Downscaled climate projections of future mesopelagic habitat in the California Current Ecosystem

Although the mesopelagic zone occupies a substantial volume of the world's oceans, our results suggest that the livable portion may compress vertically by ~40 m or ~39% by the end of the century. Using an ensemble of three downscaled climate projections from a high emissions scenario, we evaluated the connection between anthropogenic greenhouse gas emissions and changes in light and oxygen at depth, which influence the upper and lower limits of mesopelagic habitat in the central California Current. Although the model projects a small deepening (~ 2 m) of the upper light boundary consistent with increased stratification and reduced upper ocean productivity, the main driver of vertical mesopelagic habitat compression is the significant shoaling (by ~44 m) of the hypoxic boundary over the course of the 21st century. Differences in dissolved oxygen across ensemble members highlight the potential influence of equatorial dynamics and the California Undercurrent in constraining the future avai..., Downscaled Regional Climate Projections
We use an ensemble of high-resolution regional climate projections representing three different rates of warming under the RCP 8.5 high emissions scenario for the period 2000-2100. The earth system model solutions are first downscaled to 1/10° (~10 km) resolution for the broader California Current (30-48 °N)1,2 and subsequently nested at 1/30° (~3 km) resolution for the central California Current (32-44 °N) to improve the representation of local scale coastal upwelling processes3. In this approach, the 1/10° downscaled projections are forced directly by the CMIP5 earth system models using a time-varying delta method, and the high-resolution nested projections are subsequently forced by the downscaled projections using an offline nesting method (Fig. 1). The three earth system model solutions selected here are GFDL-ESM2M, IPSLCM5, and Hadley-GEM2-E as they include marine biogeochemical fields and represent the spread of the CMIP5 ensemble (GFDL-ESM..., , # Downscaled climate projections of future mesopelagic habitat in the California Current Ecosystem

[https://doi.org/10.5061/dryad.kh18932hn](https://doi.org/10.5061/dryad.kh18932hn)

## Description of the data and file structure

The following oceanographic data and R code accompany the manuscript \"Projected 21st century compression of mesopelagic habitat in the California Current\" submitted to Scientific Reports. Using an ensemble of three high-resolution downscaled climate projections for the California Current under a high emissions scenario, we evaluated potential changes in the availability of mesopelagic habitat by the end of the 21st century. The upper and lower boundaries of the mesopelagic zone are defined as the depth at which light intensity reaches (0.0217 W/m2) and the depth of the hypoxic boundary defined as ~63 mmol/m3. Additional ocean metrics include: temperature at 150 m, dissolved oxygen at 300 m, Integrated chlorophyll in the upper 100 m, maximum buoyancy frequency ...,