|Berelson, William M.||University of Southern California (USC)||Principal Investigator|
|Adkins, Jess F.||California Institute of Technology (Caltech)||Co-Principal Investigator|
|Dong, Sijia||California Institute of Technology (Caltech)||Scientist|
|Naviaux, John D.||California Institute of Technology (Caltech)||Scientist|
|Subhas, Adam V.||Woods Hole Oceanographic Institution (WHOI)||Contact|
|Heyl, Taylor||Woods Hole Oceanographic Institution (WHOI BCO-DMO)||BCO-DMO Data Manager|
|Rauch, Shannon||Woods Hole Oceanographic Institution (WHOI BCO-DMO)||BCO-DMO Data Manager|
The methodology for measuring dissolution rate follows published methods in Naviaux et al., 2019 and Dong et al., 2019. The ratio of the dissolving solid was measured following methods of Subhas et al., 2018.
Dissolution experiments were conducted in situ using modified Niskin incubators, described in detail by Naviaux et al. (2019) and Dong et al. (2019). In this study, we dissolved bleached, 13C-labeled E. huxleyi liths. A total of 20 coccolith dissolution experiments were conducted at depths between 240-1000 meters at Stations 2-5 with temperatures ranging from 2.4-4.8 degrees C and Ωcalcite from 0.96 to 0.67. We conducted one experiment with a planktic foraminiferal assemblage, cultured and 13C -labeled as described in Subhas et al. (2018). Briefly, roughly 0.5-1.5 milligrams (mg) of labeled biogenic calcite was sealed in between 47 millimeter "Nuclepore" polycarbonate membrane filters (0.8 um pore size). These packets were then mounted inside the Niskin incubators. The incubators were hung on a hydrowire, sent down to depth, and triggered closed. The Niskin reactors remained closed at depth for 24–58 hours and were sampled for silica, SRP, nitrate, alkalinity, pH, and δ13C -DIC upon recovery. Niskin data were quality checked by comparing SRP, silica, and nitrate to ambient water-column values obtained via CTD/rosette deployments on the same cruise. Saturation states in the Niskin reactors were determined from Alk- pH pairs, input into CO2SYS along with the temperature, salinity, depth, SRP, and silica concentrations at which the reactor was deployed. Dissolution rates were calculated by taking the difference between the final incubator and ambient water column 13C/12C ratios, multiplied by the [DIC] and the mass of seawater (1.126 kg) inside the incubators, and divided by the incubation time. Rates calculated in this way are in units of grams per Ca13CO3 g CaCO3 per day. Biogenic materials were not 100% labeled and rates were scaled for the extent of isotope labeling following Subhas et al. (2018). Briefly, when the amount of 13C in the dissolving material is substantially enriched above natural abundance (13C/12C~0.01), isotope ratio differences can be multiplied by a correction factor of (Rs+1)/Rs, where Rs is the 13C/12C ratio of the dissolving solid (i.e. a reduced form of Eq. 3 from Subhas et al. (2018) when Rs >> R1, R2). One batch of E. huxleyi was used for the majority of the dissolution rates shown here (Rs = 0.928). One experiment using the original batch of bleached E. huxleyi (Rs = 20, Subhas et al. 2018) was also run. The planktic foraminifera assemblage from Subhas et al. (2018) was used (Rs = 1.6). Dissolution rates were normalized further by the specific surface areas of E. huxlyei liths (10.5 m2g) and planktic foraminifera (4.3, Subhas et al., 2018).
The saturation state of the planktic experiment is anomalously low (0.64). Based on co-located coccolith and calcite dissolution experiments, both the in situ pH and alkalinity appear lower than they should be for that depth. We applied a correction factor of 0.06 to the in situ Omega value to correct for this (i.e. Oca_use = Oca + Oca_corr).
