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Fw: Cretaceous/Cenozoic Greenhouse Climate Extremes: Causes and Conseq uences II

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  • Pat N self only
    ... The abstracts below were presented at the Fall (December 14-17, 2004) Meeting....... These in particular concern the Paleocene-Eocene Thermal Maximum, a
    Message 1 of 1 , Jan 7, 2005
      ----- Forwarded Message (Sonya PLoS Medicine)
      The abstracts below were presented at the Fall (December 14-17, 2004)
      These in particular concern the Paleocene-Eocene Thermal Maximum, a
      rapid global warming event that occurred 55 million years ago....
      some of them speak to methane and the very last one concerns the modern day Sea of Japan, relating a current methane plume source.......

      The research is derived from ODP leg 208........

      Paleoceanography and Paleoclimatology [PP]
      PP14A MCC:2004 Monday 1600h Cretaceous/Cenozoic Greenhouse Climate
      Extremes: Causes and Consequences II
      Presiding:C M John, Department of Earth Sciences, University of
      California, Santa Cruz; H M Stoll, Geoscience Department, Williams
      College PP14A-01 16:00h

      Model Simulations of the Global Carbon and Sulfur Cycles: Implications
      for the Paleocene-Eocene Thermal Maximum
      * Higgins, J A (jhiggins@...) ,Schrag, D P
      (schrag@...) ,

      Extreme global warmth and an abrupt negative carbon isotope excursion
      during the Paleocene-Eocene Thermal Maximum (PETM) have been attributed
      to a rapid addition of isotopically depleted carbon to the
      ocean-atmosphere system. Potential carbon sources include the abrupt
      release of 1000-2000 Gt C as methane hydrate (\delta$^{13}$C
      ~-60\permil) from sediments on the continental slope (Dickens et al.,
      1995) and the oxidation of 8000-9000 Gt of organic carbon
      (\delta$^{13}$C ~-25\permil) in rampant global wildfires (Kurtz et al.,
      2003). Using a simple geochemical model of the global carbon and sulfur
      cycles, we investigate whether these hypotheses are consistent with
      estimates of climate warming during the PETM by considering the effects
      of atmospheric composition and climate in the Paleocene and feedbacks
      driven by changes in sulfur cycling and seawater chemistry. Modest
      increases in atmospheric CO$_{2}$ (70-150 ppm) associated with methane
      hydrate release cannot, without additional feedbacks in the climate
      system, account for a $5-6\deg$ C increase in global sea surface
      temperature during the PETM. In contrast, a significant increase in
      atmospheric CO$_{2}$ (600-700 ppm) is observed following the oxidation
      of 8000-9000 Gt of organic carbon. However, constraints on the size and
      extent of the Paleocene terrestrial carbon pool and the absence of
      geologic evidence indicative of vast wildfires argue against a global
      conflagration as an important source of depleted carbon. Instead, we
      interpret the PETM and its associated negative carbon isotope excursion
      as representing the oxidation of 8000-9000 Gt C as organic matter in
      shallow marine and near shore terrestrial sediments following the
      retreat of major epicontinental seaways in the Paleocene. This
      hypothesis is also consistent with large changes in the sulfur cycle in
      the early Eocene inferred from the \delta$^{34}$S of seawater sulfate.
      References: Dickens G.R., et al., (1995) Paleoceanography, 10, 965-971.
      Kurtz, A.C., et al., (2003) Paleoceanography, 18, 1090-1104.

      PP14A-02 16:15h Multiple Early Eocene Thermal Maximums
      * Roehl, U (uroehl@...) , Zachos, J C (jzachos@...)
      ,Thomas, E (ethomas@...) ,
      Kelly, D C (ckelly@...) , Donner, B (donner@...)
      , Westerhold, T (tho@...) ,

      Periodic dissolution horizons signifying abrupt shoaling of the
      lysocline and CCD are characteristic features of deep-sea sections and
      often attributed to Milankovitch forcing via their diagnostic
      frequencies. Prominent dissolution horizons also correspond to abrupt
      climate events, such as the Paleocene-Eocene thermal maximum (PETM), as
      a result of input of significant CH$_{4}$ - CO$_{2}$ into the
      ocean-atmosphere system. The question arises whether other significant
      dissolution horizons identified in sediments of late Paleocene and early
      Eocene age similar to the recently identified ELMO (Lourens et al.,
      2004) were formed as a result of greenhouse gas input, or whether they
      were related to cumulative effects of periodic changes in ocean
      chemistry and circulation. Here we report the discovery of a 3$^{rd}$
      thermal maximum in early Eocene (about 52 Ma) sediments recovered from
      the South Atlantic during ODP Leg 208. The prominent clay layer was
      named the "X" event and was identified within planktonic foraminifer
      zone P7 and calcareous nannofossil zone CP10 at four Walvis Ridge
      Transect sites with a water depth range of 2000 m (Sites 1262 to 1267).
      Benthics assemblages are composed of small individuals, have low
      diversity and high dominance. Dominant taxa are {\it Nuttallides
      truempyi} and various abyssaminids, resembling the post PETM extinction
      assemblages. High-resolution bulk carbonate \delta$^{13}$C measurements
      of one of the more shallow Sites 1265 reveal a rapid about 0.6 per mill
      drop in \delta$^{13}$C and \delta$^{18}$O followed by an exponential
      recovery to pre-excursion \delta$^{13}$C values well known for the PETM
      and also observed for the ELMO. The planktonic foraminiferal
      \delta$^{13}$C records of {\it Morozovella subbotina} and {\it Acaranina
      soldadoensis} in the deepest Site 1262 show a 0.8 to 0.9 per mill drop,
      whereas the \delta$^{13}$C drop of benthic foraminifera {\it Nuttallides
      truempyi} is slightly larger (about 1 per mill). We are evaluating
      mechanisms for the widespread change in deep-water chemistry, its
      connection to the surface-water response, and the relationship of the
      event, as well as the PETM and ELMO, with current astronomical solutions
      (Laskar et al., 2004; Varadi et al., 2003). References 1. Lourens, L.J.,
      Sluijs, A., Kroon, D., Zachos, J.C., Thomas, E., Roehl, U., and the ODP
      Leg 208 Shipboard Scientific Party, 2004. An early Eocene transient
      warming (~53 Ma): Implications for astronomically-paced early Eocene
      hyperthermal events.- Abstract, 8th International Conference on
      Paleoceanography (ICP), 5-10 September 2004, Biarritz, France. 2. F.
      Varadi, B. Bunnegar, M. Ghil, Astrophysical J. 592, 620-630 (2003). 3.
      J. Laskar et al., Astronomy and Astrophysics (2004).

      PP14A-03 16:30h
      An early Eocene transient warming ($\sim $53 Ma): Implications for
      astronomically-paced early Eocene hyperthermal events.
      * Sluijs, A (A.Sluijs@...) ,Lourens, L J (llourens@...) ,
      Kroon, D (kroo@...) ,
      Zachos, J C (jzachos@...) , Thomas, E
      (ethomas@...) , R�hl, U (uroehl@...-bremen.de) ,

