Net community production in the Greenland Sea: a comparative case study using Argo data of nitrate, oxygen, and DIC

In this case study, we derive and compare estimates of annual net community production (NCP) in the Greenland Sea from Argo float data of nitrate, oxygen, and dissolved inorganic carbon (DIC). We added tracers of the inorganic carbon system, nitrate, dissolved oxygen, and air-sea gas exchange to the 1-D Price-Weller-Pinkel mixing model (Price et al., 1986) tuned to the Greenland Sea (Moore et al., 2015; Brakstad et al., 2019). By reinitializing the model with every Argo profile, we were able to estimate NCP as the difference between the abiotic model output and the Argo profiles. This method has previously been employed in various other regions (Plant et al. 2016;  Briggs et al. 2017, Mork et al. 2024). While we here compare NCP estimates from both nitrate, oxygen, and DIC, previous work has considered maximum two of these concurrently. Through our comparison, we discovered quantitative discrepancies in the NCP and annual NCP (ANCP) estimates. These results were sensitive to trends in the raw data and artefacts deriving from processes that were unresolved in the model, such as internal waves. Effects from internal waves were challenging to remove without introducing new artefacts. Qualitatively, the NCP seasonal cycle was well resolved: the summer of 2019, NCP fluctuated between periods of weak net biological production and periods of weak net heterotrophy. NCP was close to zero through winter, before two strong blooms were observed in late April and May 2020. However, the amplitude of the NCP signal from DIC was somewhat larger than from nitrate and oxygen. DIC derived NCP also exhibited stronger signs of remineralization from November 2019 to January 2020 compared to the two other estimates. Thus, this work shows the importance of careful consideration when utilizing biogeochemical Argo data in the Greenland Sea.