

NEW PLANKTIC FORAMINIFERTRANSFER FUNCTION

WINTER SST 6 8 , I • I

2.0

10 12 14 I , I ,

SUMMER SST

10 20

.& 3.0'

I

2.0

2.5,

2.5"

13

ii!

,

!

30 ,

!

3.0' ÷

w

3.5'

4.0

4.0

¸

4.5

' ~

4.5 1 5.0

5,0

i

Fig. 9. W i n t e r and S u m m e r S S T estimated for Hole 552A. Vertical lines indicate approximate mean annual sea surface temperature today at the location of D S D P Site 552. Gray band indicates position of inferred hiatus.

amplitude variations about the declining mean. The coldest estimates coincide with the first unequivocal occurrence of ice-rafted detritus at about 2.45 Ma. The pattern of winter SST estimates is the

same as the summer estimates throughout the interval we have studied, but the magnitude of warmings is greater in the summer SST estimates. Current seasonality in the North Atlantic in the vicinity of Site 552 is around 5 to 6 ° C. Thus, our data suggest that seasonality increased during warm intervals, to as much as 10°C and decreased somewhat during cold intervals, to around 4°C. However, GSF18 summer SST values are sensitive to partitioning of taxa within the Neogloboquadrina plexus and winter SST values are probably biased toward colder estimates due to our grouping of Neogloboquadrina atlantica with dextral and sinistral forms of Neogloboquadrina pachyderma. Thus, our summer SST estimates and related data on seasonality must be treated with caution until we can substantiate those results.

Comparison with isotopic data Figure 10 shows the Site 552A winter SST estimates along with available oxygen isotope data from this site. The planktic record from Shackleton and Hall (1985) has been edited to include only Cibicidoides spp. data, making comparison to the Cibicidoides spp. record of Curry and Miller (in press) more direct (Fig. 10). Planktic 01sO data are from Neogloboquadrina atlantica (Shackleton and Hall, 1985). Above 3.1 Ma, the SST and planktic and benthic oxygen isotope records exhibit a good general correlation although details of the curves differ,

TABLE V Sensitivity tests No.

Description

Effect

Mean change ( ° C )

Max. change ( ° C)

Winter

Summer

Winter

Summer

Reassign 10% Globigerina bulloides to

Cooling

0.11

0.10

0.22

0.19

Neogloboquadrina atlantica Reassign 50% Neogloboquadrina acostaensis

Cooling

0.44

0.90

1.76

4.06

to "du-pac" category Reassign 20% "du-pac" category to

Warming

0.20

0.75

0.75

1.63

Neogloboquadrina acostaensis

H.J. DOWSETT

14

WINTER SST °C 4 2.2

l

6 ,

I

8 :

i

10 ,

i

12 ,

I

14 3 ,

BENTHIC

PLANKTIC ~lSO I

2

3

1 4

~

~180

BENTHIC

2

AND

R.Z. POORE

~ISO

3

2

I-

2.4

!

=E

uJ (3

2.8T---~ 3.°.+

. . . . .

t . . . .

. . . .

. . . . .

.

3.2'

3.4'

3.6

.

.

.

.

L

~

SHACKLETON

•

AND HALL 1985

J

~

,

CURRY & MILLER

in press Fig. 10. Comparison of Winter SST with benthic and planktic stable isotope data from DSDP Hole 552A. Note that we have only plotted Cibicidoides spp. data from the 552A benthic record of Shackleton and Hall {1985). Gray band indicates position of inferred hiatus.

in part, because of different sampling densities. The cooling trend indicated by faunal sea-surface temperature estimates is matched by a trend towards heavier values in the isotopic records. High amplitude variability about the general trend is seen in all data sets. The warmest SST estimates at about 3.1 Ma correlate with a light excursion in the planktic isotopic data; the available benthic data at this point do not define a clear peak. We interpret these records to indicate that following the thermal maximum at approximately 3.1 Ma, there was overall surface water cooling and gradual but continuous build up of global ice volume culminating in a Northern Hemisphere glaciation that is indicated by the presence of ice-

rafted detritus in 552A sediments at about 2.45 Ma. Between 3.1 and 3.5 Ma the isotopic records and SST estimates are not well correlated. The pronounced cool event seen in the SST estimates does not show up in either a 1sO record. Coarse fraction and percent benthic foraminifer indices (Appendix 2) and CaCO3 data (Zimmermann et al., 1985 ) do not suggest that the faunal signal is related to a period of higher dissolution. In addition, the faunal change indicating cool temperatures in this interval of 552A is compelling both within this core and in other cores from the North Atlantic. The down core abundance data (Fig. 7) document the absence or very low abundance of Globorotalia puncticulata between 3.15 and 3.35