      Here we report on a pronounced hyperthermal event approximately 2 Myrs
      after the Paleocene-Eocene thermal maximum (PETM) and place both events
      in a new orbitally-tuned framework. This previously unrecognized
      transient event and the underlying PETM were both recovered at five
      sites along a 2km depth transect on the Walvis Ridge (southeast
      Atlantic) during Ocean Drilling Program Leg 208. Similar to the PETM,
      this event, \textit{Elmo}, is marked by a red clay layer, associated
      with severe drop in CaCO$_{3}$ concentrations, suggesting a $\sim $2 km
      rise in the lysocline. High-resolution (1cm) bulk carbonate $\delta
      ^{13}$C measurements of the shallowest, and hence most complete Site
      1263 revealed a $\sim $1.5% drop in $\delta ^{13}$C and $\delta ^{18}$O.
      The negative $\delta ^{13}$C excursion is composed of three steep steps
      of which the last one corresponds to the base of the red clay layer. The
      post-\textit{Elmo} interval mirrors the typical PETM signature with an
      exponential recovery to pre-excursion $\delta ^{13}$C values. The
      planktonic foraminiferal $\delta ^{13}$C record (measured on single
      specimens of the surface dweller \textit{Acaranina soldadoensis})
      confirms the bulk pattern, although the amplitude of the excursion,
      $\sim $-2.5, is larger. The planktonic foraminiferal $\delta ^{18}$O
      record shows the same $\sim $-1% excursion as the bulk, suggesting a
      fast increase in sea surface temperature of $\sim $4 degrees C. The case
      of conditions similar to the PETM during the ELMO event is further
      strengthened by the occurrence of low diversity, diminutive benthic
      foraminifer assemblages, and a decrease in planktonic foraminifer
      diversity. Examination of published isotope, X-ray fluorescence and
      magnetic susceptibility records further indicates that this event is
      global in nature and recorded in other marine and terrestrial basins.
      Orbital tuning of the deepest Sites 1262 magnetic susceptibility and
      Sites 1262 and 1267 color reflectance records to the La2004 and R7
      astronomical solutions shows that the \textit{Elmo} is five 400-kyr
      eccentricity cycles younger than the PETM and that both events are
      linked to eccentricity-maxima. This, and the subtle resemblance between
      the \textit{Elmo} and PETM mentioned above, suggests that similar,
      astronomically modulated, mechanisms are at the root of them. The
      leading hypothesis to explain the PETM climatic event and its $\delta
      ^{13}$C excursion is the dissociation of submarine methane hydrates. If
      the \textit{Elmo} shares a similar origin, its less extreme appearance
      may be associated with the ability of the methane hydrate reservoir to
      recharge after the PETM, especially under the warm conditions that
      prevailed in the interval spanning the two events.

      PP14A-04 16:45h
      Revisiting ODP Site 690 to Assess the Responses of Marine Carbonate
      Chemistry to the Paleocene-Eocene Thermal Maximum
      * Kelly, D C (ckelly@...) , Zachos, J C
      (jzachos@...) , Bralower, T J (tjb26@...) ,
      Schellenberg, S A (schellenberg@...) ,

      The close of the Paleocene epoch (ca. 55 Ma) is punctuated by a
      transient ($ < $100 kyr) global warming event referred to as the
      Paleocene-Eocene Thermal Maximum (PETM). In the marine realm, hallmark
      signatures of the PETM are a negative carbon isotope excursion (CIE) on
      the order of 3 per mil, widespread carbonate dissolution, and a benthic
      foraminiferal mass extinction. The rapid onset and anomalous magnitude
      of the CIE has been attributed to a sudden release of some 2000 Gt of
      methane into earth's surficial carbon reservoir. Presumably, oxidation
      of this methane elevated pCO2 levels in the atmosphere/ocean system,
      fueling global greenhouse warmth and carbonate dissolution. Here we
      revisit what is arguably the most complete deep-sea record of the PETM
      recovered from ODP Site 690 to explore the dynamic coupling between
      atmospheric CO2 levels, marine carbonate chemistry, continental
      weathering and global climate. The abrupt onset of the CIE is
      accompanied by a sharp decline in wt.% carbonate, yet wt.%
      coarse-fraction ($ > $63 microns, foraminiferal shells) values remain
      fairly constant. These sedimentological shifts collectively point toward
      the selective removal of fine-fraction ($ < $63 microns) carbonate
      produced by calcareous nannoplankton during peak oceanic warmth. We
      believe this selective pattern of "dissolution" actually reflects, in
      part, reduced calcification among some calcareous nannofossil taxa. An
      important corollary of this interpretation is that rising pCO2 levels
      attained a critical threshold that inhibited nannoplankton
      calcification. Decreased surface-ocean carbonate production triggered a
      shoaling of the local lysocline and concomitantly enhanced the ocean's
      carbon-storage capacity providing an important sink for atmospheric CO2.
      The character of carbonate sedimentation is reversed during the later,
      recovery stages of the CIE. It is within this stratigraphically expanded
      portion of the CIE that wt.% carbonate values and the relative
      proportion of wt.% fine-fraction increase markedly. This secondary shift
      coincides with a 5 degrees C cooling of intermediate waters and a sharp
      influx of kaolinite. Concurrent cooling of sea-surface temperatures is
      also suggested by the disappearance of warm-water microplankton. We
      believe these changes to be interrelated. The kaolinite spike likely
      reflects intensified silicate weathering on Antarctica as well as
      increased continental runoff. Thus, enhanced silicate weathering
      reactions (CaSiCO3 + CO2 -$ > $ SiO2 + CaCO3) may have served as an
      added sink for atmospheric CO2 and a source of oceanic Ca2+ and HCO3-
      that drove an alkalinity overshoot thereby fostering increased carbonate
      sedimentation within the Weddell Sea region. The remarkable sequence of
      oceanic changes preserved in the Site 690 PETM record is consistent with
      the hypothesis that both marine carbonate chemistry and continental
      weathering acted as negative feedbacks to curb PETM warmth.

      PP14A-05 17:00h
      Barium Cycling During the Paleocene-Eocene Thermal Maximum: Evidence
      From Ba/Ca in Foraminifera
      * Hall, J M (jenney.hall@...) , Zachos, J C (jzachos@...)
      ,Turekian, K K (karl.turekian@...) ,

      The Paleocene-Eocene thermal maximum (PETM) around 55 Ma reflects
      short-term, rapid climate change during a period of intense greenhouse
      climate. This interval is characterized by a negative carbon isotopic
      shift, interpreted as a release of methane from seafloor gas hydrate
      reservoirs. This perturbation of the carbon cycle is accompanied by
      significantly greater rates of euhedral barite accumulation in deep sea
      sediment commonly believed to be a reflection of elevated primary
      productivity in surface waters. An interpretation of higher productivity
      during the PETM, however, is contrary to microfossil assemblage data
      which indicates a decrease in primary productivity. It has also been
      suggested that the increase in barite accumulation during the PETM may
      have been the result of an increase in dissolved barium concentrations
      in the deep ocean coeval with methane release. This supposition has
      support from the fact that modern gas hydrate reservoirs are surrounded
      by pore waters with dissolved barium concentrations considerably higher
      than that of seawater. This investigation utilizes the barium content of
      foraminifera as a proxy to reconstruct changes in the barium
      concentration of the ocean. At 55 Ma, Ba/Ca decreases between 25 to 28%
      in the planktic foraminifer \textit{Morozovella velascoensis},
      indicating a decrease in the barium concentration of the surface ocean.
      These results bolster the theory that there was increased biogenic
      barite precipitation during the PETM. Changes in surface water
      temperature and pH may have altered species assemblages such that
      celestite (SrSO$_4$) precipitating organisms enriched in barium as
      BaSO$_4$ (possibly acantharia) were dominant, modifying the barite
      precipitation pathways, which affected water column barite cycling.
      Ba/Ca and Cd/Ca measurements on benthic foraminifera show a positive
      correlation with Mn/Ca, indicating contamination of manganese oxide
      coatings. This contamination is in part due to the greater surface to
      volume ratio of benthic foraminifera, which are smaller than planktic
      species. Additionally, smaller quantities of benthics were available for
      analysis, which limited the intensity of pre-treatment to remove these
      coatings. After correcting for this coating contamination, no
      significant change in benthic Ba/Ca could be discerned through this
      interval. Taken together, the planktic and benthic foraminiferal Ba/Ca
      data suggests that enhanced biogenic barite accumulation during the PETM
      was primarily due to increased export from the surface waters.

