A complete high-resolution Paleocene benthic stable isotope record for the central Pacific (ODP Site 1209)



[1] We have compiled the first stratigraphically continuous high-resolution benthic foraminiferal stable isotope record for the Paleocene from a single site utilizing cores recovered at Pacific ODP Site 1209. The long-term trend in the benthic isotope record suggests a close coupling of volcanic CO2 input and deep-sea warming. Over the short-term the record is characterized by slow excursions with a pronounced periodic beat related to the short (100 kyr) and long (405 kyr) eccentricity cycle. The phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the Oligocene and Miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on Milankovitch time scales. In addition, the record documents an unusual transient warming of 2°C coeval with a 0.6‰ carbon isotope excursion and a decrease in carbonate content at 61.75 Ma. This event, which bears some resemblance to Eocene hyperthermals, marks the onset of a long-term decline in δ13C. The timing indicates it might be related to the initiation of volcanism along Greenland margin.

1. Introduction

[2] The Paleocene (65–55 Ma) represents an epoch when both the climate system and carbon cycle were undergoing dramatic shifts during a period of elevated greenhouse gas levels. Previous reconstructions based on pelagic benthic foraminifer stable isotope records reveal a rather complex history of initial long-term cooling followed by warming, with several rapid transitions and short-term events, which are changes that appear to have been driven primarily by variations in pCO2 as inferred from carbon isotope and other data [Zachos et al., 2001a] (Figure 1). The fine-scale details of these trends, particularly the key transitions, as well as the variability on orbital time scales, however, have not been resolved because of the lack of chronologically well-constrained, high-resolution data sets.

Figure 1.

Global climate evolution over the past 65 million years. Absolute ages are relative to GPTS2004 [Ogg and Smith, 2004]. (a) Stacked deep-sea benthic foraminiferal δ13C and δ18O data based on records from Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites [Zachos et al., 2008]. The raw data were smoothed by using a 1 million year running mean (thick red line). The δ18O temperature scale was computed on the assumption of an ice-free ocean; it therefore applies only to the time preceding the onset of large-scale glaciation on Antarctica (∼35 Ma). Indicated by arrows are the Mid-Miocene Climate Optimum, Mid-Eocene Climatic Optimum, Early Eocene Climatic Optimum, and the very short-lived early Eocene hyperthermals such as the PETM (ETM1) and Eocene Thermal Maximum 2 (ETM2). Note the paucity and spread of data for pre-Eocene time. (b) Zoom in on the Eocene, Paleocene, and latest Cretaceous data of the compilation. Data from various sites have been grouped to Atlantic, Pacific, Southern, and Indian oceans to highlight the sparse coverage in this interval. Shaded zone highlights the interval of study in this work.

[3] The discovery of transient global warming events in the greenhouse world of the Eocene [Kennett and Stott, 1991; Thomas et al., 2000; Cramer et al., 2003; Lourens et al., 2005; Röhl et al., 2005; Nicolo et al., 2007; Agnini et al., 2009] is important because these events can provide insight into the nature of climate and carbon cycle coupling [Zachos et al., 2008; Zeebe et al., 2009]. The largest and most thoroughly studied is the Paleocene/Eocene Thermal Maximum (PETM), which is characterized by a brief interval (few tens of thousands of years) of extreme global warmth and a pronounced negative carbon isotope excursion (CIE) [Kennett and Stott, 1991; Zachos et al., 2008]. Smaller transient warming events (a.k.a. hyperthermals) have been indentified for the Paleocene epoch including: the Dan-C2 event [Quillévéré et al., 2008] ∼65.2 Ma, the Top Chron 27n event [Westerhold et al., 2008] or Latest Danian Event (LDE) [Bornemann et al., 2009] ∼61.7 Ma, the Danian/Selandian transition event [Speijer, 2003] ∼61 Ma, the carbon isotope excursions CIE-DS1 and CIE-DS2 at Zumaia [Arenillas et al., 2008] ∼61.7 and ∼61 Ma, as well as the Early Late Paleocene Event (ELPE) [Röhl et al., 2004; Petrizzo, 2005; Bralower et al., 2006] or Mid Paleocene Biotic Event (MPBE) [Bernaola et al., 2007] ∼58.2 Ma. However, the exact character of most of these “events” (i.e., whether warming is global) has yet to be resolved. As a consequence, it is unclear whether they shared similar origins as the PETM, or even if they were truly anomalous with respect to background variability.