15

NEW PLANKTIC FORAMINIFER TRANSFER FUNCTION Appendix 1. Varimax facto~ matrix for core top samples. Negative longitude is West longitude. Site 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69

Latitude 44.35 28.00 50.93 35.72 36.13 36.13 35.78 36.22 37.65 31.83 31.65 29.77 19.40 19.92 23.93 24.80 30.78 35.77 39.13 39.27 33.57 25.83 05.28 03.65 00.58 10.55 20.72 42.47 23.75 37.22 36.85 35.05 32.60 32.28 32.20 17.55 29.28 38.92 36.90 34.67 40.77 08.23 22.95 23.02 24.27 11.18 01.75 17.00 15.48 00.85 30.52 17.93 17.27 13.25 01.97 15.40 23.33 30.00 60.03 28.48 12.38 24.97 27.97 29.62 32.75 ,58.3~7 60.73 13.73 04.23

Longitude Cornmunality -30.27 0.901 -38.78 0.960 -41.75 0,966 -67.33 0.868 -68.92 0,905 -69.13 0.964 -68.93 0.910 -69.40 0.930 -72.95 0.976 -74.35 0.925 -75.35 0,954 -76.80 0.764 -78.55 0,993 -73.83 0.829 -75.75 0.955 -75.92 0,960 -67.67 0.910 -69.08 0.919 -42.65 0.937 -36.70 0.962 -27.37 0.929 -19.30 0.951 -17.07 0.599 -18.30 0.782 -21.78 0,974 -57.33 0.986 -59.20 0.967 -54.90 0.997 -92.47 0,973 -33.13 0.889 -21.02 0.846 -11.62 0.820 -69.50 0.897 -65.12 0,827 -64.70 0.884 -63.57 0.933 -79.92 0.742 -57.13 0,987 -54.03 0.887 -61.4.5 0.958 -64.60 0.988 -37.87 0,923 -38.20 0,959 -43.80 0,964 -53.07 0,945 -36.02 0,992 -16.05 0,876 -74.38 0,989 -40.52 0,996 -32.85 0.991 -75.92 0.974 -50.35 0.995 -48.42 0.993 -40.67 0.891 -37.07 0,989 -43.40 0.993 -46.48 0.969 -51,87 0.959 -50.83 0.978 -65.05 0.946 - 18.92 0,974 -28.93 0.911 -34.13 0.951 -36.92 0.972 -41.90 0.904 -47.73 0,980 -57.83 0,979 -51.12 0.971 -47.75 0.986

Tropical 0.258 0.934 0.011 0.538 0,438 0.806 0,553 0,684 0,061 0.904 0.952 0.840 0,989 0,892 0.972 0.976 0.911 0.691 0.319 0,552 0.767 0.877 0.076 0.112 0.970 0.985 0,978 0,049 0,979 0.634 0.521 0.602 0.685 0.800 0.863 0.965 0.815 0.199 0.335 0,752 0.043 0.931 0,974 0,976 0.966 0.946 0,450 0.970 0.995 0.966 0.973 0.997 0,996 0,872 0,974 0.991 0.978 0.957 0.016 0.957 0.556 0.871 0.960 0,847 0.813 0.020 0.015 0,732 0.967

Polar 0.639 0.027 0.900 0.192 0.328 0.197 0.304 0.250 0.758 0.027 0,035 0.047 -0.007 0.023 -0.011 -0,005 0.035 0.149 0.604 0,279 0.166 0,264 0.017 -0,009 0.022 -0.017 -0.025 0,949 -0.006 0,256 0.309 0.379 0.133 0.068 0.027 -0.014 0.047 0.858 0.341 0,176 0.928 -0.002 -0.019 -0.005 -0.021 0.175 0.016 0.008 -0.010 -0.001 0,017 -0.007 -0.006 0.008 -0.010 0.003 -0.011 0.014 0,967 0,000 0.235 0.052 -0.002 0.093 0.077 0.967 0.967 0.035 -0.019

