Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean

Planktonic calcifying organisms play a key role in regulating ocean carbonate chemistry and atmospheric CO 2 . Surprisingly, references to the absolute and relative contribution of these organisms to calcium carbonate production are lacking. Here we report quantification of pelagic calcium carbonate produc- tion in the North Pacific, providing new insights on the contribution of the three main planktonic calcifying groups. Our results show that coccolitho- phores dominate the living calcium carbonate (CaCO 3 ) standing stock, with coccolithophore calcite comprising ~90% of total CaCO 3 production, and pteropods and foraminifera playing a secondary role. We show that pelagic CaCO 3 production is higher than the sinking flux of CaCO 3 at 150 and 200 m at ocean stations ALOHA and PAPA, implying that a large portion of pelagic calcium carbonate is remineralised within the photic zone; this extensive shallow dissolution explains the apparent discrepancy between previous estimates of CaCO 3 production derived from satellite observations/biogeo- chemical modeling versus estimates from shallow sediment traps. We suggest future changes in the CaCO 3 cycle and its impact on atmospheric CO 2 will largely depend on how the poorly-understood processes that determine whether CaCO 3 is remineralised in the photic zone or exported to depth respond to anthropogenic warming and acidification

From computational discovery to experimental characterization of a high hole mobility organic crystal

For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm2 V−1 s−1, respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm2 V−1 s−1 reported to date

Authigenic Formation of Clay Minerals in the Abyssal North Pacific

Funder: Blavatnik Family Foundation; Id: http://dx.doi.org/10.13039/100011643Funder: Isaac Newton Trust; Id: http://dx.doi.org/10.13039/501100004815Present estimates of the biogeochemical cycles of calcium, strontium, and potassium in the ocean reveal large imbalances between known input and output fluxes. Using pore fluid, incubation, and solid sediment data from North Pacific multi‐corer cores we show that, contrary to the common paradigm, the top centimeters of abyssal sediments can be an active site of authigenic precipitation of clay minerals. In this region, clay authigenesis is the dominant sink for potassium and strontium and consumes nearly all calcium released from benthic dissolution of calcium carbonates. These observations support the idea that clay authigenesis occurring over broad regions of the world ocean may be a major buffer for ocean chemistry on the time scale of the ocean overturning circulation, and key to the long‐term stability of Earth's climate

SOD2, the principal scavenger of mitochondrial superoxide, is dispensable for embryogenesis and imaginal tissue development but essential for adult survival

Definitive evidence on the impact of MnSOD/SOD2-deficiency and the consequent effects of high flux of mitochondrial reactive oxygen species (ROS) on pre-natal/pre-adult development has yet to be reported for either Drosophila or mice. Here we report that oocytes lacking maternal SOD2 protein develop into adults just like normal SOD2-containing oocytes suggesting that maternal SOD2-mediated protection against mitochondrial ROS is not essential for oocyte viability. However, the capacity of SOD2-null larvae to undergo successful metamorphosis into adults is negatively influenced in the absence of SOD2. We therefore determined the impact of a high superoxide environment on cell size, progression through the cell cycle, cell differentiation and cell death and found no difference between SOD2-null and SOD2+ larva and pupa. Thus loss of SOD2 activity clearly has no effect on pre-adult imaginal tissues. Instead, we found that the high mitochondrial superoxide environment arising from the absence of SOD2 leads to the induction of autophagy. Such autophagic response may underpin the resistance of pre-adult tissues to unscavenged ROS. Finally, while our data establish that SOD2 activity is less essential for normal development, the mortality of Sod2−/− neonates of both Drosophila and mice suggests that SOD2 activity is indeed essential for the viability of adults. We therefore asked if the early mortality of SOD2-null young adults could be rescued by activation of SOD2 expression. The results support the conclusion that the early mortality of SOD2-null adults is largely attributable to the absence of SOD2 activity in the adult per se. This finding somewhat contradicts the widely held notion that failure to scavenge the high volume of superoxide emanating from the oxidative demands of development would be highly detrimental to developing tissues

Meridional overturning circulation conveys fast acidification to the deep Atlantic Ocean

Since the Industrial Revolution, the North Atlantic Ocean has been accumulating anthropogenic carbon dioxide (CO2) and experiencing ocean acidification, that is, an increase in the concentration of hydrogen ions (a reduction in pH) and a reduction in the concentration of carbonate ions. The latter causes the 'aragonite saturation horizon' - below which waters are undersaturated with respect to a particular calcium carbonate, aragonite - to move to shallower depths (to shoal), exposing corals to corrosive waters. Here we use a database analysis to show that the present rate of supply of acidified waters to the deep Atlantic could cause the aragonite saturation horizon to shoal by 1,000-1,700 metres in the subpolar North Atlantic within the next three decades. We find that, during 1991-2016, a decrease in the concentration of carbonate ions in the Irminger Sea caused the aragonite saturation horizon to shoal by about 10-15 metres per year, and the volume of aragonite-saturated waters to reduce concomitantly. Our determination of the transport of the excess of carbonate over aragonite saturation ((xc)[CO3(2-)]) - an indicator of the availability of aragonite to organisms - by the Atlantic meridional overturning circulation shows that the present-day transport of carbonate ions towards the deep ocean is about 44 per cent lower than it was in preindustrial times. We infer that a doubling of atmospheric anthropogenic CO2 levels - which could occur within three decades according to a 'business-as-usual scenario' for climate change - could reduce the transport of (xc)[CO3(2-)] by 64-79 per cent of that in preindustrial times, which could severely endanger cold-water coral habitats. The Atlantic meridional overturning circulation would also export this acidified deep water southwards, spreading corrosive waters to the world ocean