| Summary: | The Southern Ocean is an important atmospheric carbon sink, and potential changes in the carbon flux in this region will affect the ocean as a whole. Thus, to monitor the variability of its physico-chemical parameters is becoming a priority. This study provides the first high-resolution all-year-round record of observed and computed physico-chemical data from a shallow coastal site in Terra Nova Bay (Ross Sea). From November 2018 to November 2019, an underwater observatory deployed at a 25 m depth under an ice pack recorded pressure (<i>p</i>), temperature (<i>t</i>), electrical conductivity (<i>C</i>), dissolved oxygen (<i>DO</i>), pH in total scale (pH<sub>T</sub>), and illuminance (<i>E</i><sub>v</sub>). Practical salinity (<i>S</i><sub>P</sub>), density (ρ), tidal constituents, carbonate system parameters (total alkalinity (TA), carbon dioxide partial pressure (<i>p</i>CO<sub>2</sub>), calcite, and aragonite (Ω<sub>Ca</sub>, Ω<sub>Ar</sub>)), together with sea ice concentration (<i>SIC</i>) and chlorophyll-a (<i>Chl</i>-a), were derived from measured and satellite data. <i>t</i>, <i>DO</i>, and pH<sub>T</sub> displayed the lowest values between July and November (–1.95 °C, 6.61 mL L<sup>−1</sup>, 7.97) whereas the highest in January (+1.08 °C, 10.61 mL L<sup>−1</sup>, 8.35). <i>S</i><sub>P</sub> had the lowest values (33.72 PSU) in February and the highest (34.87 PSU) in September. <i>E</i><sub>v</sub> peaked in March (201 lux), with the highest values (>50 lux) in correspondence to the lowest values of <i>SIC</i> and a delayed trend, between December and March, with respect to <i>Chl</i>-a values (0.2–1.1 mg m<sup>−3</sup>). Ω<sub>Ca</sub> and Ω<sub>Ar</sub> showed their highest average monthly values (±s.d.) in January (Ω<sub>Ca</sub>: 3.41 ± 0.27; Ω<sub>Ar</sub>: 2.14 ± 0.17), when <i>DO</i> had maximum values. The lowest Ω occurred in September (Ω<sub>Ca</sub>: 2.11 ± 0.02; Ω<sub>Ar</sub>: 1.32 ± 0.02), at the end of phytoplankton activity. No undersaturation for both calcite and aragonite was recorded during the study period. This study highlights that biological activities and physico-chemical variables of the investigated shallow coastal site are coupled and, in many cases, influence each other.
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