Biocomplexity and Biogeochemical Cycles of the Paleocene Eocene Thermal Maximum (BIOPE) Workshop Santa Cruz, CA - May 2-4, 2002

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1 Biocomplexity and Biogeochemical Cycles of the Paleocene Eocene Thermal Maximum (BIOPE) Workshop Santa Cruz, CA - May 2-4, 2002 Executive Summary Approximately 55 million years ago, the Earth experienced a rapid and extreme episode of global warming that was the product of an usually massive release of carbon into the ocean-atmosphere system. This event, known as the Paleocene-Eocene Thermal Maximum (PETM), had far reaching and significant impacts on both marine and terrestrial ecosystems. These impacts ranged from extinction of deep sea foraminifera to dispersal of ungulates across the continents. The combination of these climatic and biotic perturbations initiated dramatic changes in the planet s biogeochemical cycles that eventually worked to restore equilibrium to the carbon cycle. However, geologic records indicate that the recovery process took over 200,000 years, and that some changes were irreversible. Many questions arise concerning the nature of the feedbacks between the biota and the environment that were involved in these processes, and how the feedbacks compared to those occurring in response to more gradual forcings of the climate system during the early Cenozoic. To investigate the effects of this unique climatic event on the global biosphere and on the coupled biogeochemical cycles of carbon and nutrients, with support provided largely by NSF, a 5 year interdisciplinary project was launched in July of This multiinstitutional project involves over 2 dozen researchers from 6 US universities and institutions as well as researchers from over a half dozen international institutions. Expertise of the project s investigators span the following areas: modeling (biogeochemical, biosphere and climate), biogeochemistry (stable isotope, trace metal, and nutrient), marine micropaleontology (planktonic and benthic foraminifera, calcareous nannoplankton, dinoflagellates), plant physiology, paleobotany, vertebrate paleontology, and paleoecology. One of the initial activities was to assemble the working group as well other "experts" to discuss the key issues concerning the PETM as they relate to the project, and to clarify and refine the project objectives for Years 1 and 2. To this end, a workshop was held May 2-4 in Santa Cruz, California. Participants included the principle investigators, their post-docs and graduate students, as well as international coinvestigators. In addition, a half-dozen researchers who are actively working on aspects of the P-E boundary were invited to participate. Four sub- groups were assembled with focuses on 1) marine climate and geochemistry, 2) marine biota, 3) terrestrial biota and climate, and 4) climate and biogeochemical modeling. Each subgroup was charged with identifying the key issues or questions concerning the PETM, prioritizing a number of needs, grouping those that require immediate attention, and outlining specific implementation plans for addressing Years 1 & 2 objectives. The priorities and implementation plans as identified by each sub-group are provided herein.

2 TABLE OF CONTENTS EXECUTIVE SUMMARY...1 WORKSHOP...5 Objectives and Goals... 5 Organization... 5 MARINE CLIMATE, GEOCHEMISTRY, AND CHRONOSTRATIGRAPHY...5 Synopsis of recent developments:... 5 Overarching Questions:... 6 Ultimate goals for Year 1: Characterize in detail the timing and magnitude of marine biogeochemical changes for both the deep-sea and coastal oceans (2) MARINE BIOTA & ECOSYSTEMS...8 Synopsis of recent developments:... 8 Overarching question:... 8 Ultimate goals for Year 1: Generate detailed assemblage data for a variety of fossil groups in common sample sets... 9 (3) TERRESTRIAL CLIMATE AND BIOTA...9 Synopsis of recent developments:... 9 Overarching question: Ultimate goals for Year 1: Collect data for different fossil groups in North America and China (4) CLIMATE AND GEOCHEMICAL MODELING...10 Synopsis of recent developments: Overarching question: Establish the climatic and geochemical response to rapid input of a large mass of methane and/or CO Ultimate goals for Year 1: P-E Climate Simulations w/ Coupled Ocean-Atmosphere model, and compile geochemical data APPENDIX I...12 Presentation summaries: Karla Panchuk and Lee Kump, Geological Science, PSU Tim Bralower, Geological Sciences, UNC Clay Kelly, Dept. of Geological Sciences, University of Wisconsin Henk Brinkhuis, Geological Sciences, Utrecht University Chris Hollis, Institute of Geological and Nuclear Sciences, New Zealand James Zachos, Earth Sciences Dept., UCSC Gerald Dickens, Geological Sciences, Rice University Kristina Faul, Geological Sciences, Stanford University... 28

