Contrasting greenhouse gas (CO2, CH4, N2O) dynamics in two adjacent tropical estuaries: The PLUME 2024 campaign dataset

1. Overview This repository contains physical, biogeochemical, and greenhouse gas (CO2, CH4, N2O) data collected during the PLUME campaign (10 June – 9 July 2024) across southern Vietnam. The dataset covers two contrasting estuarine networks and their adjacent continental shelf waters: Saigon-DongNai River and Estuary: A tidal, urbanized river-estuary network draining Ho Chi Minh City, marked by low alkalinity and severe oxygen depletion. Mekong Delta Distributaries (Hau and Ham Luong branches): Large, well-buffered agricultural deltaic channels. Southern Vietnam Coastal Plume: The shared continental shelf receiving freshwater discharges from both systems. 2. Dataset Files Filename Format Description Records Size PLUME_2024_WetSeason_Comprehensive_Database.xlsx Excel Multi-tab workbook containing Metadata, Continuous Underway (10s), Discrete Samples, and Station Catalogs. 4 sheets 10.8 MB PLUME_2024_Continuous_Underway_Surface_QC.csv CSV High-resolution 10-second surface underway sensor measurements. 94,259 rows 17.6 MB PLUME_2024_Discrete_Bottle_QC.csv CSV Discrete surface (0.5 m) and bottom bottle samples with nutrient and gas chromatography data. 101 rows 31.3 KB PLUME_2024_Station_Metadata.csv CSV Station inventory with geographic coordinates, depths, weather, and tidal coefficients. 104 rows 12.5 KB 3. Data Dictionary 3.1 Continuous Underway Surface Dataset (PLUME_2024_Continuous_Underway_Surface_QC) Datetime_UTC: Timestamp in UTC (ISO 8601: YYYY-MM-DD HH:MM:SS). Datetime_Local_VN: Timestamp in Vietnam local time (UTC+7). Latitude, Longitude: Coordinates in WGS84 (EPSG:4326), Decimal Degrees. Platform: Survey platform (ANTEA = R/V ANTEA; Local boat = small survey vessels). System: River-estuary system (Saigon-DongNai or Mekong). Domain: Water classification (HCMC urban waters, Saigon estuarine transition, Mekong distributary waters, Continental shelf plume, Offshore marine baseline). Water_Depth_m: Total water column depth (m) recorded by vessel echosounder. Salinity_PSU: Practical salinity from flow-through WTW Cond 340i / Seabird SBE 911plus. Water_Temperature_degC: Surface water temperature (°C). pH_NBS: pH on the NBS scale. pCO2_water_uatm: Water pCO2 (µatm) measured with LI-COR 850 and marble equilibrator, corrected for temperature and water vapor. CO2_water_umol_L: Dissolved CO2 concentration (µmol/L) calculated with solubility K0 (Weiss, 1974). delta_pCO2_uatm: Air-sea pCO2 difference (µatm) relative to atmospheric baseline (423 µatm). Chlorophyll_a_ug_L: Surface fluorometer chlorophyll-a (µg/L) on R/V ANTEA. Turbidity_NTU: Optical turbidity (NTU). Continuous_CH4_nM: Continuous dissolved methane (nmol/L) from SubOcean spectrometer (Saigon network). Continuous_N2O_nM: Continuous dissolved nitrous oxide (nmol/L) from SARA spectrometer (Saigon network). Wind_Speed_ERA5_m_s: 10-meter wind speed (m/s) from ERA5 reanalysis. Hydrodynamic_Current_Velocity_m_s: Surface current velocity (m/s) simulated by 3D CROCO model for the Mekong distributaries. k600_cm_h: Gas transfer velocity normalized to Sc=600 (cm/h). k600_parameterization: Formulation used (Rosentreter_2017_Current_Wind for river/estuarine channels; Borges_2004_Wind for shelf plume). FCO2_mmol_m2_d: Diffusive air-water CO2 flux density (mmol m^-2 d^-1; positive = efflux to atmosphere). FCH4_mmol_m2_d: Diffusive air-water CH4 flux density (mmol m^-2 d^-1). QC_Flag: Quality control flag (Valid, Missing_Key_Variable). Note on Dissolved Oxygen: Flow-through underway logging did not include an in-line optical DO sensor. Dissolved oxygen was measured on all 101 discrete bottle samples. 