Dataset: Hydrography, nutrients, and mean N2 fixation rates (SPIROPA, July 2019)

Name: Hydrography, nutrients, and nitrogen uptake rates from SPIROPA cruise TN368 in July 2019
Published: 2024-05-20
Keywords: N2 fixation, diazotrophs, Mid-Atlantic bight, shelf, oceans

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Spatial Extent: N:40.5 E:-70 S:39 W:-71

Mid-Atlantic Bight shelfbreak front to the south of Massachusetts, USA. Multiple transects in the area of 70-71 degrees W longitude and 39-40.5 degrees N latitude. Sampling was restricted to waters above the 0.1% light level.

Temporal Extent: 2019-07-05 - 2019-07-18

Project:

Collaborative Research: Shelfbreak Frontal Dynamics: Mechanisms of Upwelling, Net Community Production, and Ecological Implications (SPIROPA)

Principal Investigator:

Margaret Mulholland (Old Dominion University, ODU)

Co-Principal Investigator:

Phoebe Dreux Chappell (Old Dominion University, ODU)

Student:

Corday Selden (Old Dominion University, ODU)

BCO-DMO Data Manager:

Dana Stuart Gerlach (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

Version Date:

2024-05-20

Restricted:

Validated:

Current State:

Preliminary and in progress

Hydrography, nutrients, and nitrogen uptake rates from SPIROPA cruise TN368 in July 2019

Abstract:

Continental shelves contribute a large fraction of the ocean’s new nitrogen (N) via N2 fixation; yet, we know little about how physical processes at the ocean’s margins shape diazotroph biogeography and activity. This dataset includes N2 fixation rates and hydrographic measurements collected at the Mid-Atlantic Bight shelfbreak front in July 2019. Rates were measured using the 15N2 bubble release method on repeat cross-frontal transects. This study was coordinated with the SPIROPA (‘Shelfbreak Productivity Interdisciplinary Research Operation at the Pioneer Array’) Project (https://www.bco-dmo.org/project/748894). See Selden et al. (2024, JGR-Oceans) or contact Dr. Corday Selden (crselden@marine.rutgers.edu) for further information.

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Description

This dataset is derived from Selden et al. (2024) JGR Oceans Table S1, and McGillicuddy bottle data from TN368, the third SPIROPA cruise (https://www.bco-dmo.org/dataset/849340). The mean values of nitrogen fixation rates shown here are derived from nitrogen fixation incubation data (https://www.bco-dmo.org/dataset/928568)

Glossary of terms:
A = Atom-% enrichment
APN = Atom-% enrichment of the particulate nitrogen pool
BDL = Below detection limit
DNQ = Detectable but not quantifiable
LOD = Limit of detection
LOQ = Limit of quantification
N2 = Nitrogen gas
PETG = Polyethylene Terephthalate Glycol
PN = Particulate nitrogen
NFR = Nitrogen fixation rate
SUR = Specific uptake rate
t0 = time initial
tf = time final

Methods & Sampling

Nitrogen fixation rates and hydrographic data were measured in July 2019 in conjunction with the SPIROPA (Shelfbreak Productivity Interdisciplinary Research Operation at the Pioneer Array) project cruises (Chief Scientist Dr. Dennis McGillicuddy). This case study was conducted at the Mid-Atlantic Bight shelfbreak front to the south of Massachusetts, USA to examine whether significant N2 fixation occurs in the continental shelf region. On July 5th, 2019, the vessel R/V Thomas G. Thompson (cruise TN368) departed Woods Hole, MA and performed multiple transects in the area of 70 to 71 degrees West longitude and 39 to 40.5 degrees North latitude. Sampling was restricted to waters above the 0.1% light level.

Water was collected in 10L Niskin bottles on a 24-bottle rosette. Vertical conductivity, temperature, and depth profiles were measured concurrently using a Sea-Bird 911+ CTD profiler. Samples to determine nitrate, phosphate, and silicate concentrations were filtered (0.4 um, polycarbonate) directly from the Niskin bottles into acid-washed polyethylene bottles and stored frozen until analysis. Standard colorimetric methods were performed at the Woods Hole Oceanographic Institution's Nutrient Analytical Facility using a SEAL Analytical AA3 HR discrete chemistry analyzer. Detection limits for nitrate, phosphate, and silicate methods were 0.040, 0.030 and 0.009 μM, respectively.

This dataset presents hydrographic and nutrient data plus uptake rates and nitrogen fixation rates based on the mean values of replicate samples at each collection site and depth. For full incubation data (and methods) for all replicates, please refer to BCO-DMO dataset https://www.bco-dmo.org/dataset/928568.

Nitrogen fixation rates (NFR) were measured using the ¹⁵N₂ bubble release method on repeat cross-frontal transects. Bottles were incubated on-deck for approximately 24 hours in incubators that recirculated water through aquaria chillers to maintain approximate temperature conditions for shelf, frontal, and offshore waters. At the end of the incubation period, an aliquot was collected from each bottle for isotope analysis (see https://www.bco-dmo.org/dataset/928568). The remaining incubation volume was then filtered for initial particulate nitrogen (PN) samples.