Gyre Margin 0.020 -0.107 0,052 0.316 0.419 0.224 0.349 0,270 0.282 0.172 0.102 0,017 0.119 0.097 -0.092 -0.068 -0.074 0.356 0.144 -0.010 -0,065 0.161 0.769 0.876 0.149 0.117 0.090 0.060 0.112 -0.033 0,042 -0,038 0.059 -0.071 -0.113 -0.014 0,103 0.183 0.158 0.060 0.165 0.232 -0.032 -0.077 -0.078 0.254 0.819 0.216 0.073 0.131 0.001 0.010 0.001 0,357 0,203 0,093 -0.085 -0.067 -0.002 -0.082 0,763 0,272 -0.084 -0.066 -0.054 -0.002 -0.001 0.655 0.223

SubTropical 0,646 0.268 0.389 0.576 0.652 0.426 0.616 0.538 0.423 0,278 0,183 0.126 0,032 0.086 0,055 0.057 0.262 0,538 0.607 0.706 0.537 0.280 0.020 -0.001 0.056 0.013 0.011 0.161 0,032 0.593 0.689 0.556 0.634 0,420 0.330 0,030 0,134 0.264 0.778 0.560 0.149 -0.022 0.063 0.073 0.043 0.016 -0.043 0.012 0.026 0,023 0.150 0.028 0.035 -0.045 -0.008 0,042 0.063 0.181 -0.156 0.120 0.143 0.220 0.120 0.438 0.482 -0.158 -0.158 0.037 -0,007

SubPolar 0.093 -0.056 -0.038 0,331 0,069 0.208 0,098 0.195 -0.369 0.031 0,061 0,201 -0.009 0.128 -0.008 0.016 0.074 -0.057 -0.286 0.283 0.143 -0.094 0.042 0.038 0.078 -0.028 -0,052 -0.254 0.001 0,263 0.044 0.042 0.068 -0.022 0.129 -0.017 0,215 -0.330 -0.170 0.212 -0,275 0.032 -0.0T7 0.007 -0.053 -0.025 0,026 0,045 0.007 0.038 0.064 0.009 0.016 0.008 0.011 0,025 -0,006 -0.073 -0.139 -0.092 -0.086 -0.164 -0.084 -0.221 0.034 -0.137 -0.138 0,052 -0.017

16

H.J. DOWSETT AND R.Z. POORE

Appendix I. Varimax facto/" malnx for core top samples. Negative longitude is West longitude. Site 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138

Latitude 38.75 01.42 03.65 29.02 11.53 02.00 05.32 08.47 23.37 38.28 12.75 08.72 04.67 14.40 15.02 20.70 27.92 34.75 41.52 54.20 59.95 62.65 70.05 54.25 52.58 49.87 46.00 29.80 19.88 17.20 17.48 22.60 26.78 09.32 27.92 06.27 06.02 05.83 00.30 30.45 42.78 42.27 42.73 44.15 54.00 54.03 54.72 55.97 56.72 58.18 59.13 60,70 61.93 61.37 62.85 55.03 48.28 43.78 43.97 42.68 39.70 39.58 34.18 29.48 25.93 16.53 08.80 05.10 02.25

Longitude Communality -67.55 0.911 -09,08 0.792 -15,05 0.796 -41,40 0.959 -60,52 0.979 -35,60 0.972 -33.03 0.916 -30.13 0.847 -43,65 0.973 -68.53 0.984 -45.63 0.933 -41.25 0.969 -20.92 0,957 -21.15 0.919 -23.23 0.976 -31.45 0.991 -43.63 0,961 -57.25 0.861 -45.13 0.983 -45.97 0.871 -32.85 0,879 -27.53 0.922 08.32 0.991 -16.83 0.978 -21.93 0,983 -24.25 0.964 -16.92 0.962 - 15.08 0.986 -25.53 0.950 -38.83 0.993 -40.67 0.983 -72.60 0.965 -46.68 0.958 -42.98 0.896 -47.77 0.966 -17.90 0.888 -18.23 0.716 -18.08 0.918 -14.80 0.963 -67.97 0.915 -54.33 0,991 -60.48 0.987 -43.22 0.982 -39.87 0.972 -46.20 0.892 -46.85 0.910 -53.10 0.979 -56.05 0.978 -54.68 0.979 -44.60 0.976 -41.07 0.980 -37.27 0.944 -33.27 0.972 -11.48 0.993 -17.92 0.993 -33.07 0,963 -16.97 0,989 -14.68 0,933 -15.80 0.991 - 17.07 0,969 -20.15 0.871 -13.55 0.986 -16.85 0.858 -19.60 0.956 -26.58 0.947 -28.85 0.991 -22.10 0.832 -26.65 0.891 05.72 0.838

