California Current Ecosystem LTER

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Carbon:234Thorium ratios (Process Cruise)

Title
Carbon:234Thorium ratios of sinking particles collected by sediment trap and large particles collected by in situ pump on CCE-LTER Process Cruises. 2006 - 2017 (ongoing).

Abstract
The ratio of carbon to 234Thorium on particles can be used to convert water column 234Th measurements to sinking carbon flux estimates and to investigate particle scavenging in the ocean. Carbon:234Th ratios of two types of particles are measured: true sinking particles collected by sediment trap and large (>50-µm) particles collected using a McLane in situ Pump. Sinking particles are collected in VERTEX-style particle interceptor traps (PIT) with an 8:1 aspect ratio, 70-mm diameter, and a baffle on top comprised of 13 smaller beveled tubes with a similar 8:1 aspect ratio. Tubes are deployed with a formalin-brine for a duration of 2-5 days. After recovery, samples were gravity filtered through a 200-µm filter. The 200-µm filtered was then immediately examined under a stereomicroscope and mesozooplankton swimmers were removed from the sample. On P0704, P0810, and P1106 cruises the remaining (non-swimmer) portion of the material on the >200-µm filter was then re-combined with the <200-µm portion of the sample. Samples were then filtered through a pre-combusted quartz (QMA) filter. On P1208, P1604, and P1706 cruises the >200-µm and <200-µm fractions were filtered separately onto QMA filters to determine C:234Th ratios of different size classes of sinking particles. Typically, triplicate whole PIT tubes were filtered for C:234Th ratios. However, on some cycles with very high flux, samples were first split on a Folsom splitter. On some cycles, the mesozooplankton ‘swimmers’ were saved and filtered onto a separate QMA filter to quantify the C:234Th ratio of mesozooplankton. QMA filters were all dried and mounted in RISO sample holders. >50-µm particles were also collected using McLane in situ pumps (typically deployed for a period of ~1 hour at the same depth of the sediment traps). In situ pump samples were rinsed off of the 147-mm nitex mesh filters used with the pump onto a pre-combusted QMA filter, which was similarly dried and mounted in a RISO sample holder. Samples were beta counted on a RISO beta GM multi-counter. >6 months later, samples were background counted. On P1604 and P1706 cruises additional counts were performed as the samples decayed. After background counts, carbon and nitrogen on the filters was quantified by elemental analyzer at the Scripps Institution of Oceanography Analytical Facility
Keywords
carbon, carbon cycling, marine, oceans, sediments, 234Thorium, thorium, biological carbon pump, carbon export, particle scavenging

LTER Data System Record
http://dx.doi.org/10.6073/pasta/89330ad45c3de2e962455ac5d5f25d87
Projects
California Current Ecosystem LTER

Creators
Stukel, Mike (mstukel@fsu.edu)

Contact
CCE LTER Information Manager (ccelter.im@gmail.com)

Data

table C:Th ratios
Primary data table 		Rows: 60
Columns: 20 		View / Download

Methods

Sediment Trap Deployments
Sinking particles are collected in VERTEX-style particle interceptor traps (PIT) with an 8:1 aspect ratio, 70-mm diameter, and a baffle on top comprised of 13 smaller beveled tubes with a similar 8:1 aspect ratio. Tubes are deployed with a formalin-brine for a duration of 2-5 days. After recovery, samples were gravity filtered through a 200-µm filter. The 200-µm filtered was then immediately examined under a stereomicroscope and mesozooplankton swimmers were removed from the sample. On P0704, P0810, and P1106 cruises the remaining (non-swimmer) portion of the material on the >200-µm filter was then re-combined with the <200-µm portion of the sample. Samples were then filtered through a pre-combusted quartz (QMA) filter. On P1208, P1604, and P1706 cruises the >200-µm and <200-µm fractions were filtered separately onto QMA filters to determine C:234Th ratios of different size classes of sinking particles. Typically, triplicate whole PIT tubes were filtered for C:234Th ratios. However, on some cycles with very high flux, samples were first split on a Folsom splitter. On some cycles, the mesozooplankton ‘swimmers’ were saved and filtered onto a separate QMA filter to quantify the C:234Th ratio of mesozooplankton.

In situ pump deployments
McLane WTS-LV pumps were deployed with 147-mm nitex screen (50-µm) to collect large particles that are believed to be representative of sinking particles. Nitex screens were rinsed onto 25-mm quartz (QMA) filters

C:234Th measurements
Samples were filtered onto pre-combusted quartz (QMA) filters, which where then dried and mounted in RISO sample holders. Samples were then counted in a RISO GM beta multi-counter at the University of South Carolina (2007 - 2011) or in a RISO GM beta multi-counter taken to sea (2012-ongoing). >6 months later, samples were background counted. On cruises from 2016 - ongoing, additional counts were made as the thorium decayed. After background counts, carbon and nitrogen on the filters were measured using an elemental analyzer at the SIO Analytical Facility

References

Stukel, M. R., T. B. Kelly, L. I. Aluwihare, K. A. Barbeau, R. Goericke, J. W. Krause, M. R. Landry, M. D. Ohman (2019). The Carbon:234Thorium ratios of sinking particles in the California Current Ecosystem 1: Relationships with plankton ecosystem dynamics. Marine Chemistry. doi: 10.1016/j.marchem.2019.01.003

Stukel, M. R., T. B. Kelly (submitted). The Carbon:234Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model. Marine Chemistry.

Morrow, R. M., M. D. Ohman, R. Goericke, T. B. Kelly, B. M. Stephens, M. R. Stukel (2018). Primary production, mesozooplankton grazing, and the biological pump in the California Current Ecosystem: Variability and response to El Nino. Deep-Sea Research I. 140: 52-62. doi: 10.1016/j.dsr.2018.07.012

Stukel, M. R., M. D. Ohman, C. R. Benitez-Nelson, M. R. Landry. 2013. Contributions of mesozooplankton to vertical carbon export in a coastal upwelling system. Mar. Ecol. Prog. Ser. 491: 47-65 doi: 10.3354/meps10453

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