OS14A-01 INVITED
Coccolithophore Response to CO2 Increase and Related Ecological Changes
Changes in ocean chemistry due to anthropogenic CO2 emissions affect marine life, nutrient cycles and biocalcification. Ocean acidification has been identified as a major consequence of rising atmospheric CO2 levels. This makes understanding the response of calcareous plankton, and other effects of global change, an urgent challenge. There have been controversial results from culture experiments and field observations, on the impact of CO2 increase on coccolithophore calcification and ecology. The objective of this presentation is to report the state-of-the-art on the impact of ocean acidification on coccolithophores and possible consequences on their biogeography and ecology. Results will also be reported from a workshop sponsored by the European Science Foundation (Euroclimate Program) and PAGES on Atmopheric CO2, ocean acidification and ecological changes in planktonic calcifying organisms. A wide range of experts contributed to that workshop, from the cellular and genetic to the ecological and global carbon cycle levels. Questions include how the predicted CO2 increase and acidification is likely to affect coccolithophores, what the possible secondary consequences may be, and what research is needed to allow robust predictions for the future.
OS14A-02
Cenozoic Icehouse Forcing Mechanisms on Coccolithophorid Evolution
An overall macroevolutionary size decrease in marine unicellular calcifying algae, the coccolithophores, is punctuated by distinct size responses that correlate to major climatic and paleoceanographic events during the Cenozoic. Notably, major size decreases in the ancestors of the modern blooming species Emiliania huxleyi and Gephyrocapsa oceanica are recorded at the Eocene-Oligocene transition (34 Ma) and in the late Miocene (9 Ma). Coccolithophorid cell size (as reconstructed from individual coccolith biometry) is likely influenced by a variety of passive and active evolutionary selection pressures, with specific factors, such as resource availability and climatic change, determining trends in specific intervals of time. This study presents biometric data of the Noelaerhabdacaea, Calcidiscaceae and Coccolithaceae families, which together represent the bulk of coccolith-carbonate buried in Cenozoic deep-sea sediments, from multiple Deep Sea Drilling Project and Ocean Drilling Project sites covering temperate to tropical regions in the Atlantic, Indian and Pacific oceans. Despite distinct regional ecologic responses at each site, striking correspondences within the global data set call for global forcing mechanisms on the size evolution and ecological success of coccolithophores in an ‘icehouse' world.
OS14A-03
Evolutionary Response of Planktic Foraminifera to a Pronounced Global Warming Event 40 Myr ago
A transient interval of pronounced and abrupt global warming ca. 40 Myr ago associated with major perturbations to the carbon cycle interrupts the long-term Eocene cooling trend. This interval has typically proven difficult to investigate because a near-global hiatus truncates many existing deep-sea records approximately 40.5 Myr ago, making complete recovery of planktic foraminiferal biozone E12 (P13 in previous biozonation scheme), to which this event is restricted, extremely difficult. One exception is Ocean Drilling Program (ODP) Site 1051 (Blake Nose, western North Atlantic), the most expanded and continuous sedimentary record from this interval, which also benefits from good preservation of calcareous microfossils. Here we present new high-resolution faunal records (from 40.6 Myr ago to 39 Myr ago) of all the major groups of planktic foraminifera that document the biotic response of plankton to this rapid climatic warming event. The geologically brief duration of biozone E12, to which this event is restricted, is defined by the total range of an unusual and distinctive species of planktic foraminifera - Orbulinoides beckmanni. We test the hypothesis that the origination, subsequent evolutionary development and eventual extinction of this short-lived, biozone marker species was intimately linked to environmental changes associated with this warming event.
OS14A-04
Ocean acidification in the early Eocene and Anthropocene
Anthropogenic carbon emissions have roughly doubled over the past 35 years and are now ~ 100 times larger than gross fluxes of natural carbon exchange between long-term carbon reservoirs. As the CO2 invades the ocean, the seawater pH and the carbonate mineral saturation state drop, a process termed 'ocean acidification'. The current rate of this process is likely unprecedented during millions of years of Earth's recent history. The Paleocene-Eocene Thermal Maximum (PETM, about 55 Ma ago) may constitute an analog for the future because the scale of climate and carbon cycle perturbations are potentially comparable to anthropogenic impacts within the next centuries. At the onset of the PETM, surface temperatures rose globally by 5-9 deg C, the ocean pH decreased, and the ratio of 13C/12C of the surficial carbon reservoirs dropped by about 3 per mil within a few thousand years. We will describe our recent progress in reconstructing changes in deep-sea carbonate chemistry and modeling of carbon cycle changes during the PETM. Our new results on basin-differences in chemistry and dissolution coupled with stable carbon isotope records provide important constraints for modeling the carbon release during the PETM. In particular, it will allow a quantitative comparison between carbon cycle changes in the early Eocene and the Anthropocene. We will discuss the marine biotic response of calcifying organisms to ocean acidification both during the PETM and in the near future. Our results indicate that potentially detrimental effects on marine biota under business-as-USual emission scenarios may be significantly more severe in the future than during the PETM.
