Posts Tagged 'protists'

The magnitude of surface ocean acidification and carbon release during Eocene Thermal Maximum 2 (ETM‐2) and the Paleocene–Eocene Thermal Maximum (PETM)

Eocene Thermal Maximum 2 (ETM‐2; 54.1 Ma) was the second largest Eocene hyperthermal. Like the Paleocene–Eocene Thermal Maximum (PETM), ETM‐2 was characterized by massive carbon emissions and several degrees of global warming, thus can serve as a case study for assessing the impacts of rapid CO2 emissions on ocean carbonate chemistry, biota and climate. Marine carbonate records of ETM‐2 are better preserved than those of the PETM due to more subdued carbonate dissolution. As yet, however, the magnitude of this carbon cycle perturbation has not been well constrained. Here, we present the first records of surface ocean acidification for ETM‐2, based on stable boron isotope records in mixed‐layer planktic foraminifera from two mid‐latitude ODP Sites (1210 in the N. Pacific and 1265 in the S.E. Atlantic), which indicate conservative minimum global sea surface acidification of –0.20 +0.12/–0.13 pH units. Using these estimates of pH and temperature as constraints on carbon cycle model simulations, we conclude that the total mass of C, released over a period of 15 to 25 kyr during ETM‐2, likely ranged from 2,600 to 3,800 Gt C, which is greater than previously estimated on the basis of other observations (i.e., stable carbon isotopes and carbonate compensation depth) alone.

Continue reading ‘The magnitude of surface ocean acidification and carbon release during Eocene Thermal Maximum 2 (ETM‐2) and the Paleocene–Eocene Thermal Maximum (PETM)’

Responses of symbiotic cnidarians to environmental change

As climate change intensifies, the capacity of organisms to adapt to changing environments becomes increasingly relevant. Heat-induced coral bleaching –the breakdown of the symbiotic association between coral hosts and photosynthetic algae of the family Symbiodiniaceae– is rapidly degrading reefs worldwide. Hence, there is a growing interest to study symbioses that can persist in extreme conditions. The Red Sea is such a place, known as one of the hottest seas where healthy coral reef systems thrive. Here (Chapter 1), we tested the potential of symbiont manipulation as means to improve the thermal resilience of the cnidarian holobiont, particularly using heat tolerant symbiont species from the Red Sea. We used clonal lineages of the model system Aiptasia (host and symbiont), originating from different thermal environments to assess how interchanging either partner affected their short- and long-term performance under heat stress. Our findings revealed that symbioses are not only intra-specific but have also adapted to native, local environments, thus potentially limiting the acclimation capacity of symbiotic cnidarians to climate change. As such, infection with more heat resistant species, even if native, might not necessarily improve thermotolerance of the holobiont. We further investigated (Chapter 2) how environment-dependent specificity, in this case elevated temperature, affects the establishment of novel symbioses. That is, if Aiptasia hosts are, despite exhibiting a high degree of partner fidelity, capable of acquiring more thermotolerant symbionts under stress conditions. Thus, we examined the infection dynamics of multi-species symbioses under different thermal environments and assessed their performance to subsequent heat stress. We showed that temperature, more than host identity, plays a critical role in symbiont uptake and overall performance when heatchallenged. Additionally, we found that pre-exposure to high temperature plays a fundamental role in improving the response to thermal stress, yet, this can be heavily influenced by other factors like feeding. Like climate change, ocean acidification is a serious threat to corals. Yet, most research has focused on the host and little is known for the algal partner. Thus, here we studied (Chapter 3) the global transcriptomic response of an endosymbiotic dinoflagellate to long-term seawater acidification stress. Our results revealed that despite observing an enrichment of processes related to photosynthesis and carbon fixation, which might seem beneficial to the symbiont, low pH has a detrimental effect on its photo-physiology. Taken together, this dissertation provides valuable insights into the responses of symbiotic cnidarians to future climate and ocean changes.

Continue reading ‘Responses of symbiotic cnidarians to environmental change’

Reconstructing 800 years of carbonate ion concentration in the Cariaco basin using the area density of planktonic foraminifera shells

Anthropogenically mediated ocean acidification (OA) has negative impacts on many marine organisms, especially calcifiers. However, systematic measurements of OA have only been made over the past four decades. In order to improve future predictions and understand how ongoing OA compares to natural variability on longer timescales, it is critical to extend records beyond observational time series. In the Cariaco Basin, located in the tropical Atlantic, near‐surface dissolved inorganic carbon reflects atmospheric carbon dioxide concentrations (CO2) since the Industrial Revolution, making it an ideal site for examining longer‐term variability. We extend the record of Cariaco Basin near‐surface [CO32−] back to 1240 CE, using the area density (shell weight (μg)/shell area (μm2)) of the planktonic foraminifer Globigerinoides ruber (pink). Multidecadal variability is observed throughout the record. Since the Industrial Revolution (1760–2007 CE), [CO32−] has declined by 0.22 μmol kg−1 year−1, in agreement with the magnitude and direction of change captured in the shorter instrumental time series. During the Little Ice Age (1500–1760 CE), a period marked by regional drought, substantial variability but no long‐term trend is observed, while a decrease in [CO32−] of 0.11 μmol kg−1 y−1 occurs at the end of the Medieval Climate Anomaly (MCA) (1240 – 1500 CE). Both the MCA and Little Ice Age contain substantial natural variability in near surface [CO32−] that we attribute to changes in regional upwelling and atmospheric CO2. However, the decline in [CO32−] occurring in the Post‐Industrial Period is anomalous against a backdrop of 800 years of natural variability, reflecting OA associated with anthropogenic increases in atmospheric CO2.