      PP14A-06 17:15h Coccolithophorid Productivity Response to
      Paleocene-Eocene Thermal Maximum
      * Stoll, H M (hstoll@...) , Shimizu, N (nshimizu@...)
      ,Arevalos, A (05ala@...) , Theroux, S (05smt@...) ,

      The response of marine plankton to the Paleocene-Eocene Thermal Maximum
      may have influenced the rate of uptake of greenhouse gases and recovery
      of the climate but indicators of marine productivity in the open ocean
      are sparse and have yielded conflicting results at some sites. Here we
      report on the productivity response of coccolithophorids during the PETM
      at sites from the Southern Ocean, Tropical Pacific, and Tropical
      Atlantic. A novel technique for picking individual coccoliths for
      analysis using secondary ion mass spectrometery (SIMS) allows us to
      apply the coccolith Sr/Ca productivity proxy to individual genera and
      avoid biases from changing species assemblages and noncoccolith
      carbonate in sediments. In the Southern Ocean site, Chiasmolithus
      experiences a brief surge in productivity in the first thousand years
      following the event onset, Zygrhablithus experiences an increase in
      productivity beginning about 20,000 years following the event onset and
      lasting about 50,000 years. Toweius, the dominant genera, experiences
      increased productivity beginning about 20,000 years following the event
      onset and lasting about 100,000 years and likely contributing to the
      high carbonate accumulation rates at this site during the carbon isotope
      recovery. Discoaster shows a slight decrease in productivity. In the
      Equatorial Pacific Site, Toweius experiences a dramatic decline in
      productivity after the event onset, and recovery to pre-event levels
      about 50,000 years later. Discoaster shows a slight increase in
      productivity during the PETM. In the Equatorial Atlantic site, Toweius
      shows a slight decrease in productivity during the PETM whereas
      Coccolithus is unaffected. Consequently, while published Os isotopic
      data are inferred to indicate increased global average weathering rates,
      the largest effect of such an increase may have been in higher latitude
      areas which were previously weathering-limited. Hence, the effect of
      nutrient fertilization may have been confined to these regions.

      PP14A-07 17:30h Major Transient Floral Change During the
      Paleocene-Eocene Thermal Maximum

      * Wing, S L (wings@...) , Harrington, G J
      (g.j.harrington@...) , Bloch, J I (carpo@...) , Boyer, D M
      (dboyer@...) , Smith, F (fsmith@...) ,

      New continental sections representing the Paleocene-Eocene Thermal
      Maximum (PETM) have been discovered in the southern Bighorn Basin,
      Wyoming. Three localities preserving leaves and fruits are the first
      megafossil record of plants from this geologically short (about 150ky)
      period of intense warming. The localities produce fossil pollen and
      spores as well. The plant remains are in sections that preserve
      vertebrate fossils characteristic of the Wa-0 faunal zone that elsewhere
      is restricted to the period of negative carbon isotopic values that
      occurred during the PETM. The megaflora and palynoflora from the three
      localities contain a small number of long-ranging taxa that are common
      in many late Paleocene and early Eocene localities from the Bighorn
      Basin (e.g., {\it Macginitiea}, {\it Caryapollenites}, {\it
      Ulmipollenites}, {\it Alnipollenites}), however they also produce up to
      10 taxa that have not been seen before in either the Paleocene or Eocene
      of this area. In the palynoflora, several of these previously unrecorded
      taxa (e.g, {\it Labropollis}, cf. {\it Bombax}, and a distinctive large
      tricolpate grain) are common in the Gulf Coastal Plain Paleogene.
      Although the number of dicot leaf species so far is too small to produce
      a robust physiognomic estimate of temperature or precipitation, it is
      notable that one locality near the base of the PETM is dominated by
      small-leaved legumes, and another near the top by an undetermined dicot
      leaf with an extremely long drip-tip. Preliminary analysis of the floral
      data strongly suggests that some types of plants extended their ranges
      up to 1500 km northward during the PETM, where they became sympatric
      with native mid-latitude taxa. These range extensions are restricted to
      the PETM. Furthermore, PETM floral change was essentially synchronous
      with the better-known mammalian turnover event. The unusual physiognomy
      of PETM fossil leaves raises the possibility of major changes in
      seasonality or amount of precipitation. We plan to measure stable carbon
      isotope ratios in organic matter and soil carbonates from the new
      sections in order to establish more precisely the relationship between
      biotic and geochemical change during the PETM.

      PP14A-08 17:45h New Sections and Fossils From the Southern Bighorn
      Basin, Wyoming Document Faunal Turnover During the PETM * Bloch, J I
      (jbloch@...) , Boyer, D M (dboyer@...) , Strait, S G
      (straitho@...) ,
      Wing, S L (wings@...) ,

      Though earliest Eocene (Wa-0) mammals are known from the southern
      Bighorn Basin, late Paleocene mammals are not. Recent discovery of
      latest Paleocene mammals in section with new Wa-0 faunas and floras at
      Cabin Fork allows for the first studies of terrestrial biotic change
      across the Paleocene-Eocene boundary interval outside of the northern
      Bighorn Basin. A differential GPS was used to map the area and provide a
      framework for high-resolution biostratigraphy. Least squares
      interpolation of bedding planes from points marking outcrop of beds
      reveals high r$^{2}$ coefficients (0.97-0.98). This indicates that small
      scale folding is minimal and bed traces are smoothly planar. Beds in the
      study area strike N-NW ($355\deg$) and dip shallowly W-SW ($ <
      $$1.0\deg$). Smaller scale undulations are present: to the NE beds
      strike NW and dip to the SW ($342\deg$/$1.0\deg$) whereas those to the
      SW strike NE and dip NW ($5\deg$/$1.0\deg$). Shallow dips allow us to
      approximate stratigraphic thickness with elevation. Paleocene mammals,
      including diagnostic Clarkforkian land-mammal age indicators, {\it
      Aletodon gunnelli}, {\it Apheliscus nitidus}, and {\it Haplomylus
      simpsoni}, were found in a ferruginous, grit-pebble conglomerate at the
      base of a channel sand at the top of the Fort Union Fm. The
      fossiliferous horizon is extensive and has produced over 200 specimens
      from more than 60 sites for which positions have been determined with
      sub-meter accuracy. Absence of {\it Plesiadapis cookei} and {\it
      Hyracotherium} spp., together with high relative abundance of {\it
      Phenacodus} and {\it Ectocion}, indicate this fauna is latest
      Clarkforkian ({\it Phenacodus-Ectocion} Range Zone, Cf-3). Earliest
      Eocene mammals, including diagnostic Wa-0 taxa {\it Arfia junnei}, {\it
      Copecion davisi}, {\it Hyracotherium sandrae}, and {\it Diacodexis
      ilicis}, are represented by more than 233 specimens from 70 sites at
      three levels in the lowest Willwood Formation. The lowest fossils come
      from paleosols and claygall accumulations in stringer sands
      approximately 3 meters above the top of the channel sand that is the top
      of the Fort Union Formation, and 8 meters above the Clarkforkian
      localities. The second level is a fossiliferous paleosol 6-8 meters
      above the top of the channel sand. The third level is a paleosol fossil
      accumulation approximately 22 meters above the top of the channel sand
      and 15 meters below a large and persistent red paleosol informally
      called ?Big Red.? In the Cabin Fork area, Big Red produces mammal
      fossils, including {\it Cardiolophus}, that have been used to define the
      succeeding Wa-1 faunal zone (although some Wa-0 taxa have been recovered
      from Big Red approximately 6 km to the east). The Wa-0 interval in the
      Cabin Fork area is 38-40 meters thick and bounded by distinct Cf-3 and
      Wa-1 faunas. Preliminary analyses of fossils from the Cabin Fork section
      show that the faunal shift marking the PETM was very similar to that
      seen in the northern Bighorn Basin. This suggests that previously
      documented differences between Wa-0 mammalian faunas in the southern and
      northern Bighorn Basin, including the absence of certain diagnostic Wa-0
      taxa in the south, may reflect local sampling variation or artifacts
      rather than regional variation in faunal composition.