OS14A-05
Modeling Biogeochemical Responses to Massive Carbon Releases at the Paleocene- Eocene Thermal Maximum
For the Paleocene-Eocene Thermal Maximum (55 Mya), significant changes in climate and geochemistry have been inferred from changes in temperature proxies and stable carbon isotope ratios. The comprehensive climate model CCSM-3 including a carbon and nutrient cycle model is applied to explore effects of different magnitudes and rates of carbon release into the atmosphere on the lysocline and on CaCO3 accumulation rates. Paleocene-Eocene simulations with 8xCO2 indicate significant warming in the high latitudes and reduction of downwelling in the subtropical gyres. These results coincide with environmental shifts that have been recorded in these areas, such as decreased open-ocean productivity at lower latitudes at the onset of the Paleocene Eocene Thermal Maximum.
OS14A-06 INVITED
Deep Sea Benthic Foraminifera: Love Cold, Fear Warm
The fossil record provides understanding of possible linkages between long-term environmental changes and evolution of assemblages and morphological species of deep-sea benthic foraminifera, of which the phylogeny is still little known. Deep-sea benthic foraminifera have long morphological species lives and do not commonly suffer massive extinctions: they live in the largest habitat on earth, species have large geographic ranges or are cosmopolitan, and they use motile propagules to rapidly re-populate regions where populations have been destroyed. Extinction occurs only when rapid and severe environmental change affects such a large part of the deep ocean that no refugia exist, even for common species. Deep-sea benthic foraminifera reacted to global cooling (in the earliest Oligocene, middle Miocene and middle Pleistocene) not by extinction, but by a gradual turnover of species. The most extensive turnover occurred in the late Eocene through earliest Oligocene, when some presently important ecological niches were first filled. In contrast, deep-sea benthic foraminifera suffered severe extinction (30-50% of species, including common, cosmopolitan, long-lived species) during the rapid global warming of the Paleocene-Eocene Thermal Maximum (PETM), a time of high CO2 levels and potential ocean acidification. The extinction was followed by slow recovery of faunas, but diversity never returned to pre-extinction levels. The PETM and later, less severe short-term periods of global warming (hyperthermals ETM1 and ETM2) were characterized by low diversity faunas dominated by small, thin-walled individuals. No significant net extinction occurred during the later hyperthermals. Such faunas might reflect dissolution, low oxygen conditions, or blooming of opportunistic species after environmental disturbance. Most commonly cited causes of the PETM extinction are: 1. low oxygen concentrations, 2. acidification of the oceans, 3. increase or decrease in oceanic productivity and/or transfer of food to the sea floor, and 4. increasing temperatures. All 4 factors may have contributed to the extinction, but the first three factors varied regionally and by depth, whereas only the temperature increase affected the deep-sea environment globally. High temperatures not only increase overall metabolic rates, but also affect which species of prokaryotes are most active and which labile compounds they generate, thus the compounds and the amount of labile organic matter available for foraminiferal feeding. At sites along a depth transect at Walvis Ridge (SE Atlantic) species that earlier had been abundant in neritic waters ( Tappanina selmensis) increased strongly in abundance. Some surviving deep-sea species underwent diversification and morphological evolution; during and just after the PETM and two other hyperthermal events the deep-sea genus Abyssamina became more abundant (most pronounced at the deeper sites), while evolving into several morphological species. During the warmer intervals its aperture became more irregular in shape, with an extremely asymmetrical shape at the deepest site during ETM1. The aperture in benthic foraminifera directs the streaming of pseudopods, thus the way of food intake, suggesting that the nature of benthic feeding changed during the warm periods. During the early Eocene (a period characterized by hyperthermals), faunas maintained larger differences in assemblage composition between ocean basins than before the extinction. It remains a question whether this faunal heterogeneity reflects the mode of deep-ocean circulation/ventilation during the warmest period of the Cenozoic.