[4] The characterization of these events, as well as the opportunity to place them in a high-resolution chronologic framework, was significantly enhanced by the recovery of continuous Paleogene sections from the equatorial Pacific during ODP Leg 198 (Shatsky Rise, [Bralower et al., 2002]) and the South Atlantic during ODP Leg 208 (Walvis Ridge, [Zachos et al., 2004]). These high-quality stratigraphic sections, characterized by pronounced cyclicity, have provided the basis for the development of a fully integrated and astronomically calibrated biostratigraphy and magnetostratigraphy for the Paleocene epoch [Westerhold and Röhl, 2006; Westerhold et al., 2008].

[5] Here we present a stratigraphically continuous high-resolution (4–10 kyr) benthic foraminiferal stable isotope record from a single Pacific site (ODP Site 1209) spanning the entire Paleocene (magnetic polarity chrons C24r to C30n). The record provides unprecedented insight into the detailed evolution of the climate system and the carbon cycle, and the response of each to orbital and other forcing over the entire Paleocene. This includes the presence and characteristics of short-lived climatic anomalies or thermal maxima.

2. Methods

2.1. Stable Isotopes and Coarse Fraction

[6] The Site 1209 Paleocene record was continuously sampled in 4 cm (229.70–264.58 revised meters composite depth (rmcd)) and 10 cm (216.36–233.92 rmcd) resolution, providing a temporal resolution of 4–10 kyr. In total 1276 sediment samples were soaked in a sodium metaphosphate solution to disaggregate, washed through a 38 μm mesh sieve and then oven dried. Benthic stable carbon and oxygen isotope data were generated from analysis of 1017 (230 Santa Cruz, 787 Bremen) samples of the benthic foraminifera Nuttallides truempyi picked from the >150 μm fraction. Isotope measurements were performed on a Finnigan MAT 251 mass spectrometer equipped with an automated carbonate preparation line at MARUM, University of Bremen. The carbonate was reacted with orthophosphoric acid at 75°C. Analytical precision based on replicate analyses of in-house standard (Solnhofen Limestone) averages 0.05‰ (1σ) for δ13C and 0.07‰ (1σ) for δ18O. All data are reported against VPDB after calibration of the in-house standard with NBS-19. Stable isotope analyses of multispecimen samples of Nuttallides truempyi at the UCSC SIL facilities were performed on an Autocarb coupled to a PRISM mass spectrometer. All UCSC values are reported relative to the VPDB standard. Analytical precision based on replicate analyses of in-house standard Carrara Marble and NBS-19 averages 0.06‰ (1σ) for δ13C and 0.10‰ (1σ) for δ18O.

[7] For the coarse (sand) fraction wt%, dried bulk samples were weighed and then washed and sieved using 38 μm sieves in Bremen and 63 μm in Santa Cruz. The difference in sieve size used to determine coarse fraction % (>38 μm and >63 μm) appears to create only a minor difference based on a comparison interval where the two records overlap (Figure S1 in the auxiliary material). The complete data set presented is available online in the WDC-MARE PANGAEA database (http://doi.pangaea.de/10.1594/PANGAEA.758023).

2.2. Chronology

[8] A complete astronomically calibrated stratigraphic framework for the Paleocene epoch has been developed based on the identification of the stable long-eccentricity cycle (405 kyr) in several deep-sea sites [Westerhold et al., 2008]. Compiled biostratigraphy and magnetostratigraphy was integrated with recalibrated magnetic polarity datums to establish a high-resolution calcareous nannofossil biostratigraphy for the Atlantic (ODP Site 1262) and Pacific Oceans (ODP Site 1209). Correlation of high-frequency lithologic cycles between Site 1209 to 1262 allowed for recognition of condensed intervals at Site 1209 [Westerhold and Röhl, 2006; Westerhold et al., 2008]. All absolute ages given in this paper are based on tuning option 1 of Westerhold et al. [2008] to the orbital solution of Laskar et al. [2004].