      Author(s) (2004), Title, Eos Trans. AGU, 85(47), Fall Meet. Suppl.,
      Abstract #####-##.

      part two

      Paleoceanography and Paleoclimatology [PP]
      PP11B MCC:level 1 Monday 0800h
      Cretaceous/Cenozoic Greenhouse Climate Extremes: Causes and Consequences
      I Posters
      Presiding:C M John, Department of Earth Sciences, University of
      California, Santa Cruz; H M Stoll, Geoscience Department, Williams College

      PP11B-0558 0800h
      Decoupled Shelf-Ocean Phytoplankton Productivity Responses Across the
      Paleocene-Eocene Thermal Maximum
      * Gibbs, S J (sgibbs@...) ,Bralower, T J
      (bralower@...) , Boharty, S (sbohaty@...) ,
      Zachos, J (jzachos@...) , Bybell, L M (lbybell@...) ,
      Quattlebaum, T (thomasqtl@...) ,

      Significant transformations in the global biosphere accompanied dramatic
      global warming and profound perturbation of the carbon cycle during the
      Paleocene Eocene Thermal Maximum (PETM, $\sim$55 Ma). These abrupt
      changes have been linked to a massive release of light carbon into the
      ocean-atmosphere system. Increased phytoplankton productivity has been
      cited as a mechanism responsible for subsequent CO$_{2}$ draw-down.
      However, interpretations of geochemical and biotic data differ on where
      this increased productivity occurred. Here we constrain the loci of
      increased productivity using highly detailed nannofossil assemblage
      data. Calcareous nannofossils provide an excellent basis to monitor
      changes in primary production during the PETM given their sensitivity to
      surface water conditions, especially availability of nutrients. We
      present nannofossil assemblage records from productivity end-member
      environments: a central gyre setting (ODP Site 1209, Shatsky Rise,
      paleo-equatorial Pacific), a high-latitude, open-ocean setting (ODP Site
      738, Indian Ocean sector of the Southern Ocean) and a neritic setting
      (USGS Wilson Lake drill hole, New Jersey). Nannofossil assemblages at
      all three sites display a pattern of continuous reorganization during
      the PETM. In particular, assemblage shifts at Shatsky Rise demonstrate a
      short-lived interval of extremely low productivity coincident with the
      carbon isotope excursion. In contrast, assemblages at Wilson Lake
      suggest a transient shift to more mesotrophic conditions. Combined with
      published planktonic assemblage records, these data produce a global
      picture of productivity change across the PETM with shelf areas and the
      open ocean clearly decoupled regardless of latitude. Open ocean sites
      demonstrate a global but transient increase in oligotrophy which may
      have resulted from a widespread deepening of the thermocline. Shelf
      productivity increase is localized with mesotrophic communities
      spatially restricted to areas close to nutrient sources via increased
      precipitation and runoff.

      PP11B-0559 0800h New Data On The Distribution Of Calcareous Nannofossils
      During And After The Paleocene/Eocene Transition
      * Raffi, I (raffi@...)

      Major changes occur among calcareous nannofossil assemblages at the
      transition from Paleocene to Eocene. In most known P/E boundary sections
      with complete sediment records, the changes are associated to the brief,
      intensive interval of global warming, the Paleocene-Eocene Thermal
      Maximum (PETM), and a concomitant huge perturbation of the global carbon
      budget, the Carbon Isotope Excursion (CIE). Changes in nannofossil
      assemblages include: (A) occurrence of {\it Rhomboaster} spp. - {\it D.
      araneus} correlative with the CIE; (B) decrease in diversification of
      {\it Fasciculithus} spp. at the CIE onset; (C) occurrence of {\it
      Zygrhablithus bijugatus} and {\it Fasciculithus} spp./ {\it Z.
      bijugatus} abundance cross-over within the upper part of the CIE-PETM
      interval; and (D) extiction of the Paleocene genus {\it Fasciculithus}
      just above the CIE, an event that is closely followed by the further
      evolution of {\it Rhomboaster - Tribrachiatus} plexus. The genus {\it
      Tribrachiatus} subsequently radiates over the next $\sim$1 million
      years, a time interval showing further steps in the evolutionary history
      of calcareous nannofossils (speciations among discoasters and
      sphenoliths) during the Eocene. Quantitative analyses of selected
      calcareous nannofossils in deep-sea sections recovered from the Atlantic
      (DSDP Site 550, ODP Site 929, and ODP Sites 1262 and 1263 of Leg 208)
      and paleo-equatorial Pacific (ODP Sites 1215, 1220, 1221 of Leg 199)
      provide new informations about calcareous nannofossils across the
      Paleocene/Eocene transition interval. The distinctive {\it Rhomboaster}
      spp. - {\it D. araneus} association (RD) was previously considered to
      have a marked provincialism, restricted to the Atlantic Ocean and
      partially extending to the Tethys seaway and westernmost Indian Ocean.
      Detailed study of Leg 199 sections (from equatorial Pacific) and
      preliminary analyses at the P/E boundary of ODP Site 929 (from Ceara
      Rise in western equatorial Atlantic) and ODP Sites 1262 and 1263 (from
      Walvis Ridge in southern Atlantic) indicate some difference in the RD
      distribution. The sudden appearance and short co-existence of {\it R.
      calcitrapa} gr. and {\it D. araneus}, and the lowermost occurrence of
      {\it R. cuspis} at the onset of CIE clearly can be extended to the
      equatorial regions of the Atlantic as well as the Pacific Ocean. The
      genus {\it Fasciculithus} undergoes a substantial decrease in
      diversification at the onset of CIE, and perish completely shortly
      afterwards. This significant turnover appears to represent a global
      event observed in all the known P/E boundary sections from different
      oceans and paleo-latitudes. The abundance cross-over between {\it
      Fasciculithus} spp. and {\it Z. bijugatus} has been observed to occur
      within the the CIE-PETM interval in several deep-sea sections. In the
      central paleo-equatorial Pacific Ocean, however, {\it Z. bijugatus}
      specimens were not present at all, whereas a marked increase in
      abundance of {\it R. cuspis} was observed in conjunction with the final
      decline of {\it Fasciculithus} spp. Data from the western
      paleo-equatorial Atlantic Ocean (Site 929) shows only few {\it Z.
      bijugatus}, implying that this particular early Eocene turnover is
      absent in these equatorial regions. {\it Thoracosphaera} spp. shows a
      short abundance peak immediately above the carbonate barren interval at
      the P/E boundary, during the CIE, at paleo-equatorial Pacific Site 1220,
      which probably reflects a stressed surface water environment.

      PP11B-0560 0800h Events at the Paleocene-Eocene Boundary as Recorded in
      Shelf Sediments From the Californian Margin

      * John, C M (cjohn@...) , Bohati, S (sbohaty@...) ,
      Zachos, J C (jzachos@...) ,
      Brinkhuis, H (H.Brinkhuis@...) ,Sluijs, A (A.Sluijs@...) ,
      Gibbs, S (sgibbs@...) ,
      Bralower, T (bralower@...) , McDougall-Reid, K (kris@...) ,

      The Paleocene-Eocene Thermal Maximum (PETM) is characterized by rapid
      global warming, as much as 8 degrees C, and a transient 3 per mil
      negative excursion in carbon isotopes (CIE) that has been observed in
      marine and terrestrial records worldwide. The magnitude of the CIE is
      best explained by the rapid transfer of a large mass of methane from gas
      hydrate reservoirs to the atmosphere. The rise in temperature associated
      with the addition of this greenhouse gas appears to have also altered
      global humidity and precipitation patterns, a feature which is best
      expressed in near shore depositional facies. While extensively studied
      in deep-sea sediments, the PETM has been comparatively less investigated
      in near-shore, shallow-marine records. This is particularly true for the
      Californian margin, where complications linked to syn-sedimentary and
      post depositional tectonic have so far limited paleoceanographic works
      on Paleocene-Eocene sedimentary records. Continental shelves are,
      however, a potentially important archive of the PETM event as they are
      proximal to rivers and are the principal sink for terrigenous sediments.
      The coastal marine ecosystems are also particularly sensitive to changes
      in local salinity and nutrient fluxes brought about by changing runoff.
      Here, we present data from several marine sections (claystones and
      siltstones) now exposed in the mountains of central and southern
      California and comprised of sediments deposited across the
      Paleocene-Eocene boundary. Sedimentation at these locations resulted
      from the interplay between tectonic, paleoceanographic, and climatic
      processes. The main objective of our study is to explore the relative
      timing between the CIE, possible changes in continental weathering,
      productivity and paleoceanography, and changes in regional climate (such
      as increased or decreased precipitation). The results obtained thus far
      indicate that 1) the CIE is recorded on the Western North American
      shelf, though its onset is truncated due to complex regional eustatic
      tectono-sedimentary patterns, 2) the magnitude of the isotopic excursion
      is similar to that in the deep-sea, 3) the excursion interval is
      expanded due to higher sedimentation rates, and 4) kaolinite to smectite
      ratios indicate a more complex relationship between continental
      weathering and climate than has been recorded on the U.S. East coast or
      on the southern margin of the Tethys.

