ALBERT

Description: Individual species were identified and 550 individuals per species were picked from the 〉250 µm fraction under dissecting microscope for each sample. Approximately 7 mg of picked and identified foraminifera shells were crushed between glass microscope slides and rinsed with MilliQ water. Samples were cleaned prior to δ¹⁵NFB measurement as described in Marcks et al., (2023). Once samples were clean, organic nitrogen was released into solution by acid dissolution of the foraminiferal calcite. Samples were acidified prior to measurement. Nitrate concentrations were measured by chemiluminescence on a Teledyne Instruments (Model 200E) chemiluminescence NO/NOx analyzer. δ15NFB samples, 10 nmol in size, were measured by bacterial conversion of nitrate to nitrous oxide, with measurement of the δ¹⁵N of the nitrous oxide by automated extraction and gas chromatography-isotope ratio mass spectrometry on a Thermo Delta V Plus IRMS. The potassium nitrate reference materials IAEA-N3 and USGS 34 (+4.7 ‰ and 1.8 ‰, respectively) were used to standardize results (Gonfiantini et al., 1995). Note, testing of a subset of 6 samples, each with full procedural triplicates, for a total of 18 samples, showed negligible differences in nitrogen content and δ¹⁵NFB values with and without a reductive cleaning step, and so it was omitted here to avoid unnecessary loss of sample material. Sample replicates and triplicates were analyzed when possible. Full procedural replicates were analyzed for 134 sample splits, representing 66 unique samples, when enough foraminifera were available for duplicate or triplicate analysis. The average standard deviation of procedural replicates is 0.4 ‰. Full operational blanks and amino acid standards (USGS 65 glycine) were measured in each batch. The average standard deviation of glycine standards measured in triplicate is 0.3 ‰. We estimated the δ¹⁵N value of the persulfate blank using a dilution series (5, 7.5, 10, and 20 μM of the glycine standard and the fraction of the blank in standards. We applied a blank correction to each sample based on the calculated mean δ¹⁵N value of all of the persulfate blanks for the dataset and the fraction of the blank in the N content of each sample. Data were subset to exclude N content outliers (〉2 s.d. from mean and where the blank was greater than 20 % of the sample N content, with significantly different δ¹⁵N values from other replicates). Full propagated analytical error associated with measurement and blank correction, following Higgins et al., (2009, doi:10.1021/ac8017185 ), was on average 0.6 ‰. Propagating the errors, including not only the procedural replicates and their variance, but the relative size of the blanks, the mean of the calculated blank δ¹⁵N values (5± 10 ‰). The mean value, 0.6 ‰, is used where procedural replicates were limited by sample availability. The age model is based on the benthic oxygen isotope stratigraphy presented by Starr et al. (2021, doi:10.1038/s41586-020-03094-7). This age model for Site 361-U1475 was generated with 12 radiocarbon dates and 33 benthic oxygen isotope tie points which were graphically aligned with a probabilistic stack of 180 globally distributed benthic oxygen isotope records (Starr et al., 2021, doi:10.1038/s41586-020-03094-7).

Description: Individual species were identified and ~550 individuals per species were picked from the 〉250 µm fraction under dissecting microscope for each sample. Approximately 7 mg of picked and identified foraminifera shells were crushed between glass microscope slides and rinsed with MilliQ water. Samples were cleaned and prepared for δ¹⁵NFB measurement as in Smart et al. (2020, doi:10.1029/2019gc008440). Nitrate concentrations were measured by chemiluminescence on a Teledyne Instruments (Model 200E) chemiluminescence NO/NOx analyzer (Braman & Hendrix, 1989; doi:10.1021/ac00199a007). δ¹⁵NFB was measured by bacterial conversion of nitrate to nitrous oxide (Sigman et al., 2001; doi:10.1021/ac010088e), with measurement of the δ¹⁵N of the nitrous oxide by automated extraction and gas chromatography-isotope ratio mass spectrometry (Casciotti et al., 2002; doi:10.1021/ac020113w ) on a Thermo Delta V Plus IRMS. The potassium nitrate reference materials IAEA-N3 and USGS 34 (+4.7 ‰ and 1.8 ‰, respectively) were used to standardize results (Gonfiantini et al., 1995). Sample replicates and triplicates were analyzed when possible. Full procedural replicates were analyzed for 161 sample splits, representing 77 unique samples, when enough foraminifera were available for duplicate or triplicate analysis. Precision for full procedural replicates was 1.0 ‰, this is comparable with modern shell-bound measurements of the same species taken from net tows in this region (standard error = 0.9 ‰, n=10 & 1.1 ‰, n=6, of G. bulloides and G. inflata, respectively; Smart et al., 2020). In every batch, full operational blanks and amino acid standards (USGS 65 amino acid standard) were used to correct for the persulfate oxidation blank and to ensure complete conversion of N. The age model is based on the benthic oxygen isotope stratigraphy presented by Starr et al. (2021, doi:10.1038/s41586-020-03094-7).

