Late Paleocene to Eocene Paleoceanography of the Equatorial Pacific Ocean: Stable Isotopesrecorded at Ocean Drilling Program Site 865, Allison Guyot

PALEOCEANOGRAPHY,VOL. 10, NO. 4 , PAGES 841-865, AUGUST 1995

Late Paleocene to Eocene paleoceanography of the equatorial Pacific Ocean: Stable isotopesrecorded at Ocean Drilling Program Site 865, Allison Guyot

TimothyJ. Bralower,1James C. Zachos,2 Ellen Thomas, 3,4 Matthew Parrow, 1 Charles K. Paull,• D. ClayKelly, • IsabellaPremoli Silva, 5 WilliamV. Sliter,6 and Kyger C. Lohmann 7

Abstract. An expandedand largely complete upper Paleocene to upperEocene section was recoveredfrom the pelagic cap overlying Allison Guyot, Mid-Pacific Mountains at OceanDrilling Program(ODP) Site865 (18ø26'N,179ø33'W; paleodepth 1300-1500 m). Reconstructionsshow thatthe site was within a few degreesof theequator during the Paleogene. Because no other Paleogenesections have been recovered in thePacific Ocean at sucha low latitude,Site 865 providesa uniquerecord of equatorialPacific paleoceanography. Detailed stable isotopic investigationswere conducted on three planktonic foraminiferal taxa (species of Acarinina, Morozovella,and Subbotina). We studiedbenthic foraminiferal isotopes at muchlower resolution on speciesof Cibicidoidesand Lenticulina, Nuttallides truernpyi and Gavelinella beccariiformis, becauseof theirexceptional rarity. The •5180 and •513C stratigraphies from Site 865 are generally similarto thosederived from otherPaleocene and Eocene sections. The planktonicforaminiferal recordsat Site 865, however,include significantly less short-term, single-sample variability than thosefrom higher-latitude sites, indicating that this tropical, oligotrophic location had a comparativelystable water column structure with a deepmixed layer and less seasonal variability. Low-amplitude(0.1-0.8%o) oscillations on timescalesof 250,000to 300,000years correlate betweenthe/513C records of all planktonictaxa and may represent fluctuations in the mixing intensityof surfacewaters. Peak sea surface temperatures of 24ø-25øCoccurred in theearliest Eocene,followed by a rapidcooling of 3-6øCin thelate early Eocene. Temperatures remained cool andstable through the middle Eocene. In thelate Eocene, surface water temperatures decreased further.Vertical temperature gradients decreased dramatically in thelate Paleocene and were relativelyconstant through much of theEocene but increased markedly in thelate Eocene. Intermediatewaters warmed through the late Paleocene,reaching a maximumtemperature of 10øC in the earlyEocene. Cooling in themiddle and late Eocene paralleled that of surfacewaters, with latestEocene temperatures below 5øC. Extinctionpatterns of benthicforaminifera in thelatest Paleocene were similar to those observed at other Pacific sites and were coeval with a short-term, veryrapid negative excursion in/513C values in planktonicand benthic taxa as at othersites. Duringthis excursion, benthic foraminiferal/5180 values decreased markedly, indicating warming of 4 to 6øCfor tropicalintermediate waters, while planktonictaxa show slight warming (1 øC) followedby 2øC of cooling.Convergence of/5180 values of planktonicand benthic foraminifera suggeststhat thermalgradients in the watercolumn in thistropical location collapsed during the excursion.These data are consistentwith the hypothesisthat equatorial Pacific surface waters were a potentialsource of warm, highersalinity waters which filled portionsof the deepocean in the latestPaleocene. Oxygen isotopic data indicate that equator to high southernlatitude sea surface thermalgradients decreased to as little as 4øC at the peak of the excursion,suggesting some fundamentalchange in globalheat transport.

1Departmentof Geology, University of NorthCarolina, Chapel Hill. 6Branchof Paleontologyand Stratigraphy, U.S. Geological Survey, 2EarthScience Board, University of California,Santa Cruz. Menlo Park, California. 3Departmentof Geology and Geophysics, Yale University, New 7Departmentof Geological Sciences, University of Michigan,Ann Haven, Connecticut. Arbor. 4Alsoat Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut. Introduction 5Dipartimentodi Scienza della Terra, Universita di Milano,Milan, Italy. Paleogenesediments have proven to be elusive targets for high-resolutionpaleoceanographic studies: they are too young Copyright1995 by the AmericanGeophysical Union. to be widely exposedin mountainbelts yet too old to be easily Papernumber 95PA01143. accessibleto shallow drilling technology. Most researchhas 0883- 8305/95/95PA- 01143510.00 thusbeen doneon materialrecovered by the Deep Sea Drilling 842 BRALOWERET AL.: PALEOGENE EQUATOR/AL PACIFIC PALEOCEANOGRAPHY

Project (DSDP) and OceanDrilling Program(ODP), especially in the Paleogenesubtropical Pacific Ocean [Zachos and Arthur, sedimentsfrom high southernlatitude sites such as from Maud 1986; Miller et al., 1987; Corfield and Cartlidge, 1992; Pak Rise in the southernmostAtlantic Ocean [Barker et al., 1990] and Miller, 1992]. This section accumulated at low and KerguelenPlateau in the Indian Ocean[Wise et al., 1992]. sedimentationrates and containshighly condensedintervals or These sectionshave been analyzed at a resolutioncommonly short-termhiatuses (particularly in the lower Eocene), the seen in studieson younger sections[e.g., Kennett and Stott, middleEocene is missing,and part of the uppermostPaleocene 1990; Stott and Kennett, 1990; Barrera and Huber, 1991; lies in a core break in two holes. A rotary-drilledrecord from Zachos et al., 1993; Thomas and Shackleton, 1995], DSDP Site 47.2 also on the ShatskyRise hasbeen discussed by demonstratingthat Paleogeneoceans and climate witnesseda Stott [1992], but significant drilling disturbanceprecludes pattern of short-term(103-10 4 years) fluctuationsin high-resolution studies. temperature. These short-termexcursions are superimposedon The Paleogenepelagic cap sectionat Site 865 on Allison long-term(>106 years) climatic fluctuations [e.g., Shackleton Guyot (18ø 26' N, 179ø 33' W; 1530 m waterdepth; Figure 1) and Kennett, 1975; Savin, 1977; Kennett and Stott, 1991; lies on Cretaceousshallow water limestonestargeted on Leg Corfield and Cartlidge, 1992; Miller, 1992]. During the latest 143. Calculationsusing the Pacific polar wanderpath indicate Paleocene to earliest Eocene, high-latitude surface waters paleolatitudesof about 2 ø N in thelate Paleocene to about6 ø N warmed graduallyfrom 11ø to 15øC and deep watersfrom 9 ø to in the late Eocene (R. Larson, oral communication, 1994). 13øC [Miller et al., 1987; Stott et al., 1990; Zachos et al., Conventionalpaleodepth back-tracking techniques could not 1993], but in the middle through late Eocene, high-latitude be employeddue to the unusualthermal history of the Mid- surface and deep waters cooled to 6øC and 4øC, respectively Pacific Mountains. Depth estimates based on benthic [e.g., Zachos et al., 1994]. foraminifera are not precisefor the bathyal-abyssalrange in The latest Paleocenerapid climatic change was one of the Paleogenesediments [Berggren and Miller, 1989],but detailed most dramatic warming events in the geological record. comparisonbetween Paleocene/Eocene faunas at Site 865 and Antarctic surface and deep water temperaturesincreased from those at Sites 762 (Indian Ocean, paleodepth1000-1500 m), 14øC to 20øC and from 10øC to 18øC, respectively,over less Site 577 (Pacific Ocean, paleodepthabout 1500 m), Site 752 than 10,000 years, so that vertical thermal gradientsdecreased; (Indian Ocean, paleodepth500-1000 m), Site 689 (Weddell they remained at these levels for 50,000 to several hundred Sea, paleodepthabout 1100 m), and Site 525 (Walvis Ridge, thousand years [Stott et al., 1990; Kennett and Stott, 1991; paleodepthabout 1600 m) suggeststhat the paleodepthwas in Thomas and Shackleton, 1995]. Synchronous with the the upper half of the lower bathyal, i.e., betweenabout 1300 dramaticdecrease in •180 valueswas a largenegative excursion and 1500 m [Thomas and Shackleton, 1995; E. Thomas, in the •13C recordsof planktonicand benthic foraminifera. manuscriptin preparation,1995], suggestinglittle subsidence The event is believedto have been associatedwith a temporary since the Paleogene.We presentthe isotopicstratigraphy of change in dominant deep water sources from high to low the Paleogene section at Site 865 and its general latitudes [Kennett and Stott, 1991; Pak and Miller, 1992; paleoceanographic significance. The paleoclimatic Thomas, 1992; Eldholm and Thomas, 1993] which could have implicationsof this recordare furtherexplored by J. C. Zachos been the major cause of the associated mass extinction of et al. (manuscript in preparation, 1995); the benthic benthic foraminifera [Braga et al., 1975; Schnitker, 1979; foraminiferal faunal record will be discussedby E. Thomas Tjalsmaand Lohmann,1983] possiblyresulting from decreased (manuscriptin preparation,1995). dissolved oxygen contents of warmer deep waters [e.g., Kennett and Stott, 1990; Thomas, 1990a, 1992; Kennett and Stott, 1991; Kaiho, 1991, 1994]. Methods and Procedures The short-termchanges in Eocenesea surfacetemperatures (SST)are well documented in high-latitude •80 recordsbut not Sample Selection and Preparation in the low latitudes.Low-latitude •80 recordsare essential, Samples were analyzed from the upper Paleocenethrough however, for reconstructing the low- to high-latitude upper Eocene interval of Hole 865B. Hole 865C was sampled temperature gradient, especially since inconsistenciesexist in detail only in the interval close to Paleocene/Eocene between faunal and isotopic temperatureestimates for the boundarybecause the uppermostPaleocene part of the section tropics on longer timescales [e.g., Adams et al., 1990]. A in Hole 865B is interruptedby the break betweenCores 11 and knowledge of latitudinal thermal gradients is essential to 12. One to three samplesper core section(every 0.5 m to 1.5 developinga betterunderstanding of how heat transportby the m) were selected for isotopic measurementfrom Hole 865B, ocean and atmospheremay have respondedto changesin with the densest sampling in the upper Paleoceneto lower radiative forcing [Barron, 1987; Barron and Washington, Eocene. A more detailedsample set (one sampleevery 10 cm) 1982; Rea et al., 1990; Barron and Peterson,1991]. was taken close to the benthic foraminiferal extinction horizon High-resolutiondeep-sea Paleogene stratigraphic records in theupper Paleocene in bothholes. One 20 cm3 sampleper from low latitudesare rare. Abundantchert occurring in many section was taken in Hole 865B for benthic foraminiferal low-latitude sections of this age has led to reduced core faunal analysis. All other samplesranged in volumebetween 5 recovery rates [e.g., Pisciotto, 1981]. Diagenesis has and 10 cm3. Samplesfor planktonicforaminiferal analyses overprintedisotope values in many deep burial Paleogene were split, dried, and washed with pH buffered water through sequences. The sequence from Site 577 (Shatsky Rise, sieves with screen openingsof 250, 125, 63, and 38 !.tm and paleolatitude15-20 ø N) is almostthe only proxyfor conditions then oven-dried at 60øC. The >250 t.tm fraction was dry-split BRALOWERET AL.:PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 843