      PP11B-0561 0800h
      Extreme Acidification of the Deep Sea at the Paleocene-Eocene Boundary:
      New Constraints From Ocean Drilling Program Leg 208
      * Zachos, J (jzachos@...) , Roehl, U , Hodell, D , Thomas, E ,
      Sluijs, A , Schellenberg, S , Kelly, C ,
      McCarren, H , Kroon, D , Nicolo, M ,

      A negative carbon isotope excursion and a rise in global temperature at
      the Paleocene-Eocene boundary have been attributed to the rapid release
      of as much as 2000 Gt of methane. In theory, the subsequent oxidation
      and uptake of this carbon by the ocean should have lowered deep-sea pH
      and carbonate ion content ([CO3]), thereby triggering a relatively rapid
      (~10-20 kyr) shoaling of the oceanic lysocline and calcite compensation
      depth (CCD) followed by more gradual (~40 kyr) recovery via silicate
      weathering of continental rocks. Here, we provide inorganic carbon,
      carbon isotope, and other physical property and geochemical data from a
      vertical array of deep-sea cores that constrain the timing and magnitude
      of CCD migration during the Paleocene-Eocene Thermal Maximum (PETM). The
      cores, Sites 1262, 1263, 1265, 1266, and 1267, were recovered from
      between 2.7 and 4.8 km water depth on the flanks of Walvis Ridge in the
      South Atlantic during ODP Leg 208. In each section, the Paleocene-Eocene
      boundary is marked by an abrupt transition from carbonate-rich ($ >
      $90%) chalk or ooze to a clay rich layer ($ < $1% CaCO3), the thickness
      of which increases (5-35 cm) from the shallowest to deepest core. With
      high-resolution carbon isotope and other records, we correlate the
      carbon records to each other and to the carbon isotope record of ODP
      Site 690, one of the more expanded marine P-E boundary sections. The
      comparison shows that the CCD shoaling was relatively fast coinciding
      with the initial phase of the carbon isotope excursion, while the
      recovery of the CCD over the 2 km transect took between 30-50 kyr. The
      rapid shoaling and gradual descent support the hypothesis that an
      anomalously large mass of carbon was rapidly released at the
      Paleocene-Eocene boundary. We also posit that this extreme decline in
      oceanic carbonate saturation to paleodepths shallower than 1.4 km
      contributed to the mass extinction of benthic foraminifera.


      PP11B-0562 0800h Tracers of Productivity across the PETM, Walvis Ridge,
      ODP Sites 1262 and 1263
      Quartini, J C (joequartini@...) , * Chun, C O (cchun@...)
      ,Delaney, M L (delaney@...) ,
      Zachos, J C (jzachos@...) ,

      The rapid and extreme global warming across the Paleocene-Eocene Thermal
      Maximum (PETM) is unmatched in Earth's history. We are using sedimentary
      phosphorus concentrations and geochemistry, along with barium and trace
      metals, to reconstruct nutrient burial, primary productivity, and
      paleoredox state across a depth transect for Walvis Ridge. We have
      chosen Ocean Drilling Program (ODP) Sites 1262 (4755 m water depth) and
      1263 (2717 m water depth) at a sample resolution of $\sim$ 1-2 kyr for 5
      Ma centered at 55 Ma. We are characterizing the nutrient burial history
      during the PETM by recording the associated short-term changes in ocean
      chemistry and circulation. We have measured Ba excess, a good indicator
      of export productivity in marine sediments underlying oxic conditions,
      for Site 1262 samples. Ba excess concentrations range between $\sim$ 2-5
      umol Ba/g prior to the warming event and decrease to zero at the
      boundary (140.04 mcd). Ba excess gradually recovers but does not greatly
      exceed pre-event concentrations ($\sim$ 2-5 umol Ba/g). Uranium and
      manganese enrichment factors (EF) were determined during this event for
      Site 1262. U ranges from 0.9 -1.1 relative to crustal averages
      pre-event, 0.7- 0.8 during the event, and 0.9 -1.1 after the rapid
      warming. Uranium data shows consistent recovery with calcium carbonate
      deposition over a depth range $\sim$ 0.5m. Mn EF values range between
      3.7 -8.6 prior to the event, suggesting an oxygenated depositional
      environment. At the boundary, Mn EF values drop to 1.3, then gradually
      return to pre-event values with a peak at 139.76 mcd of 13.2. We will
      compare our geochemical results with Site 1263 data.

      PP11B-0563 0800h Sedimentology, Petrology, and Volcanology of the
      Lower Aptian Selli Event (OAE1a) on the Shatsky Rise, North-Central
      Pacific Ocean * Marsaglia, K M (kathie.marsaglia@...)

      The large-scale submarine volcanism documented across the Pacific at
      ~120 Ma also affected the Shatsky Rise. The interval containing the
      lower Aptian Selli Event (OAE1a) was cored on the Shatsky Rise during
      Ocean Drilling Program Leg 198 with moderate (50%) recovery. Thin
      sections were produced from the Selli organic-rich interval, as well as
      the tuffaceous units above and below it. Mineralogy of selected samples
      was determined using X-ray diffraction analyses. On the Shatsky Rise,
      there is a pulse of ash input just prior to the deposition of the Selli
      OAE1a interval. Its texture and alteration are consistent with a mafic
      source, either a direct product of Ontong Java Plateau eruptions or more
      likely, an indirect product via reactivation of the older volcanic
      edifices on the rise. Soon after this volcanic pulse, anomalous amounts
      of organic matter accumulated on the rise forming a black shale horizon.
      The complex textures in the organic-rich intervals suggest a history of
      periodic anoxia, overprinted by bioturbation. Components include
      pellets, radiolaria, and fish debris. Petrographic observations made
      across the well-developed OAE1a interval at Site 1207 indicate that at
      the beginning of the event, the organic matter had a more globular
      texture (sapropellic algal matter) that progressively became laminated
      upsection. What this likely represents is the onset of organic matter
      accumulation and the resultant development of bacteria colonies on the
      sediment surface. These laminae are first irregular and discontinuous
      (wispy), then become more continuous and dense. The presence of
      carbonate-cemented radiolarite under the Selli interval implies
      carbonate remobilization, perhaps linked to calcareous microfossil
      dissolution. The volcanic debris in the overlying tuffaceous interval
      differs in that it is mainly epiclastic and glauconitic, likely derived
      from an emergent volcanic edifice on the Shatsky Rise. The epiclastic
      debris is mostly microlitic and locally tachylitic, suggesting that
      source lavas cooled slowly as would be expected in a subaerial setting.
      Rounding of the epiclastic debris is consistent with transport in a
      beach setting or possibly a high-energy shelf. The time frame involved
      with this interval (tuffaceous and organic-rich units) is relatively
      short, on the order of 1 million years, which would be consistent with
      the timeframe need for the rejuvenation and then subsidence of volcanic
      centers. This story, although best told through the stratigraphic
      section on the Shatsky Rise, is also represented in the Mid-Pacific
      Mountains at Site 463.

