Ocean acidification, which like global warming is an outcome of anthropogenic CO2 emissions, severely impacts marine calcifying organisms, especially those living in coral reef ecosystems. However, knowledge about the responses of reef calcifiers to ocean acidification is quite limited, although coral responses are known to be generally negative. In a culture experiment with two algal symbiont‐bearing, reef‐dwelling foraminifers, Amphisorus kudakajimensis and Calcarina gaudichaudii, in seawater under five different pCO2 conditions, 245, 375, 588, 763 and 907 μatm, maintained with a precise pCO2‐controlling technique, net calcification of A. kudakajimensis was reduced under higher pCO2, whereas calcification of C. gaudichaudii generally increased with increased pCO2. In another culture experiment conducted in seawater in which bicarbonate ion concentrations were varied under a constant carbonate ion concentration, calcification was not significantly different between treatments in Amphisorus hemprichii, a species closely related to A. kudakajimensis, or in C. gaudichaudii. From these results, we concluded that carbonate ion and CO2 were the carbonate species that most affected growth of Amphisorus and Calcarina, respectively. The opposite responses of these two foraminifer genera probably reflect different sensitivities to these carbonate species, which may be due to their different symbiotic algae.

Recent studies have remarked on the importance of direct CO 2 release from river water into the atmosphere on the global carbon cycle over a short timescale. In this study, we investigated carbonate systems, including spatial and seasonal variations of pCO 2 , in three major Himalayan rivers in Bangladesh: the Ganges, Brahmaputra, and Meghna Rivers, and their potential importance. Although pCO 2 is known to be low in the upper reaches of these rivers, owing to active chemical weathering, we observed pCO 2 values higher than the atmospheric pCO 2 level along their lower reaches, where deep soils have developed and where high air temperatures promote active soil respiration. By a simple mixing calculation, we found that seasonal variations in these river water carbonate systems are controlled by subsurface water flows. In the rainy season, most of the lowlands are inundated, and the contribution of subsurface flow to river water carbonate systems increases, resulting in higher pCO 2 values. In future research, more detailed spatial and seasonal investigations are required to clarify the role of terrestrial ecosystems, including rivers and the CO 2 flux to the atmosphere, in the global carbon cycle and to examine how that role will change under global warming.

[1] In the past 800 thousand years and before industrialization, the largest variations in atmospheric CO 2 concentration (pCO 2 ) occurred in connection with the glacial cycles that characterized Earth's climate over this period. One curious feature of at least the last four glacial-interglacial cycles is that atmospheric pCO 2 reached about the same upper limit of 280 ppm during peak interglacial periods and about the same lower limit of 180 ppm during peak glacial periods. Here, we show using a numerical model of earth system that enhanced shelf sediment weathering during glacial sea level lowstands tends to raise pCO 2 even after carbonate compensation and thus stabilize pCO 2 from further reduction. This is because not all nutrients from weathering will be utilized by biology but more importantly because the spatial distributions of carbon and phosphorus from weathering become decoupled in such a way that carbon is preferentially stored in the upper ocean and phosphorus in the deep ocean. In addition, the C:P ratios in continental margin sediments are generally much higher than the Redfield ratio due to preferential remineralization of phosphorus in shelf sediment diagenesis. When these factors are accounted for in our model, the input of organic matter, which corresponds to the observed negative shift in ocean d 13 C during glacial periods, raises pCO 2 by approximately 14 ppm. The same mechanisms operating in the opposite directions during interglacial highstand tend to lower pCO 2 and stabilize it from further increase. The impact of sea level-driven continental shelf exposure and submersion of CO 2 is therefore a negative feedback that may have contributed to limiting the variation of Pleistocene pCO 2 to the observed 100 ppm range.Citation: Ushie, H., and K. Matsumoto (2012), The role of shelf nutrients on glacial-interglacial CO 2 : A negative feedback, Global Biogeochem. Cycles, 26, GB2039,

[1] Riverine carbon transportation is an important carbon flux connecting reservoirs of the atmosphere, continents, and oceans. The flux is strongly related to the important roles of rivers such as regulation of climate change and buffering of ocean acidification. Here, to evaluate the linkage of such functions of rivers and geological characteristics of the watersheds, we present the results of a comparative hydrogeochemical study conducted on small subtropical watersheds of aluminosilicate-dominated Iriomote Island and carbonate-based Ishigaki Island, southwestern Japan. Rivers on Ishigaki Island exhibited much higher alkalinity than rivers on Iriomote Island, which was even higher than the mean value of major rivers in the world, such as the Saint Lawrence and the Mississippi. This high alkalinity was the result of carbonate dissolution enhanced by soil-originated CO 2 . As a result of this high inorganic carbon input, the ratio of inorganic carbon and nutrients of the river water was higher than that of marine organic matter such as the Redfield ratio, making the coastal seas a potential source of CO 2 for the atmosphere.