30øN

20 ø

..... ' ,.,Site'n•• _, ..•. . . . ,: J,.I..' ','l '" '•' '': • ' 865' ' ' ";""' '' • ' ' • ß ..•• .:,• • arshal,,'slands .': ß ., ß ...- • , _ •',• •'. - ]; - ...... 10 ø Mage//anR/se ' . u •• . • :Line Islands 0 o 160øE 170ø 180ø 170øW 160ø 150ø

Figure 1. Locationof ODP Site 865 on AllisonGuyot in the Mid-PacificMountains. Inset shows general locationof detailedmap. into various size fractions: >400 I.tm, 355-400 pm, 300-355 ontogeneticand other vital effects on the interpretationof I.tm, and 250-300 I.tm. stableisotopic results [e.g., Shackletonet al., 1985a;Corfield and Cartlidge, 1991; Pearson et al., 1993], almost all of our Planktonic Foraminiferal Taxa isotopic investigationswere performed on the 300-355 I.tm fraction. Initially, 25 specimensof each specieswere picked; Various taxa have been utilized for Paleogeneplanktonic however, the eight to 10 best-preserved specimens were foraminiferal isotope stratigraphy [e.g., Shackletonet al., selectedfor isotopic measurement. 1984; Boersrna et al., 1987; Stott et al., 1990; Pearson et al.,

1993]. We usedspecies of Morozovellaand Acarinina because Benthic Foraminiferal Taxa of their (1) taxonomic distinctiveness; (2) overlapping stratigraphicranges spanning the interval of interest;and (3) Stableisotopic analyses have been conductedon Nuttallides surface dwelling habitat. We selected Morozovella truernpyiand speciesof Cibicidoides (largeC. praernundulus) velascoensis (upper Paleocene), Morozovella subbotinae throughout the section and Gavelinella beccariiformis and (uppermost Paleocene to lower Eocene), Morozovella species of Lenticulina in samples from the uppermost aragonensis (lower to middle Eocene), Morozovella lehneri Paleocene. Dependingon size, betweenfive and 20 benthic (middle to upperEocene) (Figure 2), Acarinina rnckannai(upper foraminifera were picked for isotopic measurement; all Paleocene),Acarinina soldadoensis(upper Paleoceneto lower specimenswere larger than 125 I.tm in diameter. Eocene),and Acarinina spp.(lower to upperEocene) (Figure 3). These latter taxa, groupedas A. bullbrooki by Bralower et al. Isotopic Analyses [1995], include considerablemorphological variety, grading from older forms which are compressedand somewhatresemble Isotopic analyses were performed in the Stable Isotope A. soldadoensis, to younger conical forms similar to A. laboratory at the University of Michigan. Individual bullbrooki, to forms which resemble Truncorotaloides foraminifera were sonicated in distilled water to remove pseudotopilensis. We have combinedspecies of Subbotina adhering particles and roasted in vacuo at 380ø C. The (Figure 3) becauseof taxonomicuncertainties. Observationsof specimens were processedin a Kiel automated carbonate foraminiferalpreservation were made in a Leica Stereoscan440 digestiondevice. Each sample was reactedin an individual ScanningElectron Microscopein the Geology Departmentat vessel with three drops of phosphoricacid at 75 ø C. The the University of North Carolina-ChapelHill. To reduce resulting CO2 was isolated in a single-stepdistillation and 844 BRALOWER ET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY

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Figure2. Typicalspecimens of planktonic foraminifera from Site 865. Specimens1 and 2 areMorozovella velascoensis,specimen 1 is theumbilical view and specimen 2 is theside view; Sample 865C-12H-4, 10-12 cm. Specimens3 and 4 areM. subbotinae,specimen 3 is the umbilical view and specimen 4 is theside view; Sample865C-12H-4, 10-12 cm. Specimens 5 and 6 areM. aragonensis;specimen 5 is theumbilical view and specimen6 is the side view; Sample 865B-10H-2, 4-6 cm. Specimens 7 and 8 areM. quetra,specimen 7 is the umbilicalview and specimen 8 is theside view; Sample 865B-10H-2, 60-62 cm. Specimens 9 and 10 are M. lehneri,specimen 9 is theumbilical view and specimen 10is theside view; Sample 865B-4H-6, 20-22 cm. Scale bar represents100 microns. BRALOWERET AL.:PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 845 introduceddirectly to the MAT-251 mass spectrometerfor [e.g., Berggren et al., 1995], we presentthe isotopicdata from measurement. National Bureau of Standards(NBS)-18,-19, and Site 865 in plots versus depth (Figures 4-11). In order to -20 as well as an in-house standard LV-2 were measured on a comparedata from different sites,however, these depths need daily basis to monitor instrumentcalibration and analytical to be convertedto a common reference. Becausemany sites accuracy. Average precisiondetermined from 40 replicate have magnetostratigraphiccontrol, we utilize the geomagnetic analysesof planktonicforaminifera was betterthan +0.1 for polafity timescaleof Cande and Kent [1992] as a reference. We both•5180 and •513C values but significantlylower for benthic have selectedseveral nannofossiland planktonicforaminiferal foraminifera [Bralower et al., 1995]. datums which can be placed reliably in a variety of sites, In orderto calculatepaleotemperatures, we usedthe equation including Site 865 and which have been correlated to the of Erez and Luz [1983]and a •518Oswvalue of-0.98%0 for geomagneticpolarity timescale [e.g., Berggren et al., 1985; seawaterassuming an ice-free earth [Zachos et al., 1994] Wei and Wise, 1989]. The numeficalages of thesedatums were correctedrelative to the Pee Dee belemnite(PDB) standardby determined by estimating their average relative positions subtracting 0.27%0[Hut, 1985]. In addition,to adjust for within the chrons(Table 1), assumingconstant sedimentation systematicchanges in salinity as a function of latitude, we rates betweentie points. For compafison,we includethe ages appliedthe equationproposed by Zachoset al. [1994] to our of the samedatums taken from Berggrenet al. [1985] and Wei calculationof $ST. This equationis basedon the assumption and Wise [1989]. In addition,we includethe age of the latest that sea surfacesalinities were high in the subtropicsand low Paleocenebenthic foraminiferal extinction following Pak and in higherlatitudes throughout the Cenozoicas today. While it Miller [1992] and Eldholm and Thomas [1993] (58 Ma from is possiblethat the latitudinal salinity gradienthas changed Aubry et al. [1988]; 55.7 Ma from Candeand Kent, [1992]). throughtime, thereis no evidenceto suggestthat the patternor magnitude of this gradient was substantiallydifferent than Results present. Observations indicate high current velocities, winnowing, Biostratigraphy and Timescale and redepositionon top of Horizon Guyot [Lonsdale et al., Stratigraphic control is largely based on calcareous 1972]. Similar activity on Allison Guyot as it subsidedshould nannofossilbiostratigraphy [Bralower and Mutterlose,1995], have led to pervasive unconformitiesand condensedsections. indicatingthat the sequenceis largely complete,with apparent Anomalous enrichments of planktonic foraminifera over unconformitiescorrelating to lower Eocene nannofossilZone smaller particles, including calcareous nannofossils, in NP13 and an interval around the Eocene/Oligoceneboundary. sedimentsfrom Site 865 indicate winnowing. The shallow Assemblages are characterized by only minor apparent burial depths (15-135 meters below sea floor (mbsf)) of the redepositionconcentrated at the top of cores,much of which Paleogenesection at Site 865 resultedin excellent microfossil might have resultedfrom the soupynature of the sediments preservation, particularly among the foraminifera. Some when cored [Bralower and Mutterlose, 1995]. Preliminary samplescontain yellowed, corrodedbenthic foraminifera that planktonic foraminiferal biostratigraphy focused on were probablyreworked from older materials(these specimens determining the precise location of zonal and subzonal were not used in isotopic and faunal analysis). Benthic boundaries(I. Premoli Silva and W. V. Sliter, unpublisheddata, foraminiferal specimensare extremely rare in all samples,even 1994). No magnetostratigraphiccontrol is available. As is for deep-seabenthic foraminifera; about 10-100 times fewer standardin low-latitude deep-seasequences [e.g., Berggren et specimensper gram occurredat Site 865 than in samplesof al., 1985; Aubry et al., 1988; Berggren et al., 1995], we use similar age and paleodepth from Maud Rise (Weddell Sea, the last occurrenceof the planktonicforaminifer, Morozovella Antarctica [Thomas, 1990b]), and Walvis Ridge (S. Atlantic velascoensis, to recognize the Paleocene/Eoceneboundary. Ocean [Thomas and Shackleton, 1995]). Benthic foraminifera Nannofossil events which have been used to correlate this occurred at less than 500 per gram in the Paleocenethrough boundary,the first occurrencesof Tribrachiatusbramlettei and lower Eocene (below the unconformity at 79 mbsf in Hole Discoaster diastypus[e.g., Perch-Nielsen, 1985], cannotbe 865B), increasedto slightly more than 1000 per gram in the determined with confidence in Site 865 [Bralower and first half of the middle Eocene (between 57 and 79 mbsf), Mutterlose, 1995], although the last occurrence of decreasedto 500-1000 per gramin the uppermiddle Eocene (57 Fasciculithuscan be determinedprecisely. The highestsample to 35 mbsf), and increasedconsiderably (1500-2000 per gram) analyzed is from the uppermost Eocene based on the in the uppermost middle Eocene (above 35 mbsf). These occurrencesof Discoasterbarbadiensis and D. saipanensis. extremely low values for benthic foraminiferal abundance,as well as benthic foraminiferal accumulation rates in the Paleogene time scales are currently in a state of flux [Berggrenet al., 1992;Berggren and Aubry, 1995;Berggren et Paleocenethrough middle Eocene,indicate a very low transport al., 1995]. The age of the Paleocene/Eoceneboundary has of organic matter to the seafloor [Berger et al., 1994], commonlybeen placedat 57.8 Ma [Berggrenet al., 1985] or probably as a result of very low primary productivity. The 57 Ma [Aubry et al., 1988], but this value is almost certainly extremely low abundancemakes isotopic analysesvery time too high in view of newly obtainedradiometric dates [Wing et consuming. Stable isotopicdata are compiledby Bralower et al., 1991;Berggren et al., 1995]. Candeand Kent [1992] used al. [1995] and Table 2, summarizedin Table 3, and plottedin a value of 55 Ma in constructing a geomagnetic polarity Figures4-14 with more positive •5180 values to thefight in all timescale. Because of inevitable changesin the timescale figures exceptFigure 12 (versusgeneral convention). 846 BRALOWER ET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY

