211 research outputs found
High temperature decreases the PIC / POC ratio and increases phosphorus requirements in <i>Coccolithus pelagicus</i> (Haptophyta)
Rising ocean temperatures will likely increase stratification of the water
column and reduce nutrient input into the photic zone. This will increase the
likelihood of nutrient limitation in marine microalgae, leading to changes in
the abundance and composition of phytoplankton communities, which in turn
will affect global biogeochemical cycles. Calcifying algae, such as
coccolithophores, influence the carbon cycle by fixing CO<sub>2</sub> into
particulate organic carbon through photosynthesis (POC production) and into
particulate inorganic carbon through calcification (PIC production). As
calcification produces a net release of CO<sub>2</sub>, the ratio of PIC to POC
production determines whether coccolithophores act as a source (high PIC / POC)
or a sink (low PIC / POC) of atmospheric CO<sub>2</sub>. We studied the effect of
phosphorus (P-) limitation and high temperature on the physiology and the
PIC / POC ratio of two subspecies of Coccolithus pelagicus. This large
and heavily calcified species is a major contributor to calcite export from
the photic zone into deep-sea reservoirs. Phosphorus limitation did not
influence exponential growth rates in either subspecies, but P-limited cells
had significantly lower cellular P-content. One of the subspecies was
subjected to a 5 °C temperature increase from 10 °C to
15 °C, which did not affect exponential growth rates either, but
nearly doubled cellular P-content under both high and low phosphate
availability. This temperature increase reduced the PIC / POC ratio by
40–60%, whereas the PIC / POC ratio did not differ between P-limited and
nutrient-replete cultures when the subspecies were grown near their
respective isolation temperature. Both P-limitation and elevated temperature
significantly increased coccolith malformations. Our results suggest that a
temperature increase may intensify P-limitation due to a higher P-requirement
to maintain growth and POC production rates, possibly reducing abundances in
a warmer ocean. Under such a scenario <i>C. pelagicus</i> may decrease its
calcification rate relative to photosynthesis, thus favouring
CO<sub>2</sub> sequestration over release. It seems unlikely that P-limitation by
itself causes changes in the PIC / POC ratio in this species
Timing and Pacing of Indonesian Throughflow Restriction and Its Connection to Late Pliocene Climate Shifts
drier conditions. This shift fundamentally reorganized Earth\u27s climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned high‐resolution sediment geochemistry, calcareous nannofossil, and X‐ray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogue‐based interpretations of nannofossil assemblages indicate that ITF configuration culminated ~3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (~3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the Sahul‐Indian Ocean Bjerknes mechanism and increased the response to glacio‐eustatic variability
Надзор органов прокуратуры за коррупционной сферой бизнеса в России и Беларуси в современных условиях
Материалы IX Междунар. науч. конф., 21–22 мая 2015 г
Indonesian Throughflow drove Australian climate from humid Pliocene to arid Pleistocene
Late Miocene to mid-Pleistocene sedimentary proxy records reveal that northwest Australia underwent an abrupt transition from dry to humid climate conditions at 5.5 million years (Ma), likely receiving year-round rainfall, but after ~3.3 Ma, climate shifted toward an increasingly seasonal precipitation regime. The progressive constriction of the Indonesian Throughflow likely decreased continental humidity and transferred control of northwest Australian climate from the Pacific to the Indian Ocean, leading to drier conditions punctuated by monsoonal precipitation. The northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by ~2.4 Ma, well after the intensification of Northern Hemisphere glaciation. The transition from humid to arid conditions was driven by changes in Pacific and Indian Ocean circulation and regional atmospheric moisture transport, influenced by the emerging Maritime Continent. We conclude that the Maritime Continent is the switchboard modulating teleconnections between tropical and high-latitude climate systems
Decrease in coccolithophore calcification and CO2 since the middle Miocene
International audienceMarine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone εp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity
On the Origin and Trigger of the Notothenioid Adaptive Radiation
Adaptive radiation is usually triggered by ecological opportunity, arising
through (i) the colonization of a new habitat by its
progenitor; (ii) the extinction of competitors; or
(iii) the emergence of an evolutionary key innovation in
the ancestral lineage. Support for the key innovation hypothesis is scarce,
however, even in textbook examples of adaptive radiation. Antifreeze
glycoproteins (AFGPs) have been proposed as putative key innovation for the
adaptive radiation of notothenioid fishes in the ice-cold waters of Antarctica.
A crucial prerequisite for this assumption is the concurrence of the
notothenioid radiation with the onset of Antarctic sea ice conditions. Here, we
use a fossil-calibrated multi-marker phylogeny of nothothenioid and related
acanthomorph fishes to date AFGP emergence and the notothenioid radiation. All
time-constraints are cross-validated to assess their reliability resulting in
six powerful calibration points. We find that the notothenioid radiation began
near the Oligocene-Miocene transition, which coincides with the increasing
presence of Antarctic sea ice. Divergence dates of notothenioids are thus
consistent with the key innovation hypothesis of AFGP. Early notothenioid
divergences are furthermore congruent with vicariant speciation and the breakup
of Gondwana
Gender differences in the use of cardiovascular interventions in HIV-positive persons; the D:A:D Study
Peer reviewe
Résultats préliminaires sur la sédimentation pélagique de l'Atlantique tropical au Crétacé et au Tertiaire (plateau de Demerara, Leg ODP 207)
Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study
Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe
Phosphorus limitation and heat stress decrease calcification in <i>Emiliania huxleyi</i>
Calcifying haptophytes (coccolithophores) sequester carbon in the
form of organic and inorganic cellular components (coccoliths). We examined
the effect of phosphorus (P) limitation and heat stress on particulate
organic and inorganic carbon (calcite) production in the coccolithophore
Emiliania huxleyi. Both environmental stressors are related to rising CO2 levels and
affect carbon production in marine microalgae, which in turn impacts
biogeochemical cycling. Using semi-continuous cultures, we show that
P limitation and heat stress decrease the calcification rate in E. huxleyi. However,
using batch cultures, we show that different culturing approaches (batch
versus semi-continuous) induce different physiologies. This affects the
ratio of particulate inorganic (PIC) to organic carbon (POC) and complicates
general predictions on the effect of P limitation on the PIC  ∕  POC ratio. We
found heat stress to increase P requirements in E. huxleyi, possibly leading to lower
standing stocks in a warmer ocean, especially if this is linked to lower
nutrient input. In summary, the predicted rise in global temperature and
resulting decrease in nutrient availability may decrease CO2
sequestration by E. huxleyi through lower overall carbon production. Additionally, the
export of carbon may be diminished by a decrease in calcification and a
weaker coccolith ballasting effect
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