3. Results

[9] Preservation of Nuttalides truempyi at Site 1209 ranges from moderate to good in the Paleocene, whereas in the late Paleocene in Chron C24r preservation is relatively poor due to dissolution. All picked specimens were thin walled and of glassy appearance (in wet condition), optical signs of diagenetic recrystallization or secondary overgrowths could not be detected. Intervals of lower resolution are located at condensed intervals at Site 1209 [Petrizzo et al., 2005; Westerhold and Röhl, 2006; Westerhold et al., 2008] which are characterized by decreased or even no occurrence of the species.

[10] Benthic stable carbon and oxygen isotope data (Table S1 in the auxiliary material) from the Paleocene section of Site 1209 are presented versus age in Figure 2 (and against depth in Figure S2). Over the long term, values follow the general trend in benthic stable isotopes throughout the Paleocene [Zachos et al., 2008]. In the late Maastrichtian benthic δ13C data increase from 65.8 to 65.3 Ma by 0.8‰ whereas δ18O decrease from 65.8 to 65.5 Ma by 0.5‰ and then increase toward the K/Pg boundary by 0.3‰. Benthic carbon isotopes show a positive excursion from 65.3 to 64.75 Ma of more than 0.5‰ as previously recognized at Site 577 [Zachos et al., 1989]. A slight decrease in the δ13C long-term trend of 0.5‰ during the Danian Stage terminates at 61.75 Ma with a negative carbon excursion of 0.6‰, as well as a 0.5‰ excursion in oxygen. These excursions are actually composed of twin peaks and a high peak in Fe intensity at the polarity boundary C27n/C26r. The δ18O record shows a marked decrease after the K/Pg boundary of 0.3‰ until 63.0 Ma and a subsequent increase of 0.5‰ until 61.8 Ma. During the Danian the δ13C and δ18O values oscillate by 0.2 to 0.3‰, respectively, with minima in the isotopes aligning with peaks in Fe intensity and minima in coarse fraction. These variations have a dominant period of ∼400 kyr.

Figure 2.

Paleocene data from ODP Site 1209 against age (option 1 of Westerhold et al. [2008]). Benthic oxygen and carbon stable isotope data based on analysis of N. truempyi and coarse fraction at the three different holes of Site 1209. All δ18O data are adjusted by +0.45‰ [Shackleton et al., 1984]. Paleotemperature after Erez and Luz [1983]; −1.2‰ ice-free standard mean ocean water (SMOW). Fe intensity data, sedimentation rate, and condensed intervals from Westerhold et al. [2008]. Blue bars mark the Cretaceous/Paleogene (K/Pg) boundary, the Top Chron 27n event or Latest Danian event (LDE), the Early Late Paleocene Event (ELPE), and the Paleocene/Eocene Thermal Maximum (PETM).

[11] In the Selandian and Thanetian, benthic δ13C shows an initial 4.2 Myr long rise (61.7–57.5 Ma; Figure 2) of 1.6‰ followed by a 2.2 Myr long decline of 1.0‰ (57.5–55.5 Ma). This long-term rise and peak in carbon isotopes is the well known Paleocene carbon isotope maximum (PCIM) [e.g., Shackleton et al., 1984]. Benthic δ18O data show an increase during the Selandian of 0.4‰ and a decrease of 0.9‰ from 59.72 to 55.5 Ma. The decrease represents the initial phase of a larger 1.5‰ decrease between 59 and 52 Ma representing the most pronounced warming trend of the Cenozoic [Zachos et al., 2001a]. The Paleocene record terminates with the transient negative carbon (∼1.5‰) and oxygen (∼0.8‰) isotope excursions of the PETM. Amplitude and phase relation between proxies in the Selandian and Thanetian Stage are similar to the pattern observed during the Danian Stage with one notable exception; in the middle of Chron C25r, δ13C decreases by 0.4‰ from 58.2 to 58.0 Ma, as δ18O first drops, then rises by 0.4‰. This is immediately followed by a rapid 0.5‰ increase in δ13C within less than 50 kyr at 57.70 Ma. Benthic δ18O, on the other hand, decreases by 0.5‰. This pattern is observed in both Holes 1209B and 1209C coincident with a prominent rise in sedimentation rate and decrease in Fe intensity. Finally, at the onset of the long-term decrease in δ13C at 57.3 Ma, δ18O rapidly decreases by 0.4‰.