OS14A-07
Bleaching of Symbiotic Foraminifera During Extreme Global Warming at the Paleocene- Eocene Boundary
Rapid global warming during the Paleocene-Eocene Thermal Maximum (PETM, 55 Ma) is accompanied by a pronounced decrease in carbon isotopes believed to record the massive input of greenhouse gases into the biosphere. Curiously, the magnitude of this carbon isotope excursion varies between species of foraminifera, reaching as much as -4 per mil in Southern Ocean surface-dwelling species, and being distinctly smaller than this in thermocline and bottom-dwelling species. New data shows that the carbon excursion is magnified in species that bore algal symbionts because the symbiotic relationship was briefly eliminated just before and during the most intense global warming associated with the PETM. The early onset of the loss of photosymbiosis suggests that environmental change substantially preceded the whole ocean change in carbon isotopes and suggests that impact events and mass submarine slope failures reported during the PETM are not the ultimate triggers for this event. The ecological loss of photosymbiosis also explains why the magnitude of the carbon isotope excursion is larger in some species than in others and does not require either that greenhouse gases flooded the atmosphere before being mixed into the deep sea or that the input of carbon into the biosphere was substantially larger than is anticipated for a -2.5 per mil carbon isotope anomaly. The bleaching of photosymbiotic foraminifera suggests that warming was rapid enough, and severe enough, to largely or entirely eliminate symbiosis for 40 kyr.
OS14A-08 INVITED
Biotic Response of Deep-Ocean Ostracodes to the Paleocene-Eocene Thermal Maximum: An Assessment of Past, Present, and Future studies
Ostracodes are the only commonly preserved deep-ocean metazoans and provide an important perspective on benthic conditions through the global carbon cycle perturbation known as the Paleocene-Eocene Thermal Maximum (PETM). The classic global Cenozoic study of >250 micron size-fraction ostracode faunas from 1,000+ samples drawn from 150+ DSDP sites by Benson et al. (1984) revealed marked transient declines in abundance, richness, and Shannon diversity in the late Paleocene, but these data are discretized within relatively coarse one-Myr averaged bins and may have little direct temporal or causal relationship with the much shorter PETM. Following the "discovery" of the PETM by Kennett and Stott in the early 1990s, Steineck and Thomas (1994) examined the >150 micron size-fraction ostracode faunas through the PETM at upper bathyal Site 689B on Maud Rise, and argued for a marked relative increase in small, thin walled "opportunistic" taxa capitalizing upon transient conditions of increased food, decreased dissolved oxygen, and decreased carbonate saturation. However, our subsequent cm-scale bulk carbonate carbon-isotope chemostratigraphy for Site 689 confirms that only two of these faunal samples are located within the carbon-isotope excursion of the PETM. Recent high-resolution geochemical analyses of ODP PETM sections in the Southern Ocean are producing a new benchmark for integrative approaches to understanding the PETM. Cast within these environmental frameworks, our recent >63 micron size-fraction ostracode faunal analyses at Maud Rise (690B) and Kerguelen Plateau (738C) reveal marked declines in ostracode accumulation rates and resampled (abundance- corrected) generic richness coincident with the CIE onset and varying rates of recovery following the CIE minimum. Cluster and ordination analyses support major faunal perturbations through the CIE and subsequent recovery towards pre-CIE faunal composition and structure following the CIE. The relatively rapid recovery in ostracode accumulation rates near the CIE minimum does not support prolonged deleterious conditions for metazoans, though the faunal composition shows a significantly greater proportion of presumably dysoxia- tolerant suspension-feeding platycopid taxa. However, this platycopid signal may well reflect increased food availability as well as decreased oxygenation as has been suggested from benthic foraminiferal studies. The restriction of specific taxa, such as Munseyella and Palmoconcha, to specific CIE intervals within the highly stratigraphically resolved Site 690 suggests that faunal patterns reflect a true ecological signal versus pervasive artifacts from differential sedimentation rates and reworking. Ongoing single-valve stable-isotope analyses of various ostracode taxa should provide additional constraints on reworking as well as the arrival of CIE to these bathyal sites via thermohaline circulation. Ongoing logistical challenges to consolidating and expanding the PETM marine ostracode record include (1) obtaining sufficient specimen abundances at sufficient stratigraphic resolution given often low ostracode accumulation rates and limited sediment volumes; (2) adopting explicit and consistent inter-worker methods (e.g., size fraction picked, tallying adults vs. juveniles); (3) ensuring permanent archiving of complete faunal matrices; (4) establishing a consistent species taxonomy; and (5) stratigraphic expansion of such studies about the PETM to assess longer term faunal patterns and sensitivity to orbital forcing and other Paleogene hyperthermals.