Specific uptake rates were calculated following Montoya et al. (1996), with equations detailed below.

Data Processing Description

Specific N₂ uptake rates (SUR) were calculated following Montoya et al. (1996):

Equation 1: SUR = (APN_tf - APN_t0) / (AN2 - APN_t0) ] x (1/time)

where A represents the atom-% enrichment of the initial (t=0) or final (t=f) particulate nitrogen (PN) pool, or the nitrogen (N₂) pool. Across all experiments, AN2 averaged 3.89 ± 2.0%. Experiments with <1% enrichment were excluded from downstream analysis. The specific uptake rate represents the relative contribution of diazotroph-derived N to PN turnover within a given sample. Absolute N₂ fixation rates (NFR) were calculated as:

Equation 2: NFR = SUR x [PN]

where [PN] indicates the particulate nitrogen concentration. Limits of detection and quantification were calculated per incubation by propagating the minimum detectable difference between initial and final ¹⁵N atom-% enrichment of the PN pool (3σ and 10σ), three sigma and ten sigma respectively, n≥7, 12.5 µg N standards measured daily through Eqn. 2 (Ripp, 1996; White et al. 2020). A rate was only considered detectable if two of three replicate incubations yielded detectable rates.

BCO-DMO Processing

- Imported data from source file "Selden_JGR24_TableS1.xlsx" into the BCO-DMO data system.
- Changed date format from m/d/yyyy to yyyy-mm-dd (ISO Date 8601 format) and converted datetimes from EST to UTC.
- Converted latitude and longitude to decimal degrees.
- Added official cruise ID corresponding to the the provided deployment and cruise name
- Added cast number and replicate sample ids (from the incubations) based on datetime and depth.
- Rounded values according to the PI’s/submitter’s indicated precision
- Modified parameter (column) names to conform with BCO-DMO naming conventions. The only allowed characters are A-Z,a-z,0-9, and underscores. No spaces, hyphens, commas, parentheses, or Greek letters.

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-1657803

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
TN368		2019-07-05	R/V Thomas G. Thompson	Dennis J. McGillicuddy (Chief Scientist)	data info

Instruments

Aquarium chiller

Supplied Name: AquaEuroUSA Aquaria chillers (MC-1/10HP)

Supplied Description:

To avoid temperature-shocking the samples, three on-deck incubators recirculated water through aquaria chillers (MC-1/10HP, AquaEuroUSA) housed in custom casings.

Instrument Type

Generic Name: Aquarium chiller

Generic Description:

Immersible or in-line liquid cooling device, usually with temperature control.

CTD Sea-Bird SBE 911plus

Supplied Name: Sea-Bird 911 plus CTD

Supplied Description:

Vertical conductivity, temperature, and depth profiles were collected concurrently using a Sea-Bird 911 plus CTD.

Instrument Type

Generic Name: CTD Sea-Bird SBE 911plus

Acronym: CTD SBE 911plus

Community Identifier: http://vocab.nerc.ac.uk/collection/L22/current/TOOL0058/

Generic Description:

The Sea-Bird SBE 911 plus is a type of CTD instrument package for continuous measurement of conductivity, temperature and pressure. The SBE 911 plus includes the SBE 9plus Underwater Unit and the SBE 11plus Deck Unit (for real-time readout using conductive wire) for deployment from a vessel. The combination of the SBE 9 plus and SBE 11 plus is called a SBE 911 plus. The SBE 9 plus uses Sea-Bird's standard modular temperature and conductivity sensors (SBE 3 plus and SBE 4). The SBE 9 plus CTD can be configured with up to eight auxiliary sensors to measure other parameters including dissolved oxygen, pH, turbidity, fluorescence, light (PAR), light transmission, etc.). more information from Sea-Bird Electronics

Incubator

Supplied Name: incubator

Supplied Description:

To avoid temperature-shocking the samples, three on-deck incubators recirculated water through aquaria chillers.

Instrument Type

Generic Name: Incubator

Acronym: incubator (general)

Generic Description:

A device in which environmental conditions (light, photoperiod, temperature, humidity, etc.) can be controlled.

Note: we have more specific terms for shipboard incubators (https://www.bco-dmo.org/instrument/629001) and in-situ incubators (https://www.bco-dmo.org/instrument/494).

Isotope-ratio Mass Spectrometer

Supplied Name: Europa 20/20 isotope ratio mass spectrometer with automated nitrogen and carbon preparation module

Supplied Description:

Initial and final PN isotopic composition and concentration were analyzed on a Europa 20/20 isotope ratio mass spectrometer with an automated N and carbon preparation module.

Instrument Type

Generic Name: Isotope-ratio Mass Spectrometer

Acronym: IR Mass Spec; IRMS

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/LAB16/

Generic Description:

The Isotope-ratio Mass Spectrometer is a particular type of mass spectrometer used to measure the relative abundance of isotopes in a given sample (e.g. VG Prism II Isotope Ratio Mass-Spectrometer).

