Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

Water samples were collected near‐monthly from the Tapajós River upstream of Itaituba Brazil (-4.3375,-56.06953). Three water samples (1 L) were collected at 0.5 m depth from the river across the channel in equal spacing and combined into a 4 L acid‐washed carboy to make a composite sample.  The water was filtered through a 0.45 μm capsule filter with a peristaltic pump into acid‐rinsed high‐density polyethylene (HDPE) bottles. Filtered samples were kept cold during transport and immediately frozen upon transfer to the laboratory and kept in the dark until analysis.

Mass spectral peaks (>6σ root‐mean‐square (RMS) baseline noise) were exported to a peak list and processed using PetroOrg. Molecular formulae were assigned to ions constrained by C4‐75H4‐150O1‐30N0‐4S0‐2 not exceeding 300 ppb error. The resulting peak list includes all confidently assigned molecular formulae across every analyzed sample. Individual molecular formulae peaks can be compared between samples and bulk stoichiometric parameters (e.g., mean H/C , O/C ratio) can be determined for each sample in this dataset. 

* Sheet 1 of submitted file "Tapajos_FT-CR MS peaks_combined.csv" was imported into the BCO-DMO data system for this dataset.  Table will appear as Data File: 986858_v1_tapajos_mass-spec-peaks.csv (along with other download format options).

* Data table within Sheet 1 from file "Tapajos_sample dates.xlsx" was imported as supplemental file (table added to BCO-DMO page as "sample-metadata.csv"). Column "Sample Name" was adjusted to add zero-padding for samples with only one digit in order to match to the primary data table column "Sample."
* sample date and lat,lon were added to the primary data 986858_v1_tapajos_mass-spec-peaks.csv by joining on the sample identifier in both tables.

Changes made in all tables in this dataset:

* Column names adjusted to conform to BCO-DMO naming conventions designed to support broad re-use by a variety of research tools and scripting languages. [Only numbers, letters, and underscores.  Can not start with a number]

* Date converted to ISO 8601 format

* Location field contained both latitude and longitude in degrees minutes and seconds (e.g. '"4°20'15.0"S 56°04'10.3"W"') which was converted to separate lat_dd lon_dd columns (also converted to decimal degrees)

NSF Award Abstract:
The Amazon River is one of the largest sources of freshwater and carbon to the ocean. Thus, understanding the factors that influence freshwater delivery from the Amazon River is important for understanding the carbon cycle of the Amazon River and the receiving Atlantic Ocean. El Niño–Southern Oscillation (ENSO) is a periodic event that causes changes in winds and sea surface temperature over the tropical eastern Pacific Ocean and affects climate in the tropics and subtropics. The National Weather Service predicts that El Niño conditions are likely to form across the Pacific during Summer 2023. These conditions are expected to last through February 2024. This event is expected to impact precipitation and air temperatures in the Amazon Basin and freshwater delivery from the Amazon River. This project aims to study the amount and chemical composition of dissolved organic carbon delivered from the Amazon River to the Atlantic Ocean during the 2023-2024 El Niño event. Scientists involved in this project plan to collect samples from late Summer 2023 through late Summer 2024. The study will identify conditions before, during and after this event. This unique set of samples will enable the team of scientists to study how ENSO influences the delivery of organic carbon to the coastal ocean.
This project provides support for an early career researcher and promotes international cooperation and inclusivity between researchers from the United States of America and researchers in Brazil who are directly impacted by the changing Amazon River.

This project examines how El Niño Southern Oscillation (ENSO) anomalies impact the export of dissolved organic carbon (DOC) and composition of dissolved organic matter (DOM) from the Amazon River to the Atlantic Ocean. Based on recent studies, it has been hypothesized that the upcoming 2023 El Niño event will reduce the annual DOC flux and proportion of exported terrestrial DOM from the Amazon River compared to non-ENSO and La Niña years. This hypothesis will be examined by linking established state-of-the-art optical and molecular-level characterization techniques (e.g., Fourier-transform ion cyclotron resonance mass spectrometry; FT-ICR MS) with DOC flux calculations over the course of an El Niño year. Analyzing both bulk DOC fluxes and the molecular-level composition will reveal how the quantity and quality of DOM export will change monthly in response to reduced precipitation and higher temperature across the Amazon Basin and headwaters. DOC fluxes as well as detailed characterizations (FT-ICR MS, optical, fluorescence analysis) of DOM sampled from the furthest downstream Amazon River gauging station at Óbidos (Brazil) will be directly compared to results obtained from the 2011-2012 La Niña year and the following 2012-2013 hydrologically normal year to determine how global climate anomalies impact the DOC export to marine systems and to create a framework for future predictions. Data obtained from this proposed study will lay the foundations for larger studies investigating how ENSO cycles impact discharge and carbon export from other major tropical-subtropical rivers and ultimately, how ENSO cycles impact global land-ocean carbon export.

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.