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@geosc.psu.edu) , Department of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
Bralower, T J (bralower@geosc.psu.edu) , Department of Geosciences, Pennsylvania State University, University Park, PA 16802 United States
Boharty, S (sbohaty@es.ucsc.edu) , Earth Science Department, University of California, Santa Cruz, CA 95064 United States
Zachos, J (jzachos@es.ucsc.edu) , Earth Science Department, University of California, Santa Cruz, CA 95064 United States
Bybell, L M (lbybell@usgs.gov) , U.S. Geological Survey, 926 National Center, Reston, VA 20192 United States
Quattlebaum, T (thomasqtl@yahoo.com) , Earth Science Department, University of California, Santa Cruz, CA 95064 United States

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@unich.it) , Dipartimento Scienze della Terra, Universita "G.d'Annunzio" di Chieti, Campus Universitario, via dei Vestini 31, Chieti Scalo, 66013 Italy

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@es.ucsc.edu) , Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
Bohati, S (sbohaty@es.ucsc.edu) , Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
Zachos, J C (jzachos@es.ucsc.edu) , Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
Brinkhuis, H (H.Brinkhuis@bio.uu.nl) , Laboratory of Palaeobotany and Palynology, Department of Palaeoecology, Utrecht University, Budapestlaan 4, Utrecht, CD 3584 Netherlands
Sluijs, A (A.Sluijs@bio.uu.nl) , Laboratory of Palaeobotany and Palynology, Department of Palaeoecology, Utrecht University, Budapestlaan 4, Utrecht, CD 3584 Netherlands
Gibbs, S (sgibbs@geosc.psu.edu) , Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802 United States
Bralower, T (bralower@geosc.psu.edu) , Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802 United States
McDougall-Reid, K (kris@usgs.gov) , Flagstaff Science Center, U. S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001 United States

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@es.ucsc.edu) , University of California, Earth Sciences Dept., Santa Cruz, CA 95064 United States
Roehl, U , Universitaat Bremen, Dept. of Geosciences, Postfach 33 04 40, Bremen, CA 28334 Germany
Hodell, D , University of Florida, Dept. of Geology and Geophysics, Gainesville, FL 32611 United States
Thomas, E , Wesleyan University, 265 Church St., Middletown, CT 06459 United States
Sluijs, A , Utrecht University, Dept. of Geology, Budapestlaan 4, Utrecht, CA 3584CD Netherlands
Schellenberg, S , San Diego State Univ., Dept. of Geological Sciences, San Diege, CA 92182 United States
Kelly, C , University of Wisconsin, Dept. of Geology & Geophysics, Madison, WI 53706 United States
McCarren, H , University of California, Earth Sciences Dept., Santa Cruz, CA 95064 United States
Kroon, D , Vrije Universiteit, Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, HV1081 Netherlands
Nicolo, M , Rice University, Dept. of Earth Sciences, Houston, TX 77005 United States

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.

http://www-odp.tamu.edu/publications/208_IR/208ir.htm

PP11B-0562 0800h

Tracers of Productivity across the PETM, Walvis Ridge, ODP Sites 1262 and 1263

Quartini, J C (joequartini@hotmail.com) , Earth Sciences, Univeristy of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
* Chun, C O (cchun@ucsc.edu) , Ocean Sciences/Institute of Marine Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
Delaney, M L (delaney@ucsc.edu) , Ocean Sciences/Institute of Marine Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
Zachos, J C (jzachos@earthsci.ucsc.edu) , Earth Sciences, Univeristy of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States

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@csun.edu) , Department of Geological Sciences, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330-8266 United States

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@es.ucsc.edu) , Earth Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
Thomas, E (ethomas@wesleyan.edu) , Earth and Environmental Sciences, Wesleyan University, 265 Church Street, Middletown, CT 06459 United States
Zachos, J (jzachos@es.ucsc.edu) , Earth Sciences, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States

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@gns.cri.nz) , Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6315 New Zealand
Crouch, E M (e.crouch@gns.cri.nz) , Institute of Geological and Nuclear Sciences, PO Box 30-368, Lower Hutt, 6315 New Zealand
Dickens, G R (jerry@rice.edu) , Rice University, Department of Earth Sciences, Houston, TX 77005 United States

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@rice.edu) , Rice University Earth Science, 6100 Main St., MS-126, Houston, TX 77005 United States