3 Gavin, Schmidt, NASA, Columbia Univ Gabriel Bowen, Earth Sciences, UCSC Cindy Shellito and Lisa Sloan, Earth Sciences Dept., Univ. of California, Santa Cruz Meeting participants Support:... 34

4 Introduction: The current perturbation to global carbon and biogeochemical cycles is not unprecedented. Over its history, Earth has experienced several large carbon inputs through natural (i.e., nonanthropogenic) mechanisms. One of the largest and most rapid occurred 55 million years ago (Ma) near the boundary between the Paleocene and Eocene epochs. This time interval, referred to as the Paleocene Eocene Thermal Maximum (PETM), was associated with the most pronounced transient warming of the last 100 million years and with sudden, dramatic and widespread changes in many components of global biogeochemical cycles, both terrestrial and marine (Thomas and Shackleton, 1996). The balance of existing geochemical and sedimentological data support the hypothesis that the LPTM was accompanied by a rapid release of ~2000 Gt of microbially-produced methane hydrate from the seafloor. The impacts on ecosystems were widespread and significant, including both extinction and rapid evolution of marine organisms, displacement of marine and terrestrial ecosystems, and possibly a pulse of evolutionary innovation among continental mammals. The overall impacts altered the course of evolution for several major groups of organisms. Indeed, the rate and magnitude of change in all major systems appear unparalleled in the last 100 million years, except as predicted for the present and near future. The PETM provides a unique opportunity to investigate on a global scale how environmental processes, as well as physical, chemical, geological, and biological processes, function before, during and after massive injection of carbon into the oceanatmosphere system. In particular, we can examine both the short and long-term effects of rapid global warming on marine and terrestrial ecosystems. To exploit this opportunity, however, a number key challenges must be overcome. These challenges can be loosely grouped into two sets. The first set relates to the precision and completeness of our reconstructions of the biotic and biogeochemical changes of that period. Despite the recent rapid progress in piecing together the environmental responses to events, critical gaps remain, particularly concerning the timing and scale of the biotic response in near shore marine and terrestrial environments. The second set of challenges concerns limits in our conceptual understanding of how biogeochemical systems function on time scales exceeding observational. For example, most existing models of the global carbon cycle, whether simple or complex, are incapable of accurately simulating such an event for lack of a methane sub-cycle. And yet, release and oxidation of ~2000 Gt of methane from marine gas hydrate deposits seemingly provides the only plausible explanation for the extraordinary carbon excursion at the PETM. As such, biogeochemical models must be modified to include bacteriallymediated gas hydrate reservoirs that store and release enormous amounts of carbon with changes in oceanographic conditions. In addition, models must account for the many potential pathways by which carbon will enter and exit the ocean and atmosphere. To this end, consideration of global ecosystem response to carbon cycle and climatic perturbations becomes critical. Does the biosphere contribute to buffering or restoring the global carbon balance in the case of a rapid injection of carbon to the atmosphere?

5 Workshop Objectives and Goals The purpose of this workshop was to bring together a diverse group of researchers who are actively investigating the climatic, biotic and biogeochemical changes associated with the PETM using both empirical and theoretical approaches. The workshop was organized with the following objectives in mind: 1) identify the key unresolved questions concerning the PETM. 2) identify ways in which our understanding of this event, particularly in terms of the biological and biogeochemical response, should be improved through integrated theoretical and empirical approaches 3) design and implement plans for addressing short-term (within the next 2 years) objectives. In addition to the core group of participants, several researchers with expertise that could be brought to bear on these problems were invited. A list of the participants is provided in the appendix. Organization The workshop was organized in such a way as to enhance sharing and integration of new findings and ideas across disciplines. To this end, the first day was devoted to updating all participants on the latest research developments on the PETM and related areas. This involved a series of presentations by participants that focused on key unresolved issues. Participants were limited to sharing only a few key figures (3-5) so that there would be ample time for open discussion. On the second day participants were divided into 4 theme groups; Marine Climate and Geochemistry; Marine biota; Terrestrial Climate and Biota; and Geochemical and Climate Modeling. Group leaders identified key questions that came out of the previous day's presentations and discussions. Theme groups then broke out to identify short (Year 1) and long-term goals, and determine the details of how best to address these questions. This included preliminary discussion of detailed implementation plans. The entire group then reconvened to summarize morning meetings. In the afternoon, the groups were reorganized on the basis of questions and issues rather than by theme with intent of combining theoretical and empirical expertise. The questions were then refined and solutions outlined in the context of an integrated model/data approach. (1) Marine Climate, Geochemistry, and Chronostratigraphy Synopsis of recent developments: At the PETM, within a very short interval, a massive amount of carbon was added to the ocean-atmosphere system, and polar temperatures soared by as much as 8 C (Kennett et al. 1991; Thomas & Shackleton 1996). The primary evidence for these changes comes from high-resolution isotope records, which show dramatic negative excursions in δ 13 C and δ 18 O. As highlighted throughout this report, many other records across the PETM generally support massive carbon input (e.g., pronounced carbonate dissolution on the seafloor) or extreme warmth (e.g., pronounced increase in warm water nannoplankton in open ocean sites, and migration of low-latitude biota to high latitudes). Both empirical and theoretical evidence implicates a massive and rapid release of marine methane