BCO-DMO processing description:
- Adjusted field/parameter names to comply with BCO-DMO naming conventions
- Added a conventional header with dataset name, PI names, version date
- Converted dates to ISO date format YYYY-MM-DDThh:mmZ
|Station||Station number occupied (1-5)||unitless|
|Latitude||Station latitude North||decimal degrees|
|Longitude||Station longitude East (West is negative)||decimal degrees|
|Cast_ID||Cast type (FA = Floating array, HW = hydrowire)||unitless|
|ISO_DateTime_In||Date and time array deployed in GMT, in 24 hour time: YYYY-MM-DDThh:mmZ||unitless|
|ISO_DateTime_Out||Date and time array recovered in GMT, in 24 hour time: YYYY-MM-DDThh:mmZ||unitless|
|Sample_ID||sample type (benthic = benthic foraminifera Amphistegina spp., original_ehux = original batch of 13C-cultured E. huxleyi, planktic = planktic foraminifera assemblage)||unitless|
|TALK||Total alkalinity||microequivalents per kilogram seawater|
|pH||pH total scale at zero pressure, 25C, and in situ salinity||unitless|
|DIC||Calculated DIC||micromoles per kilogram seawater|
|Temperature||In situ temperature||degrees celsius|
|Oca||Calcite saturation state calculated via pH and total alkalinity||unitless|
|Oar||Aragonite saturation state calculated via pH and total alkalinity||unitless|
|Rate_ggd||Dissolution rate normalized by carbonate mass||grams per gram per day|
|Rate_gcm2d||Dissolution rate normalized by carbonate mass and surface area||grams per square centimeter per day|
|Rate_error_ggd||Dissolution rate error for Rate_ggd||grams per gram per day|
|Rate_error_gcm2d||Dissolution rate error for Rate_gcm2d||grams per square centimeter per day|
|log_rate_gcm2d||Log dissolution rate||grams per square centimeter per day|
|log_rate_error_gcm2d||Log dissolution rate error||grams per square centimeter per day|
|Oca_corr||Omega correction factor is zero except for one planktic foram assemblate experiment||unitless|
|Rs||13C ratio of the dissolving solid with Inf as infinity, meaning that there is no 12C (100% 13C-labeled)||moles 13C per mole 12C|
|Dataset-specific Instrument Name|| |
Modified Niskin incubators
|Generic Instrument Name|| |
|Dataset-specific Description|| |
A 1.6-L Niskin incubator was modified by connecting a PVC sample holder and a Seabird pump to the Niskin via threaded connections and Tygon tubing. The sample holder accommodated packets of 13C-labeled calcium carbonate, and the pump moved seawater from the Niskin interior through the sample holder and back into the Niskin interior. The Seabird pump was run using a custom-built aluminum battery housing strapped to the modified Niskin. See Naviaux et al., (2019) for details.
|Generic Instrument Description|| |
A device on a ship or in the laboratory that holds water samples under controlled conditions of temperature and possibly illumination.
R/V Kilo Moana
|Start Date|| |
|End Date|| |
Additional cruise information is available from the Rolling Deck to Repository (R2R): https://www.rvdata.us/search/cruise/KM1712
NSF Award Abstract:
Ocean acidification by anthropogenic carbon dioxide (CO2) emissions to the atmosphere will ultimately be balanced by sedimentary carbonate dissolution. The time constant for this reaction, however, is ca. 6,000 years. So, in the coming decades, the ocean's response to CO2 uptake will be based on the kinetics of supply and removal, not on the thermodynamics of the system. Unfortunately our understanding of the basic rate law for carbonate dissolution in the ocean is lacking. The order of the rate law is still argued to be anywhere from 1 to 4.5; this range represents a major difference in the sensitivity of the system to small changes in saturation state. The relative importance of aragonite vs. calcite dissolution, the influence of magnesium content in the minerals, and the sign of the role of organic matter are all still unknowns in the modern ocean. Of course, a truly useful rate law would be able to combine the relative importance of all of these factors into a predictive rule for how dissolution will respond to ocean acidification.
In this study, researchers at the California Institute of Technology and the University of Southern California will address this problem with a novel set of laboratory and in situ experiments that use carbon-13 (13C) tracer labeled biogenic carbonates to measure the dissolution rate under a wide range of saturation states. They will assemble a set of rules that will govern carbonate dissolution in sinking particles and in marine sediments. This will require two sub-projects. First, they will culture several different species of biogenic carbonate producers in the lab under the influence of a strong 13C label. With enrichments of around 30,000o/oo in the calcium carbonate (CaCO3), they will measure the change in dissolved inorganic carbon-13 at several time points over 1-2 weeks in specially built high-pressure reaction chambers. The construction of a prototype chamber is completed and it provides the means, for the first time, to control carbonate saturation state by changing seawater chemistry, pressure, and temperature independently. Experiments with pure 13C labeled inorganic CaCO3 will provide the inorganic reference frame for the biogenic carbonate results. Secondly, to check the lab-based rate data, they will also use labeled biogenic particles in a simple Niskin bottle based reactor that will be deployable on regular hydrowire. The accumulation of 13C in the Niskin dissolved inorganic carbon over 1-2 days will provide an initial rate that is directly comparable to the more extensive laboratory study on the same sorts of materials. Using the San Pedro Basin as a test bed for these in situ experiments will sample a range of saturation states in a series of 3-day cruises. This high-sensitivity approach should allow the team to unpack the various components of carbonate dissolution in seawater under rising CO2 concentrations.
Broader Impacts. Producing a better rate law for carbonate dissolution will have broad implications for the fields of marine chemistry, marine biology, paleoceanography, and for potential societal response to ocean acidification. This rate law sits at the heart of the marine carbonate cycle. In addition, this work will benefit at least two graduate students and promote US-Israel collaborations via the inclusion of Jonathan Erez and his students. The specific involvement of underrepresented high school students in scientific/oceanographic research is built into the efforts of this project as well as ongoing efforts by both PIs to communicate their science to a broad array of non-scientific audiences.
|NSF Division of Ocean Sciences (NSF OCE)|
|NSF Division of Ocean Sciences (NSF OCE)|