[12] Reduced sedimentation rates as represented by condensed intervals occur at 63.1, 60.4, 58.95 (ELPE), and 56.2 Ma (Figure 2). The intervals around 63.1, 58.95 and 56.2 Ma are characterized by both low coarse fraction and high Fe intensity values, suggesting severe dissolution of carbonate. In contrast, the condensed interval at 60.4 Ma, identified by detailed correlation to both Leg 199 and Leg 208 sites [Westerhold et al., 2008], reveals up to 10 wt% coarse fraction and low Fe intensity values, a sign of winnowing. The coarse fraction record of Site 1209 (Table S2 in the auxiliary material) shows an abrupt increase of up to 30 wt% at the K/Pg boundary and a subsequent decrease during the following 800 kyr. This was first observed at Site 577 [Zachos et al., 1989], and is similar to the pattern observed at the Walvis Ridge [Kroon et al., 2007]. The increased fraction of foraminifera in the early Paleocene has been attributed to increased saturation of the deep sea due to the extinction of calcareous plankton and reduced carbonate flux to the deep sea [Caldeira et al., 1990; D'Hondt, 2005]. The timing suggests that it took at least 800 kyr for the calcareous plankton flux to recover. After 800 kyr the CCD at Site 1209 rises and coarse fraction values drop below 20 wt%. The coarse fraction tracks the dissolution as recorded in the benthic fragmentation at Site 1209 [Hancock and Dickens, 2005] (Figure S3) with the most prominent dissolution phase in the upper Paleocene (∼59.5–58.5 Ma).

4. Discussion

[13] Our new high-resolution stable isotope, XRF, and %CF records for Site 1209 are the most detailed and complete data sets generated to date for the Paleocene. Combining the orbital chronology with the detailed stable isotope record affords a precise chronology of the major global/regional trends and events of the Paleocene at unprecedented resolution and allows us to evaluate the relation between climatic and astronomical cycles.

4.1. Key Trends in Paleocene Benthic Stable Isotope Records

[14] The Site 1209 benthic stable isotope records (Figure 3) show the well-known long-term patterns established from numerous lower-resolution records [e.g., Shackleton et al., 1985; Charisi and Schmitz, 1995; Zachos et al., 2001a; Hollis et al., 2005]. The 3°C warming and subsequent 1.5°C cooling during a 500 kyr interval in the late Maastricht just prior to the K/Pg boundary has been observed in numerous deep-sea records throughout the oceans including the North Atlantic, South Atlantic, Tropical Pacific and Indian Ocean [Stott and Kennett, 1990; Li and Keller, 1998; Barrera and Savin, 1999]. The warming is relatively fast and has been attributed to a rise in atmospheric pCO2 driven by a second phase of the Deccan Trap volcanism centered at the C30n/C29r magnetochron boundary [Caldeira and Rampino, 1990; Li and Keller, 1998; Nordt et al., 2002; Ravizza and Peucker-Ehrenbrink, 2003; Wilf et al., 2003; Chenet et al., 2007; Robinson et al., 2009; Thibault and Gardin, 2010]. Immediately after the K/Pg boundary, from 65.3 to 64.8 Ma, deep-sea temperature increased gradually by 2°C. Decreasing δ13C suggests that the warming could have been driven by the 3rd phase of the Deccan Trap volcanism [Knight et al., 2003; Baksi, 2005; Knight et al., 2005; Chenet et al., 2007; Chenet et al., 2008; Chenet et al., 2009] which occurred after the K/Pg impact till the mid of magnetochron C29n. In contrast, modeling results suggest that flood basalt volcanism might not in itself emit carbon at a sufficient rate to cause noticeable warming, particularly during the early Paleocene [Caldeira and Rampino, 1990; Self et al., 2006]. Alternatively, diminished CO2 drawn down by a reduction in oceanic export production for ∼0.5 kyr after the K/Pg impact might have contributed to warming [Hsü and McKenzie, 1985; Zachos et al., 1989; D'Hondt et al., 1998].

Figure 3.