6 hydrates as the carbon source. The key geochemical evidence is a coeval >3 negative carbon isotope excursion in marine and terrestrial reservoirs at the PETM. New data from ODP site 690 (D. Thomas and colleagues) indicates that the transition in carbon isotope values was immediate in the mixed layer, and more gradual in the deep sea. This is inferred from analyses of single specimen planktonic and benthic foraminifera collected at 1 cm intervals across the P-E boundary. These data also indicate a slight lag in the propagation of the signal from the mixed layer into the deep ocean. Evidence of large-scale and widespread changes in physical, chemical, geological, and hydrological systems, including changes in ocean and atmosphere circulation, precipitation patterns and intensity, and the global sedimentation patterns is common to most PETM horizons. Deep-sea sediment cores are characterized by pronounced carbonate dissolution at the start of the PETM (Thomas et al. 1999), followed by gradual increases in carbonate and barium accumulation at some locations (Bains et al. 2000). In near shore and shallow marine environments, increased accumulation of carbonates and clastics occurs, particularly kaolinite, a chemical weathering byproduct (Robert & Kennett 1994; Kaiho et al. 1996; Schmitz et al. 1996, 1997; Cramer et al. 1999; Gibson et al. 2000). One notable recent advance has been the development of new chronological constraints on the PETM transition. In the past, the duration of the excursion and recovery were constrained through simple interpolation of sedimentation rates between several, widely spaced and inadequately constrained biostratigraphic and reversal datums. An astronomical chronology, established at ODP Sites 690 and 1051 through analyses of Ca and Fe cycles, represented the first attempt to constrain rates on a fine-scale. These records collectively indicate the transition and recovery span some 220 kyr with the initial excursion spanning roughly 40 kyrs (Rohl & Norris, 2000; Rohl et al., 2001). More recently, a second independent technique involving He isotope ratios was also applied to Site 690 (Farley & Eltgroth, in press). This method, which can only be used to establish relative changes in accumulation rates, indicates no change in sedimentation rates at Site 690 through the peak of the excursion consistent with the orbital chronology. However, in the recovery interval, He isotopes indicate an abrupt increase in sedimentation rates, roughly double those predicted by the orbital chronology. This might explain the stasis in the carbon isotope record and the unusual thickness of the recovery interval at Site 690 compared to other pelagic locations. Overarching Questions: The theme groups identified a number of key issues or needs which were grouped under 4 categories (1) carbon cycle, (2) productivity, (3) deep-sea redox cycle, and (4) continental weathering. A high degree of emphasis was placed on the issue of open versus coastal responses to the PETM, particularly in terms of biological production, bottom water carbon, nutrient, and redox chemistry. The group focused on identifying short-term objectives that could be addressed with available sedimentary sections. The key overarching questions and solutions are outlined below.