'i,

Figure 3. Typicalspecimens of planktonicforaminifera from Site 865. Specimens1 and 2 areAcarinina mckannai,specimen 1 is theumbilical view and specimen 2 is theside view; Sample 865C-12H-4, 10-12 cm. Specimens3 and 4 areA. soldadoensis;specimen 3 is theumbilical view andspecimen 4 is the sideview; Sample865C-10H-4, 60-62 cm. Specimens5 and 6 areSubbotina spp., specimen 5 is theumbilical view and specimen6 is theside view; Sample 865B-12H-4, 70-72 cm. Specimens 7-10 are Acarinina spp., specimens 7 and8 areumbilical views and specimens 9 and 10 areside views; Sample 865B-7H-l,118-120 cm. Specimens 11and 12 are Truncorotaloides rohri; specimen 11 is theumbilical view, specimen 12 is theside view; Sample 865B-5H-5, 50-72 cm. Scalebar represents100 microns. BRALOWERET AL.: PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY 847

Table 1. Datums Used in the Estimationof Ages for Intersite Comparison

Datum Polarity Age (CK92), Age (BKF85), Depth Depth Chron* Ma Ma1. 865B•: 865C$

LO D. barbadiensis C13r.0.50 34.11 36.7 18.70 LO C. grandis C17n.ln.0.20 37.32 40.0 19.32 LO C. solitus C17r.0.00 38.50 41.3 29.40 FOR. umbilicus C19r.0.25 42.38 44.6 47.31 FO C. gigas C20r.0.50 45.08 47.4 67.70 FO D. sublodoensis C22r.0.00 49.60 52.6 79.60 LOT. orthostylus C23n.1.0.50 50.73 53.6 79.60 FO D. lodoensis C24n. ln.0.50 52.39 55.2 89.60 LO M. velascoensis C24r.0.35 55.00 57.8 100.90 98.30 Benthic foram. extinction 55.70 58.0 102.53- 102.95 103.50{} FO. D. multiradiatus C25n.0.50 56.26 59.2 116.21 114.60 FO D. mohleri C26n.0.80 58.12 60.5 125.75 FOF. •mI•an•ormis C26r.0.40 60.21 62.0 132.20 *Terminologyis takenfrom Candeand Kent [1992]. Numericalsuffix refers to relativeposition in chronat severalsites with baseat 0.00 and top at 1.00. I' Agesare taken from Berggren etal. [1985] and Wei and Wise [1989]. $ Alldepths are meters below sea floor. {}This depth isbetween Cores 11 and 12.

Planktonic foraminifera to the lower part of Zone CP6) to an averageof-2.0%0 in the lowermost Eocene (-102-84 mbsf; Zones CP9 and CP10), Acarinina: Oxygen 'isotopes t•-:•,,,gures 4- 7) . •u,•owcu by-i.•7 an increaseto -u.J•/ooin the upperEocene (-20 Oxygenisotopic values show a long-termdecrease from -1.8%o mbsf;Zone CP15). As in the recordof Acarinina, a rapid 1.0%o in the uppermostPaleocene (-115 mbsf; nannofossilZone decreasein 15180values occurs in lower EoceneZones CP10 and CP8) to -2.1%o in the lowermost lower Eocene (-102 mbsf; CP11 (-86-81 mbsf; Figure 5), and an interval with fluctuating Zone CP9) and are relativelyconstant through the lower lower values occursin Zone CP11 to the lower part of Zone CP13 Eocene (-102-84 mbsf; Zones CP9 and CP10) (Figure 4 and (-81-68 mbsf). Table3). A sharp1.0%o increase in average•5180 values occurs Oxygen isotopic values of M. subbotinaeare up to 0.2%0 in the upper lower Eocene(-84-82 mbsf; upper part of Zone heavier than those of M. velascoensis and between 0.1%o CP10 and Zone CPll), followed by an interval of fluctuating heavierand 0.2%0lighter than thoseof M. aragonensis(Figure valueswithout long-term trend in the uppermostlower Eocene 5). Oxygen isotopicvalues of M. aragonensis are between0.2 (-82-71mbsf; Zone CP12). Average {5180 values in themiddle and 0.4%0lighter than those of M. lehneri(Figure 6). and upper Eocene (Zones CP13 to CP15) show a long-term increasefrom -1.2%oto 0.2%0 (-69-20 mbsf; Figure 4). There Morozovella: Carbon isotopes (Figures 8-11). is little difference between 15180values of A. mckannaiand A. Carbon isotopic values show similar trends to those of soldadoensis measured in the same samples (Figure 5). Acarinina (Figures 8-10 and Table 3). Values increasefrom Oxygen isotopicvalues of A. soldadoensisand Acarinina spp. 3.8%0in the lower upper Paleocene(~130 mbsf; nannofossil differ to a greaterextent (Figure 5). Zone CP5) to 5.1%oin the middleupper Paleocene (-118 mbsf; Zone CP7), then decreasethrough the uppermostPaleocene and Acarinina: Carbon isotopes (Figures 8-11). lower Eocene (-118-80 mbsf; Zones CP8 to CPll) to an Carbon isotopic values show a steadydecrease from average averageof 2.5%0,followed by a gradualincrease to an average values of about 4.7%0 in the upper Paleocene(-115 mbsf; of 3.0%0 in the lower middle Eocene (-74-61 mbsf; Zone nannofossilZone CP8) to an average of 2.6%0 in the lower CP13). Uppermiddle and upper Eocene •513C values show a Eocene (-88-80 mbsf; Zones CP10 and CPll) (Figures 8 and 9 gradualdecline to 2.6%0(-20 mbsf;Zone CP15). Overlapping andTable 3). A slightincrease to averagevalues close to 3.0%0 recordsillustrate slightly different •513C values for different occursin ZonesCP12 and CP13 (~80-50mbsf). The fil3C speciesof Morozovella: M. subbotinae is up to 0.2%0heavier values of A. rnckannai and A. soldadoensis are similar, but than M. velascoensis and up to 0.5%0 heavier than M. values for A. soldadoensisand Acarinina spp. in the lower aragonensis(Figure 9). Values of M. aragonensis in turn are Eoceneare up to 0.6%0different (Figure 9). up to 0.2%0lighter than thoseof M. lehneri (Figure 10).

Morozovella: Oxygen isotopes (Figures 4-7). Subbotina: Oxygen isotopes (Figures 4-7). Oxygenisotopic values for Morozovellafrom Hole 865Bshow Oxygen isotopic values of Subbotina show more variability similar patternsto thoseof Acarinina but cover a longer than those of the other planktonicgenera (Figure 4 and Table stratigraphicinterval (Figure 4 and Table 3). Two long-term 3); averagevalues decrease from about0.0%0 in the lower upper trendsare clear: (1) a decreasefrom an averageof ~-1.4%oin the Paleocene (-128-124 mbsf; top of Zone CP5 and bottom of lowerupper Paleocene (-130-124 mbsf; nannofossil Zone CP4 Zone CP6) to --1.3%o in the uppermostPaleocene (-117-103 848 BRALOWEREl' AL.' PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY

Table 2. Additional Stable Isotopic Data for Site 865

Hole-Core Sec. Interval, mbsf Taxon Size,gm õ13C, /5180, cm %o B-13H 1 21-23 113.21 Subbotinaspp 300-355 2.77 -1.28 B-12H 4 70-72 108.70 Subbotinaspp 300-355 2.77 -1.39 B-12H 3 20-22 106.70 Subbotinaspp 300-355 2.67 -1.26

C-12H 4 20-22 103.00 A. soldadoensis 300-355 4.05 -2.18 C-12H 4 20-22D 103.00 A. soldadoensis 300-355 4.26 -1.97 C-12H 4 30-32 103.10 A. soldadoensis 300-355 4.28 -1.96 C-12H 4 40-42 103.20 A. soldadoensis 300-355 4.05 -2.03

C-11H 6 52-54 96.82 Subbotinaspp. 300-355 1.74 -0.97 C-12H 1 10-12 98.40 Subbotinaspp. 300-355 1.68 -0.96 C-12H 1 60-62 98.90 Subbotinaspp. 250-300 1.81 -1.06 C-12H 2 70-72 100.50 Subbotinaspp. 300-355 2.00 -1.02 C-12H 2 70-72 100.50 Subbotinaspp. 300-355 2.06 -1.50 C-12H 3 00-02 101.30 Subbotinaspp. 250-300 2.07 -1.39 C-12H 3 10-12 101.40 Subbotinaspp. 250-300 1.82 -1.47 C-12H 3 30-32 101.60 Subbotinaspp. 300-355 2.00 -1.47 C-12H 3 50-52 101.80 Subbotinaspp. 300-355 1.83 -1.32 C-12H 3 60-62 101.90 Subbotinaspp. 300-355 1.81 -1.16 C-12H 3 70-72 102.00 Subbotinaspp. 300-355 1.78 -1.06 C-12H 3 80-82 102.10 Subbotinaspp. 300-355 1.79 -1.18 C-12H 3 90-92 102.20 Subbotinaspp. 300-355 1.66 -0.78 C-12H 3 110-112 102.40 Subbotinaspp. 250-300 1.76 -1.04 C-12H 3 120-122 102.50 Subbotinaspp. 300-355 1.45 -0.88 C-12H 3 130-132 102.60 Subbotinaspp. 300-355 1.47 -0.80 C-12H 3 140-142 102.70 Subbotinaspp. 300-355 2.01 -0.76 C-12H 3 140-142D 102.70 Subbotinaspp. 300-355 1.93 -1.31 C-12H 4 10-12 102.90 Subbotinaspp. 300-355 1.53 -1.64 C-12H 4 20-22 103.00 Subbotinaspp. 300-355 2.26 -1.56 C-12H 4 20-22D 103.00 Subbotinaspp. 300-355 2.22 -1.28 C-12H 4 30-32 103.10 Subbotinaspp. 300-355 2.39 -1.26 C- 12H 4 40-42 103.20 Subbotinaspp. 300-355 2.14 -0.80 C-12H 4 50-52 103.30 Subbotinaspp. 300-355 2.61 -1.48 C-12H 4 60-62 103.40 Subbotinaspp. 300-355 2.17 -0.90 C-12H 4 70-72 103.50 Subbotinaspp. 300-355 2.01 -0.42 C-12H 4 80-82 103.60 Subbotinaspp. 300-355 2.55 -1.29 C-12H 4 90-92 103.70 Subbotinaspp. 300-355 3.72 -1.55 C-12H 4 110-112 103.90 Subbotinaspp. 300-355 2.77 -1.50 C-12H 4 120-122 104.00 Subbotinaspp. 300-355 2.77 -1.51 C-12H 4 130-132 104.10 Subbotinaspp. 300-355 2.54 -1.26 C-12H 4 140-142 104.20 Subbotinaspp. 300-355 2.55 -1.35 C- 12H 5 00-02 104.30 Subbotinaspp. 300-355 2.60 -1.51 C-12H 5 70-72 105.00 Subbotinaspp. 300-355 2.75 -1.10 C-12H 5 70-72D 105.00 Subbotinaspp. 300-355 2.67 -1.28 C-12H 5 130-132 105.60 Subbotinaspp. 300-355 2.30 -0.76

