Dataset: Thorium-234 along the Western Antarctic Peninsula (2016-2020)

Name: Total water-column Thorium-234 measurements collected during January cruises of the Palmer LTER program along the Western Antarctic Peninsula from 2016-2020
Published: 2024-12-04
Keywords: thorium-234, sinking particles, Carbon Export, biological carbon pump, uranium-thorium disequilibrium, oceans

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Spatial Extent: N:-63.9653 E:-64.398014 S:-69.39223 W:-78.19839

Western Antarctic Peninsula

Temporal Extent: 2016-01-11 - 2020-02-02

Project:

Quantifying Processes Driving Interannual Variability in the Biological Carbon Pump in the Western Antarctic Peninsula (WAP Carbon export)

Principal Investigator:

Michael R. Stukel (Florida State University, FSU)

BCO-DMO Data Manager:

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

Version:

Version Date:

2024-12-04

Restricted:

Validated:

Current State:

Data not available

Total water-column Thorium-234 measurements collected during January cruises of the Palmer LTER program along the Western Antarctic Peninsula from 2016-2020

Abstract:

This dataset includes total water-column Thorium-234 measurements collected during January cruises of the Palmer LTER program along the Western Antarctic Peninsula. 238U-234Th disequilibrium is used as a proxy for sinking particle flux out of the upper ocean. Vertical profiles of 234Th were measured using standard small-volume techniques on 5 Palmer LTER cruises on ARSV Laurence M. Gould during 2016-2020. Measurements typically spanned from the surface to a depth of ~200 meters, although the deepest depths were variable, based on the LTER sampling program. Typically, 12 to 20 stations were sampled per year.

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Methods & Sampling

Total 234Th was measured using standard small volume techniques (Benitez-Nelson et al., 2001; Pike et al., 2005). 4-liter (L) samples for total 234Th were sampled using a CTD Niskin rosette (typically from eight depths spanning the epipelagic). Samples were acidified to a pH of <2 with HNO3. A tracer addition of 230Th was added and samples were mixed vigorously. Samples were allowed to equilibrate for 4-9 hours and then adjusted to a pH of 8-9 with NH4OH. KMnO4 and MnCl2 were added and samples were mixed and allowed to sit for ~12 hours as Th co-precipitated with manganese oxide. Samples were then vacuum-filtered at high pressure onto QMA filters, dried, and mounted in RISO sample holders.

Samples were beta counted on a RISO low-level background beta counter at Palmer Station and re-counted >6 half-lives later. Samples for water-column 234Th were then dissolved in HNO3/H2O2 solution and 229Th tracer was added. Samples were evaporated and reconstituted in dilute nitric acid / hydrofluoric acid. They were then analyzed by inductively-coupled plasma mass spectrometry at the Woods Hole Oceanographic Institution Analytical Lab to determine the ratio of 229:230Th to determine the initial yield of the 234Th filtration. 238U activity (for estimating 238U-234Th deficiency) was estimated from a linear relationship with salinity (Owens et al., 2011).

BCO-DMO Processing

- Imported original file "Th Logs - ForBCODMO - 2024-07-03.xlsx" into the BCO-DMO system.
- Renamed fields to comply with BCO-DMO naming conventions.
- Converted the local date-time column to ISO 8160 format.
- Added a date-time column in UTC.
- Saved the final file as "945225_v1_th-234_wap.csv"

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Office of Polar Programs (formerly NSF PLR)	OPP-1951090

Deployments

Deployment	Start Date	Platform
LMG1601	2016-01-03	ARSV Laurence M. Gould	data info
LMG1701	2016-12-30	ARSV Laurence M. Gould	data info
LMG1801	2017-12-30	ARSV Laurence M. Gould	data info
LMG1901	2018-12-30	ARSV Laurence M. Gould	data info
LMG2001	2019-12-30	ARSV Laurence M. Gould	data info

Instruments

Inductively Coupled Plasma Mass Spectrometer

Supplied Name: inductively-coupled plasma mass spectrometry

Supplied Description:

Samples were analyzed by inductively-coupled plasma mass spectrometry to determine the ratio of 229:230Th

Instrument Type

Generic Name: Inductively Coupled Plasma Mass Spectrometer

Acronym: ICP Mass Spec

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/LAB15/

Generic Description:

An ICP Mass Spec is an instrument that passes nebulized samples into an inductively-coupled gas plasma (8-10000 K) where they are atomized and ionized. Ions of specific mass-to-charge ratios are quantified in a quadrupole mass spectrometer.

Niskin bottle

Supplied Name: CTD Niskin rosette

Supplied Description:

Samples for total 234Th were sampled using a CTD Niskin rosette (typically from eight depths spanning the epipelagic)

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.

Riso Laboratory Anti-coincidence Beta Counters

Supplied Name: RISO low-level GM beta multi-counter

Supplied Description:

Samples were beta counted on a RISO low-level background beta counter

Instrument Type

Generic Name: Riso Laboratory Anti-coincidence Beta Counters

Acronym: Riso Beta Counter

Generic Description:

Low-level beta detectors manufactured by Riso (now Nutech) in Denmark. These instruments accept samples that can be mounted on a 25mm filter holder. These detectors have very low backgrounds, 0.17 counts per minute, and can have counting efficiencies as high as 55%.

Typically used in laboratory analyses. Designed to measure low levels of beta particle emission. The systems work on the principle of anticoincidence.

Parameters

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

Supplied Name	Supplied description	Supplied Units	Standard Name
Cruise	The identifier for the Palmer LTER cruise from which the data was collected	unitless	cruise_id
Event	Unique cruise event number that identifies the CTD cast from which the sample was collected	unitless	event
GridLine	Palmer LTER grid line from which sample was collected	unitless	grid_line
GridStation	Palmer LTER grid station from which sample was collected	unitless	grid_sta
Latitude	Latitude of sample collection; negative values = South	decimal degrees	lat
Longitude	Longitude of sample collection; negative values = West	decimal degrees	lon
Niskin	Number of the Niskin bottle from which sample was collected	unitless	bottle
Depth	Sample collection depth	meters (m)	depth
Salinity	Salinity determined from a Seabird CTD	PSU	sal
U238	Activity of U-238 determined from a regression with salinity	decays per minute per liter (dpm/L)	U238_in_sw
ISO_DateTime_Local	Collection date and time in ISO 8601 format; Local time zone is UTC-0400 Format: %Y-%m-%dT%H:%M	unitless	ISO_DateTime_Local
ISO_DateTime_UTC	Collection date and time in ISO 8601 format in UTC Format: %Y-%m-%dT%H:%MZ	unitless	ISO_DateTime_UTC
Th234_Activity	Activity of total water-column Thorium-234	decays per minute per liter (dpm/L)	Th234
Th234_Activity_Absolute_Error	Uncertainty in Thorium-234 activity	decays per minute per liter (dpm/L)	Th234
Deficiency	238Uranium minus 234Th disequilibrium	decays per minute per liter (dpm/L)	no_bcodmo_term
Deficiency_Absolute_Error	Uncertainty in uranium-thorium disequilibrium	decays per minute per liter (dpm/L)	no_bcodmo_term

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Dataset: Thorium-234 along the Western Antarctic Peninsula (2016-2020)