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@gc.cuny.edu) , Graduate School & University Center, City University of New York, 365 Fifth Avenue, New York, NY 10016 United States
Pekar, S F (spekar@qc1.qc.edu) , Queens College, CUNY, 65-30 Kissena Blvd., Flushing, NY 11367 United States
Pekar, S F (spekar@qc1.qc.edu) , Lamont-Doherty Earth Observatory of Columbia University, Route 9W, Palisades, NY 10964 United States
Jenning, N (nfj2003@columbia.edu) , Columbia University, 3244 Lerner Hall, New York, NY 10027 United States
Taitt-Finch, N (mzfinch@earthlink.net) , Queens College, CUNY, 65-30 Kissena Blvd., Flushing, NY 11367 United States

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@es.ucsc.edu) , University of California, Santa Cruz, Earth Sciences Dept. 1156 High St., Santa Cruz, CA 95062 United States
Sloan, L C (lcsloan@es.ucsc.edu) , University of California, Santa Cruz, Earth Sciences Dept. 1156 High St., Santa Cruz, CA 95062 United States

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 experiments.

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@mines.edu) , Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401 United States
Gardner, M H (mgardner@mines.edu) , Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401 United States

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@geosc.psu.edu) , The Pennsylvania State University, Deike Building, University Park, PA 16802 United States
Bralower, T J (bralower@geosc.psu.edu) , The Pennsylvania State University, Deike Building, University Park, PA 16802 United States

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@online.sh.cn) , Laboratory of Marine Geology, Tongji University, 1239 Siping Road, Shanghai, 200092 China
Tuo, S (tuosht@hotmail.com) , Laboratory of Marine Geology, Tongji University, 1239 Siping Road, Shanghai, 200092 China
Zhao, Q (qhzhaok@online.sh.cn) , Laboratory of Marine Geology, Tongji University, 1239 Siping Road, Shanghai, 200092 China
Chen, X (xrchengk@online.sh.cn) , Laboratory of Marine Geology, Tongji University, 1239 Siping Road, Shanghai, 200092 China

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@rci.rutgers.edu) , Rutgers, the State University of New Jersey, Department of Geological Sciences, Piscataway, NJ 08854 United States
Wright, J D (jdwright@rci.rutgers.edu) , Rutgers, the State University of New Jersey, Department of Geological Sciences, Piscataway, NJ 08854 United States
Browning, J V (jvb@rci.rutgers.edu) , Rutgers, the State University of New Jersey, Department of Geological Sciences, Piscataway, NJ 08854 United States
Pusz, A (aimeep@eden.rutgers.edu) , Rutgers, the State University of New Jersey, Department of Geological Sciences, Piscataway, NJ 08854 United States

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) , UMR 8148 IDES, batiment 504, orsay, 91400 France, Metropolitan
gardin, s (gardin@ccr.jussieu.fr) , CNRS-UMR 5143 CEPAGE, tour 56-46 4, place Jussieu, Paris, 75252 France, Metropolitan
fiet, n (fiet@geol.u-psud.fr) , UMR 8148 IDES, batiment 504, orsay, 91400 France, Metropolitan
bartolini, a (chiara@ccr.jussieu.fr) , CNRS-UMR 5143 CEPAGE, tour 56-46 4, place Jussieu, Paris, 75252 France, Metropolitan
blamart, d (dominique.blamart@lsce.cnrs-gif.fr) , Laboratoire LSCE UMR CNRS-CEA, batiment 12, Avenue de la Terrasse, Gif sur Yvette, 91198 France, Metropolitan
pagel, m (pagel@geol.u-psud.fr) , UMR 8148 IDES, batiment 504, orsay, 91400 France, Metropolitan

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 perturbation.

PP11B-0574 0800h

Modeling the Impact of Forest and Peat Fires on Carbon-Isotopic Compositions of Cretaceous Atmosphere and Vegetation

* Finkelstein, D B (dafinkel@indiana.edu) , Indiana University, Geological Sciences, 1001 East 10th St., Bloomington, IN 47405 United States
Pratt, L M , Indiana University, Geological Sciences, 1001 East 10th St., Bloomington, IN 47405 United States

