The last interglacial ocean

  • Published on
    26-Aug-2016

  • View
    227

  • Download
    4

Embed Size (px)

Transcript

<ul><li><p>QUATERNARY RESEARCH 21, 123-224 (1984) </p><p>The Last Interglacial Ocean CLIMAP Project Members </p><p>Coordination and Compilation: WILLIAM F. RUDDIMAN Editor: ROSE MARIE L. CLINE </p><p>TASKGROUPLEADERS </p><p>Antarctic Ocean: JAMES D. HAYS? Indian Ocean: WARREN L. PRELL* </p><p>North Atlantic Ocean: WILLIAM F. RUDDIMANt Pacific Ocean: TED C. MOORERS </p><p>South Atlantic Ocean: NILVA G. KIPP* BARBARA E. MOLFINol </p><p>Ice Sheet: GEORGE H. DENTONS TERENCE J. HUGHES* </p><p>William L. Balsam# Charlotte A. Brunner** Jean-Claude Duplessyti- Ann G. Esmay? James L. Fastook$ </p><p>John Imbrie* Lloyd D. KeigwinO Thomas B. Kelloggs Andrew McIntyret Robley K. Matthews* </p><p>Received August 10, 1982 </p><p>Alan C. Mixi Joseph J. Morley? Nicholas J. Shackleton@ S. Stephen Streeter Peter R. Thompsonii~ </p><p>The final effort of the CLIMAP project was a study of the last interglaciation, a time of minimum ice volume some 122,000 yr ago coincident with the Substage 5e oxygen isotopic minimum. Based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean, last interglacial sea-surface temperatures (SST) were compared with those today. There are small SST departures in the mid-latitude North Atlantic (warmer) and the Gulf of Mexico (cooler). The eastern boundary currents of the South Atlantic and Pacific oceans are marked by large SST anomalies in individual cores, but their interpretations are precluded by no-analog problems and by discordancies among estimates from different biotic groups. In general, the last interglacial ocean was not significantly different from the modern ocean. The relative sequencing of ice decay versus oceanic warming on the Stage 6/5 oxygen isotopic transition and of ice growth versus oceanic cooling on the Stage Se/5d transition was also studied. In most of the Southern Hemi- sphere, the oceanic response marked by the biotic census counts preceded (led) the global ice- volume response marked by the oxygen-isotope signal by several thousand years. The reverse pattern is evident in the North Atlantic Ocean and the Gulf of Mexico, where the oceanic response lagged that of global ice volume by several thousand years. As a result, the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years. </p><p>* Brown University, Providence, Rhode Island 02912. I Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964. $ University of Maine, Orono, Maine 04473. 8 University of Rhode Island, Kingston, Rhode Island 02881. /I Exxon, Stratigraphic Prediction Section, Houston, Texas 77001. # Southampton College, Southampton, New York 11968. ** University of California, Berkeley, California 94720. t? Centre des Faibles RadioactivitCs, Laboratoire mixte CNRS-CEA, 91190 Gif sur Yvette, France. $$ Godwin Laboratory, Free School Lane, Cambridge CB2 3RS, England. 8 Chevron, Le Habra, California 90631. (/(I Arco Oil &amp; Gas Company, Dallas, Texas 75221. </p><p>123 0033-5894/84 $3.00 Copyright 0 1984 by the University of Washingtor All tights of reproduction in any form reserved. </p></li><li><p>124 CLIMAP PROJECT MEMBERS </p><p>These regional lead-lag relationships agree with those observed on other transitions and in Iong- term phase relationships; they cannot be explained simply as artifacts of bioturbational translations of the original signals. </p><p>Contenrs. Introduction. Data Base. Choice of cores. Oxygen isotopic ice volume record and chronology. Definition of the last interglaciation. Age of the last interglaciation. Sea-surface tem- perature estimates. Absolute abundance counts. Reconstruction of the last interglacial ocean. Methods. Choice of oxygen isotopic 5e level. Choice of modem SST value. Results. Lead-lag relutionships: SST and ice. Methods. Offsets in transition midpoints. Cross-correlation