Marine Carbonate Production Research Articles

Carbonate factory response through the MECO (Middle Eocene Climate Optimum) event: Insight from the Apulia Carbonate Platform, Gargano Promontory, Italy

During the Eocene, shallow-water carbonate systems were significantly impacted by climate fluctuations and hyperthermal events. Following the peak temperatures of the Early Eocene Climatic Optimum (EECO), a general cooling trend began, with short-lived (⁓200 kyr) warming events occurring alongside it. In the early Bartonian (around 40.1 Ma), a warming event known as the Middle Eocene Climatic Optimum (MECO) occurred, lasting approximately 500,000 years. In this scenario, the types and calcification rates of marine organisms such as corals and larger benthic foraminifera (LBF) were influenced by global CO2 and oceanographic changes, which had a major effect on photic carbonate factories. To better understand the effects of these factors on carbonate factories, a detailed study of shallow-water facies types, distributions, and evolution was conducted. The Middle Eocene Monte Saraceno sequence, located on the eastern margin of the Apulia Carbonate Platform (Gargano Promontory, southern Italy), was selected as a case study to investigate the relationships between carbonate factory types and climatic changes around the MECO event. This study identified two distinct intervals with different modes of carbonate production, separated by a sharp boundary. The lower interval consists of clinostratified, thick beds of rudstone to floatstone, mostly made up of various large Nummulites tests, indicating an early Bartonian age (Shallow Benthic Zone 17). Instead, the upper interval consists of coral floatstone to rudstone with a packstone matrix, rich in branching corals in association with gastropods, bivalves, and rare small larger benthic foraminifera. The appearance of Heterostegina sp. and Glomalveolina ungaroi in this interval indicates a late Bartonian age (Shallow Benthic Zone 18). By integrating biostratigraphic and stable-isotope data, the lower interval, with abundant Nummulites, was linked to the MECO event, during which higher sea-surface temperatures seem to enhance larger benthic foraminifera proliferation, as already occurred in the Early Eocene. However, in the late Bartonian, the sharp transition to a coral-dominated carbonate factory, with rare larger benthic foraminifera showing smaller sizes, could be attributed to a drop in temperature that created the conditions more favourable to corals. Overall, this study provides compelling evidence of how environmental changes can affect marine carbonate production, also highlighting the importance of investigating these relationships, to better understand climate change in the past, present and near future.

Unique evolution of foraminiferal calcification to survive global changes

Foraminifera, the most ancient known calcium carbonate–producing eukaryotes, are crucial players in global biogeochemical cycles and well-used environmental indicators in biogeosciences. However, little is known about their calcification mechanisms. This impedes understanding the organismal responses to ocean acidification, which alters marine calcium carbonate production, potentially leading to biogeochemical cycle changes. We conducted comparative single-cell transcriptomics and fluorescent microscopy and identified calcium ion (Ca 2+ ) transport/secretion genes and α-carbonic anhydrases that control calcification in a foraminifer. They actively take up Ca 2+ to boost mitochondrial adenosine triphosphate synthesis during calcification but need to pump excess intracellular Ca 2+ to the calcification site to prevent cell death. Unique α-carbonic anhydrase genes induce the generation of bicarbonate and proton from multiple CO 2 sources. These control mechanisms have evolved independently since the Precambrian to enable the development of large cells and calcification despite decreasing Ca 2+ concentrations and pH in seawater. The present findings provide previously unknown insights into the calcification mechanisms and their subsequent function in enduring ocean acidification.

