A document by Nathan J.M. Laxague. Click on the document to view its contents.

Solar heating of the upper ocean is a primary energy input to the ocean-atmosphere system, and the vertical heating profile is modified by the concentration of phytoplankton in the water, with consequences for sea surface temperature and upper ocean dynamics. Despite the development of increasingly complex modeling approaches for radiative transfer in the atmosphere and upper ocean, the simple parameterizations of radiant heating used in most ocean models are plagued by errors and inconsistencies. There remains a need for a parameterization that is reliable in the upper meters and contains an explicitly spectral dependence on the concentration of biogenic material, while maintaining the computational simplicity of the parameterizations currently in use. In this work, we assemble simple, observationally-validated physical modeling tools for the key controls on ocean radiant heating, and simplify them into a parameterization that fulfills this need. We then use observations from 64 spectroradiometer depth casts across 6 cruises, 13 surface hyperspectral radiometer deployments, and 2 UAV flights to probe the accuracy and uncertainty associated with the new parameterization. We conclude with a case study using the new parameterization to demonstrate the impact of chlorophyll concentration on the structure of diurnal warm layers, an investigation that was not possible to conduct accurately using previous parameterizations. The parameterization presented in this work equips researchers to better model global patterns of sea surface temperature, diurnal warming, and mixed-layer depths, without a prohibitive increase in complexity.

Parameterizations of gas transfer velocities are needed for climate predictions. Single parameter models typically only include wind dependence and may readily be used in climate studies. Their application is however gas specific and limited to select environments. Mechanistic parameterizations incorporating multiple forcing factors allow modelling the transfer of gases with differing solubilities for a wide range of conditions. A novel framework is put forward to model gas transfer in the open ocean in the presence of breaking waves. It incorporates both the turbulence- and bubble-mediated transfers based on statistics determined from the breaking crest length distribution ($\Lambda(c)$). Testing the mechanistic model with measurements from the HiWinGS field campaign shows promising results for both CO\textsubscript{2} and DMS. Uncertainties remain in the quantification of bubble clouds which are at the core of the formulation of the bubble-mediated transfer.

Estimates of turbulence kinetic energy (TKE) dissipation rate (ε) are key to understanding how heat, gas, and other climate-relevant properties are transferred across the air-sea interface and mixed within the ocean. A relatively new method involving moored pulse-coherent Acoustic Doppler Current Profilers (ADCPs) allows for estimates of ε with concurrent surface flux and wave measurements across an extensive length of time and range of conditions. Here, we present 9 months of moored estimates of ε at a fixed depth of 8.4m at the Stratus mooring site (20°S, 85°W). We find that shear- and buoyancy-dominant turbulence regimes are defined equally well using the Obukhov length scale ( LM ) and the newer Langmuir stability length scale (LL ), suggesting that ocean-side friction velocity (u*) implicitly captures the influence of Langmuir circulation at this site. This is illustrated by a strong linear dependence between surface Stokes drift (us) and and is likely facilitated by the steady Southeast trade winds regime. The traditional Law of the Wall (LOW) and surface buoyancy flux scalings of Monin-Obukhov similarity theory scale our estimates of well, collapsing data points near unity. We find that the newer Stokes drift scaling ( usu*2 /mixed layer depth) scales ε well at times but is overall less consistent than LOW. Scaling relationships from prior studies in a variety of aquatic and atmospheric settings largely agree with our data in destabilizing, shear-dominant conditions but diverge in other regimes.