Pteropods have been nicknamed the “canary in the coal mine” for ocean acidification because they are predicted to be among the first organisms to be affected by changing ocean chemistry. This is due ...to their fragile, aragonitic shells and high abundances in polar and subpolar regions where the impacts of ocean acidification are most pronounced. For pteropods to be used most effectively as indicators of ocean acidification, the biotic and abiotic factors influencing their shell formation and dissolution in the modern ocean need to be quantified and understood. Here, we measured the shell condition (i.e., the degree to which a shell has dissolved) and shell characteristics, including size, number of whorls, shell thickness, and shell volume (i.e., amount of shell material) of nearly 50 specimens of the pteropod species Heliconoides inflatus sampled from a sediment trap in the Cariaco Basin, Venezuela, over an 11-month period. The shell condition of pteropods from sediment traps has the potential to be altered at three stages: (1) when the organisms are live in the water column associated with ocean acidification, (2) when organisms are dead in the water column associated with biotic decay of organic matter and/or abiotic dissolution associated with ocean acidification, and (3) when organisms are in the closed sediment trap cup associated with abiotic alteration by the preservation solution. Shell condition was assessed using two methods: the Limacina Dissolution Index (LDX) and the opacity method. The opacity method was found to capture changes in shell condition only in the early stages of dissolution, whereas the LDX recorded dissolution changes over a much larger range. Because the water in the Cariaco Basin is supersaturated with respect to aragonite year-round, we assume no dissolution occurred during life, and there is no evidence that shell condition deteriorated with the length of time in the sediment trap. Light microscope and scanning electron microscope (SEM) images show the majority of alteration happened to dead pteropods while in the water column associated with the decay of organic matter. The most altered shells occurred in samples collected in September and October when water temperatures were warmest and when the amount of organic matter degradation, both within the shells of dead specimens and in the water column, was likely to have been the greatest. The hydrographic and chemical properties of the Cariaco Basin vary seasonally due to the movement of the Intertropical Convergence Zone (ITCZ). Shells of H. inflatus varied in size, number of whorls, and thickness throughout the year. There was not a strong correlation between the number of whorls and the shell diameter, suggesting that shell growth is plastic. H. inflatus formed shells that were 40 % thicker and 20 % larger in diameter during nutrient-rich, upwelling times when food supply was abundant, indicating that shell growth in this aragonite-supersaturated basin is controlled by food availability. This study produces a baseline dataset of the variability in shell characteristics of H. inflatus pteropods in the Cariaco Basin and documents the controls on alteration of specimens captured via sediment traps. The methodology outlined for assessing shell parameters establishes a protocol for generating similar baseline records for pteropod populations globally.
For over 50 years, cores recovered from ocean basins have generated fossil, lithologic, and chemical archives that have revolutionized fields within the earth sciences. Although scientific ocean ...drilling (SOD) data are openly available following each expedition, the formats for these data are heterogeneous. Furthermore, lithological, chronological, and paleobiological data are typically separated into different repositories, limiting researchers' abilities to discover and analyze integrated SOD data sets. Emphasis within Earth Sciences on Findable, Accessible, Interoperable, and Reusable (FAIR) Data Principles and the establishment of community‐led databases provide a pathway to unite SOD data and further harness the scientific potential of the investments made in offshore drilling. Here, we describe a workflow for compiling, cleaning, and standardizing key SOD records, and importing them into the Paleobiology Database and Macrostrat, systems with versatile, open data distribution mechanisms. These efforts are being carried out by the extending Ocean Drilling Pursuits (eODP) project. eODP has processed all of the lithological, chronological, and paleobiological data from one SOD repository, along with numerous other data sets that were never deposited in a database; these were manually transcribed from original reports. This compiled data set contains over 79,899 lithological units from 1,125 drilling holes from 422 sites. Over 26,000 fossil‐bearing samples, with 5,378 taxonomic entries from 13 biological groups, are placed within this lithologic spatiotemporal framework. All information is available via GitHub and Macrostrat's application programming interface, which renders data retrievable by a variety of parameters, including age, site, and lithology.
Key Points
Scientific ocean drilling has produced vast amounts of data; however, they are not archived in a way that meets the Findable, Accessible, Interoperable, and Reusable data principles
The extending Ocean Drilling Pursuits project standardizes lithology, paleontology, and age data across decades of drilling programs
This project has migrated data sets to existing, open‐access, searchable databases to enable scientific research
It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing ...3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.
The Paleocene-Eocene Thermal Maximum (PETM, ∼55 million years ago) was an interval of global warming and ocean acidification attributed to rapid release and oxidation of buried carbon. We show that ...the onset of the PETM coincided with a prominent increase in the origination and extinction of calcareous phytoplankton. Yet major perturbation of the surface-water saturation state across the PETM was not detrimental to the survival of most calcareous nannoplankton taxa and did not impart a calcification or ecological bias to the pattern of evolutionary turnover. Instead, the rate of environmental change appears to have driven turnover, preferentially affecting rare taxa living close to their viable limits.