Prevalence of wildfires or peat fires associated with seasonally dry conditions in the Cretaceous is supported by recent studies documenting the widespread presence of pyrolytic polycyclic aromatic hydrocarbons and fusinite. Potential roles of CO$_{2}$ emissions from fire have been overlooked in many discussions of Cretaceous carbon-isotope excursions (excluding K-P boundary discussions). Enhanced atmospheric CO$_{2}$ levels could increase fire frequency through elevated lightning activity. When biomass or peat is combusted, emissions of CO$_{2}$ are more negative than atmospheric CO$_{2}$. Five reservoirs (atmosphere, vegetation, soil, and shallow and deep oceans), and five fluxes (productivity, respiration, litter fall, atmosphere-ocean exchange, and surface-deep ocean exchange) were modeled as a closed system. The size of the Cretaceous peat reservoir was estimated by compilation of published early Cretaceous coal resources. Initial pCO$_{2}$ was assumed to be 2x pre-industrial atmospheric levels (P.A.L.). Critical variables in the model are burning efficiency and post-fire growth rates. Assuming 1% of standing terrestrial biomass is consumed by wildfires each year for ten years (without combustion of peat), an increase of atmospheric CO$_{2}$ (from 2.0 to 2.2x P.A.L.) and a negative carbon isotope excursion (-1.2 $\permil$) are recorded by both atmosphere and new growth. Net primary productivity linked to the residence time of the vegetation and soil reservoirs results in a negative isotope shift followed by a broad positive isotope excursion. Decreasing the rate of re-growth dampens this trailing positive shift and increases the duration of the excursion. Post-fire pCO$_{2}$ and new growth returned to initial values after 72 years. Both negative and positive isotope excursions are recorded in the model in surface ocean waters. Exchange of CO$_{2}$ with the surface- and deep-ocean dampens the isotopic shift of the atmosphere. Excursions are first recorded in the atmosphere (and new growth), followed by the ocean, vegetation, and soil reservoirs. Ten to twenty five-year cycles of drought and fire are not recorded as individual excursions in the soil reservoir as the rate of transfer between the vegetation and soil reservoirs homogenizes the signal. A wildfire-modeled excursion does not propagate a geologically significant excursion through time. Combustion of a peat reservoir is necessary to drive and validate a geologically and isotopically significant excursion. Assuming 0.5% of the standing early Cretaceous peat reservoir is consumed by fire for each year for ten years coupled with the earlier scenario, the atmospheric CO$_{2}$ increases from 2.0 to 3.1x P.A.L., atmosphere, vegetation, and the surface ocean record a negative carbon isotope excursion of -5.1 $\permil$, -3.8 $\permil$ and -1.8 $\permil$ respectively, with a duration of 741 years. Increasing the size of the vegetation reservoir translates the excursions from the centennial to millennial scale. For example, doubling the vegetation reservoir (from 1.4 to 2.8E+16 gC) for a 25 year global peat conflagration (0.5% combusted each year) results in a CO$_{2}$ increase from 2.0 to 4.0x P.A.L., and the atmosphere, vegetation, and the surface ocean reservoirs with a negative carbon isotope excursion of -5.7 $\permil$, -8.7 $\permil$ and -2.3 $\permil$ respectively. Addition of carbonaceous aerosols (black carbon and polycyclic aromatic hydrocarbons) to pelagic marine sediments could potentially serve as a high-resolution record of ancient fires and firmly tie isotopic shifts to paleofires.

PP11B-0575 0800h

Methane Plumes over a Marine Gas Hydrate System in the Eastern Margin of the Sea of Japan: a Proposed Mechanism for the Transport of Significant Subsurface Methane to Shallow Waters

