Primary productivity measurements in the Ross Sea, Antarctica: a regional synthesis

Polar systems are undersampled due to the difficulty of sampling remote and challenging environments; however, these systems are critical components of global biogeochemical cycles. Measurements on primary productivity in specific areas can quantify the input of organic matter to food webs and so are of critical ecological importance as well. However, long-term measurements using the same methodology are available only for a few polar systems. Primary productivity measurements using C-14-uptake incubations from the Ross Sea, Antarctica, are synthesized, along with chlorophyll concentrations at the same depths and locations. A total of 19 independent cruises were completed and 449 stations occupied where measurements of primary productivity (each with seven depths) were completed. The incubations used the same basic simulated in situ methodology for all. Integrated water column productivity for all stations averaged 1.10 +/- 1.20 gCm(-2) d(-1), and the maximum was 13.1 g Cm-2 d(-1). Annual productivity calculated from the means throughout the growing season equalled 146 g Cm-2 yr(-1). The mean chlorophyll concentration in the euphotic zone (the 1% irradiance level) was 2.85 +/- 2.68 mg m(-3) (maximum observed concentration was 19.1 mg m(-3)). Maximum photosynthetic rates above the 30% isolume (normalized to chlorophyll) averaged 0.98 +/- 0.71 mgC (mg chl)(-1) h(-1), similar to the maximum rate found in photosynthesis-irradiance measurements. Productivity measurements are consistent with the temporal patterns of biomass found previously, with biomass and productivity peaking in late December; mixed layers were at a minimum at this time as well. Estimates of plankton composition also suggest that pre-January productivity was largely driven by the haptophyte Phaeocystis antarctica and summer productivity by diatoms. The data set (https://doi.org/10.26008/1912/bco-dmo.863815.2, Smith, 2021) will be useful for a comparison to other Antarctic regions and provide a basis for refined bio-optical models of regional primary productivity and biogeochemical models for the Southern Ocean.