| Contributors | Affiliation | Role |
|---|---|---|
| Wang, Xingchen | Boston College (BC) | Principal Investigator |
| Landry, Kameko | Boston College (BC) | Student |
| Rauch, Shannon | Woods Hole Oceanographic Institution (WHOI BCO-DMO) | BCO-DMO Data Manager |
Data were collected on the NSF-funded 2021 "CDISP" cruise on R/V Sally Ride (SR2113). Analyses of the samples presented in this dataset were funded through Boston College.
Water samples were collected directly from the CTD Niskin bottles and filtered through 0.2-micrometer (um) PVDF syringe filters. Samples were collected from approximately 24 depths throughout the water column ranging from 7 to 2900 meters (m), with the shallowest depths being sampled first to avoid nitrate contamination from deeper, higher nitrate samples. The samples were collected in pre-cleaned acid-washed 30-milliliter (mL) HDPE bottles. The bottles and caps were rinsed three times with the sample water. The syringe was rinsed three times before attaching the PVDF syringe filter& and, once attached to the syringe, 10 mL of sample water was used to rinse the filter before filling the sample bottles. Once filled, sample bottles were labeled and parafilmed. Samples were immediately frozen on the ship and continued to be frozen until analysis.
For isotopic analysis using the denitrifier method, bacteria are grown in aerobic environments starting the seed of the bacteria Pseudomonas aurofaciens. Once all nitrate is fully consumed, the bacteria are harvested from a growth media and placed in clean pre-combusted vials. The vials are then sealed and purged with N2 gas for three hours to completely remove the N2O background. Approximately 200-500 mL of nitrate samples are then injected into a purged vial. After overnight complete conversion of nitrate to N2O in the sealed vials, the δ15N of N2O is analyzed using a customized gas bench isotope ratio mass spectrometer.
The data are processed and corrected based on amino acid standards (USGS64 and USGS65) and nitrate isotope standard (USGS34 and USGS35).
- Imported original file "CCR_d15N_1000m_data.xlsx" into the BCO-DMO system.
- Marked "N/A" and "nd" as missing data values (missing data are empty/blank in the final CSV file).
- Converted the date column to YYYY-MM-DD format.
- Renamed fields to comply with BCO-DMO naming conventions.
- Saved the final file as "933292_v1_water_column_nitrate_d15n_cocos_ridge.csv".
| Parameter | Description | Units |
| Station_ID | Cocos Ridge station number + cast number + Niskin bottle number | unitless |
| Depth_m | Sample depth | meters (m) |
| WC_d15N_avg | Averaged d15N in permille vs N2. Blank/empty values in this column mean water was not collected from this specific bottle. | permille vs N2 |
| WC_d15N_1sd | Standard deviation of measurements for samples analyzed with more than one run | permille vs N2 |
| Latitude | Latitude of sample collection | decimal degrees |
| Longitude | Longitude of sample collection; negative values = West | decimal degrees |
| Date | Date of sample collection | unitless |
| Dataset-specific Instrument Name | Thermo IV Isotope Ratio Mass Spectrometer |
| Generic Instrument Name | Isotope-ratio Mass Spectrometer |
| Generic Instrument Description | The Isotope-ratio Mass Spectrometer is a particular type of mass spectrometer used to measure the relative abundance of isotopes in a given sample (e.g. VG Prism II Isotope Ratio Mass-Spectrometer). |
| Dataset-specific Instrument Name | 24-bottle Niskin CTD rosette |
| Generic Instrument Name | Niskin bottle |
| Generic Instrument Description | A Niskin bottle (a next generation water sampler based on the Nansen bottle) is a cylindrical, non-metallic water collection device with stoppers at both ends. The bottles can be attached individually on a hydrowire or deployed in 12, 24, or 36 bottle Rosette systems mounted on a frame and combined with a CTD. Niskin bottles are used to collect discrete water samples for a range of measurements including pigments, nutrients, plankton, etc. |
| Dataset-specific Instrument Name | N2O Gas Bench |
| Generic Instrument Name | Thermo-Fisher Scientific Gas Bench II |