      PP11B-0564 0800h
      Depth Dependant Variations in Benthic Foraminiferal Assemblages and
      Stable Isotopes Across the P-E Boundary, Walvis Ridge (ODP Leg 208)
      * McCarren, H K (hmccarren@...) , Thomas, E
      (ethomas@...) , Zachos, J (jzachos@...) ,

      The Paleocene-Eocene Thermal Maximum (PETM) ($\sim$55 Ma), was
      characterized by extreme global warming, a negative carbon isotope
      excursion, intensified carbonate dissolution, and a severe mass
      extinction of benthic foraminifera. The lack of continuous, undisturbed
      cores over a wide depth range has limited efforts to place constraints
      on key aspects of the PETM event, such as changes in ocean redox and
      carbon chemistry, and depth dependent patterns of the benthic
      extinction. The P-E boundary was recovered in multiple holes at 5 sites
      from Walvis Ridge in the southeastern Atlantic (ODP Leg 208). We
      document changes in benthic assemblages and stable isotopes across the
      PETM at ODP Leg 208, and compare these with data from other PE boundary
      sections, including DSDP Sites 525 and 527 previously drilled on Walvis
      Ridge. Faunal assemblage analyses show a distinct drop in diversity
      coincident with the base of the clay layer at all sites. There is a
      clear relationship between water depth and magnitude of the benthic
      foraminifera isotope excursion along the Walvis Ridge depth transect.
      Site 1263 (2717m) records excursion values of -2.2 $\delta$$^{13}$C and
      -2.5 $\delta$$^{18}$O; whereas Site 1262 (4759m) has values of -0.2
      $\delta$$^{13}$C and -0.8 $\delta$$^{18}$O at the height of the
      excursion. This difference implies truncation of the record at deeper
      sites by carbonate dissolution, possibly as well as a depth dependent
      difference in water mass chemistry and temperature during the PETM.
      Several benthic foraminiferal species such as {\it Nuttallides truempyi}
      and various abyssaminid species that may indicate low nutrient
      availability increase in abundance at the onset of the isotope
      excursion, while the percentage of biserial and triserial species, used
      as high food/low oxygen indicators, decreases. There are thus distinct
      changes in ocean chemistry over the 2.3 km paleodepth range of the
      Walvis Ridge transect during the PETM event.

      PP11B-0565 0800h
      How Were Southwest Pacific Pelagic Ecosystems Affected by Extreme Global
      Warming During the Initial Eocene Thermal Maximum?
      * Hollis, C J (c.hollis@...) ,Crouch, E M (e.crouch@...) ,
      Dickens, G R (jerry@...) ,

      Four sections in eastern New Zealand provide the only South Pacific
      record of the initial Eocene thermal maximum (IETM): a siliciclastic
      outer shelf section (Tawanui, Hawkes Bay) and three pelagic-hemipelagic
      sections forming an outer shelf-upper slope transect across a carbonate
      ramp (Muzzle, Dee and Mead Streams, Clarence Valley). Although the rocks
      are too indurated to yield reliable oxygen isotope data, the IETM is
      identified by bulk carbonate carbon isotopes as a sharp negative
      excursion followed by gradual recovery over 0.6 to 4.0 m. In all
      sections, the excursion is mirrored by terrigenous sediment
      concentration, due to reduced biogenic (carbonate and silica) input and
      increased terrigenous input. Increased precipitation under warm humid
      conditions appears to have increased terrestrial discharge, recorded by
      deposition of smectitic marl in pelagic settings and
      illite/kaolinite-bearing smectitic mudstone in neritic settings.
      Eutrophic conditions are inferred for the IETM interval at Tawanui based
      on dysoxia, carbonate dissolution, an acme for the peridinioid dinocyst
      {\it Apectodinium} and abundant {\it Toweius} spp in nannofossil
      assemblages. Continued abundance of {\it Toweius} and replacement of
      {\it Apectodinium} by peridinioids of the {\it Deflandrea} complex
      suggests that eutrophic, albeit cooler, conditions persisted for at
      least 0.5 Ma after the IETM. In contrast, the IETM in Clarence Valley is
      marked by reduced biogenic silica content but little change in
      carbonate, and no evidence for carbonate dissolution. Sparse, poorly
      preserved palynomorphs assemblages suggest organic matter was oxidised
      under fully oxic conditions. Reduced numbers of upwelling indicators in
      the siliceous microfossil assemblage and common warm-water planktic
      foraminifera ({\it Morozovella} spp.), nannoplankton ({\it Discoaster}
      spp.) and radiolarians (e.g. {\it Podocyrtis} and {\it Theocorys} spp.)
      signal a switch from eutrophic to oligotrophic conditions and
      significant warming of near-surface waters. A progressive increase in
      neritic symbiotrophes within the radiolarian assemblage during the IETM
      recovery phase suggests warm, stratified, oligotrophic oceanic
      conditions. Radiolarians are scarce and upwelling indicators are very
      rare in sediments overlying the IETM. In the Southwest Pacific, global
      warming during the IETM increased terrestrial discharge, which enhanced
      productivity in shallow marine environments. Reduced productivity in
      deeper marine settings may have been caused by the poleward expansion of
      oligotrophic subtropical surface waters, impinging on a southern
      cyclonic system that had promoted upwelling along the eastern New
      Zealand margin through the Paleocene. Little evidence is found for local
      plankton productivity having a role in the gradual decrease in global
      temperatures that defines the upper IETM.

      PP11B-0566 0800h The Composition and Flux of Terrigenous Material from
      the late Paleocene to the early Eocene in the Indian Ocean *
      Nicolo, M J (micahn@...)

      Stable isotope records of both marine and terrestrial origin constructed
      from numerous widespread locations show a characteristic sequence of
      large amplitude variations in \delta $^{18}$O and \delta $^{13}$C
      between ca. 60 and 50 Ma, suggesting major changes in global climate and
      carbon cycling from the late Paleocene to the early Eocene. Continental
      weathering and atmospheric circulatory systems should have varied in
      response to these global fluctuations. In this regard, the flux,
      composition and grain-size of both eolian and hemipelagic (terrigenous)
      components of oceanic sediments should be affected by the intensity of
      atmospheric circulation and changes in terrestrial climate and
      weathering respectively. Deep-Sea Drilling Project Site 215 (near
      Ninety-East Ridge), Ocean Drilling Program Site 752 (Broken Ridge), and
      Ocean Drilling Program Site 762 (Exmouth Plateau) are located in the
      Indian Ocean, have well-dated early Paleogene sections, and are
      applicable to these systems in different ways (e.g. are varied by
      latitude and type of terrigenous material they likely received during
      the time interval of interest). Following early work at ODP Site 215
      (Hovan and Rea, 1992), here we present records of the terrigenous
      component at these sites, including mass accumulation rate (MAR),
      grain-size, and mineralogy (XRD). These records coupled with future work
      in the southern Atlantic and southern Pacific oceans provide a basis for
      understanding early Paleogene climate changes in the Southern
      Hemisphere, as well as constraints for future modeling.

      PP11B-0567 0800h
      Paleoceanographic changes in the western tropical Atlantic during the
      late Paleocene (59-55 Ma): high-resolution stable isotope records from
      ODP Leg 207 Site 1258
      * Romano, M (mromano1@...) ,Pekar, S F (spekar@...) ,
      Pekar, S F (spekar@...) ,
      Jenning, N (nfj2003@...) , Taitt-Finch, N
      (mzfinch@...) ,

      High-resolution isotopic records are being developed for the late
      Paleocene (59-55 Ma) from cored materials from ODP Leg 207 Site 1258 to
      evaluate oceanographic changes leading up to the Paleocene/ Eocene
      Thermal Maximum (PETM). Site 1258 is located on the western slope of the
      Demerara Rise, $\sim$380 km north of Suriname. It was drilled in 3,192
      meters of water and is the deepest water site of the paleoceanographic
      transect drilled for Leg 207. Site 1258 contains an exceptional
      sedimentary archive of late Paleocene oceanographic and climate changes
      based on high sedimentation rates and pristinely preserved benthic
      foraminifers, providing the requisite material to study deep-sea changes
      in the western equatorial Atlantic. The late Paleocene $\delta$$^{18}$O
      record at Site 1258 contains low values from 58 Ma until near the PETM
      at Site 1258, which are consistent with bottom water temperatures of up
      to 10$\deg$ to 12$\deg$C. These low $\delta$$^{18}$O values result in a
      significant gradient (up to $\sim$1$\permil$) between the equatorial
      Atlantic and the southern ocean (e.g., Site 690) bottom waters. This
      suggests at least two bottom water sources existed during this time, one
      originating from the southern ocean region and another from either the
      Tethys Sea or somewhere near the equatorial Atlantic regions. A number
      of isotopic excursions occur in both the $\delta$$^{13}$C and
      $\delta$$^{18}$O records between 57 Ma and before the PETM. These are
      characterized by $\delta$$^{13}$C changes of over 1$\permil$ and
      $\delta$$^{18}$O changes of up to $\sim$0.7$\deg$ (equivalent to $\sim$
      3$\deg$ C). Similar events were previously identified in records from
      the North Pacific Ocean Site 577, which were interpreted to be
      restricted to the Pacific basin. Although limitations in age control
      cannot unequivocally show whether these events were synchronous at both
      sites, these results indicate that these brief abrupt deep-sea warming
      events occurred in both the Atlantic and Pacific basins, indicating that
      they were global in nature.