7 Carbon Cycle: How rapidly, and to what extent did the carbon chemistry of the ocean change during the PETM? 1. Increase the resolution of isotope and other records used to constrain the relative timing of the onset C-isotope excursion in the surface and deep-ocean. High-resolution, single foraminifera approach to isolate reworking effects Orbital stratigraphy & He isotopes - Site 865, Shatsky Rise, Walvis Ridge, New Jersey (coastal sequences?) 2. Establish the rate of recovery of the C-isotope excursion relative to changes in carbonate accumulation rates. 3. Establish the spatial C-isotope patterns of the surface ocean Low to high latitudes Coastal to open ocean 4. Quantify changes in carbonate dissolution (CCD/Lysocline) as a function of depth. In the Pacific/Atlantic Determine how carbonate accumulation changed Determine changes in organic carbon accumulation rates in Tethyan and other coastal sequences. Determine the relative contributions of terrestrial versus marine. Productivity: - How did open marine oceanic productivity change (timing and magnitude) within the open and ocean and relative to coastal ocean during the PETM? Quantify changes in Ba (barite) accumulation rates in coastal and pelagic sections along with other productivity proxies (i.e., carbonate accumulation). 1. Isolate & remove the detrital contribution to Ba 2. Sediment redox conditions *INVENTORY CHANGE - test of methane hypothesis Deep-sea Redox Chemistry To what extend did the dissolved oxygen content of the deep-sea change during the PETM? What was the spatial pattern? Quantify changes in bottom water redox conditions as a function of depth in the ocean Establish changes in redox sensitive elements (Mn, U, Re, Mo) relative to changes in benthic foraminifera assemblages in deep-sea cores, particularly depth transects (Pacific & Atlantic), but also in expanded hemi-pelagic sequences Continental Chemical Weathering How did the flux of chemically weathered minerals (clays) change across the PETM? What was the spatial pattern? 1. Establish changes in the patterns of clay ratio and accumulation rates in shelf sequences and hemi-pelagic sequences N. Atlantic and Tethyan continental margins

8 Ultimate goals for Year 1: Characterize in detail the timing and magnitude of marine biogeochemical changes for both the deep-sea and coastal oceans. - Sample Wilson Lake Core - Generate bulk isotope records - Determine suitability for foram isotope studies - Generate clay accumulation curves - Identify marine P-E boundary sections exposed in California - Determine if sections are complete (do they possess the excursion/clay layers) - Sample Shatsky Rise Cores - Generate bulk and planktic foraminifera isotope records - Quantify dissolution using %sand fraction and fragmentation indexes. - Assess suitability for trace elements studies - (2) Marine Biota & Ecosystems Synopsis of recent developments: The PETM climatic/oceanographic changes clearly had profound effects on marine ecosystems. This includes the extinction of between 30 and 50% of deep-sea benthic foraminiferal species, including many large, heavily-calcified epifaunal taxa (Thomas 1990), An unusual proliferation of exotic "excursion" species of planktonic foraminifera, calcareous nannoplankton, and dinoflagellate cysts (Apectodinium) in the low to mid-latitude oceans at the event is indicative of massive shifts in oceanic fertility (Kelly et al. 1996; Aubry 1998; Bujak & Brinkhuis 1998; Crouch et al. 2001). The impact of this event on planktonic foraminifera assemblages was far more complex than first recognized. Following the proliferation of excursion taxa during the peak of the PETM, a second perturbation occurs associated with the recovery phase of the event. New data from the southern ocean show a The abundances of calcareous nannofossils assemblages also show a complex pattern of change through the P-E transition in both low and high-latitudes. A recent study of the PETM at Site 690 shows at least 4 major regime shifts in the nannofossil assemblages through the initial excursion and recovery (Bralower, in press). These shifts are inferred to reflect changes in ocean fertility. Overarching question: What was the overall marine and terrestrial biotic response to the PETM event, and how did this impact marine ecosystem energy flow on a variety of spatial and temporal scales. 1. How did productivity change in the open ocean? In marginal basins? In coastal oceans? Can we separate the effect of T/S on plankton assemblages from that of productivity? 2. Can we separate the effect of oxygenation on benthic assemblages from that of productivity? 3. How were surface and deep ocean coupled during/before/after the PETM and what was the efficiency of the biotic pump? 4. How did surface and deep ocean environments change during the onset, the peak and the recovery period of the event? 5. What was the phasing of biotic events?

