361 / 2024-09-15 03:07:31

The hydrographic and biogeochemical processes on the Ross Sea continental shelf based on BGC-Argo analysis

BGC-Argo,spring/summer process,Ross Sea continental shelf

Session 7 - Advances in the Oceanography of the Ross Sea

The Ross Sea is the most productive region in the Southern Ocean, which plays an important role in the carbon pump and elemental cycles. However, due to the challenges in sampling, continuous observations in this intermittently frozen region are rare; most research cruise emphasized spatial changes. In 2023, five BGC-Argo floats were deployed on the Ross Sea continental shelf region and recorded parameters over an entire year. Spring/summer processes were consistent with previous observations. Nitrate consumption began at the end of November and continued through mid-January when they ceased, presumably due to iron limitation under strong stratification. The decrease of dissolved inorganic carbon (DIC) and nitrate exhibited a strong linear relationship, but the ΔDIC: Δnitrate ratios were higher in the southern regions when compared to the central region. The chlorophyll increase was in prior to complete ice melt, suggesting the initial growth of phytoplankton likely occurred at locations where stratification increased but ice had not totally disappeared, allowing more radiation to enter the mixed layer. The amounts and proportions of chlorophyll and particulate organic carbon (POC) accumulation exhibited significant spatial differences, while the increased POC: chlorophyll ratios were recorded by central floats. Integrated particulate organic carbon below 100 m increased through time, suggesting that phytoplankton growth in the surface enhanced vertical carbon flux. The elevated DIC: nitrate ratios and reduced POC: chlorophyll ratios were indicative of haptophyte dominance, and combined with high chlorophyll suggests the dominance of Phaeocystis antarctica in the southern region. Spatial iron variations potentially play a significant role in the observed spatial variations of phytoplankton biomass. BGC-Argo floats provide an efficient method for continuous observations and improve our understand of annual hydrographic and biochemical changes.