Niskin bottle

Supplied Description:

A CTD rosette equipped with 24 10L Niskin bottles was used to sample water in the Mid Atlantic Bight

Instrument Type

Generic Name: Niskin bottle

Community Identifier: http://vocab.nerc.ac.uk/collection/L22/current/TOOL0412/

Generic Description:

A Niskin bottle (a next generation water sampler based on the Nansen bottle) is a cylindrical, non-metallic water collection device with stoppers at both ends. The bottles can be attached individually on a hydrowire or deployed in 12, 24, or 36 bottle Rosette systems mounted on a frame and combined with a CTD. Niskin bottles are used to collect discrete water samples for a range of measurements including pigments, nutrients, plankton, etc.

Seal Analytical AutoAnalyser 3HR

Supplied Name: SEAL Analytical AA3 HR discrete chemistry analyzer

Supplied Description:

Samples to determine nitrate, phosphate, and silicate concentrations were filtered (0.4 μm, polycarbonate) directly from Niskin bottles into acid‐washed polyethylene bottles and stored frozen until analysis via standard colorimetric methods at the WHOI Nutrient Analytical Facility using a SEAL Analytical AA3 HR discrete chemistry analyzer.

Instrument Type

Generic Name: Seal Analytical AutoAnalyser 3HR

Generic Description:

A fully automated Segmented Flow Analysis (SFA) system, ideal for water and seawater analysis. It comprises a modular system which integrates an autosampler, peristaltic pump, chemistry manifold and detector. The sample and reagents are pumped continuously through the chemistry manifold, and air bubbles are introduced at regular intervals forming reaction segments which are mixed using glass coils. The AA3 uses segmented flow analysis principles to reduce inter-sample dispersion, and can analyse up to 100 samples per hour using stable LED light sources.

Parameters

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
DateTime_EST	Datetime of sampling in Eastern Standard Time Format: %Y-%m-%d %H:%M	unitless	DateTime
Latitude	Latitude of sampling site	decimal degrees	lat
Longitude	Longitude of sampling site	decimal degrees	lon
Cruise_ID	Cruise ID	unitless	cruise_id
Cast	Cast identifier for cruise TN368 on R/V T.G. Thompson	unitless	cast
Depth	Depth at which sample was collected	meters (m)	depth
Salinity	Salinity (derived from CTD data)	psu	sal_ctd
Temperature	Temperature in degrees Celsius (derived from CTD data)	degrees Celsius (°C)	temp
SigmaTheta	Sigma theta potential density at sampling depth (derived from CTD data)	kilograms per cubic meter (kg/m3)	sigma_0
NO3	Nitrate concentration of sample water	micromolar	NO3
PO4	Phosphate concentration of sample water	micromolar	PO43-
SiO4	Silicate concentration of sample water	micromolar	SiO4
PN_mean	Mean particulate nitrate concentration of sample water	micromolar	NO3
PN_sd	Standard deviation of particulate nitrate concentrations of sample water	micromolar	NO3
Replicate_incubations	Number of replicate 15N2 incubations conducted	unitless	num_reps
Repl_spl_ids	Sample ID of replicate samples in incubation	unitless	sample_descrip
Flag	Flag for specific uptake rate/nitrogen (N2) fixation rate, where DNQ = Detected but not quantifiable; BDL = Below detection limit	unitless	flag
SUR_mean	Mean specific N2 uptake rate calculated from replicate incubations	per day	N
SUR_sd	Standard deviation of specific nitrogen uptake rates	per day	N
NFR_mean	Mean nitrogen fixation rate calculated from replicate incubations	nanomoles nitrogen per liter per day (nmol N2/L/day)	N2_fix
NFR_sd	Standard deviation of nitrogen fixation rates	nanomoles nitrogen per liter per day (nmol N2/L/day)	N2_fix
NFR_LOD	Limit of detection for nitrogen fixation rate at given sampling location	nanomoles nitrogen per liter per day (nmol N2/L/day)	N
NFR_LOQ	Limit of quantification for nitrogen fixation rate at given sampling location	nanomoles nitrogen per liter per day (nmol N2/L/day)	N
SUR_LOD	Limit of detection for specific nitrogen uptake rate at given sampling location	per day	N
SUR_LOQ	Limit of quantification for specific nitrogen uptake rate at given sampling location	per day	N
ISO_DateTime_UTC_if_EST	Datetime of sampling in UTC (if original datetimes were EST or GMT-5) Format: %Y-%m-%dT%H:%MZ	unitless	ISO_DateTime_UTC
ISO_DateTime_UTC_if_EDT	Datetime of sampling in UTC (if original datetimes were actually EDT or GMT-4) Format: %Y-%m-%dT%H:%MZ	unitless	ISO_DateTime_UTC

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Dataset: Hydrography, nutrients, and mean N2 fixation rates (SPIROPA, July 2019)