Non-spinose planktonic foraminifera (Neogloboquadrina pachyderma) cultured for geochemical and paleoceanographic applications.

摘要

Shells of two extant species of non-spinose planktonic foraminifera, Neogloboquadrina pachyderma and N. dutertrei, provide an important archive of past ocean conditions. Neogloboquadrina pachyderma is particularly important because it is the only species preserved in polar sediments, regions vital to understanding paleoceanographic change. In spite of the valuable information provided by N. pachyderma , little is known about this species lifestyle and the controls on its shell chemistry because living specimens have not been maintained in laboratory culture. This dissertation describes protocols developed to culture N. pachyderma (d.), possible ecological aspects based on collections and laboratory observations, and geochemical experiments completed under controlled conditions.; Healthy N. pachyderma (d.) from productive waters are found associated with particulate organic matter (POM) or marine aggregates. Cultured N. pachyderma (d.) surround their shells when fed Artemia nauplei, and resemble marine aggregate encapsulated specimens. Neogloboquadrinids also exhibited behavior normally associated with benthic foraminifera. Experiments reveal secondary calcification comprises approximately half of the total shell calcite and confirm thick-shelled specimens result from late ontogenetic crusting of thin-shelled non-encrusted forms. Shell crusting occurred over the entire culturing temperature range (6–19°C).; Mg/Ca and oxygen isotopes in N. pachyderma (s.) exhibited a clear dependence on temperature. Oxygen isotopes vary linearly with temperature while Mg/Ca increases exponentially with temperature. Limited data suggest N. dutertrei cultured under low light exhibit similar elemental and isotopic temperature relationships to N. pachyderma (d.). Cultured neogloboquadrinid shells have δ13C values similar to culture water δ13C_DIC, and δ 13C −δ13C_DIC did not vary with temperature. Taking into account δ13C_DIC values for surface and culture water, N. pachyderma grown in the laboratory exhibited 1‰ more positive δ13C − δ 13C_DIC compared to field collected specimens. Relative to N. pachyderma, N. dutertrei shells collected by plankton tows exhibited more positive δ13C. When we applied the temperature relationships established by culturing to shells collected by plankton tows, the calculated temperatures were consistent with SST by ±1.9°C for Mg/Ca and ±1.6°C for δ18O (95% CI).