Continue reading ‘Reconstructing 800 years of carbonate ion concentration in the Cariaco basin using the area density of planktonic foraminifera shells’

Decadal variability in twentieth-century ocean acidification in the California Current Ecosystem

Oceanic uptake of CO2 can mitigate climate change, but also results in global ocean acidification. Ocean acidification-related changes to the marine carbonate system can disturb ecosystems and hinder calcification by some organisms. Here, we use the calcification response of planktonic foraminifera as a tool to reconstruct the progression of ocean acidification in the California Current Ecosystem through the twentieth century. Measurements of nearly 2,000 fossil foraminifera shell weights and areas preserved in a marine sediment core showed a 20% reduction in calcification by a surface-dwelling foraminifera species. Using modern calibrations, this response translates to an estimated 35% reduction in carbonate ion concentration, a biologically important chemical component of the carbonate system. Assuming other aspects of the carbonate system, this represents a 0.21 decline in pH, exceeding the estimated global average decline by more than a factor of two. Our proxy record also shows considerable variability that is significantly correlated with Pacific Decadal Oscillation and decadal-scale changes in upwelling strength, a relationship that until now has been obscured by the relatively short observational record. This modulation suggests that climatic variations will play an important role in amplifying or alleviating the anthropogenic signal and progression of ocean acidification in this region.

Continue reading ‘Decadal variability in twentieth-century ocean acidification in the California Current Ecosystem’

Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact

Debate lingers over what caused the last mass extinction 66 million years ago, with intense volcanism and extraterrestrial impact the most widely supported hypotheses. However, without empirical evidence for either’s exact environmental effects, it is difficult to discern which was most important in driving extinction. It is also unclear why recovery of biodiversity and carbon cycling in the oceans was so slow after an apparently sudden extinction event. In this paper, we show (using boron isotopes and Earth system modeling) that the impact caused rapid ocean acidification, and that the resulting ecological collapse in the oceans had long-lasting effects for global carbon cycling and climate. Our data suggest that impact, not volcanism, was key in driving end-Cretaceous mass extinction.

Continue reading ‘Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact’

Reduced continental weathering and marine calcification linked to late Neogene decline in atmospheric CO2

The globally averaged calcite compensation depth has deepened by several hundred metres in the past 15 Myr. This deepening has previously been interpreted to reflect increased alkalinity supply to the ocean driven by enhanced continental weathering due to the Himalayan orogeny during the late Neogene period. Here we examine mass accumulation rates of the main marine calcifying groups and show that global accumulation of pelagic carbonates has decreased from the late Miocene epoch to the late Pleistocene epoch even though CaCO3 preservation has improved, suggesting a decrease in weathering alkalinity input to the ocean, thus opposing expectations from the Himalayan uplift hypothesis. Instead, changes in relative contributions of coccoliths and planktonic foraminifera to the pelagic carbonates in relative shallow sites, where dissolution has not taken its toll, suggest that coccolith production in the euphotic zone decreased concomitantly with the reduction in weathering alkalinity inputs as registered by the decline in pelagic carbonate accumulation. Our work highlights a mechanism whereby, in addition to deep-sea dissolution, changes in marine calcification acted to modulate carbonate compensation in response to reduced weathering linked to the late Neogene cooling and decline in atmospheric partial pressure of carbon dioxide.

Continue reading ‘Reduced continental weathering and marine calcification linked to late Neogene decline in atmospheric CO2’

Evaluating the planktic foraminiferal B/Ca proxy for application to deep time paleoceanography

Highlights

  • Paleocene seawater chemistry affects planktic foraminifer boron/calcium proxy sensitivity.
  • T. sacculifer and O. universa shell boron content is similar to that of Paleogene species.
  • We present a new framework for applying B/Ca calibrations to the early Cenozoic.
  • Our new approach allows application of calibrations from modern species to extinct ones.

Abstract

The Cenozoic Era has been characterized by large perturbations to the oceanic carbon cycle and global climatic changes, but quantifying the magnitude and cause of these shifts is still subject to considerable uncertainty. The boron/calcium (B/Ca) ratio of fossil planktic foraminifera shells is a promising tool for reconstructing surface ocean carbonate chemistry during such events. Previous studies indicate that symbiont-bearing, planktic foraminiferal B/Ca depends on the [B(OH)4− /DIC] ratio of seawater and potentially, when combined with foraminiferal δ11 B proxy reconstructions of B(OH)4− , an opportunity to reconstruct surface ocean DIC in the geologic past. There are, however, two barriers towards interpreting records from the pre-Pleistocene era: (1) changes in seawater major ion chemistry in the past might have affected foraminiferal B/Ca; and (2) modern foraminifera species show variable B/Ca calibration sensitivities that cannot be constrained in now-extinct species. Here we address these challenges with new experiments in which we have cultured modern, symbiont-bearing foraminifera Globigerinoides ruber (pink) and Trilobatus sacculifer in seawater with simulated early Cenozoic seawater chemistry (high [Ca], low [Mg], and low [B]T). We explore mechanisms that can account for the inter-species trends that are observed in foraminiferal B/Ca, and propose a framework that can be used to apply B/Ca calibrations to now-extinct species for reconstructing climate perturbations under varying seawater chemistries.

Continue reading ‘Evaluating the planktic foraminiferal B/Ca proxy for application to deep time paleoceanography’


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Ocean acidification in the IPCC AR5 WG II

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