Sediment Trap Time Series of GDGT and alkenone flux in the Gulf of Mexico

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Frequently anticipated questions:


What does this data set describe?

Title:
Sediment Trap Time Series of GDGT and alkenone flux in the Gulf of Mexico
Abstract:
The tetraether index of C86 (TEX86) and alkenone unsaturation index (Uk37Õ) molecular biomarker proxies have been broadly applied in down-core marine sediments to reconstruct past sea surface temperature (SST). Although both TEX86 and Uk37 have been interpreted as proxies for mean annual SST throughout the global ocean, regional studies of glycerol dibiphytanyl glycerol tetraethers (GDGT)s and alkenones in sinking particulate matter (SPM) are required to understand the influence of seasonality, depth distribution and diagenesis on downcore variability. USGS scientists measured GDGT and alkenone flux, as well as the TEX86 and Uk37Õ indices in a 4-year sediment trap time series (2010-2014) in the northern Gulf of Mexico (nGoM), with weekly-to-monthly resolution, and compared these data with core-top sediments at the same location. GDGT and alkenone fluxes do not show a consistent seasonal cycle; however, the largest flux peaks for both occurs in winter. Uk37 co-varies with SST over the 4-year sampling interval, but the U-SST relationship in this dataset implies a smaller slope or non-linearity at high temperatures when compared with existing calibrations. Furthermore, the flux-weighted Uk37 value from sinking particles is significantly lower than that of underlying core-top sediments, suggesting preferential diagenetic loss of the tri-unsaturated alkenone in sediments. TEX86 does not co-vary with SST, suggesting production in the subsurface ocean. The flux-weighted mean TEX86 matches that of core-top sediments, suggesting that sedimentary TEX86 in the Gulf of Mexico reflects local autochthonous production. We explore these potential sources of uncertainty in both proxies in the GoM, but demonstrate that they show nearly identical trends in 20th century SST, despite these factors.
  1. How might this data set be cited?
    Richey, Julie, 20161216, Sediment Trap Time Series of GDGT and alkenone flux in the Gulf of Mexico: U.S. Geological Survey Data Release doi:10.5066/F76M350W, US Geological Survey, St. Petersburg, FL.

    Online Links:

    This is part of the following larger work.

    Richey, Julie N., and Tierney, Jessica E., 2016, GDGT and alkenone flux in the northern Gulf of Mexico: Implications for the TEX86 and UKÕ37 paleothermometers: Paleoceanography 31.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: 91.0
    East_Bounding_Coordinate: 90.0
    North_Bounding_Coordinate: 28.0
    South_Bounding_Coordinate: 27.0
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Jan-2010
    Ending_Date: 01-Jan-2014
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: tabular digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set.
    2. What coordinate system is used to represent geographic features?
  7. How does the data set describe geographic features?
    2010_2014_NGOM_Sediment_Trap_Biomarkers.csv, 2010_2014_NGOM_Sediment_Trap_Biomarkers.xlsx
    These files contain a weekly to bi-weekly resolution 4-year time series (2010-2014) of GDGT and alkenone flux in the northern Gulf of Mexico. The TEX86 and U37K' indices are also included, which are sea surface temperature proxies based on the distribution of GDGTs and alkenones, respectively. (Source: USGS)
    Entity_and_Attribute_Overview:
    The detailed attribute descriptions for the 2010_2014_NGOM_Sediment_Trap_Biomarkers workbook are provided in the included data dictionary (Data Dictionary). This metadata file is not complete without that worksheet.
    Entity_and_Attribute_Detail_Citation:
    The entity and attribute information was generated by the individual and/or agency identified as the originator of the dataset. Please review the rest of the metadata record for additional details and information.

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Julie Richey
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Julie Richey
    US Geological Survey
    600 4th Street South
    Saint Petersburg, FL
    USA

    (727) 502-8123 (voice)
    jrichey@usgs.gov

Why was the data set created?