(top) Paleocene composite multisite deep-sea benthic foraminiferal δ18O and δ13C records against age (option 1 of Westerhold et al. [2008]). Black line is the five-point moving average of Site 1209 benthic isotope data from this study. Note that for benthic isotopes all δ13C data are corrected to N. truempyi [Katz et al., 2003], all δ18O data are corrected to N. truempyi and adjusted +0.45‰ [Shackleton et al., 1984]. Paleotemperature after Erez and Luz [1983]; −1.2‰ ice-free SMOW. Primary components of North Atlantic Igneous Province (NAIP) and Deccan Trap volcanism are adapted from Sinton and Duncan [1998] and Chenet et al. [2007], respectively. Data source are Sites 384, 527, 550, 577, 689, 690, 702, 738, 865, 1209 from Cramer et al. [2009] compilation; Site 215 from Zachos et al. [2001a] compilation; Site 761 from Quillévéré et al. [2002]; Site 1049 from Quillévéré et al. [2008]; and Sites 1262 and 1263 from McCarren et al. [2008]. (bottom) The paleogeographic reconstruction for the middle Paleocene (60 Ma) shows the location of Shatsky Rise ODP Site 1209 and different DSDP and ODP sites that make up the Paleocene portion of the stacked composite record (see Figure 1).

[15] The Dan-C2 isotope excursion which has been reported to occur near the top of C29r in a benthic δ13C record from a single Atlantic Ocean hole (1049C) [Quillévéré et al., 2008] is not present in our high-resolution benthic δ13C record from Shatsky Rise. The characteristic double peak in δ13C of bulk sediment, however, has been found at sites from Walvis Ridge (DSDP 527 and 528). Bulk sediment carbon and oxygen isotope records from the western Tethyan Contessa Highway section (Gubbio, Italy) also show the Dan-C2 event [Coccioni et al., 2010]. Either this event was restricted to the Atlantic and is thus not manifested in the deep equatorial Pacific, or Site 1209 contains an undetected stratigraphic gap or condensed interval. There is, however, no obvious evidence of the latter.

[16] Several records indicate a global change in climate and paleoceanographic conditions at 63.0 Ma. This includes the onset of a long-term global cooling trend, a systematic increase in sedimentation rates and decreasing Fe intensity or increasing carbonate content. The increase in both Atlantic and Pacific carbonate sedimentation rates [Westerhold et al., 2008] suggests higher open ocean carbonate production and/or preservation, roughly coinciding with the second stage of the post-K/Pg recovery of the open ocean carbon cycle [D'Hondt et al., 1998; Adams et al., 2004]. Carbon isotopes, on the other hand, show only a minor response at this time consistent with relatively minor changes in overall carbon fluxes.

[17] The Site 1209 record indicates that the cooling trend which initiated at 63.0 Ma and continued to the base of the ELPE event at 58.5 Ma, was temporarily interrupted at 61.75 Ma by a transient warming of more than 2°C near the termination of Chron C27n, which we refer to as the Top Chron 27n event [Westerhold et al., 2008]. This warming also marks the onset of the Paleocene carbon isotope maximum (PCIM) [e.g., Shackleton et al., 1984] which is thought to represent massive burial of organic carbon caused by enhanced marine productivity or increased burial of terrestrial biomass [Shackleton, 1986; Corfield and Norris, 1996; Thompson and Schmitz, 1997; Kurtz et al., 2003; Hilting et al., 2008]. The isotope record across the Early Late Paleocene Event (ELPE) [Röhl et al., 2004; Petrizzo, 2005; Bralower et al., 2006] or Mid Paleocene Biotic Event (MPBE) [Bernaola et al., 2007] is sparse due to strong dissolution. The few data points are insufficient to determine whether or not the ELPE was a global hyperthermal-like event [see Bernaola et al., 2007].

[18] The PCIM is punctuated by several rapid, but small shifts in the isotope record. At 58.2 Ma, δ13C and δ18O decrease in 200 kyr consistent with a gradual input of light carbon accompanied by a small rise in temperature. At 57.7 Ma a rapid positive shift of 0.5‰ in δ13C data is accompanied by a decrease of 0.4‰ in δ18O, roughly coincident with a prominent rise in carbonate sedimentation rates in both the South Atlantic and in the Pacific [Westerhold et al., 2008]. The positive shift in δ13C is fast and might be more consistent with a ventilation change that results in enhanced carbonate preservation at Site 1209. Other records are required to determine if the signal is global, in which case it could reflect a relatively rapid increase in burial rates of organic carbon countered by an increase in carbonate preservation and burial [Kump and Arthur, 1999].

