Altabet Mark A.

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Altabet

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Mark A.

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Innovative nitrogen sensor maps the North Pacific oxygen minimum zone

(The Oceanography Society, 2018-03) McNeil, Craig L. ; D'Asaro, Eric A. ; Reed, Andrew ; Altabet, Mark A. ; Bourbonnais, Annie ; Beaverson, Chris
N2 fixation in eddies of the eastern tropical South Pacific Ocean

(Copernicus Publications on behalf of the European Geosciences Union, 2016-05-18) Löscher, Carolin ; Bourbonnais, Annie ; Dekaezemacker, Julien ; Charoenpong, Chawalit N. ; Altabet, Mark A. ; Bange, Hermann W. ; Czeschel, Rena ; Hoffmann, Chris ; Schmitz, Ruth

Mesoscale eddies play a major role in controlling ocean biogeochemistry. By impacting nutrient availability and water column ventilation, they are of critical importance for oceanic primary production. In the eastern tropical South Pacific Ocean off Peru, where a large and persistent oxygen-deficient zone is present, mesoscale processes have been reported to occur frequently. However, investigations into their biological activity are mostly based on model simulations, and direct measurements of carbon and dinitrogen (N2) fixation are scarce. We examined an open-ocean cyclonic eddy and two anticyclonic mode water eddies: a coastal one and an open-ocean one in the waters off Peru along a section at 16° S in austral summer 2012. Molecular data and bioassay incubations point towards a difference between the active diazotrophic communities present in the cyclonic eddy and the anticyclonic mode water eddies. In the cyclonic eddy, highest rates of N2 fixation were measured in surface waters but no N2 fixation signal was detected at intermediate water depths. In contrast, both anticyclonic mode water eddies showed pronounced maxima in N2 fixation below the euphotic zone as evidenced by rate measurements and geochemical data. N2 fixation and carbon (C) fixation were higher in the young coastal mode water eddy compared to the older offshore mode water eddy. A co-occurrence between N2 fixation and biogenic N2, an indicator for N loss, indicated a link between N loss and N2 fixation in the mode water eddies, which was not observed for the cyclonic eddy. The comparison of two consecutive surveys of the coastal mode water eddy in November 2012 and December 2012 also revealed a reduction in N2 and C fixation at intermediate depths along with a reduction in chlorophyll by half, mirroring an aging effect in this eddy. Our data indicate an important role for anticyclonic mode water eddies in stimulating N2 fixation and thus supplying N offshore.
Vertical profiles of N2 gas concentrations in excess of equilibrium values along with the isotopic composition of total N2, NO3- and NO2- from R/V New Horizon cruise NH1410 in the Eastern Tropical North Pacific from May to June 2014

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-05-05) Altabet, Mark A. ; McNeil, Craig L.

This dataset includes vertical profiles of N2 gas concentrations in excess of equilibrium values along with the isotopic composition of total N2, NO3- and NO2- from R/V New Horizon cruise NH1410 in the Eastern Tropical North Pacific from May to June 2014. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/705567
The role of regenerated nitrogen for rocky shore productivity, Cape Flattery, Washington, 2010 & 2011

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2014-02-04) Pather, Santhiska ; Pfister, Catherine A. ; Altabet, Mark A. ; Post, David

Stable isotope tracers were added to exposed tidepools utilizing them as temporary mesocosms to quantify N transformation rates (Pather et al.,L&O). Large tracer signals were observed over the typical 4-5 hr experimental period in both the dilution of the isotope label in its added form (NH4+ or NO3-) and the appearance of the label in products (e.g. NO2-) The primary advantage was that all members of community participated in the experiment allowing us to recognize the complexity of nitrogen cycling in this system. A full dataset description is included in the supplemental file 'project-data-description.pdf'. Field names are included in the files, '*_params.csv'
Nitrate isotope data from R/V Thomas G. Thompson cruise TN303 in the Eastern Tropical Pacific in 2013 (U.S. GEOTRACES EPZT project)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-03-31) Casciotti, Karen L. ; Altabet, Mark A.

Nitrate isotope data from R/V Thomas G. Thompson cruise TN303 in the Eastern Tropical Pacific in 2013 (U.S. GEOTRACES EPZT project). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/650087
Radiocarbon dating of archived sediment cores in the Southeast Pacific from 1960 to 2000

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2023-01-17) Altabet, Mark A.