D aftercentimeter interval refers to duplicateanalysis. All analysesare reported with respectto PeeDee belemnite (PDB) standard. Sec. is section. mbsf is meters below sea floor.

mbsf;Zone CP8) and increasesteadily to -0.8 %0in the upper Benthic foraminifera Eocene (-29-20 mbsf; SubzoneCP14b and Zone CP15). Short- termdecreases of up to -1.2%oand 0.6%0 in õ180values occur Oxygen isotopes (Figures 4-7). Benthic foraminiferal measurements could not be conducted at a similar resolution as between 91 and 85 mbsf and between 60 and 70 mbsf, that of the planktonicforaminifera because of the extremeand respectively. unusualrarity of benthicforaminifera. We choseto includethe incomplete record in order to demonstrateat least to some Subbotina: Carbon isotopes (Figures 8-11). The $13C record of Subbotina resemblesthose of the other two degree the intermediatewater developments. Replicate measurementsof benthicforaminifera yield greatervariability genera(Figure 8 and Table 3). Carbonisotopic values increase than thoseof planktonicforaminifera [Bralower et al., 1995]. from -1.8%o in the lower upper Paleocene (-133 mbsf; Thisdifference averages 0.93%0 (s=0.92; n=5) for $180values nannofossilZone CP5) to -3.0%0 in the middle part of the upper Paleocene (-118 mbsf; Zone CP7) then decrease to and0.53%0 for $13Cvalues (s=0.38; n=5). We do notthink -1.0%oin the lower Eocene(-91 mbsf;Zone CP9) (Figure9). that this larger variability resultsfrom "vital effects"(either Values fluctuate between 1.0%o and 2.0%0 throughout the sizeor microhabitatrelated), because the variabilityin $180 remainder of the Eocene (-91-20 mbsf). valuesis largerthan that in $13Cvalues, while it hasbeen well BRALOWERET AL.:PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 849

i i i i i i

i i i i i

i i i i i i i i i i i i

i i i i i i i 850 BRALOWERET AL.: PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY

, , , NANNOFOSSIL• ; UJ•___..• 18 SERIESZONE • i, On' •.• -2 -1• 0(%0)

...ic•o NP21 cP161a '" '" 2H - • Benthics nu.I _•0__ .,.• 3H _- _= Morozovella • NP17 b • • I --'" '" 30 - • Subbotina •P14 -e-.,. 4H _- '" '" -- o Acarinin

NP16 a + • -- • • • • 40-- • 5H -

C3_ '" • 6H 50'•

Z OLU NP15 3P13 b• • 7H 60--: •_..• O

a ..e-..e- 8H 70 --

b.e..i. NP14CP12 7,4- ,.e-

• NP12CP10 '•• O CP11'•..e-•• 9H80'• n ._1 NP11 b• • 90"•

NP10CP9 a + • • • 100--_

LU • 110• Z NP9CP8+••• 1•._ _-- • • 120-- :) LU NP7/8 .•.• - [ O• CP6 '"'"• ..e- - • NP6NP5 CP5CP4 4-••..e- 1•.• 130---- NP4CP3 • • 115X-- Figure4. Planktonicand benthic foraminifer •180 (%o versus Pee Dee belemnite (PDB)) records of theupper Paleoceneto upperEocene of Hole 865B. Planktonictaxa are groupedinto genera,and benthictaxa are combined.Calcareous nannofossil zones of Martini[1971] and Bukry [1973, 1975] (using terminology of Okadaand Bukry [ 1980])are shown at left. Arrowindicates position of benthicforaminiferal extinction. documented that microhabitat variability very strongly (Sample865B-15X-1, 120-125cm) in which15•80 values in G. influences1513C values but not 15•80 values [e.g., McCorkle et beccariiformisand N. truempyidiffer by closeto 1.0%o(Figure al., 1990; Woodruff and Savin, 1985]. We think that the 5). There appear to be no consistent offsets between benthic variability is so much larger than that of the Cibicidoidesspp. and N. truempyi[Shackleton and Hall, 1984; planktonicsbecause the benthic sampleswere larger (thus Katz andMiller, 1991;Pak andMiller, 1992]. The 15•80record representinga longertime), and the specimensare extremely for benthicforaminifera shows the same general trends as those rare and thusrepresent the full samplethickness (representing for the planktonicforaminiferal taxa (Figure4). Oxygen 3000 to 7500 yearsthroughout most of the section). More data isotopic values in the upper Paleocene (-135-108 mbsf; are beingcollected to evaluatethis problemfully. nannofossilZones CP3 to CP8) average close to 0.0%o. Analysesof separatetaxa from the same samplesmostly Averagevalues decrease steadily in the upperPaleocene-lower differ by small amounts(0.1-0.3%o) with one exception Eocene(-108-92 mbsf; ZonesCP8 to CP9) to --0.5%o in Zones BRALOWERET AL.:PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 851

NANNOFOSSIL"• LLI• • al 8 SERIESZONE • 13..Q 0(%o)

NP14CP12 a:::J LLI .,..,..,.i

NP12 4' 4' O cP1o•.;'4,-,.I-,.I-..T.I / NP11 b • 4.4-1 90• III...... ,,!,..i..i."''"'" I [] CP9 a +*'*'l ---- .1o ;;;I -- * 4'*'l 100• ...... '" '" '" ! -- +'"'"1 -

IIIZ NP9 CP8 ••l •,•o-•

O : • NP7/8" I•• •J• 120• Q=• CP6""4';';'1 '" '" I --- -- NP5NP6CP4CP5 't::[:::1 ';4H 130-•_Z NP4CP3 -T- • •[ 15X - _i '"'" '" I --

.. 4- Cibicidoidessp. • M. velascoensis iv A. mckannai

ß Lenticulinasp. ,, M. subbotinae Cl A. soldadoensis

13 N.truempyi ••-• M.aragonensis 0 Acarininaspp. •T G.beccariiformis -- M.lehneri ••• Subbotinaspp.

Figure5. Planktonicand benthic foraminifer 8180 (%0 versus PDB) records of theupper Paleocene to lowermostEocene of Hole 865B. Planktonictaxa are separatedinto species,and benthic taxa are differentiated.See key below for symbols.Arrow indicates position of benthicforaminiferal extinction.

CP10to CP12(-90-74 mbsf;Figure 5 andTable 2). Average fairly consistentoffset, with the latter speciesrecording /5180values increase markedly in the lower part of themiddle average/5•3Cvalues 0.3-0.5%0 lighter than the former two taxa Eocene(-74-68 mbsf;Subzones CP12b and CP13a)to -0.3%0. for mostof the intervalanalyzed (Table 3 [e.g.,Pak and For the remainderof the Eocene,values increase steadily, Miller, 1992]). TheN. truempyirecord and the combinedG. attainingan averageof-0.8%0 in the uppermiddle and lower beccariiformisand Cibicidoides spp. record show similar upperEocene (-30-20 mbsf;top of ZoneCP14 and Zone CP15) trendswith an increasein averagevalues of about0.9 to 1.1%o (Figure6). In the upperPaleocene, /5180 values measured on in the upper Paleocene(-135-104 mbsf; nannofossilZones benthic foraminifera are up to 2.0%0 heavier than those CP3 to CP8), a decreaseto -0.0%0in the lowermostEocene measuredon planktonicforaminifera in the samesamples. (-91-83mbsf; Zones CP9 to CP10),stable values through Thisdifference decreases to less than 1.0%o in theupper lower muchof thelower and middle Eocene (-91-27 mbsf; Zone CP10 andmiddle Eocene (Figures 5 and6). to SubzoneCP14b), and the beginningof an increasein the upperEocene (27-21 mbsf; Subzone CP14b) (Figures 9 and 10). Carbon isotopes (Figures 8-11). Measurementson G. A negative/5•3C excursion of about1.4%o occurs in the beccariiformis,Cibicidoides spp., and N. truempyishow a Cibicidoidesspp. record between Samples 865B-12H-1, 40-42 852 BRALOWERET AL.: PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY

^ofoss,1 5 ,?,• o •E -,I 0I ,I • NP21CP16 a • 2H 2

• N•a- cP•5 .. 20 -- • 20 • • __ • 3H -

D NP17 b • • -- O

__ • --

• 30 -- CP14 • • •

NP16 a • • • 40-- .. 5H 2 -

-- • -- • 50 -

NP150P13 b -- 60 --

-- • . _

a.. 70-- --

NP14 0P12 b • •

Figure6. Planktonicand benthic foraminifer •i180 (%0 versus PDB) records of thelower to upperEocene of Hole865B. Planktonictaxa are separated into species, and benthic taxa are differentiated. See key in Figure5 for symbols. cm and -12H-l, 10-12 cm (103.9-103.6mbsf; Figure 9). The thermocline [e.g., Stott et al., 1990; Pearson et al., 1993; N. truernpyi recordshows the samegeneral trend based on a D'Hondt et al., 1994]. Data from Site 865 agreewith these coarserset of samples. establishedpatterns. Differencesbetween isotopic values of In Hole 865C, carbon isotopic measurements on deep-dwellingSubbotina and the two surface-dwellinggenera Cibicidoides spp. show a marked negativeexcursion of are between0.5 and 1.5%ofor 5180 and 1.0 and 2.0%0for •13C approximately 2.0%0 in the uppermostPaleocene from near (Figures4 and 8), similar to valuesfrom high-latitudesites 1.5%oto -0.8%0(102.9-102.7 mbsf; Figure 11). Values are [e.g., $tott et al., 1990]. Recordsof •i180 and•i13C values of offset consistentlyfrom thoseof the planktonictaxa, with the $ubbotina containconsiderably more short-termvariability exception of one sample (865C-12H-4, 10 cm; 102.9 mbsf). than the recordsfor the othertwo genera,reflecting either Theexcursion in •i13C measured onfour samples of Lenticulina greater (1) habitat variability of this taxon, (2) environmental is offsetdownward by 20 cmfrom that of Cibicidoidesspp. heterogeneityof deepersurface waters, or (3) interspecific variability within $ubbotina comparedto monospecific Discussion analysesof the otherplanktonic genera. Some intervals in the Eocene are characterizedby Relative Isotopic Values of Different Planktonic convergencein the •i13Cvalues of Acarininaspp. and Genera $ubbotinaspp. (Figures 9 and 10). In only one of eight samplesin which•i13C values for the two taxaconverge, Previous studies have demonstrated the systematic however,are •i180 values similar (Figures 5 and 6). If depth differences(hereafter termed offsets) between •i180 and•i13C habitatwas responsible for theconvergence of $ubbotina spp. values for Morozovella and $ubbotina [Boersrnaet al., 1979; andthe surfacewater species, we wouldexpect both •i13C and Shackletonet al. 1985a;Cotfield and Cartlidge,1991; Pearson •i180 valuesto converge.Therefore we postulatethat the et al., 1993;D'Hondt et al., 1994]. Lower•i180 andhigher variability in the middle-upperEocene Acarinina recordis a •i13Cvalues for Morozovella indicate that it probablylived result of changesin vital processesover time. It is possible withinthe mixedlayer, whereas higher •i180 and lower •i13C thatAcarinina increasedits depthhabitat but not to the depth values for $ubbotina suggesta habitat within or below the at which $ubbotina reside. BRALOWERET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 853

ZONE

E SERIES• NANNO :i:: 0c ELI •180(%) o EL Q -3 -2 -1 0 ß-.,.-w--w. L l•l•J, I•1• ,,, •..... 96-

' j_ '"'"'"101- ' ' Z"' '"'"'"-I--I,- -,I,, 102- UJ -I- -I,-,.!. ,.•, cO • o .,..,..,.103-

< o• .,..,..,.104 - O_ rl •.. -'--'- -'- -- z o .,..,..,.lO5

-,--,--,.106 -

-,--,--,. 107 -

Figure7. Planktonicand benthic foraminifer •5180 (%0 versus PDB) records of theuppermost Paleocene and lowermostEocene of Hole 865C. Planktonictaxa are separatedinto species,and benthic taxa are differentiated.See key in Figure5 for symbols.Calcareous nannofossil zones of Martini [1971]and Bukry [1973, 1975] are shownat left. Planktonicforaminifer subzones of Berggrenand Miller [1988] as determined by D.C. Kelly are indicated.Arrow indicatesposition of benthicforaminiferal extinction.