analysis. Results. Problems and complications. Validity of the 6t80/ice volume assumption. Temperature and dissolution overprints. Meltwater complications and oceanic mixing time. Summary of 680. Validity of the SST estimates. No-analog conditions. Discordant multiple estimates. Bioturbational and bottom-current mixing. Impact of mixing on Stage 5e SST estimates. Impact on lead-lag relationships. Summary of problems and their impacts. Stage 5e SST reconstruction. Lead-lag relationships. Other evidence 0ff3~0/SST phasing. Evidence from other transitions. Comparison with long-term phase relationships. Implications of diachronous regional responses. Additional evidence of last interglnciul climate. Extent of last interglacial ice sheets. Correlation to pollen records. Other terrestrial sequences. Shallow marine sequences. Other oceanic evidence. Sum- mary. Conclusions. Acknowledgments. References. </p><p>INTRODUCTION </p><p>In the final three years (1977- 1980) of its decade-long existence, CLIMAP (Climate, Long-Range Investigation, Mapping and Prediction) focused a considerable part of its research effort on the last interglacial ocean. That study, reported here, had two major objectives: (1) to compare the last interglacial ocean with the modern ocean and (2) to define the sequence of regional oceanographic changes that occurred during the shift both into, and out of, the last period of minimal ice volume. The latter objective involved a study of leads and lags in estimated SST in various oceanic regions relative to the oxygen iso- topic record of global ice volume. </p><p>DATA BASE </p><p>Choice of Cores </p><p>The last interglacial study is based on 52 cores (Fig. 1, Table 1). This coverage spans all the major oceans, with maximum cov- erage in the North and South Atlantic. </p><p>Three criteria primarily determined the final core coverage. First, because our stra- tigraphy is based entirely on oxygen iso- topic records, we were restricted to regions of calcareous microfossils. Areas lacking foraminifera, like the high-latitude North and South Pacific and high-latitude South- </p><p>ern Ocean, are thus blank spaces on the map. Second, to minimize problems in- volving sediment mixing (bioturbation), we only included cores with sedimentation rates in excess of 1.0 cm/1000 yr. This di- minished our coverage of mid-ocean waters in the central subtropical gyres, although temperature changes in such areas have generally been small anyway. Third, we sought to focus our major effort on regions of high-amplitude temperature change, both to maximize the signal-to-noise ratio in our temperature estimates and from the conviction that regions of maximum varia- tion are inherently important parts of the climate system. </p><p>Finally, the preexisting state of strati- graphic knowledge influenced the final cov- erage. Regions with a long history of cu- mulative research effort (e.g., the North At- lantic Ocean) naturally emerged with a larger data base than areas where the basic stratigraphic framework had to be gener- ated almost entirely within this project (e.g., the Indian Ocean). </p><p>Oxygen Isotopic Ice Volume Record and Chronology </p><p>We have relied on oxygen isotopic vari- ations in foraminifera for (1) basic strati- graphic control and (2) a first-order indi- cator of global ice volume against which to </p></li><li><p>THE LAST INTERGLACIAL OCEAN </p><p>FIG. 1. Locations and names of cores used in the last interglacial project. </p><p>TABLE 1. CORE LOCATIONS AND DEFTHS </p><p>Core Latitude Longitude Depth </p><p>Cm) Core Latitude Longitude Depth </p><p>Cm) </p><p>Al80-73 Dl17 E49-18 K-11 K708- 1 Ml2392-1 MD73025 RC8-39 RCS-145 RC 10-65 RCll-86 RCll-120 RCll-210 RCl l-230 RCl2-294 RCl2-339 RCl3-205 RCl3-228 RCl3-229 RCl5-61 RC17-69 RCl7-98 TRl26-23 TRl26-29 v12-122 Vl8-68 </p><p>0lON 4206N 4603 S 7147N 50OON 25lON 4349S 4253S 3335N O4lN </p><p>3547S 433 1 S </p><p>l49N 