* Matsumoto, R (ryo@eps.s.u-tokyo.ac.jp) , University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo, 113-0033 Japan
Okuda, Y (okuda.gsj@aist.go.jp) , Geological Survey of Japan, Higashi 1-1-3, Tukuba, 305-8567 Japan
Aoyama, C (aoyama@hotmail.com) , Independent Institute Co.Ltd, Shinbashi 3-1-10 Minato-ku, Tokyo, 105-0004 Japan
Hiruta, A (hiruta@eps.s.u-tokyo.ac.jp) , University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo, 113-0033 Japan
Ishida, Y (yasushi@eps.s.u-tokyo.ac.jp) , University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo, 113-0033 Japan
Sunamura, M (sunamura@eps.s.u-tokyo.ac.jp) , University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo, 113-0033 Japan
Numanami, H (hnuma@kasei-gakuin.ac.jp) , Tokyo Kaseigakuin University, Aihara 2600 Machida, Tokyo, 194-0292 Japan
Tomaru, H (hitoshi@earth.rochester.edu) , University of Rochester Dept. Earth and Env. Sci., 227 Hutchison Hall, Rochester, NY 14627 United States
Snyder, G T (gsnyder@rice.edu) , Rice University Earth Science-MS126, 6100 Main St., Houston, TX 77005 United States
Komatsubara, J (jkomatsu@eps.s.u-tokyo.ac.jp) , University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo, 113-0033 Japan
Takeuchi, R (lika@eps.s.u-tokyo.ac.jp) , University of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo, 113-0033 Japan
Hiromatsu, M (sti-555@mx12.freecom.ne.jp) , Nippon Kaiyo Corporation, Chiyoda-ku, Tokyo, 101-0041 Japan
Takeda, S (takeda@kaiyodai.ac.jp) , Tokyo Univ. Marine Sci. Tech., 4--5--7 Konan Minato--Ku, Tokyo, 108-8477 Japan
Koike, T (capkoike@s.kaiyodai.ac.jp) , Tokyo Univ. Marine Sci. Tech., 4--5--7 Konan Minato--Ku, Tokyo, 108-8477 Japan

R&T/V Umitaka-maru sailed to a small ridge (now named O`UT04 RidgeO_L) in the eastern margin of the Sea of Japan July to August 2004 to explore the ocean floor gas hydrates and related phenomena. The Ridge is located in the southwestern extension of JapanOs most productive hydrocarbon province. Detailed bathymetric profiles and seismic profiles have revealed a number of mud volcanoes (20 to 40 m high and 300-500 m across), pockmarks (40-70 m deep and 300 < ETH > 500 m across), and collapse structures within 3 km x 4 km on the ridge at a water depth of 910 to 980 m. Large pockmarks develop in the NNE-SSW direction, parallel to the boundary between the Eurasian and North American Plates. Fathometer and quantitative Echo sounder have depicted 36 magnificent flares of plumes over the area, each ranging 100 to 200 m in diameter and 600 to 750 m in height, reaching up to the shallow water zone of 200 m to 350 m below sea level. Onboard geochemical analysis of the interstitial waters has identified the sulfate-methane interface (SMI) at $ < $0.5 m to 4 m. Black silt and clay from the top 0.5 -3.5 m at active seep sites contained a number of chunks of gas hydrate and nodular carbonates. Gas hydrate is dominated by methane with minor ethane. Seawater sampling was conducted at every 100-200 m in the water column over the area. Onboard GC measurements have demonstrated characteristic methane profiles as 10 to 50 nmon/L for the bottom waters, 5 to 8 nmol/L for the intermediate waters, 20-45 nmol/L at 200 to 300 m, and again about 5 nmol/L for the surface water. CTD has shown anomalously low temperatures, 0.25$^{o}$ C, for the bottom and intermediate waters, and abrupt increase at around 300 m up to about 25$^{o}$ C at surface. Field observations and consideration on the stability of gas hydrates lead us to the hypothesis that methane plumes are not the columns of methane bubbles but of gas hydrate. Methane bubbles from the seeps would be converted to gas hydrate sooner or later in such a cold deep waters. Gas hydrate crystals could potentially float upward until they reach the warm waters at around 200-300 m, where gas hydrate would be dissociated, and continuously supply methane to shallow waters. This hypothesis is to be tested by submersible dives planned in 2005.

PP11B-0576 0800h

Acoustical Surveys Of Methane Plumes By Using The Quantitative Echo Sounder In The Eastern Margin Of The Sea of Japan

