Posts Tagged 'protists'

Modern planktic foraminifers in the high-latitude ocean

Highlights

  • We review the knowledge on modern high-latitude planktic foraminifers.
  • Subpolar species currently invade higher latitudes.
  • Climate change affects phenology, seawater pH, and carbon turnover.
  • Modern planktic foraminifers are briefly discussed for their paleoceanographic significance.


Abstract

Planktic foraminifers can be sensitive indicators of the changing environment including both the Arctic Ocean and Southern Ocean. Due to variability in their ecology, biology, test characteristics, and fossil preservation in marine sediments, they serve as valuable archives in paleoceanography and climate geochemistry over the geologic time scale. Foraminifers are sensitive to, and can therefore provide proxy data on ambient water temperature, salinity, carbonate chemistry, and trophic conditions through shifts in assemblage (species) composition and the shell chemistry of individual specimens. Production and dissolution of the calcareous shell, as well as growth and remineralization of the cytoplasm, affect the carbonate counter pump and to a lesser extent the soft-tissue pump, at varying regional and temporal scales. Diversity of planktic foraminifers in polar waters is low in comparison to lower latitudes and is limited to three native species: Neogloboquadrina pachyderma, Turborotalita quinqueloba, and Globigerina bulloides, of which N. pachyderma is best adapted to polar conditions in the surface ocean. Neogloboquadrina pachyderma hibernates in brine channels in the lower layers of the Antarctic sea ice, a strategy that is presently undescribed in the Arctic. In open Antarctic and Arctic surface waters T. quinqueloba and G. bulloides increase in abundance at lower polar to subpolar latitudes and Globigerinita uvula, Turborotalita humilis, Globigerinita glutinata, Globorotalia inflata, and Globorotalia crassaformis complement the assemblages. Over the past two to three decades there has been a marked increase in the abundance of Orcadia riedeli and G. uvula in the subpolar and polar Indian Ocean, as well as in the northern North Atlantic. This paper presents a review of the knowledge of polar and subpolar planktic foraminifers. Particular emphasis is placed on the response of foraminifers to modern warming and ocean acidification at high latitudes and the implications for data interpretation in paleoceanography and paleoclimate research.

Continue reading ‘Modern planktic foraminifers in the high-latitude ocean’

The survival, recovery, and diversification of metazoan reef ecosystems following the end-Permian mass extinction event

The Triassic Period records important ecological transitions in the aftermath of the end-Permian mass extinction and is a key interval in the evolution of modern coral reefs. There have been several critical developments in our understanding of Triassic reef evolution over the past decade: the timing of events and duration of stages have changed dramatically; the discovery of metazoan reefs in the Early Triassic; details about the environmental perturbations that drove the extinction; the relationship between tectonic activity and platform margin reef proliferation; and additional proxy evidence for the co-evolution of coral reef-builders and their photosymbionts. Here, we provide an up-to-date synthesis of reef collapse and recovery dynamics following the end-Permian extinction, specifically integrating recent discoveries. The evolution of reef ecosystems can be divided into five phases based on their composition. 1) Microbial-metazoan reefs represent survival communities that characterize the immediate extinction aftermath. 2) The re-establishment of reefs built by metazoans (small sponge biostromes and bivalve buildups) is observed in oxygenated settings in the Olenekian (Early Triassic). 3) Towards the end of the Olenekian and into the Anisian (Middle Triassic) low-diversity, “Tubiphytes”-dominated reefs formed, which represent the first Triassic platform-margin reefs; platform-margin reefs, however, are not widespread until the late Anisian. 4) Late Anisian reefs also record a composition change and increase in species richness with sponges and “Tubiphytes” as the main reef builders. 5) The first scleractinian corals (which are the main reef builder in modern marine reef ecosystems) evolved during the Anisian but are not reported as dominant reef builders until the Late Triassic. The radiation of coral reefs is posited to be coupled to the acquisition of photosymbionts (e.g., zooxanthellae). There is clearly a stepwise evolution of reef types during the Triassic; however, once each reef type appears it persists throughout the remainder of the Triassic. The survival, recovery, and diversification of reef ecosystems is, therefore, more complex than previously outlined, particularly with respect to the earliest post-extinction ecosystems. These recent advances highlight the need to thoroughly document the faunal compositions of understudied reef systems as well as to continue the exploration of Triassic ecosystems in underrepresented regions.

Continue reading ‘The survival, recovery, and diversification of metazoan reef ecosystems following the end-Permian mass extinction event’

Calibration of the carbon isotope composition (δ13C) of benthic foraminifera

The carbon isotope composition (δ13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ13C of foraminifera tests. Here more than 1700 δ13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ13C of dissolved inorganic carbon (δ13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between δ13CCibnat and δ13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (−2.6 ± 0.4) × 10−3‰/(μmol kg−1) [CO32−] and pressure (−4.9 ± 1.7) × 10−5‰ m−1 (depth) effects, which we use to propose a new global calibration for predicting δ13CDICnat from δ13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ13CDICnat = δ13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ13C record.