Eocene emergence of highly calcifying coccolithophores despite declining atmospheric CO2

Coccolithophores, a group of unicellular calcifying phytoplankton, have been major contributors to marine carbonate production since the calcite plates that they produce (coccoliths) first appeared in the fossil record over 200 million years ago (Ma). The response of this process to changes in environment on evolutionary timescales remains poorly understood, particularly in warm climates. Here we integrate a dataset consisting of carbon isotope ratios of size-separated coccolith calcite from marine sediments with a cell-scale model to interrogate cellular carbon fluxes and p_{{mathrm{CO}}_2} through the Eocene (~55–34 Ma), Earth’s hottest interval of the past 100 million years. We show that the large coccolithophores that rose to dominate the oceans through the Eocene have higher calcification-to-carbon fixation ratios than their predecessors while the opposite is true for smaller coccolithophores. These changes, which occurred in the context of increasing ocean alkalization, may have played a role in an apparent positive carbon cycle feedback to decreasing p_{{mathrm{CO}}_2}. Our approach also provides independent support of multiproxy-based evidence for general p_{{mathrm{CO}}_2} decline through the Eocene in step with temperature. Together, this challenges the emerging view that a general decline in p_{{mathrm{CO}}_2} reduces calcification on evolutionary timescales.

Calcification in free-living coralline algae is strongly influenced by morphology: Implications for susceptibility to ocean acidification

Rhodolith beds built by free-living coralline algae are important ecosystems for marine biodiversity and carbonate production. Yet, our mechanistic understanding regarding rhodolith physiology and its drivers is still limited. Using three rhodolith species with different branching morphologies, we investigated the role of morphology in species’ physiology and the implications for their susceptibility to ocean acidification (OA). For this, we determined the effects of thallus topography on diffusive boundary layer (DBL) thickness, the associated microscale oxygen and pH dynamics and their relationship with species’ metabolic and light and dark calcification rates, as well as species’ responses to short-term OA exposure. Our results show that rhodolith branching creates low-flow microenvironments that exhibit increasing DBL thickness with increasing branch length. This, together with species’ metabolic rates, determined the light-dependent pH dynamics at the algal surface, which in turn dictated species’ calcification rates. While these differences did not translate in species-specific responses to short-term OA exposure, the differences in the magnitude of diurnal pH fluctuations (~ 0.1–1.2 pH units) between species suggest potential differences in phenotypic plasticity to OA that may result in different susceptibilities to long-term OA exposure, supporting the general view that species’ ecomechanical characteristics must be considered for predicting OA responses.

Calcification of planktonic foraminifer Pulleniatina obliquiloculata controlled by seawater temperature rather than ocean acidification

Abstract Planktonic foraminifera represent a major component of global marine carbonate production, and understanding environmental influences on their calcification is critical to predicting marine carbon cycle responses to modern climate change. The present study investigated the effects of different environmental influences on calcification of the planktonic foraminifer Pulleniatina obliquiloculata. By correcting the dissolution effect on the size-normalized weight (SNW) of P. obliquiloculata from deep-sea sediments, we provide a means of estimating initial size-normalized weight (ISNW) from which to assess secular changes in the degree of calcification of P. obliquiloculata. Core-top ISNW in P. obliquiloculata from the global tropical oceans is significantly positively correlated with calcification temperature, suggesting that temperature is the dominant control on calcification. Using Neogloboquadrina dutertrei SNW as an independent deep-water Δ[CO32−] proxy, we present an ISNW record for P. obliquiloculata from the western tropical Pacific since 250 ka. The response of ISNW to past seawater temperature variations further confirms the dominant influence of temperature on P. obliquiloculata calcification. A potential increase in calcification as a result of ocean warming may have reduced oceanic uptake of CO2 from the atmosphere and increased atmospheric pCO2, generating a positive feedback for global warming.

Interactions between sediment production and transport in the geometry of carbonate platforms: Insights from forward modeling of the Great Bank of Guizhou (Early to Middle Triassic), south China