* Aoyama, C (aoyamac@dokken.co.jp) , Japan_fs Independent Institute Co.,Ltd., Ishii Bldg.7Fl.,3-1-10,Shinbashi,Minato-Ku, Tokyo, 105-0004 Japan
Matsumoto, R (ryo@eps.s.u-tokyo.ac.jp) , Dept. Earth and Planet Sci.,Tokyo Univ., 7-3-1,Hongo,Bunkyou-Ku,, Tokyo, 113-0033 Japan
Okuda, Y (okuda.gsj@aist.go.jp) , Inst.Geo-Resources and Env.,Nat.Inst.Adv.Ind.Sci.and Tech., 1-1-1,Higashi,Thukuba-city, Ibaraki, 305-8561 Japan
Ishida, Y (yasushi@eps.s.u-tokyo.ac.jp) , Dept. Earth and Planet Sci.,Tokyo Univ., 7-3-1,Hongo,Bunkyou-Ku,, Tokyo, 113-0033 Japan
Hiruta, A (hiruta@eps.s.u-tokyo.ac.jp) , Dept. Earth and Planet Sci.,Tokyo Univ., 7-3-1,Hongo,Bunkyou-Ku,, Tokyo, 113-0033 Japan
Sunamura, M (sunamura@eps.s.u-tokyo.ac.jp) , Dept. Earth and Planet Sci.,Tokyo Univ., 7-3-1,Hongo,Bunkyou-Ku,, Tokyo, 113-0033 Japan
Numanami, H (hnuma@kasei-gakuin.ac.jp) , Tokyo Kaseigakuin Univ., 2600,Aihara-machi,Machida-city, Tokyo, 194-0292 Japan
Tomaru, H (hitoshi@earth.rochester.edu) , Dept. Earth and Env.Sci.,Univ.Rochester, Rochester, Rochester, NY 14627 United States
Snyder, G (gsnyder@rice.edu) , Dept. Earth Sci. Rice Univ., 6100 Main Houston, Texas, Houston, TX 77005 United States
Komatsubara, J (jkomatsu@eps.s.u-tokyo.ac.jp) , Dept. Earth and Planet Sci.,Tokyo Univ., 7-3-1,Hongo,Bunkyou-Ku,, Tokyo, 113-0033 Japan
Takeuchi, R (lika@eps.s.u-tokyo.ac.jp) , Dept. Earth and Planet Sci.,Tokyo Univ., 7-3-1,Hongo,Bunkyou-Ku,, Tokyo, 113-0033 Japan
Hiromatsu, M (mhiromat@suruga-g.co.jp) , Nippon Kaiyo Corporation, 9-2,Sakae-cho,Kita-Ku, Tokyo, 114-0005_@ Japan
Aoyama, D (aoyamad@dokken.co.jp) , Japan_fs Independent Institute Co.,Ltd., Ishii Bldg.7Fl.,3-1-10,Shinbashi,Minato-Ku, Tokyo, 105-0004 Japan
Koike, Y (capkoike@s.kaiyodai.ac.jp) , Tokyo Univ. of Marine Sci. and Tech., 4-5-7,Kounan,Minato-Ku, Tokyo, 108-8477 Japan
Takeda, S (mbreeze@s.kaiyodai.ac.jp) , Tokyo Univ. of Marine Sci. and Tech., 4-5-7,Kounan,Minato-Ku, Tokyo, 108-8477 Japan
Hayashi, T , Tokyo Univ. of Marine Sci. and Tech., 4-5-7,Kounan,Minato-Ku, Tokyo, 108-8477 Japan
Hamada, H , Tokyo Univ. of Marine Sci. and Tech., 4-5-7,Kounan,Minato-Ku, Tokyo, 108-8477 Japan

The reseach and trainning/V, Umitaka-maru sailed to the methane seep area on a small ridge in the eastern margin of the Sea of Japan on July to August 2004 to survey the ocean floor gas hydrate and related acoustic signatures of methane plumes by using a quantitative echo sounder. Detailed bathymetric profiles have revealed a number of mounds, pockmarks and collapse structures within 3km x 4km on the ridge at the water depth of 910m to 980m. We mapped minutely methane plumes by using a quantitative echo sounder with positioning data from GPS. We also measured averaged echo intensity from the methane plumes both in every 100m range and every one minute by the echo integrator. We obtained the following results from the present echo-sounder survey. 1) We checked 36 plumes on echogram, ranging 100m to 200m in diameter and 600m to 700m in height, reaching up to 200m to 300m below sea level. 2) We measured the averaged volume backscattering strength (SV) of each methane plume. The strongest SV, -45dB, of the plumes was stronger than SV of fish school. 3) Averaged SV tend to show the highest values around the middle of plumes, whereas the SVs are relatively low at the bottom and the top of plumes. 4) Some of the plumes were observed to show daily fluctuation in height and width. 5) We recovered several fist-sized chunks of methane hydrate by piston coring at the area where we observed methane plumes. As a following up project, we are planning to measure SV of methane bubbles and methane hydrate floating in water columns through an experimental studies in a large water tanks.