Dataset: GP15 delta30Si Leg 2

Name: Depth profiles of the isotopic composition (δ30Si) of silicon within dissolved silicic acid from samples collected on Leg 2 of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1815) on R/V Roger Revelle from October to November 2018
Published: 2024-12-19
Keywords: oceans

Cite This Dataset

DOI:10.26008/1912/bco-dmo.946249.1

Spatial Extent: N:17.5 E:-151.9862 S:-20 W:-152.0082

Meridional Pacific Ocean

Temporal Extent: 2018-10-26 - 2018-11-23

Project:

US GEOTRACES Pacific Meridional Transect (GP-15): Resolving Silicon Isotope Anomalies in the Northeast Pacific (PMT Si)

US GEOTRACES Pacific Meridional Transect (GP15) (U.S. GEOTRACES PMT)

Program:

U.S. GEOTRACES (U.S. GEOTRACES)

Principal Investigator:

Mark A. Brzezinski (University of California-Santa Barbara, UCSB-MSI)

Contact:

Janice L. Jones (University of California-Santa Barbara, UCSB-MSI)

BCO-DMO Data Manager:

Shannon Rauch (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

Version Date:

2024-12-19

Restricted:

Validated:

Yes

Current State:

Final no updates expected

Depth profiles of the isotopic composition (δ30Si) of silicon within dissolved silicic acid from samples collected on Leg 2 of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1815) on R/V Roger Revelle from October to November 2018

Abstract:

The isotopic composition of dissolved silicon (δ30Si) has proven to be a powerful tool to better understand the marine Si cycle. The δ30Si of seawater carries information about dissolved silicon utilization in surface waters, the subsequent dissolution of sinking biogenic material as well as water mass mixing. This data set supplies information on the spatial distribution of isotopes of Si within water masses from Tahiti to Alaska along GEOTRACES section GP15. This dataset results from leg 2 of the expedition, RR1815; data from RR1814 are available in a separate BCO-DMO dataset.

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Archival Copy

Version Date	Archive	Persistent Identifier (PID)	Date PID Issued
2024-12-19	Marine Biological Laboratory/Woods Hole Oceanographic Institution Library (MBLWHOI DLA)	10.26008/1912/bco-dmo.946249.1	2024-12-19

Methods & Sampling

Seawater samples for δ30Si measurements were collected using the Oceanographic Data Facilitiy's (ODF, Scripps Institution of Oceanography) CTD-rosette mounted with Niskin samplers and a Sea-Bird Electronics CTD (SBE9plus). Seawater was gravity-filtered into polypropylene containers through in-line Supor filter capsules (0.8/0.45-micrometer (µm)) attached directly to each Niskin bottle. Sample bottles were capped and stored without preservative in the dark.

Back in the laboratory, the silicon from seawater was precipitated off as trimethylamine silicomolybdate using a high-purity triethlyamine ammonium molybdate solution (TEA-Moly). The precipitate was isolated by filtration onto a polycarbonate filter and purified by high-temperature combustion to produce solid silicon dioxide. SiO2 was then converted to solid Cs2SiF6 by dissolution in HF and addition of CsCl. The Cs2SiF6 was rinsed with ethanol, dried, and dissolved in high purity (>18MΩ) water. BaSiF6 was precipitated by the addition of BaCl, rinsed with ethanol and dried.

Isotopic ratio analysis was performed using a Nu Perspective isotope ratio mass spectrometer equipped with a Nu Sil inlet system. Samples of BaSiF6 are loaded into sample vials that are placed in a sample carousel in the Nu Sil. Samples are sequentially heated to 590 degrees Celsius (°C) to evolve.

Isotope delta values are normalized against the international standard NBS28.

Methods are further described in the Supplemental File "Natural_Abundance_Protocol.pdf".