[19] The long-term 3°C warming and decline in δ13C (∼1‰) that precedes the PETM essentially initiates at 57.3 Ma with a rapid warming of 1.5°C. The decrease might have resulted from a long-term input of 12C-enriched carbon into the atmosphere and ocean. The second phase of the North Atlantic Igneous Province (NAIP) initiated around 57.5 Ma [Sinton and Duncan, 1998]. Presumably, the increased crustal production was accompanied by increased mantle outgassing of CO2 and thus likely sustained the long-term warming trend that began at ∼57.5 Ma and lasted into the early Eocene [Vogt, 1979; Arthur, 1980; Corfield and Cartlidge, 1992; Zachos et al., 2001a; Demicco, 2004]. This gradual trend was briefly interrupted at the end of the Paleocene by the strong carbon isotope anomaly and warming of the PETM [e.g., Zachos et al., 2008].

4.2. Orbital Cyclicity in the Paleocene Benthic Isotope Record

[20] Our new data show that the deep-sea benthic isotope record is characterized by periodic cycles or excursions that are superimposed on the long-term trend. In general, carbon isotope minima are associated with oxygen isotope minima and increased dissolution, indicated by peaks in Fe intensity as well as minima in the coarse fraction (Figure 2). Carbon isotope excursions are related to the short (100 kyr) and long (405 kyr) eccentricity cycle with maxima in eccentricity being associated with carbon isotope minima (Figure 4). Wavelet analysis of benthic δ13C, benthic δ18O and coarse fraction supports the dominance of the 405 kyr cycle in the benthic Paleocene record. (Figures S5, S6, and S7). Precession and obliquity related variations in the data cannot be detected with confidence, because low sedimentation rate and bioturbation smooth signals over 10 to 25 kyr. Cross-spectral analysis (Figure 4c) between eccentricity and isotope data reveals a 40–60 kyr phase lag of δ13C and a 0–50 kyr phase lag of δ18O for long eccentricity cycles. For short eccentricity cycles we found a roughly 10 kyr lag of δ13C and almost no lag of δ18O. This frequency-dependent phase lag of δ13C has been detected previously and is attributed to a nonlinear energy transfer from precession to eccentricity bands due to the long residence time of carbon in the oceans [see Pälike et al., 2006]. A similar interaction of the carbon cycle, solar forcing, and oxygen isotope variations has been documented for the Oligocene and Miocene [Zachos et al., 2001b; Holbourn et al., 2007] as well as the Paleocene and late Cretaceous [Herbert, 1997; Zachos et al., 2010].

Figure 4.

Spectral analysis of Site 1209 benthic δ13C and δ18O data. (a) Benthic δ13C and δ18O data from Site 1209 (55–66 Ma, black line) and bulk δ13C data from Site 1262 (Walvis Ridge, South Atlantic, 55–57.5 Ma, gray line; data from Zachos et al. [2010]). The 405 kyr filter output for Site 1209 data is dashed in intervals with sparse data coverage. The software package AnalySeries 2.0 [Paillard et al., 1996] was used to filter the time series for variability at a period of 405 kyr (0.024 ± 0.0007). For comparison, we plotted the Laskar et al. [2004] solution for eccentricity and the stable 405 kyr cycle [Laskar et al., 2004, equation 47]. Note that the dashed gray grid lines are spaced by 405 kyr and that the original bulk δ13C data from Site 1262 have been offset by 1‰ to be plotted on the benthic δ13C y axis. (b) MTM power spectra for Site 1209 benthic δ13C and δ18O data. The spectra have been calculated by the kSpectra Toolkit using three tapers and a resolution of 2; bars indicate bandwidth. Background estimate and hence confidence levels (90%, 95%, and 99%) are based on a robust red noise estimation [Mann and Lees, 1996]. Spectral peaks related to the short (100 kyr) and long (405 kyr) eccentricity cycles are marked by an arrow. In preparation for analysis outliers were removed and the time series linearly resampled at 2 kyr intervals. The long-term trend was removed by a 2.5 Myr (0.0004 Hz) FFT high-pass filter. (c) Blackman-Tukey cross-spectral phase estimates between stable isotopes and the La2004 eccentricity curve, converted to lag times in kyr (with 99% confidence intervals).