Tropical 0.129 0,124 0.075 0.962 0.976 0.947 0.914 0.157 0,962 0.044 0.922 0.969 0.933 0.114 0.965 0.974 0,958 0.600 0.322 -0.005 0.029 0.037 0.017 0,045 0.039 0.045 0.113 0.948 0,872 0,962 0,968 0,979 0.968 0.836 0.966 0.132 0.449 0.135 0.617 0.919 0.019 0.010 0.221 0.134 0.002 0.004 0.016 0.015 0.015 0.012 0.015 0.027 0.024 0.016 0.014 0.054 0.043 0.011 0.015 0.151 0.442 0.186 0.722 0,926 0.873 0.902 0.729 OJBg0 0.109

Polar 0.365 0.136 -0.008 -0.003 -0.018 -0.013 0.043 0.002 -0.010 0.860 -0.003 0.005 0.052 0.037 0.082 0.047 -0.004 0.204 0.668 0.660 0.849 0.880 0.982 0.962 0.959 0.891 0.907 0.051 0.162 0.018 0.033 -0.008 -0.007 -0.010 -0.003 -0.010 0.024 -0.012 0.042 0.028 0.967 0.957 0.909 0.779 0.731 0.802 0.967 0.966 0.967 0.981 0.987 0.943 0.970 0.996 0.972 0,794 0.942 0.771 0.901 0,881 0.468 0.945 0.140 0.264 0.090 0.213 0.137 -0.010 0,029

Gyre Margin 0.351 0.869 0.888 -0.100 0.158 0.274 0.264 0.905 -0.074 0.193 0.287 0.174 0.287 0.941 0.139 0.199 -0,096 0.125 0.134 0.007 0.003 -0,006 0.000 0.034 0.026 0.055 0.029 0.012 0.389 0.259 0.016 -0,053 -0.094 0.442 -0.076 0.932 0.714 0.948 0.760 -0.072 0.047 0.103 0.039 0.079 0.010 0.007 -0.002 -0.001 -0.001 0.003 0.000 -0.002 0.000 0.012 0,019 0.006 0.030 0.060 0.030 0.050 -0.039 0.004 0.018 -0.066 0.267 0.351 0,529 0.311 0.848

SubTropical 0,651 0.048 0.044 0.151 0.007 -0.025 -0.002 0.044 0.058 0.313 -0.034 0.009 0.004 0.118 0.134 0.034 0.175 0.620 0.633 0.312 0.081 0.083 -0.147 0,189 0.227 0.353 0.343 0.268 0.105 0.008 0.065 0.057 01~ 8 -0.030 0.150 0.040 -0.068 0.024 -0.026 0.256 0.156 0.210 0.314 0.550 0.294 0.240 -0,156 -0.159 -0.158 -0.100 -0.073 -0.009 -0.032 -0,028 0,055 0,271 0.297 0.384 0.245 0.363 0.671 0.230 0.561 0.150 0.269 0,078 -0.036 -0.055 0.287

SubPolar -0.463 0.000 0.013 -0.035 -0.038 0.004 0.088 0.023 -0.012 -0.327 0.000 0.021 0.018 -0.063 0.036 -0.013 -0.068 -0.242 -0.123 0.581 0.387 0.374 -0.072 0.121 0.098 0.201 0,092 -0.113 -0.018 -0.015 0,007 0,005 -0,047 -0.018 -0.065 0.012 0.005 0.013 0.054 0.005 -0.171 -0.122 0.078 -0.196 0.520 0.458 -0.136 -0,141 -0.138 -0.048 0.004 0.234 0.173 -0.033 -0.212 0.507 -0.097 -0.434 -0.342 -0.191 -0.067 -0.078 -0.045 -0.054 -0.185 -0.052 0.013 -0.006 -0.152

17

NEW PLANKTIC F O R A M I N I F E R T R A N S F E R F U N C T I O N

Appendix 1. Varimax factor matrix for core top samples. Negative IorKiitude is West longitude. Site 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207

