Seawater carbonate chemistry, calcification and dissolution of a coral reef in the northern Red Sea, 2007

In this study we investigated the relations between community calcification of an entire coral reef in the northern Red Sea and annual changes in temperature, aragonite saturation and nutrient loading over a two year period. Summer (April-October) and winter (November-March) average calcification rates varied between 60 ± 20 and 30 ± 20 mmol·m-2·d-1, respectively. In general, calcification increased with temperature and aragonite saturation state of reef water with an apparent effect of nutrients, which is in agreement with most laboratory studies and in situ measurements of single coral growth rates. The calcification rates we measured in the reef correlated remarkably well with precipitation rates of inorganic aragonite calculated for the same temperature and degree of saturation ranges using empirical equations from the literature. This is a very significant finding considering that only a minute portion of reef calcification is inorganic. Hence, these relations could be used to predict the response of coral reefs to ocean acidification and warming.

Sr/Ca and Cd/Ca ratios of benthic foraminifera in surface deep-sea sediments

Measurements of Sr/Ca of benthic foraminifera show a linear decrease with water depth which is superimposed upon significant variability identified by analyses of individual foraminifera. New data for Cd/Ca support previous work in defining a contrast between waters shallower and deeper than ~2500 m. Measured element partition coefficients in foraminiferal calcium carbonate relative to sea water (D) have been described by means of a one-box model in which elements are extracted by Rayleigh distillation from a biomineralization reservoir that serves for calcification with a constant fractionation factor (alpha), such that D = (1 - f**alpha)/(l - f), where f is the proportion of Ca remaining after precipitation. A modification to the model recognises differences in element speciation. The model is consistent with differences between D[Sr], D[Ba], and D[Cd] in benthic but not planktonic foraminifera. Depth variations in D for Sr and Ba are consistent with the model, as are differences in depth variation of D[Cd] in calcitic and aragonitic benthic foraminifera. The shallower depth variations may reflect increasing calcification rates with increasing water depth to an optimum of about 2500 m. Observations of unusually lower DCd for some deep waters, not accompanied by similar [Sr], or D[Ba] may be because of dissolution or a calcification response to a lower carbonate saturation state.

Seawater carbonate chemistry and biological processes during experiments with a Sea Star Crassaster papposus, 2010

Ocean acidification (OA) is believed to be a major threat for near-future marine ecosystems, and that the most sensitive organisms will be calcifying organisms and the free-living larval stages produced by most benthic marine species. In this respect, echinoderms are one of the taxa most at risk. Earlier research on the impact of near-future OA on echinoderm larval stages showed negative effects, such as a decreased growth rate, increased mortality, and developmental abnormalities. However, all the long-term studies were performed on planktotrophic larvae while alternative life-history strategies, such as nonfeeding lecithotrophy, were largely ignored. Here, we show that lecithotrophic echinoderm larvae and juveniles are positively impacted by ocean acidification. When cultured at low pH, larvae and juveniles of the sea star Crossaster papposus grow faster with no visible affects on survival or skeletogenesis. This suggests that in future oceans, lecithotrophic species may be better adapted to deal with the threat of OA compared with planktotrophic ones with potentially important consequences at the ecosystem level. For example, an increase in populations of the top predator C. papposus will likely have huge consequences for community structure. Our results also highlight the importance of taking varying life-history strategies into account when assessing the impacts of climate change, an approach that also provides insight into understanding the evolution of life-history strategies.

Seawater carbonate chemistry, virioplankton and bacterioplankton in a shallow CO2-dominated hydrothermal vent (Panarea Island, Tyrrhenian Sea)

Gas hydrothermal vents are used as a natural analogue for studying the effects of CO2 leakage from hypothetical shallow marine storage sites on benthic and pelagic systems. This study investigated the interrelationships between planktonic prokaryotes and viruses in the Panarea Islands hydrothermal system (southern Tyrrhenian Sea, Italy), especially their abundance, distribution and diversity. No difference in prokaryotic abundance was shown between high-CO2 and control sites. The community structure displayed differences between fumarolic field and the control, and between surface and bottom waters, the latter likely due to the presence of different water masses. Bacterial assemblages were qualitatively dominated by chemo- and photoautotrophic organisms, able to utilise both CO2 and H2S for their metabolic requirements. From significantly lower virioplankton abundance in the proximity of the exhalative area together with particularly low Virus-to-Prokaryotes Ratio, we inferred a reduced impact on prokaryotic abundance and proliferation. Even if the fate of viruses in this particular condition remains still unknown, we consider that lower viral abundance could reflect in enhancing the energy flow to higher trophic levels, thus largely influencing the overall functioning of the system.

(Table S2) The reconstructed sea surface temperature (SST) over the eastern equatorial Pacific

Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18-15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5-1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.