Description: Neogloboquadrina pachyderma abundance was obtained by washing ~ 10 cm³ of sediment through a 150µm sieve and drying at ~ 50 ºC for 24 h. This dried fraction was split until a total of 300-400 individuals remained. From this amount, we identified the relative abundance of Neogloboquadrina pachyderma tests according to Kennett and Srinivasan (1983) and Loeblich and Tappan (1988, doi:10.1007/978-1-4899-5760-3).

Description: Biogenic silica accumulation was obtained by analyzing approximately 200 mg of homogenized and freeze dried sediment for each sample. Cleaning, chemical treatment, and measurement followed protocols outlined in (Mortlock & Froelich, 1989, doi:10.1016/0198-0149(89)90092-7). Samples were measured with a UV Vis spectrophotometer at 812 nm wavelength. Full procedural replicates were performed on 163 of the 435 samples yielding an average standard deviation of 0.2 %. Samples were referenced to RICCA VerSpec SiO32- in 1 % NaOH for intercomparison. Opal mass accumulation rates were calculated by multiplying the fraction of opal by dry bulk density and sedimentation rates from Starr et al. (2021, doi:10.1038/s41586-020-03094-7).

Description: Intense seasonal productivity and carbon drawdown on the West Antarctic Peninsula (WAP) is driven by upwelling of nutrient-rich Circumpolar Deep Water (CDW) and subsequent stratification. CDW influence on the WAP is thought to have varied dramatically during the mid-Holocene, 5-7 ka. Here, we use diatom-bound nitrogen isotopes (δ15NDB), a nutrient utilization proxy, from ODP Site 1098 in Palmer Deep to study variations in the presence of CDW on sub-millennial timescales in the mid-Holocene. CDW intrusion is synchronous with atmospheric warming over Antarctica, suggesting that stronger and/or more southerly Southern Hemisphere westerlies enhanced CDW intrusion onto the WAP shelf. Our results also suggest that bulk sedimentary nitrogen isotopes (δ15Nbulk) do not track the same processes as δ15NDB at this site and that this cannot be explained by changes in diatom assemblages.

Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 3696–3714, doi:10.1002/2016JC012460.

Description: We present 34 profiles of radon-deficit from the ice-ocean boundary layer of the Beaufort Sea. Including these 34, there are presently 58 published radon-deficit estimates of air-sea gas transfer velocity (k) in the Arctic Ocean; 52 of these estimates were derived from water covered by 10% sea ice or more. The average value of k collected since 2011 is 4.0 ± 1.2 m d−1. This exceeds the quadratic wind speed prediction of weighted kws = 2.85 m d−1 with mean-weighted wind speed of 6.4 m s−1. We show how ice cover changes the mixed-layer radon budget, and yields an “effective gas transfer velocity.” We use these 58 estimates to statistically evaluate the suitability of a wind speed parameterization for k, when the ocean surface is ice covered. Whereas the six profiles taken from the open ocean indicate a statistically good fit to wind speed parameterizations, the same parameterizations could not reproduce k from the sea ice zone. We conclude that techniques for estimating k in the open ocean cannot be similarly applied to determine k in the presence of sea ice. The magnitude of k through gaps in the ice may reach high values as ice cover increases, possibly as a result of focused turbulence dissipation at openings in the free surface. These 58 profiles are presently the most complete set of estimates of k across seasons and variable ice cover; as dissolved tracer budgets they reflect air-sea gas exchange with no impact from air-ice gas exchange.

Description: NSF Arctic Natural Sciences program Grant Number: 1203558

Description: 2017-11-05

Description: Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography: Methods 10 (2012): 631-644, doi:10.4319/lom.2012.10.631.

Description: Intercomparision of 234Th measurements in both water and particulate samples was carried out between 15 laboratories worldwide, as a part of GEOTRACES inter-calibration program. Particulate samples from four different stations namely BATS (both shallow and deep) and shelf station (shallow) in Atlantic and SAFE (both shallow and deep) and Santa Barbara station (shallow) in Pacific were used in the effort. Particulate intercalibration results indicate good agreement between all the participating labs with data from all labs falling within the 95% confidence interval around the mean for most instances. Filter type experiments indicate no significant differences in 234Th activities between filter types and pore sizes (0.2-0.8 μm). The only exception are the quartz filters, which are associated with 10% to 20% higher 234Th activities attributed to sorption of dissolved 234Th. Flow rate experiments showed a trend of decreasing 234Th activities with increasing flow rates (2-9 L min-1) for 〉 51 μm size particles, indicating particle loss during the pumping process. No change in 234Th activities on small particles was observed with increasing flow-rates. 234Th intercalibration results from deep water samples at SAFe station indicate a variability of 〈 3% amongst labs while dissolved 234Th data from surface water at Santa Barbara Station show a less robust agreement, possibly due to the loss of 234Th from decay and large in-growth corrections as a result of long gap between sample collection and processing.

