Date of Award
Doctor of Philosophy in Oceanography
Marine and Atmospheric Chemistry
Biogeochemical gas budgets at high-latitude regions and sea ice zones are a source of uncertainty in climate models. The four main processes that regulate these budgets include advection, ventilation, mixing, and accumulation/release from sea ice. Considering the scarcity of data in sea ice zones, specifically during winter time, the environment is too poorly sampled to constrain these processes through direct measurements; hence we proposed models to systematically investigate these processes. The models proposed in this dissertation consist of regional numerical ice-ocean models, 1D forward and inversion numerical models, and analytical models.
Manuscript I of this dissertation focuses on a 3D regional Arctic ice-ocean models. The models are based on MIT general circulation model (MITgcm) code. We used 36 km, 9 km and 2 km horizontal resolution of regional MITgcm configuration with fine vertical spacing to evaluate the capability of the model to reproduce the physical parameters that affect the budget. The model outputs of interest from these simulations are sea ice concentration, sea ice speed, water velocities, and mixed layer depth. From gas budget point of view, sea ice concentration and speed effect ventilation, changes in mixed layer depth lead to mixing, and resolving water velocities quantifies the effects of advection.
To assess the accuracy of model, we compared the model outputs to existing field data. We found model sea ice concentration and speed follow data with good fidelity. The model demonstrated the capacity to capture the broad trends in the mixed layer although with a significant bias. We saw improvement in mixed layer depth accuracy with reducing the horizontal resolution of the model. Finally we showed modeled water velocities have low correlation with point-wise in situ data. This correlation remained low in all three model resolution simulations and we argued that is largely due to the quality of the input atmospheric forcing.
Manuscript II of this dissertation focuses on 1D forward and inversion modeling of gas budgets. Following our results from the first manuscript, we approximated the effects of advection analytically and utilized a 1D model and its inversion code. We applied the model with combination of numerical passive tracers to reproduce the 53 radon profiles gathered in the Arctic. The optimization based on inversion model reduced the uncertainties in initial conditions and supported the 1D model. We showed mixing, if not resolved, can introduce up to 50% error in estimated budgets. When effects of mixing, melt/freeze and advection taken into the account, we show current estimates of gas exchanges under predicts surface flux in almost cover sea ice areas.
Manuscript III presents a new approach in modeling gas exchange in sea ice zones. In this study a sea state dependent gas exchange parametric model is developed based on the turbulent kinetic energy dissipation rate. After comparing this model results with data in the Open Ocean, lakes and marginal ice zones, we applied it to a numerical ice-ocean model of Arctic Ocean. Finally, it is shown that, under the present conditions, gas flux into the Arctic Ocean may be overestimated by 10% if a conventional parameterization is used.
In summary, the work presented in this dissertation evaluates and quantifies the effects of environmental forcing on gas budgets in marginal ice zones and offered insight into main factors regulating near surface gas budgets in marginal sea ice zone.
Bigdeli, Arash, "Modeling Gas Budgets in Marginal Sea Ice Zones" (2017). Open Access Dissertations. Paper 678.