Jones_19_October_2017 |
Jones_Colin_23October_2017
Graduate School of Oceanography - OCG 695
23 October, 3:30 PM, Coastal Institute Auditorium
23 October, 3:30 PM, Coastal Institute Auditorium
Colin Jones
Assessment of diatom assemblage and community nitrogen isotope fractionation in Southern Ocean diatoms
Glacial-scale pCO2 changes are well-documented, but the role of the Southern Ocean biological pump is still an open question. The sedimentary diatom-bound nitrogen isotope proxy (δ15Ndb) provides information about past surface ocean nutrient conditions and may show evidence for changes in the biological pump. Recent work has shown that the δ15Ndb proxy is impacted by species-specific isotope fractionation. This means that downcore δ15Ndb records likely reflect not only nutrient conditions in the past, but also fluctuations in diatom community composition. To disentangle these signals and generate robust records of nutrient utilization we will compare the isotopic relationship between community and monospecific cultures with the future goal of using sedimentary diatom assemblages to obtain more quantitative information from δ15Ndb values. Here I present preliminary diatom community composition and nitrate (NO3-) isotope results from two shipboard community incubations performed in the field. Assemblages were dominated by Fragilariopsis species in both incubations. Measured isotopic enrichment factors (ε) for the communities are 3.9±0.4‰ for 66°S and 4.0±0.5‰ for 61°S, similar to literature values. The next step will be to measure δ15Ndb of the shipboard incubations and continue growing monospecific cultures with diatoms isolated from the Southern Ocean.
Colin Jones received a degree in Chemistry from Willamette University in 2014. He entered GSO in Fall 2014. His major professor is Rebecca Robinson. Other core committee members are Tatiana Rynearson and Simon Engelhart.
Glacial-scale pCO2 changes are well-documented, but the role of the Southern Ocean biological pump is still an open question. The sedimentary diatom-bound nitrogen isotope proxy (δ15Ndb) provides information about past surface ocean nutrient conditions and may show evidence for changes in the biological pump. Recent work has shown that the δ15Ndb proxy is impacted by species-specific isotope fractionation. This means that downcore δ15Ndb records likely reflect not only nutrient conditions in the past, but also fluctuations in diatom community composition. To disentangle these signals and generate robust records of nutrient utilization we will compare the isotopic relationship between community and monospecific cultures with the future goal of using sedimentary diatom assemblages to obtain more quantitative information from δ15Ndb values. Here I present preliminary diatom community composition and nitrate (NO3-) isotope results from two shipboard community incubations performed in the field. Assemblages were dominated by Fragilariopsis species in both incubations. Measured isotopic enrichment factors (ε) for the communities are 3.9±0.4‰ for 66°S and 4.0±0.5‰ for 61°S, similar to literature values. The next step will be to measure δ15Ndb of the shipboard incubations and continue growing monospecific cultures with diatoms isolated from the Southern Ocean.
Colin Jones received a degree in Chemistry from Willamette University in 2014. He entered GSO in Fall 2014. His major professor is Rebecca Robinson. Other core committee members are Tatiana Rynearson and Simon Engelhart.