Description: This research is funded by NSF Chemical Oceanography program. LM will like to thank Fisheries and Oceans Canada for support. PM is supported through ICREA Academia funded by Generalitat de Catalunya. The International Atomic Energy Agency is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Durkin, C. A., Buesseler, K. O., Cetinic, I., Estapa, M. L., Kelly, R. P., & Omand, M. A visual tour of carbon export by sinking particles. Global Biogeochemical Cycles, 35(10), (2021): e2021GB006985, https://doi.org/10.1029/2021GB006985.

Description: To better quantify the ocean's biological carbon pump, we resolved the diversity of sinking particles that transport carbon into the ocean's interior, their contribution to carbon export, and their attenuation with depth. Sinking particles collected in sediment trap gel layers from four distinct ocean ecosystems were imaged, measured, and classified. The size and identity of particles was used to model their contribution to particulate organic carbon (POC) flux. Measured POC fluxes were reasonably predicted by particle images. Nine particle types were identified, and most of the compositional variability was driven by the relative contribution of aggregates, long cylindrical fecal pellets, and salp fecal pellets. While particle composition varied across locations and seasons, the entire range of compositions was measured at a single well-observed location in the subarctic North Pacific over one month, across 500 m of depth. The magnitude of POC flux was not consistently associated with a dominant particle class, but particle classes did influence flux attenuation. Long fecal pellets attenuated most rapidly with depth whereas certain other classes attenuated little or not at all with depth. Small particles (〈100 μm) consistently contributed ∼5% to total POC flux in samples with higher magnitude fluxes. The relative importance of these small particle classes (spherical mini pellets, short oval fecal pellets, and dense detritus) increased in low flux environments (up to 46% of total POC flux). Imaging approaches that resolve large variations in particle composition across ocean basins, depth, and time will help to better parameterize biological carbon pump models.

Description: This work was supported by an NSF EAGER award to C. A. Durkin (OCE-1703664), M. L. Estapa (OCE-1703422), and M. Omand (OCE-1703336), and also by the NASA EXPORTS program (80NSSC17K0662), a NASA New Investigator award to M. L. Estapa (NNX14AM01G), the Rhode Island Endeavor Program (RIEP), NASA's PACE mission, and the Schmidt Ocean Institute.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Estapa, M., Buesseler, K., Durkin, C. A., Omand, M., Benitez-Nelson, C. R., Roca-Marti, M., Breves, E., Kelly, R. P., & Pike, S. Biogenic sinking particle fluxes and sediment trap collection efficiency at Ocean Station Papa. Elementa: Science of the Anthropocene, 9(1), (2021): 00122, https://doi.org/10.1525/elementa.2020.00122.

Description: Comprehensive field observations characterizing the biological carbon pump (BCP) provide the foundation needed to constrain mechanistic models of downward particulate organic carbon (POC) flux in the ocean. Sediment traps were deployed three times during the EXport Processes in the Ocean from RemoTe Sensing campaign at Ocean Station Papa in August–September 2018. We propose a new method to correct sediment trap sample contamination by zooplankton “swimmers.” We consider the advantages of polyacrylamide gel collectors to constrain swimmer influence and estimate the magnitude of possible trap biases. Measured sediment trap fluxes of thorium-234 are compared to water column measurements to assess trap performance and estimate the possible magnitude of fluxes by vertically migrating zooplankton that bypassed traps. We found generally low fluxes of sinking POC (1.38 ± 0.77 mmol C m–2 d–1 at 100 m, n = 9) that included high and variable contributions by rare, large particles. Sinking particle sizes generally decreased between 100 and 335 m. Measured 234Th fluxes were smaller than water column 234Th fluxes by a factor of approximately 3. Much of this difference was consistent with trap undersampling of both small (〈32 μm) and rare, large particles (〉1 mm) and with zooplankton active migrant fluxes. The fraction of net primary production exported below the euphotic zone (0.1% light level; Ez-ratio = 0.10 ± 0.06; ratio uncertainties are propagated from measurements with n = 7–9) was consistent with prior, late summer studies at Station P, as was the fraction of material exported to 100 m below the base of the euphotic zone (T100, 0.55 ± 0.35). While both the Ez-ratio and T100 parameters varied weekly, their product, which we interpret as overall BCP efficiency, was remarkably stable (0.055 ± 0.010), suggesting a tight coupling between production and recycling at Station P.

Description: The authors would like to acknowledge funding support from the NASA EXPORTS program (Award 80NSSC17K0662) for all sediment trap data presented here. Net primary production data collection was supported by EXPORTS (Award 80NSSC17K568) to Oregon State University. Thorium data collection was supported by EXPORTS (Award 80NSSC17K0555) to KB, CRBN, and L. Resplandy.