3.2 Discrete Bottle Dataset (PLUME_2024_Discrete_Bottle_QC) Station_ID: Station identifier (S00–S20, M01–M18, N01–N40, C01–C10). Sample_Type: Sampling depth tier (Surface = 0.5 m; Bottom = ~1 m above seabed). Sampling_Depth_m: Sampling depth below surface (m). Station_Depth_m: Water column depth at the station (m). Datetime_UTC, Datetime_Local_VN: Timestamps in UTC and UTC+7. Latitude, Longitude: Coordinates in WGS84, Decimal Degrees. Platform, System, River_Branch: Vessel, system, and channel branch name. Salinity_PSU, Water_Temperature_degC, Conductivity_mS_cm, pH_NBS: In situ physical-chemical parameters. DO_saturation_pct, DO_concentration_mg_L: Dissolved oxygen measured with calibrated WTW Oxi probe. Total_Alkalinity_mmol_L, Total_Alkalinity_umol_kg: Total alkalinity from potentiometric titration (0.02 M HCl, endpoint pH 4.5). DOC_mgC_L, DOC_umol_L: Dissolved organic carbon measured by catalytic oxidation (Shimadzu TOC-L). NO3_umol_L, NH4_umol_L, PO4_umol_L, DSi_umol_L: Dissolved inorganic nutrients (µmol/L) via colorimetric spectrophotometry. Marine samples (S >= 20) are masked to avoid chloride interference. TN_umol_L, TP_umol_L: Total nitrogen and phosphorus (µmol/L) after alkaline persulfate digestion. Discrete_pCO2_uatm, Discrete_pCH4_uatm, Discrete_N2O_nmol_L: Headspace gas chromatography (PerkinElmer Clarus GC-FID/ECD). AOU_umol_L: Apparent Oxygen Utilization (µmol/L). deltaTA_nonconservative_umol_kg, deltaDIC_nonconservative_umol_kg: Deviations from conservative mixing lines. Matched_Continuous_pCO2_uatm: Underway pCO2 matched within 30 seconds of station sampling. k600_cm_h: Gas transfer velocity at station location (cm/h). Matched_Continuous_FCO2_mmol_m2_d: Underway CO2 flux density matched at station. Discrete_FCH4_mmol_m2_d, Discrete_FN2O_mmol_m2_d: Diffusive CH4 and N2O flux densities. Combined_Flux_CO2eq_mmol_m2_d: Combined radiative flux density (mmol CO2-eq m^-2 d^-1) using IPCC AR6 GWP100 (CH4 = 27.0, N2O = 273). 3.3 Station Metadata Dataset (PLUME_2024_Station_Metadata) Station_ID: Station code. System: Estuarine system or domain (Saigon-DongNai, Mekong, Continental Shelf / Offshore). Sampling_Area: Channel, sub-basin, or shelf sector. Platform: Sampling vessel (ANTEA or Local boat). Campaign_Leg: Cruise leg (Legs 3–5). Latitude, Longitude: Coordinates in WGS84, Decimal Degrees. Station_Depth_m: Total depth measured by echosounder (m). Date_UTC, Start_Time_UTC, End_Time_UTC: Operation time logs (UTC). Meteo_Conditions_WMO: Meteorological codes (WMO Code 4501). Sea_State_Douglas: Sea state (Douglas scale 0–9). Tidal_Coefficient: Astronomical tidal coefficient. 4. Analytical Methods Continuous Underway CO2: Equilibrator response time <120 s to 99% equilibration; LI-COR 850 calibrated with zero (N2) and span standards (1,000 ppm and 5,000 ppm). Continuous Spectrometry: SubOcean optical cavity spectrometer for CH4 and SARA cavity-enhanced absorption for N2O calibrated against certified standards. Headspace Gas Chromatography: 100 mL glass serum bottles preserved with 1% NaN3, equilibrated with high-purity N2, and analyzed on PerkinElmer Clarus GC. Thermodynamic Mixing: Carbonate calculations performed with PyCO2SYS v1.8 using Lueker et al. (2000) constants on the NBS scale. Contact: Julien Némery ([e-mail])