There were likely large changes in Southeast (SE) Pacific Ocean biogeochemistry over the last glacial cycle as a consequence of coincident changes in dust flux, oxygenation, and latitudinal position of the Subantarctic and Antarctic Fronts. However, there are few available sediment core records with reliable chronologies for this time interval despite the large number of archived cores collected between the 1960s and 1990s. The apparent reason is that, except for sites in proximity to the South American continental margin, sedimentation rates are often lower than 1 cm/kyr and calcium carbonate is only well preserved on topographic highs. As part of a project to study past nitrogen fixation, we surveyed archived cores from the SE Pacific and selected the most promising for radiocarbon dating of the planktonic foraminiferal fraction. While many cores have core tops were found to be older than detectable with radiocarbon, a number have core tops ages within the Holocene and sediment accumulation rates centering on 1.5 cm/kyr. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/886679
Microbial associations with macrobiota in coastal ecosystems : patterns and implications for nitrogen cycling

(John Wiley & Sons, 2016-05-02) Moulton, Orissa M. ; Altabet, Mark A. ; Beman, J. Michael ; Deegan, Linda A. ; Lloret, Javier ; Lyons, Meaghan K. ; Nelson, James A. ; Pfister, Catherine

In addition to their important effects on nitrogen (N) cycling via excretion and assimilation (by macrofauna and macroflora, respectively), many macrobiota also host or facilitate microbial taxa responsible for N transformations. Interest in this topic is expanding, especially as it applies to coastal marine systems where N is a limiting nutrient. Our understanding of the diversity of microbes associated with coastal marine macrofauna (invertebrate and vertebrate animals) and macrophytes (seaweeds and marine plants) is improving, and recent studies indicate that the collection of microbes living in direct association with macrobiota (the microbiome) may directly contribute to N cycling. Here, we review the roles that macrobiota play in coastal N cycling, review current knowledge of macrobial–microbial associations in terms of N processing, and suggest implications for coastal ecosystem function as animals are harvested and as foundational habitat is lost or degraded. Given the biodiversity of microbial associates of macrobiota, we advocate for more research into the functional consequences of these associations for the coastal N cycle.
N-loss isotope effects in the Peru oxygen minimum zone studied using a mesoscale eddy as a natural tracer experiment

(John Wiley & Sons, 2015-06-06) Bourbonnais, Annie ; Altabet, Mark A. ; Charoenpong, Chawalit N. ; Larkum, Jennifer ; Hu, Haibei ; Bange, Hermann W. ; Stramma, Lothar

Mesoscale eddies in Oxygen Minimum Zones (OMZs) have been identified as important fixed nitrogen (N) loss hotspots that may significantly impact both the global rate of N-loss as well as the ocean's N isotope budget. They also represent “natural tracer experiments” with intensified biogeochemical signals that can be exploited to understand the large-scale processes that control N-loss and associated isotope effects (ε; the ‰ deviation from 1 in the ratio of reaction rate constants for the light versus heavy isotopologues). We observed large ranges in the concentrations and N and O isotopic compositions of nitrate (NO3−), nitrite (NO2−), and biogenic N2 associated with an anticyclonic mode-water eddy in the Peru OMZ during two cruises in November and December 2012. In the eddy's center where NO3− was nearly exhausted, we measured the highest δ15N values for both NO3− and NO2− (up to ~70‰ and 50‰) ever reported for an OMZ. Correspondingly, N deficit and biogenic N2-N concentrations were also the highest near the eddy's center (up to ~40 µmol L−1). δ15N-N2 also varied with biogenic N2 production, following kinetic isotopic fractionation during NO2− reduction to N2 and, for the first time, provided an independent assessment of N isotope fractionation during OMZ N-loss. We found apparent variable ε for NO3− reduction (up to ~30‰ in the presence of NO2−). However, the overall ε for N-loss was calculated to be only ~13–14‰ (as compared to canonical values of ~20–30‰) assuming a closed system and only slightly higher assuming an open system (16–19‰). Our results were similar whether calculated from the disappearance of DIN (NO3− + NO2−) or from the appearance of N2 and changes in isotopic composition. Further, we calculated the separate ε values for NO3− reduction to NO2− and NO2− reduction to N2 of ~16–21‰ and ~12‰, respectively, when the effect of NO2− oxidation could be removed. These results, together with the relationship between N and O of NO3− isotopes and the difference in δ15N between NO3− and NO2−, confirm a role for NO2− oxidation in increasing the apparent ε associated with NO3− reduction. The lower ε for N-loss calculated in this study could help reconcile the current imbalance in the global N budget if representative of global OMZ N-loss.
The influence of light on nitrogen cycling and the primary nitrite maximum in a seasonally stratified sea

( 2011-07-08) Mackey, Katherine R. M. ; Bristow, Laura ; Parks, David R. ; Altabet, Mark A. ; Post, Anton F. ; Paytan, Adina