9 6. How do we separate transient biotic events from evolutionary events and does the basic environmental forcing differ for the two? Ultimate goals for Year 1: Generate detailed assemblage data for a variety of fossil groups in common sample sets Complete Site 690 assemblage studies Compete Site 738 assemblage studies. Identify New Jersey margin sections for sampling Identify California margin sections for sampling Pursue sections with silica, Site 1051? Communicate results and interact with geochemists and modelers and based on feedback, reconsider sample plan for Year 1 sites as well as sites to be studied in Year 2. (3) Terrestrial Climate and Biota Synopsis of recent developments: Terrestrial ecosystems experienced dramatic changes in faunal diversity and composition (including the first appearance of many important groups of modern mammals), body size, and guild structure, as well as a pronounced pulse of higher speciation rates in the million years following the event (Gingerich 1989; Clyde & Gingerich 1998; Alroy et al. 2000). Terrestrial floras exhibit a smaller pulse of changes, including the dispersal of low-latitude, warm-climate floras into mid- and high-latitudes (Wing et al. 2000). Although some responses were transient (e.g., temporary latitudinal displacement), others were permanent and altered the course of evolution of Holarctic terrestrial ecosystems. The PETM occurred during a gradual warming that began in the late Paleocene ~58 Ma and culminated at the early Eocene Climatic Optimum (EECO) ~51 Ma (Miller et al. 1987; Zachos et al. 1994)). This warming trend, although interrupted by at least one cool interval between 54.3 and 53.7 Ma (Wing et al. 2000), was probably caused by elevated greenhouse gas concentrations (Sloan et al. 1992). Within the context of conventional carbon cycle models, enhanced volcanic emissions provide the most probable source for this gas (Eldholm & Thomas 1993). However, given the current framework for understanding the PETM, slow release of CH 4 from the seafloor presents an interesting, unexplored alternative. An overall decline in the δ 13 C of the ocean between 58 and 53 Ma is consistent with either interpretation. Regardless, the long-term temperature rise may have brought the climate system to a threshold that, once crossed, set in motion the perturbations seen at the PETM. As with the PETM, the biotic consequences of the EECO were marked, particularly in middle and high latitudes. Mid-latitude temperate floras were supplemented and replaced by subtropical and tropical forms (Wing 1987, 1998). The presence the same warm-adapted plant genera in Asia, North America and Europe suggests that some lineages were able to expand across high-latitude land bridges (Tiffney 1985a,b, Manchester 1999). Above the Arctic Circle the very warm climates of this period permitted the growth of moderately diverse and productive deciduous forests (Basinger 1991; McIver & Basinger 1999). Tropical to sub-tropical marine organisms similarly expanded their ranges into higher latitudes. Benthic organisms fared better during this period, perhaps because forms susceptible to the environmental pressures associated with extreme warming became extinct at the PETM, leaving opportunistic taxa and post-disaster faunas (Thomas et al. 1998). Nonetheless, benthic faunas suffered several episodes of stress during the EECO with an ecological response similar to that at the PETM (Thomas et al. 1999).

10 Overarching question: What are the marine and terrestrial biotic responses to the PETM event, and in particular to recreate the long and short-term ecosystem changes on different spatial and temporal scales, 1. How did terrestrial floral assemblages change during the excursion? 2. What were the long-term impacts between terrestrial floral assemblages? 3. How did terrestrial mammals respond to this event? 4. Did Asia serve as locus of emigration during the excursion? What was the relative succession of first occurrences? 5. What was the phasing of biotic events locally and globally? 6. How do we separate transient biotic events from evolutionary events and does the basic environmental forcing differ for the two? Ultimate goals for Year 1: Collect data for different fossil groups in North America and China - Sample boundary sections in China - Construct soil nodule C-isotope stratigraphies for same sections - High density sampling of P-E layers in various locations in the Bighorn basin (4) Climate and Geochemical Modeling Synopsis of recent developments: At present, computer modeling of aspects of the PETM geochemical and climatic conditions has been limited. Climatic modeling efforts have largely focused on the impact of elevated greenhouse gas levels on temperature, precipitation, and ocean circulation (Sloan and Rea, 1995; Huber and Sloan, 2000). These simulations were carried out using atmospheric climates models coupled to a slab ocean with prescribed temperatures. As for biogeochemistry, modeling has been limited to several simulations of the carbon cycle response to input of range of masses of methane derived carbon. These simulations, conducted with a 8 box model of the carbon cycle (Dickens et al., 1997), show significant changes in the concentration of carbonate ion in the ocean, and seafloor dissolution of carbonate. Current models for understanding biogeochemical systems lack a mechanism to transfer carbon to and from marine gas hydrate reservoirs in response to oceanographic stimuli (e.g., warming). Dickens (2001) has addressed this issue by constructing a "gas hydrate capacitor" that stores and releases large quantities of 12 C-rich carbon at rates linked to environmental change, especially bottom water temperature. This capacitor, largely based on information from the well-characterized Blake Ridge hydrate system, contains three internal reservoirs: dissolved gas, gas hydrate and free gas. Carbon enters dissolved gas through decomposition of organic matter (methanogenesis), gas hydrate through saturation of pore waters, and free gas through thermal dissociation of gas hydrate. Carbon leaves as free gas to the ocean through anaerobic CH 4 oxidation in sediment or, if the overlying gas hydrate has been completely dissociated, by direct