Carbonate platforms grow through the precipitation, transport, and final deposition of carbonate sediment out of seawater. Quantifying the relative contributions of initial production versus subsequent transport in determining the growth rates and geometries of platforms remains a significant challenge. In this study, stratigraphic forward modeling is used to quantify the roles of sediment production, transport, and deposition during each growth stage of a Permian-Triassic carbonate platform with a complex growth history. Parameter optimization and sensitivity analysis show that, within the range of reasonable values, the morphology of the platform is most sensitive to sediment transport, moderately sensitive to maximum carbonate production rate, and least sensitive to the productivity-depth curve. The ramp-to-high relief, steep-sloped platform transition during Early Triassic time can be explained by any factor that limits sediment transport from shallow water areas of high production to the slope and basin. Reefs may play a role in limiting sediment transport on many platforms but other processes, such as early marine cementation or carbonate production along the slope, may be equally capable of yielding this shift in platform geometry. In this particular case, early lithification of ooid and skeletal shoals on the platform margin, perhaps facilitated by unusually high carbonate saturation state of seawater, may have inhibited sediment transport into the basin prior to the development of a reef on the platform margin. Later, Anisian progradation of the platform margin can be explained by the development of a slope factory rather than requiring increased sediment transport from the platform top. The development of an escarpment margin in the Ladinian is mainly influenced by accommodation in the slope profile created by antecedent Anisian topography. A general implication from the model results is that the growth of steep-sloped carbonate platforms lacking slope factories may often be limited by transport of sediment from the platform top to accommodation on the slope rather than by the intrinsic production capacity of the platform top factory.

Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater. Mg isotopes are significantly (up to 5‰) fractionated during carbonate precipitation by preferential incorporation of 24Mg, while hydrothermal reactions are associated with negligible Mg isotope fractionation by preferential sequestration of 26Mg. Thus, the marine Mg cycle could be reflected by seawater Mg isotopic composition (δ26Mgsw), which might be recorded in marine carbonate. However, carbonates are both texturally and compositionally heterogeneous, and it is unclear which carbonate component is the most reliable for reconstructing δ26Mgsw. In this study, we measured Mg isotopic compositions of limestone samples collected from the early Carboniferous Huangjin Formation in South China. Based on petrographic studies, four carbonate components were recognized: micrite, marine cement, brachiopod shell, and mixture. The four components had distinct δ26Mg: (1) micrite samples ranged from −2.86‰ to −2.97‰; (2) pure marine cements varied from −3.40‰ to −3.54‰, while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range (−3.27‰ to −3.75‰); (3) values for the mixture component were −3.17‰ and −3.49‰; and (4) brachiopod shells ranged from −2.20‰ to −3.07‰, with the thickened hinge area enriched in 24Mg. Due to having multiple carbonate sources, neither the micrite nor the mixture component could be used to reconstruct δ26Mgsw. In addition, the marine cement was homogenous in Mg isotopes, but lacking the fractionation by inorganic carbonate precipitation that is prerequisite for the accurate determination of δ26Mgsw. Furthermore, brachiopod shells had heterogeneous C and Mg isotopes, suggesting a significant vital effect during growth. Overall, the heterogeneous δ26Mg of the Huangjin limestone makes it difficult to reconstruct δ26Mgsw using bulk carbonate/calcareous sediments. Finally, δ26Mgsw was only slightly affected by the faunal composition of carbonate-secreting organisms, even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range (0.2‰–4.8‰) of fractionation during biogenic carbonate formation.

Proton pumping accompanies calcification in foraminifera

Ongoing ocean acidification is widely reported to reduce the ability of calcifying marine organisms to produce their shells and skeletons. Whereas increased dissolution due to acidification is a largely inorganic process, strong organismal control over biomineralization influences calcification and hence complicates predicting the response of marine calcifyers. Here we show that calcification is driven by rapid transformation of bicarbonate into carbonate inside the cytoplasm, achieved by active outward proton pumping. Moreover, this proton flux is maintained over a wide range of pCO2 levels. We furthermore show that a V-type H+ ATPase is responsible for the proton flux and thereby calcification. External transformation of bicarbonate into CO2 due to the proton pumping implies that biomineralization does not rely on availability of carbonate ions, but total dissolved CO2 may not reduce calcification, thereby potentially maintaining the current global marine carbonate production.

Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures.