Latitude 00.98 03.05 01.03 20.17 35.57 55.53 76.82 73.48 72.18 71.17 64.83 68.72 67.68 65.52 60.55 60.62 49.45 47.47 44.53 42.17 26.78 12.27 16.37 22.47 40.55 41.53 42.83 44.00 45.30 49.13 49.13 52.37 52.67 55.40 57.00 58,72 59.95 60.38 60.80 61.18 61.55 65.60 66.73 67.78 72.97 75.92 65.17 62.85 61.92 18.43 21.23 22.65 24.12 25.72 25.72 25.57 25.83 25.88 25.92 26.60 26.92 24.50 10.18 44.18 45.08 54.'07 21.30 16.57 07.63

L ~ . itude Communality 01.98 0.902 -11.80 0.938 -13.62 0.674 -26.62 0.931 -43.90 0.930 -47.10 0.973 -01.33 0.979 -00.83 0.978 05.27 0.946 01.62 0.986 -03.58 0.966 -12.72 0.979 00.23 0.983 00.20 0.959 -11.45 0.861 -15.18 0.993 -22.27 0.965 -19.98 0.979 -32.58 0.989 -42.10 0.977 -50.83 0.971 -81.70 0.989 -17.92 0.965 -20.07 0.973 -26.00 0.948 -25.70 0.975 -25.15 0.950 -24.53 0.975 -23.87 0.970 -25.50 0.984 -25.50 0.993 -17.53 0.992 -15.17 0.991 -18.73 0.995 -21.32 0.987 -15.55 0.984 - 19.20 0.958 -20.97 0.960 -22.43 0.977 -23.00 0.955 -25.12 0.921 -06.48 0.883 -06.73 0.884 -06.67 0.928 -06.98 0.980 -05.12 0.980 -00.07 0.924 -14.53 0.983 -24.05 0.992 -21.08 0.978 -21.32 0.983 -19.20 0.988 -19.10 0.922 -26.88 0.982 -19.52 0.992 -16.83 0.964 -16.92 0.970 -16.45 0.972 - 19.05 0.961 -15.15 0.955 -19.13 0.992 -16.95 0.979 -77.20 0.987 - 14.90 0.888 - 10.55 0.868 -15.38 0.954 -69.65 0.967 -79.52 0.990 -48.08 0.990

Tropical 0.289 0.801 0.189 0.794 0.6~8 0.010 0.015 0.021 0.018 0.016 0.018 0.015 0.017 0.018 0.048 0.040 0.054 0.050 0.143 0.196 0.973 0.985 0.351 0.951 0.278 0.183 0.222 0.118 0.102 0.058 0.046 0.037 0.050 0.028 0.047 0.051 0.058 0.051 0.944

0.059 0.077 0.018 0.018 0.018 0.015 0.015 0.021 0.043 0.660 0.616 0.479 0.168 0.592 0.917 0.864 0.570 0.426 0.229 0.837 0.655 0.927 0.294 0.946 0.048 0.042 0.061 0.979 0.963 0.987

Polar 0.017 0.081 0.167 0.112 0.231 0.974 0.966 0.966 0.9.56 0.972 0.965 0.966 0.975 0.969 0.862. 0.873 0.900 0.865 0.777 0.832 O.OO2 0.047 0.725 0.164 0.593 0.550 0.625 0.746 0.815 0.910 0.919 0.979 0.937 0.950 0.917 0.914 0.845 0.929 0.925 0.887 0.837 0.920 0.921 0.945 0.967 0.967 0.949 0.894 0.913 0.664 0.769 0.899 0.548 0.301 0.410 0.651 0.795

0.825 0.359 0,576 0.271 0,869 .0.014 0.914 0.869 0.905 -0.002 -0.003

-0.011

Gyre Margin 0.894 0.539 0.776 0.529 0.014 0.002 -0.001 -0.002 -0.002 -0.002 -0.003 .0.001 -0.002 -0.001 -0.003 0.006 0.030 0,027 0.008 0.072 -0.078 0.124 0.205 0.044 0.000 -0.009 -0.027 -0.002 0.002 0.018 0,018 0.016 0.009 0.011 0.012 0,003 0.008 0.010 0.004 0.003 0.005 -0.004 -0.004 -0.004 -0.002 -0.001 -0.004 .0.002 -0.002 0.179 0.130 0.087 0.201 0.060 0.027 0.072 0.052 0.021 0.150 0,079 0.044 0.076 0.303 0.038 0.062 0.025 -0.071 0.248 0.125

