Chemistry of zeolithe and clays from Central Kerguelen Plateau basalts

Ocean Drilling Program Leg 120 recovered basement samples that consisted of zeolite-facies metabasalts at Sites 747, 749, and 750 on the Kerguelen Plateau. These basalts were metamorphosed in the low to intermediate zones of the zeolite facies, as indicated by the presence of diagnostic zeolites and the absence of chlorite, epidote, prehnite, pumpellyite, and wairakite. Chabazite, natrolite, thompsonite, mesolite, stilbite, huelandite, and smectites occur as amygduloidal fillings in basalts from Holes 747C and 750B, whereas only stilbite, laumontite, and pure and mixed-layered smectites were identified in amygduloidal basalts from Hole 749C. In the lower sections of Hole 749C, only laumontite and mixed-layered smectites coexist. Based on calculations with published experimental phase equilibria, the absence of wairakite in basalts from Hole 749C and of laumontite in basalts from Holes 747C and 750B suggests that metamorphic temperatures did not exceed approximately 225° and 120°C, respectively. The presence of well-developed zeolite mineral assemblages and the absence of carbonate and clay mineral assemblages restricts XCO2 in the fluid to approximately <=0.0075. Low- to intermediate-zone zeolite-facies mineral assemblages in basalts from the Kerguelen Plateau can be accounted for by metamorphism in an active geothermal area such as present-day Iceland.

Increased carbon dioxide availability alters phytoplankton stoichiometry and affects carbon cycling and growth of a marine planktonic herbivore

Rising levels of CO2 in the atmosphere have led to increased CO2 concentrations in the oceans. This enhanced carbon availability to the marine primary producers has the potential to change their nutrient stoichiometry, and higher carbon to nutrient ratios are expected. As a result, the quality of the primary producers as food for herbivores may change. Here, we present experimental work showing the effect of feeding Rhodomonas salina grown under different pCO2 (200, 400 and 800 µatm) on the copepod Acartia tonsa. The rate of development of copepodites decreased with increasing CO2 availability to the algae. The surplus carbon in the algae was excreted by the copepods, with younger stages (copepodites) excreting most of their surplus carbon through respiration, and adult copepods excreting surplus carbon mostly as DOC. We consider the possible consequences of different excretory pathways for the ecosystem. A continued increase in the CO2 availability for primary production, together with changes in the nutrient loading of coastal ecosystems, may cause changes in the trophic links between primary producers and herbivores.