11 injection to the water column. Massive amounts of 12 C-rich carbon can escape the capacitor during bottom water warming; the capacitor refills during cooling because the amount and location of free gas depends on the geotherm. Deep ocean temperature functions will be applied to a range of potential capacitors of different C mass and distribution to generate a series of functions for CH 4 release over space and time. These possible temperature inputs and carbon outputs can be constrained with new, highresolution δ 18 O and δ 13 C records in the time domain. Ultimately, the 12 C-rich CH 4 will be oxidized to CO 2 in the ocean (via aerobic bacteria) or CO 2 in the atmosphere (via OH radicals). Overarching question: Establish the climatic and geochemical response to rapid input of a large mass of methane and/or CO 2 1. What is the planetary thermal gradient under varying levels (2-6x) of CO 2 in the atmosphere? 2. What is the planetary thermal gradient under varying levels of CH 4 in the atmosphere? a. How does the residence time of CH 4 change as the flux increases? 3. What was the fate of the CH 4 once it was released from the sea floor? Was it oxidized in the ocean, the atmosphere, or both environments? 4. How is the injection of carbon into the system buffered by dissolution of rocks on land and sediments on the seafloor? a. How rapidly does the lysocline and CCD shoal? b. How rapidly does the lysocline and CCD recover? 5. What are the effects of the climatic and geochemical changes on global chemical weathering fluxes? 6. Why is the magnitude of the carbon isotope excursion in terrestrial soil carbonate record larger than recorded in marine sections? Ultimate goals for Year 1: P-E Climate Simulations w/ Coupled Ocean-Atmosphere model, and compile geochemical data - Begin simulations of extreme greenhouse forcing on planetary meridional temperature gradients - Develop a soil carbon model that is dynamically linked to the ocean/atmosphere carbon cycle box model.

12 Appendix I Presentation summaries: Karla Panchuk and Lee Kump, Geological Science, PSU Figure above shows basic components of a spatially resolved, fully coupled, intermediate complexity biogeochemical model capable of simulations on a Ma time-scale. The model will track the masses (M) and isotopic compositions (δ) of elemental tracers C, O, and S, and the masses of reactive P and N in the ocean. Intended uses are to simulate the release of methane from gas hydrate reservoirs and to follow the propagation of the methane-derived C-isotope response throughout the system, to monitor changes in the oceanic lysocline depth, and to monitor the spread of anoxia. Components include an ocean GCM (1) with primary productivity, and carbonate and redox chemistry coupled to marine sediments (2) where dissolution of CaCO3 or remineralization of organic matter can take place, as well as the formation of pyrite. The ocean and marine sediment components are associated with a methane capacitor (3) (Dickens, 2001), which accumulates or discharges methane depending on the temperature and pressure at the sea floor. The atmosphere component (4) exchanges O2, CO2, CH4, and N 2 with the ocean, contributes O2 and CO2 to weathering reactions, and incorporates CO2 from mantle degassing (5). The atmosphere receives O 2 and CO2 from the terrestrial vegetative biomass (6) by means of photosynthesis and respiration or combustion, respectively, while contributing CO2 for photosynthesis. Gas exchange also occurs between the atmosphere and soils (7), where vegetative material accumulates and is decomposed. Finally, the ocean, atmosphere, vegetation, and soils are linked to the hydrologic cycle (8).

13 Ellen Thomas, Geology, Yale University Figure above shows detailed benthic and isotope records from ODP Site 690B. Note that benthic foraminifera (Thomas, in press) increased in absolute abundance (number of tests per gram dry sediment, indicator of food supply to the benthos) at exactly the same level in the sediment where Fasciculithus spp. (Bralower, 2002) increased in relative abundance (indicator of decreasing productivity in surface waters). This level was just below the beginning of the carbon isotope excursion (Bains et al., 1999). Blue lines indicates the level of the main phase of benthic foraminiferal extinction (Thomas, in press).