Sub-

Tropical 0.134 0.001 0.079 0.082 0.620 0.009 -0.159 -0.158 -0.172 -0.158 -0.176 -0.159 -0.162 -0.140 0.065 0.239 0.363 0.419 0.576 0.472 0.125 0.019 0.523 0.190 0.705 0.749 0.676 0.575 0.535 0.351 0.366 0.171 O.223 0.195 0,237 0.180 0,273 0,186 0,187 0.195 0.213 -0.188 -0.188 -0.182 -0.160 -0.159 -0.151 0.130 0.176 0.319 0.329 0.262 0.436 0.194 0.245 0.456 0.359 0,456 0.267 0.421 0.218 0.350 0.003 0.125 0.2~8,5 0.219 0.062 0.009 0.001

SubPolar -0.039 .0.031 0.046 -0.044 -0.066 0.158 -0.140 -0.141 -0.041 -0.123 -0.067 -0.140 -0.075 -0,013 0.336 0.414 0.137 0.228 0.178 0.137 -0,047 -0.017 O.025 -0.067 0.149 0,280 0.228 0.269 0.102 0.171 0.110 0,037 0.247 0.230 0.297 0.338 0.408 0.243 0.289 0.355 0,412 -0.028 -0.028 -0.044 -0.139 -0.137 0.010 0.405 0.353 -0.153 -0.190 .0.277 -0.203 -0.094 -0.128 0.038 0.157 -0.175 .0.196 0.104 -0.095 -0.098 -0.006 -0.185 -0.163 0.289 0.018 0.036 0,001

18

H.J. DOWSETT AND R.Z. POORE

Appendix 1. Vanmax f_=~__~matrix for core top samples. Neqative longitude is West Iorzqitude. Site 208 20g 210 211 212 213 214 215 216 217 218 21 g 220 221 222 223

L=~h =dA 04.97 02.22 00.92 01.68 30.73 38.03 13.17 01.85 01.78 04.58 03.70 04.52 02.02 59.65 53.87 63.47

Longitude Communality -45.97 0.981 -45.40 0.985 -43.77 0.983 -41.52 0.901 -75.32 0.962 -70.80 0.982 -79.82 0.994 -30.00 0.957 -25.43 0.979 -10.05 0.947 -07.72 0.923 -00.72 0.937 02.63 0.874 -22.77 0.981 -21.10 0.988 -00.07 0.982

Tropical 0.982 0.962 0,941 0.601 0.968 0.088 0.970 0.930 0.960 0,903 0.866 0.858 0.268 0.050 0.018 0.017

Polar -0.011 -0.015 -0.011 -0,005 -0.002 0.916 .0.009 0.001 0.029 0.015 0.010 0.025 0.001 0.878 0.974 0.973

Gyre Margin 0.129 0.244 0.311 0.731 0.084 0.130 0.230 0.297 0.232 0.356 0.411 0.389 0.878 0.021 0.025 -0.001

SubTropical -0.012 0.002 .0.017 -0.063 0.131 0.313 0.014 -0.008 0.009 0.067 0.057 0.200 O.157 0.217 0.182 -0.143

SubPolar -0.014 0.001 0.015 0,036 0.023 -0.142 0.012 0.060 0.048 0.021 -0.016 -0.088 -0.078 0.400 0.070 -0.123

VARIANCE CUMULATIVE VARIANCE

39.939 39,939

35.141 75.079

7.924 83.003

8.470 91.473

2.972 94.446

Ma. Globigerina buUoides shows well defined increases in abundance at the beginning and end while "cold"Neogloboquadrina show a peak in the middle of the Globorotaliapuncticulata gap. The same sequence of faunal events, including common occurrence of Globorotalia puncticulata above and below the "puncticulata gap", is a regional feature documented at several other sites in the North Atlantic (Sites 548, 606 and 607) at approximately the same time (Ehrman and Keigwin, 1986; Loubere and Moss, 1986; Raymo et al., 1986 and Dowsett et al., 1988). We conclude that the cooling indicated by our SST estimates in 552A between 3.15 and 3.35 Ma represents regional sea-surface cooling in the North Atlantic, whereas the isotopic records from this interval of 552A are reflecting a complex signal that includes global ice-volume, as well as local temperature near the surface and at the sea floor. Cooling is not seen in the Neogloboquadrina atlantica 01sO data which suggests that N. atlantica is not a surface dwelling form. Instead, N. atlantica may be a deep dwelling planktic and, as suggested by Shackleton and Hall (1985), may migrate vertically in the water column to seek a constant temperature.