Pteropods have been hailed as the “canary in the coal mine” for ocean acidification, however, questions remain about their life history, habitat, and the environmental parameters that the isotopic ...composition of their shells reflect. In order to use pteropods as recorders of ocean chemistry, it is first necessary to understand where they calcify and how this may change through the year, whether this signal is affected by dissolution, and if shells are retained in the subfossil, and eventually fossil, record. Here we create the first annual record of the stable isotopic composition of shells of the pteropod
Heliconoides inflatus
in the Cariaco Basin, Venezuela utilizing samples and data from the CARIACO time series. Sixty-four
H. inflatus
specimens from 17 sediment trap samples between November 1996 and April 1998, and 22 specimens from the late Holocene-aged CAR2000-MC-2 core were analyzed for shell condition (an assessment of the amount of dissolution that a shell has experienced), size, and carbon and oxygen isotopic composition. Carbon isotopic measurements of juveniles (< 1mm) were more variable than those in adults (>1 mm), suggesting juvenile pteropods likely have a higher growth rate, and therefore different metabolic vital effects, and a more varied diet than adult pteropods.
H. inflatus
was found to have an apparent calcification depth of 51.2 ± 34.0 m, suggesting they calcify at the shallowest part of their diurnal migration in the mixed layer (10–35 m in the Cariaco Basin).
H. inflatus
shell calcification will therefore only be impacted by changes in water chemistry at mixed layer depths. The shell condition did not impact the stable isotopic composition of the shells in either the sediment trap or core sample, suggesting the potential for using the isotopic composition of pteropod shells as oceanographic proxies when they are preserved. Comparisons between sediment trap and core sample show a 0.5°C warming that is marginally significant and a significant 0.45‰ decrease in δ
13
C between the late Holocene and the late 1990's. These measurements reflect changes in oceanic conditions linked to anthropogenic fossil fuel emissions known as the Suess effect, and lay the groundwork for establishing pteropods as paleoceanographic proxies in the future.
Aim: The latitudinal diversity gradient (LDG) is a primary emergent property of the biosphere, yet the cause(s) of this pattern are still debated. Key to many hypotheses is the origins and ...maintenance of tropical hyperdiversity, and the role of climate in driving low latitude speciation. Here, we analyse patterns of tropical and extratropical floral diversification and migration during the early Palaeogene "greenhouse" interval, to shed further light on the relationship between climatic change, latitude and floral diversity. Location: The early Palaeogene, from ∼63 to 42 million years ago, of the US Gulf Coastal Plain (GCP) and Colombia. Taxon: Terrestrial plants, using pollen and spores as a proxy. Methods: We analyse species diversity trends using coverage and sample size-based interpolation and extrapolation, Chao1 estimated richness, and evenness metrics. (CMR)Capture–mark–recapture modelling is used to estimate origination and extinction probabilities. Origination patterns on the GCP are separated into in situ speciation versus immigration. Results: While Colombian (tropical) palynofloral richness and origination rates increased in conjunction with warming, GCP richness remained stable. The single rise in GCP origination rates, coincident with the Palaeocene–Eocene Thermal Maximum, was largely driven by the immigration of Eurasian taxa, rather than in situ origination, which was the case in Colombia. Main conclusions: These results show that the relationships among climatic parameters and diversification and dispersal are not straightforward. While temperature may have driven diversification in the tropics, other factors, such as precipitation, insolation or biological interactions, may have constrained diversification in the extratropics. Furthermore, our results suggest that outward dispersal from the tropics was limited in the warm world of the early Palaeogene, with most GCP immigrants being sourced from other extratropical regions. These findings suggest that the tropics and extratropics may have functioned independently at this time.
The Paleocene‐Eocene Thermal Maximum (PETM) was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale. Here we examine the sediments, flora, and ...fauna from an expanded section at Mattawoman Creek‐Billingsley Road (MCBR) in Maryland and explore the impact of warming at a nearshore shallow marine (30–100 m water depth) site in the Salisbury Embayment. Observations indicate that at the onset of the PETM, the site abruptly shifted from an open marine to prodelta setting with increased terrestrial and fresh water input. Changes in microfossil biota suggest stratification of the water column and low‐oxygen bottom water conditions in the earliest Eocene. Formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift, while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites. This proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12C‐enriched CO2. We conclude that the MCBR site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming.
