DOI: 10.5281/zenodo.18338891
title: Nitrate and primary production dataset from the fjords around Uummannaq, Northwest Greenland

description: Data was collected from the research vessel RV Sanna, Eurofleets+ IOPD cruise, in the fjord system near Uummannaq in West Greenland, between 28 June 2022 and 10 July 2022, along in total five fjords, from the shelf edge towards the head of the fjord or until icebergs blocked the way. More details can be found in the cruise report: https://csr.seadatanet.org/report/21026654.

 

File 1 (SUNA_Nitrate)

This dataset contains nitrate concentration profiles measured using a Satlantic SUNA V2 (Submersible Ultraviolet Nitrate Analyzer). Data have been temperature-salinity corrected and validated against discrete bottle samples.

## Instrument

- **Sensor**: Satlantic SUNA V2 (Submersible Ultraviolet Nitrate Analyzer)- **Measurement principle**: UV absorption spectroscopy (190-370 nm)- **Fitting wavelength range**: 217-240 nm

## Methods

### Temperature-Salinity Correction

SUNA measurements require correction for the temperature and salinity dependence of seawater UV absorption. This dataset uses the Sakamoto et al. (2009) linear correction method:

    A_sw = (S / S_cal) * (E_SWA + (T - T_cal) * E_TSWA)    A_corrected = A_measured - A_sw

Where:- **A_sw**: Seawater absorbance contribution- **S, T**: In situ salinity (PSU) and temperature (°C) from CTD- **S_cal, T_cal**: Calibration reference values (34.5 PSU, 20°C)- **E_SWA**: Seawater extinction coefficient spectrum- **E_TSWA**: Temperature slope of seawater extinction

### CTD Data Source

- **Temperature and Salinity**: Bin-averaged CTD data (1 dbar bins) for smooth T-S correction

### Spectral Fitting

Nitrate concentration is determined by fitting the corrected absorbance spectrum to the nitrate extinction coefficient using non-negative least squares (NNLS) regression over the 217-240 nm wavelength range.

### Bottle Correction

A depth-independent offset correction is applied based on comparison with discrete bottle samples analyzed in the laboratory:

    NO3_final = NO3_SUNA + offset

The offset is calculated as the median difference between SUNA and bottle values at matched depths for each station.

### Data Processing

- **Soak period removal**: Surface equilibration period removed before processing- **Cast selection**: Both downcast and upcast data included- **Depth interpolation**: Data interpolated to standard 1-meter depth intervals

## Data File: SUNA_Nitrate_Zenodo.csv

### Column Descriptions

| Column | Unit | Description ||--------|------|-------------|| Cast | - | Station/cast identifier || Date | YYYY-MM-DD | Sampling date || Time_UTC | HH:MM:SS | Sampling time (UTC) || Latitude | degrees N | Station latitude (decimal degrees) || Longitude | degrees E | Station longitude (decimal degrees, negative = West) || Depth_m | m | Standard depth (1, 2, 3, ... m) || Temperature_C | °C | In situ temperature from CTD || Salinity_PSU | PSU | In situ salinity from CTD || Nitrate_Raw_uM | µmol L⁻¹ | SUNA nitrate before bottle offset correction || Nitrate_Corrected_uM | µmol L⁻¹ | SUNA nitrate after bottle offset correction (recommended) || Nitrate_Bottle_uM | µmol L⁻¹ | Discrete bottle nitrate (at actual sample depths only) | Subsamples (10 mL) were filtered through 0.45 um filters (Q-Max GPF) and frozen at -20C until analysis. Nutrients were measured by standard colorimetric methods on a Seal QuAAtro autoanalyzer. 

 

## Calibration

- **Factory calibration**: SUNA calibrated by manufacturer- **Field validation**: Bottle samples collected and analyzed for nitrate+nitrite

## Uncertainty

Typical uncertainty for SUNA nitrate measurements after correction:- **Precision**: ~0.3 µM (based on spectral fit residuals)- **Accuracy**: ~0.5-1.0 µM (based on bottle comparison)

## References

- Sakamoto, C.M., Johnson, K.S. & Coletti, L.J. (2009). Improved algorithm for the computation of nitrate concentrations in seawater using an in situ ultraviolet spectrophotometer. Limnology and Oceanography: Methods, 7, 132-143. DOI: 10.4319/lom.2009.7.132

- Johnson, K.S. & Coletti, L.J. (2002). In situ ultraviolet spectrophotometry for high resolution and long-term monitoring of nitrate, bromide and bisulfide in the ocean. Deep-Sea Research I, 49, 1291-1305.

## Data Processing Software

Data were processed using R (version 4.x) with the following packages:- oce (oceanographic data handling)- dplyr (data manipulation)- nnls (non-negative least squares fitting)

 

File 2 (Primary_production)

This dataset contains depth-integrated primary production (PP) estimates. Primary production was calculated using photosynthesis-irradiance (PI) curve parameters derived from 14C incubation experiments, combined with in situ chlorophyll profiles and theoretical surface PAR.

### Primary Production Calculation

Primary production was calculated using the Jassby-Platt model:

    PP = Pmax * tanh(alpha * PAR / Pmax) * Chl

Where:- **Pmax**: Maximum photosynthetic rate (mg C (mg Chl)^-1 h^-1)- **alpha**: Initial slope of PI curve (mg C (mg Chl)^-1 h^-1 (umol m^-2 s^-1)^-1)- **PAR**: Photosynthetically active radiation (umol m^-2 s^-1)- **Chl**: Chlorophyll-a concentration (mg m^-3)

### PI Curve Parameters

PI curve parameters (Pmax, alpha) were derived from 14C incubation experiments at multiple depths per station. Parameters were interpolated vertically to create continuous profiles.

### Chlorophyll Profiles

Chlorophyll profiles were constructed by calibrating CTD fluorescence measurements against discrete bottle chlorophyll samples using depth-specific correction factors.

### Light Model

- **Surface PAR**: Calculated using the incident() function from the phytotools R package (clear sky conditions)- **Underwater light attenuation**: Measured CTD PAR profiles (normalized attenuation) were used when available; otherwise theoretical exponential decay with measured Kd values

### Integration

- **Depth range**: 0-50 m (or to maximum cast depth if shallower)- **Depth resolution**: 1 m- **Time resolution**: 5 minutes- **Daily integration**: Summed over 24-hour period- **Cruise average**: Mean of daily PP values across all cruise days

### Column Descriptions

| Column | Unit | Description ||--------|------|-------------|| Cast | - | Station/cast identifier || Latitude | degrees N | Station latitude (decimal degrees) || Longitude | degrees E | Station longitude (decimal degrees, negative = West) || Cruise_Start | YYYY-MM-DD | Start date of cruise period || Cruise_End | YYYY-MM-DD | End date of cruise period || PP_cruise_avg | mg C m^-2 d^-1 | Depth-integrated primary production (cruise average) || mean_Chl | mg m^-3 | Mean chlorophyll concentration in water column |

## References

- Jassby, A.D. & Platt, T. (1976). Mathematical formulation of the relationship between photosynthesis and light for phytoplankton. Limnology and Oceanography, 21(4), 540-547.

- Platt, T., Gallegos, C.L. & Harrison, W.G. (1980). Photoinhibition of photosynthesis in natural assemblages of marine phytoplankton. Journal of Marine Research, 38, 687-701.

## Data Processing

Data were processed using R (version 4.x) with the following packages:- phytotools (PI curve fitting, PAR calculation)- openxlsx (Excel file handling)- oce (oceanographic calculations)