848S </p><p>37=16S 908N 217S </p><p>222OS 253OS 4037S 313OS 1313S 2029N 2126N 17OON 5433S </p><p>23OOW 3749 5245W 3300 9009E 3253 </p><p>l36E 2900 2345W 4053 165lW 2573 5119E 3284 422lE 4330 6223W 2743 </p><p>10837W 3588 1827E 2829 7952E 3135 </p><p>14003W 4420 1 lO48W 3259 loO6W 3308 9002E 3010 SllE 3731 </p><p>1 ll2E 3204 1 ll8E 4191 7712W 3771 3236E 3380 6537E 3409 9537W 2410 9357W 2700 7424W 2800 775lW 3982 </p><p>Vl9-29 v19-53 V21-146 V22-38 V22- 108 V22-174 V22-182 V22-196 V23-82 V25-59 V27-20 V27-86 V28-14 V28-56 V28-127 V28-238 V28-304 V28-345 V29-29 V29-179 v30-97 V32-126 V32-128 v34-88 Y71-6-12 Y72-11-l </p><p>335S 17OlS 374lN 933S </p><p>43llS loO4S O33S </p><p>1350N 5235N </p><p>l22N 54OON 6636N 6447N 6802N 1 l39N 1OlN </p><p>2832N 174OS 507N </p><p>44OON 4lOON 3519N 3628N 163lN 1626S 43lSN </p><p>8356W 3157 1133lW 3058 16302E 3968 3415W 3797 315W 4171 </p><p>1249W 2630 1716W 3937 1858W 3728 2156W 3974 3329W 3824 4612W 3510 </p><p>l07E 2900 2934W 1855 607W 2941 </p><p>8008W 3227 16029E 3120 13408E 2942 11757E 1904 7735E 2673 2432W 3331 3256W 3371 </p><p>11755E 3870 117lOE 3623 5932E 2100 7753W 2734 </p><p>12623W 3000 </p></li><li><p>126 CLIMAP PROJECT MEMBERS </p><p>phase local changes in SST. Both of these uses of the iY80 record derive from the fact that periodic preferential storage of at60 over #*O in ice sheets is the major control over al80 records in foraminifera (Shack- leton and Opdyke, 1973). As a result, the ice-volume signal dominant in all a*0 curves from the deep sea is generally con- sidered globally synchronous within the mixing time of the deep ocean, estimated to be </p></li><li><p>THE LAST INTERGLACIAL OCEAN 127 </p><p>TABLE 2. 6i*O ADJUSTMENTS USED FOR BENTHONIC FORAMINIFERA </p><p>Species Correction </p><p>(%d </p><p>Uvigerina peregrina Uvigerina senticosa Cibicides wuellerstorfi (-Planulina wuellerstorfi) Cibicides kullenbergi Melonis barleanum Melonis pompilioides (=Nonion spp.) Oridorsalis tener Oridorsalis umbonatus mixed Oridorsalis spp. Pyrgo murrhina Pyrgo depressa Pyrgo oblonga Pyrgo rotaliana Hoeglundina elegans Favocassidulina favus Globocassidulina subglobosa Gyroidina spp. </p><p>1 0.00 : j +0.64 Shackleton and Opdyke (1973) </p><p>+ 0.73 Graham et al. (1981) </p><p>+ 0.40 Streeter and Shackleton (1979) </p><p>+ 0.36 +0.15a +0.136 </p><p>0.00 </p><p>-0.51 </p><p>-0.37 -0.34 </p><p>0.00 -0.10 </p><p>0.00 I </p><p>Source </p><p>Shackleton (1974) </p><p>Shackleton (unpublished) Belanger et al. (1981) Graham et al. (1981) Shackleton (1974) </p><p>Duplessy et a/. (1975) </p><p>Belanger et a/. (1981) Graham et al. (1981) </p><p>Shackleton (unpublished) </p><p>u Derived entirely through offset relative to C. wuellerstorfi. b Derived in part through offset relative to C. wuellerstorfi. </p><p>stage 5e was the last time that there was as small a volume of ice on earth as there is today. </p><p>Oxygen isotopic records published ear- lier indicated relatively little structure within interglacial isotopic Stage 5 (Em- iliani, 1955, 1966), but later work showed major positive isotopic excursions during Substages 5d and 5b with Substages 5c and 5a never returning to the extremely light 6180 values characteristic of Substage 5e (Ninkovich and Shackleton, 1975; Shack- leton, 1977). As a result, the concept of the last interglaciation shrank from the 52,000- yr length of Stage 5 to the 11,000 yr of Sub- stage 5e (Shackleton, 1969). Oxygen iso- topic Substage 5e is thus our definition of the peak of the last interglaciation, the last time that there was as little ice as today. </p><p>Through the sequence of changes into and out of the last interglaciation, the two records in Figure 2 show an oxygen iso- topic signature that is typical of that found in benthonic foraminifera from most of the worlds oceans. The values are character- istically around 5..0%0 in Stage 6. rise to </p><p>3.0%0 in Substage 5e, and then fall to 