AlthoughAcarinina is inferred to have been a surfacedweller statistically significant, but offsets larger than 0.2%o are. [e.g., Pearson et al., 1993], previous comparisonsof its Analysesof Acarininaand Morozovella were mostlyperformed isotopic values with Morozovella have been mostly separately several months apart and have been correctedfor inconsistent. Distinguishableoffsets betweenAcarinina and long-term "machinedrift" [Bralower et al., 1995]. The fact that Morozovella exist at Site 865. Below 96 mbsf at Site 865, A. the offset between Acarinina andMorozovella in the upper mckannaiand A. soldadoensisgive •il3C valuesconsistently Paleocene-lower Eocene is oppositefrom that in the lower- 0.1 to 0.2%0lighter than speciesof Morozovella includingM. upper Eocene intervals suggeststhat this phenomenonis a velascoensisand M. subbotinae(Figure 9). A. soldadoensis result of factors other than "machine drift." •i•80 valuesare consistently lighter by 0.1 to 0.2%0than those Consistent offsets between Acarinina and Morozovella have been observedonly in two other data sets. Similar offsets to of Morozovella speciesthrough the uppermostPaleocene and those observed at Site 865 were recorded between combined lower Eocene (Figure 5), except near the Paleocene/Eocene speciesof Morozovellaand Acarinina in the upperPaleocene- boundary. In the upperlower Eoceneto upperEocene interval, lower Eocene of South Atlantic Site 524 [Oberhiinsli and species of Acarinina (mostly Acarinina spp.) contain Tourmarkine,1985]. In a studyof varioussize fractionsof late consistentlyhigher •i•80 valuesby 0.1 to 0.5%0than those of Paleoceneplanktonic foraminifera, Acarinina nitida was found Morozovella (M. aragonensisand M. lehneri), but there is no to recordlower •i•3C valuesthan Morozovella subbotinae and consistentoffset in •5•3C. The smaller(0.1%o) offsets are not M. velascoensis [D'Hondt et al., 1994]. No reasonswere 854 BRALOWERET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY

SERIES ZONE _• • • •E -1 0I 1I 2I 3I 4I 5I [ _- Benthics • NP18-cP15 • -- •• '• 3H • la cP14 • •' 4H Z o Acarinina

NP16 a • • • _ :Z 5H 40•

• •] 6H50• • NP15CP13 b O +• { 7H 60•

a -

NP140P12 a • • • • - , CP11• 9H80 • • NP12 • CP10• - a NP11b : • 90• ...... ++• 100• Z ++. 110• • NP9CP8 - • NP7/8 + + --

NP5cP4 +• 130• u NP4CP3 TT -

Figure8. Planktonicand benthic foraminifer •513C (%0 versus PDB) records of theupper Paleocene to upper Eocene of Hole 865B. Planktonic taxa are groupedinto genera,and benthic taxa are combined.Calcareous nannofossilzones of Martini [1971] andBukry [1973, 1975] are shownat left. Arrow indicatesposition of benthic foraminiferal extinction.

given for the offsets in either study. Small but consistent •5180values are offset, as in themiddle and upper Eocene, offsets between speciesmay be the result of differencesin paleohabitatdepth difference is lesslikely, and vital effectsare depth habitat, season of growth, or vital effects. Without more probable. ontogenetic information, distinguishing between these two In most other sections where joint measurements of possibilities [e.g., D'Hondt and Zachos, 1993] is difficult. Acarinina and Morozovella have been made, consistentoffsets Whenboth •5180 and •513C values are offset consistently, asin have not been observed. Boerstoa et al. [1979] showed in the upper Paleocene-lowerEocene, it is likely that paleohabitat sampleswith joint •5180analyses that in five of sevencases depthis a factor.On thebasis of present-dayprofiles in •513C values of Acarinina are lower than those of Morozovella. [e.g., Kroopnick et al., 1977], the 0.2%0 offset can be Pearsonet al. [1993] concludedthat relativeisotopic values explainedby minor (<100 m) differencesin depth. Where only between the two genera, and between individual speciesof BRALOWF_RET AL.: PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY 855

,',.Q C (%0)

ZONE -3 g •t••E oI•L•J•I•L•• 1 2 3 4 5 • NP15•P13 a '"+'•'1 70•

III NP14CP12 a "'""""1 ---- • LMZ cP11"'"'"'1'" '" '" I 80--- • NP12 "' + +1 _ •10 CP10ß+++l I- 4- 4-I LU "''" '"1 - NP11 b "'+ +1 90--__

CP9 a "'"'"'1 -- NP10 "' '" '"1 -- "''" '"1 11H -- + + +1 100• ..... +++1 -- ß'++1 -- LU NP9 CP8 +++l 12H Z ++ +J 110•-- LU + '" '"1 - O "''" '"1 - + + +l 13H -- --,jLU•' NP7/8 cP7 ••l• .... 120• _ Q_<:• CP6'"+ '"+ +l '"1 --- NP6 OP5 +++1*++l 14H --- '"+ +1 130-- •1• NP5 CP4 • •. •.1 -- :::1 - NP4 OP3.,.++1 15X _--

Figure 9. Planktonicand benthic foraminifer 813C (%0 versus PDB) records of theupper Paleocene to lowermostEocene of Hole 865B. Planktonictaxa are separatedinto species,and benthictaxa are differentiated.See key in Figure5 for symbols.Arrow indicates position of benthicforaminiferal extinction.

them, are variable in middle Eocenesamples. The apparent interval of interest. In high-latitudesites [e.g., Stott et al., lack of offsetsbetween these genera at othersites may result 1990;Barrera and Huber,1991; Lu and Keller, 1993],large, from slight diagenetic overprinting which may tend to ornate morozovellidsthat typify tropical assemblagesare homogenize sample isotope ratios. Alternatively, the absentor very rare. In temperateand low-latituderecords, equatorialwater column at Site 865 with a steeperthermal publishedlong-term 8180 records are mostly based on one or gradientmay havehad moredistinct habitat separation. two genera [e.g., Shackletonet al., 1984; Corfield and Cartlidge, 1992]. Analysis of three different low-latitude genera has been performedon short stratigraphicintervals Long-Term Isotopic Trends and Short-Term Variability: Comparison With Other Sites only [e.g., Shackletonet al., 1985a] or in single-sample comparisons [e.g., Boersrna et al., 1979; Boersrna et al., The record of upper Paleoceneto upper Eoceneplanktonic 1987]. Becausethe three generawere thoughtto inhabit and benthic 8180 and 813C valuesfor Hole 865B is similar to variablewater depths[e.g., Boersrnaet al., 1987], we can use recordsfrom other sites [e.g., Shackletonand Boersrna,1981; their8•80 and 8•3C values to interpretthe structure of surface Oberhiinsliet al., 1984;Shackleton et al., 1984;Keigwin and watersthrough time in termsof thermaland nutrient gradients. Corliss, 1986; Shackleton, 1986; Miller et al., 1987; Kennett Carbon isotopic values of planktonicforaminifera increase and Stott, 1990; Stott et al., 1990; Barrera and Huber, 1991; in theupper Paleocene, reach a peakin its uppermostpart, and Corfield and Cartlidge, 1992; Corfield et al., 1992; Pak and thendecrease gradually across the Paleocene/Eocene boundary Miller, 1992; Zachos et al., 1992a, b; Lu and Keller, 1993]. into the lower Eoceneas in othersites [e.g., Shackletonand Our data set is the only one from equatorialPacific watersand Hall, 1984;Shackleton et al., 1985b;Corfield and Cartlidge, containsdetailed measurementsof three planktonicgenera 1992] (Figure8). Our dataexhibit a slightincrease in 8•3C (Acarinina, Morozovella, and$ubbotina) throughmost of the valuesin all threegenera from the lowerto the middleEocene, 856 BRALOWERET AL.:PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY

NANNOFOSSIL"r; • I--'r•' u) •13C (%0) SERIESZONE l::: 0 ! 2 3 NP21 •. •. 2H -

LU 20 ' • • -- tT' NP18-GP15 •' •' 3H 20--- .•. • NP17 b •.• -

• 30 • CP14 •. •. 4H -

NP16 a •'• -- •'• 40•-- •' •' 5H -- u.[,Z ** _ Q O • •'"' 5o-•

LU .,..,. -

NP150P13 b

• •' • 8H 70 --

NP14 3P12 b --

Figure10. Planktonicand benthic foraminifer/513C (%0 versus PDB) records of thelower to upperEocene of Hole865B. Planktonictaxa are separated into species, and benthic taxa are differentiated. See key in Figure5 for symbols. similarto publishedreports. Middle and upper Eocene /513C preservationof the planktonicforaminifera in Site 865 than in values are fairly constant for all the planktonic and benthic several other sections(e.g., South Atlantic Sites 525-529 taxa, similar to trends from other sites [e.g., Keigwin and contain several intervals with poor to moderate preservation Corliss, 1986; Stott et al., 1990; Kennett and Stott, 1990; Pak [Boersrna,1984]). The greatervariability of the recordat high- and Miller, 1995]. latitude siteswith good preservation(e.g., Site 690) may result Althoughthe stratigraphictrends appear similar, /513C from large seasonalfluctuations in temperature,depth to the records from other sites have different average values. Some thermocline, mixing intensity, upwelling, and productivity differencesin /513Cvalues between sites are probablyreal, [e.g., Stott et al., 1990]. Tropical, oligotrophic locations reflectingregional differences in seasurface/513C and nutrient today are characterizedby comparativelystable water column structureswith a deep mixed layer and less seasonalvariability levels, while other differencesmight be artifactsof differences than high-latitude settings. in the samplingstrategies used to constructeach record. For Carbon isotopic values from Hole 865B appear to show example, minor isotopic variability can be ascribed to disparitiesin the taxonomyand size rangesof the foraminifera correlatedshort-term (1-3m) multisamplefluctuations between the different planktonic genera (Figure 9). To substantiate measured [e.g., Shackleton et al., 1985a; Corfield and Cartlidge, 1991]. thesecorrelations, we have normalizedall /513Cvalues to the The planktonicforaminiferal /518 0 and/513C recordsalso mean value for each genusfor the intervalsbetween 94.0 and show less high-amplitude (0.5-1.0%o) single sample 130.0 mbsf then carriedout a cross-correlationanalysis. We variability than other records[e.g., Shackletonand Hall, 1984; have excluded the abnormal interval around the benthic Stott et al., 1990]. This may be a resultof a numberof factors. foraminiferal extinction. Minor (0.1 to 0.8%o) fluctuationsin First, our recordis more detailedthan severalothers (e.g., Site /513Cvalues measured in all threetaxa are similarwith Pearson 738 [Barrera and Huber, 1991] (0.5-1 m.y. betweenpoints); correlation coefficients significant at the 99% interval of Site 577 [Corfield and Cartlidge, 1992] (>0.3 m.y. between confidenceand a significantdecrease in correlationcoefficients points)). Becausegenerally less time (averageof 0.15 m.y.) is when curvesare offset upward or downwardby one or more representedbetween our data points, they may record less sample. The lower-amplitudefluctuations (~0.1%o) are closeto short-term variability. Second, the lower intersample precisionlevels, but the higher-amplitudefluctuations which variability in our record may result from the generallybetter show significant correlation between different genera are BRALOWERET AL.: PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY $57

ZONE

SERIES NANNO LU 0 0rr 0rr •_'r' LUi'1 • 3C(%0) LL. .•• • -2-1 0 1 2 3 4 5

n •.-- 97- ,- T"' '"'" 98- W 13.ø • (• i-•+.,..,.-- (• Z O, /+-,--, - • |.,..,..,. __ a- |.,..,..,. /*'"'"•+• 100-- /-'- -'--'- 101-

Z -- / • I11 k•+•nu "' '" '" 102--- 0 /*-'--'- 103---' • I11 /"" '"'" .• o• /-'- -'--'- 104-

l•,, •,, •,, ••• 106-

*-,-, 107--

Figure11. Planktonicand benthic foraminifer •513C (%0 versus PDB) records of theuppermost Paleocene and lowermostEocene of Hole 865C. Planktonictaxa are separatedinto species,and benthictaxa are differentiated.See key in Figure5 forsymbols. Calcareous nannofossil zones of Martini[1971] and Bukry [1973,1975] are shown at left. Planktonicforaminifer subzones of Berggren and Miller [1988]as determined by D.C. Kelly areindicated. Arrow indicates position of benthicforaminiferal extinction.

probablynot an artifactof ontogenetic,sedimentologic, or on MaudRise, which does not showsimilar cycles in its carbon analytical factors. isotope record. Any global small amplitudeshort-term Fluctuationsin upper Paleoceneplanktonic foraminifera variability,however, may be maskedby the largeramplitude •513Cvalues suggest oscillating oceanographic conditions. variability associatedwith seasonalenvironmental variations. Giventhe stratigraphicresolution available, we cannotsay Thusit is possiblethat thesecycles are reflectingshort-term whetherthese fluctuations are truly rhythmic, but they have an variations in the mean carbon isotopic compositionof averagefrequency of about2-3 m (250,000-300,000years at a seawater. Lower correlation coefficients observed between the sedimentationrate of 6-8 m/m.y. [Bralower and Mutterlose, •5•80records of thedifferent genera and between •5•80 and •5•3C 1995]). Covariance of short-term •513C fluctuations in would tend to support this inference. These fluctuations planktonictaxa living at different depthsindicates that the disappearin themiddle and upper Eocene interval, possibly as variations may reflect changes in either surface water a result of lower sample resolution or unidentified minor conditions(productivity, nutrient levels) or the mean carbon unconformities. isotopic compositionof seawater. If the latter is the sourceof thesevariations, one wouldexpect to seesimilar variations at PaleogeneTropical Ocean Thermal History othersites. Unfortunately,most other pelagic records lack the Site 865 containsthe only available late Paleoceneto late resolutionto resolvesuch cycles. One exceptionis Site 690 Eocene15•80 record from an equatoriallocation and thus $55 BRALOWERET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY provides a potentially important record of sea surface although these sites were characterizedby colder waters (at temperature.Stratigraphic trends in therecord of 6]80 values least 0.5-1.0%o, representing~2øC) throughout this interval of planktonic foraminifera from Site 865 are similar to those [e.g., Shackleton and Kennett, 1975; Shackletonet al., 1984; from other sites [Shackletonet al., 1984; Keigwin and Corliss, Keigwin and Corliss, 1986; Zachos et al., 1994]. Sparsedata 1986; Boersrna et al., 1987; Stott et al., 1990; Barrera and indicate comparabletemperatures in other equatorial Pacific Huber, 1991; Corfield and Cartlidge, 1992; Zachos et al., (Sites 167 and 171) and Indian Ocean (Site 219) locations but 1994]. Oxygen isotope values gradually decreasedduring the Slightlyhigher temperatures in the equatorial Atlantic (Site late Paleocene reaching a minimum in the earliest Eocene 366) [e.g., Keigwin and Corliss, 1986; Zachos et al., 1994]. (Figure4). Thelower Eocene 6180 values of surface-dwellingHigh-latitude sites, on the other hand, witnessed constant cooling throughoutthe middle and late Eocene [e.g., Stott et speciesat Site865 are among the lowest recorded; 6•80 values al., 1990; Barrera and Huber, 1991; Miller, 1992; Mackensen for Acarinina andMorozovella peak at -2.3%o,which indicates and Ehrmann, 1992; Zachos et al., 1992a]. the warmest oceanic temperaturesof the last 65 m.y. [e.g., Comparisonof relative isotopic values of Acarinina and Shackleton and Kennett, 1975; Savin, 1977]. These values are Morozovella with thoseof Subbotinareveals some interesting similar to thoseobtained from Site 171 on Horizon Guyot at a trends(Figure 4), suggestingthat different parts of the surface comparablelatitude in the central Pacific but slightly lower water layer did not experiencean identicaltemperature history than values from Site 144 on DemeraraRise in the equatorial and possiblythat the depthto the thermoclinechanged through Atlantic [Shackleton and Boersrna, 1981]. Planktonic time. The difference between these groups decreased foraminifera from tropical Sites 144 and 171, however,appear throughoutthe late Paleoceneand reacheda minimum in the to have been altered by burial diagenesis which may have latest part of this epoch(Figures 5 and 7) before increasingin lowered•5•80 values [e.g., Anderson and Arthur, 1983]. The the early Eocene. This late Paleoceneminimum occurred prior lowestconsistently recorded lower Eocene6180 valuesat to the early Eoceneinterval of maximumwarmth and suggests Antarctic Site 690 and subantarctic Site 738 are about-1.0%o that water column thermal gradients were at a minimum. and -1.3%o, respectively [Stott et al., 1990; Lu and Keller, Carbon isotopic value gradients narrowed but not as 1993], and subtropical-temperateSouth Atlantic Sites 525 and significantly(Figure 9). For muchof the early Eoceneand the 527 record values close to -1.2%o [Shackleton et al., 1984]. SubtropicalPacific Sites 47.2 and 577 reach minima of-1.5%o Temperature(øC) Age and -1.25%o,respectively, the former in the upper Paleocene Epochs(Ma) 0 5 10 15 20 25 30 and the latter in the lower Eocene [Shackleton et al., 1985a; Corfield and Cartlidge, 1992; Stott, 1992]. Our data suggestthat maximumsea surfacetemperatures of 24-25øC were attained in the early Eocene in the equatorial SubbotinaAc•rininaMorozovella Pacific (Figure 12) while coeval paleotemperatureselsewhere ranged from 14øC (subantarctic)to 26øC (equatorialAtlantic) [Zachos et al., 1994]. Oxygen isotopic values from Pacific Sites865, 577 and 47.2 indicatethermal gradients of some4- 5øC within the low latitudes. 3enthic • At Site 865, 6180 valuesfor Morozovella showtwo lower Eocene peaks (100-96 mbsf and 86 mbsf) separatedby an interval of slightly higher values (Figures 5 and 12). The secondpeak includes the lowest values (-2.28%o) recordedfor this genus and separatesshort-term warming and cooling events. The warmingevent beginsat 88 mbsf and is clearestin measurementsof M. aragonensisbut is also seenat a slightly lower stratigraphiclevel in the Subbotina record; the 0.45%o decreasein 6180 valuesfor Morozovella representsa temperature change of just over 2øC. The cooling event between 86 and 80.7 mbsf includesan increasein 6180 values of over 1.10%oindicating at least 4øC of cooling over a short interval of time. Steady cooling into the middle Eocene is shownby 6•80 values(Figures 6 and12). Overall,the early and part of the middle Eocenewitnessed some 6øC of cooling, comparablewith other sites [e.g., Shackletonet al., 1984]. Temperature changed little over much of the late middle Eocene, but cooling again commenced in the latest middle Figure 12. Paleogene paleotemperaturehistory of surface Eocene and continuedinto the late Eocene (Figure 12), for an and intermediate waters at Site 865 based on 6•80 values of overall 2-3øC of cooling. Oxygen isotopic values from planktonic and benthic foraminifera (see text for discussion). subtropical and temperate sites suggestrather similar surface Note that temperature scale is inverted relative to other water cooling historiesfor much of the middle and late Eocene, figures. BRALOWERET AL.: PALEOGENEEQUATORIAL PACIFIC PALEOCEANOGRAPHY $59