Key Points
We document the response of marine flora and fauna to changing habitats in a nearshore environment during the PETM
We show that episodic hyperpycnal flow resulted in an increase in sedimentation rate, input of fresh water, and terrestrial material
We propose that authigenic carbonate resulted in a diagenetic isotope pattern that mimics a magnified negative CIE in bulk carbonates
The carbon and oxygen isotope compositions of calcium carbonate shells are widely accepted and applied proxies for tracking changes in paleoenvironmental conditions such as temperature, salinity ...and productivity. In order to accurately interpret isotopic measurements, diagenetic alteration must first be assessed. The occurrence of aragonitic shells is often taken as a first order sign of unaltered material because aragonite at the Earth's surface is metastable and converts to calcite. However, even specimens that retain an aragonitic composition and are macroscopically well preserved often exhibit subtle to considerable signs of alteration when shell microstructure is examined using scanning electron microscopy (SEM). To determine the textural and isotopic effects of progressive alteration on differing types of shell microstructure, we undertook a comparative study of aragonitic shells from two regions frequently used in paleoenvironmental reconstructions and diagenetic studies -- the Upper Cretaceous of the Gulf Coastal Plain (GCP) and the Western Interior Seaway (WIS). Because the GCP is within a passive margin setting and the WIS has experienced tectonic processes, we also evaluate how diagenetic history affects isotopic composition. Visually well-preserved ammonite, bivalve, and gastropod shells were collected from one locality in the GCP and examined using SEM. To evaluate microstructural preservation, we used a previously published scale based on WIS specimens for nacreous shell material and a complementary scale we developed for crossed lamellar microstructure. The stable carbon and oxygen isotope compositions of specimens across the preservational scale from both regions were analyzed. Isotopic composition does not change systematically with degrading preservation in the GCP specimens, a result that contrasts strongly with patterns in WIS specimens where isotopic composition systematically decreases with decreasing microstructural preservation. Dissimilar tectonic regimes that led to unique post-depositional conditions for each region are invoked to explain this difference. The WIS was a foreland basin subjected to significant meteoritic groundwater flow driven by active uplift, while the GCP was a passive margin that has remained close to sea level, with low hydraulic potential, since the time of deposition. Thus, during diagenesis the WIS shells were exposed to fluids that differed greatly from the seawater in which the organisms grew, whereas diagenetic fluids in GCP settings likely were similar to marine waters. As expected, shells with the best-preserved microstructure provide the most consistently reliable isotopic data for paleoenvironmental reconstructions, but our comparisons show that similar degrees of microstructural alteration can express very different diagenetic shifts in isotopic values.
An epicontinental sea bisected West Africa periodically from the Late Cretaceous to the early Eocene, in dramatic contrast to the current Sahara Desert that dominates the same region today. Known as ...the Trans-Saharan Seaway, this warm and shallow ocean was a manifestation of globally elevated sea level associated with the rapid break-up of the supercontinent Gondwana in the late Mesozoic. Although it varied in size through time, the Trans-Saharan Seaway is estimated to have covered as much as 3000 km2 of the African continent and was approximately 50 m deep. The edges of the sea were defined in part by the high topography of the Precambrian cratons and mobile belts of West Africa. Over its approximately 50 million year episodic existence, through six major periods of transgression and regression, the Trans-Saharan Seaway left behind extensive nearshore marine sedimentary strata with abundant fossils. The waters that yielded these deposits supported and preserved the remains of numerous vertebrate, invertebrate, plant, and microbial species that are now extinct. These species document a regional picture of ancient tropical life that spanned two major Earth events: the Cretaceous-Paleogene (K-Pg) boundary and the Paleocene-Eocene Thermal Maximum (PETM). Whereas extensive epeiric seas flooded the interior portions of most continents during these intervals, the emerging multicontinental narrative has often overlooked the Trans-Saharan Seaway, in part because fundamental research, including the naming of geological formations and the primary description and analysis of fossil species, remained to be done. We provide such synthesis here based on two decades of fieldwork and analyses of sedimentary deposits in the Republic of Mali. Northern parts of the Republic of Mali today include some of the farthest inland reaches of the ancient sea. We bring together and expand on our prior geological and paleontological publications and provide new information on ancient sedimentary rocks and fossils that document paleoequatorial life of the past. Ours is the first formal description of and nomenclature for the Upper Cretaceous and lower Paleogene geological formations of this region and we tie these names to regional correlations over multiple modern territorial boundaries. The ancient seaway left intriguing and previously unclassified phosphate deposits that, quite possibly, represent the most extensive vertebrate macrofossil bone beds known from anywhere on Earth. These bone beds, and the paper shales and carbonates associated with them, have preserved a diverse assemblage of fossils, including a variety of new species of invertebrates and vertebrates, rare mammals, and trace fossils. The shallow marine waters included a wide range of paleoenvironments from delta systems, to hypersaline embayments, protected lagoons, and carbonate shoals. Our overarching goal has been to collect vertebrate fossils tied to a K-Pg stratigraphic section in Africa. We provide such a section and, consistent with prior ideas, indicate that there is a gap in sedimentation in Malian rocks in the earliest Paleocene, an unconformity also proposed elsewhere in West Africa. Our phylogenetic analyses of several vertebrate clades across the K-Pg boundary have clarified clade-by-clade species-level survivorship and range extensions for multiple taxa. Few macrofossil species from the Trans-Saharan Seaway show conspicuous change at either the K-Pg boundary or the PETM based on current evidence, although results are very preliminary. Building on our earlier report of the first record of rock-boring bivalves from the Paleocene of West Africa, we further describe here a Cretaceous and Paleogene mollusk fauna dominated by taxa characteristic of the modern tropics. “This abstract has been truncated. To view the complete abstract please download the PDF”
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