Multicores from 14 different stations along the Guianas mudbanks coast (NE S. America, Brazil, French Guiana, and Suriname) were extruded and frozen aboard the R/V F.G. Walton Smith in the summer of 2023. Samples were subsequently portioned, with some portions dried, acid-treated, and/or ground. Samples were analyzed in duplicate on an elemental analyzer connected to an isotope ratio mass spectrometer (IRMS) for nitrogen quantity and stable nitrogen isotope values and for carbon quantity, stable carbon isotope values, and carbon:nitrogen ratios. A subset of samples was analyzed for bulk radiocarbon content. A subset of samples was run for surface area, inorganic elemental content. and grain size distribution. These data will be useful for marine chemists interested in particulate-aqueous exchange in a mobile mudbank setting as well as goechemists interested in the exchange of carbon between terrigenous particulate matter, minerals, and the water column in a dynamic shelf sedimentary system with high fluvial inputs. The data were collected by shipboard scientists Brad Rosenheim (chief scientist, co-PI), Christopher Hein, Manuel Colombo, Brenna Boehmann, Evan Flynn, Andrea de Lima Oliveira, Calyn Crawford, Ronmel Rugama-Montenegro, Davide Calvarese, and Jose Moura da Souza Mauro, and land-based scientists Valier Galy (co-PI), Orion Schomber, Theresa King, Devon Firesinger, Ethan Goddard, Ann Dunlea, and Timothy Eglinton. Measurements were made in the Marine Environmental Chemistry Laboratory of the College of Marine Science at the University of South Florida (EA-irMS, Brad Rosenheim), Woods Hole Oceanographic Institution (surface area, inorganic geochemistry), Virginia Institute of Marine Science (grain size), and ETH-Zurich (radiocarbon values).

Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Curation Notes
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Multicores from 14 different stations along the Guianas mudbanks coast (NE S. America, Brazil, French Guiana, and Suriname) were extruded and frozen aboard the R/V F.G. Walton Smith in the summer of 2023. Samples were subsequently portioned, with some portions dried (freeze-drying and oven-drying), acid-treated, and/or ground. Samples were analyzed in duplicate (acid-treated and not acid-treated) on an elemental analyzer connected to an isotope ratio mass spectrometer (IRMS) for nitrogen quantity and stable nitrogen isotope values (not acid-treated) and for carbon quantity, stable carbon isotope values, and carbon:nitrogen ratios (acid-treated). 

A subset (n=35) of acid-treated samples was analyzed for bulk radiocarbon content. A subset (n=25) of non-acid-treated, unground samples was run for surface area, and all non-acid-treated and unground samples were measured for inorganic elemental content and grain size distribution. Sample names in this dataset include the code for the seagoing expedition (WS23-139), the multicore number, and the extrusion depth (in centimeters) from the multicore. Columns are provided with station numbers, latitude, longitude, and station name. The 14 stations aligned in sets of 3 cross-shelf transects (inner, middle, and outer) at 6 different locations along this coast. 

Sediment samples were extruded on board the ship after cores were recovered. Extruded intervals were measured using a rotating core table on a calibrated threaded rod (Schwing et al., 2016). Extruded samples were placed in pre-combusted glass jars with pre-combusted foil covers and threaded lids, and they were frozen on board the ship. Upon return to the laboratories at the University of South Florida, samples were thawed and separated into three aliquots: acid treatment, no acid treatment, and archive.

Archive aliquots were refrozen.

Acid treatment consisted of rinsing with 1N HCl in pre-combusted glass beakers and rinsing with distilled water until pH testing strips rose to a stable pH when contacted with siphoned rinse water from the sediments. The sediments were dried at 50 degrees Celsius and ground. This aliquot was used for carbon isotopes, %TOC, C:N ratios, and radiocarbon measurements.

The non-acid-treated samples were divided for grain size analysis, surface area analysis, and inorganic geochemistry (undried, unground) and for nitrogen isotope, %C, and %N analyses (dried and ground). The %CaCO3 of the samples was calculated using the difference between %C and %TOC measurements, the latter of which had carbonate minerals removed by acid treatment, and the %TOC values were corrected for the missing mass of CaCO3 by multiplying the measured values by the term (1-%CaCO3). Both corrected and measured %TOC values are provided.

Stable isotope data were transferred to the international stable isotope scales of PDB (carbon isotopes) and AIR (nitrogen isotopes) by measuring laboratory reference materials that were calibrated to those scales. Radiocarbon data were transferred to fraction modern values using standards offered by the International Atomic Energy Association. Nitrogen and carbon composition of the organic matter was calculated from...

Calculation of the amount of CaCO3 and correction of %TOC are explained under the methods section. Data from different sources were merged using the pandas package (v. 2.2.2) of Python (v. 3.14.0) and output as a single .csv file.

This section documents curation actions performed prior to publication review with the submitter, and additional information relevant to understanding and reusing this dataset. It distinguishes changes made to the submitted (meta)data from unresolved issues and/or enhancements that improve future reuse and interoperability.