[21] For a short interval at Shatsky Rise (230–234 rmcd; about 9 eccentricity cycles) helium isotope data [Marcantonio et al., 2009] and dust flux estimates [Woodard et al., 2011] show that changes in eolian dust flux are synchronous with Fe intensity data and thus likely eccentricity driven. In addition, the extraterrestrial 3He data from Site 1209 point to climate-forced changes in carbonate preservation anti-phased to the dust flux [Marcantonio et al., 2009]. Coarse fraction data presented here document enhanced preservation of calcium carbonate in eccentricity minima, supporting the helium isotope results. Our data from the central Pacific, along with the new bulk isotope data from the South Atlantic [Zachos et al., 2010], confirm the importance of eccentricity oscillations in driving Paleocene climate variations. Simple box modeling using parameterized forcing suggests that the climate system responses to complex orbital variations via expansion and contraction of biosphere productivity [Pälike et al., 2006]. The pronounced 100- and 405-kyr periodicity observed in the data might be a result of the long residence time of carbon in the ocean (∼100 kyr) which acts like a low-pass filter that dampens the signal, particularly at high frequencies [Cramer et al., 2003]. It is not known if the climatic response in the Paleocene and Eocene is achieved through ocean export production or carbon accumulation in the ocean or on land [Zachos et al., 2010]. The subdued amplitude of the 405-kyr cycles in benthic δ13C in the interval 2–3 Myr after the K/Pg might be consistent with observation that export of carbon to the deep sea had not fully recovered to preextinction levels [Coxall et al., 2006]. This dampening, the condensed intervals and the limited resolution of stable isotope data from 55.5 to 58 Ma in Site 1209 also hamper the clear recognition of the very long 2.4 Myr eccentricity cycle.

4.3. Top Chron C27n Event

[22] The Site 1209 benthic foraminiferal stable isotope record also provides unprecedented insight into the climatic processes around the Danian/Seladian boundary, in particular the Top Chron 27n event at 61.75 Ma [Westerhold et al., 2008]. The Top Chron C27n Event has also been identified in detailed cyclostratigraphic records from ODP Leg 208 on Walvis Ridge (South Atlantic) and ODP Leg 199 on Shatsky Rise (Western Pacific) and is characterized by exceptionally high peaks in iron concentration close to the top of magnetochron C27n. The Site 1209 benthic record (Figure 5 and Figure S4) shows that the event is characterized by a double peak in carbon isotopes with a total duration of 200 kyr, a feature common to subsequent early Eocene hyperthermals [Zachos et al., 2010]. The onset is transient with a 0.6‰ decrease in δ13C and a 0.5‰ decrease in δ18O (2°C increase in deep-sea temperature) right at the Chron C27n/C26r boundary and planktic foraminiferal zone P3a/P3b boundary. The sudden decrease in carbonate in combination with a clear negative excursion in δ13C and δ18O indicates that this event may represent an early Paleocene global warming episode. This event clearly corresponds to the Latest Danian Event (LDE) of Bornemann et al. [2009], the Danian/Selandian transition event of Speijer [2003] (Neo-Duwi event), and the carbon isotope excursions CIE-DS1 of Arenillas et al. [2008] at Zumaia as well as ODP 761B off NW Australia [Quillévéré et al., 2002] (Figure 5). New paleomagnetic data from Zumaia show that the onset of the transient δ13C excursion CIE-DS1 occurred exactly at the C27n/C26r magnetochron boundary [Dinarès-Turell et al., 2010], identical to the data from Shatsky Rise. The characteristic double peak in carbon isotopes is also present in bulk δ13C data from Walvis Ridge Site 1262 (at 195 mcd in the work by Kroon et al. [2007, Figure F11]). Our isotope data as well as micropaleontological work at other sections [Speijer, 2003; Youssef Ali, 2009] suggests that this event represents an exceptional perturbation of the carbon cycle associated with a 2°C warming of the deep ocean.

Figure 5.

Benthic foraminiferal δ13C and δ18O and stratigraphy from ODP Site 1209, Gebel Aweina in the Nile Basin (Egypt) [Bornemann et al., 2009], and ODP Site 761B (offshore NW Australia) [Quillévéré et al., 2002] and bulk rock δ13C from Zumaia (Spain) [Arenillas et al., 2008] across the Top Chron 27n event or Latest Danian Event (LDE). Please note that the Danian/Selandian boundary definition at Zumaia is ∼870 kyr above the C27n/C26r magnetochron boundary according to Bernaola et al. [2009]; the Danian/Selandian boundary at Site 1209 is after GTS2004 [Luterbacher et al., 2004], close to the C27n/C26r magnetochron boundary. The peak LDE δ13C and δ18O values are coincident with the base of the planktonic foraminifera zone P3b (Igorina albeari subzone). Blue shaded area represents the correlation between sections for the LDE with duration of 200 kyr. Red lines mark correlation ties between Zumaia and Site 1209.