early part of the middleEocene, the differencebetween/5180 early Eocene, assumingjust the salinity effect, the maximum valuesof Subbotina and the surface-dwellingtaxa remained SST value would increaseby 3øC. In either caseSST would still constant,with two brief intervalswhere gradientsappeared to not exceed presentday at this latitude. diminishbriefly, in the middle part of the early Eoceneand in the early part of the middle Eocene(Figure 4). Surfacewater Tropical Intermediate Water Evolution thermalgradients lessened gradually through the middlepart of the middle Eocene,reaching a minimumin SubbiochronCP14a Oxygen isotopicvalues of Cibicidoidesspp. and Nuttallides (35-40 mbsf). Thereafter,the deeperpart of the surfacewater truempyi decreasethrough the upperPaleocene and reachtheir layercooled dramatically as indicatedby an increasein/5180 lowest levels (-0.5%0) in the lower Eocene (Zones CP10 to CP12; Figure 5), but thesevalues are slightlyhigher than those valuesof Subbotinatoward benthic values, whereas the upper part of the surfacewater layer cooledmore gradually. Thusthis measuredon the sametaxa from severalother sitesincluding pattern indicatesa steeper,more shallow thermocline. Benthic Sites 401 (Bay of Biscay), 524 (Cape Basin), 577 (Shatsky foraminiferal accumulation rates suggest that surface Rise; paleodepthabout 1500 m)), and 738 (KerguelenPlateau; productivity increasedat this time. paleodepthabout 1600 m) [Oberhansli et al., 1984; Oberhansli and Tourrnarkine,1985; Miller et al., 1987; Barrera and Huber, The combinedplanktonic /5180 record from Hole 865B 1991; Pak and Miller, 1992; Zachoset al., 1993]. All of these (Figures4-6) suggeststhat after the graduallate Paleoceneto sites possessvalues between -0.7 and -1.2%o in this interval. early Eocenewarming, cooling occurred from the late early The fact that the values are lighter at the other sites, all of Eocene to late Eocene in a seriesof steps. Intervals of rising or which are from higher latitudes and most of which are from of constant surface water temperatureswere accompaniedby greater water depths, is puzzling. One viable explanation is reduction of surface water thermal gradientswhile periods of thatthe low •5•80interval is simplynot represented at Site 865 cooling were accompaniedby increasedthermal gradients0.e., due to a combination of factors including: (1) inadequate the increaseswere larger in Subbotina). The fact that equatorial Pacific temperatures at this time of dramatically reduced sampling resolution and (2) the presenceof a brief hiatus in latitudinal thermal gradientswere slightly cooler than those of ZoneNP13. Alternatively,the differences in/5•80 values may today(mean temperatures are 27-28øC; •180 vahmqare 0•5%o) be reflectingdifferences in the temperatureand salinity of water is unexpected. This result is consistentwith other supposed masses.The lowerSite 865 •5•80values may result from a indices of tropical temperature [Adams et al., 1990] but is mixture of cool and warmer but more saline waters [e.g., extremelydifficult to explain in climate modelingefforts [e.g., Kennett and Stott, 1991]. Oxygen isotopic data combined Sloan et al., 1995]. Is it possible that our temperature from Cibicidoides spp. and Nuttallides truempyi indicatethat estimatesare biasedtoward coolertemperature because we have about 4øC of warming of intermediatewaters took placein the underestimatedthe /5•80 compositionof tropicalsurface late Paleocene-early Eocene and that maximum temperatures seawater? There are potentially two ways this could be were close to 11øC (Figure 12). Cooling of intermediatewaters achieved. The first requires that sea surface salinity and at Site 865 in the late early Eocene to late Eocene occurredat tropicalsea surface/5•80 values were much higher than present. similar rates to other sites suggesting a similar source or sourcesof deep water [Pak and Miller, 1992; 1995]. The latest Increasingsalinity by one part per thousand(ppt) over typical equatorial values today would lead to a decreasein calculated Eoceneintermediate water temperaturesat Site 865 were around paleotemperatureof roughly 1-2øC (assuming0.35%dppt). It 5øC (Figure 12). is very difficult to envisagewhy the salinity would be so high, Carbon isotopic values for Nuttallides truernpyi and many however, since climate models consistently show higher Cibicidoides spp. are lighter (between0.1 and 0.5%0)at Site precipitation than evaporation in the equatorial belt [e.g., 865 than at most other sites at comparable depths. This Sloan and Barron, 1992; Sloan et al., 1995]. differencesuggests that deep watersat Site 865 were older than those at these other locations. The lowest Eocene benthic Another possibility is that the assumedvalue of-0.98%0 for /5•8Oswis lowerthan the actual value for anice-free Earth or /5•3Cvalues, however, have been measured at PacificSite 577 that the Earth was in fact not ice-freeduring the Eocene. The [Pak and Miller, 1992], where the oldestdeep waters would be value used here, however, is the most conservative of available expectedif circulationwent from high to low latitudes. estimatesfor mean15•8Osw of an ice-freeEarth. All other Isotopic Excursions and Events in the Latest estimates are lower (e.g., -1.2%o [Shackleton and Kennett, Paleocene 1975]), which would only decreasethe computedtemperatures by anotherIøC. As for ice volume,underestimating ice would The latest Paleocene decrease in the meridional thermal also tend to bias temperatureestimates toward cooler values. gradient precededone of the most rapid intervals of warming There is somephysical evidence for ice sheetsappearing in the observed in the geologic record, the late Paleocene thermal late Eocene but not in the early Eocene [Wise et al., 1991]. maximum, [Zachos et al., 1993] toward the end of the late Thus, if we assume these extreme conditions in the late middle Paleocene long-term warming episode. Substantialdecreases Eocene, sea surface salinity 2 ppt higher (+0.7%o), and ice in •5180 values of benthic foraminifera at sites at different volume 50% of presentday (+0.5%o),these effects combined depths in different oceans indicate widespread long-term wouldincrease the value for/S18Osw by 1.2%oadding a totalof warming of deep waters to close to 16øC [e.g., Kennett and 5øC to the computedtemperatures, resulting in a maximum $tott, 1991; Corfield and Cartlidge, 1992; Hovan and Rea, value of less than 25øC for the late middle Eocene. For the 1992; Pak and Miller, 1992]. Correlative with the short-term 860 BRALOWERET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY

•5180 excursion is a marked decreasein •j13C values and the this interval, maintaining values close to -1.5%o (19.5øC most dramatic extinction of deep-sea benthic foraminifera [Stott,1992]). The•5180 data suggest similar temperatures in since the Cenomanian/Turonianboundary (Late Cretaceous) these locations in the Antarctic and tropical Pacific separated [e.g., Tjalsma and Lohmann, 1983; Thomas, 1990a, 1992; by some 50ø of latitude. Severe drilling disturbanceat Site Kaiho, 1991, 1994]. These data have been interpretedin terms 47.2 raises the chance that the stratigraphic record is not of short-termwarming of high latitudesand possiblya change entirelycomplete, even though •513C values clearly record the in the source of deep waters from high to low latitudes [e.g., negative excursion. Thus oxygen isotopic data from Thomas, 1990a; Katz and Miller, 1991; Kennett and Stott, planktonic foraminifera from Site 865, which occupied an 1991; Eldholm and Thomas, 1993], although local equatorial latitude at this time, are critical in establishing productivitychanges may have played a role in the extinctions changesin low-latitude SST during this event. [Thomasand Shackleton,1995]. Consequentchanges in deep A recent biostratigraphicstudy by Aubry et al. [1995] has water chemistry,particularly oxygen capacity, may have led to thrown into doubt the stratigraphic completenessof the a mass extinction of benthic foraminifera in all oceans. uppermostPaleocene in all sequences,including Site 690 where Comparedto the abundantbenthic isotopicdata acrossthis the record appearsto be the most expandedacross the benthic event, planktonicdata are relatively sparse. Kennettand Stott extinction but where there appears to be a hiatus across [1991] discussedthe recordsfor Acarinina prepentacamerata paleomagneticchron C24r-1, higher in the section. At Site and Subbotinaspp. from Site 690, which showclose to 2.0%0 690, the last occurrence (LO) of the late Paleocene fasciculith decreasein •5180values in this time period(Figure 13a). A nannofossils lies 23 m above the level of the benthic singlevalue of-2.2%0 for the formergenus represents a surface extinctionand •513C shift [Pospichal and Wise, 1990; Thomas, water temperatureof close to 19øC, and a few values for 1990b; Thomas et al., 1990; Kennett and Stott, 1991]. At Site Morozovella convexaat Sites 689 and 690 rangefrom -2.05 to 865, and at many other sections (e.g., Sites 577 and 527 -2.15%o [Thomas and Shackleton, 1995]. Oxygen isotopic [Backman, 1986]), these events almost correlate. Although values measuredon A. soldadoensisdecrease by 1.0%oat Site there is potential that reworking at Site 690 [e.g., Pospichal 738 [Lu and Keller, 1993] to a minimumvalue of-1.6%o (16øC). and Wise, 1990] could have raised the level of the LO of the The record of Morozovella velascoensis from Site 47.2 from fasciculiths or that diachrony occurs in the ranges of taxa theShatsky Rise showed virtually no change in •5180values in between high and low latitudes, the possibilityexists that a

(a) •180 •13C (%0) Planktonic foram. Planktonic foram. AGE(Ma)-2.5 -1.5 -0.5 0.5 -2 -1 0 I 2 3 4 5 • 865C ,•N.Pacific I ; (2øN)

+•z.'x - - - 6x.....

• 690B Maud Rise • • (65øS)

865C 690B * Acarinina o Acarinina x Morozovella (Kennett & Stott, 1991)

Figure 13. (a) Planktonic and (b) benthic stable isotopic recordsof the latest Paleoceneinterval in Hole 865C comparedto recordsfrom other sitesincluding Site 527 in the SouthAtlantic [Thomasand Shackleton, 1995; J. C. Zachos and D. K. Rea, unpublisheddata, 1994] and Site 690 on Maud Rise [Kennett and Stott, 1991]. BRALOWERET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 861

(b) b80 b3C Benthic foram. Benthic foram. AGEtMa) -2 -1 0 1 -2 -1 0 55.1 865 • 527

I I 55.3 I

I I I I 55.516øC 55.7

55.9

690

56.1 Illllllll]lllllllll[lllllllll

Figure 13. (continued)

minor unconformity lies right above the benthic extinction •513Cgradients decreased strongly, suggesting that the effects level in many sections. The interval in which benthic of local productivity changesare superimposedon the global foraminiferal faunas have abnormally low diversity after the 8•3C shift[Thomas and Shackleton,1995]. In addition,it is extinctionis considerablythicker at Site 690 than at Site 865, extremely difficult to comparethe maximummagnitude of such supportingthe idea that a minor unconformityor condensed a short-lived excursion, because isotope values changed interval occursjust above the extinctionlevel. extremely rapidly and even very minor unconformities or The planktonic foraminiferal isotopic record from the differences in sampling resolution can cause comparisonof Paleocene/Eocene boundary interval of Hole 865C is of noncoeval data. sufficiently high resolutionto identify a warming event some In the latest Paleocene interval there was also a 1.5%o several tens of thousands of years in duration or greater decreasein/5•80 valuesin benthicforaminifera (Figures 13b (Figures 13 and 14). Unfortunately,the benthicforaminiferal isotopicrecord is less detailedbecause specimens are extremely and 14), illustrating that low-latitude intermediate waters rare andtheir collection is time-intensive.A negative813C warmed by 4 to 6øC, with one sample reaching a value of roughly 16øC. Oxygen isotopic changes in planktonic excursion measured on both benthic (2.2%o) and planktonic foraminifera are far more subtle (Figures 13a and 14), foraminifera (2.4-2.7%o) indicates that the Paleocene/Eocene suggesting that surface water stratification, as indicated by boundary event is recorded at Site 865 over a relatively thin differences in the isotopic values between Acarinina and stratigraphicinterval (-20 cm). The condensedinterval may have been causedby a reductionin carbonateaccumulation rates Morozovella,disappeared fora short(-105 years) period of which would occur if there had been a regional decline in time. The Morozovella recordshows a 0.4%odecrease in 8•80 productivity or increased dissolution [Zachos et al., 1993; values Oust over IøC warming), whereasthe Acarinina record Thomas, 1992; Thomasand Shackleton,1995] or by a brief exhibitsan increasein 8180 values,indicating a similar hiatus. amount of cooling. These changesare insignificantcompared The 813C excursionmeasured on planktonicforaminifera at to the 8øC of warming that occurredin high-latitude surface Site 865 is smallerin magnitude(1.9%o) than in other sites waters [e.g., Kennett and Stott, 1991; Thomasand Shackleton, (Figure13a). At Sites689 and 690, the 8•3C excursion for 1995]. The lowest8•80 valuesof Acarininafrom Site 690 are Acarinina measuresclose to 4.0%o [Kennett and Stott, 1991; -2.2%o (19øC), compared to -2.3%o (25øC; both of the Thomasand Shackleton,1995]; valuesfor Morozovella at Site temperature values have been corrected [Zachos et al., 1994]) 47.2 decreaseby morethan 3.0%o [Stott, 1992]. At Sites689 for this genus at Site 865 (Figure 13a). In the absenceof and 690, however, the excursionwas much smaller in the exceptional changes in the physical properties of the water benthicforaminifera (about 2%o) than in the planktonicsand accompanying this dramatic event, these relative values 862 BRALOWERET AL.: PALEOGENE EQUATORIAL PACIFIC PAJ_,E•••••