CURATION ACTIONS PERFORMED ON DATA

- Imported original file "MUDBENCS_MC_data_repository.csv" into the BCO-DMO data processing system.
- Deleted the unnamed column containing row numbers.
- Renamed columns to comply with BCO-DMO naming conventions.
- Replaced a non-standard character in the station_name value "Uaça Outer" with "Uaca Outer".
- Converted format and renamed column "on_station_time" to "on_station_time_local" (no timezone conversion, format change of %Y-%m-%d %H:%M:%S to %Y-%m-%dT%H:%M:%S).
- Converted "off_station_time" to local datetime "off_station_time_local" similarly.
- Converted "on_station_time" with input timezone of UTC-3 to UTC and named the new column "on_station_time_UTC".
- Converted "off_station_time" with input timezone of UTC-3 to UTC and named the new column "off_station_time_UTC".
- Deleted original on_station_time and off_station_time columns after creating local/UTC variants.
- Saved the final file as "1009552_v1_guiana_mudbanks_multicore.csv".

CURATION ACTIONS PERFORMED ON METADATA

- BCO-DMO's standard metadata entry and text formatting steps were performed. See: https://www.bco-dmo.org/how-to/standard-curation-edits

ISSUES POTENTIALLY IMPACTING REUSE

- The "Data Processing" section is incomplete.
- C to N mass ratio appears twice in the dataset as columns "C_to_N_mass_ratio" and "C_to_N_mass_ratio2". It is not known if or how these differ.

Not all analyses were performed on all samples. Quality control flags pertain to the analysis of general organic geochemistry variables (C, N, d15N, d13C, and derived quantities) by elemental analyzer isotope ratio mass spectrometer. Flags are for samples where the unacidified sample N content was near the instrument detection limits, and therefore both the nitrogen quantity and isotope values may be inaccurate.

Coverage: Atlantic Ocean coastal waters, Brazil, French Guiana, Suriname

NSF Award Abstract:
The Amazon River is one of the largest and most important rivers in the world. It not only carries water through the Amazon rain forests, it also carries mud - lots of mud. This mud settles when the river joins the ocean, forming the Amazon delta. Waves and wind re-suspend some of this mud, which forms mud banks that slowly move from the coast of Brazil, to French Guiana, Suriname, and Guyana. Not only do these mud banks shape the coastlines of these areas, but they also serve as a storage for carbon that had been removed from the atmosphere by the Amazon rainforest, dropped to the forest floor and washed into the river, ultimately transported on particles of mud into the Amazon delta. Normally, this represents a transfer of carbon from the atmosphere to the sediment and rock record, hiding it away for thousands to millions of years and participating in the natural regulation of atmospheric carbon dioxide concentration. However, the Amazon's special case of mud banks that travel hundreds of miles along the coast has long been believed to stir up this carbon and release most of it back to the atmosphere. This idea has held for decades, but if wrong, may have a large impact on our understanding of the ocean's carbon cycle. This research will use new science and technology to change the way we look at river carbon cycling in the ocean by sampling the mud banks, ocean waters, and Amazon River waters more thoroughly than has been previously done, with the aim to understand and quantify the storage of land-derived carbon in marine mudbank sediments offshore the Amazon River. This research will serve as the core of two Ph.D. dissertations and will interface with the Woods Hole Partnership Educational Program (PEP) to provide under-represented minority college students an opportunity to gain practical experience in marine and environmental sciences. The project will also be incorporated into the Saint Petersburg Science Fest, an event that brings several thousand school children to University of South Florida campus during one weekend every autumn to showcase different research projects and initiatives.

Twenty years ago, John Hedges posed a seminal question pertaining to the role of the ocean in the carbon cycle: "what happens to terrestrial organic matter in the oceans?" That question was set upon a conundrum - because riverine organic matter is highly degraded, it should be expected to suffer minimal respiration in the ocean, yet by most accounts continental margins seem to be incinerators of terrestrial organic matter. However, much of this paradigm was originally built upon biogeochemical studies of the Amazon sub-aqueous delta and the mobile fluidized mudbanks along the Guianas coast. However, preliminary state of the art characterizations of organic carbon in Amazon River and mudbank sediments suggest that a fraction of terrestrial organic carbon is actually not refractory and as such is rapidly and efficiently oxidized in the ocean, whereas another fraction is refractory and is in fact quantitatively preserved in marine sediments. Overall, the data suggest an underestimation of burial efficiency in the realm of 50-100%. This proposal focuses on gaining a transformative mechanistic and quantitative understanding of the fate of terrestrial organic carbon in the coastal ocean offshore of the Amazon River. This will be done through i) sampling the marine province offshore of the Guianas coast (the Guianas mudbanks) as well as the Amazon River delta, using a shallow-draft research vessel and ii) using novel state of the art geochemical analysis of organic carbon - in particular ramped oxidation and compound specific radiocarbon analysis - and elemental composition to demonstrate the selective nature of terrestrial organic carbon oxidation and provide new estimates of burial efficiency of this system - with implications for the global inventory of terrestrial organic carbon in the ocean.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.