Summary and conclusions A reorganized and simplified modern Atlantic core-top data set for planktic foraminifers

has been used to develop a transfer function for SST estimates. The new transfer function (GSF18) and faunal groupings it uses give modern SST estimates that are as accurate as F13, the standard Atlantic transfer function used by CLIMAP, but are more readily applied to Pliocene foraminifer assemblages. Application of GSF18 to total faunal analysis of a Pliocene record spanning the interval of 4.6 to 2.3 Ma in DSDP 552A has identified two intervals in which mean winter SST exceeded modern and isotopic stage 5e temperatures by about 2 ° C. These warm intervals are dated in Hole 552A as 4.0 to 3.5 Ma and 3.15 to 2.95 Ma. SST estimates from faunal data and oxygen isotope data on benthic and planktic foraminifers show parallel trends between 3.1 and 2.2 Ma. SST estimates and isotopic data from intervals older than 3.1 Ma are not well correlated.

Acknowledgements

We thank T.M. Cronin, W.F. Ruddiman, M.E. Raymo and R.S. Thompson for reviewing drafts of this manuscript and for discussions which greatly improved the final version. Linda Gosnell provided assistance with drafting and various aspects of data reduction.

NEW PLANKTIC FORAMINIFER TRANSFER FUNCTION

Explanation of counting category abbreviations In Appendix 2. Category

Comments

Globigennabulloides (d'Orbigny) and G. praebulloides Blow Globigerina falconensisBlow Globigerinapseudobesa (Salvatodni) Globige#naincisa (Bronnimann and Resig) Globigennadigitata Brady Globigerinaprae~gitata Parker Globige#naeamsi Blow Globigedna woo~Jenkins and G. apertura Cushman Globige#nasp. 1. Taxon resembles G. falconensisbut has reticulate surface texture similar to G. woodi group. aequi G/obiget~nellaaequi/aterak's(Brady) gluti G/obigerinitaglu~nata (Egger) s.L obliq Globigerinoides ob#quusBolli and G. extrernus Bolli and Bermudez Globigerinoides tuber (crOrbigny) ruber Gnoid G/obigerinoidesspp. Representatives of Globigerinoides(usually small) that could not be confidently assigned to G. tuber, G. ob/iquus(s.l.) or G. cong/obatus. conom Globorotalia conomiozeaKennett crass Globorotaliacrass~ormis (Galloway and Wissler). This category includes G. ronda Blow and G oceanica Cushman and Bermudez. Specimens with a distinct keel on the entire ultimate whod are tabulated separately under "kcras'. kcras Globerotaliacrassaformiswith fully keeled ultimate whorl. hirsu Globorotalia hirsuta (d'Orbigny) plata G/oborotaHainflata (d'Orbigny) and G. punc~cu/ata(Deshayes) marga Globerotala margantaeBolli and Bermudez menar G/o~rota/ia menardii(Parker, Jones, and Brady) s.L Globorotaliascitula (Brady) scitu acost Neogloboquadfinaacostaensis (Blow) and N. continuosa (Blow) satca Neog/oboquaddnaatlanUca(Berggren) left-ceiling. datca Neogloboquadnnaatlantica (Berggren) right-coiling spach Neogloboquadrinapachydenna (Ehrenberg) left-coifing. Relatively small, compact Neogloboquadfinawith 4-5 chambers in the ultimate whorl, kummerform ultimate chamber, and a slightly to distinct oval equatorial outflne are included here. dpach Neogloboquadfinapachyderma (Ehrenberg) fight-coiling. dupac This category is used for specimens of dght-coiling Neogloboquadfinawith mere than four chambers in the ultimate whorl that are transitional between N. pachydermaand N. acostaensis or N. atlantica. Orbul Orbulina universad'Orbigny quinq Turborotalita quinqueloba(Natland) OTHER This category includes rare unidentified specimens and taxa Reworked Reworked specimens from Eocene sediments TOTAL PLANK Total number of planktJc forams in counting split frags Fragments of planldic foraminifers rocks Ice-rafted detritus bforrn Benthic foraminifers bulls falce pseud incis digit praed earnsi woodi sp. 1

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