Posts Tagged 'paleo'

Influences of coral genotype and seawater pCO2 on skeletal Ba/Ca and Mg/Ca in cultured massive Porites spp. corals

Highlights

• KD Ba/Ca vary significantly between massive Porites spp. coral genotypes.
• Seawater pCO2 affects KD Ba/Ca significantly in 1 of 3 coral genotypes.
• KD Mg/Ca varies significantly between some duplicates of the same coral.

Abstract

Coral skeletal Ba/Ca is a proxy for seawater Ba/Ca, used to infer oceanic upwelling and terrigenous runoff while [Mg2+] is implicated in the control of coral biomineralisation. We cultured large individuals (>12 cm diameter) of 3 genotypes of massive adult Porites spp. corals over a range of seawater pCO2 to test how atmospheric CO2 variations affect skeletal Ba/Ca and Mg/Ca. We identified the skeleton deposited after a 5 month acclimation period and analysed the skeletal Ba/Ca and Mg/Ca by secondary ion mass spectrometry. Skeletal Mg/Ca varies significantly between some duplicate colonies of the same coral genotype hampering identification of genotype and seawater pCO2 effects. Coral aragonite:seawater Ba/Ca partition coefficients (KD Ba/Ca) do not vary significantly between duplicate colonies of the same coral genotype. We observe large variations in KD Ba/Ca between different massive Porites spp. coral genotypes irrespective of seawater pCO2. These variations do not correlate with coral calcification, photosynthesis or respiration rates or with skeletal KD Mg/Ca or KD Sr/Ca. Seawater pCO2 does not significantly affect KD Ba/Ca in 2 genotypes but KD Ba/Ca is significantly higher at 750 μatm seawater pCO2 than at 180 μatm in 1 P. lutea genotype. Genotype specific variations in KD Ba/Ca between different Porites spp. could yield large errors (~250%) in reconstructions of seawater Ba when comparing Ba/Ca between corals. Analysis of fossil coral specimens deposited at low seawater pCO2, may underestimate past seawater Ba/Ca and ocean upwelling/freshwater inputs when compared with modern specimens but the effect is small in comparison with the observed difference between coral genotypes.

Continue reading ‘Influences of coral genotype and seawater pCO2 on skeletal Ba/Ca and Mg/Ca in cultured massive Porites spp. corals’

Determining climate change impacts on ecosystems: the role of palaeontology

Climate change is projected to change the ecosystems on land and in the sea at rates that are unprecedented for millions of years. The most commonly used approach to derive projections of how ecosystems will look in the future are experiments on living organisms. By their nature, experiments are unlike the real world and cannot capture the ability of organisms to migrate, select and evolve. They are often limited to a select few species and drivers of environmental change and hence cannot represent the complexity of interactions in ‘real’ ecosystems. The fossil record is an archive of responses to climate change at a global ecosystem scale. If, and only if, fossil assemblage variation is combined with independent information of environmental changes, sensitives of species or higher taxa to a specific magnitude of change of an environmental driver can be determined and used to inform future vulnerabilities of this species to the same driver. While records are often fragmented, there are time intervals which, when thoroughly analysed with quantitative data, can provide valuable insights into the future of biodiversity on this planet. This review provides an overview of projected impacts on marine ecosystems including: (1) the range of neontological methods, observations and their challenges; and (2) the complementary information that palaeontologists can contribution to this global challenge. I advocate that, in collaborations with other disciplines, we should aim for a strong visibility of our field and the knowledge it can provide for policy relevant assessments of the future.

Continue reading ‘Determining climate change impacts on ecosystems: the role of palaeontology’

Past carbonate preservation events in the deep Southeast Atlantic ocean (Cape Basin) and their implications for Atlantic overturning dynamics and marine carbon cycling

Micropaleontological and geochemical analyses reveal distinct millennial‐scale increases in carbonate preservation in the deep Southeast Atlantic (Cape Basin) during strong and prolonged Greenland interstadials that are superimposed on long‐term (orbital‐scale) changes in carbonate burial. These data suggest carbonate oversaturation of the deep Atlantic and a strengthened Atlantic Meridional Overturning Circulation (AMOC) during the most intense Greenland interstadials. However, proxy evidence from outside the Cape Basin indicates that AMOC changes also occurred during weaker and shorter Greenland interstadials. Here we revisit the link between AMOC dynamics and carbonate saturation in the deep Cape Basin over the last 400 kyr (sediment cores TN057‐21, TN057‐10, and Ocean Drilling Program Site 1089) by reconstructing centennial changes in carbonate preservation using millimeter‐scale X‐ray fluorescence (XRF) scanning data. We observe close agreement between variations in XRF Ca/Ti, sedimentary carbonate content, and foraminiferal shell fragmentation, reflecting a common control primarily through changing deep water carbonate saturation. We suggest that the high‐frequency (suborbital) component of the XRF Ca/Ti records indicates the fast and recurrent redistribution of carbonate ions in the Atlantic basin via the AMOC during both long/strong and short/weak North Atlantic climate anomalies. In contrast, the low‐frequency (orbital) XRF Ca/Ti component is interpreted to reflect slow adjustments through carbonate compensation and/or changes in the deep ocean respired carbon content. Our findings emphasize the recurrent influence of rapid AMOC variations on the marine carbonate system during past glacial periods, providing a mechanism for transferring the impacts of North Atlantic climate anomalies to the global carbon cycle via the Southern Ocean.