Biological activity is a major factor in Earth's chemical cycles, including facilitating CO2 sequestration and providing climate feedbacks. Thus a key question in Earth's evolution is when did life arise and impact hydrosphere-atmosphere-lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800-3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals from the Isua supracrustal belt (ISB), southwest Greenland. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1-4-cm-high stromatolites-macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3,700 million years ago (Ma), near the start of Earth's sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).

Microfacies, paleoenvironments and development pattern of Neoproterozoic cap carbonates in the Niari–Nyanga Basin (Congo and Gabon Republics, Central Africa)

In the Niari–Nyanga Basin, the Neoproterozoic SCI Formation of the Schisto-Calcaire Group includes a lower member (SCIa), made up of carbonates and corresponding to the cap carbonate that unconformably overlies the Marinoan glacial diamictite. Petrographic analysis of carbonate and terrigenous rocks from seven stratigraphic sections of the Niari–Nyanga Basin led to define six microfacies (MF0 to MF5). The vertical and lateral variations of the cap carbonate microfacies suggest a shallow-water carbonate system with a dominating microbial carbonate factory. The area of carbonate production migrated through time to the South-West prior to the final demise of the carbonate system in the basin. Such a transition is marked by a sharp negative excursion in bulk carbon and oxygen isotope ratios, that is widely correlatable across the basin, at the top of the SCIa dolostones. The presence of depositional features, such as oolites, peloidal stromatolites with fenestral structures, together with evidences of early leaching of carbonate grains within the SCIa member and at the base of the SCIb member strongly suggest a peritidal marine carbonate production in the Niari–Nyanga Basin, during the deposition of the cap carbonate.

Climatic and eustatic signals in a global compilation of shallow marine carbonate accumulation rates

AbstractTwo of the most important factors that control the accumulation rate of material in carbonate platform environments on geological time scales are climate and eustasy. Accurately assessing the importance of these inter‐related factors through the study of both modern and ancient carbonate facies, however, is problematic. These difficulties arise from both the complexities inherent in carbonate depositional systems and the demonstrable incompleteness of the stratigraphic record. Here, a new compilation of more than 19 000 global Phanerozoic shallow marine carbonate accumulation rates derived from nearly 300 individual stratigraphic sections is presented. These data provide the first global holistic view of changes in shallow marine carbonate production in response to climate and eustasy on geological time scales. Notably, a clear latitudinal dependence on carbonate accumulation rates is recognized in the data. Moreover, it can also be demonstrated that rates calculated across the last glacial maximum and Holocene track changes in sea‐level. In detail, the data show that globally averaged changes in carbonate accumulation rates lagged changes in sea‐level by ca 3 kyr, reflecting the commonly observed delay in the response of individual carbonate successions to sea‐level rise. Differences between the rates of carbonate accumulation and sea‐level change over the past 25 kyr ostensibly reflect changing accumulation mode, with platform drowning (give‐up mode) pervasive during peak Early Holocene sea‐level rise, followed by a switch to catch‐up mode accumulation from ca 9 ka to the present. Carbonate accumulation rates older than the Quaternary are typically calculated over time spans much greater than 100 kyr, and at these time spans, rates primarily reflect long‐term tectonically mediated accommodation space changes rather than shorter term changes in climate/eustasy. This finding, coupled with issues of stratigraphic incompleteness and data abundance, tempers the utility of this and other compilations for assessing accurately the role of climate and eustasy in mediating carbonate accumulation rates through geological time.