4.0%. in Substage 5d. Many other records show changes with smaller or larger amplitudes but a similar pattern. In some other cores, the total amplitude may be maintained but with the absolute values systematically shifted toward lighter or heavier values. Oxygen isotopic signals in surface-dwelling planktonic foraminifera often show some- what smaller amplitudes of change. In cores with both benthonic and planktonic records, the two oxygen isotopic signals are usually in phase. In those cores where the two signals are out of phase, we relied on the benthonic foraminiferal signal rather than the planktonic. These, then, are the basic signals we have used to define the last interglacial level in these cores. </p><p>Age of the last interglaciation. The basic chronologic framework of the oxygen iso- topic record of the last 130,000 yr was de- fined by the work of Broecker et al. (1968). They placed the Stage 5 boundaries at 127,000 and 75,000 yr B.I? , creating a time scale some 25% longer than that previously used by Emiliani (1%6). This assessment </p></li><li><p>128 CLIMAP PROJECT MEMBERS </p><p>lSOTOPlC STAGES </p><p>+5 </p><p>v19-29 </p><p>8*0 vs. P.D.B. +4 </p><p>Ml2392 -1 </p><p>8O vs. P. D.B. +4 </p><p>I i </p><p>3 DEPTH I IN CORE (ml 4 </p><p>MORE LESS MORE LESS GLOBAL- GLOBAL GLOBAL- GLOBAL </p><p>ICE ICE ICE ICE </p><p>FIG. 2. Oxygen isotopic records of the last 150,000 yr from Pacific core Vl9-29 and Atlantic core Ml2392-1 (data from Shackleton (1977)). Last interglacial level (Substage 5e) marks the last time that isotopic values were as light as they are today, suggesting global ice volumes at least as small as those today. </p><p>depended both on 231Pa/23cTh dating within deep-sea cores and on correlation of iso- topic Substages Sa, 5c, and 5e with Bar- bados high sea-level terraces I, II, and III. This chronology has passed the test of a decades vigorous application and is widely accepted. It has been corroborated by iso- topic work on Barbados mollusks (Shack- leton and Matthews, 1977). It has also pro- vided plausible links between orbitally con- trolled insolation changes and climatic responses on earth (Hays et al., 1976; Moore et al., 1977; Imbrie and Imbrie, 1980; Ruddiman and McIntyre, 1981a). </p><p>The major challenge to the Broecker/Ku chronology is the frequency of dates on high sea-level terraces in the range 140,000-130,000 yr B.P. Several papers argue that this concentration of U-series dates on apparently unaltered corals is real (Chappell, 1974; Moore, 1982). Moore </p><p>argues that a high stand of sea level 2 m above the modern levels occurred at -135,000 yr B.P. </p><p>The oxygen isotopic record, however, shows no large-amplitude negative excur- sions just prior to the Stage 60 boundary at -127,000 yr B.P. (Fig. 2); it certainly shows no full-scale excursion to full-inter- glacial values. Such a sea-level excursion could only exist within the Broecker/Ku time scale if oxygen isotopes were con- cluded to be totally insensitive as monitors of ice volume. This is not a reasonable con- clusion. </p><p>Alternatively, these high sea levels might argue for a different time scale, with the lower boundary of Stage 5 at -140,000 in- stead of -127,000 yr B.P. This, however, would raise many other problems. It would mean that the large body of work that con- vincingly links orbital forcing and the cli- </p></li><li><p>matic response on earth at the Broecker/Ku three biotic components of the sediments: time scale over the last 130,000 yr is invalid foraminifera, radiolaria, or coccoliths, (2) and must be some totally fortuitous acci- selection or development of the appropriate dent. It would also require that a major de- regional transfer function to apply to the glaciation occurred at a time (140,000 yr biotic counts, and (3) estimation of SST for BP) when orbital forcing provides no un- the winter and summer seasons. usu...</p></li></ul>