[23] The Top Chron C27n event marks the beginning of the long-term increase in δ13C and coincides with the major deceleration of South Atlantic spreading rates indicating a possible causal relationship. Interestingly this event is synchronous with two major land mammal turnovers (Shanghuan-Nongshanian Asian Land Mammal boundary and the Torrejonian-Tiffanian North American Land Mammal boundary) and thus lends support to the idea that the turnover was driven by environmental changes [Clyde et al., 2008]. Although the causal mechanism for the Top Chron 27n event is uncertain, the proximity to the first phase of the NAIP (Figure 3) [Saunders et al., 1996; Larsen and Saunders, 1998; Jolley and Bell, 2002; Pedersen et al., 2002] points to a similar triggering mechanism as proposed for the PETM with initial warming caused by a pulse in volcanic CO2 input and subsequent warming due to positive feedback loops in the climate system [Svensen et al., 2004; Zachos et al., 2005; Sluijs et al., 2007; Storey et al., 2007]. Increased productivity and deep-sea cooling starting more than 1 million years earlier, at around 63.0 Ma, should have favored the expansion of reduced carbon reservoirs (e.g., gas hydrates), one or more of which then rapidly released excess carbon in response to initial warming.[Dickens et al., 1995; Dickens, 2003]. While there are other subsequent thermal excursions, for example at 61.35 Ma, none are associated with a prominent carbon isotope excursion and dissolution horizon features that imply tight coupling between climate and the carbon cycle.

5. Conclusions

[24] Our ∼11 Myr long benthic carbon and oxygen isotope record from the equatorial Pacific ODP Site 1209 is the first high-resolution, continuous record covering the entire Paleocene. The combination of the integrated astronomically calibrated stratigraphic framework and high-resolution benthic stable isotope data at Site 1209 provides new detailed information about climate variability during the Paleocene epoch. The long-term trend in our record reveals a close coupling of volcanic CO2 input by Large Igneous Provinces (LIPs) and subsequent deep-sea warming, and suggests that the Deccan Trap phase 2 and 3 around the K/Pg boundary might have contributed to deep-sea warming of ∼0.5°C. Moreover, the North Atlantic Igneous Province (NAIP) phase 1 at 61–62 Ma reversed the late Danian cooling, and phase 2 starting around 57.5 Ma lead to a long-term deep-sea warming of 3–4°C up to the PETM.

[25] The Paleocene deep-sea benthic isotope record of Site 1209 is characterized by periodic slow excursions superimposed on the long-term trend. These swings in the carbon cycle and deep-sea temperature are dominated by orbital forcing, especially by the long (405 kyr) eccentricity cycle. As in the late Paleocene and early Eocene [Zachos et al., 2010] negative carbon isotope excursions are in phase with maxima in eccentricity.

[26] Our record also documents a transient carbon isotope excursion (CIE) associated with a 2°C warming of the deep ocean at 61.75 Ma coincident with the planktic foraminiferal zone P3a/P3b boundary and close to the magnetochron C26r/C27n boundary. This event is characterized by an abrupt onset, a double peak in both isotopic records, a negative carbon isotope excursion of 0.6‰ and a 0.5‰ decrease in δ18O. The duration of the event is ∼200 kyr which is similar in duration to the PETM and subsequent hyperthermals, but of significantly smaller magnitude.


[27] We thank Monika Segl and her team for carefully analyzing the stable isotopes at the MARUM in Bremen and Jason Newton and Robert Becker at UCSC. The manuscript benefited from feedback by two anonymous reviewers. This research used samples and/or data provided by the Ocean Drilling Program (ODP). Funding for this research was provided by the Deutsche Forschungsgemeinschaft (DFG), the DFG-Leibniz Center for Surface Process and Climate Studies at the University of Potsdam, and the National Science Foundation (NSF).