Continue reading ‘Past carbonate preservation events in the deep Southeast Atlantic ocean (Cape Basin) and their implications for Atlantic overturning dynamics and marine carbon cycling’

Surface ocean pH variations since 1689 CE and recent ocean acidification in the tropical South Pacific

Increasing atmospheric CO2 from man-made climate change is reducing surface ocean pH. Due to limited instrumental measurements and historical pH records in the world’s oceans, seawater pH variability at the decadal and centennial scale remains largely unknown and requires documentation. Here we present evidence of striking secular trends of decreasing pH since the late nineteenth century with pronounced interannual to decadal–interdecadal pH variability in the South Pacific Ocean from 1689 to 2011 CE. High-amplitude oceanic pH changes, likely related to atmospheric CO2 uptake and seawater dissolved inorganic carbon fluctuations, reveal a coupled relationship to sea surface temperature variations and highlight the marked influence of El Niño/Southern Oscillation and Interdecadal Pacific Oscillation. We suggest changing surface winds strength and zonal advection processes as the main drivers responsible for regional pH variability up to 1881 CE, followed by the prominent role of anthropogenic CO2 in accelerating the process of ocean acidification.

Continue reading ‘Surface ocean pH variations since 1689 CE and recent ocean acidification in the tropical South Pacific’

Reconstructing coral calcification fluid dissolved inorganic carbon chemistry from skeletal boron: An exploration of potential controls on coral aragonite B/Ca

The boron geochemistry of coral skeletons reflects the dissolved inorganic carbon (DIC) chemistry of the calcification fluid from which the skeletons precipitates and may be a valuable tool to investigate the effects of climate change on coral calcification. In this paper I calculate the predicted B/Ca of aragonite precipitating from seawater based fluids as a function of pH, [DIC] and [Ca2+]. I consider how different co-precipitating DIC species affect aragonite B/Ca and also estimate the impact of variations in the B(OH)4-/co-precipitating DIC aragonite partition coefficient (KD), which may be associated with changes in the DIC and Ca2+ chemistry of the calcification fluid. The coral skeletal B/Ca versus calcification fluid pH relationships reported previously can be reproduced by estimating B(OH)4- and co-precipitating DIC speciation as a function of pHCF and assuming that KD are constant i.e. unaffected by calcification fluid saturation state. Assuming that B(OH)4- co-precipitates with CO32-, then observed patterns can be reproduced by a fluid with approximately constant [DIC] i.e. increasing pHCF concentrates CO32-, as a function of DIC speciation. Assuming that B(OH)4- co-precipitates with HCO3- only or CO32- + HCO3- then the observed patterns can be reproduced if [DIC]CF and pHCF are positively related i.e. if DIC is increasingly concentrated in the calcification fluid at higher pHCF probably by CO2 diffusion into the calcification site

Continue reading ‘Reconstructing coral calcification fluid dissolved inorganic carbon chemistry from skeletal boron: An exploration of potential controls on coral aragonite B/Ca’

Push from the Pacific

Enhanced upwelling and CO2 degassing from the subpolar North Pacific during a warm event 14,000 years ago may have helped keep atmospheric CO2 levels high enough to propel the Earth out of the last ice age.

Continue reading ‘Push from the Pacific’

Deglacial upwelling, productivity and CO2 outgassing in the North Pacific Ocean

The interplay between ocean circulation and biological productivity affects atmospheric CO2 levels and marine oxygen concentrations. During the warming of the last deglaciation, the North Pacific experienced a peak in productivity and widespread hypoxia, with changes in circulation, iron supply and light limitation all proposed as potential drivers. Here we use the boron-isotope composition of planktic foraminifera from a sediment core in the western North Pacific to reconstruct pH and dissolved CO2 concentrations from 24,000 to 8,000 years ago. We find that the productivity peak during the Bølling–Allerød warm interval, 14,700 to 12,900 years ago, was associated with a decrease in near-surface pH and an increase in pCO2, and must therefore have been driven by increased supply of nutrient- and CO2-rich waters. In a climate model ensemble (PMIP3), the presence of large ice sheets over North America results in high rates of wind-driven upwelling within the subpolar North Pacific. We suggest that this process, combined with collapse of North Pacific Intermediate Water formation at the onset of the Bølling–Allerød, led to high rates of upwelling of water rich in nutrients and CO2, and supported the peak in productivity. The respiration of this organic matter, along with poor ventilation, probably caused the regional hypoxia. We suggest that CO2 outgassing from the North Pacific helped to maintain high atmospheric CO2 concentrations during the Bølling–Allerød and contributed to the deglacial CO2 rise.

Continue reading ‘Deglacial upwelling, productivity and CO2 outgassing in the North Pacific Ocean’


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