100-year ecosystem history elucidated from inner shelf sediments off the Pearl River estuary, China

In this paper, we analyze the organic geochemistry of four sediment cores recovered from a cross-shelf transect offshore from the Pearl River Estuary, China, in an attempt to determine the impact of anthropogenic activity on carbon burial and phytoplankton community structure over the past century. Downcore total organic carbon (TOC) was found to be predominantly of marine origin, as indicated by the TOC:TN ratio, δ13Corg, and the branched and isoprenoid tetraether (BIT) index. Profiles of degradation-corrected marine organic carbon (MOCcorr) show an asynchronous history, with a gradual increase beginning in the 1940s at the proximal sites (A9 and A7), in the 1970s at the central site (A6), and after 2000 at the distal site (A5). Following this gradual increase, a concurrent but more rapid rise in MOCcorr occurred after about 1980, except at site A5. This rise in MOCcorr is probably associated with enhanced primary productivity related to an increase in the fluvial nutrient influx, as indicated by upcore increases in δ13Corg, δ15N, and phyto-sterol lipids. At sites A7 and A6, phyto-sterol compound ratios suggest a progressive decrease in diatoms, but an increase in non-diatom algae in the community since the 1940s. However, inshore at site A9, the community structure, as well as δ15N, remained almost unchanged. Distance from the shore may be one cause of the asynchronous increase in MOCcorr along the cross-shelf transect. However, our results imply that changes in community structure may also modulate MOC burial by partially offsetting the effect of growth in primary productivity. In addition, the CaCO3:MOCcorr ratio decreased significantly at sites A7 and A6 over the past 30years, which may suggest a relative decrease in marine carbonate production that may have acted as a negative feedback to limit atmospheric CO2 rises.

Incorporating nutrients as a limiting factor in carbonate modelling

Nowadays, the use of process-based numerical models to predict facies distribution and stratal architecture constitutes an essential tool in sedimentary basin analysis. One of these models, the SIMSAFADIM-CLASTIC program, simulates clastic transport and sedimentation in three dimensions together with autochthonous marine carbonate production. In this code, carbonate modelling mainly follows predator–prey relationships among species associations based on Lotka–Volterra equations. The carbonate model also considers other environmental factors such as the presence of siliciclastic sediments and carbonate mud in suspension and water depth. Although these parameters are important, carbonate producers are largely conditioned by other variables, which have to be taken into account in order to obtain a more realistic approach. In this contribution, nutrient availability is added as a new limiting environmental parameter, which exerts control over carbonate producing organisms. A synthetic sample experiment is used to show that inclusion of nutrient availability is critical to reproduce carbonate lithofacies heterogeneity in a more accurate temporal and spatial disposition as a function of trophic resources.

Orbitally forced climate and sea-level changes in the Paleoceanic Tethyan domain (marl–limestone alternations, Lower Kimmeridgian, SE France)

High-resolution analysis of multiple climatic proxies was carried out on a ∼ 8.5-m Lower Kimmeridgian interval of a pelagic marl–limestone succession at Châteauneuf-d'Oze (Vocontian Basin, southeastern France). The aim of the study was to characterize the orbitally controlled sedimentary cyclicity and to decipher paleoclimatic and paleoceanographic changes. All analysed proxies (magnetic susceptibility, carbonate content, manganese content, and bulk carbon and oxygen stable isotopes ( δ 13C and δ 18O) respond in synchrony to orbitally forced climate change. Precession index cycles modulated by short (∼ 100 kyr) eccentricity cycles are strongly expressed in magnetic susceptibility, carbonate and Mn contents but less so in δ 18O. Obliquity cycles are expressed in manganese and particularly in δ 13C. The orbital forcing was conferred to these rhythmic pelagic sediments via paleoclimatic and paleoceanographic changes as follows. Detrital input and marine carbonate production are recorded by the magnetic susceptibility and carbonate signals with strong precession cyclicity. Calcareous nannofossil analysis shows the omnipresence of coccoliths and debris of coccoliths in the marls and limestones, suggesting that the carbonate production was in largest part in situ. Precession index may exert oscillations in the antagonist marine surface productivity and detrital flux processes via solar radiation change. Oxygenation of the seafloor leading to redox cycles is detected in the manganese signal and supported by the δ 13C record, with a strong expression of the obliquity. Finally, paleotemperature variations were deduced from the δ 18O record, although this latter has been in part perturbed by diagenesis. In sum, the variations in the studied proxies suggest a depositional model of combined climate and sea-level cycles forced in concert by Earth's orbital parameters. In particular, the limestones represent warmer climates and higher sea-levels and the marls colder climates and lower sea-levels. This depositional model concurs with a previous depositional model of deep-water carbonates of the German Kimmeridgian, while is in opposition to a previous one of the same section in the Vocontian Basin.

