A study of several aspects of the marine carbon cycle: (1)~Sea-air flux of carbon dioxide in the North Pacific using shipboard and satellite data, (2)~Chloropigments and labile organic carbon at the equatorial Pacific seafloor and (3)~Late Holocene calcium carbonate dissolution from the equatorial Pacific seafloor
Date of Award
Doctor of Philosophy (Ph.D.)
First Committee Member
David C. Kadko - Committee Chair
This dissertation consists of three studies involving fluxes and processes of the marine carbon cycle operating on widely differing timescales. First, a method is developed in which estimates of the surface water partial pressure of CO$\sb2$ (pCO$\sb2$) can be improved using satellite sea surface temperature (SST) data. It is applied to the North Pacific using relationships between pCO$\sb2$ and SST obtained from ship observations. The method is most successful in the subtropical gyre region, where the main control on pCO$\sb2$ is SST. It is somewhat less successful in the subpolar region because of changes in $\Sigma$CO$\sb2$ caused by seasonal variations in mixing and primary productivity. The use of additional satellite data and a mixed layer model might lead to improvements there. The North Pacific (north of 10$\sp\circ$N) is found to be a net source to the atmosphere of 0.02-0.07 Gt C/yr.Second, the degradation of chlorophyll-a and pheopigments at the equatorial Pacific seafloor is investigated. These pigments hold promise as solid phase tracers of recently arrived labile organic matter, which is responsible for substantial benthic chemical fluxes. Degradation rate constants obtained from a majority of the pigment profiles are $\rm k=8$-54 /yr. Several profiles show evidence of much slower degradation at depths below 0.5 cm ($\rm k=0.002$-0.79 /yr), which suggests that a fraction ($\le$1%) of the pigments and, possibly, other labile organic matter escapes rapid degradation near the sediment-water interface.Third, the glacial-Holocene CaCO$\sb3$ record within equatorial Pacific sediments is studied. The application of a numerical model to CaCO$\sb3$, C-14, and Th-230 reveals that the sedimentation and CaCO$\sb3$ accumulation rates have declined by 1-1.5 cm/kyr and 1.5-2 g/cm2/kyr, respectively, within the past 3-4 kyr (late-Holocene). The ratios of Th-230 to Pa-231 within the sediment, though, indicate that particle fluxes and primary productivity have not changed significantly during the Holocene. This suggests that the decreased accumulation rates result from intensified CaCO$\sb3$ dissolution rather than decreased rain rates. The organic carbon to CaCO$\sb3$ molar rain ratios for the region ($<$1.0) require that bottom water undersaturation caused the heightened dissolution.
Physical Oceanography; Geochemistry
Stephens, Mark Patrick, "A study of several aspects of the marine carbon cycle: (1)~Sea-air flux of carbon dioxide in the North Pacific using shipboard and satellite data, (2)~Chloropigments and labile organic carbon at the equatorial Pacific seafloor and (3)~Late Holocene calcium carbonate dissolution from the equatorial Pacific seafloor" (1996). Dissertations from ProQuest. 3413.