Time series measurements of dissolved nitrous oxide, nutrients, and chlorophyll at stations in the South Shetland Islands

The data set comprises concentrations of dissolved nitrous oxide (N2O), an important green house gas, d nutrients and chlorophyll-a from surface ocean. Seawater samples collected in a time series stations located in Greenwich Island within the South Shetland Islands, an area n of the western Antarctic Peninsula influenced by the circumpolar current system and adjacent to Bellinghausen. Two specific marine sampling points (Station P1: -62,489S; -59,683W and station P3: -62,461; -59,677 W) were monitored over four late summer periods (February and early March) in the years 2017, 2018, 2019, and 2020. Physical variables were measured with a Conductivity Temperature Depth profiler (CTD; SeaBird19 plus). Seawater samples for biological and biogeochemical variables were superficially collected at a depth of 2, 5 or 10 meters using a handheld pump or Niskin bottles (5 and 10 m depth) aboard a Zodiac boat for nitrous oxide, nutrient, and chlorophyll analysis. Simultaneously, a CTD instrument was deployed to obtain temperature (°C) and salinity profiles. For chlorophyll a (Chl-a) measurements, triplicate 1-L samples of seawater from both 2 and 30 m depth were prefiltered with a 150-µm net to exclude large organisms, and then the remaining biomass was collected by subsequent filtration with 0.7-µm GF/F glass fiber filters. Each filter was frozen until processing, using acetone extraction protocols, after which extracts were analyzed by fluorometric (measured with a 10-AU Turner fluorometer (Turner, USA). ([Holm-Hansen & Riemann, 1978] techniques, respectively. Samples for the determination of inorganic nutrients (nitrite (NO2−), nitrate (NO3−) and phosphate (PO43−)) were also taken in triplicate stored in 15 mL polyethylene tubes and frozen at −20 °C in the dark until analysis. NO2−, NO3− and PO4−3 concentrations were measured with a Seal AutoAnalyzer 3 (AA3, SEAL Analytical, Mequon, WI, USA) [Grashoff et al., 2009]. N2O samples were taken in triplicate in 20 mL vials and carefully sealed to avoid air bubbles. They were then preserved with 50 μL of saturated HgCl2 and stored in darkness until analysis. N2O was analyzed by creating a 5 mL headspace of ultrapure Helium (He) and then equilibrated within the vial and measured by gas chromatography (Shimadzu 17A) using an electron capture detector (ECD). The calibration curves were made before each measurement with five points using pure He, 0.1, 0.5, and 1 of N2O standards and dry air (Farias et al., 2015). The ECD detector linearly responded to this concentration range and the analytical error for N2O measurements was ~3%. The uncertainty of the measurements was calculated from the standard deviation of the triplicate measurements by depth. Samples with a variation coefficient above 10% were not considered in the N2O database. Procedures of calibration were used following Wilson et al. (2018)