Estimation of in situ distribution of carbonate produced from cold-water octocorals on a Japanese seamount in the NW Pacific

The importance of the deep, cold-water hexacorals as cold-water bioherms and their contribution to marine carbonate production has been demonstrated elsewhere. However, no research has been carried out to examine the contribution of carbonate production by deep, cold- water octocorals (CWOC), even though this group comprises a major component of cold-water coral fauna in the NW Pacific. To assess the contribution of CWOC carbonate production on the Shiribeshi Seamount (43° 34-36' N, 139° 31-35' E), Sea of Japan, remotely operated vehicle (ROV) dive video archives and deposited specimens of Primnoa pacifica (Octocorallia, Primnoidae) were analysed. To estimate the carbonate weight per colony, the diameter of cross-sections of branches or stems and the carbonate weight per volume of specimens were measured. Colony volumes were then calculated from the video footage. The amount of carbonate standing stock (CSS) was calculated at each dive line by analysing the distribution of CWOC and specimen data. The average (± SD) weight percent- age of sclerites per colony of P. pacifica was 37.93 ± 7.45%, with the range 25.47 to 49.19%. It was estimated that the total amount of CSS of coral would be over 0.65 t at all dive lines (22 753 m 2 ) at the seamount. Maximum CSS was 70.64 g m -2 and maximum carbonate production was up to 3.61 ± 0.06 g m -2 yr -1 . In comparison with the other CSS in non-tropical areas, our results show that CWOC may potentially contribute to carbonate production in cold-water environments.

Secular environmental precursors to Early Toarcian (Jurassic) extreme climate changes

The Early Toarcian Oceanic Anoxic Event (T-OAE), about 183 myr ago, was a global event of environmental and carbon cycle perturbations, which deeply affected both marine biota and carbonate production. Nevertheless, the long-term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood. Here we present a similar to 8 myr-long record of Early Pliensbachian-Middle Toarcian environmental changes from the Lusitanian Basin, Portugal, in order to address the long-term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the T-OAE. Paleotemperature estimates derived from the oxygen isotope compositions of well-reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees C cooling in the Late Pliensbachian (margaritatus-spinatum ammonite Zones boundary). This cooling event is followed by a marked similar to 7-10 degrees C seawater warming in the Early Toarcian that, after a second cooling event in the mid-polymorphum Zone, culminates during the T-OAE. Calcium carbonate (CaCO3) contents, the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer Schizosphaerella, all largely covary with paleotemperatures, indicating a coupling between climatic conditions and both pelagic and neritic CaCO3 production. Furthermore, the cooling and warming episodes coincided with major marine regressions and transgressions, respectively, suggesting that the growth and decay of ice caps may have exerted a strong control on sea-level fluctuations throughout the studied time interval. This revised chronology of environmental changes shows important similarities with Neogene and Paleozoic episodes of deglacial black shale formation, and thus prompts the reevaluation of ice sheet dynamics as a possible agent of Mesozoic events of extinction and organic-rich sedimentation. (C) 2010 Elsevier B.V. All rights reserved.

SIMSAFADIM-CLASTIC: A new approach to mathematical 3D forward simulation modelling for terrigenous and carbonate marine sedimentation

