Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

DIC, DOC, POC, Zoopl Carbon concentration & isotopic data.
For POC and zooplankton C/N ratios also included.

Related files and references:
Sampling procedures, instrumentation, discussion of blanks, etc, included in Zigah, P.K., E.C. Minor, J.P. Werne, and S. L. McCallister, 2011. Radiocarbon and stable carbon isotopic insights into provenance and cycling of carbon in Lake Superior. Limnology and Oceanography 56(3), 867-886.

Because the samples are initially processed on deck and radiocarbon is being measured, the engines of the R/V Blue Heron are shut down during this time allowing the vessel to drift (engines not going and thus less possibility for contamination from the stack), until the processing of the samples has been completed.

Related files and references:
Sampling procedures, instrumentation, discussion of blanks, etc, included in Zigah, P.K., E.C. Minor, J.P. Werne, and S. L. McCallister, 2011. Radiocarbon and stable carbon isotopic insights into provenance and cycling of carbon in Lake Superior. Limnology and Oceanography 56(3), 867-886.

Isotopic data were processed as described in Radiocarbon Data & Calculations.

Concentration data for DOC and DIC are from a Shimadzu TOC-Vcsh Analyzer.

For DIC, the analyzer was calibrated using primary standard grade sodium carbonate and ACS reagent grade sodium bicarbonate. The inorganic carbon in the sample was volatilized with 25% H₃PO₄ (by weight) in a CO₂-free closed reaction vessel, and the CO₂ evolved was measured by a non-dispersive infrared (NDIR) gas detector.

For DOC, the samples were acidified to pH 2 with ACS reagent grade HCl at the time of sampling. The TOC analyzer was run in NPOC mode and calibrated with potassium hydrogen phthalate (KHP). Deep seawater from Florida Strait at 700 m (Batch-8 2008) reference waters obtained from the DOC Consensus Reference Program (Hansell laboratory, University of Miami, USA) and additional KHP standards were interspersed and analyzed along with the samples to assess instrumental performance.

Our mean DOC value of the external reference sample was 43.9 ± 3.9 μM (n = 5), and agrees with the consensus value of 41-43 μM. For each sample and standard, three injections were performed. If the standard deviation was not ≤ 2.5%, two more injections were performed and the closest three of the five injections were averaged to yield sample concentration.

Particulate organic samples (on GF/F filters) were fumigated with HCl, dried, then loaded into tin capsules and analyzed for particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations using a Costech ECS 4010 elemental analyzer (EA) coupled to Finnigan Delta Plus XP isotope ratio mass spectrometer (IRMS). The EA was calibrated with acetanilide (Costech Analytical Technologies Inc., Valencia, CA, USA) and caffeine (SigmalUltra; Wheaton Science Products, NJ, USA) reference standard materials; C and N were quantified using the IRMS. Typical instrumental precisions for POC and PON measurements were respectively, 0.2% and 0.4% of the measured concentrations.

BCO-DMO Processing Notes
Generated from original .xls file "August09cruise_collatedC14_OC.xls" contributed by Elizabeth Minor

BCO-DMO Edits
- Column inserted with cruise_id
- Location values split into separate Lat/Lon values
- Lat/Lon values converted to decimal degrees
- Date converted to YYYYMMDD
- Time converted to HHMM
- "time_range" column inserted to preserve start/end time range in time cell ("nd" if no range)
- "time" contains the start time of the time range
- "nd" (no data) value inserted in blank cells
- Commas in various fields converted to semicolons
- "<" symbol changed to "lt"
- ">" symbol changed to "gt"
- Parameter names modified to conform to BCO-DMO convention
- Misc leading and trailing spaces and tabs in various fields removed
- Blank lines removed
- Lat/Lon for data collected at 2009/08/14 1959 CDST corrected to Lat/Lon from CTD station data srg/18April2013
- Data columns and parameters "error_calc_1" and "error" removed. 19July2013, srg

Organic carbon present in aquatic ecosystems has the potential to either be sequestered by sedimentary organic matter or recycled and contributed to the atmosphere through microbial respiration. Ultimately, the fate of organic matter is dependant upon its source, as well as the physical transport mechanisms and biogeochemical transformations it is exposed to in the water column. Because these processes vary significantly within aquatic systems, such as the ocean, it is difficult to assess the biogeochemical importance of organic carbon; however, it is a problem of critical importance whose results could be utilized to resolve key issues in global biogeochemical carbon cycles and to determine the net heterotrophy of most aquatic environments.

Scientists from the University of Minnesota-Duluth and Virginia Commonwealth University would address this problem by studying organic carbon dynamics in Lake Superior because its biogeochemistry is similar to that of the world ocean. Using Lake Superior as a natural laboratory, the researchers plan to carry out radiocarbon measurements of particulate organic carbon (POC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and bacterially-respired CO2, as well as obtain the chemical composition of DOC and POC during stratified and non-stratified periods. Results would be used to identify the sources of carbon in the lake and determined transformations of carbon between POC, DOC, DIC, and bacterially-respired CO2.

Educational impacts include workshops and presentation for K-12 audiences as well as research and training opportunities for graduate and undergraduate students in Water Resources Science and Biochemistry classes.

Cruise pictures and info (for a general audience)