A budget approach is used to disentangle drivers of the seasonal mixed layer carbon cycle at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) in the North Pacific Subtropical Gyre (NPSG). The budget utilizes data from the WHOTS (Woods Hole - Hawaii Ocean Time-series Site) mooring, and the ship-based Hawai‘i Ocean Time-series (HOT) in the North Pacific Subtropical Gyre (NPSG), a region of significant oceanic carbon uptake. Parsing the carbon variations into process components allows an assessment of both the proportional contributions of mixed layer carbon drivers, and the seasonal interplay of drawdown and supply from different processes. Annual net community production reported here is at the lower end of previously published data, while net community calcification estimates are 4- to 7-fold higher than available sediment trap data, the only other estimate of calcium carbonate export at this location. Although the observed seasonal cycle in dissolved inorganic carbon (DIC) in the NPSG has a relatively small amplitude, larger fluxes offset each other over an average year, with major supply from physical transport, especially lateral eddy transport throughout the year and entrainment in the winter, and biological carbon uptake in the spring. Gas exchange plays a smaller role, supplying carbon to the surface ocean between Dec-May, and outgassing in Jul-Oct. Evaporation-precipitation (E–P) is variable with precipitation prevailing in the first- and evaporation in the second half of the year. The observed total alkalinity signal is largely governed by E–P, with a somewhat stronger net calcification signal in the wintertime.

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.