      PP11B-0568 0800h
      Using a Dynamic Global Vegetation Model to Simulate the Response of
      Vegetation to Warming at the Paleocene-Eocene Boundary
      * Shellito, C J (shellito@...) , Sloan, L C (lcsloan@...) ,

      A major turnover in benthic marine and terrestrial fauna marks the
      Initial Eocene Thermal Maximum (IETM) (~55Ma), a period of ~150 ky in
      which there was a rapid rise in deep sea and high latitude sea surface
      temperatures by 5-8C. Curiously, no major responses to this warming in
      the terrestrial floral record have been detected to date. Here, we
      present results from experiments examining the response of the global
      distribution of vegetation to changes in climate at the IETM using the
      NCAR Land Surface Model (LSM1.2) integrated with a dynamic global
      vegetation model (DGVM). DGVMs allow vegetation to respond to and
      interact with climate, and thus, provide a unique new method for
      addressing questions regarding feedbacks between the ecosystem and
      climate in Earth's past. However, there are a number of drawbacks to
      using these models that can affect interpretation of results. More
      specifically, these drawbacks involve uncertainties in the application
      of modern plant functional types to paleo-flora simulations,
      inaccuracies in the model climatology used to drive the DGVM, and lack
      of available detail regarding paleo-geography and paleo-soil type for
      use in model boundary conditions. For a better understanding of these
      drawbacks, we present results from a series of tests in the NCAR
      LSM-DGVM which examine (1) the effect of removing C4 grasses from the
      available plant functional types in the model; (2) model sensitivity to
      a change in soil texture; and (3), model sensitivity to a change in the
      value of pCO2 used in the photosynthetic rate equations. We consider our
      DGVM results for the IETM in light of output from these sensitivity

      PP11B-0569 0800h
      Does rapid climate change affect sedimentation in a fluvial system?
      Documenting the PETM using pedogenic carbonate in the Wasatch Formation
      of Western Colorado
      * Blecha, A M (ablecha@...) , Gardner, M H (mgardner@...) ,

      While the Paleocene/Eocene Thermal Maximum (PETM) has been identified in
      numerous terrestrial systems across North America, little work has been
      done relating landform evolution to this event. The Wasatch Formation of
      western Colorado is an ideal setting for this investigation, with
      extensive exposures and conspicuous lithological variability straddling
      the Paleocene/Eocene boundary. In addition, comparisons between the
      basin axis and the western margin provide conflicting environmental
      interpretations. Data collected from an isotopic study of pedogenic
      carbonate from the western margin of this outcrop attempts to identify
      the PETM in relation to these lithologic discrepancies. Pollen data
      constrain the PETM to the conspicuous increase in sand volume within the
      basin axis of the Wasatch Formation. Tectonic forcing has been
      attributed to this change, but we are investigating the possible
      influence of climate on this system. The integration of an isotopic
      record will provide a high-resolution time scale, allowing for direct
      comparison between lithologic shifts and this global climatic event. The
      200 meter thick Wasatch Formation in the western margin study area
      consists of an upward increase in sand, transitioning from clay
      dominated mudstone to pebbly sandstone, then returning to a sand poor
      environment. This sand increase also mirrors the general drying trend of
      the system. The sand poor organic-rich mudstones located at the basal
      unconformity contains algal laminae of a shallow lacustrine origin. This
      wet, poorly drained environment grades both laterally and vertically
      into more arid and better drained conditions evidenced by red mudstones
      with carbonate nodules. These mudstones show abundant rooting,
      burrowing, and slickenlines indicative of soil forming processes. This
      red bed sequence, averaging 70-90 meters thick, is characterized by
      isolated point bars and splays increasing upsection in abundance.
      Capping the red beds are sheet sands with conglomeratic lags. A sequence
      of minor channelized sandstones follow, interbedded with purple and grey
      mudstones. These mudstones do not contain carbonate, indicating a return
      to the previous poorly drained conditions. Carbonate nodules have been
      collected through the red beds in the western reaches of the outcrop
      belt. Sampling was at a 0.5 to 8 m resolution, with an average of 2
      meters throughout the section. These nodules are currently being
      analyzed for carbon isotopes to attempt to determine if the negative
      \delta $^{13}$C shift indicative of the PETM in other basins can be
      detected in this formation. Assuming the PETM occurs within the red bed
      interval, lateral tracing to the basin axis correlates these strata to
      the thick (100 meter) fluvial sandstones of the Molina Member. Whereas
      the red mudstones along the basin margin indicate drying conditions, the
      contemporaneous aggradational fluvial system in the basin axis suggests
      an increase in discharge. This conundrum may reflect the limitations of
      one dimensional analysis when evaluating the signature of climate in
      landform evolution.

      PP11B-0570 0800h
      Evolutionary Events and Phytoplankton Recovery After the K/T Mass Extinction
      * Fuqua, L M (lfuqua@...) , Bralower, T J
      (bralower@...) ,

      The recovery of the open ocean ecosystem after the Cretaceous-Tertiary
      boundary mass extinction (65 Ma) was extremely slow. The surface to deep
      carbon isotopic gradient remained below latest Cretaceous levels for
      more than three million years after the boundary event, suggesting
      suppressed rates of carbon cycling and low phytoplankton productivity.
      There is a rapid change in the carbon isotopic gradient between 62 and
      61 Ma, indicating the final recovery of surface water production levels
      (D'Hondt et al., 1998). We are investigating nannoplankton communities
      in the interval from 61.5 to 62.5 Ma to determine the relationship
      between the recovery and changes in productivity and carbon cycling.
      Samples were collected at high resolution from Ocean Drilling Program
      Site 1209 in the western Pacific, and Deep Sea Drilling Project Sites
      384 in the North Atlantic and 528 in the South Atlantic. Results show
      major diversification of two dominant Cenozoic nannoliths (non-coocolith
      bearing, calcite-secreting nannoplankton), {\it Fasciculithus} and {\it
      Sphenolithus}, occurred shortly after carbon gradients were restored.
      The first occurrences of these two genera are associated with
      significant changes in calcareous nannoplankton communities, indicative
      of abrupt changes in surface water circulation. A rapid evolutionary
      sequence of early forms of {\it Fasciculithus} has been identified at
      Sites 1209 and 384. Two unidentified taxa were found before the first
      occurrence of the earliest documented species, {\it F. pileatus}. SEM
      work currently underway is designed to elucidate the evolution of this
      genus. At the Pacific site, the diversification is associated with an
      interval of dissolution, presumably resulting from a change in deep
      water circulation. The significance of this relationship is currently
      not understood. D'Hondt, S. et al., Organic carbon fluxes and ecological
      recovery from the Cretaceous-Tertiary mass extinction, Science, 282,
      276-279, 1998.