(%o) -3 -2 -1 0 -2 0 2 I ,I I I , I

Io114 /

104

Figure14. Planktonicand benthic foraminifer •513C and •5180 records (%0 versus PDB) of theuppermost Paleoceneof Hole 865C. Scaleis metersbelow sea floor. Planktonictaxa are separatedinto species,and benthictaxa are differentiated.See key in Figure5 for symbols.Arrow indicatesposition of benthic foraminiferal extinction. indicate that equator-to-pole temperature gradient was water flow, the notion that densesurface waters might have substantiallydiminished. been sinkingin the equatorialPacific is compatiblewith (1) The finding that temperaturesat Site 865 were either similar theobservation that /5180 values of Acarinina,and especially to or cooler than presentduring all of the late Paleoceneand $ubbotina,actually increase during the excursion(the latter Eocene, including during the brief warming in the latest approachingvalues from benthic foraminifera(Figure 14)) Paleocene,is significant.These data suggestthat in the past indicating cooling of about 2øC for waters close to the the ocean/atmospheresystem operated in sucha manneras to thermocline (or slightly increasedsalinity), and (2) the maintain cool tropics while allowing high-latitude convergenceof /513C values of shallowand deep planktonic temperatures to vary substantially. However, no climate foraminiferalgenera (Figure 14). Althoughit is difficult to modelshave been able to producethe low gradientssuggested estimatethe buoyancyof surfacewaters, the convergenceof by theseisotopic data: increased heat transportby oceansand /5180values of $ubbotinaand benthic foraminifera over a 50- atmosphereis difficult to accomplishat low temperature gradients[Barron, 1987;Rea, 1994;$1oan and Rea, 1995]. cm interval(Figure 14) indicatesthat surfacewaters may have How good a sourcefor deepwaters was the surfacewater in been dense (saline) enough to sink at least to intermediate the equatorialPacific? Althoughthe magnitudeof the •513C water depths. If surfacewaters indeed were sinking, the excursion measured on benthic foraminifera is similar at physicalproperties of the deeperpart of this layer where $ubbotinalived wouldbe expectedto changemore drastically numeroussites, values at thepeak of the /513Cexcursion are than the shallowerpart. The isotopicrecord of $ubbotina is slightly different (Figure 13b). The significanceof such intriguingin its potentialbearing on surfacewater stability; differences, however, is hard to evaluate for such a short-term however,convergence of/5180 values of $ubbotinaand benthic event:parts of the recordrepresented in data from differentsites foraminiferacan also be explainedby a short-termhiatus in the may representevents occurringat different times, especially becausehiatuses may occur at many locations[Aubry et al., upper part of the excursioninterval, possiblyleading to 1995]. The problemis exacerbatedbecause at SouthernOcean bioturbationof postexcursion$ubbotina which have higher /5180values into the excursioninterval. and Pacific sites(including 690 and 865) N. truempyiis absent for a shortinterval just at the extinction.The lowest/513C values measured on N. truempyi are as follows: Site 525: Conclusions -1.47%o, Site 527: -1.53%o[Thomas and Shackleton,1995]; Site 577 (where a short unconformityalmost certainly is 1. Long-termlate Paleocene-Eocene/518 0 and/513 C records present): 0.15%o [Pak and Miller, 1992]; Site 690: -1.25%o at Site 865 are similar to those at other sites. However, the [Kennettand $tott, 1991]; Site 865:0.39%0 (Sample865B- planktonicrecord at Site 865 includessignificantly less short- 11H-CC). For Lenticulina spp.the lowestvalue at Site 690 is term, single-samplevariability than those at higher-latitude - 1.89%o,for Site 689 - 1.23%o[Thomas and Shackleton,1995], sites, suggestinga comparativelystable water column structure comparedto -1.7%o at Site 865 (Sample 865C-12H-4, 10- with a deep mixed layer and less seasonalvariability. Small- 12cm). scale (0.1-0.8%o)multisample oscillations are observedin the Although the benthic carbon isotopic values thus cannot •j13Crecords of all planktonicgenera. help in determiningthe agingpatterns of deepand intermediate 2. The/5180and •j13C values for genera(Acarinina and BRALOWER ET AL.: PALEOGENE EQUATORIAL PACIFIC PALEOCEANOGRAPHY 863

Morozovella) living within the mixed layer are consistently Barron, E. J., Eocene equator-to-polesurface ocean temperatures:A offsetfrom thosemeasured on Subbotina,which lived deeperin significantclimate problem, Paleoceanography,2, 729-740, 1987. Barron, E. J., and W. H. Peterson, The Cenozoic ocean circulation based the water column. The õ180 and õ13C valuesof Acarinina and on GeneralCirculation Model results,Palaeogeogr. Palaeoclimatol. Morozovella are slightly offset from one anotherfor large Palaeoecol., 83, 1-18, 1991. stratigraphicintervals as a result of depth-of-habitator vital Barron,E. J., andW. M. Washington,The atmosphericcirculation during. processes. warm geologic periods: Is equator-to-polesurface temperature gradientthe controllingfactor?, Geology,10, 633-636, 1982. 3. Peak sea surfacetemperatures of 24-25øC are recordedin Berger, W. A., J. C. Herguera, C. B. Lange, and R. Schneider, the lowermost Eocene; this interval of dramatically reduced Paleoproductivity:Flux proxiesversus nutrient proxies and other latitudinal thermal gradients was not accompanied by problemsconcerning the Quaternaryproductivity record, in Carbon substantiallyhigher equatorialSSTs as inferred from oxygen Cycling in the Glacial Ocean: Constraintson the Ocean'sRole in isotopes. This warm interval was terminated by a sharp Global Change,edited by R. Zahn, T. F. Pedersen,M. A. Kaminski, andL. D. Labeyrie,pp. 385-411, Springer-Verlag,New York, 1994. cooling event of 4øC in the latest middle Eocene. Vertical Berggren,W. A., and M.-P. Aubry, A late Paleocene- early Eocene thermal gradientsdecreased dramatically in the late Paleocene NW Europeanand North Sea magnetobiostratigraphiccorrelation and reacheda minimumin the latestpart of this period. network:A sequencestratigraphic approach, Spec. Publ. Geol. Soc. 4. A short-term,strong, negative excursion in õ•3C values London,in press,1995. Berggren,W. A., and K. G. Miller, Paleogeneplanktonic foraminiferal occurredin planktonic and benthic taxa at the time of the latest biostratigraphyand magnetobiochronology,Micropaleontology, 34, Paleocenebenthic foraminiferalextinction, but õ•80 data 362-380, 1988. indicate that only intermediate waters warmed (4 to 6øC). Berggren, W. A., and K. G. Miller, Cenozoic bathyal and abyssal calcareousbenthic foraminiferal zonation, Micropaleontology, 35, Increasein õ•80 valuesof certainplanktonic foraminiferal 308-320, 1989. genera suggestscooling or an increase in salinity in this Berggren,W. A., D. V. Kent, andJ. J. Flynn,Jurassic to Paleogene,Part interval;convergence of fi•80 valuesfor planktonicsand 2, Paleogene geochronologyand chronostratigraphy,in The Chronologyof the GeologicRecord, edited by N.J. Snelling,Geol. benthicssuggests that the thermoclinein this tropical location Soc. London Mem., 10, 141-195, 1985. weakened strongly. This collapse of thermal gradientsmay Berggren, W. A., D. V. Kent, J. D. Obradovich, and C. C, Swisher III, have been coincidentwith sinkingof theselow-latitude surface Toward a revisedPaleogene geochronology, in Eocene-Oligocene wator• tn at lon•t intorrnoctinto etonthe Climatic and Biotic Evolution, edited by D.R. Protheroand W.A. Berggren,pp. 29-45, PrincetonUniv. Press,Princeton, N.J., 1992. 5. The finding that temperaturesat Site 865 were either Berggren, W. A., D. V. Kent, C. C. Swisher III, and K. G. Miller, A similar to or cooler than presentduring all of the late Paleocene revised Paleogene geochronologyand chronostratigraphy,in and Eocene, including during the brief warming in the latest Geochronology, Time Scales and Stratigraphic Correlations: Paleocene,is significant. These data suggestthat in the past Frameworkfor an Historical Geology,edited by W. A. Berggren,D. V. Kent, and J. Hardenbol, Spec. Publ. Soc. Econ. Paleontol. the ocean/atmospheresystem operated in such a manner as to Mineral., in press,1995. maintain cool tropics while allowing the high-latitude Boersma, A., Cretaceous-Tertiaryplanktonic foraminifers from the temperaturesto vary substantially. southeasternAtlantic, Walvis Ridge area,Deep Sea Drilling Project Leg 74, editedby T. C. MooreJr., et al., Initial Rep.Deep SeaDrill. Acknowledgments. We gratefullyacknowledge discussions with S. Proj., 74, 501-532, 1984. D'Hondt and U. Rohl and critical reviewsby R. Corfield, K. Miller, D. Boersma,A., N. Shackleton,M. Hall, andQ. Given,Carbon and oxygen Pak, L. Stott, J. Winterer, and an anonymousreviewer. Research isotope records at DSDP Site 384 (North Atlantic) and some supportedby JOI-USSAC and NSF EAR-9405784 awardsto Bralower Paleocenepaleotemperatures and carbonisotope variations in the and EAR-9406099 award to Zachos and Thomas. AtlanticOcean, Initial Rep.Deep Sea Drill. Proj., 43, 695-717, 1979. Boersma, A., I. 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