In the seasonally stratified Gulf of Aqaba Red Sea, both NO2- release by phytoplankton and NH4+ oxidation by nitrifying microbes contributed to the formation of a primary nitrite maximum (PNM) over different seasons and depths in the water column. In the winter and during the days immediately following spring stratification, NO2- formation was strongly correlated (R2=0.99) with decreasing irradiance and chlorophyll, suggesting that incomplete NO3- reduction by light limited phytoplankton was a major source of NO2-. However, as stratification progressed, NO2- continued to be generated below the euphotic depth by microbial NH4+ oxidation, likely due to differential photoinhibition of NH4+ and NO2- oxidizing populations. Natural abundance stable nitrogen isotope analyses revealed a decoupling of the δ15N and δ18O in the combined NO3- and NO2- pool, suggesting that assimilation and nitrification were co-occurring in surface waters. As stratification progressed, the δ15N of particulate N below the euphotic depth increased from -5‰ to up to +20‰. N uptake rates were also influenced by light; based on 15N tracer experiments, assimilation of NO3-, NO2-, and urea was more rapid in the light (434±24, 94±17, and 1194±48 nmol N L-1 day-1 respectively) than in the dark (58±14, 29±14, and 476±31 nmol N L-1 day-1 respectively). Dark NH4+ assimilation was 314±31 nmol N L-1 day-1, while light NH4+ assimilation was much faster, resulting in complete consumption of the 15N spike in less than 7 hour from spike addition. The overall rate of coupled urea mineralization and NH¬4+ oxidation (14.1±7.6 nmol N L-1 day-1) was similar to that of NH¬4+ oxidation alone (16.4±8.1 nmol N L-1 day-1), suggesting that for labile dissolved organic N compounds like urea, mineralization was not a rate limiting step for nitrification. Our results suggest that assimilation and nitrification compete for NH4+ and that N transformation rates throughout the water column are influenced by light over diel and seasonal cycles, allowing phytoplankton and nitrifying microbes to contribute jointly to PNM formation. We identify important factors that influence the N cycle throughout the year, including light intensity, substrate availability, and microbial community structure. These processes could be relevant to other regions worldwide where seasonal variability in mixing depth and stratification influence the contributions of phytoplankton and non-photosynthetic microbes to the N cycle.
Methods for measuring denitrification : diverse approaches to a difficult problem

( 2005-07-15) Groffman, Peter M. ; Altabet, Mark A. ; Bohlke, John K. ; Butterbach-Bahl, Klaus ; David, Mark B. ; Firestone, Mary K. ; Giblin, Anne E. ; Kana, Todd M. ; Nielsen, Lars Peter ; Voytek, Mary A.

Denitrification, the reduction of the nitrogen (N) oxides, nitrate (NO3-) and nitrite (NO2-), to the gases nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2), is important to primary production, water quality and the chemistry and physics of the atmosphere at ecosystem, landscape, regional and global scales. Unfortunately, this process is very difficult to measure, and existing methods are problematic for different reasons in different places at different times. In this paper, we review the major approaches that have been taken to measure denitrification in terrestrial and aquatic environments and discuss the strengths, weaknesses and future prospects for the different methods. Methodological approaches covered include; 1) acetylene-based methods, 2) 15N tracers, 3) direct N2 quantification, 4) N2/Ar ratio quantification, 5) mass balance approaches, 6) stoichiometric approaches, 7) methods based on stable isotopes, 8) in situ gradients with atmospheric environmental tracers and 9) molecular approaches. Our review makes it clear that the prospects for improved quantification of denitrification vary greatly in different environments and at different scales. While current methodology allows for the production of accurate estimates of denitrification at scales relevant to water and air quality and ecosystem fertility questions in some systems (e.g., aquatic sediments, well defined aquifers), methodology for other systems, especially upland terrestrial areas, still needs development. Comparison of mass balance and stoichiometric approaches that constrain estimates of denitrification at large scales with point measurements (made using multiple methods), in multiple systems, is likely to propel more improvement in denitrification methods over the next few years.
N2 gas concentration in excess of saturation determined by N2:Ar ratiometry from samples collected in the Bering Sea, Chukchi Sea, and Western Arctic on cruise HLY1702 from August to September 2017

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-05-05) Altabet, Mark A.

N2 gas concentration in excess of saturation determined by N2:Ar ratiometry from samples collected in the Bering Sea, Chukchi Sea, and Western Arctic on cruise HLY1702 from August to September 2017. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/812052

Altabet Mark A.

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