| Generic Instrument Description | An on-line gas preparation and introduction system for isotope ratio mass spectrometry that is designed for high precision isotope and molecular ratio determination of headspace samples, including water equilibration, carbonates and atmospheric gases. The instrument allows for the use of a dual viscous flow inlet system of repetitive measurements of sample and standard gas on a continuous flow isotope ratio mass spectrometer (CF-IRMS) system. The sample volume is the sample vial (instead of a metal bellows), and the reference gas volume is a pressurized gas tank. The instrument consists of a user programmable autosampler, a gas sampling system, a maintenance-free water removal system, a loop injection system, an isothermal gas chromatograph (GC), an active open split interface, a reference gas injection system with three reference ports, and one or two optional LN2 traps for cryofocusing. The gas sampling system includes a two port needle which adds a gentle flow of He into the sample vial, diluting and displacing sample gas. Water is removed from the sample gas through diffusion traps. The loop injector aliquots the sample gas onto the GC column, which separates the molecular species. The reference gas injection system allows accurate referencing of each sample aliquot to isotopic standards. The system can be used with several options including a carbonate reaction kit that allows injection of anhydrous phospohric acid into sample vials. |
| Website | |
| Platform | R/V Sally Ride |
| Start Date | 2021-11-20 |
| End Date | 2021-12-20 |
NSF Award Abstract:
The uptake of anthropogenic CO2 by the ocean will eventually be mitigated by the dissolution of CaCO3 on the sea floor. Dissolution is an important component of the carbon cycle in models used for climate projections though the relative importance of where it occurs (water column versus sediments) and the rates and processes involved are not fully understood. This ambitious field and laboratory study is designed to advance our knowledge of the important factors that control carbonate dissolution/ preservation in deep ocean sediments. Using a novel tracer approach and multiple in situ sampling strategies, the project will investigate sea floor dissolution rates, their kinetic controlling factors, the depth in sediments at which dissolution occurs, the role that oxidation of particulate organic carbon plays, and the ramifications of solid phase alteration for the use of geochemically-based paleoceanographic proxies. The project will foster further development of benthic lander technology and yield key information relating sea floor conditions to carbonate dissolution rate, thereby helping to constrain the rate at which the ocean can neutralize the impacts of ocean acidification. Graduate and undergraduate students will be trained and the research team will use film and animation to bring this work to a broader audience through a collaboration with the Los Angeles Natural History Museum.
The research team has developed a new approach to quantify calcium carbonate dissolution rates based on 13-C labeled carbonate substrates, a technique which is significantly more sensitive than traditional approaches based on alkalinity and/or calcium measurements. This has opened a range of new opportunities and insights into the governing mechanisms and rates of calcium carbonate dissolution, a challenging and long-standing geochemical problem. Carbonate dissolution rates on the sea floor will be directly assessed by benthic chamber flux measurements of alkalinity and calcium as well as pore water models of TCO2 and alkalinity and their isotopic composition. The potential impacts of organic carbon remineralization will be measured through oxygen and nutrient flux determinations, pore water gradients and modeling. Labeled 13C-enriched calcite will serve as a tracer of near surface dissolution processes when added to benthic chambers and of down-core dissolution processes using 13C-labeled rods inserted into the sediment column. These in situ experiments of labeled carbonate dissolution will be the first of their kind. To complement these measurements, the team will continue development of a rhizon-based pore water sampler that works on a multi-corer at all ocean depths. Field experiments will be conducted at sea at 4-6 sites in a transect through water column supersaturation to undersaturation between Panama and the Galapagos. Dissolution rate measurements, coupled with analyses of cation/Ca ratios in CaCO3 foraminiferal shells will help calibrate the impact of dissolution on paleo-proxy interpretations. Further, analyses of sediment calcite and aragonite fractions will help explain net dissolution and sediment response with time. The results from this study should help to better parameterize sediment variables in ocean-climate models (GCMs), which has important implications for predicting the consequences of ocean acidification and the modeling of paleoceanographic records. The methodologies and new techniques will surely be adopted by other researchers, therefore impacting the larger geochemical community.
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.
| Funding Source | Award |
|---|---|
| Boston College |