Data Processing Description

Depths (represented as pressure in decibars), date-times, and locations (lat/lon) in the dataset were obtained from the cruise's CTD bottle file based on the unique GEOTRACES sample number for each sample. However, there were sometimes multiple bottles tripped for a single GEOTRACES sample number. In those cases, if the Niskin/Go-Flo number was also recorded by the data provider, the metadata information for that bottle was used. If the Niskin/Go-Flo number was not recorded along with the GEOTRACES number, the rosette bottle number that had both O2 and salinity data was used to obtain the metadata information for the sample, as advised by the cruise's lead PIs.

Quality flags were assigned according to the following definitions:

1 = Good; passed documented required QC tests.
2 = Not evaluated, not available or unknown. Used for data when no QC test performed or the information on quality is not available.
3 = Questionable/suspect; failed non-critical documented metric or subjective test(s).
4 = Bad; failed critical documented QC test(s) or as assigned by the data provider.
9 = Missing data. Used as place holder when data are missing.

BCO-DMO Processing

- Imported original file "RR1815_silicon.xlsx" into the BCO-DMO system.
- Marked "nd", "no data", "#N/A" , and "small n" as missing data values (missing data values are empty/blank in the final CSV file).
- Renamed fields to comply with BCO-DMO naming conventions.
- Created date-time field in ISO 8601 format.
- Rounded values in the SILICATE_30_28_D_DELTA_BOTTLE_1foxwp and SD1_SILICATE_30_28_D_DELTA_BOTTLE_1foxwp columns to 3 decimal places.
- Removed the following empty columns: End_Date_UTC, End_Time_UTC, End_Latitude, End_Longitude.
- Saved the final file as "946249_v1_gp15_delta30si_leg2.csv".

Data Files

File
946249_v1_gp15_delta30si_leg2.csv (Comma Separated Values (.csv), 26.93 KB) MD5:0f5495df01d62f74ce07af67b7ffccf3 Primary data file for dataset ID 946249, version 1

Supplemental Files

File
Natural_Abundance_Protocol.pdf (Portable Document Format (.pdf), 284.37 KB) MD5:9220bce254d78da1714d456b5bed38ae Supplemental file for dataset IDs 946242 (version 1) and 946249 (version 1).

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-1732139

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
RR1815	GP15 GP15 Leg 2 33RR20180918 PMT US GEOTRACES PMT	2018-10-24	R/V Roger Revelle	Gregory A. Cutter (Chief Scientist) Karen L. Casciotti (Co-Chief Scientist) Phoebe J. Lam (Co-Chief Scientist)	data info

Instruments

Isotope-ratio Mass Spectrometer

Supplied Name: Nu Perspective isotope ratio mass spectrometer

Supplied Description:

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 Name: Niskin bottles on the GEOTRACES ODF CTD-rosette system

Supplied Description:

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.

Parameters

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

Supplied Name	Supplied description	Supplied Units	Standard Name
Station_ID	sampling station	unitless	station
Start_Date_UTC	cast date Format: %d/%m/%Y	unitless	date
Start_Time_UTC	cast time (UTC) Format: %H:%M	unitless	time
Start_ISO_DateTime_UTC	cast date and time (UTC) in ISO 8601 format Format: %Y-%m-%dT%H:%MZ	unitless	ISO_DateTime_UTC
Start_Latitude	cast latitude (negative values = South)	decimal degrees	lat
Start_Longitude	cast longitude (negative values = West)	decimal degrees	lon
Event_ID	GEOTRACES event number	unitless	event
Sample_ID	GEOTRACES sample number	unitless	sample
Sample_Depth	Pressure at depth of sample collected; obtained from CTD data provided by from chief scientist	decibars (db)	press
SILICATE_30_28_D_DELTA_BOTTLE_1foxwp	mean delta30Si(OH)4 relative to the NBS28 standard	per mil	Si
SD1_SILICATE_30_28_D_DELTA_BOTTLE_1foxwp	Standard deviation of SILICATE_30_28_D_DELTA_BOTTLE_1foxwp	per mil	Si
Flag_SILICATE_30_28_D_DELTA_BOTTLE_1foxwp	Quality flag for SILICATE_30_28_D_DELTA_BOTTLE_1foxwp	unitless	q_flag