This dataset was generated to address the modern variability of GDGT and alkenone flux from a sediment trap time series in the Gulf of Mexico.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 02-Nov-2016 (process 1 of 1)
    Methods: Sediment Trap The McLane PARFLUX Mark 78 automated sediment trap is moored at 700 meters water depth in the northern Gulf of Mexico (27.5 ¼N and 90.3 ¼W) in 1,150 meters water depth. The trap is equipped with 21 collection cups, all mounted on a rotating plate programmed to rotate every 7 to 14 days. Sample cups were prefilled with a buffered formalin solution made with filtered seawater, formalin (3.7%) and sodium borate. The trap was recovered and redeployed every 6-9 months, a sampling gap occurred between early February 2012 and late March 2012. Sediment-trap samples were wet-split into four aliquots using a precision rotary splitter at the University of South Carolina, stored in buffered, deionized water, and then refrigerated.
    Biomarker analysis Sediment trap samples were filtered onto 0.45 micron pre-combusted glass fiber filters, freeze dried, then extracted using a Dionex Accelerated Solvent Extractor (ASE 200) in 9:1 methylene chloride (DCM) to Methanol (MeOH). The total lipid extract was separated into acid and neutral fraction using aminopropyl gel columns, with neutrals eluting in 3:1 DCM:IPA and Acids eluting in 4% Acetic Acid in DCM. The neutral fraction was then separated into hydrocarbon, ketone and polar fractions via silica gel column chromatography using the elution scheme: hexane (hydrocarbons), DCM (alkenones), and MeOH (GDGTs). The polar fraction, containing the GDGTs, was dissolved in a 99:1 (vol:vol) mixture of hexane:isopropanol, then filtered through 0.45 micron polytetrafluoroethylene (PTFE), filters. Analyses of GDGTs for TEX86 and branched and isoprenoid tetraether (BIT) index determination were performed by high?pressure liquid chromatography?mass spectrometry (HPLC?MS) at Woods Hole Oceanographic Institution. Samples were analyzed on an Agilent 1260 HPLC coupled to an Agilent 6120 MSD according to the method of Schouten et al. (2007). Briefly, A Prevail Cyano column (150 x 2.1 mm, 3 micron) was used with 100% hexane (A) and 90:10 hexane:isopropanol (v:v) (B) as eluents. Samples were injected then eluted isocratically for the first 5 minutes (min) with A, after which the eluent increased by a linear gradient up to 18% B over the next 35 min at a flow rate of 0.2 mL/min. Detection was performed in single ion monitoring mode (SIM). Synthetic C46 GDGT obtained from Purdue University was used as an internal quantification standard. All GDGT samples were analyzed in duplicate. Long-term analyses of an external laboratory standard yield a precision of 0.004 TEX86 units. Alkenone fractions were analyzed via gas chromatography with a flame ionization detector (GC-FID) at the U.S. Geological Survey St. Petersburg Coastal and Marine Geology Center. GC-FID conditions were: split/splitless injection (inlet temperature: 300 ¼C), DB-1 capillary column (60 m, 0.32 mm i.d., 0.10 ?m film thickness), 1.5mL/min He carrier gas, with 1 microliter sample injection volume, and the following oven temperature program: 60 ¼C to 270 ¼C at 30 ¼C/minute, 270 ¼C to 310 ¼C at 1.2 ¼C/minute, and 310 ¼C to 325 ¼C at 10 ¼C/minute. Identification of alkenones was verified using GC-MS (Agilent 7890B gas chromatograph coupled to an Agilent 5977A mass spectrometer with the same column and method), and based on comparisons with a purified alkenone standard from cultured Emiliania huxleyi. Both hexatriacontane and heptatriacontane were added to samples as internal quantification standards for alkenones.
  3. What similar or related data should the user be aware of?
    Schouten, Stefan, et al., 2007, Gradistat: Towards calibration of the TEX 86 palaeothermometer for tropical sea surface temperatures in ancient greenhouse worlds: Organic Geochemistry 38(9).

    Online Links:

    Other_Citation_Details: Pages 1537-1546

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    No formal attribute accuracy tests were conducted
  2. How accurate are the geographic locations?
    No formal positional accuracy tests were conducted
  3. How accurate are the heights or depths?
    No formal positional accuracy tests were conducted
  4. Where are the gaps in the data? What is missing?
    Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    No formal logical accuracy tests were conducted

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
Use_Constraints:
Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. The U.S. Geological Survey requests to be acknowledged as originator of these data in future products or derivative research.
  1. Who distributes the data set? (Distributor 1 of 1)
    Julie Richey
    600 4th Street South
    Saint Petersburg, FL
    USA

    (727) 502-8123 (voice)
    jrichey@usgs.gov
  2. What's the catalog number I need to order this data set? 2010_2014_NGOM_Sediment_Trap_Biomarkers.csv, 2010_2014_NGOM_Sediment_Trap_Biomarkers.xlsx
  3. What legal disclaimers am I supposed to read?
    Although these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The USGS shall not be held liable for improper or incorrect use of the data described or contained herein. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?
  5. Is there some other way to get the data?
    Contact U.S. Geological Survey for details.

Who wrote the metadata?

Dates:
Last modified: 20-Mar-2019
Metadata author:
Julie Richey
US Geological Survey St. Petersburg Coastal and Marine Science Center
Research Geologist
600 4th Street South
Saint Petersburg, FL
USA

(727) 502-8123 (voice)
jrichey@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

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