Most sedimentary modelling programs developed in recent years focus on either terrigenous or carbonate marine sedimentation. Nevertheless, only a few programs have attempted to consider mixed terrigenous-carbonate sedimentation, and most of these are two-dimensional, which is a major restriction since geological processes take place in 3D. This paper presents the basic concepts of a new 3D mathematical forward simulation model for clastic sediments, which was developed from SIMSAFADIM, a previous 3D carbonate sedimentation model. The new extended model, SIMSAFADIM-CLASTIC, simulates processes of autochthonous marine carbonate production and accumulation, together with clastic transport and sedimentation in three dimensions of both carbonate and terrigenous sediments. Other models and modelling strategies may also provide realistic and efficient tools for prediction of stratigraphic architecture and facies distribution of sedimentary deposits. However, SIMSAFADIM-CLASTIC becomes an innovative model that attempts to simulate different sediment types using a process-based approach, therefore being a useful tool for 3D prediction of stratigraphic architecture and facies distribution in sedimentary basins. This model is applied to the neogene Valles-Penedes half-graben (western Mediterranean, NE Spain) to show the capacity of the program when applied to a realistic geologic situation involving interactions between terrigenous clastics and carbonate sediments.

Modeling the marine aragonite cycle: changes under rising carbon dioxide and its role in shallow water CaCO<sub>3</sub> dissolution

Abstract. The marine aragonite cycle has been included in the global biogeochemical model PISCES to study the role of aragonite in shallow water CaCO3 dissolution. Aragonite production is parameterized as a function of mesozooplankton biomass and aragonite saturation state of ambient waters. Observation-based estimates of marine carbonate production and dissolution are well reproduced by the model and about 60% of the combined CaCO3 water column dissolution from aragonite and calcite is simulated above 2000 m. In contrast, a calcite-only version yields a much smaller fraction. This suggests that the aragonite cycle should be included in models for a realistic representation of CaCO3 dissolution and alkalinity. For the SRES A2 CO2 scenario, production rates of aragonite are projected to notably decrease after 2050. By the end of this century, global aragonite production is reduced by 29% and total CaCO3 production by 19% relative to pre-industrial. Geographically, the effect from increasing atmospheric CO2, and the subsequent reduction in saturation state, is largest in the subpolar and polar areas where the modeled aragonite production is projected to decrease by 65% until 2100.

Antarctic records of precession‐paced insolation‐driven warming during early Pleistocene Marine Isotope Stage 31

Precisely dated Antarctic continental margin and Southern Ocean geological records show that the early Pleistocene interglacial Marine Isotope Stage 31 (MIS‐31) was characterized by warmer than present surface waters with reduced sea‐ice and enhanced high latitude marine carbonate production. Micropaleontologic, isotopic, and paleomagnetic evidence from drill cores at 77°S (Cape Roberts Project‐1) and 53°S (ODP Site 1094) indicate circumantarctic changes in sea surface temperature and water mass stratification that are in phase with high southern latitude insolation changes during MIS‐31. These changes imply a significant, though as yet unquantifiable reduction in Antarctic ice volume. This study supports the hypothesis that the interhemispheric antiphased relationship of the precession cycle attenuates a potentially significant Antarctic ice volume signal in the deep sea oxygen isotope record. The implications are that Antarctic marine ice sheets may be more susceptible to warming and high insolation driven retreat than has been widely recognized.

Assessing the potential long-term increase of oceanic fossil fuel CO<sub>2</sub> uptake due to CO<sub>2</sub>-calcification feedback

Abstract. Plankton manipulation experiments exhibit a wide range of sensitivities of biogenic calcification to simulated anthropogenic acidification of the ocean, with the "lab rat" of planktic calcifiers, Emiliania huxleyi apparently not representative of calcification generally. We assess the implications of this observational uncertainty by creating an ensemble of realizations of an Earth system model that encapsulates a comparable range of uncertainty in calcification response to ocean acidification. We predict that a substantial reduction in marine carbonate production is possible in the future, with enhanced ocean CO2 sequestration across the model ensemble driving a 4–13% reduction in the year 3000 atmospheric fossil fuel CO2 burden. Concurrent changes in ocean circulation and surface temperatures in the model contribute about one third to the increase in CO2 uptake. We find that uncertainty in the predicted strength of CO2-calcification feedback seems to be dominated by the assumption as to which species of calcifier contribute most to carbonate production in the open ocean.