Abstract: We present the sensitivity of the Theia experiment to low-energy geo- and reactor antineutrinos. For this study, we consider one of the possible proposed designs, a 17.8-ktonne fiducial volume Theia-25 detector filled with water-based liquid scintillator placed at Sanford Underground Research Facility (SURF). We demonstrate Theia’s sensitivity to measure the geo- and reactor antineutrinos via inverse-beta decay interactions after one year of data taking with $$11.9 \times 10^{32}$$ 11.9 × 10 32 free target protons. Considering all uncertainties on input throughout the whole analysis chain, the expected number of geo- and reactor antineutrinos is $$220\,^{+30}_{-24}$$ 220 - 24 + 30 (stats+syst) and $$168\,^{+26}_{-24}$$ 168 - 24 + 26 (stat+sys), respectively, after one year of data taking. The corresponding expected fit precision of a sole experiment is evaluated at 8.7% and 10.1%, respectively. We also demonstrate the sensitivity towards fitting individual Th and U contributions, with best fit values of $$N_\text {Th}=40^{+26}_{-22}$$ N Th = 40 - 22 + 26 (stat+sys) and $$N_\text {U}=180^{+30}_{-24}$$ N U = 180 - 24 + 30 (stat+sys). Finally, from the fit results of individual Th and U contributions, we evaluate the mantle signal to be $$S_\text {mantle} = 9.3\,\pm [5.2,5.4]$$ S mantle = 9.3 ± [ 5.2 , 5.4 ]  NIU (stat+sys). This was obtained assuming a full-range positive correlation ($$\rho _c\in [0, 1]$$ ρ c ∈ [ 0 , 1 ] ) between Th and U, and the projected uncertainties on the crust contributions of 8.3% (Th) and 7.0% (U).

Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatio-temporal patterns of mixing are largely driven by the geography of generation, propagation and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last five years and under the auspices of US CLIVAR, a NSF- and NOAA-supported Climate Process Team has been engaged in developing, implementing and testing dynamics-based parameterizations for internal-wave driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here we review recent progress, describe the tools developed, and discuss future directions.