      PP11B-0571 0800h
      Marine carbonate dissolution event across the Eocene/Oligocene boundary:
      the Walvis Ridge transect, South Atlantic (ODP Leg 208)
      * Liu, Z (lzhifei@...) , Tuo, S (tuosht@...) , Zhao, Q
      (qhzhaok@...) , Chen, X (xrchengk@...) ,

      Sediments recording the response of South Atlantic to global cooling and
      marine carbonate dissolution during the Eocene-Oligocene transition were
      recovered across a broad range of depths of five sites on the
      northeastern flank of Walvis Ridge during ODP Leg 208. Although the
      Eocene/Oligocene (E/O) boundary is not well preserved
      biostratigraphically, especially at two deepest sites (Sites 1262 and
      1267), oxygen and carbon stable isotopes of benthic and/or planktonic
      foraminifers have determined the exact boundary position for most of
      sites. High-resolution carbonate content and foraminiferal grain size
      combined with coarse fraction and siliciclatic element geochemistry
      reveal that the strongest carbonate dissolution event occurred just
      above the E/O boundary, leading the global Earliest Oligocene Glacial
      Maximum (EOGM). This carbonate dissolution event may take up abundant
      atmospheric CO2 into the deep ocean by the calcium carbonate pump
      system, and then induces the global cooling during the earliest
      Oligocene. The recovery of the foraminiferal preservation does not
      appear to be immediate with rapid cooling; however, it lags behind about
      500 kyr, implying that the shift in carbonate preservation was triggered
      by changes in climate. The carbonate dissolution event is associated
      with deepening of carbonate compensation depth (CCD) and falling of sea
      level. Moreover, the event has a close relationship with continental
      weathering rates indicated by element geochemistry, implying the
      possible carbon cycle-forced global cooling event across the E/O boundary.

      PP11B-0572 0800h Visions of Ice Sheets in a Greenhouse World
      * Miller, K G (kgm@...) , Wright, J D
      (jdwright@...) , Browning, J V (jvb@...) , Pusz,
      A (aimeep@...)

      The warmest global climates of the last 200 m.y. occurred in late
      Cenomanian-early Turonian (ca. 95-93 Ma) and latest Paleocene-early
      Eocene (ca. 55-50 Ma), with bottom-water and high-latitude temperature
      exceeding 15$\deg$C. These intervals of peak warmth were punctuated by
      cool snaps associated with sea-level drops. The late Cenomanian-early
      Turonian $\delta^{18}$O minimum was bracketed by two large ($ > $0.75%)
      deep-sea $\delta^{18}$O increases (92-93 Ma, mid-Turonian and 96 Ma,
      mid-Cenomanian recorded at Site 1050). New surface dwelling planktonic
      $\delta^{18}$O data from equatorial Site 1259 also record a similar the
      mid-Turonian increase, suggesting a global compositional change in
      seawater. Backstripped eustatic estimates from New Jersey and the
      Russian platform show large ($ > $25 m) and rapid ($ < $1 m.y.)
      sea-level changes in the Late Cretaceous to early Eocene (99-49 Ma) that
      must be attributed to glacioeustasy. The mid-Cenomanian and mid-Turonian
      $\delta^{18}$O increases are associated with major eustatic lowerings,
      implicating ice growth despite the warm interval bracketing these
      events. We reconcile records of warm high latitudes with glacioeustasy
      by proposing that Late Cretaceous-early Eocene ice sheets generally
      reached maximum volumes of 8-12 x 10$^{6}$ km$^{3}$ (20-30 m
      glacioeustatic equivalent), but did not reach the Antarctic coast;
      hence, coastal Antarctica (hence deep water) remained warm even though
      there were significant changes in sea level as the result of glaciation.
      Unlike the Oligocene and younger icehouse world, these ice sheets only
      existed during short intervals ($ < $100 k.y.) of peak Milankovitch
      forcing, leaving Antarctica ice-free during much of the greenhouse Late
      Cretaceous to middle Eocene. These results highlight the need to
      re-evaluate the paradigm that continental ice sheets did not exist
      during times of warm high-latitude climates.

      PP11B-0573 0800h
      Calcareous Nannofossil Paleofertility Indicators During the Valanginian
      Carbon Perturbation in an Epicontinental Basin System (Vocontian, SE France)
      * duchamp, s (duchamp@geol.u-psud.fr) , gardin, s
      (gardin@...) , fiet, n (fiet@geol.u-psud.fr) ,
      blamart, d (dominique.blamart@...-gif.fr) , pagel, m
      (pagel@geol.u-psud.fr) ,

      A major and global delta 13C positive excursion is recognized in
      sediments of the Late Valanginian-Hauterivian interval. This
      perturbation coincides with a widespread eutrophication of marine
      ecosystems associated with organic carbon rich deposits and a crisis of
      carbonate producing biota. Subaerial volcanism of the Parana-Etendeka
      large igneous province (ca. 132 Ma) was presumably responsible for an
      increase of CO2, triggering greenhouse conditions, increased weathering
      and elevated nutrient transfer rates to oceans. High resolution carbon
      isotope stratigraphy coupled with a quantitative calcareous nannofossils
      study has been done at Angles section, located in an epicontinental
      basin of the northern margin of the Tethys (Vocontian basin, SE France).
      In this kind of environment we can unravel the influence of weathering
      on delta 13C variations and on abundance fluctuations of primary
      producers (calcareous nannofossils). We test open sea calcareous
      nannofossils described in the litterature as good paleofertility
      indicators to elaborate new nutrient index and reconstruct sea surface
      trophic conditions in this epicontinental basin. Some calcareous
      nannofossil taxa fluctuations appear very sensitive to delta 13C
      variations. The beginning of the delta 13C perturbation (minimim delta
      13C values in Hirsutus ammonite biozone) is associated with relatively
      abundant {\it Watzauneria sp.}, generally considered as an oligotrophic
      taxon. The slow increase of delta 13C values in Hirsutus to Campylotoxus
      ammonite biozone is paralleled by the progressive decline of {\it
      Watzauneria sp.} and by instantaneously rise of specimens considered as
      mesotrophic indicators such as {\it Discorabdus rotatorus.} and {\it
      Lithraphidites sp.}. The abrupt increase of the delta 13C signal to a
      peak (Campylotoxus to Verrucosum biozone) is marked by the definitive
      decline of {\it Watzauneria sp.} whereas nannofossils usually indicating
      high fertility conditions ({\it Zeughrabdotus fissus.} and {\it Biscutum
      sp.}) abound significantly. The plateau of maximum delta 13C values
      seems to correspond to mesotrophic conditions, with some fluctuations
      towards more oligotrophic conditions, as testifyed by the ponctual
      slight abundance of {\it Discorabdus rotatorus.} and {\it Lithraphidites
      sp.} associated with the ponctual high abundance of {\it Watzauneria
      sp.}. At last, the return to post-perturbation low delta 13C values
      (Nicklesi to Callidiscus biozone) is characterized by a continuously
      rise of the oligotrophic indicator. {\it Biscutum sp.} wanes
      progressively whereas {\it Zeughrabdotus fissus} definitively exctincts.
      Most of open sea nannofossils paleofertility indicators seem to have
      coherent pattern with the variations of the delta 13C signal. Thus, they
      can be used as nutrient index in epicontinental basin systems. This is
      not the case for {\it Rhagodiscus asper}, generally considered as an
      oligotrophic taxon in open sea, while in an epicontinental basin system
      such as the Vocontian basin, it seems to have the same behaviour as
      mesotrophic open sea indicators (such as {\it Discorabdus rotatorus.}
      and {\it Lithraphidites sp.}). In this specific environment, calcareous
      nannofossils show some "local" response to the global Valanginian

      PP11B-0574 0800h
      Modeling the Impact of Forest and Peat Fires on Carbon-Isotopic
      Compositions of Cretaceous Atmosphere and Vegetation
      * Finkelstein, D B (dafinkel@...) , Pratt, L M ,

      Prevalence of wildfires or peat fires associated with seasonally dry
      conditions in the Cretaceous is supported by recent studies documenting
      the widespread pre<br/><br/>(Message over 64 KB, truncated)
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