Continue reading ‘Calibration of the carbon isotope composition (δ13C) of benthic foraminifera’

Combined impacts of ocean acidification and dysoxia on survival and growth of four agglutinating foraminifera

Agglutinated foraminifera create a shell by assembling particles from the sediment and comprise a significant part of the foraminiferal fauna. Despite their high abundance and diversity, their response to environmental perturbations and climate change is relatively poorly studied. Here we present results from a culture experiment with four different species of agglutinating foraminifera incubated in artificial substrate and exposed to different pCO2 conditions, in either dysoxic or oxic settings. We observed species-specific reactions (i.e., reduced or increased chamber formation rates) to dysoxia and/or acidification. While chamber addition and/or survival rates of Miliammina fusca and Trochammina inflata were negatively impacted by either dysoxia or acidification, respectively, Textularia tenuissima and Spiroplectammina biformis had the highest survivorship and chamber addition rates with combined high pCO2 (2000 ppm) and low O2 (0.7 ml/l) conditions. The differential response of these species indicates that not all agglutinating foraminifera are well-adapted to conditions induced by predicted climate change, which may result in a shift in foraminiferal community composition.

Continue reading ‘Combined impacts of ocean acidification and dysoxia on survival and growth of four agglutinating foraminifera’

Size-dependent response of foraminiferal calcification to seawater carbonate chemistry (update)

The response of the marine carbon cycle to changes in atmospheric CO2 concentrations will be determined, in part, by the relative response of calcifying and non-calcifying organisms to global change. Planktonic foraminifera are responsible for a quarter or more of global carbonate production, therefore understanding the sensitivity of calcification in these organisms to environmental change is critical. Despite this, there remains little consensus as to whether, or to what extent, chemical and physical factors affect foraminiferal calcification. To address this, we directly test the effect of multiple controls on calcification in culture experiments and core-top measurements of Globigerinoides ruber. We find that two factors, body size and the carbonate system, strongly influence calcification intensity in life, but that exposure to corrosive bottom waters can overprint this signal post mortem. Using a simple model for the addition of calcite through ontogeny, we show that variable body size between and within datasets could complicate studies that examine environmental controls on foraminiferal shell weight. In addition, we suggest that size could ultimately play a role in determining whether calcification will increase or decrease with acidification. Our models highlight that knowledge of the specific morphological and physiological mechanisms driving ontogenetic change in calcification in different species will be critical in predicting the response of foraminiferal calcification to future change in atmospheric pCO2.

Continue reading ‘Size-dependent response of foraminiferal calcification to seawater carbonate chemistry (update)’

Extinction, dissolution, and possible ocean acidification prior to the Cretaceous/Paleogene (K/Pg) boundary in the tropical Pacific

Biotic perturbations and changes in ocean circulation during the Maastrichtian stage of the latest Cretaceous raise questions about whether the biosphere was preconditioned for the end-Cretaceous mass extinction of calcareous plankton. A brief acme of inoceramid clams at ~ 71 Ma on Shatsky Rise in the tropical North Pacific was followed by their extinction during the “mid-Maastrichtian event” at 70.1 Ma associated with an abrupt warming of deep waters. This was later followed by an interval of intense dissolution beginning ~ 67.8 Ma at ODP Site 1209 (2387 m). The late Maastrichtian dissolution interval was initially gradual, and is characterized by a low planktic/benthic (P/B) ratio, highly fragmented planktic foraminifera, mostly an absence of larger taxa, low abundances of smaller taxa, extremely low planktic foraminiferal numbers, and low planktic foraminiferal and nannofossil species richness. A partial recovery in carbonate preservation and calcareous plankton simple diversity began ~ 250 kyr prior to the K/Pg boundary associated with the incursion of a younger (more enriched δ13C) deep water mass, although total abundances of planktic foraminifera in the sediment remained a tiny fraction of their earlier Maastrichtian values. A second, brief dissolution event occurred ~ 200 kyr before the boundary evidenced by renewed increase in planktic fragmentation, but without a decrease in P/B ratio. Our data show that changing deep water masses, coupled with reduced productivity and associated decrease in pelagic carbonate flux was responsible for the first ~ 1.6-Myr dissolution interval, while Deccan Traps volcanism (?) may have caused surface ocean acidification ~ 200 kyr prior to the K/Pg mass extinction event.

Continue reading ‘Extinction, dissolution, and possible ocean acidification prior to the Cretaceous/Paleogene (K/Pg) boundary in the tropical Pacific’

Sulfur in foraminiferal calcite as a potential proxy for seawater carbonate ion concentration

Sulfur (S) incorporation in foraminiferal shells is hypothesized to change with carbonate ion concentration [ ], due to substitution of sulfate for carbonate ions in the calcite crystal lattice. Hence S/Ca values of foraminiferal carbonate shells are expected to reflect sea water carbonate chemistry. To generate a proxy calibration linking the incorporation of S into foraminiferal calcite to carbonate chemistry, we cultured juvenile clones of the larger benthic species Amphistegina gibbosa and Sorites marginalis over a 350–1200 ppm range of pCO2 values, corresponding to a range in [ ] of 93 to 211 μmol/kg. We also investigated the potential effect of salinity on S incorporation by culturing juvenile Amphistegina lessonii over a large salinity gradient (25–45). Results show S/CaCALCITE is not impacted by salinity, but increases with increasing pCO2 (and thus decreasing [ ] and pH), indicating S incorporation may be used as a proxy for [ ]. Higher S incorporation in high-Mg species S. marginalis suggests a superimposed biomineralization effect on the incorporation of S. Microprobe imaging reveals co-occurring banding of Mg and S in Amphistegina lessonii, which is in line with a strong biological control and might explain higher S incorporation in high Mg species. Provided a species-specific calibration is available, foraminiferal S/Ca values might add a valuable new tool for reconstructing past ocean carbonate chemistry.

Continue reading ‘Sulfur in foraminiferal calcite as a potential proxy for seawater carbonate ion concentration’


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Ocean acidification in the IPCC AR5 WG II

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